Excretory Product | Zoology Optional Notes for UPSC PDF Download

Excretory Product and their Elimination

• Excretion involves getting rid of waste substances from an organism's body. These waste products, which can be harmful and unwanted, are expelled to uphold homeostasis and safeguard the body from their toxic effects.
• Defaecation refers to the elimination of undigested food remnants from the digestive tract, while secretion involves releasing specially synthesized products like hormones from endocrine glands or saliva from salivary glands.
• Osmoregulation pertains to the control of water levels and salt concentrations within an organism's body.
• Homeostasis is the process of maintaining a stable and favorable internal environment despite variations in water levels, concentrations of solutes, and the production of potentially harmful metabolic waste products.

Osmolarity

• Osmolarity refers to the concentration of solutes in a solution, expressed either as molarity or moles of solute per liter. The unit of measurement is the milliosmole, equivalent to 1000 osmoles, representing the amount of solute that forms one mole of active particles. In fresh water, the osmolarity typically falls below 50 mosm per liter, freshwater vertebrates exhibit osmolarities ranging from 200 to 300 mosm per liter, and human blood maintains a constant osmolarity of around 300 mosm per liter. Conversely, seawater has a higher osmolarity, approximately 1000 mosm per liter.
• Solutions with the same osmolarity are considered isotonic. A solution with a higher osmolarity or concentration is termed hypertonic, while a solution with a lower concentration or a more diluted state is known as hypotonic.

Metabolic Waste Products

• Nitrogenous Waste Products:
  • Originating from the metabolism of surplus proteins, amino acids, nucleic acids, alkaloids, etc.
  • Examples include ammonia, urea, uric acid, creatine, creatinine, hippuric acid, xanthine, guanine, trimethylamine oxide, and allantoin.
• Non-nitrogenous Waste Products:
  • Includes substances such as oxalic acid and lactic acid.
• Excess Chemicals:
  • Various chemicals, including sodium, calcium, magnesium, lead, chloride, phosphate, iodine, pigments, drugs, cholesterol, hormones, vitamins, and wax, are eliminated as excretory products.
• Bile Pigments:
  • Bilirubin, biliverdin, and urochrome are breakdown products of hemoglobin formed by the liver.
• CO₂ (Carbon Dioxide):
  • Released as a waste product during metabolic processes.
• Excess Water:
  • Elimination of surplus water from the body.

Types of animals based on excertory products

Ammonotelic Animals

• These animals excrete nitrogenous wastes primarily in the form of ammonia, a product of protein metabolism.
• Ammonia is highly soluble in water and can be caustic, requiring significant water loss for its elimination.
• Well-suited for aquatic organisms with constant access to water.
• Examples include protozoans, sponges, cnidarians, liver flukes, tape worms, Nereis, earthworms, aquatic arthropods, mollusks, bony fish, amphibian tadpoles, salamanders, and crocodiles.
• Approximately 300 to 500 ml of water is needed to eliminate 1 gm of ammonia.

Uricotelic Animals

• These animals excrete nitrogenous wastes mainly in the form of uric acid.
• Uric acid is less soluble and less toxic than ammonia, requiring less water for elimination.
• Primarily observed in terrestrial animals that have limited access to water.
• Uric acid is synthesized from ammonia in the liver through the ionosinic pathway.
• Reptiles, birds, land snails, and insects excrete uric acid, often in pellet form.
• About 10 ml of water is needed to eliminate 1 gm of uric acid.

Ureotelic Animals

• These animals excrete nitrogenous wastes mainly as urea.
• Urea is less toxic and less soluble in water than ammonia, allowing for storage in the body.
• Urea formation requires energy expenditure and occurs in the liver through the ornithine cycle.
• Urea is eliminated in the form of urine.
• About 50 ml of water is required to eliminate 1 gm of urea.
• Exhibited by semi-terrestrial animals, including some earthworms, adult amphibians, cartilaginous fishes, semi-aquatic reptiles like turtles and alligators, and mammals, including humans.
• Sharks retain high levels of urea in their blood, matching the osmotic pressure of sea water and minimizing water loss.

