Module 13: The Digestive System Flashcards
Mastication
The process of chewing.
Describe the physical changes food goes through in the body.
- Mastication breaks food down into smaller, more manageable chunks.
- The stomach churns and breaks food into smaller pieces.
- Food dissolves in the fluids of the digestive system, which separates molecules from each other.
Digestion
The breakdown of food molecules into their individual components.
Why must food be chemically broken down into smaller components?
The body cannot absorb food molecules through physical changes because they are still too big, so it must undergo further separation through digestion.
What do proteins break down into?
They break down into individual amino acids.
What do carbohydrates break down into?
Most of the carbohydrates you eat are disaccharides or polysaccharides, and these must be broken down into monosaccharides (simple sugars).
What do fats break down into?
Fats break down into their constituent fatty acid molecules.
What are the two parts of the digestive system?
The alimentary canal (the canal through which food travels on its way from the mouth to the anus) and the accessory organs.
What is the role of the stomach in digestion?
The stomach churns and mixes food with digestive fluids. It temporarily stores the food, but once it has been thoroughly mixed, it sends the mixture, now called chyme, into the small intestine.
What is the role of the small intestine in digestion?
In the small intestine, the food molecules are digested, and most of the nutrients are absorbed into the bloodstream through its lining.
What is the role of the liver in digestion?
The liver stores nutrients, makes proteins for the blood such as fibrinogen and prothrombin, cleanses the blood of toxins and wastes, and produces a fluid called bile, which aids in the mechanical digestion of fats.
What is the role of the gallbladder in digestion?
The gallbladder concentrates and stores bile from the liver. It releases this concentrated bile into the small intestine, where it aids in the digestion of fats coming from the stomach.
What is the role of the pancreas in digestion?
The pancreas produces its own digestive juice, which is released into the small intestine to aid in the digestion of the food molecules.
What is a possible role of the vermiform appendix in digestion?
It may be responsible for housing good bacteria, and if the biofilms are shed in the intestines, the good bacteria could emerge from the appendix and repopulate the lining of the intestine before more harmful bacteria could take hold.
Biofilm
A delicate layer of beneficial microbes, mucus, and immune system molecules exist on what are known as biofilms in the intestines and appendix.
What are the components of saliva?
Water (about 99%), mucus, amylase, lysozyme, and antibodies.
What is the purpose of saliva?
Saliva dissolves food. Also, it is essential to the sense of taste. In order for the taste buds to function, the food you are eating must be dissolved in the the saliva so it can enter the taste pore of the taste bud.
What is the role of mucus in saliva?
The mucus provides for lubrication so the food can travel more easily down the alimentary canal.
What is the role of amylase in saliva?
Amylase is a digestive enzyme that helps to break down starch into maltose, which is a disaccharide.
Name the three major pairs of salivary glands.
The parotid salivary glands, the sublingual salivary glands, and the submandibular salivary glands.
Bolus
A soft lump of food that has been chewed.
Deglutition
The act of swallowing.
To make food go down the esophagus safely, what steps steps must happen automatically?
The airway must be closed off. Therefore, when you swallow, the soft palate rises up and closes off the nasal cavity, which opens into the upper part of the pharynx. At the same time, the larynx rises and the epiglottis drops, sealing off the larynx so that food cannot travel down into the trachea.
What are the three stages of deglutition?
The voluntary oral stage, the pharyngeal stage, and the esophageal stage.
Summarize the voluntary oral stage of deglutition.
The bolus is pushed toward the back of the mouth by the tongue. As the bolus reaches the pharynx, the pharyngeal stage begins.
Summarize the pharyngeal stage of deglutition.
The soft palate lifts up and blocks the nasal cavity. At the same time, the larynx lifts up to meet the epiglottis, closing off the larynx and trachea below ti. The vocal folds also move together to form a tight seal in the trachea. Then, the pharyngeal muscles constrict to push the bolus toward the esophagus.
Summarize the esophageal stage of deglutition.
Rings of muscle contract and relax to push the bolus down the esophagus. This process is called peristalsis.
Peristalsis
The process of contraction and relaxation of circular smooth muscle that pushes food through the alimentary canal.
How is peristalsis controlled?
The reflex is initiated by the bolus. The pressure of the bolus at the pharynx sends a message to the pons and medulla oblongata.
What are the two main functions of the stomach?
It acts as a storage chamber and can expand considerably without much increase in pressure, and it acidifies the food entering it.
What two things does acidifying the food in the stomach do?
