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Chapter 18: The Urinary System
Terms in this set (31)
List the three steps involved in performing a urinalysis
The three major steps in a urinalysis are:
a. A gross examination of the physical properties of the sample.
b. A chemical analysis of substances dissolved in the urine.
c. A microscopic examination of the solid components in the urine.
What are the six structures that make up the urinary system?
Two kidneys, two ureters, one urinary bladder, and one urethra
Nitrogenous waste materials from protein breakdown are eliminated from the body primarily as what?
Name one hormone whose release is regulated by the kidney, one hormone that directly affects kidney function, and one hormone produced by the kidney.
The release of antidiuretic hormone is regulated by the kidneys, aldosterone directly affects kidney function, and erythropoietin is produced by the kidneys.
What is the difference between the hilus of the kidney and the renal pelvis?
The hilus is the area on the medial side of each kidney where blood and lymph vessels, nerves, and the ureter enter and leave the kidney.
The renal pelvis is inside the hilus and is a urine collection chamber at the beginning of the ureter.
What is meant by the term retroperitoneal?
Retroperitoneal means outside of the abdominal cavity, between the parietal peritoneum and the dorsal abdominal muscles.
List, in order, the parts of the nephron. Indicate whether each specific part is found in the cortex or the medulla of the kidney.
1. Renal corpuscle (cortex)
2. Proximal convoluted tubule (cortex)
3. Loop of Henle (medulla and cortex)
4. Distal convoluted tubule (cortex)
What is the difference between glomerular filtrate and tubular filtrate?
Glomerular filtrate is the fluid that leaves the glomerular capillaries and enters the capsular space. It is similar to plasma, but without proteins. It contains waste products that need to be cleared from the body, as well as important substances that the body needs, such as sodium, potassium, calcium, magnesium, glucose, amino acids, chloride, bicarbonate, and water. Glomerular filtrate enters the proximal convoluted tubule and is termed tubular filtrate, which travels through the tubular part of the nephron. The important substances are reabsorbed from the tubular filtrate back into the body along with some urea. The body eliminates some waste products by secreting them into the tubular filtrate. Examples include hydrogen, potassium, ammonia, and some drugs.
What is the function of the brush border on the epithelial cells of the proximal convoluted tubule?
The brush border increases the cellular surface area exposed to the fluid in the tubule by a factor of about 20. This is especially important to the PCT's reabsorption and secretion functions.
How does the blood in the efferent glomerular arteriole differ from the blood in the afferent glomerular arteriole?
Blood in the afferent glomerular arteriole of the kidney gives up all of the small molecules that can fit easily through fenestrations in the glomerulus. These include electrolytes, bicarbonate, glucose and water.
Consequently, the blood of efferent glomerular arterioles is composed of large molecules such as proteins and blood cells including platelets. An exception is oxygen, which is not given up by the red blood cells until the blood has entered the efferent arteriole. Here oxygen nourishes the cells of the nephron. Ultimately, the valuable electrolytes, buffers, glucose and water needed by the body are resorbed by the nephron and put back into the blood stream.
What is the difference between tubular reabsorption and tubular secretion?
The glomerular filtrate contains substances found in plasma that the body doesn't want to lose because it needs them to maintain homeostasis. Tubular reabsorption involves removing these substances from the tubular filtrate. The useful substances are reabsorbed from the tubules into the peritubular capillaries.
Many waste products and foreign substances are not filtered from the blood in sufficient amounts from the glomerular capillaries. The body still needs to get rid of these substances, so it transfers them from the peritubular capillaries into the tubular filtrate in the tubules to be eliminated in urine.
How does ADH deficiency affect urine volume? What is the mechanism?
Insufficient ADH will increase urine volume. ADH acts on the distal convoluted tubules to promote water reabsorption into the body. If ADH is absent, water will not be reabsorbed and will be lost in urine.
What is the mechanism by which glucose and amino acids are reabsorbed out of the proximal convoluted tubule and back into the body?
As the glomerular filtrate enters the lumen of the PCT, sodium is actively pumped out of the fluid and back into the bloodstream. Sodium in the tubular filtrate attaches to a carrier protein that carries it into the cytoplasm of the PCT epithelial cell. The transfer of sodium from the tubular lumen into the epithelial cell requires energy. At the same time glucose and amino acids attach to the same protein as sodium and follow the sodium into the epithelial cell by passive transport. Glucose and amino acids passively diffuse out of the tubular epithelial cell into the interstitial fluid and then into the peritubular capillaries.
Explain the concept of the renal threshold of glucose.
The renal threshold of glucose is the amount of glucose that can be reabsorbed by the proximal convoluted tubules. If the blood glucose level gets too high, the amount of glucose that is filtered through the glomerulus exceeds the amount that can be reabsorbed (the renal threshold) and the excess is lost in urine. Fortunately, the renal threshold exceeds the normal amount of glucose found in blood, so 100% of the glucose filtered through the glomerulus is reabsorbed back into the body, and no glucose is lost in the urine. However, in pathologic conditions such as uncontrolled diabetes mellitus, where blood glucose levels can be extremely high because of insufficient insulin production, the amount of glucose filtered through the glomerulus exceeds the limit that can be reabsorbed by the PCT.
