URINARY SYSTEM KIDNEY FUNCTION

What are the three main functions of the Kidney?

1. Regulate water concentration, inorganic ions, ph, and blood volume

2. Remove metabolic waste and foreign chemicals from blood, excreting them in urine

3. Produce hormones: Erythropoietin: controls RBC production

• renin: influences blood pressure and Na+ balance

• 1,25-dihydroxyvitamin: influences Ca2+ balance

What is the flow of the urinary system? Where are the kidneys located?

Two kidneys → Ureters→ Bladder→ Urethra

Two kidneys located in the retroperitoneal space

What are the two main layers of the kidney, and what does each contain?

Renal Cortex (outer):

• Contains the renal corpuscle and tubules which are single layer of epithelial cells, that add and removes substances)

Renal Medulla (inner):

• Contains the Loop of Henle and collecting duct

The overall functional unit of the kidney.

It is located in both the cortex and medullary regions.

Nephron

What are the components of the renal corpuscle?

1. Glomerulus: Glomerular capillaries, where filtration occurs

2. Bowman’s Capsule:

   • Parietal: Surrounds the glomerulus

   • Visceral: Lies in contact with capillaries (these are podocytes)

3. Afferent Arteriole: Blood enters here

4. Efferent Arteriole: Blood leaves here

How do the afferent and efferent arterioles affect filtration?

Afferent Arteriole (blood in):

• Dilated → Increases filtration

• Constricted → Decreases filtration

Efferent Arteriole (blood out):

• Constricted → Increases filtration

• Dilated → Decreases filtration

What gets filtered at the renal corpuscle, and what does not?

Freely filtered:

• Molecules less than 8nm

• Molecules not highly negative

• 20% of plasma becomes ultrafiltrate

Not filtered:

• Erythrocytes (red blood cells)

• Most plasma proteins

What three layers must filtrate cross, and what determines if a substance is filtered?

1. Capillary Endothelial Cells (have fenestrations/holes)

2. Basement Membrane

3. Podocyte Filtration Slits

Determining factors:

• Size

• Charge

visceral layer of Bowman's capsule.

They lie in direct contact with the glomerular capillaries and contain filtration slits that plasma passes through.

Podocytes

Trace the path of blood through the renal corpuscle.

Afferent Arteriole(blood enters) → Glomerulus(filtration) → Efferent Arteriole(blood leaves)

Trace the path of filtrate from Bowman's space to the renal pelvis

Nephron Ultrafiltrate flow

Bowman's Space → Proximal Convoluted Tubule → Loop of Henle → Distal Convoluted Tubule → Collecting Duct → Renal Pelvis

What are the two types of nephrons?

Cortical Nephrons (85%):

• Short Loop of Henle

Juxtamedullary Nephrons (15%):

• Located next to the medulla

• Long Loop of Henle

• Peritubular capillaries are called Vasa recta

BOTH CONTAIN GLOMECULAR CAPILLARIES(in renal corpuscle) AND PERITUBULAR CAPILLARIES(surround tubules)

• All secreted, none reabsorbed, all excreted

para-aminohippurate

• None secreted, some reabsorbed, some excreted

Sodium

• None secreted, all reabsorbed, none excreted

Glucose

bulk flow process; plasma filtered from the glomerular capillaries → Bowman's space, creating ultrafiltrate.

filtrate has virtually the same substance concentrations as plasma.

regulated by pressure and is under physiological control.

glomerular filtration

What are the Opposing Starling forces that determine glomerular filtration?

Favors Filtration: (Glomerular capillary hydrostatic pressure/blood pressure) HIGHEST

OPPOSING FILTRATION

• Hydrostatic pressure in Bowman’s space- LOWEST

• Osmotic pressure of blood (due to higher protein concentration in blood than in Bowman’s capsule)- MIDDLE

• NET FILTRATION= PGC-PBS-πGC

How does constricting the afferent arteriole affect filtration?

Constricting the afferent arteriole decreases the amount of blood entering glomerulus.

Decreases glomerular capillary hydorostatic pressure→decreases filtration

How does dilating the afferent arteriole affect filtration?

Dilating the afferent arteriole increases the amount of blood entering the glomerulus

Increases glomerular capillary hydrostatic pressure→increase filtration

How does constricting the efferent arteriole affect filtration?

Makes it harder for blood to leave glomerulus, causing blood to back up

Increases glomerular capillary hydrostatic pressure→increase filtration

How does dilating the efferent arteriole affect filtration?

Makes it easier for blood to leave glomerulus

Decreases glomerular capillary hydrstaic pressure→decreases filtration

Filtered from Glomerular capillaries into the Bowman’s Capsule

PLASMA

What are the 3 basic renal processes

1. Glomerular Filtration: blood to tubule

2. Tubular Secretion: blood to tubule

3. tubular Reabsorption: tubule to blood

What is the equation for a given subtance that appears in urine?

Amount excreted (urine)= Amount filtered + Amount secreted - Amount Reabsorbed

(ALL THREE PROCESSES DONT APPLY TO ALL SUBSTANCES)

Renal Handling of Various substances

1. Para-aminohippurate

2. Soidum

3. Glucose

ALL UNDER PHYSIOLOGICAL CONTROL

Glomerular filtration is described as a “Tug of War”, Net filtration flows towards ____ for (+) and _____for (-)

Bowmans Capsule

Glomerular Capillary