First, it kills most bacteria and other microorganisms that may be in the food. Second, the enzymes within the stomach that are used to digest proteins work better at an acidic pH so acidifying the food enhances the digestion of proteins.
What are the four main regions of the stomach?
The cardiac region, the fundus, the body, and the pylorus.
Visceral peritoneum (the serosa)
The outer layer of the stomach made of a thin layer of connective tissue and a thin layer of simple squamous epithelium.
What three layers of smooth muscle make up the muscularis?
The longitudinal muscularis, the circular muscularis, and the oblique muscularis.
The submucosa
A layer of connective tissue that contains blood vessels and nerves that loosely binds the muscularis to the mucosa.
Gastric juice
The acidic secretions of the stomach.
Why doesn’t the strong acid in the stomach hurt it?
Cells near the top of the gastric pits secrete an enormous amount of mucus, so much that the gastric juice never actually touches the tissues of the stomach.
What is the acid in gastric juice called?
Hydrochloric acid (HCl).
Pepsin
An enzyme activated by the acid in gastric juice which breaks proteins down into smaller chains of amino acids called peptides.
Why do the gastric glands make pepsinogen?
This chemical, when mixed with HCl and other pepsin molecules, can be converted into pepsin. A cell cannot make active enzyme (pepsin) because it would break down its own proteins, so instead, it makes pepsinogen.
What role does intrinsic factor play in gastric juice?
Without intrinsic factor, the body could not absorb vitamin B12. IF binds to B12 in order for it to be absorbed later on by the small intestine.
Adventitia
A thin layer of loose connective tissue that binds an organ to surrounding tissues or organs.
How does the stomach make chyme?
It mixes the boluses with gastric juice to form chyme. The smooth muscle of the stomach contracts and relaxes in a rhythmic pattern to form mixing waves. These waves blend the boluses with the gastric juice to make chyme. As the liquefied food mixes with the gastric juice, it also mixes with pepsin so that the proteins can be broken down into peptides.
How is peristalsis different from mixing waves in the stomach?
Peristalsis forces the chyme down the stomach into the pylorus, but peristaltic waves are weak. The mixing waves swish the chyme back and forth in the stomach while slow, weak peristaltic waves push the chyme through the pyloric sphincter into the small intestine.
Explain the process of vomiting.
When the lining of the alimentary canal becomes irritated, action potentials travel to the medulla oblongata, which initiates the vomit reflex. The larynx elevates; the soft palate closes off the nasal cavity; the upper and lower esophageal sphincters open; and the diaphragm and abdominal muscles contract strongly. This compresses the stomach and forces the contents of it to travel back up the esophagus and out the mouth.
What does the hormone gastrin do?
Secreted by the stomach, it increases lower esophageal sphincter tone. This makes the sphincter contract more strongly and avoid having gastric juice back up into the esophagus, which causes gastroesophageal reflux, or heartburn. It also decreases the pyloric tone, which increases the rate at which the stomach empties. It increases the rate of secretion from the gastric pits and the rate of mixing waves of the stomach.
What are the three main functions of the small intestine?
- To mix and propel the chyme.
- To digest the food.
- To absorb the nutrients.
What are the three regions of the small intestine?
The duodenum, the jejunum, and the ileum.
How are the layers of the small intestine different from the stomach?
They are the same except the small intestine has no oblique muscularis and the duodenum has adventitia instead of serosa.
What is the purpose of intestinal villi?
They increase the amount of intestinal surface that comes into contact with the food, speeding up the absorption process.
Microvilli
Microscopic extensions of the cell membrane that cover the epithelial cells of the villi.
Where do fatty acids (the components of fats) go after being absorbed by the villi of the small intestine?
They do not enter the blood capillaries. Instead, lacteals carry fat-soluble nutrients to the blood by making them part of the lymph. When lymph ultimately gets returned to the bloodstream, the fat-soluble nutrients enter the circulatory system as well.
Lumen
The space in the center of a tube.
Mucous goblet cells
Exocrine glands which secrete mucus. This mucus protects the tissue of the intestine from the chyme, as well as from the digestive enzymes. These cells can be found all over the small intestine.
Why do the duodenal glands secrete an alkaline (basic) mucus?
The chyme has just come from the stomach and is very acidic. The alkaline mucus helps to neutralize the acidity of the chyme.
What secretes secretin, and where is it secreted?
The duodenum secretes secretin. Instead of being secreted into the lumen like exocrine secretions, it is secreted into the blood capillaries within the wall of the duodenum.
