Hormones Flashcards
(73 cards)
1
Q
List the functions of calcium
A
- structural component of bones and teeth
- maintains normal excitability of nerve and muscle cells
- involved in neurotransmitter and hormone release
- muscle contraction
- activation of many enzymes
- coagulation of blood
- milk production
2
Q
What determines plasma calcium levels?
A
- protein-bound calcium cannot diffuse through membranes and not usable by tissues
- ionized or free calcium is the physiologically active form
- complexed or chelated calcium is bound to phosphate, bicarbonate, sulfate, citrate and lactate
3
Q
What is hypocalcemia?
A
- calcium levels are too low - involuntary muscle contraction
- neuronal hyper-excitability
- low ionized extracellular fluid increased the permeability of neuronal membranes to sodium ions
- causes a progressive depolarization, which increases the possibility of action potentials
4
Q
What is hypercalcemia?
A
- calcium levels are too high
- neurons less excitable
5
Q
What are the function of osteoblasts?
A
Synthesize and secrete collagen and promote deposition of calcium phosphate crystals - secrete factors that activate osteoclasts
6
Q
List the control points for calcium
A
absorption - via intestines
excretion - via kidney/urine
temporary storage - via bones
7
Q
What are the function of osteoclasts?
A
Promote resorption of bone
8
Q
What are the function of osteocytes?
A
Play essential role in exchange of calcium between ECF and bone
9
Q
Describe the role of acute control in calcium regulation
A
- must maintain constant free Ca2+ concentration in the plasma
- mostly by rapid exchange between bone and ECR
10
Q
Describe the role of chronic control in calcium regulation
A
- maintains total level in the body long term
- adjust GIT absorption and urinary excretion
11
Q
What factors determine plasma calcium concentration?
A
- net absorption of Ca2+ from the GIT
- net excretion of Ca2+ in urine
- exchange of Ca2+ with bone
12
Q
Which hormones control plasma calcium concentration?
A
parathyroid hormone
1,25-dihydroxycholecalciferol (calcitriol)
calcitonin
13
Q
What is the role of parathyroid hormone?
A
Monitors the concentration of calcium in the blood perfusing the glands
14
Q
Describe the features of parathyroid hormone
A
- peptide hormone
- stored within chief cells
- half-life of 5 minutes
- secreted continuously at a low rate
- released in response to low blood calcium
- affects bone, gut and kidneys
- main target is kidneys and bone
- increases reabsorption of calcium from the urine
- fast-acting
- increases expression of enzyme 1a-hydroxylase
- increases osteoclast activity (indirectly) causing increase in bone resorption
15
Q
Where can vitamin D2 and D3 be found?
A
D2 can be found in plant sources, whereas D3 can be obtained from the diet, food supplements and synthesised in the skin from sunlight
16
Q
Describe the actions of calcitriol
A
- acts on cells in the GIT
- increases production of calcium transport proteins - increase in calcium uptake from GIT
- only mechanism that can increase calcium stores
- increases rate of bone resorption - increases secretion of osteoclast activating factors
- has a minor effect in decreasing urinary loss of calcium in the kidneys
- works by increasing how much calcium we can absorb from food
17
Q
Describe the actions of calcitonin
A
- secreted by the C-cells (parafollicular cells) of the thyroid gland
- lowers the level of free plasma calcium
- inhibition of osteoclast activity - bone resorption reduced
- increased excretion of calcium and phosphate by kidneys
18
Q
What is hyperparathyroidism?
A
- inappropriate secretion of PTH - results in hypercalcemia
- elevated PTH and raised serum calcium and low level phosphate
- most caused by a single parathyroid adenoma
- presentation: bones, stones, abdominal groans, psychic moans
19
Q
What causes rickets?
A
- vitamin d deficiency
- bone remodelling impaired
- failure of calcification
- skeletal deformities of weight bearing bones in children
20
Q
List possible causes of vitamin d deficiency
A
- poor diet
- malabsorption
- decreased sunlight
- liver or kidney disease
21
Q
What is osteomalacia?
A
vitamin d deficiency leading to softening and weakening of bones
22
Q
Describe the features of a steroid hormone
A
- cholesterol composition
- receptor located in cytosol or nucleus
- bind DNA/modify transcription
- slow speed
- more permanent effects
- e.g. testosterone, oestrogen
23
Q
Describe the features of a peptide hormone
A
- composed of amino acids
- receptor located on cell surface
- 2nd messengers
- rapid response
- temporary effects
- e.g. ADH, growth hormone
24
Q
What is the function of the anterior lobe (pars distalis)?
