7.4 Hypothalamus and Pituitary

Question 1

Connections and involvement of hypothalamus

Answer 1

Nervous and endocrine involvement
Connected to limbic lobe (emotion)
Extensive connection between hypothalamus and rest of brain

Question 2

Pituitary gland gross anatomy

Answer 2

Pituitary gland is about 1cm in diameter.
Pituitary gland sits in ‘sella turcica’ inferior to the optic chiasm.
Posterior and anterior sections, joined to the hypothalamus via the stalk/infundibulum

Question 3

Posterior pituitary gland anatomy

Answer 3

Neurohypophysis
Extension of hypothalamus
Made of terminals of neurons from hypothalamus.

Question 4

What are the two nuclei that make hormones in the hypothalamus to be released by the neurohypophysis?

Answer 4

Nuclei of the cell bodies are the supraoptic nucleus and paraventricular nucleus.

Question 5

Two hormones made in hypothalamus and secreted from posterior pituitary gland?

Answer 5

Oxytocin and ADH/vasopressin

Question 6

Pathway of ADH/oxytocin production and release (anatomical)

Answer 6

Hormones made by supraoptic nucleus and paraventricular nucleus -> packaged into vesicles -> sent down axons into posterior pituitary gland -> stored in nerve terminals -> released upon stimulus -> secreted into ECS -> capillaries -> systemic circulation

Question 7

When is ADH released?

Answer 7

Release is stimulated by and increase in osmolarity (concentration of solutes), decrease in BP, increase in stressors (adrenergic).

Question 8

ADH’s effect in V2 receptors?

Answer 8

Binds to V2 receptors on kidney tubules:
Increase in cAMP (cyclic adenosine monophosphate) ->
Increase in insertion of aquaporins in collecting ducts ->
Increase in water reabsorption (less water lost in urine)

Question 9

ADH’s effect in V1 receptors?

Answer 9

Binds to V1 receptors on blood vessels (inc. renal vessels):
Increase in IP3 (inositol) and DAG (diacylglycerol) ->
Increase in [Ca2+] (from intracellular calcium stores) ->
Increase in vascular tone (contraction of smooth muscle in blood vessels)
Vasoconstriction

Question 10

ADH’s effect in V3 receptors?

Answer 10

Binds to V1b/V3 receptors on anterior pituitary corticotrophs (cells that produce and release ACTH):
Increase in IP3 (inositol) and DAG (diacylglycerol) ->
Increase in ACTH (adrenocorticotropic hormone) secretion ->
Increase in aldosterone (ACTH is only a part of the main regulation of aldosterone) ->
Increase in Na+ and water reabsorption (water follows salt)

Question 11

Main actions of oxytocin

Answer 11

Stimulates childbirth and breast feeding in positive feedback loops.

Question 12

Pathway for release of oxytocin after cervical stretch detected:

Answer 12

Cervical stretch -> sensory afferent neurons -> received in brain -> activation of hypothalamic neurons -> message to posterior pituitary gland -> release of oxytocin

Question 13

Childbirth feedback loop

Answer 13

Fetus drops lower -> cervical stretch -> uterine contractions

Cervical stretch -> Oxytocin from posterior pituitary -> Prostaglandins from uterine wall -> uterine contractions

Oxytocin from posterior pituitary gland -> uterine contractions

Uterine contractions -> cervical stretch

Question 14

Breast feeding pathways (controlled by different hormones):

Answer 14

Child’s cry -> Higher brain centers -> Hypothalamus -> PIH cell -> PIH decreased (dopamine) -> Anterior pituitary -> prolactin no longer inhibited, prolactin released -> milk produced

Child’s cry -> Higher brain centers -> Hypothalamus -> Oxytocin neuron -> Posterior pituitary -> oxytocin release -> smooth muscle contraction -> milk ejected

Question 15

What types of hormones are oxytocin and ADH?

Answer 15

Peptide hormones

Question 16

Anterior pituitary gland anatomy

Answer 16

Made of glandular epithelial tissue and actually produces hormones.
Larger than posterior.
Vascular connection with hypothalamus.
Also called adenohypophysis.

Question 17

Name the 7 hypophysiotropic hormones, their acronyms, and their effect

Answer 17

• Thyrotropin releasing hormone (TRH) - stimulates release of thyroid stimulating hormone (TSH) and prolactin
  
  • Corticotropin-releasing hormone (CRH) - stimulates release of adrenocorticotropic hormone (ACTH or corticotropin)
  • Gonadotropin releasing hormone (GnRH) - stimulates release of follicle-stimulating hormone (FSH) and luteinising hormone (LH)
  • Growth hormone releasing hormone (GHRH) - stimulates release of growth hormone
  • Growth hormone inhibiting hormone (GHIH) - inhibits release of growth hormone and TSH
  • Prolactin releasing hormone (PRH) - stimulates release of prolactin
    Prolactin-inhibiting hormone (PIH or dopamine) - inhibits release of prolactin

Question 18

Main pathway of hypophysiotropic hormone release:

Answer 18

In hypothalamus, short axon neurons which terminate in median eminence of the pituitary stalk -> release into capillaries of hypothalamic-hypophyseal portal system

Question 19

What hormones do hypophysiotropic hormones control?

Answer 19

Anterior pituitary hormones

Question 20

Features of a neuroendocrine system

Answer 20

Fast
Specific
Not diluted in systemic blood

Question 21

Anterior pituitary gland (cells, hormones, target, function)

Answer 21

Thyrotrophs (3-5%) - TSH - Thyroid - stimulates T3 and T4 secretion

Corticotrophs (15-20%) - ACTH - adrenal cortex - stimulates cortisol secretion

Somatotrophs (40-50%) - GH/somatotropin - bones, tissues, liver - essential for growth

Gonadotrophs (10-15%) - FSH and LH - ovaries and testes - essential for reproduction

Lactotrophs (10-15%) - Prolactin (PRL) - mammary glands - milk secretion