NEET Biology - Unit 5- Breathing and Respiration- Study Notes - New Syllabus
NEET Biology – Unit 5- Breathing and Respiration- Study Notes – New Syllabus
Key Concepts:
- Breathing and Respiration: Respiratory organs in animals (recall only); Respiratory system in humans; Mechanism of breathing and its regulation in humans-Exchange of gases, transport of gases and regulation of respiration Respiratory volumes; Disorders related to respiration-Asthma, Emphysema, Occupational respiratory disorders.
Breathing and Respiration
🌱 Introduction
Breathing and respiration often sound similar, but in biology they are two different processes.
Breathing deals with air movement, while respiration deals with energy release inside cells.
🫁 What is Breathing?
- Simple physical process.
- Taking in oxygen and giving out carbon dioxide.
- Also called ventilation.
- Happens through respiratory organs.
🔋 What is Respiration?
- A catabolic breakdown of food (usually glucose) inside cells.
- Releases usable energy (ATP) for all life activities.
- Takes place in mitochondria.
- Final products: CO2, water, ATP.
Mnemonic: B = Body movement of air, R = Release of energy inside cells.
🐾 Respiratory Organs in Animals
Different animals use different organs depending on habitat (aquatic/terrestrial) and complexity.
1. Cutaneous Respiration (Skin breathing)
- Used by soft-bodied or moist-skinned animals.
- Earthworm
- Frog (also uses lungs later)
- Skin stays moist to allow diffusion of gases.
2. Tracheal System
- Used mainly by insects.
- Network of tracheae and tracheoles
- Air enters through spiracles
- Direct supply of oxygen to tissues
- No involvement of blood in gas transport.
3. Gills (Branchial Respiration)
- Used by aquatic animals.
- Fish, prawns, tadpoles
- Gills have filaments rich in blood capillaries
- Oxygen dissolved in water diffuses into blood
4. Lungs (Pulmonary Respiration)
- Used by land animals with higher metabolic needs.
- Reptiles, birds, mammals, humans
- Lungs have internal pockets to increase surface area
- Suitable for breathing dry air
🫀 Human Respiratory System
Air Passage
Nostrils → Nasal chamber → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
Protective Features
- Epiglottis prevents food from entering windpipe.
- Pleural membranes reduce friction around lungs.
🫁 Mechanism of Breathing
Inspiration (Breathing in)
- Active process
- Diaphragm contracts and moves down
- External intercostal muscles raise ribs
- Chest cavity volume increases
- Pressure inside lungs becomes lower than atmosphere
- Air rushes in
Expiration (Breathing out)
- Passive process
- Diaphragm relaxes and moves up
- Ribs move down
- Chest cavity volume decreases
- Pressure inside lungs becomes higher than atmosphere
- Air moves out
📏 Respiratory Volumes and Capacities
| Term | Meaning | Average Value |
|---|---|---|
| TV | Air in normal breath | ~500 ml |
| IRV | Extra air inhaled forcefully | 2500–3000 ml |
| ERV | Extra air exhaled forcefully | 1000–1100 ml |
| RV | Air left after forceful exhalation | 1100–1200 ml |
| IC | TV + IRV | Air inhaled after normal exhalation |
| EC | TV + ERV | Air exhaled after normal inhalation |
| FRC | ERV + RV | Air left in lungs after normal exhalation |
| VC | Maximum air breathed out after deep inhalation | TV + IRV + ERV |
| TLC | Total volume lungs can hold | TV + IRV + ERV + RV |
💨 Exchange of Gases
Where it happens
In alveoli, across a very thin diffusion membrane.
Gas movement occurs by simple diffusion.
Partial pressures
- pO2 alveoli: 104 mmHg
- pO2 blood (deoxygenated): 40 mmHg
- pCO2 alveoli: 40 mmHg
- pCO2 blood: 45 mmHg
So, oxygen moves into blood, carbon dioxide moves out of blood.
