Respiratory System

Human needs energy to do activities everyday such as working and studying. Do you know how the body produces the energy for us?

The body produces energy by Respiration. It is the oxidation or breakdown of food substances with the release of energy. It oxidized glucose from the food that we eat to convert it into energy that we used in our daily lives.

Cellular Respiration

There are two kinds of Respiration: Aerobic and Anaerobic Respiration

Aerobic Respiration

Aerobic respiration involves oxygen to produce a large amount of energy. It releases Water and Carbon dioxide as its waste product.

Here is the overall reaction of aerobic respiration of glucose:

C₆H₁₂O₆+ 60₂ –> 6CO₂ + 6H₂O + Energy

The actual process is more complicated than the equation above since it involves series of steps with the help of the enzymes. These enzymes are found in the mitochondria in the cells. Thus, the mitochondria are important in aerobic respiration.

Human respires aerobically. Our complex body needs a lot of energy to survive. Examples of energy-consuming processes are:

– The synthesis of proteins from amino acids;

– Cell division;

– Muscular contractions such as heartbeats and respiratory movements;

– Active transport in the absorption of food substances by the small intestine;

– Transmission of nerve impulses;

During respiration, some energy is also released as heat. This het is circulated around our body by blood to keep our body warm.

Anaerobic Respiration

Anaerobic respiration is the breakdown of food molecules in the absence of oxygen. It produces less energy than aerobic respiration.

There are two types of anaerobic respiration: Alcoholic fermentation and lactic acid fermentation.

Alcoholic fermentation usually happens in yeast. The equation is:

Glucose –> Ethanol + Carbon dioxide + Small Amount of Energy

The amount of energy is small because it is only partially broken down. The ethanol (Alcohol) still contains much energy.

Lactic Acid fermentation happens in muscle cells. During exercise, our muscle cells first respire aerobically but as we start panting, the body needs more oxygen to be brought to the muscle cells yet there is a limit to our heartbeat and heart rate. Even maximum aerobic respiration can’t cover the energy needed so the muscle cells respire anaerobically to gain extra energy. Lactic acid is formed in this respiration.

Here is the chemical equation of anaerobic respiration:

C₆H₁₂O₆ –> 2C₃H₆O₃ + Small Amount of Energy

With the extra energy from the anaerobic respiration, the muscle cells are able to contract during vigorous exercise.

When anaerobic respiration occurs, lactic acid is produced and it will build up in our muscles and eventually cause muscular pain and fatigue. The body needs to rest to recover after doing exercise.

Gas exchange system in humans

Human do gas exchange to live. We inhale oxygen then exhale carbon dioxide. There are vital parts in human gas exchange system. Here is how the air enters our body:

External nostrils –>Nasal passages –>Pharynx –>Larynx –>Trachea –>Bronchi –>Bronchioles –> Alveoli

The nose

Air enters our body through the two external nostrils, which are lined with moist mucous membrane. Here are the ad vantages of breathing through our nose:

– Dust and foreign particles are trapped by the hairs in the nostrils and mucus on the mucous membrane

– The air is warmed and moistened before it enters the lungs by the nasal passages

– Harmful chemicals may be detected by small sensory cells in the mucous membrane

Nose to Trachea

From the nasal passages, air enters the pharynx. From there, it passes into the larynx and then into the trachea through an opening known as the glottis.

Trachea to Bronchi

From there, the air enters the trachea. The trachea is placed in front of the oesophagus and it is supported by C-shaped rings of cartilage that ensure the trachea is always kept open. The lower end of the trachea divides into two tubes, the bronchi, one to each lung. Each bronchus divides repeatedly and ends in very fine bronchioles. Each bronchiole ends in a cluster of air sacs, the place where gas exchange happens.

Thinner walls of trachea and bronchi are lined by epithelium bearing cilia. Gland cells in the epithelium secrete mucus that traps dust particles and bacteria. The cilia help to sweep mucus up the bronchi and trachea into the pharynx. From here, they are swallowed into the oesophagus.

The Lungs

Each lung lies in the pleural cavity, within which the lung expands. It is lined by two transparent elastic membranes called the pleura or pleural membranes. The inner pleuron covers the lung while the outer pleuron is in contact with the walls of thorax and the diaphragm. A thin layer of lubricating fluid allows the membranes to glide over each other easily when the lungs expand and contract during breathing.

Alveoli, or also called air sacs, provide a very large surface area for gaseous exchange. The alveoli are well supplied with blood capillaries for gaseous exchange.

Gaseous Exchange in the alveoli

Gaseous exchange in our lungs takes place by diffusion. Blood entering our lung has lower concentration of oxygen but higher concentration of carbon dioxide than atmospheric air entering the alveoli in the lungs. A concentration gradient for the two gasses is set up between blood and alveolar air. Oxygen diffuses from the alveolar air into the blood capillaries while carbon dioxide diffuses in the opposite direction.

Lungs adaptation for efficient gaseous exchange

– Numerous alveoli provide a large surface area.

– The wall of alveolus is only one-celled thick that ensures faster rate of gaseous exchange.

– A thin film of moisture covers the surface of alveolus to allow the oxygen to dissolve in it.

– It is richly supplied with blood capillaries and it maintains the concentration gradient of

gases.

Here is a video about cell respiration.