Topics to be learn :
  • Introduction
  • Excretion and Excretory Products
  • Excretory System in Human Beings
  • Urine Formation
  • Concentration of Urine
  • Composition of Urine
  • Role of Other Organs in Excretion
  • Disorders and Diseases

Introduction
  • Metabolism: The total sum of all chemical reactions occurring in an organism's body.
  • Metabolic Waste Products: By-products formed during metabolic processes, known as metabolic waste.
  • Types: Fluid, gaseous, organic, or inorganic waste. Produced within body cells.
Excretion and Excretory Products

Excretion: The elimination of waste products from the body.

Main Excretory Products:
  • Fluids: Water.
  • Gaseous wastes: Carbon dioxide (CO₂).
  • Nitrogenous wastes: Ammonia, urea, uric acid, creatinine.
  • Minerals & Salts: Sodium, potassium, calcium (eliminated if in excess).
  • Pigments: Breakdown of hemoglobin creates: Bilirubin (excreted via feces). Urochrome (excreted via urine).
  • Food and Drug Pigments: Certain foods (e.g., beetroot), vitamins, hormones, and drugs.
  • Volatile Substances: From spices (eliminated through lungs).
Conditions Causing Deeply Colored Urine
  • Severe Dehydration: Leads to concentrated urine.
  • Diet: Foods like beetroot with high pigment.
  • Medications: Certain drugs can change urine color.
Deamination Process
  • Deamination:The breakdown of excess amino acids in the body.
  • Purpose: Necessary because the body cannot store extra amino acids.
Process:
  • Amino group is removed from amino acid, forming ammonia.
  • Ammonia is either excreted directly or converted into less toxic forms (e.g., urea, uric acid) before excretion.
Role of Water in Excretion
  • Ammonia: Primary by-product of deamination.
  • Highly toxic, must be diluted immediately.
Water Access:
  • Abundant Water: Ammonia can be excreted directly.
  • Limited Water: Ammonia must be converted into less toxic forms (e.g., urea, uric acid) to conserve water.
Three Main Modes of Excretion: 1.Ammonotelism, 2.Ureotelism, 3.Uricotelism
(i) Ammonotelism

Definition: Excretion of nitrogenous waste as ammonia.

Characteristics:

  • Ammonia: Basic and highly toxic, disturbs pH balance and enzyme reactions if not removed quickly.
  • Water Requirement: Requires large amounts of water (300-500 ml per gram of ammonia) to dilute and reduce toxicity.
  • Energy Efficiency: Energy-saving excretion method due to minimal conversion steps.

Examples:

  • Aquatic animals: Tadpoles, aquatic invertebrates, bony fishes, aquatic or larval amphibians.
  • Excretion Pathways: Skin, gills, kidneys.
  • Protozoa: Also use ammonotelism as they lack a specialized excretory system.
(ii) Ureotelism

Definition: Excretion of nitrogenous waste as urea.

Characteristics:

  • Urea: Less toxic and less soluble than ammonia; can be concentrated in the body with minimal water.
  • Water Requirement: Only about 50 ml per gram of urea, allowing better water conservation.
  • Energy Use: Requires energy for conversion from ammonia, using the urea cycle in the liver (3 ATP per molecule of urea).
  • Organ Involved: Liver—primary site for the urea cycle with specialized enzymes.

Examples:

  • Terrestrial animals: Mammals (e.g., humans), cartilaginous fishes (e.g., sharks, rays), many reptiles, and adult amphibians.
  • Ureotelic Adaptation: Useful for animals that need to conserve water.
(iii) Uricotelism

Definition: Excretion of nitrogenous waste as uric acid.

Characteristics:

  • Uric Acid: Least toxic and can be stored in concentrated form, requiring minimal water (5-10 ml per gram).
  • Water Conservation: Ideal for animals needing extreme water conservation.
  • Energy Cost: Higher energy needed for conversion, using the inosinic acid pathway in the liver.
  • Adaptation for Flight: Reduces body weight in birds, aiding in flight.

