Endocrine System

endocrine and nervous system

• direct
• paracrine
• synaptic
• endocrine

• neighboring cells in direct contact with each other, communicate by the exchange of ions and molecules, through gap junctions in the cell membrane
• electrical transmission of impulse
• extremely small distances
• (very few)

• uses chemical messengers to carry info from cell to cell within the same tissue
• occurs over small distances

• a specialized cell (neuron) releases a neurotransmitter very close to the target cell (effector) at the synapse
• effects usually short-lived
• (most)

• release of hormones into circulatory system where they are carried to the target cells, tissues, or organs
• targets have specialized receptor sites to which the hormone must bind before it exerts its effects
• a single hormone may have effects on multiple tissues/organs
• long-acting
• cover massive distances

• endocrine= slower response, long-acting
• nervous= rapid response, short-lived

• pituitary gland (1)
• parathyroid gland (2)
• thyroid gland (2)
• adrenal gland (2)
• kidney (2)
• ovary (2)
• pancreas (1)
• testis (2)

unilateral

hormone has only one organ it acts on

(and that target organ is the only one with receptors for that hormone)

chemical messenger released by a tissue which is carried in circulation to reach specific target cells in other tissues around the body

similar in structure to amino acids

epinephrine, norepinephrine, thyroid hormones,melanin

• antidiuretic hormone, oxytocin (short chains)
• growth hormone, prolactin (longer chains)
• follicle stimulating hormone, luteinizing hormones (amino acid chain with carbohydrate molecule attached:glycoprotein based hormones)

• 2 groups
• similar in structure to cholesterol: steroid hormones
• derived from the essential fatty acid arachidonic acid: eicosanoids

• reproductive hormones (estrogens, testosterone)
• glucocorticoids (released by adrenal gland)

• transported in the blood bound to carrier proteins rather than free molecules
• remain in circulation longer than other hormones

synthetic glucocorticoid

(have on shelf to inject)

pure steroid hormones produced by adrenal gland

activate, or deactivate an existing enzyme within any cell or affect the rate of synthesis of a structural protein or enzyme

areas that have a large capillary network so they can quickly enter circulation, where they will circulate either freely or bound to a carrier protein

• change in extracellular fluid (hypoglycemic)
• secretion or removal of another hormone
• release of neurotransmitter that affects the endocrine gland

Negative Feedback

*discussion question*

• Thyroid Stimulating Hormone
• thyrotropin

(stimulates the production of the thyroid hormones by the thyroid gland)

• to prevent dehydration
• reabsorbs water and sodium

(dehydrated do not urinate very much bc the body is reabsorbing any water it can)

hypothalamus

• secretes regulatory hormones that control the hormonal activity of the anterior pituitary gland, affecting the activity of thyroid gland, cortex of adrenal gland, and reproductive organs
• autonomic nervous control over hormones secreted by the medulla of adrenal glands
• also acts as a endocrine gland itself by releasing hormones into circulation via the posterior pituitary gland

hypothalamus (then passed down/stored in posterior pituitary gland)

• or hypophysis
• two parts: anterior and posterior

• posterior lobe
• pars nervosa
• neurohypophysis 

• anterior lobe
• adenohypophysis

• pars tuberalis
• pars intermedia
• pars distalis

• (anterior pituitary)
• formed from Rathkes Pouch-a structure derived from mucous membranes of the embryonic pharynx

• (posterior pituitary)
• originated from embryonic brain
• connected to brain by pituitary stalk
• allows for production of posterior pituitary hormones to be produced in the hypothalamus and transported via nerves to posterior lobe to be stored and later used

• adrenocorticotropic hormone
• adrenocorticotropin
• corticotropin

Growth Hormone

Prolactin

• lutenizing hormone (in female)
• interstitial cell stimulating hormone, ICSH (in male)

• luteotropic hormone
• luteotropin
• lactogenic hormone
• prolactin

follicle stimulating hormone

• Antidiuretic Hormone
• Vasopressin

• somatotropic hormone
• somatotropin
• growth hormone

• oxytocin
• antidiuretic hormone (ADH) or vasopressin

(both synthesized in the hypothalamus)

• ADH
• affects kidneys, causing an increase in absorption of water by the tubules
• reduces the volume of urine
• increases water retention and volume of blood

causes contraction of the smooth muscle of the uterus during labor and stimulates milk production at lactation

"pop" (causes contractions to "pop" out the puppies!!)

