MNSR 43 - Islets of Langerhans Adrenal glands Flashcards
pancreas
organ with both a digestive exocrine and endocrine function
Exocrine
secretes digestive juices containing enzymes and bicarbonate
2 major hormones released from pancreas as endocrine
- two major hormones insulin and glucagon
what cells in pancreas secrete insulin and glucagon
These are secreted by the cells of the Islets of Langerhans which are scattered throughout the exocrine
acinar tissue.
how are islets of langerhans arranged in pancreas
islets, the cells are arranged in irregular chains
and cords separated by a rich blood supply;
3 main cell types
alpha -20%
beta - 70%
sigma - 10%
what hormone does alpha cell secrete
glucagon - more peripherally arranged
what hormone does beta cell secrete
insulin
what hormone does sigma cell secrete
somatostatin
what does insulin and glucagon regulate
glucose levels - main target organ is liver
what causes diabetes
cause when body is state of hyperglycaemia - blood has glucose levels over renal threshold of 180mg/100ml
describe insulin structure
small protein made of 2 linked peptides
21 and 30 aa
effects carbohydrate metabolism
name three methods in which insulin decreases blood glucose levels
- Glucose transport is increased across all cell membranes in the body particularly muscle and liver
- Excess glucose is converted into glycogen in muscle and liver and into fatty acids in the liver
- Gluconeogenesis - the production of glucose from amino acids and glycerol in the liver, is reduced
what does glucagon hormone consist of
hormone consists of a single chain
protein of 29 amino
how is glucagon made
Synthesised as proglucagon, which is cleaved by protease enzymes to release active glucagon as well as several other signalling proteins
functions of glucagon
Glycogen breakdown in the liver is promoted,
glycogenolysis;
Gluconeogenesis (the production of glucose) is increased;
Lipolysis (breakdown of lipids) within adipose tissue is
promoted.
how does body react when there is a rise in blood glucose levels
beta cells are stimulated and release insulin
decrease in alpha cells secreting glucagon
liver takes up glucose - stored as glycogen
blood glucose levels decline
How does body react when there is a drop in blood glucose levels
alpha cells stimulated and release glucagon in blood
decrease in activity of beta cells - lowers release of insulin
blood glucose levels rise
how is glucose stored
stored as glycogen thru process of glycogenesis or stored as fats thru process lipogenesis
describe histology of adrenal medulla
a relatively homogenous,
well vascularised tissue with irregularly arranged cells often referred to as
chromaffin cells
contain small granules of hormone molecules in cytoplasm
lot of myelinated fibres of sympathetic nervous system
cell type of adrenal medulla
modified postganglionic neurons (neuroendocrine)
how fast or slow is adrenal medulla and why
The response of the medulla is very rapid due to the direct
sympathetic innervation.
what does adrenaline bind to
binds and activates both a and b adrenergic receptors to cause the following effects;
what effect does adrenaline have in the body when adrenaline activates alpha and beta adrenergic receptors
• Increased cardiac output (b1-adrenoreceptors)
• Increased lipolysis and glycogenolysis (a1 & b1-
adrenoreceptors)
• Bronchodilatation and vasodilatation (b 2 adrenoreceptors
in smooth muscle in the bronchial tree and skeletal blood
vessels)
what are adrenaline and noradrenaline derived from and what are they referred to as
Adrenalin(e) [epinephrine] and noradrenalin(e) [norepinephrine] which,
like thyroxine, are derivatives of tyrosine and often referred to as
catecholamines
what percentage of the secretion is adrenlaine and what %age is noradrenaline
80%adrenaline
20%noradrenalien
physiological effect of secretion of hormones of adrenal medulla
- Bronchodilation
- Decreased peristalsis in GIT
- Increased heart beat
- Increased blood flow to brain and muscle
- Decreased blood flow to skin and GIT
- Increased mental alertness
- Increased lipolysis and glycogenolysis
3 layers of adrenal cortex
zona reticularis (inner) zona fasciculata zona glomerulosa (outer)
how many steroids have been isolated from adrenal cortex
30
3 groups of adrenocortical hormones
glucocorticoids
mineralcorticoids
androgens
site of production and hormone released from glucocorticoids group
Produced in zona fasciculata.
