Digestive System S.1.4

· The digestive system involves a series of process that break down the food we eat into structures that can delivered and then used by the cells. - Food is first ingested into the mouth chewed, and then swallowed. - Food is then digested through mechanical digestion, the physical breakdown of food through chewing and mixing movements in the stomach.

- Chemical digestion breaks food down further through the use of enzymes so that the nutrients can be absorbed. - The absorption process transports the digested food through the intestine into the circulatory system. - Lastly, undigested food is eliminated.

- The digested material then passes into the cecum and into large intestine or colon. The vermiform appendix projects from cecum, which is located at the junction of the small and large intestines. BOOK

A lot of water and nutrients are absorbed in the small intestine, and the large intestine absorbs remaining water and salt from digested food. The waste of bacterial fermentation in the colon. Vitamin K is absorbed in the large intestine. The waste accumulates in the rectum and is ejected through the anus.

- The gastrointestinal system starts at the mouth and ends at the anus. BOOK

Appreciating regional specialization is the key to understanding the structure and function of the gastrointestinal system. After food is ingested, mechanical digestion by chewing and grinding in the mouth increases surface area by breaking it down to smaller pieces

3.) Fill in the table below with the names of the structure, hormone or enzyme that matches the characteristics.

Carbohydrates- digesting enzyme produced by salivary glands. Salivary gland Zymogen form of protease produced by the stomach Pepsinogen Cells that produce acid in the stomach Parietal cells Valve through which chyme passes from stomach to duodenum Pyloric sphincter Hormone produced by stomach induces stomach secretion Gastrin Hormone that induces bile and pancreatic juice secretion Cholecystokinin Second section of small intestine where majority of absorption occurs. Jejunum Blood vessel that carries nutrients directly from small intestine to liver. Hepatic portal vein Substance mainly absorbed from waste in large intestine. Water

- Mucus in salvia lubricates the food. Salvia also provides amylase and lipase to intimate chemical digestion of starch and lipids. BOOK

Food then is packaged into small parcels called "Bolus" and swallowed (deglutition). As it passes through the pharynx, the epiglottis closes the tracheal opening, and the food passes into the esophagus.

- Hormones regulate many aspects of nutrition. Ghrelin induces hunger, and leptin causes the sensation of satiety. BOOK

Hormones induce secretions and speed up the movement of food through the small intestine. Insulin induces cellular uptake of glucose, and glucagon stimulates breakdown of stored glycogen. Other hormones and nerve function modulate digestive action.

Organ: Mouth Enzymes: Salivary amylase, salivary lipase Major hormones: None Organ: Stomach Enzymes: Gastric Lipase, pepsin(ogen), HCI Major hormones: Gastrin, Ghrelin Organ: Liver Enzymes: Bile (stored in gallbladder) Major Hormone: None

Organ: pancreas Enzymes: Pancreatic juice (bicarbonate, lipase, trypsin(ogen), proteases and amylase) Major hormones: Secretin, somatostatin, insulin, glucagon Organ: Small intestine Enzyme: Brush border enzymes (proteases, lactase, disaccharidases) Major hormones: Cholecystokinin, somatostatin, secretin, motilin Organ: Large intestine Enzymes: None Major hormones: None

· Digestive tract, or gastrointestinal (GI) Tract, is about eight to nine meters long and begins with the mouth, where food enters, and ends at the anus, where waste is eliminated. In between, the GI tract is made up of various organs through which food passes and is broken down.

The sequence of the GI tract includes the mouth, throat, esophagus, stomach, small intestine, large intestine. Most digestion take place in small intestine.

1.) Which of the following physiological response follows eating a large meal? a. Pulse rate increases b. Peristalsis rate increases** c. Enzyme production decreases d. Parasympathetic nervous activity decreases

b. Peristalsis rate increases**

2.) Which of the following describes why liver failure is a critical health emergency? a. The liver produces the majority of digestive enzymes b. Food is filtered through the liver before digestion takes place c. The liver helps digested food products to be pumped around the body d. The liver filters digestion products and produces urea as wastes.**

d. The liver filters digestion products and produces urea as wastes.**

- Peristalsis moves the bolus down to the stomach through the BOOK

gastric sphincter, which prevents reflux of food back in the esophagus.

