Urinary System Pt.1 Flashcards
Components of the Urinary System
2 Kidneys, 2 Ureters, 1 Bladder, 1 Urethra.
Kidney Function
Filters blood to remove wastes; creates urine.
Homeostasis Role of the Urinary System
Manages blood volume, controls fluid balance, maintains proper blood composition, regulates pH levels.
What is Osmolarity?
Measure of the total number of dissolved particles per liter of solution.
Breakdown of the Urinary System Components
2 Kidneys, 2 Ureters, 1 Bladder, 1 Urethra.
Functions of the Kidneys
Blood filter, urine creation, blood chemistry control, blood pressure regulation, hormone production.
Osmolarity’s Importance
Keeps proper concentration of dissolved particles in blood, controls water balance, maintains fluid levels between blood and tissues.
Urinary System as a Filtration Plant
Cleans and maintains proper balance of body fluids.
What are the 4 main functions of the urinary system?
Excretion of metabolic wastes
Regulation of blood ionic composition
Regulation of blood pH
Regulation of blood volume
What metabolic wastes does the urinary system excrete?
• Body-produced wastes:
Urea and ammonia (from amino acids)
Uric acid (from nucleic acids)
Urobilin (from hemoglobin)
• External wastes:
Drugs
Environmental toxins
What ions does the urinary system regulate?
Cations (positive):
Sodium (Na+)
Potassium (K+)
Calcium (Ca2+)
Anions (negative):
Chloride (Cl-)
Phosphate (HPO42-)
How does the urinary system regulate blood pH?
• Removes hydrogen ions (H+) as needed
• Retains bicarbonate ions (HCO3-) to buffer acids
How does the urinary system regulate blood volume?
• Controls water balance by:
Retaining water when needed
Removing excess water through urine
Adjusting urine concentration
What are the nitrogen-containing compounds excreted?
• Urea and ammonia (from amino acids)
• Uric acid (from nucleic acids)
• Urobilin (from hemoglobin breakdown)
What role does the urinary system play in drug elimination?
Removes foreign substances including:
• Drugs
• Environmental toxins
Through excretion in urine
What are the 4 additional functions of the urinary system?
Regulation of blood pressure
Maintenance of blood osmolarity
Production of hormones
Regulation of blood glucose
How does the urinary system regulate blood pressure?
• Secretes enzyme renin
• Activates the Renin-Angiotensin-Aldosterone (RAA) pathway
• Helps maintain proper blood pressure levels
What is the target blood osmolarity and how is it maintained?
• Target: 300 mOsm/liter
• Maintained by:
- Regulating water loss
- Controlling ion loss
- Independent regulation of both in urine
What hormones does the urinary system produce?
Calcitriol:
Active form of vitamin D
Regulates calcium homeostasis
Erythropoietin:
Stimulates red blood cell production
Maintains blood cell levels
What is gluconeogenesis and its role in the urinary system?
• Process of making new glucose
• Uses amino acid glutamine
• Helps maintain stable blood sugar levels
• Occurs when blood glucose is low
What is the role of Calcitriol?
• Active form of vitamin D
• Important for:
- Calcium homeostasis
- Bone health
- Calcium absorption
What is the function of Erythropoietin?
• Stimulates bone marrow
• Triggers production of red blood cells
• Maintains adequate oxygen delivery to tissues
• Helps prevent anemia
How does the urinary system maintain osmotic balance?
• Regulates water and ion loss separately
• Adjusts urine concentration
• Maintains blood osmolarity at ~300 mOsm/liter
• Responds to changes in blood concentration
What is the basic description of kidneys?
• Reddish, bean-shaped organs
• Located above waist
• Behind abdominal lining (retroperitoneal)
• Between last thoracic and third lumbar vertebrae
What does ‘retroperitoneal’ mean?
Located behind the peritoneum (abdominal lining), not within the abdominal cavity
How are the kidneys protected?
• Partially protected by lower ribs (11th and 12th ribs)
• Surrounded by fat and connective tissue
• Located deep in the back muscles
Why is the right kidney lower than the left?
Due to the position of the liver above the right kidney, pushing it slightly lower
What vertebrae are the kidneys located between?
Between the last thoracic vertebra and the third lumbar vertebra
What is the injury risk to kidneys?
Fractured lower ribs can damage kidneys, potentially causing serious injury due to their proximity
What is the color and shape of kidneys?
• Reddish in color
• Bean-shaped organs
What anatomical structures protect the kidneys?
