Overview and Homeostasis



Overview and Homeostasis

Nervous System and Drugs

Skeletal, Muscular and Integumentary

Circulatory and Respiratory

Digestive and Excretory

Endocrine and Reproductive

Immune System and Disease

Vocabulary: cell, tissue, organ, organ system, homeostasis/dynamic equilibrium/steady state, dynamic equilibrium, feedback mechanism, stimulus, response, insulin, glycogen

Levels of Organization
Living things have different levels of organization. The simplest level of organization is that of the cell. A group of cells with a similar function is called a tissue. Groups of tissues working together to perform a common function are called organs. An example of this would include the nervous, muscle, and other tissues which make up the heart. Groups of organs working together to perform a common function are referred to as a system or organ system. The blood vessels, blood, and the heart are organs which work together to form the circulatory system. Many different systems function together to allow a complex organism to function.

All the components of the living things, from the cells and the organelles within them to the organ systems of complex organisms must interact to maintain a balanced internal environment within the organism. Organisms possess many control mechanisms to detect internal and external changes and make changes to correct any deviations. This maintenance of a stable internal environment by an organism is called homeostasis. Homeostasis in an organism is constantly threatened. Failure to respond effectively can result in disease or death. 

The ability to carry on the life processes allow a living thing to maintain dynamic equilibrium or homeostasis with their surroundings. Homeostasis is a state of balance or steady state between a living thing and its environment.   Homeostasis in an organism is constantly threatened. Failure to respond effectively to a failure of homeostasis can result in disease or death. 

Feedback Mechanisms
Dynamic equilibrium
or homeostasis results from the ability of organisms to detect and respond to stimuli. Feedback mechanisms are specific ways which have evolved in different living things to respond to internal or external environmental changes and maintain homeostasis. A feedback mechanism is a process where the level of one substance or activity of an organ or structure influences another substance or structure in some manner.

Dynamic Equilibrium and Feedback
is the maintenance of a stable internal state within an organism. Homeostasis is also known as steady state. Organisms must respond and maintain homeostasis in relation to many factors.

Stimulus and Response

Organisms detect changes in their environment and respond to these changes in a variety of ways. These changes may occur at the cellular or organism level.

The graphic above shows the response of a human to being struck on the knee with a hammer. A change in the environment is called a stimulus. In this situation, the stimulus is the being struck with the hammer. A response is the manner in which the organism reacts to the stimulus. The knee jerk reflex which is pictured at the right is the response of this individual to being hit with this hammer.

Feedback Mechanism Examples
Feedback mechanisms have evolved in living things as a mechanism by which they maintain homeostasis or dynamic equilibrium.    

A feedback mechanism occurs when the level of one substance influences the level of another substance or activity of another organ.   

An example of a feedback mechanism in humans would be the increase in heart rate and respiratory rate which occurs in response to increased exercise or other increased muscle cell activity. Some other examples of feedback mechanisms in living things appear below.

Temperature Homeostasis

Humans maintain a relatively constant body temperature of about 37 C.

  • when we "heat up" we sweat if possible
  • the evaporation of this perspiration returns the body to its original temperature


Blood Sugar Regulation

The pancreas is an endocrine gland which produces hormones which regulate blood glucose (sugar) levels

An increase in blood sugar level triggers the release of the hormone insulin by the pancreas

the hormone insulin lowers blood sugar level restoring the body to its original blood glucose level in two major ways:

  • it increases the ability of body cells to take in glucose from the blood
  • it converts blood glucose to the compound glycogen -- this compound is also called animal starch and is stored in our liver and muscles

Back to Top      Next page


Copyright 1999-2011 Oswego City School District Regents Exam Prep Center
RegentsPrep and StudyZone are FREE educational resources.