英文题 第八章 （2006. 3. 23）
Ⅰ. 选择题
1. The main difference between primary urine and blood plasma is: D
A. Glucose concentration.
B. Crystal osmotic pressure.
C. NaCl concentration.
D. Plasma protein concentration.
E. pH value.
2. Site of renin secretion is at A
A. Juxtaglumerular cells.
B. Extraglomerular mesangial cells.
C. Juxtaglomerular apparatus.
D. Macula densa.
E. Glomerular capillary
3. Macula densa is a A
A. Chemical receptor.
B. Baroreceptor.
C. Stretch receptor.
D. Volume receptor.
E. Osmoreceptor.
4. Characteristic of renal blood circulation is: A
A. Double capillary beds.
B. Low capillary hydrostatic pressure.
C. High peritubular capillary hydrostatic pressure.
D. Smaller blood flow of renal cortex.
E. Greater blood flow of renal marrow (medulla).
5. Which of the following descriptions about urine of a normal adult is true ? D
A. Daily urine quantity is 2 to 3 L/ day.
B. Its osmotic pressure is equal to that of plasma.
C. It contains a large amount of NaCl.
D. Urine does not contain glucose.
E. Urine contains protein.
6. Which of the followings can increase the glomerular filtration rate ? C
A. Arterial blood pressure rises from 80 to 180 mmHg.
B. Arterial blood pressure declines from 180 to 80 mmHg.
C. A large amount of normal saline is given intravenously.
D. Excitation of sympathetic nerve.
E. Constriction of afferent arteriole.
7. The driving force for glumerular filtration is: A
A. Glomerular capillary hydrostatic pressure.
B. Arterial blood pressure.
C. Plasma colloid osmotic pressure.
D. Bowman’s capsular hydrostatic pressure.
E. Blood pressure of efferent arteriole.
8. The main barrier of glomerular filtration membrane is located on B
A. Capillary endothelial cell layer.
B. Basement membrane.
C. Visceral epithelial cell (“foot cell ” or podocyte) layer.
D. Parietal epithelial cell layer.
E. Negatively charged elements of capillary endothelial cell layer.
9. If some diseases damage the negatively charged elements of glomerular membrane, which of the following will occur ? B
A. Glomerular filtration rate increases.
B. Proteinuria (protein in urine).
C. Hematuria ( hematuresis or blood in the urine).
D. Renal blood flow increases.
E. Plasma protein concentration increases.
10. Glucose concentration of the ultrafiltrate (primary urine) is: A
A. Similar to blood plasma.
B. Higher than that of plasma.
C. Lower than that of plasma.
D. Similar to urine.
E. Similar to tubular fluid in distal tubule.
11. Normally, which of following substances can not move through (pass across or penetrate) glomerular filtration membrane? A
A. Plasma protein
B. Glocose
C. Creatinin
D. urea
E. Inulin
12. When noradrenaline (norepinephrine ) is given intravenously, the main cause of urine quantity decreasing is: B
A. Boeman’s capsule hydrostatic pressure increases.
B. Renal arteriole constricts.
C. Release of ADH increases.
D. Release of renin decreases.
E. Release of aldosterone decrease.
13. Which of the following descriptions about glomerular filtration membrane is wrong? E
A. It consists of capillary endothelium, basement membrane, and epithelial cell.
B. It is quite porous.
C. It is structural base of glomerular filtration.
D. The basement membrane is major barrier for plasma protein.
E. The negatively charged protein move easily through the filtration membrane.
14. If reabsorption of renal tubule and collecting duct to water decreases 1%, the quantity of urine will increase D
A. 1%
B. 2%
C. 50%
D. 100%
E. 300%
15.Which of the following descriptions about the reabsorption of Na+ and Cl- at the proximal
tubule is wrong? E
A. The intracellular Na+ are transported by Na+ - K+ pump to interstitial fluid
B. The process by which Na+ move from tubular fluid into cell is passive transport.
C. In second half of proximal tubule, Na+ and Cl-diffuse from tubular lumen into intercellular fluid mainly via the tight junction.
