Endocrine System Flashcards
Endocrine
Ductless glands that secrete hormones
Hormones are released from endocrine glands into surrounding tissue fluid and then enter the circulatory system. Circulate within body via bloodstream to affect cells in a specific organ
Hormones (Examples. Can be…)
Proteins (Insulin), glycoproteins (LH, FSH, TSH), or polypeptides (oxytocin, prolactin)
Amino Acids: T3, T4; catecholamines (epi and norepi)
Steroids: testosterone, estrogen, progesterone, cortisol, aldosterone
Hormones Path
Hormones travel to target cells by bloodstream where most will bind to receptors on target cell surface.
Steroids pass through plasma membrane of target cell and bind the nucleus.
Hormones produce slow sustained response
An endocrine system
Stimulus -> endocrine gland -> Hormone -> target tissue -> response
Hormone Functions (endocrine system controls..)
Body energy levels and metabolism
Internal balance of body systems (homeostasis)- ions and water balance
Responses to surroundings, stress, and injury
Reproduction
Growth and development
Primary Endocrine Organ
First function is to secrete hormones
Primary Endocrine Organ Examples
- Pituitary gland, hypophysis cerebri
- Pineal gland, Epiphysis cerebri
- Thyroid gland
- Parathyroid gland
- Adrenal glands
Hypothalamus
Secondary Endocrine Organ
A secondary function is to secrete hormones
The first function is something else
Secondary Endocrine Organ Examples
Pancreas Testes Ovaries Kidneys Stomach Intestines Thymus Heart Placenta Adipose Tissue
Overview of Major endocrine organ function
Growth and development
Internal environment
Energy production, storage, and utilization
Reproduction
Hypothalamus
Portion of the brain that links the nervous system to the endocrine system via the pituitary gland/hypophysis
Hypothalamic nuclei
Collections of neurons
Control distant cells via hormones in 2 ways:
1. Production of releasing hormones- released into portal system to target cells in the adenohypophysis
2. Hormones axonally transported and stored in the neurohypophysis, then released into the blood to target distant sites (ADH and Oxytocin)
Endocrine Pathway ??/
In hypothalamus, releasing hormones are secreted into a portal blood system. They stimulate a variety of cells in the anterior (adenohypophysis) pituitary and secondary hormones released to effect other organs.
OR ADH/oxytocin is produced in nerves and stored in axons extending into the neural lobe of pituitary and is released directly into blood stream
Origin of Pituitary
Adenohypophysis: Epithelial- Roof of pharynx
Neurohypophysis: Neuroectodermal (from diencephalon)
Neurohypophysis: Important Portions
Pars Nervosa (Pars posterior, posterior pituitary) Infundibular stalk (Infundibulum)
Neurohypophysis
Cell bodies of large neurons (magnocelluolar neurons) in hypothalamus nuclei produce: ADH (vasopressin) and oxytocin
Their axons comprise the infundibulum and pars nervosa (posterior pituitary)
Swellings along these axons known as herring bodies- where hormones are accumulated
Herring Bodies
Swelling along axons in neurohypophysis where hormones are accumulated.
Neurohypophysis- Pars nervosa
Axons terminate on vessels and blood then transports hormones to target organs
Oxytocine
Causes release of milk
Calf suckling is the stimulus that causes a release of oxytocin from herring bodies into the blood and to the mammary glands. The oxytocin stimulates contraction of myoepithelial cells to let milk down
Adenohypophysis Portions
Pars distalis
Pars intermedia
Pars tuberalis
Adenohypophysis- Pars distalis
The bulk of adenohypophysis and secretes majority of hormones Cells: Acidophils (red) Basophils (bluish) Chromophobes (no color)
Cells in the anterior pituitary are difficult to differentiate.
Adenohypophysis
Relative size and orientation depend on species
Require a releasing hormone from hypothalamus
Hypothalamic neurons produce releasing hormones into portal vessels which travel to Adenohypophysis (esp pars distalis) where they stimulate acidophils or basophils to produce another hormone.
The second hormone travels to a target endocrine organ where a third hormone is produced. This will cause an effect on the target organ/cell.
Adenohypophysis- Pars intermedia
Source of melanocyte-stimulating hormone (MSH)
Contains large pale cells that produce large molecule POMC which can be sectioned into a number of hormones including endorphins, melanotropins, and lipotropins
Can have an interglandular cleft (remnant of Rathke’s Pouch cavity
Acidophils
Found in pars distalis
Somatotropes secrete Growth Hormones
Mammotropes secrete prolactin (lacticotropes)
Basophils
Found in Pars Distalis
Thyrotropes secrete thyrotropin (TSH)
Gonadotropes secrete FSH, LH
Adrenocorticotropes secrete ACTH
Pineal Gland
One on each side in brain near middle
Epiphysis
Main function is to regulate daily rhythms of bodily activity and have pinealocytes that secrete melatonin
Pinealocytes
Secretory cells in epiphysis. They produce melatonin.
