Lecture 19: Renal 2 — The Nephron, Glomerular Activity & Filtration -

What is a nephron?

The structural and functional unit of the kidney.

Approximately how many nephrons are in each kidney?

More than one million.

What are the four basic kidney processes?

Filtration, reabsorption, secretion, and excretion.

What is glomerular filtration?

Movement of fluid from glomerular blood into Bowman's capsule.

What is tubular reabsorption?

Movement of substances from tubule fluid back into blood.

What is tubular secretion?

Movement of substances from blood into tubule fluid.

What is excretion?

Elimination of urine from the body.

What are the two main parts of a nephron?

Renal corpuscle and renal tubule.

What structures form the renal corpuscle?

Glomerulus and Bowman's (glomerular) capsule.

What is the glomerulus?

A tuft of capillaries where blood is filtered.

What is Bowman's capsule?

A cup-shaped structure that collects filtrate.

Which arteriole brings blood into the glomerulus?

Afferent arteriole.

Which arteriole carries blood away from the glomerulus?

Efferent arteriole.

What are fenestrated capillaries?

Capillaries with pores that facilitate filtration.

What are podocytes?

Cells around glomerular capillaries that form filtration slits.

Why is the filtration barrier selective?

It allows water and small solutes through but limits cells and large proteins.

What is the proximal convoluted tubule (PCT)?

The tubule segment immediately after Bowman's capsule, specialized for reabsorption.

What is the distal convoluted tubule (DCT)?

A later tubule segment involved in fine-tuning fluid and electrolyte balance.

What is the nephron loop?

A descending and ascending segment that helps establish a medullary osmotic gradient.

What are cortical nephrons?

The common nephron type, mainly in cortex, with relatively short loops.

About what percentage of nephrons are cortical?

About 85%.

What are juxtamedullary nephrons?

Nephrons near the cortex-medulla boundary with long loops extending into the medulla.

Why are juxtamedullary nephrons important?

Their long loops help concentrate urine.

What are peritubular capillaries?

Capillaries surrounding renal tubules that exchange substances with them.

What are the vasa recta?

Capillaries associated with long loops of juxtamedullary nephrons.

What is glomerular filtration rate (GFR)?

The volume of filtrate formed by both kidneys per minute.

What mainly drives glomerular filtration?

Hydrostatic pressure in glomerular capillaries.

What does glomerular blood hydrostatic pressure do?

Pushes fluid out of blood into Bowman's capsule.

What does capsular hydrostatic pressure do?

Opposes filtration by pushing back against fluid entering the capsule.

What does glomerular blood oncotic pressure do?

Opposes filtration by pulling water toward blood proteins.

What is net filtration pressure (NFP)?

The combined pressure favoring filtration minus pressures opposing it.

How does higher net filtration pressure affect GFR?

It tends to increase GFR.

What is the juxtaglomerular apparatus (JGA)?

A region where the DCT contacts arterioles and helps regulate filtration.

What is the macula densa?

DCT cells that sense tubular NaCl and signal the JGA.

What is the myogenic autoregulatory response?

Afferent arterioles constrict when stretched by higher pressure.

How does afferent arteriolar constriction affect GFR?

It reduces glomerular pressure and tends to lower GFR.

What happens when afferent arteriolar pressure rises?

The arteriole stretches and constricts to resist an increase in GFR.

What is tubuloglomerular feedback?

The macula densa uses tubular NaCl information to adjust afferent arteriolar tone.

What does high NaCl at the macula densa usually indicate?

Filtration and tubular delivery are high.

What happens after the macula densa senses high NaCl?

Signals promote afferent constriction, reducing GFR.

Why is GFR autoregulated?

To keep filtration relatively stable despite changes in arterial pressure.

About how much cardiac output goes to the kidneys?

About 20%, roughly 1 L/min if output is 5 L/min.

Where does the renal artery originate?

The abdominal aorta.

Where does the renal vein drain?

The inferior vena cava.