Chapter 3 terms

Given the following information, calculate the creatinineclearance: 24-hour urine volume = 720 mL, plasma creatinine = 1.5 mg/dL, and urine creatinine = 300 mg/dL.

100 mL/min.

Given the following information, calculate the effective renal plasma flow: urine volume = 240 mL in 2 hours, urine PAH = 150 mg/dL, and plasma PAH = 0.5 mg/dL.

600 mL/min.

vasa recta

A network of capillaries surrounding the loop of Henle.

Define the term ultrafiltrate of plasma.

A solution containing the same concentration of low-molecular-weight substances as plasma.

List four substances reabsorbed by active transport and two substances reabsorbed by passive transport.

Active transport: glucose, amino acids, sodium, chloride, phosphorus, calcium; passive transport: water, urea.

Explain the relationship of tubular secretion to tests for renal blood flow.

Adequate renal blood flow must be present for nonfiltered substances to reach the capillaries for secretion.

Why is the result obtained in Question #27 called effective renal plasma flow rather than renal blood flow?

Approximately 8%of the renal blood flow does not come in contact with functional renal tissue.

Given the following information, calculate the free water clearance and interpret the result: urine volume = 720 mL in 6 hours, urine osmolarity = 75 mOsm, and plasma osmolarity = 300 mOsm.

Cosm= 0.5 mL/min; CH2O= + 1.5 mL/min and excretion of excess water.

How will bacterial breakdown of urine creatinine, increased plasma chromogens, and an incomplete urine collection affect the results of a creatinine clearance test?

Creatinine clearance results are lowered.

State whether the following are endogenous or exogenous test substances: creatinine, beta2microglobulin,and radionucleotides.

Endogenous substances: creatinine, beta2microglobulin; exogenous substances: radionucleotides.

Why is the glomerulus referred to as a nonselective filter?

Filtration is controlled only by particle size.

Statethe two colligative properties measured by clinical osmometers.

Freezing point and vapor pressure depression.

Why is the creatinine clearance test not useful for detecting early renal disease?

Healthy glomeruli are capable of increasing their filtering capacity in response to a decrease in functional glomeruli.

Name a chemical that is filtered by the glomerulus and reabsorbed and secreted by the tubules.

Hydrogen

titratable acidity

Hydrogen ions in the urine that can be quantitated by titration with a base to a pH of 7.4.

Following administration of ammonium chloride to a normal person, will the levels of titratable acidity and urinary ammonia be decreased or increased?

Increased.

When the body is dehydrated, is the production of ADH increased or decreased?

Increased.

A random urine sample has a urine osmolarity of 305 mOsm and a serum omolarity of 295 mOsm. Is this normalor abnormal?

Normal.

Why is urine osmolarity more representative of urine concentration than specific gravity?

Osmolarity represents the number of particles present and is not influenced by particle size and density.

renin-angiotensin-aldosterone system (RAAS)

Regulates flow of blood to and within the kidneys by responding to changes in blood pressure and plasma sodium content. A sustained fall in blood pressure causes the kidney to release renin. This is converted to angiotensin which then raised blood pressure directly by constricting the arterioles and stimulating the suprarenal gland to produce aldosterone which promotes sodium and water retention by the kidney, such that blood volume and blood pressure increase.

Why do tests for renal concentrating ability incorporate water deprivation?

Renal concentration is regulated by body hydration.

How does tubular secretion maintain the buffering capacity of the blood?

Secretion of hydrogen ions facilitates the reabsorption of bicarbonate ions.

How do the capillary endothelial cells in the glomerulus differ from other capillary endothelial cells?

The glomerular endothelial cells contain pores.

Define the term renal tubular acidosis.

The inability to produce an acid urine in the presence of metabolic acidosis

How will failure of the distal convoluted tubule to produce ammonia affect urine pH?

The pH is consistently alkaline.

Why is water not always reabsorbed from the collecting duct when it passes through the medulla?

