Kidney Anatomy and Functions

Kidney Functions

• The kidney performs several functions, including filtering blood, regulating blood pressure, and electrolyte balance.
• It also regulates pH, produces hormones, and eliminates waste.

Kidney Anatomy and Function

• Renal Artery: Transports unfiltered blood to the kidney.
• Renal Vein: Transports filtered blood away from the kidney.
• Urethra: Carries urine from the bladder to the outside of the body.
• Bladder: Stores urine.
• Kidney: Filters blood and produces urine.
• Ureter: Carries urine from the kidney to the bladder.
• Adrenal Gland: Endocrine gland located on top of the kidney, produces hormones.
• Renal Hilus: Indentation in the kidney where blood vessels and the ureter enter and exit.
• Renal Capsule: Protective outer covering of the kidney.
• Adipose Capsule: Layer of fat that surrounds the kidney, providing protection.
• Renal Fascia: Connective tissue that anchors the kidney in place.
• Cortex: Outer region of the kidney, contains the glomeruli and convoluted tubules.
• Medulla: Inner region of the kidney, contains the loops of Henle and collecting ducts.
• Papillae: Tip of the renal pyramid, where urine is excreted into the calyces.
• Renal Pelvis: Funnel-shaped structure that collects urine from the calyces.
• Calyces: Cup-like structures that collect urine from the papillae.
• Renal Pyramid: Conical-shaped tissue in the medulla, contains the loops of Henle and collecting ducts.
• Segmental Artery: Branch of the renal artery that enters the kidney.
• Collecting Duct: Tube that collects urine from several nephrons.
• Lobular Artery: Branch of the segmental artery that supplies a lobe of the kidney.
• Lobular Vein: Drains blood from a lobe of the kidney.
• Arcuate Artery: Artery that arches around the base of the renal pyramid.
• Arcuate Vein: Vein that drains blood from the arcuate artery.
• Interlobular Artery: Artery that extends from the arcuate artery into the cortex.
• Interlobular Vein: Vein that drains blood from the interlobular artery.
• Afferent Arteriole: Supplies blood to the glomerulus.
• Efferent Arteriole: Drains blood from the glomerulus.
• Peritubular Capillaries: Capillaries that surround the proximal and distal convoluted tubules.
• Vasa Recta: Capillaries that run parallel to the loops of Henle in the medulla.
• Glomerulus: Network of capillaries where filtration occurs.
• Bowman's Capsule: Cup-shaped structure that surrounds the glomerulus and collects filtrate.
• Glomerular Capillary: Capillary within the glomerulus where filtration occurs.
• Glomerular Endothelium: Inner lining of the glomerular capillary.
• Podocytes: Cells that surround the glomerular capillaries and help filter blood.
• Proximal Convoluted Tubule: First section of the renal tubule, where most reabsorption occurs.
• Loop of Henle: U-shaped part of the renal tubule, responsible for the concentration of urine.
• Distal Convoluted Tubule: Last section of the renal tubule, where further reabsorption and secretion occur.

Cortical vs. Juxtamedullary Nephrons

• Cortical nephrons are primarily in the cortex.
• Juxtamedullary nephrons have loops of Henle that extend deep into the medulla and help concentrate urine.

Glomerular Capsule Cells - Mesangial

• Mesangial cells play a role in immune response and structural support.

Glomerular Capsule Cells - Juxtaglomerular

• Juxtaglomerular cells secrete renin to regulate blood pressure.

Macula Densa Function

• Macula densa cells monitor sodium chloride levels in the distal tubule and regulate GFR.

Glomerular Capillaries

• Glomerular capillaries act as a filter for fluid flow.

Kidney Blood Flow

• Order of blood flow through the kidney: interlobular artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta → interlobular vein.

Urine Formation

• Urine formation starts in the Bowman's capsule.
• Flow: Bowman's capsule → proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting duct.

Glomerular Filtration Rate (GFR)

• Rate of urine excretion is determined by GFR, reabsorption, and secretion.

Fates of a Filtered Molecule

• Filtered molecules can be reabsorbed, excreted, secreted, or metabolized.

Normal GFR

• Normal GFR is approximately 125 mL/min.
• GFR can vary depending on factors such as age, sex, and kidney function.

Glomerular Filtration Forces

• Forces that favor glomerular filtration: glomerular capillary hydrostatic pressure.
• Opposing forces: Bowman's capsule hydrostatic pressure and plasma oncotic pressure.

Calculating GFR

• GFR = Kf x Net Filtration Pressure (NFP)

Kf Representation

• Kf represents the filtration coefficient, a measure of the permeability of the glomerular capillaries.

