The Application of Endocrinology to Selected Animals and Humans (Chapter 11) Efficient production – dependent on effective bodily function Effective bodily function – dependent on endocrine glands

Science of Endocrinology Endocrine glands – secrete hormones Ductless – release directly into blood stream Exocrine glands Ducts that lead to body surfaces or into other organs Pancreas – unique organ that is both endocrine (insulin) and exocrine (pancreatic juice into stomach)

Science of Endocrinology Hormone – means “to stimulate” Secreted in very small quantities 1/1,000,000 g of oxytocin will cause milk ejection Important in: growth and efficiency reproduction lactation

Endocrine Glands Anterior pituitary Affects secretions of many other endocrine organs Posterior pituitary Stores and releases some hypothalamus hormones Hypothalamus Small area of brain that regulates hormonal activity Several others scattered around body

Chemical Nature of Hormones Proteins and glycoproteins Peptides Amines Steroids Non-steriodal

Hypothalmus Hormones Growth hormone-releasing hormone (GnRH) Stimulates release of growth hormone Growth hormone inhibiting hormone (somatostatin) Inhibits release of growth hormone Prolactin-releasing hormone (PRH) Stimulates release of prolactin

Hypothalmus Hormones Prolactin-inhibiting hormone (PIH) Inhibits release of prolactin Oxytocin Ejection of milk, expulsion of eggs, uterine contractions Vasopressin Constriction of peripheral blood vessels and water resorption in the kidney tubules

Anterior Pituitary Hormones Growth hormone (GH, somatotropin) Promotes growth of tissues Adrenocorticotropin (ACTH) Stimulates secretion of steroids (especially glucocorticoids (from adrenal cortex) Thyroid-stimulating hormone (TSH) Stimulates thyroid gland to secrete thyroxine

Anterior Pituitary Hormones Prolactin Initiates lactation and stimulates maternal behavior Follicle stimulating hormone (FSH) Stimulates follicle development in the female and sperm production in the male Luteinizing hormone (LH) Maturation of follicles and ovulation in female, testosterone production in testes by male

Thyroid Hormones Thyroxine, triiodothyronine Increases metabolic rate Calcitonin Lowers concentration of calcium in the blood and promotes incorporation of calcium into the bone

Parathyroid Hormones Parathyroid Hormone Maintains or increases the level of blood calcium and phosphorus

Adrenal Cortex Hormones Glucocorticoids Mobilizes energy, increases blood glucose, antistress Mineralocorticoids Maintains salt and water balance in the body

Adrenal Medulla Hormones Epinephrine Stimulates heart muscles and rate and strength of their contraction Norepinephrine Stimulates smooth muscles and glands and maintains blood pressure

Ovarian Follicle Hormone Estrogens Growth of the reproductive tract and mammary duct system

Ovarian Corpus Luteum Hormones Progesterone Prepares reproductive tract for pregnancy, maintains pregnancy and causes development of mammary lobule-alveolar system Relaxin Causes relaxation of ligaments and cartilage in pelvis, assists in parturition

Uterus Hormone Prostaglandin F 2α (PGF 2α ) Causes luteolysis and a decrease in progesterone

Testicular Hormones Androgens (testosterone) Causes maturation of sperm Promotes development of male accessory glands Promotes development of secondary sex characteristics

Pancreatic Hormones Insulin Lowers blood glucose Glucagon Raises blood glucose

Placenta (in some species) Hormones Gonadotropins, estrogen, progesterone Promotes maintenance of pregnancy Some names for placental gonadotropins Pregnant mare serum Equine chorionic gonadotropin Human chorionic gonadotropins

Functions of Hormones Small amounts needed Affect growth, body shape, food use, reproduction Many quickly deactivated when administered May disappear in few hours Act quickly but effect may not be noticeable until later

Mechanism of Hormone Action Hormones released into, and travel through circulatory system Attach to receptors that are specific to each hormone Once attached to receptor, action will be carried out in the cell

Regulation of Hormone Secretion Endocrine activity must be carefully balanced Regulation is important Feedback mechanism Interaction between two hormones may regulate secretion of both Chemical homeostasis Blood level of non-hormone chemicals affected by hormones may regulate secretion

Uses of Natural and Synthetic Hormones Birth control pills Many have combination of synthetic progesterone and synthetic estrogen Synchronize estrus - Progestins, PGF 2α Superovulation – Gonadotropins Treatment of cystic ovaries – Gonadotropin releasing hormone

Uses of Natural and Synthetic Hormones Induction of lactation (not approved by FDA) Administration of estrogen and progesterone Increase rate and efficiency of gain Estrogens and synthetic estrogens Melengestrol acetate (MGA) – synthetic progesterone

Hormones and Public Health Possibility of residues in food produced by animals treated with hormones Has not become a public health problem Prevention of residues is high priority