GI Tract Flashcards
Constituents of the GI tract
Mouth oesophagus, stomach, duodenum, jejunum, ileum, colon, rectum anus
Which regions make up the small intestin
Duodenuim, jejunum, ileum
Which regions make up the large intestin
Colon rectum anus
Accessory structures
Parotid, sub-mandibular, sublingual, pancrease, liver, gallbladder, tounger
What is the GI tract function
Breakdown of ingested food which can be taken up into the body tissues
What are the two aspects the the role of the GI tract
Digestion and absorption
How is the GI tract organised structurally
Mucosa, sub mucosa, muscularise and serosa
Which is the innermost layer of the Gi tract and what does it consist of
Mucosa - Consists of mucous epithelium, lamina propria and muscularis mucosae
What two layers make up the muscularis
Circ muscle layer
Longitudinal muscle layer
Which layer is referred to as the peritoneum and consists of connective tissue
Serosa
What is meant by the pylorus
Opening form stomach into duodenum
What are the main roles of the stomach
Storage
Mechanical digestion
What region does most absorption occur
Small intestin
What is special about the jejunum and ileum
3 strata of folding, no definable boundary
Define chyme
Semifluid mass of partially digested food that is expelled from the stomach into the duodenum
Describe the chyme found in the large intestin
Very little nutrients
What is the roel of the large intestin
Absorb of salt, water and sugar
Name the regions of the colon
Caecum, ascending, transverse, descending and sigmoid
Main control mechanisms of the GI tract
ANS - symp inhib digestion, para stim
Enteric - Independent from the CNS
Gut peptides - paracrine or hormonal
What are the nerve plexus involved in enteric nervous control of the GI tract
Myenteric and sub mucosal plexus
What are the roles of the nerve plexus
Sense luminal contents and controls muscles and glands
Where are gut peptides secreted from
Enteroendocrine cells in the mucosa
Name some gut peptides
Gastrin
Secretin
Cholecystokinin
What is motility and secretion controlled by
Reflexes
Main differences between intrinsic and extrinsic control reflexes
Int - Short - local stim - local nerve circuits
Ext - Long - ext stimuli - CNS involvement
What are enteroendocrine cells
Single cells scattered throughout the GI tract
What is the role of EE cells
Detect luminal contents and respond by releasing peptide transmitteres
How do EE cells act
Humourally or paracrine
What stimulates peristalsis
Distension of the GI tract by bolus
What structure mediates peristalsis
Myenteric plexus
What are the aspects of peristalsis
Oral contraction followed by aboral relaxation
If the bolus is moving away from the anus
Vomitting
Does peristalsis require CNS input
No
What is Hirchsprungs disease
Congenital disorder due to the absent development of the myenteric plexus, lack of GI innervation, enlarged colon requires surgical removal
What is the role of saliva
Solvent or taste
Cleans/protects teeth LUbrication
Antimicrobial
What is the role of the parotid gland
Secretion of saliva into the parotid duct
What is the name of the gland that secretes below the tounge
Sub lingual
Which salivary gland located below the mandible
Sub mandibular
What are the component parts of slaiva
Water, mucous, a-amylase, lipase
Which enzyme secreted by the parotid gland
A amylase
Which enzyme secreted by the sub lingual
Lipase
Descibe salivary gland structure
12+ aciniar cells around central lumen
Describe the process of slaivation
Acinar cells produce primary saliva and secrete it into the intercalated duct. The saliva then travels through the striated duct where the ductal cells modify it by reabsorbing Na+ and Cl- and secreting HCO3-. After the striated duct the saliva then passes into the excretory duct where myoepithelial cells contract following nervous system stimulation to bring the saliva into the mouth
What are zymogen granules, why are they useful
Zymogen granules are vesicles containing inactive proenzymes that are to be secreted. Only once secreted are these proteins cleaved to their active forms. These prevent damage to our own cells by the protease activity of some of the enzymes.
