Anatomy of the Digestive System:
Functions of the digestive system:
Digestive tract: tube extending from the mouth to the anus, and associated organs that secrete fluids into digestive tract
Gastrointestinal tract: stomach and intestine
The Path of Food
Oral cavity, or mouth
first part of digestive system
Bounded by lips, cheeks, teeth, and tongue
Function to masticate, chew, moisten the food
Pharynx, or throat
Esophagus
Stomach
Cardiac sphincter
Rugae
-Exit of stomach is pyloric sphincter
Small intestine
6 meters long, consists of duodenum, jejunum, and ileum
Duodenum has more villi (finger-like projections), ahs larger diameter, and is thicker than the other two parts
This increases the surface area in the duodenum, allowing for more absorptions of nutrients
Small intestine is the primary site for diffusion of nutrients into the blood
Large intestine

Accessory Organs
Liver: located in upper right quadrant of abdomen, divided into the right and left lobe, helps:
Digest: bile salts emulsify and he;p break down fats into fatty acids and glycerol
Excretion: bile contains excretory products from the hemoglobin breakdown
Nutrient storage: liver removes sugar from the blood and stores fats, vitamins, copper, and iron
Nutrient conversion: liver converts some nutrients into others
Detoxification of harmful chemicals: liver removes ammonia from the blood and converts it to urea
Synthesis of new molecules: liver synthesizes new blood proteins such as albumins and fibrinogens
Pancreas: composed of both endocrine and exocrine tissues that perform several functions
Secretes bicarbonate ions, neutralizing acids
Secretes digestive enzymes that are important to all classes of food
Produces insulin and glucagon, which regulate blood sugar levels
Gallbladder: nestled under liver, stores concentrated bile
Tongue: muscular organ that occupies most of the oral cavity, moves food in the mouth with help of lips and checks to hold the food in place during mastication
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, mixture of serous (watery) and mucus fluids that contain digestive enzymes
Digestion
Digestion: breakdown of food into molecules that are small enough to be absorbed into the bloodstream
Types of digestion:
Mechanical: breaks down large food particles into smaller ones, person’s teeth grinds food into smaller pieces
Chemical: digestive enzymes break covalent chemical bonds into organic molecules
Carbohydrates broken down to -> monosaccharides
Proteins broken down to -> amino acids
Fats/Lipids broken down to -> fatty acids and glycerol
Digestive enzymes break covalent chemical bonds into organic molecules
Monosaccharides, fatty acids, and glycerol are small enough to diffuse across membranes of the digestive system to enter the bloodstream or places where they are needed
Absorption
Begins in stomach where small lipid soluble molecules like aspirin can pass the stomach epithelium into circulation
Most absorption occurs in duodenum and jejunum, some in the ileum
Some molecules can diffuse through intestinal wall others must be transported across intestinal wall
Transport requires carrier molecule, active transport required energy to move transported molecules across intestinal wall
Enzymes
Amylase | Produced in the mouth and breaks down carbohydrates |
Pepsin | Produced in the stomach and breaks down protein |
Lipase | Produced in the pancreas and secreted into the small intestine to break down lipids |
Peptidase | Produced in the pancreas and secreted into the small intestine to break down peptides into amino acids |
Sucrase | Produced in the small intestine and breaks down sucrose into glucose |
Lactase | Produced in the small intestine and breaks down lactose into glucose |
Disorders of the Digestive System
Stomach:
Liver
Cirrhosis: disease in which there is damage or death of liver cells, which are replaced by connective tissue
Hepatitis: inflammation of the liver
Intestine
Irritable bowel disease: term for Crohn’s disease or ulcerative colitis
Irritable bowel syndrome (IBS): disorder of unknown cause causing intestinal mobility to be abnormal
Malabsorption syndrome: spectrum of disorders of the small intestine that result in abnormal nutrient absorption
Appendicitis: inflammation of the appendix usually occurs b/c of obstruction
The digestive system begins with the mouth and then proceeds throughout the abdominal cavity to the anus.
The oral cavity at the entry to the alimentary canal.

mouth |
First, food is ingested through the mouth where mechanical digestion begins.
Digestion begins in the mouth with mechanical and chemical digestion. The other organs play a role but do not start digestion. (quiz) |
Protein break down in stomach |
With the help of pepsin, protein starts to break down in the stomach. |
Small intestine | The small intestine also breaks down proteins with the secretion of trypsin from the pancreas, but this is after the food passes through the stomach. |
Large intestine | Vitamin K is absorbed in the large intestine |
Interaction with nervous system | The smooth muscle involved in mechanical digestion and movement of food through the digestive system is controlled by the parasympathetic nervous system. |
hormone and nerve | hormones and nerve function modulate digestive action. Hormones Involved in Digestion |
Digestion | both mechanical (physical) and chemical (enzymatic) digestion. |
Digestive system Function | to break down food for absorption and distribution of nutrients to the rest of the body.
function of the digestive system organs, as well as the secreted enzymes and hormones that control digestion. |
Cardiac sphincter | The esophageal (cardiac) sphincter prevents reflux of food back into the esophagus. |
Peristalsis | A series of muscle contractions that move food through the digestive tract called peristalsis
Muscle contractions that move food through the digestive tract.
Peristalsis refers to the muscle contractions that move food through the digestive tract. |
chyme | Stomach muscle contractions mechanically break down food even further and mix with secretions to form a substance called “chyme.” |
chyme | The semifluid mass of partly digested food that moves from the stomach to the small intestine. |
chyme | chyme is neutralized by bicarbonate from pancreatic secretions. |
Duodenum | The first part of the small intestine is the duodenum. |
Neutralize acidic enzyme | The duodenum receives alkaline bile juices from the gallbladder, which helps neutralize acidic chyme. |
Villi and Microvilli in small intestine | Villi and microvilli in the small intestine (largely the ileum) absorb water-soluble (polar, hydrophilic) digested nutrients into blood, lipids into lacteals as chylomicrons, and vitamin B12 |
Microvilli | Microvilli absorb nutrients in the small intestine. Enzymes and hormones aid in digestion, but they do not absorb. |
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Liver enzyme function | Blood, carrying nutrients, passes from the small intestine to the liver through the hepatic portal duct, allowing liver enzymes to deaminate amino acids, convert ammonia to urea, metabolize consumed toxins, and store glucose as glycogen. |
Enzyme | A substance produced by a living thing that acts as a catalyst. A catalyst that speeds up a chemical reaction by lowering the activation energy; in cells, most enzymes are proteins. |
Enzyme | Enzymes are proteins produced by the body that catalyze and speed up the breakdown of food so that nutrients are available for the body. |
Amylase and lipase | Mucus in saliva lubricates the food and provides the enzymes amylase and lipase to initiate chemical digestion of starch and lipids, respectively. |
Pepsin | Pepsin is a stomach enzyme that breaks down proteins
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Ghrelin | Ghrelin induces hunger, and leptin causes the sensation of satiety. |
Leptin | leptin causes the sensation of satiety. |
Hormones | Hormones induce secretions and speed up the movement of food through the small intestine. |
Glucagon | glucagon stimulates the breakdown of stored glycogen |
Protease and Lactase | the duodenum produces a large number of “brush border” enzymes, including proteases, lactase and other disaccharidases, and bicarbonate |