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Excretory Products and Their Elimination - Human excretory system

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Modes of Excretion: Organisms are classified as Ammonotelic (excreting NH3NH_3), Ureotelic (excreting Urea NH2CONH2NH_2CONH_2), or Uricotelic (excreting Uric acid C5H4N4O3C_5H_4N_4O_3) based on their nitrogenous waste.

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Human Excretory System: Consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. Kidneys are situated between the levels of the T12T_{12} and L3L_3 vertebrae.

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Nephron Structure: The functional unit of the kidney, consisting of the Glomerulus and the Renal Tubule (Bowman's capsule, Proximal Convoluted Tubule (PCT), Henle's loop, and Distal Convoluted Tubule (DCT)).

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Glomerular Filtration Rate (GFR): The amount of filtrate formed by the kidneys per minute. In a healthy individual, it is approximately 125 mL/min125 \text{ mL/min}, which totals 180 L/day180 \text{ L/day}.

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Urine Formation: Involves three main processes: Ultrafiltration (occurring in the Malpighian corpuscle), Reabsorption (mostly in the PCT where 70−80%70-80\% of electrolytes and H2OH_2O are reclaimed), and Secretion (H+H^+, K+K^+, and NH3NH_3 into the filtrate).

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Counter Current Mechanism: Operates between the Henle's loop and Vasa recta to maintain an osmolarity gradient in the medullary interstitium, increasing from 300 mOsmolL−1300 \text{ mOsmolL}^{-1} in the cortex to 1200 mOsmolL−11200 \text{ mOsmolL}^{-1} in the inner medulla.

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Regulation of Kidney Function: Controlled by the Antidiuretic Hormone (ADH), the Renin-Angiotensin-Aldosterone System (RAAS), and the Atrial Natriuretic Factor (ANF).

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Micturition: The process of release of urine, regulated by the central nervous system through the micturition reflex.

📐Formulae

NFP=GHP−(BCOP+CHP)NFP = GHP - (BCOP + CHP) (Net Filtration Pressure)

GFR=125 mL/min=180 Litres/dayGFR = 125 \text{ mL/min} = 180 \text{ Litres/day}

Urine Excreted=Glomerular Filtration−Tubular Reabsorption+Tubular Secretion\text{Urine Excreted} = \text{Glomerular Filtration} - \text{Tubular Reabsorption} + \text{Tubular Secretion}

Concentration of Medullary Interstitium≈1200 mOsmolL−1\text{Concentration of Medullary Interstitium} \approx 1200 \text{ mOsmolL}^{-1}

💡Examples

Problem 1:

Calculate the Net Filtration Pressure (NFPNFP) if the Glomerular Hydrostatic Pressure (GHPGHP) is 60 mmHg60 \text{ mmHg}, the Blood Colloidal Osmotic Pressure (BCOPBCOP) is 30 mmHg30 \text{ mmHg}, and the Capsular Hydrostatic Pressure (CHPCHP) is 20 mmHg20 \text{ mmHg}.

Solution:

NFP=60−(30+20)=10 mmHgNFP = 60 - (30 + 20) = 10 \text{ mmHg}

Explanation:

The Net Filtration Pressure is the total pressure that promotes filtration. It is calculated by subtracting the opposing pressures (BCOPBCOP and CHPCHP) from the promoting pressure (GHPGHP).

Problem 2:

Explain why only 1.5 L1.5 \text{ L} of urine is excreted daily even though 180 L180 \text{ L} of filtrate is formed.

Solution:

180 L (Filtrate)−1.5 L (Urine)=178.5 L (Reabsorbed)180 \text{ L (Filtrate)} - 1.5 \text{ L (Urine)} = 178.5 \text{ L (Reabsorbed)}

Explanation:

Nearly 99%99\% of the filtrate is reabsorbed by the renal tubules through active and passive transport mechanisms to prevent the loss of essential water and solutes like Na+Na^+, Glucose, and Amino Acids.