Human Biology Essentials: Digestion, Blood, and Mitosis

The Human Digestive Process

There are three phases in the processing of food: digestion, absorption, and expulsion of waste. This process, driven by peristaltic movements, involves several key steps:

1. Mouth: Digestion begins in the mouth as a result of mastication (chewing) and salivation. Saliva is a liquid produced by the salivary glands in the mouth.
2. Stomach: After swallowing, the food reaches the stomach where gastric digestion begins, and chyme is produced.
3. Small Intestine: The duodenum continues the chemical digestion of the food. Chyme is mixed there with intestinal juices, resulting in chyle, which is then absorbed.

Respiration and Blood Composition

The Respiratory Cycle

During inspiration, the air enters the lungs. During expiration, the air leaves the lungs. The interchange of gases between the air and the blood occurs in the alveoli.

Components of Blood

The blood transports substances through the human body and other vertebrates. It is made up of various blood cells which float in a liquid called the blood plasma.

• Erythrocytes (Red Blood Corpuscles): These are cells without a nucleus. In a healthy person, there are between 4.4 and 5.5 million erythrocytes per cubic millimeter of blood. They are responsible for transporting oxygen and carbon dioxide.
• Leukocytes (White Blood Corpuscles): These are cells with a nucleus that defend the body from infection. There are five kinds: neutrophils, basophils, eosinophils, lymphocytes, and monocytes.
• Platelets: These are not complete cells but small bits of cytoplasm from other cells. Platelets are involved in the coagulation of the blood.

The Stages of Mitosis

Mitosis is the process of cell division that results in two identical daughter cells. The phases are:

1. Interphase: When the cell is not dividing, it is in interphase. At the end of this phase, it prepares for division and duplicates the DNA fibers of its nucleus.
2. Prophase: The nuclear envelope begins to disappear and chromosomes are formed.
3. Metaphase: The X-shaped chromosomes join together in the center of the cell, forming what is known as the metaphase plate or "mother star."
4. Anaphase: The two bars (chromatids) which make up each chromosome separate. Each one goes to a different pole of the cell.
5. Telophase: A nuclear envelope is formed around each group of chromosomes. These begin to disappear as the DNA fibers are re-formed. Finally, the cell completes its division into two.

The result is two daughter cells which grow until they are identical to the mother cell.