• oxytocin
• antidiuretic hormone

Up.

• hypothyroidism
• hyperadrenal cortism
• hyperestrogenism

• composed of epithelial cells and connective tissue separated by sinusoids of blood
• has 6 types of cells

• precursor to cells that produce the hormones of the anterior lobe
• (produce chromophils)

separated by their staining properties

• acidophils (stain red)
• basophils (stain blue)

• somatotrophs-produce STH
• lactotrophs- produce Prolactin

*stain red

• FSH gonadotrophs- produce FSH
• LH gonadotrophs- produce LH
• Thyrotrophs- produce TSH
• Corticotrophs- produce ACTH

*stain blue

series of veins that carry blood from the pituitary stalk and the brain to the adenohypophysis of the pituitary gland

these veins break up into small capillaries and actually account for the control of the hormones released by the adenohypophysis

growth hormone

• oxytocin
• antidiuretic hormone

• STH
• ACTH
• TSH
• FSH
• LH
• LTH
• MSH

(secretes a total of 7 different hormones, all under control of regulatory hormones secreted by hypothalamus)

• T4- thyroxine
• T3- liothyronine
• thyrocalcitonin

the thyroid hormones: T3, T4, thyrocalcitonin


TRH > TSH >Thyroid > T3&T4&Thyrocalcitonin

thyroxine

liothyronine

thyrocalcitonin

removal of calcium from bones

colloid

(the majority of which consists of a protein-iodine complex:thyroglobulin)

the blood level of calcium

raises calcium blood level by absorbing calcium from the bone 

(antagonistic to calcitonin)

parathormone

(raises calcium blood level)

2:1

levothyroxine sodium (tetraiodotyrosine)- T4 brand name: Soloxine & Synthroid

liothyronine sodium (triiodotyrosine)- T3 brand name: Cytobin

Iodine to form T3&T4 and be biologically active. 

(thyroid gland can concentrate and store iodine to levels 25-50 times that of circulatory blood)

iodides

Iodine or Oxidized Iodine

the thyroid gland traps iodide in the colloid and oxidizes it to iodine

iodine then incorporated into the amino acid, tyrosine, to form monoiodotyrosine  (MIT) and diiodotyrosine (DIT)

T4

(formed and stored in thyroid gland)

less than 20% of T3 formed in thyroid gland, remaining T3 formed from deiodination of T4

• control of enzymes and proteins for metabolism
• maintenance of normal hair growth and skin condition
• normal fetal development

Iodide (in blood) >> Oxidized Iodine (in thyroid gland)

Monoiodotyrosine (MIT) >> Diiodotyrosine (DIT) >>

• Iodothyronines (T3&T4) 1. Liothyronine Sodium (triiodotyrosine)
• 2. Levothyroxine Sodium (tetraiodotyrosine)

• lethargic
• anemia
• bilateral alopecia
• cold

• nervous
• fatigue
• hunger
• weight loss

• cabbage
• rutabagas
• turnips

adenohypophysis

neurohypophysis

hyperthyroidism

• mental dullness
• lethargy
• exercise intolerance 
• weight gain with no increase in appetite
• cold intolerance  

carotid artery

• bilateral alopecia
• seborrhea- flaky, dry, oily
• pyoderma- pus in and under skin
• myxedema- thickening of skin (face)

most brought in for hair loss. caused by thyroid gland not producing sufficient amounts of thyroid hormones to stimulate new hair growth

• most common form (95%)
• result of destruction of thyroid gland
• develops gradually=not noticeable until 75% of thyroid destroyed

most common symptoms of divided into 2 areas: metabolic (no energy bc not burning calories) dermatological (hair loss, etc)

activity as metabolism of all the tissues

(so it makes sense that when their function or amount decreases, the skin and hair are affected)