🚚 Transport of Gases
Transport of Oxygen
- 97 percent carried by hemoglobin
- Forms oxyhemoglobin
- One Hb carries 4 O2 molecules
- High pO2 in lungs → binding
- Low pO2 in tissues → release
- Graph of percent Hb saturation vs pO2 is a sigmoid curve.
Transport of Carbon Dioxide
- 70 percent as bicarbonate (HCO3-)
- 23 percent as carbamino-hemoglobin
- 7 percent dissolved in plasma
- Enzyme carbonic anhydrase (in RBCs) converts CO2 → bicarbonate quickly
🧠 Regulation of Respiration
- Controlled by centers in medulla and pons
- Responds to CO2 levels, not oxygen
- High CO2 → stronger breathing signal
📘 Summary Table: Breathing vs Respiration & Respiratory Organs
| Topic | Key Points |
|---|---|
| Breathing | Physical movement of air in and out |
| Respiration | Cellular breakdown of food to release energy |
| Cutaneous Respiration | Earthworm, frog (skin based) |
| Tracheal System | Insects (tracheae, spiracles) |
| Gills | Aquatic animals (fish, prawns) |
| Lungs | Higher vertebrates, humans |
📦 Quick Recap
Breathing = air exchange
Respiration = energy release inside cells
Earthworm → skin; insects → tracheae; fish → gills; humans → lungs
Inspiration = active, diaphragm down
Expiration = passive, diaphragm up
Gas exchange in alveoli by diffusion
O2 carried by hemoglobin, CO2 mainly as bicarbonate
Control centers in medulla + pons
Respiratory System in Humans
🌱 Introduction
Humans need a continuous supply of oxygen because every cell performs aerobic respiration to release energy.
The respiratory system is designed to take in air, filter it, warm it, exchange gases, and transport them efficiently.
Its main job is to ensure oxygen enters the body and carbon dioxide leaves it.
🫁 Parts of the Human Respiratory System
A. External Structures
1. Nostrils (External nares)
- First opening through which air enters.
- Two nostrils separated by a nasal septum.
- Have hair and mucus to trap dust.
2. Nasal Chamber
- Air is filtered, warmed, moistened.
- Lined with ciliated epithelium.
- Opens into the pharynx.
B. Passage of Air Inside the Body
3. Pharynx
- Common passage for air and food.
- Conducts air to the larynx.
4. Larynx (Voice Box)
- Produces sound with vocal cords.
- Epiglottis covers the larynx during swallowing so food does not enter the windpipe.
5. Trachea (Windpipe)
- A 12 cm long straight tube.
- Supported by C-shaped cartilaginous rings to prevent collapse.
- Lined with mucus and cilia which push dust upwards.
6. Bronchi
- Trachea divides into right and left primary bronchi.
- Each enters a lung and divides repeatedly into smaller tubes.
7. Bronchioles
- Finer branches of bronchi.
- No cartilage.
- End in tiny sacs called alveoli.
C. Lungs
8. Structure of Lungs
- Two spongy, elastic organs located in the thoracic cavity.
- Right lung has 3 lobes, left has 2 lobes (space for heart).
9. Pleura and Pleural Fluid
- Each lung is enclosed by two membranes:
- Outer pleura
- Inner pleura
- Space between them has pleural fluid to reduce friction during breathing.
10. Alveoli – Main Site of Gas Exchange
- Balloon-like clusters at the end of bronchioles.
- Enormous surface area (approx 70 square meters).
- Surrounded by dense capillary network.
- Exchange of gases occurs across a thin diffusion membrane.
📘 Summary Table: Human Respiratory System
| Part | Function |
|---|---|
| Nostrils | Entry of air; filtration |
| Nasal chamber | Warm, moisten, filter air |
| Pharynx | Common passage |
| Larynx | Voice production; protected by epiglottis |
| Trachea | Air passage with cartilage rings |
| Bronchi | Carry air to lungs |
| Bronchioles | Fine tubes ending in alveoli |
| Alveoli | Main gas exchange site |
| Lungs | Elastic organs for breathing |
| Pleura | Reduces friction |
📦 Quick Recap
Air path: Nostrils → nasal chamber → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
Lungs protected by double pleura
Breathing involves diaphragm + intercostal muscles
Gas exchange depends on partial pressure differences
O2 carried by hemoglobin; CO2 mostly as bicarbonate
Brainstem controls respiration using CO2 levels
Mechanism of Breathing and Its Regulation in Humans
🌱 Introduction
Breathing is the physical process of moving air in and out of the lungs. It ensures a continuous supply of oxygen and removal of carbon dioxide so that cellular respiration can run smoothly in all tissues.
