Kids Research Express

If the body produces too much pituitary hormone or too little insulin, the amount of sugar in the blood rises abnormally, producing a condition known as hyperglycemia. In hyperglycemia the blood may contain as much as four times the normal amount of sugar. Hyperglycemia in itself is not lethal, but it is a symptom of a serious disease, diabetes mellitus. Diabetes is sometimes caused by a tumor or other condition in the pancreas that prevents the formation of insulin. Diabetic patients do not die of hyperglycemia, but if they are not given injections of insulin they may die from such causes as the accumulation of poisons in the body, produced by altered metabolism of fats; the body of the diabetic consumes fats as a substitute for the sugar that it cannot use. If an excessive amount of insulin is injected into the body, the amount of sugar is reduced to a dangerously low level, a condition known as hypoglycemia or insulin shock. Controlled insulin shock is sometimes used in the tre

The interconversion between glucose and glycogen is catalyzed by a number of different enzymes. Phosphorylase is responsible for the release of glucose-1-phosphate from glycogen; the reaction is enhanced by the hormones adrenaline and glucagon. Glucose-1-phosphate is converted to glucose-6-phosphate, which can either be metabolized or converted to free glucose, which enters the bloodstream. The uptake of glucose by cells is stimulated by insulin . Before glucose is used it is converted to glucose-6-phosphate (by hexokinase), which may be metabolized or (in the liver and in muscle) converted to uridine diphosphate glucose. From the latter compound glucose is transferred to glycogen, in a reaction catalyzed by glycogen synthetase and stimulated by insulin. By as yet unknown mechanisms, cortical and pituitary hormones as well as thyroxin are also involved in the control of carbohydrate metabolism. More Articles: DIGESTION, ASSIMILATION, AND STORAGE GLYCEMIA AND GLYCOSURIA  FERMENTA

Carbohydrates such as starch, dextrin, glycogen (animal starch), sucrose (cane sugar), maltose (malt sugar), and lactose are broken down in the digestive tract into simple, six-carbon sugars that pass easily through the intestinal wall. Fructose (fruit sugar) and glucose are unchanged in the digestive tract and are absorbed as such. Cellulose, a common constituent of many foods, is an important nutritional element for some animals, notably cattle and termites, but has no value in human nutrition (see Nutrition, Human ). The digestion of carbohydrates is performed by various enzymes (see Enzyme ). Amylase, found in saliva and in the intestine, breaks starch, dextrin, and glycogen into maltose, a 12-carbon sugar. Other sugar-converting enzymes in the small intestine break 12-carbon sugars into 6-carbon sugars. Maltase breaks maltose into glucose; sucrase, or invertase, breaks cane sugar into glucose and fructose; lactase breaks milk sugar into glucose and galactose. The six-carb

Sugar Metabolism, process by which the body uses sugar for energy. Carbohydrates, one of the three principal constituents of food, form the bulk of the average human diet. The end product of the digestion and assimilation of all forms of carbohydrate is a simple sugar, glucose , commonly called grape sugar when found in food, or blood sugar when found in the human body. The metabolism of fats and of certain protein substances also sometimes leads to the production of glucose. Glucose is the principal fuel that the muscles and other portions of the body consume to produce energy. It is present in every cell and almost every fluid of the body, and its concentration and distribution are among the most important processes in human physiology. A few other sugars are of comparatively minor importance in human physiology, notably lactose , or milk sugar, which is formed in the mammary glands of all lactating animals and is present in their milk. See Metabolism ; Sugar. More Articles: D

Thalamus, a brain part, consists of two rounded masses of gray tissue lying within the middle of the brain, between the two cerebral hemispheres. The thalamus is the main relay station for incoming sensory signals to the cerebral cortex and for outgoing motor signals from it. All sensory input to the brain, except that of the sense of smell , connects to individual nuclei of the thalamus.

Phagocytosis (Greek -phagos, “one that eats”; kytos, “cell”), process of ingestion of matter by cells known, in this context, as phagocytes. Single-celled life forms that bodily engulf and ingest foreign matter—whether other cells, bacteria, or nonliving material—display phagocytosis. In multicellular organisms the process is relegated to specialized cells, generally for the purpose of defending the organism as a whole from potentially harmful invaders. In humans and other higher animals, phagocytes are wandering cells that occur throughout the body. Larger phagocytes, called macrophages, are particularly important in the lymph system, liver, and spleen; amoeboid macrophages also travel throughout the body's tissues, feeding on bacteria and other foreign matter. Smaller phagocytes, which are known as granular leukocytes—a type of white blood cell—are carried throughout the body by the bloodstream (see Blood ). Attracted to sites of infection by chemicals which are emitted by t

Brain, portion of the central nervous system contained within the skull. The brain is the control center for movement, sleep, hunger, thirst, and virtually every other vital activity necessary to survival. All human emotions —including love, hate, fear, anger, elation, and sadness—are controlled by the brain. It also receives and interprets the countless signals that are sent to it from other parts of the body and from the external environment. The brain makes us conscious, emotional, and intelligent. THE HUMAN BRAIN The human brain has three major structural components: the large dome-shaped  cerebrum (top), the smaller somewhat spherical cerebellum (lower right), and the brainstem (center). Prominent in the brainstem are the medulla oblongata (the egg-shaped enlargement at center) and the  thalamus (between the medulla and the cerebrum). The cerebrum is responsible for intelligence and reasoning. The cerebellum helps to maintain balance and posture. The medulla is involve