Physiology 3120 Lecture 57: Lec 57 - GI Physiology
15 May 2018
School
Department
Course
Professor
Lecture 57 – Gastrointestinal Physiology
Four processes of the GI tract
1. Digestion: chemical and mechanical
- Mechanical digestion of food:
o Crushing of food into smaller fragments
o Occurs in the mouth and stomach
- Stomach crushes the food particles into very small fragments
- Chemical digestion:
o Take particles we are eating which are in large forms (complex carbohydrates or
intact proteins) and they must be broken down into individual monosaccharides
and individual AA
o Occurs by actions of enzymes from the digestive tract
2. Absorption
- Occurs optimally in the small intestine
- Majority of nutrient absorption occurs in the small intestine
o Maximised in structure and the cells it contains to absorb majority of nutrients
- A small amount of absorption occurs in the large intestine
- VERY little absorption can occur in the mouth and stomach – very minimal
3. Motility
- Don’t want food staying in one part of the digestive tract
- Mouth → esophagus → food stays in the stomach (stomach knows how long food should
stay there based on the composition, volume, whether or not something is in the small
intestine yet) → first part of the small intestine where other organs make secretions →
large intestine (fairly rapid but not too rapid)
- Motility in the stomach varies based on composition, volume and what is happening in the
rest of the tract
- Other organs of the digestive tract that don’t come into contact with food but make
important secretions: liver (makes biles), gallbladder, exocrine pancreas
- Motility is controlled by neurons and by hormones
4. Secretion
- Exocrine secretions go into the digestive tract
o Water, mucous, ions, enzymes
o Cells → lumen of the tract
- Endocrine secretions go into the blood
o Hormones are triggered for release into blood based on what is occurring in the GI
tract
- Approximately 20 feet in the digestive tract that the food particles must travel
find more resources at oneclass.com
find more resources at oneclass.com
Organs of the GI tract
- Organs are the ones that physically come into contact with food
- Mouth
- Pharynx: common passage that connects to esophagus and trachea
o Closes when eating so only food goes down the esophagus
- Stomach: holds food for the right period of time
- Small intestine: chemical digestion + nutrient absorption
- Large intestine: bacteria control digestive health
- Accessory glands: structures and organs that connect to the digestive tract
o Make important secretions into the digestive tract to help with nutrient digestion
- Sphincters along the tract close off entry at any time
o Upper esophageal sphincter: top part of the esophagus, opens we eat food but want
it to stay closed in other times so air does not enter tract
o Lower esophageal sphincter: boundary for the stomach so stomach contents stay in
there (acids, foods)
▪ Only triggered to open when food is going down esophagus
▪ Stays closed most of the time
▪ If it opens inappropriately, get acid reflux
o Pyloric sphincter: muscular, usually closed in the stomach → as soon as food enters,
it opens to allow for small particles of liquefied food to pass into the intestine
▪ Controls the rate of emptying out of the stomach
▪ Meal high in fat: don’t want it to exit stomach too quickly = it will stay mostly
closed
▪ Control gastric emptying by changing opening of the spinchter
o Ileocecal valve: separates small intestine from large intestine
▪ Closed most of the time except when you want to empty contents
▪ Don’t want large intestinal contents to go back into small intestine because
large intestine is full of bacteria (most are good) but small intestine is not
designed to hold too much bacteria (can cause sickness)
▪ Small intestine has some bacteria but not a lot
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Four processes of the gi tract: digestion: chemical and mechanical. Mechanical digestion of food: crushing of food into smaller fragments, occurs in the mouth and stomach. Stomach crushes the food particles into very small fragments. Majority of nutrient absorption occurs in the small intestine: maximised in structure and the cells it contains to absorb majority of nutrients. A small amount of absorption occurs in the large intestine. Very little absorption can occur in the mouth and stomach very minimal. Don"t want food staying in one part of the digestive tract: motility. Motility in the stomach varies based on composition, volume and what is happening in the. Other organs of the digestive tract that don"t come into contact with food but make important secretions: liver (makes biles), gallbladder, exocrine pancreas. Motility is controlled by neurons and by hormones: secretion. Exocrine secretions go into the digestive tract: water, mucous, ions, enzymes, cells lumen of the tract.