• Lower ribs (11th and 12th)
• Back muscles
• Retroperitoneal fat
• Connective tissue
What is the renal hilum?
Indented area on kidney’s medial side
Acts as kidney’s ‘gateway’
Located at concave medial border
Main entry/exit point for vessels and structures
What structures pass through the renal hilum?
Renal artery
Renal vein
Ureter
Nerves
Lymphatic vessels
What is the renal sinus?
Large hollow space inside kidney
Expansion of the hilum
Filled with protective fat tissue
Contains renal pelvis, calyces, and vessel branches
What are the functions of structures entering/exiting the hilum?
Renal Artery: Brings oxygen-rich blood
Renal Vein: Removes filtered blood
Ureter: Transports urine to bladder
Nerves: Control kidney function
Lymphatics: Drain fluid and immune cells
What structures are found in the renal sinus?
Renal Pelvis (funnel-shaped urine collector)
Calyces (major and minor)
Blood vessel branches
Nerve branches
Protective fat tissue
What are calyces and their function?
Cup-shaped structures that collect urine
Two types:
Major calyces (larger collection spaces)
Minor calyces (smaller collection spaces)
What is the renal pelvis?
Funnel-shaped structure in renal sinus
Collects urine from calyces
Connects to ureter
Beginning of urinary drainage system
What is the role of nerve branches in the renal sinus?
Control kidney function
Regulate blood flow
Monitor blood pressure
Maintain homeostasis
What are the 3 layers of kidney protection (from superficial to deep)?
Renal fascia (outermost), Perirenal adipose capsule (middle), Renal (fibrous) capsule (innermost)
Describe the renal fascia.
Composition: Dense irregular connective tissue, Collagen and elastic fibers.
Functions: Anchors kidneys to abdominal wall, Connects to surrounding structures, Lies beneath peritoneum.
What is the perirenal adipose capsule?
Composition: Mass of fatty tissue.
Functions: Acts as shock absorber, Provides cushioning protection, Holds kidneys in position, Stabilizes kidney in abdominal cavity.
Describe the renal (fibrous) capsule.
Composition: Smooth, transparent sheet, Rich in collagen, Continuous with ureter outer coat.
Functions: Maintains kidney shape, Provides protective barrier, Protects against trauma.
Which layer anchors the kidney to the abdominal wall?
The renal fascia (outermost layer).
Which layer provides cushioning protection?
The perirenal adipose capsule (middle layer).
Which layer maintains the kidney’s shape?
The renal (fibrous) capsule (innermost layer).
What is the main component of the middle layer?
Fatty tissue (adipose tissue).
What are the two main regions of the kidney?
Renal cortex (superficial, light red)
Renal medulla (deep, dark red)
What is the functional unit of the kidney?
The nephron
What are the two main parts of a nephron?
Renal corpuscle (filtering unit)
Renal tubule (processing unit)
Describe the glomerulus
• Ball-shaped capillary network
• First filtration site
• Receives blood from afferent arteriole
• Filters blood into Bowman’s capsule
Describe Bowman’s capsule
• Double-walled cup
• Surrounds glomerulus
• Collects filtered fluid (glomerular filtrate)
• Directs filtrate to renal tubules
Describe the proximal convoluted tubule (PCT)
• Tightly coiled
• First processing section
• Reabsorbs useful substances
• Located in cortex
Describe the loop of Henle
• Hairpin-shaped
• Extends into medulla
• Descending and ascending limbs
• Crucial for urine concentration
Describe the distal convoluted tubule (DCT)
• Final processing section
• Fine-tunes filtrate composition
• Regulates pH and mineral balance
What are cortical nephrons?
• 80-85% of nephrons
• Located in cortex
• Short loops of Henle
• Handle routine filtration
What are juxtamedullary nephrons?
• 15-20% of nephrons
• Located near medulla
• Long loops of Henle
• Specialized for urine concentration
What is the function of collecting ducts?
• Receive processed fluid from nephrons
• Control final urine concentration
• Respond to hormones
What is the function of papillary ducts?
• Larger ducts formed from collecting ducts
• Transport urine to calyces
• Lead to ureter
What are the overall functions of the nephron?
• Blood filtration
• Waste removal
• Fluid balance
• Blood pressure regulation
• pH control
• Mineral balance
What percentage of the body’s mass do kidneys comprise?
Less than 0.5%
What percentage of cardiac output do kidneys receive?
