Hormones Flashcards
What are hormones?
HORMONES fall under a group of are chemical substances that control and regulate metabolic and other cellular activities
Describe the types of hormones
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
Give a brief overview on the endocrine system
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
List the classes of hormones
Peptide
Catecholamine
Eicosanoid
Steroid
Vitamin D
Retinoid
Thyroid
Nitric oxide
List the peptide hormones
They include the pancreatic hormones insulin, glucagon, and somatostatin, the parathyroid hormone, calcitonin, and all the hormones of the hypothalamus and pituitary
Describe peptide hormones
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
Describe catecholamine hormones
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
Describe eicosanoid hormones
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
List the eicosanoid hormones
Prostaglandins (PG)
Leukotrienes (LT)
Prostacyclin (PGI2)
Thromboxane (TXA2)
Describe the steroid hormones
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
Describe the thyroid hormones
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.
Describe the biosynthesis of peptide hormones
Describe the biosynthesis of catecholamine hormones
Describe the biosynthesis of eicosanoid hormones
Describe the biosynthesis of steroid hormones
Describe the vitamin D hormone
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
Describe the biosynthesis of vitamin D hormone
Describe retinoid hormones
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
Describe the biosynthesis of retinoid hormones
Describe the biosynthesis of thyroid hormones
Describe nitric oxide hormone
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
Describe the mechanisms of hormone release
(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
What are the physiological effects of thyroid hormone
