My Histology Notes

L1 Epithelial tissue

1. Tissue

Cells work together in functionally related groups 

Types:

a. Epithelial--lining and covering

General characteristics:

Covers a body surface or lines a body cavity

Forms most glands

Functions:

Protection, Absorption, Secretion, Ion transport, Filtration, Forms slippery surfaces

Special characteristics:

i. cellularity: cells are in close contact with each other with little or no intercellular space between them

ii. specialized contacts: may have junctions for both attachment and communication

iii. polarity: epithelial tissues always have an apical and basal surface

iv. support by connective tissue: both tissue contribute to the basement membrane at the basal surface

v. avascular: nutrients must diffuse

vi. regeneration: epithelial tissues have a high capacity for regeneration

Lateral surface features:

Factors holding epithelial cells together

i. adhesion proteins link plasma membranes of adjacent cells

ii. contours of adjacent cell membranes

iii. special cell junctions: 

#Tight (zone occludens)-close off intercellular space

found at apical region of most epithelial types

some proteins in plasma membrane of adjacent cells are fused

prevent molecules from passing between cells of epithelial tissue

#Adherens

#Desmosomes-2 disc-like plaques connected across intercellular space

plaques of adjoining cells are joined by proteins called cadherins

proteins interdigitate into extracellular space

intermediate filaments insert into plaques from cytoplasmic side

#Gap-passageway between 2 adjacent cells

let small molecules move directly between neighboring cells

cells are connected by hollow cylinders of proteins

Basal surface features: Basal Lamina

non-cellular supporting sheet between the epithelium and the connective tissue deep to it

consists of proteins secreted by the epithelial cells

acts as a selective filter, determining which molecules from capillaries enter epithelium

basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane

Classifications:

a. first name of tissue indicates number of layers

simple-one layer of cells

stratified-more than one layers of cells

b. last name of tissue describes shape of cells

squamous-cells wider than tall (plate or "scale" like)

cuboidal-cells are as wide as tall, in cubes

columnar-cells are taller than their wide, like columns

Naming epithelia:

-includes both the layer (1) and the shape of cells (2)

-may also include any accessory structures, e.g. goblet cells, cilia, keratin

-special epithelial tissue (don't follow naming convention), e.g. pseudostratified, transitional

2. Simple Squamous Epithelium

Description: single layer of flat cells with disc-shaped nuclei

Special types: endothelium (inner covering; slick lining of hollow organs), mesothelium (middle covering; lines peritoneal, pleural, and pericardial cavities; covers visceral organs of those cavities)

Function: passage of materials by passive diffusion and filtration; secretes lubricating substances in serosae

Location: renal corpuscles, alveoli of lungs, lining of heart, blood and lymphatic vessels, lining of ventral body cavity (serosae)

3. Simple Cuboidal Epithelium

Description: single layer of cube-like cells with large, spherical central nuclei

Function: secretion and absorption

Location: kidney tubules, secretory portions of small glands, ovary and thyroid follicles

4. Simple Columnar Epithelium

Description: single layer of column-shaped (rectangular) cells with oval nuclei--some bear cilia at their apical surface--may contain goblet cells

Function: absorption, secretion of mucus, enzymes, and other substances, ciliated type propels mucus or reproductive cells by ciliary action

Location: non-ciliated form--lines digestive tract, gall bladder, ducts of some glands; ciliated form--lines small bronchi, uterine tubes, uterus

5. Pseudostratified  Columnar Epithelium

Description: all cells originate at basement membrane, only tall cells reach apical surface, may contain goblet cells and bear cilia, nuclei lie at varying heights within cells (gives false impression of stratification)

Function: secretion of mucus, propulsion of mucus by cilia

Locations: non-ciliated type--ducts of male reproductive tubes and large glands; ciliated variety--lines trachea and most of upper respiratory tract

6. Stratified Epithelia

contain 2 or more layers of cells

regenerate from below

major role is protection

named according to shape of cells at apical surface

7. Stratified Squamous Epithelium

Description: many layers of cells-squamous in shape, deeper layers of cells appear cuboidal or columnar, thickest-adapted for protection

Specific types: keratinized-contain protective protein keratin (surface cells are dead and full of keratin); non-keratinized-forms moist lining of body openings

Functions: protects underlying tissues in areas subject to abrasion

Location: keratinized-forms epidermis; non-keratinized-forms lining of esophagus, mouth, and vagina

8. Transitional Epithelium

Description: basal cells usually cuboidal or columnar, superficial cells dome-shaped or squamous

Function: stretches and permits distension of urinary bladder

Location: lines ureters, urinary bladder and part of urethra

9. Glandular Epithelium

ducts carry products of exocrine glands to epithelial surface

include diverse glands, e.g. mucus-secreting, sweat and oil, salivary, liver and pancreas, mammary

may be uni/multicellular

10. Unicellular Exocrine Glands (Goblet Cells)

produce mucin

mucin+water→mucus

protects and lubricates many internal body surfaces

11. Multicellular Exocrine Glands 

classified by structure (branching and shape) of duct

can also be classified by mode or type of secretion

i. Merocrine-secretory vesicles released via exocytosis (salivary glands)

ii. Apocrine-apical portion of the cell is lost, cytoplasm+secretory product (mammary glands)

iii. Holocrine-entire cell is destroyed during secretion (sebaceous glands)

12. May also be classified by types of secretions from exocrine glands

i. serous--mostly water but also contains some enzymes, e.g. parotid glands, pancreas

ii. mucous--mucus secretions, e.g. sublingual glands, goblet cells

iii. mixes--serous and mucus combined, e.g. submandibular gland

SUMMARY:

https://www.youtube.com/watch?v=jxpfFSgSRrA

https://www.youtube.com/watch?v=P3714_a3l0w

https://www.youtube.com/watch?v=c3COBYNC3sQ

L2 Connective Tissue

b. Connective--support

Description:

Binds together, supports and strengthens other body tissues

Protects and insulates internal organs

Compartmentalizes structures such as skeletal muscle

The major transport system within the body

Site of stored energy reserves

Main site of immune responses

General features:

 2 basic parts: Cells and Matrix

Matrix – material between widely spaced cells

Consists of protein fibers and ground substance

Ground substance – material between cells and fibers secreted by the cells and determine the tissue qualities

Does not occur on free surfaces

Has a nerve supply (except cartilage)

Highly Vascular (except cartilage and tendons)

Cells: 

Fibroblasts – large flat cells with branching processes. Migrate throughout connective tissue secreting the fibers and ground substance

Macrophages – develop from white blood cells. Surround and engulf material by phagocytosis

Mast Cells – alongside blood vessels that supply connective tissue. Produce histamine – a chemical that dilates blood vessels.

Adipocytes – “fat cells” store triglycerides.

Matrix:

Ground Substance – component of a connective tissue between the cells and fibers, supports cells, binds them together, and provides a medium through which substances are exchanged.

Ex. Hyaluronic Acid

Strengthens and supports connective tissue

i. Collagen Fibers

Strong, resist pulling forces, flexible

Made of the protein collagen which is the most abundant protein in your body

ii. Elastic Fibers

smaller in diameter than collagen fibers, branch to form network

Made of the protein elastin

iii. Reticular Fibers

Provide support for the walls of blood vessels

Made of collagen with a glycoprotein covering

Types:

There are 6 types of connective tissue that vary by the fibers, ground substance and cells contained in it. Each type has a very specific structure and function.

Loose Connective Tissue:

Fibers are loosely intertwined among many cells.

3 types of loose connective tissue

i. Areolar Connective Tissue – one of the most widely distributed connective tissues in the body.

Contains fibroblasts, macrophages, plasma cells, mast cells, adipocytes and a few white blood cells as well as all 3 types of fibers

Helps to form the subcutaneous layer

ii. Adipose Tissue – The cells, called adipocytes, are specialized for storage of triglycerides. Adipocytes fill up with a large fat droplet so the nucleus gets pushed to one side of the cell.

