Urinary SystemLecture 2, Q3 2011

Nephronfunctional unit of the kidney

Parts of the nephronParts of the nephron A normal kidney contains 800,000 to one million nephrons

• Renal corpuscle consists of

• Glomerulus – a tuft of capillaries associated with a renal tubule

• Bowman’s capsule – a cup-like sac that houses the glomerulus

Glomerulus inside Bowman’s capsule together called Renal Renal CorpuscleCorpuscle

Renal Tubule

• PCT - Proximal convoluted tubule – reabsorbs water and solutes from filtrate & secretes substances into it

• Loop of Henle – part of the PCT that is hairpin shaped

• DCT - Distal convoluted tubule – functions more for secretion than reabsorption

Nephron types

• Cortical nephrons – 85% of nephrons located in the renal cortex

• Juxtamedullary nephrons – located at the cortex-medulla junction– Loops of Henle deeply invade the medulla– Extensive thin segments produce highly

concentrated urine

Vasa recta

• After the efferent arterioles descend into the medulla they divide into long thin STRAIGHT capillaries called the vasa recta (Latin for straight vessels)

Urine formationThe 3 big-picture processes

Glomerular filtration Glomerular filtration –– Tubular absorption Tubular absorption ++ Tubular secretion Tubular secretion == Excretion Excretion

Glomerular filtration

• Separates plasma fluid and small solutes from larger proteins and blood cells

• High blood pressure in glomerular capillaries forces fluid through capillary walls into Bowman’s capsule

Tubular reabsorption

• Returns filtered water and nearly all major nutrients to the blood

• Primary active transport of Na+ across cell membrane drives diffusion of Cl- and water; provides energy for reabsorption by secondary active transport or passive diffusion of other substances

Tubular secretion

• Removes harmful or excess substances from blood

• Substances move by active transport or passive diffusion from capillaries into the tubule

Filtrate contents = glomerular filtrate

• Contains all plasma components except protein

• Loses water, nutrients, and essential ions to become urine

• The urine contains metabolic wastes and unneeded substances

Countercurrent mechanism: Tubes that interact to make the excretory process work.• Involves sodium pumps that create an area of high

sodium concentration deep in the medulla, near the collecting duct

• This allows the kidneys to produce dilute or concentrated urine depending on your body’s needs

• Interaction between the flow of filtrate through the loop of Henle (countercurrent multiplier) and the flow of blood through the vasa recta blood vessels (countercurrent exchanger) allow this process to work

Urinary infections UTIs

• Pyelitis - Acute inflammation of the pelvis of the kidney, caused by bacterial infection.– the renal pelvis, the central part of the kidney

is where urine accumulates before discharge.

– It is more common in women than in men.

Pyelonephritis• pyelonephritis is when a urinary tract infection

has reached the pyelum (pelvis) of the kidney

• Symptoms include:

• Loin pain, often severe

• Fever and shivers

• Blood-stained urine

• Foul-smelling and cloudy urine

• Painful and frequent urination

• Nausea and vomiting

Volume of blood filtered daily

• 200 liters!

• The kidneys filter the body’s entire plasma volume 60 times each day