Endocrine System Part II Flashcards
the hypothalamus is connected to the pituitary gland (hypophysis) via the
infundibulum
pituitary gland
- secretes at least 8 major hormones
- has 2 major lobes
posterior pituitary lobe
composed of neural tissue that secretes neurohormones
- neurohypophysis: posterior lobe of the pituitary + infundibulum
anterior pituitary
composed of glandular tissue; called the adenohypophysis
the anterior lobe is vascularly connected to the hypothalamus via the
hypophyseal portal system
hypophyseal portal system
- primary capillary plexus
- hypophyseal portal veins
- secondary capillary plexus
the hypothalamus regulates hormone secretion by
secreting, releasing, and inhibiting hormones to the anterior pituitary gland
the posterior pituitary gland is made of
neural tissue - derived from a downgrowth of the brain
hypothalamic hypophyseal tract
- maintains neural connection to the hypothalamus
- tract arises from neurons in the paraventricular and supraoptic nuclei and runs through infundibulum
- secretes 2 neurohormones (oxytocin + ADH)
paraventricular neurons in the posterior pituitary
produce oxytocin
supraoptic neurons in the posterior pituitary
produce ADH
hormones are stored in _________ and released into the blood when _________
- axon terminals
- neurons fire
Oxytocin
- released during childbirth; stimulant of uterine contractions
- hormonal trigger for milk ejection
- ^ both are positive feedback loops
- acts as neurotransmitter in brain
- uses pip2 calcium 2nd messenger system
Anti diuretic hormone (ADH)
- hypothalamus contains osmoreceptors that monitor solute concentrations
- when concentration is high, posterior pituitary secretes ADH
- target is kidney tubules - triggered to reabsorb more water and inhibit urine formation
- release of ADH is also triggered by pain, low blood pressure, and drugs; inhibited by alcohol and diuretics
anterior pituitary hormones
- all 6 hormones of the AP are peptide hormones
- all but growth hormone (GH) activate target cells via cAMP second-messenger system
- all but 2 are tropic hormones (tropins) - they regulate the secretion of other hormones
6 hormones of the anterior pituitary
- growth hormone - GH
- thyroid-stimulating hormone - TSH
- adrenocorticotropic hormone - ACTH
- follicle-stimulating hormone - FSH
- luteinizing hormone - LH
- prolactin - PRL
growth hormone
- also called somatotropin
- produced by somatotrophic cells
- has direct actions on metabolism and indirect growth-promoting actions
direction actions on metabolism
- decreases rate of cellular glucose uptake and metabolism (glucose sparing, anti insulin effects)
- triggers the liver to break glycogen down into glucose
- increases blood levels of fatty acids to use as fuel; encourages cellular protein synthesis
indirect actions on growth
- triggers liver, skeletal muscle, and bone to produce insulin-like growth factors (IGFs)
- IGFs stimulate the cellular uptake of nutrients used to synthesize DNA and the proteins needed for cell division and formation of collagen and deposition of bone matrix
- GH stimulates most cells to enlarge and divide, but its major targets are bone and skeletal muscle
regulation of secretion of gh
release or inhibition of gh is chiefly regulated by 3 hypothalamic hormones with antagonistic effects - ghrh and ghih
growth hormone releasing hormone - GRHR
stimulates GH release
- secreted on daily cycle - highest amounts are secreted during sleep; total amount secreted daily peaks during adolescence
- ghrh is triggered by low blood gh or glucose levels
growth hormone inhibiting hormone - ghih
inhibits gh release (also called somatostatin)
- triggered by increased levels of gh and igf
- produced in various locations within the gut
* release of GH is also stimulated by ghrelin - the hunger hormone
thyroid stimulating hormone - TSH
- tropic hormone; also called thyrotropin - produced by thyrotropic cells
- stimulates normal development and secretory activity of thyroid gland
- release triggered by secretion of of thyrotropin releasing hormone (TRH) from the hypothalamus
- inhibited by rising blood levels of thyroid hormones acting on pituitary and hypothalamus; also inhibited by GHIH
adrenocorticotropic hormone (ACTH)
- also called corticotropin; secreted by corticotropic cells
- stimulates the adrenal cortex to release corticosteroids
regulation of acth release
- triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm - highest levels in morning
- rising levels of corticosteroids feed back and block secretion of crh
- internal and external factors that alter the release of crh include fever, hypoglycemia and stressors
- cushing syndrome
gonadotropins (FSH and LH)
- secreted by gonadotropic cells of anterior pituitary
- fsh and lh are both absent from blood in prepubescent adolescents
regulation of gonadotropin release
- during and after puberty, fsh and lh are triggered by gonadotropin releasing hormone (GnRH) from the hypothalamus
