Human Body Systems: Digestion, Respiration, and Excretion

The Human Digestive System: Function and Components

The digestive system transforms food into nutrients, which are then transported by the circulatory system through the blood to the cells. It is a set of organs and structures, including the digestive tract and accessory glands.

Key Components of the Digestive System

• Mouth
• Pharynx
• Oesophagus
• Stomach
• Small Intestine
• Large Intestine
• Appendix
• Salivary Glands
• Liver
• Pancreas

Initial Digestion: Mechanical and Chemical Processes

Digestion is the transformation of food into nutrients so that cells can benefit from them. It can be mechanical or chemical. Digestion begins in the mouth immediately after food is ingested.

Processes and Elements in Oral Digestion

• Mastication (Chewing)
• Food
• Tongue
• Salivary Glands
• Bolus formation (Insalivation)
• Deglutition (Swallowing)

Stomach, Intestine, and Nutrient Absorption

The majority of food digestion takes place in the stomach and the small intestine.

Absorption and Faeces Formation

Absorption is the passage of the nutrients obtained during digestion through the intestinal wall and into the blood, allowing them to be transported to the cells. Undigested material forms faeces.

Common Digestive Ailments

Gastroenteritis

Gastroenteritis is an illness involving inflammation of the mucosae. It usually results from infections caused by viruses, bacteria, or Protozoa, often due to the consumption of contaminated food or water or contact with an infected person.

Constipation

Constipation is characterized by the infrequent or difficult expulsion of faeces.

The Human Respiratory System: Gas Exchange

The respiratory system takes oxygen from the air, provides cells with the oxygen they need to produce energy, and expels carbon dioxide produced by the cells. It is made up of the respiratory tract and two main organs: the lungs.

Structure and Function of the Lungs

The lungs are elastic organs located in the thoracic cavity on each side of the heart. They are covered by a double membrane called the pleura, which facilitates the movement of the lungs during respiration and contains pleural fluid.

Pulmonary Ventilation and Alveolar Gas Exchange

Pulmonary Ventilation

This process renews the air in the lungs and the respiratory tract, allowing air to flow in and out of the lungs (inhalation and exhalation).

Gas Exchange

Oxygen from the air in the alveoli passes into the pulmonary blood capillaries. Conversely, carbon dioxide passes from the blood capillaries into the alveoli. Gases pass through the walls of the alveoli and blood vessels in one direction or another.

The Impact of Tobacco on Respiratory Efficiency

Tobacco produces thousands of substances, many of which are toxic, such as tar, carbon monoxide, and nicotine. Nicotine is an addictive drug. Tobacco use makes gas exchange in the respiratory system less efficient.

Excretory Organs and Kidney Anatomy

Excretory Organs

The primary excretory organs include the Kidneys, Lungs, Sweat Glands, and organs of the digestive system.

Kidneys

These organs measure approximately 10–12 cm. They are located behind the abdomen, above the waist, and beside the spine on each side of the body.