108.2

Filtration

first step in urine formation; filters excess fluid and waste products out of blood

reabsorption

renal tubules return nutrients and water back into capillaries

secretion

waste ions and hydrogen ions pass from the capillaries into the renal tubules

25%

The kidneys receive approximately what percentage of the blood pumped through the heart at all times?

1200 mL/min

How much blood flows through the kidneys per minute?

600-700 mL/min

How much plasma flows through the kidneys per minute?

The afferent arteriole supplies blood to the kidneys; the efferent arteriole carries the blood leaving the kidneys

What is the difference between the efferent and afferent arterioles?

Enters through C (renal artery) leaves through D (renal vein)

Map the renal blood flow from the renal artery to the renal vein.

1.73 m^2

What is the average BSA?

size; filters out molecular weights smaller than 70,000

What is non-selective filtration in Bowman's capsule based on?

cellular structure of capillary walls and Bowman's capsule; hydrostatic and oncotic pressure; RAAS

What other factors influence filtration in Bowman's capsule?

capillary wall - endothelial cells have pores (fenestrated) that block large molecules and cells

basement membrane- further restricts large molecules

Bowman's capsule inner layer - intertwining podocytes and membrance covered filtration slits

What are the three cellular layers of the Glomerulus?

shield of negativity

repels molecules with a negative charge; filters molecules that would otherwise pass through barrier

renin starts RAAS which helps maintain a consistent glomerular blood pressure; if systemic blood pressure is low, it dilates the afferent arteriole and constricts the efferent arteriole; if system BP is high, afferent arteriole constricts and efferent arteriole dilates

How does renin affect renal blood flow?

ultrafiltrate has proteins filtered out

How does ultrafiltrate differ from plasma?

proximal convoluted tubule

When does reabsorption of ultrafiltrate begin?

active transport

transport in tubular reabsorption in which substance must combine with a carrier protein

passive transport

transport in tubular reabsorption that takes place due to concentration or electrical potential differences

renal threshold

The concentration at which a substance in the blood that is not normally excreted by the kidneys begins to appear in the urine

tubules

where concentration of plasma ultrafiltrate mainly takes place in the nephron

descending loop of henle

part of loop of henle in which water reabsorbs due to osmotic pressure

ascending loop of henle

part of loop of henle in which chloride and sodium are actively reabsorbed; water impermeable

aldosterone

hormone that controls sodium reabsorption

collecting duct

where final concentration of filtrate takes place

anti-diuretic hormone

hormone that regulates reabsorption of water in collecting ducts; prevents dehydration

decreased ADH levels, increased urine output

How is ADH levels and urine output affected when the body is well hydrated?

increased ADH levels, decreased urine output

How is ADH levels and urine output affected when the body is dehydrated?

secretion

from blood to tubule

reabsorption

from tubules to blood

tubular secretion

eliminates waste products; regulates acid-base balance in body

phosphate and ammonia

two compounds that H+ ions combine with in urine elimination

glomerular, tubular, intersitial

three categories of renal disease

immunologic disorders, nephrotic syndrome, chemical exposure

examples of glomerular renal disease

damaged tubules, acute tubular necrosis, metabolic and hereditary disorders

examples of tubular renal disease

infections, UTI, inflammatory conditions, Pyelonephritis

examples of interstitial renal disease

Renal Lithiasis

kidney stones

urinary stasis, chemical concentration, pH

causes of renal lithiasis

filtering capacity of glomeruli

what glomerular filtration tests measure

it cannot be reabsorbed or secreted by tubules

what is an important criteria for substances used in filtration tests

endogenous

substance that is already present in body

exogenous

substance that must be added to body

urea

substance that is present in all urine specimens

40% of urea is reabsorbed

Why is Urea Clearance test not considered the best to measure filtration?

creatinine clearance test

most common laboratory test used for measuring renal filtration

must be a 24 hour urine specimen; urine must be refrigerated to prevent bacterial breakdown; tubular secretion increases with high blood creatinine levels; highly pigmented urine affects results

disadvantaged of creatinine clearance test

serum creatinine, cystatin C, Beta2microglobulin

What are some newer tests being used for filtration rate?

mL/min

unit of measure for creatinine clearance

to determine the amount of creatinine completely cleared from the plasma in one minute

principle of creatinine clearance test

C = UV/P x 1.73/BSA

formula for creatinine clearance test

can be used for routinely screening patients as part of a metabolic profile, to monitor patients already diagnosed with renal disease, and when prescribing medicine that require adequate renal clearance

clinical significance of glomerular filtration rate tests

1: GFR greater than or equal to 90 ml/min/1.73 m

2: GFR 60-89

3: GFR 30-59

4: GFR 15-29

5: GFR less than or equal to 15

stages of chronic kidney disease

Renal concentrating ability

what does renal reabsorption tests measure?

osmolality

most common renal concentration ordered in lab?

osmometer

what measures osmolality

freezing point/vapor pressure

two types of osmometers

evaluates renal concentration ability, monitors course of renal disease, monitors fluid or electrolyte therapy, differentiates between hyponatremia (not enough Na+2) and hypernatremia (too much Na2+), evaluates secretion and response to ADH

clinical significance of monitoring osmolality

3:1

normal urine to blood ration when monitoring hydration controlled osmolality

tubular secretion test

test used to measure complete blood flow through nephrons

p-aminohippuric acid (PAH)

example of tubular secretion test

Osmolarity

total concentration of all solute particles in a solution

1. calyx

2. renal pelvis

3. medulla

4. cortex

5. ureter

6. renal vein

7. renal artery

label

1. glomerulus

2. renal cortex

3. cortical nephron

4. renal medulla

5. juxtamedullary nephron

6. collecting duct

7. loop of henle

8. renal tubule

label