55.1 Functions of the Hypothalamus

Question 1

What are examples of the functions of the hypothalamus?

Answer 1

• Endocrine
• Autonomic
• Survival functions (eating, sleep, sexual behaviour, aggression)

Question 2

What are the different hypothalamic nuclei?

Answer 2

Question 3

What are the roles of the hypothalamic nuclei?

Answer 3

Homeostasis, rhythms, development (e.g. puberty), metabolism, control of ANS, and endocrine system control

Question 4

How is the circuitry of the hypothalamus different to other brain areas?

Answer 4

• There are both neural and extensive non-neural interconnections
• Interconnections are bidirectional (besides a few exceptions like retinal input)

Question 5

Which systems is the hypothalamus interconnected with?

Answer 5

• Limbic circuits
• Sensory and autonomic circuits
• Neurohumoral systems: Pituitary gland, circumventricular organs

Question 6

What do the connections to the pituitary gland and circumventricular organs allow?

Answer 6

Monitoring of plasma levels of hormones, metabolites, and plasma osmolarity

Question 7

How do hypothalamic neurons connect to the anterior posterior pituitary gland?

Answer 7

Secrete releasing factors into primary capillary plexus in the median eminence
Travel via hypothalamic-hypophyseal portal vessels to anterior pit

Question 8

How do hypothalamic neurons connect to the posterior pituitary gland?

Answer 8

Directly travel down into posterior pit
Secrete vasopressin/oxy into blood supply

Question 9

What are the circumventricular organs and their role?

Answer 9

Structures in the brain with extensive and highly permeable capillaries (no BBB)
Either sensory or secretory
In contact with CSF and blood so permit communication between CNS and peripheral blood

Question 10

What are examples of sensory circumventricular organs?

Answer 10

Area postrema
Subfornical organ (SFO)
Organum vasculosum of Lamina terminalis (OVLT)

Question 11

What are examples of secretory circumventricular organs?

Answer 11

Pituitary gland
Median eminence
Pineal gland

Question 12

How does the hypothalamus control metabolism?

Answer 12

• Appetite control - leptin, insulin etc signalling
• Thyroid (T3) action
• Glucose sensing
• Amino acid sensing

Question 13

What is the role of the hypothalamus in growth?

Answer 13

Releases GHRH to stimulate GH release
Releases somatostatin to inhibit GH release

(GH stimulates IGF-1 release from liver)

Question 14

What is the role of the hypothalamus in triggering puberty?

Answer 14

Kisspeptin activates GnRH neurons to start releasing GnRH in 90 min pulses
Causes FSH and LH release from anterior pit

Question 15

Which hypothalamic nuclei is involved in blood pressure and volume control?

Answer 15

Paraventricular
Supraoptic

Question 16

Which circumventricular organ senses changes to blood osmolarity?

Answer 16

OVLT

Question 17

What exactly does the OVLT sense?

Answer 17

Extracellular NaCl and angiotensin II concentrations

Question 18

Describe the circuitry response to high dietary salt intake

Answer 18

Increases plasma sodium and osmolality - activates OVLT (and other sodium sensors)
Excites PVN and SON in hypothalamus
Triggers vasopressin release from posterior pit
Causes vasoconstriction and water retention in kidney
Activates arterial baroreceptors which inhibit firing - decreases BP

Question 19

Which are the two main nuclei controlling the anterior pituitary gland?

Answer 19

Arcuate nucleus and paraventricular nucleus

Question 20

Which hormones are under control by the arcuate nucleus?

Answer 20

GnRH
GHRH
Prolactin

Question 21

Which hormones are under control by the paraventricular nucleus?

Answer 21

TRH
CRH
Oxytocin
Vasopressin (AVP)

Question 22

What are the two release-inhibiting factors released by the hypothalamus?

Answer 22

Dopamine
Somatostatin

Question 23

What does dopamine inhibit?

Answer 23

Prolactin secretion

Question 24

What does somatostatin inhibit?

Answer 24

Growth hormone secretion

Question 25

What does TRH stimulate?

Answer 25

TSH secretion from anterior pit

Question 26

What does TSH stimulate?

Answer 26

T3 and T4 release from thyroid gland Iodine uptake

Question 27

Which molecules provide negative feedback of TRH/TSH release?

Answer 27

T3 and T4

Question 28

What does CRH stimulate?

Answer 28

ACTH release from anterior pit

Question 29

What does ACTH stimulate?

Answer 29

Glucocorticoid secretion from adrenal gland

Question 30

How is stimulation of ACTH controlled by systemic circulation?

Answer 30

Inhibited by glucocorticoid --> negative feedback

Question 31

What stimulates CRH release from the hypothalamus?

Answer 31

Stress, hypoglycaemia

Question 32

What are the two types of feedback signals?

Answer 32

- Peripheral hormones - Metabolic signals (e.g. leptin)

Question 33

What is a common local effect of pituitary tumours?

Answer 33

Bitemporal hemianopia (and other visual disturbances) Compression on optic chiasm

Question 34

What is the most common pituitary tumour?

Answer 34

Prolactinoma - excessive growth of lactotrophs

Question 35

What are the symptoms of prolactinoma? (women/men/both)

Answer 35

Women: low oestrogen - irregular periods, acne, excessive body and facial hair Men: low testosterone - erectile dysfunction, decreased body and facial hair, enlarged breasts Both: low bone density, headaches, visual disturbances, infertility

Question 36

What does somatotroph adenoma cause?

Answer 36

Acromegaly (a rare condition where the body produces too much growth hormone, causing body tissues and bones to grow more quickly)

Question 37

What does corticotroph adenoma cause?

Answer 37

Cushing's syndrome

Question 38

How does a tumour of some pituitary cells affect the other cells?

Answer 38

Impairs their survival So less secretion of hormones from other cells

Question 39

What are the main releasing and inhibitory hormones produced by the hypothalamus that act on the anterior pituitary? [IMPORTANT]

Answer 39

Releasing: * GnRH * GHRH * TRH * CRH Inhibitory: * Somatostatin * Dopamine

Question 40

What are the roles of the hypothalamus in thermoregulation?

Answer 40

* Stimulating thermogenesis * Shivering, piloerection, skin vasoconstriction * Behaviours that increase body temperature * Stimulating heat loss * Sweating, skin vasodilation * Behaviours that promote body temperature cooling * Inducing fever

Question 41

Which part of the hypothalamus determines the body temperature set point? How can this set point be changed?

Answer 41

* Anterior hypothalamus * Set point can be elevated by pyrogens -\> PGE2 acting on EP3 receptors

Question 42

How can the supraoptic and paraventricular nuclei in the hypothalamus detect changes in blood osmolarity?

Answer 42

* They receive input from intrinsically osmosensitive neurons in the circumventricular organs (OVLT and SFO) and the nucleus tractus solitarius (NTS) * The supraoptic and paraventricular nuclei are also osmosensitive but are less well understood

Question 43

How can a cell be intrinsically osmosensitive?

Answer 43

* A change in osmolarity will cause cell swelling or shrinking, resulting in increased or decreased stretch of plasma membrane * This causes opening/closing of membrane ion channels via: * Direct stretch-activation of the ion channels * The ion channel being tethered to the ECM or the cytoskeleton, which causes it to open as the cell stretches * Indirect activation of the ion channels via a mechano-sensitive

Question 44

What does the posterior pituitary secrete?

Answer 44

Oxytocin and ADH