15 - Hypothalamic Pituitary Axis Flashcards
Where is the HPA found?
- Hypothalamus below the thymus
- Pituitary gland below the hypothalamus in a bone socket called sella turcica
What are some of the processes that the HPA modulates?
What is the anatomy and origin of the pituitary gland?
- Anterior = adenohypophysis, grows upwards from roof of mouth
- Posterior = neurohypophysis, connected to hypothalamus through infundibulum as grows downwards from diencaphalon of developing brain
Where is oxytocin produced?
Oxytocin and ADH synthesised by neurosecretory cells in the supraoptic and paraventricular nuclei of hypothalamus
NOT pituitary
What is contained in the posterior pituitary gland?
- Axons and terminals from hypothalamus (pituitary stalk)
- Specialised glial cells called pituicytes
What is the neurocrine system of the posterior pituitary gland?
- Oxytocin and ADH transported down nerve cell axons
- Stored and released from posterior pituitary into the bloodstream to act on distant targets
- Not technically a gland
How does the anterior pituitary gland function?
- Tropic hormones synthesised and stored in median eminence of hypothalamus travel to hypophyseal portal system
- These hormones stimulate endocrine cells in anterior pituitary
- Endocrine cells secrete hormones into blood stream to act on distant and autocrine/paracrine targets
What hormones do each part of the pituitary gland release?
Posterior: Oxytocin and ADH
Anterior: FSH, LH, TSH, ACTH, PRL, GH
When is oxytocin released and what effect does it have?
- Breast feeding: stimulus of suckling let-down reflex sends signals to hypothalamus from breast. Release of oxytocin from posterior, travels to mammary gland and activates oxytocin receptors on myoepithelial cells causing them to contract and release milk
- Birth: Pressure of baby head on cervix sends signal to hypothalamus to release oxytocin. Travels in blood stream and binds to uterine smooth muscle cells causing contraction
How can synthetic oxytocin be used?
After childbirth to increase uterine tone and control bleeding, pitocin
When is ADH released and what effects does it have?
- High blood osmolality ADH is released and acts on receptors in distal tubular epithelium of collecting ducts in kidneys
- Translocates aquaporin channels so more water reabsorbed
- ADH receptors also on smooth muscle of blood cells so causes vasoconstriction increasing arterial blood pressure so restores b.p in hypovoelemic shock
- Drinking alcohol inhibits it’s release
What are the seven tropic hormones that act on the anterior pituitary gland, what type of receptors do they bind to and what do they stimulate a release of?
GPCR
What are the hormones produced and released by the anterior pituitary gland and what effect do they have?
What are the different types of negative feedback
Give the example of HPA adrenal for negative feedback.
What is GH and its main function?
- Growth-promoting effects mainly by binding to liver and skeletal muscle which produces and secretes IGF’s that stimulate body growth and regulate metabolism
- Protein hormone that has signal peptide that needs to be cleaved
- Secreted mainly at night
What effect do IGF and GH have on children and on adults?
What inhibits and stimualtes GH release?
What is the long loop and short loop negative feedback mechanism of GH secretion?
How does GH have an effect on cells?
- Directly through own receptor (JAK) and indirectly by producing IGF’s
How do IGF’s cause a response in their target tissue?
- Bind to binding proteins and insuline like receptor
- Endocrine/paracrine/autocrine
- IGF2 in fetal growth/development and IGF1 in adults
Why are IGF-1 receptors often found in tumours?
IGF-1 can inhibit apoptosis, allows them to proliferate
What other hormones apart from GH influence growth?
