Chapter 11 TERMS - The Endocrine System

parathyroid gland

4 small pale nodules in, on, or near thyroid gland that secrete parathyroid hormone/parathormone - varies from animal to animal, species to species - opposite effect of calcitonin - prevents hypocalcemia

FIGURE 11-1 Relative locations of major endocrine glands in the cat.

FIGURE 11-1 Relative locations of major endocrine glands in the cat.

FIGURE 11-2 Hormone receptor binding. A, Water-soluble hormones: peptides and catecholamines - receptors are on cell membrane B, Lipid-soluble hormones steroid and thyroid hormones - receptors are in cytoplasm or nucleus

FIGURE 11-2 Hormone receptor binding. A, Water-soluble hormones: peptides and catecholamines - receptors are on cell membrane B, Lipid-soluble hormones - steroid and thyroid hormones: receptors are in cytoplasm or nucleus

FIGURE 11-3 Structure of steroid hormones.

FIGURE 11-3 Structure of steroid hormones.

Table 11-1: Comparison of Endocrine and Nervous System Characteristics

Table 11-1: Comparison of Endocrine and Nervous System Characteristics

positive feedback systems

a change in a given direction causes additional change in the same direction For example, an increase in the concentration of a substance causes feedback that produces continued increases in concentration. - not common - potential to lead to vicious cycles of hormone production - do play specific limited roles: female estrous cycle

hypothalamus

an endocrine gland that regulates the pituitary gland - part of diencephalon - important nervous system functions: > appetite control > temp regulation > wake/sleep cycles - links conscious mind with rest of body - links cerebrum with endocrine system by regulating pituitary gland - important bridge btwn nervous system/endocrine system

Melanocyte-Stimulating Hormone/ MSH/MH

assoc w/control of color changes in pigment cells (melanocytes) of reptiles, fish, amphibians released by: anterior pituitary -- administration of lg amts to higher mammals can cause skin darkening from melanocyte stimulation

endocrine glands

basic units of endocrine system ductless glands that secrete tiny amts of hormones directly into bloodstream - located thruout body - effects produced where specific receptors are found

both endocrine & nervous systems use this to control functions of the body

both use chemical messaging

epinephrine & norepinephrine

catecholamines that affect heartrate, blood pressure, air passageways, and GI function in the fight/flight response released by: adrenal medulla - effects: ~ ↑ heartrate/output ~ ↑ blood pressure ~ ↑ dilation of air passageways in lungs ~ ↓ GI function epinephrine/norepinephrine is all three: - neurotransmitter - hormone - drug

hormones

chemical messengers produced by endocrine glands - secreted into blood vessels - travels bloodstream to all parts of body - produce effects only when bound to their particular receptors within/on cells

what is the precursor to the following types of hormones? > glucocorticoids > mineralocorticoids > sex hormones

cholesterol

endocrine & nervous systems share:

controlling/coordinating functions of the body for homeostasis

hypoxia

decrease in oxygen content of blood

an ADH deficiency can cause:

diabetes insipidus/bitter diabetes: ~ other disease conditions produce similar symptoms, so complete workup needed for proper diagnosis effects: - produce lg. qty of very dilute urine (polyuria) ~ drink lots of water (polydipsia) treatment: administering drug with ADH activity for life

hypercalcemia

excessively high blood calcium level

Adrenocorticotropic Hormone/ACTH

stimulates adrenal cortex development & release of adrenal cortex hormones released by: anterior pituitary -- regulates: response to stress -- regulated by: hormonal feedback from adrenal cortex -- in sudden stress, is released quickly: other parts of brain stimulate hypothalamus → burst of ACTH-releasing factor sent to anterior pituitary → ACTH then released

produced by beta cells of pancreas:

insulin

example of negative feedback:

like a thermostat regulating the temperature of a room: - thyroid gland = heater > produces thyroid hormone as result of thyroid stimulating hormone (TSH) from anterior pituitary - if level of thyroid hormone drops below the 'thermostat setting', anterior pituitary produces more TSH, stimulating thyroid gland to produce more thyroid hormone - thyroid hormone level reaches the 'setting' needed, and production of TSH is shut down

