hormones Flashcards
What are organs that secrete a hormone into the blood called?
endocrine glands
What are the three types of hormone?
steroid hormones, peptide hormones, amino acid derived hormones
What is the mechanism of action of steroid hormones?
bind DNA/modify transcription
What is the mechanism of action of peptide hormones?
second messengers
What is the mechanism of action of peptide hormones?
second messengers
Where is the pituitary gland?
at the base of the brain, below the hypothalamus with the optic chiasm between
What are the two parts of the pituitary gland?
anterior lobe (pars distalis) and posterior lobe (pars nervosa)
What hormones does the posterior pituitary release?
oxytocin and vasopressin
What does oxytocin do?
controls milk release from lactating breast and controls uterine contractions at onset of labour
What does vasopressin do?
acts on kidney to reabsorb water
What does the interaction of oxytocin with its receptors do?
raises the level of intracellular calcium in the myoepithelial cells of the mammary gland
How many hormones does the anterior pituitary secrete?
six
Which hormones does the anterior pituitary secrete?
growth hormone, prolactin, ACTH, TSH, FSH, LH
What vessels are in the anterior pituitary?
portal vessels
What are the five different cell types for the hormones?
somatotrophs (growth hormone), lactotrophs (prolactin), corticotrops (ACTH), gonadotrophs (FSH, LH), thyrotrophs (TSH)
What controls the secretory activity of the anterior pituitary?
the hypothalamus
Where is growth hormone synthesised and stored?
somatotrophs
What are the principle targets of growth hormone?
targets bone and skeletal muscle
What does growth hormone do in children and adults?
stimulates growth in children and adolescents but continues to exert important effects throughout adult life
What are direct effects of growth hormone on muscle?
decreases glucose uptake, stimulates amino acid uptake/protein synthesis, inhibits protein breakdown = increased muscle mass
What are the direct effects of growth hormone on adipose tissue?
decreases glucose uptake, increases lipolysis = decrease in fat deposits
What are the direct effects of growth hormone on liver?
increases gluconeogenesis, increases protein synthesis = stimulates IGF (insulin-like growth factor) production
What does insulin-like growth factor do?
skeletal growth - cartilage formation, bone deposition. soft tissue growth - protein synthesis and cell proliferation
What is somatopause?
decrease in lean body mass, decline in bone mineral density, increase in body fat
What is gigantism?
abnormally high linear growth due to excess action of IGF while the epiphyseal growth plates are open (children). they have normal body proportions due to soft tissue also being affected
What is acromegaly?
increased growth hormone later in life after fusion of growth plates
What are features of someone with acromegaly?
course facial features, enlarged hands and feet, protruding jaw, enlarged tongue, deep voice, diabetes
What is pituitary dwarfism?
GH insufficiency in children, growth rate below third centile on age/height, normal body proportions, poor muscle development
What does GH insufficiency in adults?
no major symptoms
Where is the thyroid gland?
discrete organ, adheres to the trachea - 2 large flat lobes connected by isthmus
When is the thyroid gland fully developed?
by week 12 of gestation - responsive to TSH at 22 weeks - capable of producing T3/T4 by 14 weeks
What is the functional unit of the thyroid gland?
follicles (200-300 um in diameter) - 1000’s in each gland
What are the thyroid hormones?
triiodothyronine (T3) and thyroxine (T4)
How much of each is secreted by day?
80-100 ug of T4, 5 ug of T3
Which thyroid hormone has the greatest biological activity?
T3
In what hormone class is thyroid hormones?
amino acid derived, tyrosine & iodinated
In plasma, what are T3 and T4 bound to?
thyroxine-binding globulin, albumin
What does synthesis of thyroid hormones require?
tyrosines - provided by thyroglobin and secreted by follicle cells into lumen as colloid. iodine - essential requirement, pumped into follicular cells against concentration gradient
How is monoiodotyrosine (MIT) and diiodotyrosine (DIT) formed?
when iodine is attached to tyrosine in the colloid it forms MIT and DIT
How is T3 and T3 formed?
by MITs and DITs linking together
What is the advantage of the thyroid system?
it is capable of storing many weeks worth of thyroid hormone - if no iodine is available for this period, thyroid hormone secretion will be maintained
What are the effects of thyroid hormones?
they bind to intracellular receptors. form a complex with thyroid response elements (TRE) that bind to DNA and influence gene expression. enzymatic conversion of T4 into T3 in peripheral tissue
What do the transcribed proteins do? (after thyroid hormones increase gene expression & transcription)
increased: cellular metabolism, oxygen consumption, cellular glucose, circulation and respiration
What are cardiovascular thyroid hormone effects?
increased cardiac output, increased heart rate and contractility
What are the thyroid hormone effects of growth and maturation?
bone growth, synergy with growth hormone, CNS development and function
What does TSH stimulate?
promotes the release of thyroid hormones into the blood, increasing the activity of the iodide pump and iodination of tyrosine
What is hypothyroid?
underactive thyroid. in general metabolic rate increases weigh gain
What is hyperthyroid?
overactive thyroid, in general metabolic rate increases weight loss
What are symptoms of hypothyroidism?
dry, cold skin, weight gain but loss of appetite, impaired memory, mental dullness, lethargy
What are the levels of T3 and T4 with hypothyroidism?
low plasma levels of ‘free’ T3 and T4
How do you treat hypothyroidism?
thyroxine, dose determined by TSH monitoring
What does iodine deficiency cause?
endemic goitre
What causes endemic goitre?
insufficient dietary iodine, insufficient T3 & T4, abnormally high TSH