Urinary Flashcards
The urinary consists of 4 parts of the body. What are the 4 parts and what are each of their functions?
- Kidneys - Form Urine
- Ureters - Transport Urine
- Urinary Bladder - Store Urine
- Urethra - Carries Urine to Outside of Body
What are some of the major functions and characteristics of the kidneys? (There are 4 of them)
- Regulates composition of body fluids (i.e., water balance)
- Rids body of wastes of metabolism
- Removes foreign chemicals, drugs and food additives
- Minor endocrine organs (i.e., renin-angiotensin system and erythropoietin)
Where are the kidneys located in the body?
Either side of vertebral column in abdominal cavity between 12th and 3rd lumbar vertebrae.
What is the outer portion of the kidney called and what does it contain?
- Renal Cortex
2. Contains capillary tufts and convoluted tubules
What is the inner portion of the kidney called and what is it composed of?
Renal Medulla
Composed of a series of triangular masses (renal pyramids) which are separated by renal columns.
What are the symptoms of acute renal failure?
A sudden loss of kidney function, usually associated with shock or intence renal vasoconstriction. It can last for several days to a long as weeks
What is cystitis?
Inflammation of the urinary bladder
What is hemoturia?
Blood in the urine
What is Hemodialysis?
It is a method of clearing waste products from the blood in which blood passes by the semipermeable membrance of the artificial kidney and waste products are removed by diffusion
What is nocturia?
“night urination” or during sleep
What is oliguria?
the condition of having urinary volumes of less than 500 ml/day
What is plyuria?
Excessive urine output
What is uremia?
The retention of urinary constituents in the blood, owing to kidney dysfunction
What are the six parts of the nephron?
The Glomerulus Bowman's Capsule (glomerular capsule) Proximal Convoluted Tubule Loop of Henle (Nephron Loop) Distal Convoluted Tubule Collecting Duct
About how many nephrons are there per kidney?
Over 1 million
True or false: One collecting duct can serve several nephrons
TRUE
Describe the make-up a the glomerulus
A network of 50 capillaries with many circular fenestrations (pores)
Why is the glomerulus more permeable than typical capillaries and by how much?
The pores have a diameter of 50-100 nm.
100-1000 times more permeable
Describe the Bowman’s capsule (glomerular capsule)
It is a double-walled cuplike structure composed of squamous epithilium.
What is the difference between the inner and out layers of epithelium in the glomeruluar capsule?
The outer layer is continuous with the epithelium of the proximal tubule whereas the innter layer is composed of modified cells called podocytes that are closely associated with the glomerular capillaries
What is unique about the proximal convoluted tubule?
It is continuous with the epithelium of the glomerular capsule and consists of a single layer of cuboidal cells containing microvilli to greatly increase the surface are
What the nephron loop composed of?
A descending and ascending thin limb and an ascending thick portion.
The thin segments are lined with flat squamous cells without microvilli
The cubodial cells in the thick segment also lack microvilli
Where is the thick segment of the nephron loop located?
It runs between the afferent and efferent arterioles
What is the macula densa?
A mass of specialized epithelial cells of the tubule wall located next to the afferent arteriole
True or false: The distal convoluted tubule is longer than the proximal convoluted tubule
FALSE- the distal convoluted tubule is shorter than the proximal convoluted tubule and contains fewer microvilli
Where is the distal convoluted tubule located?
It starts at the macula dens and terminates as it empties into the collecting duct.
It is the last segment of the nephron
Why does the proximal convoluted tubule have a lot of mitochondria?
Because is uses active transport which requires a lot of energy
What are the three major functions of the nephron?
1) Glomerular Filtraion
2) Tubular Reabsorption
3) Tubular Secretion
What is the portion of the blood plasma that enters the glomerular capsule?
Glomerular Filtrate
How much glomerular filtrate enters the glomerular capsule each day?
180 L (45 gallons)
What two mechanisms cause 180 L of fluid to be filtered each day in the glomerular capsule?
1) The high hydrostatic pressure of the blood (45 to 60 mmHg) in the glomerulus
2) The large numbers of pores, which are larger than most pores in blood capillaries
What substances in the blood are present in the glomerular filtrate?
Water, electrolytes, glucose, amino acids, urea, hormones, and vitamins
Why are RBC’s, WBC’s, and platlets excluded from passage in the glomerular filtrate?
Because of their large size
What does the presence of RBC’s or protein in the urine indicate?
It indicates that the hydrostatic pressure in the glomerular capillaries is excessively high or that there is a defect in the glomerular
What is the average glomerular filtration rate (GFR) per minute? Per hour? Per day?
120 ml per minute or
7.5 L per hour or
180 L per day
What two mechanisms regulate GFR via vasoconstriction or vasodilation?
