Homeostasis

What is Homeostasis?

Things you did not know about Homeostasis

The concept of homeostasis is widely used, in physiology and psychology, to identify what seems to be a general attribute of living organisms: the tendency to maintain and restore certain steady states or conditions of the organism. An obvious example is that of body temperature, which in the human tends to fluctuate only in a narrow range about the value 98.6° F. When the temperature rises above the normal range, corrective reflexes (perspiration, reduced metabolism, etc.) go into action to restore the steady state. Persistent deviation may initiate other actions (moving into the shade, plunging into water, etc.). If body temperature drops, other corrective actions are observed.

Many bodily steady states follow this pattern. Blood glucose level, blood pH, and osmotic pressure are examples. The key concepts are: an observable steady state that persists over time with minor changes; thresholds above and below this normal range; a sensory input that reports changes in the steady state; and effector mechanisms for restoring the steady state.

When a deviation goes beyond either the upper or the lower threshold, energy is mobilized to restore the steady state to its optimal value. Physiologists have been concerned mainly with the reflexes triggered by such deviations, but psychologists have emphasized those homeostatic actions that are seen in learned behavior. Man will exert considerable energy to protect optimal states. He may take restorative action (building a fire when cold) or forestalling action (moving south before winter arrives). The simple reflex level and the complex learned response to homeostatic disturbance are often labeled differently: Stagner and Karwoski (1952) called the former “static homeo-stasis” and the latter “dynamic homeostasis”; Cofer and Appley (1964) used the terms “physiological homeostasis” and “behavioral homeostasis.”

The biochemical and reflex defenses function adequately to protect some constancies; if blood osmotic pressure drops too low or vitamin concentration is too high, kidney mechanisms correct the situation. In other cases, the reflex machinery may fail, and learned behavior is activated. There are probably two thresholds in the system, one for reflexive response and another (further from optimum) that initiates voluntary action.

Damaging the biochemical mechanism forces increased reliance on the learned systems of defense. Thyroidectomized rats build nests to protect against heat loss; parathyroidectomy or adren - alectomy leads to increased drinking of solutions containing calcium or sodium. It seems reasonable, therefore, to consider the cerebral cortex as the highest level of a homeostatic protective mechanism

Muscular System

There are three distinct types of muscles: skeletal muscles, cardiac or heart muscles, and smooth (non-striated) muscles. Muscles provide strength, balance, posture, movement and heat for the body to keep homeostasis.


Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening every sarcomere. The best proposed model for understanding contraction is the sliding model of muscle contraction. Actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped heads that project toward the actin filaments.


Larger structures along the myosin filament called myosin heads are used to provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style, they swivel toward the center of the sarcomere, release and then reattach to the nearest active site of the actin filament. This is called a rachet type drive system. This process consumes large amounts of adenosine triphosphate (ATP).


Energy for this comes from ATP, the energy source of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must continuously recycle the discharged adenosine diphosphate molecule (ADP) into ATP rapidly. Muscle tissue also contains a stored supply of a fast acting recharge chemical, creatine phosphate which canhelp initially producing the quick regeneration of ADP into ATP.

The Circulatory system

The circulatory system is often seen both the cardiovascular system, which distributes blood, and the lymphatic system, which circulates lymph These are two separate systems. The passage of lymph for example takes a lot longer than that of blood. Blood is a fluid consisting of plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the vertebrate vascular system, carrying oxygen and nutrients to and waste materials away from all body tissues. Lymph is essentially recycled excess blood plasma after it has been filtered from the intersititial fluid (between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning 'heart' and 'vessel') system comprises the blood, heart, and blood vessels. The lymph, lymph nodes, and lymph vessels form the lymphatic system, which returns filtered blood plasma from the interstitial fluid (between cells) as lymph

The Digestive System

The digestive system is a group of organs working together to convert food into atp and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the gastrointestinal tract (GI tract). The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines.