Lecture 21: HPA & GH

Question 1

Describe the role of the hypothalamus in the control of the pituitary function.

Answer 1

Hypothalamus releases hormones that can stim/inhibit pituitary hormone secretions via the hypophyseal portal system.
Releasing RH and IH can control the pituitary’s hormone secretion: hence function.

Question 2

Name all 6 (+2) hormones secreted by the hypothalamus and describe the role of each.

Answer 2

GHRH (somatotropin)= stim. GH release
GHIH (somatostatin)= inhibit GH release
GnRH= stim. FSH & LH
GnIH= inhibit FHS & LH
TRH= stim. TSH
CRH= stim. ACTH

ADH= reduce urine production by less H20 reabsorbed into kidney collecting ducts to the blood
Oxytocin= stim. milk let down & uterine contraction

Question 3

A GP notices one of her patients has developed coarse facial features: broader nose, thicker lips over the 5yrs she’s known them. Upon questioning, they have needed to buy larger sized shoes recently and their wedding ring is too tight.
What is your diagnosis and what factor would normally control this hormone?

Answer 3

Acromegaly as they have abnormal growth even after the epiphyseal plates have closed (hence coarser features, enlarged hands and feet).

Normally, hypothalamic GHRH and GHIH would control the anterior pituitary secretion of GH. To cause this excessive growth, there could a GH-secreting pituitary tumour so there are higher levels of GH if there is a normal level of GHRH.

Question 4

Your 47yrs patient comes in with coarse features and enlarged hands and feet. When questioning, they tell you that their friends have noticed that their voice has deepened. You suspect that they have acromegaly.

What would you do to further confirm your diagnosis?

Answer 4

OTT with GH response (normally: higher plasma glucose/FA= decrease GH secretion)

If you failed to suppress GH< 1μg/L

Elevated IGF-1 levels in relation to age

GH day curve - find the mean elevated GH

-PET scan to confirm that there is a pituitary adenoma

Question 5

A GP diagnoses her patient with acromegaly which is a condition in which there is excessive GH secretion.

What types of treatment can the GP discuss with the patient?

Answer 5

• Surgical removal of pituitary adenoma
• Radiotherapy removal
• Prescribe dopamine agonists (cabergoline, bromocriptine)
• Prescribe somatostatin analogues (octreotide, lanreotide)
• Block the GH receptor using pegvisomant

Question 6

Explain why the pituitary gland is considered the “master endocrine gland”.

Answer 6

Pituitary secretes tropic hormones that control (stim/inhibit) other endocrine glands/tissues’ secretions.

Question 7

Name all 6 APG hormones and describe what each does.

Answer 7

ACTH= aldosterone, cortisol, androgens
TSH= T3 + T4
Prolactin= milk production
GH= growth
FSH= ovary and testis' function
LH= ovary & testis' hormone production

Question 8

What does the term “short-loop” negative feedback refer to regarding the control of hormonal secretions from the HPA?

Answer 8

A negative feedback loop, in terms of HPA, is where the hypothalamus secretes tropic hormones that will start a chain of hormone secretions in other endocrine glands. Their secretions will then inhibit the hypothalamus from secreting any more tropic hormones.

Short loop is where a pituitary hormone inhibits the hypothalamic hormone secretion so it negates the overall response.

Question 9

Explain the mechanism by which GH can exert a direct effect on target tissues.

Answer 9

GH binds to plasma membrane receptors that directly causes intracellular responses within target tissues.

Question 10

Explain the mechanism by which GH can exert an indirect effect on target tissues.

Answer 10

IGF hormones are produced from liver & MSK cells: as a response to GH production.
Mainly IGF-1 stimulate body growth and metabolism regulation by binding to IGF receptors on target cell membranes.

Question 11

Briefly explain why a non-functioning pituitary tumour can cause problems in vision.

Answer 11

The pituitary is in close proximity to the optic chiasm. If the pituitary adenoma grows and compresses the optic chiasm, it will cause vision problems like peripheral vision loss (tunnel vision).

Question 12

Which condition is caused by excess GH secretion in adults (after epiphyseal growth plates closure in long bones)?

Give as many symptoms and signs you can.

Answer 12

Acromegaly.

• coarser facial features (broader nose, thicker lips)
• deepened voice
• enlarged hands and feet
• greasy skin (excessive sweating)
• prominent supraorbital ridge

Question 13

What is the embryological origin of the APG?

Answer 13

The APG arises from an up-growth of ectodermal cells from the roof of the primitive pharynx.

Evagination of oral ectoderm (Rathke’s pouch/ primitive gut tissue)

Question 14

A 25yrs woman and her 26yrs male partner present to their GP concerns around conceiving. Subsequent investigations reveal that the man has a low sperm count.

Which hormone is deficient for this to occur?

Answer 14

FSH: responsible for ovaries and testis function

Question 15

In which nuclei of the hypothalamus are the neurones, that synthesise ADH & Oxytocin, located?

Answer 15

Supraoptic and paraventricular nuclei.

Question 16

Describe how the hypophyseal portal system works to release APG hormones.

Answer 16

1. Hypothalamic tropic hormones are secreted.
2. These are transported down axons and stored in the median eminence.
3. The hormones are released into the 1˚ then 2˚ capillary bed of the hypophyseal portal system into the APG.
4. The tropic hormones interact with the target endocrine cells in the APG.
5. Endocrine hormones secreted from the APG into the bloodstream to act on distant target tissues.

Question 17

A 32yrs woman with BMI=30kg/m² has been trying to conceive for 2nd child but has been unsuccessful. She is experiencing galactorrhoea and has had no menses for 11 months.

What is galactorrhoea and why might this patient have this symptom?

Answer 17

Milky discharge = galactorrhoea

There is more prolactin secretion from possibly a prolactin-secreting pituitary adenoma.