5. Glands Flashcards
What is the definition of a gland?
An epithelial cell or aggregate of epithelial cells that are specialised for the secretion of a substance
What is secretion?
Production and release by a cell or aggregate of cells
Where do glands receive their stimuli from?
From the brain (CNS) and chemicals in blood and from neighbouring cells
What are endocrine glands?
Ductless
Secrete directly into the blood
Release hormones
Describe the pituitary gland
Endocrine
Anterior - produces hormones that regulate most glands of endocrine, prolactin which stimulates milk production, somatrophin regulates body and tissue growth
Posterior - produces vasopressin that prevents water loss from kidneys oxytocin signals uterus for delivery
Describe the thyroid gland
Produces thyroid hormones T3 and T4 that control metabolism
Produces calcitonin involved in calcium homeostasis
Endocrine
Describe the parathyroid gland
Produces parathyroid hormones, calcium homeostasis
Endocrine
What are exocrine glands?
Ducted
Secrete into a location or region of body through a duct, secretions are mostly enzymes or lubricants
Describe the salivary gland
In buccaneers cavity secrete saliva
Function of saliva include partial digestion of food and lubrication
Exocrine
Describe the pancreas
Secretes enzymes - amylase, trypsin and lipase - that digest carbs, proteins and fats
Exocrine
Describe the mammary glands
Produces colostrum and milk in response to prolactin and oxytocin to nourish neonates
Exocrine
Describe the sweat glands
Secrete sweat which regulates body temp and excretion
Exocrine
Describe the sebaceous gland
Secretes sebum onto skin an in ear to protect tissues from pathogens
Exocrine
Describe the lachrymal glands
In eyes, secrete water to moisten cornea
Produces lysozyme
Exocrine
Which cells in the gland secrete products?
Epithelial cells
Only cells at apex of duct
When does the generation of glands begin in utero development?
Week 4-5
Describe the 5 stages of generation of glands in utero development
- Growth signal received
- Proliferation of daughter cells occurs and extracellular protein degradation enzymes produced
- Epithelial cells invade space created
- Exocrine gland: central cells die off to produce duct
- Endocrine gland: produce angiotensin factors to stimulate blood vessel growth in and around epithelial cells, link to mother cells broken by apoptosis
What are the 2 types of epithelial cells in exocrine glands?
Cells lining ducts
Cells that make secretory products
What happens to some cells at secretory end of ducts?
Change into myoepithelial cells
What are myoepithelial cells?
Have features of both epithelial cell and smooth muscle cell
Help to eject secretions from duct
What are the 2 types of secretion from salivary glands?
Mucous
Serous
What are merocrine glands?
Fusion of vesicles with apical membrane (form of exocytosis)
E.g. pancreas
What re the 2 pathways of merocrine glands?
Regulated secretion (needs Ca2+ ions to work), e.g. beta cells of pancreas Constitutive secretion (secretory product in vesicles and released continuously)
What are apocrine glands?
Partial loss of cytoplasm
E.g. lactating mammary gland, sweat glands in axilla (armpit), external genitalia
What are the holocrine glands?
Complete loss of cytoplasm or cell
E.g. sebaceous gland in skin and tarsal glands in eyelid
How do holocrine glands work?
Secretory cell gradually fills with secretory granules, cell organelles degenerate, cell dies, plasma membrane breaks and contents empty, dead cells replaced by mitotic division of basal cells
What is the role of Golgi in secretion?
Proteins move from RER to cis face of Golgi
Golgi modifies the protein and glycosylation takes place where sugars are added
Glycoproteins leave the trans face of Golgi via vesicles
What is the definition of glycosylation?
Covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids
What is the role of glycosylation?
Aid protein folding
Prevent protein/lipid digestion by intracellular proteases/lipase
Cells recognition (blood groups)
Cell to extracellular matrix attachment
What is glycation?
Covalent attachment of sugars to proteins and lipids to form glycoproteins and glycolipids without the use of enzymes
What is the definition of exocytosis?
Secretion of molecules outside the cell via a vesicle fusing to a membrane
What is the definition of endocytosis?
Engulfing of molecules inside the cell via vesicle formation
What is the definition of phagocytosis?
Process by which cells envelop or engulf other cells or particles
What is the definition of pinocytosis?
Process in which liquid droplets are ingested by cells, used especially by smooth muscle cells
What are the 4 types of transepithelial transport (transcytosis)?
- Molecules can move through aqueous channels in intercellular junction
- Can move through lipid cell membranes
- Molecules with appropriate characteristic may be transported by carrier proteins
- Pit system
Describe the pit system
Molecules that are impermeable may bind to cell surface receptors, be engulfed by cell membrane, then released inside cells or expelled via membrane-limited vesicles
What are the 4 types of glandular control
Humoral stimulus through feedback loops
Hormonal stimulus
Neural stimulus (adrenaline and noradrenaline)
Neurocrine communication (hypothalamus to pituitary)