Examples:

  • Uricotelic Animals: Birds, some insects, many reptiles, and land snails.
  • Adaptation: Helps conserve water in arid environments and for flight efficiency in birds.
Osmoregulation, and Homeostasis
1. Excretory Adaptations in Different Animals

Sharks (Urea Retention):

  • Sharks retain more urea in their blood to make it isotonic with surrounding seawater.
  • Purpose: Maintains osmotic balance, preventing water loss through exosmosis.

Terrestrial Animals (Ureotelic/Uricotelic):

  • Cannot be ammonotelic because ammonia requires too much water for safe excretion.
  • Adaptation: Terrestrial animals conserve water by excreting less toxic nitrogenous waste (urea or uric acid).

Guanotelic Animals:

  • Excrete guanine instead of urea or uric acid.
  • Examples: Spiders, scorpions, penguins.
2. Plasma Creatinine
  • Source: Breakdown of creatine phosphate in muscles during contraction.
  • Purpose: Provides high-energy phosphate for muscle contraction.
  • Importance: Blood levels of plasma creatinine are steady, matching muscle production and renal excretion.
  • Indicator: Elevated levels indicate poor kidney function.
3. Homeostasis
  • Maintains the body’s internal environment.
  • Relies on osmoregulation (regulation of water and salt).
  • Role of Excretion: Excretory organs manage blood composition, impacting homeostasis.
4. Osmoregulation in Fish and Marine Organisms

Freshwater Fish:

  • Challenge: Higher salt concentration inside fish than in freshwater.
  • Water Intake: Water enters by osmosis, risking swelling.
  • Solution: Kidneys produce large urine volumes to remove excess water.
  • Salt Retention: Specialized chloride cells in gills absorb salts from water into the blood.

Marine Fish:

  • Challenge: Blood salt level is lower than seawater, leading to water loss.
  • Solution: Drink seawater to replenish water loss.
  • Salt Excretion: Small kidneys and chloride cells in gills excrete excess salts.

Marine Organisms with Salt Glands:

  • Marine Birds (e.g., Albatross):
  • Salt Glands: Near nostrils, secrete salts to balance osmotic pressure.
  • Examples: Albatross, sea turtles, marine iguanas, sea birds, gulls.
5. Osmoconformers and Osmoregulators

Osmoconformers:

  • Have body fluids isoosmotic to surroundings.
  • Common in marine organisms.

Osmoregulators:

  • Control internal environment independently of the surroundings.
  • Typical of freshwater and terrestrial organisms
Excretory Methods in Various Organisms
1. Excretory Methods by Organism Type
  • Unicellular Organisms: Method: Use contractile vacuoles to collect and discharge waste outside the cell.
  • Sponges: Method: Waste diffuses into water and exits through the osculum.
  • Bilateral Symmetry Organisms: Common Structure: Simple or branched tubes that open outside via nephridiopores. Examples: Annelids, Amphioxus, earthworms.
  • Insects: Method: Use Malpighian tubules—blind-ended tubules for excretion.
  • Crustaceans: Method: Use green glands as excretory organs.
  • Echinoderms: Method: Lack specialized excretory organs; waste diffuses directly into water or through tube feet.
  • Mammals: Organ: Kidneys, comprised of functional units called nephrons, for efficient waste excretion.
2. Types of Nephridia
  • Nephridia: Simple or branching tubes for excretion, opening outside through nephridiopores.
Protonephridia:
  • Structure: Network of dead-end tubes called flame cells.
  • Location: In animals without a true body cavity.
  • Examples: Platyhelminthes, rotifers, some annelids, Amphioxus.
Metanephridia:
  • Structure: Unbranched coiled tubes connected to the body cavity by nephrostomes (funnel-like openings).
  • Process: Body fluid enters through the nephrostome and is discharged via nephridiopores.
  • Example: Earthworms.
Excretory System in Humans
Components of the Human Excretory System
  1. Kidneys
  2. Ureters
  3. Urinary Bladder
  4. Urethra
1. Kidneys

Structure:

  • Shape and Location: Bean-shaped organs, positioned on either side of the spine from the 12th thoracic to the 3rd lumbar vertebra.
  • Retroperitoneal: Located behind the peritoneum.
  • Size and Weight: ~10 x 5 x 4 cm; 150g in males, 135g in females.
  • Hilum: Notch on the inner surface where the renal artery enters, and the renal vein and ureter exit.
  • Nephrons: Each kidney contains approximately 1 million nephrons, the functional units for filtration.

