Anatomy & Physiology 2A

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Endocrine Glands

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an endocrine gland produces a chemical substance (hormone) that is carried by the circulation to a target organ at some distance from the original endocrine gland.

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Endocrine Glands

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ae ductless glands that influence variuos vital functions of the animal from before birth until death.

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hormone

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chemical messengr released by a tissue which is carried in the circulation to reach specific cells.

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steroids -

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derived from lipids
- produced by the gonads, & certain fetal membranes

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Proteins

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peptide hormones (polypeptides)

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Amino acids

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adrenaline, noradrenalin, thyroid

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Chemical Classification

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each cell has an equal chance of coming into contact with any hormone. The cell must have a receptor for a given hormone to cause a response by the cell.

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Hormonal Actions

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actions of hormones are slower and more sustained then the actions of the nervous system (although autonomic nerves tend to act over a longer period of time then other peropheral nerves)

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Examples of the combination of nerve action and hormone action include:

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-induced ovulatio following coitus in rabbits
-the suckling stimulus for milk let down
-effect of light on seasonally bredding species

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Factors the influence hormoe activity include:

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Majority of the hormones are controlled by a neg. feedback

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potentiation or synergistic action:

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is when some hormones increase the activity of other hormones

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Antagonistic action

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is when one hormone inhibits the action of another hormone

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Hypothalamus located in

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brain

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Hypothalamus called the

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master gland

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Hypothalamus

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secretes regulatory hormones to control the anterior pituitary

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Master gland (hypothalamus)

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because of the large number of hormones it releases into
the blood stream to control either directly or indirectly most of the functions of the body

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Pituitary (hypophysis cerebri)

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located at the base of the brain on the floor of the cranial cavity

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Hormones produced by the anterior pituitary -

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all are polypeptides and TSH, FSH, and LH contain CHO, so are mucoproteins

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GH (growth hormone) or STH (somatotropic hormone)

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- stimulates growth of all body cells that can grow
- especially effective on bone and muscle

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GH

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increases the breakdown of glycogen and increases gluconeogenesis

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ACTH (adrenocorticotropic hormone)

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greatest effect in stimulating the adrenal cortex (not adrenal medulla)
stimulates the increased production of cortical steroid hormones
indirectly affects other tissues

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ACTH

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regulated by feedback mechanism: as adrenal cortical hormones increase, ACTH decreases; as adrenal cortical hormones decrease, ACTH increases

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TSH (thyroid stimulating hormone

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primary action on the thyroid gland
controlled by feedback mechanism and by TRF (thyroid releasing factor) from the hypothalamus

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FSH (follicle-stimulating hormone)

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causes follicles in the ovary to develop and enlarge
estrogen will then be produced by the follicle and have a negative feedback on the production of FSH
also stimulates gametogenesis in the seminiferous tubules of the testis of the male; this requires testosterone and ICSH

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LH (luteinizing hormone or interstitial-cell-stimulating hormone)

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production of this hormone increases as production of FSH decreases
correlated with estrogen secretion, maturation of the ovum, ovulation and formation of the corpus luteum
the CL produces progesterone, which inhibits the production of LH and prevents more follicle growth and ovulation

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LH (luteinizing hormone or interstitial-cell-stimulating hormone)

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production of this hormone increases as production of FSH decreases
correlated with estrogen secretion, maturation of the ovum, ovulation and formation of the corpus luteum
the CL produces progesterone, which inhibits the production of LH and prevents more follicle growth and ovulation

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LH

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also called ICSH (interstitial-cell-stimulating hormone) due to stimulation of the interstitial cells in the male, which produce testosterone, the male sex hormone

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LTH (luteotropic hormone or prolactin)

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associated with the initiation and maintenance of milk secretion

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intermediate lobe produces MSH (melanocyte-stimulating hormone or intermedin)

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associated with the control of pigment cells (melanocytes) in lower forms of animals (fish, amphibians, and reptiles)
incomplete knowledge of affect in mammals

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intermediate lobe produces MSH (melanocyte-stimulating hormone or intermedin)

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associated with the control of pigment cells (melanocytes) in lower forms of animals (fish, amphibians, and reptiles)
incomplete knowledge of affect in mammals

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ADH (antidiuretic hormone)

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functions in control of water loss from kidney by facilitating reabsorption of water
release is stimulated by increased osmotic pressure in blood reaching the hypothalamus; conditions requiring conservation on water

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ADH

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low osmotic pressure of blood inhibits ADH release and allows diuresis to occur

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oxytocin

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acts on the uterine muscle and on the mammary glands
causes contraction of the uterus during parturition, helping to expel the fetus

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Adrenal Glands

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located close to the kidneys
consists of an outer zone - the cortex, and an inner zone - the medulla
hormones of the adrenal cortex - steroid hormones

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glucocorticoids

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cortisol, corticosterone, cortisone, and 11-dehydro-corticosterone
promote blood glucose levels

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mineralocorticoids

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most effective is aldosterone, also deoxycorticosterone
aid in sodium retention and potassium excretion

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androgens

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are masculinizing sex hormones

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Adrenal Glands

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other actions include during stress
decrease the number of eosinophils & lymphocytes in circulating blood
decrease inflammation
increase time of wound healing

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ACTH stimulates

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the release of the adrenal cortical hormones

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hormones of the adrenal medulla – catecholamines

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epinephrine

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hormones of adrenal medulla catecholamines

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- norepinephrine
- dopamine
- animals exposed to stresses of ordinary living cannot adapt to the environment if deprived of both adrenal medulla

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if the adrenal glands are removed, the following happens

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-young animals stop growing
- reduction in blood suger
- reduction in blood pressure
- reduction in body temp
- kidneys cannot function properly

