Endocrine Physiology Flashcards
List the 3 types of hormones
- Steroids
- Peptides
- Altered amino acids
List the 3 types of hormone receptor
- Cell surface
- Cytoplasmic
- Nuclear (thyroid hormone)
Where is the hypothalamus situated
In the forebrain in the floor of the third ventricle between thalamus above and pituitary below
What links the hypothalamus to the pituitary gland
Hypophyseal stalk
Embryological origin of the anterior pituitary
Outpouching of tissue from the oral cavity (ectoderm)
Embryological origin of the posterior pituitary
Derived from a downgrowth of neural tissue, continuous with the hypothalamus
How is anterior pituitary hormone secretion regulated
By hormones secreted along the hypophyseal tract from the hypothalamus
List the hormones secreted from the anterior pituitary gland (6)
- ACTH
- TSH
- FSH
- LH
- Prolactin
- Growth hormone
List the hormones secreted from the posterior pituitary gland (2)
- Oxytocin
2. ADH
What stimulates secretion of ACTH
Corticotropin-releasing hormone from the hypothalamus
Function of ACTH
- Stimulates release of glucocorticoids from the adrenal cortex
- Stimulates release of beta-endorphin and precursors of melanin-releasing hormone
What stimulates secretion of FSH and LH
Gonadotrophin-releasing hormone (GnRH)
What stimulates secretion of prolactin
Factors that decrease dopamine lead to the release of prolactin
What inhibits the release of growth hormone
- Growth hormone-inhibiting hormone
- Somatostatin
Which cells produce oxytocin
Cells of the paraventricular nucleus of the hypothalamus
What stimulates the secretion of oxytocin
Sensory stimuli activating mechanoreceptors in the breast during suckling
Function of oxytocin
- Milk ejection
- Uterine contraction
- Sexual arousal
Which cells produce ADH
Cells of the supraoptic nucleus of the hypothalamus
Why does amenorrhoea occur in hyperprolactinaemia
Inhibitory effect of high prolactin on GnRH production
Disorders caused by raised growth hormone
- Children = gigantism
- Adults = acromegaly
Diagnostic criteria for SIADH
- Hyponatraemia
- Reduced plasma osmolality
- Raised urine osmolality
- Urinary Na >30
List the causes of SIADH
- Tumours - lung, pancreas, lymphomas
- TB
- Lung abscess
- CNS lesions e.g. meningitis
- Metabolic e.g. alcohol withdrawal
- Drugs e.g. Carbamazepine
What is Kallman Syndrome
LH and FSH deficiency
What is Sheehan’s Syndrome
Pituitary infarction following post-partum haemorrhage
Microscopic structure of the thyroid gland
Outer layer of cuboidal epithelium filled with colloid
Which cells secrete Calcitonin
Parafollicular C cells
What are Thionamides
- Antithyroid drugs
- e.g. Carbimazole, propythiouracil
- Competitively inhibit the peroxidase-catalysed reaction (iodide to iodine)
What are anion inhibitors
- Antithyroid drugs
- e.g. Perchlorate
- Competitively inhibit the uptake of iodine
Significant side effect associated with Perchlorate
Aplastic anaemia
Outline the process by which thyroid hormones are secreted
- Hypothalamus releases thyrotropin-releasing hormone
- Transported to endocrine cells of anterior pituitary which secrete TSH
- TSH stimulates thyroid hormone production and secretion
- T3 and T4 have a negative feedback effect on TRH
What is the majority of thyroid hormone in the circulation bound to
Thyroglobulin
In which phase of thyroiditis would a patient be found to be hyperthyroid and why
- Acute phase
- Early phase of cell injury causes release of stored thyroid hormone
What drug is classically associated with hyperthyroidism
Amiodarone
What is Plummer’s disease
Hyperthyroidism secondary to solitary toxic adenoma/nodule
Which ovarian tumour is associated with secondary hyperthyroidism
Struma ovarii
Which drug is classically associated with hypothyroidism
