Levels of Organization: Introduction to Human Anatomy and Physiology
1. Define homeostasis.
2. Why is homeostasis essential for survival? 3. Describe two homeostatic mechanisms.
Homeostasis
The internal environment of the human body must remain relatively stable for the person to survive. Homeostasis is a term that describes a stable internal body environment. It requires a constant balance. There should be normal concentrations of nutrients, oxygen, and water. Heat and pressure should be regulated to tolerable levels. Homeostatic mechanisms regulate the body through negative or positive feedback.
homeostatic control
For homeostasis to occur, the body primarily uses the nervous and endocrine systems. These systems allow forms of communication that control homeostasis. The nervous system uses neural electrical impulses for these activities, while the endocrine system uses blood-borne hormones. The nervous system handles rapid, short-term, and extremely specific responses. The endocrine system responds more slowly, but its effects last longer. The event or factor that is controlled (regulated) is called a variable.
The two basic components of homeostatic control are as follows:
■ Self-regulation: Also known as intrinsic regulation, it occurs when a body structure or system adjusts its activities due to some change in its environment. For example, decreased oxygen levels in the tissues cause cells to release chemicals that widen local blood vessels, thereby increasing blood flow, delivering more oxygen to the Extrinsic regulation: Related to the activity of the nervous or endocrine system, these systems influence the activities of many other body systems simultaneously. For example, increased exercise causes the nervous system to raise the heart rate and circulate blood faster. It also reduces blood flow to the digestive tract and other less active organs. The oxygen in the circulating blood is then available to the active muscles, which are the ones that need it most.
All mechanisms used for homeostatic control involve at least three components:
■ Receptors:
These are "sensors" that monitor the body's internal environment and respond to stimuli. The receptors send information to the control center along the afferent pathway. You can remember this more easily because the afferent pathway carries information that "closes" to the control center.
■■ Control Center:
This is a point on the body that determines the set point (the range or level in which a variable should be held). Analyzes input from receivers to determine appropriate responses or actions. It then sends information to the effectors through the efferent pathway. You can remember this more easily because the efferent pathway carries information that is “coming out” of the control center . The benchmark for average body temperature, for example, is 98.6°F (37°C). Another set point is normal blood pressure in adults, which is ideally below 120 (systolic) and below 80 (diastolic).
