Breathing and Exchange of Gases

Beginner - Story ModeTopper - Revision

1. Respiratory Organs & Human System

Imagine breathing through skin like frog, gills like fish, trachea like insects, lungs like us. Human has conducting part nose to bronchioles cleans warms, and respiratory part alveoli where actual exchange happens.

Nose → Pharynx → Larynx voice box with vocal cords → Trachea C-shaped cartilage incomplete dorsally, lined with ciliated epithelium mucus traps dust → Bronchi → Bronchioles → Alveoli bunch like grapes, thin squamous epithelium, capillary network. Pleura double membrane, pleural fluid reduces friction. Diaphragm dome muscle main inspiratory. Think of airway as tree upside down trunk trachea branches bronchi leaves alveoli.

Part 1A - Respiratory Organs Overview

Part 1B - Human Respiratory System Detailed Zoom

Revision: Conducting zone nose to bronchioles no exchange, Respiratory zone alveoli exchange. Trachea C-cartilage, ciliated epithelium, pleura fluid, alveoli squamous, diaphragm main muscle.

2. Mechanism of Breathing - Inspiration & Expiration

Breathing is physical movement of air, driven by pressure difference. Air goes from high pressure to low pressure like wind.

Inspiration active: Brain sends signal phrenic nerve to diaphragm, diaphragm contracts flattens down, external intercostals contract ribs up out, thoracic volume ↑, intrapulmonary pressure ↓ 756 vs 760 atmospheric, air rushes in. Boyle law P1V1=P2V2. Expiration passive at rest: Diaphragm relaxes dome up, internal intercostals contract ribs down in, volume ↓ pressure ↑ 762, air out. Forced expiration abdominal muscles + internal intercostals. Think of lungs as balloon inside box, box expands balloon inflates.

Part 2A - Inspiration - Diaphragm Contracts

Part 2B - Expiration - Pressure Volume Zoom

Revision: Inspiration active diaphragm + external intercostals volume ↑ pressure ↓ air in. Expiration passive diaphragm relax volume ↓ pressure ↑ air out. Forced expiration abdominal + internal intercostals. Boyle law.

3. Pulmonary Volumes & Capacities

How much air you can hold? Like water in bottle measured with spirometer. Volumes small units capacities sum of volumes.

TV tidal volume 500ml normal breath. IRV inspiratory reserve 2500-3000ml extra you can inhale forcefully. ERV expiratory reserve 1000-1100ml extra you can exhale. RV residual volume 1100-1200ml stays after forceful expiration never zero else lung collapse. Capacities: IC = TV+IRV 3500ml, EC = TV+ERV 1600ml, FRC = ERV+RV 2300ml air left after normal expiration, VC = IRV+TV+ERV 4000-4500ml max exhale after max inhale, TLC = VC+RV 5800ml total. Spirometry graph shows up down.

Part 3A - TV IRV ERV RV Volumes

Part 3B - Capacities VC TLC Spirometry Zoom

Revision: TV 500 IRV 2500-3000 ERV 1000-1100 RV 1100-1200 IC TV+IRV EC TV+ERV FRC ERV+RV VC IRV+TV+ERV TLC VC+RV. RV prevents collapse.

4. Exchange of Gases - Alveoli

Alveoli is where O2 meets blood. Diffusion is simple high to low pressure like perfume spreads.

Alveolar wall is 3 layers: squamous epithelium alveoli + endothelium capillary + basement membrane fused = 0.5mm diffusion membrane very thin. Partial pressures: Atmospheric pO2 159 pCO2 0.3, Alveolar pO2 104 pCO2 40, Arterial blood pO2 95-100 pCO2 40, Venous blood pO2 40 pCO2 45. So O2 104→40 diffuses into blood, CO2 45→40 diffuses out. Solubility CO2 20-25 times more than O2 so diffuses faster despite small gradient. Diffusion depends on thickness, surface area, gradient.

Part 4A - Alveoli Gas Exchange Membrane

Part 4B - Partial Pressures Table mmHg Zoom

Revision: Diffusion membrane alveolar epithelium + endothelium + basement. pO2 Atmospheric 159 Alveolar 104 Arterial 95 Venous 40, pCO2 Atm 0.3 Alv 40 Art 40 Ven 45. O2 in CO2 out gradient, CO2 20x soluble faster.

