- Nerve response signals hormone.
- Suckling stimuli travels up spinal cord to hypothalamus
- neurocrines secrete oxytocin
- travels down axon, released in blood
- contraction of smooth muscle of mammary gland
- milk to teat
Endocrine vs Neuro
- NS fast, short duration
- ES cellular metabolism, growth and reproduction. Long term, slow-acting.
- Interact closely--dopamine, histamine, somatostatin are in endocrine and neuro. Endocrine cells can be controlled by neurons.
a cell or group of cells that secretes a chemical messenger (hormone) directly into the bloodstream.
a chemical messenger that is produced by one or a group of cells, secreted directly into the bloodstream and transported to distant target cells, eliciting a response
- neurohormones. Chemical messengers secreted by axonal terminal of neuron directly into bloodstream.
- can act on distant cell. Oxytocin.
a chemical messenger secreted by a cell into ISF that acts on a DIFFERENT type of neighboring cell.
a chemical messenger secreted by a cell into ISF that acts on the cell of origin or an identical neighbor.
Endocrine hormone classification
- 2 kinds:
- Peptide hormone: peptides, polypeptides, proteins, produced by adrenal medulla, pituitary gland, hypothalamus, thyroid gland, parathyroid gland, pancreas, placenta, endometrium
- Steroid hormone: derived from cholesterol. Produced by gonads, adrenal cortex, fetal membranes (placenta).
Protein hormone synthesis
synthesized as preprohormones, cleaved in rough ER to make prohormones, golgi apparatus to form active hormones, STORED in granules, released in response to stimuli
steriod hormone synthesis
- made from cholesterol in the liver
- released AS SYNTHESIZED
Transport of hormones in blood
- Peptide/protein hormones are hydrophilic, dissolve in plasma
- steroid and thyroid hormones are lipophilic carried in plasma bound to proteins. Must unbind before it can penetrate a target cell.
Peptide hormone-cell interaction
- receptors are on or next to membrane (outside).
- changes enzymatic activity in target cell if stimulated
- effect occurs fast, lasts less than 1 hour
steroid hormone-cell interaction
- intracellular receptors
- stimulated receptor changes synthesis of specific proteins
- effect occurs slow, lasts hours to days
Functions of the endocrine system
- control of physiologic functions like
- metabolism (energy and mineral)
Hormones in energy metabolism
- thyroid hormone
- growth hormone
hormones in mineral metabolism
- parathyroid hormone
hormones in growth
- growth hormone
- thyroid hormone
- growth factors
hormones in reproduction
- luteinizing hormone (LH)
- Follicle stimulating hormone (FSH)
- Prolactin (PRL)
small amount of hormone produces significant effects due to gain of signal
Negative feedback control
when the released hormone can go back up to the hypothalamus and pituitary to stop production of the tropic hormone
Adrenal axis negative feedback
- Hypothalamus secretes CRH
- CRH acts on anterior pituitary
- anterior pituitary secretes ACTH
- ACTH goes to adrenals
- adrenals produce cortisol
- cortisol tells hypothalamus and pituitary to stop producing
- less common than negative feedback
- when production of the final hormone stimulates more hormone to be produced.
- Seen in ovulation (estrogen makes more estrogen and progesterone)
Hormone patterns change based on light rhythms as well as negative feedback
- Interface between ES and NS.
- Produces peptides and amines to influence pituitary
- Part of diencephalon, floor of third ventricle, connected to hypophysis.
- made up of anterior (adenohypophysis) and posterior (neurohypophysis).
- anterior made from pouch of pharyngeal mucosa
- posterior made from outgrowth of hypothalamus. Remains connected by stalk.
- direct axonal connection.
- Hormones secreted by posterior pituitary are synthesized by hypothalamus, carried by axon, posterior secretes into veins, then systemic. Called neurocrines. Vasopressin (ADH) and Oxytocin. Peptide hormones. Direct hormones.
- Secreted into blood, cause response not more hormone.
- released by posterior pituitary.
- contraction of smooth muscle (mammary gland and uterus)
- released by posterior pituitary.
- conservation of water, increased blood pressure.
- disorder of water metabolism characterized by polyuria, dilute urine and polydipsia.
- caused by defective secretion of ADH (Central) or renal lack of response to ADH (nephrogenic)
- partial or complete
Central diabetes insipidus
lack of secretion of ADH causes water disorder with dilute urine and dehydration.
nephrogenic diabetes insipidus
when kidneys don't respond to ADH, leads to dehydration and dilute urine
Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
- hypersecretion of vasopressin (ADH).
