2021-Physiology-Digestive System notes PDF

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2021-Physiology-Digestive System notes...

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Intermediate Physiology Digestive System Lab 3 Pre-Worksheet Label the following: A. B. C. D. E. F. G. H. I. J. K. L.

The Mechanical and Chemical Events of Digestion Mechanical digestion is a physical process that increases the surface area of ingested food and prepares it for chemical digestion by enzymes. The chewing of food in the mouth and the churning of food in the stomach are examples of the mechanical breakdown of food. Chemical digestion, by contrast, involves the action of hydrolytic enzymes that chemically break macromolecules (carbohydrates, proteins, lipids, and nucleic acids) into their building blocks.

Digestive Processes The digestive system performs six basic processes. Describe the following and state which organ is primarily responsible for each process: Note: One organ may perform multiple functions. Ingestion

Secretion

Motility

Digestion

Absorption

Defecation

The Stomach The stomach is a highly muscular organ that is located in the upper left quadrant of the abdominal cavity, under the diaphragm. This organ uses hydrochloric acid and enzymes to digest food, creating a fairly harsh environment, and its mucosa is quite thick to prevent autodigestion. When the stomach is full it is said to be distended or flexed, however, when it is empty structures called rugae form in the lining of the stomach. Rugae are simply folds found within the stomach when it is not fully distended. One of the major processes that begins in the esophagus and continues into the stomach is peristalsis. Peristalsis is the rhythmic contraction of smooth muscle that propels food toward the stomach from the esophagus, and once in the stomach, peristalsis continues and churns the food into the duodenum of the small intestines. This churning of the food is under autonomic control and is continuously being done by the smooth muscle lining the esophagus and stomach. The churning aids in the digestion of the bolus in the stomach, as well as the movement of the bolus.

In the figures above you can see the peristalsis occurring within the esophagus as well as the stomach and the rugae. 1. What is peristalsis and in which organs does it primarily occur? Be specific.

2. Why does the stomach need to have a thick mucusa layer? What role does it play?

3. What is rugae and under which conditions is the rugae present in the stomach?

Breakdown In The Digestive Tract Match each word with its corresponding sentence. Word Bank Bicarbonate-rich Fluid

HCl

Mucus

Bile

Hormonal Stimulus

Pepsin

Brush border enzymes

Lipases

Psychological stimulus

Chewing

Mechanical stimulus

Churning

Mouth

Salivary Amylase

1. Starch digestion begins in the mouth when ________ is ducted in by the salivary glands. 2. Gastrin, which prods the stomach glands to produce more enzymes and HCl represents a _________.

3. The fact that the mere thought of a relished food can make your mouth water is an example of ___________. 4. Many people chew gum to increase saliva formation when their mouth is dry. This type of stimulus is a ___________. 5. Protein foods are largely acted on in the stomach by ____________. 6. For the stomach protein-digesting enzymes to become active, ____________ is needed. 7. Since living cells of the stomach (and everywhere) are largely protein, it is amazing that they are not digested by the activity of stomach enzymes. The most important means of stomach protection is the ____________ it produces. 8. The third layer of smooth muscle found in the stomach wall allows mixing and mechanical breakdown by _______________. 9. Important intestinal enzymes are the _______________. 10. The small intestine is protected from the corrosive action of hydrochloric acid in chyme by ____________, which is ducted in the pancreas. 11. The pancreas produces protein-digesting enzymes, amylase, and nucleases. It is the only important source of ______________. 12. A nonenzyme substance that causes fat to be dispersed into smaller globules is _____________.

The Small and Large Intestines The small intestines are composed of three major parts: The duodenum, jejunum, and ileum. The duodenum is the first section of the small intestine and it is primarily involved in chemical digestion. It contains disaccharidases and peptidases that break down disaccharides and peptides, respectively. It also works hand-in-hand with secretin and cholecystokinin (CCK), both of which are hormones that aid in digestion. Secretin stimulates the release of pancreatic juices into the digestive tract, it also causes the liver to increase its production of bile. CCK stimulates the release of bile from the gallbladder as well as pancreatic juices. The jejunum and ileum mostly function in absorption. They are lined with villi, which increase the surface area available for absorption. The large intestine absorbs excess water and salts, forming semi solid feces. It consists of the cecum, colon, and rectum. All three have similar functions, but it is important to note that it is in the rectum where the feces is stored and it is excreted via the anus.

1. Describe the flow of food (chyme) through the small intestines. Be specific as to what occurs at each subunit. 2. Label the following structures on the image below and give a brief description of their function.

● ● ● ●

Cecum Colon Rectum Anus

Protein and Fat Digestion Protein digestion begins in the stomach. The gastric mucosa contains cells that secrete both hydrochloric acid (HCl) and pepsinogen. Pepsinogen reacts with the HCl to become its active form, pepsin. Pepsin hydrolyzes proteins into large polypeptides, which then enter the small intestine. The pancreatic enzymes trypsin and chymotrypsin chemically break down the large polypeptides to smaller polypeptides and peptides. Finally, brush border enzymes such as aminopeptidase and dipeptidase cleave the peptides to release the final products: small oligopeptides and amino acids.

Lipids include triglycerides, steroids, and phospholipids, in addition to other lipoid substances. Triglycerides, also called neutral fats, are the most abundant dietary lipids. Lipids are difficult to chemically digest because they are hydrophobic and thus tend to aggregate in large spherical droplets within the aqueous fluid in the digestive tract. The formation of droplets greatly reduces the surface area of lipid on which the water-soluble lipases (fat-digesting enzymes) can act, because the enzymes can contact lipid molecules only on the outer surface of the droplets. For the digestion of triglycerides to occur efficiently, large fat droplets in the stomach must first be separated by stomach churning (peristalsis) and gastric lipases into smaller fat globules. Most digestion of triglycerides occurs in the small intestine. When chyme entering the duodenum contains fat, intestinal cells there release the hormone cholecystokinin (CCK), which stimulates the gallbladder to contract and release bile (which contains bile salts). When bile arrives in the small intestine, the bile salts emulsify the fat droplets into still smaller fat droplets, enabling pancreatic lipase to hydrolyze fats into their building blocks: free fatty acids and glycerol. Bile salts remain associated with the digested fats to form small spheres of lipids called micelles.

Hormones Word choices can be used more than once: A. Cholecystokinin (CCK) B. Gastrin C. Secretin _____________1. These two hormones stimulate the pancreas to release its secretions. _____________2. This hormone stimulates increased production of gastric juice. _____________3. This hormone causes the gallbladder to release stored bile. _____________4. This hormone causes the liver to increase its output of bile....