D. The first half of proximal tubule does not reabsorb Cl- .
E. It is regulated by aldosterone
16. Proximal tubule of kidneys reabsorbs C
A. 85% of filtrated water.
B. 85% of filtrated Na+.
C. 65~70% of filtrated Na+ and water.
D. 65~70% of filtrated glucose.
E. 65~70% of filtrated HCO3-.
17. Location reabsorbing glucose is at: A
A. Proximal tubule.
B. Descending limb of Henle’ loop.
C. Ascending limb of Henle’ loop.
D. Distal convoluted tubule.
E. Collecting duct.
18. Normally, proximal tubule reabsorbs: E
A. 20% of filtrated glucose.
B. 50% of filtrated glucose.
C. 65~70% of filtrated glucose.
D. 80% of filtrated glucose.
E. 100% of filtrated glucose.
19. The reason for that the filtration occurs only in afferent
arteriole end of the glomerular capillary is: B
A. Blood pressure at the efferent arteriole end of glomerular capillary is low
B. Plasma colloid osmotic pressure gradually increases along the glomerular capillary
C. Plasma crystal osmotic pressure gradually decreases along the glomerular capillary
D. Plasma crystal osmotic pressure gradually increases along the glomerular capillary
E. Hydrostatic pressure in Bowman’s capsular gradually increases
20. Key dynamic of the solute and water reabsorption at the proximal tubule is: A
A. Na+-K+ pump
B. Carbonic anhydrase
C. Concentration gradient
D. Potential gradient
E. Osmotic pressure gradient
20. Site that is high permeable to water and impermeable to Na+ and Cl- is C
A. Ascending limb thick segment of Henle’ s loop
B. Ascending limb thin segment of Henle’ s loop
C. Descending limb thin segment of of Henle’s loop
D. Descending limb thick segment of of Henle’s loop
E. Distal convoluted tubule
21. Site that can actively reabsorb Na+, Cl- and K+ but is impermeable to water is: A
A. Ascending limb thick segment of Henle’ s loop
B. Ascending limb thin segment of Henle’ s loop
C. Descending limb thin segment of of Henle’s loop
D. Descending limb thick segment of of Henle’s loop
E. Collecting duct
22. Site that is high permeable to urea is: D
A. Distal convoluted tubule
B. Cortical segment of collecting duct
C. Outer medullary segment of collecting duct
D. Inner medullary segment of collecting duct
E. Descending limb thin segment of of Henle’s loop
23. Cause of polyuria (quantity of urine increases) in patient with diabetes mellitus mainly is: C
A. Glumerular filtration rate increases
B. Colloid osmotic pressure of plasma decreases
C. Osmotic pressure of tubular fluid increases
D. Crystal osmotic pressure of plasma increases
E. Secretion of ADH decreases
24. Location in which Na+ is passively reabsorbed is: B
A. The first half of proximal tubule
B. The second half of proximal tubule
C. Ascending limb thick segment of Henle’ s loop
D. Distal convoluted tubule
E. Collecting duct
25. Mechanism forming osmolarity gradient in the outer medulla mainly is A
A. NaCl reabsorption in the ascending limb thick segment of Henle’ s loop
B. Urea circulation
C. NaCl reabsorption in the descending limb thin segment of of Henle’s loop
D. NaCl reabsorption in the descending limb thick segment of of Henle’s loop
E. Urea reasorption in the ascending limb thick segment of Henle’ s loop
26. Which of the following descriptions about H+ secretion is wrong ? D
A. Proximal tubule secretes H+ by H+-Na+ exchange (antiport of H+ and K+)
B. Intercalated cell in distal tubule and collecting duct secretes H+ via proton pump( H+- ATPase)
C. Intercalated cell distal tubule and collecting duct secretes H+ via H+-K+ ATPase
D. When pH value of internal environment lowers, the activity of carbonic anhydrase decreases
E. H+ secretion promotes the reabsorption of HCO3- and the secretion of NH3
27. Which of the following descriptions about NH3 secretion is wrong D
A. NH3 derives mainly from the deamination of glutamine
B. NH3 is a lipid-soluble weak base
C. NH3 diffuses readily from epithelial cell into tubular fluid
D. NH3 secretion inhibits H+ secretion
E. NH3 secretion promote the reabsorption of HCO3-
28. Which of the following description about K+ secretion is wrong D
A. K+ in end-urine derives mainly from the secretion of distal convoluted tubule and collecting duct.
B. Principal cells secrete K+
C. Aldosterone promotes K+ secretion
D. Antidiuretic hormone inhibit K+ secretion
E. K+ secretion is a passive transport
29. Location in which the glomerulotubular balance occurs is: A
A. Proximal tubule.
B. Descending limb of Henle’s loop.
C. Ascending limb of Henle’s loop.
D. Henle’s loop.
E. Distal convoluted tubule and collecting duct.
30. Which of the following factors does not concerned with the osmotic diuresis E
A. Increased solute concentration of tubular fluid.
B. Hyperosmotic glucose solution is given intravenously.
C. Mannitol is given intravenously.
D. Diabetes mellitus
E. Diabetes insipidus
31. Location in which water is regulatory reabsorbed is in: E
A. Proximal tubule
B. Descending limb of Henle’s loop
C. Ascending limb of Henle’s loop
D. Henle’s loop
E. Distal convoluted tubule and collecting duct
32. Normally, hormone regulating the reabsorption of water is: D
Normally, hormone maintaining the water balance of body is D
A. Renin
B. Adrenaline (epinephrine)
C. Angiotensin Ⅱ
D. ADH ( antidiuretic hormone)
E. Aldosterone
33. Normally, the Na+ reabsorption and K+ secretion are regulated by: E
Normally, hormone maintaining the Na+ and K+ balance is: E
A. Renin