- often neoplastic or drug reaction
- hyponatremia (low NA+) because body is SO dilute.
- concentrated urine, over-hydration
- portal system links anterior hypophysis with hypothalamus.
- hypothalamic releasing factors stimulate endocrine cells within anterior pituitary to secrete hormones into capillary system
- capillary systems in hypothalamus and in anterior pituitary that coalesce and drain into systemic veins.
Hypothalamic releasing hormones (7)
- released from hypothalamus into portal system, stimulate anterior pituitary to secrete hormones into capillaries
- Thyrotropin-releasing hormone (TSH)
- Gonadotropin releasing hormon (GnRH)
- Growth hormone inhibiting hormone (GHIH)
- Growth hormone releasing hormone (GHRH)
- Corticotropin-releasing hormone (CRH)
- Prolactin-releasing factor (PRF)
- Prolactin-inhibiting hormone (dopamine) (PIH)
Anterior pituitary hormones (6)
- all are peptide hormones. All are tropic except prolactin.
- Growth hormone (somatotropin)
- Thyroid stimulating hormone (TSH)
- Follicle-stimulating hormone (FSH)
- Lutenizing hormone (interstitial-cell-stimulating hormone) (LH or ICSH)
- Prolactin (PRL) *only direct hormone
- Corticotropin (adrenocorticotropic hormone) (ACTH)
- Stimulate a target endocrine gland to secrete increased amounts of its own hormone
- stimulated from anterior pituitary
- feedback inhibition.
- FSH, LH, TSH, ACTH, GH
- NOT prolactin
Thyroid stimulating hormone (TSH)
thyrotropin releasing hormone stimulates anterior pituitary to release TSH (tropic hormone) that travels to thyroid.
- thyroid gland is composed of follicles lined by epithelium filled with a fluid known as colloid
- Thyroid hormones are stored extracellularly as part of thyroglobulin, main part of colloid
most numerous cells in epithelium of thyroid follicle and secretes thyroid hormones and thyroglobulin (glycoprotein)
- thyroid glycoprotein containing tyrosine
- precurser to T4 and T3
- Present in colloid of thyroid follicles
- two tyrosines contain 3 or 4 iodines, making thyroid hormone
parafollicular cell or C cell
- located outside thyroid follicle
- secretes calcitonin
- Secreted in response to TSH
- T4 - thyronine (4 iodines) (90%)
- T3 - triiodothyronine (3 iodines) (10%, rest made from T4 in muscles/liver/kidneys)
- thyroglobulin and enzymes synthesized in follicular cell, sent into colloid
- iodine co-transported in with Na+, sent to colloid
- Enzymes add iodine to thyroglobulin making T3 and T4
- thyroglobulen returns to cell, enzymes separate T3 and T4
- T3 and T4 enter circulation
- negative feedback (thermostat)
- T3 and T4
- selective absorption of iodide from circulation by follicular cells in thyroid gland.
- Brought in by cotransport with Na+, sent to colloid
- Iodine then used to synthesize T3 and T4
another type of T3, formed outside thyroid, few bio effects
T3 and T4 travel
- must combine with plasma proteins
- T3 is less tightly bound, more is released to tissue cells
- T3 is more potent but shorter-duration than T4
Function of thyroid
- Basal metabolism #1
- O2 consumption = heat production
- glucose absorption and uptake
- glycogen storage or lysis
- with GH for normal growth
- lipid metabolism (lipolysis)
- Enhances symp NS
- CNS development
- maintains cardiac contractility (nerves)
- Increase heart rate/contraction
- normal metabolic functions of all tissues
inability to secrete adequate amounts of thyroid hormone leading to enlargement of thyroid gland
- decrease in thyroid hormone.
- Common in dog
- lethargy, weight gain, symmetrical alopecia, cold sensitivity
- overproduction of thyroid hormone
- common in cats
- hyperactivity, tachycardia, aggression, polyphagia, weight loss, PUPD
- AKA somatotropin and somatotrophic hormone
- Stimulates liver to form somatomedins which promote bone growth, elongation and thickness
- stimulates growth in all body cells that can grow
- most important for controlling stature
- conserves protein and breaks down fat to provide energy and increases blood glucose levels
- milk production in cows
somatomedins (insulin-like growth factors)
- produced by liver in response to growth hormone from anterior pituitary.