Used for insulation, protection and as an energy reserve

iii. Reticular Connective Tissue – made of interlacing reticular fibers and reticular cells that connect to each other to form a network.

Used to bind together smooth muscle cells and to filter out worn out blood cells and bacteria

Dense Connective Tissue:

Contains more numerous, thicker and denser fibers but fewer cells than loose connective tissue.

3 types:

i. Dense Regular Connective Tissue

Bundles of collagen fibers are arranged regularly in parallel patterns that give it strength.

Withstands pulling from the ends, but unravels when pulled from the side

Silvery white in appearance. Tough and pliable

Found in tendons and ligaments

ii. Dense Irregular Connective Tissue

Collagen fibers are packed closely together in an irregular, random pattern

Found in parts of the body where pulling forces are exerted in various directions

Usually found in sheets

Examples: Dermis of the skin, heart valves, perichondrium and periosteum

iii. Elastic Connective Tissue

Contains branching elastic fibers and fibroblasts

Yellowish in color

Strong, can regain shape after stretching

Found in lungs and arteries

Cartilage:

Dense network of collagen fibers and elastic fibers embedded in chondroitin sulfate (a rubbery component of the ground substance)

Can withstand more stress than the dense and loose connective tissue.

Collagen fibers make the tissue strong, chondroitin sulfate makes it resilient

Chondrocytes – mature cartilage cells

Lacunae – holes in the matrix in which the cells sit

Perichondrium – dense irregular connective tissue that surrounds cartilage

3 types – hyaline, fibrocartilage and elastic

Cartilage is AVASCULAR and NO nerve supply (but the perichondrium does)

i. Hyaline Cartilage:

Gel like ground substance, collagen fibers (not visible with normal stains) and prominent chondrocytes

Most abundant cartilage in the body

Found at the end of long bones to cushion joints and at epiphyseal plates (growth plates in bones)

Weakest of the 3 types of cartilage

ii. Fibrocartilage: 

Chondrocytes scattered among visible bundles of collagen fibers

No perichondrium

Strongest of the 3 types of cartilage

Found in the intervertebral discs

iii. Elastic Cartilage: 

Chondrocytes located in a threadlike network of elastic fibers

Provides strength, elasticity and maintains the shape of certain structures (like the external ear)

Bone Tissue (osseous tissue): 

2 types – compact and spongy

i. Compact

Osteon – basic unit of compact bone

Lamellae – concentric circles of matrix

Lacunae – spaces in the matrix that house cells

Osteocytes – mature bone cells

ii. Spongy

Trabeculae – columns of bone with spaces filled with red bone marrow

Blood Tissue: 

Connective Tissue with a liquid matrix

Red Blood Cells (erythrocytes) – transport oxygen

White Blood Cells – function in immunity

Neutrophils, Eosinophils, Basophils, T and B leukocytes, natural killer cells and Monocytes

Platelets – participate in blood clotting

SUMMARY:

https://www.physio-pedia.com/Connective_Tissue_Disorders

L3 Muscle Tissue

c. Muscle--movement

Types :

Skeletal muscle:

 Multinucleated (having long, multinucleate cells running the length of muscle).

 Function: Voluntary movement.

 Location: Skeletal muscle.

 Cell: Skeletal muscle cell/muscle fiber.

i) Usually attached by tendons to bones, when muscle contract--cause the bones to move at their joints.

ii) Each skeletal muscle contains numerous muscle fibers--a single muscle cell--muscle fiber.

iii) Each muscle fiber encloses a bundle of myofibrils. 

iv) Each myofibril is composed of thick & thin myofilaments.

https://www.youtube.com/watch?v=aSO0z-Ev9G8

Cardiac muscle:

Striated, branched, responsible for the contraction of the heart (involuntary).

 Function: increasingly interconnected cells, promotes rapid spread of signal initiating contraction.

 Location: Walls of heart.

 Cell: Cardiac cell/cardiomyocyte.

i) Cardiac muscle composed of smaller, interconnected cells, each with a single nucleus.

ii) Interconnections between adjacent cells (appear as dark lines)--intercalated discs.

iii) Enable cardiac muscle cells to form a single functioning unit--myocardium.

https://www.youtube.com/watch?v=8HYfcUDR4qw

Smooth muscle:

Lack striations, cigar-shaped nucleus & spindle-shaped cells.

 Function: -involuntary contraction commanded by the CNS.

-e.g. churning of the stomach & constriction of arteries.

 Location: Wall of BVs, stomach & intestines.

 Cell: Smooth muscle cell.

https://www.youtube.com/watch?v=yh4bUdnU2MQ

SUMMARY:

Kenhub

https://www.youtube.com/results?search_query=histology+of+skeletal+muscle+ken+hub+

https://www.youtube.com/watch?v=a-BTPEWYftA

L4 Nervous Tissue

d. Nervous--control 

Nerve tissue:

-Neurons:(nerve cell)

 Fx: produce, receive & transmit electrochemical messages/ “impulses”.

4 distinct part:

i) dendrite-collect incoming messages.

ii) cell body-comprise the nucleus & surrounding cytoplasm.

iii) axon-transmit messages to target cell.

iv) Synaptic terminals-attaches to another neuron/the target cell.

 Perikaryon: soma, cell body; receive signals from axons of other neurons through synaptic terminal (terminal bouton).

 Nucleus: large, central & euchromatic; has prominent nucleolus.

 Cytoplasm: abundant RER & free polyribosomes appear as clumps of basophilic material  Nissl bodies.

 Axon hillock: absence of Nissl-related basophilia.

Sensory neuron

Unipolar

 Fx: carry impulses (info from internal/external environment) from sensory receptors to interneurons.

 Location: eyes, ears, skin.

 Characteristic of cell type

rods & cones (eyes).

Interneuron

Bipolar

 Fx: Integrate information, conduct impulses between neurons & CNS.

 Location: Brain & spinal cord.

Motor neuron

Multipolar

 Fx: Carry impulses away from CNS, activate muscle/glands.

 Location: Brain & spinal cord.

-Supporting Cells:

Neuroglia/glial cells

 Fx: 

i) support & insulate neurons (forms myelin sheath).

ii) eliminate foreign materials (in & around neurons).

iii) do NOT conduct electrical impulses.

Neuroglia Neuron

 Types:

 in CNS: astrocytes, oligodendrocytes, microglia & ependymal cells.

 in PNS: Schwann cells & satellite cells.

SUMMARY:

https://www.youtube.com/watch?v=NsBaPtemAjs

https://www.youtube.com/watch?v=gotqQ7RxT_U

https://www.youtube.com/watch?v=2reeT7kX1H4

https://www.youtube.com/watch?v=ZWxm2A0TFxM

https://www.youtube.com/watch?v=cUGuWh2UeMk

https://www.kenhub.com/en/library/anatomy/peripheral-nerves-histology

L5 Integumentary System

Objectives:

1. Describe the functions of the integumentary system.

2. Identify the major structures found in the three layers of the skin.

3. Describe the anatomy and physiology of hair and nails

4. Define some common dermatopathological disorders.

This system is divided into:

1. Skin

• Skin is an organ because it consists of different tissues that are joined to perform a specific function.

• Largest organ of the body in surface area and weight.

• Dermatology is the medical specialty concerning the diagnosing and treatment of skin disorders.

Anatomy (structure)

• Epidermis (thinner outer layer of skin)

• Dermis (thicker connective tissue layer)

• Hypodermis (subcutaneous layer or Sub-Q)

• Muscle and bone

Physiology (function)

A. Protection

• Physical barrier that protects underlying tissues from injury, uv light and bacterial invasion.

• Mechanical barrier is part non specific immunity (skin, tears and saliva).

