Hypothalamo-pituary gland axis

Question 1

Where is the pituitary/hypophysis gland located?

Answer 1

Underneath the hypothalamus, in a small bone growth called Sella Turcica

Question 2

How many lobes does the hypophysis have ? What are their names (2 each) and loosely mention what type of tissue they are derived

Answer 2

2 lobes
Posterior lobe-neurohypophysis-derived from neural tissue
Anterior lobe-adenohypophysis-derived from mouth tissue

Question 3

What are hypothalamic nuclei? Where are they located? What types exist? Where do their axons go to?

Answer 3

Hypothalamic nuclei are dense bundle of cell bodies in the hypothalamus.
Supra-optic nuclei have magnocellular axons only going to the posterior lobe
Paraventricular nuclei can have magnocellular axons, or some are parvocellular with axons going to the median evidence primary capillary plexus

Question 4

How does blood flow within/between the hypothalamic-adreno axis?

Answer 4

Blood comes in from the superior hypophysial artery, then forms a bundle of leaky vessels at the median evidence (primary capillary plexus). The capilaries then straighten (long portal veins)-then secondary capillary plexus around the secreting cells, and onto circulartion (cavernous sinus, jugular)

Question 5

What are 3 steps of adrenohypopphysial secretion?

Answer 5

1) Hypothalamic neurosecretion
hypothalamic neurone is activated, and releases neurosecretion in median eminance through axons
2) Neurosecretion flows down and acts on target cells
3) Targetted cells release protein hormone into circulation

Question 6

What are the 5 hormones produced by adenophysial cells? And their targets

Answer 6

SOMATOTROPHS-Growth Hormone (Somatotrophin)-general tissue and mainly liver
LACTOTROPHS-prolactin-breast
THYROTROPHS-Thryroid stimulatinf hormone (TSH, Thryrotrophin) - Thyroid
GONADOTROPHS-Lutenising hormone or follicule stimulating hormone (LH, LSH) - Testes/ovaries
CORTICOTROPHS-Adrenocorctocotrphic hormone (ACTH) - Adrenal complex

Question 7

What are prohormones? Can you classify the 5 adrenophysial hormones?

Answer 7

Prohormones are precursors of protein hormones, inactive, and with extra part that are cleaved before secretion
Protein hormones-
Growth hormone-191aa
prolactin-199aa

Glycoproteins-an 99a subunit common to all, different B subunit
TSH
Gonadotrophins (LH, FSH)

Polypeptides
ACTH 39aa

Question 8

Describe the hypothalamic hormones, their targets, and their effect on the adrenophysial hormones?

Answer 8

Growth hormone-on switch is Growth hormone releasing hormone (GHRH), off switch is somatostatin
Prolactin-constant negative by dopamine (need low dopamine to lactate). Thyroid Releasing hormone has small effect
TSH-activated by TSH
Gonadotrophins-activated by Gonadotrophins releasing hormone (GnRH)
ACTH-activated by Corticotrophin releasing hormone, vasopressin

Question 9

Explain the different effects of GH (somatotrophin)

Answer 9

GF targets general tissues in the body, especially muscle and bone for growth, leading to increasing growth and development
But GF also targets the liver with produces SOMATOMEDINS (IGF1/2)-they also target body tissues with similar effect
=>double effect
Both have a metabolic effect: increase aa intake and protein synthesis, increased gluconeogenesis, increased lypolysis, increase growth

Question 10

Describe the different levels of negative feedback on Growth hormone

Answer 10

Growth hormone is released after GHRH is produced, and then leads to IGF1 production
GH will negativly impact production of GHRH and increase somatostatin production in hypothalamus
IGF1 levels negative feedback on hypothalamus nuclei,. It also negativly regulates GH secretion from adenalprophysis
Stomach hormine ghrelin reduces Somatostatin, free FFA increases

Question 11

What are the main effector of increased GH

production?

