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Homeostatic control system

-A homeostatic control system is a functionally interconnected network of body components that operate to maintain a given factor in the internal environment relatively constant around an optimal level. -To maintain homeostasis, the control system must be able to: 1. Detect deviations from the norm 2. Integrate this information with any other relevant information. 3. Make appropriate adjustments in the activity of the body parts responsible for restoring this factor to a desired value.

Basic cell functions

-All cells perform certain basic functions necessary for their own survival, which include: 1. Obtaining nutrients and O2 from the environment. 2. Using the nutrients and O¬2 obtained. 3. Eliminating CO¬2 and other by products (wastes). 4. Synthesizing necessary proteins. 5. Controlling exchanges of materials between the cell and its environment. 6. Moving materials internally (some cells can move themselves). 7. Sensitivity and responsiveness to environmental changes. 8. Most cells reproduce.

Homeostasis

-Cells can live and function only when the extracellular fluid is compatible with their survival. -Thus, the chemical composition and physical state of this internal environment must be maintained within narrow limits. -Nutrients must constantly be replenished, and wastes must constantly be removed from the internal environment. -Other aspects of the internal environment (such as pH and temperature) also must be kept relatively constant. -Maintenance of a relatively stable internal environment is termed homeostasis.

Multicellular organism nutrient supply

-Cells in a multicellular organism cannot live and function without contributions from the other body cells because the vast majority of cells are not in direct contact with the external environment. -A cell in a multicellular organism has the same need for life supporting nutrients and O2 uptake and waste elimination, yet the cell is isolated from the external environment surrounding the body. -The internal environment is the fluid that surrounds the cells and through which they make life sustaining exchanges and provides a bridge from the external environment.

Tissue level

-Cells of similar structure and specialized function combine to form tissues. -There are four primary types of tissues: 1. Muscle 2. Nervous 3. Epithelial 4. Connective -Each tissue consists of cells of a single specialized type along with varying amounts of extracellular material.

Organism level

-Each body system depends on the proper functioning of other systems to carry out its specific responsibilities. -The whole body of a multicellular organism consists of the various body systems structurally and functionally linked as an entity that is separate from its surrounding environment. -Thus, the body is made up of living cells organized into life-sustaining systems.

Cell functions

-Each cell performs specialized activities in addition to fundamental activities required of all cells. -Specialized contributions among the cells of multicellular organisms are essential for survival of the whole body. -Cells are organized into tissues, organs, body systems, and finally the whole body.

Cells, body systems, and homeostasis

-Functions performed by each body system contribute to homeostasis, thereby maintaining an environment in the body necessary for the survival and function of cells. -Cells, in turn, make up body systems. -Therefore, homeostasis is essential for the survival of each cell, and each cell, through its specialized activities, contributes as part of a body system to the maintenance of the internal environment shared by all cells. -Homeostasis is a reinforcing effect.

Body system level

-Groups of organs are further organized into body systems. -Each system is a collection of organs that perform related functions and interact to accomplish a common activity that is essential for survival of the whole body. Ex. - The digestive organs break down food into small nutrient molecules that can be absorbed into the blood for distribution to all cells.

Classes of homeostatic control systems

-Homeostatic control systems can be grouped into two classes: 1. Intrinsic controls - aka Local controls, are built into or are inherent in an organ. 2. Extrinsic controls - regulatory mechanism initiated outside an organ to alter the organs activity. -Extrinsic control of the organs and body systems is accomplished by the nervous and endocrine systems. -Extrinsic control permits coordinated regulation of several organs toward a common goal, while intrinsic controls serve only the organ in which they occur.

Positive feedback

-In positive feedback control systems, the output enhances or amplifies a change so that the controlled variable continues to move in the direction of the initial change. -Positive feedback does not occur nearly as often as negative feedback. Ex. Positive feedback plays a role in the birth of children - when contractions begin, the fetus is pushed against the cervix. -The resulting stretching of the cervix causes more hormones to be released causing more powering contractions until the baby is born. -All other positive feedback systems in the body also have mechanisms for stopping the cycle.

