Week 9- Upper GI Tract Flashcards
Define digestion
The process of breaking down macromolecules to allow absorption
Define absorbtion
The process of moving nutrients and water across a membrane
What are the 4 layers of the gut wall?
Mucosa
Submucosa
Muscularis
Serosa
Describe the mucosa layer
Epithelium, loose connective tissue, muscularis mucosae
Describe the submucosa layer
Connective tissue containing nerve plexus
Describe the muscularis layer
Smooth muscle containing nerve plexus
Describe the serosa layer
Connective tissue, may have epithelium
What are the 3 salivary glands?
Parotid, sublingual and maxillary gland
How many body cavities does the oesophagus traverse?
3
What is the function of the oesophagus?
Conduit for food, drink and swallowed secretions from pharynx to stomach
What type of epithelium is present on the oesophagus?
Non keratinising
What sphincters are present in the oesophagus?
Upper and lower oesophageal sphincters
What is gastro oesophageal reflux disease?
When stomach acid refluxes into the oesophagus
What is oesophagitis?
Swelling of the oesophagus
What defence mechanism does the oesophagus have against acid reflux?
Change from squamous to columnar epithelium (Barrets syndrome when goes too far)
What muscle is present in the oesophagus?
Circular muscle
At the gastro oesophageal junction what prevents reflux/
The diaphragm
What are gastric folds at the gastro oesophageal junction called?
Rugae
How does the pressure change from the thorax to the abdomen? How is this significant?
Goes from negative to positive keeping the oesophagus in the abdominal cavity collapsed
Why are gastric folds present?
Plays a role in absorptive function- increases surface area greatly
What are the 4 phases of swallowing?
Oral phase
Pharyngeal phase
Upper oesophageal phase
Lower oesophageal phase
What is the function of the stomach?
Breaks food into smaller particles (acid and pepsin)
Holds food, releasing it in a controlled steady rate into duodenum
Kills parasites and certain bacteria
What does the stomach release food into?
Duodenum
How much acid does the stomach secrete a day?
2L
What is the pH of the stomach at the epithelial surface?
6-7
What is the pH of the stomach at the lumen?
1-2
What is a stomach chief cell?
Protein secreting epithelial cells
Abundant RER
Secretes pepsinogen
Masses of apical secretion granules
What converts pepsinogen to pepsin?
Hcl
What is the difference between pepsinogen and pepsin?
Pepsin is the active form
What is a parietal stomach cell?
Many mitochondria
Cytoplasmic tubulovesicles
Internal caniculi
What is gastrin?
A hormone secreted by G cells, stimulates histamine release from chromaffin cells
How many teeth do humans have in total?
32
What are the 4 types of teeth and how many of each do humans have?
Incisors (8)
Canines (4)
Premolars (8)
Molars (12)
What is the largest jaw muscle?
Masseter muscle
What does saliva contain?
Aqueous secretion and digestive enzymes
What enzymes does saliva contain and what do they do?
Lingual lipase (fat digestion) Salivary amylase (carbohydrate digestion)
What 2 types of muscle are present in the tongue and what do they do?
Intrinsic- for fine motor control and movement of food
Extrinsic- for moving the tongue itself, aids mechanical digestion
What does the oesophagus traverse in the spine?
C5-T10
How does food move down the oesophagus?
Via peristalsis
Describe the oral phase
Chewing and saliva prepare the bolus, both oesophageal sphincters are constricted
Describe the pharyngeal phase
Pharyngeal muscles guide the bolus towards the oesophagus, both oesophageal sphincters open
Describe the upper oesophageal phase
Upper sphincter closes
Superior circular muscle rings contract and inferior rings dilate
Sequential contractions of longitudinal muscle
Describe the lower oesophageal phase
Lower sphincter closes as food passes through
What are the 3 sections of the stomach?
Cardia and pyloric region
Body and fundus
Antrum
What do the cardia and pyloric regions of the stomach secrete?
Mucus only
What do the body and fundum of the stomach secrete?
Mucus, Hcl and pepsinogen
What does the antrum of the stomach secrete?
Gastrin
What ion is found trapped in the mucus from the stomach?
HCO3-
What are the 2 types of stomach muscle contraction?
Peristalsis and segmentation
Which stomach muscle contraction is more powerful?
Peristalsis
Which stomach muscle contraction is more common?
Segmentation
Describe peristalsis in the stomach
Makes up 20% of muscle contractions
Is more powerful as chyme is pushed to the colon, movement from LOS to pyloric sphincter
ANS is essential
What is required for peristalsis in the stomach?
Autonomic nervous system involvement
Describe segmentation in the stomach
Makes up 80% of muscle contraction
Is weaker as solid chyme pushed back to the body and fluid chyme pushed towards pyloric sphincter
Stretching activates the enteric nervous system
How is the enteric nervous system activated?
Via stretching during segmentation in the stomach
How is HCL synthesised in the gastric lumen?
CO2 moves into the parietal cell
CO2 combines with water to form carbonic acid
Carbonic acid dissociates into H+ and HCO3-
K+ moves into the parietal cell, Na+ moves out
K+ carried to the gastric lumen via H+/K+ ATPase
HCO3- moves out of the cell via pump and Cl- moves into gastric lumen
H+ from dissociation of carbonic acid moves into gastric lumen, K+ pumped back into the parietal cell
H+ and Cl- in the gastric lumen can now combine to form HCl
What are the 3 phases of gastric secretion?
Cephalic phase
Gastric phase
Intestinal phase
Describe how the cephalic phase causes stimulation of stomach secretory activity
Sight/thought/smell of food or stimulation of taste on receptors on tongue cause stimulation via vagus nerve to the stomach
Describe how the cephalic phase causes inhibition of stomach secretory activity
Loss of appetite/depression causes lack of stimulation to the parasympathetic centre inhibiting secretory activity
Describe how the gastric phase causes stimulation of stomach secretory activity
Stomach distention activates stretch receptors, food chemicals and rising pH activates chemoreceptors which leads to stimulation via the vagus nerve
Describe how the gastric phase causes inhibition of stomach secretory activity
Excessive acidity causes decline of gastric secretion or emotional distress activates sympathetic system which overides parasympathetic controls and inhibits activity
Describe how the intestinal phase causes stimulation of stomach secretory activity
Presence of low pH and partially digested food in the duodenum stimulates stomach secretory activity
Describe how the intestinal phase causes inhibition of stomach secretory activity
Distention of the duodenum, presence of fatty acidic or hypertonic chyme inhibits secretory activity