A
portal blood vessels connect pituitary and hypothalamic capillary beds
25
What is the function of the posterior lobe (pars nervosa)
nerve fibers originate in the hypothalamus and transport hormones to posterior pituitary
26
Describe the action of oxytocin
- released by the posterior pituitary
- hormone produced in the supraoptic nucleus
- controls milk release from lactating breast
- controls urine contraction at onset of labour
- interaction of oxytocin raises the level of intracellular calcium in the myoepithelial cells of the mammary gland
- myoepithelial cells contract forcing milk out --> neuro-endocrine reflex
27
Describe the action of vasopressin (ADH)
- released by the posterior pituitary
- hormone released in the paraventricular nucleus
- acts on kidneys to reabsorb water
- regulates blood osmolarity and urine output
- increased plasma osmolarity (hemorrhage/dehydration) stimulates osmoreceptors in hypothalamus
28
List the six hormones released by the anterior pituitary
- growth hormone
- prolactin
- andernocorticotropic hormone (ACTH)
- thyroid stimulating hormone (TSH)
- follicle stimulating hormone (FSH)
- luteinising hormone (LH)
29
List the cell type for each hormone produced by the anterior pituitary
somatotrophs - growth hormone
lactotrophs - prolactin
corticotrophs - ACTH
gonadotrophs - FSH, LH
thyrotrophs - TSH
30
List the hormones released from the hypothalamus
- corticotrophin releasing hormone (CRH)
- gonadotropin releasing hormone (GRH)
- thyrotropin releasing hormone (TRH)
- growth releasing hormone (GHRH)
- dopamine (DA)
- somatostatin (SS)
31
Describe the action of growth hormone
- synthesised and stored in somatotrophs
- principle targets bone and skeletal muscle
- stimulates growth in children and adolescents
32
Describe the metabolic effects of GH on muscle
- decreases glucose uptake
- stimulates amino acid uptake/protein synthesis
- inhibits protein breakdown
- increased muscle mass
33
Describe the metabolic effects of GH on adipose tissue
- decreases glucose uptake
- increases lipolysis
- decrease in fat deposits
34
Describe the metabolic effects of GH on the liver
- increases gluconeogenesis
- increases protein synthesis
- stimulates IGF production
35
What is somatopause?
- decrease in lean body mass
- decline in body mineral density
- increase in body fat
36
What is gigantism?
refers to abnormally high linear growth due to excessive action of IGF while the epiphyseal growth plates are open
37
What is acromegaly and what are its symptoms?
- increased growth hormone later in life after fusion of epiphyses (growth plates)
- coarse facial features
- enlarged hands and feet
- protruding jaw and separation of teeth
- enlarged tongue and thickened lips
- deep voice
- cardiomegaly
- diabetes
- usually due to pituitary tumour
38
Describe the complications of GH insufficiency in children
- pituitary dwarfism
- slow growth rate below 3rd centile on age/height or bone chart
- normal body proportions
- poor muscle development, excess subcutaneous fat
39
What are the adrenal glands?
- a pair - lie above the kidney
- each gland enclosed in a fibrous capsule surrounded by fat
- each gland equivalent to 2 endocrine glands
- inner = adrenal medulla
- outer = adrenal cortex
- function independently but share a common blood supply and play a role in response to stress
- rich blood supply - blood flows through the cortex and drains into the medulla
40
What is the adrenal medulla and what are its functions?
- enlarged and specialised sympathetic ganglion
- secrete catecholamine hormones
- adrenaline --> epinephrine
- noradrenaline --> norepinephrine
- not under hormonal control
- medulla chiefly composed of chromaffin cells
- specilaised postganglionic neurons
- preganglionic = splanchnic nerve fibres
- neurotransmitter is acetylcholine
41
What is the purpose of adrenaline and noradrenaline?
- catecholamine release occurs as part of a general sympathetic stimulation
- important in fight or flight response and prepared body for acute stress
42
What are the cardiovascular effects of adrenaline?
- increased heart rate or stroke volume
- increase in blood pressure - systolic
- vasodilation of coronary and skeletal muscle blood vessels
- vasoconstriction of blood vessels to non-essential tissues
- bronchodilation
43
What are the metbaolic effects of adrenaline?
- increases the amount of energy for immediate use
- liver converts glycogen to glucose
- metabolic rate increases
- blood flow changes, reducing digestive system activity and urine output
44
List the hormones produced by the adrenal cortex and where they are produced from.
zona glomerulosa - mineralocorticoids (aldosterone) --> salt
zona fasciculata - glucocorticoids (cortisol) --> sugar
zona reticularis - gondocorticoids (androgens) --> sex
45
What is the result of high circulating testosterone levels?
masculinization of fetal external genitalia
46
Describe the action of adrenal androgens
- insignificant amounts of testosterone
- produce dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S) and androstenedione
- testosterone and oestrogen precursors
- converted to testosterone in peripheral tissues
- DHEA and DHEA-S bind less efficiently to the androgen receptors
- controlled by ACTH
47
Describe the effects of testosterone in females from the adrenal glands
- secrete half of total androgenic requirement
- responsible for growth of pubic and axillary hair and sex drive
- kick start puberty
- maintain muscle and bone mass
48
Describe the effects of excessive production of adrenal androgen
- overproduction of ACTH, adrenal tumor, cushing's syndrome
- masculinisation of females
- acne, hirsutism, irregular periods, breast shrinkage
- play a role in PCOS
- anti-androgen blocks androgen receptors - cyproterone acetate and ethinylestradiol
49
What regulates aldosterone secretion?
- response to renin-angiotensin system
- decreased ECF volume and decreased renal blood flow
- response to high plasma protein
50
What are the principal actions of aldosterone?