20-25%
Why is the high blood flow to the kidneys important?
Essential for: • Waste removal • Blood volume regulation • Ion balance control
What is the origin of the renal nerves?
Renal ganglion, travel through the renal plexus
What type of nerve fibers are predominantly found in the renal nerves?
Sympathetic nerve fibers
What is the main function of the renal nerves?
Primarily vasomotor; regulate blood flow to the kidneys
How do renal nerves influence blood pressure?
By regulating blood flow, they influence blood pressure homeostasis
Trace the path of blood vessels in the kidneys
Renal arteries → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate arteries → afferent glomerular arterioles
What is vasomotor control?
The regulation of blood vessel diameter, which affects blood flow and blood pressure within the kidneys. Nerves primarily control blood vessels and help maintain blood pressure.
What would happen if blood flow to the kidneys was significantly reduced?
Waste removal and blood pressure regulation would be severely affected, potentially leading to acute or chronic kidney failure.
What is the afferent arteriole?
Brings blood into the nephron. Branches from cortical radiate arteries. First point of blood entry into the nephron.
What is the glomerulus?
Ball-shaped capillary network. Formed by branching afferent arteriole. Primary filtration site. Unique: positioned between two arterioles (afferent and efferent).
What is the efferent arteriole?
Formed when glomerular capillaries reunite. Carries filtered blood away from glomerulus. Continues to other kidney structures (peritubular capillaries or vasa recta).
What are the two main types of nephrons?
Cortical nephrons. Juxtamedullary nephrons.
Describe cortical nephrons
Located in outer cortex. More numerous. Shorter loops of Henle. Responsible for most of the filtration.
Describe juxtamedullary nephrons
Located near the medulla. Fewer in number. Long loops of Henle. Important for concentrating urine. Create osmotic gradient in medulla.
What are peritubular capillaries?
Branches of efferent arterioles. Surround renal tubules in cortex. Involved in reabsorption and secretion.
What are vasa recta?
Long, loop-shaped capillaries. Supply tubular portions in medulla. Part of the countercurrent exchange system.
Trace the blood flow from glomerulus to renal vein
Glomerulus → Efferent arterioles → peritubular capillaries/vasa recta → cortical radiate veins → arcuate veins → interlobar veins → renal vein.
mnemonic “Great Elephants Prefer Climbing Around In Rain”
How do renal nerves regulate blood flow?
Via vasomotor nerves. Cause vasodilation or vasoconstriction of renal arterioles. Maintain appropriate blood pressure and filtration rate.
What percentage of nephrons are cortical nephrons?
80-85%
Where are the renal corpuscles of cortical nephrons located?
Outer portion of the renal cortex
How far do the loops of Henle extend in cortical nephrons?
Only into the outer region of the medulla (short loops)
What is the osmolarity of urine produced by cortical nephrons?
Similar to blood osmolarity (approximately 300 mOsm/L)
What is the primary function of cortical nephrons?
Routine filtration and maintenance of normal fluid balance. They handle most of the daily filtration needs.
How does the length of the loop of Henle affect the cortical nephron’s function?
The shorter loop limits their ability to concentrate urine.
Compared to juxtamedullary nephrons, cortical nephrons have what structural difference?
Shorter loops of Henle
What is the blood supply for cortical nephrons?
Peritubular capillaries that branch from efferent arterioles
Where are the renal corpuscles of juxtamedullary nephrons located?
Deep in the cortex, near the medulla
Describe the loops of Henle in juxtamedullary nephrons
Long loops extending deep into the medulla
What is the primary function of juxtamedullary nephrons?
Concentrating urine
What blood vessels supply juxtamedullary nephrons?
Peritubular capillaries and vasa recta
What is the significance of the vasa recta?
Maintain the medullary osmotic gradient for urine concentration
Describe the ascending limb of the loop of Henle
Has thick and thin segments; thin segment is permeable to ions but not water, the thick segment actively transports ions.
How does the structure of the juxtamedullary nephron contribute to urine concentration?
Long loops create a concentration gradient in the medulla; the vasa recta help maintain this gradient; the collecting duct reabsorbs water based on the gradient.
What is the osmolarity of urine produced by juxtamedullary nephrons?
Significantly higher than blood osmolarity (much more concentrated)
What is the clinical significance of juxtamedullary nephrons?
Essential for maintaining hydration and electrolyte balance, especially in conditions of water scarcity. Their function is critical for conserving water.
