Chapter 22 Digestive
Describe the alimentary canal with its accessory organs:
The organs of the digestive system can be grouped into: 1.) alimentary canal 2.) accessory organs
The alimentary canal (gastrointestinal tract ‑ G.I.) is a continuous, coiled, hollow, muscular tube that winds through the ventral body and is open Cal both ends. It digests food and absorbs the fragments through its lining into the blood.
Organs include: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
Accessory digestive organs include: teeth, tongue, gallbladder, salivary glands, liver, pancreas. The accessory digestive glands produce saliva, bile, and enzymes.
What is the role of the gall bladder?
The gallbladder is a small storage organ located inferior and posterior to the liver. Though small in size, the gallbladder plays an important role in our digestion of food. The gallbladder holds bile produced in the liver until it is needed for digesting fatty foods in the duodenum of the small intestine. Bile in the gallbladder may crystallize and form gallstones, which can become painful and potentially life threatening.
What is the role of the liver in digestion?
its main function within the digestive system is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. In addition, the liver is the body’s chemical "factory." It takes the raw materials absorbed by the intestine and makes all the various chemicals the body needs to function. The liver also detoxifies potentially harmful chemicals. It breaks down and secretes many drugs.
What is the role of the pancreas in digestion?
The pancreas secretes digestive enzymes into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolizing sugar.
What is deglutition?
The action or process of swallowing. Its a complicated process that involves 22 separate muscle groups. It has 2 major phases: 1.) the buccal phase (occurs in mouth & is voluntary) 2.) The pharyngeal-esophageal phase (involuntary)
How much fluid enters the digestive tract each day and where does it come from?
About 9 liters of fluid pass through the GI system each day, and only about 2 liters are ingested, the rest represent secretions from the system itself. About half, 3.5, liters is secreted from the exocrine glands, the salivary glands, the pancreas and the liver, the other half is secreted by the epithelial cells of the of the digestive tract it self.
What are the major functions of the digestive tract?
1.) Ingestion 2.) Propulsion 3.) Mechanical breakdown 4.) Digestion 5.) Absorption 6.) Defecation
Describe what happens to a cheeseburger as it passes through the digestive system:
1.) Ingestion: taking food into the mouth
2.) Propulsion: includes swallowing (voluntary) and then peristalsis (involuntary process) which involves alternating waves of contraction and relaxation of muscle in the organ walls.
3.) Mechanical breakdown: chewing, mixing food with saliva by the tongue, churning food in the stomach and segmentation. Segmentation mixes food with digestive juices and makes absorption more efficient.
4.) Digestion: a series of catabolic steps in which enzymes secreted into the lumen of the alimentary canal breakdown complex food molecules
5.) Absorption: is the passage of digested end products from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph.
6.) Defecation: Large intestine eliminates indigestible substances from the body via the anus
which components of the cheeseburger are digested in which regions of the digestive systems?
Some absorption occurs in the duodenum, but the majority takes place in the other two sections of the small intestine: the jejunum and the ileum.
As the food travels down the gut, the smaller molecules are absorbed through the lining of the intestine and into the circulatory system (for carbohydrates and proteins) or into the lymphatic system (for fats). By the time the food makes its way through the 20+ feet of small intestine, almost all of the nutrients have been absorbed and all that you have left is undigestible material (such as fiber) and bile salts.
Describe the enzymes that breakdown the components of the cheeseburger?
In the mouth, salivary amylase in saliva begins chemical breakdown of starch.
In the stomach pepsin beings to breakdown proteins.
Additionally, lingual lipase is released by the minor salivary glands to digest some triglycerides in the stomach.
In the small intestine enzymes from pancreas and brush border enzymes attached to microvilli membranes complete digestion of all classes of foods.
How are the digested components of the cheeseburger absorbed by the digestive tract?
Stomach: absorbs a few fat-soluble substances (aspirin, alcohol, some drugs)
Small Intestine: breakdown products of carbs, proteins, fat and nucleic acid digestion plus vitamins, electrolytes, and water are absorbed by active and passive mechanisms.
Large Intestine: absorbs most remaining water, electrolytes (largely NaCl), and vitamins produced by bacteria.
Describe how fats, carbohydrates and proteins are digested and absorbed?
Proteins: The chemical side of digestion for proteins starts in the stomach where enzymes such as pepsin begin to break the proteins down into tinnier sections of amino acids.
