Digestive+and+Endocrine+System


 * Digestive and Endocrine System **


 * Functions of the Digestive System **

The main function of the digestive system is to dissemble all of the food you eat into its component molecules so that it can be used as energy for your body. First it takes ingested food and begins moving it through the digestive tract. During this, it digests, or breaks down, chemically and mechanically the complex food molecules. Next the system absorbs the digested food and distributes it to the cells of the body. Finally, it eliminates undigested materials from your body.


 * The Mouth **


 * What Happens As You Chew **

As you chew, your tongue moves the food around and helps to position it between your teeth. This is a form of mechanical digestion, which is the physical process of breaking food into smaller pieces. It prepares food for chemical digestion.


 * Chemical Digestion Begins in the Mouth **

As you eat, salivary glands in your mouth secrete saliva which contains a digestive enzyme called amylase, which breaks down starch into smaller molecules such as DI or monosaccharide. In the stomach the amylase continues to digest starch in the swallowed food for about thirty minutes.


 * Swallowing Your Food **

After you’ve chewed your food, the tongue shapes it into a ball and moves it to the back of your mouth to be swallowed. The food is forced into the throat, then to the esophagus. Then the food moves down the esophagus by way of peristalsis. The food is moved from the mouth to the stomach by contractions occurring in waves. Circular muscles relax and longitudinal muscles contract, then circular muscles contract and longitudinal muscles relax. The epiglottis closes over the opening to the respiratory tract as you swallow, preventing food from entering.


 * The Stomach **

A muscular pouch-like enlargement of the digestive tract.


 * Muscular Churning **

Three layers of involuntary muscles contract to physically break down the swallowed food creating smaller pieces. During that time, they mix them with digestive juices produced by the stomach.


 * Chemical Digestion in the Stomach **

The inner lining of the stomach contains millions of glands that secrete a mixture of chemicals called gastric juices. It contains pepsin and hydrochloric acid. Pepsin is an enzyme that begins the chemical digestion of proteins in food. It increases the acidity of the stomach contents to PH2. The Stomach is protected from that with a lining of mucus that secretes and forms a protective layer between it and the acidic environment of the stomach. Food stays in the stomach for two to four hours. When the food is to leave the stomach, peristaltic waves gradually become more vigorous and begin to force small amounts of liquid out of the lower end of the stomach and into the small intestine.


 * The Small Intestine **

The small intestine is a muscular tube about 6 meters wide. The digestion of a meal is completed within the small intestine. Muscle contractions contribute to further mechanical breakdown of carbohydrates and proteins, undergo further chemical digestion with the enzymes produced and secreted by the pancreas and liver.


 * Chemical Action **

Enzymes and chemicals that function in the duodenum enter it through ducts that collect juices from the pancreas, liver, and gall bladder.


 * Secretions of Pancreas **

A soft flattened gland that secretes both digestive enzymes and hormones. The mixture of enzymes secretes and breaks down carbohydrates, proteins, and fats. Alkaline pancreatic also help to neutralize the acidity of the liquid food, stopping any further action of pepsin.
 * Secretions of Liver **

Large complex organ that has many functions. It can produce bile, which is a chemical substance that helps break down fats. Once made in the liver, bile is stored in the gallbladder and from there passes into the duodenum. Bile causes further mechanical digestion by breaking apart large drops of fat into smaller droplets.


 * Absorption of Food **

Liquid food stays in the small intestines for 3-5 hours and is slowly moved along its length by peristalsis. The digested food passes over villi, which is a single projection on the lining of the small intestine that functions in the absorption of food. The villi greatly increase the surface area of the small intestine, which allows a greater absorption rate. When the food is in the form of small molecules, it can be absorbed directly into the cells of the villi. Afterwards, the food molecules diffuse into the blood vessels of the villus and enter the bloodstream. The villi are the link between the digestive system and the circulatory system.


 * The Large Intestine **

The indigestible materials from meals pass through the muscular tube that is also called the colon.