B. Regulation of body temperature

• High temperature or strenuous exercise; sweat is evaporated from the skin surface to cool it down.

• Vasodilation (increases blood flow) and vasoconstriction (decrease in blood flow) regulates body temp.

C. Sensation

• Nerve endings and receptor cells that detect stimuli to temp., pain, pressure and touch.

D. Excretion

• Sweat removes water and small amounts of salt, uric acid and ammonia from the body surface

E. Blood reservoir

• Dermis houses an extensive network of blood vessels carrying 8-10% of total blood flow in a resting adult.

F. Synthesis of Vitamin D (cholecalciferol)

• UV rays in sunlight stimulate the production of Vit. D. Enzymes in the kidney and liver modify and convert to final form; calcitriol (most active form of Vit. D.) Calcitriol aids in absorption of calcium from foods and is considered a hormone.

Epidermis

• Keratinized stratified squamous epithelium with four distinct cell types and five distinct layers.

Cells in the epidermis:

Keratinocytes

• Most abundant

• Produce keratin (fibrous protein)

• Protective; waterproofing the skin

• Continuous mitosis

• Form in the deepest layer called the stratum basale

• Cells push their way up to the surface where they are dead cells filled with keratin; will slough off.

• Regenerates every 25-45 days.

Melanocytes

• Cells produce brownish/black pigment

• Called melanin. (8% of epidermal cells)

• Stratum basale

• Branching processes (dendrites)

• Melanin accumulates in melanosomes and transported along dendrites of the melanocytes to keratinocytes.

• Melanin accumulates on the superficial aspect of the keratinocyte shielding its nucleus from harmful UV light.

• Lack of melanin: albino

Merkel cells

• Stratum basale

• Attach to keratinocytes by desmosomes

• Make contact with a sensory neuron ending called a Merkel disc (touch).

Langerhans’ cells

• Star-shaped cells arising from bone marrow that migrate to epidermis.

• Epidermal dendritic cells (macrophages)

• Interact with a WBC called a T- helper cell

• Easily damaged by UV light.

5 layers of the epidermis:

A. Stratum corneum (horny layer)

• Layer has many rows of dead cells filled with keratin

• Continuously shed and replaced (desquamation)

• Effective barrier against light, heat and bacteria

• 20-30 cell layers thick

• Dandruff and flakes

• anucleated

• 40 lbs. Of skin flakes in a lifetime (dust mites!)

B. Stratum lucidum: clear layer

• Seen in thick skin of the palms and soles of feet

• 3-5 rows of clear flat dead cells

• Keratohyalin (precursor) to keratin

C. Stratum granulosum: granular layer

• 3-5 rows of flattened cells

• Nuclei of cells flatten out

• Organelles disintegrate cells eventually die

• Keratohyalin granules (darkly stained) accumulate

• Lamellated granules secrete glycolipids into extracellular spaces to slow water loss in the epidermis

D. Stratum spinosum: “spiny/prickly layer”

• 8-10 rows of polyhedral (many sided) cells

• Appearance of prickly spines

• Shrink when prepared for slide

• Melanin granules and Langerhans’ cell predominate

E. Stratum basale: deepest epidermal layer

• Attached to dermis

• Single row of cells

• Mostly columnar keratinocytes

• With rapid mitotic division

• Stratum germinativum

• Contain merkel cells and melanocytes

• 10-25%

SUMMARY:

https://www.youtube.com/watch?v=CC15024Qz9U

https://www.youtube.com/watch?v=acXjaANVK4M

https://www.youtube.com/watch?v=yQQ2Dmz42Vs

https://www.youtube.com/watch?v=63YdIH2S2ls

Dermis

• Flexible and strong connective tissue

• Elastic, reticular and collagen fibers

• Cells: fibroblasts, macrophages (WBC), mast cells (histamine).

• Nerves, blood and lymphatic vessels

• Oil and sweat glands originate

• Two layers: papillary and reticular

Papillary layer (dermis)

• Loose connective tissue with nipple like surface projection called dermal papilla.

• Capillaries

• Contain pain receptors

• Contain touch receptors (Meissner’s corpuscles

• Dermal ridges- epidermal ridges-pattern called fingerprints

Reticular layer

• Dense irregular C.T.

• Collagen fibers offer strength

• Holds water

• Dermal tearing causes stretch marks.

Hypodermis

• Called subcutaneous, Sub-Q or superficial fascia

• Anchors skin to underlying structures

• Contains adipose tissue and blood vessels

• Common site for injection

Skin color:

• attributed to melanin, hemoglobin and carotene.

• Race is determined by amount of melanin not # of melanocytes.

• Local accumulation of melanin will result in freckles and pigmented moles.

• UV light stimulates melanin production. Excessive UV light can damage DNA and cause solar elastosis (elastin fibers clump)

• Carotene is formed from Vit. A and deposits in stratum corneum and imparts an orange tone to skin

Freckles

2. Hair

Hair color:

• Dark hair: mostly melanin

• Blond and red hair: melanin with Fe and S.

• Gray hair: loss of pigment (decr. tyrosinase)

• White hair: air bubbles in the medullary hair shaft.

Hair (pili):

• Main function is protection

• Hair root nerve plexus for touch

• Normal hair loss in adult 70-100 hairs/day

Hair anatomy:

• Composed of dead columns of keratinized cells.

• Shaft: is the superficial portion of hair

• Root: below the surface in the dermis

• Shaft and root are composed of three layers: inner medulla, middle cortex and outer cuticle.

• Inner medulla has 2-3 rows of polyhedral cells where pigment is located

• Cortex is major portion of shaft

• Cuticle is scaly and heavily keratinized

• Vellus hair: fine hair

• Terminal hair : coarser hair; axillary and pubic region. Grow in response to sex hormones

• Hirsutism: excessive hairiness: incr. androgens

• Hair follicle surrounds the root.

• Bulb is the enlargement at the end of the follicle.

• Also houses the germinal layer

• Papilla (nipple like) is located in the bulb and is where the blood supply nourishes the hair.

• Arrector pili (pl. pilorum) is smooth muscle located in the dermis and is attached to the side of the hair shaft.

• Fright, cold and emotions will contract muscle and pull hair in vertical position.

“Goose bumps”.

3. Glands

• Two types of glands exist in the integument.

• Sebaceous glands (oil glands)

• Sudoriferous glands (sweat glands)

• Sebaceous glands: (holocrine glands)

• connected to hair follicle

• not found on palms and soles of feet

• Secretes sebum (fats, cholesterol and proteins

• Keep hair from drying out, keeps skin moist

• Whiteheads, blackheads and acne

Whitehead: When the trapped sebum and bacteria stay below the skin surface, a whitehead is formed.

Blackhead: A blackhead occurs when the trapped sebum and bacteria partially open to the surface and turn black due to melanin, the skin's pigment. Blackheads can last for a long time because the contents very slowly drain to the surface.

Sudoriferous glands: exocrine glands

• Millions located throughout the skin

• Two types:

A. Eccrine: more common (merocrine)

• originate in subQ layer

• duct empties on skin surface

• palms and soles of feet

• sweat is watery (99% H20)

• sweating regulated by sympathetic nervous system

B. Apocrine: axillary and pubic region

• duct empties onto hair follicle

• viscous fluid

• causes body odor when bacteria break it down

4. Nails

5. Nerve endings

• Pacinian (lamellated) corpuscles: deep pressure and stretch

• Meissner’s (tactile) corpuscles: light touch, vibration and discriminative touch.