Homeostasis as a dynamic condition

-Internal environments must be kept stable, but composition, temperature, and other characteristics are constantly fluctuating. -Both external and internal factors continuously threaten to disrupt homeostasis. -When any factor starts to move the internal environment away from optimal conditions, the body systems initiate counteractions to minimize the change. -Thus, homeostasis is not a rigid, fixed state but a dynamic steady state where changes that occur are minimized by compensatory physiological responses.

Levels of bodily organization

-Levels of organization make life as we know it possible. -The levels build upon each other, going from simplest to most complex. 1. Chemical level 2. Cellular level 3. Tissue level 4. Organ level 5. Body System level 6. Organism level (the whole body).

Factors that are homeostatically regulated

-Many factors of the internal environment must be homeostatically maintained, including: 1. Concentration of nutrients 2. Concentration of O¬2 and CO2 3. Concentration of waste products 4. Changes in pH 5. Concentrations of water, salt, and other electrolytes 6. Volume and pressure 7. Temperature

Negative feedback

-Negative feedback opposes an initial change and is widely used to maintain homeostasis. -Homeostatic control primarily utilizes negative feedback. -Negative feedback occurs when a change in a homeostatically controlled factor triggers a response that seeks to restore the factor to normal by moving the factor in the opposite direction of its initial change. -Thus, negative feedback opposes the original deviation from the normal desired level.

Cellular level

-Nonliving chemical components must be arranged and packaged in very precise ways to from a living entity. -The cell is the fundamental unit of both structure and function in a living being and is the smallest unit capable of carrying out the processes associated with life. -Complex, multicellular organisms have many different kinds of cells. -During development, each cell differentiates (becomes specialized to carry out a particular function). -The human body has about 200 different specialized cell types.

Organ level`

-Organs consist of two or more types of primary tissue organized together to perform a particular function or functions. Ex. - The stomach is made up of all 4 tissue types: -The stomach is lined with epithelial tissue. -The wall of stomach contains smooth muscle tissue. -The wall of stomach also contains nervous tissue to control muscle contraction and gland secretion. -Connective tissue binds all these tissues together.

Physiology

-Physiology is the study of the functions of living things, specifically how the human body works. -Physiological mechanisms are made possible by the structural design and relationships of the various body parts that carry out various functions (Functional Anatomy). -Works by using both physical and chemical signals as well as multiple levels of organization. -Physiology works 24/7 and varies with the time of day and season. -Physiology is important because abnormal physiology is directly related to disease.

Extracellular fluid

-The extracellular fluid is the internal environment of the body. -Extracellular fluid is made up to two components: 1. Plasma - fluid portion of the blood 2. Interstitial fluid - surrounds and bathes the cells -No matter how remote a cell is from the external environment, it can make life sustaining exchanges with its own surrounding fluids. -The extracellular fluid allows nutrients and O¬2 (obtained from the external environment) to be collected by cells and also allows for wastes and by products of cells to be discarded.

Organ systems of the body

-The human body has 11 organ systems. 1. Circulatory 2. Digestive 3. Respiratory 4. Urinary 5. Skeletal 6. Muscular 7. Integumentary 8. Immune 9. Nervous 10. Endocrine 11. Reproductive

Components of negative feedback

-There are 3 components of negative feedback control systems: 1. Sensor - monitors the magnitude of the regulated variable. -The sensor typically converts the original signal regarding a change into a signal that the integrator can understand. 2. Integrator - aka control center, which compares the sensors input with the set point the cells/organs require. -The integrator then sends instructions to the effector. 3. Effector - the component of the control system commanded to bring about the desired effect (bringing the regulated variable back to normal). -Negative feedback control systems detect a change away from the ideal value in a regulated variable, initiates a mechanism to correct the situation, then shuts itself off. (Can occur in either direction).

Feedback and feedforward control

-To stabilize the physiological factor being regulated, homeostatic control systems must be able to detect and resist change. -Feedback refers to responses made after a change has been detected. -Feedforward is used for responses made in anticipation of a change.

Pathophysiology

-When one or more of the body's systems malfunction, homeostasis is disrupted, and all the cells suffer because they no longer have an optimal environment in which to live and function. -Pathophysiology refers to the abnormal functioning of the body associate with disease. -When a homeostatic disruption becomes so severe that it is no longer compatible with survival, death occurs.