L7) Glands 1 (introduction) ✔ Flashcards
what is the definition of a gland?
an epithelial cell
or an aggregate of epithelial cells
that are specialised for the secretion of a substance
what is secretion?
the production and release of materials
by a cell or aggregate of cells
what is the function of glands?
to regulate human physiology
by homeostasis - via stimulus from CNS or via circulating levels of chemicals or via neighbouring cells
how are glands classified?
their structure
mode of secretion
what are the two types of glands?
endocrine
exocrine
what are endocrine glands?
ductless glands
secrete directly into blood flowing through them
to let the secretion function at distant parts of the body
their secretions are called hormones.
what is are some examples of endocrine glands?
pituitary gland - anterior and posterior
thyroid gland
parathyroid gland
what is the function of the thyroid gland?
produce:
thyroid hormones T3 & T4 = control metabolism
calcitonin = calcium homeostasis
what is the function of the parathyroid gland?
produce:
parathyroid hormone = calcium homeostasis
what is the function of the anterior pituitary gland?
produces:
ACTH, LH, FSH, TSH = regulate most endocrine glands
prolactin = stimulates milk production in mothers
somatotrophin = regulates growth of body and tissues
what is the function of the posterior pituitary gland?
produces:
vasopressin (ADH) = prevents water loss from kidneys
oxytocin = signals uterus for delivery at end of gestation and ejection of milk during breast feeding
what are exocrine glands?
ducted glands
secrete into a location or region of the body through a duct
their secretions are mostly enzymes or lubricants
what are some examples of exocrine glands?
salivary gland
pancreas
mammary
sweat glands
sebaceous glands
lachrymal glands
what is the function of the salivary gland?
secretes saliva into the oral cavity
functions include partial digestion of food and lubrication
what is the function of the pancreas?
secretes enzymes: amylase, trypsin, lipase
functions include digesting of carbs, proteins and fats
what is the function of the mammary?
produces colostrum and milk in response to prolactin and oxytocin (hormones)
to nourish neonates
what is the function of the sweat glands?
secretes sweat
functions include regulation of body temperature and excretion
what is the function of the sebaceous gland?
secretes sebum onto skin and ear (earwax)
functions to protect these tissues from pathogens
what is the function of the lachrymal glands?
secrete aqueous fluid in eye
functions to moisten the eye and also produce lysozyme (an enzyme to attack bacteria)
which parts of the endocrine and exocrine gland secrete hormones/products?
endocrine = all epithelial cells in the gland
exocrine = only cells at the apex of the duct
how does andenogenesis (gland development) of exocrine glands occur?
in utero development
growth signal received
proliferation of (daughter) cells occurs and extracellular protein degradation enzymes produced
epithelial cells invade space
→ canalicularisation - central cells die off to produce duct
→ link to (mother) cells remains
→ significant amount of branching
how does andenogenesis (gland development) of endocrine glands occur?
in utero development
growth signal received
proliferation of (daughter) cells occurs and extracellular protein degradation enzymes produced
epithelial cells invade space
→ 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? (lungs)
FGF10 released by immature fibroblasts (mesenchymal stem cells)
Epithelial cells move towards the signal
Two different fates:
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 Sonic the Hedgehog (Shh)
what are the different shapes of exocrine glands?
tubular:
simple tubular/simple branched tubular
compound tubular
alveolar:
simple alveolar/simple branched alveolar
compound alveolar/compound tubuloaveolar
what are the two types of epithelial cells in exocrine glands?
cells lining the duct
cells that make secretory products
what is the significance of secretory cells of ducts changing morphology?
turn into myoepithelial cells
have features of both epithelial and smooth muscle cell
help to eject secretions from duct
give examples of tubular secretory structures
simple tubular: intestinal glands
simple branched tubular: stomach glands
compound tubular: duodenal glands
give examples of alveolar secretory structures
simple alveolar: none important
simple branched: sebaceous glands
compound alveolar: mammary glands
compound tubuloalveolar: salivary glands
what are the four modes of secretion?
merocrine
apocrine
holocrine
cytocrine
what type of gland is a merocrine gland?
whereby fusion of vesicles occurs with apical membrane (exocytosis)
e.g. acinar and endocrine pancreatic glands
what type of gland is a apocrine gland?
