7 Epithelium

Question 1

Epithelium:
Definition?
Origin?

Answer 1

Sheets of contiguous cells, varied embryonic. Origin, that cover the external surface of the body and line the internal surfaces including the body’s vessels

Origin:derived from all the embryological germ layers: ectoderm, endoderm, mesoderm.

Question 2

Surfaces with epithelial linings:
Exterior surface?
Interior spaces opening to exterior?
Interior spaces which do not open to the exterior?

Answer 2

1. Skin
2. GI, resp, urinary tract
3. pericardial sac, peural sac, blood and lymphatic

Question 3

Simple cell types (one cell thick)

Answer 3

Simple squamous, cuboidal, columnar and pseudostratified columnar

Question 4

Striated/ compound (more than one cell layer thick)

Answer 4

Squamous, cuboidal, columnar and transitional (only found in the urinary tract)

Question 5

Simple Squamous Epithelia

Function and location??

Answer 5

Function: fast material exchange and barrier to fluids. Also barrier in the brain and CNS.
Example: mesothelium

Location: bowmans capsule, lungs, heart and viscera serosa.

Question 6

Simple cuboidal
Function?
Location?

Answer 6

All look equal, like squares.
Functions: absorption, conduit, barrier, hormone synthesis, storage and mobilisation.
Examples of location: pancreatic duct, collecting ducts of kidney, in the thyroid follicle.

Question 7

Simple columnar
Function?
Location?

Answer 7

Functions: mainly absorption of nutrients as have microvilli, secretion and lubrication.
Location examples: intestinal glands (crypts of Lieberkuhn) —> stomach lining, gastric glands, small intestine and colon.

Question 8

Pseudostratified epithelia

Answer 8

Cells have to make contact with basement membrane but not all reach cell surface so gives the impression of multiple cell layers.
Function: secretion and conduit, particle trapping and removal.
Locations include: nasal cavity, trachea and bronchi

Question 9

Striated squamous non keratinised epithelia

Answer 9

Multiple layers of cells and the outmost are thin squamous epithelial cells
Function: protection against abrasion, reduces water loss but remains moist
Location: vagina, oesophagus, oral cavity, anal canal

Question 10

Stratified squamous keratinised epithelium

Answer 10

Contains multiple layers of cells and the outmost of which are squamous cells which have lost there nuclei and cornified. Contain keratin.
Outmost layer reduces water loss and prevents toxins getting in

Question 11

Epidermis layering and psoriasis

Keratinocytes

Answer 11

Stratified squamous keratinised epithelium is made up of mostly keratinocytes. The mitosis of keratinocytes is in the basal layer. The daughter keratinocytes move towards surface, differentiating and eventually losing their ability to divide.
They produce. Keratin to help strengthen epidermis.

Normal transit time to surface is 28-40 days. But in psoriasis its 2-4 days.

Question 12

Other cells in the epidermis:

Answer 12

Melanocytes: occur at intervals (1:8 of basal layer), produce melanin.

Langerhans cells: highly specialised capacity to present antigens to T cells, therefore mediating immune reactions

Question 13

Transitional epithelium
Function?
Location?

Answer 13

Surface cells vary in shape from columnar/cuboidal to flattened.
Function: distensibility, protection of underlying tissue from toxic chemicals
Location: urinary tract, renal pelvis