Function:

  • Eliminates nitrogenous waste, excess water, and toxins.
  • Regulates osmoregulation and body fluid pH, maintaining homeostasis.
  • Produces calcitriol, renin, and erythropoietin (important for RBC production).
2. Ureters

Structure:

  • Quantity: One pair, arising from each kidney’s hilum.
  • Length: Muscular tubes about 25–30 cm long.
  • Bladder Connection: Opens obliquely into the bladder, preventing backflow as the bladder fills.

Function: Transports urine from the renal pelvis to the urinary bladder.

3. Urinary Bladder

Structure:

  • Shape: Pear-shaped, hollow, muscular organ in the pelvic cavity.
  • Trigone Area: An inverted triangular region at the bladder’s base, with the urethra at the apex and ureter openings at the base.
Layers:
  • Outer Layer: Covered by peritoneum.
  • Muscular Layer: Detrusor muscle composed of three layers (longitudinal-circular-longitudinal).
  • Inner Layer: Transitional epithelium that allows bladder expansion.

Function: Serves as a temporary storage for urine and aids in micturition (urine expulsion).

4. Urethra

Structure:

  • A fibromuscular tube extending from the bladder to the exterior.
  • Length: Shorter in females (~4 cm) than in males (~20 cm), which increases susceptibility to urinary tract infections (UTIs) in females.
Urethral Sphincters:
  • Internal Sphincter: Involuntary, formed by detrusor muscles.
  • External Sphincter: Voluntary, formed by striated muscles.

Function: Discharges urine from the body; also serves as a urinogenital organ in males.

Floating Kidney (Nephroptosis):
  • Definition: Inferior displacement of the kidney.
  • Causes: Common in individuals with low body fat or weak renal fascia, leading to kidney slippage from its position.
  • Impact: Can obstruct urine flow due to ureter distortion, potentially causing urine backup, which strains kidney tissue.
Micturition
  • Definition: Micturition is the process of releasing urine from the urinary bladder.
  • Bladder Capacity: The bladder typically holds around 700 ml of urine.
Process:
  • When the bladder is about half full, stretch receptors in the bladder wall send signals to the spinal cord.
  • This triggers a conscious desire to urinate.
  • The spinal cord’s micturition reflex center then sends signals to the bladder wall muscles and the internal urethral sphincter.
  • Bladder Muscles: Contract to help push urine out.
  • Internal Urethral Sphincter: Relaxes, allowing urine to pass toward the urethra.
  • External Sphincter: Controlled voluntarily; relaxes as per signals from the brain, resulting in urine elimination.
Longitudinal Section (L.S.) of Kidney

Each kidney is covered by three tissue layers:

  1. Renal Fascia: Outermost layer made of fibrous connective tissue.
  2. Adipose Capsule: Middle layer of fatty tissue attaching the kidney to the abdominal wall. Serves as shock absorber to protect the kidneys.
  3. Renal Capsule: Innermost smooth, fibrous membrane. Connects to the ureter's outer layer and acts as a barrier against infections.
Internal Structure of Kidney (Histology)

The kidney contains two distinct regions:

1. Renal Cortex:

  • Location: Outer, reddish-brown, and granular.
  • Contains: Malpighian bodies, convoluted tubules, and blood vessels.

2. Renal Medulla:

  • Location: Inner region with a pale, striated appearance.
  • Contains: Loops of Henle and collecting ducts arranged in a conical formation to create renal pyramids.
  • Renal Pyramids: Each pyramid has a narrow tip called the renal papilla. Renal papillae open into the minor calyx.
  • Cortex Extensions: Known as columns of Bertini or renal columns, they extend into the medulla between the pyramids.
Pathway of Urine Flow
  1. Renal Papillae → Minor Calyx
  2. Minor Calyces (merge) → Major Calyces
  3. Major Calyces (merge) → Renal Pelvis
  4. Renal Pelvis: A funnel-shaped cavity that transitions into the ureter at the hilum, allowing urine to exit the kidney.
Nephrology
  • Definition: Branch of biology that studies the structure, function, and disorders of the urinary system in both males and females.
Nephrons
  • Definition: Nephrons are the structural and functional units of the kidney.
Components:
  • Renal Tubule (4-6 cm long) and Glomerulus (a bunch of capillaries).
  • Divided into Bowman’s Capsule, Proximal Convoluted Tubule (PCT), Loop of Henle (LoH), Distal Convoluted Tubule (DCT), and Collecting Tubule (CT).
Renal Corpuscle: The combination of Bowman’s capsule and glomerulus is known as the renal corpuscle or Malpighian body.
Structure of Nephron

