This is known as Muscular Fatigue. If Oxygen is available, Lactic acid is converted into Pyruvic acid again and then into Acetyl Co-A.

- In case of Bacteria, Pyruvic acid converts into Lactic acid.

Acidic Fermentation

C6H12O6 2C3H6O3 + 2ATP

- In case of Yeast fungus, or in some plant cells, Pyruvic acid is reduced into Ethyl alcohol and Carbon dioxide. This process is called Alcoholic Fermentation and is used in the industry of some products.

Alcoholic Fermentation

C6H12O6 2C2H5OH + 2CO2 + 2ATP

The Respiratory System in Man

1. An air entrance:

Air enters the body through the nose or the mouth. It’s preferable for air to enter through the nose because:

A. This passage is warm, as it is lined with numerous blood capillaries.

B. This passage is moist, as it secretes mucous.

C. This passage serves as a filter, as it contains hairs that act as a filter.

2. The Pharynx:

Pharynx is a common passage for both air and food.

3. The Larynx:

Larynx is also known as the voice box.

4. The Trachea:

Air enters the trachea through the larynx. The trachea wall contains a series of cartilage ¾ rings which prevent the trachea wall from collapsing, thus maintaining an open passageway for air.

The inner surface of the trachea is lined with cilia which beat upwards to create air and mucous currents; this impedes the entry of small foreign bodies and moves them to the pharynx, where they may be swallowed. The trachea is divided at its lower end into two bronchi.

5. The two bronchi:

Each bronchus enters a lung, where it divides and sub-divides into progressively smaller and smaller bronchioles. Each bronchiole finally opens into one of the many alveoli (air sacs), of which there are about 600 millions per lung.

N.B.: 1. The thin alveolar walls are considered the actual respiratory surface, as they are surrounded with a large network of blood capillaries. Blood receives Oxygen from the alveolar air and carries it to the rest of the body. It gives out CO2 to the alveoli in return, so that it may get rid of it.

N.B.: 2. The whole group of alveoli, and bronchioles connected to them, together with the huge network of capillaries, constitute the lung. Each animal, and also Man possesses two lungs, a right lung, and a left lung.

Mechanism of respiration in Man

Mechanism of respiration in Man is the responsibility of:

1. The diaphragm: The respiratory muscle.

2. The intercostals muscles: Two groups of internal and external chest muscles that move the ribs.

In case of inspiration:

- The internal muscles between the ribs contract, thus moving them up.

- The diaphragm muscle below the lungs contracts.

- The chest cavity increases.

- The internal pressure of air inside the lungs is reduced.

- The outside air flows from the outside through the nose and downwards through the trachea and finally into the lungs.

In case of expiration:

- The ribs muscles relax.

- The diaphragm relaxes.

- The volume of the chest cavity is reduced.

- The internal pressure increases.

- Air is forced outside the lungs.

N.B.:

1. During each respiratory cycle (inspiration and expiration), the aeration of the lungs does not exceed 10% of its capacity. This ratio varies according to:

Date: 2015-12-11; view: 809