- Somatomedin C (insulin-like growth factor 1) most important
- stimulates systemic growth, growth in almost every cell in body
- regulates cell growth/development (nerves, DNA synthesis)
- somatotropin deficiency in dog. Destruction of pituitary gland.
- slow growth, dwarfism, mental retardation, others
- somatotropin excess in adult cat.
- uncontrolled diabetes melitus (insulin resistance), organomegaly (big organs), enlargement of extremities (body size, jaw, tongue, forehead)
- small paired structures immediatly cranial to kidneys
- two glands wrapped around each other.
- Cortex and medulla
Zones of adrenal cortex
- Zona glomerulosa (aldosterone)
- Zona Fasciculata (cortisol and glucocorticoids)
- Zona Reticularis (sex hormones and few glucocorticoids)
two types of steroid hormones produced by adrenal cortex
glucocorticoids and mineralcorticoids
- steroid hormones produced by adrenal cortex.
- Electrolyte balance (blood pressure) (sodium reabsorption and potassium excretion)
- zona glomerulosa
regulation of aldosterone/mineralcorticoids
- increased potassium ion concentration***
- increased activity of renin-angiotensin system
- increased sodium ion concentration (decrease aldosterone secretion)
- ACTH from anterior pituitary is necessary for secretion of aldosterone--does not affect rate
- released mainly in zona fasciculata of adrenal cortex
- secretion regulated by ACTH from anterior pituitary; negative feedback loop
- Stimulated by stress
- cortisol most important
- glucocorticoid released by zona faciculata of adrenal cortex
- essential for body's response to stress (sick, fear, etc)
- increases blood glucose levels by increasing protein catabolism, increasing lipolysis and increasing gluconeogenesis
- also anti-inflammatory, immunosuppressive
- decreases ADH secretion, diluting urine
cortisol and circadian rhythms
- sleep and activity patterns are superimposed on negative feedback system
- lowest at night and highest in early morning
- Stressors cause hypothalamus to secrete CRH
- CRH makes anterior pituitary secrete ACTH
- ACTH makes adrenal cortex secrete cortisol
- cortisol goes to liver, fat, muscle, lymphocytes etc
- cortisol goes to hypothalamus to stop CRH production
- cortisol goes to anterior pituitary to stop ACTH production
- Cushing's disease
- hypersecretion of adrenal cortex.
- Caused by pituitary tumor, adrenal tumor or iatrogenic (give too much cortisol, turns off system)
- Signs are PUPD, polyphagia, lethargy, pot belly, panting, alopecia, thin skin
- hyposecretion of adrenal cortex
- lack of mineralcorticoids and glucocorticoids
- waxing and waning signs, vomiting, diarrhea, anorexia, weakness, bradycardia, electrolyte abnormalities
- Conn's syndrome
- adrenal glands produce excess aldosterone
- results in hypertension or hypokalemia. Uncommon
Hormones of adrenal medulla
- catecholamines (epinephrine and norepinephrine)
- Flight or fight
- metabolism, increase concentration of glucose
- secretion initiated by ACH from preganglionic
- tumor of adrenal medulla, secretes epinephrine, norepinephrine or both.
- PU/PD, increased heart rate, restlessness, distended abdomen, sometimes hypertension. Sometimes no signs.
Follicle stimulating hormone
- protein hormone, stim by anterior pituitary. Gonadotropin (with LH). Dominant in growth of follicles. Stimulates growth of oogenesis and spermatogenesis
- controlled by GnRH (gonadotropin releasing hormone from hypothalamus)
- Causes secretion of estrogen, progesterone and inhibin.
- protein hormone stimulated by anterior pituitary. Gonadotropin (with FSH). Dominant during final follicular maturation and ovulation.
- Assists in ovulation and develops functional corpus luteum. Simulates testosterone secretion in males.
- Controlled by GnRH (gonadotropin releasing hormone) from hypothalamus.
- Causes secretion of estrogen, progesterone and inhibin.
process by which mammary alveolar cells aquire ability to secrete milk.
establishment of milk secretin--start
continued production of milk by mammary glands.
- adenohypophysis hormone creates lactation (produce milk). Stimulates and maintains milk production (sheep and non-ruminants). Not so much needed to maintain in ruminants.
- pulsatile (always releasing some)
- inhibited by Dopamine (ventral hypothalamus)
- stimulated by vasoactive intestinal peptides
- Increases right before parturition (when progesterone drops)
Process of teat stimulation
- stimulation of nipple sends impuse to hypothalamus
- Hypo blocks release of dopamine and stimulates vasoactive intestinal peptides
- prolactin released from anterior pituitary
- causes contraction of myoepithelial cells surrounding alveolus
- milk enters ducts and cisterns (milk letdown)
- Promotes contraction of uterus during parturition (if uterus has been exposed to adequate estrogen).