• Hair root plexus

• Free (naked) nerve endings: nociceptors (pain) and thermoreceptors ( hot and cold surface)

• Ruffini’s corpuscles: deep pressure

6. Dermatopathological terms

• Macule – flat spot on skin with color (freckle)

• Wheal – round and temp. elevation of skin (hives)

• Papule - solid elevated area, epidermal and papillary (insect bite)

• Nodule - large papules extending into subcutaneous layer (cyst)

• Vesicle - papule with fluid core (varicella zoster virus)

• Pustule - papule with pus core (acne)

• Erosion - ruptured vesicle (ulcer)

• Xeroderma - "dry skin"

• Hemangiomas - benign tumor in the dermis (capillary and cavernous)

• Sebaceous hyperplasia - enlargement of the sebaceous gland

• Pruritis - irritating itching sensation of the skin

• Seborrheic dermatitis - inflammation around abnormally active sebaceous glands

• Basal cell carcinoma - malignant cancer originating in the germinative layer

• Squamous cell carcinoma - malignant cancer originating in the top layer of the skin

• Malignant melanomas - metastasizing melanocytes

Skin disease

https://kikoxp.com/posts/5084/public

https://www.youtube.com/c/JeradGardnerMD/videos

SUMMARY:

https://www.youtube.com/watch?v=EGoakiTAW5A

https://www.youtube.com/watch?v=Orumw-PyNjw

https://www.youtube.com/watch?v=p4hnFf_jmvU

L6 Reproductive Organs

Female Reproductive Organ

The Ovary

Learning Objectives

• Explain the regular progression of follicular development and atresia occurring in a cyclic fashion in the primary ovary

• Describe the role of FSH and LH in driving follicular development.

• Diagram how estrogen is produced by cells of the theca interna and zone granulosa.

1. Introduction

• The histological appearance of the organs that compose the female reproductive system undergo cyclical structural changes that are not pathological.

• These organs include the ovary and uterus, and the histological changes in these organs are driven largely by four hormones:

• Follicle-stimulating hormone (FSH)

• Leutenizing hormone (LH)

• Estrogens

• Progesterone

2. Ovary

• The human ovary consists of an inner medulla and outer cortex with indistinct boundaries.

• The medulla contains the blood vessels and nerves, while the cortex is occupied by developing follicles.

• A cross-section of an ovary will reveal follicles in various stages of development.

3. Ovarian Follicle Development

A. Primordial Follicle

• An ovarian follicle progresses through several distinct phases before it releases its ovum.

• During the first five months of development, a finite number of primordial follicles form in the fetal ovary.

• These follicles consist of oocytes surrounded by a single layer of squamous follicular cells.

• These primordial follicles remain in the process of the first meiotic division.

• At puberty, they begin to develop further and become primary follicles.

B. Early Primary Follicle

• At the start of each menstrual cycle a limited number of primordial follicles are triggered to develop.

• The first apparent histological stage is the early primary follicle that consists of a central oocyte surrounded by a single layer of follicular cells which have become cuboidal.

• The zona pellucida is a thin band of glycoproteins that separates the oocyte and follicular cells.

• Proteins on the surface of sperm will bind to specific glycoproteins in the zona pellucida.

 C. Late Primary Follicle

• The late primary follicle stage is reached when the follicular cells proliferate into a stratified epithelium known as the zona granulosa.

• The zona pellucida enlarges and can be seen even more clearly.

D. Secondary Follicle

• The characteristic feature that distinguishes secondary from primary follicles is the appearance of a follicular antrum within the granulosa layer.

• The antrum contains fluid which is rich in hyaluronan and proteoglycans. There is increase in cell layers of the zone granulosa, the thicker zona pellucida, and larger oocyte.

• At this stage, a layer of cells outside the follicle become evident. These cells compose the theca interna and contribute to the production of estrogens.

Secondary Follicle (cont’d)

• The production of estrogen requires both the cells of the theca interna and granulosa cells.

• Estrogens are produced from cholesterol through a multi-step process that requires several different enzymes.

• Neither the cells of the theca interna nor the granulosa cells contain all of the enzymes necessary to convert cholesterol into estrogens.

• Theca cells contain enzymes that catalyze the initial conversion of cholesterol into androgens but lack aromatase that carries out the final steps of converting androgens into estrogens.

• Consequently, androgens produced by theca cells diffuse into the granulosa cells which contain aromatase but lack the enzymes for the initial steps in estrogen synthesis.

• The theca cells are in a better position to catalyze the initial steps in estrogen synthesis because they are closer to blood vessels and can take up LDL to obtain cholesterol.

E. Graafian Follicle

• The Graafian follicle is the stage after the first meiotic division has completed but before ovulation.

• The oocyte is now a 2N haploid (secondary oocyte) and located eccentrically. The follicle is characterized by a large follicular antrum that makes up most of the follicle.

• The oocyte is surrounded by the zona pellucida and a layer of several cells known as the corona radiata.

• When released from the Graafian follicle and into the oviduct, the ovum will consist of three structures: oocyte, zona pellucida and corona radiata.

F. Corpus Luteum

• After release of the ovum, the remaining cells of the granulosa and theca interna form the corpus luteum.

• The center contains the remains of the blood clot that formed after ovulation.

• Surrounding the clot are glanulosa lutein cells and on the outside theca lutein cells. These cells produce progesterone and to a lesser extent cholesterol.

Corpus Luteum (Cont’d)

• The granulosa lutein cells have an appearance characteristic of steroid-producing cells, with pale cytoplasm indicating the presence of lipid droplets.

• Theca lutein cells are smaller and more deeply stained. Blood vessels penetrate into region of the granulosa lutein cells allowing them to take up cholesterol to be used to synthesize progesterone.

• The activity of the cells of the corpus luteum is sustained by luteinizing hormone.

• If the ovum is fertilized and implants in the uterine wall, human chorionic gonadotropin replaces leutenizing hormone to sustain the activity of the cells in the corpus luteum.

G. Corpus Albicans

• If fertilization does not occur, the cells of the corpus luteum remain active for roughly 14 days until the levels of LH fall and the corpus luteum involutes to form the corpus albicans.

• The secretory cells of the corpus luteum degenerate, are phagocytosed by macrophages and replaced by fibrous material.

H. Atretic Follicle

• Each menstrual cycle, several primordial follicles are stimulated to continue development but only one follicles completes development to release an ovum.

• The other follicles degenerate through a process called atresia which can occur at any stage of development.

• During atresia, granulosa cells undergo apoptosis and are replaced by fibrous material.

• The oocyte degenerates and the basement that separated the oocyte from granulosa cells thickens to become the glassy membrane.

Male Reproductive Organ

The Testis

Learning Objectives

• Describe the histological organization of the testis and the process of spermatogenesis in the germinal epithelium of the seminiferous tubule.

• Explain the importance of each portion of the duct system and accessory glands of the male reproductive tract.

• Explain the structural and functional significance of the blood-testis barrier.

1. Testis

• The testis contain several important cell types that are important to understand. The first two of these are found in the germinal epithelium , the layer of the seminiferous tubule in which gamete production and development occurs.

2. The Convoluted Seminiferous Tubules

• These tubules are enclosed by a thick basal lamina and surrounded by 3-4 layers of smooth muscle cells (or myoid cells).

• The insides of the tubules are lined with seminiferous epithelium, which consists of two general types of cells: spermatogenic cells and Sertoli cells.

3. Spermatogenic cells

A. Spermatogonia

• The first cells of spermatogenesis.

• Spermatogonia remain dormant until puberty. They are always in contact with the basal lamina of the tubule.

• Two types of spermatogonia can be distinguished in the human seminiferous epithelium:

• Type A spermatogonia have a rounded nucleus with very fine chromatin grains and one or two nucleoli. They are stem cells which divide to form new generations of both type A and type B spermatogonia.

• Type B spermatogonia have rounded nuclei with chromatin granules of variable size, which often attach to the nuclear membrane, and one nucleolus. Although type B spermatogonia may divide repeatedly, they do not function as stem cells and their final mitosis always results in the formation of primary spermatocyte.

B. Primary spermatocytes

• Lie in the cell layer luminal to the spermatogonia.

