Most hormones are amino-acid based. Size varies from simple amino acid derivatives which include amines and thyroxine constructed from the amino acid tyrosine, to peptides (short chains of amino acids), to proteins (long polymers of amino acids).
Steroids are synthesized from cholesterol. Of the hormones produced by the major endocrine organs, ONLY gonadal & adrenocortical hormones are steroids.
Eicosanoids, include leukotrienes and prostaglandins, we must add a third class. These biologically active lipids(made from arachidonic acid) are released by nearly all cell membranes. Leukotrienes are signaling chemicals that mediate inflammation and some allergic reactions. Prostaglandins have multiple targets & effects, ranging from raising blood pressure & increasing the expulsive uterine contractions of childbirth to enhancing blood clotting, pain, and inflammation. Eicosanoids are highly localized, affecting only nearby cells, they generally act as paracrines and autocrines and do not fit the definition of the true hormones, which influence distant targets.
Is a protein hormone structurally similar to GH. Produced by the lactotrophs, PRL stimulates the gonads of some animals (other than humans) and is considered a gonadotropin. Its effect in humans is to produce milk. (pro=for; lact=milk) The release of PRL is controlled primarily by an inhibitory hormone, (PIH) prolactin inhibiting hormone, now known to be dopamine (DA) which prevents prolactin secretion. Decreased PIH secretion leads to surge in PRL release. There are a number of prolactin releasing factors, including TRH. In females, prolactin levels rise and fall in rhythm with estrogen blood levels. Estrogen stimulates prolactin release, both directly and indirectly. A brief rise in prolactin levels just before the menstrual period partially accounts for the breast swelling and tenderness but because it is so brief breasts do not produce milk. In pregnant women, PRL blood levels rise dramatically toward the end of pregnancy, milk production becomes possible. After birth, the infant's suckling stimulates release of prolactin-releasing factors in the mother, encouraging milk production & availability. They influence the energy metabolism of most body cells and help us to resist stressors.
NORMAL Circumstances - they help body adapt to intermittent food intake by keeping blood glucose levels fairly constant, and maintain blood pressure by increasing the action of vasocontrictors.
STRESS - due to hemorrhage, infection or physical/emotional trauma evokes a higher output of glucocorticoids which helps the body negotiate crisis.
Glucocorticoid hormones include corisol (hydrocortisone), cortisone, and corticosterone, but only cortisol is secreted in significant amounts in humans.
Basic Mechanism of glucocorticoid action is to modify gene activity. Glucocorticoid secretion is regulated by negative feedback. Cortisol is released by ACTH, triggered by hypothalamus releasing CRH. Rising cortisol levels feed back to act on both the hypothalamus and the anterior pituitary, preventing CRH release and shutting off ACTH and cortisol secretion. Cortisol secretory bursts, driven by patterns of eating and activity, occur in a definite pattern throughout the day & night.
Normal cortisol rhythm is interrupted by acute stress as CNS centers override the inhibitory effects of elevated cortisol levels and trigger CRH release. The increase in ACTH blood levels causes an outpouring of cortisol from the adrenal cortex. Stress results in a dramatic rise in blood levels of glucose, fatty acids, and amino acids, all provoked by cortisol. Cortisol's prime metaboic effect is to provoke gluconeogenesis, the formation of glucose from fats and proteins. Cortisol mobilizes fatty acids from adipose tissue and encourages their increased use for energy to save glucose for the brain. Under cortisol's influence, stored proteins are broken down to provide building blocks for repair or for making enzymes to be used in metabolic process. Cortisol enhances the sympathetic nervous system's vasoconstrictive effects, and the rise in blood pressure and circulatory efficiency that results helps ensure that these nutrients are quickly distributed to the cells.
Cortisol excess is associated with significant ant-inflammatory and anti-immune effects.
Excessive levels of glucocorticoids:
1. Depress cartilage and bone formation
2. Inhibit inflammation by deceasing the release of inflammatory chemicals.
3. Depress the immune system
4. Promote changes in cardiovascular, neural and gastrointestinal function.
Glucocorticoid drugs control symptoms of many chronic inflammatory disorders, such as rheumatoid arthritis or allergic responses. Although they relieve some of the symptoms of these disorders, they also cause the undesirable effects of excessive levels of these hormones.
Michelle Provost-Craig, Susan J. Hall, William C. Rose 12th EditionDavid N. Shier, Jackie L. Butler, Ricki Lewis 9th EditionElaine N. Marieb