+Endocrine System Review Chapter 38

Important Tables and Pages

• Page 741: Grid comparison for A&P review.

• Table 39.5 (Page 755): Comparison group.

• Table 39.6 (Page 758).

• Table 39.7 (Page 761): Summary of endocrine disorders, functions, and effects of too little or too much hormone, including medications.

• Table 40.1 (Page 767): Important comparison.

• Table 40.4: Different types of insulin.

• Tables 40.5 (Pages 774-775): Very important.

• Table 40.7 (Page 778): Compare/contrast hypoglycemia and hyperglycemia.

Review of A&P

• Most hormone levels are regulated by negative feedback (when levels are too low, the body secretes more).

• Hypothalamus connects the nervous system to the endocrine system via the pituitary gland.

• Anterior pituitary gland secretes hormones in response to hypothalamus signals.

• Growth hormone:

  • Regulated by growth hormone releasing hormone and growth hormone inhibiting hormone.

  • If the level is too high, a signal is sent to the inhibiting hormone to pull it back.

  • If the level is too low, a signal is sent to the releasing hormone to release more.

Antidiuretic Hormone (ADH) / Vasopressin

• Antidiuretic hormone: stops you from peeing.

• Also known as vasopressin.

• Given when someone is hypotensive; it constricts.

• If blood volume is low, the body secretes antidiuretic hormone to hold on to fluid.

• Increases water reabsorption by the kidney tubules, which decreases urine output.

• In cases of severe hemorrhage, ADH is important because it causes arterial vasoconstriction, increasing blood pressure to homeostatic levels.

• Vasopressors are blood pressure medications that help save lives.

Oxytocin

• Causes contractions of the uterus.

• Operates on a positive feedback loop.

  • When stimulated, it releases more (e.g., breastfeeding releases oxytocin, contracting the uterus and causing more milk flow).

  • The more you breastfeed or pump, the more milk your body makes.

Thyroid Gland

• T3 and T4 increase metabolism of glucose and fatty acids, which increases energy and heat production.

• Low T3 and T4 lead to decreased metabolism, decreased heat production (feeling cold), and decreased energy (lethargy).

• Hypothyroid: low energy, low metabolism, cold.

• Hyperthyroid: lots of energy, lots of metabolism, hot all the time.

Thyroid Levels During Pregnancy

• Thyroid levels can be affected due to hormonal release.

• Metabolism slows down because the baby takes all the nutrients.

• Thyroid levels are essential for normal physical growth, mental development, and reproductive maturation.

Iodine

• Sufficient iodine intake is required for T3 and T4 production.

• The biggest source of iodine in the diet in the United States is iodized salt.

• Sea salt and pink Himalayan salt are not typically iodized, which can lead to iodine deficiency.

Thyroid Stimulating Hormone (TSH)

• The direct stimulus for secretion of T3 and T4 is TSH from the anterior pituitary.

• A decrease in metabolic rate causes the hypothalamus to secrete TRH, which stimulates the release of TSH. TSH stimulates the thyroid to secrete T3 and T4.

• All glands have a stimulating hormone that either releases or inhibits their hormone. It's a constant loop, re-evaluating and adjusting levels as needed.

Calcitonin

• Works with the reabsorption of calcium and phosphorus into the blood, especially during childhood.

• Inhibits the reabsorption of calcium and phosphorus into the blood so that they stay in the bones.

• Maintains normal blood levels of calcium and phosphate and maintains strong, stable bones.

• When hypercalcemic, calcitonin puts calcium back into the bones.

• Calcitonin tones down serum calcium.

Parathyroid Hormone (PTH)

• Antagonist to calcitonin.

• Raises blood calcium levels.

• Pulls calcium from the bones and puts it into the blood.
  *
  For older patients, excessive PTH can cause osteoporosis.

Adrenal Glands

• Located above the kidneys.

• Adrenal medulla releases catecholamines (epinephrine, norepinephrine) as part of the sympathetic nervous system during stress (fight or flight).

• Adrenal cortex secretes steroid hormones: mineralocorticoids, glucocorticoids, and gonadocorticoids.

Aldosterone

• A mineralocorticoid that promotes the reabsorption of sodium and the excretion of potassium by the kidney tubules.

• As sodium ions are reabsorbed, water follows, maintaining normal blood volume and blood pressure.

• Aldosterone releases or holds on to water, and is stimulated when dehydrated with low blood volume.

Cortisol

• The most abundant glucocorticoid that stimulates gluconeogenesis in the liver, increases lipolysis, and protein catabolism for energy production.

• Ensures glucose availability for the brain.

• Released at higher levels during stress (including exercise).

• Has an anti-inflammatory effect.

• Excess cortisol decreases the immune response and delays healing.

• Cortisol levels causes a delay in healing.

Gonadocorticoids

• Male androgens that get converted to estrogen in females. They are the only source of estrogen after menopause.

• Contribute to libido in both genders.

Pancreas

• Secretes insulin and glucagon.

• Hypoglycemia stimulates the release of glucagon, which raises blood glucose.

• Hyperglycemia stimulates beta cells to release insulin.

• Insulin and glucagon work as antagonists to keep blood glucose levels normal.

• The body thrives on equilibrium and tries to fix high or low levels.

Regulation of Glucose

• After eating, blood glucose levels rise.

• High glucose levels stimulate beta cells to secrete insulin.

• Insulin stimulates cells to take up more glucose and causes the liver to store extra glucose as glycogen.

• When blood glucose drops, alpha cells release glucagon.

• Glucagon stimulates the liver to break down glycogen into glucose.

Aging System

• Decreased growth hormone causes decreased muscle mass and increased fat storage.

• Decreased TSH and thyroid hormone cause decreased metabolic rate and decreased energy.

• Decreased insulin secretion leads to decreased glucose tolerance.

Assessment

• Weight changes (unplanned weight loss or weight gain).

• Excessive thirst or urination.

• Heat or cold tolerance.

• Mood and memory changes.

• Family history.

• Exophthalmos (bulging eyes).

• Fat pads.

• Thyroid enlargement (bulging).

• Skin changes.

• Tremors.

Common Tests

• Thyroid tests: check TSH, T3, and T4.

• PTH level.

• Hormone levels.

Thyroid Scan

• Ultrasound to check for tumors or nodules.

• Radioactive material (drink or IV) is absorbed by the thyroid.

• Hot spots (concentrated areas of radioactive material uptake) indicate nodules.

• Cold spots (no radioactive material uptake) may indicate malignancy. Biopsy to confirm.

• Radioactive iodine uptake test to see how the thyroid is functioning.

TSH, T3 and T4

• If T3 and T4 levels are off, check TSH to determine if the problem is with hormone production or stimulation.

• If TSH levels are normal, but t3 and t4 levels are low, replace the actual hormone.

• If TSH levels are not normal, the stimulator is malfunctioning.