Pituitary Gland And Regulation Of The Endocrine System

Question 1

How are the pituitary gland and the hypothalamus connected?

Answer 1

The pituitary lies inferior to the hypothalamus, and is connected to it by a slender pituitary stalk called the infundibulum

Question 2

Name the three main places in the hypothalamus that neurons travelling to the pituitary arise.

Answer 2

Ventral hypothalamus
Paraventricular nuclei
Supraoptic nuclei

Question 3

When all the neurons from the hypothalamus join together, what do they form?

Answer 3

The hypothalamic hypophyseal tract - becomes the posterior pituitary lobe

Question 4

What is the name of the circulation system in the hypothalamus/pituitary that carriers hormones from one to the other?

Answer 4

Hypophyseal portal system

• primary capillary plexus
• hypophyseal portal vein
• secondary capillary plexus

Question 5

What are the secretly cells of the anterior pituitary called?

Answer 5

Secretory cells of the adenohypophsysis

Question 6

What is the neurophypophysis?

Answer 6

A storage for hypothalamic hormones in the posterior pituitary

Question 7

What happens in the primary capillary plexus?

Answer 7

Hormones from the hypothalamus are released into the hypophyseal portal system, and flow down, mainly towards the anterior pituitary

Question 8

What is the blood supply to the infundibulum and pituitary?

Answer 8

Superior hypophyseal artery

Inferior hypophyseal artery

Question 9

Which cells in the anterior pituitary react to growth hormone releasing hormone (GHRH), and what do they release?

Answer 9

Somatotrophs (50%)

- release growth hormone

Question 10

Which cells in the anterior pituitary react to gonadotropin releasing hormone (GnRH) and what do they release?

Answer 10

Gonadotrophs (10%)

• follicle stimulating hormone (FSH)
• luteinising hormone (LH)

Question 11

Which cells in the anterior pituitary react to corticotrophic releasing hormone (CRH), and what do they release?

Answer 11

Corticotrophs (10-15%)

- adrenocorticotrophic hormone (ACTH)

Question 12

Which cells in the anterior pituitary react to thyroid releasing hormone (TSH), and what do they release?

Answer 12

Thyrotrophs (5%)

- Thyroid stimulating hormone (TSH)

Question 13

Which cells in the anterior pituitary react to dopamine, and what do they release?

Answer 13

Lactotrophs (20%)

- dopamine inhibits prolactin release

Question 14

Briefly describe the growth hormone axis.

Answer 14

The hypothalamus releases growth hormone releasing hormone and somatostatin
GHRH induces GH release from the anterior pituitary and somatostatin inhibits GH release
GH acts on the liver, bone, adipose tissues and metabolism
The liver produces IGF-1 - which excerpts an indirect effect on bone, adipose tissue and metabolism
GH and IGF-1 both have a negative feedback effect on the pituitary and hypothalamus

Question 15

What is notable about GH secretion?

Answer 15

It is pulsatile - and mainly only has effects in childhood

Question 16

Which physiological occurrences increases GHRH release?

Answer 16

Stress
Exercise
Sleep
Hypoglycaemia

Question 17

Which physiological occurrences increase the amount of CRH?

Answer 17

The time of the day
Illness
Stress

Question 18

What large molecule is ACTH a derivative of?

Answer 18

POMC - Pro-opiomelanocorticotrophin

Question 19

What effects does testosterone have on the HPG axis?

Answer 19

It stimulates Sertoli cells (which produce inhibin)

It has a negative effect on the hypothalamus and the anterior pituitary

Question 20

What are the actions of prolactin, and when is it upregulated?

Answer 20

It develops the mammary gland and stimulates lactation

- only physiologically active in pregnancy

Question 21

What hormones have a positive and a negative effect on prolactin release?

Answer 21

Positive - oestrogen

Negative - dopamine (from hypothalamus)

Question 22

Which two hormones does the posterior pituitary release?

Answer 22

ADH

Oxytocin

Question 23

What is the function of oxytocin?

Answer 23

Important in labour and breastfeeding
Stimulates cervical dilation and uterine contractions by increasing prostaglandin production
Important in sexual arousal, recognition, trust, anxiety and mother-infant bonding - the love hormone
‘Let-down’ reflex in response to suckling

Question 24

Name two disorders of the posterior pituitary.

Answer 24

Diabetes insipidus - lack of ADH release

Syndrome of inappropriate ADH (SIADH - too much ADH)

Question 25

Name two general pituitary disorders.

Answer 25

Pituitary tumours | Hypopituitarism

Question 26

Which hormones form the antiretroviral pituitary can easily be produced in excess

Answer 26

ACTH TSH GH Prolactin

Question 27

Describe the normal action of ADH.

