Endocrine System Flashcards
What are the different types of endocrine organs?
Pituitary, thyroid, parathyroid, adrenal, pineal
Sole function is to synthesize and secrete hormones
Hormones
Chemical messengers that are carried via blood to distant target cells
Water-soluble hormones
Act via specific cell-surface receptors, then activate a second messenger
Lipid soluble hormones
Diffuse across the cell membrane
Endocrine hormones
Hormones released into the blood and acts on distant cells (pituitary hormones)
Paracrine hormones
Hormones diffused locally and acts on neighboring cells (NTs)
Autocrine hormones
Acts on cell that is producing it (T lymphocyte proliferation)
Where are diffuse endocrine cells distributed?
Individually or in small groups within the epithelium of the digestive system
(argentaffin cells)
Pituitary is connected via ________ with the hypothalamus
Infundibulum (funnel-like structure)
Adenohypophysis (anterior lobe)
Develops from Rathke’s pouch (pharyngeal ectoderm)
Consists of Pars distalis, tuberalis and intermedia
Neurohypophysis (posterior lobe)
Hypothalamus invagination (diencephalons)
Consists of Pars nervosa and infundibulum
What is the space between the pars intermedia and distalis?
A remnant of the cavity of Rathke’s Pouch
Where is the only true division of the anterior and posterior lobe?
Human and to some extent bovine and porcine
Pars distalis
Cells arranged in irregular cords that lie adjacent to sinusoids
Two cell types: chromophils (acidophils and basophils) and chomophobes
Acidophils
PAS negative with protein secretion
Somatotroph (GH) and lactotroph/mammotroph (prolactin)
Basophils
PAS positive with glycoprotein secretion
Gonadotroph (FSH and LH), thyrotroph (TSH) and corticotroph (ACTH)
Percentage of different cell types
Somototroph 50%
Mammotroph 20%
Corticotroph 20%’
Gonadotroph 5%
Thyrotroph 5%
Pars intermedia
Melanotrophs secrete MSH
Contain colloid-containing cysts (remannt of Rathke’s pouch)
What other cells does pars intermedia have?
Coricotrophs
Can hypertrophy/ hyperplasia in horse –> excessive secretin of ACTH –> excessive secretion of cortisol from adrenal cortex –> Cushing’s syndrome
Where are MSH, ACTH and B endorphin derived from?
Pro-opiomelanocortin
Pars nervosa
Contains axons of supraoptic (SO) and paraventricular nuclei (PV) whose cells bodies are in the hypothalamus
Pars nervosa cells
Oxytocin and vasopressin transported to distal ends of axons stored in sites called Herring bodies
What are axons of pars nervosa surrounded by?
Oligodendrocyte called pituicyte
Hypothalamic hypophyseal portal system
- Hypothalmic secretions (GnRH, GHRH, CRH) enter capillary plexus
- Drain into hypothalamus-hypophyseal portal vein
- Drained into a secondary capillary plexus with surrounding acidophils and basophils
Portal vein
Vein interposed between two capillary networks
Hypophseal vein interposed between primary capillary plexus and secondary capillary plexus
What are the anterior pituitary hormones?
GnRH
CRH
TRH
PRH
GHRH
GnRH
Pituitary hormone: LH, FSH
Target: reproductive system
Effects: stimulates production of sex hormone by gonads, stimulates production of sperm and eggs
TRH
Pituitary hormone: TSH
Target: thyroid gland
Effects stimulates release of thyroid hormone, regulates metabolism
PRH
Inhibited by PIH
Pituitary hormone: PRL
Target: Mammary glands
Effects: promotes milk production
GHRH
Inhibited by GHIH
Pituitary hormone: GH
Target: Liver, bone, muscle
Effects: induces targets to produce insulin-like GF! Stimulate body growth and higher metabolic rate
CRH
Pituitary hormone: ACTH
Target: Adrenal glands
Effects induces targets to produce glucocorticoids, regulate metabolism and stress response
What is the posterior pituitary hormone?
ADH
Pituitary hormone: stores ADH
Target: kidneys, sweat glands, circulatory system
Effects: water balance
Dwarfism, Gigantism, and acromegaly
Lower GH before puberty
Higher GH before pubert
Higher GH after puberty
Hypo or hyperthyroidism
Lower TSH or higher TSH
Cushing’s syndrome and Addisons disease
Higher ACTH
Lower ACTH
Prolactinemia
Higher prolactin due to tumor of mammotrophs
Common in humans
Leads to male infertility
Diabetes insipidus
Lower ADH
Thyroid gland
2 lobes connected by isthmus that envelope from endoderm
Made of follicles
Filled with thyroglobulin glycoprotein (colloid)
What is the follicle of the thyroid gland lined by?
Simple cuboidal epith. that contains follicular cells (98%) and parafollicular cells (2%)
What is unique about the thyroid gland?
Only endocrine gland where secretion is first stored extracellularly in lumen then reabsorbed and secretes into blood
What stain is used for parafollicular cells?
Immunicytochemical stain
Follicular cells epithelium
Cuboidal then columnar when stimulated by TSH and squamous when inactive
What are follicular cells involved in?
The synthesis and release of thyroid hormones T4 (abundant) and T3 (more potent)
Resting follicle
Large
Lined by squamous with microvilli
Dark nucleus
Large amount of acidophillic colloid in lumen
Active follicle
Small
Lined by cuboidal to low columnar with more microvilli
Pale nucleus
Little colloid with scalloped border
What are the steps involved in synthesis and release of thyroid hormone
- Synthesis of thyroglobulin
- Uptake of iodide
- Oxidation of iodide
- Tyrosine iodination
- Resorption if thyroglobulin and release of T4 and T3 into circulation
TRH
Thyrotropic releasing hormone
Stimulates TSH secretion from pituitary
TSH
Thyroid stimulating hormone
Stimulates thyroid gland to secrete T3 and T4
What does the release of T3 and T4 cause?
