Week 3: Digestion

List the secretions that break down fats during digestion

1) Bile 2) Pancreatic lipase, 3) Gastric lipase >Minimal in the mouth, hard fats begin to melt once they meet body temperature >Small intestine bile emulsifies fats and fluids and pancreatic and intestinal >Lipases break down fat to smaller fragments in order to be absorbed through the intestinal walls

Organs that make up the GI TRACT

1) Mouth 2) Esophagus 3) Stomach 4) Small intestine 5) Large intestine 6) Rectum

List the parts of the gastrointestinal (digestive) tract in order from the mouth to the colon

1) Mouth: Mechanical breakdown of food, saliva -- which starts to break down carbs 2) Esophagus: Passes food from mouth to stomach, food is now called bolus 3)Stomach: Food is now chyme, stomach muscles church food to liquids, adds enzymes, acids, and liquids -- gastric juice >Gastric juice denatures proteins so highly acidic >Converts pepsinogen to pepsin 4) Small Intestine: Secretes pancreatic enzymes that digest all energy yielding nutrients to smaller nutrient particles >Cells on the wall, (villi), absorb the nutrients into the blood and lymph system >Most nutrients are absorbed in small intestine, food digested 5) Large intestine (colon): What is left from small intestine goes to large -- mostly waste >Short chain fatty acids promote a healthy colon >Absorbs water and minerals and passes waste Rectum: >Stores waste prior to elimination Anus >Holds rectum closed and opens to allow elimination

List the secretions that break down proteins during digestion.

1) Pepsin 2) Hydrochloric Acid (HCl) 3) Pancreatic Protease >Stomach acid denatures proteins, mixed with gastric acids making proteins available to gastric protease enzymes to digest >Small fragments of the proteins are absorbed in the small intestine

List the secretions that break down carbohydrates during digestion

1) Salivary amylase (in saliva) 2) Pancreatic amylase

Organs that assist digestion, but are NOT part of the digestive tract (and their functions)

1) Salivary glands >Secretes saliva to moisten food >Provides lubrication for swallowing >Enzymes in saliva begin the process of chemical digestion 2) Pancreas >Secretes digestive juices containing enzymes to the small intestine to help digest nutrients. >Releases bicarbonate to neutralize acidic chyme that enters the small intestine 3) Liver >Liver produces and secretes bile, which emulsifies fats in the small intestine. 4) Gallbladder >Gallbladder stores bile from the liver until needed

3 ways in which nutrients can be absorbed into the cells lining the GI tract following their digestion

1) Simple diffusion: Nutrient moves freely into cell 2) Facilitated diffusion: Nutrient meets specific character to be transported through cell wall (requires help of a transport protein) 3) Active transport/diffusion: Some nutrients must be absorbed actively so they move against the concentration gradient which requires energy (requires hep of a transport protein)

Enzymes

>All enzymes are proteins >Enzymes speed up chemical reactions >Each enzyme acts on a specific substrate

Common Digestive Tract Problems

>Choking >Heartburn >Ulcers >Constipation >Diarrhea >Vomiting >Gas

Bile

>Formed in liver >Stored in gallbladder

Water souble vs Fat soluble

>Vitamins are classified into two groups: water-soluble and fat-soluble. >Water-soluble vitamins, which include all of the B vitamins, are easily absorbed into the body.

Peristalsis

A coordinated muscular contraction that propels food down the GI tract is called

3 major hormones that control digestion and absorption.

A. Gastrin B. Secretin C. Cholecystokinin (CCK)

Sphincter Muscle Function

Control the passage of food through the GI tract

Dietary fats will enter the ____ system?

Enter the lymphatic system.

Gastrin

Gastrin Responds to: food in stomach Secreted from: stomach wall Stimulates: stomach glands Response: Secretion of gastric acid (hydrochloric acid)

When nutrients are transported from intestinal epithelial cells to the vascular system, what organ is first to receive them?

Liver

Explain the role of the circulatory (blood) system vs. the lymphatic system in the transport of nutrients around the body following their absorption.

Lymphatic >Has no pump, lymph circulates between the cells >fat soluble nutrients, vitamins A, D, E, K and fatty acids, >loose and organized system of vessels and ducts which conveys fluids to the heart and GI track of the lymphatic system carries the products of fat digestion into the bloodstream

Mechanical digestion vs Chemical digestion and point out where these processes occur along the digestive tract.

Mechanical Digestion: mechanical actions that break down food >chewing in the mouth >stomach churning and mixing in fluid to break down >food moving along tract's content by peristalsis >after digestion wastes are excreted. Chemical Digestion: >begins in the mouth, where food is mixed with saliva, breaks down carbohydrates >stomach acids break down protein >liver and gallbladder contribute bile that emulsifies fat in the small intestine >pancreas and small intestine donate enzymes that continue digestion so that absorption can occur.

Chyme

Partially digested food in the stomach

Cholecystokinin (CCK)

Responds to: fat or protein in the small intestine Secreted from: intestinal wall Stimulates: gallbladder and pancreas Response: >pancreatic response is the release of bile and slowing of GI motility >gallbladder response is bile being secreted into the small intestine to maintain a slightly alkaline ph

Secretin

Secretin Responds to: acidic chyme in the small intestine Secreted from: duodenal wall Stimulates: pancreas Response: secretion of bicarbonate rich pancreatic juice (neutralizes acidity of chyme), digests fats and proteins

Which action is associated with the presence of fat in the GI tract?

Slowing of the process of digestion and absorption

Mucus

The substance that protects the stomach lining from damage due to digestive juices

Cells lining small intestine drain into either:

Vascular system (Blood) >Water-soluble and small particles Intestines to portal vein to liver Lymphatic system (Lymph) >Fat-soluble and large particles Intestines to thoracic duct to subclavian vein >Enters bloodstream, eventually reaches liver

What two circulatory systems transport absorbed nutrients around the body? Water-soluble nutrients and fat-soluble nutrients prefer which route of transportation?

Vascular system (blood circulatory system): carries water-soluble nutrients Lymphatic system: carries fat-soluble nutrients