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Questions and Answers
Which type of excretion method is characteristic of reptiles, birds, land snails, and insects?
What is the primary excretory structure in Platyhelminthes?
Which excretory structure is responsible for nitrogenous waste removal in earthworms?
In humans, which organ is directly responsible for filtering blood to produce urine?
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What form do the nitrogenous wastes take when excreted by most insects?
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Which of the following structures performs excretory functions in crustaceans like prawns?
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What type of waste do ureotelic animals primarily excrete?
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Which excretory structure is primarily involved in ionic and fluid volume regulation in certain invertebrates?
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What is the primary function of the glomerulus in urine formation?
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Which type of nephron has a long loop of Henle that extends deep into the medulla?
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What constitutes the filtration slits in the Bowman’s capsule?
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What is the glomerular filtration rate (GFR) in a healthy individual, on average?
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Which of the following statements is true regarding the components filtered through the glomerulus?
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What percentage of blood pumped by the heart is filtered by the kidneys per minute?
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Which of the following structures are found in the capillary network surrounding the renal tubule?
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What mechanism regulates the glomerular filtration rate (GFR)?
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What initiates the micturition reflex in humans?
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Which of the following substances, when present in urine, indicates a possible diagnosis of diabetes mellitus?
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Which organ is primarily responsible for the secretion of bile, which helps in excretion?
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How much urine does an average adult human excrete per day?
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What is the pH level of normal urine in humans?
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Which of the following describes the micturition process?
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Which of the following excretory products is eliminated by the lungs?
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What daily volume of CO2 do human lungs remove approximately?
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What is the primary function of the nephrons in the kidney?
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What is the role of Bowman’s capsule in the nephron?
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Which nitrogenous waste forms are commonly excreted by animals?
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In which part of the nephron does the majority of reabsorption occur?
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What is the most significant factor affecting kidney transplant success?
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Which of the following statements correctly describes glomerulonephritis?
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What structure connects the kidneys to the urinary bladder?
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What is the primary composition of renal calculi?
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What is primarily responsible for maintaining the increasing osmolarity from the cortex to the inner medulla?
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How does NaCl move within the nephron structure according to the counter current mechanism?
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What role does the concentration gradient in the medullary interstitium play?
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Which of the following correctly describes the osmolarity levels from cortex to inner medulla?
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What is the primary substance that enters the thin segment of the ascending limb of Henle's loop during the counter current mechanism?
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Which part of vasa recta is responsible for returning NaCl to the interstitium?
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Which mechanism facilitates the concentration of urine within the nephron?
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What is the impact of the counter current mechanism on the transport of substances in the nephron?
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Study Notes
Excretion in Animals
- Ureotelic Animals: Many mammals, amphibians, and marine fishes excrete urea, which is synthesized from ammonia in the liver and filtered by kidneys; some urea may be retained for osmolarity.
- Uricotelic Animals: Reptiles, birds, land snails, and insects excrete nitrogenous wastes as uric acid, allowing for water conservation; these wastes are expelled as pellets or paste.
Excretory Structures in Invertebrates and Vertebrates
- Protonephridia: Found in flatworms (e.g., Planaria), rotifers, and some annelids; involved in osmoregulation.
- Nephridia: Tubular structures in earthworms that remove nitrogenous wastes and maintain fluid and ionic balance.
- Malpighian Tubules: Present in most insects, assist in excretion of nitrogenous wastes and osmoregulation.
- Antennal Glands: Also known as green glands, perform excretory functions in crustaceans like prawns.
Human Excretory System
- Comprised of a pair of kidneys, ureters, urinary bladder, and urethra; kidneys filter blood and produce urine.
- Nephrons: Functional units of the kidneys, consisting of glomerulus and renal tubule; some nephrons are juxtamedullary, having long loops of Henle.
- Vasa Recta: Capillary networks surrounding Henle’s loop, crucial for counter-current exchange mechanisms.
Urine Formation
- Processes Involved: Glomerular filtration, reabsorption, and secretion occur in different nephron segments.
- Glomerular Filtration: Blood filtration occurs at the glomerulus; approximately 1100-1200 ml of blood is filtered per minute.
- Filtration Rate (GFR): In a healthy individual, GFR averages around 125 ml/min (180 liters per day).
- Counter Current Mechanism: Facilitates concentration gradient maintenance in renal medulla, aiding in water reabsorption from collecting tubules.
Micturition
- Urine stored in the urinary bladder triggers a micturition reflex upon stretching; involves CNS signaling to contract bladder muscles and relax urethral sphincter.
- An adult human typically excretes 1 to 1.5 liters of urine daily, which is light yellow, slightly acidic (pH ~6), and contains approximately 25-30 g of urea.
- Urine analysis is key for diagnosing conditions like diabetes (presence of glucose and ketone bodies).
Role of Other Organs in Excretion
- Lungs: Excrete CO2 (~200 mL/min) and water vapor, contributing to waste elimination.
- Liver: Secretes bile with substances like bilirubin and cholesterol; plays a role in detoxification.
- Kidney Transplantation: Method for correcting acute renal failure, preferably using a close relative as a donor to minimize rejection risk.
Summary of Excretory Processes
- Excretion mechanisms vary among animals based on habitat (water availability); ammonia, urea, and uric acid are common nitrogenous wastes.
- Excretory organs include protonephridia, nephridia, Malpighian tubules, green glands, and kidneys, vital for waste elimination and maintaining body fluid balance.
- In humans, kidneys contain over a million nephrons which filter blood via glomeruli and renal tubules, resulting in urine formation.
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