Excretory organs in different animal groups

• Protozoans:
  • Excretory Organs: Plasmalemma, pellicle.
  • Nitrogenous Waste: Ammonia.
• Poriferans:
  • Excretory Organ: General body surface.
  • Nitrogenous Waste: Ammonia.
• Coelenterates:
  • Excretory Organs: General body surface.
  • Nitrogenous Waste: Ammonia.
• Platyhelminths:
  • Excretory Organ: Protonephridium with flame cells.
  • Nitrogenous Waste: Ammonia.
• Aschelminths:
  • Excretory Organ: Renette cells (Ascaris).
  • Nitrogenous Waste: Ammonia, urea.
• Annelids:
  • Excretory Organs: i) Metanephridia (Nereis and leech). ii) Metanephridia and chloragogen cells (earthworm).
  • Nitrogenous Waste: i) Ammonia. ii) Ammonia, urea on land.
• Molluscs:
  • Excretory Organ: Renal gland or organ of Bojanus (Pila and unio) and Keber’s organ (Unio).
  • Nitrogenous Waste: Ammonia in aquatic forms and uric acid in land forms.
• Arthropods:
  • Excretory Organs: i) Malpighian tubules, uricose gland, urate cells, nephrocyte. ii) Malpighian tubules, coxal gland, hepato-pancreas, and nephrocytes (spiders and scorpions). iii) Green glands or antennary glands in crustaceans.
  • Nitrogenous Waste: i) Uric acid in land forms and ammonia in aquatic forms. ii) Guanine, some xanthine, and uric acid. iii) Ammonia.
• Echinoderms:
  • Excretory Organs: Tube feet (podia) and dermal branchiae (thin walls of gills).
  • Nitrogenous Waste: Ammonia.
• Hemichordates:
  • Excretory Organ: Glomerulus (Balanoglossus).
• Chordates:
  a) Urochordates: Excretory Organ: Neural gland (Herdmania).
  b) Cephalochordates: Excretory Organ: Pharyngeal nephridia and Hatschek’s nephridium (Amphioxus).
  c) Vertebrates: Excretory Organ: One pair of kidneys as the main excretory organs. Lungs, liver, skin, and intestine serve as accessory excretory organs in many vertebrates.
• Nitrogenous Waste: Ammonia, urea, uric acid.

Human Excretory System

The mammalian ( human) urinary system consists of two kidney which form the urine, two ureters which conduct the urine from kidney to urinary bladder, a urinary bladder for storage of urine and a urethra through which the urine is voided by bladder contractions. 

Kidneys

• Mesodermal in origin, developing from linearly arranged mesodermal somites.
• Positioned in the abdominal cavity just behind the vertebral column, termed retroperitoneal (located outside the peritoneal cavity).
• Situated between the last thoracic and third lumbar vertebrae near the dorsal inner wall of the abdominal cavity, protected by the last two pairs of ribs (floating ribs).
• Average size: 10-12 cm in length, 5-7 cm in width, 3-4 cm in thickness. Weight is around 150 gm in males and approximately 135 gm in females. The right kidney is typically smaller and positioned slightly lower due to the presence of the liver on the right side.
• Covered by protective layers: renal capsule (fibrous connective tissue), adipose capsule (layer of fat), and renal fascia (outer fibrous membrane).
• Internally consists of the cortex (outer dark region) and medulla (inner light region), both containing uriniferous tubules or nephrons.
• Renal cortex appears granular due to convoluted tubules (proximal and distal convoluted tubules) containing Malpighian corpuscles.
• Medulla comprises 10 to 15 multilobular conical masses called medullary pyramids or renal pyramids. Papillae at the apices of pyramids project into minor calyces, which lead into major calyces. Major calyces join to form the renal pelvis, connecting to the ureter.
• Renal columns of Bertin extend between the medullary pyramids into the medulla.
• The medial concave border of the kidney has a notch known as the hilus, serving as the entry point for the renal artery and the exit points for the renal vein and ureter.

Urinary System Components

• Ureters: Conduct urine from the kidneys to the urinary bladder.
• Urinary Bladder: Stores urine.
• Urethra: Passageway through which urine is voided by bladder contractions.

