Transcript Renal Physiology

Renal Physiology: Chapter Goals
After studying this chapter, students should be able to . . .
1. describe the different regions of the nephron tubules and explain the
anatomic relationship between the tubules and the gross structure of the
kidney.
2. describe the structural and functional relationships between the nephron
tubules and their associated blood vessels.
3. describe the composition of glomerular ultrafiltrate and explain how it is
produced.
4. explain how the proximal convoluted tubule reabsorbs salt and water.
5. describe active transport and osmosis in the loop of Henle and explain how
these processes produce a countercurrent multiplier system.
6. explain how the vasa recta function in countercurrent exchange.
7. describe the role of antidiuretic hormone (ADH) in regulating the final urine
volume.
8. describe the mechanisms of glucose reabsorption and explain the meanings
of the terms transport maximum and renal plasma threshold.
Renal Physiology: Chapter Goals
9. define the renal plasma clearance, and explain why the clearance of inulin is
equal to the glomerular filtration rate.
10. explain how the clearance of different molecules is determined and how the
processes of reabsorption and secretion affect the clearance measurement..
11. explain the mechanism of Na+ reabsorption in the distal tubule and why this
reabsorption occurs together with the secretion of K+.
12. describe the effects of aldosterone on the distal convoluted tubule and how
aldosterone secretion is regulated.
13. explain how activation of the renin-angiotensin system results in the
stimulation of aldosterone secretion.
14. describe the interactions between plasma K+ and H+ concentrations and
explain how this affects the tubular secretion of these ions.
15. describe the role of the kidneys in the regulation of acid-base balance.
16. describe the different mechanisms by which substances can act as diuretics
and explain why some cause excessive loss of K+.
Renal Physiology
• Functional Relationships
• Urinary System Anatomy
• Nephron
Functional Relationships
Urinary System Anatomy
• Kidneys
• Nephrons
14.1a
14-1b
14-3
Juxtamedullary Nephron
Cortical Nephron
14-5
14-8
Nephron Function
• Filtration
• Tubular Secretion
• Selective Reabsorption
14-6
14-7
Filtration
• Analysis of Glomerular Capillary Dynamics
– Blood Pressure
=55.0 mm Hg O (vs 35
normally)
– Plasma Coll O.P. =30.0 mm Hg I
– BC Hydrostatic P. =15.0 mm Hg I
10.0 mm Hg O = Filtration
Pressure
Table 14-1
Regulation of Filtration Pressure
14-10
Regulation of Filtration Pressure
14-11
Filtration (cont’d)
• Regulation of Filtration Pressure - via
juxtaglomerular apparatus
14-12
Autoregulation of High Filtration Pressure
14-13
Tubular Secretion/Selective
Reabsorption
• Tubular Maximum
• Urine = (Filtration - reabsorption) + Secretion
14-21
Fox 17.20
Regulation of Blood Composition
• 1. Electrolytes and Solutes
• a. Na+ high in blood; low in cells
• b. K+ high in cells; low in blood
• c. Aldosterone (from adrenal gland)  Na+ uptake
and K+ uptake (into blood)
Saving Sodium
14-18
14-19
Losing Sodium
14-20
14.24
14-25
14-26a
14-26b
14-26c
14-26d
Regulation of Blood Composition
• 2. pH: too low - H+to tubule; too high - H + to blood
– a. Definition - pH = -log [H+]
– b. How buffers work - e.g. tie up H+ from a strong acid with the
salt of a weak acid, which forms a weak acid.
Regulation of Blood Composition
15-8a
Regulation of Blood Composition
15-8b
Regulation of Blood Composition
15-10
Regulation of Blood Composition
15-11
Regulation of Blood Composition
3. Water
– 80% reabsorbed by elevated osmotic pressure
of blood in capillaries of efferent renal arteriole
following filtration by the glomerulus
– Countercurrent Mechanism - salvages water
from glomerular filtrate, so produces a
concentrated urine
Water Reabsorption
17-22
Countercurrent Mechanism
– i. Produce Na+ concentration gradient via
active transport in ascending branch of the
Loop of Henle.
– ii. Maintain Na+ concentration gradient against
tendency to diffuse.
– iii. Use Na+ concentration gradient to salvage
water
Countercurrent Mechanism
14-27
14-28a
14-28b
14-28c
14-28d
14-28e
14-28f
14-28g
14-29
14-31a
14-31b
Chapter Summary
Structure and Function of the Kidneys
I. The kidney is divided into an outer cortex and inner medulla.
A. The medulla is composed of renal pyramids, separated by renal columns.
B. The renal pyramids empty urine into the calyces that drain into the renal pelvis. From
there urine flows into the ureter and is transported to the bladder to be stored.
II. Each kidney contains more than a million microscopic functional units called
nephrons. Nephrons consist of vascular and tubular components.
A. Filtration occurs in the glomerulus, which receives blood from an afferent arteriole.
B. Glomerular blood is drained by an efferent arteriole, which delivers blood to peritubular
capillaries that surround the nephron tubules.
