renal

HUBS1404 Biomedical Science Part 2: The Renal System I Anatomy Lecture Notes

Lecture Plan

  • Gross Anatomy of the Kidney

  • Nephron Structure

  • Blood Supply to and from the Nephrons

  • Role of the Renal Corpuscle and Renal Tubules

  • Structure of the Ureters, Urinary Bladder, and Urethra

Key Functions of the Kidney

  • Removal of Waste Products:

    • Excretes nitrogenous wastes such as urea and creatinine.

  • Regulation of Fluid and Electrolyte Levels:

    • Maintains balance of fluids and essential ions like sodium, potassium, and calcium.

  • Regulation of pH:

    • Helps maintain acid-base balance in the body.

  • Maintaining Blood Pressure:

    • Regulates blood volume and systemic resistance.

  • Maintaining Blood Osmolarity:

    • Controls the concentration of solutes in the blood.

  • Production of Hormones and Renin:

    • Endocrine functions including erythropoietin and angiotensinogen.

  • Gluconeogenesis:

    • Produces glucose from non-carbohydrate sources during fasting.

Introduction to the Renal System

  • Role in Homeostasis:

    • The kidneys are vital for maintaining homeostasis through filtration, reabsorption, and secretion.

  • Renal Blood Flow:

    • Approximately 1200 ml/min, representing 20-25% of cardiac output despite the kidneys constituting only 0.5% of body mass.

Components of the Renal System

  • Kidneys (x2):

    • The active renal organs.

  • Ureters (x2):

    • Convey urine from kidneys to the bladder.

  • Bladder:

    • Acts as a temporary storage for urine.

  • Urethra:

    • Serves as the exit tube for urine.

Kidney Structure

  • Dimensions: Approximately 10-12 cm long, 5-7 cm wide, and 3 cm thick.

  • Hilum:

    • A notch on the medial side, serves as the entry/exit point for blood vessels and ureters.

  • Renal Cortex:

    • The outer region containing nephron structures.

  • Renal Medulla:

    • The inner region with renal pyramids and renal columns.

Anatomy of the Kidney

  • Frontal Section of the Kidney:

    • Includes components like renal hilum, renal pelvis, major/minor calyx, and renal sinus.

  • Renal Pyramids:

    • Located in the renal medulla, separated by renal columns.

  • Nephrons:

    • Functional units of the kidney comprising renal corpuscles and renal tubules.

Blood Supply

  • Key Vessels:

    • Renal artery, Interlobar artery, Arcuate artery, Interlobular artery (cortical radiate artery), Afferent arterioles, Efferent arterioles, Glomerulus, Renal vein, etc.

  • Blood Flow Functionality:

    • Blood flows into the renal corpuscle via afferent arterioles, filtering takes place, and then passes through the efferent arterioles towards peritubular capillaries.

Nephrons

  • Quantity: Each kidney contains between 1-1.25 million nephrons.

  • Types of Nephrons:

    • Cortical Nephrons (80-85%):

    • Located mainly in the cortex, shorter nephron loops.

    • Juxtamedullary Nephrons:

    • Located closer to the medulla, longer nephron loops for concentrated urine.

  • Nephron Structure:

    • Renal Corpuscle:

    • Site of filtration including the glomerulus and Bowman’s capsule.

    • Renal Tubule:

    • Divided into proximal tubule, loop of Henle, and distal tubule for reabsorption and secretion.

Renal Corpuscle

  • Glomerulus:

    • A network of fenestrated capillaries where blood is filtered.

  • Bowman's Capsule:

    • Comprises an inner visceral layer (podocytes) and an outer parietal layer (squamous cells).

    • Pedicels: Extensions forming filtration slits for selective filtration.

Renal Tubule Function

  • The tubular journey begins in the capsular space becoming tubular fluid as it moves through the three main sections:

    1. Proximal Convoluted Tubule (PCT)

    2. Nephron Loop (Loop of Henle)

    3. Distal Convoluted Tubule (DCT)

    • Final urine is formed as fluids reach the collecting ducts.

Processes in the Nephron

Proximal Convoluted Tubule (PCT)

  • Reabsorption: Most active site for reabsorption, reclaiming 65% of water, 100% of glucose and amino acids, 65% of Na+ and K+ ions.

  • Cell Structure:

    • Simple cuboidal epithelium with microvilli for increased reabsorption surface area.

Nephron Loop (Loop of Henle)

  • Thick Ascending Limb:

    • Reabsorbs 25% of Na+ and Cl-, impermeable to water.

  • Thin and Thick Segments:

    • Specialized for different absorption processes (water and solutes).

Distal Convoluted Tubule (DCT)

  • Function: Regulates composition of fluids, final adjustments in ion and water levels.

  • Receptors for Hormones: Cells respond to ADH and aldosterone for Na+ and water reabsorption.

Urine Pathway and Storage

  1. Collecting Ducts:

    • Collect urine from nephrons.

  2. Minor Calyces:

    • Collect urine from collecting ducts.

  3. Major Calyces:

    • Join into the renal pelvis.