steroid hormones

lipid hormones synthesized from cholesterol -- includes: ~ androgens (e.g., testosterone) ~ estrogens (e.g., estradiol) ~ glucocorticoids (e.g., cortisol) ~ mineralocorticoids (e.g., aldosterone) ~ progestins (e.g., progesterone) -- hydrophobic: bind to hydrophilic transport proteins to travel in plasma -- lipid structure allows passage thru cell membrane -- receptors: within target cell, in cytoplasm or nucleus

hypocalcemia

low blood calcium level

Follicle-Stimulating Hormone/FSH

stimulates oogenesis & estrogens; spermatogenesis released by: anterior pituitary -- named for effect in females

Homeostasis of Blood Pressure

maintained by pressure receptors in walls of certain arteries - detect increase in BP - blood pressure = force of blood on walls of vessels -- brain (control center) receives input, signals heart and blood vessels -- effector - heart: rate slows, arterioles dilate -- BP returns to normal

sex hormones

male and female sex hormones released by: adrenal cortex -- in both males and females: - produce small amts of sex hormones - both androgens (male sex hormones) and estrogens (female sex hormones) are produced - very small amt - minimal effects

hormone secretions are commonly controlled by these systems:

negative feedback systems

TH Calorigenic Effect

regulates metabolic rate of all body cells -- calorigenic effect allows heat generation, enabling animals to maintain constant internal temp ~ TH production increases in cold temps ~ nutrients burn faster - outdoor animals in cold temps need more calories -- can be inhibited by emotional or physical stresses, would cause difficulty maintaining body temp, compounding stress, opens door to disease

gonads

reproductive organs: testes, ovaries - produce male and female reproductive cells and important hormones

ovulation

rupture of follicle/release of ovum into oviduct

produced by delta cells of pancreas:

somatostatin

lipid soluble hormones

steroid and thyroid hormones

the 7 anterior pituitary hormones

- Thyroid-stimulating hormone/TSH - Prolactin - Follicle-stimulating hormone/FSH - Luteinizing hormone/LH - Adrenocorticotropic hormone/ACTH - Growth hormone/GH - Melanocyte-stimulating hormone 'TP FLAGM'

pancreatic hormones

- insulin and glucagon: important in controlling metabolism and use of glucose, with opposite effects for balance - somatostatin: > inhibits secretion of insulin, glucagon, and GH > diminishes GI activity

3 chemical categories of hormones:

- peptides - steroids - monoamines

erythropoietin

- secreted by: kidney - stimulates: bone marrow to produce erythrocytes /RBCs

TH Effect on Protein, Carbohydrate, and Lipid Metabolism

-- affects metabolism of proteins, carbs, and lipids much like GH does: ~ proteins: • encourages anabolism/synthesis of proteins if diet contains adequate energy sources • if deficient in energy foods, or amt of TH is excessive, opposite can occur - protein catabolism/breakdown ~ carbohydrates:: • hyperglycemic effect • helps maintain blood glucose ~ lipids: • encourages catabolism

summary of thyroid hormone effects:

-- maintains body temp, metabolism -- stimulates gut motility -- bone and muscle growth -- hair growth, healthy skin -- hyperglycemic effect -- stimulates cardiac output, increases heart rate

TH Effect on Young, Growing Animals

-- necessary for normal growth and development in young animals > dev/maturation of CNS > growth/dev of muscles/bones.

Thyroid Hormone (TH)

-- produced when TSH from anterior pituitary stimulates the thyroid -- is really TWO hormones: ~ T4: thyroxine - prohormone, a circulating reservoir ~ T3: triiodothyronine - active hormone *** names derived from # of iodine atoms ea. molecule contains -- thyroid gland produces far more T4 than T3, as T4 functions as a circulating reservoir: ~ converted to T3 in peripheral tissues (mainly liver, kidney, muscle) as needed

thyroid gland

-- two lobes - either side of larynx -- depending on species - may be connected by isthmus/narrow band -- the only endocrine gland that stores large amts of hormone precursor for later use -- produces two hormones: > thyroid hormone: helps with metabolic rate > calcitonin: helps regulate blood calcium levels

anemia

= RBC deficiency ~ often accompanies serious kidney disease or failure ~ inability to produce enough erythropoietin ~ patient becomes increasingly hypoxic: • old red blood cells continue to be removed • not enough new red blood cells produced to replace them ~ blood transfusions often necessary to support patients while other therapies are administered ~ synthetic forms of erythropoietin often used therapeutically in human patients w/kidney failure ~ high $$ limits veterinary uses

