Respiration

What is respiration?
Respiration is the breakdown of food substances such as glucose to release energy in form of ATP (adenosine triphosphate) in all living cells.

Aerobic respiration: Aerobic respiration is the breakdown of food substances e.g. glucose to release energy in form of ATP in presence of oxygen.

Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP)

Anaerobic respiration: Anerobic respiration is the breakdown of food substances e.g. glucose to release energy in form of ATP in absence of oxygen.

Equation (in mammals and bacteria): C6H12O6 → 2C3H6O3 + energy (ATP)

Equation (in plants, microorganism and yeast): C6H12O6 → C2H2OH + 2CO2 + energy (ATP)

Uses of energy from respiration:

Muscle contraction
Protein synthesis
Cell division
Active transport
Growth
Contraction of heart
Conduction of nerve impulse
Maintenance of constant body temperature

Respiratory system consists of:

Nose and mouth
Larynx
Trachea
Bronchus
Bronchiole
Alveoli

**Alveoli is the main gaseous exchange surface in humans.

**Trachea is made of C cartilage

Percentage composition of substances in inspired and expired air:

Breathing: Breathing is the mechanical process which involves taking in of oxygenated air into the lungs and taking out of deoxygenated air from lungs

Mechanism of breathing

Breathing in:

Diaphragm contracts and become flatten.
External intercostal muscles contracts and pulls the ribcage upwards and outward. This increases the volume of the lungs.
Increase in volume of lungs results in decrease in pressure within the lungs, as a result air from the environment rushes into the lungs.

Breathing out:

Diaphragm relaxes and becomes dome shaped.
Internal intercostal muscles contract and pulls the ribcage downwards and inwards. This decreases the volume of the lungs.
Decrease in volume of lungs results in increase in pressure within the lungs, as a result air from the lungs is forced out of the lungs.

Gaseous Exchange: Gaseous exchange is the exchange of oxygen and carbon dioxide between alveolus and capillaries. Alveolus is the main gaseous exchange surface in humans.

How are the alveoli adapted to carry out its function?

Wall of both alveolus and the capillary is very thin, only one cell thick, this makes the diffusion distance short and increases the rate of diffusion of gases.
Difference in concentration of gases between the alveolus and the capillaries is very large, this increases the rate of diffusion of gases.
Alveolus is shaped like a balloon which gives it a large surface area for faster diffusion of gases.
Walls of alveolus are lined by a thin film of moisture in which gases dissolve during diffusion, this makes the gaseous exchange fast.
Alveolus has many capillaries, so more oxygen can be transported from lungs to body.

How does the respiratory system ensure a supply of clear germ-free air during breathing?

Respiratory system contains specialized cells such as goblet cells and cilia.
Goblet cells are specialized secretory cells which secrete mucus, mucus traps germs and dust that come along with air breathed in.
Cilia are tiny hair like projections which are on the trachea and bronchus, they beat the mucus trapped with dust and germs upwards and outwards towards the throat to be coughed out.

The relationship between physical activity, rate and depth of breathing:

When a person runs, muscles in his legs use up a lot of energy. Cells in the muscle need a lot of oxygen very quickly. They combine oxygen and glucose as fast as they can to release energy for muscle contraction, so a lot of oxygen is needed. As a result, the person breathes deeper and faster to get more oxygen into his blood. Person’s heart beats faster to get oxygen to the leg muscles as fast as possible. A limit is reached, the heart can’t supply oxygen to the leg muscles faster than this limit. Respiration is switched to anaerobic from aerobic. Some extra energy is produced by anaerobic respiration. Glucose is broken down without oxygen.

C6H12O6 → 2C3H6O3 + energy

Increased oxygen and lactic acid concentration in tissue and blood causes decrease in blood pH. Brain detects the change and sends nerve impulses to the diaphragm and intercostal to contract harder and more frequently, as a result deeper breathing occurs. The oxygen is used to oxidize lactic acid, volume of oxygen needed to oxidize lactic acid completely is known as oxygen debt.