Control Systems of the Body

-
The human body has thousands of control systems in it. The most intricate of these are the genetic control systems that operate in all cells to help control intracellular function as well as extracellular function.
Many other control systems operate within the organs to control functions of the individual parts of the organs; others operate throughout the entire body to control the interrelations between the organs. For instance, the respiratory system, operating in association with the nervous system, regulates the concentration of carbon dioxide in the extracellular fluid. The liver and pancreas regulate the concentration of glucose in the extracellular fluid, and the kidneys regulate concentrations of hydrogen, sodium, potassium, phosphate, and other ions in the extracellular fluid.
Examples of Control Mechanisms
Regulation of Oxygen and Carbon Dioxide Concentrations in the Extracellular Fluid
Because oxygen is one of the major substances required for chemical reactions in the cells, it is fortunate that the body has a special control mechanism to maintain an almost exact and constant oxygen concentration in the extracellular fluid. This mechanism depends principally on the chemical characteristics of hemoglobin, which is present in all red blood cells. Hemoglobin combines with oxygen as the blood passes through the lungs. Then, as the blood passes through the tissue capillaries, hemoglobin, because of its own strong chemical affinity for oxygen, does not release oxygen into the tissue fluid if too much oxygen is already there. But if the oxygen concentration in the tissue fluid is too low, sufficient oxygen is released to re-establish an adequate concentration. Thus, regulation of oxygen concentration in the tissues is vested principally in the chemical characteristics of hemoglobin itself. This regulation is called the oxygen-buffering function of hemoglobin.


Carbon dioxide concentration in the extracellular fluid is regulated in a much different way. Carbon dioxide is a major end product of the oxidative reactions in cells. If all the carbon dioxide formed in the cells continued to accumulate in the tissue fluids, the mass action of the carbon dioxide itself would soon halt all energy-giving reactions of the cells. Fortunately, a higher than normal carbon dioxide concentration in the blood excites the respiratory center, causing a person to breathe rapidly and deeply. This increases expiration of carbon dioxide and, therefore, removes excess carbon dioxide from the blood and tissue fluids. This process continues until the concentration returns to normal.
Regulation of Arterial Blood Pressure
Several systems contribute to the regulation of arterial blood pressure. One of these, the baroreceptor system, is a simple and excellent example of a rapidly acting control mechanism. In the walls of the bifurcation region of the carotid arteries in the neck, and also in the arch of the aorta in the thorax, are many nerve receptors called baroreceptors, which are stimulated by stretch of the arterial wall. When the arterial pressure rises too high, the baroreceptors send barrages of nerve impulses to the medulla of the brain. Here these impulses inhibit the vasomotor center, which in turn decreases the number of impulses transmitted from the vasomotor center through the sympathetic nervous system to the heart and blood vessels. Lack of these impulses causes diminished pumping activity by the heart and also dilation of the peripheral blood vessels, allowing increased blood flow through the vessels. Both of these effects decrease the arterial pressure back toward normal.

Conversely, a decrease in arterial pressure below normal relaxes the stretch receptors, allowing the vasomotor center to become more active than usual, thereby causing vasoconstriction and increased heart pumping, and raising arterial pressure back toward normal.

Comments

Post a Comment

Popular posts from this blog

Pleural Effusion

-
Image
Pleural effusion , sometimes referred to as “water on the lungs,” is the build-up of excess  fluid  between the layers of the pleura  outside the lungs. The  pleura  are thin membranes that line the lungs and the inside of the chest cavity and act to lubricate and facilitate breathing. Differential Diagnosis Exudative malignancy, infections, connective tissue disease, pulmonary embolism, hemothorax, pancreatitis, chylothorax Trabsydatuve HF, hypoalbuminemia (GI losing enteropathy, cirrhosis, nephrotic syndrome, malnutrition), SVC obstruction, hepatohydrothorax, urinothorax, atelectasis, trapped lung, peritoneal dialysis, hypothyroidism, pulmonary embolism Note: pulmonary embolism, malignancy, and sar coidosis can present as either exudative or transudative effusions. HF following diuresis may become ‘‘pseudo exudative’’ (check albumin gradient) Clinical Features History dyspnea, cough, hemoptysis, chest pain, weight loss, fever, trauma, occup...
Read more

FNAC of Salivary Gland Tumors

-
Image
Fine Needle Aspiration Cytology (FNAC) of Salivary Gland Tumors Introduction: Salivary gland neoplasms though relatively uncommon are by no means rare, accounting for 3 % of all head and neck tumors. Distribution wise 80% of the tumors occur in parotid gland, 15% in submandibular gland and less than 1% in sublingual glands. The World Health Organization (WHO) has classified the tumors of salivary gland as primary or secondary, malignant or benign and by the tissue of origin. The five broad – categories of salivary gland tumors are: Malignant tumors: e.g. Mucoepidermoid Carcinoma, Acinic cell Carcinoma and Adenoid Cystic Carcinoma, Benign tumors: e.g. Pleomorphic Adenoma, Warthin’s tumor, Myoepithelioma, Soft Tissue tumors: e.g. Hemangioma, Hematolymphoid tumors: e.g. Hodgkin’s Lymphoma & Secondary tumors. Of the malignant tumors Mucoepidermoid Carcinoma is the most common neoplasm occurring most frequently in the parotid gland. Exposure to radiation has been thought to play or...
Read more

Crohn's Disease

-
Image
Crohn's disease causes inflammation of the small intestine. Although it may involve any part of the digestive tract from the mouth to the anus, it most commonly affects the last part of the small intestine, called the ileum, and the large intestine, including the colon and rectum. This is considered a chronic condition because it may recur at various times throughout your lifetime, with periods of remission in which you are free of symptoms. There is no consistently accurate way to predict when a remission may occur or when symptoms will return. The disease may occur in people of all ages, although most are diagnosed before the age of 30. However, it also can affect young children and older people in their seventies or beyond. Crohn's disease occurs most commonly in people living in northern climates and affects men and women equally. The condition can be inherited and is common in some families. About 20 percent to 25 percent of those with Crohn's disease have a close r...
Read more