Box 11-1: Chemical Categories of Hormones

Box 11-1: Chemical Categories of Hormones

FIGURE 11-4 Relationship of hypothalamus and anterior pituitary (adenohypophysis)

FIGURE 11-4 Relationship of hypothalamus and anterior pituitary (adenohypophysis) - Hormones from hypothalamus are secreted into portal blood vessels that carry them to the anterior pituitary. - There they stimulate or inhibit release of anterior pituitary hormones. ~ some anterior pituitary hormones influence all body cells, so hypothal indirectly affects whole body ~ therefore animal's state of mind can influence its susceptibility and reaction to illness

FIGURE 11-5 Relationship of hypothalamus and posterior pituitary (neurohypophysis)

FIGURE 11-5 Relationship of hypothalamus and posterior pituitary (neurohypophysis) - Neurosecretory cells (modified neurons) in hypothalamus produce hormones that are transported down nerve fibers to the posterior pituitary, where they are stored. - Their release is controlled by nerve impulses from the hypothalamus. - secrete: • antidiuretic hormone (ADH) • oxytocin

Figure: Nervous System vs. Endocrine System

Figure: Nervous System vs. Endocrine System

Figure: Regulation of Blood Glucose

Figure: Regulation of Blood Glucose

Figure: nervous/endocrine system connection

Figure: nervous/endocrine system connection

kidney characteristics

In addition to filtering blood, this organ produces erythropoietin: > stimulated by hypoxia > effect: increases oxygen-carrying red blood cell production ~ red blood cells ▲ in response → oxygen level ▲ → feeds back to kidneys → production of erythropoietin slows ~ helps maintain long term homeostasis of blood's oxygen carrying ability

oxytocin

a hormone that causes contractions in the uterus and milk letdown in mammary glands, aka 'cuddle hormone' -- contractions in uterus: ~ at breeding & parturition -- milk letdown in mammary glands: • nursing/milking stimulates release into bloodstream, circulates to myoepithelial cells in mammary gland, causing contraction -- lag time - sensory stimulation to brain → signals hypothalamus → oxytocin from posterior pituitary → oxytocin reaches mammary gland via blood circulation -- use as a drug: - for prolonged labor ~ to shrink uterus after a cesarean ~ to expel afterbirth -- recent studies ~ may play roles in human/other animal behaviors: • social group recognition • pair connection • 'cuddle/bonding hormone'

glucagon

a hormone that helps regulate blood glucose levels with a hyperglycemic effect released by: pancreas - two main mechanisms: 1. stimulates liver cells to convert glycogen to glucose 2. stimulates gluconeogenesis/glycogenesis (conv. of fat, protein breakdown products to glucose) - glucagon deficiency not devastating like insulin deficiency > GH and glucocorticoid have similar hyperglycemic effects

insulin

a hormone that helps regulate blood glucose levels with a hypoglycemic effect released by: pancreas - causes glucose, amino acids, fatty acids to be absorbed into body cells for energy: lowers glucose - overall effect on glucose: move it out of bloodstream

pancreas

a long, flat, abdominal organ near the duodenum (first portion of small intestine) with both endocrine AND exocrine functions - most of mass: ~ exocrine glandular tissue ~ produces important digestive enzymes - small % of mass: ~ endocrine component: islets of Langerhans ~ produces hormones regulating glucose

feedback system

a method of maintaining hormone levels; the level of hormone in the blood directly or indirectly "feeds back" info to the gland that produced it, affecting the activity of the gland

fight/flight response

a response produced by: 1. direct sympathetic nerve stimulation of target tissues 2. epinephrine, norepinephrine release into bloodstream by adrenal medulla -- after threat passes: ~ body takes time to relax from excited state; epinephrine/norepinephrine still circulating ~ must metabolize and dissipate

colloid

a thyroid hormone precursor (raw material for thyroid hormone) produced by thyroid cells