• hypothyroidism
• hyperadrenocortism
• hyperestrogenism

4-6 yrs

(can be seen 2-9)

thyroxine (T4) test

T3 rarely deficient, usually T4

name brand thyroxine: Synthyroid or Levothyroxine

methimazole

lowers thyroxine (T4) by blocking uptake of iodine by thyroid

• tachycardia
• hyperactivity
• weight loss
• polyphagia
• polyuria
• polydipsia

• 5 mg per os bid
• topical cream to inner pineal surface of each ear

so as not to suppress the bodies natural hormones it produces it at night

adrenal gland

corticotropin releasing hormone (CRH) from the hypothalamus

• glucocorticoids (cortisol, corticosterone)
• mineralocorticoids
• sex hormones 

(all are steroid-based hormones that affect cellular metabolism)

• capsule
• zona glomerulosa
• zona fasiculata
• zona reticularis
• adrenal medulla

zona glomerulosa

• cortisol
• corticosterone

• capsuleadrenal cortex (outer-made up of 3 layers)
• adrenal medulla

zona fasiculata

zona reticularis

producing no hormones/steroids

producing too much steroids

glucocorticoids

corticosteroids

ex: Dexamethasone, Prednisone

ACTH- Adrenal corticotropic hormone

secreted in response to production of gonadotropin releasing hormone (GnRH) from the hypothalamus

• gonadotropin
• FSH
• ICSH

female- acts on ovarian follicles to stimulate its development and maturation

male- promotes maturation of sperm

female- stimulates ovulation and development of corpus luteum 

male- regulates production of the hormone testosterone by the interstitial cells of Leydig in the testes

• stimulates development of mammary glands of pregnant female
• active role in lactation 

hypothalamic hormones that control it's secretion: prolactin releasing factor (PRF) and prolactin inhibiting hormone (PIH)

• cellular growth
• regulates production of proteins by cells
• controls energy used within body 

during times of poor food supply will stimulate gluconeogenesis

production regulated by: growth hormone releasing hormone (GH-RH) and growth hormone inhibiting hormone (GH-IH) produced by the hypothalamus 

• ACTH
• MSH
• TSH
• GH
• PRL
• LH
• FSH

• antidieuretic hormone/vasopressin 
• oxytocin

melanocyte-stimulating hormone 

(former intermediate lobe hormone)

production of skin pigments in fish, amphibia, reptiles, many mammals (not primates)

its target cells are melanocytes within epidermis-stimulates these to produce skin pigment known as melanin

secretion controlled by melanocyte-stimulating hormone inhibiting hormone (MSH-IH) produced by hypothalamus

"third eye" 

contains neurons, neuroglia, and specialized secretory cells called pinealocytes

secrete an enzyme called seratonin which under influence from light can increase or decrease the production of melatonin 

reproductive behaviors

melatonin high

melatonin low

horses- spring (melatonin decrease bc light exposure is increasing)

sheep- fall (melatonin increase bc less light exposure)

• PTH
• parathormone

parathyroid hormone in response to falling levels of calcium ions in the blood.

PTH secretion causes an increase in circulating calcium

• stimulates activity of osteoclasts within bone to cause breakdown of bone matrix
• osteoblast activity inhibited-calcium into blood instead of bone
• urinary secretion of calcium ions reduced
• stimulates secretion of calcitrol by kidney-increases calcium absorption from digestive tract

 kidney

calcitonin (decreases calcium blood level)

• neoplasia of parathyroid gland
• secondary indirect hyperparathyroidism (kidney problem)
• secondary nutritional hyperparathyroidism (lack of proper diet)

• causes overproduction of PTH
• demineralization of bone causing bones to weaken and fracture

• chronic renal failure
• body attempts to maintain calcium level by absorbing it from the bone resulting in rubbery bones "rubber jaw"

meat only diet (meat is low in calcium levels for dogs so their bodies adjust with over-production of PTH)

calcitonin (decreases calcium blood level)

• thyroxine (T4)
• liothyronine (T3)
• thyrocalcitonin 

• calcitrol&calcitonin
• parathyroid gland&thyroid gland
• ANP (reduce blood vol)&Aldosterone (increase blood vol)

peptide similar to ANP secreted by Left ventricle in response to Left ventricle wall stretch/stress

• canine test available through ANTECH
• dog&cat through IDEXX

• 0-900 normal
• above 1800=heart failure

causes fall in calcium ion concentration by inhibiting osteoclast activity in bone (thereby increasing bone deposition) and by promoting secretion of calcium ions by kidney in urine