- Chemical digestion of protein is initiated in the stomach by action of the enzyme pepsin, which is activated by acid and autocatalysis. There are three main secretions of the stomach: BOOK

pepsinogen (chief cells), mucus (goblet cells), and hydrochloric acid (parietal cells). Following the digestion in the stomach, the contents (now called chyme) pass through the pyloric sphincter into the duodenum, which is the first part of the small intestine.

· Hormones play a vital in digestion as well. They cause the secretions necessary for digestion. They stimulate muscle contraction and relaxation to move digested matter through the small intestine. They regulate to flow of water and electrolytes between the digestive system and the bloodstream and they increase blood flow for the absorption of nutrients. Specific hormones perform other functions as well. - For examples, the hormones ghrelin stimulates appetite, leptin inhibits hunger, insulin causes the storage of glucose, and glucagon stimulates the breakdown of stored glycogen. Without hormones, the system cannot function.

· Other vital organs necessary of the digestion and absorption of food are the pancreas and liver. The pancreas secretes pancreatic juice, which helps to break down fasts into useful nutrients for the body. The liver produces bile, which is important in the digestion of fats. The bile is stored in the gallbladder until it is needed.

- Anus: the opening of the rectum from which solid waste is expelled - Bolus: A mass of food that has been chewed and swallowed - Chyme: The semifluid mass of partly digested food that moves from stomach to the small intestine - Enzymatic digestion: The breakdown of food by enzymes for absorption - Gallbladder: The organ that stores bile - Large intestine: Also known as the colon, where vitamins and water area absorbed before feces is stored prior to elimination - Liver: The organs that produces bile, regulated glycogen storage, and performs other bodily function - Mouth: The oral cavity at the entry to the alimentary canal - Pancreas: The gland of the digestive system and endocrine systems that produces insulin and secretes pancreatic juices.

- Peristalsis: A series of muscle contractions that move food through the digestive tract. - Rectum: The last section of the large intestine, ending with the anus. - Saliva: The clear liquid found in the mouth, also known as spit - Small intestine: The part of the GI tract between the stomach and large intestine that includes the duodenum, jejunum, and ileum, where digestion and absorption of food occurs. - Stomach: The organ between the esophagus and small intestine in which the major portion of digestion occurs.

The process of digestion is another complex series of events. · The process of digestion begins in the mouth, where the salivary glands secrete saliva as food is chewed and broken down. Enzymes such as lipase and amylase in the salvia begin chemical digestion of lipids and starches. · Swallowed food mixed with saliva (bolus) then moves through the esophagus and into the stomach. The gastric sphincter prevents the reflux of food back into the esophagus. The enzyme pepsin initiates chemical digestion the stomach.

Secretions in the stomach further help the food to digest. · Once the food is digested in the stomach, the product is called chyme (acidic fluid that passes from the stomach to the small intestines) and it passes through pyloric sphincter into the duodenum, the first part of the small intestine. · Absorption of nutrients occurs primarily in the small intestine, where the gallbladder secretes bile made in the liver, and the pancreas secretes additional enzymes essential to digestion. · The digested material then passes into the cecum and then into the large intestine. The large intestine preforms the role of absorbing water, vitamin K, and salt from digested food matter and creating wastes through bacterial fermentation in the colon. These wastes then pass through the body via the rectum and the anus.

- From the small intestine, blood carrying nutrients passes to the liver through the hepatic portal duct, allowing the liver enzymes to deaminate amino acids, convert ammonia to urea, metabolize consumed toxins, and store glucose as glycogen. BOOK

The digested material then passes into the cecum and into large intestine or colon.

- In the duodenum, chyme is neutralized by bicarbonate in pancreatic secretions. BOOK

The duodenum receives alkaline bile juices from the gallbladder, which helps neutralize acid chyme. In addition, the duodenum produces a large number "brush border" enzymes, including proteases, lactase and other disaccharidases, and bicarbonate. Villi and Microvilli in the small intestine (largely the ileum) absorb polar digested nutrients into blood, lipids into lacteals as chylomicrons, and vitamin B12.