How many juxtamedullary nephrons are there compared to cortical nephrons?
Fewer than cortical nephrons (15-20% of total nephrons)
What are nephrons?
The functional units of the kidneys; responsible for filtering blood, excreting waste, and regulating fluid/electrolyte balance.
Approximately how many nephrons are in each kidney?
Approximately one million.
What are the two main parts of a nephron?
Renal corpuscle (filtration) and renal tubule (further processing).
What is the renal corpuscle?
The initial filtering component of a nephron, consisting of the glomerulus and Bowman’s capsule.
What is the glomerulus?
A network of capillaries where blood plasma is filtered.
What is Bowman’s capsule?
A double-walled structure surrounding the glomerulus that collects the glomerular filtrate.
What is the renal tubule?
A long, coiled tube where the glomerular filtrate undergoes further processing via reabsorption and secretion.
What is the proximal convoluted tubule (PCT)?
The first segment of the renal tubule; where most reabsorption of nutrients, water, and ions occurs.
What is the loop of Henle?
A U-shaped structure extending into the medulla; crucial for establishing the osmotic gradient needed for urine concentration.
What is the distal convoluted tubule (DCT)?
The final segment of the renal tubule; fine-tunes the filtrate composition via reabsorption and secretion; responds to hormones.
What is the overall function of the nephron?
To filter blood, reabsorb essential substances, secrete waste products, and produce urine. This helps maintain fluid and electrolyte balance and overall body homeostasis.
What are the two main parts of the renal corpuscle?
Glomerulus (capillary network) and Glomerular (Bowman’s) capsule (double-walled cup)
What is the glomerulus?
A ball-shaped network of capillaries; receives blood from the afferent arteriole and drains into the efferent arteriole.
What cells help regulate glomerular filtration?
Mesangial cells (contractile cells within the glomerulus)
What is the glomerular (Bowman’s) capsule?
A double-walled epithelial cup that surrounds the glomerulus; collects the glomerular filtrate.
What are the layers of Bowman’s capsule?
Visceral layer (podocytes) and Parietal layer (outer layer)
What are podocytes?
Specialized cells in the visceral layer of Bowman’s capsule; have foot-like projections (pedicels) that wrap around glomerular capillaries, creating filtration slits.
Where is the glomerular filtrate collected?
In the space between the visceral and parietal layers of Bowman’s capsule (Bowman’s space).
What is the function of mesangial cells?
To regulate glomerular filtration by contracting and changing the surface area available for filtration. This helps to maintain appropriate filtration pressure.
What is the overall function of the renal corpuscle?
To filter blood and collect the resulting filtrate (glomerular filtrate). This is the first step in urine formation.
What forms the inner layer of Bowman’s capsule?
Podocytes and their pedicels.
What forms the outer layer of Bowman’s capsule?
Parietal layer of the glomerular capsule.
Where does filtered fluid collect in the renal corpuscle?
Capsular space (between parietal and visceral layers).
What are pedicels?
Foot-like projections of podocytes forming filtration slits.
What is the function of mesangial cells?
Regulate blood flow and remove debris in the glomerulus.
What are filtration slits?
Gaps between pedicels allowing selective filtration.
What is the role of the renal corpuscle?
To filter blood, producing the glomerular filtrate.
What vessel brings blood into the glomerulus?
Afferent arteriole.
What vessel carries blood away from the glomerulus?
Efferent arteriole.
What are the three main sections of the renal tubule?
Proximal Convoluted Tubule (PCT), Nephron Loop (Loop of Henle), Distal Convoluted Tubule (DCT)
Where is the PCT located and what is its structure?
Located in renal cortex, attached to glomerular capsule, highly coiled with brush border, has microvilli for efficient absorption
What does the PCT reabsorb?
100% of glucose, 100% of amino acids, 65-70% of water, most minerals, bicarbonate ions
Describe the Loop of Henle’s structure
U-shaped tube connecting PCT to DCT, has descending limb (water permeable), has ascending limb (pumps out sodium/chloride)
What is the main function of the Loop of Henle?
Creates concentration gradient in medulla, essential for concentrating urine, maintains water-salt balance
Where is the DCT located and what are its key features?
Located in cortex, contains principle cells, has hormone receptors (ADH and aldosterone), connects to collecting duct
What are the main functions of the DCT?
Fine-tunes urine composition, responds to hormones, maintains acid-base balance, regulates electrolytes, controls blood pressure
What hormones affect the DCT?
