02: Hypothalamus-Pituitary Axis

Where does most hormone regulation start

In the brain

Portions of the brain involved in hormone secretion and regulation

Hypothalamus and pituitary

How are the hypothalamus and pituitary connected

A thin stalk

Types of hormones produced by the hypothalamus

Neurohormones

Function of hypothalamic hormones

Controls hormone release from other organs, particularly the anterior pituitary

Main hormones released by the posterior pituitary

ADH/vasopressin and oxytocin

What is the major control center of the body

Hypothalamus

Processes that the hypothalamus regulates

• Thermoregulation

• Thirst and appetite

• Emotions

• Sleep

• Sex drive

• Birth

• GIT secretions

• etc.

Fate of neurohormones once they leave the hypothalamus

• Stored by the posterior pituitary

• Acts on anterior pituitary

Neurohormones that act directly on their target hormones (not a releasing hormone)

• GH

• Oxytocin

• ADH

Neurohypophysis

Posterior pituitary

Adenohypophysis

Anterior pituitary

Types of cells in the anterior pituitary

• Acidophils

• Basophils

• Alpha cells

• Gamma cells

Patterns of release from the pituitary

• Repetitive fashion (every 1-3 hours)

• Circadian rhythm

What controls all secretions from the pituitary

Hypothalamus

Signaling pathway of a pituitary hormone that binds to a G_sPCR

Hormone binds → GDP swaps for GTP → activated G protein activates adenylyl cyclase → ATP converted to cAMP → activates PKA → cellular response

Major effect of growth hormone on the liver

Stimulates the release of insulin-like growth factor 1 (IGF-1)

IGF-1 function

Acts exactly like GH, but has a way longer half life

General affects of GH/IGF-1

• Increased bone and tissue growth

• Increased protein synthesis

• Decreased protein catabolism

• Increased lipolysis

• Decreased glucose utilization

Are most of the physiological affects mediated by GH or IGF-1

IGF-1

Normal pattern of GH release

Circadian rhythm (sleep!)

What additional factor stimulates GH release

Exercise

Why is low protein associated with increased levels of GH

The body is trying to stimulate protein synthesis

How to measure GH in blood

You don’t, go measure the IGF-1

What other hormone acts with GH to stimulate growth

Insulin

Action of GH in the cell

Controls gene expression

Hormone that controls GH release

GH releasing hormone (GHRH)

Hormone that inhibits GH release

Somatostatin

Condition associated with too much GH as a juvenile with open growth plates

Gigantism

Condition associated with too much GH as an adult with closed growth plates

Acromegaly

Condition associated with too little growth hormone

Dwarfism

Panhypopituitarism

Low GH secretion

Causes of panhypopituitarism

• Tumor

• Head trauma

• Brain surgery

• Radiation tx

• Stroke/hemorrhage

GH affect on cartilage and bone

Increases proliferation and activity of chondrocytes and oosteocytes

Bone changes due to gigantism

Growth the elongates the long bones

Bone changes due to acromegaly

Enlarged soft bones in face and head

Blood markers for patients with acromegaly

Consistently high GH in body

Hormone that causes water retention

ADH (anti-diuretic hormone/vasopressin)

What causes the release of ADH

High ion concentration in the interstitial fluid is sensed by osmoreceptors in the hypothalamus

What other receptors are triggered alongside the osmoreceptors involved in ADH release

Thirst receptors

Type of channel that moves water

AQP

What organ releases ADH

Posterior pituitary gland

What receptor does ADH bind to in the nephron tubules

V2 receptor

What type of receptor is the V2 receptor

G_sPCR

Result of ADH on nephron tubules

Upregulation of AQP2 in epithelial cells

How does ADH increase the presence of AQP2

ADH binds to V2 → activated adenylyl cyclase → cAMP production → activates PKA → phosphorylates AQP2 reservoirs in the cell → AQP2 moves to the plasma membrane

Diabetes insipidus

Decrease in ADH action, causing lots of water loss in urine

Types of diabetes insipidus

• Central

• Nephrogenic

Central diabetes insipidus

Defect in ADH secretion from the posterior pituitary → no water reuptake → PU/PD

Nephrogenic diabetes insipidus

Problem with V2 receptor or the signaling pathway → kidney resistance to ADH

Which type of diabetes insipidus can be reversed with exogenous ADH

Central diabetes insipidus

General physiological cause of nephrogenic diabetes insipidus

Kidney disease

Oxytocin hormone structure

Peptide hormone

Where is oxytocin released from

Posterior pituitary

Common causes of oxytocin release

• Labor

• Exercise

• Physical touch

• Breast feeding

Effect of oxytocin

• Uterine contractions

• Milk let down

• Positive bonding emotions

Oxytocin also stimulates the release of what hormone

Insulin