The Gastrointestinal System
The Gastrointestinal System
The following video will provide a review on the Gastrointestinal System.
Anatomy of the Digestive System
This lesson introduces the structures and functions of the digestive system.
The following are the functions of the digestive system:
- Take in food.
- Break down food.
- Absorb digested molecules.
- Provide nutrients.
- Eliminate wastes.
The digestive system consists of the digestive tract, which is a tube extending from the mouth to the anus, and the associated organs, which secrete fluids into the digestive tract. The term gastrointestinal tract technically refers to only the stomach and intestines.
The Path of Food
Food takes the path outlined below as it moves through the body.
The oral cavity, or the mouth, is the first part of the digestive system. It is bounded by the lips and cheeks and contains the teeth and tongue. Its primary function is to masticate, or chew, and moisten the food.
The pharynx, or throat, connects the mouth to the esophagus.
Gastrointestinal System Anatomy
Stomach Diagram
The esophagus is a muscular tube about 25 centimeters long. Food travels down it to the cardiac sphincter of the stomach.
The stomach is an enlarged segment of the digestive tract.
The opening of the stomach is the cardiac sphincter.
The muscular layer of the stomach is different from other regions because it has folds called rugae that increase the surface area.
The exit of the stomach is the pyloric sphincter.
The small intestine is about 6 meters long and consists of three parts: duodenum, jejunum, and ileum.
- The duodenum has more villi (finger-like projections), has a larger diameter, and is thicker than the other two parts.
- This increases the surface area in the duodenum, which allows for more absorption of nutrients.
- The small intestine is the primary site for diffusion of nutrients into the blood.
The large intestine consists of the cecum, colon, rectum, and anal canal. The cecum is located where the small and large intestine meet.
- The colon is about 1.5 to 1.8 meters long and consists of four parts: the ascending, transverse, descending, and sigmoid colon.
- The primary function of the large intestine is to compress the waste and collect any excess water that can be recycled.
Accessory Organs
Accessory organs contribute to the process of digestion. Food does not pass through these organs, but they play critical roles in the digestion of food. The accessory organs are listed below.
The liver weighs about 1.36 kilograms and is located in the upper-right quadrant of the abdomen. It is divided into two major lobes: the right lobe and left lobe. The liver has multiple functions:
- Digestion: Bile salts emulsify and help break down fats into fatty acids and glycerol.
- Excretion: Bile contains excretory products from the hemoglobin breakdown.
- Nutrient storage: The liver removes sugar from the blood and stores fats, vitamins, copper, and iron.
- Nutrient conversion: The liver converts some nutrients into others. For example, it coverts amino acids to lipids or glucose.
- Detoxification of harmful chemicals: The liver removes ammonia from the blood and converts it to urea.
- Synthesis of new molecules: The liver synthesizes new blood proteins such as albumins and fibrinogens.
The pancreas is a complex organ composed of both endocrine and exocrine tissues that perform several functions:
- It secretes bicarbonate ions, which neutralize acids.
- It secretes digestive enzymes that are important to all classes of foods.
- It produces insulin and glucagon, which regulate blood sugar levels.
The gallbladder, nestled under the liver, stores concentrated bile.
The tongue is a large, muscular organ that occupies most of the oral cavity. It moves food in the mouth and, in cooperation with the lips and cheeks, holds the food in place during mastication.
Saliva keeps the oral cavity moist and begins the process of chemical digestion with the enzyme amylase. There are three pairs of salivary glands:
- Parotid (largest, located in front of the ears)
- Submandibular (located below the mandible)
- Sublingual (smallest, located in the bottom of oral cavity)
These glands produce saliva, which is a mixture of serous (watery) and mucus fluids that contain digestive enzymes.
Digestion
Digestion is the breakdown of food into molecules that are small enough to be absorbed into the bloodstream. There are two types of digestion: mechanical and chemical. Mechanical digestion breaks down large food particles into smaller ones and is evident as a person’s teeth grind food into smaller pieces. During chemical digestion, digestive enzymes break covalent chemical bonds into organic molecules.
Carbohydrates are broken down into monosaccharides, proteins are broken down into amino acids, and fats or lipids are broken down into fatty acids and glycerol. Monosaccharides, amino acids, fatty acids, and glycerol molecules are small enough to diffuse across the membranes of the digestive system and enter the bloodstream, to be taken where they are needed.
Absorption begins in the stomach, where small, lipid-soluble molecules, such as alcohol and aspirin, can pass through the stomach epithelium into circulation. Most absorption occurs in the duodenum and jejunum, although some occurs in the ileum. Some molecules can diffuse through the intestinal wall. Others must be transported across the intestinal wall. Transport requires a carrier molecule. If the transport is active, energy is required to move the transported molecule across the intestinal wall.
Enzymes:
Most enzymes are recognizable by the -ase ending. Here are some of the most common enzymes:
- Amylase is produced in the mouth and breaks down carbohydrates.
- Pepsin is produced in the stomach and breaks down proteins.
- Lipase is produced in the pancreas and secreted into the small intestine to break down lipids.
- Peptidase is produced in the pancreas and secreted into the small intestine to break down peptides into amino acids.
- Sucrase is produced in the small intestine and breaks down sucrose into glucose.
- Lactase is produced in the small intestine and breaks down lactose into glucose.
Disorders of the Digestive System
The following are disorders of the digestive system.
Stomach:
- Vomiting results primarily from irritation of the stomach and small intestine. After the vomiting center has been stimulated, a sequence of events occurs that result in vomiting.
- Ulcers occur from a specific bacterium, Helicobacter pylori. Ulcers were previously thought to be caused by stress, but they can be treated successfully with antibiotics.
- Peptic ulcers is a condition in which the stomach acids digest the mucus lining of the duodenum. These ulcers are sometimes called duodenal ulcers. People who experience a great deal of stress tend to secrete as much as 15 percent more HCl than normal, which causes the chyme, semifluid food mass, to be highly acidic. There are not enough sodium bicarbonate ions to neutralize the acidic chyme, and it eats away at the mucus lining, causing ulcers.
Liver:
- Cirrhosis is a disease characterized by damage or death of liver cells, which are replaced by connective tissue. This causes abnormal blood flow in the liver and interferes with normal liver functions.
- Hepatitis is an inflammation of the liver. Liver cells can die and be replaced with scar tissue.
Intestine:
- Irritable bowel disease is the general term for Crohn’s disease or ulcerative colitis.
- Crohn’s disease includes a localized inflammatory degeneration that causes the wall of the small intestine to thicken. This disease causes diarrhea, abdominal pain, and weight loss.
- Ulcerative colitis is limited to the mucosa of the large intestine. The involved mucosa exhibits inflammation, including edema, vascular congestion, and hemorrhaging.
- Irritable bowel syndrome (IBS) is a disorder of unknown cause in which intestinal mobility is abnormal. Patients exhibit pain in the left lower quadrant, especially after eating, and have alternating bouts of diarrhea and constipation.
Use the diagram to identify the main organs affected by the described disorders.
- Malabsorption syndrome is a spectrum of disorders of the small intestine that result in abnormal nutrient absorption.
- Appendicitis is an inflammation of the appendix that usually occurs because of an obstruction.
Let’s Review
- The digestive system consists of the digestive tract, which is a tube extending from the mouth to the anus, and accessory organs.
- Accessory organs contribute to the process of digestion.
- Food does not pass through the accessory organs.
- Digestion is the breakdown of food into molecules that are small enough to be absorbed into the bloodstream.
- The two types of digestion are mechanical and chemical.
Gastrointestinal System Flashcards
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