C. The glomerular (Bowman’s) capsule and the proximal and distal convoluted tubules are
located in the cortex.
D. The loop of Henle is located in the medulla.
E. Filtrate from the distal convoluted tubule is drained into collecting ducts, which plunge
through the medulla to empty urine into the calyces.
Chapter Summary
Glomerular Filtration
I. A filtrate derived from plasma in the glomerulus must pass though a basement
membrane of the glomerular capillaries and through slits in the processes of the
podocytes, the cells that compose the inner layer of the glomerular (Bowman’s)
capsule.
A. The glomerular ultrafiltrate, formed under the force of blood pressure, has a low
protein concentration.
B. The glomerular filtration rate (GFR) is the volume of filtrate produced by both
kidneys each minute. It ranges from 115 to 125 ml/min.
II. The GFR can be regulated by constriction or dilation of the afferent arterioles.
A. Sympathetic innervation causes constriction of the afferent arterioles.
B. Intrinsic mechanisms help to autoregulate the rate of renal blood flow and the
GFR.
Chapter Summary
Reabsorption of Salt and Water
I. Approximately 65% of the filtered salt and water is reabsorbed across the proximal
convoluted tubules.
A. Sodium is actively transported, chloride follows passively by electrical attraction, and
water follows the salt out of the proximal tubule.
B. Salt transport in the proximal tubules is not under hormonal regulation.
II. The reabsorption of most of the remaining water occurs as a result of the action of
the countercurrent multiplier system.
A. Sodium is actively extruded from the ascending limb, followed passively by chloride.
B. Since the ascending limb is impermeable to water, the remaining filtrate becomes
hypotonic.
C. Because of this salt transport and because of countercurrent exchange in the vasa recta,
the tissue fluid of the medulla becomes hypertonic.
D. The hypertonicity of the medulla is multiplied by a positive feedback mechanism
involving the descending limb, which is passively permeable to water and perhaps to salt.
Chapter Summary
Reabsorption of Salt and Water
III. The collecting duct is permeable to water but not to salt.
A. As the collecting ducts pass through the hypertonic renal medulla, water leaves
by osmosis and is carried away in surrounding capillaries.
B. The permeability of the collecting ducts to water is stimulated by antidiuretic
hormone (ADH).
Chapter Summary
Renal Plasma Clearance
I. Inulin is filtered but neither reabsorbed nor secreted. Its clearance is
thus equal to the glomerular filtration rate.
II. Some of the filtered urea is reabsorbed. Its clearance is therefore less
than the glomerular filtration rate.
III. Since almost all the PAH in blood going through the kidneys is
cleared by filtration and secretion, the PAH clearance is a measure of
the total renal blood flow.
IV. Normally all of the filtered glucose is reabsorbed. Glycosuria occurs
when the transport carriers for glucose become saturated as a result of
hyperglycemia.
Chapter Summary
Renal Control of Electrolyte and Acid-Base Balance
I. Aldosterone stimulates sodium reabsorption and potassium secretion in the distal
convoluted tubule.
II. Aldosterone secretion is stimulated directly by a rise in blood potassium and
indirectly by a fall in blood sodium.
A. Decreased blood flow through the kidneys stimulates the secretion of the
enzyme renin from the juxtaglomerular apparatus.
B. Renin catalyzes the formation of angiotensin I, which is then converted to
angiotensin II.
C. Angiotensin II stimulates the adrenal cortex to secrete aldosterone.
III. Aldosterone stimulates the secretion of H+, as well as potassium, into the filtrate in
exchange for sodium.
Chapter Summary
Renal Control of Electrolyte and Acid-Base Balance
IV. The nephrons filter bicarbonate and reabsorb the amount required to maintain acidbase balance. Reabsorption of bicarbonate, however, is indirect.
A. Filtered bicarbonate combines with H+ to form carbonic acid in the filtrate.
B. Carbonic anhydrase in the membranes of microvilli in the tubules catalyzes the
conversion of carbonic acid to carbon dioxide and water.
C. Carbon dioxide is reabsorbed and converted in either the tubule cells or the red
blood cells to carbonic acid, which dissociates to bicarbonate and H+.
D. In addition to reabsorbing bicarbonate, the nephrons filter and secrete H+, which
is excreted in the urine buffered by ammonium and phosphate buffers.
Chapter Summary
Clinical Applications
I. Diuretic drugs are used clinically to increase the urine volume and thus
to lower the blood volume and pressure.
A. Loop diuretics and the thiazides inhibit active Na+ transport in the
ascending limb and early portion of the distal tubule, respectively.
B. Osmotic diuretics are extra solutes in the filtrate that increase the
osmotic pressure of the filtrate and inhibit the osmotic reabsorption
of water.
C. The potassium-sparing diuretics act on the distal tubule to inhibit
the reabsorption of Na+ and secretion of K+.
II. In glomerulonephritis the glomeruli can permit the leakage of plasma
proteins into the urine.
III. The technique of renal dialysis is used to treat people with renal
insufficiency.