Different types of kidneys in vertebrates

Archinephric or Holonephric Kidney

• Extends throughout the entire length of the coelom.
• Hypothetical kidney found in the larvae of certain cyclostomes (e.g., Myxine).
• It is believed to be the precursor to all other types of kidneys.

Pronephric or Head Kidney

• Located dorsal to the anterior end of the coelom.
• Associated with pronephric tubules.
• In the pronephric kidney, the glomerulus is external and naked.
• Functional only during embryonic and larval stages, and is soon replaced by the next developmental stage.

Mesonephric or Middle Kidney

• Develops from the middle part of the intermediate mesoderm, also known as Wolffian body.
• Functional in both larvae and adults of most fishes and amphibians.
• In amniotes, it is functional during the embryonic stage and gets replaced by the metanephric kidney in adults.

Opisthonephric or Tail Kidney

• Functional nephrons in this kidney are from the posterior region of the coelom, displaced from their original position.
• Found in sharks and caecilians.

Metanephric Kidney

• In the metanephric kidney, functional posterior nephrons are displaced to an anteriolateral position.
• Nephrons of this kidney are highly differentiated, forming the loop of Henle in mammals.
• Functional in all amniotes, including reptiles, birds, and mammals.

Function of Kidney

The kidney performs several crucial functions in the body:

• Osmoregulation: The kidney regulates water balance by removing excess water from the body.
• Elimination of Nitrogenous Waste: It removes nitrogenous waste, such as urea and uric acid, from the blood.
• Maintenance of pH: Kidneys play a role in maintaining the proper pH of the blood (approximately 7.4) by removing excess acids and alkalies.
• Maintenance of Salt Contents: They help maintain the appropriate levels of mineral salts, including sodium and potassium, in the body.
• Removal of Other Substances: Kidneys eliminate toxic substances, drugs, pigments, and excess vitamins from the blood.
• Maintenance of Blood Pressure: By controlling fluid balance in the body, the kidney helps regulate and maintain blood pressure.
• Secretion of Renin: The kidney secretes the enzyme renin, which acts as a hormone. Renin converts angiotensinogen (produced by the liver) into angiotensin. Angiotensin stimulates the adrenal cortex to release aldosterone, a hormone that increases the rate of Na+ reabsorption in the nephrons.
• Erythropoietin Production: Kidneys produce erythropoietin, a hormone that stimulates the formation of red blood cells. Erythropoietin secretion is triggered by low oxygen levels in the blood (hypoxia) and is also influenced by male sex hormones and cobalt salt.
• Homeostasis: By removing various unwanted materials from the blood, the kidney contributes to maintaining the constant internal environment of the body, known as homeostasis.

Nephrons

• General Description:
  • Nephrons are the functional units of the kidney, and a human kidney typically contains approximately one million of these tubular units.
  • These nephrons, also known as uriniferous tubules, are thin, long, and highly convoluted tubular structures.
• Types of Nephrons:
  • There are two main types of nephrons in the kidney: cortical nephrons (constituting about 85%) and juxtamedullary nephrons (making up around 15%).
  • Cortical nephrons are located in the renal cortex, with their glomeruli situated in the outer cortex. They have a shorter loop of Henle and a peritubular capillary network, lacking Vasa recta. These nephrons regulate plasma volume under normal water supply conditions.
  • Juxtamedullary nephrons are positioned at the junction of the renal loop of Henle and Vasa recta. They control plasma volume in situations of reduced water supply.
• Nephron Structure:
  • Each nephron consists of two primary components: the renal corpuscle, also known as the Malpighian corpuscle, and the renal tubule. Both components are composed of simple cuboidal epithelium.
  • Renal Corpuscle (Malpighian Corpuscle):
    • Functions as the initial filtering component.
    • Composed of a glomerulus, a network of capillaries, and Bowman's capsule, a cup-shaped structure that surrounds the glomerulus.
  • Renal Tubule:
    • Represents the long tubular component of the nephron.
    • Composed of simple cuboidal epithelium.

