General Physiology (PDF)

GENERAL PHYSIOLOGY CELL: Cell is defined as the structural and functional unit of the living body because it has all the characteristics of life. TISSUE: The tissue is defined as the group of cells having similar function. The tissues are classified into four major types which are called the primar...

GENERAL PHYSIOLOGY CELL: Cell is defined as the structural and functional unit of the living body because it has all the characteristics of life. TISSUE: The tissue is defined as the group of cells having similar function. The tissues are classified into four major types which are called the primary tissues: 1. Muscle tissue: Skeletal muscle, smooth muscle and cardiac muscle. 2. Nervous tissue: Neurons and supporting cells. 3. Epithelial tissue: Squamous, columnar and cuboidal epithelial cells. 4. Connective tissue: Connective tissue proper, cartilage, bone and blood. ORGAN: An organ is defined as the structure that is formed by two or more primary types of tissues. Some organs are composed of all the four types of primary tissues. The organs may be tubular like intestine or hollow like stomach. SYSTEM: The system is defined as group of organs functioning together to perform a specific function of the body. For example, digestive system is made out of groups of organs like esophagus, stomach, intestine, etc., which is concerned with digestion of food particles. STRUCTURE OF THE CELL: Each cell is formed by a cell body and a cell membrane or plasma membrane that covers the cell body. The important parts of the cell are (Fig. 1-1): 1. Cell membrane. 2. Nucleus. 3. Cytoplasm with organelles. 1 FIGURE 1-1: Structure of the cel 2  Homeostasis  ‘Homeostasis’ means the maintenance of constant internal environment.  The internal environment in the body is the ECF which contains nutrients, ions and all other substances necessary for the survival of the cells and in this environment the cells live. It includes the blood and interstitial fluid.  Fortunately, body is provided with appropriate detectors or sensors, which recognize the deviation and alert the integrating center. The integrating center immediately sends information to the concerned effectors to either accelerate or inhibit the activity so that the normalcy is restored. COMPONENTS OF HOMEOSTATIC SYSTEM The homeostatic system in the body acts through self-regulating devices, which operate in a cyclic manner (Fig. 2-1). This cycle includes three components: 1. Detectors or sensors, which recognize the deviation. 2. Transmission of this message to an integrating unit or control center. 3. Transmission of the information from the control center to the effectors for correcting the deviation. 3 HOMEOSTASIS AND VARIOUS SYSTEMS OF THE BODY One or more systems are involved in homeostatic mechanism of each function. Some of the functions in which the homeostatic mechanism is well established are given below: 1. The pH of the ECF has to be maintained at the critical value of 7.4. The tissues cannot survive if it is altered. Thus, the decrease in pH (acidosis) or increase in pH (alkalosis) affects the tissues markedly. The respiratory system, blood and kidney helps in the regulation of pH. 2. The body temperature must be maintained at 37.5°C. Increase or decrease in temperature alters the metabolic activities of the cells. The skin, respiratory system, digestive system, excretory system, skeletal muscles and nervous system are involved in maintaining the temperature within normal limits. 3. Adequate amount of nutrients must be supplied to the cells for various activities and growth of the tissues. Digestive system and circulatory system play major roles in the supply of nutrients. 4. Adequate amount of oxygen should be supplied to the cells for the metabolic processes. And carbon dioxide and other metabolic end products must be removed from the cells. Respiratory system and excretory systems involved in these activities. 5. Many hormones are essential for the metabolism of nutrients and other substances necessary for the cells. The hormones are to be synthesized and released from the endocrine glands in appropriate quantities and, these hormones must act on the body cells appropriately. Otherwise, it leads to abnormal signs and symptoms. 6. Water and electrolyte balance should be maintained optimally. Otherwise it leads to dehydration or water toxicity and alteration in the osmolality of the body fluids. Kidneys, skin, salivary glands and gastrointestinal tract take care of this. 4  MECHANISM OF ACTION OF HOMEOSTATIC SYSTEM The homeostatic mechanism acts through feedback mechanism. Feedback is a process in which some proportion of the output signal of a system is fed (passed) back to the input. There are two types of feedback mechanisms: 1. Negative feedback mechanism. 