24.4 Blood Flow and Filtered Fluid Flow

At least ___ of the resting cardiac output (1 liter per minute) typically flows through the kidneys for the purpose of removing unwanted substances.

20-25%

A filtrate is formed

when blood flows through the glomerulus, and some components of the plasma enter the capsular space.

Resulting in 2 fluid flow patterns:

• The flow of blood into and out of the kidney

• The flow of filtrate, tubular fluid, and urine through the nephron and other urinary system structures.

Blood is delivered to each kidney by way of a

renal artery

that arises from the abdominal aorta.

The renal artery branches as it enters the renal sinus into

segmental arteries.

Within the renal sinus, the segmental arteries branch to form the

interlobar arteries, which are located between the renal lobes (within the renal columns).

The interlobar arteries extend to the

corticomedullary junction.

The corticomedullary junction branches to form

arcuate arteries.

Arcuate arteries (definiton)

• arch-shaped

• projects parallel to the base of the medullary pyramid at the corticomedullary junction.

The arcuate arteries extend branches called

interlobular arteries or cortically radiate arteries

they project peripherally into the cortex (where renal lobules are located)

As the interlobular arteries extend into the cortex,

numerous small afferent arterioles branch from them.

Each afferent arteriole supplies blood to a

glomerulus.

Some blood plasma is filtered at the

glomerulus

this fluid enters the glomerular capsule of the renal corpuscle.

After this filtration event, most blood(which was unfiltered and remains within the glomerulus) exists the glomerulus through

an efferent arteriole.

Each efferent arteriole now branches into

a second capillary network, either the

• peritubular capillaries

• vasa recta.

The peritubular capillaries

associated with and intertwined around both the

• proximal convoluted tubules

• distal convoluted tubules

they primarily reside in the cortex of the kidney.

vasa recta capillaries

• “straight vessels” associated with the nephron loop

primarily reside in the medulla of the kidney.

When the blood reaches the 2nd capillary bed (peritubular capillaries or vasa recta),

the exchange of gases, nutrients, and wastes occurs between the tissues of the kidney and the blood.

They then drain into the network of veins.

Blood drains from both particular and vasa recta capillary beds into

small veins.

The smallest of these veins:

• interlobular veins

interlobular veins merge to form

arcuate veins at the base of the medullary pyramids

arcuate veins then form into

interlobular veins, which extend through the renal columns.

Interlobar veins merge in the renal sinus to form

the renal vein.

The renal vein,

which extends from the kidney at its hilum, drains blood into the inferior vena cava.

When blood flows through the glomerulus and is filtered, both water and solutes move from the blood plasma across the filtration membrane and into the capsular space to form:

filtrate.

Filtrate

plasma minus large solutes (most proteins)

Filtrate then enters the proximal convoluted tubule, where it is now called:

tubular fluid.

Tubular fluid flows through the proximal convoluted tubule, nephron loop and

distal convoluted tubule.

Tubular fluids from several distal convoluted tubules enter into small collecting tubules that empty into

larger collecting ducts.

Tubular fluid is not changed further after leaving the collecting ducts, and it is now called:

urine

Urine enters a papillary duct located within a renal papilla and then los progressively through spaces:

within the renal sinus of the kidney.

The specific spaces in order:

• minor calyx

• major calyx

• renal pelvis

The renal pelvis transports urine from the kidney into a

ureter

A ureter from each kidney transports urine into the

urinary bladder, where it is stored until it is excreted from the body through the urethra.