Anatomy & Physiology: Endocrine System

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hormone

a chemical substance that is carried by the circulation from and endocrine gland in one part of the body to another part of the body where it exerts a specific observable effect

2 types of hormones

steroid hormones (made from fat), protein hormones(made from amino acids)

hormone-like substances

similar to hormones but not "exactly" like them. May mimic them to a certain extent like tofu(soybean) or certain clovers.. contains estrogen-like compound.

how hormones work

1. Leaves gland and enters bloodstream 2. Reaches "target tissue" 3. Binds to "receptor sites" 4. A specific response occurs in the cell

Master gland

Pituitary gland

Pituitary gland

Controls other glands in the body by secreting hormones that either turn them on or off.

Hypothalamus

Connects pituitary gland to the ventral portion of the brain. Sends releasing factors or inhibitory factors to the pituitary gland by direct blood vessels

Positive feedback

If levels of a particular hormone are low in the blood the hypothalmus senses this and tells the pituitary to send out releasing factors which turn on the gland that makes that particular hormone.

Negative feedback

If hormone levels are found to be too high the hypothalamus tells the pituitary to send out inhibitory factors which tell the gland that makes the hormone to stop producing so much.

Adenohypophysis

anterior lobe of the pituitary gland- produces 7 hormones

Neurohypophysis

Posterior lobe of the pituitary gland- produces 2 hormones

Growth Hormone (GH)

Stimulates growth of body cells, especially bone and muscle. Causes protein synthesis and prevents protein breakdown. Increases milk production in cattle (bST).

ACTH

Stimulates cortex of the adrenal glands to make cortisol/ cortisone which is needed in stressful situations

Thyroid Stimulating Hormone (TSH)

Stimulates the thyroid gland in the neck to make thyroid hormones

Prolactin

Stimulates milk production in females. Released in response to nursing offspring

Follicle Stimulating Hormone (FSH)

Causes follicles with eggs in them on the ovaries to grow near estrus cycles and make estrogen. Stimulates sperm production in males.

Luteinizing Hormone (LH)

Causes follicles on ovaries to rupture (ovulation). If not enough released some follicles don't ovulate and turn into "cysts." Stimulates testosterone production in testes in males.

MSH

Causes color change in reptiles, fish and amphibians to allow them to blend into their enviroment.

Anti-diuretic Hormone (ADH or vasopressin)

Makes collection ducts in kidney absorb more water from the urine to conserve water in the body.

Oxytocin (Pitocin)

Stimulates smooth muscle to contract. Helps in birthing process/ expel placenta. Uterus for sperm movement cranially. Udder for milk letdown.

Adrenal Glands

Near hilus of kidneys. Has a cortex and medulla like the kidney.

Cortex Hormones

Steroid hormones- made from cholesterol, are essential for life.

Glucocorticoids

cortisol (natural), prednisone, cortisone, dexamethasone (synthetic). Increase blood sugar levels. Decrease inflammation. Helpful in times of stress to maintain homeostasis.

Mineralocorticoids

Aldosterone - Made in response to renin-angiotensin when water needs to be conserved. Causes sodium retention n PCT and water follows.

Androgens

Male hormones- testosterone. Made by both sexes. Ratio of male to female hormones is improtant for sex drive in females

Cushing's Disease

Hyperadrenocorticism- too many hormones especially cortisol. Pot belly, thirst, appetite, urination, weight gain.

Addison's Disease

Hypoadrenocorticism- Not enough hormones. Low blood sugar, weak, shake, V/D, easily stressed.

Medullary Hormones

Catecholamines -Epinephrine/ Adrenaline, Norepinephrine. Fight or flight hormones. Needed daily to handle "stress."

Thyroid Gland

Consists of 2 lobes often connected with a band of tissue. Fluid filled "follicles" make T3 and T4.

T3

Tri-iodothyronine, the active hormone of the thyroid gland.

T4

Thyroxine, the hormone of the thyroid gland that is usually measured in the lab.

