Epithelial Tissues Flashcards
3 germ layers of the embryo
ECTODERM - epidermis of skin and corneal epithelium of eye
MESODERM - Urinary tract, blood and lymphatic vessel lining, pericardial and pleural sac lining and peritoneal lining
ENDODERM - epithelial of respiratory tract, GI tract, liver, and many glands - thyroid, salivary
Basement membrane
Thin, flexible, acellular layer - lies between epithelial cells and the subtending connective tissue
Consists of a basal lamina - laid down by the epithelial cells
Cellular and molecular filter
The degree to which malignant cells penetrate basement membrane is highly relevant to prognosis
Simple Squamous Epithelium
- lining of blood and lymph vessels - ACTIVE TRANSPORT
- lining of body cavities (pericardium, pleura, peritoneum) - LUBRICATION
- respiratory epithelium - pulmonary alveoli - GAS EXCHANGE
- Bowman’s capsule and Loop of Henlé of kidney
- inner and middle ear
Simple Cuboidal Epithelium
- thyroid follicles - HORMONE SYNTHESIS, STORAGE & MOBILISATION
- small ducts of many exocrine glands - ABSORPTION & CONDUIT
- kidney tubules - ABSORPTION & SECRETION
- germinal epithelium (surface of ovary) - BARRIER
Simple Columnar Epithelium
- stomach lining & gastric glands - SECRETION
- small intestine & colon - SECRETION, ABSORPTION & LUBRICATION
- gallbladder - ABSORPTION
- large ducts of some exocrine glands
- oviducts - TRANSPORT
- uterus
- ductuli efferentes of testis
Pseudostratified Epithelium
- lining of nasal cavity, trachea,bronchi and bronchioles - MUCUS SECRETION FOR PARTICLE TRAPPING AND REMOVAL
- epididymis - ABSORPTION
- ductus deferens - SECRETION AND COMDUIT
- lacrimal sac
- large excretory ducts
Stratified Squamous Non-Keratinized Epithelium
- oral cavity
- oesophagus
- larynx
- vagina
- part of anal canal
- surface of cornea
- inner surface of eyelid
PROTECTION AGAINST ABRASION ADN REDUCES WATER LOSS WHILST REMAINING MOIST
Stratified Squamous Keratinised Epithelium
- surface of skin
- limited distribution in oral cavity
PROTECTION AGAINST ABRASION AND PHYSICAL TRAUMA, PREVENTS WATER LOSS, PREVENTS INGRESS OF MICROBES, SHIELDS AGAINST UV LIGHT DAMAGE
Transitional (Urinary) Epithelium
- renal calyces
- ureters
- bladder
- urethra
DISTENSIBILITY, PROTECTION OF UNDERLYING TISSUES FROM TOXIC CHEMICALS
Renewal rates of epithelium
Turnover differs depending on location and function - speeds up if injury occurs
Epidermis - from cell division in basal layer (differentiation, migration, keratinisation and death) to being sloughed off is ~ 28 days
Lining of the small intestine - replaced by regenerative cells in the base of the crypts every 4-6 days
Other epithelia only are renewed in adult hood if there is physical damage or acute toxic injury
Microvilli
Apical extensions which greatly increase the surface area for selective absorption
Stereocilia
- like very long microvilli
Have an absorptive function
Cilia
- bigger than microvilli
9: 2 structure of microtubules
Epithelia
Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line internal surfaces