• They appear larger than spermatogonia.

• A large number of primary spermatocytes is always visible in cross-sections through seminiferous tubules.

• Cell divisions, from the formation of primary spermatocytes and onwards, to the production of the spermatocytes, are incomplete. The cells remain connected by bridges of cytoplasm.

• The completion of the first meiotic division results in the formation of secondary spermatocytes.

C. Secondary spermatocytes

• Smaller than primary spermatocytes.

• They rapidly enter and complete the second meiotic division and are therefore seldom seen in histological preparations.

• Their division results in the formation of spermatids.

D. Spermatids

• Lie in the luminal part of the seminiferous epithelium.

• They are small (about 10 µm in diameter) with an initially very light (often eccentric) nucleus.

• The chromatin condenses during the maturation of the spermatids into spermatozoa, and the nucleus becomes smaller and stains darker.

• The terminal phase of spermatogenesis is called spermiogenesis and consists of the differentiation of the newly formed spermatids into spermatozoa

F. Spermatozoa

• The mature human spermatozoon is about 60 µm long and actively motile. It is divided into head, neck and tail.

4. Spermatogenesis

• It takes about 48 days from the time cells enter meiosis until morphologically mature spermatozoa are formed. Depending on the length of reproduction of spermatogonia (which is not precisely determined) it takes approximately 64 days to complete spermatogenesis.

• Spermatogenesis is regulated by follicle stimulating hormone (FSH), which in males stimulates the spermatogenic epithelium, and luteinizing-hormone (LH), which in males stimulates testosterone production by Leydig cells in the interstitial tissue.

5. Sertoli cells

• Far less numerous than the spermatogenic cells and are evenly distributed between them.

• Their shape is highly irregular - columnar is the best approximation.

• Sertoli cells extend from the basement membrane to the luminal surface of the seminiferous epithelium.

• Processes of the Sertoli cells extend in between the spermatogenic cells (cell limits are therefore not clearly visible in the LM).

• The nucleus of Sertoli cells is ovoid or angular, large and lightly stained and often contains a large nucleolus.

• The long axis of the nucleus is oriented perpendicular to wall of the tubule. A fold in the nuclear membrane is characteristic for Sertoli cells but not always visible in the LM.

Sertoli cells (cont’d)

• Lateral processes of Sertoli cells are interconnected by tight junctions, which are likely to be the structural basis for the blood-testis barrier.

• Spermatogonia and primary spermatocytes are located in the basal compartment, other cellular stages of spermatogenesis are located in the adluminal compartment.

• Tight junctions may temporarily open to permit the passage of spermatogenic cells from the basal into the adluminal compartment.

• Sertoli cells provide mechanical and nutritive support for the spermatogenic cells.

6. Interstitial tissue

• Leydig cells

• Located in the interstitial tissue between the convoluted seminiferous tubules, constitute the endocrine component of the testis.

• They synthesise and secrete testosterone.

• Leydig cells occur in clusters , which are variable in size and richly supplied by capillaries.

• The cytoplasm is strongly acidophilic and finely granular. The nucleus is large, round and often located eccentric in the cell.

7. Ducts of the Testis

• Spermatozoa pass via the tubuli recti (low columnar epithelium) and the rete testis (flattened or cuboidal epithelium) into numerous ductuli efferentes, which are lined by a columnar epithelium, which consists of both absorptive and ciliated cells.

• The height of the two cells types which form the epithelium of the ductuli efferentes is variable which gives the lumen a characteristic wavy outline.

• The ductuli efferentes leave the testis and open into a common duct, the ductus epididymidis (about 6 m long!).

• It is lined by a very tall pseudostratified columnar epithelium. Most cells of the epithelium, also called principal cells, have long stereocilia. Stereocilia are non-motile structures, which in the EM resemble large microvilli.

• Towards the basal lamina we see a number of small nuclei, which belong to the basal cells of the ductus epididymidis. These cells regenerate the epithelium.

• Peristaltic contractions of smooth muscle cells surrounding the ductus epididymidis move the spermatozoa towards the middle segment of the duct, which is the site of final functional maturation of the spermatozoa - now they are motile.

• The terminal segment of the ductus epididymidis is the site of storage of the mature spermatozoa. Smooth muscle fibres of the terminal part of the ductus epididymidis do not contract spontaneously.

• They contract during sexual stimulation concurrently with the contraction of the musculature of the duct into which it opens, the vas deferens.

8. The Vas deferens (or ductus deferens)

• The mucosa of the vas deferens forms low longitudinal folds. It is

lined by a pseudostratified columnar epithelium. Similar to the epididymis, cells have long stereocilia.

• The lamina propria is unusually rich in elastic fibres.

• The muscularis is well developed (up to 1.5 mm thick) and consists of a thick circular layer of smooth muscle between thinner inner and outer longitudinal layers.

• The vas deferens is surrounded by an adventitia.

SUMMARY:

https://www.youtube.com/watch?v=1cskfSs7mAs

https://www.youtube.com/watch?v=QUY9pJsvNlU

https://www.youtube.com/watch?v=EQj0wogxa_Q

https://www.youtube.com/watch?v=krSMZDsjLuU

https://www.youtube.com/watch?v=QtCjQYosj_g

https://www.youtube.com/watch?v=nLmg4wSHdxQ

https://www.youtube.com/watch?v=yAy1-RrOKG4

https://www.youtube.com/watch?v=PV5ADdZ3PMg

https://www.youtube.com/watch?v=V2z6wpCbqjg

https://www.youtube.com/watch?v=6iFe7noKujI

https://www.youtube.com/watch?v=mUVy9-dclQU

https://www.youtube.com/watch?v=XiOPMzq34N0

L7 The Digestive Tract

Learning Outcomes:

 Name the parts of the GIT & the primary function of each.

 Compare the GIT organs in terms of the four(4) layers comprising their walls & relate any structural variations to differences in organ function.

 Know the distinguishing regional structure of each GIT component.

 Identify the organ, region, cell types present & type of section in a micrograph of any part of the GIT.

1. Components of GIT

 Series of organs forming a long muscular tube –continuous lumen opens to the exterior at both ends.

2. Fx. of GIT system

 Aids ingestion, mastication & salivation of food in the oral cavity.

 Transports & digest food material (bolus) from the oral cavity through the esophagus into the stomach & SI.

 Mixes bolus with gastric juices to form chyme in the stomach.

 Absorbs nutrients in the SI that are transported by the bloodstream to the liver for metabolism.

 Reabsorbs water from digested food & eliminates indigestible material in the LI.

 Stores feces in the rectum for defecation through anal canal.

 Mechanical digestion:

chewing food in mouth.

action of 3 smooth muscle layers of stomach.

 Chemical digestion (secretion of):

gastric juices (mucus, HCl, pepsin).

pancreatic enzymes.

 Movement of food material through GI system:

1-way, wave-like smooth muscle motility/peristalsis of esophagus, stomach & intestines.

 Passage of food from 1 organ to another

reflexes (swallowing & defecation).

relaxation & closure of sphincter (esophageal & pyloric sphincter).

valves (ileocecal).

3. General structure features of GIT

 Each organ has 4 concentric layers:

 Mucosa (epithelium, lamina propria, muscularis mucosae).

 Submucosa.

 Muscularis externa (inner circular, outer longitudinal).

 Serosa/adventitia.

4. Simplified schematic diagram of the layers in the walls of GIT

5. Mucosa layer

 Borders the lumen.

 Has 3 parts:

 Epithelium

 Stratified squamous = oral cavity, esophagus & anal canal.

 Simple columnar = stomach, intestines & rectum.

 Lamina propria

 Loose CT (BVs & LVs).

 Muscularis mucosae

 Thin, smooth muscle layer (bordering submucosa).

6.  Submucosa layer

 Dense, irregular CT (BVs , LVs & submucosal (Meissner’s) plexus of nerves).

