AUBF - Renal Function

the approximate no. of nephrons in each kidney

1-1.5M

functional units of kidney

nephrons

2 types of nephrons

cortical nephron and juxtamedullary nephron

85% of nephrons

cortical nephron

responsible for removal of waste products and reabsorption of nutrients

cortical nephron

funtion is concentration of urine

juxtamedullary nephron

The ability of the kidneys to clear waste products selectively

from the blood and simultaneously to maintain the

body's essential water and electrolyte balances is controlled in

the nephron by the following renal functions:

renal blood flow

glomerular filtration

tubular reabsorption

tubular secretion

supplies blood to the kidney

renal artery

The human kidneys receive approximately ___ of the blood pumped through the heart at all times

25%

Blood enters the capillaries of the nephron through the ___then flows through the ____ and into the ____

afferent arteriole

glomerulus

efferent arteriole

The __ help to create the hydrostatic pressure differential important for glomerular filtration and to maintain consistency of glomerular capillary pressure and renal blood flow within the glomerulus

varying sizes of these arterioles

renal blood flow

Afferent arteriole, peritubular capillaries, vasa recta, efferent arteriole

surround the proximal and distal convoluted tubules, providing

for the immediate reabsorption of essential substances

from the fluid in the proximal convoluted tubule and final adjustment of the urinary composition in the distal convoluted

tubule.

peritubular capillaries

are located adjacent to the ascending and descending loop of Henle in juxtamedullary nephrons. In this area, the major exchanges of water and salts take place between the blood and the medullary interstitium.

vasa recta

necessary for renal concentration.

osmotic gradient

Based on an average body size of 1.73 m2 of surface, the

total renal blood flow is approximately

1200 mL/min

total renal plasma flow ranges

600 to 700 mL/min

consists of a coil of approximately eight capillary

lobes

glomerulus

capillary lobes

capillary tuft

forms the beginning of the renal tubule

glomerulus

Plasma filtrate must pass through three cellular layers:

the capillary wall membrane

the basement membrane (basal

lamina)

the visceral epithelium of Bowman's capsule

endothelial cells of the capillary wall

fenestrated

increase capillary permeability but do

not allow the passage of large molecules and blood cells.

pores

thin membranes

covering the filtration slits formed by

intertwining foot

processes of the podocytes

maintains the glomerular blood pressure at a relatively

constant rate regardless of fluctuations in systemic blood

pressure.

autoregulatory mechanism within the juxtaglomerular apparatus

an increase in blood pressure results in ____ to prevent overfiltration or damage to the glomerulus

constriction of the afferent arterioles

controls the regulation of the flow of blood to and within the glomerulus.

renin-angiotensin-aldosterone system (RAAS)

responds to changes in bp and plasma Na content

raas

decreases water retention within the circulatory system,

resulting in a decreased overall blood volume and subsequent

decrease in blood pressure

Low plasma sodium content

produce a constant pressure within the nephron

actions of angiotensin II

the only difference between the compositions of the filtrate and

the plasma is

the absence of plasma protein, any proteinbound

substances, and cells

body cannot lose ___ of water-containing essential

substances every minute

120 ml

___ to occure the substance to be reabsorbed must combine

with a carrier protein contained in the membranes of the renal

tubular cells

active transport

responsible for the reabsorption of glucose, amino acids and salts in the proximal convoluted tubule

chloride in the ascending loop of Henle, and

sodium in the distal convoluted tubule

Active transport

is the movement of molecules across a

membrane as a result of differences in their concentration or

electrical potential on opposite sides of the membrane

Passive transport

physical differences

gradients

Passive reabsorption

of water takes place in all parts of the nephron except the

ascending loop of Henle

the walls of which are impermeable

to water

ascending loop of Henle

passively reabsorbed in the proximal convoluted

tubule and the ascending loop of Henle

urea

accompanies the active transport of chloride in the ascending loop.

