The endocrine system part 2 Flashcards
lecture 10 week 5
What is the structure of the hypothalamus
- the hypothalamus sits above the pituitary gland
- controls a number of bodily functions; body temperature, regulates the pituitary gland, appetite and food intake
- contains several nuclei which all have different roles
- paraventricular and supraoptic nuclei (regulates water balance, produces ADH and oxytocin)
- anterior nucleus (thermal regulation- dissipates heat)
- preoptic area (releases gonadotrophic hormones)
- superachiaomatic nucleus (retina input)
- arcuate nucleus (produces hypothalamic releasing factos)
- ventromedial nucleus (feel full after eating)
- mammillary body (input from hippocompal formation)
- lateral nucleus (stimulates appetite)
- posterior nucleus (thermal regulation - conserves heat)
What is the hypothalamic-pituitary axis (HPA)
- anterior pituitary (adenohypophysis): connected to the hypothalamus by a network of capillaries that transfer releasing hormones
- posterior pituitary (neurohypophysis):stores and secretes hormones directly from neurones arising in the hypothalamus
- the pituitary gland lies beneath the hypothalamus
- anterior pituitary gland makes and secretes: ACTH, GH, TSH, LH, FSH, prolactin
in immunostaining of the anterior pituitary gland you can see the structure that secretes hormones (antibodies bind to targets causing stain)
What are the cells within the pituitary gland and the hormones they secrete
somatotrophic hormones
- hormones that have a single peptide chain
- growth hormone (GH) made and secreted by somatotrophs
- prolactin (PRL) made and secreted by lactotrophs
corticotrophin related
- peptide hormones all derived from a single common precursor
- corticotrophin (ACTH), B-lipotrophin, B-endotrophin, alpha- melanocyte-stimulating hormone (alpha-MSH) all made and secreted by corticotrophs
glycoprotein hormones
- composed of a common alpha-peptide chain associated with a variable beta-peptide chain
- thyrotrophin (TSH) from thyrotrophs, FHS and LH from gonadotrophs
What is the feedback control of hormones
releasing hormone —> hormone 1 (pituitary gland) —> endocrine target gland —> hormone 2 (from endocrine organ)
TRH —> TSH —> thyroid gland —> thyroid hormones
CRH —> ACTH —> adrenal cortex —> glucocorticoids
GnRH —> FSH —> testes/ovaries —> inhibin (t) inhibin and estrogen (o)
GnRH —> LH —> testes/ ovaries —> androgens (t) progesteron and estrogen (o)
(LH can be inhibited)
What is the thyroid gland
- the thyroid gland lies on the trachea just below the larynx
- it is butterfly shaped with a rich blood supply
- T3 and T4 are the thyroid hormones
- formed from the attachment of iodine to tyrosine residues on thyroglobulin
- thyroglobulin is produced by follicular cells
- T3 and T4 are only molecules in the body containing iodine
What is the mode of action of thyroid hormones
- thyroid hormones have intracellular receptors which are widely distributed throughout the body
- effects have been deducted by studying hypothyroidism and hyperthyroidism
- thyroid hormones have cellular and whole body effects including regulating temperature and stimulating insulin secretion
What are the actions of the T3 and T4 hormones
- calorigenesis
- fat and carbohydrate metabolism
- protein synthesis and degradation
- enhance cardiac output/increase heart rate
- promotes growth/brain development
What are the disorders of the thyroid gland
hyperthyroidism (overreactive)
- increased O2 consumption, weight loss, protrusion of eye balls
- treatment: thyroidectomy or ingestion of radioactive iodine
hypothyroidism (under activity)
- hair loss, weight gain, swelling, memory loss
- treatment: iodine supplement or hormone replacement therapy
from autoimmune disease, causing antibodies to attack cells in the thyroid gland
How does the parathyroid gland help with the regulation of Ca2+
- parathyroid hormone with calcitonin and vitamin D (1,25- dihydroxycholecalciferol metabolites) regulate plasma Ca2+
decreased plasma calcium —> detected lower Ca2+ levels by calcium receptors on chief cells on parathyroid gland —> increased PTH secretion
then
increased bone resorption (breaking down on bone tissue to release Ca2+) —> INCREASED PLASMA CALCIUM
increased calcium reabsorption and decreased phosphate reabsorption by kidneys —> INCREASED PLASMA CALCIUM
increased synthesis of 1,25-dihydroxycholecalciferol by kidneys —> increased calcium absorption by gut —> INCREASED PLASMA CALCIUM
What are the components of the adrenal gland
- the adrenal gland sits on top of two kidneys
- cortex
- capsule (surrounds glands)
- zona glomerulosa (mineralocorticoid hormone)
- zona fascuiculata (cortisol, DHEA and andostenedione)
- zona reticularis (same as zona fascuiculata)
- medulla (preganglionic sympathetic termine - adrenaline)
- medullary vein
What does the adrenal medulla do
- innervated by preganglionic neurone
- receives cholinergic fibres by the splanchnic nerve
- splanchnic nerve secretes acetylcholine onto chromaffin cells
chromaffin cells a secretory vesicle filled with catecholamines (eg adrenaline), ATP and Ca2+
adrenaline promotes glycogenolysis, glucagon secretion, lipolysis, calorigeneis, increased heart rate and insulin secretion
What is the pathway of the adrenal medulla
sympathetic nervous system (splanchnic nerve) —> release of acetylcholine —> acetylcholine binds to nicotinic acetylcholine receptor —> membrane depolarisation occurs —> Ca2+ influx —> adrenaline granules fuse with plasma membrane —> adrenaline is released into the bloodstream
What is cortisol
- helps the body respond to chronic stress
- increases blood glucose levels which promotes gluconeogenesis and increases lipolysis
cortisol = chronic stress
adrenaline = acute stress
Information about stress
- stress in any response that threatens the bodies ability to maintain homeostasis
- stressors can be physical, chemical, physiological, psychological, emotional and social and trauma
- the hypothalamus then detects a stressor and responds by releasing CRH to stimulate anterior pituitary gland to produce ACTH
- pro-opicmelanocortin (POMC) is a protein precursor that is proteclytically cleaved to produce ACTH, B-lipotrophin, alpha-MSH and B-endotorphin
What is the negative feedback mechanism
- stress/other factors
- hypothalamus
- secretion of CRH (stimulates)
- ATCH secretion by anterior pituitary
- increased plasma ACTH
- increased secretion of cortisol by adrenal cortex
cortisol when chronically elevated can result in various health issues such as high blood sugar, indigestion, weak immune system
