Biology Mcat

Front 1

1) Explain the functinon of the angiotensinogen-renin-angiotensinogen pathway and how that affects aldosterone.

2) What counters the effect of aldosterone?

Back 1

1) Renin is an enzyme secreted by the juxtaglomerular cells in the kidneys that converts angiotensinogen (a zymogen) to angiotensin I which then is converted to angiotensinogen II by ACE (angiotensin converting enzyme) in the lungs. Angiotensinogen II causes blood vessels to constrict, increasing b.p. and also releasing aldosterone which acts on the distal convoluted tubule to increase the reabsorption of Na+ (which also means increases water retention) causing blood volume and blood pressure to increase.

2) ANF (Atrial natriuretic Factor), a hormone secreted by the heart counters the effects of renin. (It is secreted when the body has "too much blood." The major result is a decrease in b.p. The aferent glomerular arteriole is dilated and the efferent is constricted increasing filtration rate, decreasing Na+ absorption

Front 2

What happens when the blood is too concentrated?

Back 2

**ADH (antidiuretic hormone) or vasopressin [secreted by the posterior pituitary] increases H2O reabsorption by making the distal convoluted tubule more permeable to H2O, increasing water retention and blood volume.

Front 3

How does alcohol affect ADH?

Back 3

It inhibits release of ADH causing causing dilute urine to be produced.

Front 4

Explain how the pancreas acts as an exocrine and endocrine organ. What enzymes/hormones does it secrete as such.

Back 4

As an exocrine organ it secretes amalase, lipase, nuclease, proteases, and trysinogen (converted into trypsin in the intestine). These secretions are controlled by CCK and secretin.

As an endocrine gland, the Islets of Langerhans (a collection of pancreatic cells) secrete three different hormones:
1) the alpha cells secrete glucagon which is released when blood glucose levels are low. (Glucagon stimulates the liver to break down glycogen stores and release glucose into the bloodstream.)

2) beta cells secrete insulin. Insulin is stimulated when glucose levels in the bloodstream are high causing glucose storage in the liver and muscle cells.

3) Delta cells secrete somatostatin which inhibits many digestive processes.

Front 5

What are the two types of Diabetes and how do they differ?

Back 5

Type I Diabetes or Juvenile Onset Diabetes occurs as a result of an autoimmune disorder. The body destroys its own insulin-producing cells. The treatment is insulin injections.

Type II Diabetes occurs when the body does not secrete insulin in response to high glucose levels in the blood. This is often the result of insulin production deficiency or metabolic deficiency in glucose-insulin responses. This type often manifests in middle age.

Front 6

Cholesterol is not a precursor for which of the following?

a) aldosterone
b) cortisol
c) vasopressin
d) estrogen

Back 6

Cholesterol is only a precursor for steroid hormones. Vasopressin (also known as ADH) is a pituitary peptide hormone. All other choices are steroids. The passage specifically states that cholesterol is the precursor for the adrenocortical hormones. These include mineralocorticoids (aldosterone), glucocorticoids (cortisol), and gonadocorticoids (estrogen).

Front 7

Which of the following are correct regarding the inter­actions of insulin, glucocorticoids, and glucose?

I. Insulin and glucocorticoids function com­ple­mentarily.

II. Insulin and glucocorticoids function antago­nistically.

III. Glucocorticoids facilitate the generation of glucose by the liver.

IV. Glucocorticoids facilitate conversion of glu­cose to fatty acids and protein.

Back 7

Insulin reduced blood glucose levels. Glucocorticoids increase blood glucose levels.

Front 8

Explain the hormones involved in bone resorption and reabsorption.

Back 8

Bone resorption occurs when serum Ca2+ levels are low. The parathyroid hormone causes Ca2+ to be released from the bone into the blood, increasing serum Ca2+ levels. PTH also acts on th kidney to reabsorb more Ca2+ from the urine and activates VitD so that more Ca2+ is reabsorbed in the intestine.

Calcitonin, secreted by the thyroid gland, causes Ca2+ deposition in bones. When too much serum Ca2+ is present, calcitonin is secreted.