Wk 3 Flashcards
Tissues Epithelia: Structure & Function
What is epithelia?
A sheet of cells that covers a body surface or cavity (dense - lack of extracellular matrix).
Structure:
- Apical (top which faces a lumen)
- Basal (bottom which is bound to basement membrane)
- Lateral (cell to cell junctions form boundaries)
Function:
- Selective barrier
- Secretory surface
- Protective surface
What are the two types of epithelial tissue?
Covering epithelia tissues - line and cover structures.
Glandular epithelia tissue - secretes stuff.
What are the types of covering epithelia?
- Mucous membrane
- Serous membrane
What is a mucous membrane?
Lines a body cavity that opens directly to the exterior.
What are the 3 layers that mucosa consists of?
- Epithelium
- Lamina propria
- Muscularis mucosae
What is a serous membrane?
Lines a body cavity that does NOT open directly to the exterior.
- Covered by mesothelium that secrete fluid (reduces friction)
What are the two types of glandular epithelial tissue?
- Exocrine glands
- Endocrine glands
Can glands be unicellular OR multicellular?
Yes
Unicellular:
Exocrine - Goblet/Paneth cells
Endocrine - Enteroendocrine
Multicellular:
Brunners glands
What are exocrine glands?
Will empty their contents into a duct which opens into the lumen of the organ (simple or stratified cuboidal).
Function: digestive enzymes aid digestion, reduce body temperature by sweating.
E.g.
- Pancreas
- Sweat glands
- Digestive glands
What are the types of ducts of exocrine glands?
Unbranched - simple
Branched - compound
What are the modes of secretion of exocrine glands? (multicellular)
- Merocrine glands
- Apocrine glands
- Holocrine glands
What are merocrine glands?
- Synthesised by ribosomes on ER
- Packaged and processed by golgi complex
- Released from cell by exocytosis
E.g. salivary glands
What are apocrine glands?
- Top of cell (apical) is pinched off by exocytosis
- Cell then repairs itself
E.g. mammary glands
What are holocrine glands?
- Whole cell ruptures to form secretory product
E.g. sebaceous gland
What are endocrine glands?
Release hormones into the bloodstream (simple cuboidal and others).
Function: hormones help maintain homeostasis.
E.g.
- Pituitary (stores hormones)
- Pancreas
- Adrenal glands
What are the epithelia cell shapes?
- Squamous cells (flat and thin)
- Columnar cells (rectangular)
- Cuboidal cells (square shaped)
- Transitional cells (change shape)
What are the epithelia cell layers?
- Simple epithelium (single layer)
- Stratified epithelium (2 or more layers)
- Pseudostratified epithelium (appears to be multiple but only 1 layer)
What is simple squamous epithelia?
Structure:
- Single layer of cells
- Nuclei lay flat
Function:
- Filtration, diffusion
E.g.
- Epithelium of blood vessels
- Lung alveoli (1 cell thick so gases can diffuse easily)
What is simple cuboidal epithelia?
Structure:
- Cells with square shape
- Nuclei are round and central
Function:
- Secretion
- Absorption
E.g.
- Capsule of lens
- Collecting tubules of kidney
What is simple columnar epithelia?
Structure:
- Cells are rectangular shape
- Nuclei are oval shaped, generally at same level
Function:
- Secretion
- Absorption
E.g.
- Lining the gastrointestinal system (GIT)
What is stratified squamous?
Structure:
- Two or more layers
- Nuclei are flat, often bulges
- Can be keratinised/non-keratinised
Function:
- Provides protection (forms physical barrier)
E.g.
- Skin
- Vagina
- Oral cavity
What is transitional (urothelium) epithelia?
Structure:
- Round/pear shaped cells
Function:
- Changes shape, located in organs that stretch
- Relaxed (several layers thick)
- Stretched (only 2-3 layers thick)
E.g.
- Ureters and urinary bladder
What is stratified cuboidal epithelia? (rare)
Structure:
- Two or more layers of square shaped cells
- Nuclei are round/central
Function:
- Protection (limited secretion and absorption)
E.g.
- Ducts of sweat glands
What is stratified columnar epithelia? (rare)
Structure:
- Two or more layers of rectangular shaped cells
- Nuclei are oval shaped
Function:
- Protection
- Secretion
E.g.
- Parts of conjunctiva of eye
- Ducts of salivary gland