 * Water Absorption **

Water and salts are absorbed by the intestinal walls, leaving behind a more solid material. Second function of the large intestines is vitamin synthesis. Anaerobic bacteria synthesize some B vitamins and vitamin K, which are absorbed as needed by the body. The bacteria also stop harmful bacteria from colonizing, reducing the risk of intestinal infections.


 * Elimination of Wastes **

After 18-24 hours in the large intestine, the remaining material, feces, reaches the rectum which is the last part of the digestion system. Feces are eliminated from the rectum through the anus.


 * The Vital Nutrients **

Six basic kinds of nutrients can be found in the body: carbohydrates, fats, proteins, minerals, vitamins, and water. These are essential for body function.


 * Carbohydrates **

Contains important energy for cells. During digestion, complex carbs are broken down into simple sugars. They’re absorbed into the bloodstream through the villi of the small intestine and circulate to fuel body functions. Some are carried to the liver to be stored as glycogen.


 * Fats **

Necessary for energy and body building materials, such as cell membranes. They also synthesize hormones, protect body organs from injury, and insulate the body from cold. In the digestive system, the fats are broken down into fatty acids and glycerol and absorbed by the villi of the small intestines. Some end up in the liver, where it either converts it into glycogen or stored as fat throughout the body.


 * Proteins **

Enzymes, antibodies, many hormones, and substances that help the blood clot are all proteins. They form part of the muscles, and cell structures, including the cell membrane. During digestion, proteins are broken into amino acids. After they’ve been absorbed by the small intestines, they enter the bloodstream and enter the liver. The liver either converts it into fat or glucose. The body only uses amino acids when the other energy sources are depleted. Most of them are absorbed by cells and used for protein synthesis. The human body needs 20 amino acids to carry out protein synthesis.


 * Minerals and Vitamins **

A mineral is an inorganic substance that serves as a building material, or takes part in a chemical reaction in the body. They make up about four percent of the total body weight, mostly in the skeleton. Minerals aren’t used as an energy source. Vitamins are organic nutrients that are required in small amounts to maintain growth and metabolism. The two main groups are water-soluble, which can’t be stored in the body and fat-soluble, which can be stored in the liver.


 * Water **

Is the most abundant substance in the body- between 45 and 75 percent of the total body mass. It facilitates the chemical reactions in the body and is necessary for the breakdown of foods during digestion. Water’s also a solvent; oxygen and nutrients from food couldn’t enter the cells otherwise.


 * Calories and Metabolism **

The energy content of the food measured in units of heat. A calorie is the amount of heat required to raise the temperature of 1mL of water by 1 degree Celsius. Some foods contain more calories than others. The number of calories needed each day varies from person to person, depending on the rate at which energy is burned, or metabolism. Body mass, age, weight, gender, and physical activity affect the metabolism rate.


 * Calories and Health **

When the energy taken in is greater than the energy expended, the extra energy is stored as body fat and a person gains weight. If less energy is taken in, the body’s stored energy is used and the person loses weight. Determined by physicians, most Americans are overweight. Overweight and obesity increases the risk of developing health problems, such as high blood pressure, diabetes, and heart disease. Being underweight has an increased risk of developing anemia, fatigue, and decreased ability to fight illness and diseases.


 * Control of the Body **

Internal control of the body is controlled by two systems: the nervous system and the endocrine system, which is made up of glands called endocrine glands that release chemicals directly into the bloodstream. The chemicals act as messengers relaying info to other parts of the body.

**Interaction of the Nervous System and the Endocrine System**

Both systems work together to maintain homeostasis within the body. Hypothalamus is the portion of the brain that connects the endocrine and nervous systems. It receives messages from other areas of the brain and from internal organs. When a change in the homeostasis is detected, it stimulates the pituitary gland, which is the main gland in the endocrine system. It releases its own chemicals or stimulates other glands to release theirs. Other endocrine glands under control of the pituitary include the thyroid gland, the adrenal gland, and glands associated with reproduction.

