Renal Physiology: Nephron Filtration, GFR Regulation & Kidney Functions Flashcards | Quizlet

What are the major functions of the kidneys?

Regulate blood ionic composition, pH, osmolarity, glucose, volume, and pressure; release EPO and calcitriol; excrete wastes.

Which ions do the kidneys regulate in the blood?

Na+, K+, Ca2+, Cl−, and phosphate.

How do the kidneys regulate blood pressure?

By secreting renin and adjusting renal vascular resistance.

What hormone do the kidneys release to stimulate RBC production?

Erythropoietin (EPO).

What vitamin do the kidneys activate?

Calcitriol (active vitamin D).

What substances do the kidneys excrete?

Wastes and foreign substances.

What is the functional unit of the kidney?

The nephron.

What are the three basic processes performed by nephrons?

Glomerular filtration, tubular reabsorption, and tubular secretion.

Where does glomerular filtration occur?

Renal corpuscle.

Where does tubular reabsorption occur?

Renal tubules and collecting duct.

Where does tubular secretion occur?

Renal tubules and collecting duct.

What is glomerular filtrate?

Fluid that enters the glomerular capsular space.

Approximately how much filtrate is produced daily?

About 48 gallons per day.

How much urine is normally produced daily?

About 1–2 quarts.

What is the filtration fraction?

The fraction of plasma entering afferent arterioles that becomes filtrate.

What is the normal filtration fraction?

Approximately 20% of plasma.

What three features enhance glomerular filtration?

Thin filtration membrane, large capillary surface area, and high glomerular blood pressure.

What is the endothelial-capsular membrane?

The filtering unit of a nephron.

What are the three layers of the filtration membrane?

Glomerular endothelium, glomerular basement membrane, and slit membranes between podocyte pedicels.

What does the glomerular endothelium prevent from filtering?

All blood cells and platelets.

What does the glomerular basement membrane prevent from filtering?

Large plasma proteins.

What do slit membranes between podocyte pedicels prevent from filtering?

Medium-sized plasma proteins.

What is the principle of glomerular filtration?

Pressure forces fluids and solutes through a membrane.

What pressure promotes glomerular filtration?

Glomerular blood hydrostatic pressure (GBHP).

What are the two pressures opposing glomerular filtration?

Capsular hydrostatic pressure (CHP) and blood colloid osmotic pressure (BCOP).

What causes capsular hydrostatic pressure?

Back pressure from fluid entering the capsular space.

What causes blood colloid osmotic pressure?

Plasma proteins that cannot be filtered.

What is the typical GBHP?

55–60 mmHg.

What is the typical CHP?

15 mmHg.

What is the typical BCOP?

30 mmHg.

What is the formula for net filtration pressure?

NFP = GBHP − (CHP + BCOP).

What is the typical net filtration pressure?

10 mmHg.

How is NFP calculated using typical values?

55 − (15 + 30) = 10 mmHg.

Why is glomerular blood pressure high?

The efferent arteriole is smaller in diameter than the afferent arteriole.

What is glomerular filtration rate (GFR)?

The amount of filtrate formed in all renal corpuscles of both kidneys per minute.

What is the average adult male GFR?

125 mL/min.

What affects GFR?

Changes in net filtration pressure.

At what GBHP does filtration stop according to the lecture?

45 mmHg.

At what mean arterial pressure do kidneys function normally according to the lecture?

80–180 mmHg.

What are the three principal mechanisms controlling GFR?

Renal autoregulation, neural regulation, and hormonal regulation.

What is renal autoregulation?

Mechanisms that maintain relatively constant GFR despite changes in arterial blood pressure.

What are the two mechanisms of renal autoregulation?

Myogenic mechanism and tubuloglomerular feedback.

What is the myogenic mechanism?

Increased blood pressure stretches the afferent arteriole, causing smooth muscle contraction and reduced diameter.

How quickly can the myogenic mechanism adjust GFR?

Within seconds.

What happens to the afferent arteriole when systemic blood pressure rises?

It stretches and constricts.

How does afferent arteriole constriction affect GFR?

It decreases GFR.

What is tubuloglomerular feedback?

A mechanism where the macula densa detects changes in tubular Na+, Cl−, and water delivery.

What does the macula densa detect during elevated GFR?

Increased Na+, Cl−, and water flow through the renal tubule.

What does the macula densa release during tubuloglomerular feedback?

A vasoconstrictor from the juxtaglomerular apparatus.

What is the effect of tubuloglomerular feedback on the afferent arteriole?

It constricts the afferent arteriole and reduces GFR.

Which nervous system supplies blood vessels of the kidneys?

The sympathetic nervous system.

How does sympathetic stimulation affect renal arterioles?

