Digestion

Purpose of digestive system: to break down food into small enough molecules that the cells can absorb the nutrients and eliminate wastes.

Mouth Mouth: Opening to digestive system Taste buds: receptors on the tongue activated by the presence of food. Taste mostly due to smell. Hard palate: several bones forming the roof of the mouth Soft palate: located behind the hard palate, made entirely of muscle

Salivary glands: secretes saliva that contains the enzyme salivary amylase. Salivary amalyse begins the digestion of starch

Teeth: chew and tear food. They begin the mechanical digestion of food. Dental carries--"cavities" when enamel is destroyed.

Tongue: mixes food with saliva. Forms mixture into a mass called a "bolus" in order to for it to be swallowed

Pharynx: The region at the back of the mouth that receives food from the mouth and air from the nose. The epiglottis closes the trachea (windpipe) when swallowing

Esophagus: A long muscular tube that takes food from the pharynx to the stomach

Stomach

Entrance to stomach--Bolus enters though a small circular muscle called a sphincter acts as a valve to prevent food and acid from backing up into the esophagus. Heart burn or acid reflux is when stomach acid leaks from the stomach back into the esophagus.

Stomach The stomach is J-shaped. It stores food, and mechanically churns to break down food.

Digestion in Stomach--Stomach produces gastric juices contains the enzyme pepsin, and HCL. Pepsin: digests protein HCL: Hydrochloric acid – kills most bacteria in food pepsin and HCl work together synergistically.

Walls of stomach lined with mucus for protection against gastic juices Ulcer: When HCL penetrates mucous and the walls of the stomach break down, causing an open sore. Most of the time it is caused by an infection but can be worsened with stress.

Stomach churns and mixes food with gastric juice in to a soupy mixture called “chyme”. Exit: food leaves as chyme through a sphincter small amounts at a time

Small Intestine: Where most chemical digestion and nutrient absorption occurs. The small intestine is about 7 meters long.

Bile: contains enzymes that help to break down fats. It is produced in the liver and stored in the gall bladder Villi: finger like projections in the small intestine that help absorb nutrients from fats, glucose, and amino acids. Glucose and amino acids are absorbed into the circulatory system. Fats are absorbed into the lymphatic system.

Digestive juices are regulated by hormones that keep a balance between too many digestive juices and too few.

Large Intestine (colon): absorbs water, salts, vitamins, and stores indigestible Material until eliminated, it is about 1.5 meters long

Consists of colon (three parts), rectum, and anal canal Excretion of feces--3/4 water 1/4 solids. Solids are indigestible remains like bacteria and fiber (roughage). Bacteria--break down indigestible material--help us. (e.coli) Total length of the digestive tract is about 9 meters

Accessory Organs Pancreas: Produces enzymes. The pancreas secretes pancreatic juice, a mix of digestive enzymes and sodium bicarbonate. Digestives enzymes include pancreatic amylase for starch digestion, trypsin for protein digestion, and lipase for fat digestion.

Liver: Produces bile The liver functions as a gatekeeper to the blood. The liver stores glycogen, which can be readily mobilized when blood glucose is low. The liver produces bile, which emulsifies fats in the small intestine.

Gallbladder- A muscular sac lying within the lobes of the liver. Bile is stored here. It is commonly removed if it becomes impaired

Problems : Diarrhea: when too little water is absorbed. Caused by infection or nervous stimulation. Constipation: too much water is absorbed. Can be prevented by consuming more H20 and fiber.

Hemorrhoids: inflamed blood vessels. Ulcerative Colitis: IBD (Inflammatory Bowel Disease) affects inner lining of the Lg. intestine Chron’s Disease : IBD (Inflammatory Bowel Disease) affects the inner and outer linings of the Lg. intestine. Colon Cancer : genetic and environmental

Serious liver disorders. jaundice – many causes- results in a yellow cast to the skin and eyes. Hepatitis – inflammation of the liver – various types. cirrhosis of the liver – progressive replacement of active liver tissue by scar tissue often due to chronic alcoholism..

cirrhosis Liver cancerLiver cancer Jaundice- hepatitis

After eating a meal there is more glucose than the body can use. Insulin is released from the pancreas and this extra glucose is converted into glycogen (the storage form of glucose). The liver stores the glycogen, and when blood glucose drops, glucagon,(another hormone produced in the pancreas) is released to break down glycogen into sugar which is then released into the blood stream.

6 major nutrients and functions

Carbohydrates: digestion of carbohydrates begins in the mouth with salivary amylase and continues in the small intestine with pancreatic amylase. Carbohydrates contain the most readily available form of energy needed to sustain life. 4cal/gram

Protein: digestion begins in the stomach with pepsin and is completed in the small intestine with pancreatic trypsin. Proteins are needed for growth and repair. 4cal/gram

Fat: digestion begins in the small intestine with pancreatic lipase after bile has emulsified the fats. It is most important for energy storage. 9cal/gram

Water: is needed to aid digestion and cellular metabolism. Water is absorbed in the large intestine. Vitamins: small molecules that aid metabolism and are required in small amounts Minerals: Needed in trace amounts to prevent diseases. (calcium, Zinc, Iron, Magnesium, phosphorous, potassium)