ADH (controls water reabsorption), Aldosterone (regulates sodium/potassium)
What problems can occur if the renal tubule malfunctions?
Electrolyte imbalances, water balance issues, pH problems, kidney stones, high blood pressure
What is the correct order of filtrate flow through the renal tubule?
Glomerular capsule, Proximal Convoluted Tubule, Nephron Loop (descending then ascending limb), Distal Convoluted Tubule
What are the key features of the PCT?
• Located in renal cortex • Has microvilli for increased absorption • Reabsorbs 65% of water • Reabsorbs glucose, amino acids, and ions • Connected to glomerular capsule
How does the descending limb of the Loop of Henle function?
• Permeable to water • Not permeable to salts • Water leaves the filtrate here • Increases filtrate concentration
How does the ascending limb of the Loop of Henle function?
• Impermeable to water • Actively pumps out salts • Decreases filtrate concentration • Sets up concentration gradient
What are the main functions of the DCT?
• Fine-tunes filtrate • Reabsorbs sodium and calcium • Secretes potassium and hydrogen • Responds to hormones (ADH and aldosterone) • Regulates pH and blood pressure
What hormones affect the DCT and how?
• Aldosterone: Increases sodium reabsorption • ADH: Increases water reabsorption
What is the main function of the Loop of Henle?
Creates and maintains concentration gradient in medulla for concentrating urine
Where does the filtrate go after leaving the DCT?
Into the collecting duct, where final adjustments are made before becoming urine
What happens in the PCT regarding reabsorption?
Reabsorbs most filtered substances: • Water (65%) • Glucose • Amino acids • Ions (sodium, chloride)
What is the overall purpose of the renal tubule system?
To process filtrate by selectively reabsorbing useful substances and removing wastes, maintaining body homeostasis
What is the macula densa?
A region of crowded cells where the ascending loop contacts the afferent arteriole; senses sodium concentration.
What are juxtaglomerular cells?
Modified smooth muscle cells in the wall of the afferent arteriole near the macula densa.
What is the juxtaglomerular apparatus (JGA)?
The combination of macula densa and juxtaglomerular cells; regulates blood pressure in the kidney.
How do nephrons develop?
Number is fixed at birth; kidney growth occurs through enlargement of existing nephrons, not formation of new ones.
What happens if nephrons are damaged?
They cannot be replaced; new nephrons do not form.
How do kidneys compensate for nephron loss?
Remaining nephrons adapt to filter more; symptoms often don’t appear until 75% of function is lost.
What happens if one kidney is removed?
The remaining kidney can enlarge and function at about 80% of two normal kidneys’ capacity.
What regulates kidney blood pressure?
The juxtaglomerular apparatus (JGA) in conjunction with the autonomic nervous system (ANS).
Where is the macula densa located?
At the end of the ascending limb of the nephron loop where it contacts the afferent arteriole.
What is the clinical significance of fixed nephron number?
Once nephrons are damaged or lost, they cannot be replaced, making prevention of kidney damage crucial.
What are the three basic processes of urine formation?
Glomerular filtration, Tubular reabsorption, Tubular secretion
What is the equation for solute excretion?
Excretion = Filtration + Secretion - Reabsorption
What is glomerular filtration?
The initial filtering of blood plasma through the glomerulus, where small molecules pass into the renal tubule to form filtrate.
What is tubular secretion?
Process where substances are actively transported from blood into the renal tubule after initial filtration.
What is tubular reabsorption?
Transport of substances from the filtrate back into the bloodstream to conserve essential materials.
What substances are typically reabsorbed?
• Essential nutrients (glucose, amino acids) • Water • Electrolytes (sodium)
Why is secretion important?
Helps eliminate compounds that: • Weren’t filtered initially • Need additional removal • Require active transport out of blood
Example: If 100 units are filtered, 20 secreted, and 30 reabsorbed, how many are excreted?
90 units
Calculation: 100 + 20 - 30 = 90 units
What is the purpose of reabsorption?
To conserve necessary substances and maintain fluid/electrolyte balance in the body.
What determines the final composition of urine?
The combined effects of: • Initial filtration • What gets secreted • What gets reabsorbed
What is the filtration membrane made of?
• Glomerular capillaries
• Podocytes
• Three filtering layers:
- Glomerular endothelial cells
- Basement membrane
- Filtration slits
What is the filtration fraction?
The percentage of blood plasma that becomes filtrate (normally 16-20%)
How much filtrate is produced daily?