- controls ECF volume
- conserve body sodium
- stimulates reabsorption of sodium in renal distal convoluted tubules in exchange for potassium
51
Describe the functions of cortisol?
- stress is a stimulator of cortisol production
- mediates the body's response to stress
- metabolic effects
- increased plasma glucose and FFA concentration
- provide energy substrates to body tissues
- increased catabolism - skeletal muscle, amino acids converted to glucose
- increased lipolysis - liberate free fatty acids and triglycerides from adipose tissue
- increased intake - stimulated appetite
- anti-inflammatory
- immunosuppressive
52
What is cushing's syndrome
- overproduction of cortisol
- result of adrenal or pituitary tumour
- redistribution of body fat
- muscle wastage
- thin skin, bruising, abnormal pigmentation
- changes in CHO and protein metabolism
- hyperglycaemia
- hypertension
53
What is Conns disease?
- mineralocorticoid excess
- rare
- overproduction of aldosterone
- retention of sodium, loss of potassium and alkalosis
- hypertension through expansion of plasma volume
54
What is addison's disease?
- rare
- damage to adrenal glands, autoimmune disease or pituitary damage
- deficits in glucocorticoids and mineralocorticoids
- progressive weakness, lassitude and weight loss
- pigmentation of the skin and mucosal membranes
55
Describe the features of the thyroid gland
- a discrete organ, adheres to the trachea
- 2 large asymmetrical flat lobes connected by the isthmus
- regulated by the hypothalamus and pituitary
- fully developed by week 12 of gestation
- responsive to TSH at 22 weeks
- capable of producing T3/T4 at 14 weeks
- thyroid hormones crucial for fetal growth and development
56
Describe the histology of the thyroid gland
- functional unit = follicle
- 1000s in each gland
- each follicle consists of a layer of follicular cells (simple cuboidal epithelial) surrounding a colloid-filled cavity
57
List the thyroid hormones and their hormone class
- Triiodothyronine (T3) and thyroxine (T4)
- T4 and T3 contain four and three atoms of iodine per molecule respectively
- amino acid derived
- tyrosine
- iodinated
58
Describe the action of tyrosines
- provided by thyroglobulin
- secreted by follicular cells into lumen of follicle as colloid
59
How is iodine obtained for thyroid hormone synthesis?
- iodine pumped into follicular cells against concentration gradient
- dietary iodide is oxidized to iodine
60
What is the majority of thyroid hormone released as?
T4
61
Where does the enzymatic conversion of T4 to T3 take place
in peripheral tissues
62
What does thyroid hormone generally increase?
- cellular metabolism
- cardiac output, heart rate and contractility
- cellular oxygen consumption - increases mobilization and utilisation of glucose, fat and protein
- circulation and respiration
- promotes nervous system and skeletal development
63
What does thyroid hormone help maintain?
- energy levels
- weight
- thermoregulation
- heart rate
- GI motility
- mood
64
How does TSH stimulate thyroid function?
- promotes the release of thyroid hormones into blood stream
- increases activity of the iodine pump and iodination of tyrosine to increase production of thyroid hormones
65
What causes hypothyroidism and what are its symptoms
- underactive thyroid
- iodine deficiency --> endemic goitre
- autoimmune disease --> hashimoto's thyroiditis
- dry, cold skin
- sensitivity to cold
- weight gain despite lack of appetite
- impaired memory
- mental dullness
- lethargy
66
What clinical exams can diagnose hypothyroidism and what is the clinical diagnosis?
- reduced metabolic rate
- reduced cardiac output
- low plasma levels of 'free' T3 and T4
67
What is the treatment for hypothyroidism
thyroxine
68
Describe the causes and effects of iodine deficiency (endemic goitre)
- insufficient dietary iodine
- insufficient amounts of T3 and T4
- abnormally high TSH
- abnormal growth of the thyroid due to trophic effects of TSH
69
What is Hashimoto's disease?
- common cause of hypothyroidism
- autoimmune disease
- antibodies against thyroglobulin or thyroid peroxidase
- interferes with thyroid hormone synthesis
- antibodies against TSH receptor
- prevents stimulation of T3 and T4 release
70
Describe the symptoms of congenital hypothyroidism
- cretinism
- intellectual disability
- short disproportionate neck
- thick neck and tongue
- lack of gland or incorrect hormone biosynthesis
71
What are the symptoms of hyperthyroidism and what clinical exams can be done to diagnose?
- loss of weight
- excessive sweating/intolerance to heat
- palpitations and irregular heartbeat
- anxiety and nervousness
- exophthalmos (bulging eyes)
- raised metabolic rate and oxygen consumption
- increased heart rate
- hypertension
72
What is the treatment for hyperthyroidism?
- surgical removal of all or part of the thyroid
- ingestion of radioactive iodine that selectively destroys the most active thyroid cells
- drugs that interfere with the gland's ability to make T3/T4
73
What is Grave's disease?
- autoimmune disease
- abnormal antibodies that mimic TSH
-induces T3/T4 release
- characterised by goitre, exophthalmos and lid retraction
- muscle weakness, heart palpitations, irritability
