Final-Chapter 18-19 Urinary System

Question 1

What are some functions of the kidneys?

Answer 1

The kidneys function to
1. Maintain H2O balance in the body(most important).
2. Maintain proper osmolarity of body fluids, primarily through regulating H2O balance.
3. Regulate the quantity and concentration of most ECF ions.
4. Maintain proper plasma volume.
5. Help maintain proper acid-base balance in the body.
6. Excreting (eliminating) the end products (wastes) of bodily metabolism.
The main purpose of the kidneys it to produce perfect blood.

Question 2

What is the urinary system?

Answer 2

The urinary system consists of:

1. Urine forming organs-kidneys
2. The structures that carry urine from the kidneys to the outside for elimination from the body-Ureters, Urinary bladder, and Urethra.

Question 3

What are ureters?

Answer 3

The Ureters is the smooth muscle-walled duct that xit each kidney and carry urine to the urinary bladder.

Question 4

What is the urinary bladder?

Answer 4

The Urinary Bladder is a hollow, distensible, smooth muscle-walled sac that temporarily stores urine. It periodically empties to the outside of the body through the urethra.

Question 5

What is the Urethra?

Answer 5

The urethra conveys urine to the outside of the body. The Urethra is straight and short in females, but in males it is much longer and follows curving course from bladder to outside. It serves a dual function in providing a route for eliminating urine from bladder, but also a passageway for semen from reproductive organs.

Question 6

What does Renal mean?

Answer 6

Renal means kidneys. Renal arteries carries blood from the heart to the kidney to be filtered. Renal vein carry blood away from kidney and to the heart.

Question 7

What s a nephron?

Answer 7

Nephron has two component:

1. A Vascular component: pertaining to blood vessels and carrying blood.
2. A Tubular component: is a hollow, fluid-filled tube formed by a single layer of epithelial cells. Filled with filtrate and used to carry urine.

The combined vascular and tubular component is the juxtaglomerular apparatus which produces substances involved in the control of kidney function. The Glomerulus is a ball of capillaries, part of vascular component and Bowmans capsule is surrounding the Glomerulus and is part of the Tubular component.

Question 8

What are the components of the vascular component?

Answer 8

The vascular component is composed of:

1. Afferent arterioles which carries blood to the glomerulus.
2. Glomerulus, a tuft of capillaries that filters a protein free plasma into the tubular component. Blood enters the glomerulus where it is filtered and it enters the bowmans capsule. It then moves to the proximal tubule.
3. Efernt arteriole which carries blood from the glomerulus.
4. Pertubular capillaries that supply the renal tissues involved in exchanges with the fluid in the tubular lumen.

The dominant part of the vascular component is the glomerulus- a ball of capillaries where water and solutes are filtered through glomerulus as blood passes through it.

Question 9

What are the components of the tubular component?

Answer 9

The tubular component is composed of:

1. Bowman’s capsule is responsible for collecting the glomerular filtrate.
2. Proximal tubule is where the uncontrolled reabsorption and secretion of selected substances occur.
3. The Loop of Henle establishes an osmotic gradient in the renal medulla that is important in the ability to produce urine of various concentrations. There is an descending and ascending limb.
4. Distal tubule and collecting is where the variable, controlled reabsorption of sodium and water and secretion of potassium and Hydrogen ions occur here. Fluid leaving the collecting duct is urine, which enter the renal pelvis.

Question 10

What is the main function of the kidneys?

Answer 10

The kidney is primarily responsible for maintaining stability of ECF (extracellular fluid-water, proteins, salts) volume, electrolyte composition, and osmolarity. This is the body’s main route for eliminating potentially toxic metabolic wastes and foreign compounds from the body.

Question 11

What four processes must occur to form urine?

Answer 11

1. Glomerular filtration.
2. Tubular reabsorption-leave urine (out of tubule) and gets reabsorbed into blood.
3. Tubular secretion-Things leaving blood and entering urine.
4. Concentration

Question 12

Why is only 20 percent of blood filtered at one time?

Answer 12

If all blood was filtered passing through the glomerulus, you would have a long line of blood waiting to be filtered and you wouldn’t have blood filtering through other organs. We cannot survive without more than a few ounces of blood.

Question 13

What is glomerular filtration?

Answer 13

Fluid filtered from the glomerulus into Bowman’s capsule pass through three layers of the glomerular membrane. During this step, almost everything that CAN be removed from the blood is removed. Filtrate, which will become urine, is formed in this process.

Question 14

What is tubular re-absorption?

Answer 14

Tubular re-absorption involves the transfer of substances from tubular lumen into peritubular capillaries. It is a highly selective and variable process that involves trans-epithelial transport. The reabsorbed substance must cross five barriers.
Must leave tubular fluid by crossing luminal membrane of tubular cell.
Must pass through cytosol from one side of tubular cell to the other.
Must cross basolateral membrane of the tubular cell to enter interstitial fluid.
Must diffuse through interstitial fluid.
Must penetrate capillary wall to enter blood plasma

Question 15

What five barriers must reabsorbed substances cross?

Answer 15

During tubular reabsorption, reabsorbed substance must cross five barriers:

1. Must leave tubular fluid by crossing luminal membrane of tubular cell.
2. Must pass through cytosol from one side of tubular cell to the other.
3. Must cross basolateral membrane of the tubular cell to enter interstitial fluid.
4. Must diffuse through interstitial fluid.
5. Must penetrate capillary wall to enter blood plasma.

