Chapter Outline

Human Biology

Human biology—the special part of life science that focuses on human life

The Human Brain

The ability to think distinguishes human beings from other organisms. The human brain has many features that contribute to the thought process:

• brain size and shape
• neurons
• localization of brain functions—left hemisphere and right hemisphere

Taking Care of Your Body

The following steps can help you to lead a healthful lifestyle:

• Avoid fatty animal products.
• Reduce or stop smoking.
• Reduce alcohol consumption.
• Reduce sugar consumption.
• Reduce stress.
• Reduce body weight.
• Exercise regularly.
• Keep aware of advances in health education.

Nutrition is the study of the health value of food. Calories are a measure of food energy and are directly related to weight gain and weight loss. Nutrients are important food substances that every healthy body needs. Nutritionists classify food in five main groups:

• carbohydrates—a main source of slow-burning energy
• fats—an important energy source that should be eaten in limited amounts
• proteins—a substance that is vital to body growth and body repair
• vitamins and minerals—important chemicals that are used by the body in small amounts
• water—a substance that is used in the digestion of food, in the production of blood, in the elimination of wastes, and to help regulate body temperature

Systems of the Human Body

A group of organs working together to perform related body functions is called an organ system. Nine important human organ systems are listed below:

• skeletal system—approximately 200 bones and numerous joints that give form and strength to the body
• muscular system—a fibrous system that makes movement possible
• nervous system—nerve tissue that enables messages from the brain and spinal cord to travel back and forth to all parts of the body
• digestive system—the system that is used for breaking down food into the nutrients used by cells.
• excretory system—the system used for eliminating body waste products
• respiratory system—the breathing system used for getting oxygen into the blood stream
• circulatory system—the heart and major arteries and veins that transport blood with its water, nutrients, and oxygen to all cells in the body
• reproductive system— a system composed of the organs used for human reproduction
• endocrine system—a network of glands that produce hormones which regulate blood chemicals that control body processes

Reproduction and Human Genetics

Reproduction results in a new individual who has many of the same characteristics as the parents. These characteristics are passed by the parents to the offspring through genes, coded chemical messengers that make up the chromosomes of DNA. Much has been learned about human genetics during the last 50 years:

• Every human body cell, except the female egg cell and male sperm cell, contains 46 chromosomes in sets of two. Of the 23 sets, one set is a special pair that determines the sex of the child.
• Identical twins form from a single fertilized egg cell and have identical sets of chromosomes.
• Fraternal twins develop when two egg cells are fertilized by two sperm cells. Good prenatal care is necessary to ensure a healthy baby at birth. A pregnant woman should not smoke, drink, or take any drugs that have not been prescribed by her doctor.
• A genetic disorder is any disease, disability, or difference caused by an abnormal gene. By using a process called amniocentesis, doctors can examine fetal cells and determine many common genetic disorders. Many of these disorders can now be treated by gene therapy.
• Examples of serious genetic disorders are sickle-cell anemia and hemophilia. An example of a less serious genetic trait is color blindness.