Renal Corpuscle

• Name Origin: The term "Malpighian corpuscle" is named after Marcello Malpighi.
• Filtration Process: The renal corpuscle is responsible for filtering out large solutes from the blood while delivering water and small solutes to the renal tubule for further modification.
• Components: Comprising the renal corpuscle are two main structures: the glomerulus, a capillary network, and Bowman's capsule, also known as the glomerular capsule.
• Aglomerular Nephrons: Marine fishes and desert amphibians lack Bowman's capsule and glomeruli in their nephrons, earning them the term "aglomerular."
• Bowman’s Capsule:
  • Named after Sir William Bowman, a British surgeon and anatomist.
  • It is a double-layered, cup-shaped structure whose lumen is continuous with the narrow lumen of the renal tubule.
  • Comprises two layers: outer parietal layer (simple squamous epithelium) and inner visceral layer (layer of special epithelial cells) called podocytes, which contain filtrate filters.
• Glomerulus:
  • The glomerulus is a capillary network located within Bowman’s capsule.
  • Blood enters the glomerular capillaries through afferent arterioles and exits through efferent arterioles. The diameter of the glomerulus is much greater than that of the efferent arteriole.
• Juxtaglomerular Cells: The walls of the afferent and efferent arterioles contain juxtaglomerular cells, which secrete renin.

Renal Tubule

• General Description: Attached to each Bowman’s capsule is a long, thin tubule with three distinct regions: proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT).
• Proximal Convoluted Tubule (PCT):
  • The first segment is the proximal convoluted tubule.
  • Approximately 14 mm long, lined by a single layer of brush-bordered cuboidal epithelium to increase surface area.
  • Contains mitochondria for energy provision, facilitating the active transport of salt reabsorption.
• Loop of Henle:
  • Henle’s loop, a U-shaped tube, plays a crucial role in maintaining the high osmolarity of the surrounding tissue.
  • Comprises a descending limb and an ascending limb.
  • The descending limb is lined by flat cells (simple squamous epithelium) permeable to water but impermeable to electrolytes, leading to concentration of the filtrate.
  • The ascending limb is thicker, composed of flattened cuboidal epithelium, and is impermeable to water but permeable to electrolytes such as K+, Cl-, and Na+.
• Distal Convoluted Tubule (DCT):
  • Located in the cortex region of the kidney, approximately 4.5 – 5.5 mm long with a diameter of 20 – 50 μm.
  • Lined by cuboidal epithelium with elevations but lacking a true brush border.
  • Conditional reabsorption of Na+, water, and HCO3- occurs in this segment.
• Collecting Duct:
  • The final part of the nephron is the collecting duct, approximately 20 mm long, lined by cuboidal cells.
  • Multiple collecting tubules from different nephrons join successively to form the duct of Bellini or papillary duct, opening at the apex of the renal pyramid.

Nephron’s Blood Supply

• Intimate Association:
  • A close association exists between the blood vessels and the nephrons in the kidney, facilitating extensive filtration from the blood and selective reabsorption back into the blood.
• Renal Artery Branching:
  • Upon entering each kidney, the renal artery undergoes repeated branching, forming smaller arteries that eventually reach each of the 1 million nephrons.
  • An afferent arteriole delivers blood to the glomerulus for filtration, while an efferent arteriole drains filtered blood away from the same glomerulus.
• Peritubular Capillaries:
  • The efferent arteriole connects to the second network of capillaries, known as peritubular capillaries, closely associated with the nephron tubule.
  • These peritubular capillaries serve as the site for reabsorption of water, ions, and nutrients from the filtrate in the nephron tubule.
• Vasa Recta:
  • From the peritubular capillary network, arise the capillaries of vasa recta, extending parallel to the loops of Henle and collecting ducts in the medulla.
  • The vasa recta includes both descending and ascending capillaries.
• Formation of Renal Venules:
  • All the capillary networks join to form renal venules.
  • Renal venules then combine to form the renal vein, ultimately opening into the inferior vena cava.

