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Flashcards in this deck (80)
  • The kidneys have three main functions: excretory, regulatory, and endocrine.

    physiology kidneys functions
  • The excretory function of the kidneys involves the removal of metabolic products and foreign substances such as urea, uric acid, and creatinine.

    physiology kidneys excretory
  • The regulatory function of kidneys includes maintaining body fluid osmolality and volumes, electrolyte balance, and acid-base balance.

    physiology kidneys regulatory
  • The endocrine function of the kidneys includes the production of hormones like renin, erythropoietin, and the active form of Vitamin D (1,25-dihydroxycholecalciferol).

    physiology kidneys endocrine
  • The nephron consists of several parts, including the Renal Corpuscle, Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule, and Collecting Duct System.

    physiology nephron structure
  • The glomerular filtration rate (GFR) is an important measure, and its estimation can involve methods like creatinine clearance.

    physiology gfr kidneys
  • The kidneys help regulate electrolyte balance and acid-base balance as part of their regulatory functions.

    physiology kidneys balance
  • The term Renal Clearance refers to the volume of plasma from which a substance is completely removed by the kidneys per unit time, often expressed with equations.

    physiology renal_clearance equations
  • The normal filtration fraction is defined and quantified as part of kidney function studies.

    physiology filtration_fraction kidneys
  • Osmolarity, osmolality, and tonicity are important concepts in understanding fluid movement between intracellular and extracellular compartments.

    physiology osmolarity fluid_movement
  • Urine formation involves three major processes: Glomerular filtration, Reabsorption, and Secretion.

    physiology kidneys urine
  • The first step in urine formation is ultrafiltration of plasma by the glomerulus, resulting in glomerular filtrate.

    physiology urine glomerulus
  • The Renal Corpuscle consists of the Glomerulus and Bowman's capsule.

    anatomy kidneys nephron
  • The glomerulus is a network of capillaries supplied by the afferent arteriole and drained by the efferent arteriole.

    anatomy glomerulus capillaries
  • The filtration membrane includes the endothelium, basement membrane, and epithelium (podocytes).

    physiology filtration membrane
  • The glomerular filtration barrier restricts molecules based on both size and electrical charge.

    physiology filtration barrier
  • Neutral molecules with a radius < 20 Å are filtered freely, while molecules > 42 Å are not filtered.

    physiology filtration molecules
  • Serum albumin, an anionic protein with a molecular radius of 35.5 Å, is poorly filtered due to its negative charges.

    physiology filtration albumin
  • The composition of glomerular filtrate is nearly protein-free and contains salts & organic molecules like glucose and amino acids.

    physiology filtrate composition
  • The Starling forces drive the process of ultrafiltration in the kidneys.

    physiology starling ultrafiltration
  • The glomerular filtrate is nearly protein-free and contains no cellular elements such as RBC, WBC, and platelets.

    kidney filtrate composition
  • Starling forces drive ultrafiltration across the glomerular capillaries, and changes in these forces alter the GFR.

    kidney starling_forces gfr
  • The clinical importance of the negative charges on the filtration barrier is to restrict the filtration of plasma proteins.

    kidney clinical filtration
  • In glomerular diseases, the negative charges on the filtration barrier are reduced, leading to proteinuria.

    kidney disease proteinuria
  • The GFR can be calculated using the formula: GFR = Kf [ (PGC - PBS) – (πGC) ].

    kidney gfr formula
  • The layers of the glomerular filtration barrier include the endothelium, basement membrane, and podocytes.

    kidney filtration_barrier anatomy
  • The composition of the glomerular filtrate is similar to plasma, containing salts and organic molecules such as glucose and amino acids.

    kidney filtrate plasma
  • The Starling forces include forces favoring filtration and those opposing filtration, affecting fluid movement across the glomerular capillary wall.

    kidney starling_forces filtration
  • In the case of a 6 year-old boy with dark urine and swollen feet, the condition is likely related to post-infectious glomerulonephritis.

    kidney clinical_case glomerulonephritis
  • The formula for Glomerular Filtration Rate (GFR) is GFR = Kf [ (PGC - PBS) – (πGC )].