1. Malpighian Body: Contains Bowman’s Capsule and Glomerulus.

Glomerulus:

  • Blood Capillaries: A network formed by the afferent arteriole branching extensively in Bowman’s capsule.
  • Pressure: The larger diameter of the afferent arteriole compared to the efferent arteriole creates high hydrostatic pressure necessary for ultrafiltration.

Bowman’s Capsule:

  • Structure: Double-walled, cup-like structure with an outer parietal wall (simple squamous epithelium) and an inner visceral wall with podocytes.
  • Function: Forms the initial filtrate through filtration slits between podocytes.

2. Renal Tubule

Neck: Transition from Bowman’s capsule to the PCT, lined with ciliated epithelium.

Proximal Convoluted Tubule (PCT):

  • Function: Major site for selective reabsorption of water, ions, and nutrients.
  • Structure: Lined with cuboidal cells with microvilli (brush border) for increased absorption.

Loop of Henle (LoH):

  • Structure: U-shaped, with a thin descending limb (permeable to water) and a thick ascending limb (impermeable to water).
  • Function: Sets up a counter-current system for osmoregulation.

Distal Convoluted Tubule (DCT):

  • Function: Tubular secretion and pH regulation of body fluids.
  • Structure: Lined with simple cuboidal epithelium.

Collecting Tubule:

  • Function: Water reabsorption and proton secretion.
  • Connects to the collecting duct, which transports urine to the renal pelvis.
Types of Nephrons

1. Cortical Nephrons:

  • Shorter Loop of Henle that extends minimally into the medulla.
  • Most common type, with peritubular capillaries surrounding PCT, DCT, and Loop of Henle.

2. Juxtamedullary Nephrons:

  • Longer Loop of Henle, extending deep into the medulla.
  • Vasa recta forms around the Loop of Henle, aiding in water reabsorption.
Juxtaglomerular Apparatus (JGA)
  • Location: Near the point where DCT contacts the afferent arteriole.
  • Function: The JGA plays a crucial role in blood pressure regulation within the kidney.
Components:
  • JG Cells: Smooth muscle cells in the afferent arteriole wall with granular cytoplasm.
  • Macula Densa: Densely packed cells in the DCT wall.
Urine Formation

Urine formation occurs through three main steps:

  1. Ultrafiltration / Glomerular Filtration
  2. Selective Reabsorption
  3. Tubular Secretion / Augmentation
1. Ultrafiltration / Glomerular Filtration

Arteriole Comparison:

  • Afferent Arteriole: Larger diameter than the efferent arteriole.
  • Efferent Arteriole: Smaller diameter.
  • Capillaries: Diameter smaller than both arterioles.

Glomerular Hydrostatic Pressure (GHP):

  • Definition: Pressure in the glomerulus.
  • Normal Value: Approximately 55 mmHg.

Opposing Pressures:

  • Osmotic Pressure of Blood: About 30 mmHg.
  • Capsular Pressure: About 15 mmHg.

Net / Effective Filtration Pressure (EFP):

Filtration Process:

  • High pressure makes capillary walls permeable (excluding blood cells and proteins).
  • Plasma (except proteins) oozes out through capillaries.

Filtration Rate:

  • Blood Flow: About 600 ml per minute per kidney.
  • Glomerular Filtrate Rate: 125 ml/min (or 180 L/day).

Composition of Glomerular Filtrate:

  • Type: Deproteinized plasma / primary urine.
  • Characteristics: Alkaline.
  • Contents: Contains urea, amino acids, glucose, pigments, and inorganic ions.