B. Adrenaline (epinephrine)
C. Angiotensin Ⅱ
D. ADH ( antidiuretic hormone)
E. Aldosterone
34. After drinking a large amount of water, the reason for increased quantity of urine is that: C
A. Glomerular filtration rate increases
B.. Aldosterone secretion decreases
C. ADH secretion decreases
D. Arterial blood pressure rises
E. Plasma colloid osmotic pressure decreases
35. After a large amount of sweating, the cause resulting in the decreased quantity of urine is that: C
A. Plasma crystal osmotic pressure declines
B. Plasma colloid osmotic pressure elevates
C. ADH secretion increases
D. Aldosterone secretion increases
E. Renal blood flow decreases
36. Main reason for that excitation of sympathetic nerve results in decreasing of urine quantity is: A
A. Renal blood flow decreases
B. Plasma colloid osmotic pressure elevate
C. ADH secretion increases
D. Aldosterone secretion decreases
E. Glomerular filtration rate increases
37. Location in which urine concentration occurs is: D
A. Ascending limb thick segment of Henle’s loop
B. Distal convoluted tubule
C. Cortical segment of collecting duct
D. Medullary segment of collecting duct
E. Descending limb thin segment of Henle’s loop
38. Which of followings is not related to (concerned with) the urine dilution E
A. Ascending limb thick segment of Henle’ s loop
B. Distal convoluted tubule
C. Cortical segment of collecting duct
D. Inner medullary segment of collecting duct
E. Proximal tubule
39. Which of followings does not initiate ADH secretion ? B
A. Dehydration (deficit of water)
B. Decreased plasma colloid osmotic pressure
C. Increased plasma crystal osmotic pressure
D. Severe pain
E. A large mount of hemorrhage
40. Which of the followings does not initiate renin secretion ? E
A. Reduction of afferent arteriolar transmural pressure
B. Reduction of NaCl flowing through the macula densa
C. Increased sympathetic nerve activity
D. Elevated plasma adrenaline and noradrenaline
E. Decreased intrarenal prostaglandin E2 formation.
41. Which of the followings does not cause aldosterone secretion ? D
A. Decreased arterial blood pressure
B. Angiotensin Ⅱ
C. Angiotensin Ⅲ
D. Increased plasma Na+ concentration
E. Increased plasma K+ concentration
42 Normally, which of the following substances has the minimal renal clearance? A
A. Glucose
B. Urea
C. Endogenous creatinine
D. Inulin
E. NaCl
Ⅱ. Define following word
1. Glomerular filtration When blood flows through the glomerular capillary, under driving of glomerular effective filtration pressure, the water and low-molecular weight solute in plasma move through filtration membrane into the Bowman’s capsule, this process is termed as glomerular filtration. The filtrate formed in glomerulus is ultrafiltrate, is also called the primary urine.
2. Glomerular filtration rate (GFR) The quantity of ultrafiltrate formed by both kidneys per unit time(each minute) is called GFR. In normal adult human, GFR average 125ml /min, 180L/day.
3. Filtration fraction(FF) The ratio between glomerular filtration rate and renal plasma flow per a minute is termed FF. FF = GFR/RPF(renal plasma flow). In normal human , FF is 19~20%
4. Glomerular effective filtration pressure (GEFP)
GEFP is the net dynamics of glomerular filtration.
GEFP = glomerular capillary hydrostatic pressure (GCHP) – glomerular capillary plasma colloid osmotic pressure ( GCOP) – Bowman’s capsular hydrostatic pressure
5. Autoregulation of renal blood flow (RBF) When the arterial blood pressure is varied between 80 and 180 mmHg, the RBF, GCHP and GFR keep constant, which is called the autoregulation of RBF and GFR.
6. Electrostatic barrier of glomerular filtration membrane. The three layers of glomerular filtration membrane contain negatively charged glycoprotein, these negatively charged elements impede the passage of same charged plasma protein, which is called electrostatic barrier.
7. Filtration coefficient(Kf) Kf means the quantity of filtrate per unit time and per unit GEFP
8. Filtration equilibrium When the force opposing filtration become equal to the force driving filtration, the GEFP is zero, filtration ceases, which is called the filtration equilibrium.
9. Osmotic diuresis When a large amount of solute are present in tubuar fluid, the increased osmotic pressure caused by the solute retards reabsorption of water and sodium, as a result, the quantity of urine increases, which is called osmotic diuresis.
10. Glomerulotubular balance The proximal tubular always reabsorbs the 65~70% of filtrated water and Na+ in despite of the GFR increasing and decreasing, this phenomenon is called glomerulotubular balance.
11. Water diuresis Drinking a large amount of water causes the quantity of urine to increase, which is called water diuresis.
12. renal clearance(Cx) The renal clearance of a substance is the volume of plasma that is completely cleared of this substance by kidneys per unit time.
Ⅲ. Answer following question
1. Describe the characteristics of renal blood circulation.
Answer:
(1). Double capillary bed: The renal blood circulation has two capillary bed in series, glomerular capillary and peritubular capillary. The glomerular capillary has an high hydrostatic pressure (blood pressure), which is favorable to fluid filtration. The peritubular capillary have lower hydrostatic pressure and higher plasma colloid osmotic pressure, which is favorable to fluid reabsorption.