During secretion these five steps occur in reverse.

Question 16

What is the difference between passive and active tubular reabsorption?

Answer 16

Passive reabsorption requires no energy for the substance’s net movement and occurs down electrochemical or osmotic gradients.
On the other hand, active reabsorption occurs if any one of the steps in transepithelial transport of a substance requires energy. Active transports movement occurs against electrochemical gradient. If any step requires energy all the steps require energy, i.e. the whole thing is active.

Question 17

Describe Sodium re-absorption .

Answer 17

A Na+/ K+ ATPase pump in basolateral membrane is essential for sodium reabsorption. Of total energy spent by kidneys, 80% is used for sodium transport. Sodium is not reabsorbed in the descending limb of the loop of Henle. Water follows reabsorbed sodium by osmosis which affects blood volume and blood pressure. Sodium reabsorption is active.

Question 18

What is the role of reabsorption in areas of the tubule.

Answer 18

In the proximal tubule 67 percent of sodium is reabsorbed that plays a role in reabsorbing glucose, amino acids, water, chlorine, and urea.

In the ascending limb of the loop of henle, 25 percent of sodium is absorbed that plays a critical role in the kidneys ability to produce urine of varying concentrations.

In the distal and collecting tubules 8 percent or sodium is absorbed and is variable and subject to hormonal control and also plays a role in regulating ECF volume.

Question 19

How is glucose and amino acids re-absorbed.

Answer 19

Glucose and amino acids are reabsorbed by sodium-dependent, secondary active transport. The re-absorption of water into the blood surrounding the proximal tubule increases the concentration of urea inside the tubule, as water is lost from the tubule. This produces a concentration gradient for urea from the tubule into the interstitial fluid. The process of reabsorbing water, glucose, and amino acids back into our blood also means reabsorbing a little urea.

Question 20

Describe the process of passive re-absorption of urea at the end of the proximal tubule.

Answer 20

Sodium and water is being absorbed back into the blood stream at the beginning of the proximal tubule. So by the end of the proximal tubule the concentration of urea has built up in the proximal tubule and passive transport of some urea occurs back into the blood stream.

Question 21

What is tubular secretion?

Answer 21

Tubular secretion is the transfer of substances from peritubular capillaries into the tubular lumen. It involves trans-epithelial transport where the steps are reversed. Kidney tubules can selectively add some substances to the filtrate. Tubular secretion gets rid of anything we have extra of including ions and water.

Question 22

What are the most important substance secreted into the tubules?

Answer 22

Most important substances secreted into the tubules are:

1. H ions which areI important in regulating acid-base balance and is secreted in proximal, distal, and collecting tubules.
2. Potassium ions keeps plasma potassium concentration at appropriate level to maintain normal membrane excitability in muscles and nerves and is secreted only in the distal and collecting tubules.
3. Organic ions are secreted only in the proximal tubule.

Question 23

Give a summary of what happens in the nephron.

Answer 23

1. Filtration: Water and small dissolved substances removed from glomerular capillaries. Filtrate collected in Bowman’s capsule.
2. Tubular re-absorption: In the proximal tubule, sodium, water, and nutrients are transported from the filtrate to the blood.
3. Secretion: Occurs in the proximal and distal tubule and actively moves H+, K+, some drugs, and organic ions from the blood back into the filtrate.
4. Concentration: Maintenance of a large osmotic gradient around the Loop of Henle allows for water to be retained and urine to become highly concentrated.

Question 24

What happens in the loop of henle?

Answer 24

1. Descending limb is highly permeable to water, but not to NaCl. As filtrate flows down, water leaves the tubule as the osmolarity of the extracellular fluid increases. Loss of water increases the osmolarity of the filtrate. At the bottom of the loop, the concentration of the filtrate and the extracellular fluid is equal (1200 mOsm).
2. Ascending limb is impermeable to water, but permeable to NaCl. As highly concentrated filtrate flows up, NaCl diffuses, then is actively transported out of the tubule. But water does not follow. Filtrate becomes more dilute than extracellular fluid.

This gives the body an opportunity to regain water if we need to at distal tubule and collecting duct. We do this by inserting protein channels into Distal tubule membrane called aquaporins. The aquaporins allow water to leave tubule, although it is not usually permeable to water.

Question 25

What is the purpose of the Loop of henle?

Answer 25

The purpose of the loop of henle is to maintain sodium gradient outside the distal tubule and regain water if needed.

Question 26

What is the role of vasopressin?

Answer 26

Vasopressin-controlled, variable water re-absorption occurs in the distal tubule and the collecting duct. 65 percent of water re-absorption is obligatory in the proximal tubule. In the distal tubule and collecting duct it is variable, based on the secretion of ADH (anti-diuretic hormone / vasopressin).
The secretion of vasopressin increases the permeability of the tubule cells in the distal tubule and collecting duct to water by inserting aquaporins. An osmotic gradient exists outside the tubules for the transport of water by osmosis.
Vasopressin is produced in the hypothalamus and stored in the posterior pituitary. The release of this substance signals the distal tubule for the re-absorption of water.
During a water deficit, the secretion of vasopressin increases. This increases water re-absorption. Alcohol is a vasopressin inhibitor (frequent urination)
During an excess of water, the secretion of vasopressin decreases. Less water is reabsorbed. More is eliminated. For every 250 mLs of alcohol consumed, your body eliminates about 1,000 mLs of water in your urine.