T3: triiodothyronine

active hormone, one of the parts of thyroid hormone, converted from T4

adrenal medulla

adrenal gland portion developed from nervous tissue that secretes epinephrine, norepinephrine -- modified neurons secrete directly to bloodstream -- secretion controlled by sympathetic portion of autonomic nervous system: 'fight/flight'

negative feedback systems

when the activity of a gland is decreased by rising levels of the hormone it produces - most common feedback system

Luteinizing Hormone (LH)

females: completes follicle dev. in ovary, then causes ovulation when levels are at peak • after ovulation, high LH level stimulates cells of empty follicle to multiply, develops corpus luteum males: : stimulates interstitial cells in testes to produce testosterone -- sometimes called ICSH: interstitial cell-stimulating hormone released by: anterior pituitary FSH and LH are sometimes grouped together under gonadotropins because they stimulate growth, dev. of gonads - ovaries and testes

duodenum

first portion of small intestine

follicles

fluid filled structures in which female reproductive cells develop

adrenal gland characteristics

glands named for cranial proximity to kidneys (renal = kidneys) - two glands in one: > outer adrenal cortex > inner adrenal medulla - different origins/structure/function

produced by alpha cells of pancreas:

glucagon

major endocrine glands:

gonads hypothalamus pancreas pituitary adrenal parathyroid thyroid Glands Have Particular Products And Particular Targets

progestins

group of hormones produced by the corpus luteum ~ principle progestin: progesterone, necessary for maintaining pregnancy ~ helps prepare uterus to receive fertilized ovum - if pregnancy is successful: > corpus luteum continues to produce progestin - if no pregnancy: - no signal received - corpus luteum shrinks/disappears - often used therapeutically, esp. horses: ~ synchronize estrus in mares for concurrent breeding ~ help maintain pregnancy in mares w/deficient natural progesterone levels THINK: 'pro-GEST-terone': gestation

thymus

helps kick start immune system early in animal's life -- extends cranially from heart level up into neck region along both sides of trachea -- large in young animals; atrophies after puberty -- function involves hormones or hormone-like chemical substances: ~ thymosin ~ thymopoietin • seem to cause primitive cells in thymus and other lymphoid organs to be transformed into T lymphocytes (T for 'thymus-derived') aka T cells -- important part of cell-mediated immunity; portion of immune system that produces 'killer cells' that directly attack foreign invaders

corpus luteum

helps prep uterus for fertilized ovum & maintains pregnancy; used to synchronize estrous periods in mares ~ produces progestins/progesterone, 'pregnancy-promoting steroid' ~ "yellow body"

Antidiuretic Hormone/ADH

helps prevent diuresis, conserving water in short supply released by: posterior pituitary -- hypothalamus is triggered by receptors that detect dehydration/hemoconcentration: 1. detection of hemoconcentration: a condition where osmotic pressure of blood increases (its more concentrated) 2. triggers nerve impulses down to posterior pituitary to release ADH 3. travels to kidneys, causing them to reabsorb more water from urine back into bloodstream, making urine more concentrated & conserving water -- ADH release inhibited by alcohol and caffeine; they will not relieve thirst; allow more water to flow out w/urine -- desert animals have increased ADH

relaxin

hormone that causes ligaments btwn bones surrounding birth canal to soften/relax in prep for parturition (birth process) released mainly by: corpus luteum, see below - produced late in pregnancy - role in mammary development in some species - productive organ depends on the species; can be: > corpus luteum > placenta > uterus → THINK 'relaxing' the birth canal

