Biology Chapter: Respiratory System

Human Breathing System

• Respiration involves the intake of oxygen and release of carbon dioxide.
• Gas exchange in Amoeba involves oxygen diffusing into the cell and carbon dioxide diffusing out.
• The process of respiration in humans occurs through a combination of a breathing system and transport systems.
• The human breathing system includes the nasal cavity, nostrils, pharynx, epiglottis, larynx, trachea, bronchi, bronchioles, intercostal muscles, ribs, air sacs, inner and outer pleural membrane, and pleural cavity, and lungs, diaphragm.

Airflow and Nostrils/Mouth

• Breathing through nostrils is better than the mouth because hairs and mucus in the nasal cavity filter incoming air, trapping dust and microorganisms. The mouth cavity lacks these features.

Cells in Nasal Cavity

• Ciliated epithelial cells and mucus-secreting cells line the nasal cavity.
• Ciliated epithelial cells remove trapped particles and microorganisms and mucus-secreting cells produce mucus to trap these particles, and thus protect the body from bacterial invasion.

Trachea, Bronchi, and Bronchioles

• The trachea is supported by C-shaped cartilages, while bronchi are supported by circular rings of cartilage .
• The trachea's posterior wall lacks cartilage, allowing flexibility during swallowing.
• Bronchioles have smooth muscles but no cartilage. This allows them to constrict and dilate, regulating airflow.

Lung Tissue and Air Movement

• Lung tissue is soft and spongy, supported by cartilage (in the trachea only).
• Air sacs (alveoli) within the lungs increase in volume when air is pumped in and decrease during exhalation.
• The air sacs in the lungs have high density owing to the presence of air.

Importance of Elastic Fibres

• Elastic fibres in lung tissue allow expansion during inhalation and recoil during exhalation, facilitating efficient air movement.

Comparison of Inhaled and Exhaled Air

• Inhaled air contains 21% oxygen and exhaled air contains 16% oxygen.
• Inhaled air contains 0.04% carbon dioxide, and exhaled air contains 4% carbon dioxide.
• Inhaled air is less saturated with water molecules than exhaled air, and exhaled air is warmer than inhaled air.

Hydrogencarbonate Indicator

• Expired air has more carbon dioxide than inhaled air, which is visible in a experiment using a hydrogencarbonate indicator.
• Exhaled air turns a hydrogencarbonate indicator yellow, while inhaled air remains red. A similar result is observed if a lime water test is performed.

Lung Tissue Structure and Function

• The alveoli, air sacs in the lungs, have thin walls and a large surface area.
• The thin walls and a large surface area in the alveoli facilitate efficient gas exchange.
• The abundance of capillaries surrounding the alveoli enables rapid gas transport to and from the blood.

Oxygen and Blood (in Gas Exchange)

• Oxygen diffuses from the air sacs into the capillaries.
• Carbon dioxide diffuses from the blood into the air sacs, facilitating gaseous exchange.

Ventilation (Breathing)

• Inhalation: Intercostal muscles contract, causing ribs to move upwards and outwards, and the diaphragm flattens increasing the volume of the thoracic/chest cavity. This causes air pressure in the lungs to decrease, so air moves into the lungs.
• Exhalation: Intercostal muscles relax, causing ribs to move downwards and inwards. The diaphragm relaxes and returns to dome shape, and this decreases the thoracic cavity/chest volume increasing the pressure inside the lungs, so air moves out of the lungs.