whereby there is a partial loss of cytoplasm
e.g. lactating mammary gland, sweat glands in the axilla and external genitalia
what type of gland is a holocrine gland?
whereby there is a complete loss of cytoplasm [or cell]
e.g. sebaceous gland in skin and tarsal glands in eyelid
what type of gland is a cytocrine gland?
whereby cells are released as a secretion
e.g. spermatid (spermatozoa) in the seminiferous tubule (testis)
what are the two pathways involved in merocrine secretion?
regulated secretion
constitutive secretion
what is regulated merocrine secretion?
secretory granules accumulate in large vesicles and are released by exocytosis upon stimulation
requires Ca2+ ions to work
e.g. insulin secretion
what is constitutive merocrine secretion?
secretory product is not concentrated into granules but packaged into small vesicles
continuously released to the cells surface
mainly used to repopulate the plasma membrane with plasma proteins
how does regulated secretory mechanism occur?
uses energy
cargo can be anything within the cell
active secretion requires specific signal - Ca2+
vesicle migrates to cell surface along microtubules
in presence of Ca2+ ions, membrane of vesicle fuses with plasmalemma
cargo released to extracellular space
how does apocrine secretion occur - during neonatal period?
fats are secreted by apocrine secretion (signet fragment)
milk proteins made in RER and on free ribosomes are packed into vesicles produced by the Golgi apparatus and then released by merocrine secretion
how does apocrine secretion occur - during lactation?
both fats and proteins are released by apocrine secretion
how does apocrine secretion occur - sebaceous glands?
the secretory cell gradually fills up with secretory granules
cell organelles degenerate and cell dies
plasma membrane breaks off and the contents (secretum) empties
dead cell is replaced by mitotic division of the basal cells
what is the role of the Golgi apparatus in secretion?
critical - packs the proteins into the constitutive pathway or regulated pathway
glycosylation of protein determines the pathway
how does the Golgi apparatus aid secretion?
proteins made on the ribosomes of RER
packaged into vesicles and passed to the Golgi
vesicle fuses with cis region membrane
enzymes glycosylate the protein as it passes from the cis region to the trans region
signalling and glycosylation regulate
what is glycosylation?
covalent attachment of sugars
by enzymes to proteins and lipids
to form glycoproteins and glycolipids
what is the difference between glycosylation and glycation?
glycosylation = attachment of sugars with enzymes
glycation = attachment of sugars without enzymes
what is the function of glycosylation?
to aid protein folding
prevent protein digestion by intracellular proteases
prevents lipid digestion by intracellular lipases
cell recognition
role on cell to extracellular matrix mattachment
what is the role of glycosylation in secretion?
glycosylation of protein in golgi determines pathway taken
if glycosylation by right sugars → pathways taken
if signal is recieved → the vesicle takes the regulated pathway
if no signal → the constitutive pathway taken
what is exocytosis?
secretion of molecules outside the cell via a vesicle fusing to a membrane
what is endocytosis?
engulfing of molecules inside the cell via vesicle formation
what are the two types of endocytosis?
phagocytosis
pinocytosis
what is phagocytosis?
process by which cells (phagocytes) engulf other cells or particles
used by cells of immune system: macrophages, dendritic cells, neutrophils, basophils and eosinophils
what is pinocytosis?
process by which liquid droplets are ingested by cells
used by all cells, esp smooth muscle cells
how is transepithelial transport conducted?
via transcytosis:
paracellular transport -
how are secretions regulated?
through negative feedback mechanisms
hormonal, humoral and neural
describe hormonal control mechanism of hormone release
refers to the release of hormones in response to hormones released by other endocrine glands
describe neural control mechanism of hormone release
refers to release of hormones in response to a stimuli from the nervous system
describe humoral control of secretions
refers to the control of hormone release in response to changes in extracellular fluids
give examples of humoral, hormonal and neural glandular control?
humoral: secretion of PTH
hormonal: secretions by endocrine glands
neural: secretion of catecholamines
where are each of the control mechanisms of hormone release most prevelant?
humoral: endocrine
neural: only in salivary (exocrine) glands (but also oxytocin and ADH)
hormonal: endocrine
what is neurocrine communication?
different form of eural communication
neurones release something into blood on target
