Chapter 19: Excretory Products and their Elimination - Class 11 NCERT | NEET Notes

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Today we will study Chapter 19 of Class 11 NCERT Biology:

*Excretory Products and their Elimination*

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Chapter 19: Excretory Products and their Elimination - Class 11 NCERT*  

_Detailed Short Notes for NEET - Expanded Version_

### *1. EXCRETION*

*Definition*: Removal of nitrogenous wastes and other toxic metabolic by-products from the body.

*Why needed?* 

To maintain *homeostasis* - constant internal environment for proper functioning of enzymes and cells.

*Mode of excretion depends on*: Habitat, water availability, and evolutionary adaptation.

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### *2. EXCRETORY PRODUCTS*

Based on main nitrogenous waste

Product Example Animals Toxicity Water Needed Solubility

**Ammonia** Aquatic animals, bony fishes, tadpole Most toxic Very high Highly soluble

**Urea** Mammals, amphibians, cartilaginous fishes Less toxic Moderate Soluble

**Uric acid** Birds, reptiles, insects Least toxic Very less Insoluble

#### *Types of animals based on excretion*

1. *Ammonotelic*: Excrete ammonia. Ex: Bony fishes, aquatic amphibians, aquatic insects

2. *Ureotelic*: Excrete urea. Ex: Mammals, amphibians, cartilaginous fishes

3. *Uricotelic*: Excrete uric acid. Ex: Birds, reptiles, insects. Adaptation for less water loss

4. *Aminotelic*: Excrete amino acids directly. Ex: Some molluscs, echinoderms

5. *Guanotelic*: Excrete guanine. Ex: Spiders

6. *Caprinotelic*: Excrete creatine. Ex: Some amphibians

*Note*: Birds are ureotelic in embryonic stage, uricotelic in adult stage.

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### *3. HUMAN EXCRETORY SYSTEM*

*Organs:*

1. *Kidneys* - 1 pair, reddish brown, bean shaped. *Retroperitoneal*

2. *Ureters* - 1 pair, 25-30 cm long, carry urine to bladder

3. *Urinary bladder* - Muscular, stores 300-500 ml urine

4. *Urethra* - Carries urine outside. Longer in males 15cm, shorter in females 4cm

#### *KIDNEY - Detailed*

- *Location*: Abdomen, between *T12 to L3 vertebra*. Right kidney slightly lower due to liver

- *Weight*: 120-170g. *Length*: 10-12 cm

- *Coverings*: 3 layers from outside - *Renal fascia → Adipose capsule → Renal capsule*

- *Hilum*: Medial notch. Structures entering: Renal artery, nerve. Exiting: Renal vein, ureter, lymphatics

*Internal structure:*

1. *Outer Cortex* - Reddish, granular. Contains renal corpuscles

2. *Inner Medulla* - Divided into *10-18 Renal pyramids*. Base towards cortex, apex = *Renal papilla*

3. *Renal columns of Bertini*: Cortex extends between pyramids

4. *Renal pelvis*: Funnel shaped, formed by union of 2-3 calyces. Continues as ureter

*Functional unit: Nephron* - *1 million in each kidney*

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### *4. NEPHRON - Structural & Functional unit*

*2 parts: Renal corpuscle + Renal tubule*

*A. Renal corpuscle / Malpighian corpuscle*

1. *Glomerulus*: Tuft of capillaries formed by *afferent arteriole*. Efferent arteriole is narrower → High GFR

2. *Bowman's capsule*: Double walled cup. 

   - *Inner layer*: Podocytes with foot processes. Form filtration slits

   - *Outer layer*: Parietal layer

*B. Renal tubule - 4 parts*

1. *PCT - Proximal Convoluted Tubule*: Lies in cortex. Cuboidal epithelium with *brush border microvilli*. Major site of reabsorption

2. *Loop of Henle*: Hairpin shaped, runs into medulla

   - *Descending limb*: Thin, permeable to water, impermeable to solutes

   - *Thin Ascending limb*: Impermeable to water, permeable to ions

   - *Thick Ascending limb*: In medulla, active transport of Na+, K+, Cl-

3. *DCT - Distal Convoluted Tubule*: In cortex. Cuboidal, selective reabsorption. Under hormonal control

4. *Collecting duct*: Many DCTs open into one CD. Passes through medulla to pelvis. Permeable to water under ADH

*Types of Nephrons:*

1. *Cortical nephrons*: 85%. Loop of Henle in cortex only. Short loop

2. *Juxtamedullary nephrons*: 15%. Loop runs deep into medulla. Long loop. *Important for concentration of urine*

*Juxtaglomerular apparatus/JGA*: Formed by DCT + Afferent arteriole. 

