Epithelia Flashcards
Name the external surface of the body
- Skin
- Cornea of the eye
Define Epithelia
A sheet of contiguous cells of varied embryoinic origin which cover the external surface of the body and line the internal surfaces
Name the interior spaces of the body which open to the environment
- Gastrointestinal tract
- Respiratory tract
- Genitourinary Tract
Name the interior spaces of the body which do not open to the environment
- Pericardium
- Pleural Sacs
- Peritoneum
- Blood Vessels
- Lymphatics
Which epithelia are of ectodermic origin?
- Skin
- Cornea
Which epithelia are of mesodermic origin?
- All the interior spaces closed to the environment and the genitourinary tract
Which epithelia are of endodermic origin?
- Respiratory tract
- GI tract
- liver
- Many glands
What is the structure and function of the basement membrane?
- A thin, flexible, acellular layer consisting of basal lamina and reticular fibres
- It lies between epithelia and the underlying connective tissue and serves as a cellular and molecular filter as well as for adherence of epithelia
Describe simple squamous epithelia, indicating their function and a named example
- One layer thick flattened squamous cells
- Allow diffusion in the alveoli
- Line the body cavities and aid lubrication
- Line the blood and lymph vessels and allow gas exchange and cell migration
- Bowmans capsule - allow exchange
Describe simple cuboidal epithelia, including their function and named example
- Centrally located nuclei
- Main function is for secretion
- Small ducts of exocrine glands, eg pancreatic duct
- Many glands, eg thyroid
- collecting duct of nephrons
Describe simple columnar epithelia, including its function and a named example
- Basally located nuclei
- main function is for absorption
- GI tract, eg small intestine, colon, crypts of Lieberkhun, gall bladder
- Fallopian tube, ciliated
- Microvilli increase surface area
Describe Pseudostratified epithelia, including its function and named example
- One layer thick, however looks like many layers
- Found in upper respiratory tract - ciliated to assist movement of mucus to immobilise particles and lubricate larynx. Goblet cells present
- Form mucocillary esculator to eliminate trapped particles and pathogens
Are epithelia vascular or avascular?
Avascular - receive nutrients via diffusion
Describe Stratified Squamous non-keratinised epithelia, including its function and a named example
- Multiple layers of squamous cells
- Resist abraision
- Reduces water loss
- Found in Buccal Cavity and Oesophagus
- Vagina and Anal Canal
What is special about epiglottis epithelia?
-Lined with Stratified squamous on one side and Pseudostratified on the other
What is special about the epithelia of the cornea?
-Lined with stratified squamous on the outside and simple squamous on the inside
Why is it important that the vagina has a high source of glycogen?
Helps maintain the pH balance in the vagina as lactobacilli thrive under rich glycogen conditions. This maintains the pH and controls other bacteria
Why are there no goblet cells in the narrower tracts of the respiratory tract?
- Goblet cells produce mucus
- If mucus was secreted in these narrow lumens they would become blocked
- cells secrete surfactant instead
Describe keratinised stratified squamous epithelia, including its function and a named example
- Skin
- Multiple layers of cells. Cells at the apical membrane loose their nucleus and die due to lack of nutrients, water loss and keratin
- Resists abrasion
- Prevents water loss
- Barrier to microbes
- Curved edge on basolateral side of epidermis stops shearing
Describe transitional epithelium, including its function and a named example
- Multiple layers
- Distensibility
- Protection from toxic chemicals
- Urothelium (found only in urinary tract), eg ureter, urethra, renal calyces
How often is the epithelia of the skin renewed?
- From the basal layer through differentiation, migration, keratinisation and shedding it is approximately 28 days
How often is the epithelia of the small intestine renewed?
- Every 4-6 days by regenerative cells in the base of the crypts
What are cilia?
- Actin extensions which protrude from the cell and are use to mobilise particles for extrusion
What are microvilli?
- Apical extensions which greatly increase surface area for selective absorption
- Also known as ‘brush border’
What is metaplasia?
- Epithelia which are under stress undergo a change from one cell type to another in order to better cope with its surroundings
- eg pseudostratified to stratified squamous in heavy smokers
What is neoplasia?
- Tumour formation, specifically known as carcinoma in epithelia
- Benign tumours represent cellular origin
- Malignant tumours have an altered cellular structure