- suppressed via feedback of the gonadal hormones
Follicle stimulating hormone - fsh
stimulates the production of gametes (egg/sperm)
Luteinizing hormone (LH)
promotes production of gonadal hormones
- in females, lh helps to mature egg containing follicles, triggers ovulation, and creates + releases estrogen + progesterone
- in males lh stimulates production of testosterone
prolactin - PRL
- Secreted by prolactin cells in the anterior pituitary; structurally like GH
- Simulates milk production in females; its role in males is not fully understood
- Regulation is primarily controlled by prolactin-inhibiting hormone (PIH) AKA dopamine
- PIH prevents release of PRL until it is needed; decreased levels of PIH leads to lactation
- In females, PRL levels rise and fall in rhythm with estrogen - reason for breast swelling and tenderness during menstruation
- Blood levels of PRL dramatically rise at the end of pregnancy
- Nursing stimulates the release of prolactin-releasing factors and promotes continued milk production
thyroid gland
butterfly shaped gland in anterior neck, located on trachea just inferior to the larynx
- largest pure endocrine gland in body
parts of thyroid gland
- Isthmus: median mass connecting 2 lateral lobes
- Follicles: hollow spheres of epithelial follicular cells – produce glycoprotein thyroglobulin
- Colloid: fluid in the follicle lumen, contain thyroglobulin + iodine – a precursor to thyroid hormone
- Parafollicular Cells: produce the hormone calcitonin
thyroid hormone - TH
- body’s metabolic hormone, stored extracellularly in follicle lumen
- affects virtually every cell in the body - enters target cells, binds to intracellular receptors within nucleus, triggers transcription
- effects of thyroid hormone include increasing basal metabolic rate and hear production - calorigenic effect
thyroid hormone is found in two forms:
- Thyroxine (T4): major form; consists of 2 tyrosine molecules with 4 bound iodine atoms
- Triiodothyronine (T3): form of TH that has 2 tyrosine molecules with 3 bound iodine atoms
- T3 must be converted to T4 at the tissue level
- both t3 and t4 are iodine containing amine hormones
thyroid hormone pt 2
- regulates tissue growth and development; essential for normal development of skeletal and nervous systems and reproductive capabilities
- maintains blood pressure - increases adrenergic receptors in blood vessels
regulation of thyroid hormone
release is triggered by thyroid stimulating hormone (TSH)
- tsh is regulated by negative feedback
- falling amounts of th stimulate release of tsh
- rising amounts of th inhibit tsh
- tsh can also be inhibited by ghih, dopamine, and increased levels of cortisol and/or iodine
calcitonin
- produced by the parafollicular cells in response to high ca2+ levls
- antagonist to parathyroid hormone (pth)
- does not have a known physiological role at normal levels
elevated calcitonin levels
- inhibits osteoclast activity
- prevents release of ca2+ from bone matrix
- stimulates the uptake of ca2+ by bone matrix
parathyroid gland
- 4 to 8 tiny yellow-brown glands embedded in posterior aspect of thyroid
- contains oxyphil and parathyroid cells
- parathyroid cells secrete parathyroid hormone
parathyroid hormone - pth
- most important hormone in ca2+ homeostasis - secreted in response to low blood levels of ca2+ and inhibited in response to rising blood levels of ca2+
- target organs are skeleton, kidneys, and intestines
functions of pth
- stimulate osteoclasts to digest bone matrix and release ca2+ into blood
- enhance reabsorption of ca2+ and secretion of phosphate (PO34-) by the kidneys
- promote activation of vitamin D by the kidneys - leads to increased absorption of ca2+ by intestinal mucosa
adrenal gland
- paired, pyramid shaped organs sitting atop kidneys
- sometimes called suprarenal glands
- structurally and functionally, they are 2 glands in 1
adrenal cortex
3 layers of glandular tissue - synthesize and secrete several different hormones
- produce over 24 different hormones known as corticosteroids
adrenal medulla
nervous tissue - part of the sympathetic nervous system
steroid hormones
not stored in cells - their rate of release is dependent on their rate of synthesis
3 layers of cortical cells that produce different types of corticosteroids:
- zona glomerulosa - mineralocorticoids
- zona fasciculata - glucocorticoids
- zona reticularis - gonadocorticoids
mineralocorticoids
regulate electrolyte concentrations in the ECF - primarily Na+ and K+
aldosterone
most potent mineralocorticoids
- stimulates reabsorption of Na+ by the kidneys; results in increased blood volume and pressure
- stimulates elimination of K+ by the kidneys
factors that regulate the secretion of aldosterone
- renin-angiotensin-aldosterone mechanism
- plasma concentration of K+
- adrenocorticotropic hormone (ACTH)
- atrial natriuretic peptide (ANP)