(2). Renal blood flow (RBF) is large. RBF of two kidney in a resting, young man，is about 1200ml /min, is about 20~25% of cardiac output.
(3). RBF is not uniformly distributed. Renal cortex receives 94% of RBF. This blood flow is necessary to sustain a high glomerular filtration rate (GRF). Outer marrow receives 5% of RBF . Inner marrow receives 1% of RBF. The relative low blood flow in the marrow preserves the osmotic gradient in this region.
(4). Characteristics of regulation of RBF
1) Autoregulation: When the arterial blood pressure is varied between 80 and 180 mmHg, the RBF, GCHP and GFR keep constant, which is called the autoregulation of RBF and GFR.
2) Nervous regulation and humoral regulation:
Sympathetic nerve: The renal sympathetic nerves innervate the renal vascular smooth muscle. In response to the state of emergency (critical condition), the increased activity of sympathetic nerve causes the renal blood vessel to constrict, RBF decreases.
Adrenaline (epinephrine ) and noradrenaline (norepinephrene ) causes the renal blood vessel to constrict, RBF decreases.
Prostaglandin E2 (PGE) , prostacyclin(PGI2), NO, bradykinin, atrial natriuretic peptide (ANP) cause renal vessel to relax, RBF increasing.
2. What is glomerular filtration membrane? What are characteristics of glomerular filtration membrane (GFM)?
Glomerular filtration membrane means the membranous structure between the glomerular capillary blood and Bowman’s capsula cavity.
GFM consists of three layers- capillary endothelium, basement membrane, and epithelial cell(podocytes). They are both structural base and barrier of glomerular filtration,
(1). The capillary endothelial cell layer has many round, window-like holes , which is called fenestrea , its diameter is about 50~100 nm. Because the diameter of fenestrea is relatively large, the endothelial layer is not a major barrier for filtration.
(2). The basement membrane consist of meshwork of fine fibrils ( collagen and proteoglycan fibrils) embedded in a gel-like matrix. The basement membrane contains mesh holes about 2~8 nm in diameter. The mesh holes prevents effectively filtration of plasma protein, and is major barrier for plasma protein.
(3). The epithelial cell layer consist of “foot cell ” or podocytes. The epithelial cell layer contains slit pores about 4~12 nm in diameter.
Accordingly, GFM is quite porous, has high permeability to water and low-molecules solute, but restricts passage of the plasma protein.
The three layers of GFM contain negatively charged glycoprotein, these negatively charged elements impede the passage of same charged plasma protein, which is called electrostatic barrier.
3. Describe factors determining glomerular filtration rate.
Answer:
(1). GEFP (glomerular effective filtration pressure):
1) GCHP (glomerular capillary hydrostatic pressure): The GCHP is the only driving force for filtration. GCHP is determined by the arterial blood pressure and the contractile state of afferent and efferent arteriole. .
When the arterial blood pressure is varied between 80 and 180 mmHg, the RBF, GCHP and GFR keep constant, which is called the autoregulation of RBF and GFR.
If arterial pressure is lowered below 80mmHg, the GCHP will markedly fall, and thus GFR will reduce.
If arterial pressure is declined below 50mmHg, the GEFP falls to zero, GFR is zero, the patient or animal will be anuria.
When constriction of the afferent arteriole strengthen, the precapillary resistance increase; GCHP declines, GEFP decreases; GFR decreases. When the constriction of efferent arteriole strengthen, postcapillary resistance increases; GCHP elevates; GFR increases.
2) GCOP (glomerular capillary plasma colloid osmotic pressure): The GCOP is force opposing filtration; normally, it is stable.
With intravenous infusion of a large volume of normal saline, a decreased GCOP increases the GEFP and GFR.
3) Boeman’s capsule hydrostatic pressure: Boeman’s capsule hydrostatic pressure is the force opposing filtration. Normally, Bowman’s capsule hydrostatic pressure is stable. In certain pathological state, such as obstruction of urinary tract, Bowman’s capsule pressure increases, GFR reduces.
(2). Renal plasma flow (RPF)
GFR is in direct proportion to RPF.
Mechanism : As mention above, the GCOP will increase due to prior filtration. When RPF increases, the increase of GCOP along the length of glomerular capillary will become slow, the location at which the filtration equilibrium is achieved nears the efferent arteriolar end. The effective filtration membrane area increases, GFR increases. Conversely, if the RPF decreases, GFR decreases.
(3). Filtration coefficient ( KF)
GFR is in direct proportion to Kf. GFR = Kf × GEFP
Kf means the quantity of filtrate per unit time and per unit GEFP .
Kf is in direct proportion to both the fluid permeability and surface area of filtration membrane.
If there is a decrease in either permeability or surface area of filtration membrane, GFR will decrease. In chronic renal disease, the glomeruli are destroyed, leading to a reduction in filtration membrane area and a diminished GFR. If some diseases damage the mechanical and electrostatic barrier, the permeability of filtration membrane increases, leading to hematuria and proteinuria.
