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Questions and Answers

Which specific action does aldosterone NOT perform in principal cells to enhance sodium reabsorption?

Stimulates the synthesis of sodium channels

Increases the permeability of cell membranes to sodium (correct)

Enhances the activity of Na+/K+ ATPase pumps

Upregulates sodium-hydrogen exchangers

What hormone primarily acts to elevate potassium levels in the blood despite aldosterone's role in the distal convoluted tubule?

Insulin (correct)

Atrial natriuretic peptide

Epinephrine

Cortisol

Which mechanism does NOT play a role in urea reabsorption in the collecting ducts?

Concentration gradient established by the thick ascending limb

Facilitated diffusion through transporters

Active transport via ATP consumption (correct)

Effects of antidiuretic hormone

What physiological condition triggers the release of ADH from the posterior pituitary?

Slight changes in ECF osmolarity Signup and view all the answers

Which statement correctly describes the water permeability of the late distal convoluted tubule?

It is impermeable to water under normal conditions. Signup and view all the answers

What role does ADH play in the function of aquaporin-2 in the collecting ducts?

Stimulates its insertion into the apical membrane Signup and view all the answers

What is the primary effect of aldosterone on potassium secretion in the distal convoluted tubule?

Increases potassium secretion into the lumen Signup and view all the answers

Which condition describes hyperkalemia and its implications?

Elevated potassium leading to potential cardiac complications Signup and view all the answers

Which of the following contributes to the countercurrent multiplication in the loop of Henle?

Active transport of sodium and chloride in the thick ascending limb Signup and view all the answers

What is the primary reason for the tight regulation of potassium levels in the blood?

High potassium levels can disrupt electrical potentials across cell membranes Signup and view all the answers

What is the primary mechanism for glucose reabsorption in the nephron?

Active transport via Na+/glucose symporters Signup and view all the answers

How much urea is typically reabsorbed in the nephron?

50% Signup and view all the answers

Which function is performed by the ascending limb of the Loop of Henle?

Reabsorption of sodium Signup and view all the answers

What percentage of sodium is reabsorbed in the early Distal Convoluted Tubule?

5% Signup and view all the answers

What role does aldosterone play in the nephron?

Stimulates reabsorption of sodium in the late Distal Convoluted Tubule Signup and view all the answers

In the Loop of Henle, which segment is primarily responsible for water reabsorption?

Descending limb Signup and view all the answers

What is the primary reason proteins are not found in the filtrate of Bowman’s capsule under normal physiological conditions?

Proteins are too large to pass through the filtration membrane. Signup and view all the answers

Which structure is NOT involved in the renin-angiotensin-aldosterone system?

Peritubular capillaries Signup and view all the answers

What is the effect of ADH on the nephron?

Increases water reabsorption in the collecting ducts Signup and view all the answers

Which transporters are involved in glucose reabsorption in the proximal convoluted tubule?

SGLT1/2 on the apical membrane and GLUT on the basolateral membrane. Signup and view all the answers

What is unique about urea reabsorption in the nephron?

It is reabsorbed, despite being a waste product, to maintain osmotic balance. Signup and view all the answers

Which factor contributes to the net filtration pressure in the glomerulus?

Glomerular capillary hydrostatic pressure Signup and view all the answers

Which cellular feature is crucial for filtration in the glomerulus?

Fenestration Signup and view all the answers

In the Loop of Henle, which limb is primarily involved in the reabsorption of water?

Thin descending limb. Signup and view all the answers

What is the significance of the NKCC2 transporter in the thick ascending limb of the Loop of Henle?

It facilitates the reabsorption of Na, K, and Cl, contributing to the vertical osmotic gradient. Signup and view all the answers

Which hormones primarily regulate calcium reabsorption in the early distal convoluted tubule?

Parathyroid hormone and calcitriol. Signup and view all the answers

Which cells in the late distal convoluted tubule are primarily responsible for responding to aldosterone?

Principal cells. Signup and view all the answers

How is the renin-angiotensin-aldosterone system (RAAS) primarily activated?

Decreased sodium concentration detected by macula densa cells. Signup and view all the answers

What is the primary outcome of the RAAS system?

Increasing blood pressure and sodium retention. Signup and view all the answers

What type of transport mechanism is primarily utilized in the reabsorption processes of the proximal convoluted tubule?

Secondary active transport. Signup and view all the answers

What is the primary mechanism for glucose reabsorption in the nephron?

Active transport via SGLT Signup and view all the answers

Which statement best describes the reabsorption process of urea in the nephron?

