Homeostasis.pptx
- 1. Homeostasis -By Dr. N. Revanth
- 3. Homeostasis: • Homeo- similar ; Stasis – standing still • Homeostasis is the maintenance of the nearly constant conditions in the internal environment.
- 4. Introduction: • The fact that we remain alive is the result of complex control systems. • Hunger makes us seek food, and fear makes us seek refuge. • Sensations of cold make us look for warmth. • Other forces cause us to seek fellowship and to reproduce. • The fact that we are sensing, feeling and knowledgeable beings is part of this automatic sequence of life; these special attributes allow us to exist under widely varying conditions that otherwise would make life impossible.
- 5. • The basic living unit of the body is the cell. • Each tissue or organ is an aggregate of many different cells held together by intercellular supporting structures. • Different cells may markedly differ from one another, but all have certain basic characteristics which are alike. • Almost all cells have the ability to reproduce additional cells of their own type, so if one type of cells are destroyed the remaining cells of this type generate new cells.
- 6. EXTRACELLULAR FLUID—THE “INTERNAL ENVIRONMENT” • 50% to 70% of the adult human body is fluid, mainly a water solution of ions and other substances. • Most of the fluid is inside the cells and is called INTRACELLULAR FLUID. • 1/3rd fluid is outside the cells – Extracellular fluid.
- 7. • ECF is in constant motion throughout the body. • In this there are ions & nutrients required for basic functioning of a cell. • Hence all cells live in similar environment called the Extra-Cellular Fluid. • Hence the name Internal environment of the body or milieu interieur. • Milieu Interieur – coined by the great French physiologist “Claude Bernard”. 1813 - 1878
- 8. Difference between ECF & ICF: • The ECF contain large amounts of sodium, chloride and bicarbonate ions + nutrients for cells. • It also contains CO2 that is being transported to from cells to lungs to be excreted & also other cellular waste to be excreted by kidneys. • Where as the ICF contains large amounts of potassium, magnesium and phosphate ions.
- 9. HOMEOSTASIS • Homeostasis is the maintenance of the nearly constant conditions in the internal environment. • Walter Bradford Cannon – an American physiologist coined the term Homeostasis. 1871 - 1945
- 10. • Essentially all organs & tissues of the body perform functions that help maintain these relatively constant conditions. • various ions, nutrients, waste products and other constituents of the body are normally regulated within a range of values, rather than at fixed values. • Powerful control systems exist for maintaining concentrations of ions, nutrients and substances in the body at levels that permit the cells, tissues and organs to perform their normal functions, despite wide environmental variations and challenges from injury and diseases. • Disease is often considered to be the state of disrupted homeostasis.
- 11. ECF Transport and mixing system: • Transported in two stages • • - Movement of blood through the body in the blood vessels • • - Movement of fluid between the blood capillaries and the intercellular spaces.
- 13. • As blood passes through the capillaries continuous exchange of ECF takes place between the plasma and intercellular spaces. • Capillary walls are permeable to most molecules in the blood plasma except plasma proteins, which are too large to pass through capillaries readily. • Large amounts of fluid and its dissolved constituents diffuse back and forth between the blood and the tissue spaces. • The extracellular fluid everywhere in the body is continually being mixed, thereby maintaining homogeneity of extracellular fluid throughout the body. • Respiratory system – O2 for cell functioning. • Gastro-intestinal system – Dissolved nutrients absorbed from food into ECF. • Liver- Metabolism • Musculoskeletal system - motility.
- 14. Regulation of Body Functions: Nervous System: Sensory Input Portion Central Nervous System or Integrative Portion Motor Output Portion Hormone Systems: Endocrine organs Hormones Via ECF Target organs
- 15. Control Systems of Body: • Human body has thousands of control systems. • Many – within the organ • Some – control the interrelationships between the organs. • Ex: Respiratory system – co2 concentration in ECF. • Liver & Pancreas : Glucose concentration. • Kidneys : H+, K+, Na+, PO4- & Other ions.
- 16. Examples: Oxygen required for major chemical reactions in cell Haemoglobin + Oxygen Tissues If O2 more- does not disassociate If less- sufficient O2 is released Oxygen-buffering function of Hemoglobin Carbon dioxide has different pathway: CO2 Respiratory centre is excited Breathing rapidly & deeply CO2 Excretion
- 19. Characteristics of Control Systems: 1. Negative Feed Back Mechanism: • Most of the systems act via negative feedback. • Negative feed-back consists of a series of changes opposite to the initiating stimulus that return the factor towards a certain mean value, thus maintaining homeostasis. Gain of a Control System: Gain = Correction/ Error • The degree of effectiveness with which a control system maintains constant conditions is determined by the gain of negative feedback.
- 21. 2. Positive Feed- back Mechanism: • Most of systems follow negative feed back cause positive feed back does more damage than stabilising the system.
- 22. • In positive feed-back initiating stimulus causes more of the same. • It is sometimes known as vicious- cycle. • But in some cases Positive Feed-back can be useful, like blood clotting. • When blood vessel ruptures, clot begins to form and multiple enzymes called clotting factors are activated within clot. • Some of these enzymes act on adjacent inactivated factors and activate them resulting in furthermore clot formation. • This continues until the hole is plugged. • But unwanted clot formations may result in acute attacks like MI.
- 23. • Child birth is another example of positive feedback mechanism. • When uterine contractions becomes strong enough to bring the babys head towards the cervix => cervix sends signals back to uterus body => further strong uterine contractions. • Uterine contractions causes cervix stretch, these in turn causes further strong uterine contractions. • Another important example is Nerve signal transmission. • Stimulation of nerve causes => Leakage Na+ via Na+ channels => Na+ into fibre interior => changes membrane potential => more Na= channels opening => more change of potential => and so on=> action potential generation. • In each part where there is positive feed back is useful, it is a part of an overall negative feed back process.
- 24. 3. Feed Forward Control Mechanism: • Homeostasis is controlled by many interconnected simple yet complex mechanisms. • For example, some movements of the body occur so rapidly that there is not enough time for nerve signals to travel from the peripheral parts of the body all the way to the brain and then back to the periphery again to control the movement. • Therefore, the brain uses a mechanism called feed-forward control to cause required muscle contractions. • Sensory nerve signals from the moving parts apprise the brain about whether the movement is performed correctly. • If not, the brain corrects the feed-forward signals that it sends to the muscles the next time the movement is required. • if still further correction is necessary, this process will be performed again for subsequent movements. This process is called adaptive control.