GI anatomy overview (lecture) Flashcards
What is the mouth otherwise referred to as?
Oral cavity
Buccal cavity
What type of epithelium is the “oral mucosa”?
stratified squamous epithelium
(Thick and resistant to abrasion)
Where is the oral mucosa found?
Lining the oral cavity
What are childhood “milk” teeth called?
Deciduous teeth
What does the oral mucosa produce and secrete?
Defensins to inhibit bacterial growth
What is the role of defensins produced by the oral muscosa?
Inhibit bacterial growth
How many deciduous teeth does a child have?
20
When do deciduous teeth come in?
First 6-24 months of life
What are adult teeth called?
Permanent teeth
At what age should all deciduous teeth have been replaced, roughly?
Approx 12 yrs old
What is the bony ridge called that hold the sockets of the teeth?
Alveolar ridge of the maxilla (top) and mandible (bottom)
How many permanent teeth does an average person have?
32
How many incisors are in an adult mouth?
8
- 4 top (2 each side)
- 4 bottom (2 each side)
What is the action of incisors?
Slice and cut
How many canines does an adult mouth have?
4
- 2 top (1 each side)
- 2 bottom (1 each side)
What is the action of canines?
Tear and rip
How many premolars are in an adult mouth?
8
- 4 top (2 each side)
- 4 bottom (2 each side)
What is the action of premolars?
Grind and crush
How many molars does an adult mouth have?
12
- 6 top (3 each side)
- 6 bottom (3 each side)
What is the action of molars?
Grind and crush (mainly grind)
What are cavities?
Gradual demineralisation of enamel
What causes cavities?
Acid production from bacteria in plaque
What is the formula for types of teeth in 1 quadrant of the mouth (e.g the top left side) ?
2I, 1C, 2PM, 3M
2 incisors
1 canine
2 premolars
3 molars
Name the 4 types of teeth in an adult mouth…
- incisors
- canines
- premolars
- molars
Name the teeth in 1 quadrant of the mouth in order, front to back…
- central incisor
- lateral incisor
- cuspid (canine)
- first premolar (bicuspid)
- second premolar (bicuspid)
- first molar
- second molar
- third molar
What is another name for cavities?
Dental caries
What can missing teeth cause?
Excessive wear on the corresponding teeth above/below the abscess
What are the 3 main salivary glands?
Parotid
Sublingual
Submandibular
What % of saliva is water?
Approx 99%
Is saliva acidic, neutral or alkaline?
Slightly acidic (pH 6.75 - 7) to provide optimal conditions for enzyme action
What enzymes does saliva contain?
- lipase
- alpha-amylase
- lysozyme
What does saliva contain?
- water (99%)
- lipase
- amylase
- lysozyme
- mucoproteins (mucin for lubrication)
- immunoglobulins (esp, IgA)
- electrolytes
- calcium and phosphate (dental repair)
Which immunoglobulin is most abundant in saliva?
IgA
What approximate pH is saliva at?
6.75 - 7
Which element in saliva acts to lubricate the passage of food ?
Mucoprotiens (mucin)
Where are the salvatory nuclei located?
Pons and medulla
What type of receptors in the mouth stimulate watery saliva production ?
Mechanoreceptors
Chemoreceptors
Which type of receptors trigger saliva production when non-food objects enter the mouth?
Mechanoreceptors
What is the composition like of saliva produced in reaction to:
a) non-food stimuli ?
b) food stimuli ?
High water content = non-food stimuli
High enzyme content = food stimuli
Name the 2 intrinsic nerve plexuses in control of gut function …
Myenteric nerve plexus
Submucosal nerve plexus
Are the myenteric/submucosal nerve plexuses sympathetically or parasympathetically innervated?
Parasympathetic innervation
Which cranial nerve regulates the enteric nervous system (ENS)?
CN X = Vagus
What are the 3 divisions of the autonomic nervous system ?
Sympathetic NS
Parasympathetic NS
Enteric NS
What is the Enteric Nervous System (ENS) ?
The nervous system exclusively influencing the GI system
What are the 2 principle components of the enteric nervous system ?
- myenteric (Auerbach’s) plexus
- submucosal (Meissner’s) plexus
What is the function of the myenteric plexus?
Controls digestive tract motility
Increase muscular tone/strength/velocity of muscular contractions in peristalsis
What is the function of the submucosal plexus?
Controls absorption
Controls localised secretions, local muscular action, blood flow and, therefore, absorption of nutrients
What are the layers of the wall of the GI tract?
- lumen of GI tract
- mucosa
- submucosa (containers submucosal plexus)
- muscularis externa (circular muscular layer -> myenteric plexus -> longitudinal muscular layer)
- serosa
What 2 layers make up the muscularis externa in the GI tract wall?
- circular muscular layer (inner)
- longitudinal muscular layer (outer)
What action does contraction of the circular muscular layer have in the gut?
Squeezes gut contents
What action does contraction of the longitudinal muscular layer have in the gut?
Shortens that portion of the gut
Are the smooth muscle layers in the gut (muscularis externa) regulated or spontaneously active?
Smooth muscle in the gut is spontaneously active
regulated by enteric or extrinsic neurones
What are the pace maker cells of the gut called?
Interstitial cells of cajal (found in circular smooth muscle)
Where are the pacemaker cells (cells of cajal) found in the gut lining?
In the circular muscle layer of the muscularis externa
What can a loss of interstitial cells of cajal result in?
Gut motor dysfunction disorders
How long is the average oesophagus in adults?
Approx. 25cm long
(Pharynx to stomach)
What structures are contained within the submucosal layer of the GÌ tract?
