MCAT BIO/BIOCHEM: Endocrine System Flashcards

Question 1

Define Endocrine Gland.

Accepted Answer

A ductless gland that secretes hormones directly into the bloodstream, which carries them to target cells that may be far from the gland.

Question 2

What is Hormone?

Accepted Answer

A chemical messenger released into the blood by a gland or specialized cells that changes the activity only of target cells carrying a receptor for it.

Question 3

Define Peptide Hormone.

Accepted Answer

A water-soluble hormone built from amino acids, stored in vesicles and released by exocytosis; it binds cell-surface receptors and usually acts quickly through second messengers.

Question 4

Define Steroid Hormone.

Accepted Answer

A lipid-soluble hormone made from cholesterol that crosses the cell membrane, binds an intracellular receptor and changes gene transcription, so its effects are slower but longer-lasting.

Question 5

Define Amino Acid-Derived Hormone.

Accepted Answer

A hormone made from tyrosine or tryptophan; catecholamines act like peptide hormones at surface receptors, while thyroid hormones act like steroids inside the cell.

Question 6

Define Second Messenger.

Accepted Answer

A small intracellular molecule, such as cAMP, calcium ions or IP3, that relays and amplifies a signal from a cell-surface receptor to proteins inside the cell.

Question 7

Define G Protein-Coupled Receptor.

Accepted Answer

A seven-pass membrane receptor that, when its ligand binds, activates a heterotrimeric G protein, which then changes enzymes such as adenylyl cyclase or phospholipase C.

Question 8

Define Tropic Hormone.

Accepted Answer

A hormone whose main target is another endocrine gland, which it stimulates to release a hormone of its own.

Question 9

What is Hypothalamus?

Accepted Answer

The brain region linking the nervous and endocrine systems; it releases hormones that control the anterior pituitary and makes ADH and oxytocin for the posterior pituitary.

Question 10

Define Hypophyseal Portal System.

Accepted Answer

A network of blood vessels that carries releasing and inhibiting hormones from the hypothalamus directly to the anterior pituitary, without diluting them in the general circulation.

Question 11

Define Anterior Pituitary.

Accepted Answer

The glandular front lobe of the pituitary, which makes and secretes FSH, LH, ACTH, TSH, prolactin and growth hormone under control from the hypothalamus.

Question 12

Define Posterior Pituitary.

Accepted Answer

The neural back lobe of the pituitary, which stores and releases ADH and oxytocin made by hypothalamic neurons whose axons end there.

Question 13

Define Antidiuretic Hormone (ADH).

Accepted Answer

A posterior pituitary peptide, also called vasopressin, released when blood osmolarity rises; it inserts aquaporin-2 channels in collecting duct cells so more water is reabsorbed.

Question 14

What is Oxytocin?

Accepted Answer

A posterior pituitary peptide that stimulates uterine contractions during labor and milk ejection during breastfeeding, both driven by positive feedback.

Question 15

What is Prolactin?

Accepted Answer

An anterior pituitary hormone that stimulates milk production in the mammary glands; unlike the other anterior pituitary hormones, it is mainly held in check by hypothalamic dopamine.

Question 16

Define Growth Hormone.

Accepted Answer

An anterior pituitary hormone that promotes growth of bone and muscle, largely through IGF-1 made by the liver, and raises blood glucose by opposing insulin.

Question 17

Define Thyroid-Stimulating Hormone (TSH).

Accepted Answer

An anterior pituitary tropic hormone that stimulates the thyroid gland to take up iodine and to make and release T3 and T4.

Question 18

Define Thyroxine (T4).

Accepted Answer

The main hormone secreted by the thyroid, carrying four iodine atoms; tissues convert it to the more active T3, which raises the basal metabolic rate.

Question 19

What is Calcitonin?

Accepted Answer

A peptide hormone from the thyroid's parafollicular (C) cells that lowers blood calcium by inhibiting osteoclast bone resorption; its role in adult humans is minor.

Question 20

Define Parathyroid Hormone (PTH).

Accepted Answer

A peptide hormone from the parathyroid glands that raises blood calcium by stimulating bone resorption, calcium reabsorption in the kidney and activation of vitamin D.

Question 21

What is Cortisol?

Accepted Answer

The main glucocorticoid, a steroid from the adrenal cortex's zona fasciculata that raises blood glucose, breaks down protein and fat, and suppresses inflammation and immunity during stress.

Question 22

What is Aldosterone?

Accepted Answer

The main mineralocorticoid, made in the zona glomerulosa; by adding sodium channels and pumps to distal tubule and collecting duct cells, it retains sodium and water and excretes potassium.

Question 23

Define Adrenal Medulla.

Accepted Answer

The inner part of the adrenal gland, made of modified sympathetic neurons, that releases epinephrine and norepinephrine into the blood during the fight-or-flight response.

Question 24

Define Adrenal Cortex.

Accepted Answer

The outer part of the adrenal gland, which makes steroid hormones in three zones: mineralocorticoids, glucocorticoids and androgens, from the outside in.

Question 25

What is Insulin?

Accepted Answer

The main storage hormone of the fed state, secreted by beta cells of the pancreatic islets; it lets muscle and fat take up glucose and drives synthesis of glycogen, fat and protein.

Question 26

What is Glucagon?

Accepted Answer

The main hormone of the fasting state, secreted by alpha cells of the pancreatic islets; in the liver it switches on glycogenolysis and gluconeogenesis to stop blood sugar dropping too low.

Question 27

Define Islets of Langerhans.

Accepted Answer

Clusters of endocrine cells scattered through the pancreas, with alpha cells that secrete glucagon, beta cells that secrete insulin and delta cells that secrete somatostatin.

Question 28

What is Melatonin?

Accepted Answer

A hormone made from serotonin by the pineal gland and released at night that helps set the body's sleep-wake rhythm; bright light suppresses its secretion.

Question 29

Define Renin-Angiotensin-Aldosterone System.

Accepted Answer

A hormone cascade in which kidney renin turns angiotensinogen into angiotensin I, ACE converts it to angiotensin II, and angiotensin II triggers aldosterone release and vasoconstriction.

Question 30

Define Hypothalamic-Pituitary-Adrenal Axis.

Accepted Answer

The three-step hormone chain in which hypothalamic CRH triggers pituitary ACTH, which triggers adrenal cortisol, and cortisol in turn inhibits both CRH and ACTH.

Question 31

Define Gonadotropins (FSH and LH).

Accepted Answer

The anterior pituitary hormones FSH and LH, released in response to hypothalamic GnRH, that control gamete production and sex-steroid secretion in the ovaries and testes.

Question 32

Define Paracrine Signaling.

Accepted Answer

Signaling in which a cell releases a chemical that diffuses to and acts on nearby cells, instead of traveling through the blood to distant targets.

Question 33

Define Diabetes Insipidus.

Accepted Answer

A condition of large volumes of dilute urine and intense thirst, caused by too little ADH (central) or by kidneys that do not respond to it (nephrogenic).

Question 34

What is Goiter?

Accepted Answer

An enlargement of the thyroid gland, which can occur with too little or too much thyroid hormone; worldwide, iodine deficiency is the most common cause.