Gastrointestinal tract Flashcards
What is the general structure of the GI tract wall?
Long muscular tube with variations on basic structure related to function
What is the mucosal layer made up of?
Epithelial cells
Lamina propria
Muscularis mucosae
What is the submucosal layer?
Collagen
Elastin
Glands
Blood vessels
What is the enteric nervous system?
Collection of nerve plexuses surrounding the GI tract including the pancreas and biliary system
Very complex and 1/3 of the divisions of the ANS
How is the GI tract intrinsically and extrinsically controlled by the nervous system?
Intrinsic- ENS primary mechansism of ganglia in submucosal and myenteric plexuses
Extrinsic- sympathetic and parasympathetic innervation
What is the structure of the contractile tissue of the GI system?
Unitary muscle- smooth muscle cells connected by gap junctions so there is a rapid spread of APs that allow coordinated contraction
What acts as the GI pacemaker?
Interstitial cells of cajal
How is food broken down in the mouth?
Teeth and tongue mechanically break down food to be ready for swallowing
Saliva lubricates and contains a-amylase which hydrolyses starch
What are slow waves in terms of the GI systems motility?
Subthreshold membrane depolarisation and then repolarisation
Produce weak/tonic contractions
What is the purpose of GI tract motility?
Regulation of antegrade and retrograde transport
Separation of low pressure organs by sphincters
What are mastication muscles innervated by?
Madibular nerve of cranial nerve V
What are the three phases of swallowing?
Oral
Pharygeal
Oesophageal
What is the function of the oesophagus in digestion?
Swallowing reflex- closes upper oesophageal sphincter and initiates primary peristaltic wave of coordinated sequential contractions
Continued distension stimulates secondary paristaltic wave by the ENS
Lower oesophageal sphincter opening mediated by the vagus nerve releasing VIP
What is the first phase of motility in the stomach?
Receptive relaxation in thin walled orad to receive food
What is the second stage of motility in the stomach?
3 muscular layers of the caudad region contract to mix food with gastric juice from mucosal glands through ANS control which forms chyme- HCl, pepsinogen, intrinsic factor and mucus
What is the third stage of motility in the stomach?
Gastric emptying through pyloric sphincter into the small intestine- fat content and H+ slow emptying
What is the function of the small intestine?
Digestion and absorption of nutrients- carbs, amino acids, fats, water and ions
Chyme is mixed with digestive enzymes and pancreatic solutions
What are the three parts of the small intestine?
Duodenum
Jejunum
Ileum
How is the surface area of the small intestine increased?
Plicae
Villi
microvilli
What is the function of the pancreas as an accessory organ?
1L of exocrine solution secreted every day which includes:
Solution rich in HCO3- secreted from centroacinar and ductal cells to neutralise H+ delivered from the stomach
Enzymes secreted from acinar cells
How does the ANS control the activity of the pancreas?
Parasympathetic NS stimulates secretion and sympathetic NS inhibits secretion
What are the three stages of pancreatic secretion?
Cephalic
Gastric
Intestinal