GI system Flashcards
Function of GI tract
Digestion and absorption of nutrients
What cells are in the mucosal layer?
Epithelial cells
Lamina propria
Muscularis mucosae
Function of lamina propria
Connective tissue
Blood and lymph vessels
What does muscularis mucosae contraction cause?
Change in the shape of the epithelial layer
What is the submucosal layer composed of?
Collagen
Elastin
Glands
Blood vessels
What is the enteric nervous system?
Collection of nerve plexuses surrounding the gi tract
Is the ENS intrinsic or extrinsic?
Intrinsic
Are parasympathetic postganglionic neurones cholinergic or peptidergic or adrenergic?
Cholinergic & Peptidergic
Are sympathetic postganglionic neurons cholinergic, peptidergic or adrenergic?
Adrenergic
What are the 3 gi peptide classes?
Hormones
Paracrine
Neurocrine
What is the gi hormone cascade?
Endocrine cell at the end of GI tract ->
Secretion ->
Portal circulation ->
Liver ->
Systemic circulation ->
Target cell
What is the gi paracrine cascade?
Endocrine cell ->
Diffusion ->
Target cell
What is the gi neurocrine cascade?
Neuron ->
Action potential ->
Target cell
What is most contractile tissue in the gi tract?
Unitary smooth muscle electrically coupled via gap junctions
What are the 2 subsections of contractions?
Phasic
Tonic
What is a phasic contraction?
A periodic contraction or relaxation, lasting between 3-12 mins
What is a tonic contraction?
A constant level of contraction/ tone due to slow waves
What generates a true action potential?
An extension to threshold
What is the gi pacemaker?
Interstitial cells of cajal
What are low pressure organs separated by?
Sphincters
What is the mastication muscle innervated by?
Mandibular nerve (V3) of cranial nerve 5
What are the 3 phases of swallowing?
Oral
Pharyngeal
Oesophageal
What is lubricated food ready for swallowing called?
Bolus
What does saliva contain? What is
Alpha amylase to hydrolyse starch
What are mechanoreceptors?
Receptors which relay sensory info to the brainstem
What is the oesophagus lumen lined with?
Stratified squamous epithelia
What is the swallowing reflex?
The upper oesophageal sphincter is closed ->
This initiates primary peristaltic waves which coordinates sequential contractions
What triggers a secondary peristaltic wave?
Continued distension causing contractions to move the bolus along
What are the 3 motility phases in the stomach?
- Receptive relaxation in orad
- Caudad contraction
- Gastric emptying
What is force of contraction in the caudad region controlled by?
Due to action potentials
What is chyme composed of?
HCL
Pepsinogen
Intrinsic factor
Mucus
Describe gastric emptying
Chyme empties through the pyloric sphincter into the small intestine
Function of the small intestine
Digestion and absorption of nutrients
How long (approx) is the small intestine?
6 1/2 meters long
What are the sections of the small intestine?
Duodenum
Jejunum
Ileum
What increases surface area in the small intestine?
Plicae
Villi
Microvilli
Function of the pancreas
Excretes 1l of exocrine pancreatic secretion into duodenum per day
What are the secretion phases in the pancreas?
Cephalic
Gastric
Intestinal
Where are enzymes secreted from in the pancreas?
Acinar cells
What is the cephalic phase initiated by?
Initiated by smell, taste and conditioning
What is the gastric phase initiated by?
Initiated by distension of the stomach
Where is bile produced?
In hepatocytes
What is bile composed of?
Bile salts
Pigments
Cholesterol
Bilirubin
Function of the gall bladder
Stores, concentrates and ejects bile
What can bile form to emulsify lipids?
Form micelles to aid digestion and absorption of lipids
Function of CCK in the gallbladder
Contracts the gallbladder by relaxing the sphincter of Oddi
What cells release serotonin in the small intestine? What for?
Enterochromaffin cells for peristaltic reflex
What happens to material not absorbed in the small intestine?
Passes through ileocecal sphincter into the caecum of large intestine
What process exposes Chyme to secretions?
Segmentation contractions opposing in circular and longitudinal layers
What are the functions of the large intestine?
Absorbs water and electrolytes
Makes and absorbs vitamins K&B
Forming and propelling faeces (ferments indigestible foods)
What is a crypt?
Glands that secrete mucus to protect the lining from digestive fluids
