AP Biology : Excretory Physiology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #24 : Excretory System

Which section of the nephron is most directly affected by antidiuretic hormone?

Possible Answers:

Collecting duct

Glomerulus

Proximal convoluted tubule

Loop of Henle

Correct answer:

Collecting duct

Explanation:

In the presence of antidiuretic hormone (ADH), water is reabsorbed and the urine is concentrated. Antidiuretic hormone plays the biggest role on the collecting duct and distal tubule, allowing water to diffuse into the medulla by increasing the production of aquaporin proteins. These proteins become embedded in the membranes of the nephron epithelium and allow water to pass through the usually impermeable cells.

The other important regulator of water balance is aldosterone, which works by a different mechanism. Aldosterone increases production of sodium channels, allowing sodium to exit the filtrate in the distal tubule. Water diffuses to follow the reabsorbed sodium ions.

Example Question #25 : Excretory System

Which regulatory mechanism functions to increase water reabsorption and maintain homeostasis when blood pressure is below normal?

Possible Answers:

Atrial natriuretic peptide

Adrenocorticotropic hormone

Substance P

Renin-angiotensin-aldosterone system (RAAS)

Correct answer:

Renin-angiotensin-aldosterone system (RAAS)

Explanation:

There are two main systems designed to regulate water reabsorption in the kidney: antidiuretic hormone (vasopressin) and the renin-angiotensin-aldosterone system (RAAS). The RAAS system includes a combination of substances that raise blood pressure through arteriole constriction and sodium reabsorption. It employs a specialized tissue that supplies blood to the glomerulus, called the juxtaglomerular apparatus (JGA), which produces the enzyme renin when stimulated by a drop in blood pressure.

Renin secretion is the first step in a series of reactions that serve to lower blood pressure. Renin enters the bloodstream, where it interacts with angiotensinogen and produces angiotensin I. Angiotensin-converting enzyme in the lungs further converts angiotensin I into angiotensin II. Angiotensin II has two primary functions: it acts as vasoconstrictor and stimulates release of aldosterone from the adrenal cortex. Vasoconstriction helps to immediately increase local blood pressure. Aldosterone interacts with the distal tubule of the nephron to increase sodium reabsorption. The increase in interstitial osmolarity helps pull water out of the filtrate, concentrating the urine and enhancing water conservation, which can increase blood volume and pressure.

Atrial natriuretic hormone serves to inhibit the RAAS system when blood pressure is low.

Example Question #26 : Excretory System

How would production of vasopressin be affected after consuming a large amount of water?

Possible Answers:

It would decrease

It would increase

None of the other answers

Vasopressin would be inactivated by renin

Correct answer:

It would decrease

Explanation:

Vasopressin, also called antidiuretic hormone (ADH), is part of the hormonal control of urine excretion and functions to enhance water reabsorption and limit the excretion of water in urine. Vasopressin is released when osmoreceptor cells in the hypothalamus detect a rise in the osmolarity or solute concentration of the blood above a threshold level.

Conversely, intake of a large quantity of water will lower blood osmolarity and signal that water conservation is not needed. When blood volume or pressure increases and blood osmolarity decreases, production of vasopressin is inhibited in order to promote water excretion.

Example Question #11 : Excretory Physiology

Which of the following is the mechanism of action of vasopressin?

Possible Answers:

Mobilize aquaporin receptors from storage vesicles

Internalize aquaporin receptors

Stimulate release of potassium ions in the proximal tubule

Inhibit the function of sodium ion channels

Correct answer:

Mobilize aquaporin receptors from storage vesicles

Explanation:

Vasopressin, also called antidiuretic hormone (ADH), is part of the hormonal control of urine excretion and functions to enhance reabsorption of water, limiting the excretion of water in urine. Vasopressin is released when osmoreceptor cells in the hypothalamus detect a rise in the osmolarity (solute concentration) of the blood above a threshold level. Upon release, vasopressin reaches the kidney and binds to receptors on cells in the collecting duct, which stimulates release of aquaporin water channels from storage vesicles within the cells. Aquaporin channels are selectively permeable to water, and allow the flow of water out of the filtrate/urine. This water is then reclaimed by the body and used to increase blood volume, increase blood pressure, and reduce blood osmolarity.

Example Question #12 : Excretory Physiology

What are the two primary solutes that affect and produce osmolarity gradients within the nephron?

Possible Answers:

Potassium and water

Ammonia and sodium

Sodium and urea

Bicarbonate and glucose

Correct answer:

Sodium and urea

Explanation:

One of the key adaptations of the mammalian kidney is the ability to conserve water through reabsorption and excretion of concentrated urine. This is accomplished by maintenance of an osmolarity gradient, suitable for extracting water from the filtrate. The two primary solutes are sodium, which is deposited in the renal medulla by the loop of Henle, and urea, which crosses the epithelium of the collecting duct in the inner medulla. The increased osmolarity of the interstitial fluid enables water to be extracted and conserved through aquaporin proteins in the collecting duct.

