Tutorial 6 Endocrine Disorders

Question 1

Define a feedback system and explain why endocrine feedback mechanisms are so important for maintaining homeostasis

Answer 1

1. Feedback system can consist of a negative or positive feedback loop
2. Most are negative feedback loops
3. Feedback systems allow for the required levels of hormones to be maintained so as not to result in disease/imbalance.

Question 2

Define a negative feedback (blood glucose regulation)

Answer 2

1. Stimulus: Rising BGL e.g. after eating
   a. Beta cells of pancreas stimulated to release insulin into the blood
   b. Insulin stimulates:
   - body cells take up more glucose
   - liver takes up and stores it as glycogen
   c. Blood glucose level declined to a set point; stimulus for insulin release diminishes
2. Stimulus: Falling BGL e.g. skipping a meal
   a. Alpha cells of pancreas stimulated to release glucagon into the blood
   b. Glucagon stimulates:
   - liver releases glycogen and releases glucose into the blood
   c. BGL rises to set point; stimulus for glucagon release diminishes

Question 3

Define a positive feedback loop (oxytocin in childbirth)

Answer 3

1. The baby pushes against the cervix, causing it to stretch
2. The stretch of cervix causes nerve impulses to be sent to the brain
3. The brain stimulates the pituitary to release oxytocin
4. Oxytocin causes the uterus to contract to push the baby out

Question 4

State the common pathophysiological mechanisms of endocrine disorders

Answer 4

Three groups:
1. Endocrine hypersecretion - excess hormone production

2. Endocrine hyposecretion - hormone insufficiency
3. Tumours of the endocrine glands

Question 5

Describe the common hypothalamic-pituitary disorders and the main hormones involved

Answer 5

1. Hyperpituitarism or hypopituitarism
2. Acromegaly (pituitary) - excessive growth hormone
3. Prolactin secreting tumours
4. Diabetes insipidus due to ADH secretion
5. Syndrome of inappropriate ADH secretion
6. Hypothalamic disease may cause deficiencies in any downstream hormone e.g. TSH (thyroid-stimulating hormone), adrenocorticotrophic hormone, beta-endorphin, luteinizing hormone, FSH, MSH

Question 6

Describe two main thyroid and parathyroid disorders and discuss the main hormones involved

Answer 6

1. Graves disease (toxic diffuse goitre) - hyperthyroidism
   An autoimmune disorder where thyroid-stimulating immunoglobulins bind to the thyroid cells and stimulate the production of too much thyroid hormone
2. Hashimoto’s disease
   Autoimmune thyroiditis - inflammation damages the gland leading to decreased thyroid production
3. Hyperparathyroidism
   excess PTH and too much calcium in the blood
4. Hypoparathyroidism
   not enough PTH and low calcium in the blood

Question 7

Describe 2 main adrenal gland disorders including symptoms and causes and discuss the main hormones involved

Answer 7

1. Cushing’s syndrome - too much cortisol
   a. Symptoms include: rapid weight gain (central obesity), buffalo hump, moon face, hirsutism, baldness, depression and anxiety
   b. Causes: May be from exogenous administration of glucocorticoids or endogenous pituitary adenoma, adrenal tumours, paraneoplastic Cushing’s common from small cell lung cancer.
2. Addison’s disease - too little cortisol
   a. Symptoms include: chronic fatigue, muscle weakness, weight loss, loss of appetite sometimes, N&V, fainting and low BP
   b. Causes: adrenal insufficiency, secondary adrenal insufficiency caused by ACTH deficiency e.g. removal of the pituitary, tuberculosis which can destroy the adrenal glands, cancer and chronic fungal infection

Question 8

Define diabetes mellitus, and explain how it differs from diabetes insipidus?

Answer 8

1. Patient with both types will feel thirsty and urinate frequently
2. DM is caused by a lack of insulin or insulin resistance whereas diabetes insipidus is caused by a lack of hormone vasopressin (ADH)
3. Diabetes insipidus is uncommon

Question 9

Define metabolic syndrome

Answer 9

1. Combination of conditions that increase the risk of cardiovascular disease
2. Diagnostic criteria include 3 or more of the following:
   a. abdominal obesity (waist circumference)
   b. elevated triglyceride
   c. HTN
   d. glucose intolerance/insulin resistance
   e. Decreased HDL cholesterol

Question 10

State 3 common complications of diabetes mellitus and describe the pathophysiological causes?

Answer 10

1. Heart and blood vessel disease:
   excess glucose binds to the blood vessel wall causing thickening and hardening to occur.
2. Neuropathy (nerve damage):
   excess glucose can damage the capillaries that nourish the nerves
3. Nephropathy:
   damage to the nephrons
4. Retinopathy (eye damage):
   blood vessels at the back of the eye balloon into pouches, this can ultimately lead to bleeding and loss of vision
5. Osteoporosis:
   Diabetes can decrease your bone mineral density and increase your risk of osteoporosis
6. Hearing impairment
7. Alzheimer’s disease:
   Caused by blocking blood blow to the brain or by increased insulin causing brain-damaging inflammation

Question 11

Describe the risk factors/causes, pathophysiology and clinical manifestation of Inappropriate Anti-diuretic Hormone Secretion

Answer 11

1. Causes: head injury, pituitary surgery, pulmonary diseases and lung tumours etc.
2. Pathophysiology:
   a. increased ADH (antidiuretic) or vasopressin, causing inability to excrete dilute urine
   b. retention of free water
   c. expansion of extracellular volume
   d. dilutional hyponatremia
3. Clinical manifestation:
   oliguria, weight gain, anorexia, N&V, muscle weakness, seizures, coma

Question 12

Describe the pathophysiology of T2DM

Answer 12

1. Genetic and environmental factors:
   increased appetite, nutrient intake, metabolic sufficiency
2. Physiological changes:
   a. increased adiposity:
   low grade inflammation, reactive oxygen species, dyslipidemia, adipokines, beta cell stress
   b. Insulin resistance: liver and muscle
   c. beta cell dysfunction
3. Excess glucose production, impaired glucose uptake and utilisation lead to T2DM

Question 13

How do we diagnose an alteration in endocrine function?

Answer 13

1. Signs and symptoms: coma, oedema
2. Blood tests:
   a. BGL for diabetes
   b. T3, T4 tests for thyroid function
   c. other elevated hormone levels
3. Diagnostic imaging of the endocrine organ
   e. g. MRI, CT