2. Positive feedback mechanism. Negative Feedback Mechanism Negative feedback mechanism is the one by which a particular system reacts in such a way as to stop the change or reverse the direction of change. After receiving a message, the effectors send the inhibitory signals back to the system. Now, the system stabilizes its own function either by stopping the signals or by reversing the signals. For example, thyroid-stimulating hormone (TSH) released from pituitary gland stimulates thyroid gland, which in turn secretes thyroxin. When thyroxin level increases in blood, it inhibits the secretion of TSH from pituitary so that, the secretion of thyroxin from thyroid gland decreases (Fig. 2-2). On the other hand, if thyroxin secretion is less, it induces pituitary gland to release TSH. Now, TSH stimulates thyroid gland to secrete thyroxin. Another example for negative feedback mechanism is maintenance of water balance in the body. 5 FIGURE 2-2: Negative feedback mechanisms 6 Positive Feedback Mechanism Positive feedback mechanism is the one in which the system reacts in such a way as to amplify (increase the intensity of) the change in the same direction. Positive feedback is less common than the negative feedback. However, it has its own significance, particularly during emergency conditions. One of the positive feedbacks occurs during the blood clotting. Blood clotting is necessary to arrest bleeding during injury and it occurs in three stages: A. Formation of prothrombin activator. B. Conversion of prothrombin into thrombin. C. Conversion of fibrinogen into fibrin by thrombin. Thrombin formed in the second stage stimulates the formation of more prothrombin activator in addition to converting fibrinogen into fibrin. It causes formation of more and more amount of prothrombin activator so that the blood clotting process is accelerated and blood loss is prevented quickly 7  BODY FLUIDS Body is formed by solids and fluids. The fluid part is more than 2/3 of the whole body. Water forms most of the fluid part of the body. In human beings, the total body water varies from 45 to 75% of body weight. In a normal young adult male, body contains 60 to 65% of water and 35 to 40% of solids. In a normal young adult female, the water is 50 to 55% and solids are 45 to 50%. The total quantity of body water in an average human being weighing about 70 kg is about 40 L. COMPARTMENTS OF BODY FLUIDS - DISTRIBUTION OF BODY FLUIDS Compartments and distribution of body fluids with the quantity is given in Table 1. Water moves between different compartments (Fig. 3-1). Total body water (40 L) is distributed into two major fluid compartments: 1. Intracellular fluid (ICF) forming 55% of the total body water (22 L). Extracellular fluid (ECF) forming 45%X of the total body water (18L). FIGURE 3-1: Body fluid compartments 8  COMPOSITION OF BODY FLUIDS Body fluids contain water and solids. Solids are organic and inorganic substances. 1. ORGANIC SUBSTANCES Organic substances present in body fluids are glucose, amino acids and other proteins, fatty acids and other lipids, hormones and enzymes. 2. INORGANIC SUBSTANCES The inorganic substances present in body fluids are sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate and sulfate. Body water balance A. Daily water intake (gain) (2500 ml): 1- Ingested liquids and water in food (2300 ml / day) 2- Synthesized in the body as a result of metabolism of food (200 ml / day) B. Daily water loss from the body (2500 ml): 1- Water loss through urine (1500 ml / day) 2- Water loss in feces (200 ml / day) 3- Water loss in sweet (100 ml / day) 4- Insensible water loss by evaporation from respiratory tract (700 ml / day) 9 APPLIED PHYSIOLOGY (BODY WATER IMBALANCE) 1. DEHYDRATION Definition: Significant decrease in water content of the body is known as dehydration. Causes 1. Severe diarrhea and vomiting. 2. Excess water loss through urine. 3. Insufficient intake of water. 4. Excess sweating. 5. Use of laxatives or diuretics. Signs and Symptoms Mild and moderate dehydration 1. Dryness of the mouth. 2. Excess thirst. 3. Decrease in sweating. 4. Decrease in urine formation. Severe dehydration 1. Decrease in blood volume. 2. Decrease in cardiac output. 3. Cardiac shock. Very severe dehydration 1. Damage of organs like brain, liver and kidneys. 2. Mental depression and confusion. 3. Renal failure. 4. Coma. 10 OVERHYDRATION OR WATER INTOXICATION Definition Over hydration, hyper hydration, water excess or water intoxication is defined as the condition in which body has too much water. causes Over hydration occurs when more fluid is taken than that can be excreted. It also develops in some conditions such as heart failure, renal disorders and hyper secretion of antidiuretic hormone. Signs and Symptoms 1. Behavioral changes. 2. Drowsiness and inattentiveness. 3. Nausea and vomiting. 4. Sudden loss of weight followed by weakness and blurred vision. 5. Anemia, acidosis, cyanosis, hemorrhage and shock. 6. Muscular weakness, cramps and paralysis. 7. Severe conditions of over-hydration result in: - Delirium (extreme mental condition characterized by confused state and illusion). - Seizures (sudden uncontrolled involuntary muscular contractions). - Coma (profound state of un-consciousness in which person fails to respond to external stimuli and cannot perform voluntary action). 11