The permeability of the walls of the collecting duct to water is controlled by ADH in response to body hydration.

When calculating creatinine clearance tests performed on children, are any additional calculations required? Why or why not?

The results must be corrected for body size.

Glomerular Filtration Rate (GFR)

The volume of plasma that is filtered by the glomerulus in a specified time.

State two major processes associated with the peritubular capillaries.

Tubular reabsorption and secretion.

If a waste product is not filtered at the glomerulus, how can it be removed from the blood?

Tubular secretion.

With which clinical osmometer is specimen evaporation of greatest concern?

Vapor pressure osmometer.

How does reabsorption in the descending loop of Henle differ from reabsorption in the ascending loop? What is the primary reason for this difference?

Water is passively reabsorbed from the descending loop, chloride is actively reabsorbed, and sodium is passively reabsorbed from the ascending loop; the walls of the ascending loop are impermeable to water, which maintains the osmotic gradient of the medulla.

When is the kidney stimulated to produce renin? What is the primary chemical affected by the renin-angiotensin-aldosterone system?

When blood pressure decreases, renin is produced to stimulate the retention of sodium.

When will a substance that is usually completely reabsorbed by active transport appear in the urine?

When the blood level of that substance reaches its renal threshold

nephron

a functional unit of the kidney that forms urine

aldosterone

a hormone that regulates reabsorption of sodium in the distal convoluted tubule

Countercurrent mechanism

a selective urine concentration process in the ascending and descending loops of Henle

afferent arteriole

a small branch of the renal artery through which blood flows to the glomerulus of the kidney

Creatinine

a substance formed by the breakdown of creatine during muscle metabolism

beta2-microglobulin

a subunit of the class I major compatibility antigens that enters the blood at a constant rate

Free water clearance

a test to determine the ability of the kidney to respond to the state of body hydration

podocytes

epithelial cells of the inner lining of Bowman's capsule that contain foot-like processes

antidiuretic hormone (ADH)

hormone produced by the hypothalamus regulate water reabsorption in the collecting duct

Active transport

movement of a substance across cell membranes into the bloodstream by electrochemical energy

passive transport

movement of molecules across cell membrane by diffusion because of a physical gradient

Shield of negativity

negative ions in the glomerular filtration barrier that prevent small proteins such as albumin from entering the urine filtrate

distal convoluted tubule

part of the nephron between the ascending loop of Henle and the collecting duct where the final concentration of urinary filtrate begins

Collecting duct

part of the nephron where the final concentration of urine take place through the reabsorption of water

renal threshold

plasma concentration of a substance at which active transport stops and increased amounts are excreted in the urine

renin

proteolytic enzyme produced by the kidney that reacts with angiotensinogen to produce angiotensin to increase blood pressure

Cystatin C

small protein produced at a constant rate by all nucleated cells

juxtaglomerular apparatus

specialized cells located on the afferent arteriole that regulate secretion of renin

glomerular filtration barrier

structure of the walls of the glomerular capillaries that prevents the filtration of large molecules from the blood into the the urine filtrate

tubular reabsorption

substances moved from the tubular filtrate into the blood by active or passive transport

Loops of Henle

the U-shaped part of renal tubule that consists of a thin descending limb and a thick ascending limb

peritubular capillaries

the capillaries that surround the renal tubules

Maximal reabsorptive capacity (Tm)

the maximum reabsorption ability for a solute by renal tubules

proximal convoluted tubule (PCT)

the nearest tubule to the glomerulus where reabsorption of essential substances begins

osmolality

the osmotic pressure of a solution expressed in milliosmoles per liter; it is only affected by the number of particles present

tubular secretion

the passage of substances from the blood in the peritubular capillaries to the tubular filtrate

efferent arteriole

the small renal artery branch through which blood flows away from the glomerulus

renal plasma flow

the volume of plasma passing through the kidneys per minute

glomerulus

tuft of capillary blood vessels located in Bowman's capsule where filtration occurs