    physiology gfr formulas
  • Kf is a measure of the product of the intrinsic permeability of the glomerular capillary to water and the glomerular surface area available for filtration.

    physiology kf glomerular_filtration
  • The rate of glomerular filtration is higher in glomerular capillaries than in systemic capillaries mainly because Kf is approximately 100 times greater in glomerular capillaries.

    physiology glomerular_filtration kf
  • Diseases can lower Kf by reducing the number of functional glomerular capillaries or by increasing the thickness of the glomerular capillary membrane.

    physiology diseases kf
  • In normal individuals, the GFR is physiologically regulated by alterations in PGC, where an increase in PGC leads to an increase in GFR.

    physiology gfr regulation
  • Constriction of the afferent arteriole leads to a decrease in Renal Plasma Flow (RPF), PGC, and GFR.

    physiology afferent_arteriole gfr
  • Constriction of the efferent arteriole causes a slight decrease in RPF, but an increase in PGC and GFR.

    physiology efferent_arteriole gfr
  • An increase in plasma protein concentration leads to an increase in πGC and a decrease in GFR.

    physiology plasma_protein gfr
  • The normal GFR in an adult male is between 90 - 140 mL/min, while in an adult female it is 80 - 125 mL/min.

    physiology gfr normal_values
  • GFR can be estimated using the creatinine clearance test, where the amount of creatinine excreted in urine per minute equals the amount filtered at the glomerulus.

    physiology creatinine gfr
  • The excretion rate is the amount of creatinine filtered at the glomerulus each minute, represented as:

    GFR = ( \frac{U_{Cr} \times V}{P_{Cr}} ). Where: - PCr = plasma [creatinine] - UCr = urine [creatinine] - V = urine flow.

    gfr creatinine kidney
  • The clearance of creatinine provides a means for determining the GFR in clinical practice, and is important when kidney disease is suspected because a decline in GFR may be the first clinical sign of kidney disease.

    gfr clearance clinical
  • To measure GFR, a substance must meet the following criteria: 1. Be freely filtered across the glomerulus into Bowman's space 2. Not be reabsorbed or secreted by the nephron 3. Not be metabolized or produced by the kidney 4. Not alter the GFR if infused. Example: Inulin is a fructose polymer that measures GFR.

    gfr criteria inulin
  • A 50% loss of functioning nephrons only reduces the GFR by about 25%, because the remaining nephrons compensate. This is crucial for understanding kidney disease progression.

    nephrons gfr kidney
  • Kidney function is assessed by measuring PCr, which is inversely related to GFR. A fall from 120 to 100 mL/min in GFR is accompanied by a small increase in PCr from 1.0 to 1.2 mg/dL, indicating a significant decline in GFR.

    pcr gfr kidney
  • During pregnancy, the GFR increases by 50%, with a normal GFR of 125 mL/min rising to 188 mL/min and creatinine levels dropping from 1 mg/dL to 0.5 mg/dL.

    pregnancy gfr creatinine
  • The filtration fraction is the fraction of plasma filtered through the glomerular capillaries, calculated as:

    Filtration Fraction = ( \frac{GFR}{RPF} ) Where ~20% of the plasma flowing through the kidneys is filtered.

    filtration gfr rpf
  • Typical renal blood flow (RBF) is 1.1 L/min, with renal plasma flow (RPF) calculated as 0.55 x 1.1 L/min, resulting in 605 mL/min. Of this, 125 mL/min filters into Bowman's space, which is 20% of the total.

    rbf rpf filtration
  • Today's topics include: - Overview of kidney functions - Glomerular Filtration (GFR) - Estimation of GFR via creatinine clearance - Clinical importance of GFR.

    kidney gfr topics
  • The volume of plasma completely cleared of a substance (x) by the kidneys per unit time is known as renal clearance.

    renal clearance
  • The formula for renal clearance is C x = U x X V / P x.

    renal formula
  • In the formula for renal clearance, U x represents the urine concentration of substance x (mg/ml).

    renal urine
  • If U x = 100 mg/ml and V = 1 ml/min, then the excretion rate of x is 100 mg/min.

    renal excretion
  • The clearance of inulin is used to estimate GFR because it is freely filtered but neither reabsorbed nor secreted.