Carbs- Digestion for carbs begins in the mouth with the secretion of saliva from the salivary glands which breaks down complex sugars like starch into simple sugars like glucose. not much occurs enzyme wise in the stomach for carbs. next the they reach the small intestine where the pancreas secretes a slurry of enzymes simply referred to as the pancreatic juices but the main one that deals with carbs is carboxypeptidase. Also in the intestinal enzymes of the alkaline mucosal membranes in the small intestine help to digest carbs. These enzymes include: maltase, lactase and sucrase. All of the breaking down forms simple sugars that can easily diffuse into the blood stream or by products like the indigestible carb cellulose which is the fiber in your diet
Fats- Bile emulsification to small fat droplets
Enzymes: lipases, colipases & phospholipases
Triglycerides monoglycerides & free fatty acids
How are glucose and amino acids transported across the mucosa?
Carb Absorption: The Na+K+ pump stores energy that drives glucose and galactose uptake by creating a steep concentration gradient for Na+ entry into intestinal cells. As Na+ moves across the membrane through a membrane co-transporter protein, it drives glucose against its concentration gradient into the cells.
**Fructose enters the cell by facilitated diffusion.
**Monosaccharides exit across membrane via facilitated diffusion on the GLUT2 sugar transporter.
Amino Acids: Proteins are digested to amino acids. The amino acids are then absorbed by active transport into the absorptive cells and move their opposite side. The amino acids leave the epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts.
How many teeth do humans have?
most adults have 32 teeth. Among these teeth are 8 incisors, 4 canines, 8 premolars, and 12 molars (including 4 wisdom teeth).
What happens to nucleic acids in the digestive tract?
Absorption: active transport via membrane carriers
Absorbed in villi and transported to liver via hepatic portal vein
Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestines
Describe the roles of teeth in the mechanical breakdown of food
Masticate or chew by opening and closing our jaws, moving them from side to side while using our tongue to move the food between our teeth. In the process our teeth tear and grind the food, physically breaking it down into smaller fragments.
Describe the role of the stomach in the mechanical breakdown of food
Further degrades food both physically and chemically. HCl produced by the stomach glands chemically breaks down proteins and food is converted into a creamy paste called chyme thats delivered to the small intestine. PEPSIN being the most important protein-digesting enzyme produced by the gastric mucosa.
The only stomach function essential to life is the secretion of Intrinsic factor which is required for intestinal absorption of B12... needed to produce red blood cells.
Describe the role of the small intestine in the mechanical breakdown of food
As chyme slowly enters the duodenum, Carbohydrates and proteins are only partially digested. No fat digestion has taken place.
Duodenum: is a segment of intestine between the stomach and the jejunum that is very active in digestion where many different enzymes mix from the stomach, liver, gallbladderand pancreas.
Jejunum: The mucous membrane on the inner surface of the jejunum is covered with hair-like projections termed villi. These are instrumental in the absorption of nutrients such as proteins, carbohydrates, amino acid, sugar, fatty acid particles, vitamins, minerals, electrolytes and water. It is interesting to note that the villi in the jejunum are longer than those in the duodenum and the ileum. The surface are of the jejunum is also increased due to large circular folds called plicae circulares present in the submucosa.
Ileum: absorbs mainly vitamin B12, other water soluble vitamins, bile salts, and nutrients that were not absorbed in the jejunum. More specifically, the absorption of the vitamins takes place at the terminal ileum – the last part of the ileum. Removal of this portion of the ileum will necessitate supplementary vitamin B12 doses for rest of the life.
Describe the role of the large intestine in the mechanical breakdown of food
No further food breakdown occurs in the large intestine. The large intestine harvests vitamins made by the bacterial flora and reclaims most of the remaining water and some of the electrolytes (Na+ and chloride)
*Major function are propulsive activities that force fecal material toward the anus and eliminate it from the body.
Describe the swallowing reflex Buccal Phase:
Occurs in the mouth and is voluntary. We place the tip of the tongue against the hard palate and then contract the tongue to force the bolus into the oropharynx.
Describe the swallowing reflex Pharyngeal Esophageal Phase:
Involuntary. Once food enter the pharynx all routes except the desired one are closed off. Wavelike peristaltic contracts create pressure waves that propel food through the pharynx and into the esophagus. Solid foods pass from the oropharynx to the stomach in about 8 seconds.
What are deciduous teeth?
baby teeth, temporary teeth and now more commonly primary teeth, are the first set of teeth in the growth development of humans and other diphyodont mammals.
Consider the following dental formula: 2I, 1C, 2PM, 3M
Primary: 2I (incisors), 1C (canine), 2M (molars)
Permanent: 2I, 1C, 2PM (premolars), 3M
Hormones produced by the stomach