T3 and T4

Exert a lot of control over metabolism. 1. Absorption and use of glucose 2. Synthesis of protein 3. Synthesis of cholesterol 4. Heat production 5. Need for normal growth and reproduction.

Hypothyroidism

(Dogs and Humans). Lethargic, cold intolerance, weight gain, hair loss "rat tail," thick greasy skin, metal dullness, reproductive problems. Treat with T4.

Hyperthyroidism

(Cats and Humans) Fast metabolism, thin, tachycardia, hyperactive, bulging eyes (humans). Treat with surgery, radioactive Iodine, drugs- Tapazole.

Goiter

Enlargement of thyroid. Due to excessive stimulation of thyroid gland by pituitary due to iodine deficiency. Due to tumor, due to excess iodine in diet.

Parathyroid gland

On or near edges of thyroid glands (4 total). Make parathormone (PTH)- increases blood calcium. Stimulates osteoclasts to remove Ca+ from bones. Increases GI absorption of Ca++. Increases renal absorption.q

Pancreas

Exocrine function- amylase, lipase and trypsin. Endocrine function- Islets of Langerhans.

Glucagon

Alpha cells. Works opposite of insulin. Works to break down glycogen in liver to raise bood sugar levels when fasting or inappetance

Insulin

Beta cells- forces glucose into cells for energy after we eat. Stimulates glycogen formation. Released in response to a rise in blood glucose after a meal. Not depended on pituitary gland.

Diabetes Mellitus

P/U & P/D due to loss of glucose in urine. Juvenile and Adult onset.

Thymus

Located in caudo-ventral neck area near base of heart. Seen in young animals, tends to atrophy with age. Makes hormones needed for normal develpoment of cellular immunity and WBC function.

Pineal Body

Gland on the top of the brain. Makes melatonin at night. Helpful in nocturnal (especially reptiles) animals for night activity. Decreases gonad activity in winter.

Photo-period

length of day

Horses

Long-day breeders (spring and summer)

Sheep/Goats

Short-day breeders (fall and winter)

Sex Glands

Testes, Ovaries and Uterus

Testes

Interstitial cells make testosterone/sperm when stimulated by FSH and LH from the pituitary gland.

Testosterone

Leads to secondary sex characteristics. Voice change, heavy bones, thick neck, muscle development, sperm formation, sex drive.

Ovaries

Make estrogen and follicle cells around egg.

Estrogen

Gives female body shape, mammary development, signs of estrus.

Corpus Luteum

Yellow body. Makes progesterone after egg as left follicle

Progesterone

Quiets uterus to prepare it for the fertilized egg. Stops further heat cycles if pregnant. Maintains pregnancy.Causes mammary development for milk production.

Relaxin

Hormone made by ovaries and uterus for pregnant animals. Blood tests for pregnancy in *****es after 21st day of pregnancy. Levels increase near parturition. Relaxes cervix, vagina, ligaments around birth canal- absorb more water.

HCG

Human chorionic gonadotrophin-- Urine pregnancy test kits.

PMSG

Pregnant mare serum gonadotrophin - Made by endometrial cups in uterus of pregnant mare.

Estrone Sulfate

Found in blood of pregnant mare > 90 days with a healthy placenta/live fetus.

Prostaglandin

Many types made by different organs. Hormone of inflammation.

PG F 2 alpha

Made by non-pregnant uterus to start another heat cycle. Man made now also to help manipulate heat cycles. Causes luteolysis so progesterone levels drom and the hypothalamus senses it and causes the pituitary gland to release FSH

Erythropoietin

Made by the kidney to stimulate RBC formation in the bone marrow.

Secretin

Stimulates pancreatic, bile and duodenal secretion of fluids to mix with ingesta

Pancreozymin

Stimulates pancreas to make enzymes

Cholecystokinin

Stimulates the gall bladder to contract and send bile into the duodenum.

Hyperadrenocorticism

Cushing's Disease

Hypoadrenocorticism

Addison's Disease

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