Chapter 10 The Digestive System Overview
Animals use energy released from, carbohydrates, lipids, proteins, and nucleic acids – known as macromolecules- to perform metabolic functions. These macromolecules are broken down during the process of digestions. Water, vitamins, and minerals are also essential for metabolic function.
The alimentary canal varies among animals. In general, herbivores have longer intestines than carnivores to accommodate their different diets. As food moves through the human alimentary canal, it is processed in four stages.
1. Ingestion: takes place in the mouth.
2. Digestion: begins in the mouth and continues through the small intestine.
3. Absorption: takes place in the small and large intestines.
4. Elimination: takes place at the anus.
Physical digestion breaks food down into smaller pieces. In chemical digestion, enzymes and acids break macromolecules down into smaller molecules that can be absorbed through the cells that line the small intestine.
Several disorders such as peptic ulcers, hepatitis, and diabetes can affect the functioning of the digestive system. We have developed diagnoses and treatments for many of these diseases and research is ongoing.
Chapter 11 The Respiratory System Overview
Body cells need a constant supply of oxygen to carry out metabolic functions. The respiratory system is responsible for bringing oxygen into the body, delivering it to cells in all parts of the body, and carrying carbon dioxide away from the cells and out of the body.
Animals in different environments have a variety of types of respiratory systems. Fish obtain oxygen by passing water over gills, earthworms obtain oxygen through their skin, and insects have a network of branching tracheae that bring air close to tall their body cells, where diffusion can occur.
In many animals, including humans, inhaling brings air into the lungs. Air travels through the nasal passages, pharynx, and larynx; into the bronchus; and through two bronchioles into two lungs protected by the ribs.
In the alveoli of the lungs, oxygen diffuses from the air into tiny capillaries. Oxygen-rich blood is then transported by the circulatory system to cells around the body. Carbon dioxide-rich blood is transported to the lungs, where the carbon dioxide diffuses from the capillaries into the air. The air is then released from the body by exhaling.
Some disorders of the respiratory system, such as pneumonia and bronchitis, can often be treated with antibiotics. For other disorders – including asthma, cystic fibrosis, and emphysema – treatments are used to relieve symptoms. Gene therapy is being explored as a cure for cystic fibrosis.
Chapter 12 The Circulatory System
In multi-celled animals, the circulatory system transports gases, nutrients, wastes and other chemical substances from one part of the body to another. It also regulates body temperature and protects against blood loss and disease.
Vertebrates and other large complex animals have closed circulatory systems. A heart pumps blood into thick, elastic arteries, which carry the blood to small, thin capillaries. Materials diffuse from the capillaries into body cells and from body cells into the capillaries. Veins carry blood back to the heart.
Humans have a double circulatory system – the circulation of blood around the body (systemic circulation) is separate from the circulation of blood to the lungs (pulmonary circulation). Separate chambers in the heart pump blood in each part of the system. To pump the blood, the SA node and the AV node (two areas of specializes tissue in the heart) emit electric signals that cause the heart muscle to contract and relax rhythmically. We experience this rhythmic pumping as a heart beat. Valves in the heart and in the veins prevent blood from flowing backward.
Many factors can be measured to help monitor the health of the circulatory system, including electrical activity in the heart, blood pressure, stroke volume, and cardiac output.
Disorders of the circulatory system include arteriosclerosis, arrhythmias, congenital heart defects, stroke, hemophilia, and leukemia. Many common disorders can be prevented and controlled by lifestyle choices. Some, however, have other causes. Hemophilia is caused by a genetic sex-linked trait. Most causes of congenital heart defects are unknown.
Medical technology has brought some creative solutions to the treatment of circulatory system disorders, including angioplasty, bypass surgery, pacemakers, and xenotransplants.