 Some organs contain glands & lymphoid nodules.

7. Muscularis externa

 Consist of 2 layers of smooth muscle throughout most GIT :

 Inner circular& outer longitudinal layer.

 In betw. lies myenteric (Auerbach’

s) plexus.

8. Serosa & adventitia...

 Outer covering – differs to location.

i) Adventitia = esophagus & rectum.

=retroperitoneal organs (duodenum, ascending & descending colon)

merges with surrounding CT 

ii) Serosa = intraperitoneal organs (stomach, jejunum, ileum, transverse & sigmoid colon).

9. Stomach

 Fx: temporarily holds ingested food, adding mucus, acid & digestive enzyme pepsin.

 Contractions blend the mixture--chyme.

General structure:

 Mucosa:

 Epithelium: Simple columnar epithelium.

 Lamina propria: numerous gastric glands.

 Muscularis mucosae: 2-3 layers.

 Submucosa:

 Loose CT, BVs & LVs.

 Muscularisexterna:

 3 layers.

 Serosa

Gastric mucosa:

3 regions of a gland:

Mucosa epithelial cell types:

A. Surface mucous cells--simple columnar epithelium.

 Loc: lines the stomach, gastric pits & much of the isthmus.

 Fx: secrete neutral mucus – protect stomach’s surface from HCl.

B. Undifferentiated cells--low columnar cells.

 Loc: lines the neck.

 Move upward/deeper& differentiate.

C. Mucous neck cells

 Loc: in betw. parietal cells in the neck.

 Fx: secrete acidic mucus.

D. Parietal (oxyntic) cells

 Loc: in betw. mucous neck cells in the neck.

 Large, round--pyramidal, with 1 or 2 central nuclei.

 Pale, acidophilic cytoplasm.

 Fx: secrete HCl & intrinsic factor.

E. Chief (zymogenic) cells

 Loc: predominate in base.

 Smaller than parietal cells.

 Basophilic cytoplasm.

 Fx: secrete pepsinogen & some lipase.

F. Enteroendocrine cells

 Loc: In base.

 Fx: produce histamine & gastrin - enhancing acid production.

Regional differences:

A. Cardia

a) Surrounds the entry of the esophagus.

b) Cardiac glands = shallow pits & coiled baseswith wide lumen.

c) Fx: produce mainly mucus & lysozyme.

B. Fundus & body

a)stomach’s largest region, cardia: pylorus.

b)fundic glands = shallow pits & long glands.

c)abundant parietal & chief cells.

C. Pylorus

a) 4-5 cm before duodenum.

b)pyloric glands = deep pits & short glands.

c)less parietal & chief cells.

d)large, pale-staining mucus-secreting cells.

10. Small intestine

 Receives:

i) chyme from stomach.

ii) bile from liver.

iii) digestive enzymes from pancreas.

 Fx: absorb hydrolyzed nutrients & transfer to blood & lymphatic capillaries.

General structure:

 Mucosa:

 Villi with epithelial lining.

 Lamina propria – intestinal gland.

 Muscularis mucosae.

 Submucosa:

 Submucosal (Brunner’s) gland.

 Plicae circulares (valves of Kerckring)--both mucosa & submucosa.

 Muscularis externa:

 2 layers.

 Adventitia & serosa.

Mucosa of the SI:

A. Villi:

a) Epithelium = simple columnarepithelium, fingerlike mucosal projections.

b) L.propria = loose CT, blood capillaries & central lacteal.

c) M.mucosae.

B. Intestinal glands (crypts of Lieberkuhn):

a) Extend into l.propria below villi.

b) Lined by absorptive, Goblet cells, Paneth, enteroendocrine & undifferentiated cells.

Mucosa epithelial cell types:

A. Enterocytes (absorptivecells):

a) Loc: Predominant cells covering villi & small no.s in crypt.

b) Microvilli extending from apical surfaces.

B. Goblet cells:

a) Loc: betw. absorptive cells.

 increase from duodenum to ileum.

b) Fx: secrete mucus on epithelial surface, protect from pancreatic enzyme & bacterial invasion.

C. M cells:

a) Loc: overlie solitary lymphoid nodules (Peyer’s patches).

b) apical surface have small folds (not microvilli).

c) Fx: endocytose Ag from lumen & pass to lymphoid cells.

D. Paneth’s cells:

a) acidophilic secretory granules containing lysozymes.

b) Loc: base of crypts.

b) fx: host defence against microbes.

E. Enteroendocrine cells:

a) Loc: crypts.

b) Fx: i) produce secretin - increase pancreatic, biliary bicarbonate & H2O secretion.

ii) cholecystikinin - increase pancreatic secretion & gallbladder contraction.

iii) gastric inhibitory peptide - decrease gastric acid production.

iv) motilin - increase gut motility.

F. Undifferentiated (stem) cells:

a) Loc: base of crypts.

b) Fx: replace mucosal epithelial cells – turnover – mitosis of stem cells.

c) Mitotic activity - increasingly staining dark-staining chromosome.

Stem cells differentiates into:

Regional differences:

 Duodenum:

A. Mucosa:

a) epithelial cells: produce alkaline secretion (pH 8.1-9.3).

b) prominent villi & few goblet cells.

B. Submucosa: duodenal (Brunner’s) gland.

 Jejunum:

A. Mucosa:

a) Villi, many plicae circulares & intermediate number goblet cells.

B. Submucosa:

a) No Brunner’s gland.

 Ileum:

A. Mucosa:

a) Fewer villi; short & broad-tipped (club-like).

b) Epithelial cells: abundant goblet cells.

c) L.propria: lymphoid nodule clusters (Peyer’s patches).

SUMMARY:

https://www.youtube.com/watch?v=_kvoEDmEK2I

https://www.youtube.com/watch?v=WBkEf8PWcxg

https://www.youtube.com/channel/UC57M7uN2OITkb5CCILXhduA/videos

https://www.youtube.com/watch?v=djScwPnPeG8

https://www.youtube.com/watch?v=E4Eq_Zvli48

https://www.youtube.com/c/DrNaveenaSwargam/videos

https://www.youtube.com/watch?v=J7-0mo0b26Q

https://www.youtube.com/watch?v=Dq8FkYH9VvY

https://www.youtube.com/watch?v=FciRqrV-L6w

https://www.youtube.com/watch?v=cArB7k8ROZc

L8 The Respiratory System

1. Learning Outcomes

 Name the three divisions of the respiratory system and the components of each.

 Compare the right and left lungs.

 Describe the respiratory tract walls in terms of the arrangement, composition and function of their layers and cells.

 Distinguish between respiratory tract components based on differences in wall structure.

 Identify the organ, tissues and cell types present and distinguish among the various components of the respiratory system.

 The respiratory system extends from:

-nasal orifices--periphery of the lungs & pleura.

2. Structure & fx of the lungs

 Fx: exchange gases between inspired air &the blood.

A) Inspired air passes from trachea to left & right bronchus.

B) Each bronchus branches giving rise to smaller airways.

C) BronchiolesTerminal bronchiolesRespiratory bronchiolesAlveolar ducts.

D) Blind-ended alveolar sac (gas exchange occurs).

3. Three principle subdivisions of the respiratory system & their fx.s

A. AIR CONDUCTING PORTION

walls of this system of tubes are specialized to carry air to & from the site of gas exchange.

conditions the air; warms moisten & cleans it.

B. RESPIRATORY PORTION

structures which allow gas exchange betw air & blood.

C. VENTILATION APPARATUS

 used for moving air in & out of the lungs.

-diaphragm, rib cage, intercostal muscles & lung’s elastic CT.

4. Components of the 2 basic portions

 Conducting portion:

a. Nasal cavity & oral cavity.

b. Nasopharynx & larynx.

c. Trachea.

d. Bronchi.

e. Bronchioles.

f. Terminal bronchioles.