Urine Formation in Kidney

• Uropoiesis Process: The creation of urine is referred to as uropoiesis.
• Three Steps in Urine Formation: The kidney's urine formation process can be categorized into the following three distinct steps:
  • Glomerular Filtration or Ultrafiltration: This step involves the filtration or ultrafiltration of blood in the glomerulus. It serves as the initial stage in urine formation.
  • Selective Reabsorption: In this phase, specific substances are selectively reabsorbed from the filtrate back into the bloodstream. This process ensures that essential elements are retained while unnecessary materials continue through the urinary system.
  • Tubular Secretion: Tubular secretion involves the active transport of certain substances from the blood into the renal tubules. This step allows for the elimination of additional waste products and fine-tuning of the urine composition.

Glomerular filtration or ultarfiltration

• Blood Pressure Influence: The primary driver of ultrafiltration is blood pressure. In the kidney, the glomerular capillary is identified as a high-pressure bed, while the peritubular network is considered a low-pressure bed.
• Pressure Variations:
  • Blood pressure measures around 100 mm Hg in the glomerulus, decreases to approximately 70 mm Hg within the glomerulus, and further diminishes to about 18 mm Hg in the efferent arteriole.
  • Within the peritubular network, pressure is around 14 mm Hg around the proximal convoluted tubule (PCT) and 6 mm Hg around the distal convoluted tubule (DCT). The pressure is lowest, around 2 mm Hg, around the collecting tubule.
• Filtration Mechanism:
  • As blood enters the glomerulus, the pressure forces water and dissolved components out through the filtration membrane.
  • The resultant fluid is termed filtrate, containing almost all blood constituents except cells, proteins, certain drugs, pigments, and dyes.
• Filtrate Composition: The glomerular filtrate mirrors the composition of blood, excluding specific elements present in the blood.
• Glomerular Filtration Rate (GFR):
  • The quantity of filtrate produced by the kidneys per minute is known as the Glomerular Filtration Rate (GFR).
  • In a healthy individual, the typical GFR is 125 mL/minute, equivalent to 180 L/day.

Selective Reabsorption

• Filtrate Movement:
  • Following ultrafiltration in the Bowman’s capsule, the glomerular filtrate progresses into the Proximal Convoluted Tubule (PCT).
  • Simultaneously, both processes, reabsorption and secretion, occur in the tubular region.
• Reabsorption in PCT:
  • Approximately 65% of the glomerular filtrate is typically reabsorbed in the PCT before reaching the loop of Henle.
  • Reabsorbed substances include glucose, amino acids, vitamins, hormones, sodium, potassium, chlorides, phosphates, bicarbonates, most of the water, and some urea.
• Reabsorption Mechanisms:
  • Na+ and K+ undergo reabsorption through active transport.
  • Glucose and amino acids are reabsorbed via passive transport.
  • Water reabsorption occurs through osmosis.
  • Cl-, urea, and other solutes undergo reabsorption through simple diffusion.
• Secretion in PCT:
  • Alongside reabsorption, the PCT also facilitates the active secretion of certain substances.
  • This includes creatinine, hippuric acid, pigments, drugs, as well as H+ and NH3.
  • Reabsorption refers to the transport of substances from the filtrate back into the blood (flowing in the peritubular network) through tissue fluid.
  • Tubular secretion involves the transport of substances from the blood toward the filtrate through tissue fluid (from the peritubular network to renal tubules).

Tubular Secretion

• Selective Reabsorption and Tubular Secretion:
  • Substances not reabsorbed during selective reabsorption are excreted into the filtrate through the process of secretion.
  • Tubular secretion stands in contrast to tubular reabsorption.
• Secretion Process:
  • Tubular cells actively secrete substances like H+, K+, and ammonia into the filtrate.
  • While K+ ions enter the filtrate from the glomerulus and are nearly entirely reabsorbed, they are also secreted into the lumen of the distal convoluted tubule and collecting ducts.
  • The active secretion of K+ ions is coupled with the active reabsorption of Na+ ions.
  • Most other substances entering the tubule through tubular secretion move through active transport.
• Role of Tubular Secretion:
  • Tubular secretion plays a relatively minor role in the overall function of human kidneys.
  • In certain animals like marine fishes and desert amphibians, where nephrons lack developed glomeruli, urine is primarily formed through the tubular secretion of urea, creatinine, and mineral ions.
• Reabsorption Process:
  • The process of reabsorption involves both active and passive pathways.