  4. Ureters:

    • Transport urine to the bladder.

  5. Bladder:

    • Stores urine until voided through urethra.

Ureters Structure

  • Length: Approximately 25-30 cm.

  • Layer Composition:

    • Mucosa: Transitional epithelium with mucous secretion.

    • Muscularis: Circular and longitudinal smooth muscle layers.

    • Adventitia: Loose connective tissue anchoring the ureters.

Urinary Bladder Structure

  • Capacity: Can hold 700-800 ml of urine, expands with filling.

  • Mucosa and Rugae Structure: Allows distension without damage.

  • Muscular Layers:

    • Comprised of detrusor muscle with an inner longitudinal, central circular, and outer longitudinal layer.

Urethra Description

  • Function: Carries urine from the bladder to the exterior.

  • Epithelium Variation: Different types present in males and females; in males, it runs through the prostate and perineal muscles.

Summary of Learning Outcomes

  • Ability to define the key functions of the kidneys.

  • Description of the gross structures including renal cortex, medulla, and pyramids.

  • Explanation of nephron structure and blood flow from renal artery to renal vein.

  • Discussion of the glomerular capsule and renal tubule functions.

  • Identification of the ureters, bladder, and urethra components.

HUBS1404 Biomedical Science Part 2: The Renal System II Filtration Lecture Notes

Lecture Plan

  • Three Factors of Net Glomerular Filtration

  • Importance of Glomerular Filtration Rate (GFR)

  • Autoregulation Mechanisms: Myogenic, Neural, Hormonal

  • Consequences of Glomerular Disease

Introduction

  • The kidneys perform a range of homeostatic functions mainly through the nephron operations:

    • Filtration

    • Reabsorption

    • Secretion

Overview of Filtration Process

  • Glomerular Filtration: Occurs in the renal corpuscle.

  • Tubular Reabsorption: Along the renal tubule and collecting duct.

  • Tubular Secretion: Occurs to modify fluid composition.

Maintaining Blood Solute Concentrations

  • Ions to Monitor: Sodium (Na+), Potassium (K+), Hydrogen ions (H+).

  • Nitrogenous Waste Removal: Primarily through urea and uric acid derived from protein metabolism.

Filtration Details

Filtration Membrane Composition

  • Components:

    • Fenestrated capillaries and podocytes.

  • Filtration Criteria:

    • Size and charge determine if substances can pass through; most proteins and cells are too large to filter.

  • Measurements:

    • Fenestration size: 0.07−0.1extµm0.07-0.1 ext{ µm}; filtration slit size: <0.007 ext{ µm}.

Factors Driving Net Filtration

Glomerular Blood Hydrostatic Pressure (GBHP)

  • Average GBHP: 55 mmHg — enables fluid exit from glomerular capillaries.

Capsular Hydrostatic Pressure (CHP)

  • Average CHP: 15 mmHg — opposes fluid exit from capillaries.

Blood Colloid Osmotic Pressure (BCOP)

  • Average BCOP: 30 mmHg — opposes fluid loss due to solute concentration.

Net Filtration Pressure (NFP)

  • Calculated as:
    NFP=GBHP−CHP−BCOP=55extmmHg−15extmmHg−30extmmHg=10extmmHgNFP = GBHP - CHP - BCOP = 55 ext{ mmHg} - 15 ext{ mmHg} - 30 ext{ mmHg} = 10 ext{ mmHg}

Glomerular Filtration Rate (GFR)

  • Importance of GFR: Constant flow ensures waste removal; GFR must be maintained for proper kidney function.

  • Normal GFR Values:

    • Males: 125 ml/min

    • Females: 105 ml/min

  • Risks of Abnormal GFR:

    • High GFR: Loss of important solutes.

    • Low GFR: Accumulation of waste products affecting blood composition.

Stages of Renal Failure by GFR

  • Normal GFR: 125 ml/min

  • Impaired GFR: 60 - 100 ml/min

  • Mild Renal Failure: 30 - 60 ml/min

  • Moderate to Severe Renal Failure: 15 – 30 ml/min

  • End-Stage Renal Failure: <15 ml/min

Daily Filtration Volume

  • Filtrate per day:

    • Males: 180 liters/day

    • Females: 150 liters/day

  • Reabsorption: 99% of the filtered fluid is reabsorbed, resulting in 1-2 liters of urine based on hydration levels.

Regulation of GFR

  • Mechanisms:

    • Renal Autoregulation (local adjustments)

    • Neural Regulation

    • Hormonal Regulation

Myogenic Mechanism

  • Function: Adjusts afferent and efferent arterioles to regulate blood flow in response to pressure changes.

Tubuloglomerular Feedback Mechanism

  • Macula Densa Cells: Detect changes in tubular fluid flow. They inhibit nitric oxide release, resulting in vasoconstriction of the afferent arteriole, reducing blood flow to the glomerulus.

Neural Regulation

  • Sympathetic Activation: Increases vasoconstriction via norepinephrine, particularly affecting afferent arterioles, reducing GFR and urine output to retain blood volume and pressure.

