the endocrine system - primary endocrine glands Flashcards
thyroid gland anatomy
-below larynx
-made up single layer of epithelial cells called thyroid follicular epithelial cells
hormones of the thyroid gland
-T3/T4
-calcitonin
thyroid follicular epithelial cells
-have receptors for TSH from anterior pituitary gland
-TSH stimulates synthesis of thyroid hormones (T3 & T4)
thyroxine (T4) & triiodothyronine (T3)
-T4: about 90% produced
-T3: about 10% produced
-produced by thyroid follicles
-regulates basal metabolic rate (BMR) of all cells
-influences physical/mental development + growth
HYPOsecretion of T3/T4
LOW basal metabolic rate (BMR)
-put on weight easier
-feel cold easier
-low cardiac output
-sluggish tendon reflexes
-muscle weakness
HYPERsecretion of T3/T4
HIGH basal metabolic rate (BMR)
-weight loss
-feel agitated frequently
-high cardiac output (hear beats stronger/faster)
calcitonin
-produced by parafollicular cells (outside thyroid follicles)
-influences bone + calcium metabolism
-regulates blood calcium levels
parathyroid gland
-two pairs of parathyroid glands located on dorsal (back) side of the thyroid gland
-secretes parathyroid hormone (PTH)
parathyroid hormone (PTH)
plays role in calcium balance alongside calcitonin in a counter-regulatory manner
blood calcium level too high
-thyroid gland releases more calcitonin in response
-calcitonin acts to stimulate fall in blood calcium levels (is taken up by bone)
blood calcium level too low
-activates parathyroid glands to release PTH
-encourage mobilisation of calcium from bone to restore blood levels to homeostatic setpoint
pancreas anatomy
-an exocrine and endocrine gland
-much of its tissue made up of acinar cells (exocrine)
-small clusters of cells called islets of Langerhans (endocrine)
exocrine gland
-specialises in producing fluid into a ductile system
-that fluid goes off to drain in its respective structure
acinar cells
-manufacture sodium bicarbonate (to create alkaline conditions)
-secrete digestive enzymes that are deposited in the duodenum
islets of Langerhans
-manufacture and secrete two key hormones
-beta cells: insulin
-alpha cells: glucagon
glucagon
-facilitates the breakdown of glycogen to glucose
-puts glucose back into circulation to raise blood sugar levels
insulin
-essential for maintenance of normal blood sugar levels
-stimulates glucose uptake by many tissues
-inadequate levels result in diabetes mellitus
adrenal glands anatomy
-situated on top of each kidney
-inside is called medulla
-outside layer is called the cortex
adrenal cortex
produces two key hormones:
-cortisol
-aldosterone
cortisol (a glucocorticoid)
-regulates carbohydrate, protein + fat metabolism
-works in conjunction with insulin/glucagon
-has an anti-inflammatory effect (dampens immune system)
-helps body cope during times of stress (mobilises glucose)
aldosterone (a mineralocorticoid)
-promotes sodium and chloride retention
-promotes potassium excretion
regulation of cortisol secretion from adrenal cortex
-hypothalamic-pituitary-adrenal (HPA) axis
-corticotropin-releasing hormone (CRH)
-CRH neurons activated (by stress) secrete CRH
-CRH reaches corticotrope cells in ant. pituitary gland
-corticotropes produce adrenocorticotropic hormone (ACTH)
-ACTH enters peripheral circulation to act on adrenal cortex to stimulate cortisol production (and aldosterone but lesser extent)
regulation of aldosterone
local mechanism in kidney called renin-angiotensin-aldosterone system (RAAS)
adrenal medulla
produces:
-adrenaline (epinephrine)
adrenaline
-raises systolic blood pressure, heart rate + cardiac output
-speeds up release of glucose from liver
-dilates bronchial tubes + relaxes airways
-together with noradrenaline promotes ‘fight/flight’ response
regulation of adrenal medulla via autonomic nervous system
-hypothalamus stimulated by stress, physical activity, low blood glucose
-action potentials travel down sympathetic nerves activating adrenal medulla
-promote release of adrenaline (+noradrenaline from sympathetic nerves)
-adrenaline+noradrenaline reach target tissues