- Release stimulated by posterior pituitary. NEUROCRINE, when tactile stimulation of nipple.
- main organ involved in calcium and phosphorus metabolism (raises Ca to normal when low)
- 4 pairs at base of thyroid
- Chief cells secrete hormone.
- hormone secretion controlled by calcium concentrations in blood (less calcium turns on, too much turns off), epinephrine, magnesium and sleep.
actions of parathyroid hormone
- frees Ca2+ and phosphate from bone
- increases production of active vitamin D by kidneys, promoting absorption of Ca and Phosphate from GI tract
- causes kidneys to excrete P and keep Ca2+
- works WITH Calcitriol and against calcitonin(action reaction pair with calcitonin)
- activated vitamin D
- important for absorption of Calcium from the gut.
- works with parathyroid hormone and against calcitonin
- hormone of the thyroid gland that works against parathyroid hormone and calcitriol.
- Causes lowering of calcium levels in the blood.
- inhibits bone resorption and may increase excretion of Ca and phosphate in kidney
- secreted by parafollicullar cells or C cells
- stimulated by hypercalcemia and hypermagnesemia.
- excessive secretion of PTH by one or more abnormal glands
- Primary (parathyroid adenoma usu.)
- Secondary (renal disease or nutrition, takes from bones. "rubber jaw", can have normal blood levels)
- signs are hypercalcemia, PUPD, weakness, vomiting, urinary incontinence
- absolute or relative deficiency in the secretion of PTH
- usually we did it (when we took out thyroid), idiopathic
- causes hypocalcemia and hyperphosphatemia
- neuromuscular signs (nervousness, seizures, focal twitching, ataxia, weakness
Four hormone-secreting cells of endocrine pancreas
- cells in Islets of Langerhans
- alpha cells secrete glucagon
- beta cells secrete insulin
- delta cells secrete somatostatin
- F cells secrete pancreatic polypeptides
- PANCREATIC HORMONES ARE POLYPEPTIDES
- lowers concentration of blood glucose, fatty acids and amino acids and converts to their storage forms (glycogen, triglycerides and protein) and decreases breakdown of storage.
- allows transport of glucose across cell membrane (out of blood)
- stimulated by LOTS of stuff
- inhibited by somatostatin
- also epinephrine, norepinephrine
- deficiency of insulin
- high glucose in blood and urine
- PUPD, anorexia or polyphagia, weight loss, vomiting, diarrhea, lethargy, weight loss, diabetic neuropathy
- opposite of insulinoma
- increased production of insulin by islet cell tumors
- Opposite of diabetes mellitus (causes low glucose in blood and urine, lots of storage).
- LOTS in ferrets
- produced by alpha cells in islets of langerhans
- increases blood glucose levels. (opposite of insulin. Action/reaction pair)
- decreases glycogen synthesis, increases glycogenolysis and increases gluconeogenesis.
- Stimulated by low glucose, Symp NS and Para NS,
- INHIBITED BY SOMATOSTATIN
Glucagon and insulin
work together to keep blood glucose levels steady. After a meal, blood glucose is high, insulin released. Hours later, glucagon released.
- extremely rare tumor of alpha cell of islets of langerhans causing increased secretion of glucagon
- superficial necrolytic dermatitis (on feet and hock area), hyperglycemia
- inhibitor of secretion of pancreatic hormones (insulin, glucagon, pancreatic polypeptide). inhibitor of growth hormone secretion, inhibitor of digestive process, decreasing absorption, secretion and motility.
- secreted by D cells of pancreas, brain and GI tract.
- Secretion stimulated by nutrients, neurotransmitters (ACH, epinephrine, norepinephrine)
- tumor of delta cells of endocrine pancreas
- extremely rare (bearded dragons).
- anorexia, vomiting, hyperglycemia, anemia
- secreted by F cells of endocrine pancreas.
- effects in GI tract (not exactly sure how--inhibits pancreatic/gallbladder secretions,increases gastric emptying and motility)
- secretion stimulated by intestinal hormones (CCK, Secretin, Gastrin), vagus, and ingestion of protein.
- Inhibited by SOMATOSTATIN
Pancreatic polypeptide disease
pancreatic polypeptidomas are very rare. Pancreatic tumors can cause multiple hormone problems
exocrine hormones of the pancreas.