• Females: ~150 liters
• Males: ~180 liters
• 99% is reabsorbed
• Only 1-2 liters becomes urine
What are the three filtering layers?
• Fenestrated endothelium
• Basement membrane
• Slit membrane between pedicels
What can pass through the filtration membrane?
Water and small solutes (salts, glucose, waste products)
What cannot pass through the filtration membrane?
Blood cells and most proteins
What is the function of fenestrations?
Allow plasma components to pass while blocking blood cells
What is the function of the basement membrane?
Prevents larger proteins (like albumin) from passing through
What are pedicels?
“Arms” of podocytes that create filtration slits
What happens to the glomerular filtrate?
Enters Bowman’s capsule for further processing in the nephron
What are the three filtration barriers in order?
- Glomerular endothelial cells (with fenestrations)
- Basement membrane (basal lamina)
- Filtration slits (between podocyte pedicels)
What are the characteristics of glomerular endothelial cells?
• Have large pores (fenestrations) 0.07-0.1 µm
• Allow plasma and solutes through
• Block blood cells
• Considered ‘leaky’
What is the composition and function of the basement membrane?
• Made of collagen and glycoproteins
• Located between endothelium and podocytes
• Allows water and small solutes
• Blocks plasma proteins
What are filtration slits?
• Gaps between podocyte pedicels
• Allow molecules < 0.006-0.007 µm
• Let through water, glucose, vitamins, amino acids
• Block larger proteins
What is the role of mesangial cells?
• Located between glomerular capillaries
• Regulate glomerular filtration rate (GFR)
• Can contract to control blood flow
What substances can pass through all three barriers?
• Water
• Small solutes
• Glucose
• Vitamins
• Amino acids
• Small proteins
• Ions
What substances are blocked by the filtration membrane?
• Blood cells
• Large proteins (like albumin)
• Most plasma proteins
Why are glycoproteins in the basement membrane important?
Their negative charge helps repel proteins, preventing them from passing through
What are pedicels?
Foot-like processes of podocytes that wrap around capillaries and create filtration slits
How efficient is the filtration system?
• Produces 150-180L filtrate daily
• 99% is reabsorbed
• Only 1-2L becomes urine
What are the three main pressures affecting glomerular filtration?
Glomerular Blood Hydrostatic Pressure (GBHP) - promotes filtration
Capsular Hydrostatic Pressure (CHP) - opposes filtration
Blood Colloid Osmotic Pressure (BCOP) - opposes filtration
What is GBHP and what’s its value?
Blood pressure inside glomerular capillaries
Value: ~55 mmHg
Promotes filtration by pushing fluid out
What is CHP and what’s its value?
Pressure from fluid in capsular space
Value: ~15 mmHg
Opposes filtration as ‘back pressure’
What is BCOP and what’s its value?
Pressure from proteins in blood
Value: ~30 mmHg
Opposes filtration by pulling water back to blood
How is Net Filtration Pressure (NFP) calculated?
NFP = GBHP - CHP - BCOP = 55 - 15 - 30 = 10 mmHg
What are the three features that make filtration efficient?
Large surface area of glomerular capillaries
Thin and porous filtration membrane
High glomerular blood pressure
Why is glomerular blood pressure high?
Efferent arteriole is smaller than afferent arteriole
Creates resistance to outflow
Forces more blood into smaller space
What makes the filtration membrane efficient?
Only 0.1 mm thin
50x more porous than other capillaries
Has three filtering layers
What can pass through the filtration membrane?
Water
Glucose
Amino acids
Ions
Vitamins
Small molecules
What can’t pass through the filtration membrane?
Blood cells
Large plasma proteins
Albumin
What determines the amount of plasma filtered in the glomerulus?
Net Filtration Pressure (NFP)
How is NFP calculated?
NFP = GBHP - CHP - BCOP
What does GBHP stand for, and what is its function?
Glomerular Blood Hydrostatic Pressure; pushes fluid out of the glomerulus
What does CHP stand for, and what is its function?
Capsular Hydrostatic Pressure; pushes fluid back into the glomerulus
What does BCOP stand for, and what is its function?
Blood Colloid Osmotic Pressure; pulls fluid back into the glomerulus (via osmosis)
What are the normal values for GBHP, CHP, and BCOP?
• GBHP = 55 mmHg • CHP = 15 mmHg • BCOP = 30 mmHg
Using the normal values, calculate NFP.
