8: Endocrine System II Flashcards
vascular arrangement
vascular arrangement of the hypophyseal portal system provide efficient means of ensuring that all hypothalamic hormones will reach target cells in the anterior pituitary before being diluted in general circulation
posterior pituitary hormones
ADH is regulated by osmoreceptors of which determine the concentration of the blood
ADH effects the kidneys, which increases the reabsorption of water, elevates blood pressure and volume
oxytocin occurs through sensory stimulation
in males it affects smooth muscle in ductus deferens and prostate glands
in females it causes labour contractions and stimulates lactation
pineal gland
small gland in brain - has lots of neural tissue and cells called pinealocytes
contains neurons - branches from the visual pathways so signalling from the amount of light
pinealocytes secrete melatonin - low production during day and more at night
functions of melatonin - influences circadian rhythms and is an antioxidant
thyroid gland
in neck, anterior to thyroid cartilage of larynx
two lobes connected by narrow isthmus
stores and secretes thyroid hormones thyroxine (T4) and triiodothyronine (T3)
thyroid hormones increase sodium potassium ATPase production
important for producing energy, controlling out metabolic rate and controlling heat
effects of thyroid hormones
increase oxygen and energy consumption
increase heart rate
increase sensitivity to sympathetic stimulation
stimulates RBC formation
affects activity of other endocrine tissues
increase bone turnover
thyroid follicles
thyroid follicles = hollow spheres lined by cuboidal epithelium (which produce thyroid hormone) and surrounded by capillaries
contain colloid which is protein rich fluid
follicle cells synthesise tyrosine rich thyroglobulin which is stored in colloid
iodine is then incorporated to from thyroxine and triiodothyronine
thyroid gland and iodine deficiency
iodine deficiency called Derbyshire neck or Goitre is a swelling of the thyroid gland
rate in the country because iodine is now added to drinking water
swelling caused by build up of thyroglobulin in follicles
C cells
sit just outside on the rim of follicles
C cells produce calcitonin - which controls the level of calcium in body
reduced serum calcium by deposition in bone and increased excretion by kidneys
when calcium levels too low, parathyroid glands secrete parathyroid hormone which causes reabsorption of calcium by kidneys, calcium is released from bone and increased calcitriol production causes calcium absorption by digestive system to elevate calcium levels again
parathyroid glands
small glands on posterior thyroid
parathyroid cells produce parathyroid hormone (PTH)
PTH is released to increase serum calcium when levels decline
connective tissue capsule around outside
blood vessels in for good blood supply to distribute hormone
adrenal glands
two glands - one of top of each kidney
outer capsule, outer layer called cortex, and inner layer called medulla
cortex = produces a range of steroid hormones
layer called zona reticularis produces androgen (type of steroid) that has anabolic effect
layer called zona fasciculata produces glucocorticoids that promote glucose synthesis, fat and protein catabolism, anti-inflammatory effects
zona glomerulosa produces mineralocorticoids which affect electrolyte composition
adrenal medulla = produces catecholamines (adrenal and nonadrenal), fight or flight hormones that increase blood glucose and heart rate, neural innervation from hypothalamus
the pancreas
pancreatic islet contain
- alpha cells that produce glucagon to increase blood glucose
- beta cells produce insulin which lowers blood glucose
insulin effects
increased rate of glucose transport into target cells
increased rate of glucose utilisation and ATP generation
increased conversion of glucose to glycogen
increased amino acid absorption and protein synthesis
increased triglyceride synthesis in adipose tissue
glucagon effects
increased breakdown of glycogen to glucose (in liver and skeletal muscle)
increased breakdown of fat to fatty acids (in adipose tissue)
increased synthesis and release of glucose (by liver)
diabetes mellitus
abnormally high glucose (hyperglycaemia) could result in: kidney damage, retinal damage, peripheral nerve damage, increased CV disease risk
type 1 (insulin dependent) diabetes: 5-10% of cases, often diagnosed in childhood, pancreatic insulin production is inadequate, insulin injection required
type 2 (non-insulin dependent) diabetes: most common, most often diagnosed in middle/older ages, reduced tissue response to insulin, often managed with diet and exercise
pattern of hormonal interaction
antagonistic effects e.g. PTH and calcitonin work in balance to maintain calcium homeostasis
synergist effects e.g. GH and glucocorticoids
permissive effects meaning one hormone is necessary for another to produce effect
integrative effects meaning hormones produce different but not complementary results
hormones and growth
growth hormone: protein synthesis and cellular growth
thyroid hormones: nervous system development
insulin: supply of energy and nutrients
parathyroid hormone and calcitriol: calcium absorption/deposition in bones
reproductive hormones: cell growth & differentiation / secondary sexual characteristics
organs with secondary endocrine functions
heart - secretes natriuretic peptide to reduce blood pressure and volume
thymus - secretes thymosin to promote lymphocyte development
adipose tissue - secretes leptin to suppress appetite
digestive tract - hormones involved in the coordination of system functions, glucose metabolism and appetite
kidneys - secrete erythropoietin for RBC production, calcitriol promotes calcium absorption and renin is involved in control of BP and volume
testes - androgens and inhibin
ovaries - oestrogen, progestins, and inhibin
general adaptive system: alarm phase
fight or flight
mainly coordinated by adrenal medulla that produces epinephrine and norepinephrine
also general sympathetic activation
causes:
- mobilisation of glucose reserves
- changes in circulation
- increases in HR and respiratory rates
- increased energy use by all cells
general adaptative system: resistance phase
long term metabolic adjustments
sympathetic stimulation of kidneys, adrenal cortex, pancreas
causes:
- mobilisation of remaining energy reserves (lipids released by adipose tissue, amino acids released by skeletal tissue)
- conservation of glucose (peripheral tissue breaks down lipids to obtain energy)
- elevation of blood glucose concentrations (liver synthesises glucose from other carbs, amino acids and lipids)
- conservation of salts and water, loss of K+ and H+
general adaptive system: exhaustion stage
collapse of vital organs
causes may include:
- exhaustion of lipid reserves
- inability to produce glucocorticoids
- failure of electrolyte balance
- cumulative structural or functional damage to vital organs
