PHYSIO EXAM 4

What organs carry urine from kidney to bladder via waves of contractions?

Ureters

What organ is composed of smooth muscle and expands as it fills?

Bladder

What is total renal blood flow?

1200mL/min

How is blood delivered to the kidneys?

Via renal arteries

How does blood enter the nephron into the glomerulus?

Through the afferent arteriole

How does blood exit from the glomerulus?

Through efferent arteriole

What vessel supplies the peritubular capillaries that travel alongside the nephron?

Efferent arteriole

How does blood exit the kidneys?

Via venules and out through the renal vein

What are the roles of the kidney?

• Filtration of blood

  • Removes wastes

  • Body’s water balance

  • Conc. of electrolytes

  • Acid/base balance

• Regulation of blood volume and pressure

• Activation of Vitamin D

• Production of erythropoietin

What are the components of the nephron?

• Glomerulus

  • Afferent arteriole

  • Efferent arteriole

  • Peritubular capillaries

• Bowman’s capsule

• Proximal convoluted tubule

• Loop of Henle

• Distal convoluted tubule

• Collecting duct

What structure within the nephron detects sodium levels and is in close contact with the afferent arteriole?

Macula densa

What is the nonselective filter of plasma substances?

Glomerulus

What is the part of the nephron that encases the glomerulus?

Bowman’s capsule

What are the three layers that plasma filtrate must pass through?

• Capillary wall membrane of glomerulus

• Basement membrane

• Podocytes surround the outer surface of the basement membrane

What is the area of the nephron with the highest reabsorption levels and a very small amount of secretion?

Proximal tubule

What substances are mostly absorbed in the proximal tubule?

• 65% of Na and Water

• 98% Glucose

• 80% Bicarbonate

• 80% K

What portion of the loop of Henle is highly permeable to water, and its main function is to allow simple diffusion?

Thin descending

What portions of the loop of Henle is virtually impermeable to water?

Thin and thick ascending

What portion of the loop of Henle?:

• Virtually impermeable to water

• Epithelial cells with high metabolic activity capable of active reabsorption

  • 25% Na, Cl, and K

  • Others: calcium, bicarb, and magnesium

Thick ascending

What is the first portion of the distal tubule?

Macula densa

What part of the distal tubule has a similar reabsorption characteristics of the thick ascending limb of the loop of Henle?

Distal convoluted tubule

What part of the distal tubule has principal cells and intercalated cells?

Late distal/Cortical collecting tubules

What cells in the late distal tubule reabsorb Na and water and secretes K?

Principal cells

What cells in the late distal tubule plays a major role in acid-base regulation by secreting or reabsorbing hydrogen, bicarbonate, and K?

Intercalated cells

What is the final site for processing urine and plays a critical role in final urine output of water and solutes?

Medullary collecting duct

What hormone controls permeability of water in the medullary collecting duct?

ADH

What hormone stimulates Na and Water absorption and K and H secretion?

Aldosterone

These are stimuli for what hormone?:

• Low BP, Low sodium, Low volume

• Increased extracellular K concentration

• Increased angiotensin II levels

Aldosterone

What hormone works on the distal tubule/collecting duct and stimulates water reabsorption by increasing water permeability?

ADH

Without what hormone is water permeability low in the distal collecting ducts which results in large amounts of dilute urine to be excreted?

ADH

What does decreased BP and volume stimulate?

ADH

What is the relationship between osmolarity and solute concentration?

Increased osmolarity → Increased solute concentration

What causes a large volume of diluted urine where ADH is not needed?

Low osmolarity

What causes a small volume of concentrated urine where ADH is stimulated?

High osmolarity

What osmolarity?:

• More solute in blood/water deficit

• Causes more concentrated urine

• ADH stimulated

High osmolarity

What osmolarity?:

• Less solute in blood/excess water

• Causes more dilute urine

• ADH not stimulated

Low osmolarity

What hormone acts on the proximal tubule, thick ascending limb, distal/collecting tubule, and stimulates Na and water reabsorption and H secretion?

Angiotensin II

What hormone increases Na and Water reabsorption by:

• Indirectly by stimulating aldosterone secretion, which also increases Na reabsorption

• Constricts efferent arteriole

• Directly stimulates Na reabsorption along the nephron

Angiotensin II

What is the adequacy of renal function clinically defined by?

Glomerular filtration rate (GFR)

What should the glomerular filter NOT allow passage?

• Blood cells

• Plasma proteins

What is the GFR’s stability due to?

Autoregulation of renal blood flow

Effects on what arteriole?:

• Constriction

  • Decrease pressure, decrease GFR, decrease tubular blood flow, decrease RBF

• Dilation

  • Increase pressure, increase GFR, increase tubular blood flow, increase RBF

Afferent arteriole

Effects on what arteriole?:

• Constriction

  • Increase pressure, increase GFR, increase tubular blood flow, decrease RBF

• Dilation

  • Decrease pressure, decrease GFR, decrease tubular blood flow, increase RBF

Efferent arteriole

What are molecules that release H+ in solution (acidosis)?

Acids

What are molecules or ions that accept H+ (alkalosis)?

Bases

What is normal pH?

7.4

What is the acid-base physiology regulated by?

• Varying CO₂ excretion in the lungs

• Varying the rate of H and bicarb production in the kidney

Where is most of the bicarb reabsorbed?

Proximal tubule

Where is most of the H secreted by?

Proximal tubule

What system responds to changes in blood pressure and plasma sodium content as monitored by the juxtaglomerular apparatus?

Renin-Angiotensin-Aldosterone System (RAAS)

What structure in the kidney senses drops in BP and releases renin?

