Functions of the Digestive System
Chemical digestion is when enzymes catalyze the chemical reactions that lead to the breakdown of food molecules. This includes the secretion of saliva from the salivary glands (parotid gland, submandibular gland, and the sublingual glands). Saliva dissolves chemical in food so that they can be detected by the taste buds, but also moistens food so that it can be swallowed. Saliva also contains salivary amylase, which is a digestive enzyme which breaks down starch into maltose.
Mechanical digestion is when your teeth physically break down the food. This is also known as mastication. The main tools used to mastication are the teeth, which contain three layer: enamel (the outermost layer made of calcium phosphate), dentin (similar to bone, but without living cells), and the pulp cavity (the living cells of the tooth). There are various types of teeth used though for mastication:
Mechanical digestion is when your teeth physically break down the food. This is also known as mastication. The main tools used to mastication are the teeth, which contain three layer: enamel (the outermost layer made of calcium phosphate), dentin (similar to bone, but without living cells), and the pulp cavity (the living cells of the tooth). There are various types of teeth used though for mastication:
- Incisors clipping or cutting
- Canines tearing or slashing
- Molars crushing, mashing, or grinding
- Wisdom Teeth additional set of molars that develop later on
After the food is chewed up, and moistened, it forms a ball, which is called a bolus. The bolus is then pushed back towards the pharynx with the tongue. The uvula moves backwards, blocking the nasal cavity, and the epiglottis folds down, blocking the trachea. All passageways except to the esophagus are blocked.
The Esophagus
The bolus moves through the esophagus by a series of smooth muscle contractions called peristalsis. The bolus eventually enters the stomach through the cardiac sphincter.
The Stomach
The stomach contains various regions: cardiac, fundus, body, and pyloric. The cardiac is the region closest to the esophogus and heart. The fundus is the superior bulge in the stomach, and under it is the body, which is the middle section. The last section, the pyloric section, is the inferior region closest to the small intestine. The stomach contains rugae, which are the internal folds that increase the surface area for digestion. The lining of the stomach is simple columnar epithelium. The stomach contains the cardiac sphincter, which is a ring of smooth muscles that allow for food to enter the stomach, but not leave. When food enters the stomach, gastrin is stimulated and causes the stomach glands to produce this. Pepsiongen is an inactive enzyme produced by chief cells, which converts to pepsin, which breaks down proteins into amino acids. Mucus is also contained in the stomach, which protects the stomach from being digestion or dissolved. Hydrochloric acid also lowers the pH level of the stomach contents, activating pepsin. This is produced by parietal cells. No absorption, however, occurs in the stomach except for aspirin and alcohol. Food is then turned into chyme, which is partielly digested food. The chyme then goes through the pyloric sphincter, which releases chyme into the small intestine 30 mL at a time.
Small Intestine
The duodenum is the place where the most digestion occurs. Most hormones are secreted from the pancreas and the liver are sent to the duodenum. Bicarbonate is released and neutralizes the stomach acid, stopping the action of pepsin. Pancreatic amylase converts starch to maltose, lipase converts lipids to fatty acids, nuclease converts DNA and RNA to nucleotides, and trypsin converts proteins into amino acids. The liver, however, releases bile, which separates fats into smaller droplets to increase the rate of digestion by lipase.
Food is moved through the Jejunum and Ileum by peristalsis, and absorption occurs here. Villi are present in all the cells along the intestines to absorb, and active transport moves the nutrients across membranes. Substances are then transported to the liver by the peptic portal vein.
Food is moved through the Jejunum and Ileum by peristalsis, and absorption occurs here. Villi are present in all the cells along the intestines to absorb, and active transport moves the nutrients across membranes. Substances are then transported to the liver by the peptic portal vein.
Large Intestine
The large intestine contains the cecum, with the appendix attached, as well as the ascending, transverse, and descending colons. It then ends with the rectum. No digestive enzymes are present here. E. Coli resides in the large intestine to digest some of the remaining nutrients, producing vitamins K, B and some gases. Water and vitamins are absorbed here. The remaining material is eliminated as feces. This includes undigested food residue, mucus, bacteria, and water. There are two different defecation reflexes used. First, the internal anal sphincter is the involuntary smooth muscle and must be relaxed. The external anal sphincter is the voluntary muscle that must be relaxed before defecation can actually occur.
Working with Other Body Systems
- The endocrine system sends signals to tell the system how much it should digest.
- The muscular system allows for the muscles to contract in order to stimulate peristalsis.
- Fats are stored in the skeletal system if there is an excess digested.