• in mediastinum of thorax
• size decreases with age
• produces hormone: Thymosin

hormone that promotes development and maturation of lymphocytes

(contributing factor to immune response in young, its deterioration with age may account for being more prone to disease as grow older)

• T lymphocytes
• B lymphocytes "plasma cells" produce immunoglobulins (antibodies)

atrial natriuretic peptide (ANP)

(over-stretching of atria walls occurs when circulating blood vol is too high. ANP helps to reduce circulating blood vol-vasodilation) 

reduces blood volume

• secretion of Na ions&water secretion increased by kidney
• suppression of thirst
• release of rennin, ADH, Aldosterone is suppressed
• angiotensin 2 and norepinephrine cause vasoconstriction, ANP prevents this and consequently promotes vasodilation=reduce in blood pressure

• calcitrol
• erythropoietin

Cushing's Disease

Addison's

• released by kidney when circulating blood oxygen levels are low
• job-produce more RBC

• glomerulosa (outer)
• fasiculata (middle)
• reticularis (inner)

adrenal medulla

• 24
• all steroid based
• carried in circulation bound to carrier proteins so have longer duration of action than other hormones
• these hormones effect the genes of cells that control the production of enzymes
• overall effect on cellular metabolism as a whole

corticosteroid- synthetic glucocorticoid (ex:dexamethazone)

glucocorticoid- hormones naturally produced by zona fasiculata

• mineralocorticoids
• *aldosterone
• contributes to regulation of electrolytes in body, primarily sodium and potassium

• fall in levels of sodium ions in circulation below the threshold level
• fall in blood vol or blood pressure
• rise in potassium ions in the extracellular fluid

(aldosterone is secreted in order to conserve sodium ions within the body and excrete potassium ions)

• glucocorticoids
• *cortisol and corticosterone
• secreted at times of stress
• help to spare glucose by mobilizing other sources of energy such as amino acids and lipis (gluconeogenisis)

zona fasiculata producing cortisol and corticosteroids or from veterinarian giving too many steroids long time (iatrogenically induced cushing's syndrome) 

glucocorticoids either due to over-production of ACTH from pituitary gland or production of excess cortisol as a consequence of neoplasia of adrenal gland

• polyphagia
• polydipsia
• polyurea
• hair loss
• pot belly
• thinning of skin

• bilateral adrenal hyperplasia due to pituitary stimulation
• unilateral functional neoplasm
• secondary adrenal secretions due to pituitary stimulation, either pituitary hyperplasia or functional pituitary tumor
• prolong administration of large amounts of adrenocorticosteroids- iatrogenically induced

(85-90% due to pituitary tumors-other 10-15% adrenal tumors)

• Low Dose Dexamethasone Screening Test (LDDS)
• give 0.01-0.15 mg dex IV if has cushing's cortisol levels remain high. if does not have cortisol levels will subside immediately

Anipryl (L-Deprenyl & Selegiline HCl)

as animal ages MAOB (monoamine oxidase-type B) production increases resulting in the decrease of the catecholamine dopamine which in turn results in hyperadrenocorticism. Anipryl is given, inhibiting production of MAOB. dopamine metabolism is restored and clinical signs of cushing's are minimized

release of glucocorticoids

(when glucocorticoids allowed to roam free=cushing's)

• older treatment for cushing's
• necrosis of fasiculata and reticularis
• hard to control but safer than vetoryl and more effective than anipryl

• enzyme blocker of steroids synthesis specifically on zona fasiculata to prevent production or release of glucocorticoids
• attacks all 3 zones
• "latest and greatest" but expensive, short lived, not as safe

Selegiline Hydrochloride 

used for Hyperadrenocorticism  or Cushing's Disease

Enalapril Maleate

an ACE inhibitor used to treat Congestive Heart Failure

• Addison's Disease
• adrenal cortices cannot produce adequate levels of Aldosterone resulting in increase in retention of Potassium in circulation (as it is not excreted by kidneys-bc no aldosterone) 

signs: vomiting, diarrhea, lethargy, weight loss, general weakness progressing to collapse, in severe cases, coma and death

• androgens
• testosterone
• some converted into estrogens in both male and female

sympathetic nervous system to produce epinephrine and norepinephrine.

