NHM 101 Lecture 3: Ch 3 - Digestion, Absorption, and Transport
2 May 2018
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Chapter 3: Digestion, Absorption, and Transport
Importance and Challenges
Every cell needs a continuous supply of nutrients, but foods must be broken down first.
Definitions
● Digestion: Process by which food is broken down
● Absorption: Uptake of nutrients by the cells of the small intestine for transport into either
the blood or the lymph system
● Gastrointestinal (GI) Tract: the digestive tract
○ Flexible, muscular tube that extends from the mouth to the anus
○ Lumen: inner space within the GI tract and is continuous from one end to the other
Anatomy of the Digestive Tract
Mouth
● Chewing & crushing foods
● Fluids from food/beverages and saliva blend
with food for easy swallowing
Carbohydrate digestion begins here
1. Food is swallowed
2. Passes through pharynx (short tube shared
by both the digestive and respiratory system)
3. Epiglottis closes off the airway
4. Food enters the esophagus as the upper
esophageal sphincter opens
Sphincter
- circular muscle that is able to open and close that surrounds a body opening
- Keeps the flow of food in 1 direction
- Multiple sphincters in the GI tract:
a. Upper Esophageal Sphincter
- Mouth/Pharynx ---> Esophagus
b. Lower Esophageal Sphincter
- Esophagus ---> Stomach
c. Pyloric Sphincter
- Stomach ---> Small Intestine
d. Ileocecal Valve
- Small Intestine ---> Large Intestine
e. 2 Sphincters of the Anus
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Esophagus
● Upper esophageal sphincter opens and food enters into the esophagus
● Food moves through the esophagus and passes through a hole in the diaphragm
● Lower esophageal sphincter opens to allow food into the stomach
Stomach
● Strongest muscle of the GI tract
● Thickest walls
● Food particles enter through the opening of the lower esophageal sphincter
● Food slowly transfers from the upper portion of the stomach to the lower portion
○ Gastric juices released from the stomach wall are added to the food and it is ground
into a semi-liquid mass (chyme)
● Chyme is released from the stomach through the pyloric sphincter
● Pyloric sphincter opens about 3 times/minute to allow chyme into the small intestine
Digestion of carbohydrates continued here
Digestion of protein and fat begin here
Small Intestine
● 10 feet of tubing
● Chyme enters into the small intestine as the pyloric sphincter opens
○ The pyloric sphincter only allows a small amount of food at one time to pass by
● Chyme bypasses the opening of the common bile duct, which drips fluid from the
gallbladder and the pancreas
● Chyme travels through the 3 segments:
○ Duodenum
○ Jejunum
○ Ileum
Most digestion occurs here
Large Intestine (colon)
● Remaining contents enter the large intestine through the ileocecal valve
● Large intestine withdraws water as intestinal contents pass to the rectum
○ Leaves a semisolid waste
Rectum & Anus
● Rectum/anal muscles hold back waste until rectal muscles relax and 2 anal sphincters open
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Every cell needs a continuous supply of nutrients, but foods must be broken down first. Digestion: process by which food is broken down. Absorption: uptake of nutrients by the cells of the small intestine for transport into either the blood or the lymph system. Flexible, muscular tube that extends from the mouth to the anus. Lumen: inner space within the gi tract and is continuous from one end to the other. Fluids from food/beverages and saliva blend with food for easy swallowing. Carbohydrate digestion begins here: food is swallowed, passes through pharynx (short tube shared by both the digestive and respiratory system, epiglottis closes off the airway, food enters the esophagus as the upper esophageal sphincter opens. Sphincter- circular muscle that is able to open and close that surrounds a body opening. Keeps the flow of food in 1 direction. Multiple sphincters in the gi tract: upper esophageal sphincter. Mouth/pharynx ---> esophagus: lower esophageal sphincter.
