Glands Flashcards
Gland definition
An epithelial cell or an aggregate of epithelial cells that are specialised for the secretion of a substance.
Secretion definition
The production and release of materials by a cell or aggregate of cells.
Two types of gland
Endocrine (ductless)
Exocrine (ducted)
Endocrine glands
Secrete directly into the blood flowing through them, to let the secretions function at distant parts of the body - secretions are hormones.
Eg pituitary gland
All epithelial cells in the gland secrete the hormone.
Exocrine glands
Secrete into a location/region of the body through a duct; their secretions are mostly enzymes or lubricants.
Eg salivary gland, mammary glands, sweat glands
Only cells at apex of duct secrete the products.
Endocrine gland - histology
Blood vessels close by
Hormone producing epithelial cells
Larger lumen
Exocrine gland - histology
Stratified cuboidal cells
Two layers of cells
Lumen of duct
Adenogenesis
Gland development in utero
1. Growth signal received
2. Proliferation of cells occurs and extracellular protein degradation enzymes produced
3. Epithelial cells invade space created
=> exocrine gland - central cells die off to produce duct (canalicularisation); link to mother cells remains; significant amount of branching
=> endocrine glands - produce angiogenic factors to stimulate blood vessel growth in and around epithelial cells; link to mother cells broken through apoptosis; virtually no branching
How does branching occur?
FGF10 released by immature fibroblasts.
Epithelial cells move towards signal.
Causes:
1 - tubule elongation (growth factor 1 active; growth factor 2 inactive)
2 - tubule branching (growth factor 1 inactive; growth factor 2 active)
Elongation and branching stopped by Shh.
Simple tubular duct structure
Duct does not branch
a) simple tubular - intestinal glands
b) simple branched tubular - gastric glands
Cuboidal epithelial cells
Alveolar secretory duct structure
Duct does not branch
a) simple alveolar - no examples in adult humans, some in foetus
b) simple branched alveolar - sebaceous glands (only found where there is hair)
Compound tubular duct structure
Duct branches
a) compound tubular - duodenal glands of small intestine
Epithelial cells with muscle so as to contract
Compound alveolar secretory duct structure
Duct branches
a) compound alveolar - mammary glands
b) compound tubuloalveloar - salivary glands
Epithelial cells with muscle so as to contract
Stages of growth and development of glands
Prebud
Initial bud
Pseudoglandular
Canalicular
Terminal bud
Two types of secretion
Mucous
Serous
Interlobular duct
Located between lobules,
Intercalated duct
Between acinus and striated duct.
Myoepithelial cells
Cells that have features of both an epithelial cell and a smooth muscle cell - help to eject secretions from the duct.
Merocrine gland
Fusion of vesicles with apical membrane - a form of exocytosis
Apocrine gland
Partial loss of cytoplasm eg lactating mammary gland.
Holocrine gland
Complete loss of cytoplasm eg sebaceous gland in skin.
Cytocrine gland
Cells are released as a secretion eg spermatid
Merocrine secretion
Secretion from cells via exocytosis - secretory vesicles joining with membrane.
Apocrine secretion
Pinched off portion of cell is the secretion.
Holocrine secretion
Mature cell dies and becomes secretory product.
Cytocrine secretion
Lose whole cell but cell doesn’t die.
Types of merocrine secretion
Regulated secretion: secretory granules accumulate in cell and are released by exocytosis upon stimulation - needs Ca2+ ions.
Constitutive secretion: product not concentrated into granules but packaged into small vesicles and continuously released to cells surface - used mainly to repopulate the plasma membrane with plasma proteins.
Example of merocrine secretion
Release of insulin from beta cells in Islet of Langerhans
Glycosylation
The covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids.
Roles of glycosylation
To aid protein folding.
Prevents protein digestion by intracellular proteases.
Prevents lipid digestion by intracellular lipases.
Cell recognition (blood groups).
Role of cell to extracellular matrix attachment.
Glycation
Covalent attachment of sugars to proteins and lipids to form glycoproteins and glycolipids.
Same as glycosylation without enzymes.
3 ways of control mechanisms
Hormonal
Neural
Humoral
Striated duct - H + E
Simple columnar epithelium
Striations in cells
Nucleus near lumen
Function of striated duct
Contain a number of ion transporters to keep ions balanced to prevent water loss.
Parotid gland
Almost totally serous - serous acini - look like acinar in pancreas.
Almost totally purple
Submandibular gland
Mostly serous, more mucous.
Mix of pink and gray.
Sublingual gland
Almost totally mucous.
Pale acini - like a dappled grey/purple
Saliva production - what type of stimulus?
Neuronal stimulus - control is neural only
Is the liver endo or exocrine?
The largest exocrine gland.
Hepatic blood supply
Hepatic portal vein
Hepatic artery
Liver lobule
Hexagonal shaped lobule with portal triad at each point.
Kupffer cells
Macrophages in the liver; form part of sinusoidal lining
Trap and phagocytose at damaged or aged erthryocytes that were missed by spleen.
After splenectomy, these cells take over removal of 120 day old (aged) RBC.
Blood flow and bile flow in liver
Blood flows from the outside of the lobule inside towards the central canal.
Bile flows from inside out, through the bile duct.
Sinusoids
Cells that line portal vein.
They have large gaps between them.
Three types of capillary vessel
Continuous
Fenestrated
Sinusoid
Continuous capillary vessel
(From outside in):
Intact basement membrane; endothelial layer (tunica intima) with intercellular clefts.
- in brain and most of body
Fenestrated capillary vessel
Intact basement membrane; endothelial layer (tunica intima) with fenestrations
- pituitary, small intestine, kidneys
Sinusoid capillary vessel
Incomplete basement membrane; endothelial layer (tunica intima) with intercellular gaps (whole cell can pass through)
- spleen, bone marrow, liver, lymph nodes
Portal triad
Vein - biggest
Bile duct - stains purple
Artery - similar size to bile duct
Canaliculi
Narrow spaces between cells in liver lobule.
Route of bile
Canaliculi -> interlobular tributaries -> periportal bile ductules -> bile ducts -> left and right hepatic ducts
Space of Disse
Space between sinusoid and hepatocytes.
Pit cells
Kill tumour cells that enter sinusoids.
The most active form of NK (natural killer) cells.
Stellate (Ito) cell
Cells found in space of Disse.
Cytoplasmic vacuoles containing vit A.
In liver cirrhosis, they lose vit A storage abilities and differentiate in myofibroblasts, which synthesis and deposit collagen within perisinusoidal space => liver fibrosis.
Hepatocytes (compared to other cells)
Many mito
Many peroxisomes
Many free ribosomes
A lot to RER and SER
Many Golgi
Glycogen deposits
Rate of liver regeneration
Low to mild damage - 7-8 days
Mild to medium damage - 30-40 days
Medium to severe damage - never
Functions of liver
Storage: iron and copper; vit A (Ito cells), D, E, K (hepatocytes); sugars (glucose as glycogen)
Anabolism: >60% of body’s proteins (plasma proteins, enzymes, apolipoproteins); a.a synthesis; haemopoiesis in the embryo/foetus
Catabolism: drugs; hormones; Hb; poisons/toxins; sugars; removal of old/damaged RBC after splenectomy
Other: bile production; filter cell debris from blood; hormones/growth factors (endocrine); modifies hormones for excretion or function