Lithium
Biochemical presentation of sick euthyroid syndrome
- Low T4/T3
- Low TSH
How does Calcium affect the permeability of the Na channel in nerve and muscle
- Low Calcium = Increased permeability to Na causing increased depolarisation
- High Calcium = Reduced permeability, decreasing nerve and muscle activity
Why is Calcium essential for clotting
Co-factor to several clotting factors
What stimulates PTH release
Fall in extracellular fluid Calcium level
List the ways in which PTH causes calcium to rise
- Stimulates release from bone
- Increases uptake from renal tubules
- Stimulates urinary phosphate excretion
- Increases rate of vitamin D activation in the kidney
How is Calcium released from bone in response to TSH
- Initially = rapid Calcium release from osteocytes mobilising the exchangeable bone calcium
- Long-term = osteoclasts release Calcium from the bone pool
What stimulates the conversion of Vitamin D into its active form
- PTH
2. Low phosphate levels
How does Vitamin D increase plasma Calcium levels
- Increases Calcium and phosphate absorption from the gut
- Increases renal tubular absorption of calcium and phosphate
- Stimulates osteoclastic bone resorption
- Promotes mineralisation of osteoid
How does Calcitonin reduce serum calcium levels
- Reduces calcium and phosphate reabsorption from the renal tubules
- Stimulates osteoblasts to mineralise bone
What regulates phosphate levels
- PTH reduces phosphate levels
- Vitamin D increases phosphate levels
Most common cause of primary hyperparathyroidism
Single adenoma
Describe secondary hyperparathyroidism
- Conditions such as chronic renal failure cause prolonged hypocalcaemia
- Causes parathyroid gland hypertrophy
- Results in low/normal Calcium and raised PTH
Difference between PTH and PTH-rp
- PTH = 84 amino acid polypeptide
- PTH-rp = 141 amino acid polypeptide
What is the result of vitamin D deficiency
- Adults = osteomalacia
- Children = rickets
(Inadequate mineralisation of bone)
List the causes of Vitamin D deficiency
- Dietary e.g. vegans
- Lack of sunlight
- Malabsorption e.g. post-gastric surgery, Coeliacs
- Renal disease
- Hepatic failure
- Vitamin-D resistant rickets
Describe the symptoms of hypocalcaemia
Symptoms related to neuromuscular irritability:
- Paraesthesia
- Numbness
- Cramps
- Tetany
- Chovtek’s sign
- Trousseau’s sign
ECG features of hypocalcaemia
Prolonged QT interval
ECG features of hypercalcaemia
Reduced QT interval
List the common causes of hypercalcaemia
- Excess PTH
- Excess Vitamin D
- Sarcoidosis
- Milk-Alkali syndrome
- Drugs e.g. Thiazides
- Malignancy
Symptoms of hypophosphataemia
- Confusion
- Convulsions
- Muscle weakness
- Reduced 2,3-DPH causes left shift of oxygen dissociation curve
List the causes of hypophosphataemia
- Hyperparathyroidism (PTH reduces renal tubule absorption)
- Vitamin D deficiency
- TPN
- DKA
- Alcohol withdrawal
- Acute liver failure
- Paracetamol overdose (phosphaturia)
How is the adrenal cortex divided and what does each division secrete
- Zona Glomerulosa = mineralocorticoids
- Zona Fasciculata = glucocorticoids
- Zona Reticularis = sex hormones
What are Chromaffin cells
Specialised sympathetic post-ganglionic neurones situated in the adrenal medulla
What stimulates the adrenal medulla to secrete catecholamines
Sympathetic stimulation via splanchnic nerves which secrete ACh
What is produced by the adrenal medulla
- Epinephrine (adrenaline)
- Norepinephrine (noradrenaline)
- Dopamine
- Beta-hydroxylase
- ATP
- Opioid peptides
What stimulates aldosterone secretion
- RAS system (specifically angiotensin 2)
- Hyperkalaemia
- ACTH
List the actions of aldosterone
- Stimulates Na+ reabsorption from DCT
- Secretion of K+ in DCT
- Secretion of H+ in DCT