Pathway: Glomerular filtrate passes through filtration slits into capsular space and moves to the proximal convoluted tubule (PCT).

2. Selective Reabsorption

Location: Occurs in the proximal convoluted tubule (PCT).

Structure:

  • Highly coiled to slow down glomerular filtrate passage.
  • Columnar Cells: Equipped with microvilli to increase absorptive surface area.

Reabsorption Processes:

  • Active Reabsorption (ATP-mediated): Substances like glucose, amino acids, vitamin C, Ca²⁺, K⁺, Na⁺, Cl⁻ are absorbed against the concentration gradient.
  • Passive Reabsorption: Low-threshold substances like water, sulphates, nitrates, etc., are absorbed through simple diffusion.

Reabsorption Efficiency: About 99% of glomerular filtrate is reabsorbed in PCT and distal convoluted tubule (DCT).

3. Tubular Secretion / Augmentation

Pathway: Filtrate moves from the PCT to the distal convoluted tubule (DCT) via the loop of Henle.

Surrounding Structure: Peritubular capillaries surround the DCT.

Secretion Process:

  • Cells in DCT and collecting tubule (CT) actively absorb wastes (e.g., creatinine) and ions (K⁺, H⁺) from peritubular capillaries.
  • Wastes are secreted into the lumen of DCT and CT, concentrating urine and changing its pH from alkaline to acidic.
  • Homeostatic Mechanism: Secretion of H⁺ ions in DCT and CT is crucial for blood pH regulation.
  • Special Note: Tubular secretion is the primary excretion method in marine bony fishes and desert amphibians.
Distinction Between Selective Reabsorption and Tubular Secretion


Concentration of Urine

Countercurrent Mechanism Overview:

  • Humans can produce concentrated urine, particularly in low water intake or significant water loss (e.g., sweating). Concentration can be up to 1200 mOsm/L, compared to blood at 300 mOsm/L.
  • The countercurrent mechanism is crucial in the nephrons, specifically within the Loop of Henle and vasa recta.

Mechanism Details:

1. Countercurrent Flow:

  • Fluid flows in opposite directions through the descending and ascending limbs of Henle’s loop.
  • In the vasa recta, blood also flows in a countercurrent manner from ascending to descending parts.

2. Descending Limb:

  • Thin and Water-Permeable: Water diffuses from the tubular fluid into tissue fluid, concentrating the tubular fluid.
  • Effect: As water is lost, the osmolarity of tubular fluid increases gradually.

3. Ascending Limb:

  • Thick and Impermeable to Water: Na⁺ and Cl⁻ are actively reabsorbed from the tubular fluid into the tissue fluid.
  • Effect: This reduces the osmolarity of tubular fluid as it flows up.

4. ADH Influence:

  • When water retention is necessary, the pituitary gland secretes ADH (Antidiuretic Hormone).
  • ADH increases water permeability in the collecting ducts, leading to further water reabsorption and concentrated urine formation.

5. Urea Recycling:

  • In the deep medullary part of the collecting ducts, urea is permeable.
  • Concentrated urine flows through, allowing urea to diffuse into tissue fluid.
  • Urea then diffuses back into the tubular fluid in the ascending limb of Henle’s loop.
  • This recycling promotes further water reabsorption and results in small volumes of concentrated urine.

6. Osmotic Gradient Maintenance:

  • The osmotic gradient in the renal medulla is essential for water reabsorption.
  • The vasa recta maintains this gradient through a countercurrent exchange system.

7. Adaptations in Desert Mammals:

  • Desert mammals, like camels, have longer Henle loops to maximize water reabsorption, leading to the excretion of highly concentrated urine.
Composition of Urine

Normal Urine Characteristics:

  • Volume: Typically 1-2 liters in 24 hours; varies with fluid intake, activity, and temperature.
  • Color: Pale yellow, due to urochrome (a pigment from bile breakdown); color can vary with concentration and diet.
  • Appearance: Clear and transparent; no sediments or crystals are typically present.
  • pH: Generally acidic, around 6.0 (range: 4.6 to 8.0); can vary with diet.
  • Specific Gravity: Average of 1.02 (range: 1.001 to 1.035).
  • Normal urine does not contain: Albumin, Sugar, Bile Salts, Bile Pigments, Ketone Bodies, Occult Blood
Regulation of Urine Composition

