Glandular Tissues And How Cells Secrete Flashcards
Gland
An epithelial cell or collection of cells specialised for secretion
Exocrine
Glands with ducts - secrete onto an epithelial surface
Endocrine
‘ductless glands’ - secrete (hormones) into bloodstream
Unicellular glands
e.g. Goblet cell
CF
cystic fibrosis transmembrane regulator (CFTR) is not present in the apical membranes of the epithelial cells
Chloride ion transport across the membrane is compromised
RESPIRATORY TRACT - water does not leave the epithelium in sufficient quantities to adequately hydrate the secreted mucus
The mucus becomes viscous and can less readily be moved to the oropharynx for swallowing - serious pulmonary infection often occurs
GI TRACT - mucus also becomes too viscous
SWEAT GLANDS - poor reabsorption of chloride ions - sweat is rich in chloride and sodium ions - SALTY SWEAT
PANCREAS - the gut receives insufficient pancreatic digestive enzyme and malabsorption results
Acinar
alveolar
e.g. Pancreatic
Compound
If ducts branch
Combined tubular - mucous glands in mouth
Compound alveolar - mammary glands
Compound tubuloalveolar - salivary glands, pancreas
Mucous glands
secretions contain mucus - rich in mucking (highly glycosylated polypeptides)
Stain poorly with H&E - lightly stained
Serous glands
secretions (often enzymes) are watery and free of mucus
Pink in H&E sections (darker than mucous glands)
Merocrine secretion
(exocytosis)
(apocrine and eccrine sweat glands)
- membrane bound component approaches cell surface
- vesicle fuses with the plasma membrane
- contents are released into extracellular space
- plasma membrane is transiently larger
- membrane is retrieved, stabilising cell surface area
Apocrine secretion
e.g. lactating mammary glands
- non-membrane bound structure (e.g. lipid) approached the cell surface
- makes contact and pushes apical membrane
- thin layer of apical cytoplasm drapes around droplet
- membrane surrounding droplet pinches off from cell
- plasma membrane transiently smaller
- membrane has to be added to to regain original area
Holocrine Secretion
e.g. sebaceous glands fill hair follicle with sebum
- disintegration of cell
- release of contents
- discharge of whole cell
Endocytosis
- engulfing of material that is initially outside of the cell
- opposite of merocrine secretion
- Endo- and Exo-cytosis are coupled in transepithelial transport
Transepithelial transport
- material endocytosed at one surface
- transport vesicle shuttles across cytoplasm
- material exocytosed at opposite surface
Golgi Apparatus
Structure
- stack of disc-shaped cisternae
- one side of discs are flattened, other concave
- disks have swellings at their edges - distal swellings pinch off as migratory Golgi Vacuoles
Function
- sorting of proteins into different comparments
- adding of sugars to proteins and lipid (Glycosylation)
- transport of resultant vesicles
Golgi product destinations
- majority extruded in secretory vesicles
- some retained for use in cells (e.g. Lysosomes)
- some entries the plasma membrane - glycocalyx
Glycosylation
- branching sugars offer complex shapes for specific interactions in the glycocalyx
- destruction of this layer by enzymes alters many specificity based properties of the cells:
- adhesion to substrates and neighbouring cells
- mobility of cells
- communication with neighbouring cells
- contact inhibition of movement and division
Control of Secretion
NERVOUS - Sympathetic nervous stimulation of medullary cells leads to the release of adrenaline
ENDOCRINE CONTROL - ACTH - simulates the cortex of the adrenal gland to secrete hormones
NEURO-ENDOCRINE CONTROL - nervous cells of the hypothalamus control ACTH secretion from the anterior pituitary gland
NEGATIVE FEEDBACK CHEMICAL MECHANISM - the inhibitory effect of high thyroxine levels on thyroid stimulating hormone synthesis by the anterior pituitary gland
Salivary Glands
Parotid - (2x cheeks)
Sublingual - (2x side of tongue)
Submandibular - (1x under tongue)
Thyroid
4 parathyroid glands - chief cells secrete parathyroid hormone (PTH) - controls the amount of calcium in the blood
Adrenal or Suprarenal Glands
On top of the kidney
THE CORTEX - has three layers (zona glomerulosa, zona fasciculata, zona reticularis (then medulla))
- secretes corticosteroid hormones
THE MEDULLA - secretes adrenaline and noradrenaline