4. When a person have a large amount of haemorrhage and thus his arterial blood pressure decreases markedly, how change his quatity of urine? Why?
Answer:
His quantity of urine decreses.
Mechanism:
(1) GFR decreses: The declined excessively arterial blood pressure result in the glomerular capillary hydrostatic pressure to decline, the glomerular effective filtration pressure reducing, glomerular filtration rate (GFR) decreasing.
(2) Renal plasma flow decreases: Both declined arterial blood pressure and the activity of sympathetic nerve causes the renal plasma flow to decrease; the increase of the plasma colloid osmotic pressure along the length of glomerular capillary will become quick, the location at which the filtration equilibrium is achieved nears the afferent arteriolar end. Consequently, effective filtration membrane area decreases, GFR decreases.
(3) Release of ADH increases：The stimulation of the decreased excessively blood volume to the volume receptors located on left atrium and thoracic large vines decreases; the afferent signals of the vagus nerve decreases; the release of ADH increases reflexly. The increased ADH plasma concentration elevates the permeability of distal convoluted tubule and collecting duct to water, thereby increasing water reabsorption, the quantity of urine decreasing and urine concentrates.
(4) Release of aldosterone increases: The decreased blood pressure at the afferent arteriole and the excessive activity of sympathetic nerve causes the juxtaglomerular cell to release rennin. The rennin-angiotensin-aldosterone system is started. Release of aldosterone increases. The aldosterone promotes the distal convoluted tubule and collecting duct to reabsorb Na+ and water.
5. Describe the process of reabsorption of N+ and Cl- at proximal tubule.
Answer:
The N+ - K+ pump located on basolateral membrane of epithelial cell of the proximal tubule actively transports Na+ from cell to interstitial fluid and K+ from interstitial fluid into cell. The operation of Na+-K+ pump carries out the reabsorption of Na+, maintains the low Na+ and the high K+ of intracellurar fluid and creates a negative potential within cell. This electrochemical gradient will provides energy for symport , antiport .
In the apical membrane of epithelial cell of the first half of proximal tubule, Na+ is reabsorbed mainly by symport along with glucose and by antiport with H+ from tubular fluid into epithelial cell；HCO3- is preferentially reabsorbed, Cl- is not reabsorbed. Therefore, the Cl- concentration increases gradually. In second half of proximal tubule, the Cl- diffuse from tubular lumen into intercellular fluid via the tight junction down concentration difference, creating a transtubular potential difference that is positive in tubular lumen and is negative in interstitial fluid, this potential difference causes Na+ to diffuse into interstitial fluid. This is passive transport..
6. Describe the process of reabsorption of N+ and Cl- at thick segment of Henle’s loop ascending limb
Answer:
The N+ - K+ pump located on basolateral membrane of epithelial cell of the thick segment of Henle’s loop ascending limb actively transports Na+ from cell to interstitial fluid and K+ from interstitial fluid into cell. The operation of Na+-K+ pump carries out the reabsorption of Na+, maintains the low Na+ and the high K+ of intracellurar fluid and creates a negative potential within cell. This electrochemical gradient will provides energy for symport , antiport .
There are a symporter of Na+, K+, Cl- on apical membrane of the cell of the thick segment ascending limb; Cl-. Na+, K+, Cl- combine with the sympoter in the proportion of 1-Na+:2-Cl-:1K+, then the Na+ and Cl- moves down its electrochemical gradient, while K+ against their electrochemical gradient from tubular fluid into the cell.
The increased intracellular Na+ is actively transported by Na+-K+ pump on basolateral membrane into interstitial fluid, the Cl- diffuses passively into interstitial fluid, the K+ partly into interstitial fluid and partly diffuses back tubular fluid and thus cause the tubular fluid to be positive potential. The positive potential in tubular fluid promotes Na+, K+ and Ca2+ to be passively reabsorbed via the paracellular transport (50%).
7. Describe the process of reabsorption of N+ and Cl- at the distal convoluted tubule and collecting duct.
Answer:
The Na+ - K+ pump located on basolateral membrane of the principal cell of the distal convoluted tubule and collecting duct actively transports Na+ from cell to interstitial fluid and K+ from interstitial fluid into cell. The operation of Na+-K+ pump carries out the reabsorption of Na+, maintains the low Na+ and the high K+ of intracellurar fluid and creates a negative potential within cell. This electrochemical gradient will provides energy for symport of Na+ - Cl-.
There are a symporter of Na+ - Cl- on the luminal membrane of of the initial segment of distal convoluted tubule. The Na+ and Cl- are transported across the luminal membrane from tubular fluid into cell by the symport.
There are a Na+ channel on the luminal membrane of principal cell in the latter second half segment of distal convoluted tubule and collecting duct. The Na+ in tubular fluid diffuse into cell through the Na+ channel, and thus creates a negative potential in the tubular fluid. The negative potential drives the Cl- reabsorption via paracelluar transport and K+ secretion.
