Hormonal Axis Physiology Flashcards
Where does the hypothalamus sit?
Above the pituitary gland
What does the anterior pituitary gland secrete?
- Thyroid stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle stimulating hormone (FSH) & Luteinising hormone (LH)
- Growth hormone (GH)
- Prolactin
What does the posterior pituitary gland secrete?
- Oxytocin (vasopressin)
- Antidiuretic hormone (ADH)
What hormone does the hypothalamus release in the thyroid hormone axis?
Thyrotropin releasing hormone (TRH)
What does TRH stimulate?
The anterior pituitary to release thyroid stimulating hormone (TSH)
What does TSH do?
Stimulates thyroid gland to release triiodothyronine (T3) and thyroxine (T4)
Summary of the thyroid hormonal Axis?
Hypothalamus releases TRH (thyrotropin releasing hormone)
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This stimulates the anterior pituitary to release thyroid stimulating hormone (TSH)
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This stimulates the thyroid gland to release triiodothyronine (T3) and thyroxine (T4)
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T3 & T4 suppress the release of TRH and TSH, resulting in lower amounts of T3 and T4
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Lower levels of T3 & T4 offer LESS suppression of TRH and TSH
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Therefore more TSH and TRH are released, equalling a rise in T3 and T4
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This is negative feedback
What organs sense T3 and T4?
Sensed by hypothalamus and anterior pituitary
What is the role of T3 and T4 ?
Suppress the release of TRH and TSH, resulting in lower amounts of T3 & T4
What does suppressing TRH and TSH result in?
Lower amounts of T3 and T4
What happens when there are lower levels of T3 and T4?
Offer less suppression of TRH and TSH, therefore more TSH and TRH are released equalling a rise in T3 and T4
The level of thyroid hormone is regulated by?
Negative feedback
What secretes cortisol?
2 Adrenal glands which sit above the kidneys
What is release of cortisol controlled by?
Hypothalamus
What is a trigger for cortisol release?
Stress
Cortisol is released in a _______ variation?
Diurnal variation
What does diurnal variation mean?
Increase and decrease at different times of day
When is the cortisol at peak?
Early morning (triggers wake up)
When is cortisol low?
Late night- triggers sleep
What does the hypothalamus release in the adrenal axis?
Corticotrophin release hormone (CRH)
What does CRH stimulate the release of?
Anterior pituitary to release adrenocorticotrophic hormone (ACTH)
What does ACTH stimulate the release of?
Cortisol from the adrenal gland
The series of hormone stimulation on the adrenal hormone axis?
CRH > ACTH > Cortisol
What is cortisol sensed by?
Hypothalamus and anterior pituitary
What does cortisol do to hormones?
Suppress the release of CRH and ACTH, resulting in lower amounts of cortisol
Actions of cortisol?
- Inhibits immune system
- Inhibits bone formation
- Increases metabolism
- Raises blood glucose
- Increases alertness
Where is growth hormone releasing hormone (GHRH) released from?
Hypothalamus
What does GHRH stimulate?
Growth hormone release from anterior pituitary
What does GH stimulate?
Release of insulin-like growth factor 1 (IGF-1) from the liver
Where releases IGF-1?
Liver
Functions of growth hormone?
- Stimulates muscle growth
- Increases bone density
- Stimulates cell regeneration & reproduction
- Stimulates growth of internal organs
What releases parathyroid hormone (PTH)?
4 parathyroid glands
What triggers PTH release?
Low serum calcium and low Mg and high serum phosphate
What does PTH do?
- Increases the activity and number of osteoclasts in bone, causing reabsorption of Ca from bone into blood therefore increasing serum calcium concentration
- Stimulates increase in calcium reabsorption in kidneys- meaning less calcium in urine
-Stimulates kidneys to convert Vit D3 into calcitriol (active form of Vit D3) which PROMOTES Ca absorption from food in the small intestine
3 effects of PTH?
- Increased calcium absorption from bone
- Increase calcium absorption from kidneys
- Increase calcium absorption from small intestine
What do the effects of PTH overall do?
Help to raise level of serum calcium
What happens when serum calcium is high?
Suppresses release of PTH (via negative feedback) reducing serum calcium level
Where is renin secreted from?
Juxtaglomerular cells that sit in afferent (some efferent) arterioles in the kidneys
What do juxtaglomerular cells do?
Sense the BP in vessels they secrete more renin in response to LOW BP and secrete less renin in response to HIGH BP
What does renin do?
Enzyme which acts to convert angiotensinogen (released by liver) into angiotensin 1
Where is angiotensinogen released from?
Liver
What does angiotensin 1 convert to?
Angiotensin 2 in the lungs with the help of angiotensin converting enzyme (ACE)
What does angiotensin cause?
Vasoconstriction by acting on blood vessels, resulting in increased Blood pressure
What does angiotensin 2 also stimulate release of?
Aldosterone from the adrenal glands
Mineralocorticoid steroid hormone acts on?
Nephrons in kidneys
What is the role of mineralocorticoids?
- Increase Na reabsorption from distal tubule
- Increase K secretion from distal tubule
- Increase H secretion from collecting ducts
What happens when Na is reabsorbed in the kidneys?
Water follows it by osmosis, leading to increase intravascular volume & subsequently BP