It undergoes both passive reabsorption and secretion. Signup and view all the answers

What role does the Loop of Henle play in urine concentration?

It generates a concentration gradient through the countercurrent multiplication mechanism. Signup and view all the answers

Which action occurs primarily in the distal convoluted tubule?

Secretion of potassium ions Signup and view all the answers

What triggers the renin-angiotensin-aldosterone system to activate?

Decreased blood volume or pressure Signup and view all the answers

How does sympathetic nervous system stimulation affect GFR?

It decreases GFR by constricting afferent arterioles. Signup and view all the answers

Which of the following does NOT contribute to the formation of the net filtration pressure (NFP)?

Oncotic pressure of the interstitial fluid Signup and view all the answers

What effect does tubuloglomerular feedback (TGF) have on GFR?

It decreases GFR when the flow of filtrate is too high. Signup and view all the answers

Which components contribute to the filtering membrane of the glomerulus?

Endothelial cells, basement membrane, and podocytes Signup and view all the answers

Which physiological response occurs when the afferent arteriole is constricted?

Decreased hydrostatic pressure in the glomerulus Signup and view all the answers

Study Notes

Late DCT - Aldosterone and Na+ Reabsorption

Aldosterone increases Na+ reabsorption in principal cells of the late DCT via three mechanisms:
- Increased synthesis of Na+ channels on the apical membrane, allowing more Na+ to enter the cell.
- Increased synthesis of Na+/K+ pumps on the basolateral membrane, enhancing Na+ transport out of the cell and into the blood.
- Stimulation of K+ secretion into the lumen, creating an electrochemical gradient favorable for Na+ reabsorption.

Late DCT - Aldosterone and K+ Secretion

Aldosterone promotes K+ secretion into the urine through principal cells of the late DCT by:
- Increasing the number of K+ channels on the apical membrane, facilitating K+ movement from the cell into the lumen.
- Stimulating Na+/K+ pumps on the basolateral membrane, increasing K+ entry into the cell, which then drives K+ secretion.
- Increasing K+ permeability in the apical membrane, further enhancing K+ secretion.

K+ Homeostasis

K+ levels in the blood are tightly regulated due to its critical role in various physiological processes, including nerve impulse transmission and muscle contraction.
Most K+ in the body resides within cells, and only a small proportion is found in the extracellular fluid (ECF).
Hyperkalemia (elevated K+ levels) is a medical emergency, potentially leading to cardiac arrhythmias and death.
Hormones that regulate K+ balance include:
- Insulin, which promotes K+ uptake into cells.
- Epinephrine, which also stimulates K+ entry into cells.
- Aldosterone, indirectly affecting K+ by enhancing its secretion into urine.

K+ Shift into ECF

Factors causing K+ to enter the ECF include:
- Increased cell lysis (cell death) releasing K+ into the ECF.
- Acidosis, driving K+ out of cells in exchange for H+ ions.

K+ Homeostasis Response

Immediate Response: The body's immediate response to elevated K+ levels in the blood involves shifting K+ into cells using insulin and epinephrine, temporarily lowering ECF K+ levels.
Long-Term Response: The kidneys, under the influence of aldosterone, enhance K+ secretion, effectively eliminating excess K+ from the body.

Alpha-Intercalated Cells of Late DCT

Alpha-intercalated cells are specialized cells in the late DCT that secrete H+ ions into the urine, contributing to acid-base regulation.

Collecting Ducts

Vertical Osmotic Gradient (VOG): The collecting ducts rely on the action of the thick ascending limb of the loop of Henle to create a VOG, allowing the kidneys to concentrate urine.
VOG Strength: A weak VOG is created by only the thick ascending limb of the loop of Henle. A strong VOG involves both the thick ascending limb and the collecting duct's ability to move urea into the interstitial space.

Water Permeability in Different Nephron Segments

PCT: Freely permeable to water.
Descending Limb of Henle: Permeable to water.
Ascending Limb of Henle: Impermeable to water.
DCT: Impermeable to water under normal conditions.
Collecting Ducts: Variable water permeability regulated by ADH.

ADH's Influence on Collecting Ducts

Antidiuretic Hormone (ADH) or Vasopressin: Increases water permeability in the collecting ducts by promoting the insertion of aquaporin-2 (AQ2) water channels into the apical membrane.
AQ2: An aquaporin protein that allows water to pass through the cell membrane. It is located in the apical membrane of collecting duct cells and is dependent on ADH for its insertion.

