Physiology: hypothalamus and pituitary gland

Question 1

ANATOMY AND PHYSIOLOGY
Hypothalamus
- What section of the brain is it from
- What ventricle is it associated with?

Pituitary gland
- Lies within what structure?

Answer 1

The diencephalon
The third ventricle

The sella turcica

Question 2

ANATOMY AND PHYSIOLOGY
Label the adjacent structures

Answer 2

Question 3

ANATOMY AND PHYSIOLOGY
If the pituitary gland compresses these structures, what are some potential consequences?
- Optic chiasm
- Carotid artery (intracranial)
- Carotid artery (intracavernous)
- Cranial nerves III, IV, V1, V2, VI

Answer 3

Optic chiasm: bitemporal hemianopia
- Compresses nasal parts of optic nerve, hence temporal visual fields are impacted
Carotid artery (intracranial): very occasionally, strokes
Carotid artery (intracavernous): headaches
Cranial nerves: palsy

Question 4

HYPOTHALAMUS PHYSIOLOGY
The hypothalamus has two types of neurons. What are these?

Answer 4

Magnocellular and parvocellula r

Question 5

HYPOTHALAMUS PHYSIOLOGY
Complete this table

Answer 5

Question 6

ANTERIOR PITUITARY
- Aka. what?
- Is it a true endocrine organ? Why?
- Name of the cells that produce hormones?

Answer 6

• Adenohypophysis
• Yes; lacks direct neural connections with the hypothalamus, made of epithelial cells and is highly vascularised
• ___ trops (eg. gonadotrophs…)

Question 7

POSTERIOR PITUITARY
- Aka. what?
- What tissue is it made of, and why?

Answer 7

Neurohypophysis
Neural tissue - as it’s an extension of the hypothalamus

Question 8

DEVELOPMENT OF THE PITUITARY
- Which of the 3 germ layers contributes to it?
- Origin of the anterior and posterior pituitary?

Answer 8

Ectodermal

Anterior pituitary: develops as an upgrowth of the pharynx (roof of mouth) from Rathke’s pouch, which rises upwards to meet the developing posterior pituitary

Posterior pituitary: develops as a downgrowth from the hypothalamus

Question 9

GROWTH HORMONE
Complete this diagram

Answer 9

Question 10

GROWTH HORMONE
- What daily pattern does it follow?
- Does its production increase or decrease over the lifespan?
- Are blood tests a reliable measure of GH? Alternative?

Answer 10

Circadian rhythm - peaks during sleep, lowest in early morning
Decreases
No - GH levels fluctuate a lot. IGF-1 is a better measure

Question 11

GROWTH HORMONE
- GhRH and dopamine increase GH production. What else increases GH production?
- Somatostatin decreases GH production. What else decreases GH production?

Answer 11

Increased by: hypoglycemia, trauma/stress/excitement, serotonin
Decreased by: hyperglycemia, obesity, increased blood FFA

Question 12

GROWTH HORMONE
In the liver, GH promotes IGF production.
Half lives of GH vs IGF?

Answer 12

IGF: ~20 hours
GH: <20 minutes

Question 13

DISORDERS
GH hypersecretion leads to what condition
- In children?
- In adults?

Answer 13

In children: gigantism
In adults: acromegaly

Question 14

DISORDERS
GH hyposecretion leads to what effects:
- In children?
- In adults?

Answer 14

Children: growth retardation, short stature, fasting hypoglycemia
Adults: abdominal obesity, reduced strength/exercise capacity

Question 15

PROLACTIN
- Label

Answer 15

Prolactin is aka. prolactin inhibiting hormone

Question 16

PROLACTIN
- What are the functions of prolactin?

Answer 16

• Breast development (ducts and glands) to produce milk

Question 17

PROLACTIN
- What happens to prolactin levels over pregnancy?
- What is the effect of suckling on prolactin secretion?
- Impact of oestrogen on the amount of lactotrophs
- Impact of prolactin on GnRH and estrogen? Implication of this?

Answer 17

Increase towards the end of pregnancy
Promotes prolactin secretion and milk production
Probably increases
Prolactin suppresses GnRH and estrogen synthesis - hence why you don’t ovulate during breastfeeding

Question 18

OXYTOCIN
- What receptors does it act on? What impact does it have?

Answer 18

Oxytocin receptors inhibit adenylyl cyclase/stimulates phospholipase C depending on the tissue

Question 19

OXYTOCIN
- Functions?

Answer 19

• Pregnancy: uterine SMC contraction during childbirth
• Contracts myoepithelial cells surrounding the alveoli in the mammary gland, triggering milk let down and ejection
• Promotes maternal behaviour towards the neonate
• Positive social interactions

Question 20

OXYTOCIN
- Describe the positive feedback of SMC contraction during childbirth

Answer 20

Head of the fetus pushes against the cervix - distending the cervix

Nerve impulses from the cervix are transmitted to the brain

The brain stimulates the posterior pituitary gland to secrete oxytocin

Oxytocin stimulates uterine contractions and pushes the fetus towards the cervix

Question 21

ADH
V1 receptors
- Where are they located?
- What signalling pathway is associated with it?

Answer 21

In vascular SMC
Phospholipase C
Vasoconstriction

Question 22

ADH
V1 receptors
- V1A receptor activation leads to what?
- V1B receptor activation?

Answer 22

V1A receptor: leads to vasoconstriction (via phospholipase C)

V1B: phospholipase C –> ACTH release –> behavioural and endocrine responses to anxiety/stress

Question 23

ADH
V2 receptors
- What signalling pathway is it associated with?
- Outcome of V2 activation?

Answer 23

Adenylyl cyclase

Inserts aquaporins into the luminal cell membrane in cells of the distal tubules of kidney –> increased water permeability –> increased water reabsorption

Question 24

DISORDERS
Syndrome of inappropriate ADH
- What happens to ADH secretion?
- What happens to serum osmolarity (and sodium concentration) versus urine osmolarity?

Answer 24

ADH secretion increases
Decreased serum osmolarity (and hyponatremia), increased urine osmolarity

Question 25

DISORDERS
Syndrome of inappropriate ADH
- Causes?

Answer 25

Ectopic ADH
Non neoplastic diseases of the lung
CNS disorders
Injury to hypothalamus or pituitary gland

Question 26

DISORDERS
Diabetes insipidus
- What happens to ADH secretion?
- Thus, what happens to serum osmolarity and urine osmolarity?
- Two key symptoms?
- Two key types?

Answer 26

Decreased ADH secretion
Serum osmolarity increases (and hypernatremia), decreased urine osmolarity

Polyuria and polydipsia
Nephrogenic (kidneys don’t respond to ADH) and central (decreased hypothalamic ADH production)

Question 27

DISORDERS
Pituitary adenomas
- Rank ACTH, GH and prolactin in terms of prevalence

Answer 27

Prolactin > GH > ACTH