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Thyroid Gland

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consists of two lobes on either side of the trachea near the larynx

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T3 *triiodothyronine)
T4 thyroxine

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thyroid-binding globulin (TBG)
hormones contain iodine in the molecule

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T3 *triiodothyronine)
T4 thyroxine

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T3- more biologically active
T4 has a slower onset of action

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T3 & T4

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facilitate cellular metabolism - increases adsorption and use of glucose, increase the synthesis of protein in all cells, have

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facilitate cellular metabolism

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increases adsorption and use of glucose, increase the synthesis of protein in all cells, have

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goiter

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enlargement of the thyroid gland, usually due to increased TSH when the gland cannot respond by producing thyroid hormone (hypothyroidism)

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hypothyroidism

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- lack of thyroid hormones

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lack of thyroid hormones

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in young animals causes a dwarf condition called cretinism
interferes with metabolism of carbohydrates, fats, proteins and electrolytes

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hypothyroidism can cause....

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can cause delayed puberty, irregular estrus and decreased fertility in males and females
in adult animals see lowered metabolism, lethargy, loss of hair and a tendency to gain weight

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calcitonin (aka thyrocalcitonin)

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produced by the “C” cells of the thyroid

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regulates the concentration of calcium in blood -

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- it inhibits the resorption of bone and decreases the release of calcium from bone to the blood - lowers blood calcium levels

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Parathyroid Gland

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small nodules located within or near the thyroid gland, usually two on each side; exact number and location vary with species

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PTH - parathyroid hormone

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is the main factor controlling the level of blood calcium
lack of PTH is especially a problem for carnivorous animals since their diet is high in phosphorus and low in calcium

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PTH
function to

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mobilize calcium from the skeleton, promote absorption of calcium and phosphorus from the GI tract, and cause the kidneys to excrete phosphorus while retaining calcium by reabsorption

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PTH

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low blood calcium concentrations affects the neuromuscular system leading to twitchings, tremors, spasms of the muscles and finally to convulsions; tetany can result in increased body temperature, rapid breathing and alkalosis of the blood – can eventually lead to death

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PTH – cont.
excess PTH causes

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bone to soften as calcium is removed – leading to osteitis fibrosa or von Recklinghausen’s disease (calcium deposits in soft tissues such as the kidneys, lungs, heart, stomach, intestines and blood vessels)

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Parathyroid Gland
mechanisms controlling blood calcium levels are

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hypercalcemia releases calcitonin while inhibiting PTH secretion
hypocalcemia releases PTH while inhibiting calcitonin

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insulin

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is produced by the beta-cells of the pancreas

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diabetes mellitus

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disease characterized by the lack of insulin or inability to use insulin - see sharp rise in blood glucose levels

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insulin

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stimulates protein synthesis
reduces ketone formation
increases the storage of glycogen by the liver and muscles
control depends on blood sugar levels

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insulin – cont.
control

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release also stimulated by amino acids
in sheep butyrate and proprionate stimulate insulin secretion (short chain fatty acids)

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glucagon

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produced by the alpha cells of the islets of Langerhans
elevates the blood sugar level by stimulating glycogenolysis (formation of glucose from glycogen) in the liver
relationship with insulin is antagonistic
is a counterinsulin substance, along with cortisol, epinephrine and GH
has been isolated from the pancreas of swine and cattle

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Pineal Body

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located above the thalamus and is attached to the roof of the third ventricle

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Thymus Gland

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is the true sweetbread
is a lymphoid organ found on both sides of the trachea along the neck for a variable distance, depending on the age and species of animal

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Thymus Gland resembles an

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endocrine gland, but production of a hormone has not been proven
does have a crucial role in the normal development and maintenance of the immune system

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androgens

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male hormones, major one is testosterone

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estrogens

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female hormones

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progestins

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major is progestrone (two others have been isolated)
secreted by the ovaries and in pregnancy the placenta

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Prostaglandins

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exert effects either within the organ in which they are synthesized or on an organ that is reached by the venous blood from the originating organ

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prostaglandin F2alpha (PGF2alpha)

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is the natural leuteolytic substance which in the absence of pregnancy, ends one estrous cycle in the female animal by destroying the CL and allows the next one to begin

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PGF2alph is essentially a

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blood vessel constrictor, whereas PGE1 and PGE2 are blood vessel dilators (in the kidney cortex causing diuresis)

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gastrin

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causes parietal cells to secrete HCl and intrinsic factor (IF) and the chief cells to secrete pepsinogen
also acts on the liver to increase the volume of bile secreted

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secretin

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synthesized in duodenal mucosa and is released into the blood when an acid enters the duodenum from the stomach
acts on the pancreas to stimulate a copious watery secretion

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secretin

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stimulates bicarbonate synthesis in the pancreatic duct cells
also acts on the liver to increase the volume of bile secretion

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gastric inhibitory peptide (GIP) and vasoactive intestinal peptide (VIP) are both released by the duodenum

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decrease secretion of HCl, pepsinogen and IF by the stomach
GIP also reduces contraction of the gastric smooth muscle
VIP also enhances blood flow to the digestive tract

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renin

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a hormone-like substance secreted from the kidneys (the cells of the juxtaglomerular apparatus) whenever the mean arterial pressure or the blood flow volume through the kidneys is reduced, or whenever the sodium concentration of the extracellular fluid is reduced
activates the formation of angiotensin

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angiotensin

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acts on the adrenal gland to secrete aldosterone (to conserve sodium)

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renal erythropoietic factor (REF)

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is an enzyme that catalyzes the production of the hormone erythropoietin (also known as hemopoietin or erythropoietic stimulating factor)