Parathyroid Hormone/parathormone (PTH) characteristics

hormone that helps maintain blood calcium levels by affecting the kidneys, intestines, and bone released by: parathyroid glands - opposite effect of calcitonin (which is released by thyroid) - prevents hypocalcemia - increases calcium levels, causing: > kidneys to retain calcium > intestine to absorb calcium from food > withdrawal of calcium from bones

monoamine hormones

hormones derived from amino acids that retain an amino group: ~ catecholamines (epinephrine/nor) ~ thyroid hormones -- catecholamines are hydrophilic like peptide hormones > transported dissolved in plasma > receptors: on target cell membranes -- thyroid hormones are hydrophobic like steroid hormones > require transport proteins > receptors: in the nucleus like some steroid hormones

peptide hormones

hormones that are chains of amino acids - arranged like pearl necklace - a few to 200 or more in chain - hydrophilic (water soluble); travel easily in blood plasma - receptors: on target cell membrane

glucocorticoids

hormones that help resist stress effects, maintain blood pressure, and affect protein and lipid catabolism - released by: adrenal cortex - several mechanisms involved: > gluconeogenesis - protein, lipid catabolism > BP maintenance > helps resist stress effects > hyperglycemic effect - name derived from effect on blood glucose levels - examples: > cortisol > cortisone > corticosterone

mineralocorticoids

hormones that regulate electrolyte/mineral salt levels released by: adrenal cortex -- principle mineralocorticoid: aldosterone (works with ADH) affects: ~ sodium/potassium/hydrogen ion levels (electrolytes) ~ water levels: because water follows sodium back into bloodstream -- targets kidneys to ↑ Na+ retention & reduce urine volume -- sodium level needs to be fairly high -- much less potassium needed ~ toxic if accumulates too high ~ some drug preparations used to euthanize contain very high levels ~ stops heartbeat -- hydrogen ions affect acid-base balance; needs careful control mineral - minerals cortico - cortex coid - steroid

estrogens

hormones that: 1. Initiate physical/behavioral changes in prep for breeding/pregnancy 2. signal that breeding time is approaching released by: ovaries - FSH (from anterior pituitary) stimulates follicle development in ovaries: > follicle cells produce/release estrogens to bloodstream > as follicle grows: estrogen production grows, accelerating physical/behavioral change > anterior pituitary reduces FSH, increases LH production > when follicle is mature: • LH level peaks • ovulation occurs

testes

housed in scrotum, sac of skin in inguinal region - coiled seminiferous tubules: produce spermatozoa - interstitial cells: groups of endocrine cells that produce androgens: male sex hormones, principally testosterone - stimulated by: luteinizing hormone/LH from anterior pituitary - aka interstitial cell stimulating hormone/ICSH in males

small intestine

in response to chyme in the duodenum, cells of small intestine produce two hormones: ~ secretin: stimulates pancreas to secrete sodium bicarbonate-rich fluid into the duodenum to neutralize acidic chyme ~ cholecystokinin: stimulates pancreas to release digestive enzymes from pancreas into duodenum ~ both also: • inhibit gastric gland secretions & stomach motility, slowing chyme mvmt to small intestine • stimulate gallbladder to contract; sends bile into small intestine to aid digestion/absorption of fats & fat-soluble vitamins

stomach

in response to the presence of food: ~ gastrin is produced & secreted by cells in stomach wall and acts on stomach wall: > stimulates gastric glands to secrete hydrochloric acid and digestive enzymes > encourages muscular contractions of stomach wall

calcitonin

one of two hormones involved in maintaining blood calcium levels (the other is parathyroid hormone). released by: thyroid gland -- produced by C cells located btwn thyroid follicles -- calcium important in muscle contraction, blood clotting, milk secretion, bone formation/maintenance ~ levels must be kept in narrow range -- prevents hypercalcemia by encouraging excess calcium to be deposited in the bones for later use.

ovaries

organs that release female reproductive cells (ova) and hormones in cycles - cycles controlled by two anterior pituitary hormones: > follicle stimulating hormone (FSH) > luteinizing hormone (LH) - hormone groups: > estrogens: prep for pregnancy * estradiol * estrone > progestins: hormone of pregnancy > relaxin: produced late in pregnancy

the gland of the body with both endocrine and exocrine functions

pancreas

Islets of Langerhans:

pancreatic cells that secrete insulin, glucagon, and somatostatin

pineal body

part of brain at caudal end of deep cleft separating cerebrum, just rostral to cerebellum produces melatonin -- affects moods, wake/sleep cycles -- possible role in timing of seasonal estrous cycles in some species

chyme

partially digested material from stomach

water soluble hormones

peptides and catecholamines

adrenal cortex

portion of the adrenal glands that is directed by ACTH and other mechanisms - develops from & looks like normal glandular tissue - produces assorted hormones, classified in 3 main groups: > glucocorticoids > mineralocorticoids > sex hormones - all are steroids because chemical structure is based on cholesterol

testosterone

primary androgen from the testes -- stimulates: ~ male secondary sex characteristics: • muscular male body shape • male libido/sex drive ~ dev. of male accessory sex glands • penis growth ~ activates spermatogenesis -- is a steroid hormone with an overall anabolic effect - stimulation of the buildup of proteins in muscle and bone