Respond to stimuli detected in the retina; darkness stimulates secretion of melatonin= circadian 24 hour rhythm
Melatonin
Manufactured by pinealocytes
Mainly secreted at night (in darkness) and is exclusively involved in signaling the time of day and time of year
Effective antioxidant
Immune-enhancing and oncostatic properties
Melatonin- Seasonal Breeders
Long-day Breeders: Horses. Cycle when days are getting longer: late spring, summer, early fall
Short-day breeders: Sheep, goat, deer, elk. Cycle when days are getting shorter: fall. Anestrus in spring and summer
Thyroid Gland
Bilateral- one on each side except in dogs where they do not connect
Thyroid Gland: Follicles
Lining cells produce thyroglobulin which is stored in follicle lumen (colloid) and combined with iodine
Lining cells endocytose thyroglobulin and covert to active T3/T4
Synthesis, iodination, proteolysis of thyroglobulin regulated by TSH
Single layer of cuboidal cells (follicular cells) that secrete into the lumen
Thyroid Gland: C cells
In between follicular cells and have a neural crest origin.
Parafollicular cells
Secrete calcitonin in response to high blood calcium
Target organs are bone, kidney
Main function is to lower serum calcium
(calcitonIN brings Calcium IN)
Parathyroid Gland: location
1 internal parathyroid embedded in each thyroid lobe, and 1 external parathyroid beside each lobe.
Parathyroid Gland: Chief Cell
The endocrine secretory cell
Parathyroid Gland: Function
Composed of tightly packed chief cells
Secrete parathormone (PTH) into capillaries
PTH increases Ca via effects in SI, bone, kidney. Increased intestinal and renal Ca resorption.
Stimulates osteoclasts for bone resorption
Adrenal Gland: Location
Above kidneys
Separation between cortex and medulla only seen in mammals
Adrenal Gland: Cortex
Arises from mesoderm
Secretes steroid: mineralocorticoid, corticosteroids, and sex hormones
Zona Glomerulosa: mineralocorticoids (aldosterone) (typical steroid secreting appearance)
Zona Fasciculata: corticosteroids (cortisol) (Spongiocytes)
Zona reticularis: weak androgens (more cellularly dense) (lipid vacuoles and vascularity)
GFR. Salt, sugar, sex
Adrenal Gland: Medulla
Arises from neural crest
Secretes catecholamines
Epinephrine»_space; norepinephrine
Adrenal Medulla
Large sympathetic ganglion, composed of modified neurons with no axons.
Chromaffin cells secrete epinephrin and norepinephrine, stored in secretory granules
Columnar to cuboidal cells, do not have distinct vacuoles
Endocrine pathway???
Corticotropin-releasing hormone (CRH) exocytosed from hypothalamic neurons, enters primary plexus of portal system, en route to pars distalis
CRH, delivered to corticotrophs by the secondary plexus, binds its GPCR on corticotrophs and signals exocytosis of ACTH
ACTH stimulates zona faciculata
ACTH binds to its GPCR, signaling via cAMP, glucocorticoid synthesis; these hormoens diffuse from cortical cells into peripheral target cells
Release of glucocorticoids and effects a lof of cells: Hepatocytes, adipocytes etc
Glucocorticoids enter cells by diffusion, bine to their cytoplasmic receptor, enter the nucleus, bind to their hormone response element, and effect transcription of responsive genes
Pancreas
Has Endocrine and exocrine functions In fascium near duodeum Empties into duodeum- exocrine Endocrine portion produces hormones Composed of exocrine acinar and endocrine tissue Exocrine=98% Endocrine= 2%
Pancreas: Islets of Langerhan
Islets of Langerhan have multiple cells types Alpha: glucagon, CCK, GIP Beta: Insulin, IAPP Delta: Somatostatin Other: Gastrin
Gastrointestinal Endocrine Tissue
Pyloric region of the stomach secretes gastrin
Enteroendocrine cells in epithelium mucosae of the small intestine secrete hormones such as cholecystokinin (CCK) for gall bladder contraction
Secretin and Gastric inhibitory polypeptide are also secreted by endocrine cells within the small intestine
Kidney
2 hormones: Renin and Erythropoietin
Kidney: renin
a hormone and an enzyme
Produced by juxtaglomerular cells (smooth muscle in wall of glomerular afferent arterioles)
secreted in response to decrease in BP in aa. and increase in Na concentration in distal tubule
part of RAAS
Kidney: Erythropoietin
Produced by interstitial fibroblasts in kidney = O2 concentration
It is a cytokine for RBC precursors
Increase in erythropoiesis is an increase in RBC production
Atrial Myocardium
Atrial muscle cells contain membrane bound granules that are especially numerous in right atrium
Atrial granules have an endocrine function due to presence of atrial natriuretic peptide (ANP)
Increase stretch of atrial myocytes -> increase ANP -> promotes Na and water loss -> decreased BP
ANP target: distal tubules of kidneys
Components of adenohypophysis
Pars tuberalis, pars intermedia, pars distalis
Components of Neurohypophysis
Pars nervosa, infundibular stalk, eminetia mediana
Cells of Pars Distalis
acidophile (GH, PRL)
Basophils (TSH, FSH, ACTH, LH)
Chromophobes
Cells of pars intermedium
Secrete melanocyte stimulating hormone
Cells of Pars Nervosa
Store ADH and oxytocin. Both originate from nuclei in the hypothalamus.
Pineal gland secretes what hormone
Melatonin
Colloid contains
thyroglobulin. Converted to thyroxine
Follicular lining cells function
secretion of thyroglobulin and conversion into thyroxine
Clear cell
Secretes calcitonin which reduces serum C
Chief Cells
Part of parathyroid. Secrete parathyroid hormone
Increases serum calcium. Targets bone, intestines, and kidneys
Chromaffin Cells
Adrenal medulla. Form Neural crest and secrete noradrenaline, and adrenaline