Breathing happens due to pressure changes created by the diaphragm and intercostal muscles.
🌿 1. Mechanism of Breathing
Breathing includes two opposite movements:
A. Inspiration (Breathing In)
- Air enters the lungs.
- It is an active process (muscles contract).
What happens during inspiration
- Diaphragm contracts and moves downwards.
- External intercostal muscles contract, lifting the rib cage up and outward.
- Thoracic cavity volume increases.
- Lung pressure becomes lower than atmospheric pressure.
- Air rushes inside.
Key idea: More thoracic volume gives less pressure, so air flows in.
B. Expiration (Breathing Out)
- Air leaves the lungs.
- A passive process (muscles relax).
What happens during expiration
- Diaphragm relaxes and moves upwards.
- Ribs move down and inward.
- Thoracic cavity volume decreases.
- Lung pressure becomes higher than atmospheric pressure.
- Air is pushed out.
Key idea: Less thoracic volume gives more pressure, so air flows out.
🫁 2. Exchange of Gases
Gas exchange occurs at two places:
- In the alveoli (lungs)
- In the tissues
A. Exchange of gases in alveoli
- Occurs by simple diffusion.
- Depends on partial pressure gradients.
Partial pressures
- pO2 (oxygen in alveoli): 104 mmHg
- pO2 (oxygen in blood): 40 mmHg
- pCO2 (blood): 45 mmHg
- pCO2 (alveoli): 40 mmHg
What diffuses where
- O2 diffuses from alveoli to blood.
- CO2 diffuses from blood to alveoli.
Diffusion membrane layers
- Alveolar squamous epithelium
- Capillary endothelium
- Fused basement membrane
Thin membrane allows fast diffusion.
B. Exchange of gases in tissues
- pO2 is higher in blood, so oxygen moves from blood to tissues.
- pCO2 is higher in tissues, so CO2 moves from tissues to blood.
🚚 3. Transport of Gases
A. Transport of Oxygen
- 97 percent transported by hemoglobin as oxyhemoglobin.
- 3 percent dissolved in plasma.
Factors that help O2 bind hemoglobin
- High pO2
- Low pCO2
- Low temperature
In tissues
- Opposite conditions cause hemoglobin to release O2.
B. Transport of Carbon Dioxide
Three forms:
- 70 percent as bicarbonate in plasma
- 23 percent as carbaminohemoglobin
- 7 percent dissolved in plasma
Role of Carbonic Anhydrase
Inside RBCs, CO2 combines with water forming carbonic acid, then bicarbonate. The reaction is reversed in alveoli to release CO2.
🧠 4. Regulation of Respiration
A. Respiratory Centres
- Medulla oblongata: controls basic rhythm of breathing.
- Pneumotaxic center (pons): modulates breathing rate and prevents over inflation.
B. What stimulates breathing?
- High CO2 concentration in blood is the strongest stimulus.
- Even a slight rise in CO2 increases breathing rate.
- Oxygen plays a lesser role unless it drops very low.
