Endocrine System

Question 1

describe the different hormonal classifications

Answer 1

steroid
- cholesterol ring structure
- can enter cells
- cortisol
- aldosterone
- testosterone
- oestrogen
- progesterone

non steroid - amino acid derivatives

• amines: adrenaline, noradrenaline, melatonin
• iodinated amino acids: T3/T4

non steroid - peptides
- short chain: ADH, MSH, TRH, GRH, ANH, somatostatin and oxytocin
- long chain: GH, PTH, ACTH, prolactin, calcitonin, insulin, glucagon, secretin, CCK, gastrin

non steroid - glycoproteins
- proteins with attached carbohydrate groups to amino acids
- FSH, TSH, chorionic gonadotropin, LH

local tissue hormones
- hormone like substances with paracrine effects
- prostaglandins, leucotrienes, thromboxanes
- vascular tone, haemostasis, inflammation, mucosal protection in the stomach

Question 2

describe the link between the hypothalamus and the pituitary gland, including hormonal involvement

Answer 2

hypothalamus
- found above pituitary in midbrain
- thermoregulation, hormone secretion, circadian rhythm, motivation, emotions
- CRH, GRH, TRH, GHRH, SS, PLRH, dopamine (aka PLIH)

anterior pituitary
- hypothalamus can produce releasing hormones which pass to the AP via blood vessels
- hypothalamic pituitary portal vessels
- secretion is triggered
- ACTH, FSH, TSH, LH, GH, PL

posterior pituitary
- hormones produced from hypothalamus pass to PP via nerve axons
- ADH and oxytocin released
- oxy released from supraoptic nucleus
- ADH released from paraventricular nucleus

Question 3

describe the roles of the pituitary hormones

Answer 3

corticotropin
- CTRH from hypothalamus leads to ACTH release
- cortisol production from adrenal cortex

gonadotropin
- GTRH from hypothalamus stimulate FSH and LH release
- FSH in ovaries: ovum maturation and oestrogen production
- LH in ovaries: ovulation and production of oestrogen and progesterone
- LH in testes: testesterone production
- FSH: sperm production

thyrotropin
- TTRH from hypothalamus stimulate TSH from pituitary
- TH from thyroid gland

somatotropin
- growth hormone releasing hormone leads to growth hormone production

prolactin
- prolactin production causing breast development and milk production

ADH
- vasopressin
- water reabsorption

oxytocin
- stretch of uterus leads to oxytocin along axons to produce oxytocin into plasma
- uterus contracts (parturition)
- OR
- infant suckling produces oxytocin to lead to milk ejection

Question 4

describe the thyroid gland and the actions of its hormones

Answer 4

• situated in anterior neck
• thyroid hormone is produced from cells around the follicles
• calcitonin is produced by para follicular c cells

actions of thyroid hormone
- increase metabolic rate of all cells
- determines basal metabolic rate
- normal fetal and childhood growth
- permissive effect on the action of adrenaline

graves disease
- hyperthyroidism
- exophthalmos - bulging eyes

hashimotos
- hypothyroidism
- cretinism
- myxoedema

goitre
- iodine deficiency
- low levels of thyroid leads to increased TSH release

Question 5

describe the parathyroid glands

Answer 5

• 4-5 glands
• deep surface of the thyroid gland
• PTH increases blood calcium
• produced from chief cells

Question 6

describe the production, function and control of isle of langerhans in the endocrine pancreas

Answer 6

INSULIN

produced from beta cells in the islets of langerhans

released in response to raised blood glucose, amino acids, glucose dependent insulinotropic peptide, and vagus nerve activity

lowers blood glucose

actions of insulin:
- facilitate uptake of glucose into myocytes, adipocytes
- promote formation of glycogen, triglycerides, facilitates protein synthesis

control

increased secretion
- increased blood glucose
- increased blood amino acids
- glucose dependent insulinotropic peptide
- vagus nerve activity

inhibited secretion
- adrenaline
- sympathetic nerves
- somatostatin

GLUCAGON

• response to low glucose
• alpha cells

action:
- glycogenolysis
- gluconeogenesis
- lipolysis and ketone synthesis

promoted by
- decreased blood glucose
- increased blood amino acids
- cholecystokinin
- autonomic nerve activity

inhibited by
- insulin
- somatostatin

Question 7

describe diabetes mellitus

Answer 7

leads to elevated blood glucose due to reduced cellular uptake

leads to gluconeogenesis and lipolysis

clinical features
- polyuria (increased urine)
- polydipsia (increased fluid intake)
- glycosuria (glucose in urine)
- diabetic neuropathy
- periodontitis
- xerostomia

type 1
- insulin dependent
- reduced insulin secretion
- beta cells destroyed
- 10% of cases
- early onset
- treated by insulin replacement therapy and diet

type 2
- insulin independent
- normal insulin levels
- reduced target cell responsiveness
- obesity and poor diet
- late onset
- oral hypoglycaemic agents and diet is treatment

Question 8

describe the adrenal glands

Answer 8

suprarenal glands

cortex
- corticosteriods
- aldosterone - zona glomerulosa - mineralcorticoid hormone. controlled by RAAS. actions: promote reabsorption of sodium and water. increase excretion of hydrogen and potassium ions.
- cortisol - zona fasiculata, controlled by ACTH, glucocorticoid hormone. actions: metabolic, permissive, anti inflammatory, immunosuppressant
- androgens - zona fasiculata and reticularis. growth and sexual characteristics, pubertal growth spurt.

medulla
- modified sympathetic ganglion controlled by pre ganglionic sympathetic nerves
- adrenaline is the main hormone
- catelochomines

disorders

cushings: excess cortisol, glucocorticoid, moon face, weight gain, poor wound healing and muscle development

adreno-genital: excess androgens, balding, small breasts, large clitoris, heavy arms and legs

addisons: reduced glucocorticoids and mineralcorticoids. very serious.