The major hormone is cortisol (hydrocortisone) the minor, corticosterone
site of production and hormone released from mineralocorticoid group
- Produced in
zona glomerulosa. The major
hormone is aldosterone
site of production and hormone released from androgen group
Produced in zona
reticularis. A minor hormone -
androstenedione.
what causes 95% of the glucocorticoid activity of adrenal
cortisol
main glucocorticoid effect of cortisol
stimulation of gluconeogenesis and reduction in glucose utilization by cells
rise in blood glucose levels
promotes breakdown of protein in all cells except liver where it is increased
amino acid transport in muscles decrease but in liver increase
when is the cortisol hormone released
pain injury blood loss fear must release ACTH first
therapeutic effect of cortisol
decrease in inflammatory response - treat certain immune response
treat eczema or anaphylaxis
aldosterone accounts for what %age of mineralcorticoid
95%
what effect does corticosterone and cortisol have
have a weak effect
main effect of aldosterone
The main effect is to increase sodium reabsorption in the distal convoluted tubule and
the collecting duct while promoting the secretion of potassium and hydrogen ions
• Also prevents Na+ loss by the sweat glands, the salivary glands and the colon
what controls aldosterone secretion
Aldosterone secretion is controlled by the circulating blood volume
how does body react when Aldosterone drops
When this falls, the hormone is secreted along with pituitary ADH
• The renin-angiotensin system also stimulates aldosterone release
renin-angiotensin system
drop in blood pressure and fluid volume
renin release from kidney and angiotensinogen released from liver
renin + angiotensinogen = angiotensin I
ACE (angiotensin-converting enzyme) from lungs + angiotensin I = angiotensin II
Angiotensin II acts on adrenal gland - release aldosterone
Aldosterone acts on kidney and start reabsorption of salt and water
Angiotensin II also acts on blood vessels - vasoconstriction
what is the main male hormone secreted by cortex
androstenedione
effects of androstenedione
Precursor in the synthesis pathways of both androgens (testosterone) as well as oestrogens (estrone)
• Exerts weak androgenic activity on its own
example of hypoactivity in adrenal cortex
glucocorticoid insufficiency - addison’s disease
causes of addisons disease
caused by an autoimmune destruction of the cortex; a third of cases are due to tuberculosis
prevalence of addison’s disease and female:male ratio
Found in 3 per 100,000 (0.003%) population;
female/male ratio 2:1.
symptoms of addison’s disease
- Hypotension, sodium and fluid loss, hypoglycaemia, nausea, vomiting, diarrhoea and coma
- The acute state (adrenal crisis) may be fatal in 24 hours
- Slower onset may result in increased ACTH secretion which can increase skin pigmentation (MSH release)
treatment of Addison’s disease
Replacement therapy with oral synthetic steroids
such as hydrocortisone
example of hyperactivity of adrenal cortex
conn’s syndrome - hyperaldosteronism
increased secretion of aldosterone
cushing’s syndrome - increased secretion of glucocorticoids
causes of hyperaldosteronism
This may be caused by a tumour within the zona glomerulosa
prevalence of hyperaldosteronism
Occurs in less than 0.2% of the population, onset between 30 – 60 years
symptoms of hyperadlosteronism
Hypertension due to sodium and fluid retention and overstimulation of the renin-angiotensin system
• Muscle weakness due to potassium deficiency
at what age is cushing’s syndrome commonly present
30-40years
causes of cushing’s syndrome
75% of cases due to overproduction of ACTH, one third of these are due to a pituitary tumour
• 20% are due to an adrenal cortical tumour
symptoms of cushing’s syndrome
Hyperglycaemia, which may lead to excessive urine production (polyuria) which leads to excessive thirst (polydipsia)
• Muscle loss occurs due to protein usage for gluconeogenesis
physical characteristics of of cushing’s syndrome
thin limbs fat in abdomen and enlargement of torso
moon face
protein removal of bone - osteoporosis
increased body hair in females
treatment of conn’s and cushing’s syndrome
For both conditions surgical removal of the tumour
and hormone replacement therapy