Increase the basal metabolic rate of almost all cells of the body
Promotes heat production
Broad effects of gene expression and induction of protein synthesis
Simple Goiter (hypothyroid)
Enlarged thyroid gland due to iodide deficiency
Follicle is filled with thyroglobulin without iodination
Blood test: low T3, T4 and high TSH
What are other names for simple goiter?
Myxedema in adults
Cretinism in young
Graves’ disease (exopthalmic goiter, hyperthyroid)
Autoimmune disease from binding of autoimmune antibodies to TSH receptors on follicle cells
Increase synthesis and secretion of T3 and T4
What are the symptoms of Graves’ disease?
Weight loss, bulging eyes, nervous excitability
Blood test: high T3 and T4 and low TSH
What are the 2 cells in the parathyroid gland?
Chief cells and oxyphil cells
Chief cells
Most numerous
Secrete parathyroid hormone to raise blood calcium levels and stimulate osteoclast activity
How do chief cells worK?
By increasing the reabsorption of calcium and decreasing reabsorption of phosphates at the PT of the kidney
Oxyphil cells
Lightly stained and few
In horse and large ruminants, rare in other species
Hypocalcemia
Stimulates chief cells to increase parathyroid hormone secretion —> stimulates osteoclasts —> stimulates calcium uptake in kidney —> increases calcium uptake in intestine —> increases blood calcium level
Hypercalcemia
Stimulates parafollicular cells to increase calcitonin secretion —> inhibits osteoclasts —> stimulates calcium deposition in bones —> reduce calcium uptake in kidney —> decreased blood calcium level
Adrenal Gland
Located at the anterior pole of each kidney
Covered by a capsule with a cortex and medulla
Parenchymal cells
Parenchymal cells
Secrete steroid hormones
Abundant SER, mitochondria with tubular cristae and lipid droplets
Cortex of the adrenal gland
Originates from mesoderm
Divided into Zona glomerulosa, fasciculata and resticularis
Zona Granulosa
Secretes aldosterone and regulates electrolyte balance
Stimulated by hypovolemia, hyponatremia and hyperkalemia
What is ZG hormone production stimulated by?
Angiotensin II and ACTH (limited control)
How is ZG arranged?
Arranged in arches for horses, carnivores and pigs
Clusters for ruminants and man
Zona fasciculata
Largest region (80% of vol)
Regulate carb metabolism
Stimulated by ACTH
How is ZF useful?
In treating stress, autoimmune diseases, chronic inflammation and promoting acceptance of heterologous grafts
What are the 3 side effects of long-term glucocorticord therapy?
Lymphopenia, eosinopenia and neutrophilia
Outer fasciculata
Spongiosa (spongiocytes) because cells appear empty due to high lipid (vacuolated)
Inner fasciculata
Secretes glucocorticoids (cortisol and corticosterone)
Zona Reticularis
Deepest layer of the cortex (7%)
Secretes androgens and small amount of glucocorticoids stimulated by ACTH
What is the important role of ZR?
Onset of puberty in humans especially in growth of pubic and axillary hairs
What controls the 3 layers of the adrenal gland?
Renin-angiotenson controls ZG
Hypothalamus- pituitary control ZR and ZF
Medulla of the adrenal gland
Originates from ectodermal neural crest cells (modified postgang. sympathetic neurons)
Medulla location (adrenal gland)
Present as a second organ in lower vertebrates
Randomly mixed with cortical tissue in birds
Centrally located in mammals
What does the medulla secrete? (Adrenal gland)
Epinephrine and some norepinephrine
Catecholamine release under nervous control (pregang sympath)
Cortical capillaries
Fenestrated sinusoids
Drain into medullary vein
Medullary artery
Drain into medullary and suprarenal vein
Clin sigs of adrenal gland
Cushing’s: Higher ACTH and Cortisol
Addison’s: Lower ACTH, aldosterone, and cortisol
Hirsutism or Virilization (F): Higher ACTH and adrogens
Pineal Gland
From root of diencephalon
Composed of pinealocytes and neuroglia cells
What are pinealocytes function?
Secrete melatonin responsible for seasonal cyclicity in horses (long) and sheep and goats (short-day breeder)
Enteroendocrine (argentaffin) cells
In basal area of the crypt
Released into adjacent capillaries
Chromaffin-positive
What do enteroendocrine (argentaffin) cells secrete?
Gastrin, secretin, CCK, somatostatin, vasoactive intestinal peptide
Islets of Langerhans (pancreas)
Alpha (20%)- glucagon
Beta (70%)- insulin
Delta (5%)- somatostatin
JG cells
Secrete renin in repsonse to low BP, hypovolemia, or hyponatremia
Erythropoietin
Secreted in response to decreased oxygen supply to the kidney
Leydig and Sertoli cells
Secrete testosterone
Secrete estrogen and inhibin
Theca interna
Have LH receptors and secrete testosterone
Granulosa cells
Have FSH receptors and convert T into estrogen (released into antrum and blood)
Endometrial cups
Consists of modified chronic epithelial cells that secrete eCG (FSH-like)
What happens when pregnancy doesn’t occur?
Endometrium secretes PGF2-alpha that causes corpus lutem and begins the new estrus cycle
Chorionic epithelium
Secretes HcG (LH-like)
Placenta
Secretes estrogen and progesterone