The composition of urine is influenced by the intake of food and liquids. Two primary mechanisms regulate this composition:

1. Regulating Water Reabsorption through ADH
  • Osmoreceptors in the hypothalamus detect changes in blood osmolarity.
Increased Osmolarity:
  • If blood osmolarity rises (due to dehydration or high salt intake), osmoreceptors stimulate the release of Antidiuretic Hormone (ADH) from the posterior pituitary.
ADH Function:
  • Increases water reabsorption in the distal convoluted tubule (DCT) and collecting ducts by making their walls more permeable.
  • Reduces urine volume and decreases blood osmolarity.
Negative Feedback Mechanism: Once osmolarity returns to normal, the secretion of ADH decreases.
Diabetes Insipidus: In the absence of ADH, the body produces large amounts of dilute urine.
 
2. Electrolyte Reabsorption through RAAS
  • The Renin-Angiotensin-Aldosterone System (RAAS) is activated by the Juxtaglomerular Apparatus (JGA).
  • Trigger: Decrease in blood supply to the afferent arteriole (e.g., low blood pressure or dehydration).
Process:
  • JGA cells release Renin, which converts angiotensinogen (from the liver) to Angiotensin I.
  • Angiotensin-Converting Enzyme (ACE) transforms Angiotensin I into Angiotensin II, which has multiple functions:
  • Constricts arterioles in the kidneys, increasing blood pressure.
  • Stimulates proximal convoluted tubule (PCT) cells to enhance reabsorption of Na⁺, Cl⁻, and water.
  • Stimulates the adrenal cortex to release aldosterone, promoting further reabsorption of Na⁺ and water in the DCT and collecting ducts, increasing blood volume and pressure.
3. Atrial Natriuretic Peptide (ANP)
  • Increased blood volume and pressure lead to the secretion of ANP from the atrial wall.
ANP Functions:
  • Inhibits reabsorption of Na⁺ and Cl⁻ from the collecting ducts.
  • Reduces renin release, leading to decreased aldosterone and ADH secretion.
  • Promotes natriuresis (increased Na⁺ excretion) and diuresis (increased urine production).
Functions of Angiotensin II
  • Vasoconstriction: Narrows arterioles in the kidney, reducing blood flow but increasing blood pressure.
  • Enhanced Reabsorption: Stimulates PCT cells to reabsorb more Na⁺, Cl⁻, and water.
  • Aldosterone Stimulation: Promotes Na⁺ and water reabsorption in the DCT and collecting ducts, increasing blood volume and pressure.
Hormones and Factors Involved in Regulation of Kidney Function
  • ADH: Regulates water reabsorption.
  • Aldosterone: Promotes Na⁺ and water reabsorption.
  • ANP: Inhibits Na⁺ and water reabsorption.
  • Renin: Initiates the RAAS pathway.
  • Calcitriol: Active form of Vitamin D synthesized by kidneys, essential for calcium absorption.
Role of Other Organs in Excretion
1. Skin
 
Sweat Glands:
  • Distributed throughout the skin; prominent in palms and face.
  • Produce sweat for thermoregulation and excrete water, NaCl, lactic acid, and urea.
Sebaceous Glands:
  • Located at hair follicles; secrete sebum which lubricates and protects the skin.
2. Lungs
  • Excrete volatile substances like CO₂ and water vapor from cellular respiration.
  • Also expel volatile compounds from food, including spices.
Disorders and Diseases of the Excretory System

  • Albuminuria: Excessive albumin in urine → Indicates injury to endothelial-capsular membrane due to: Increased blood pressure, Injury or irritation of kidney cells (toxins/heavy metals) 
  • Ketonuria: High levels of ketone bodies in urine → Caused by: Diabetes, Malnutrition, Low carbohydrate diet
  • Leucocytes in Urine: Indicates risk of kidney or urinary organ infection.
Related Disorders:

