Physiology 3120 Lecture Notes - Lecture 1: Duodenum, Common Bile Duct, Mechanoreceptor
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr. Woods
GI – Lecture 1
- Food travels about 20ft in the digestive tract
4 Processes of the GI Tract
1. Digestion
o mechanical digestion crushing of food into smaller pieces in the mouth and stomach
o chemical digestion take the particles of food and break them down into individual
monosaccharides and amino acids, and smaller fragments of fats (this is done by
enzymes of the digestive tract)
2. Absorption
o Happens the best in the small intestine
o We have a little bit in the large intestine
o Very little bit of absorption happens in the mouth/stomach
3. Motility
o Essential bc we don’t want food staying in one part of the digestive
tract
o Move from the mouth, down the esophagus, then the food stays in the
stomach for the right amount of time (depending on the composition
of the food, the volume of the food and whether or not something is in
the small intestine yet)
o Then you move from the stomach to the small intestine where other
organs secrete stuff into the stomach (liver makes bile, bile is held in
the gallbladder, exocrine pancreas)
o Then in the large intestine, we want to make room for the next meal and so motility is
rapid but not too rapid
o So in the large intestine, motility is regulated by neurons and hormones
4. Secretion
o Exocrine secretions (go into the digestive tract)
▪ Water
▪ Mucous
▪ Ions
▪ Enzymes
o Endocrine secretions (go into the blood)
▪ Hormones that will be triggered for release into the blood dueot what is going
on in the digestive tract
Organs of the GI Tract
- Pharynx is the common passage way
- Stomach – holds the food for the right period of time
- Small intestine – chemical digestion and nutrient absorption
- Large intestine
- Accessory glands – Structures and organs that connect into the digestive tract
o Secrete important into the digestive tract that help with nutrient digestion
- Along the tract we have sphincters
o Permit or close off entry at any time
o Upper esophageal sphincter
▪ opens when you are eating food but other than that its closed so air doesn’t get
into GI tract
o Lower esophageal sphincter
▪ opens when food is coming down the esophagus but other than that its closed
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▪ If it opens when its not supposed to, you get acid reflex
o Pyloric sphincter:
▪ Muscular sphincter
▪ Usually closed in the stomach
▪ When food enters, it opens to allow small particles of liquified food to pass
▪ Controls the rate of emptying out of the stomach
▪ If you eat a meal that is high in fat, you don’t want that to exit the stomach too
quickly sot he pyloric sphincter will stay shut more frequently
▪ So we can control gastric emptying by changing the opening of the sphincter
o Ileocecal valve
▪ Separates the small and large intestine
▪ Should be closed most of the time
▪ Open when you want to empty contents from the small to the large intestine
▪ Don’t ever want the large intestine contents to go back into the small intestine
bc large intestine has all this bacteria that is good for you but this bacteria is not
meant for the small intestine (it would cause sickness)
o Anal sphincter (internal and external)
▪ Kids don’t have the ability to control this sphincter
General Layers of the GI Tract
- lower part of the esophagus, stomach, small intestine and majority of the large intestine look
similar
o sometimes the lumen is narrow like the small intestine or sometimes its large like the
stomach
o the top part of your esophagus is structurally different – it has skeletal muscle and some
striated epithelial
- skeletal muscle is present in:
o top part of the small intestine
o last part of the large intestine
- mucosa:
o inner layer
o 3 distinctive subdivisions:
▪ mucous membrane
• single layer of epithelial cells (enterocytes)
• the epithelial cells are variable in the tube
• in the stomach, they secrete HCl,
• in the small intestine, they cant secrete acid (this is good)
▪ lamina propria
• supports the epithelial cells
• small lymphatic vessels (lacteals) and blood vessels are present here
▪ muscularis mucosa
• thin layer of smooth muscle
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Food travels about 20ft in the digestive tract. Ions: endocrine secretions (go into the blood, hormones that will be triggered for release into the blood dueot what is going on in the digestive tract. Stomach holds the food for the right period of time. Small intestine chemical digestion and nutrient absorption. Accessory glands structures and organs that connect into the digestive tract: secrete important into the digestive tract that help with nutrient digestion. If it opens when its not supposed to, you get acid reflex: pyloric sphincter: Muscularis externa: contain myenteric plexus neurons. Serosa: most outer layer of gi tract, thin layer of connective tissue holding everything together, continuous with the mesentery (connective tissues that binds the abdominal cavity and keeps all the organs in place) Mesentery: connective tissue that lines the oral cavity and keeps all the organs in place. Enteric nervous system is made of the submucosal plexus and myenteric plexus neurons.
