Mod8-Obj6: Hormonal secretion is regulated via negative feedback

Question 1

Concentrations of circulating hormones depend on:

Answer 1

1. ) Rate of release
2. ) Speed of inactivation
3. ) Rate of metabolism and excretion

Question 2

Negative feedback

Answer 2

Involves the production of a signal from the target cell, which “feeds back” to the hormone producing cell (endocrine gland) to decrease the production and secretion of the hormone

-Maintains hormonal homeostasis

Question 3

Example of negative feedback

Answer 3

• The β-cells within the pancreas releases insulin in response to rising blood glucose levels (i.e. after a meal).
• Insulin acts on target cells, causing the uptake of glucose into cells, reducing blood glucose levels.
• The reduction in blood glucose levels “feeds back” to the β-cells of the pancreas to inhibit the release of insulin

Question 4

Positive feedback

Answer 4

Endocrine cell releases a hormone which acts on target tissue

-Signal feeds back to the endocrine cell and signal it to secret more of the same hormone, increase the levels circulating in the blood

Question 5

Example of positive feedback

Answer 5

Childbirth

• Posterior pituitary releases oxytocin which acts on the uterus leading to contraction of the uterus
• Stretch receptors on the cervix, feeds back to the posterior pituirary, leading to more oxytocin being released

Question 6

Stimuli that control the production and release of hormones from endocrine cells (3 types)

Answer 6

1. ) Humoral stimulus (ions or nutrients)
2. ) Hormonal stimulus (hormones)
3. ) Neural stimulus (neurotransmitters)

Question 7

Humoral stimulus

Answer 7

Secretion is controlled in direct response to changes in plasma levels of certain ions or nutrients

E.g.) Ca2+ (when levels decrease, the parathyroid gland is stimulated to secrete PTH, increasing plasma Ca2+ restoring it to normal)

Question 8

Neural stimulus

Answer 8

secretion is controlled by neurotransmitters released from nerve fibres ending on an endocrine cell

E.g.) Increased activity of preganglionic sympathetic fibres on the adrenal medulla which stimulates the release of adrenalin and noradrenalin

Question 9

Hormonal stimulus

Answer 9

Secretion is controlled in response to hormones produced by other endocrine cells

E.g.) Releasing hormones (RH) secreted from the hypothalamus, which stimulate the anterior pituitary gland to secrete hormones that stimulate other endocrine glands (thyroid gland adrenal cortex, gonads) to secrete their own hormones