Juxtaglomerular apparatus

What enzyme, produced in the kidneys (JGA), coverts angiotensinogen to angiotensin I?

Renin

Where is angiotensin I converted to angiotensin II by ACE?

Lungs

What are the three ways angiotensin II corrects blood flow?

1. Causes vasoconstriction of renal arterioles (inc. BP)

2. Stimulates reabsorption of sodium in proximal convoluted tubule (Inc. BP)

3. Triggers the release of aldosterone which causes distal convoluted tubule to reabsorb Na+ and the release of ADH (Inc. BP)

As BP and the sodium levels rise, what happens to renin secretion?

Decreases

What is a decrease in extracellular volume counteracted by?

• Activation of RAAS

• Stimulation of SNS

• Increased ADH secretion → Increase renal fluid retention

What is an increase in extracellular volume counteracted by?

• Secretion of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)

  • Promotes loss of Na and water in urine

  • Inhibits secretion of ADH, renin, and aldosterone

How does calcitriol conserve calcium in the body?

• Increasing intestinal calcium absorption

• Reducing urinary calcium loss

• Promoting bone formation

What glycoprotein hormone produced by fibroblasts in the renal interstitium and is released in response to low oxygen perfusion (hypoxia)?

Erythropoietin

What protein stimulates RBC formation in bone marrow?

Erythropoietin

Where is the majority of glucose, sodium, and amino acids reabsorbed?

Proximal convoluted tubule

How is glucose transported in the proximal convoluted tubule?

SGLT2 transporter

What portion of the loop of Henle works by Na+/K+/Cl- transporter?

Ascending loop

What part of the nephron reabsorbs approximately 65% of filtered Na+?

Proximal tubule

What is the final excretion of Na+ determined by?

Variable reabsorption along the distal tubule and the collecting duct

What is the controlled plasma range?

3.5 → 5.5 mEq/L

What is the central hormone controlling K+ balance?

Aldosterone

Increased ECF K+ directly stimulates aldosterone secretion. How does aldosterone restore normal plasma K+?

Increases cellular uptake of K+ in skeletal muscle and increases renal K+ excretion

What are considered the other factors that affect K+?

• Insulin

  • Stimulates ingested K+ to move from ECF to ICF

  • Causes K+ uptake by liver and skeletal muscle

• Epinephrine

  • Stimulates K+ movement from ECF to ICF

  • During exercise, epinephrine secretion stimulates K+ reuptake into skeletal muscle

What stimulates an increase in ADH?

• Increased plasma osmolarity

• Decreased BP

• Decreased blood volume

What stimulates a decrease in ADH?

• Decreased plasma osmolarity

• Increased BP

• Increased blood volume

A patient’s afferent arteriole constricts while all other variables remain inchanged. What is the expect effect?

Decreased renal blood flow and decreased GFR

The thick ascending limb of the loop of Henle has which characteristic?

Active sodium, potassium, and chloride reabsorption with water impermeability

Which hormone directly increases water permeability of the collecting ducts?

Antidiuretic hormone (ADH)

A healthy patient has an increase in plasma osmolarity. What is the initial physiologic response?

Increased ADH release

Which nephron segment reabsorbs the largest percentage of filtered sodium under normal physiologic conditions?

Proximal convoluted tubule

The juxtaglomerular apparatus detects decreased sodium chloride delivery to the macula densa. What is the expected response?

Increased renin secretion

A healthy adult has reduced renal blood flow due to mild dehydration. Which hormone released by the kidney initiates activation of the RAAS?

Renin

The kidneys play a major role in vitamin D metabolism. Which process occurs within the proximal tubule?

Conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

The primary effect of calcitriol is to

Increase intestinal absorption of calcium

Erythropoietin production by the kidneys is primarily stimulated by

Renal hypoxia

Which nephron segment is impermeable to water but highly permeable to sodium chloride?

Thick ascending limb

Which hormone primarily increases sodium reabsorption in the principal cells of the collecting duct?

Aldosterone

A medical student asks why kidney disease often leads to both anemia and bone disease. Which explanation is most accurate?

The kidneys activate vitamin D and produce erythropoietin

Unlike skeletal cells, what cardiac cells form a highly branched network?

Myocytes

Where do myocyte-to-myocyte connections occur?

At intercalated disks

What do the gap junctions in the intercalated disks provide?

Low electrical resistance

What does a single adequate stimulus for action potential in one myocyte results in?

A rapid spread of excitation to all myocytes via gap junctions

What structure in the heart is able to contract both atria?

Bachmann’s bundle

The AV node and septum is the only place for signals to pass from the atria to the ventricles. What prevents other places in the heart from doing this?

Endocardial cushion

What is the resting electrical membrane potential that the axon maintains?

The outside if more positive than the inside

Mechanism of what?:

• Moves 3 sodium outside the cell for every 2 potassium brought in

Na/K pump

What molecule in the Na/K pump leaks back outside the cell more easily?

Potassium

What occurs during depolarization?

Sodium rushes into the cell

As the depolarization signal spreads, the axon recovers due to shutting off the sodium gates and the opening of the voltage dependent potassium gates, allowing for what?

Potassium to rush out, restoring membrane potential (Repolarization)

What occurs when repolarization happens and the signal cannot fire again until membrane potential is restored?

Refractory period

What cation always wants to move into the cell?

Calcium

What cation is normally much higher extracellularly than intracellularly due to a pump that pumps it outside of the cell?

Calcium

Voltage-dependent opening of the sodium channels may be accompanied by the voltage-dependent opening of the calcium channels, which causes what?

Further depolarization

What channels are slower than sodium channels?

Calcium