Endocrine system Flashcards
What does the endocrine system consist of?
endocrine glands (e.g. pituitary, thyroid, parathyroid, adrenal, pineal)
organs and tissues containing cells that secrete hormones (hypothalamus, thymus, pancreas, ovaries, testes, kidneys, liver, stomach, small intestine, skin, heart)
What are hormones?
chemical messengers secreted into the blood or ECF by one cell and have an effect on the functioning of other cells in other parts of the body
How do hormones function?
hormones circulate in the blood and come into contact with almost every cell in the body
they only exert their specific effect on cells that have receptors for that hormone (target cells)
What are the five modes of hormone action?
classical endocrine, paracrine, juxtacrine, autocrine, intracrine
What is the paracrine mode of action?
hormones secreted act on other cells in the neighbourhood
What is the juxtacrine mode of action?
hormones from one cell act on receptors on their immediate neighbours
What is the autocrine mode of action?
hormones act on the cells which produce them
What is the intracrine mode of action?
activation of the hormones occurs within the cell where they are created
they bind with nuclear receptors to modify the function of that cell
What are the three types of hormones?
steroid, protein/polypeptide, modified amino acids
What are some examples of lipid-soluble hormones?
steroid, thyroid
What are some examples of water-soluble hormones?
adrenaline, noradrenaline, insulin, human growth hormone
What are steroid hormones?
formed from cholesterol (produced in liver and acquired from diet)
transferred in the blood with carrier proteins in equilibrium with a small amount free in the blood
the free hormone can pass through cell membranes, combine with receptors inside the cell and modulate cell function
this is mainly through regulating transcription of specific genes in DNA and formation of mRNA and/or proteins
onset of steroid hormone function may take several hours due to the time taken in transcription
longer half-life than other hormones
eventually metabolised and excreted by the liver
Which organs produce steroid hormones?
adrenal cortex, ovaries, testes
What are some examples of steroid hormones?
oestradiol, testosterone, progesterone, cortisol
What are protein/polypeptide hormones?
vary in size from three amino acids (e.g. TSH) to larger chains with a sub-structure (e.g. LH)
molecules are formed from the genes coding for them in the endocrine cell, processed into the hormone, and stored within vesicles or secretory granules until needed
secretion is stimulated by environmental triggers (e.g. Ca2+ ions) and can be increased rapidly
short half-life and not transferred with carrier proteins
combine with protein/glycoprotein receptors on the cell membrane but interact in ICF or ECF
initiate a series of interactions leading to changes in the cell (e.g. initiating secretion of a substance from the cell, increasing uptake of a substance into the cell, stimulating mitosis)
What are modified amino acids?
small group of hormones formed by modification of the amino acids tyrosine or tryptophan
Which hormones are produced from tyrosine?
thyroid hormones, catecholamines
What are the thyroid hormones?
thyroxine (T4) and triiodothyronine (T3)
produced and stored in the thyroid gland as part of the large molecule thyroglobulin
thyroglobulin is taken up into the cells of the thyroid gland and the thyroid hormones are released and secreted from the cells
What are catecholamines?
adrenaline and noradrenaline
tyrosine is modified by chemical reactions and secreted from the adrenal medulla into the bloodstream as free hormone
act via receptors on the cell surface and have very short half-lives (<5 mins)
Which hormone is produced from tryptophan?
serotonin - a neurotransmitter which is converted to the hormone melatonin in the pineal gland
What are the three main ways by which endocrine secretion is stimulated or inhibited?
via the hypothalamus and pituitary gland
through the influence of factors in the bloodstream
by nervous stimulation
How does the hypothalamus send information to the anterior and intermediate pituitary gland?
via the hypophyseal portal system
hormones are secreted into the bloodstream and delivered to the gland where hormone secretion is enhanced or inhibited by hypothalamic hormones
How does the hypothalamus send information to the posterior pituitary gland?
along nerve axons in which the hormones are stored until their release is initiated
What are some examples of hormones secreted in direct response to the level of substance that they control?
insulin and glucagon from the pancreas are secreted in response to blood glucose level
PTH and calcitonin are secreted in response to serum Ca2+ levels, which they maintain within normal limits
What is an example of a hormone secreted in response to nervous stimulation?
adrenaline from the adrenal medulla
What are the major endocrine organs?
hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, pancreas, adrenal glands, ovaries, testes
Thyrotrophin RH produced in the hypothalamus regulates the secretion of which hormone in the anterior pituitary gland?
thyroid-stimulating hormone (TSH)
What is the function of TSH?
