Digestive system

 

Anatomy of the Digestive System:

Functions of the digestive system:

• Take in food

• Break down food

• Absorb digestive molecules

• Provide nutrients

• Eliminate waste

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

• Connects mouth to esophagus

Esophagus 

• Muscular tube about 25cm long

• Food travels down to cardiac sphincter of the stomach

Stomach

• Enlarged segment of the digestive tract 

Cardiac sphincter

• Opening of the stomach

Rugae

• Muscular layer of stomach is diff from other regions b/c it contains folds to increase the surface area

-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

• Consists of cecum (located where small and large intestine meet), colon, rectum, and anal canal

• Colon is 1.5-1.8 meters long consisting of

• Ascending, transverse, descending, and sigmoid colon

• Function of large intestine is to compress waste and collect any excess water that can be recycled

Accessory Organs

• Organs  that contribute to the process of digestion

• Food doesn't pass this organs but they play an important role digestion

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

• Ex: amino acid -> lipids or glucose

• 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

• Saliva keeps oral cavity most and begins the process of chemical digestion with enzyme amylase

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

• Enzymes have -ase ending 

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:

• Vomiting: from irritation of the stomach and small intestine

• After vomiting center is stimulated, sequence of events occurs so you vomit

• Ulcers:

• Occur from specific bacterium, Helicobacter pylori, treated with antibiotics

• Peptic ulcer:

• Condition where stomach acids digest the mucus lining of the duodenum

• Ulcers are sometimes called duodenal ulcers

• More HCl tha normals causes chyme, semifluid food mass, to be highly acidic, but enough sodium bicarbonate ions to neutralize the acidic chyme and eats mucus lining causing ulcers

Liver 

• Cirrhosis: disease in which there is damage or death of liver cells, which are replaced by connective tissue 

• Causes abnormal blood flow in the liver and interferes with normal liver functions

• Hepatitis: inflammation of the liver

• Liver cells can die and be replaced with scar tissue

Intestine

• Irritable bowel disease: term for Crohn’s disease or ulcerative colitis

• Crohn’s disease: localized inflammatory degeneration that cause the wall of the small intestine to thicken

• Disease causes diarrhea, abdominal pain, and weight loss

• Ulcerative colitis: limited to the mucosa of the large intestine 

• Involved mucosa exhibits inflammation, including edema, vascular congestion, and hemorrhaging

• Irritable bowel syndrome (IBS): disorder of unknown cause causing intestinal mobility to be abnormal

• Patients exhibit pain in the left lower quadrant after eating, having alternating bouts of diarrhea and constipation

• 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.

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
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