L4 Pituitary Gland Flashcards
(27 cards)
What are endocrine glands?
Oragns that secrete hormones directly into the blood stream.
What levels can hormones act on?
- Cellular level (e.g. mitosis, apoptosis, secretion)
- Molecular level (e.g. protein synthesis, enzyme activity)
- Whole body level (e.g. growth and development)
What is the difference between autocrine and paracrine signalling?
Autocrine: cell which produces a hormone and is influenced by that hormone itself
Paracrine: hormone has an effect on neighbouring cells, it’s not released into circulation
What type of chemical nature can hormones be of?
- Steroid
- Peptide
- Single amino acid derived hormones
Do hormones travel free in plasma?
Yes, some do.
Others are bound to a carrier protein to prolong the half-life of the hormone.
Where is the pituitary gland located?
Close to the optic chiasm, inferior to the hypothalamus.
Describe the stucture of the pituitary gland.
- Anterior lobe: connected to hypothalamus by blood vessels
- Posterior lobe: connected to nerve fibres which originate in the hypothalamus, these nerve fibres transport hormones to the posterior pituitary (intra-axonal transport)
What is the overall function of the pituitary gland?
“The master gland” which secretes hormones that carry out important bodily functions and also controls the activity of other hormone glands
Which 2 hormones does the posterior pituitary release?
- Oxytocin
- Vasopressin (anti-diuretic hormone)
What is the function of oxytocin?
- Controls uterine contraction during labour
- Controls milk release from lactating breasts
Explain the action of oxytocin.
- Child attaches to breast, sends nerve impulses to hypothalamus
- Hypothalamus produces and releases oxytocin through nerve fibres to posterior pituitary which releases oxytocin to general circulation
- Oxytocin binds to receptors on myoepithelial cells
- Intracellular calcium increases, milk is forced out
Neuro-endocrine reflex
What is the function of vasopressin/ADH?
Acts on kidneys to resorb water.
Regulates blood osmolarity and urine output.
Explain the action of vasopressin.
- Increased plasma osmolarity stimulates osmoreceptors in the hypothalamus to produce ADH
- Posterior pituitary releases ADH and water is selectively resorbed in distal tubule of kidney
- Urine becomes more concentrated and lower volume
- Decreases plasma osmolarity
Neuro-endocrine reflex
Which 6 hormones does the anteiror pituitary release?
- Growth hormone
- Prolactin
- Adrenocorticotropic hormone
- Follicle stimulating hormone
- Lutenising hormone
- Thyroid stimulating hormone
What type of hormones does the anterior putuitary secrete?
Tropic hormones: regulate secretions of other endocrine organs.
Prolactin and growth hormones are exceptions, they are not tropic hormones.
What is the function of prolactin?
Stimulates milk production.
Explain the release of hormones from the anterior pituitary.
- Stimulatory hormones are produced and released from the hypothalamus to control the secretory activity of the anterior pituitary (inhibit or stimulate).
e. g. dopamine, somatostatin, corticotrophin releasing hormone
Which hormones from the hypothalamus inhibit and stimulate secretion of growth hormone?
Inhibit: somatostatin
Stimulate: growth hormone releasing hormone
Extent of growth is not entirely dependent on growth hormone, which other hormones play a role?
- Thyroxine inhibits growth
- Cortisol inhibits growth in excess
- Insulin stimulates growth in excess
Which cells synthesise and store growth hormone?
Somatotrophs
Which tissues does growth hormone target?
Bone and skeletal muscle
What are the direct metabolic effects of growth hormone?
- Decreases glucose uptake in muscles
- Stimulates AA uptake and protein synthesis in muscles, inhibits protein breakdown therefore increasing muscle mass
- Decreases glucose uptake in adipose tissue and increases lipolysis so there’s a decrease in fat deposits
- Increases gluconeogenesis, protein synthesis and IgF production in the liver
GH is important in protecting against hypoglycaemia.
Which factors increase and decrease GH release?
Decrease: somatostatin
Increase: exercise, stress, sleep, fasting, hypoglycaemia, GHRH
Describe gigantism.
- Usually seen in children with pituitary tumours
- Excess GH secreted
- High IgF makes them abnormally tall as growth plates are still open until age 18
- Normal body proportions also affected