    renal gfr
  • In a 24-hour period, if 1.44 L of urine is collected and the inulin concentration is 150 mg/ml in urine and 1 mg/ml in plasma, the inulin clearance is 150 ml/min.

    renal inulin clearance
  • For sodium clearance, if 450 ml of urine is collected in 1 hour with a Na+ concentration of 15 mmol/L and plasma Na+ concentration of 145 mmol/L, the Na+ clearance is 0.78 ml/min.

    renal sodium clearance
  • A substance not normally filtered across the glomerular capillaries will have a clearance of approximately zero, such as large plasma proteins.

    renal clearance
  • Substances that are filtered but partially reabsorbed, like Na+, have a clearance higher than zero.

    renal na+ clearance
  • Organic acids like para-aminohippuric acid (PAH) are both filtered and secreted, resulting in the highest clearance values.

    renal organic_acids
  • Acid (PAH) is both filtered & secreted, therefore has the highest clearance values.

    renal clearance pah
  • Creatinine is preferred over inulin for estimating GFR because it is secreted to a small extent and slightly overestimates GFR, while inulin is neither reabsorbed nor secreted.

    renal gfr creatinine
  • The use of inulin clearance is limited in clinical situations due to requirements such as: - an intravenous injection followed by constant infusion - complete emptying of the bladder - high urine flow to permit analysis.

    renal inulin clearance
  • Creatinine is an end product of protein metabolism and its concentration remains fairly constant over a 24-hour period, eliminating the need for an intravenous infusion.

    renal creatinine metabolism
  • Plasma creatinine can be used to follow changes in GFR in a patient with chronic renal disease.

    renal gfr chronic
  • The clearance period for creatinine can extend for as long as 24 hours, allowing for adequate urine collection.

    renal clearance urine
  • Cimetidine can inhibit tubular secretion of creatinine, thereby reducing creatinine clearance but not affecting actual GFR.

    renal creatinine cimetidine
  • The glomerular capillaries are involved in glomerular filtration, while the peritubular capillary is involved in tubular reabsorption and tubular secretion.

    renal filtration reabsorption
  • The filtration membrane consists of three layers: capillary endothelium, basement membrane, and foot processes of podocyte.

    anatomy physiology kidneys
  • The glomerular capsule contains a visceral layer made up of podocytes that have cytoplasmic extensions called foot processes.

    anatomy kidneys glomerulus
  • Fenestrations in the glomerular capillary endothelium allow for filtration, while filtration slits between podocyte foot processes further regulate this process.

    anatomy filtration kidneys
  • The relative filterability of substances is influenced by their effective molecular radius. For example, polycationic dextran has different filterability compared to neutral dextran.

    physiology filterability molecules
  • At the arterial end of the capillary, the net filtration pressure is positive, leading to fluid exiting the capillary due to higher capillary hydrostatic pressure compared to blood colloidal osmotic pressure.

    physiology capillaries filtration
  • A constriction of the afferent arteriole leads to an increase in renal plasma flow (RPF) and glomerular filtration rate (GFR).

    physiology arterioles kidneys
  • A thickened glomerular basement membrane and reduced endothelial glycocalyx can affect the filtration process in the kidneys.

    anatomy pathology kidneys
  • The venous end of the capillary has a net filtration pressure that can be zero or negative, depending on the balance between hydrostatic pressure and osmotic pressure.

    physiology capillaries filtration
  • The constriction of the efferent arteriole leads to a decrease in GFR and an increase in RPF.

    physiology kidneys arterioles
  • The amount filtered in the kidneys is equal to the amount excreted, expressed as Po x RPF.

    physiology kidneys filtration
  • In the context of creatinine, there is no tubular reabsorption or secretion, which means Po x RPF is used to calculate GFR.

    physiology creatinine gfr
  • The formula for GFR can be represented as Po x GFR = Ug x V.

    physiology gfr formulas
  • Plasma creatinine levels are measured in mg/dL and have a direct relationship with GFR measured in mL/min.

    physiology creatinine gfr
  • The clearance of substances such as urea, penicillin, and glucose is measured in mL/min.

    physiology clearance substances