Lesson 18 - Digestion and the Absorption of Food

Digestive System

process ingested foods into molecular food that are transferred to the body’s circulatory system; distributes cells for uses

What are the components of the Digestive System?

1. Gastrointestinal Tract (GI) / Alimentary Canal: mouth, pharynx, esophagus, stomach, small/large intestine, anus

2. Accessory Organs and Tissues: salivary glands, liver, gall bladder, pancreas

What systems are in the Gastrointestinal Tract (GI)?

mouth, pharynx, esophagus, stomach, small/large intestine, anus

What are the functions of the Gastrointestinal Tract (GI)?

1. Digestion: dissolve/break particles into smaller molecules for absorption

2. Secretion of digestive enzymes and other chemicals by exocrine glands

3. Absorption of small molecules → lumen of GI tract to interstitial fluid (transported to different vessel systems)

4. Motility: specific movement through GI tract (peristaltic movement)

Peristaltic Movement

wavelike muscle contraction

What systems are considered Accessory Organs and Tissues?

salivary glands, liver, gall bladder, pancreas

Rate: secrete substances into GI tract via connecting ducts

What is the process of the Digestive System?

1. Digestion begins in the mouth: chewing (large → smaller pieces) and salivary gland mixing (forms bolus/chewed food)

2. Food swallowed due to muscular contractions of pharynx and esophagus, and collects in stomach

3. Stomach stores and partially digests macromolecules with secretions of HCl (Chyme)

4. Small Intestine: major site of digestion and absorption

   1. Secretions of liver and pancreas are used to digest macromolecules → smaller molecules

5. Once absorbed: different molecules are taken up by different vessel systems (blood and lymph)

6. Large Intestine: concentrates undigested material by absorbing most of its remaining ions and water

   1. Rich microbiome, metabolizes some unabsorbed substances into forms that can be absorbed by blood

What systems are in charge of Homeostatic Regulation after blood absorption?

kidney (glucose, FA, ions, water) and hormones from other endocrine glands (insulin) control [] of substances in the blood

What are the components of the GI Tract Structure (wall)?

1. Mucosa

2. Submucosa

3. Muscularis Externa

4. Serosa

5. Ducts from accessory organs

Mucosa

where much digestion and absorption occur; faces the lumen

• Epithelial Layer: endocrine cells (hormone secretion) + exocrine mucous glands

• Connective Tissues: contain small capillaries

• Thin Smooth Muscle Layer

• Convulsions increase SA by about 600x over flat surfaces

Submucosa

connective tissue layers

• blood and lymphatic vessels

• nerve network that controls glandular secretion

Muscularis Externa

regulates forces that move and mix GI content (motility)

• muscular layer + nerve network (controls smooth muscle activity)

Serosa

thin out layer of connective tissue

Enteric Nervous System

GI system own local neurons control control (division of ANS)