Impact of Glomerular Capillary Hydrostatic Pressure

• Increased glomerular capillary hydrostatic pressure increases NFP and GFR.

Impact of Protein Loss

• Loss of protein in renal diseases lowers plasma oncotic pressure, increasing NFP and GFR.

Impact of Kidney Stone Blockage

• Blockage in renal tubules increases renal tubular hydrostatic pressure and Bowman's capsule hydrostatic pressure, which decreases NFP and GFR.

Impact of Glomerulonephritis

• Glomerulonephritis increases permeability of glomerular capillaries, increasing NFP and GFR.

Filtration Fraction

• Filtration fraction decreases with increased blood flow because reabsorption mechanisms become saturated.

Renal Plasma Flow Decreases

• Decreased renal plasma flow decreases GFR because there is less plasma to filter.

Vasoconstriction - Afferent Arteriole

• Vasoconstriction of the afferent arteriole decreases NFP and GFR.

Vasoconstriction - Efferent Arteriole

• Vasoconstriction of the efferent arteriole increases NFP and GFR.

Vasodilation - Afferent Arteriole

• Vasodilation of the afferent increases NFP and GFR.

Vasodilation - Efferent Arteriole

• Vasodilation of the efferent arteriole decreases NFP and GFR.

Renal Blood Flow

• Renal blood flow is determined by the pressure gradient between the renal artery and vein, and renal vascular resistance.

Arterial Pressure Increases

• Increased arterial pressure increases renal blood flow.

Total Renal Vascular Resistance

• Total renal vascular resistance is regulated by the afferent and efferent arterioles.

Sympathetic Nervous System and GFR

• Sympathetic nervous system activation decreases GFR.

Angiotensin and GFR

• Angiotensin decreases GFR.

GFR Regulation

• Juxtaglomerular apparatus regulates GFR through the release of renin.

Myogenic Reflexes

• Myogenic reflexes predict vasoconstriction in response to a sudden increase in blood flow.

Tubular Reabsorption

• Glucose is completely reabsorbed after filtration.
• Creatinine is not reabsorbed at all after filtration.

Types of Diffusion

• Three types of diffusion: simple, facilitated, and osmosis.
• Diffusion is driven by a concentration gradient for molecules across a membrane.

Primary Transport ATP

• ATP is necessary for primary active transport because it provides the energy to move molecules against their concentration gradients.

Secondary Active Transport

• Secondary active transport uses the electrochemical gradient created by primary active transport to move other molecules across the membrane.

Secondary Active Transport Dependence

• Secondary active transport ultimately uses ATP because the primary active transport that creates the electrochemical gradient requires ATP.

Endocytosis

• Proteins and large molecules pass through renal tubules via endocytosis.

Paracellular vs Transcellular Movement

• Paracellular movement occurs between cells.
• Transcellular movement occurs through cells.

Tubular Epithelium

• Luminal side: faces the tubular lumen (also called apical).
• Basolateral side: faces the interstitial fluid.

Osmolarity

• Water will move into the cell if osmolarity inside a cell is greater than outside.

Osmolarity in Capillary and Tubule

• Osmolarity in the capillary: 500mOsm.
• Osmolarity in the tubular lumen: 300mOsm.
• Water will flow from the tubule into the capillary, increasing the lumen's osmolarity.

Sodium Reabsorption

• Sodium reabsorption results in water, amino acid, glucose, urea, and chloride reabsorption.

Epithelial Cells in Renal Structures

• Epithelial cells differ in structure and function in the PCT, thin descending loop of Henle, and collecting duct cells.

Proximal Convoluted Tubule Reabsorption Role

• The PCT plays a major role primarily in reabsorption.

PCT Concentrations

• Sodium, glucose, amino acid, and bicarbonate concentrations decrease in the PCT.

Thin Descending Limb

• The thin descending limb of the Loop of Henle is highly permeable to water.
• Water is primarily reabsorbed here.
• Lumen osmolarity increases.

Thin Ascending Limb

• The thin ascending limb of the loop of Henle is impermeable to water

Thick Ascending Limb

• The thick ascending limb of the loop of Henle primarily reabsorbs sodium, potassium, and chloride.
• This decreases lumen osmolality.

Countercurrent Blood Flow

• Countercurrent blood flow permits the concentration of urine in the thin descending limb.

Distal Convoluted Tubule

• Early and late portions of the distal convoluted tubule differ in their function.

Distal Convoluted Tubule (DCT)

• The DCT regulates GFR.

Urine Concentration

• Urine is concentrated in the collecting duct.

Peritubular Pressure

• Peritubular pressure influences reabsorption.

GFR and Reabsorption

• GFR influences reabsorption.

Angiotensin Secretion in Response to Low Blood Flow

• Angiotensin increases sodium and water reabsorption.

