Lecture 2.1: Epithelial Tissues Flashcards
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
Exterior epithelial surfaces
Skin
Surface of the cornea
Interior spaces opening to exterior with epithelial linings
Gastrointestinal Tract
Respiratory Tract
Genitourinary Tract
Interior spaces that do not open to the exterior with epithelial linings
Pericardial Sac
Pleural Sacs
Peritoneum
Blood and Lymphatic Vessels
3 Germ Layers of Embryo that epithelia derive from
Ectoderm
Mesoderm
Endoderm
Ectoderm: what epithelia derive from it?
Epidermis of skin
Corneal epithelium of eye
Mesoderm: what epithelia derive from it?
Urogenital Tract
Blood and Lymphatic Vessel Lining
Pericardial and Pleural Sac Lining
Peritoneal Lining
Endoderm: what epithelia derive from it?
Respiratory Tract
GI Tract
Liver
Glands (thyroid, thymus, salivary glands)
What are all epithelia anchored too?
An underlying basement membrane
This makes the epithelia polarised
What is a basement membrane (BM)?
Strong, flexible, sheet-like layer of extracellular matrix (ECM)
It is important in epithelial support and cellular signalling
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
Classification of Epithelia
SLIDE 10 of Lecture 2.1
Simple Squamous Epithelium: Structure
Thin ‘scale-like’ flat cells
Nuclei bulge from cell surface
Single Layer
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
Simple Squamous Epithelium: Function
Lubrication
Gas Exchange
Barrier
Passive transport of water and ions
Active transport
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