Urine Production in Different ADH States

Absence of ADH: Large volumes of dilute urine (low osmolarity) are produced due to the lack of water reabsorption in the collecting ducts.
Presence of ADH: Small volumes of concentrated urine (high osmolarity) are produced because ADH enhances water reabsorption in the collecting ducts.

ADH Insertion Mechanism

ADH inserts AQ2 into the apical membrane of the collecting duct cells through a complex process involving the binding of ADH to its receptor, stimulating a signaling cascade that ultimately leads to the translocation of AQ2 from intracellular stores to the cell surface.

ADH Secretion

ADH is released from the posterior pituitary gland in response to slight increases (1%) in ECF osmolarity.
ADH is secreted by specialized osmoreceptors in the brain, which are highly sensitive to changes in ECF osmolarity.

Summary of ADH and Urine Concentration

ADH promotes water reabsorption, leading to concentrated urine and water conservation.
In the absence of ADH, water is lost, resulting in large volumes of dilute urine.

Key Terms

Cortex: Outer layer of the kidney.
Medulla: Inner layer of the kidney.
Renal Artery: Blood vessel supplying blood to the kidney.
Renal Vein: Blood vessel carrying blood away from the kidney.
Pyramids: Cone-shaped structures in the medulla.
Calyx: Funnel-shaped structure collecting urine from pyramids.
Renal Pelvis: Funnel-shaped structure collecting urine from the calyces.
Ureter: Tube carrying urine from the kidney to the bladder.
Nephron: Functional unit of the kidney responsible for urine formation.
Afferent Arteriole: Blood vessel supplying blood to the glomerulus.
Glomerulus: Capillary network where filtration occurs.
Efferent Arteriole: Blood vessel carrying blood away from the glomerulus.
Peritubular Capillaries: Capillary network surrounding the renal tubules.
Vasa Recta: Blood vessels running parallel to the loop of Henle.
Bowman's Capsule: Cup-like structure surrounding the glomerulus.
PCT: Proximal convoluted tubule.
Loop of Henle: Descending and ascending limbs of the nephron.
DCT: Distal convoluted tubule.
Collecting Ducts: Tubules collecting filtrate from nephrons.
Superficial or Cortical Nephrons: Nephrons with short loops of Henle.
Juxtamedullary Nephrons: Nephrons with long loops of Henle.
Vertical Osmotic Gradient: Concentration gradient established in the renal medulla.
Detrusor Muscle: Smooth muscle in the bladder wall.
Internal Sphincter: Smooth muscle surrounding the urethra.
External Sphincter: Skeletal muscle surrounding the urethra.
Net Filtration Pressure (NFP): Pressure difference that drives filtration.
Fenestration: Pores in capillary walls.
Glomerular Basement Membrane: Specialized membrane surrounding the glomerulus.
Podocytes: Specialized cells surrounding the glomerular capillaries.
Filtration Slits: Gaps between podocyte foot processes.
Nephrotic Syndrome: Condition characterized by proteinuria and edema.
Macula Densa Cells: Specialized cells in the DCT that monitor filtrate osmolarity.
Juxtaglomerular Cells: Specialized cells in the afferent arteriole that secrete renin.
Isosmotic Reabsorption: Reabsorption of water and solutes in equal proportions.
Secondary Active Transport: Transport process that utilizes the energy stored in the electrochemical gradient of another molecule.
Osmosis: Movement of water across a semipermeable membrane.
Aquaporins: Water channels embedded in cell membranes.
Transport Maximum (Tm): Maximum rate of transport of a substance across a membrane.
Renal Threshold: Concentration of a substance in the blood that exceeds the Tm.
BUN Test: Blood urea nitrogen test used to assess kidney function.
Organic Ion Secretion: Process by which organic anions and cations are transported from the blood into the tubular fluid.
Loop Diuretics: Drugs that block the NKCC2 transporter in the thick ascending limb, increasing urine production.
Parathyroid Hormone (PTH): Hormone that increases calcium reabsorption in the DCT.
Aldosterone: Hormone that regulates Na+ and K+ balance.
Juxtaglomerular Apparatus: Specialized structure in the nephron that regulates blood pressure and GFR.
Hyperkalemia: High potassium levels in the blood.
Insulin: Hormone that promotes K+ uptake into cells.
Epinephrine: Hormone that promotes K+ uptake into cells.

