Posterior Pituitary – ADH and Oxytocin, insulin

Where are ADH and oxytocin synthesized and released?

Synthesized in the hypothalamus
Released by the posterior pituitary (neurohypophysis)

What does ADH stand for and what is its main function?

Antidiuretic Hormone (Vasopressin)
Conserves water by increasing water reabsorption in the kidney (collecting ducts)

What stimulates ADH secretion?

↑ Plasma osmolality
↓ Blood volume or pressure
Angiotensin II

What is the receptor mechanism for ADH in the kidney?

V2 receptors → ↑ cAMP → Insertion of aquaporin-2 channels in the collecting duct

What are the effects of oxytocin?

Stimulates uterine contractions during labor
Stimulates milk ejection (let-down reflex) from mammary glands

What is the mechanism of oxytocin action?

Acts on Gq protein-coupled receptors
Increases IP3 and intracellular Ca²⁺ → muscle contraction

What are the main cell types in the pancreatic islets and their hormones?

Alpha cells → Glucagon
Beta cells → Insulin
Delta cells → Somatostatin
F cells → Pancreatic polypeptide

What are the main effects of insulin?

↓ Blood glucose
↑ Glucose uptake (GLUT4)
↑ Glycogen, lipid, and protein synthesis
Inhibits gluconeogenesis, lipolysis, and proteolysis

What are the main effects of glucagon?

↑ Blood glucose
↑ Glycogenolysis
↑ Gluconeogenesis
↑ Lipolysis

What is the role of GLUT4 and where is it found?

Insulin-responsive glucose transporter
Found in muscle, adipose tissue, heart

What is the role of GLUT2 and where is it found?

Bidirectional transporter (high Km)
Found in liver, pancreatic beta cells, kidney, intestine

What is the physiological role of insulin after meals?

• Promotes glucose uptake and storage

• Supports anabolism (energy storage)

• Prevents hyperglycemia