Endocrine Physio

What is the pineal gland?

Also known as the epiphysis. Regulates circadian rhythms via melatonin. It is stimulated by darkness and inhibited by light. Precursors to melatonin are serotonin and tryptophan.

What is the pancreas?

Both an endocrine and exocrine organ. Endocrine cells are found on the islets of Langerhans. Alpha cells: Secrete glucagon - stimulated by hypoglycemia. Beta cells: Secrete insulin - stimulated by hyperglycemia.

What is diabetes mellitus?

Characterized by constant hyperglycemia. Can lead to Alzheimer's, nerve degeneration, etc. Type I DM: Insulin dependent, "born with it", it is also known as adolescent onset diabetes. Autoimmune disorder due to a destruction of beta cells so there is a lack of insulin secretion and the body is in a constant state of hyperglycemia. Smaller amount of diabetes, also not correlated with body weight. Type II DM: Non insulin dependent, "maturity onset diabetes". Due to insulin resistance since the target cells no longer respond to it because of normal or elevated insulin levels. Strong correlation with body weight (obese patients). Larger amount of diabetics.

What are hormones? Are they all the same?

Chemical messengers that are secreted in order to influence metabolic activity of the body so that homeostasis can be maintained. There are two major classes of hormones: Amino acid based: Synthesized from amino acids (amines and peptides). Water soluble so it cannot cross the plasma membrane. Steroids: Synthesized from cholesterol - these are only gonadal and adrenocortical hormones. Lipid soluble so it can cross the plasma membrane.

Explain the adrenal gland, make sure to mention the different layers.

Composed of two parts: the adrenal cortex and the adrenal medulla. Adrenal cortex: Releases corticosteroids. Has three layers: Zona glomerulosa: Secretes mineralocorticoids. Zona fasciculata: Secretes glucocorticoids. Zona reticularis: Secrete sex hormones (androgens). Girls From Russia Make Good Soup Adrenal medulla: Regulated by the nervous system - secretes epinephrine and norepinephrine.

Growth hormone (GH)

Regulates body growth and metabolism in the body. The target tissues are the muscles, bones, etc.

Adrenocorticotropic hormone (ACTH)

Stimulate the secretion of glucocorticoids, mineralocorticoids and androgens. The target tissue is the adrenal cortex.

Oxytocin

Stimulates contractions during labor and initiates milk ejection during breastfeeding. The target tissue is the uterine smooth muscle and mammary glands.

Prolactin (PRL)

Stimulates lactation. The target tissue is the mammary glands.

Follicle-stimulating hormone (FSH

Stimulates ovarian follicle maturation and estrogen production in women and sperm production in men. The target tissue are the ovaries and testes.

Luteinizing hormone (LH)

Stimulates ovulation in women and testosterone production in men. The target tissue are the ovaries and testes.

Antidiuretic hormone (ADH)

Stimulates reabsorption and inhibits diuresis. The target tissue are the kidneys.

Thyroid-stimulating hormone (TSH)

Stimulates the secretion of T3 (triiodothyronine) and T4 (thyroxine). The target tissue is the thyroid.

What is the endocrine system? What is the difference between primary and secondary endocrine organs?

The endocrine system is comprised of organs that release hormones to regulate the body in order to maintain homeostasis. Primary endocrine organs: Main function is to produce and secrete hormones. Ex. Pituitary gland. Secondary endocrine organs: Have another main function but are able to produce hormones in addition. Ex. Hypothalamus.

Explain the posterior pituitary hormones.

The hypothalamic neurons THEMSELVES synthesize oxytocin and ADH.

What is the relationship between the hypothalamus and pituitary gland?

The hypothalamus stimulates the pituitary gland and therefore is able to control the release of certain hormones in two different ways. Anterior pituitary: Also called the adenohypophysis. More of an endocrine based action - the hypothalamus secretes hormones into the hypophyseal portal system of the pituitary gland which controls the production of these anterior pituitary hormones. Posterior pituitary: Also called the neurohypophysis. More of a neural based action - axon potential travels down the hypothalamic neurons which causes the hormones to be released from those axon terminals.

What is the thyroid gland? What about the parathyroid gland?

The thyroid gland produces the thyroid hormones (T3 and T4) - they increase basal metabolic rate and body heat production as well as regulating growth and development. Calcitonin: Released from the parafollicular cells of the thyroid gland due to a high concentration of blood calcium. It will promote osteoblast activity (build up) and inhibit osteoclast activity (break down) in order to balance out the blood calcium levels. The parathyroid gland secretes parathyroid hormone, which is released when there are low levels of calcium in the blood. Stimulates three organs to increase calcium levels: skeleton (stimulates osteoclasts to digest some of the bony matrix and release calcium into the blood), kidneys (reabsorption of calcium) and intestine (activation of vitamin D).