8. Describe the identical points and different points of reabsorption of N+ and Cl- at proximal tubule, thick segment of Henle’s loop ascending limb, distal convoluted tubule and collecting duct.
Answer:
The identical points: The N+ - K+ pump located on basolateral membrane of epithelial cell of the proximal tubule, distal tubule, and collecting duct primarily actively transports Na+ from cell to interstitial fluid and K+ from interstitial fluid into cell. The operation of Na+-K+ pump carries out the reabsorption of Na+, maintains the low Na+ and the high K+ of intracellurar fluid and creates a negative potential of about -70 mv within cell. This electrochemical gradient will provides energy for symport , antiport . Reabsorption of Cl- is passive transport.
The different points:
① In the epithelial cell apical membrane of the first half of proximal tubule, Na+ is reabsorbed mainly by symport along with glucose and by antiport with H+ from tubular fluid into epithelial cell；HCO3- is preferentially reabsorbed, Cl- is not reabsorbed. Therefore, the Cl- concentration increases gradually. In second half of proximal tubule, the Cl- diffuse from tubular lumen into intercellular fluid via the tight junction down concentration difference, creating a transtubular potential difference that is positive in tubular lumen and is negative in interstitial fluid, this potential difference causes Na+ to diffuse into interstitial fluid. This is passive transport..
②The apical membrane of the cell of the thick segment ascending limb has a symporter of Na+, K+, Cl-. Na+, K+, Cl- combine with the sympoter in the proportion of 1-Na+:2-Cl-:1K+, then the Na+ and Cl- moves down its electrochemical gradient, while K+ against their electrochemical gradient from tubular fluid into the cell. The increased intracellular Na+ is actively transported by Na+-K+ pump on basolateral membrane into interstitial fluid, the Cl- diffuses passively into interstitial fluid, the K+ partly into interstitial fluid and partly diffuses back tubular fluid and thus cause the tubular fluid to be positive potential. The positive potential in tubular fluid promotes Na+, K+ and Ca2+ to be passively reabsorbed via the paracellular transport (50%).
③There are a symport Na+ - Cl- on the luminal membrane of of the initial segment of distal convoluted tubule. The Na+ and Cl- are transported across the luminal membrane from tubular fluid into cell by the symport.
There are a Na+ channel on the luminal membrane of principal cell in the latter second half segment of distal convoluted tubule and collecting duct. The Na+ in tubular fluid diffuse into cell through the Na+ channel, and thus creates a negative potential in the tubular fluid. The negative potential drives the Cl- reabsorption via paracelluar transport and K+ secretion.
9. Describe Na+-glucose symport and Na+-H+ antiport in the proximal tubule.
Answer:
The Na+ - K+ pump located on basolateral membrane of epithelial cell of the proximal tubule, distal tubule, and collecting duct transports Na+ from cell to interstitial fluid and K+ from interstitial fluid into cell. The operation of Na+-K+ pump carries out the reabsorption of Na+, maintains the low Na+ and the high K+ of intracellurar fluid and creates a negative potential within cell. This electrochemical gradient will provides energy for symport and antiport .
In the epithelial cell luminal membrane (apical membrane) of proximal tubule, Na+ is reabsorbed by symport along with glucose and by antiport with H+, from tubular fluid into epithelial cell. Na+-glucose symport: The Na+ and glucose of tubular fluid bind with the same co-transporter of luminal membrane, then, the Na+ moves into the cell down its electrochemical gradient while the glucose is pulled into cell against its concenteation difference. Then, this increased intracellular glucose diffuse via facilitated diffusion via carrier into interstitial fluid and blood.
Na+-H+ antiport : The intracellular H+ and Na+ in tubular lumen bind with the same antiporter of luminal membrane, then, the Na+ move into cell down its electrochemical gradient while the H+ is pushed out of cell against its electrochemical gradient into tubular lumen, which is called H+-Na+ exchange.
10.describe the process of reabsorption of water in the renal tubule and collecting duct.
Answer:
The manner of water reabsorption is osmosis, is passive transport. The direct driving force for water reabsorption is the osmolarity gradient between interstitial fluid and tubular fluid. The osmolarity (or osmotic pressuere) of the interstitial fluid is higher than that of the tubular fluid, then water penetrates down the osmolarity gradient from the tubular fluid to the interstitial fluid. This osmolarity gradient result from the reabsorption of Na+, Cl- ,and other solutes. Therefore, reabsorption of water is directly related to the reabsorption of solute. The proximal tubule is high permeable to water. The reabsorption of water in proximal tubule is iso-osmotic reabsorption. The descending limb of Henle’s loop is high permeable to water, water diffusing from tubular fluid to medulla interstitial fluid and thus causing the osmolarity of tubular fluid to be increased. The ascending limb of Henle’s loop is impermeable to water, water can not being reabsorbed at this portion. The reabsorption of water in proximal tubule and Henle’s loop is relatively fixed and is not affected by regulatory factors.
