Introduction to GI tract and motility Flashcards
What is the basic structure of the GI tract?
It is a series of hollow organs running from the mouth to the anus
What structures separate the hollow organs?
Sphincters
What is the function of the mouth and oropharynx?
The food is made into smaller pieces and lubricated. Fat and carbohydrate digestion starts and food is propelled to the oesophagus during swallowing
What is the function of the oesophagus?
Delivers food to the stomach
What is the function of the stomach?
Temporary food storage, continues carbohydrate and fat digestion, initiates protein digestion and regulates the delivery of chyme to the small intestine
What is chyme?
A pulpy acid fluid which passes from the stomach to the small intestine. It is made up of gastric juices and partly digested food
What is the function of the small intestine?
Principle site of digestion and absorption of nutrients
What is the function of the large intestine?
Reabsorbs fluids and electrolytes, stores faecal matter before regulated expulsion
What are the accessory structures of the digestive tract?
Salivary glands
Liver and gall bladder (hepatobiliary system)
Pancreas
What type of muscle drives motility of the GI tract?
Smooth muscle
What areas of the GI tract have skeletal muscle?
Mouth, pharynx, upper oesophagus and external anal sphincter
What are the three different mechanical activity of the GI tract?
Propulsive movements
Mixing movements
Tonic contractions
What controls secretions into the lumen of the digestive tract?
Hormonal and neural signals
What is the primary protective secretion throughout the length of the GI tract?
Mucus
What are the secretions required for?
Digestion and protection
What do the digestive secretions contain?
Water, electrolytes and organic compounds
What is digestion?
It is the biochemical breakdown of complex foodstuffs to smaller, absorbable units
What are carbohydrates broken down into?
Polysaccharides and disaccharides are converted to monosaccharides
What enzymes mediate the breakdown of carbohydrates?
Amylase and disaccharidases
What are proteins broken down into during digestion?
Amino acids, dipeptides and tripeptides
What enzymes mediate the breakdown of protein?
Proteases and dipeptidases
What are triglycerides (majority or fats) broken down into?
Monoglycerides and free fatty acids
What enzymes mediate the breakdown of triglyercides/
Lipases
What is absorption?
The transfer of absorbable products of digestion from the digestive tract to the blood or lymph
What are the four layers of the digestive tract wall?
Mucosa
Submucosa
Muscularis externa
Serosa
What is the mucosa comprised of?
Epithelial cells Exocrine cells Endocrine cells Lamina propia Muscularis mucosa
What does the submucosa contain?
Connective tissue
Large blood and lymph vessels
Nerve network - submucous plexus
What is the muscularis externa comprised of?
Circular muscle later
Nerve network
Longitudinial muscle layer
What does the serosa contain?
Connective tissue
Where foes the myenteric plexus lie?
Between the inner and outer layers or smooth muscle in the muscularis externa
What is the result of circular muscle contraction?
Lumen becomes narrower and longer
What is the result of longitudinal muscle contraction?
Intestine becomes shorter and fatter
What is the function of muscularis mucosae contraction?
Change in absorptive and secretory area of mucosa
What is the function of gap junctions?
Connect adjacent smooth muscle cells allowing the spread of electrical currents from cell to cell.