Glands Flashcards
Define a gland
An epithelial cell or aggregate of cells specialised for the secretion of a substance
Exocrine and endocrine definitions
Exocrine; secretes contents into ducts
Endocrine; (ductless) secretes contents into bloodstream or interstitial fluid
Merocrine, apocrine and Holocrine are 3 modes of secretion. What are each of their definitions
Merocrine; (exocytosis)
Apocrine; SOME of the cytoplasm and contents released
Holocrine; organelles all die, and ALL cytoplasm and contents released. Cell replaced by division of adjacent epithelial/basal cell
Mechanisms for merocrine secretions?
Merocrine secretion (exocytosis:)
- Vesicle approaches and fuses with plasma membrane
- Contents dispersed by diffusion into extracellular space
- Plasma membrane transiently larger before being retrieved and stabilising cell surface area
How does endocytosis and secretion combine to give transepithelial transport?
Transepithelial transport is when a substance enters a cell by endocytosis and exits via (merocrine) secretion/exocytosis at the opposite surface
Often used with material too large to directly diffuse though the plasma membrane
Mechanism and importance of glycosylation of newly synthesised proteins in the Golgi apparatus
Glycolysation is when carbohydrates/sugars are added to proteins and lipids. GLYCO-LY-SATION
What can be the roles of secretion in cell functions?
?
What are the simple mechanisms of control of secretion
Most mechanisms will operate by negative feedback Can be: -neural/nervous -hormonal/endocrine -humoral
Another type of neural communication is neuro-endocrine communication (hypothalamus to pituitary)
Method for apocrine secretions?
- non membrane bound substance (eg lipid) makes contact with plasma membrane, pushing against apical surface
- apical cytoplasm envelopes itself around substance
- membrane surrounding droplet of substance is pinched off
- membrane transiently smaller, membrane added to regain original area
Method for holocrine secretions
- disintegration of cell
- release of contents
- ALL contents released into extracellular space
- Secretory cell fills with secretory granules
- Organelles degenerate and cells die.
- Plasma membrane breaks and secretum (contents) empties
- Dead cells replaced by mitotic division of basal cells
What is the significance of glycosylation?
Create complex shapes for better specificity.
This is important for
-adhesion to substrate by neighbouring cells
-mobility of cells
-communication between cells/ other proteins and chemicals
(Intra cellular protein trafficking)
-movement an inhibition
-cell survival
What are diffuse neuroendocrine cells that are a part of the diffuse neuroendocrine system? (DNES)
Rarer forms of endocrine epithelial cells
These don’t aggregate together
Have microvilli, secrete some serotonin and found in the conducting and respiratory portions of the respiratory tract.
(Considered a part of the endocrine system as they are stimulated by the nervous system)
Difference between uni and multicellular cells in exocrine glands
Unicellular; release secretion(mucus) onto surface epithelium. Eg goblet cells in digestive (to lubricate) and respiratory epithelium (moisten air and trap dust and carbon particles)
Multicellular: duct system. Extend from epithelial surface to connective tissue. Discharge secretory products into the lumen of the organ via ducts
How can exocrine glands be classified
- by their modes of secretion (merocrine, holocrine or apocrine)
- by the organisation of their epithelial components (simple, compound, branched, coiled, acinar, tubular)…
What are the functions and examples of mixed exocrine and endocrine glands?
These are glands, eg pancreas, that discharge secretions into a duct system and into blood vessels.
The exocrine glands also allows for both serous and mucus production. Eg tubuloacinar glands
What are tubuloacinar glands?
Glands with branching tubules each of which ends in a secretory acini (acini- a rounded secretory unit)
These glands often contain a cap at the end of the gland (demilune) that has a myoepithelial (contractile epithelial cell) attached to the serous surface. This contracts, releasing a watery substance that assists in the release of the mucous secretions through the connecting duct.
Eg pancreas acinar glands, the submandibular salivary gland and the breast milk ducts
How long does it take for gland cells to regenerate
Cells in mucous membrane of digestive, respiratory and urinary tracts: continually replaced;
Cells of liver, thyroid, pancreas: stop multiplying by puberty but can multiply in certain circumstances eg tissue injury.
(Exception are cells of the islets of langerhans in the pancreas that cannot regenerate once destroyed)
Those in the small intestine regenerate every 4-6 days
What does Neoplasia mean
The prescence or formation of new, abnormal growth of tissue
What’s a adenocarcinoma
A malignant neoplasm derived from glandular epithelium
Examples of endocrine glands
- pituitary gland
- thyroid gland
- parathyroid gland.
ALL epithethelial cells secrete hormones in the gland
Examples of exocrine glands
- salivary glands
- pancreas
- mammary
- sweat
- sebaceous gland
- lachrymal gland
Only cells at APEX of the duct secrete the products
What’s canalicularisation
When forming exocrine glands, canalicularisation is when the central cells die off to product the duct.
What’s pinocytosis
When liquid droplets are ingested by cells
What’s the difference between hormonal, neural and humoral methods of controlling gland secretions?
?Hormonal; hypothalamus and pituitary gland involved. Most prevalent in endocrine glands
Nervous: nervous system involved (solely controls salivary exocrine gland secretion
Humoral; changing level of substance in plasma stimulates the endocrine glands. Through feedback loops most prevents in endocrine glands
Example of neurocrine communication
The hypothalamus to the pituitary
In endocrine glands, what’s the cell number, secretory products and mode of secretion
Cell number: unicellular (DNES cells), multicellular (thyroid)
Secretory products: hormones (peptide- insulin, steroid-adencorticoids), plasma proteins (by the liver)
Mode of secretion: merocrine (like exocytosis)
Difference between serous and mucosal membrane secretions
Mucous: thick, viscous
Serous: watery
Where are steroid hormones synthesised
Adrenal glands and in the gonads
