Hormonal axis physiology

Question 1

The pituitary gland is made up of…

Answer 1

• Anterior pituitary

- Posterior pituitary

Question 2

What is the mnemonic to remember which hormones are produced and released by the anterior pituitary?

Answer 2

FLAT PiG:

• Follicle stimulating hormone (FSH)
• Luteinising hormone (LH)
• Adrenocorticotrophic hormone (ACTH)
• Thyroid stimulating hormone (TSH)
• Prolactin
• (ignore)
• Growth hormone (GH)

Question 3

Which hormones are stored and released by the posterior pituitary gland?

Where are these hormones produced?

Answer 3

• Oxytocin
• Antidiuretic hormone (ADH)

These hormones are produced in the hypothalamus

Question 4

Describe the thyroid axis

How is the thyroid axis regulated?

Answer 4

• Hypothalamus releases thyrotropin releasing hormone (TRH)
• TRH stimulates the anterior pituitary to release thyroid stimulating hormone (TSH)
• TSH stimulates the thyroid to release T3 and T4
• This is regulated by a negative feedback loop

Question 5

Describe the adrenal axis

How is the adrenal axis regulated?

Answer 5

• Hypothalamus releases corticotrophin releasing hormone (CRH)
• CRH stimulates the anterior pituitary to release adrenocorticotrophic hormone (ACTH)
• ACTH stimulates the adrenal gland to produce cortisol
• This is regulated by a negative feedback loop

Question 6

What is cortisol?

Answer 6

Cortisol is a steroid hormone which is produced by the adrenal gland in response to stressful stimuli

Question 7

How do cortisol levels vary throughout the day?

Answer 7

Diurnal variation (typically highest in the morning and lowest in the evening)

Question 8

Describe the growth hormone axis

How is the growth hormone axis regulated?

Answer 8

• Hypothalamus releases growth hormone releasing hormone (GHRH)
• GHRH stimulates the anterior pituitary to release growth hormone (GH)
• GH stimulates the liver to release insulin-like growth factor 1 (IGF-1)
• This is regulated by a negative feedback loop

Question 8

What effect does parathyroid hormone have on the body?

Answer 8

Increases serum calcium via the following mechanisms:

• In the bone (by increasing osteoclast activity)
• In the kidney (by increasing reabsorption of calcium)
• In the small intestine (by stimulating the kidneys to convert vitamin D3 into calcitriol, which is the active form of vitamin D that promotes calcium absorption in the small intestine)

Question 9

Describe the parathyroid axis

How is the parathyroid axis regulated?

Answer 9

Parathyroid hormone (PTH) is released from the four parathyroid glands in response to:

• Low serum calcium
• Low serum magnesium
• High serum phosphate

This is regulated by a negative feedback loop

Question 10

What happens to angiotensin I?

Answer 10

Angiotensin I is converted to angiotensin II in the lungs with the help of an enzyme called angiotensin converting enzyme (ACE)

Question 11

What is renin?
Where is it produced?
What is it produced in response to?
What is its function?

Answer 11

• Renin is an enzyme produced by the juxtaglomerular cells in the afferent arterioles in the kidney in response to low blood pressure
• Renin converts angiotensinogen (produced by the liver) into angiotensin I

Question 12

What effect does angiotensin II have on the body?

Answer 12

Angiotensin II causes:

• Vasoconstriction, which increases blood pressure
• Aldosterone to be released by the adrenal glands

Question 14

What is aldosterone?

What effect does aldosterone have on the body?

Answer 14

Aldosterone is a steroid hormone produced by the adrenal glands in response to aldosterone

Aldosterone acts on the nephrons in the kidney to:

• Increase REABSORPTION of sodium (and therefore water) thereby increasing blood pressure
• Increase ELIMINATION of potassium and hydrogen ions