Lecture #33 - Pituitary and hypo connection Flashcards
Where’s the hypotalamus?
Here
Hypothalamus and Pituitary gland - location
-What’s the pituitary made up of?
Pituitary split into
- Anterior lobe of pituitary gland (adenophypophysis)
- Posterior lobe of pituitary gland (neurohypophysis)
- Hypo and pit are located in close proximity
- Two endocrine glands that control other endo glands
- Ant and Post have different manner of releasing and different hormones
Pituitary hormones (7)
Ant:
- Growth Hormone (GH)
- bones
- has direct & indirect effects - Adrenocoticotropic hormone (ACTH)
- adrenal cortex
- releases cortosol - Thyroid-stimulating hormone (TSH)
- thyroid gland
- goes to thyroid gland to stimulate secretion of thyroid hormone - Gonadotropic hormones (FSH and LH)
- testis and ovaries
- Goes to gonads and stimulates estradiol and testosterone - Prolactin (PRL)
- mammary glands
- Milk synthesis (direct)
Post:
- Ocytocin (OT)
- mammary glands and uterus smooth muscle
- Strong effect on uterine muscle and mammary gland (suckling = milk ejection)
- good example of a positive feedback control (all others are -ve feedback) - Antidiuretic hormone (ADH)
- kidney tubules
Anterior pituitary hormones
Name the 12 hormones
Action of hypothalamic hormones: Hypothalamic hormones have releasing or inhibiting effects on the various cells of the anterior pituitary, this regulating anterior pituitary secretion and thus ultimately regulating effects of ant pit hor throughout the body
- GnRH = gonadotropin-releasing hormone
- GHRH = growth hormone-releasing hormone
- SS = somatostatin
- TRH = thyroid-releasing hormone
- PIH = prolactin-inhibiting hormone
- PRH = prolactin-releasing hormone
- CRH = corticotropin-releasing hormone
- FSH = follicle-stimulating hormone
- LH = luteinizing hormone
- TSH = thyroids-timulating hormome
- ACTH = adrenocorticotropic hormone
- T3 = triiodothyronine
- T4 = thyroxine
- -Hypo receives neuronal/feedback trigger*
- -Signal releases hormone from hypo e.g. cortisol releasing hormone (CRH) - stimulates cells in pituitary to release ACTH - gets travelled to adrenal and then secretion (HPA axis). There’s also HPG axis (the first one)*
- -First block is what hypo releases*
- -Second block is what anterior releases*
- -negative if too much in system so turn off*
- -R = releasing (there’s also inhibitory hormone) and S = stimulatory*
- -For prolactin and growth hormone; actual hormone released from pituitary, not another endocrine organ. It’s the primary efferent thing*
The hypothalamus and posterior pituitary gland
- How is hypo connected to the post lobe?
- Hypo uses _____ ____ with the post lobe: how does frequency of APs relate to rate of hormone secretion?
- Post pit hormones are made in? Travel down? Stored at?
- In the posterior; cell bodies in the hypo and the axons are in the pituitary (no bloodstream involved). In the anterior; releasing hormone from hypo goes to blood and then pituitary
- Neruons vs bloostream - different modes of activation
- The hypothalamus is connected to the posterior lobe by neurons: cell bodies in the hypothalamus, axons terminate in the posterior lobe
- Hypothalamus uses neural communication with the posterior lobe: frequency of action potentials to the posterior lobe determines rate of hormone secretion
- Posterior pituitary hormones:
- are made in the hypothalamus (cell body of neuron - no specific cell as per say. The cell types exist in ant pit for those hormones)
- travel down the axon
- stored at the axon endings until required (OT and ADH)
What’s special about SS?
Released from hypo, goes to ant pit and switches off GH release.
This happens when signal reached that there’s too much GH in bloodstream so swtiched off by SS
So how does hypo talk to the ant pituitary?
Axonal projections to the median eminence:
Have neurons (bright freen).
The cell bodies are up in the hypotalamus and that’s where they receive the signal.
The axons project down into the median eminence region
AP is sent down to the median eminence - here, there is a portal system (blood stream that connects the hypo and anterior pituitary)
At the median eminence, the hormones are relased and they travel in that little bloodstream stright to anterior pituitary
So this is what it looks like for GnRH (ant)
AP signal sent in the GnRH neuron to the axon terminal and GnRH is relased in the portal blood stream that then travels to the ant pit and LH is released and it goes to ovaries and then ovaries produce estradiol and if conc of estradiol increases too much, it stops the loop (-ve feedback)
Oxytocin and vasopressin cells in the hypothalamus (post)
Hormones synthsised and stored in axon endings —> signal releases them —-> don’t enter blood bw hypo and post pit bc go straight
Basically, the axon endings are in the posterior pituitary so essentially, “Hypothalamus makes the hormones and they are stored in the posterior pituitary until required” - non-tropic hormones because they are secreted from the posterior pituitary gland to initiate its functions and not to another organ like tropic hormones do
Also, in the hypothalamus, supraoptic and paraventricular nuclei make the ADH and OT
Hormoes released by the post pit
1. Antidiuretic hormone (ADH; vasopressin)
-stimulates the…….
2. Oxytocin
- stimulates the……..
- stimulates………
1. Antidiuretic hormone (ADH; vasopressin)
-stimulates the kidneys to reabsorb water (the kidneys to conserve water when the body dehydrates)
2. Oxytocin (regulated by +ve feedback stimulation)
- stimulates the contraction of uterine muscles during childbirth (an example of positive feedback)
- stimulates milk release in breastfeeding (milk ejection reflex: another example of positive feedback)
Note: both hormones are made in the hypothalamus and stored in the posterior pituitary gland until required.
ADH: Redgulation of plasma osmolality
Dehydration - plasma volume falls
Conserve water - don’t urinate it out
Appreciate
That “basal” is pointing to set point - ADH secreted around that point
ADH and water and kidneys
ADH absent - water not reabsorbed through the tubular cells in the kidney
It moves the water channels into the membrane so water can travel through the tubular cells.
If no ADH, water channels stay inside the cell and so water can’t enter the body
If ADH, water channels move to the membrane which allows the water to move to the body and goes back into bloodstream and it wont get urinated out
Oxytocin: positive feedback in childbirth
Crucial for contracting in uterus
Cycle gets stronger until baby born bc then no more stimulus bc birth canal has been stretched so OT release will stop
Stronger signals sent to hypothalamus
Oxytocin: milk ejection reflex
- Baby suckling sends signal to hypo
- AP sent to post pit to release OT
- travels to breast tissue and then release of milk
- stronger suckling = stronger signal (+ve feedback)