List the glucocorticoids released from the Zona Fasciculata
- Cortisol
- Corticosterone
- Cortisone
What is the majority of cortisol bound to
- Transcortin (75%)
- Albumin (15%)
What stimulates the release of cortisol
- ACTH
- Circadian rhythm
- Stress
- Trauma
- Burns
- Infection
- Exercise
- Hypoglycaemia
List the metabolic effects of cortisol
(Generally oppose those of insulin)
- Breakdown of protein into amino acids
- Gluconeogenesis
- Storage of glucose as glycogen
- Lipolysis
What is the cardiovascular significance of cortisol
Required for vasopressors to work
What stimulates the release of androgens from the zona reticularis
ACTH
Which amino acid are epinephrine and norepinephrine synthesised from
Tyrosine
Which receptors does norepinephrine mainly bind to
Alpha receptors (alpha-1)
Which receptors does epinephrine mainly bind to
Beta receptors
Which enzymes inactivate catecholamines
- Monoamine oxidase
- Catechol-0-methyltransferase
Mineralocorticoid deficiency features of Addison’s disease
- Dehydration from increase Na+ loss
- Hyponatraemia
- Hypotension
- K+ retention causing hyperkalaemia
- H+ retention causing acidosis
Glucocorticoid deficiency features of Addison’s disease
- Weight loss
- Anorexia
- Lethargy
- Hypoglycaemia during fasting
What is the most common cause of primary hyperaldosteronism
Adrenal adenoma (Conn’s) - 60-70%
Describe secondary hyperaldosteronism
Results from excess secretion of renin due to:
- Renal artery stenosis
- CCF
- Cirrhosis
Outline the effects of hyperaldosteronism
- Sodium and water retention causing HTN
- Renal K+ loss causing hypokalaemia
- Renal H+ loss causing metabolic alkalosis
What is Cushing’s disease
ACTH-secreting pituitary tumour
What is the cause of Adrenogenital syndrome (Congenital adrenal hyperplasia)
- Genetic deficiency in the enzymes involved in cortisol synthesis
- Results in reduced cortisol but increased ACTH
- Unused cortisol precursors are driven into the androgenic hormone synthetic pathway
Phaeochromocytoma is a tumour of
Chromaffin cells of the adrenal medulla
List the effects of increased circulating catecholamines
- Palpitations and arrhythmias
- Tremors
- Sweating and flushing
- Episodic HTN
- Episodic hyperglycaemia
When is the most growth hormone released in the day
During periods of deep sleep
List the causes of GH stimulation
- Hypoglycaemia
- Anxiety
- Pain
- Hypothermia
- Haemorrhage
- Trauma
- Fever
- Exercise
Role of growth hormone in the adult
- Increased glycogenolysis
- Reduced glucose uptake by cells
- Promotes amino acid uptake into cells
- Promotes protein synthesis
- Increases lipolysis
- Reduced LDL cholesterol
Role of growth hormone in children/adolescents
Stimulates skeletal growth through stimulating mitosis in the cartilage cells of the epiphyseal plates
List the hormones that increase with stress
- GH
- Cortisol
- Renin
- ACTH
- Aldosterone
- Prolactin
- ADH
- Glucagon
List the hormones that decrease with stress
- Insulin
- Testosterone
- Oestrogen
List the hormone that are unaffected by stress
- TSH
- LH
- FSH
Sympathetic response following trauma
- Sympathetic stimulation
- Caused catecholamine release
- Results in tachycardia/HTN
- Blood is redistributed to heart/muscle/brain
How is insulin release inhibited by stress
Beta-cells are inhibited by the alpha-2 adrenergic inhibitory effects of catecholamines
Effect of trauma on glucose
Initial hyperglycaemia
Effect of trauma on salt and water metabolism
ADH causes water retention, concentrated urine, and potassium loss which can continue for 3-5 days
Which cytokine is mainly associated with surgery
IL-6 (peaks 12-24 hours following surgery
How can spinal anaesthesia affect the response to surgery
Reduces changes in:
- Glucose
- ACTH
- Cortisol
- GH
- Epinephrine