Extrinsic (sympathetic nerves) and
Intrinsic (locally produced chemicals)
How do you measure GFR?
Multiply urine volume by inulin concentration in urine.
Then divide both by inulin concentration in plasma
What is inulin?
A polymer of fructose that is extracted from plants
What is tubular reabsorption?
The transfer of fluid and solutes out of the lumen of the nephron through the interstitial space and into the peritubular capillaries
In comparison to how much glomerular filtrate is produced, how much do the kidneys normally excrete?
180 L/day is produced
only 1 to 2 L of urine is excreted
How much filtrate is reabsorbed from the renal tubules?
99%
How is urine volume regulated?
According to the needs of the body
True or false: tubules have a high reabsorptive capacity for substances needed in the body.
True. But tubules have little or no reabsorptive capacity for substances of no vlaue
Why are essential substances sometimes still secreted in the urine?
When there is an excess amoung present, like glucose or electrolytes for example
Large percentages of what are present in the urine?
Filtered waste products
What is the primary location of tubular reabsorption?
In the proximal convoluted tubule, though it occurs throughout the renal tubules
What is the term that describes the transport of substances?
trans-epithelial transport
What are the two primary modes of transport used to absorb specific substances?
1) diffusion- no energy required
2) active transport- requires energy
Of the Na+ that is filtered, how much is normally reabsorbed? And how much in the different sections of the nephron?
99.5% overall
67% in the proximal tubule
25% in the loop of Henle
8% in the distal tubule
What hormone regulates the reabsorption of Na+ in the distal and collecting ducts?
Aldosterone
Under normal conditions, how much glucose filtered is reabsorbed?
100%
What method of transport is used to filter glucose?
Carrier-mediated transport, which requires energy
What is the normal glucose concentration in the plasma?
100 mg of glucose/100 ml of plasma
What is the property of saturation and what substance commonly displays it?
It can only carry a certain amount at once
Glucose displays this property
What the Transport maximum (Tm)?
The concentration of transported molecules needed to saturate the carriers and thus achieve maximal transport rate
What is the Tm for glucose?
375 mg/minute filtered
What happens to glucose above the Tm?
It will not be reabsorbed and will appear in the urine. This mainly occurs in diabetics
What is the Law of the Kidney?
Filtration (calculated mg/min) - reabsorption+secretion (375 mg/min)= excretion in urine (mg/min)
Of the fluid going through the nephron, how much is reabsorbed in the proximal convoluted tubule?
the nephron loop?
the distal convoluted tubule?
the collecting duct?
Proximal- 80%
Nephron loop- 6%
Distal- 9%
Collecting- 4%
Which portions of the nephron are under ADH control?
Distal convoluted tubiles and collecting duct
What percent of urea is excreted in the urine?
50%
What percent of phenol is reabsorbed?
0%; all 100% is excreted in the urine
Define tubular secretion
The secretion of movement of substances from the peritubular capillaries into the lumen of the tubule.
This is a mechanism to selectively move substanves into the lumen for excretion in the urine.
In tubular secretion does transepithelial transport move fluids into or out of the tubule?
What about in tubular reabsorption?
Into the tubule in secretion
Out of the tubule in reabsorption
What are the three most important substances secreted by the tubules?
H+
K+
organic anions- food additives, pesticides, penicillin and other drugs
Why is H+ so important for secretion?
H+ regulates acid-case balance. The extent of H+ secretion depends on how acidic the body is and H+ can be secreted in all tubular regions
Where is K+ secreted and where is reabsorbed?
Secreted in the distal tubiles and collecting duct
Reabsorbed in the proximal tubule
Which hormone stimulates K+ secretion which is coupled with Na+ reabsorption?
Aldosterone
True or false: The amount of H+ secreted is independent of the amount of bicarbonate reabsorbed
False: The amounts of H+ secreted and bicarbonate reabsorbed are interdependent. The reabsorption of bicarbonate occurs as a result of the filtration and secretion and H+
What is acidosis?
The ration of CO2 to HCO3- in the extracellular fluid is increased because of the production of CO2 or an increase in the H+ formation from metabolism.
What is the renal response to acidosis?
1) increased amounts of CO2 enter the tubular cells from the extracellular fluid
2) increased amounts of H+ secreated into the lumen of the nephron; some combines with the HCO3- and one Na+ is reabsorbed for each H+ secreted
3) HCO3- in the lumen of the nephron is reabsorbed into the extracellular fluid.
The net result is that H+ ions are exreted in the urine and Na+ and HCO3- ions are retained
What is alkalosis?
The ration of HCO3- increases as the pH rises
What is the renal response to alkalosis?
1) decreased amounts of CO2 enter the tubular cells from the extracellular fluid
2) decreased amounts of H+ are secreted into the lumen of the nephron; with less H+ to combine with HCO3-, less HCO3- is reabsorbed.