It causes vasoconstriction of afferent arterioles.

What happens to renal blood vessels at rest?

They are maximally dilated due to minimal sympathetic activity.

What happens during moderate sympathetic stimulation?

Both afferent and efferent arterioles constrict equally, decreasing GFR.

What happens during extreme sympathetic stimulation?

Afferent arteriole constriction reduces GFR and urine output.

Why does extreme sympathetic stimulation reduce urine output?

It allows blood flow to be redirected to other tissues.

What hormone increases GFR according to the lecture?

Atrial natriuretic peptide (ANP).

What stimulates ANP release?

Stretching of the atria due to increased blood volume.

How does ANP increase GFR?

It relaxes glomerular mesangial cells, increasing capillary surface area.

How does angiotensin II affect GFR according to the lecture?

It reduces GFR by constricting both afferent and efferent arterioles.

Why must nephrons reabsorb approximately 99% of filtrate?

Normal GFR is so high that excessive fluid would be lost without reabsorption.

What is tubular reabsorption?

Movement of water and useful substances from tubular fluid into the blood.

What is tubular secretion?

Removal of wastes from blood and secretion into urine.

What are the two routes of tubular reabsorption?

Paracellular and transcellular.

What is paracellular reabsorption?

Movement between adjacent tubule cells by diffusion.

What percentage of reabsorbed material moves paracellularly in some tubule parts?

Approximately 50%.

What is transcellular reabsorption?

Movement through a tubule cell across its apical and basolateral membranes.

What are the four passive transport mechanisms?

Simple diffusion, facilitated diffusion, osmosis, and filtration.

What is primary active transport?

Transport that uses ATP directly to pump substances across a membrane.

What is secondary active transport?

Transport using energy stored in an ion's electrochemical gradient.

What is the role of apical and basolateral membranes?

They contain different transport proteins for movement across tubule cells.

Why is sodium reabsorption important?

It drives the reabsorption of many other solutes and water.

Where is the Na+/K+ ATPase located in tubule cells?

Basolateral membrane.

What does the Na+/K+ ATPase do?

Pumps Na+ out of the tubule cell cytosol.

How is water reabsorbed in the kidneys?

Only by osmosis.

What is obligatory water reabsorption?

Water is obliged to follow solutes being reabsorbed.

What is facultative water reabsorption?

Water reabsorption in the late DCT and collecting duct controlled by ADH.

Where does most solute and water reabsorption occur?

Proximal convoluted tubule (PCT).

Why are sodium levels low inside PCT cells?

The basolateral Na+/K+ pump maintains low intracellular sodium.

What substances are normally 100% reabsorbed in the first half of the PCT?

Glucose, amino acids, lactic acid, water-soluble vitamins, and other nutrients.

What transporters reabsorb glucose in the PCT?

Na+ symporters.

How do Na+ symporters reabsorb glucose?

They move Na+ and glucose together into PCT cells.

What do Na+/H+ antiporters accomplish in the PCT?

Na+ reabsorption, HCO3− reabsorption, water reabsorption, and H+ secretion.

How do PCT cells produce H+ for Na+/H+ antiporters?

CO2 combines with water to form H2CO3, which dissociates into H+ and HCO3−.

What does caffeine do to Na+ reabsorption according to the lecture?

Caffeine inhibits Na+ reabsorption.

What is the electrical effect of Cl− diffusion into interstitial fluid?

It makes tubular fluid more positive than interstitial fluid.

What does the electrical potential difference promote?

Passive paracellular reabsorption of Na+, K+, Ca2+, and Mg2+.

How does solute reabsorption promote water reabsorption?

It creates an osmotic gradient that draws water by osmosis.

Which nephron regions are especially permeable to water?

PCT and descending limb of the loop of Henle.

Which water channels are abundant in the PCT and descending limb?

Aquaporin-1 channels.

What can substitute for H+ on Na+/H+ antiporters?

Ammonium (NH4+).

What is secreted when NH4+ substitutes for H+?

NH4+ is secreted into tubular fluid.

Where are urea and ammonia filtered?

At the glomerulus.

Where are urea and ammonia also secreted?

By proximal convoluted tubule cells into the tubules.

What transporter is found in the thick ascending limb?

Na+-K+-Cl− symporter.

What ions are reabsorbed by the thick ascending limb symporter?

Na+, K+, and Cl−.

Why is the main effect of the thick ascending limb symporter Na+ and Cl− reabsorption?

K+ leakage channels return much of K+ to tubular fluid.

What is the charge of interstitial fluid and blood around the thick ascending limb according to the lecture?

Negative.

Where do cations passively move around the loop of Henle?

Into the vasa recta.

What happens to water in the descending limb?

Filtered water is reabsorbed.