Functional Anatomy and General Principles Flashcards
What does the GI tract consist of?
Alimentary tract and associated glandular organs
What is the overall function of the GI tract?
absorb nutrients and water into circulation
excrete waste
What are the 4 major physiological processes?
motility secretion digestion absorption excretion of waste
What is motility required for?
Reduce size of food particles -> increase surface area for chemical digestion by enzymes
Mix food particles with enzymes
Propel food from mouth towards rectum
What causes motility?
contraction of layers of smooth muscle cells in GI tract
What happens in secretion in GI system?
release of enzymes, biological detergents, mucus, ions, and water in GI lumen to aid in digestion and absorption
What is digestion?
process in which ingested macromolecules are converted to smaller, absorb-able molecules (carbs, amino acids, lipids)
What are absorbed through the GI system?
nutrients, water, electrolytes
What are the absorbed particles used for?
energy source
components of biological structures
metabolic pathways
physiologic activities
What are some products from the liver that the GI system excretes?
cholesterol
steroids
drug metabolites
The GI tract is an open/closed environment?
Open to external environment
Does the GI system have an immune function?
Yes. It is the largest immune organ in the body and has immune cells and other non-specific defense mechanisms
What are the major functional segments of the GI system?
Mouth/Pharynx - Esophagus-Stomach-Sm Intestine (DJI)-Lg Intestine- Rectum-Anus
What are the associated glandular organs of the GI system?
Salivary Pancreas Liver Gall Bladder Endocrine Glands/Cells
What are sphincters?
specialized circular muscle structures (smooth or skeletal) that mediate control over the flow of the GI contents between structures
Where is the upper esophageal sphincter?
between pharynx and esophagus
Where is the lower esophageal sphincter?
between esophagus and stomach
Where is the pyloric sphincter?
between the stomach and duodenum
where is the ileocecal sphincter?
between the sm intestine and cecum
Where is the internal and external anal sphincters?
anus
What are the 3 features of the splanchnic circulation?
large blood flow
large reservoir of blood
diverse organs perfused
What are the blood vessels that supply the GI system?
Splanchnic circulation
What are the 3 major arteries supplying the abdominal organs?
Celiac Artery: liver, spleen, stomach
Superior Mesenteric Artery: pancreas, small intestine, proximal colon
Inferior Mesenteric Artery: distal colon
Where does the venous drainage of the GI tract go to?
To the liver via portal vein into the portal circulation
Where does the venous blood from the liver go to?
Portal Vein - Hepatic Vein - IVC
How does the liver act as a defense mechanism for the GI tract?
Toxins/viruses/bacteria from GI tract are sent to liver for processing -> thus it is not sent directly into systemic circulation
What role does the lymphatic system play in GI functions?
transport of lipids and lipid soluble molecules that are too large to enter the capillaries
Where do the lymph drain ?
Via thoracic duct and then into the systemic circulation
What are the layers of the gut wall?
Mucosa
Submucosa
Muscularis External
Serosa
What is the mucosal layer made up of?
Epithelium
Lamina Propria
Muscularis Mucosae
What kind of cells are found in the epithelium of the mucosa? What are their functions?
Absorptive Enterocytes: digestion and absorption
Enteroendocrine Cells: release regulatory peptides, amines, and regulate GI function
Gastric Mucosal Cells: produce protons
Mucin-Producing Cells: produce mucin (glycoprotein)
What kind of junctions connects the epithelium of the GI tract?
tight junctions
What type of epithelial cell makes up the esophageal epithelium? What is it used for?
Helps transport swallowed food (no absorption)
Squamous Type
What type of epithelial cell makes up the intestinal epithelium? What is it used for?
Helps with absorption and selective uptake of nutrients, ions, and water
Columnar Type
What lines the epithelia on the surface?
Villi and Crypts
How often is the epithelial linings removed and where?
the cells at the tip of the villus are shed approx every 3-5 days
What are found in the crypts of the villus?
Intestinal stem cells: proliferative cells
What are found on the epithelial cells on the surface of a villus?
Microvilli/Brush Border: numerous cytoplasmic extensions
What purpose do the mucosal folds, villi, and microvilli serve?
Increase surface area of small intestine drastically
What happens with celiac disease?
flattened villi causes a reduced surface area and thus the malabsorption of nutrients -> malnutrition
The microvillar membrane has a high/low % of cholesterol and sphingolipids
High
Describe the mucosal lamina propria
Immediately below epithelium
Connective tissue: collagen and elastin
Lots of glands and has lymph vessels, nodes, capillaries, and nerve fibers
What is found in the muscularis mucosae?
thin layer of smooth muscle cells in a folding configuration due to contractions
What’s found in the submucosa?
Connective Tissue: collagen and elastin
Glands
Large nerve trunks and large blood and lymph vessels
Submucosal Plexus
What is the submucosal plexus?
aka Meissner’s Plexus; Part of the enteric nervous system that can work autonomously from the CNS as well as help with integration of motor and secretory activities
What makes up the muscularis propria?
Inner circular muscle layer
Myenteric Plexus (Auerbach’s Plexus)
Outer Longitudinal Muscle Layer
What’s the function of the muscularis propria?
To help in mixing and propelling contents of GI tract via contractions of the muscle layers
What is the Serosa?
Outermost layer of the GI that consists of squamous mesothelial cells
What are the functions of the serosa?
Lines the surface of the abdominal wall to protect as well as lubricated via viscous secretion to reduce friction between abdominal organs during the contraction/relaxation processses of the GI tract
How is GI function regulated?
Periods of relative quiescence and increased activity based on food intake/fast
Meal composition
Endocrine/Paracrine/Neural
What are the components for endocrine regulation of GI?
Sensor Cells
Blood stream circulation
Target Cell
What are EECs?
Enteroendocrine cells: act as sensor cells of the GI system that respond to a stimuli by secreting a regulatory peptide or hormone into circulation
What does it mean to be an open type EEC
apex of the cell is in contact with the GI lumen for sensing and the base releases hormone to diffuse into local capillaries
What does it mean to be a closed type EEC
do not have contact with GI luminal surface
What do the target cells need to work with EECs?
Specific receptors for the hormone being secreted
