Question 1

A PATIENT HAS HIGH TSH AND LOW T4. WHERE IS THE PROBLEM MOST LIKELY TO BE?

Accepted Answer

THE THYROID GLAND. Low T4 removes negative feedback, so a healthy pituitary raises TSH. TSH is already high, so the pituitary is responding; the thyroid is failing to answer it. This is primary hypothyroidism.

Question 2

A PITUITARY TUMOR SECRETES EXCESS ACTH. WHAT HAPPENS TO CORTISOL AND CRH?

Accepted Answer

CORTISOL RISES AND CRH FALLS. Extra ACTH drives the adrenal cortex to make more cortisol. The high cortisol then feeds back on the hypothalamus and lowers CRH, but the tumor keeps releasing ACTH regardless.

Question 3

A PATIENT TAKES A HIGH DOSE OF PREDNISONE, A SYNTHETIC GLUCOCORTICOID, FOR MONTHS. WHAT HAPPENS TO THE CORTISOL-MAKING ZONE OF THEIR ADRENAL CORTEX?

Accepted Answer

IT SHRINKS BECAUSE ACTH IS SUPPRESSED. The drug acts like cortisol and suppresses CRH and ACTH. Without ACTH stimulation the zona fasciculata atrophies, which is why long courses are tapered rather than stopped suddenly.

Question 4

SUCKLING TRIGGERS RELEASE OF ___ FROM THE POSTERIOR PITUITARY, WHICH SQUEEZES MILK INTO THE DUCTS.

Accepted Answer

OXYTOCIN. Nerve signals from the nipple reach the hypothalamus, and oxytocin released from the posterior pituitary contracts the cells around the milk glands. It is a positive feedback loop.

Question 5

IODIZED SALT PREVENTS GOITER BECAUSE THE THYROID NEEDS IODINE TO MAKE ___.

Accepted Answer

THYROXINE. Thyroxine (T4) carries four iodine atoms. Without iodine the thyroid cannot make enough, TSH rises from lost feedback, and the constant stimulation enlarges the gland.

Question 6

WHY CAN CORTISOL REACH RECEPTORS INSIDE ITS TARGET CELLS WHILE INSULIN CANNOT?

Accepted Answer

CORTISOL IS A LIPID-SOLUBLE STEROID. Steroids are made from cholesterol and diffuse through the lipid bilayer to reach intracellular receptors. Insulin is a charged, water-soluble peptide, so it must signal through a receptor on the cell surface.

Question 7

A HORMONE BINDS A RECEPTOR THAT ACTIVATES ADENYLYL CYCLASE. WHICH MOLECULE THEN CARRIES THE SIGNAL INSIDE THE CELL?

Accepted Answer

CAMP. Adenylyl cyclase converts ATP into cyclic AMP, a second messenger that activates protein kinase A. Glucagon and epinephrine both signal this way.

Question 8

THE PARATHYROID GLANDS ARE REMOVED BY ACCIDENT DURING THYROID SURGERY. WHAT HAPPENS TO BLOOD CALCIUM?

Accepted Answer

IT FALLS, CAUSING MUSCLE CRAMPS AND TETANY. PTH is the main hormone that raises blood calcium. Without it calcium falls, nerves and muscles become overexcitable, and cramps and tetany follow. Calcitonin lowers calcium, so it cannot compensate.

Question 9

DURING AN OVERNIGHT FAST, PANCREATIC ALPHA CELLS SECRETE ___ TO KEEP BLOOD GLUCOSE UP.

Accepted Answer

GLUCAGON. Glucagon makes the liver break down glycogen and run gluconeogenesis, releasing glucose into the blood when no food is coming in.

Question 10

A PATIENT SECRETES VERY LITTLE ADH. WHAT URINE WOULD YOU EXPECT?

Accepted Answer

LARGE VOLUMES OF DILUTE URINE. ADH makes the collecting ducts permeable to water. Without it water is not reabsorbed, so large volumes of dilute urine are lost. This is central diabetes insipidus.

Question 11

AN AUTOIMMUNE ATTACK DESTROYS THE PANCREATIC BETA CELLS. WHICH CONDITION RESULTS?

Accepted Answer

TYPE 1 DIABETES MELLITUS. Beta cells make insulin, so destroying them causes absolute insulin deficiency: type 1 diabetes. Type 2 is mainly insulin resistance; diabetes insipidus involves ADH; Addison's disease destroys the adrenal cortex.

Question 12

HIGH CORTISOL LOWERS THE RELEASE OF CRH AND ACTH. THIS IS AN EXAMPLE OF ___ FEEDBACK.

Accepted Answer

NEGATIVE. The end product of the axis inhibits the steps that produced it, which keeps cortisol within a set range.

Question 13

IN GRAVES' DISEASE, ANTIBODIES STIMULATE THE TSH RECEPTOR ON THE THYROID. WHAT HAPPENS TO THE PATIENT'S TSH LEVEL?

Accepted Answer

IT FALLS. The antibodies drive the thyroid to make excess T3 and T4. These feed back on the pituitary and hypothalamus, so TSH secretion is suppressed to very low levels.

Question 14

ALDOSTERONE SECRETION RISES. WHAT CHANGES IN THE DISTAL NEPHRON?

Accepted Answer

MORE SODIUM IS REABSORBED AND MORE POTASSIUM IS SECRETED. Aldosterone increases sodium channels and sodium-potassium pumps in the distal tubule and collecting duct. Sodium is reabsorbed (water follows), and potassium is secreted into the urine.

Question 15

A PERSON IS SUDDENLY FRIGHTENED. WHICH GLAND RELEASES EPINEPHRINE INTO THE BLOOD WITHIN SECONDS?

Accepted Answer

THE ADRENAL MEDULLA. Sympathetic nerves stimulate the adrenal medulla, made of modified sympathetic neurons, to release epinephrine and norepinephrine almost at once. The cortex makes steroids, which act more slowly.

Question 16

A FALL IN BLOOD PRESSURE MAKES THE KIDNEY RELEASE ___, STARTING THE CHAIN THAT ENDS WITH ALDOSTERONE.

Accepted Answer

RENIN. Renin converts angiotensinogen to angiotensin I, which ACE converts to angiotensin II. Angiotensin II constricts vessels and stimulates aldosterone release.

Endocrine System