Counter current mechanism of urine concentration

• Evolutionary Adaptation:
  • Higher vertebrates, including birds and mammals (including humans), have developed a counter-current mechanism to excrete hypertonic urine, which is urine more concentrated than blood. This adaptation is crucial for conserving body water, especially in terrestrial environments.
• Counter-Current Flow:
  • The term "counter-current" signifies that fluid flows in opposite directions in the two sides of the loop—down one side and up the other. Henle’s loop and the capillary loop (vasa rectae) play pivotal roles in this mechanism.
• Ion and Water Movement in Loop of Henle:
  • As the filtrate moves through the ascending limb of the loop of Henle, it loses NaCl to the interstitial fluid in the renal medulla through both diffusion in the narrow region and active transport in the wide region.
  • The increased solute concentration in the interstitial fluids causes water to be drawn out by osmosis from the narrow region of the descending limb and the collecting duct—both permeable to water.
  • This water quickly enters the vasa rectae and is carried away. This process maintains a high concentration of solutes in the interstitial fluid around the loop of Henle and the collecting duct, transforming the isotonic glomerular filtrate into hypertonic urine.
• Permeability of Vasa Rectae:
  • Endothelial cells forming the walls of the vasa rectae are freely permeable to ions, water, and urea.
• Osmotic Exchange in Vasa Rectae:
  • As blood flows in the descending capillary of the vasa rectae towards the renal medulla, water is drawn out from the blood plasma by osmosis due to the increasing concentration of interstitial fluid sodium, chloride ions, and urea. Simultaneously, these substances enter the plasma by diffusion.
  • As blood flows in the ascending capillary towards the renal cortex, the reverse occurs—water reenters the plasma, while Na+, Cl-, and urea leave it due to a decreasing concentration of interstitial fluid.

Regulation of kidney functions 

Control by juxtaglomerular apparatus (jga)

• Juxtaglomerular Apparatus (JGA) operates through the Renin Angiotensin Aldosterone System.
• When blood pressure decreases in the afferent arteriole of the glomerulus, characterized by a fall in glomerular filtration rate, renin is released from JG cells.
• Renin acts on angiotensinogen, produced by the liver, converting it into angiotensin I, which is further converted into angiotensin II.
• Angiotensin II increases blood pressure by causing arteriolar constriction and enhancing blood volume through increased water and NaCl reabsorption in the proximal convoluted tubule (PCT) and stimulation of aldosterone secretion by the adrenal glands, acting on the distal convoluted tubule (DCT).

Atrial Natriuretic Factor (ANF)

• ANF, produced by the walls of the atria in the heart, opposes RAAS when there is higher blood volume and pressure.
• ANF inhibits renin secretion by juxtaglomerular cells and ADH by the pituitary gland, leading to decreased NaCl reabsorption and concentration of urine.

Antidiuretic Hormone (ADH) Control

• ADH, secreted by the neurohypophysis and produced by the hypothalamus, is released when osmoreceptors detect an increase in blood osmolarity.
• ADH increases water reabsorption in the DCT and collecting duct.
• Excess water signals the posterior pituitary to stop ADH release, decreasing water reabsorption and producing abundant urine.
• Insufficient water, as in dehydration, stimulates ADH release, increasing water reabsorption and concentrating urine.

Micturition

• Expulsion of urine from the urinary bladder is called micturition.
• A reflex process involving the contraction of smooth muscles in the bladder wall and relaxation of the urethral sphincter.
• Stretch receptors in the bladder wall generate nerve impulses, producing the sensation of fullness.
• Inhibition of motor impulses releases sphincters, allowing bladder contraction.

Composition of Urine

• Physical Characteristics:
  • Transparent, amber-colored, hypertonic fluid with a slightly acidic pH (around 6.0).
  • Yellow color due to urochrome, a breakdown product of hemoglobin.
  • Volume depends on fluid intake, external temperature, and physical activity (1-2 liters per day).
  • Standing urine may develop a pungent smell due to bacterial conversion of urea into ammonia.
• Components:
  • Water (96%), Urea (2-6%), Uric acid (0.3%), Salts (1.5%), Traces of creatinine, ammonia, creatine, hormones, water-soluble vitamins, etc.

