Lecture 29 - loss of homeostasis Flashcards
Growth hormone disorders
Excess GH = gigantism (often caused by a pituitary gland tumour)
Normal level = normal height
Deficiency of GH = primordial dwarfism
Infantile hypothyroidism
Hyposecretion of thyroid hormone (there is not enough of it)
Not enough thyroid hormone in newborns leads to low metabolic rate, cold intolerant, growth is retared (short in stature) and brain development is inhibited.
Most commonly caused by …
Lack of iodine in the mother’s diet (mother does not need to show symptoms of hypothyroidism for the baby to have infantile hypothyroidism
Maternal iodine supplementation is recommended leading up to and during pregnancy
Iodine deficiency disorder (aka simple goitre)
Hyposecretion
Iodine deficiency - the thyroid gland is unable to make enough thyroid hormone (TH). When stored TH is depleted, TRH and TSH secretion increase to stimulate the thyroid gland to make more TH. Without iodine, TH cannot be made.
The continual stimulation of the thyroid gland leads to the growth of the thyroid gland. Thyroid gland enlarges with continual stimulation by TSH (loss of negative feedback control as there is an inadequate concentration of iodine to make TH)
The net result is that there is a loss of negative feedback control and overstimulation of the thyroid gland. Excess TSH stimulates growth of the thyroid gland.
Iodine deficiency disorder (aka simple goitre) - what happens to the control system?
Loss of negative feedback control
The continual stimulation of the thyroid gland leads to the growth of the thyroid gland. Thyroid gland enlarges with continual stimulation by TSH (loss of negative feedback control as there is an inadequate concentration of iodine to make TH)
There is the loss of the mechanism that prevents TRH and TSH
Graves disease
Hyper secretion of the thyroid hormone (there is too much)
Symptoms include high metabolic rate, weight loss, thyroid swelling ( because in grave’s disease the thyroid is continually being stimulated by the immune system so we sometimes also see swelling of the thyroid), exophthalmos - bulging out of the eyes due to swelling of the tissue behind the eye, increased heart rate, heat intolerant etc.
The cause of it - autoimmune disorder
Hyperparathyroidism
Leads to excess PTH secretion (hypersecretion)
Usually caused by a parathyroid tumour
Bones become soft, deformed and fragile
Raises the blood levels of calcium and phosphate ions
Promotes formation of kidney stones composed of calcium phosphate
Hypercalcaemia
Nerve and muscle cells less responsive and excitable
Blood calcium is too high
Can lead to depression of the nervous system, emotional disturbances, muscle weakness, sluggish reflexes
If plasma levels are significantly elevated can lead to cardiac arrest
Hypocalcaemia
Increased excitability of the nervous system
Blood calcium is too low
Leads to muscle tremors, spasms or cramps (tetany)
When very low - get paraesthesia (tingling/burning sensation) in hands and face (because the axons that relay tingling and burning sensations information are so close to threshold that they spontaneously fire), muscle cramps, and in some cases the muscles of the larynx may contract tightly (laryngospasm), which can shut off air flow and cause suffocation and therefore death.
Caused by
Vitamin D deficiency (absence of vitamin D means that calcium absorption in the gut is greatly affected and therefore we end up with low calcium in the body)
Diarrhoea (leads to an excess loss of calcium)
Thyroid tumours
Underactive (or removal of) parathyroid glands
Pregnancy and lactation (calcium heads towards foetus/infant instead)
How does blood calcium cause hypercalcaemia?
Increase in extracellular calcium causes excitable cells to be further from threshold/less responsive
Now the difference between the outside and the inside of the cell is much further away from the point of threshold
How does blood calcium cause hypocalcaemia?
Decrease in extracellular calcium causes excitable cells closer to threshold/more responsive
Makes outside more negative, will make the inside potential go closer to threshold for firing therefore need less stimuli to reach the threshold for firing of our excitable cells and they become more responsive
Diabetes mellitus
Two types - type one and type two diabetes
Type I diabetes mellitus
Hyposecretion of insulin - too little or no insulin is secreted
Cause can be caused by autoimmunity - destruction of pancreatic beta cells by the immune system
Glucosuria (glucose in the urine which leads to an osmotic force causing more water in the urine i.e. polyuria), polyuria (excess urine production which can lead to thrist/dehydration which is polydipsia), polydipsia (excessive thrist) etc.
Insulin injections or infusion
Onset is often early in life (childhood)
For type I diabetics why is it best for insulin to be injected rather than taken orally?
Since it is a peptide hormone it is not taken as a tablet as it would be broken down in the digestive system into its amino acid constituents. Therefore insulin must be given by injection or infusion
Type II diabetes mellitus
Hyposensitive receptors to insulin - too little or no response to insulin
Also called insulin resistance diabetes
Reduced sensitivity to insulin or developed insulin resistance
Associated with obesity (high levels of glucose in the blood constantly means that the receptors stop responding appropriately). Densenitisation of the insulin reception
Glucosuria, polyuria, polydipsia etc.
Treated by changes in diet and exercise or medication (metformin-encourages glucose loss)
How is diabetes mellitus diagnosed?
Pathological change of a homeostatic system
Cannot take a single blood glucose meansurement - need to check response to glucoses (glucose tolerance test - person does not eat anything but water and they then have a sugary drink and glucose levels are watched over a couple of hours), insulin levels, and longer-term exposure (HbA1C test)
HbA1C test is very common in NZ. When glucose is high it can bind to haemoglobin. Can determine diabetics and prediabetics. There is no fasting required and can be taken any time.