10 mmHg (55 - 15 - 30 = 10)
What does a positive NFP indicate?
Filtration will occur; fluid will move from the glomerulus into Bowman’s capsule
If NFP were negative, what would happen?
Net reabsorption would occur; fluid would move from Bowman’s capsule back into the glomerulus
What is the significance of the 10 mmHg NFP?
Sufficient to filter large volumes of fluid from the glomerulus into Bowman’s space.
What is GFR and what are normal rates?
Amount of filtrate formed by both kidneys per minute. Males: ~125 mL/min. Females: ~105 mL/min. Daily total: 150-180 liters.
What happens if GFR is too high?
Substances move too quickly through renal tubules. Inadequate reabsorption of nutrients and ions. Loss of important substances in urine.
What happens if GFR is too low?
Most filtrate gets reabsorbed. Insufficient waste excretion. Potential toxicity from waste buildup.
How do afferent arterioles affect GFR?
Dilation → increases GFR. Constriction → decreases GFR. Controls blood entering glomerulus.
How do efferent arterioles affect GFR?
Narrower diameter → increases pressure → increases GFR. Controls blood leaving glomerulus.
What role do mesangial cells play in GFR?
Relaxed → more surface area → increases GFR. Contracted → less surface area → decreases GFR.
What are the three main regulatory mechanisms for GFR?
Renal autoregulation, Neural regulation (sympathetic nervous system), Hormonal regulation (angiotensin II, ANP).
At what blood pressure does filtration stop?
Filtration stops if GBHP drops to 45 mmHg.
How much of the daily filtrate becomes urine?
Only 1-2 liters becomes urine; 99% is reabsorbed.
What factors affect GFR?
Blood pressure, Blood volume, Arteriole constriction/dilation, Mesangial cell contraction, Hormones, Sympathetic nervous system.
What are the two main ways to adjust GFR?
Adjusting blood flow through arterioles
Altering filtration surface area via mesangial cells
What are the three main mechanisms controlling GFR?
Renal autoregulation
Neural regulation
Hormonal regulation
What are the two processes of renal autoregulation?
Myogenic mechanism
Tubuloglomerular feedback
How does the myogenic mechanism work?
• High BP → arteriole contracts → reduces flow → lowers GFR
• Low BP → arteriole relaxes → increases flow → raises GFR
How does tubuloglomerular feedback work?
• High GFR → macula densa detects more Na⁺/Cl⁻ → reduces NO → constricts arteriole → lowers GFR
• Low GFR → opposite occurs
How does neural regulation affect GFR?
• Via sympathetic nerves releasing norepinephrine
• Low stimulation: minimal effect
• Moderate: slight GFR reduction
• High: significant GFR reduction
What are the two main hormones affecting GFR?
Angiotensin II: constricts arterioles, lowers GFR
ANP: relaxes mesangial cells, raises GFR
What happens during high sympathetic stimulation?
• Significant afferent arteriole constriction
• Major reduction in GFR
• Blood redirected to vital organs
How does Angiotensin II affect GFR?
• Constricts both afferent and efferent arterioles
• Reduces blood flow
• Lowers GFR
How does ANP affect GFR?
• Released when blood volume is high
• Relaxes mesangial cells
• Increases filtration surface area
• Raises GFR
What is the purpose of renal autoregulation?
To maintain consistent renal blood flow and glomerular filtration rate (GFR) despite changes in blood pressure during daily activities.
What triggers the myogenic mechanism?
Stretching of smooth muscle cells in the afferent arterioles due to changes in blood pressure.
What happens to the afferent arteriole when blood pressure increases?
Blood pressure increases renal blood flow and GFR.
Afferent arteriole stretches, causing smooth muscle contraction.
Diameter of the arteriole decreases (vasoconstriction).
Result: Reduced blood flow and GFR return to normal.
What occurs in the afferent arteriole when blood pressure decreases?
Blood pressure decreases renal blood flow and GFR.
Less stretching leads to smooth muscle relaxation.
Diameter of the arteriole increases (vasodilation).
Result: Increased blood flow and GFR return to normal.
How quickly does the myogenic mechanism respond to changes in blood pressure?
It normalizes GFR within seconds after a change in blood pressure.
Why is the myogenic mechanism important?
• Prevents excessive fluid and solute loss when blood pressure rises
• Ensures adequate filtration of waste products when blood pressure drops
• Stabilizes GFR and renal blood flow efficiently
What role do smooth muscle cells play in the myogenic mechanism?