Vasopressin (ADH) Secretion

• Vasopressin (ADH) is secreted in response to low blood osmolarity and increases water reabsorption.

Aldosterone Secretion

• Aldosterone is secreted in response to Angiotensin II and increases sodium reabsorption.

Atrial Natriuretic Factor (ANF) Secretion

• Atrial natriuretic factor secretion is stimulated by increased blood volume and decreases sodium reabsorption.

Electrolytes and Nonelectrolytes

• Electrolytes dissociate into ions in water.
• Nonelectrolytes do not.

NaCl Solution

• A 140 mM solution of NaCl in water has an osmolar concentration of 280 mOsM.

Sodium and Chloride Solution

• The milliequivalent value determines the concentration of sodium and chloride in a 3.0 g/L solution.

Dominant Ions

• Sodium and chloride dominate in the extracellular fluid.
• Potassium dominates in the intracellular fluid.

Thirst Trigger - Percentage Loss

• A 1-2% loss in plasma volume and total body fluid triggers the feeling of thirst.

Thirst Trigger - Blood Volume Change

• A thirst response is triggered by decreased blood volume.

Thirst Trigger - Blood Osmolality Change

• A thirst response is triggered by increased blood osmolality.

Negative Feedback - Thirst

• Three factors that provide negative feedback to inhibit the thirst response are:
• ingestion of water
• distension of the stomach
• decreased blood osmolality

ADH Triggers

• Two mechanisms that trigger ADH release by the posterior pituitary are:
• increased blood osmolality
• decreased blood volume

ADH Influence

• ADH influences kidney function by increasing water reabsorption in the collecting ducts.

Aquaporins

• Aquaporins are water channels that facilitate water movement across cell membranes.

Water Transfer

• Water gets transferred from a hyperosmotic lumen into the interstitial space through aquaporins.

Rennin Release Triggers

• Factors that trigger rennin release from the JGA are: decreased blood pressure, decreased sodium chloride in the distal tubule, and sympathetic nervous system activation.

Angiotensin II Effects

• Angiotensin II affects kidney function by increasing sodium reabsorption, aldosterone secretion, and vasoconstriction of the efferent arterioles.

Basolateral Na-K ATPase Pump

• An increase in Na-K ATPase pump activity in the basolateral membrane increases water reabsorption by creating an osmotic gradient that drives water movement from the tubular lumen into the interstitial fluid.

Angiotensin II and Efferent Arterioles

• Constriction of efferent arterioles by angiotensin increases water reabsorption by increasing the glomerular filtration fraction and raising the oncotic pressure in the peritubular capillaries, which promotes water movement from the tubular lumen.

Aldosterone Secretion Triggers

• Factors that trigger aldosterone secretion are: increased angiotensin II, increased potassium levels, and decreased sodium levels.

Aldosterone Impact

• Aldosterone impacts kidney function by increasing sodium reabsorption and potassium secretion in the collecting ducts, which increases water reabsorption and expands extracellular fluid volume.

ANP Secretion

• Increased blood volume and atrial stretch triggers the secretion of ANP.

Target Organs for ANP

• Three target organs for ANP:
• Kidneys (increases sodium excretion)
• Adrenal glands (decreases aldosterone secretion)
• Blood vessels (vasodilation) These effects decrease blood volume and blood pressure.

Over/Underproduction of Hormones

• Over or underproduction of hormones will have an impact on body physiology depending on their specific functions.

Hydrogen Ion Production

• Hydrogen ions are produced in the body through metabolic processes.

Body pH Regulation

• Body pH is regulated by chemical buffer systems, the respiratory system, and the kidneys.

Weak vs. Strong Acid

• A weak acid only partially dissociates in solution
• A strong acid completely dissociates in solution.

Chemical Buffer Systems in Body

• The three chemical buffer systems for acids in the body are:
• bicarbonate buffer system
• phosphate buffer system
• protein buffer system

Respiratory Acidosis/Alkalosis

• Respiratory acidosis is caused by hypoventilation.
• Respiratory alkalosis is caused by hyperventilation.

Metabolic Acidosis/Alkalosis

• Metabolic acidosis is caused by excessive production of acids or loss of bicarbonate.
• Metabolic alkalosis results from excessive loss of acids or increase in bicarbonate.

Bicarbonate Reabsorption

• Bicarbonate reabsorption in the kidney occurs through a process involving carbonic anhydrase.

H Secretion

• H+ secretion in the kidney occurs via primary and secondary active transport mechanisms in the proximal tubule, distal tubule, and collecting ducts.

Ammonium Excretion

• Ammonium excretion in the kidney is regulated by glutamine metabolism and transport in the proximal tubular cells.