Lecture 2.1: Epithelial Tissues Flashcards by Purva Shegunshi

What surfaces have epithelial linings? (3)

1) Exterior Surfaces
2) Interior spaces opening to exterior
3) Interior spaces that do not open to the exterior

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Exterior epithelial surfaces

Skin
Surface of the cornea

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Interior spaces opening to exterior with epithelial linings

Gastrointestinal Tract
Respiratory Tract
Genitourinary Tract

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Interior spaces that do not open to the exterior with epithelial linings

Pericardial Sac
Pleural Sacs
Peritoneum
Blood and Lymphatic Vessels

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3 Germ Layers of Embryo that epithelia derive from

Ectoderm
Mesoderm
Endoderm

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Ectoderm: what epithelia derive from it?

Epidermis of skin
Corneal epithelium of eye

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Mesoderm: what epithelia derive from it?

Urogenital Tract
Blood and Lymphatic Vessel Lining
Pericardial and Pleural Sac Lining
Peritoneal Lining

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Endoderm: what epithelia derive from it?

Respiratory Tract
GI Tract
Liver
Glands (thyroid, thymus, salivary glands)

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What are all epithelia anchored too?

An underlying basement membrane

This makes the epithelia polarised

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What is a basement membrane (BM)?

Strong, flexible, sheet-like layer of extracellular matrix (ECM)

It is important in epithelial support and cellular signalling

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What is the BM made of?

Consists of a basal lamina (type IV collagen), laid down by epithelial cells

Augmented by a layer (variable thickness) of reticular fibrils (type VII collagen), synthesised by the underlying connective tissue

The BM forms a thin, flexible, acellular layer that separates epithelial cells from the subtending connective tissue

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Classification of Epithelia

SLIDE 10 of Lecture 2.1

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Simple Squamous Epithelium: Structure

Thin ‘scale-like’ flat cells
Nuclei bulge from cell surface
Single Layer

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Simple Squamous Epithelium: Location

Lining of blood and lymph vessels
Lining of body cavities
Respiratory epithelium
Bowman’s capsule
Loop of Henle
Inner and middle ear
Intercalated pancreatic ducts

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Simple Squamous Epithelium: Function

Lubrication
Gas Exchange
Barrier
Passive transport of water and ions
Active transport

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Endothelium

Is simple squamous epithelium lining vasculature such as arteries, veins, capillaries and lymphatic vessels

Can exchange gases and nutrients, allow certain blood cells to enter tissues and can regulate platelet coagulation

Mesothelium

Is epithelium lining the body cavities (pleural and abdominal)

Simple Cuboidal Epithelium: Structure

Simple Cuboidal Epithelium: Location

Thyroid follicles
Small ducts of many exocrine glands
Kidney tubules
Respiratory bronchioles
Mesothelium of ovary

Simple Cuboidal Epithelium: Functions

Absorption and conduit (exocrine glands)
Absorption, conduit and secretion (kidney tubules)
Barrier/ covering (ovary)
Hormone synthesis and mobilisation (thyroid)

Simple Columnar Epithelium: Structure

Single Layer
Tall/ Elongated
Slender

Simple Columnar Epithelium: Function

Secretes acid, digestive enzymes and mucus
Concentrates bile by absorbing water and electrolytes
Removes sodium ions
Lubrication
Transport
Lining of some larger exocrine ducts

Simple Columnar Epithelium: Locations

Stomach lining and gastric glands
Small intestine and colon
Gallbladder
Large ducts of some exocrine glands
Oviducts
Uterus
Ductuli efferentes of testis

How is surface area of small intestine increased?

Plicae circulares
Villi
Microvilli

What are cillia?

They are 'hair like' organelles Can be motile or non-motile They are longer and wider than microvilli Transient actions between dynein and microtubules allow ciliary movement

Pseudostratified Columnar Epithelium: Location

Nasal cavity Bronchi, trachea Epididymis (extending into ductus vas deferens) Large excretory ducts (salivary glands) Auditory tube and tympanic cavity Lacrimal sac Male urethra

Pseudostratified Columnar Epithelium: Structure

Appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. Nuclei of neighbouring cells appear at different levels rather than clustered in the basal end.

Pseudostratified Columnar Epithelium: Function

Secretion and conduit Absorption Particle trapping and removal

Stereocilia

They are giant microvilli Long Immotile Supported by actin They increase SA for absorption/phagocytosis and secretion

Stratified Squamous Epithelium (non-keratinised): Locations

Oral Cavity Oesophagus Larynx Vagina Part of anal canal Surface of cornea Parts of the inner surface of eyelid Distal urethra

Stratified Squamous Epithelium (non-keratinised): Functions

Protection from abrasion Reduces water loss (but is moist itself) Secretion (vagina)

Stratified Squamous Epithelium (non-keratinised & keratinised): Structure

Flattened epithelial cells arranged in layers upon a basal membrane Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity.

Stratified Squamous Epithelium (keratinised): Functions

Protection against abrasion and physical trauma Prevention of water loss Prevention of microbe ingress Shield against UV damage

Stratified Squamous Epithelium (keratinised): Location

Skin Epidermis of palm of hand (thin skin) Epidermis of sole of foot (thick skin) Masticatory Mucosa

Transitional Epithelium (Urothelium): Location

Renal Calyces Ureters Bladder Proximal Urethra

Transitional Epithelium (Urothelium): Structure

Organisation changes from small basal to intermediate layers of columnar cells, with a superficial layer of bulbous umbrella cells (arrowed) The epithelium is distensible

Transitional Epithelium (Urothelium): Function

Distensibility (stretching by internal pressure-e.g. for urine) Protection of underlying tissue (from cytotoxic effects of urine)

Renewal of epithelia

There continue to proliferate through life to Maintain protective layers Cell renewal rates of epithelia tend to be higher than other (permanent) tissues Cell division in basal layer to it being sloughed off is c. 28 days Enterocytes (intestinal lining) replaced c. 3.48 days (+ SD 1.55) Respiratory epithelium takes longer to regenerate