passive reabsorption of sodium

maximal re-absorptive capacity

Tm

is the plasma concentration at

which active transport stops

renal threshold

renal threshold of glucose

160 to 180 mg/dL

where the filtrate is exposed to the high osmotic gradient of the renal medulla

descending and ascending lh

Water is removed by

osmosis in the descending loop of Henle

sodium and chloride are reabsorbed in the

ascending loop

Excessive reabsorption of water as the filtrate passes through the highly concentrated medulla is prevented by

the water-impermeable walls of the ascending loop

selective reabsorption process is called the

countercurrent mechanism

maintain the osmotic gradient of the medulla

countercurrent mechanism

Maintenance of this osmotic gradient is essential for the final concentration of the filtrate when it reaches the

collecting duct

final concentration of the filtrate through the reabsorption of water begins in the ___ and continues in the ___

late distal convoluted tubule

collecting duct

Reabsorption depends on the osmotic

gradient in the medulla and vasopressin

increases permeability, resulting in increased reabsorption of water, and a lowvolume concentrated urine

high level of ADH

is actually the final determinant of urine volume and concentration

chemical balance in the body

↑Body Hydration = _ADH = ↑Urine Volume

↓

↓Body Hydration = _ADH = ↓Urine

↑

Tubular secretion serves two major functions:

elimination of waste products not filtered by the glomerulus

and

regulation of the acid-base balance in the body through

the secretion of hydrogen ions

major site for removal of these nonfiltered

substances is the

proximal convoluted tubule

buffering capacity of the blood depends on

bicarbonate (HCO3-) ions

prevents the filtered bicarbonate from being excreted in the urine and causes the return of a bicarbonate ion to the plasma

secretion of hydrogen ions by the renal tubular cells into the filtrate

how many filtered bicarbonates are reabsorbed, occurs primarily in PCT

100%

readily filtered and reabsorbed

hydrogen ions

A disruption in these secretory functions can result in

metabolic acidosis or renal tubular acidosis

inability to produce an acid urine

metabolic acidosis or renal tubular acidosis

standard test used to measure the filtering capacity of

the glomeruli is the clearance test

Glomerular Filtration Tests

measures the rate at which the kidneys are able

to remove (to clear) a filterable substance from the blood

clearance test

the substance analyzed must be one that is

neither reabsorbed nor secreted by the tubules

approximately __ of the filtered urea is reabsorbed

40%

the use of urea as a test substance for glomerular filtration has

been replaced by the measurement of other substances

such as

creatinine, inulin, beta2 microglobulin, cystatin C,

or radioisotopes

a polymer of fructose, is an extremely stable substance

that is not reabsorbed or secreted by the tubules

inulin

A test that requires an infused substance is

exogenous procedure

suitable test substance is already present in the body

endogenous procedure

a waste product of muscle metabolism that is normally found at a relatively constant level in the blood

creatinine

greatest source of error in any clearance procedure

utilizing urine is

the use of improperly timed urine specimens

is used to determine the extent of nephron damage in known cases of renal disease, to monitor the effectiveness of treatment designed to prevent further nephron damage, and to determine the feasibility of administering medications, which can build up to dangerous blood levels if the GFR is markedly reduced

creatinine clearance

most frequently used formula was developed by

Cockcroft and Gault

is a small protein (molecular weight

13,359) produced at a constant rate by all nucleated cells

Cystatin C

readily filtered by the glomerulus and reabsorbed and

broken down by the renal tubular cells

Cystatin C

is often the first function affected in renal disease

the loss of tubular reabsorption capability

Tests to determine the ability of the tubules to reabsorb

the essential salts and water that have been nonselectively

filtered by the glomerulus

concentration tests

ultrafiltrate that enters the tubules has a

specific gravity of

1.010

is largely determined by the body's state of hydration, and the normal kidney will reabsorb only the amount of water necessary to preserve an adequate supply of body water

urine concentration

patients were deprived of fluids for 24 hours prior to measuring specific gravity

Fishberg test

compares the volume and specific gravity of day and

night urine samples to evaluate concentrating ability

Mosenthal test

persons with normal concentrating ability should have a specific gravity of __ when deprived of fluids for 16 hours

1.025

a urine osmolarity of 800 mOsm or above indicates

normal concentrating ability

depends on the number of particles present in

a solution and the density of these particles

Specific gravity

is affected only by the number of particles present

osmolarity

will contribute more to the specific gravity than

will the sodium and chloride molecules

urea

Solute dissolved in solvent causes the following

changes in colligative properties:

lower freezing point, higher boiling point, increased osmotic pressure, and lower vapor pressure