Aim: How does digestion take place in humans?

Alimentary Canal – the “tube” digestion takes place in.

Four Stages of Food Processing: Ingestion – the act of eating or drinking. Digestion – the process of breaking food down into molecules small enough for the body to absorb. Absorption – certain cells take up (absorb) the small molecules. Elimination – undigested material passes out of the body.

Digestion The process by which food products are broken down. Types: MECHANICAL: The physical breakdown of food into smaller pieces (Ex: chewing) CHEMICAL: Enzymes breakdown food into smaller pieces (Ex: amino acids)

Chemical Digestion: Enzymes play a critical role in the digestion (hydrolysis) of nutrients.

Mouth: Intake of food through the mouth! Both mechanically (teeth and tongue) and chemically (salivary amylase – an enzyme that breaks down starch) digestion occurs. Then the food mixes with saliva and travels down through the esophagus.

Esophagus Peristalsis Long muscular tube that connects the stomach to the pharynx (upper portion of the throat). No Digestion takes place here! Peristalsis Process by which muscular contractions move food through the esophagus to the stomach.

Stomach Both mechanically (churning) and chemically (pepsin) digestion occur. Stomach Glands Gastric Juice Enzyme specificity HCL (Hydrochloric Acid) Acidic pH Kill Bacteria Pepsin Digestion of proteins

Which stomach will work? 1 = water 2 = water + pepsin 3 = water + acid 4 = acid + pepsin

What is the optimum pH and temperature for pepsin?

Small Intestine Most digestion takes place and is completed here chemically. Enzymes: Amylase Trypsin Lipase Digests Starch Digests Proteins Digests Lipids

Small Intestine Responsible for digestion and absorption of nutrients. The enzymes (amylase, trypsin, and lipase) are produced by accessory organs.

Absorption The S.I. is ideal for absorption because: Its very long (about 21 feet) Many folds Has villi (finger like projections)

Villi Nutrients diffuse into the bloodstream! Blood Vessels Carry Nutrients away from the digestive system to the parts of the body that require them. Nutrients diffuse into the bloodstream!

Accessory Organs Make and store enzymes, no food passes through them Liver Gallbladder Pancreas

Accessory Organs No Food Passes Through Them (H)Liver – makes bile (G)Gallbladder – stores and releases bile into S.I. (D)Pancreas – makes and releases (pancreatic juice) amylase, trypsin, and lipase into S.I.

Bile Emulsifies fats Breaks into smaller droplets (mechanical digestion) Increases surface area of fats

Large Intestine Undigested material passes into the L.I No digestion occurs here The major function is to reabsorb water & vitamins. Stores waste (feces) in the rectum. Elimination through the anus.

What is the major role of the Digestive System (How does it help us maintain homeostasis? The digestive system breaks down nutrients into smaller parts so they can enter our bloodstream & small enough to our cells & can diffuse across the cell membrane. STARCH Proteins Lipids Diffusion GLUCOSE Cell Amino Acids Fatty Acids & Glycerlol

It's a Gas Scientists estimate that the average adult releases between 12 and 122 cubic inches of intestinal gas each day. Most of that gas is made up of hydrogen and methane produced by the bacteria as they ferment the fiber that was not digested in the stomach or small intestine. Many fruits and vegetables, especially beans, contain these polysaccharides, which cannot be broken down by the enzymes in the stomach or small intestine. As the bacteria decompose these complex sugars, gas is released. Most of the gas is passed without notice. Common wisdom tells us that beans give us a lot of gas—more than could pass without notice. Ever questing for eternal answers, scientists in one study measured the intestinal gas produced by people who ate a control diet and compared them to those who ate a meal that was half pork and beans. The folks in the control group released .9 cubic inches per hour of flatus (intestinal gas) while the pork and beans group released a whopping 10.7 cubic inches.

Weird Science Fact Alexis St. Martin, a French Canadian, was accidentally wounded by a short gun blast in 1822. Fortunately, Dr. William Beaumont, an army surgeon, was nearby and began treatment of the wound immediately. St. Martin’s recuperation lasted nearly three years, and the enormous wound healed except for a small opening leading into his stomach. A fold of flesh covered this opening; when this was pushed aside the interior of the stomach was exposed to view. Dr. Beaumont began a series of expeeriments and observations that formed the basis of our modern knowledge of digestion.