15. GI Tract Introduction Flashcards
What are the layers of the gut tract wall from outer to inner?
- serosa
- longitudinal smooth muscle
- myenteric plexus
- circular smooth muscles
- meissner’s corpuscle
- submucosa
- mucosa
What is the serosa layer?
- outer layer of connective tissue and simple squamous epithelium
- continuous with the mesentery (pathway for blood to gut tube)
Where is the serosa layer missing in the GI tract?
- esophagus, where it is replaced with adventitia to connect to abd wall
What is the submucosa?
- lamina propria but thicker
2. incorporates the blood vessels and submucosal plexus
What layers does the mucosa include in order to form a continuous sheet that lines the entire GI tract?
- lamina propria: loose CT with nerve, blood vessel, glands
2. muscularis mucosa: thin smooth muscles, form mucosal ridge
What type of cells help form the mucosa layer of gut?
- simple columnar epithelium with goblet cells
2. line entire gut tract
What forms the enteric nervous system?
- myenteric and meissners plexuses
2. neurons are supported by intrinsic glial cells
How does the enteric nervous system operate?
- intrinsic regulation and sensory reflexes
- parasympathetic increase GI activity
- sympathetic decrease GI activity
Where are myenteric plexus and what does it control?
- in between longitudinal and smooth muscles
- tonic and rhythmic contraction of smooth intestinal muscles
- excitatory (Ach, NO)
- inhibitory (VIP)
Activation of the myenteric plexus will lead to what effects?
- increased tonic contraction of gut wall
- more intense rhythmic contractions
- increased rate of contractions
- increased velocity
What does the Meissner’s plexus mostly control?
- GI secretion, absorption, and local blood flow
2. mostly local effects not long distant.
What is peristalsis?
- propulsion of food along the gut tract forcing bolus from one direction to the other
How does peristalsis work?
- circular muscles contract to prevent backflow
- longitudinal muscle will propel the bolus forward, causing distension of the tube
- distension will cause contraction of next circular ring, and the next segment of longitudinal muscle
What is receptive relaxation?
- vagovagal reflex, which activated by food and casues distension of the proximal region of stomach
- CCK is then released causing distal distention of stomach
What is the role of the distal stomach with mixing food and beginning digestion?
- contraction of distal region mixes food with gastric secretions
- contraction seals off distal end and propels food back into the “body” of stomach for mixing
What will increase gastric contractions, to improve mixing?
- stimulation of vagus nerve (parasympathetic)