📊 5. Respiratory Volumes and Capacities
| Term | Meaning | Approx Value |
|---|---|---|
| Tidal Volume (TV) | Air inhaled or exhaled in normal breathing | 500 ml |
| IRV | Extra air inhaled in deep breath | 2500–3000 ml |
| ERV | Extra air exhaled forcibly | 1000–1100 ml |
| Residual Volume (RV) | Air left after forceful exhalation | 1100–1200 ml |
| Inspiratory Capacity (IC) | TV + IRV | – |
| Expiratory Capacity (EC) | TV + ERV | – |
| Functional Residual Capacity (FRC) | ERV + RV | – |
| Vital Capacity (VC) | Max air exhaled after deep inhalation | – |
| Total Lung Capacity (TLC) | TV + IRV + ERV + RV | – |
📦 Quick Recap
Inspiration: diaphragm down, ribs up, pressure low
Expiration: diaphragm up, ribs down, pressure high
Gas exchange: occurs in alveoli by diffusion
O2 carried by hemoglobin, CO2 mostly as bicarbonate
Medulla and pons control breathing
TV = 500 ml; RV = 1100–1200 ml
Respiratory Disorders: Asthma, Emphysema, Occupational Respiratory Disorders
🌱 Introduction
The respiratory system can be affected by several disorders that interfere with normal airflow, gas exchange, or lung elasticity.
Here’s a clean, friendly, exam-oriented set of notes covering three major disorders you need to recall.
🌬️ 1. Asthma
What is Asthma?
A chronic disorder in which the bronchi and bronchioles become inflamed, leading to narrowing of airways and difficulty in breathing.
Why it happens (Causes)
- Allergy to dust, pollen, smoke
- Cold air
- Respiratory infections
- Stress and exercise
- Genetic tendency
What happens inside the lungs?
- Smooth muscles of bronchioles constrict
- Lining swells up
- Excess mucus is produced
→ Airflow becomes limited, especially while exhaling.
Symptoms
- Wheezing (whistling sound during breathing)
- Shortness of breath
- Tightness in chest
- Coughing, especially at night
Treatment / Management
- Bronchodilators (inhalers) to relax bronchioles
- Anti-inflammatory medications
- Avoiding allergens
🌬️ 2. Emphysema
What is Emphysema?
A chronic disorder in which alveolar walls are destroyed, causing abnormally large air spaces and loss of lung elasticity.
Why it happens (Causes)
- Long-term smoking (major cause)
- Exposure to harmful gases or pollutants
- Rare genetic cause (alpha-1 antitrypsin deficiency)
What happens inside the lungs?
- Alveoli lose their walls and merge into large sacs
- Surface area for gas exchange decreases
- Lungs remain over-inflated due to trapped air
Symptoms
- Chronic breathlessness
- Barrel-shaped chest due to over-inflated lungs
- Reduced oxygen levels
- Difficulty exhaling
Treatment / Management
- Stopping smoking
- Breathing exercises
- Bronchodilators
- Oxygen therapy in severe cases
Key idea: “Emphysema = destroyed alveoli + trapped air”
🏭 3. Occupational Respiratory Disorders
What are they?
Respiratory problems caused by long-term exposure to industrial dust, chemicals, or fumes at workplace.
These particles irritate the lungs and may cause permanent damage.
Common Occupations at Risk
- Miners (coal dust)
- Stone/Granite workers (silica dust)
- Textile workers (cotton dust)
- Welders, chemical industry workers
Examples of Disorders
- Silicosis – due to inhaling silica dust
- Asbestosis – due to asbestos fibres
- Byssinosis – from cotton dust (common in textile workers)
What happens inside?
- Inhaled dust particles accumulate in lungs
- Inflammation and fibrosis (hardening) of lung tissues
- Elasticity reduces
- Breathing becomes difficult
Symptoms
- Persistent cough
- Breathing difficulty
- Chest tightness
- Weakness due to low oxygen uptake
Prevention / Management
- Wearing protective masks
- Proper ventilation
- Reducing dust levels
- Regular medical checkups
📦 Quick Recap
Asthma
– Inflamed bronchioles
– Excess mucus + narrowed airways
– Symptoms: wheezing, breathlessness
Emphysema
– Alveolar walls destroyed
– Reduced surface area and trapped air
– Caused mainly by smoking
Occupational Respiratory Disorders
– Due to inhaling dust (silica, asbestos, cotton)
– Leads to fibrosis and reduced elasticity
– Seen in miners, textile workers