Human Respiration System

Nostrils

Entrance to respiratory track

Nasal Cavity

Cleaning, moistening, and warming the incoming air

• Hairs on walls of nostrils: filters dust and bacteria from the inhaled air

• Mucus secreting cells/ Goblet cells: Mucus traps bacteria and dust

• Blood Capillaries: close to the surface of cavity, warms inhaled alr

Larynx

Contains vocal cords

Trachea

Supported by C-shaped rings of cartilage: prevents trachea from collapsing during breathing due to change in air pressure

Bronchus

Trachea divides into 2 tubes, bronchi. Each bronchus divides into numerous fine tubes, bronchioles. Each bronchiole ends in a cluster of alveoli (singular: alveolus)

Trachea —> Bronchus —> Bronchiole —> Alveolus

What are inner walls of trachea and bronchus lined with + their functions?

Gland cells: secrete mucus that trap dust particles and bacteria

Ciliated cells: Have hair like structures called cilia on their surface; sweep the dust trapped mucus up the bronchi and trachea away from the lungs into the pharynx, where they can be swallowed or expelled

What happens during inhalation?

Diaphragm contracts and flattens

External intercostal muscles contract

Internal intercostal muscles relax

Rib cage moves upwards and outwards

Lung expands, as volume of lung increases, air pressure within the lungs decreases

Air is drawn into lungs as air move from higher atmospheric pressure to lower air pressure in lungs

What happens during exhalation?

Diaphragm relaxes and arches upwards to form a dome shape

External intercostal muscles relax

Internal intercostal muscles contract

Rib cage moves downwards and inwards

Lungs are compressed, as volume of lung decreases, air pressure within the lung increases

Air is expelled out of lungs as air moves from higher pressure in lungs to lower atmospheric pressure

Alveolar walls are one cell thick

Provide shorter distance for faster rate of diffusion of gases into the blood

Each alveolus is covered with a thin film of moisture

Enable gas to dissolve, increases rate of diffusion

Each alveolus is surrounded by numerous blood capillaries

Blood capillaries transport diffused oxygen away from lungs and carbon dioxide from bloodstream to the lungs for removal

Alveoli are present in large quantities

Provide a large surface are to volume ratio to increase rate of diffusion of gases

Describe how oxygen is transported from lungs

1. Alveolar air contains a higher concentration of oxygen than blood

2. Oxygen dissolves in the thin film of moisture on the surface of the alveoli

3. Oxygen then dissolves through the walls of the alveoli and blood capillaries into blood, where it diffuses into the red blood cell

4. Oxygen binds with haemoglobin in red blood cells to form oxyhaemoglobin

   • Reaction is reversible

   • Direction in which this takes place is dependent of the concentration of oxygen in the surroundings

5. When blood passes through oxygen-poor tissues, the oxyhaemoglobin releases oxygen which will then diffuse through the walls of the capillaries into the tissue cells

Describe carbon dioxide transport from the body cells to the lungs

From body cells:

1. Tissue cells produce a large amount of carbon dioxide as a result of aerobic respiration

2. As blood passes through these tissues, carbon dioxide diffuses into the blood. Most carbon dioxide enters the red blood cells. A small amount is carried in the plasma as dissolved carbon dioxide.

3. The carbon dioxide then reacts with water in the cytoplasm of the red blood cells to form carbonic acid. This reaction is catalysed by an enzyme, carbonic anhydrase

4. Carbonic acid then dissociates to form hydrogen ions and hydrogencarbonate ions

5. Hydrogen ions remain in the red blood cells, while the hydrogencarbonate ions diffuse out of the red blood cells to be carried in the plasma

At the lungs:

1. Hydrogencarbonate ions diffuse back into the red blood cells and combines with the hydrogen ions to form carbonic acid

2. Carbonic anhydrase catalyses the conversion of carbonic acid to carbon dioxide and water

3. Carbon dioxide diffuses out of the red blood cell, into the blood, through the capillaries and alveolar wall to be removed to the environment during exhalation

Composition of air in inhaled and exhaled air

Component in air	Inhaled Air	Exhaled Air
Oxygen	~21%	~16%
Carbon Dioxide	~0.03%	~4%
Nitrogen	~78%	~78%
Water Vapour	Variable (rarely saturated)	Saturated
Temperature	Variable	~37°C
Dust Particles	Variable but usually present	Little, if any

Harmful components of tobacco smoke

Nicotine, carbon monoxide, tar, irritant chemicals (e.g. hydrogen cyanide, formaldehyde)

Effects of Nicotine

Properties of chemical:

• Addictive stimulant drug that causes the release of adrenaline

• Makes blood clot easily

Effects on body:

• Increase heart rate and blood pressure

• Increases risk of blood clots in the arteries, if blood clots in the coronary artery will result in coronary heart disease

Effects of carbon monoxide

Properties of chemical:

• Combines permanently with haemoglobin to form carboxyhaemoglobin

Effects on body:

Reduces the ability of blood to carry oxygen

Effects of Tar

Properties of chemical:

• Carcinogenic

• Paralyses cilia lining air passage

Effects on body:

• Increases risk of lung cancer

• Dust particles trapped in the mucus lining the air passage cannot be removed, increasing risk of chronic bronchitis and emphysema

Irritant Particles

Effect on body:

• Causes the cells in lining bronchi and bronchioles to increase the production of mucus

• Dust particles trapped in the mucus lining the air passage cannot be removed, increasing risk of chronic bronchitis and emphysema

Chronic Bronchitis

Prolonged exposure to irritant particles that are found in tobacco smoke may chronic bronchitis

• Epithelium lining of airways become inflamed

• Excessive production of mucus by the epithelium

• Cilia on the epithelium become paralysed, unable to remove mucus and foreign particles

• Airflow becomes blocked, making breathing difficult

• Decreases the efficiency of gaseous exchange process

• Persistent coughing to clear the air passages, in order to breathe

Emphysema

Persistent and violent coughing due to bronchitis may lead to emphysema

• The walls of the alveoli break down, due to persistent and violent coughing, decreases surface area for gaseous exchange

• Lungs lose their elasticity and ability to effectively expel air, causing a build-up of carbon dioxide

• Oxygen uptake and carbon dioxide removal is impaired, severe breathlessness is experienced