Explain why proteinuria occurs with renal failure.
In a normal kidney, large molecules such as protein are too big to fit through glomerular fenestrations and are retained in blood. During some types of kidney disease, the glomerulus is damaged, resulting in enlarged fenestrations and protein passing through them into urine.
Why are clinical signs of renal failure not observed until the disease process is advanced?
There are often no clinical signs of chronic renal failure until 65% to 75% of the nephrons in both kidneys are nonfunctional. For this reason, long-term kidney disease is often not detected until very late in the disease.
Diabetes insipidus gets its name from what physical characteristic of urine produced by patients with this disease?
The word insipid means tasteless. The disease diabetes insipidus was given its name because clinically it looked similar to diabetes mellitus, but the urine was "tasteless" rather than sweet because it didn't contain glucose.
How do the kidneys respond to a decrease in blood pressure?
When blood pressure falls, the juxtaglomerular cells within the renal cortex release an enzyme called renin. Renin causes the formation of angiotensin I from angiotensin. Angiotensin I is subsequently converted to angiotensin II by another enzyme, angiotensin converting enzyme (ACE). Angiotensin II causes the arteries in the body to constrict. It also causes and the release of aldosterone from the adrenal gland, which is located near the kidney. Aldosterone stimulates the kidney to reabsorb sodium and water back into the bloodstream, which increases both blood volume and blood pressure.
Why is it important that the ureters have an inner lining of transitional epithelium?
The transitional epithelium allows the ureters to stretch as urine is passed through them on its way to the urinary bladder.
What prevents urine from backing up into the ureters when the bladder wall contracts to expel urine?
The ureters enter the urinary bladder at such an oblique angle that when the bladder is full it collapses the opening of the ureter, preventing urine from backing up into the ureter. However, it doesn't prevent more urine from entering the bladder, because the strength of the peristaltic contractions is enough to force the urine through the collapsed opening into the urinary bladder.
The ureter is continuous with what structure in the kidney (except in cattle)?
The renal pelvis
How does the bladder know when to empty itself?
The urinary bladder constantly accumulates urine until the pressure of the filling bladder reaches a certain "trigger" point that activates stretch receptors in the bladder wall. When the trigger point is reached, a spinal reflex is activated that returns a motor impulse to the bladder muscles. The muscles of the bladder wall contract. These contractions are responsible for the sensation of having to urinate. In animals that are not housebroken, emptying of the bladder will occur at this point.
What part of the urinary bladder is under voluntary control and allows an animal to be housebroken?
The muscular sphincter around the neck of the bladder
Does urine production stop when the urinary bladder is full?
No, the kidneys continue to produce urine regardless of the volume of urine present in the bladder.
Besides its urinary function, what other function does the urethra play in a male animal?
In males the urethra also has a reproductive function. The vas deferens and accessory reproductive glands enter the urethra as it passes through the pelvic canal. Here spermatozoa and seminal fluid are discharged into the urethra during ejaculation and pumped out as semen. At the beginning of ejaculation the sphincter at the neck of the urinary bladder closes, preventing semen from entering the bladder and mixing with urine.
How much kidney function must be destroyed before clinical signs of renal dysfunction become evident?
Two thirds of the total nephrons in both kidneys must be nonfunctional before clinical signs of renal dysfunction start to become evident.
Explain the difference between prerenal uremia and postrenal uremia.
Prerenal uremia is associated with decreased blood flow to the kidneys and may be caused by conditions such as dehydration, congestive heart failure, or shock if these conditions are left untreated. In these cases the kidneys are functioning normally but not enough blood is reaching them, so waste materials can't be adequately removed.
Postrenal uremia is usually associated with an obstruction that prevents urine from being expelled from the body. Tumors, blood clots, or uroliths (stones) can cause the obstruction. Eventually urine backs up into the kidney pelvis and then into the nephrons, increasing pressure in the nephrons and causing nephron damage.
What is a urolith?
A stone anywhere in the urinary system (kidneys, ureters, urinary bladder, or urethra)
Name two conditions that can predispose an animal to urolith production.
Diet and the presence of certain bacteria associated with urinary tract infections can influence the pH of urine to favor the precipitation of crystals and, eventually, uroliths. A housebroken animal that must consistently hold its urine for long periods of time has a decreased crystal transit time through the lower urinary tract (bladder and urethra) and is predisposed to urolith production.
How do uroliths in cats differ from uroliths in other species?
They are much smaller and resemble sand rather than large stones.
What is the chemical composition of a struvite crystal?
Struvite crystals are composed of magnesium, ammonium, and phosphate.
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