 Respiratory portion:

a. Respiratory bronchioles.

b. Alveolar ducts.

c. Alveoli used for gas exchange.

5. Wall structure of respiratory tract

A. Epithelium composed of

various types depending on what part of the respiratory tree.

B. Lamina propria composed of

fibroelastic tissue containing lymphocytes.

C. Smooth muscle (1 layer)

lies deep to the mucosa (except in trachea).

regulates luminal diameter.

D. Submucosal layer

underlying smooth muscle layer.

contains serous & mucous glands.

E. Cartilage

lies outside submucosa.

prevent tract from collapsing.

F. Adventitia composed of

collagen & elastic fibers.

allow for expansion followedby passive contraction.

6. Eg. Wall structure of trachea 

7. Respiratory epithelium components

 Mostly ciliated pseudostratified columnar with goblet cells.

 As resp. tract branches & luminal diameter decrease:

a) decrease epithelium height.

b) loses goblet cells, followed by cilia.

 Epithelial cell types:

a) ciliated columnar cells--sweep contaminated mucus.

b) mucous goblet cells--secrete mucus.

c) basal cells-small round cells on lying on the basal lamina.

8. Epithelial cell types

9. Lamina propria & submucosa components

 Consist of loose CT – contains mucous & serous glands in upper tract (from nasal cavity to bronchi).

 Lymphoid aggregates of variable sizes.

 Blood & lymph vessels.

 Elastic fibre content - increase towards alveoli.

10. Skeletal CT components

 Fx: as support.

– cartilage & bone in nasal cavity.

- cartilage (only) in larynx & gradually decrease.

- disappears at bronchioles.

11. Smooth muscle

 Begins in trachea – joins open ends of the C-shaped tracheal cartilage.

 Bronchi – many layers encircle the walls in a spiral.

 Muscle layer thickness decrease - disappears at alveolar ducts.

12. Smooth muscle of trachea

C=cartilage

M=mucosal layer

T=muscular layer

13. Trachea

 ~10 cm in length.

 16-20 C-shaped cartilage rings (open ends directed posteriorly).

 Opening is bridged by: 

a)fibroelastic ligament.

b)smooth muscle bundles (trachealis muscle).

Mucosal epithelium (E) - the majority of the cells form tall

pseudostratified, columnar, ciliated epithelium.

Sits on unusually thick basement membrane (BM).

Interspersed among the columnar, ciliated epithelial cells are a number of different cell types including, e.g.:

i) Goblet cells (G)

ii) Basal cells (B)

Lamina propria - contains many lymphocytes that are supported by a meshwork of elastic & collagen fibers.

A band of elastic fibers called the membran elastica interna separates the mucosa from the sub mucosa.

The submucosa - composed of loose CT & contains the secretory components of serous & mucous glands whose ducts empty into the tracheal lumen.

The adventitia - most prominent due to presence of cartilage.

14. Primary bronchi

 Basic structure of bronchi similar to trachea, but differs in several details:

 Respiratory epitheliumless tall & decrease goblet cells.

 Lamina propriamore dense with increase elastin quantity.

separated from submucosa by a discontinuous layer of smooth muscle.

 Smooth muscleprogressively more prominent in smaller airways.

 Submucosal layerdecrease serous & mucous glands.

 CartilageFlattened, interconnected plates (not C-shaped).

15. Cytology specimen by bronchial brushing

 Tapered shape of the tall columnar ciliated epithelial cells.

 Nuclei located towards the base.

16. Secondary bronchi

3 in right lung & 2 in left lung.

Each extend into a pulmonary lobe of the lung & thus are sometimes called lobar bronchi (3 lobes on the right, 2 on the left).

The intrapulmonary bronchi are histologically similar to the trachea & primary bronchi.

17. Tertiary bronchi

 Cartilage ringsdecrease to irregular plates of cartilage.

 A band of spirally wound smooth muscle present in lamina propria.

 Epitheliumsimple columnar cells decrease height & decrease cilia. decrease goblet cells.

 Adventitialymphatic nodules may be present.

18. Bronchiole

 Diameter < 1mm.

 Bronchioles lack cartilage.

 Smooth muscle layerrelatively thicker (relative to lumen size).

 Epitheliumnon-ciliated Clara cells present. simple columnarsimple cuboidal with fewer cilia.

 Submucosano glands.

19. Clara cells

20. 3 types of bronchiole

A) Large (muscular) bronchioles - branch repeatedly, final branches are the terminal bronchioles.

Epitheliumciliated simple columnar--cuboidal with interspersed clara cells.

B) Terminal bronchioles - form connection between  “larger” bronchioles & respiratory bronchioles. 

Epitheliumlow columnar/simple cuboidal with lots of clara cells.

C) Respiratory bronchioles - form connection betw terminal bronchioles & alveolar ducts.

- transitional structure connecting the conducting zone--respiratory zone.

- interrupted by thin-walled saccular evaginationsalveoli.

EpitheliumClara cells are abundant , a few ciliated cells, no goblet cells.

21. Gas exchange Spaces & the Interalveolar Wall

22. Alveolar ducts

 Walls of the ducts consist entirely of alveolar openings.

 Epithelium

squamous--called alveolar epithelium.

lining decrease to small knobs of smooth muscle.

small knobs resting atop a thin septum that separates adjacent alveoli.

 Duct terminates in a cluster of alveoli that share a common, dilated chamber - called an alveolar sac.

23. Alveoli

 Alveoli lined by:

squamous epithelium (Type I pneumocytes).

Fx: remove pulmonary surfactant & small particles from alveolar surfaces.

cuboidal-like (Type II pneumocytes).

Fx: produce surfactant.

alveolar macrophages (dust cells).

Fx: -remove debris that escapes mucus & cilia. -phagocytose blood cells entering alveoli due to heart failure.

 Beneath pneumocytes lie a CT membrane:

-separates the alveoli from pulmonary capillaries BUT allows rapid & efficient gas diffusion.

SUMMARY:

https://www.youtube.com/watch?v=xvbn8VrxSNM

https://www.youtube.com/watch?v=ne6sJa6sOu8

https://www.youtube.com/watch?v=ywMqgeyzUU8

https://www.youtube.com/watch?v=kacMYexDgHg

https://www.youtube.com/watch?v=AnT_1wLIzFM

https://www.youtube.com/watch?v=trW_5riT0Kk

https://www.youtube.com/watch?v=zDIdIo-WERs

https://www.youtube.com/watch?v=W1wHxgpxTlA

https://www.youtube.com/watch?v=mgFRoC3LRfI

https://www.youtube.com/watch?v=S59JwFCjNhc&list=PL2rpvfNeooNHjnQSPIEf9iajPFv8oNuPQ

https://www.youtube.com/watch?v=fuw2UyTj14o&list=PL2rpvfNeooNE5E4jKX9JOrXITW-kIfZCc

L9 Renal System

1. Learning Outcomes

List the organs of the urinary system & describe the role of each in the system’sfunctions.

Identify the structures & regions visible in a frontal section of a kidney & describetheir functions.

Describe the structure, function & location of each component of a nephron &identify these components in histologic sections.

Describe the function of juxtaglomerular apparatus & identify its components.

Trace the flow of urinary filtrate from Bowman’s space to the exterior, naming inorder the tubules & components of the urinary tract & describing any changes infiltrate composition & epithelial lining that occur in each component.

2. General features of the system

Urinary tract

3. Kidney

Paired, bean-shaped, retroperitoneal organs.

Fx: to remove waste & excess water from the body.

Structural & functional subdivisions

A) Outer cortex -underlies dense CT capsule.

B) Inner medulla –partly surrounds renal hilum.

C) Medullary rays –extensions of medulla into cortex.

D) Renal column –extensions of the cortex into medulla region.

E) Renal pyramid.