T4: tetraiodothyronine/thyroxine

prohormone (before hormone), one of the parts of thyroid hormone; a circulating reservoir

Growth Hormone (GH) (somatotropic hormone)

promotes growth in young, helps regulate protein, carb, and lipid metabolism in all cells released by: anterior pituitary -- effect on protein metabolism: > anabolism > supplies materials for growth, repair of tissue -- effect on lipid & carb metabolism is linked: > catabolism of lipids discourages carbohydrate use, esp. glucose, as energy source :: therefore: hyperglycemic effect: level of glucose in blood tends to rise :: opposite to insulin, which tends to lower blood glucose :: GH/insulin balance imptnt to glucose levels

Thyroid-Stimulating Hormone/TSH/Thyrotropic Hormone

stimulates thyroid gland development and TH production released by: anterior pituitary -- secretion regulated by both: > feedback from thyroid > interaction btwn hypothalamus, anterior pituitary, & thyroid -- if thyroid hormone level rises above needs: ~ TSH production diminishes → TH production diminishes → level drops

additional endocrine glands

stomach small intestine kidneys placenta thymus pineal body Some Say Kidneys Produce The Pee

exocrine glands:

sweat, oil, mucous, & salivary glands, and oddly, the pancreas

pituitary (hypophysis)

the 'master endocrine gland': many of its hormones direct activity of other endocrine glands -- size of a pea -- housed in pituitary fossa of the sphenoid bone -- two separate glands (anterior/posterior) completely different in: ~ structure ~ function ~ embryologic origin

the endocrine gland that uses direct stimulation from the nervous system instead of a feedback mechanism:

the adrenal medulla - stimulated by sympathetic nerve impulses when animals feel threatened, contributing to fight/flight response

posterior pituitary (neurohypophysis)

the caudal portion of pituitary gland that stores and periodically releases two hormones produced in hypothalamus - developed from embryonic nervous tissue - no hormone production - nerve impulses from hypothalamus stimulate the release into bloodstream - think neuro for nervous - 'AO', for 'All Others" ~ antidiuretic hormone ~ oxytocin

pancreatic islets/islets of Langerhans

the endocrine portion of pancreas - tiny clumps of cells scattered thruout the organ - main endocrine cells: > alpha cells: produce glucagon > beta cells: produce insulin > delta cells: produce somatostatin

placenta

the life support system surrounding fetus -- an interface with maternal circulation -- also an important endocrine organ -- secretions vary among species, but hormones it produces help support/maintain pregnancy: ~ small amts estrogen, progesterone ~ significant amts chorionic gonadotropin (some species) • notably, humans, horses • detection is basis of pregnancy tests for humans and blood tests for horses • other species produce too little to make it a method of pregnancy diagnosis ~ relaxin (some species) • late in pregnancy; helps relax ligaments btwn bones around birth canal in prep for parturition • may be produced by placenta, uterus, corpus luteum of ovary, depends upon species

diuresis

the loss of large qty of water in urine

anterior pituitary (adenohypophysis)

the rostral portion of the pituitary gland ~ developed from embryonic glandular tissue ~ produces 7 known hormones when stimulated by either: • hypothalamus -or- • direct feedback from target organs/tissues ~ a good way to remember the hormones it produces: - 'stimulating' hormones - 'trophic' or 'tropins' hormones - 'TP FLAGM' adeno- = 'gland'

Prolactin

triggers, maintains lactation released by: anterior pituitary -- release continues with teat stimulation ~ once ceases, prolactin production ceases ~ mammary gland dries up, shrinks, milk prod. stops -- in males: no function