Lecture 12 : Endocrine System

Question 1

Major Endocrine Organs

Answer 1

Pineal Gland - Melatonin synthesis
Pituitary Gland - FSH, GH, LH, AVP, Oxyt
Thymus - Thymopoletin and thymosin (T cell maturation)

Adrenal Gland - cortisol, epinephrine/ norepinephrine

Pancreas - Insulin and somatostatin

Ovary/Testis - Testosterone and Oestrogen/pogesterone

Question 2

cell communication: Endocrine Signalling

Answer 2

Definition: Hormones are released by endocrine glands into the bloodstream to reach distant target cells.
Key feature: Long-distance communication.
Speed: Slower, but effects are longer-lasting.
Examples:
Insulin (from pancreas) acting on muscles and liver.
Thyroid hormones (T3/T4) regulating metabolism.

Question 3

Cell Communication: Paracrine Signalling

Answer 3

Definition: Chemical messengers act on nearby (neighboring) cells without entering the bloodstream.
Key feature: Local signaling.
Speed: Fast and localized.
Examples:
Somatostatin released by pancreatic delta cells acts on nearby alpha and beta cells.
Growth factors affecting nearby tissue repair.

Question 4

Cell signalling: Autocrine signalling

Answer 4

Definition: The cell releases a signal that acts on itself by binding to its own receptors.
Key feature: Self-regulation.
Examples:
Immune cells (like T cells) releasing interleukins that promote their own activation.
Tumor cells releasing growth signals to stimulate their own proliferation.

Question 5

Neurocrine (Neuroendocrine) Signaling

Answer 5

Definition: A neuron releases a hormone or neuropeptide into the blood or onto target cells.
Key feature: Combines neural signaling with hormonal effects.
Examples:
Vasopressin and oxytocin released by neurons in the hypothalamus and secreted into the blood via the posterior pituitary.
Norepinephrine released by sympathetic neurons onto the heart.

Question 6

Metabolism of hormones:

Answer 6

Hormones circulate either bound to a carrier protein or ‘free’

● Free hormone concentration dictates availability

● Bound hormone increases half life

● Free hormone concentration dictates physiological response

● Kidney/Liver primary sites of hormone catabolism

● Target cell also breaks down hormone

Question 7

Control of Endocrine activity: The Hypothalamic pituitary axis

Answer 7

Infundibulum (stalk) connects pituitary to brain

Posterior pituitary (neurohypophysis)-extension of neural tissue

● Anterior Pituitary (epithelial lineage)-true endocrine gland