Kidney Stones
  • Definition: Also called renal calculi; can form in any part of urinary tract.
  • Process: Urolithiasis → Formation of stones in kidney, bladder, or urethra.
Types of Kidney Stones:
  • Calcium Stones: Calcium oxalate or phosphate.
  • Struvite Stones: Caused by bacterial infections from urea-splitting bacteria; grow rapidly.
  • Uric Acid Stones: Affected by low water intake/high protein diet.
  • Cystine Stones: Genetic disorder causing excess amino acid excretion.
Symptoms of Kidney Stones:
  • Intermittent pain below rib cage (back and sides)
  • Hazy, brownish, reddish, or pinkish urine
  • Frequent urge to urinate
  • Pain during micturition
Diagnosis:
  • Uric Acid Content: Blood test
  • Urine Color: Observation
  • Kidney X-ray: Imaging test
  • Sonography: Ultrasound of kidney
Uremia
  • Normal Urea Levels: 0.01 to 0.03%
  • Uremia: Urea levels above 0.05% → Can lead to kidney failure.
Nephritis
  • Definition: Inflammation of kidneys; characterized by proteinuria.
  • Causes: Increased permeability of glomerular capsule membrane → Proteins escape into urine.
  • Effect: Changes in blood colloidal osmotic pressure → Fluid moves to interstitial spaces (edema).
Renal Failure
 
Acute Renal Failure (ARF):
  • Sudden renal function worsening (often after severe bleeding).
  • Oliguria: Decreased urine output (<400 ml/day).
  • Causes: Acute obstruction, nephrotoxic drugs.
  • Detection: Elevated serum creatinine levels.
Chronic Kidney Disease (CKD):
  • Progressive, generally irreversible decline in glomerular filtration rate (GFR).
  • Causes: Chronic glomerulonephritis.
  • Detection: Reduced kidney size; possibility of anemia.
Haemodialysis and Kidney Transplantation
Haemodialysis: Definition: Artificial filtration of blood when renal function falls below 5-7%.

Process of Haemodialysis:

1. Blood Removal:Blood is typically drawn from the radial artery.

2. Filtration:

  • Blood passes through a cellophane tube (semipermeable membrane).
  • Tube is immersed in dialysate (isosmotic to normal blood plasma).
  • Excess salts move from blood into dialysate.
  • Waste substances move from blood into dialyzing fluid.

3. Return of Filtered Blood:

  • Filtered blood is returned to a vein.
  • Anticoagulant (e.g., heparin) is added during the process.
  • Anti-heparin is mixed before returning blood to circulation.

Drawbacks of Haemodialysis:

  • Hormonal Functions: Cannot secrete erythropoietin, renin, or calcitriol.
  • Process Speed: Blood moves slowly through the tube → Slow process.
Peritoneal Dialysis:
  • Definition: Dialysis method using the peritoneal membrane.

Process of Peritoneal Dialysis:

  1. Fluid Introduction: Dialyzing fluid is introduced into the abdominal (peritoneal) cavity.
  2. Filtration: Peritoneal membrane acts as a semipermeable membrane. Toxic wastes and excess solutes pass into the fluid.
  3. Fluid Drainage: Fluid is drained out after a set time.

Characteristics:

  • Repetition: Can be repeated as needed.
  • Convenience: Can be done at home, work, or while traveling.
  • Efficiency: Less efficient than haemodialysis.
Kidney Transplantation:
  • Definition: Transplant of a healthy kidney into a patient with end-stage renal disease.
Types of Kidney Transplant:
  • Cadaveric: From deceased donor.
  • Living Donor: Genetically Related: Living-related transplant. Non-Related: Living non-related transplant.
Precautions:
  • Rejection Risk: Recipient's immune system may reject the foreign kidney.
  • Immunosuppressive Medications: Given to lower the chance of transplant rejection.
Dietary Restrictions for Kidney Patients:
  • Water Consumption: Avoid excessive intake.
  • Oxalate-rich Foods: Reduce intake (e.g., soy products, rhubarb, beets, okra, spinach, Swiss chard, sweet potatoes, almonds, tea).
  • Animal Protein and Salt: Eat a low diet.
  • Calcium Intake: Reduce supplements; ensure adequate calcium from diet.