Accessory Excretory Organs

• Liver:
  • Urea Formation: Liver synthesizes urea, a nitrogenous waste, which is eliminated through the kidneys.
  • Hemoglobin Degradation: Liver cells break down hemoglobin from worn-out red blood corpuscles into bile pigments (bilirubin and biliverdin).
  • Excretion of Various Substances: Liver cells also excrete cholesterol, certain products of steroid hormones, some vitamins, and numerous drugs. These substances are secreted into the bile, transported to the intestine, and expelled with feces.
• Skin:
  • Role in Aquatic Animals: Assists in eliminating excess water, salts, and waste like ammonia in aquatic animals.
  • Mammalian Skin Features: Sweat glands and sebaceous glands in mammalian skin contribute to excretion.
• Intestine:
  • Salt Excretion: Epithelial cells of the colon excrete excess salts of calcium, magnesium, and iron with feces.
• Lungs:
  • Gaseous Waste Removal: Lungs aid in eliminating gaseous excretory wastes such as CO2 and a small amount of water vapor during respiration.
• Salivary Glands:
  • Excretion in Saliva: Salivary glands contribute to excretion by secreting saliva that contains heavy metals and drugs.

Disorders of excretory glands

• Renal Calculi:
  • Causes: Excessive hormonal imbalance, elevated uric acid formation, high milk intake, dehydration, and metabolic disturbances contribute to the formation of renal calculi or stones.
  • Composition: These stones result from the precipitation of uric acid or oxalate.
• Cystitis:
  • Definition: Inflammation of the urinary bladder often caused by bacterial infection.
• Nephritis (Bright’s Disease):
  • Definition: Inflammation involving the renal pelvis, calyces, and interstitial tissue due to local bacterial infection.
  • Infection Route: Bacteria enter these organs through the urethra and ureter.
  • Impact on Kidney Function: Inflammation disrupts the counter-current mechanism, leading to an inability to concentrate urine.
  • Symptoms: Back pain, frequent, and painful urination are characteristic symptoms.
• Polyuria:
  • Description: Excessive production of urine, surpassing normal levels.
• Haematuria:
  • Definition: Presence of blood in the urine.
• Anuria:
  • Definition: Kidneys fail to produce urine.
• Pyuria:
  • Description: Presence of pus or white blood cells in the urine.
• Glycosuria:
  • Definition: Presence of glucose in the urine, often associated with diabetes mellitus.
• Ketosis:
  • Description: Presence of ketones in the urine due to the metabolism of fatty acids instead of glucose, occurring in conditions like diabetes, starvation, and pregnancy.
• Uraemia:
  • Description: Elevated levels of urea in the blood.
• Diuresis:
  • Definition: Condition characterized by an increased volume of urine excretion.

Artificial Kidney

• Definition: An artificial kidney, known as a hemodialyzer, serves as a machine designed to filter the blood in cases of kidney damage, a process termed hemodialysis.
• Hemodialysis Process: Hemodialysis involves the separation of small molecules from large molecules in a solution by introducing a semi-permeable membrane between the solution and water.
• Components of Hemodialyzer: The hemodialyzer consists of a cellophane tube immersed in a saltwater solution, mirroring the normal blood plasma but lacking urea.
• Blood Circulation: The patient's blood is pumped from an artery into the cellophane tube, after being cooled to 0°C and combined with an anticoagulant (heparin).
• Permeable Membrane: Pores in the cellophane tube enable the diffusion of urea, uric acid, creatinine, excess salts, and surplus H+ ions from the blood into the surrounding solution.
• Purification Process: The purified blood is then warmed to body temperature and mixed with an anticoagulant to restore normal clotting ability.
• Return to Patient: The treated blood is subsequently pumped back into a vein of the patient.
• Exclusion of Plasma Proteins: Plasma proteins remain within the blood, as the pores in the cellophane tube are too small to permit the passage of their larger molecules.