Answer 27

ADH binds to vasopressin receptor 2 on the basolateral membrane of the kidney collecting duct cells This promotes insertion of aquaporin 2 channels on the apical membrane, increasing water reabsorption from the tubule - decreases urine volume - maintains blood pressure

Question 28

What is diabetes insipidus?

Answer 28

Either a lack of ADH, or a resistance to ADH | Leads to massive water loss in the urine

Question 29

What are the clinical features of diabetes insipidus?

Answer 29

Polyuria Polydipsia Nocturia - DM and hypercalcaemia must be excused first

Question 30

What are the cranial and nephrogenic causes of DI?

Answer 30

Cranial - lack of ADH production by the posterior pituitary - can be genetic or caused by trauma, infections or inflammatory conditions of the posterior pituitary Nephrogenic -resistance to ADH - can be genetic or secondary to drugs (e.g. Lithium), metabolic upset or renal disease

Question 31

To test for DI, you must perform a water deprivation test. What is this?

Answer 31

The patient is deprived of fluid for 8 hours | The plasma and urine osmolality must be checked every 2-4hrs

Question 32

What results would you expect from a water deprivation test, if the patient has DI?

Answer 32

Their starting plasma osmolality will be high | Their final urine osmolality will be less than 300mOsmol/l (compared to a normal person - over 600mOsmol/l)

Question 33

To assess whether the problem is cranial or nephrogenic, what should you do after the 8 hours?

Answer 33

Give a synthetic ADH (ddAVP) and asses urine osmolality - if the cause is cranial, the osmolality should rise back to normal levels - if the cause is cranial, the osmolality will remain low

Question 34

What is the treatment of cranial DI?

Answer 34

Desmopressin (ADH analogue) - can be given orally, nasal spray, injection - keep monitoring plasma sodium and osmolality to ensure they aren't taking too much and retaining too much water

Question 35

How is nephrogenic DI treated?

Answer 35

This is more difficult because the kidney isn't responding to ADH, whether it is present or not. Try and treat the underlying cause Try very high doses of ddAVP

Question 36

How common are pituitary adenomas, and how serious are they?

Answer 36

10% of the population has one - relatively not dangerous - asymptomatic

Question 37

If a pituitary adenoma is found, what tests need to be done to make sure it isn't causing a problem?

Answer 37

Check for any hormone excess Check for hypopituitarism Assess visual fields - pituitary is located just below the optic chiasm - tumour can extend up and push on chiasm, reducing peripheral vision (bitemporal hemianopia)

Question 38

Give some examples of secretory pituitary adenomas.

Answer 38

Prolactin - Prolatinoma - 30% ACTH - Cushing's disease - 20% GH - Acromegaly - 15% TSH - TSHomas - very rare, less than 1%

Question 39

What are the clinical features of a prolactinoma?

Answer 39

Galactorrhoea Menstrual disturbance and sub-fertility in women Reduced libido and erectile dysfunction in men

Question 40

How are prolactinoma's managed?

Answer 40

Dopamine agonists, increase dopamine to keep prolactin down - cabergoline Surgery if the tumour is large and has visual field effects

Question 41

What are the signs and symptoms of acromegaly?

Answer 41

Sweats, headache, tiredness, increasing ring/shoe size, joint pains Coarse facial appearance, enlarged tongue, hand + feet and visual field loss

Question 42

What are some of the complications associated with acromegaly?

Answer 42

Hypertension Diabetes or impaired glucose tolerance Increased risk of bowel cancer Heart failure

Question 43

How do you diagnose acromegaly?

Answer 43

Glucose tolerance test - normally glucose administration reduces GH levels dramatically, adenomas of the somatotrophs don't allow this feedback -may show underlying DM or IGT IGF-1 test - long half life, so better than measuring GH levels Pituitary MRI - tumour usually a macroadenoma (>1cm), extending into surrounding structures

Question 44

How is acromegaly managed?

Answer 44

``` Surgery - by transsphenoid route - often not curative Medical therapy - before and after surgery - somatostatin analogues to inhibit GH secretion Pituitary radiotherapy - to treat residual tumour - risk of hypopituitarism and long term problems ```

Question 45

What is hypopituitarism

Answer 45

``` Failure of (anterior) pituitary function Most commonly affects a single hormone axis (normally FSH/LH), but can affect all of them (parahypopituitarism) ```

Question 46

What does hypopituitarism lead to?

Answer 46

Secondary gonadal/adrenal/thyroid failure

Question 47

In hypopituitarism, hormone replacement is needed. If all the axis are affected, which hormone should be replaced first?

Answer 47

Cortisol

Question 48

List some of the causes of hypopituitarism.

Answer 48

Tumours - sometimes maintained or slightly increased prolactin Radiotherapy Infarction - called Sheehan's syndrome if postpartum Infiltration (e.g. Sarcoid) - can also affect posterior pituitary Trauma