The reabsorption of water at distal convoluted tubule and collecting duct is regulated by ADH. In the presence of high concentration ADH, the permeability of these tubule to water increases markedly, water being reabsorbed. The increased water and solutes in the intercellular fluid elevates the hydrostatic pressure in this region and thereby drives fluid into peritubular capillary.
11. Describe the process of secretion of K+ in distal convoluted and collecting duct.
Answer:
The vast majority of filtrated K+ is reabsorbed in proximal tubule and Henle’s loop. The K+ in end-urine derives mainly from secretion of principal cell in distal convoluted tubule and collecting duct.
The positions of K+ secretion are the distal convoluted tubule and collecting duct.
The manner of K+ secretion is a passive transport.
The driving force of K+ secretion is the negative potential in tubular fluid created by the active reabsorption of Na+.
The Na+-K+ pump located on basolateral membrane of principal cell of distal convoluted tubule and collecting duct actively transports Na+ from cell into interstitial fluid and causes the high K+ and low Na+ of the intracellular fluid. Na+ of tubular fluid diffuses down electrochemical gradient into cell, and thus creates a negative potential in the tubular fluid. This negative potential and increased intracellular K+ drives K+ from cell into tubular fluid. Therefore , K+ secretion is positively related to the activity of Na+-K+ pump and the permeability of luminal membrane to Na+.
12. Describe the process of H+ secretion and HCO3- reabsorption in renal tubule, collecting duct and deacribe its sinificance.
In proximal tubule and thick segment of Henle’s loop ascending limb, H+ is secreted by Na+-H+ exchange.
Na+-H+ antiport : The intracellular H+ and Na+ in tubular lumen bind with the same antiporter of luminal membrane, then, the Na+ move into cell down its electrochemical gradient while the H+ is pushed out of cell against its electrochemical gradient into tubular lumen, which is also called H+-Na+ exchange. The H+ secretion couples with the reabsorption of HCO3-.
The HCO3-(bicarbonate) filtrated can not permeate the luminal membrane, therefore HCO3- can not be directly reabsorbed.
In tubular fluid Carbonic
Anhydrase of
apical membrane
, HCO3- + H+ ← ——— → H2CO3 → H2O +CO2
The CO2 diffuses down its concentration difference into tubular cell .
In tubular cell Carbonic
anhydrase
CO2 + H2O ←———→ H2CO3 → H+ + HCO3-
The majority of HCO3- are transported along with Na+ into interstitial fluid and then blood, while the H+ is actively secreted into tubular fluid by Na+-H+ exchange.
Therefore, the manner of HCO3- reabsorption is CO2 .
In the distal tubule and collecting duct, the intercalated cell actively secretes H+, its process is following:
There are much CO2 in the intercalated cells. These CO2 are from both the metabolism of cell and blood.
In intercalated cell Carbonic
anhydrase
CO2 + H2O ←———→ H2CO3 → H+ + HCO3-
The HCO3- is reabsorbed into interstitial fluid, while the H+ is actively transported by proton pump( H+- ATPase)and H+-K+ ATPase into tubular fluid.
Significance: ①Whenever a H+ is secreted , there must be a HCO3- is generated or reabsorbed. Kidneys maintains the acid-base balance of internal environment by reabsorbing HCO3- and secreting H+. When pH value of internal environment lowers, the activity of carbonic anhydrase increases, secretion of H+ and reabsorption of HCO3- increasing. .② It promotes NH3 secretion. H+ in tubular fluid bind with NH3 to form NH4+. NH4+concentration of tubular fluid decreasing, NH3 secretion increasing.
13. Giving intravenously hyperosmotic glucose solution to a animal (or person), how changes its (or his ) quantity of urine ? why ?
Answer:
Giving intravenously hyperosmotic glucose solution to a animal (or person) leads to the osmotic diuresis. The quantity of urine increases.
Mechanesm: When the hyperosmotic glucose solution is injected intravenously, the blood glucose concentration rises excessively and is higher than the renal glucose threshold. The glucose can not be reabsorbed completely. The excessive glucose remains in the tubular fluid, the osmotic pressure of tubular fluid increases, which retards water reabsorption, the quantity of urine increasing. For the same reason, the quantity of urine of the most of parients with diabetes increases(hyperuria).
14. When a person is subjected a large amount of sweating and deprivation of drinking water, how change his quantity of urine? Way?
Answer:
His quantity of urine decreases.
Mechnism: The reasons for this are: (1) His plasma crystal osmotic pressure increases. The increased plasma crystal osmotic pressure stimulates the osmoreceptor in hypothalamus and thus causes posterior pituitary to release ADH. The increased ADH plasma concentration elevates the permeability of distal convoluted tubule and collecting duct to water, thereby increasing water reabsorption, the quantity of urine decreasing and urine concentrates.