Defiene swallowing
Process by which food passes from mouth to stomach
What are the phases of deglutination
Oral, pharyngeal and oesophageal
NS 1 peri wave
ANS
NS 2 peri wave
ENS
What are the four roles of the stomach
Motilitiy, digestion, protection and absorption
3 types of motility by the stomach
Accomodation
Trituration
Emptying
Which bio mole does the stomach digest
Protein
What is absorbed in the stomach and how
Alcohol and fat soluble drugs
By diffision
What are the components of gastric juice
Water Ions HCL Pepsinogen Intrinsic factor Mucus Gastrin
Role of HCL secreted
Lower pH to prevent bacterial grouth and catlayses pepsinogen to pepsin
What is the function of pepsinogen
Proenzyme of pepsin
What role does intrinsic factor play
Prevent vit B12 breakdown so it can be absorbed in the ileum
What does the cephalic phase of gastric secretion represent
Sight, thought, smell of food triggers secretion of acid, mucus and enzymes as well as increased gastric motility
what initiates the cephalic phase
PARA - vagus fibres
What does the gastric phase of secrection represent
Food entering stomach causes streching and tiggers secretion and motility
What initiates gastric pahse
Long vagal fibres and short myenteric reflexes
What does the intestinal phase of gastric secretion represent
Food in the intestine induces the release of hormones that inhibit motility
What initiates the intestinal phase
Hormones
- Which cells in the gastric pit are responsible for secreting mucus and HCO3-?
Mucus neck
Which cells secrete acid and intrinsic factor
Parietal cells
Which cells secrete gastrin
G-enteroendocrine
Which cells secrete pepsinogen
Chief
Which cells secrete somatostatin
D-enteroendocrine
What does gastrin do
Stimulate acid secretion
What does somatostatin do
Unhibit gastrin secretion and acid secretion
- What is the pH of the lumen of the GI tract compared to that of the mucus gel
Lumen - 1.5
Mucus-gel neutral zone 7.0
What is gastric/peptide ulcer disease
Breakdown in the mucus gel neutralisation barrier causing damage to the lining of the stomach/small intestine
The parietal cells exchnge what ions
K in H out
Why do pariental cells contain many mitochondria
active transport of H+ against steep gradient
How is acid secretion controlled by the NS
ACh from vagus causes secretion
How can acid secretion be controlled by the paracrine system
Histamine released from from nearby cells can stimulate acid secretion
What causes G enteroendocrine cells to secrete gastrin
Detection of increased protein levels
What causes D enteroendocrine cells to release somatostatin
Acidity of the stomach becomes too low
Which type of cells releases histamin
Enterochromaffin-like cells
What are symptoms of gastric/peptic ulcer disease
Abdo pain
Bloating
Nause/vomiting
Haemorrhage
Give an example of an endogenous cause of peptic ulcer diease
Stress- leads to decrease of HCO3- and thinning of the mucus layer
How can alcohol and coffee lead to gastric ulcer disease
Stimulate parietal cell leading to increasing in acidity
How can NSAIDs lead to gastric ulcer disease
Secretion of proteases and endotoxins that degrade tissue of the stomach
How can peptic ulcer disease be treated
Antacids - neutralise stomach acid, histamine antagonists - ranitide, cimetidine, proton pump inhibitors - omerpraxole, antibiotics, - kill H
Name given to the functions regions of the stomach, how do they differ
Reservoir – top 2/3, tonic contractions, relax during gastric accommodation to store increased volume of food. Antral Pump – bottom 2/3, phasic contractions, trituration of food
Which sphincter allows food into the stomach
Lower oesophageal sphincter
What happens when food enters the stomach
Accommodation by receptive relaxation of corpus and fundus
Describe peristalsis in the stomach
Muscle contraction pushes food toward the pylorus mixing in the antrum
Retropulsion
During peristalsis in the stomach food is pushed up against the closed pyloric sphincter resulting in being pushed back away
Descibe antral systole
Peristaltic waves pushed contents of the stomach back towards the body – trituration. Some chyme enters the duodenum where cells detect what is coming out of the stomach
Descibe the intestinal phase of gastric motility
Arrival of food in the duodenum triggers the release of the hormones CCK and secretin