- *Macula densa*: Specialized DCT cells

- *JG cells*: Secrete *Renin*. Regulate GFR

*Blood supply*: Renal artery → Afferent arteriole → Glomerulus → Efferent arteriole → *Peritubular capillaries + Vasa recta* → Renal vein

*Vasa recta*: Hairpin loop of capillaries. Maintains medullary osmolarity

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### *5. URINE FORMATION* - 3 Steps

*1. Glomerular Filtration*

- Occurs in glomerulus

- *GFR - Glomerular Filtration Rate*: *125 ml/min = 180 L/day*

- Only 1-1.5 L urine formed. Rest reabsorbed

- *Filtration barrier*: 3 layers - Endothelium of glomerulus + Basement membrane + Podocytes

- *Filtration membrane is permeable to*: Water, glucose, AA, Na+, urea. *Impermeable to*: Proteins, RBC, WBC

*2. Tubular Reabsorption*

Selective reabsorption in PCT, Loop, DCT, CD. 99% filtrate reabsorbed

- *PCT*: 100% Glucose, AA. 70% Na+, 75% water, HCO3-. *Most important site*

- *Descending Loop*: Only water by osmosis

- *Ascending Loop*: Na+, K+, Cl- by active transport. Impermeable to water

- *DCT*: Na+, Cl-, HCO3- under Aldosterone

- *Collecting duct*: Water under *ADH*, Na+ under Aldosterone

*3. Tubular Secretion*

Active transport from blood → filtrate

- *Sites*: PCT and DCT

- *Substances*: H+, K+, NH4+, creatinine, drugs, pigments

- *Importance*: Ionic balance, pH maintenance, removal of waste

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### *6. FUNCTION OF TUBULES - Summary Table*

Segment Reabsorption Secretion Permeability

**PCT** Glucose, AA, Na+, K+, water, HCO3-, Cl- H+, NH4+, drugs, toxins All

**Descending Loop** Water only - Water

**Ascending Loop** Na+, K+, Cl- - Ions only

**DCT** Na+, Cl-, HCO3- H+, K+ Hormone regulated

**Collecting duct** Water, Na+ K+, H+ Water under ADH

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### *7. MECHANISM OF CONCENTRATION OF URINE*

*Counter Current Mechanism* - Done by *Loop of Henle + Vasa recta + CD*

*How it works:*

1. *Loop of Henle*: 

   - Descending: Water moves out → filtrate becomes hypertonic

   - Ascending: NaCl moves out → filtrate becomes hypotonic

   - This maintains *high osmolarity in medulla*: 300 → 1200 mOsm/L

2. *Vasa recta*: Preserves osmotic gradient. Blood flows opposite to Loop

3. *ADH*: Increases water permeability of DCT and CD. More water reabsorbed

4. *Aldosterone*: Increases Na+ reabsorption from DCT

*Result*: Human can produce *urine 4 times concentrated* than blood plasma. *1200 mOsm/L*

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### *8. REGULATION OF KIDNEY FUNCTION*

*1. RAAS - Renin Angiotensin Aldosterone System* 

Low BP / Low Na+ → JG cells release *Renin* → Angiotensinogen → Angiotensin I → Angiotensin II → 

- Vasoconstriction → ↑BP

- Aldosterone release from adrenal cortex → Na+ and water reabsorption

*2. ANF - Atrial Natriuretic Factor* 

From *atria of heart* when BP high → Vasodilation → ↓Na+ reabsorption → ↑Na+ excretion

*3. ADH - Antidiuretic Hormone / Vasopressin* 

From *posterior pituitary*. Increases water reabsorption. Prevents diuresis

*4. Neural regulation*: SNS causes vasoconstriction of afferent arteriole → ↓GFR

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### *9. MICTURITION*

Process of urination.  

Urine collected in bladder → Stretch receptors activated → Signal to CNS → Voluntary relaxation of *urethral sphincter* → Urination

Infants: Involuntary. Adults: Voluntary control

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### *10. ROLE OF OTHER ORGANS IN EXCRETION*

1. *Liver*: Deamination → Urea. *Bile pigments* - bilirubin, biliverdin. Cholesterol

2. *Lungs*: CO2, water vapor

3. *Skin*: *Sweat glands* - water, NaCl, urea, lactic acid. *Sebaceous glands* - wax, sterols, hydrocarbons

4. *Salivary glands*: Small amount of nitrogenous waste

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### *11. DISORDERS OF EXCRETORY SYSTEM*

1. *Uremia*: High urea in blood. *Treated by Dialysis or Kidney transplant*

2. *Kidney stones / Renal calculi*: Crystallized salts - calcium oxalate in kidney

3. *Glomerulonephritis*: Inflammation of glomeruli due to infection

4. *Renal failure*: Kidney can't filter. *Causes*: Infection, obstruction

5. *Dialysis / Hemodialysis*: Artificial kidney. Uses *principle of diffusion* through semipermeable membrane

   - *Dialysing fluid*: Has same composition as plasma except nitrogenous waste

*Kidney transplant*: Best option for renal failure. Donor and recipient should have matching antigens

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#### *NEET HIGH-YIELD POINTS TO REMEMBER*

- *Functional unit*: Nephron. *1 million nephrons/kidney*

- *GFR*: 125 ml/min, *180 L/day*

- *RPF*: Renal plasma flow = 650 ml/min

- *ADH* increases water reabsorption. *Aldosterone* increases Na+ reabsorption

- *Loop of Henle + Vasa recta* = Counter current system for urine concentration

- *Urea* is main excretory product in humans - produced in liver

- *Podocytes* are cells of Bowman's capsule inner layer

- *JGA* secretes Renin

- *Normal urine*: pH 6.0, straw yellow, 1.5L/day