The net result is that H+ ions are retained and bicarbonate ions are excreted.
The kidneys keep the pH of the blood between what two values?
7.37 and 7.45
What are the two major mechanisms that kidneys use to regulate the concentration of urine?
1) Producing osmotic gradient between the tubular lumen and the surrounding interstitial fluid
2) Amount of ADH secreted from the posterior pituitary
At normal fluid balance and solute concentration, what is the value at which body fluids are isotonic?
300 millosmols/liter
True or false: The osmolarity of the interstitial fluid throughout the renal cortex is equal to the osmolarity of the fluid in the renal medulla.
FALSE: The osmolarity is 300 mosm/L in the renal cortex, but the it increases progressively until it reaches the deepest regions of the medulla and reaches an osmolarity of 1200 to 1400 mosm/L
In most basic terms, what are the six mechanisms that cause the osmolarity to increase deep in the renal medulla?
1) Ascending limb transports Cl, Na+, K+ into the medullary insterstitium
2) Ascending limb is impermeable to water
3) Fluid in the ascending limb becomes more dilute
4) Urea passively diffuses into the interstitium
5) Peritubular capillaries function as countercurrent exchanges
6) Capillary circulation carries only a minute amount of medullary interstitial solutes away from the renal medulla
What hormone plays a major role in the regulation of the final urine concentration?
ADH
What is the effect of having low levels of ADH?
The distal tubules and collecting ducts become impermeable to water and despite the high osmotic gradient, little water is pulled out into the medulla
When there are low levels of ADH, how dilute can the concentration of urine get?
100 mosm/L
What is considered highly concentrated urine?
1200 mosm/L
What is the effect of high levels of ADH?
The distal tubule and collecting ducts become highly permeable to water, which is pulled by the high osmotic gradient into the interstitium. There is a small amount of urine, but it is very concentrated
What is the definition of plasma clearance analysis?
The ability of the kidneys to “clear” the plasma of substances in a specific length of time (usually ml/min)
What percentage of filtrate fluid is reabsorbed along the tubular system?
99%
True or false: The concentration of cleared (removed) substances from the plasma in the renal veins leaving the kidneys is higher than the concentration in the blood entering the kidneys in the renal artery.
FALSE: The concentration is LOWER in the renal veins leaving the kidneys than in the blood entering the kidneys in the renal artery
How do you find volume of cleared plasma per minute?
Clearance in ml/min= (UxV)/ P
U= concentration of the substance in 1 ml of urine
V= volume of urine formed per minute
P= concentration of the substance in 1 ml of plasma
How much plasma is filtered per minute?
GFR= 120 ml/min (determined by the inulin clearance rate)
What causes the GFR to be less than 120 ml/min?
If a substance is filtered and reabsorbed but not secreted, its plasma clearance rate is always less than the GFR
What causes the GFR to be greater than 120 ml/min?
If a substance is filtered and secreted but not reabsorbed
True or false: If the amount of a substance in the urine is less than the amount that is filtered in the same time, then tubular reabsorption has taken place.
TRUE
True or false: If the amount of a substance excreted in the urine is greater than the amount that is filtered at the same time, tubular reabsorption has taken place.
FALSE! Tubular secretion has taken place is the amount excreted is greater than the amount filtered
What part of the nephron produces and secretes renin?
Juxtaglomerular apparatus
Where is the juxtaglomerular apparatus located?
Where the distal concoluted tubule makes contact with the afferent arteriole near Bowman’s capsule
What causes the release of renin?
Either a decrease in blood volume or blood pressure in the afferent arteriole sensed by juxtaglomerular cells or
An increase in sodium chloride concentration of fluid in the distal tubules sensed by the macula densa
What is the macula densa?
The wall of the distal tubule
What is the blood pressure in the glomerulus capillaries?
45-60 mm Hg
What percent of glomerula filtrate of fluid is reabsorbed?
99%
What percent of water is reabsorbed under the control of ADH?
13%
Osmotic concentration is highest in the what?
MEDULLA
The ascending limb of the NEPHRON is impermeable to what?
H2O (WATER)
If a substance is filtered and secreted, but NOT reabsorbed, its plasma clearance rate is always what?
GREATER THAN THE GFR (GLOMERULAR FILTRATION RATE)
Cystisis is what?
INFLAMMATION OF THE URINARY BLADDER
The cells that form the inner layer of Bowman’s capsule that hold the capillaries in place are called what?
PODOCYTES
The ‘Transport Maximum’ (TM) for GLUCOSE in the ‘proximal tubule’ is what?
375 mg/minute
When the body is in a state of ACIDOSIS the kidneys will do what?
SECRETE MORE H+
RETAIN HCO3-