to stimulate the thyroid gland to secrete thyroid hormones (T4 and T3)
Corticotrophin RH produced in the hypothalamus regulates the secretion of which hormone in the anterior pituitary gland?
adrenocorticotrophic hormone (ACTH)
What are the functions of ACTH?
to stimulate the adrenal cortex to secrete glucocorticoid hormones
response to stress
Gonadotrophin RH produced in the hypothalamus regulates the secretion of which two hormones in the anterior pituitary gland?
luteinising hormone (LH) and follicle-stimulating hormone (FSH)
What are the functions of LH and FSH?
to stimulate male and female gonads
LH causes ovulation (female) and release of testosterone (male)
FSH regulates oogenesis (female) and spermatogenesis (male)
Prolactin RH and prolactin IH produced in the hypothalamus regulate the secretion of which hormone in the anterior pituitary gland?
prolactin
What is the function of prolactin?
to stimulate milk production from breasts
Growth hormone RH and growth hormone IH (somatostatin) produced in the hypothalamus regulate the secretion of which hormone in the anterior pituitary gland?
human growth hormone (hGH)
What is the function of hGH?
to stimulate the growth of cells, bones, muscles
Supraoptic and paraventricular nuclei nerve impulses in the hypothalamus regulate the secretion of which hormone in the posterior pituitary gland?
oxytocin
What are the functions of oxytocin?
mainly neuromodulator in brain
‘bonding hormone’ (orgasm, social recognition, pair bonding, anxiety, etc.)
role in childbirth and breastfeeding
Suprachiasmatic nucleus nerve impulses in the hypothalamus regulate the secretion of which hormone in the posterior pituitary gland?
antidiuretic hormone (ADH) (vasopressin)
What are the functions of ADH?
water retention, vasoconstriction (raised BP)
Which hormone in the intermediate pituitary gland is regulated by a number of different factors?
melanocyte-stimulating hormone (MSH)
What are the functions of MSH?
production and release of melanin from melanocytes in skin and hair
helps activation of T-regulator cells in immune system
What is the structure of the pineal gland?
develops from the roof of the third ventricle of the brain under the posterior end of the corpus callosum
well vascularised
What is the function of the pineal gland?
to secrete melatonin (at higher levels in the dark and lower levels in daylight)
cycle of melatonin secretions is thought to control the circadian rhythm of endocrine secretion and enhances sleep patterns
What is the structure of the thyroid gland?
located at the front of the neck
four parathyroid glands embedded in it
thyroid gland tissue is composed of follicles containing the colloid thyroglobulin (a gelatinous glycoprotein containing suspended particles) surrounded by the follicular cells which make it
What is the function of the thyroid gland?
to secrete T4 and T3
What are the six stages in the formation of thyroid hormones?
iodine is trapped and absorbed into the follicular cells
thyroglobulin is formed in the follicular cells
iodine attaches to the amino acid tyrosine in the thyroglobulin to form monoiodotyrosine (MIT) and diiodotyrosine (DIT)
two DITs combine to form T4, one MIT and one DIT form T3
small amounts of thyroglobulin are taken back into the follicular cells and digested
T3 and T4 exit the thyroid follicle and transported into the bloodstream
What are the parathyroid glands?
four parathyroid glands embedded in the posterior of the four lobes of the thyroid gland secrete PTH
blood calcium levels are raised by PTH and lowered by calcitonin by acting on bone, intestine and kidneys
How does PTH raise blood calcium levels by acting on bone?
enhances calcium release from bones into bloodstream by increasing bone resorption (the normal destruction of bone by osteoclasts)
How does calcitonin lower blood calcium levels by acting on bone?
inhibits osteoclast activity and stimulates osteoblasts
this reduces calcium released into the blood
How does PTH raise blood phosphate levels by acting on bone?
enhances uptake of phosphate from bones
How does PTH raise blood calcium levels by acting on the kidneys?
enhances reabsorption of calcium and magnesium from DCT and ascending limb of loop of Henle
How does calcitonin lower blood calcium levels by acting on the kidneys?
inhibits renal tubular cell reabsorption of calcium
How does PTH lower blood phosphate levels by acting on the kidneys?
reduces reabsorption of phosphate from PCT
How does PTH raise blood phosphate levels by acting on the intestine?
enhances uptake of phosphate from intestine into blood
How does PTH raise blood phosphate levels by acting on the intestine?
enhances uptake of phosphate from intestine into blood
What is the structure of the thymus gland?
