Hormone Chemistry PDF

Hormone Chemistry Three chemical classes: 1. Steroids Derived from cholesterol Sex steroids (such as estrogen) from gonads and corticosteroids (such as cortisol) from adrenals 2. Monoamines (biogenic amines) Made from amino a...

Hormone Chemistry Three chemical classes: 1. Steroids Derived from cholesterol Sex steroids (such as estrogen) from gonads and corticosteroids (such as cortisol) from adrenals 2. Monoamines (biogenic amines) Made from amino acids Dopamine, epinephrine, norepinephrine, melatonin, thyroid hormone Figure 17.14a,b © McGraw Hill 1  Hormone Chemistry 3. Peptides and glycoproteins Created from chains of amino acids Glycoproteins have a short carbohydrate chain with the polypeptide Examples: Hormones from both lobes of the pituitary Releasing and inhibiting hormones from hypothalamus Insulin is a large peptide hormone Figure 17.14c © McGraw Hill 2  Hormone Synthesis—Steroids Figure 17.15 © McGraw Hill 3  Hormone Synthesis—Peptides Synthesized in same way as any protein Gene is transcribed to mRNA Peptide is assembled from amino acids at ribosome Rough ER and Golgi may modify peptide to form mature hormone Example: Insulin begins as a single amino acid chain called proinsulin. A connecting portion is removed and converts proinsulin to insulin. Figure 17.16 © McGraw Hill 4  Hormone Synthesis—Monoamines Thyroid hormone is composed of two tyrosines (amino acid) Thyroid follicles actively accumulate iodine The iodine is attached to tyrosines within a thyroglobulin molecule One iodine produces monoiodotyrosine (MIT) Two iodines produce diiodotyrosine (DIT) MIT and DIT attach together: DIT + DIT = T4 DIT + MIT = T3 These are still bound to thyroglobulin They dissociate from thyroglobulin when the thyroid gland is stimulated by TSH to release them into the blood stream. Only process in human body that uses iodine Lack of iodine causes a thyroid disorder called goiter © McGraw Hill 5  Thyroid Hormone Synthesis and Secretion Figure 17.17 © McGraw Hill 6  Hormone Secretion Levels in the bloodstream fluctuate throughout the day Some are secreted on a daily (circadian) rhythm Some on a monthly rhythm (in a woman’s ovarian cycle) Others under the influence of stimuli that signify a need for them Neural stimuli Hormonal stimuli Humoral stimuli © McGraw Hill 7  Hormone Secretion Neural stimuli Nerve fibers supply some endocrine glands and elicit the release of their hormones – epi/norepi, OT Hormonal stimuli Hormones from the hypothalamus regulate secretion by the anterior pituitary gland Pituitary hormones stimulate other endocrine glands to release thyroid hormone, sex hormones, and cortisol Humoral stimuli: Refers to blood-borne stimuli Rising blood glucose concentration stimulates the release of insulin Low blood osmolarity stimulates the secretion of aldosterone Low blood calcium level stimulates the secretion of parathyroid hormone © McGraw Hill 8  Hormone Secretion Peptide hormones and catecholamines are stored in secretory vesicles of the endocrine cell When needed, they are released by exocytosis when the cell receives a stimulus to do so Steroid hormones are not stored or released by exocytosis They are released as fast as they are synthesized by diffusion through the cell surface Thyroid hormone (TH) also diffuses freely through plasma membranes It does accumulate in the gland awaiting a stimulus for secretion It is in the extracellular spaces enclosed by the thyroid follicles The stimulus (TSH) causes secretion © McGraw Hill 9  Hormone Transport Most monoamines and peptides are hydrophilic Mix easily with blood plasma Can leave capillaries and reach target cell Steroids and thyroid hormone are hydrophobic Bind to transport proteins to help them circulate through watery bloodstream Transport proteins protect circulating hormones Protection from being broken down by enzymes in the plasma and liver Protection from being filtered out of the blood by the kidneys © McGraw Hill 10  Hormone Receptors and Mode of Action Each target cell has a few thousand receptors for a given hormone Receptors act like switches turning on metabolic pathways when hormone binds to them Receptor–hormone interactions exhibit specificity and saturation Specific receptor for each hormone Saturated when all receptor molecules are occupied by hormone molecules © McGraw Hill 11  Hormone Receptors and Mode of Action Peptides and catecholamines Cannot penetrate target cell Bind to surface receptors and activate intracellular processes through second messengers Steroids and thyroid hormone Penetrate plasma membrane and bind to internal receptors (usually in nucleus) Influence expression of genes of target cell Take several hours to days to show effect due to lag for protein synthesis © McGraw Hill 12  Hormone Receptors and Mode of Action Figure 17.18 © McGraw Hill 13  Peptides and Catecholamines – Mode of Action Figure 17.19 © McGraw Hill 14  Peptides and Catecholamines – Mode of Action Figure 17.20 © McGraw Hill 15  Steroids and Thyroid Hormone – Mode of Action These behave differently – simple and direct Estrogen binds to nuclear receptors in cells of uterus Thyroid hormone enters target cell by means of an ATP- dependent transport protein These require several hours to days to show an effect Needs time for genetic transcription, translation and product accumulation to effect target-cell metabolism © McGraw Hill 16  Signal Amplification Hormones are extraordinarily potent chemicals One hormone molecule can activate many enzyme molecules Very small stimulus can produce very large effect Circulating hormone concentrations in blood are relatively low Figure 17.21 © McGraw Hill 17  Modulation of Target-Cell Sensitivity Up-regulation means number of receptors is increased Sensitivity is increased Down-regulation reduces number of receptors Cell less sensitive to hormone Happens with long-term exposure to high hormone concentrations © McGraw Hill 18  Hormone Interactions Synergistic effects—multiple hormones act together for greater effect Synergism between FSH and testosterone on sperm production Permissive effects—one hormone enhances the target organ’s response to a second later hormone Estrogen prepares uterus for action of progesterone Antagonistic effects—one hormone opposes the action of another Insulin lowers blood glucose and glycogen raises it © McGraw Hill 19  Hormone Clearance Hormone signals must be turned off when they have served their purpose Most hormones are taken up and degraded by liver and kidney Excreted in bile or urine Metabolic clearance rate (MCR) Rate of hormone removal from the blood Half-life: time required to clear 50% of hormone from the blood The faster the MCR, the shorter the half-life © McGraw Hill 20