Important Numbers

Kidney Blood Flow: 20-25% of cardiac output (1-1.2 L/min or 1000-1200 mL/min).
Glomerular Filtration Rate (GFR): 100-120 mL/min.
Urine Flow Rate: 1 mL/min.
Urine Production: 1.0-1.5 L/day, with a range of 0.5-15 L/day.

PCT Reabsorption

Na+: 67%.
Glucose: 100%.
Water: 67%.
HCO3-: 80%.
Electrolytes: 67%.
Urea: 50%.

Loop of Henle Reabsorption

Descending Limb: 15% of water reabsorbed.
Ascending Limb: 25% Na+ reabsorbed.

DCT Reabsorption

Early DCT: 5% Na+ reabsorbed.
Late DCT: Variable 2-3% Na+ reabsorbed, regulated by aldosterone.

Collecting Ducts Reabsorption

Collecting Ducts: 8-17% of water reabsorbed, regulated by ADH.

Bowman's Capsule Filtrate Composition

The filtrate in Bowman's capsule reflects the composition of the blood because the glomerular filtration barrier is selectively permeable, allowing water and small solutes to pass while preventing the passage of large molecules like proteins.
Under normal conditions, proteins are not present in the filtrate because they are too large to pass through the filtration barrier.

Secondary Active Transport in PCT

Na+ is required for glucose reabsorption in the PCT. The transport of glucose across the apical membrane of the proximal tubule cells is coupled to the movement of Na+ down its electrochemical gradient, creating a driving force for glucose uptake.
This process is known as secondary active transport.

Water Reabsorption in PCT

Water is reabsorbed in the PCT through two mechanisms:
- Osmosis: Water moves passively from the tubule lumen into the interstitial space, driven by the osmotic gradient created by the reabsorption of solutes.
- Bulk Flow: Water is dragged along with solutes as they are reabsorbed, a process called bulk flow, due to the hydrostatic pressure gradient between the lumen and the interstitial space.

Glucose Reabsorption in PCT

SGLT1/2 Transporter: This transporter protein is located on the apical membrane of proximal tubule cells and is responsible for the co-transport of glucose and Na+ into the cell.
GLUT Transporter: This transporter protein is located on the basolateral membrane and facilitates the passive movement of glucose from the cell into the interstitial space.
Na+/K+ Pump: This pump is located on the basolateral membrane, maintaining the concentration gradient for Na+ movement across the apical membrane.
Transport Maximum (Tm): This is the maximum rate at which a substance can be reabsorbed. For glucose, there is a limited number of SGLT1/2 transporters. If the blood glucose concentration exceeds the Tm, glucose will not be completely reabsorbed and will appear in the urine.
Under normal physiological conditions, glucose should not be present in the urine.

Urea Reabsorption in PCT

Approximately 50% of urea is reabsorbed in the PCT.
Urea reabsorption is a passive process that occurs via diffusion down its concentration gradient.
Urea is a waste product, and reabsorption is a mechanism to conserve water and maintain the concentration gradient in the medulla.

Major Secretion in PCT

The PCT primarily functions in reabsorption, but it also secretes a small amount of organic ions, such as creatinine and uric acid.

Active vs. Passive Transport

ATP is required for active transport, which moves substances against their concentration gradient, requiring energy.
Passive transport does not require ATP and relies on the concentration gradient or electrochemical gradient.

Osmolarity Changes in the Loop of Henle

Descending Limb: The osmolarity of the filtrate increases as water moves out of the descending limb, driven by the higher osmolarity of the interstitial space.
Ascending Limb: The osmolarity of the filtrate decreases as Na+ and Cl- are actively reabsorbed in the thick ascending limb.

Reabsorption in the Descending Limb

The descending limb of the loop of Henle is permeable to water but impermeable to solutes, allowing water to move out of the tubule, driven by the osmotic gradient created by the high osmolarity of the interstitial space.

Reabsorption in the Ascending Limb

The ascending limb is impermeable to water, but permeable to solutes.
The thick segment actively reabsorbs Na+ and Cl- via the NKCC2 transporter.
Thin and Thick Segments: The thin ascending limb is less permeable to solutes compared to the thick ascending limb.

Na+ Reabsorption in the Thick Ascending Limb

NKCC2 Transporter: This transporter protein is located on the apical membrane and moves Na+, K+, and 2 Cl- ions from the lumen into the cell, using the energy of the Na+ concentration gradient.
Na+/K+ Pump: This pump is located on the basolateral membrane and maintains the concentration gradient for Na+ movement across the apical membrane.
Cl- Channel: This channel is located on the basolateral membrane and facilitates Cl- movement from the cell into the interstitial space.
K+ Channel: This channel is located on the basolateral membrane and allows K+ to exit the cell and return to the lumen, contributing to the positive voltage gradient.