• causes increase in heart rate, rate&depth of respiration, blood pressure
• blood glucose levels also increase due to increased breakdown of glycogen
• blood vessels dilated

Enacard (Enalapril Maleate)

mitral valve insufficiency: allowing blood to escape from left ventricle into left atrium and then backing up into the lungs

• produces "cardiac cough" 
• pulmonary edema 

regurgitation and consequently pulmonary edema and "cardiac cough"

• BP drops, detected by Juxtaglomerular cell which in response releases Renin
• Renin takes Angiotensinogen and converts to Angiotensin I
• Angiotensin I is converted into Angiotensin II by Angiotensin Conversion Enzyme (ACE)
• Angiotensin II goes to the adrenal gland and causes the outer layer (zona glomerulosa) to release Aldosterone
• Aldosterone goes to the kidney to cause absorption of Na
• So goes sodium, so goes water: As Na is absorbed, water comes with it increasing the volume of blood thereby raising BP

once BP increased, circulates (60 sec) up to kidney, where it is measured, once normal kidney will stop releasing Renin (negative feedback)

reduce the volume of blood 

(by reducing Na we reduce water. by reducing water we are able to drop the BP down so as blood is regurgitated from the left ventricle into the left atrium and then into the lungs, we will get less fluid absorbed into the lungs)

Enacard (enalapril maleate)

Enacard is an ACE inhibitor- blocks the conversion of Angiotensin I to Angiotensin II. This stops the Renin-Angiotensin System in its tracks and allows the animals BP to remain lower than normal, controlling the pulmonary edema that comes with mitral valve insufficiencies.

• heart rate goes up
• respirations go up
• vasoconstriction

• heart rate goes down
• respirations go down
• vasodilation

• neutrophilia
• eosinopenia
• lymphopenia

• cushing's syndrome
• addison's disease

pancreas

endocrine function through secretion of hormones (insulin, glucagon)

exocrine function through secretion of enzyme-rich fluids into digestive tract (amylase, trypsin, lipase)

Islets of Langerhans

• Alpha- secrete hormone glucagon
• Beta- insulin
• Delta- somatostatin
• F- pancreatic peptide

exocrine- produce digestive juice

(lipase, amylase, trypsin)

• endocrine
• secrete hormone: glucagon
• causes increase in blood glucose levels by stimulating breakdown of glycogen in muscle and liver.
• secreted in response to a fall in blood glucose detected by alpha cells themselves

• endocrine
• secrete hormone: insulin
• secreted in response to a rise in blood glucose

to get glucose of out the blood stream and into the tissues

• endocrine
• secrete hormone: somatostatin
• secreted in response to peaks of insulin or glucagon
• helps balance them out

• endocrine
• secrete hormone: pancreatic peptide
• thought to affect production of some pancreatic digestive enzymes

bile (digests fat)

• 1-lack of insulin
• 2-lack of insulin receptors 

• mellitus- lack of insulin or insulin receptors
• cannot regulate blood glucose levels, rise above renal threshold resulting in glucose in urine

• insipidus- lack of ADH
• inability to produce adequate amounts of ADH which causes retention of water within the body. consequently, cannot control amount of water secreted in urine and produce abundant quantities of dilute urine

• testes
• ovaries

testes produce hormones testosterone&estrogen

testosterone secreted by interstitial cells of Leydig

function of testosterone: develop&maintain viable spermatozoa, secretory cells of reproductive tract, and determine male secondary sexual characteristics (musculature, territorial scent marking)

LH or ICSH from anterior pituitary gland

(the hormone inhibin, produced by testis and ovary has a negative feedback upon production of FSH from anterior pituitary in both male and female)

ovaries produce 2 hormones in different amounts depending on stage of ovulation

estrogen&progesterone 

support maturation of oocyte and help prepare reproductive tract for mating and conception

• produced by developing cells of follicle
• prior to ovulation under direct control of FSH

maintain pregnancy by ensuring uterus stays in suitable condition to support developing embryo 

produced by corpus luteum of ovary following ovulation

hormone produced by female during pregnancy in corpus luteum placenta and uterus

• function: prepare body for birth process
• laxity of pubic symphysis