F) Renal hilum:

i) renal sinus.

ii) renal artery & vein.

iii) renal pelvis.

iv) adipose tissue.

3. Flow of Urine

Urinary space

↓

Proximal convoluted tubule (PCT)

↓

Loop of Henle: Descending thick limb

↓

Loop of Henle: Descending thin limb

↓

Loop of Henle: Ascending thin limb

↓

Loop of Henle: Ascending thick limb

↓

Distal convoluted tubule (DCT)

↓

Collecting duct

↓

Papillary duct

4. Blood supply of nephron

Interlobular arteries.

↓

Afferent arteriole.

↓

Glomeruli(cortex).

↓

Efferent arteriole.

↓

Peritubularcapillaries (cortex).

↓

Vasarecta (medulla).

↓

Interlobular veins.

5. Components distinguished grossly

Renal cortex

Renal medulla

Renal column

Renal pelvis

Major calyx

Fat

Renal sinus

Minor calyx

6. Components of renal cortex & renal medulla

A) Renal cortex comprises:

i) renal corpuscle.

ii) PCT& DCT.

iii) peritubular capillaries.

iv) medullary rays.

B) Renal medulla comprises:

i) 8-10 renal lobes (pyramid).

ii) collecting ducts.

iii) loops of Henle.

iv) vasa recta.

D) Medullary rays –extension of medullary tissue penetrating cortex.

-comprise clusters of collecting tubules & ducts.

-1medullary ray occupies centre of each renal lobule.

E) Renal lobes –each lobe: medullary pyramid + associated cortex.

-contains numerous renal lobules.

F) Renal lobules –each lobule: central medullary ray & all of nephrons emptying into its collecting tubules.

1 = kidney cap.        4 = Arcuate artery.

2 = medullary ray.   5 = Renal corpuscles.

3 = PCTs & DCTs.

7. Nephron Structure

Nephron: regulates water & soluble substances by filtering blood.

A. Renal corpuscle:filters out water & tiny particles in blood.

a) Consist of:

i) a glomeruluscovered by Bowman’s capsule (filtration barrier).

ii) vascular pole.

iii) urinary pole.

b) Glomerulus:

i) small tuft of capillaries with fenestrae covered by diaphragms.

ii) modified smooth muscle--mesangial cells.

--fx mesangial cell: clears off occasional build-up of cellular debris & some Ag-Ab complexes by phagocytosis.

c) Bowman’s capsule (double-walled epithelial chamber):

i)inner wall: visceral layer--consist of podocytes (have long primary processes, from which arise interdigitating foot processes (pedicels) that grasp glomerular capillaries).

ii)outer wall: parietal layer--simple squamous epithelium.

iii)chamber between visceral & parietal layer: urinary/Bowman’s space.

Filtration barrier

m= mesangialcell

p= podocyte

e= endothelial cell

B= Bowman's space

c= capillary

podocytes= have long primary processes, from which arise interdigitating foot processes (pedicels) that grasp glomerular capillaries.

pedicels

Primary processes

podocyte

c) Vascular pole:

i) Afferent arterioleglomerularcapillariesefferentarteriole.

ii) Lies opposite urinary pole.

d) Urinary pole:

i) Side of corpuscle where PCT exits.

e) Glomerularbarrier component DON’T ALLOW

x blood cells & large proteins from entering urinary space.

--trapped molecules in basal lamina removed by--mesangial cells.

B. PCT:fluid absorption, Na resorption & pH regulation.

a) Begins at urinary pole.

b) Epithelial lining: 

simple low-columnar-to-cuboidal cell.

have abundant long microvilli (forms brush border).

c) Fx: i) absorb approximately 2/3 Na from filtrate; water follows passively.

ii) All glucose, aa, acetoacetate, vits & small proteins reabsorbed.

d) Convoluted partlies in cortex.

Straight portionalso called thick descending limb of the loop of Henle.

e) PCT=longest part of nephron& most often encountered tubule type in cortical sections.

C. Loop of Henle: reabsorbs water & certain ions from urine.

a) U-shaped epithelial tube.

b) Consist of: 

thick & thin descending limbs.

thin & thick ascending limbs.

c) Extends from PCT (cortex)--dips into medulla--returns to cortex.

d) Epithelial lining: 

-thick limbs--simple low-columnar-to-cuboidal cells.

-thin limbs--simple squamous cells.

e) Fx:

-descending limbreabsorbs water & certain ions from urine.

-ascending limb impermeable to water & pumps out ions.

1 -thin limb = simple squamous.

2 –thick limb = simple cuboidal.

Thick descending limb? Thick ascending limb?

D. DCT: transports ions.

a) Last segment of nephron; lies in cortex.

b) Epithelial lining: 

low cuboidal cells.

lack brush border (lumen appear wider).

c) Fx: -transports ion.

i) presence of aldosterone (adrenal cortex)epithelium remove more Na from & add K to the fluid.

ii) presence of atrial natriuretic factor (right atrium of the heart)increases Na excretion.

d) Presence of macula densa

tightly packed columnar cells at the point near vascular pole.

point of the contact between DCT & an afferent arteriole.

Macula densa?

Which is PCT? Which is DCT?

E. Cortical & juxtamedullary nephrons

a) Renal corpuscles (2 types):

i) throughout cortex.

called cortical nephrons (85%).

ii) closest to medulla.

called juxtamedullarynephrons (15%).

It is located throughout the cortex.

8. Collecting tubules (CT) & ducts (CD)

A) CT fx: receive hypotonic/isotonic urine from nephron

B) Empty into largerCD.

CD fx: -final role in forming hypertonic urine.

-withADH--becomepermeabletowater.

C) Blocklike lining cells

distinct intercellular borders.

D) Cuboidal in smaller tubules & columnar in larger (papillary) ducts.

E) Cytoplasm stains poorlylining cells appear clear/white.

9. Renal calyces & renal pelvis

A) Fx: Carry urine from papillary duct--minor calyx--major calyx--renal pelvis.

B) Wall layer consist of:

i) mucosa.

epithelial lining: urinary (transitional) epithelium.

CT lamina propria.

ii) muscularis.

helical meshwork of smooth muscle.

iii) adventitia.

blends into adipose tissue in renal sinus.

10. Ureters

a. Fx: Carry urine from renal pelvis to urinary bladder.

b. Ureters < lumen < renal pelvis; but wall structure similar.

c. Wall structure:

i) mucosa: epithelial lining--transitional epithelium.

ii) muscularis: helical--longitudinal near bladder.

iii) adventitia: outer layer CT.

d.Thickness of wall increases as it reaches bladder.

11. Urinary bladder

A)Fx: to store urine before being expelled; distensible muscular sac.

B) 

i) Mucosa: 

-epithelial liningtransitional epithelium.

-lamina propriainner layer(part1)&outer layer (part2).

ii) Muscularis: 

-initiallyevery direction.

-bladder neck3 layers.

iii) Serosa: 

upper part of bladder.

C) 3 layers of smooth muscle at bladder neck:

i) Inner longitudinal.

ii) Middle circular.

iii) Outer longitudinal.

#Muscularis layer-bladder neck

12. Urethra

Male urethralonger than female’s.

a) Fx: conducts both urine & seminal fluid.

b)3 main parts:

prostatic segment:

-transitional epithelium.

membranous segment:

-pseudostratified columnar epithelium.

cavernous segment:

-stratified squamous epithelium.

Female urethra

a) Fx: carries only urine.

b) Lined by: stratified squamous+patches of pseudostratified columnar.

SUMMARY:

https://www.youtube.com/watch?v=QsSdAXv5BEM

https://www.youtube.com/watch?v=HMqzOQR2QaY

https://www.youtube.com/watch?v=AlegaeaH938

https://www.youtube.com/watch?v=mxWg-jepAko

https://www.youtube.com/watch?v=-Of88XpYM3E