Hypothalamus and post pituitary KAAP630

Parts of the pituitary gland

Anterior pituitary and posterior pituitary

Anterior = Adenohypohysis

Posterior = neurohypophysis

How many hormones are released from the anterior pituitary?

6 hormones

How many hormones are released from the posterior pituitary?

2 hormones

Why is the posterior pituitary called neurohypophysis?

It is an extension of neuronal tissue from the hypothalamus. Part of the hypothalamus that extends down.

True or false

Hypothalamus regulates the release of hormones of the pituitary gland

True

The hypothalamus releases hormones that act on the pituitary

“releasing hormones”

What are the 6 hormones secreted by the anterior pituitary?

Adrenocorticotropic hormone (ACTH)

Follicle stimulating hormone (FSH)

Luteinizing hormone (LH)

Thyroid stimulating hormone (TSH)

Growth hormone (GH)

Prolactin

What are the 2 hormones secreted by the posterior pituitary?

Oxytocin

Antidiuretic hormone (ADH) or Arginine Vasopressin (AVP)

What are responsible for making hormones in the posterior pituitary?

Paraventricular and supraoptic nucleus in the hypothalamus (they are clusters of neurons in the hypothalamus that extend down to the posterior pituitary)

Function of oxytocin?

Stimulates smooth muscle contraction

-For childbirth and lactation

What is the synthetic form of oxytocin?

Pitocin and it is given to stimulate labor

Function of antidiuretic hormone (ADH); vasopression

Reduces water loss from the body to maintain plasma volume

-favors reabsorption of water from kidney tubules to capillaries to maintain body fluid

What are the 2 stimuli of antidiuretic hormone?

High plasma osmolality and low plasma volume

Steps to oxytocin binding to receptor

1. (Suckling or contraction) oxytocin binds to Gprotein coupled receptor

2. G protein is activated

3. G protein alpha subunit is cleaved off

4. binds to phospholipase C

5. breaks down PIP2 to IP3 and DAG

6. IP3 stimulates calcium release in sarcoplasmic reticulum

7. Increase in intracellular calcium, Ca2+ binds to calmodulin

8. This activates myosin light chain kinase

9. Stimulates smooth muscle contraction and actin myosin binding

How does the hypothalamus sense changes in osmolality and water concentration?

osmoreceptors in hypothalamus

Example of osmoreceptors working

High osmolality and low water concentration causes osmoreceptors to shrink. This causes a neural reflex in hypothalamus to release ADH which causes kidney to hold on to water

What happens if osmolality is normal but plasma volume is low?

Stretch receptors in the heart initiate a reflex to cause ADH release and cause vasoconstriction

What is the primary target of ADH?

Collecting duct of a nephron in the kidney (For water reabsorption)

How does ADH allow for water reabsorption in kidney

It allows for the insertion of aquaporins in the collecting duct of the kidney which allows for water absorption.

How would you expect the urine to be after ADH?

Smaller volume but more concentrated bc less water

What if there was no ADH acting on kidney?

Large volume of urine but diluted

Steps of ADH binding

1. High osmolality or Low plasma concentration is sensed by the neurons in the hypothalamus

2. Stimulates the release of ADH from the posterior pituitary

3. ADH binds to V2 receptor

4. G protein is activated and the alpha subunit is cleaved off

5. stimulates adenylate cyclase which drives conversion of cAMP

6. ATP → cAMP

7. cAMP stimulates protein kinase A

8. protein kinase A makes and mobilizes the aquaporin channels

9. Inserts them in the apical membrane of the collecting duct which allows for H20 reabsorption

10. Aquaporin-2 channels allow for H20 reabsorption in the kidney, aquaporin-3 channels allow h20 to exit and go back into the blood system

What types of aquaporins are used and created with ADH?

aquaporin-2 channels

What if osmolality is normal and plasma volume is low?

The heart baroreceptors in the carotid and aorta send signals to the brain (hypothalamus) to release ADH to cause vasoconstriction

Steps of (ADH) AVP binding

1. AVP binds to V1 receptor

2. G protein is activated and alpha subunit is cleaved off

3. stimulates phospholipase C which breaks down PIP2 into ip3 and dag

4. IP3 stimulates calcium release from sarcoplasmic reticulum and DAG stimulates protein kinase C

5. Protein kinase C allows the voltage gated Ca2+ channels to open which allows influx of calcium into the cell

6. This influx of calcium binds to calmodulin and activates myosin light chain kinase

7. Causes smooth muscle contraction which results in vasoconstriction

What is more sensitive to secretion of ADH

plasma osmolality or plasma volume

Plasma osmolality

What are the two targets of ADH

Kidney for water reabsorption and peripheral vasculature to cause vasoconstriction.

What is the 2nd messenger system for ADH in kidney and vasculature

Kidney = Adenylate cyclase (cAMP)

Vasculature = phospholipase C

Two major actions of ADH

Water reabsorption and vasoconstriction

What are the disorders of AVP?

Excess = hold too much fluid (Heart failure or nephrotic syndrome)

Deficiency = Can’t form concentrated urine - excess excretion (diabetes insipidus)

What are the two causes of diabetes insipidus?

Neurogenic and nephrotic

What is neurogenic caused by?

Most common. caused by trauma, cancer, inflammation or infection (AVP cant be released)

What is nephrotic/renal caused by?

Mutations in the receptor or Aquaporin 2 so can’t reabsorb water