Excretory Products And Elimination, Locomotion And Movement NEET Notes By PW

Excretory Products and Elimination and Locomotion and Movement cover different but important areas of human physiology. From understanding how the kidneys filter blood and maintain fluid balance to learning how muscles contract and bones enable movement, these chapters involve several processes, structures and terms that can be difficult to recall during revision.

PW’s Excretory Products and Elimination, Locomotion and Movement one-shot lecture brings together important concepts, tricks and PYQs to support your NEET Biology preparation. Use the chapter notes alongside the video to revise key processes, understand the functions of different structures and revisit concepts that need more practice.

Need For Excretion

Metabolic reactions include catabolic reactions and anabolic reactions. These processes, along with excess ingestion, may cause the accumulation of toxic substances such as:

• Ammonia

• Urea

• Uric Acid

• Excess sodium, potassium, and chloride ions

Excretion is the continuous removal of potentially harmful substances from the body.

Classification Based On Nitrogenous Waste

Ammonia is approximately 100,000 times more toxic than urea. Aquatic animals commonly eliminate ammonia, while terrestrial and egg-laying animals often eliminate urea or uric acid to conserve water.

Examples include:

• Bony fishes and aquatic amphibians: ammonotelic

• Humans and mammals: ureotelic

• Birds, reptiles, land snails, and terrestrial insects: uricotelic

The waste product depends mainly on habitat and water availability. Aquatic and terrestrial members of the same group may differ.

Human Excretory System

The human excretory system consists of:

• One pair of kidneys

• One pair of ureters

• Urinary bladder

• Urethra

The right kidney lies slightly lower because of the liver. The renal artery, a branch of the aorta, supplies blood to the kidney. The renal vein carries blood to the inferior vena cava.

The urine pathway is:

Kidney to ureter to urinary bladder to urethra

The male urethra is approximately 20 to 25 centimetres long and carries urine and semen. The female urethra is approximately 2 to 4 centimetres long and carries urine only.

Internal Structure Of The Kidney

The kidney is covered by a renal capsule. Its outer region is the renal cortex, while its inner region is the renal medulla.

The medulla contains triangular renal pyramids. Their ducts open into:

• Minor calyces

• Major calyces

• Renal pelvis

• Ureter

The hilum is the opening on the concave side of the kidney through which blood vessels enter and leave. The cortex extends between the medullary pyramids as renal columns of Bertin.

Nephron: Structural And Functional Unit

Each kidney contains approximately one million nephrons. A nephron consists of:

• Glomerulus

• Bowman’s capsule

• Proximal convoluted tubule, or PCT

• Loop of Henle

• Distal convoluted tubule, or DCT

The glomerulus and Bowman’s capsule together form the renal corpuscle, also called the Malpighian body. A collecting duct receives fluid from several nephrons and is not considered part of one individual nephron.

Blood reaches the glomerulus through the afferent arteriole and leaves through the efferent arteriole. The afferent arteriole is wider.

Memory Tip: Afferent means Arrival, while Efferent means Exit.

Bowman’s Capsule And Filtration Membrane

Bowman’s capsule is double-walled:

• Parietal layer: outer layer of simple squamous epithelium

• Visceral layer: inner layer containing modified cells called podocytes

Podocytes have extensions called pedicels. The spaces between pedicels are filtration slits.

The filtration membrane has three layers:

1. Glomerular endothelium

2. Basement membrane

3. Visceral layer with podocytes

The basement membrane is the only non-cellular layer.

Types Of Nephrons

The vasa recta and loop of Henle are especially important for producing concentrated urine.

Urine Formation

Urine formation occurs through:

1. Ultrafiltration

2. Tubular Reabsorption

3. Tubular Secretion

Ultrafiltration

High pressure in glomerular capillaries filters the plasma portion of blood. Blood cells and proteins normally remain in the blood.

The glomerular filtration rate, or GFR, is the amount of filtrate formed per unit time. It is approximately 125 millilitres per minute, or 180 litres per day.

Ultrafiltration is a passive process and does not require energy.

Tubular Reabsorption

Approximately 99% of the filtrate is reabsorbed. Although about 180 litres of filtrate are formed daily, only about 1 to 1.5 litres of urine are passed.

The PCT is the site of maximum reabsorption. Its brush-border cuboidal epithelium contains microvilli that increase surface area.

The PCT reabsorbs:

• Water and electrolytes

• Glucose

• Amino acids

• Sodium, potassium, and chloride

• Bicarbonate

• Some urea

Glucose and amino acids are mainly reabsorbed actively. Water, chloride, urea, and bicarbonate may be reabsorbed passively.

Loop Of Henle And Counter-Current Mechanism

The descending limb is permeable to water and less permeable to electrolytes. Water leaves the filtrate, so its osmolarity increases.

The ascending limb is not permeable to water but allows electrolyte reabsorption. The thin ascending limb mainly carries out passive electrolyte movement, while the thick ascending limb carries out active electrolyte reabsorption.

The loop of Henle and vasa recta carry fluids in opposite directions. This is the counter-current mechanism. It maintains a medullary osmolarity gradient from approximately 300 to 1200 milliosmoles and helps produce concentrated urine.

Memory Tip: More solvent lowers osmolarity, while more solute raises osmolarity.