Hormonal Regulation

Atrial Natriuretic Peptide (ANP)

  • Action: Secreted in response to atrial stretch (increased blood volume) to increase GFR by dilating afferent arterioles and relaxing mesangial cells.

Angiotensin II

  • Action: A potent vasoconstrictor in response to low blood volume; constricts both afferent and efferent arterioles resulting in decreased GFR.

Glomerular Diseases

  • It is critical to maintain a normal GFR; diseases affecting the glomerulus may reduce filtration efficiency.

  • Often caused by:

    • Infections, autoimmune disorders, or drug reactions.

    • Can lead to inflammation, impacting filtration efficacy.

Glomerulonephritis in Children

  • Common Cause: Post-streptococcal infection leading to inflammation and increased permeability of the filtration membrane allowing proteins like albumin to leak into urine, leading to edema.

Summary of Learning Outcomes

  • Discuss the mechanisms and importance of glomerular filtration.

  • Explain the factors influencing net filtration.

  • Define the autoregulation, neural and hormonal processes that affect GFR.

  • Describe the effects of glomerular inflammation on health.

HUBS1404 Biomedical Science Part 2: The Renal System III Tubular Reabsorption and Secretion Lecture Notes

Lecture Plan

  • Processes of Tubular Reabsorption and Secretion

  • Differences in Reabsorption Across PT, Nephron Loop, and DT

  • Transport Methods Used for Solute Transport

Introduction to Tubular Processes

  • Focus on tubular reabsorption and secretion as remaining nephrons' main functions.

  • Most filtrate components are returned to the bloodstream providing control over urine composition.

Tubular Reabsorption Overview

  • Reabsorption Amount: 99% of filtrate reabsorbed into bloodstream.

  • Specific absorption properties vary among nephron sections resulting in unique regulatory capabilities.

Mechanisms of Solute Transport

  • Movement of solutes through renal tubules is unidirectional.

  • Differing transporter proteins present on apical vs. basolateral surfaces help facilitate absorption.

  • Example: Sodium-potassium pumps are primarily located on the basolateral surface, enabling sodium reabsorption into nearby capillaries.

Pathways of Reabsorption

  • Paracellular Transport: Fluid and solutes move between tubule cells.

  • Transcellular Transport: Solutes pass through tubule cells via specific membrane proteins.

Types of Transporters

  • Active Transport: Pumps relying on ATP to move solutes across membranes.

  • Co-transporters (Symporters): Transporting multiple solutes together in the same direction.

  • Antiporters: Move solutes in opposite directions.

Proximal Tubule (PT) Reabsorption

  • Significant reabsorption occurs:

    • Water: 65%

    • Glucose and Amino Acids: 100%

    • Sodium and Potassium Ions: 65%

    • Bicarbonate: 80-90%

    • Urea: 50%

Water Reabsorption

  • Driven mostly by osmosis as water follows solute reabsorption.

  • Aquaporins: Channels facilitating water transport across PT walls.

Nephron Loop Functions

  • Osmolarity Changes: Continuity of solute and water reabsorption alters osmolarity of tubular fluid.

  • Water Reabsorption:

    • 15% of water in descending limb (permeable to water).

    • Na+ and Cl- reabsorption in ascending limb (impermeable to water).

  • Reabsorbed Items:

    • 20-30% Na+ and Cl- ions

    • 10-20% HCO3- ions

Distal Tubule (DT) Reabsorption

  • Greater regulatory role in fluid composition:

    • Early Section:

    • Reabsorbs 10-15% of water.

    • 5% Na+ and Cl- ions.

    • Late Section:

    • Requires hormone receptors (aldosterone and ADH) to modulate Na+ and water resorption.

Collecting Duct Functions

  • Primarily Na+ transport; also modulated by ADH for water permeability.

  • Substantial water reabsorption occurs via aquaporins.

Tubular Secretion Overview

  • Solutes actively secreted into tubular fluid from blood/tubular cells for excretion.

  • Major Solutes:

    • H+, K+, NH4+, Creatinine, Urea, Drug Metabolites.

Importance of Tubular Secretion

  • Homeostasis Maintenance:

    • Aids in blood pH regulation (H+) and solute concentration normalization.

  • Helps eliminate metabolic waste and foreign substances (toxins, drugs).

Locations of Secretion

  • PT: Primary site for secretion (creatinine, urea, etc.).

  • Minimal Secretion: Occurs in the nephron loop.

  • DT and Collecting Duct: Focused control over ion secretion (H+, NH4+, K+).

Summary of Nephron Filtration, Reabsorption, and Secretion

  • Filtration in Renal Corpuscle:

    • GFR: 105-125 mL/min of isotonic fluid.

  • Reabsorption varies by nephron segment.

  • Collecting Duct:

    • Urine formation is concentrated in response to hydration state (influence of ADH).

Learning Outcomes

  • Discuss blood vessels involved in reabsorption and secretion.

  • Explain structural functions of renal tubule subdivisions.

  • List key substances reabsorbed in specific renal tubule areas.