Question

11. For each of the following hormones indicate whether it is tropic, which endocrine structure secretes it, what its major targets are, and how its release is regulated.

Antidiuretic hormone

Glucagon
Prolactin

Thyroid-stimulating hormone

Growth hormone

T3
GHRH

ACTH

Cortisol

FSH & LH

PIH

Oxytocin

Aldosterone

Insulin

Epinephrine

Answer 1

Anti diuretic hormone (Non-tropic)

Source- Anterior Pituitary Gland

Target- Tubular cells of Kidney (Mainly on DCT and principal cells of Collectiong duct)

Regulation- When their is fall in body water levels, ADH is secreted, and it helps in increased reabsorption of water from nephrons.

Glucagon (Non-tropic)

Source- Alpha cells of Pancreas

Target- Liver and adipose tissue

Regulation- When the concentration of glucose in blood falls, glucagon is secreted in blood stream to convert stored glycogen to glucose.

Prolactin (Non-tropic)

Source- Anterior pituitary gland

Target- Mammary gland

Regulation- Stimulation of nipples and mammary gland, as occurs during nursing of a baby results in release of prolactin.

Thyroid Stimulating Hormone(TSH) (Tropic)

Source- Anterior pituitary gland

Target- Thyroid gland

Regulation- TSH secretion is regulated by negative feedback mechanism of thyroid hormones. Higher the levels of thyroid hormone in blood, lower is the TSH release and vice versa.

Growth Hormone (GH) (Non-tropic)

Source- Anterior pituitary gland

Target- Liver, Adipocytes (For IGF-1 secretion)

Regulation- It is regulated by hypothalamus and mediators of GH actions. Major regulatory factors include GHRH, Somatostatin, GH releasing peptide, IGF-1.

T3 (Tri-iodothyronine) (Non-tropic)

Source- Thyroid gland

Target- Brain, bone, heart, muscles

Regulation- It is primarily regulated by TSH. As the blood concentration of thyroid hormones increases, they inhibit both TSH and TRH(Thyroid Release Hormone) leading to a halt of thyroid hormone producrion.

GHRH (Growth hormone- releasing hormone) (Tropic)

Source- Neurosecretory nerve terminals in brain

Target- Anterior pituitary gland

Regulation- Secretion of GHRH increses in response to physical and emotional stress. It is blocked by Somatostatin (Hypothalamic neurohormone)

ACTH (Adrenocorticotropic Hormone) (Tropic)

Source- Anterior pituitary gland

Target- Adrenal Cortex

Regulation- ACTH is secreted in response to Corticotropin-release hormone. CRH itself is inhibited by Glucocorticoids, making it a part of classical negative feedback mechanism.

Cortisol (Non-tropic)

Source- Adrenal Cortex

Target- Liver cells and Adipocytes

Regulation-When cortisol levels are incresed, it sends a negative feedback and release of CRH is decreased from hypothalamus which in turn decreases release of ACTH. Due to low levels of ACTH the level of Cortisol comes back to normal.The vice-versa scenario can also be appreciated.

FSH and LH (Tropic)

Source- Anterior pituitary gland

Target- Testes and ovaries

Regulation- Negative feedback mechanism is seen in regulation of FSH & LH hormones by GnRH. Product hormones of testes and ovaries (Testosterone, Progesterone and Estrogen) inhibits release of GnRH and also of FSH & LH.

PIH (Prolactin inhibitory hormone)

Source-  Hypothalamus

Target- Mammary glands

Regulation- In non pregnant female, PIH (now known to be dopamine) inhibits the prolactin activity on mammary glands.

Oxytocin (Non-tropic)

Source- Hypothalamus (Released from Posterior pituitary gland)

Target- Myoepithelial cells of Breast, Gravid uterus

Regulation- Oxytocin is controlled by a positive feedback mechanism where release of the hormone causes an action that stimulates more of its own release.

Aldosterone (Non-tropic)

Source- Adrenal Cortex

Target- DCT (Distal convulated tubules) of Kidney

Regulation- Production of aldosterone in adrenal cortex is regulated by the renin-angiotensin-aldosterone system. Renin is secreted from the kidneys in response to variations in BP, volume and plasma Na⁺ and K⁺ levels.

Insulin (Non-tropic)

Source- Beta cells of Pancreas

Target- Liver, Skeletal muscle, fat

Regulation- When the blood glucose levels are increased, insulin is employed to send glucose inside the cell. When the blood glucose levels are low, insulin concentration is decreased so adequate amount of glucose reaches the brain cells.

Epinephrine (Non-tropic)

Source- Adrenal medulla

Target-Liver, Adipocytes

Regulation- The major physiologic triggers of epinephrine release is upon stresses such as physical threat, excitement, noise, bright lights, fight.