Answer 11

Sleep, stress, oestrogen, exercise; fasting (hypoglyceamia), amino acid act on hypothalamus
Ghrelin (stomach) acts on adrenal gland directly

Question 12

Describe the characteritics of prolactin regulation

Answer 12

Dopamine inhibits prolactin release constantly
Breast suckling (post-partum) stimulated tactile receptors, and the afferent neural pathway links back to hypothalamic dopaminergic neurones-stopping dopamine production; This causes milk production

Question 13

Describe the location of the posterior pituitary, its vascular specificity

Answer 13

Posterior pituary is underneath the hypothalamus, stuck next to the anterior pituitary. It possesed a capillary plexus of veins near the bottom, connected to the hypophyseal artery and leading into general circulation

Question 14

Describe the 2 type of neurons in the hypothallamic nuclei that interact with the posterior pituitary

Answer 14

Supra-optic nuclei are megacellullar (large axons) that only go the the posterior pit capilaries. Paraventricularr nucclei can be magnocellular; but also parvocellular, with axons feeding into the median emergence and adenohypophesys, or even in the brain
They can both produce oxytocin or vasopresson

Question 15

What are Herring bodies of neurons?

Answer 15

Along the axon, stores of vesicles with the hormones in a vesicle-ready for release when activated. As the vesicles go down, hormone is cleaved and prepared for release

Question 16

Describe the structure of Vasopressin, oxytocin and recall their differences

Answer 16

Both are nonamers, with a cyclic ring of 6aa and a tail of 3. The similarity causes oxytocin to cross activate some vasopressin pathway
Vasopressin has phe (in cycle) and Arg (in tail)-where it gets it name Arginine vasopressin
While oxytocin has ile instead of phe and leu instead of arg

Question 17

Describe synthesis of vasopressin and oxytocin

Answer 17

Vasopressin is made from pre-provasopressin mRNA
The pre-prohormone has a golgi localisation segment-moves there where its cleaved of to make pro-vasopressin
Packed in vesicles with enzymes. Cleaved into AVP (Arg vasopress), neurophysin, glycopeptide before release (all together)
Oxcytocin is exactly the same except neurophysin is different and no glycopeptide

Question 18

What receptors can Vasopressin bind to? How do they act and where are they located?

Answer 18

Vasopressin can bind V1 and V2 receptors
V1 receptors are linked to PLC, using IP3 to increase intracellular Ca2+ and DAG for PKC
V2 are GCPR linked to adenylyl cyclase, cAMP and PKA
V1a receptors mostly act in smooth muscle cells for vasoconstriction. V1b in corticotrophs (ACTH)
V2-Kindey collecting duct cells, lead to water reabsorption

Question 19

How does Vasopressin produce its anti diuretic effect?

Answer 19

Vasopressin effect in kindey collecting ducts caused stimulation water reabsorption-ANTIDIURETIC
AVP causes GCPR activation, cAMP increase, PKA activation. Leads to aquaporin 2 synthesis increase. Some already exist in aggaraphores (vesicle), and are brought to surface
Osmotic gradient pulls water in the pores, in the cell, then into blood throught AQP3/4

Question 20

What are the different effects of oxytocin?

Answer 20

Major effects/therapeutic advantages-Uterus contraction for giving birth and Mammary gland myoepithelial contraction to eject milk
Minor/unwanted effect-Cadiovascular, Kidney, CNS

Uterus effects- rhythmic contraction, increase local prostanoid production, dilation of cervix-supressed by progesterone, enhances by oestrogen (effect get high as pregancy get late)
Mammary gland-contraction of Myoepithelial cells
Other-Cadio-like vasopressin-vasodilation, tachycardia
Renal-Anti-diuresis
CNS-maternal behavior, tend and befriend

Question 21

How is Vasopressin homeostasis regulated?

Answer 21

Vasopressin
For the anti-diruetic effect, osmolality is measured by Osmoreceptors (in hypothalamus). When water drops, osmolality increase shrinks the cell-transmit effect to hypothalamic nucleic-increase vasopressin. At the same time, send message for thrist
When water is high/taken in, reduce osmolality, and swell osmoreceptors->reduce vasopressin

For the blood pressure, sensed by baroreceptors (normally inhibits with activation pulses. As BP drops, pulses get rarer-release inhibition and release vasopressin-vasoconstriction

Question 22

How is Oxytocin homeaostasis regulated?

Answer 22

Breast suckling cause neural receptors-afferent to brain, that links back to hypothalamus and neuropophysis->release oxytocin

Question 23

Can you decribe dyregulation effects for oxytocin and vasopressin?

Answer 23

For oxytocin-replaced by other means-barly important
Vasopressin-Diabetes Insipidus (low vaso)
Syndrome of innapropriate ADH (high Vaso)
Diabetes insipidus-very thristy (polydipsia), lot of urine (polyuria), dilute urine)
DI can be central/cranial (lack of vasopressin production) or Nephrogenic (kindey resistance to vasopressin)