They contract or relax in response to blood pressure changes, adjusting the diameter of the afferent arteriole.
What is the end result of the myogenic mechanism?
A consistent GFR that allows for proper kidney filtration and maintenance of fluid and waste balance.
What is tubuloglomerular feedback?
A renal autoregulation mechanism where kidneys adjust GFR based on feedback from the macula densa cells detecting changes in Na⁺, Cl⁻, and water flow.
What happens when GFR is too high?
• Blood flows quickly through renal tubules • Less time for reabsorption • Increased delivery of Na⁺, Cl⁻, and water to macula densa
What role does the macula densa play?
• Detects increased levels of Na⁺, Cl⁻, and water • Signals the JGA • Triggers inhibition of nitric oxide release
How does nitric oxide (NO) affect this process?
• NO normally causes vasodilation • When inhibited, arterioles constrict • Reduction leads to decreased blood flow and GFR
Describe the complete feedback loop for high GFR:
High GFR → fast flow
Less reabsorption
Macula densa detects increased solutes
NO inhibited
Afferent arterioles constrict
Blood flow decreases
GFR returns to normal
What happens during low GFR?
• Macula densa triggers increased NO release • Afferent arterioles dilate • Blood flow increases • GFR rises back to normal
How does tubuloglomerular feedback compare to the myogenic mechanism?
It’s slower than the myogenic mechanism but provides longer-term stability.
What is the main purpose of tubuloglomerular feedback?
• Prevents overfiltration • Protects against loss of essential solutes • Maintains stable GFR • Ensures proper reabsorption time
What is the role of the juxtaglomerular apparatus (JGA)?
Acts as the control center, receiving signals from macula densa and regulating NO release.
What indicates successful tubuloglomerular feedback?
• GFR returns to normal • Tubules have adequate time for reabsorption • Balance of fluid and solutes is restored.
What is the purpose of neural regulation of GFR?
To control GFR during situations where body priorities shift (exercise, stress, blood loss) by redirecting blood flow to vital organs.
How do sympathetic nerves affect kidney blood vessels?
• Release norepinephrine • Binds to α1 receptors • Causes vasoconstriction of arterioles
What happens during moderate sympathetic stimulation?
• Both afferent and efferent arterioles constrict equally • Blood flow restricted evenly • GFR decreases slightly • Kidney function continues at slower pace
What happens during strong sympathetic stimulation?
• Afferent arterioles constrict more than efferent • Significant reduction in renal blood flow • Decreased urine output • Blood redirected to vital organs
What are the main effects of strong sympathetic stimulation?
Reduced urine output (conserves water)
Decreased GFR
Blood redirected to vital organs (heart, brain, muscles)
How does neural regulation differ from autoregulation?
• Autoregulation maintains stable filtration normally • Neural control overrides autoregulation during emergencies • Neural control is temporary
Why is reduced urine output beneficial during emergencies?
• Helps conserve water • Maintains blood volume • Supports circulation to vital organs
What role do α1 receptors play?
• Located on arteriole smooth muscle • Respond to norepinephrine • Trigger vasoconstriction when activated
What organs receive redirected blood during strong stimulation?
• Heart • Brain • Muscles
What are the two main hormones regulating GFR?
Angiotensin II (decreases GFR)
Atrial Natriuretic Peptide/ANP (increases GFR)
How does Angiotensin II affect GFR?
• Constricts afferent and efferent arterioles
• Decreases blood flow to glomerular capillaries
• Results in decreased GFR
How does ANP affect GFR?
• Relaxes mesangial cells
• Increases capillary surface area
• Results in increased GFR
What triggers ANP release?
• Stretch of cardiac atria
• Increased blood volume
What is the relationship between surface area and GFR?
• Increased surface area = increased GFR
• Decreased surface area = decreased GFR
What is the purpose of Angiotensin II’s effects?
• Helps conserve water
• Restores blood pressure
• Useful during dehydration or blood loss
What is the purpose of ANP’s effects?
• Reduces blood volume
• Lowers blood pressure
• Increases urine output
• Counteracts fluid overload
How do mesangial cells affect GFR?
• When relaxed (by ANP): increase filtration surface area
• When contracted: decrease filtration surface area
• Control amount of surface area available for filtration
What conditions might trigger Angiotensin II release?
• Dehydration
• Low blood pressure
• Blood loss
What conditions might trigger ANP release?
• High blood volume
• Fluid overload
• High blood pressure