5. Transport of Gases - O2 and Bohr Effect

Blood is truck carrying O2. Hb is seat, 4 seats per truck, 97% O2 goes sitting on Hb, 3% dissolved in plasma.

O2 binds Hb as oxyhemoglobin Hb4+4O2→Hb4(O2)4 reversible. In alveoli high pO2 low CO2 high pH binding, in tissues low pO2 high CO2 low pH release. Oxyhemoglobin dissociation curve S-shaped sigmoid. P50 25-26mmHg 50% saturation. Factors shifting right release more O2: High CO2, Low pH acidic Bohr effect, High temp, High 2,3-BPG in RBC. Shift left more affinity retains O2: Low CO2 high pH low temp low 2,3-BPG. In lungs left shift loads O2, in tissues right shift unloads O2 where needed. Fetal Hb left shift higher affinity to get O2 from mother.

Part 5A - O2 Transport 97% HbO2

Part 5B - OxyHb Curve & Bohr Effect Zoom

Revision: O2 transport 97% HbO2 3% dissolved. S-curve P50 26mmHg. Right shift high CO2 low pH high temp high 2,3-BPG Bohr effect releases O2 tissues. Left shift lungs loads O2. Fetal Hb left shift.

6. Transport of CO2 & Regulation

CO2 return journey: 70% as bicarbonate in plasma, 20% as carbaminohemoglobin bound to Hb amino group, 7% dissolved. CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- by carbonic anhydrase inside RBC super fast.

At tissues CO2 enters RBC carbonic anhydrase makes HCO3- HCO3- goes out to plasma Cl- goes in to maintain charge chloride shift Hamburger phenomenon. In lungs reverse Cl- out HCO3- in → CO2 released to alveoli exhaled. Regulation: Respiratory rhythm centre medulla dorsal DRG inspiration basic rhythm, ventral VRG expiration forced. Pons has pneumotaxic limits inspiration increases rate and apneustic prolongs inspiration. Chemosensitive area medulla sensitive to CO2 H+ in CSF. Carotid and aortic bodies peripheral chemoreceptors sensitive to O2 CO2 H+ pH low O2 high CO2 low pH → signals via glossopharyngeal vagus to medulla increase ventilation. Voluntary control cortex can override up to limit.

Part 6A - CO2 Transport Bicarbonate & Chloride Shift

Part 6B - Regulation Medulla Pons Chemoreceptors Zoom

Revision: CO2 70% HCO3- 20% carbamino 7% dissolved. Carbonic anhydrase RBC, chloride shift Hamburger HCO3- out Cl- in tissues reverse in lungs. Regulation DRG VRG medulla rhythm, pons pneumotaxic apneustic, central chemoreceptors CO2 H+, peripheral carotid aortic O2 CO2 pH.

7. Disorders & Summary

Asthma allergic bronchioles inflamed constricted wheezing. Emphysema alveolar wall destroyed elasticity lost surface area reduced smoking cause. Occupational silicosis asbestosis dust fibrosis. Hypoxia less O2.

Asthma - airway hyperreactivity allergens irritants smooth muscle spasm mucus, reversible with bronchodilators. Emphysema - irreversible alveolar septa destroyed air trapping barrel chest, common in smokers. Occupational - silica dust sand mining, asbestos fibers, fibrotic scarring, wear mask N95 ventilation no smoking. Breathing vs Respiration difference: Breathing physical in out, Respiration biochemical breaking glucose ATP. Summary: Volumes capacities exchange transport regulation disorders all linked. For NEET remember TV 500 VC 4000 TLC 5800 pO2 gradient O2 transport 97% Hb Bohr effect right shift CO2 transport 70% bicarbonate chloride shift regulation medulla pons chemoreceptors.

Part 7A - Disorders Asthma Emphysema Occupational

Part 7B - Final Revision Summary Table

Revision: Asthma reversible broncho constriction allergy, Emphysema irreversible alveolar destruction smoking, Occupational silicosis asbestosis fibrosis dust. Breathing physical Respiration biochemical. TV 500 VC 4000 TLC 5800 O2 97% Hb CO2 70% HCO3- chloride shift regulation medulla pons.