**Endocrine Control of the Body**

The chemicals secreted by endocrine glands into the bloodstream are called hormones. They convey info to other cells in the body, giving them instructions regarding metabolism, growth, development and behavior. Once released, they travel in the bloodstream and then attach to specific binding sites found on the plasma membranes, or in the nuclei of target cells, which are called receptors.

**Example of Endocrine Control**

An example would be the human growth hormone (hGH). When the body is actively growing, blood glucose levels are slightly lowered as the growing cells use up the sugar. The low blood glucose level is detected by the hypothalamus, which stimulates the production and release of hGH from the pituitary into the bloodstream. They bind to receptors on the plasma membranes of liver cells, stimulating them to release glucose into the blood.


 * Negative Feedback Control **

When the regulation of the endocrine system is controlled most often through one type of internal feedback mechanism. The hormones, or their effects, are fed back to inhibit the original signal. When homeostasis is reached, the signal is stopped and the hormone is no longer released.

**Feedback Control of Hormones**

Majority of endocrine glands operate under negative feedback systems. A gland secretes a hormone, which travels through the blood to target cells where the appropriate response occurs. Info regarding the hormone level or its effect on target cells is fed back, usually to the hypothalamus or pituitary gland, to regulate the gland’s production of the hormone.

**Control of Blood Water Levels**

An example of a hormone controlled by the negative feedback system. The hypothalamus can sense the concentration of water in the blood and determines that the body is dehydrated. In response, the pituitary gland is stimulated to release antidiuretic hormone (ADH). ADH reduces the amount of water in the urine. It binds to receptors in kidney cells, promoting reabsorption of water and reducing the amount of water excreted in urine. If the body becomes overhydrated, the hypothalamus stops stimulating the release of ADH.

**Control of Blood Glucose Levels**

The pancreas isn’t controlled by the pituitary gland. When blood glucose levels are high, the pancreas releases the hormone insulin. That signals the liver and muscle cells to take in glucose, lowering the level. When they become too low, the glucagon is released.


 * Hormone Action **

Can be grouped into two basic types according to how they act on their target cells: steroid hormones and amino acid hormones.

**Action of Steroid Hormones**

Hormones made from lipids are called steroid hormones. They’re lipid soluble, so they can diffuse freely into cells through their plasma membranes, where they bind to a hormone receptor.

**Action of Amino Acids Hormones**

Some hormones are long chains of amino acids and others in short. When secreted into the bloodstream, they bind to receptors embedded in the plasma membrane of the target cell. They open ion channels in the membrane, or route signals down from the surface of the membrane to activate enzymes inside the cell.


 * Adrenal Hormones and Stress **

The adrenal glands consist of two parts: an inner and outer portion. The outer portion secretes steroid hormones, including glucocorticoids and aldosterone. They cause an increase in available glucose and raise blood pressure, which helps combat fright, temperature extremes, bleeding, infection, disease and even test anxiety. The inner portion secretes two amino acid hormones: epinephrine (adrenaline) and norepinephrine. The hypothalamus relays impulses to the nervous system, which stimulates the adrenal glands to increase their output of the two amino acid hormones. It increases heart rate, blood pressure, respiration rate; increase efficiency of muscle contractions; and increase blood sugar levels.


 * Thyroid and Parathyroid Hormones **

Helps regulate metabolism, growth, and development. The main metabolic and growth hormone of the thyroid is thyroxin, which affects the rate the body uses energy and determines food intake requirements. The thyroid gland secretes a calcitonin that regulates calcium levels in the blood. It binds to the membranes of kidney cells and causes an increase in calcium excretion. It also binds bone-forming cells, causing them to increase calcium absorption and synthesize new bone. Involved in the mineral regulation, parathyroid hormone (PTH) is produced by the parathyroid glands which are attached to the thyroid gland. The release of PTH leads to an increase in the rate of calcium, phosphate, and magnesium absorption in the intestines. It causes the release of calcium and phosphate from bone tissue and increases the rate at which the kidneys remove calcium and magnesium from urine and return them to the blood.