Tubular Secretion

Tubular secretion adds substances to the filtrate. It is an active process that helps maintain acid-base balance.

Hydrogen ions, ammonia, and potassium may be secreted by different parts of the renal tubule. Hydrogen ion secretion makes urine slightly acidic.

Hormonal Regulation Of Kidney Function

ADH

ADH, or vasopressin, is released from the posterior pituitary. It acts on the DCT and collecting duct to increase water reabsorption.

Memory Tip: Antidiuretic means against water loss through urine.

RAAS

When blood volume and GFR decrease:

1. Juxtaglomerular cells release renin.

2. Renin helps form angiotensin II.

3. Angiotensin II causes vasoconstriction.

4. It stimulates aldosterone release.

5. Aldosterone increases sodium reabsorption in the DCT.

6. Water follows sodium, increasing blood volume and pressure.

ANF

Atrial natriuretic factor is released when blood volume is high. It inhibits RAAS, promotes sodium loss, and helps reduce excess fluid volume.

Important Excretory Disorders

• Glomerulonephritis: Inflammation of glomeruli; proteins may appear in urine.

• Renal Calculi: Kidney stones, commonly formed from calcium oxalate.

• Uraemia: Excessive accumulation of urea in blood.

• Diabetes Insipidus: Lack of ADH causes excessive water loss.

• Haemodialysis: Removes nitrogenous wastes through an artificial kidney.

• Kidney Transplantation: May be required in severe renal failure.

Locomotion And Movement

Locomotion is movement that changes body position. Movement may change posture without changing position.

All locomotions are movements, but not all movements are locomotions.

The three major types of movement are:

• Amoeboid movement

• Ciliary movement

• Muscular movement

Amoeba uses pseudopodia, white blood cells show amoeboid movement during diapedesis, cilia move mucus in the trachea, and muscles produce limb movement.

Skeletal Muscle Structure

Muscles form approximately 40 to 50% of body weight and are mesodermal in origin. Their important properties are:

• Excitability

• Contractility

• Elasticity

• Extensibility

The organisation of skeletal muscle is:

Complete muscle to fascicle to muscle fibre to myofibrils and myofilaments

• Epimysium surrounds the complete muscle.

• Perimysium surrounds a fascicle.

• Endomysium surrounds a muscle fibre.

• Myofilaments contain actin and myosin.

Memory Tip: Epi, Peri, Endo represents the coverings from the largest structure to the smallest.

Sarcomere And Muscle Contraction

A sarcomere is the functional unit of muscle contraction. It lies between two Z lines.

• I band contains thin filaments only.

• A band contains thick filaments and overlapping regions.

• H zone contains thick filaments only.

• M line lies at the centre of the H zone.

During contraction:

• Thin filaments slide inward over thick filaments.

• Z lines move closer.

• Sarcomere shortens.

• I band becomes shorter.

• H zone decreases or disappears.

• A band remains unchanged.

Memory Tip: I band decreases, H zone disappears, and A band remains the same.

Calcium released from the sarcoplasmic reticulum binds to TnC of troponin. This shifts tropomyosin and exposes myosin-binding sites on actin.

ATP hydrolysis provides energy for the myosin head to form a cross-bridge. A fresh ATP molecule breaks the existing cross-bridge. Lack of ATP after death causes rigor mortis.

Human Skeleton And Joints

The human skeleton has 206 bones:

• Axial skeleton: 80 bones

• Appendicular skeleton: 126 bones

The axial skeleton includes the skull, vertebral column, ribs, and sternum. The appendicular skeleton includes limbs and girdles.

There are 12 pairs of ribs:

• 1st to 7th: true ribs

• 8th to 10th: false ribs

• 11th and 12th: floating ribs

The vertebral column has 26 adult bones. The atlas is the first cervical vertebra, while the axis is the second.

Types Of Joints

Synovial joints include:

• Ball-and-socket: shoulder and hip

• Hinge: knee and elbow

• Pivot: atlas-axis

• Gliding: carpals and tarsals

• Saddle: thumb joint

• Condyloid: atlanto-occipital joint

Skeletal And Muscular Disorders

• Gout: Deposition of uric acid crystals in joints.

• Osteoporosis: Loss of bone minerals, causing porous and weak bones.

• Tetany: Uncontrolled muscle spasms due to low extracellular calcium.

• Myasthenia Gravis: Autoimmune damage to acetylcholine receptors at the neuromuscular junction.

• Muscular Dystrophy: Genetic disorder involving defective dystrophin and progressive muscle degeneration.

Watch PW’s EXCRETORY PRODUCTS & ELIMINATION, LOCOMOTION & MOVEMENT in ONE SHOT | Concept, Trick & PYQ Video to revisit important concepts, memory tricks and previous year questions from both chapters. Strengthen your understanding of excretion, kidney function, muscle contraction and skeletal movement while identifying topics that need further revision.

 Revising Excretory Products and Elimination, and Locomotion and Movement requires a clear understanding of biological processes, organ functions and the mechanisms behind them. Focus on key terms, revise important diagrams and practise questions to reinforce your understanding. PW’s one-shot video can help you revisit essential concepts, tricks and PYQs as part of your NEET Biology preparation.

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