K+ Movement in the Thick Ascending Limb

The NKCC2 transporter moves K+ into the cell, but most of the K+ leaks back into the lumen via K+ channels on the apical membrane, because of the positive voltage gradient created by Na+ reabsorption.
This movement generates a positive voltage gradient in the lumen, which drives movement of other cations, such as Ca2+ and Mg2+, across the apical membrane into the interstitial space.
Key Concept: This process ensures that the lumen remains positive, promoting reabsorption of Na+ and other cations.

Vertical Osmotic Gradient (VOG)

The Loop of Henle creates the vertical osmotic gradient (VOG) by reabsorbing Na+ and Cl- in the ascending limb, concentrating solutes in the interstitial space, and by moving urea into the interstitial space from the collecting duct.
This VOG is essential for the kidney's ability to concentrate urine.

Loop Diuretics (Lasix/Furosemide)

Loop diuretics, like Lasix (furosemide), block the NKCC2 transporter in the thick ascending limb of the Loop of Henle.
This leads to increased urine production by inhibiting Na+ and Cl- reabsorption and thus, water reabsorption.

Early vs. Late DCT

Early DCT: Predominantly functions in reabsorption, but also secretes a small amount of K+ and H+.
Late DCT: Primarily involved in the regulation of Na+, K+, and Ca2+ balance.

DCT Secretion

The DCT secretes K+ and H+ ions into the urine.

Na+ Reabsorption in the Early DCT

Na+/Cl- Co-transporter: This transporter is found on the apical membrane of early DCT cells, moving Na+ and Cl- ions from the tubule lumen into the cell. This process is driven by the electrochemical gradient of Na+.

Ca2+ Reabsorption in the Early DCT

The early DCT reabsorbs Ca2+ through hormone-regulated Ca2+ channels in the apical membrane.
PTH (parathyroid hormone) increases Ca2+ reabsorption in the DCT by increasing the number of these Ca2+ channels.

Principal Cells of the Late DCT

Principal Cells: These are the main cells in the late DCT and regulate the reabsorption of Na+ and the secretion of K+ in response to aldosterone.
Aldosterone: This hormone increases Na+ reabsorption and K+ secretion via the mechanisms described previously.

Macula Densa Cells and Juxtaglomerular Cells

Macula Densa Cells: These are specialized cells located in the DCT that sense changes in filtrate osmolarity.
Juxtaglomerular Cells: Specialized cells found in the afferent arteriole that secrete renin.
The macula densa cells communicate with the juxtaglomerular cells, sensing changes in filtrate osmolarity and regulating renin secretion.

Renin

Renin is an enzyme produced by the juxtaglomerular cells in response to various stimuli including:
- Low blood pressure.
- Low NaCl concentration in the DCT.
- Sympathetic nerve stimulation.

Renin's Role in RAAS System

Renin is released into the blood and converts angiotensinogen, a protein produced by the liver, into angiotensin I.

RAAS System

The Renin Angiotensin Aldosterone System (RAAS) is a complex hormonal system that regulates blood pressure, fluid balance, and electrolyte balance.
Components of RAAS: Renin , Angiotensinogen, Angiotensin I, Angiotensin II, and Aldosterone.
Activation of RAAS: The RAAS system is activated in response to low blood pressure or low blood volume, which triggers the release of renin from the kidneys.
Effects of RAAS:
- The RAAS system increases blood volume and vasoconstriction by enhancing blood pressure.
- Angiotensin II stimulates the release of aldosterone from the adrenal cortex, leading to sodium reabsorption and potassium secretion.

Main Kidney Functions

Filtration: The kidneys remove waste products and excess water from the blood, producing urine.
Regulation of Blood Pressure: The kidneys contribute to the regulation of blood pressure by regulating blood volume and vascular tone.
Regulation of Electrolytes: The kidneys maintain the balance of electrolytes, such as sodium, potassium, and calcium, in the blood.
Acid-Base Balance: The kidneys regulate the pH of the blood by removing excess acid and bicarb.

Blood Flow Through the Kidney

The kidney receives blood via the renal artery, which branches into the afferent arterioles.
The afferent arterioles carry blood to the glomerulus, where filtration occurs.
Blood exits the glomerulus via the efferent arterioles.
The efferent arterioles form the peritubular capillaries that surround the renal tubules.
The tubules, surrounded by peritubular capillaries, engage in reabsorption and secretion before the blood leaves the kidneys via the renal vein.

