Homeostasis

• Internal environment — environment of the cells.

  • Coined by Claude Bernard, he noted that body cells survived in a healthy condition only when the temperature, pressure, and chemical composition of their fluid environment remained relatively constant.

• Homeostasis — relatively constant states maintained by the body.

  • Coined by Walter B. Cannon, he suggested that every regulatory mechanism of the body exists to maintain homeostasis, or constancy, of the body’s internal fluid environment.

    • “means a condition that may vary, but which is relatively constant” the maintenance of relatively constant internal conditions despite changes in either the internal or the external environment.

  • Examples of Homeostasis:

    • Temperature regulation

    • Regulation of blood carbon dioxide level.

    • Regulation of blood glucose level.

• Set point — the normal reading or range of normal.

  • also called as setpoint range.

  • The body naturally changes some set points to different values at different times of the day.

  • Circadian rhythms — any process that originates within an organism and responds to the environment.

    • It is a natural oscillation that repeats roughly every 24 hours.

Models of Homeostasis

• In the fishbowl model of homeostasis, the body is the bowl of fluid that must be kept constant, the cells of the body are like fish, and the organ systems are like the accessories used to maintain stability

• In the Wallenda model of homeostasis, the body is compared to a circus highwire walker.

• In the heating system model, the body is like a home with a thermostat acting as a control centre to regulate the electric heater and keep the interior constantly warm.

Homeostatic Functions of Body Systems

Homeostatic control mechanisms

• Homeostatic control mechanisms — the processes for maintaining or restoring homeostasis.

  • If circumstances occur that require changes or more active regulation in some aspect of the internal environment, the body must have appropriate control mechanisms available that respond to these changing needs and then restore and maintain a healthy internal environment.

• Feedback control loop — communication networks for maintaining or restoring homeostasis by self-regulation through feedback

  • Information may be transmitted in these control loops by nervous impulses or by hormones.

  • Afferent communication — This means going toward a control centre or other point of reference.

  • Efferent communication — This means going away from a control centre or other point of reference

Basic components of control systems

• Four Basic Components in Every Feedback Control Loop:

  1. Sensor Mechanism — the process wherein a sensor must be able to identify the condition being controlled.

     • It must be able to respond to any changes that may occur from normal setpoint.

     • If deviation occurs, the sensor generates an afferent signal to transmit information to the integrator.

     • Variable — any state or condition in the body that can change or vary.

  2. Integrator or control centre — this receives and analyse the input from a homeostatic sensor; the value of a variable is compared with the setpoint value.

     • First, the level or magnitude of the variable being measured by the sensor is compared with the normal setpoint level that must be maintained for homeostasis.

     • If significant deviation from that predetermined level exists, the integration sends its own signal to the effector mechanism.

  3. Effector mechanism

     • Effectors — these are organs that directly influence controlled physiological variables.

     • Its activity is regulated by feedback of info regarding their own effects on a controlled variable.

  4. Feedback — process of information about a variable constantly flowing back from the sensor to the integrator

     • Stimulus — a change in a variable that elicits a reaction in a feedback loop.

     • Response — the reaction—the operation of the effector in a feedback loop.

     • Negative Feedback Mechanism — this feedback are inhibitory and opposes a change by creating a response that is opposite in direction to the initial disturbance.

       • It stabilises physiological variables by keeping them from straying too far outside their normal ranges.

       • They are responsible for maintaining a constant internal environment.

     • Positive Feedback Mechanism — this feedback are stimulatory and tends too amplify or reinforce the change that is occurring.

       • This causes an ever increasing rate of events to occur until something stops the process.

       • It does not promote constancy of the internal environment.

       • It is helpful on delivering newborns—it’s amplification of labour contractions speeds up the delivery of the baby and lowers the risk of complications for both the mother and the baby.

       • It is also helpful when blood vessels are damaged, and platelets stick together to form a plug to slow the loss of blood.

• Feed-forward control — the concept that information may flow ahead to another process to trigger a change in an anticipation of an event that will follow.

  • It causes a feedback loop to anticipate a stimulus before it actually happens.