positioned in the anterior mediastinum in front of the great vessels
grows throughout childhood reaching its largest at puberty and decreasing in size until about 50 years of age
What is the function of the thymus gland?
to produce polypeptide hormones which contribute to the function of the immune system
this includes differentiation of T-cells
What is the structure of the adrenal glands?
the two adrenal glands are positioned on the top of the kidneys
each one consists of an outer layer (adrenal cortex) and an inner layer (adrenal medulla)
The adrenal cortex consists of which three layers?
zona glomerulosa (outer), zona fasciculata, zona reticularis (inner)
What is the function of the zona glomerulosa?
to secrete aldosterone (main mineralocorticoid hormone) involved in regulation of fluid and electrolyte balance and blood pressure
What is the function of the zona fasciculata?
to secrete glucocorticoids including cortisol involved in the stress response
What is the function of the zona reticularis?
to produce androgens (male sex hormones)
What is the adrenal medulla?
functionally part of the SNS with the secretion of catecholamines (80% adrenaline and 20% noradrenaline) formed from tyrosine
involved in fight-or-flight response to stress
secretion of these hormones is controlled by the SNS from the preganglionic fibres from the thoracic spinal cord
What is the exocrine function of the pancreas?
to secrete enzymes into the duodenum for digestion of carbohydrates, proteins and lipids
What is the endocrine function of the pancreas?
to secrete hormones from the specialised cells of the islets of Langerhans involved in glucose metabolism
What are the endocrine functions of the ovaries and testes?
the overall function of reproduction and sexual differentiation
Which other organs/tissues in the body with important non-endocrine functions secrete hormones?
heart, kidneys, adipose tissue, skin, GI tract
Specialised cardiac cells in the atria of the heart respond to increased blood volume by releasing which hormone?
atrial natriuretic peptide (ANP)
The kidneys secrete which two sets of hormones?
angiotensin II (RAAS) and erythropoietin (EPO)
Adipose tissue produce which hormone?
leptin
What is leptin?
‘satiety hormone’
regulates how much fat is stored in the body by adjusting the sensation of hunger and the amount of energy expended
leptin is released and circulated when fat stores reach a certain level and activates leptin receptors in the hypothalamus, inhibiting hunger
opposite to ghrelin - the ‘hunger hormone’
The skin produces which hormones?
sex hormones from precursors
The skin is the only organ to synthesise which hormones from cholesterol in the presence of sunlight?
cholecalciferol (a form of vitamin D3) and ergocalciferol (vitamin D2)
What happens to vitamin D after it is synthesised?
transported to the liver and metabolised to specific modified vitamin D molecules
some molecules are converted to the biologically active form of vitamin D in the kidney
involved in regulation of calcium and phosphate with PTH and calcitonin
What are some of the risk factors for vitamin D deficiency?
old age - due to reduced synthesis of vitamin D and less exposure to sunlight
dark skin - the larger amounts of melanin in the skin limit UVB light for vitamin D production
season, latitude and time of day - influence the amount of UVB reaching the skin
sunscreen use - reduces vitamin D formation
What are the five major hormones of the GI tract?
gastrin, cholecystokinin, secretin, somatostatin, ghrelin
Which cells produce gastrin?
G-cells in antrum of stomach
What factors stimulate gastrin secretion?
distension of stomach
products of protein digestion in stomach
vagus nerve activity
adrenaline and calcium
What factors inhibit gastrin secretion?
stomach acid
somatostatin
secretin
glucagon
What processes are stimulated by gastrin?
acid and pepsin secretion
gastric motility
insulin secretion after protein meal
growth of GI mucosa
Which cells produce cholecystokinin?
mucosal I-cells of upper small intestine
What factors stimulate cholecystokinin secretion?
products of digestion (particularly in proteins) acting on intestinal wall
fatty acids in duodenum
What factors inhibit cholecystokinin secretion?
digestive products moving to lower portions of GI tract
What processes are caused by cholecystokinin?
contraction of gallbladder to release alkaline bile
secretion of pancreatic juices
inhibits gastric emptying
Which cells produce secretin?
mucosal S-cells in glands of upper small intestine
What factors stimulate secretin secretion?
products of protein digestion and acid in upper small intestine
What factors inhibit secretin secretion?
by neutralisation of acid entering small intestine
What processes are caused by secretin?
secretion of bicarbonate from pancreas
decrease in gastric acid secretion
contraction of pyloric sphincter (?)
Which cells produce somatostatin?
