Functional Anatomy and General Principles Flashcards
What is the sphincter of oddi?
The sphincter between the common bile duct/pancreatic duct and the duodenum. It controls the amount of bile and pancreatic juices released into the duodenum
What are the three major arteries of the splanchnic circulation?
Celiac, SMA and IMA
What organs are supplied by the celiac artery?
Liver, spleen and stomach
What organs are supplied by the Superior mesenteric artery?
Pancreas, small intestine and proximal colon
What organs are supplied by the IMA?
Distal colon
What happens to large molecules that are too large to pass into capillaries?
They are taken up by the lymphatic system and returned to the systemic circulation through thoracic duct –> subclavian vein
Name the four layers of the gut wall from inside to outside
Mucosa, Submucosa, muscularis externa, serosa
What individual components make up the mucosa of the gut wall?
Mucosa is the innermost layer. It is made up of epithelium, the lamina propria, and the muscularis mucosae
What are absorptive enterocytes?
The are the most abundant cell of the GI tract epithelium. They play a vital role in digestion and absorption
What is produced in gastric mucosal cells?
Protons
What type of cells are found in the mucosal epithelium of the esophagus?
Squamous cells- they help in the transportation of swallowed food
What type of cells are found in the mucosal epithelium of the intestine?
Columnar- helps in absorption or selective uptake of nutrients, ions, water
Describe the architecture of the small intestinal epithelium
The surface area of the small intestinal epithelium consists of villi and crypts.
What is the average life span of a cell at the villus tip in the GI tract?
3-5 days. The epithelial lining of the GI tracts is continously renewed
What is the consequence of a reduced surface area in the intestinal epithelium, such as in celiac disease?
Malabsorption
What is the lamina propria?
The layer immediately below the epithelium- it consists of loose connective tissue (collagen and elastin fibrils).
It is rich in glands, contains lymph vessels and nodes, capillaries, nerve fibers.
What three layers make up the mucosa?
Epithelium, lamina propria, and the muscularis mucosa
What is the muscularis mucosae?
This this layer of smooth muscle cells directly below the lamina propria
In what layer of the GI tract is the submucosal plexus of the enteric nervous system found?
The submucosae
In what layer of the GI tract is the myenteric plexus of the enteric nervous system found?
Between the two layers of the muscularis externa (muscularis propria)
Describe the muscularis externa
It consists of two layers of smooth muscle cells:
Inner circular layer
Outer longitudinal layer
Responsible for mixing and propelling contexts of the GI tract
What is the outermost layer of the GI tract?
The Serosa
What cell type makes up the serosa?
Squamous mesothelial cells- secretes a viscous fluid in order to reduce friction between organs in the abdominal cavity
Which are the “sensor cells” of the GI system?
Enteroendocrine cells- they respond to a stimulus by secreting a peptide or hormone
Which are target cells of paracrine regulation?
smooth muscle, absorptive enterocytes, secretory cells in glands and other EECs
Enterochromaffin-like cells in the stomach release what hormone? What is the effect?
Histamine. When released, the histamine binds to nearby parietal cells which can then release HCl
What is the role of serotonin released in the GI tract?
Regulation of smooth muscle contractility in the GI
What cells release serotonin?
Enteric neurons, mucosal mast cells and enterochromaffin cells
When and where is cholecystokinin released?
Cholecystokinin is released from the I cells in duodenum in response to dietary protein and fatty acids
What is celiac disease?
Allergic response to gliadin, a component of gluten. It causes an inflammatory response which results in a reduction of density and length of microvilli
Differentiate the extrinsic from the intrinsic nervous system in the gut
Extrinsic: nerves that innervate the gut, with cell bodies outside of the gut wall- part of the ANS (parasympathetic and sympathetic)
Intrinsic: The enteric nervous system- includes the submucosal and myenteric plexus
What parts of the gut does the vagus nerve innervate?
Everything except for the distal colon and anorectal region
Esophagus, stomach, gallbladder, pancreas, 1st part of the intestine, cecum, proximal part of the colon
Describe the general impact of parasympathetic stimulation on GI function
Activation
What two neurotransmitters are released by peptidergic neurons?
Substance P and VIP
What are vagovagal reflexes?
Both afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli
Which gut muscles are activated by sympathetic innervation?
GI sphincter muscles
Differentiate how the parasympathetic and sympathetic nerves interact with the ENS.
Parasympathetic fibers all affect the gut indirectly, through synapsing on the ENS
Sympathetic fibers can either directly stimulate cells, or indirectly through stimulation of the ENS
Where is the myenteric plexus?
Between the inner circular and outer longitudinal muscle layer (muscularis externae)
Where is the submucosal plexus?
In the submucosal layer of the gut wall
Is the ENS autonomous?
The ENS can act autonomously, but also receives information from the ANS
Is all of the muscle of the GI tract smooth muscle?
No- the pharynx, upper 1/3 of the esophagus and the external anal sphincter are striated muscle
What permits rapid cell-cell spread of action potentials in GI smooth muscle?
Gap Junctions formed with interstitial cells of Cajal (ICC’s)
Differentiate phasic from tonic conctractions
Phasic: periodic contractions followed by relaxation
Tonic: Constant level of contraction- generally found in sphincters that only relax when told to do so
Which cells act as the pacemaker for the gut?
Interstitial cells of cajal- ICCs: They generate the slow waves.
How do slow waves of the GI tract relate to contraction?
Slow waves that do not reach threshold still lead to tonic contractions. When action potentials occur, it is followed by a much stronger phasic contraction
Where do segmentation contractions occur?
Predominantly in the small and large intestines
What is the purpose of segmental contractions?
These allow mixing of the luminal contents with GI tract secretions and increase exposure to the mucosal surfaces where absorption occurs
Which neurotransmitters are involved in orad contraction of peristalsis?
ACh and substance P
Which neurotransmitters are involved in caudad relaxation of peristalsis?
VIP and NO