Example Question #13 : Excretory Physiology

Antidiuretic hormone (ADH) controls the concentration of urine by manipulating the permeability of the collecting ducts.

Alcohol consumption generally leads to greater urine volume. How does alcohol affect urine concentration in the body?

Possible Answers:

Alcohol inhibits ADH, and causes water to diffuse into the renal medulla from the collecting duct.

Alcohol inhibits ADH, and prevents water from leaving the collecting duct and entering the renal medulla.

Alcohol inhibits ADH, which results in the movement of ions from the collecting duct into the renal medulla.

Alcohol stimulates ADH and causes the urine to become very concentrated.

Alcohol stimulates ADH, which causes an increase in renin secretion

Correct answer:

Alcohol inhibits ADH, and prevents water from leaving the collecting duct and entering the renal medulla.

Explanation:

Antidiuretic hormone (ADH) is responsible for concentrating the urine. This is accomplished by making the collecting duct permeable to water, and allowing it to passively diffuse into the renal medulla. Alcohol will inhibit the function of ADH, which means that the urine will be less concentrated because water is unable to leave the collecting duct, thus also increasing the volume.

Example Question #14 : Excretory Physiology

Diabetes insipidus occurs when the body is unable to secrete antidiuretic hormone (ADH). ADH acts on the collecting tubule of the kidney to allow for water reabsorption. The reabsorption of water will raise the blood volume and as a result, the blood pressure will also increase. Diabetes mellitus occurs when the blood glucose level is uncontrollably high. Normally when the blood glucose level is too high, the pancreas secretes insulin. Insulin reduces glucose levels because it allows the muscles and the liver to take in glucose from the circulatory system.

Which of following represent(s) common symptoms shared by the two diseases?

I. Frequent urination

II. Hyperglycemia

III. Glucose in the urine

Possible Answers:

I only

III only 

All of these

I and II

II and III

Correct answer:

I only

Explanation:

In diabetes insipidus, ADH is not available to reabsorb the water from the collecting tubule of the renal system. As a result, more fluid will be lost and frequent urination will occur. In diabetes mellitus the osmolarity of the blood is high due to a constant high concentration of glucose in the blood. Due to the increase in osmolarity, water will be drawn from the tissues and into the blood. When the blood reaches the kidneys, it will be filtered and result in more water in the urine. More water into the urine increases its volume and leads to frequent urination. Hyperglycemia and glucose in the urine only occurs in diabetes mellitus and not in diabetes insipidus. In diabetes insipidus, the problem is not the blood glucose level but the inability to secrete ADH. The term "diabetes" does not automatically mean a problem related to sugar.

Example Question #15 : Excretory Physiology

Which of the following functions does antidiuretic hormone (ADH) serve?

Possible Answers:

None of these

Increases water permeability of the collecting ducts

Induces vasoconstriction and increases blood pressure

All of the choices

Decreases water volume in the urine

Correct answer:

All of the choices

Explanation:

ADH is a hormone that increases permeability to water in the collecting ducts and therefore increases water reabsorption from the urine. This decreases the volume of water in the urine. Additionally, it can induce vasoconstriction in high concentrations, which narrows blood vessels and thereby increasing blood pressure. 

Example Question #16 : Excretory Physiology

The natural antacid that protects the intestines against stomach acid is produced by the ______ .

Possible Answers:

small intestine

stomach

pancreas

esophagus

liver

Correct answer:

pancreas

Explanation:

Parietal cells in the stomach release hydrochloric acid, activating pepsin and aiding in digestion. This creates a highly acidic environment in the stomach that could be harmful to other regions of the body. When the stomach contents, or chyme, is transported out of the stomach and enters the small intestine it must be neutralized. The first segment of the small intestine is the duodenum, where digestive enzymes from the pancreas are secreted to help digest fats and proteins.

Along with these enzymes, bicarbonate is secreted by the pancreas into the small intestine. The bicarbonate reacts with the remaining acid, producing water, salt, and carbon dioxide.

Example Question #17 : Excretory Physiology

What is the functional unit of the kidney?

Possible Answers:

A nephron

A neuron

A chief cell

A sarcomere

Correct answer:

A nephron

Explanation:

The functional unit of the kidney is the nephron. Blood is filtered into the nephron to create filtrate. As the filtrate flows through the nephron tubules, its concentration is tightly regulated and ions and water are added and removed. The end result is a highly-concentrated filtrate that is transported to the bladder for excretion.

Neurons are the functional unit of the nervous system, not the kidney. Sarcomeres are the basic contractile unit of skeletal muscle, and chief cells are specialized stomach cells that secrete digestive enzymes, such as pepsinogen.

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