(2) His blood volume decrease. The stimulation of the decreased blood volume to the volume receptors located on left atrium and thoracic large vines (such as vena cava, pulmunary vines) decreases; the afferent signals of the vagus nerve decreases; the release of ADH increases reflexly. Finally, the quantity of urine decreases for the same reason.
Conversely, when a person drinks a large amount of water, the opposite sequence of events occurs.
15. When a person drinks a large amount of water, how change his quantity of urine? Way?
Answer:
His quantity of urine increases
Mechanism: (1) After drinking a large amount of water, his plasma is diluted. The stimulation of decreased plasma crystal osmotic pressure to the osmoreceptor in hypothalamus weaken and thus causes the release of ADH to reduce. The decreased ADH plasma concentration reduces the permeability of distal convoluted tubule and collecting duct to water. The reabsorption of water decreases, the quantity of urine increasing.
(2) After drinking a large amount of water, his blood volume increases. The increased blood volume stimulates the volume receptors located on left atrium and thoracic large vines, the afferent signals of the vagus nerve increasing, the release of ADH reducing reflexly. For the same reason, the quantity of urine increases.
16. Describe the function and its functional mechanisms of aldosterone on renal tubule and collecting duct
The aldosterone promotes the Na+ reabsorption and K+ secretion in distal convoluted tubule and collecting duct.
Mechanism: Aldosterones enter the principal cells; bind with the receptor in cytoplasm to form a hormone-cytoplasm receptor complex. The complex are transported into the nucleus, then bind with the receptor in the nucleus to form hormone-nucleus receptor complex and thus activates the transcription（转录）process of specific genes to form specific mRNA. The mRNA diffuses into cytoplasm, where it promotes the translation（转化）process to form aldosterone-induced proteins. The latter ① increase the number of the Na+ channels and thus increase the Na+ permeability of the luminal membrane , ② enhance the activity of the Na+ - K+ ATPase pump on the basolateral membrane, ③ increase the synthesis of ATP.
17. Describe the mechanism by which the renal medullary osmolarity gradient formed.
(1). Mechanism forming osmolarity gradient in outer medulla
In outer medulla, the increased osmolarity of interstitial fluid result mainly from the active reabsorption of Na+ and Cl-, while water can not be reabsorbed in the ascending limb thick segment of Henle’s loop. The ascending limb thick segment of Henle’ s loop is impermeable to water, actively reabsorbs Na+ and Cl-, consequently, the NaCl concentration in interstitium is increased, rising osmolarity of interstitial fluid in outer medulla .
(2) . Mechanism forming osmolarity gradient in inner medulla
In inner medulla, the increased concentration of NaCl and urea contribute equally to the increased osmolarity of interstitial fluid .
The process forming the osmolarity gradient of inner medulla is countercurrent multiplication, is following:
1)The descending limb thin segment of of Henle’s loop is impermeable to urea and NaCl, is highly permeable to water. As tubular fluid flow through this region, water is net reabsorbed, the concentration of NaCl in tubular fluid progressively increases.
2)When this tubular fluid rounds the bend of Henle’s loop and flow into ascending limb thin segment, because the ascending limb thin segment is highly permeable to NaCl and is impermeable to water, NaCl diffuses down concentration difference from tubular fluid into inner medullary peritubular fluid, thereby increasing its osmolarity.
3) Urea circulation increases the urea concentration of inner medulla
The distal convoluted tubule and cortical segment and outer medullary segment of collecting duct is impermeable to urea. In the presence of high concentration ADH, water is reabsorbed from these segments, increasing urea concentration in tubular fluid.
Because the inner medullary collecting duct is highly permeable to urea, then urea diffuses down its concentration difference from tubule into peritubular interstitium and thus increase the urea concentration and osmolarity of peritubular fluid in the inner medulla.
The urea in inner medulla diffuses into ascending limb thin segment, then flow through ascending limb thick segment, distal convoluted tubule, outer medullary segment of collecting duct , and finally back to the inner medullary collecting duct where urea diffuses into interstitial fluid again, this process is called urea circulation .
18. Describe the process of urine dilution and concentration.
(1) Urine dilution
In the ascending limb thick segment of Henle’s loop, Na+, K+, Cl- are avidly reabsorbed, however, this portion of tubule is impermeable to water, therefore the tubular fluid become dilute , its osmolarity is about 100mmol/L. As these dilute fluid flows through the distal tubule and collecting duct, the Na+, K+，Cl- is continuously reabsorbed. In the absence of ADH, these tubule are also impermeable to water. Therefore, the tubular fluid become even more dilute, its osmolarity lowers as low as 50 mOsm/L.
(2) Urine concentration.
The urine concentration occurs in the medullary segment of collecting duct. In presence of high concentration ADH, the distal convoluted tubule and collecting duct is high permeable to water. When tubular fluid flow through the medallary segment of collecting duct, because there is a osmolarity gradient in the interstitial fluid of renal medalla, water moves down osmotic pressure difference from tubular fluid into renal medullary interstitial fluid, up to osmotic equilibrium is achieved, consequently, the quantity of urine decreases and urine osmolarity increases.