Nephron Anatomy

Vascular Components: Afferent Arteriole, Glomerulus, Efferent Arteriole, Peritubular Capillaries, Vasa Recta.
Tubular Components: Bowman's Capsule, Proximal Convoluted Tubule (PCT), Descending Limb of Henle, Ascending Limb of Henle, Distal Convoluted Tubule (DCT), Collecting Ducts.
Two Types of Nephrons:
- Superficial or Cortical Nephrons: These are more numerous, with short loops of Henle that extend only into the outer medulla.
- Juxtamedullary Nephrons: These have long loops of Henle that extend deep into the inner medulla.

Urine Production

The kidneys filter blood, reabsorb essential substances, and secrete waste products, ultimately producing urine.

Reabsorption vs. Secretion

Tubular Reabsorption: Process of moving substances from the tubular fluid back into the bloodstream.
Tubular Secretion: Process of moving substances from the blood into the tubular fluid.

Micturition Reflex

Micturition refers to the process of urination.
Detrusor Muscle: This smooth muscle is located in the bladder wall and is responsible for contraction during urination.
Internal Sphincter: This smooth muscle is located at the junction of the bladder and urethra and is responsible for involuntary control of urine flow.
External Sphincter: This skeletal muscle is located at the end of the urethra and is controlled voluntarily.

Micturition Reflex: Sympathetic vs. Parasympathetic Activity

Sympathetic activity constricts the internal sphincter and relaxes the detrusor muscle, inhibiting urination.
Parasympathetic activity contracts the detrusor muscle and relaxes the internal sphincter, promoting urination.

Glomerular Filtration

Bulk Flow: The movement of fluid across a membrane driven by pressure gradients.
Glomerular Filtration: Filtration of blood plasma across the glomerular capillaries into the Bowman's capsule.
Hydrostatic Pressure Greater Than Colloid Osmotic Pressure: Leads to filtration, as seen in the glomerulus.
Hydrostatic Pressure Less Than Colloid Osmotic Pressure: Leads to reabsorption, as seen in the peritubular capillaries.

Glomerular Filtration Rate (GFR)

GFR: The volume of fluid filtered from the blood into Bowman's capsule per unit time.
GFR is a measure of kidney function.

Factors Affecting GFR

Constricting the afferent arteriole: Reduces blood flow to the glomerulus, decreasing GFR.
Constricting the efferent arteriole: Decreases blood flow out of the glomerulus, but increases hydrostatic pressure within the glomerulus, increasing GFR.
Dilating the afferent arteriole: Increases blood flow to the glomerulus, increasing GFR.
Dilating the efferent arteriole: Increases blood flow out of the glomerulus, but decreases hydrostatic pressure within the glomerulus, decreasing GFR.

Net Filtration Pressure (NFP)

NFP: The pressure difference that drives filtration across the glomerular capillaries.
NFP is calculated by subtracting the pressures opposing filtration from the forces favoring filtration.
Three pressures contribute to NFP:
- Glomerular capillary hydrostatic pressure (PGC): The pressure exerted by blood within the glomerular capillary.
- Bowman's capsule hydrostatic pressure (PBS): The pressure exerted by fluid inside Bowman's capsule.
- Glomerular capillary colloid osmotic pressure (πGC): The pressure exerted by proteins within the glomerular capillary.

Regulation of GFR

Renal Autoregulation: The kidneys have the ability to maintain a relatively constant GFR despite changes in blood pressure.
Sympathetic Stimulation: Sympathetic nerve stimulation decreases GFR by constricting the afferent arterioles, reducing blood flow to the glomerulus.
Tubuloglomerular Feedback (TGF): A mechanism by which the DCT senses changes in filtrate osmolarity and provides feedback to the afferent arteriole, regulating GFR.
Macula Densa Cells: These cells are involved in TGF and detect changes in filtrate osmolarity and communicate this information to the juxtamedulary cells.

Filtering Membrane

The glomerular filtration barrier is composed of three layers:
- Fenestrated endothelium: The inner layer of the capillary wall with pores that allow water and small solutes to pass.
- Glomerular basement membrane: A specialized membrane that surrounds the capillaries, providing a barrier to large molecules, like proteins.
- Podocytes: Specialized cells that surround the capillaries and contain foot processes that intertwine, forming filtration slits, which further restrict the passage of large molecules.

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