D-cells in GI mucosa (as well as in pancreas)
What factors stimulate somatostatin secretion?
acid in lumen
What processes are inhibited by somatostatin?
secretion of gastrin, secretin and others
pancreatic exocrine secretion
gastric acid secretion and motility
gallbladder contraction
Which cells produce ghrelin?
stomach cells
What processes stimulate ghrelin secretion?
fasting
What processes inhibit ghrelin secretion?
eating food
What are the functions of ghrelin?
to increase food intake (in the opposite way to leptin)
What are the six main groups of hormone functions?
reproduction and sexual differentiation development and growth maintenance of the internal environment regulation of metabolism nutrient supply stress response
What are the five major hormones involved in development and growth?
human growth hormone (hGH) Insulin-Like Growth Factor-1 (IGF-1) and insulin thyroid hormones calcitonin, PTH, vitamin D reproductive hormones
What is the function of hGH?
to regulate growth
What is the function of IGF-1 and insulin?
IGF-1 is a primary mediator of the effects of hGH
essential in growth throughout childhood and continues to have anabolic effects in adulthood
children with inadequate insulin secretion may be short in stature
What are the functions of thyroid hormones?
essential for normal growth (do not initiate growth without hGH)
essential for development of the bones of the nervous system
What are the functions of calcitonin, PTH, and vitamin D?
essential for normal calcium metabolism and normal growth and calcification of bones
What are the functions of reproductive hormones?
essential for normal development of reproductive organs and secondary sex characteristics of the adult body
The causes of restricted growth can be divided into which two main groups?
disproportionate - with some body parts relatively larger or smaller than the rest of the body (e.g. achondroplasia - limbs are abnormally short and the head is larger than average)
proportionate - with a small body but normally proportioned (e.g. pituitary dwarfism - lack of hGH)
What is the primary cause of excessive hGH secretion?
pituitary tumour
What is acromegaly?
swelling of soft tissue with enlargement of hands, feet, nose, lips and ears, and thickening of the skin
enlargement of the face, jaw and skull
when this is caused by a tumour of the pituitary gland (pituitary adenoma), the tumour can be removed by neurosurgery, accessing the skull via the nasal cavity (transsphenoidal hypophysectomy)
What is the normal blood glucose level?
4.0-7.8 mmol/L
What happens if blood glucose levels rise?
insulin released from pancreas
glucose entry to cells and metabolism increased
glucose converted into glycogen in liver for storage
blood glucose levels fall
What happens if blood glucose levels fall?
glucagon released from pancreas
glycogen broken down into glucose
glucose released from liver into blood
blood glucose levels rise
Which other hormones are involved in the regulation of metabolism?
adrenaline increases metabolism
thyroid hormones interact with catecholamines and increase heart response to catecholamines
thyroid hormones regulate the basal metabolic rate (BMR) (the amount of calories needed by the body at rest)
What are the symptoms of hypothyroidism?
reduced metabolic rate, person feels cold, slower in physical and mental functioning, weight gain, coarse hair, husky voice
babies do not grow to expected milestones and can become intellectually disabled (if not treated appropriately before birth)
What are the symptoms of hyperthyroidism?
increased metabolic rate, intolerance of heat, weight loss, nervousness, sweating, raised heart rate
Graves’ disease is the most common type of hyperthyroidism and is an autoimmune disorder
the person can develop exophthalmos (protruding eyeballs)
What are the two main hormones involved in the regulation of appetite?
leptin and ghrelin
What are some examples of stressors which disrupt homeostasis?
environmental stressors events in daily living life events stressors at work chemical stressors social and psychological events
What are the two main stress responses?
acute stress response and long-term stress response
What is the acute stress (fight or flight) response?
regulated by the SNS which stimulates the adrenal medulla to secrete adrenaline and noradrenaline (catecholamines)
these hormones increase heart rate, respiratory rate and depth, blood supply to muscles and release of glucose from glycogen in the liver and muscles
plasma half-life of adrenaline is 2-3 mins so the physiological changes only last a short time
What is the long-term stress response?
corticosteroids stimulate gluconeogenesis (mainly from protein) for neural cells which require glucose
fat metabolism provides energy for most other body tissues
mineralocorticoid actions of glucocorticoids and aldosterone cause sodium and water retention which increases blood volume and blood pressure
glucocorticoids inhibit the function of the immune system and act as anti-inflammatory agents
What are the symptoms of Cushing’s syndrome (hypersecretion)?
fat storage areas shift which leads to a puffy face and neck, hyperglycaemia
What are the symptoms of Addison’s disease (hyposecretion)?
bronzing of the skin, reduced electrolyte levels, hypoglycaemia
