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 F2α (PGF2α )

• 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, PGF2α

• 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