Hormones

Question 1

What are hormones?

Answer 1

HORMONES fall under a group of are chemical substances that control and regulate metabolic and other cellular activities

Question 2

Describe the types of hormones

Answer 2

Autocrine: these exert their effects within the tissues where they are produced. These are compounds such as cytokines that faciltate inflammation reactions an immune mechanism against bacteria
Paracrine: these exert their effects in the surrounding tissues where they are produced. Examples include the eicosanoids- prostaglandins,
Endocrine : these are called hormones and exert their effects at a distant site from where they are produced

Question 3

Give a brief overview on the endocrine system

Answer 3

System of ductless glands that secrete hormones
Hormones are “messenger molecules”- 1st messengers.
Transported in the blood
Act on distant target cells.
Target cells respond to the hormones for which they have receptors
The effects are dependent on the programmed response of the target cells
Hormones are just molecular triggers

Question 4

List the classes of hormones

Answer 4

Peptide
Catecholamine
Eicosanoid
Steroid
Vitamin D
Retinoid
Thyroid
Nitric oxide

Question 5

List the peptide hormones

Answer 5

They include the pancreatic hormones insulin, glucagon, and somatostatin, the parathyroid hormone, calcitonin, and all the hormones of the hypothalamus and pituitary

Question 6

Describe peptide hormones

Answer 6

Peptide hormones may have from 3 to 200 or more amino acid residues.
These hormones are synthesized on ribosomes in the form of longer precursor proteins (prohormones), then packaged into secretory vesicles and proteolytically cleaved to form the active peptides

Question 7

Describe catecholamine hormones

Answer 7

The water-soluble compounds epinephrine (adrenaline) and norepinephrine (noradrenaline) are catecholamines, named for the structurally related compound catechol.
They are synthesized from tyrosine.
Catecholamines produced in the brain and in other neural tissues function as neurotransmitters, but epinephrine is a h hormone, synthesized and secreted by the adrenal glands.
Like the peptide hormones, catecholamines act through surface receptors to generate intracellular second messengers.
They mediate a wide variety of physiological responses to stress

Question 8

Describe eicosanoid hormones

Answer 8

The eicosanoid hormones (prostaglandins, thromboxanes, and leukotrienes) are derived from the 20-carbon polyunsaturated fatty acid arachidonate.
Unlike the hormones described above, they are not synthesized in advance and stored; they are produced, when needed, from arachidonate enzymatically released from membrane phospholipids by phospholipase A2.
The enzymes of the pathway leading to prostaglandins and thromboxanes are very widely distributed in mammalian tissues.
The eicosanoid hormones are paracrine hormones, secreted into the interstitial fluid and acting on nearby cells

Question 9

List the eicosanoid hormones

Answer 9

Prostaglandins (PG)
Leukotrienes (LT)
Prostacyclin (PGI2)
Thromboxane (TXA2)

Question 10

Describe the steroid hormones

Answer 10

The steroid hormones (adrenocortical hormones and sex hormones) are synthesized from cholesterol in several endocrine tissues such as adrenal cortex, ovaries and testes.
They are transported to their target cells through the bloodstream bound to carrier proteins

Question 11

Describe the thyroid hormones

Answer 11

The thyroid hormones T4 (thyroxine) and T3 (triiodothyronine) are synthesized from the precursor protein thyroglobulin.

Up to 20 Tyr residues in thyroglobulin are enzymatically iodinated in the thyroid gland, then two iodotyrosine residues condense to form the precursor to thyroxine.
When needed, thyroxine is released by proteolysis.
Condensation of monoiodotyrosine with diiodotyrosine produces T3, which is also an active hormone released by proteolysis.
The thyroid hormones act through nuclear receptors to stimulate energy-yielding metabolism, especially in liver and muscle, by increasing the expression of genes encoding key catabolic enzymes.

Question 12

Describe the biosynthesis of peptide hormones

Question 13

Describe the biosynthesis of catecholamine hormones

Question 14

Describe the biosynthesis of eicosanoid hormones

Question 15

Describe the biosynthesis of steroid hormones

Question 16

Describe the vitamin D hormone

Answer 16

Calcitriol works in concert with parathyroid hormone in Ca2+ homeostasis, regulating [Ca2+ ] in the blood and the balance between Ca2+ deposition and Ca2+ mobilization from bone.
Acting through nuclear receptors, calcitriol activates the synthesis of an intestinal Ca2+-binding protein essential for uptake of dietary Ca2+.
Inadequate dietary vitamin D or defects in the biosynthesis of calcitriol result in serious diseases such as rickets, in which bones are weak and malformed

Question 17

Describe the biosynthesis of vitamin D hormone

Question 18

Describe retinoid hormones

Answer 18

Retinoids are potent hormones that regulate the growth, survival, and differentiation of cells via nuclear retinoid receptors.
All tissues are retinoid targets, as all cell types have at least one form of nuclear retinoid receptor.
In adults, the most significant targets include cornea, skin, epithelia of the lungs and trachea, and the immune system.
Retinoic acid (RA) regulates the synthesis of proteins essential for growth or differentiation.
Excessive vitamin A can cause birth defects

Question 19

Describe the biosynthesis of retinoid hormones

Question 20

Describe the biosynthesis of thyroid hormones

Question 21

Describe nitric oxide hormone

Answer 21

Nitric oxide is a relatively stable free radical synthesized from molecular oxygen and the guanidino nitrogen of arginine in a reaction catalyzed by NO synthase.
This enzyme is found in many tissues and cell types: neurons, macrophages, hepatocytes, myocytes of smooth muscle, endothelial cells of the blood vessels,and epithelial cells of the kidney.
NO acts near its point of release, entering the target cell and activating the cytosolic enzyme guanylyl cyclase, which catalyzes the formation of the second messenger cGMP

Question 22

Describe the mechanisms of hormone release

Answer 22

(a) Humoral: in response to changing levels of ions or nutrients in the blood
(b) Neural: stimulation by nerves
(c) Hormonal: stimulation received from other hormones

Question 23

What are the physiological effects of thyroid hormone