Digestive Anatomy

Alimentary Canal organs thru which food actually passes oral cavity pharynx esophagus stomach small intestine large intestine

Accessory Organs assist in digestion, but no food actually passes through them teeth tongue salivary glands pancreas liver gallbladder

Wall of the Digestive Tract Mucosa: mucous epithelium Submocosa: muscular tissue Muscularis: 2 or 3 layers of smooth muscle Serosa: serous membrane that covers the outside of the abdominal organs  It attaches the digestive tract to the wall of the abdominopelvic cavity by forming folds called mesenteries.

6 ACTIVITIES OF THE DIGESTIVE SYSTEM

Ingestion - Taking food into the body Propulsion - Moving food thru the alimentary canal. This occurs primarily via peristalsis - involuntary waves of contraction/relaxation of the smooth muscle of the organ wall. Mechanical Digestion - Physically breaking large food molecules into smaller pieces. Increases the surface area upon which digestive enzymes can then act. Chemical Digestion - Enzymatic hydrolysis of food molecules into absorbable building blocks, such as monosaccharides, amino acids, fatty acids, etc. Absorption - Passage of absorbable end-products of digestion, as well as vitamins, minerals, and water from the lumen of the GI tract into the blood or lymph. The majority of absorption occurs in the small intestine. Defecation - Elimination of indigestible materials as feces.

Mouth The oral cavity begins behind the teeth and extends to the pharynx. The tongue occupies most of the closed oral cavity and is primarily skeletal muscle. Tongue movements mix food with saliva to form a compact mass called a bolus.

Salivary Glands Produce saliva which cleanses, moistens, and dissolves food. Saliva is 99% water but also contains enzymes, salts, and antibodies.

Esophagus The "food tube" that connects the pharynx to the stomach.

Stomach

Stomach Functions storage of ingested food chemical and mechanical digestion that turns the bolus into a paste known as chyme.

Stomach Anatomy nearly hidden by the liver when empty, the stomach is J-shaped with impermanent folds known as rugae

The Major Regions of the Stomach Cardiac Region. Fundus Body Pylorus

Stomach Secretions HCl is necessary to activate pepsin Pepsinogen is converted to pepsin by HCl. HCl also helps deal with any ingested bacteria Pepsin: a protein-digesting enzyme. Intrinsic factor: necessary for absorption of vitamin B12

Small Intestine

Structures of the Small Intestine Plicae Circulares - large deep, permanent folds that slow the movement of chyme and increase surface area. Villi - Fingerlike projections that increase the surface area Microvilli - further increase the available surface area

Liver Synthesis and secretion of bile Bile: emulsifies fat Gall Bladder Concentration and storage of bile

Pancreas secretion of insulin (decrease) and glucagon (increase) secretion of digestive enzymes secretion of bicarbonate rich fluid

Large Intestine receives indigestible material from the small intestine. absorbs water from the food residues and then eliminates them as feces

Anatomy of the Large Intestine divided into the cecum, appendix, colon, rectum, and anal canal external opening = anus. Internal and external anal sphincters control the anus contains significant numbers of bacterial colonies bacteria metabolize and ferment indigestible carbohydrates and synthesize B vitamins and vitamin K

Thursday March 3

Friday March 4 Anatomy of Small Intestine Small Intestine Functions Anatomy of the Large Intestine Functions of the Large Intestine

Digestion of Carbohydrates Monosaccharides are readily absorbed and need no further digestion. Disaccharides and polysaccharides need to be broken down into monosaccharides. Chemical digestion of starch begins in the mouth with salivary amylase which breaks starch down into oligosaccharides (2-8 monosaccharides bonded together). Chemical digestion of starch continues in the small intestine with pancreatic amylase. Oligosaccharides and disaccharides will be broken down by enzymes such as sucrase and lactase.

Digestion of Proteins Composed of amino acids. digestion begins in the stomach with pepsin. In the small intestine, protein digestion continues with trypsin, chymotrypsin, carboxypeptidase, dipeptidase, and aminopeptidase. The end result of the protein digestion is free amino acids.

Digestion of Fats Most ingested fats are triglycerides - a molecule of glycerol with 3 fatty acids attached. A VERY small amount of digestion begins in the stomach Most fats are not digested until the small intestine. There they are first emulsified by bile and then acted upon by pancreatic lipase. Most ingested fats are broken down into glycerol, monoglycerides, and fatty acids.