Levels of Homeostatic Control

• Intracellular control mechanisms — operate at the cell levels; these regulate functions within it, often by means of genes and enzymes.

  • The homeostatic balance of the cells depends on the actions of the cells itself.

• Intrinsic control mechanisms — operate at the tissue and organ levels; these make use of chemical signals.

  • It is also called autoregulation, it may also be built into the tissue or organ.

• Extrinsic control mechanisms — operates at the system and organism levels, it usually involves nervous and endocrine regulation.

  • Regulation from organ to organ.

Mechanisms of Disease

• Pathology — the study of disease.

• Pathophysiology — the organised study of the underlying physiological processes associated with disease.

  • Pathophysiologists — people who study pathophysiology.

  • Pathogenesis — a process by which an infection leads to a disease.

• Disease conditions — usually diagnosed or identified by signs and symptoms.

  • Signs — objective abnormalities that can be seen or measured by someone other than the patient.

    • It is something a doctor, or other person, notices.

  • Symptoms — subjective abnormalities that are felt only by the patient.

    • It is something an individual experiences.

  • Syndrome — a collection of different signs and symptoms that occur together.

  • Acute Disease — a disease that occurs when signs and symptoms appear suddenly, persist for a short time, and then disappear.

  • Chronic Disease — a disease that develops slowly and last for a long time (perhaps for life).

  • Subacute Disease — a disease with characteristics somewhere between acute and chronic.

• Aetiology — study of all the factors involved in causing a disease.

  • Idiopathic disease — a disease with undetermined causes.

  • Communicable disease — a disease that can be transmitted from one person to another.

  • Incubation period — the time it takes for an infection to develop after a person has been exposed to a disease-causing organism.

  • Remission — the reversal of a chronic disease; if it gets permanent, it can be said that a person is “cured.“

• Epidemiology — the study of the occurrence, distribution, and transmission of diseases in human populations.

  • Endemic — a disease that is native to a local region.

  • Epidemic — a disease that spreads to many people in a relatively short time.

  • Pandemic — a disease that affects large geographic regions (or spreading worldwide).

• If homeostasis is disturbed, various negative feedback mechanisms usually return the body to normal.

  • When a disturbance goes beyond the normal fluctuation of everyday life, we can say that a disease condition exists.

  • In acute conditions the body recovers its homeostatic balance quickly.

  • In chronic diseases a normal state of balance may never be restored.

  • If the disturbance keeps the body’s internal environment too far from normal for too long, death may result.

• Pathogenic Organisms

  • Prions — proteins that may cause misfolding of protein molecules, thus converting normal proteins of the cell into different proteins.

  • Viruses — intracellular parasites that consist of a DNA or RNA core surrounded by a protein coat and, sometimes, a lipoprotein envelope; they invade human cells and cause them to produce viral components..

    • Virion — the complete virus particle existing outside the host cell.

  • Bacteria — tiny, primitive cells that lack nuclei; cause infection by parasitizing tissues or otherwise disrupting normal function.

  • Fungi — simple organisms similar to plants but lack the chlorophyll pigments that allow plants to make their own food.

    • They parasitise other tissues to make their own food.

  • Protozoa — protists, one-celled organisms larger than bacteria whose DNA is organized into a nucleus.

  • Pathogenic animals — large, multicellular organisms such as insects and worms; parasitising human tissues, bite or sting, or disrupt normal body functions.

• Tumours and cancer — abnormal tissue growths, or neoplasms, can cause various physiological disturbances.

• Malnutrition — insufficient or imbalanced intake of nutrients which causes diseases.

• Autoimmunity — occurs when the immune system attacks one’s own body.

• Inflammatory response — a normal mechanism that usually speeds recovery from an infection or injury.

• Degeneration — occurs when tissues break apart.

• Risk Factors of Diseases

  • Age

  • Lifestyle

  • Stress

    • Psychogenic — conditions caused by psychological factors.

  • Environmental factors

  • Microorganisms

  • Pre-existing conditions — Here, the primary conditions putting a person at risk for a development of a secondary condition.