- blood vessels
- lymphatics
- nerves
- lymphoid tissue
- mucus glands
Which sections of the oesophagus are voluntary/involuntary with regards to innervation of muscularis externa muscle?
- first 1/3 = voluntary skeletal muscle (decide to swallow)
- last 1/3 = involuntary smooth muscle (food pushes through involuntarily)
- middle third = mixed
What is adventitia?
The outer layer of fibrous connective tissue surrounding an organ
What is the outer layer of the oesophagus mainly made up of?
Adventitia fixed to adjacent structures via connective tissue
(fibrous connective tissue)
Which part of the oesophagus is cover with serosa (rather than adventitia?)
Serosa = past the diaphragm
Is the oesophagus held open or closed during relaxation periods?
The oesophagus is closed until food/an object pushes through it
What is the mucosa like within the oesophagus?
Highly folded (when oesophagus is closed)
What kind of epithelium is found in the oesophagus?
Stratified squamous epithelium
resists abrasion
What is the epithelium like in the GI tract after the oesophagus (at gastro-oesophageal junction) ?
Columnar epithelium (glandular)
What is a condition called that is seen in some patients prior to developing oesophageal cancer?
Barrett’s oesophagus
What is Barrett’s Oesophagus?
Unusual change of the epithelium within the oesophagus (from normal stratified to the columnar epithelium seen in gastric tract) due to to repeated damage from gastric reflux
What can cause Barrett’s Oesophagus ?
Acid/gastric reflux
Which general part of the stomach undergoes peristalsis?
Lower part of stomach
Which valve in the stomach acts in response to peristalsis?
Pyloric valve
What features of the stomach cause vigorous churning and slow gastric emptying of the stomach?
- peristalsis
- pyloric valve
What are the longitudinal mucosal folds called in the stomach ?
Rugae
Are the stomach’s mucosal and submucosal layers thin or thick?
Thick
What is one factor that controls the rate of gastric emptying of the stomach?
The caloric value of the contents in the duodenum
(duodenum = the next part of GI tract connected to stomach)
Which valve separates the stomach and the duodenum?
Pyloric valve / pylorus
What is the period/state between meals called?
Interdigestive state
When does the migrating motor complex (MMC) occur?
Between meals, in the interdigestive state
How long can it take for the migrating motor complex (MMC) to pass along the small intestine?
Up to 2 hours
What is the role of the migrating motor complex (MMC) ?
“House keeping” role = sweeps undigested material through the gut after eating
What is the migrating motor complex (MMC)?
Small irregular contractions of the small intestine during a period of ‘fasting’
What acts as a signal to stop the migrating motor complex (MMC)?
Release of gastrin and cholecystokinin in response to eating
eating triggers peristalsis which is better suited to nutrient absorption
Where is gastrin released from ?
The stomach
What is gastrin?
Peptide hormone that aids in gastric motility
Where is cholecystokinin (CCK) released from ?
The small intestine
What is cholecystokinin (CCK)?
A peptide hormone that stimulates fat and protein digestion
Which peptide hormone is a potent inhibitor of gastric emptying? What is it responding to?
Cholecystokinin (CCK)
Stops gastric emptying in response to high caloric value in the duodenum
What are the 3 parts of the small intestine in order?
- duodenum (closest to stomach)
- jejunum
- ileum
What are the parts of the large intestine, in order ?
- cecum
- ascending colon
- transverse colon
- descending colon
- rectum
- anus
What is another term for the large intestine?
The colon
Which part of the colon has the longest transit time?
The transverse colon
What is the average transit time in the colon?
2-3 days !
Is the colon active:
a) constantly ?
b) spontaneously ?
c) during eating ?
d) during fasting ?
The colon is active constantly
Haustral contractions Vs peristalsis in the colon?
Haustral contractions
= circular muscle contractions every 20/25 mins
= move food along the colon, from one haustra (pocket/bulge) to the next
= slow and continuous
Peristalsis
= circular + longitudinal muscle contractions 1/2 times a day
= shifts formed faecal matter from colon to rectum/anus
= relatively fast/forceful and infrequent
What does contraction of circular muscles in the colon cause?
Haustra = the rippled-looking bulges/pockets of the gut that are full of food
What is a haustrum?
A pocket in the colon formed by circular muscle contraction on either side of food
gives the colon it’s rippled/bulging appearance
What is the gastrocolic reflex ?
Powerful propulsive contractions are initiated in the colon when food enters the stomach
= dispels waste products to allow space for the new food entering
Where is gastrin produced/secreted?
Pyloric antrum (just before the valve)
Which cells produce gastrin in the stomach?
G cells
What are the functions of the stomach ?
- mix food
- act as a reservoir
- synthesise intrinsic factor
- start digestion (activates enzymes)
- destroy some bacteria/pathogens
- absorb some water, alcohol and B12
What is the only essential function of the stomach ?
Synthesis of intrinsic factor
(Intrinsic factor allows B12 absorption)
What does intrinsic factor do?
Allows for B12 absorption in the intestines
What is the rough pH of the stomach?
pH 1 - 2
(very acidic)
Which acid is found in the stomach?
Hydrochloric acid
Where is the majority of alcohol absorbed in the GI tract?
Duodenum and jejunum
(Small intestine)
Name the exocrine and endocrine gastric (stomach) secretions …
EXOcrine secretions:
- hydrochloride acid
- mucus
- Pepsinogen
- intrinsic factor
ENDOcrine secretions:
- gastrin
- somatostatin
What do goblet cells secrete in the stomach?
Alkaline mucus
(to protect the epithelium from acidic conditions within stomach)
What do mucous cells secrete in the stomach?
- Mucus
- Pepsinogens
What do parietal cells secrete in the stomach?
- gastric acid
- intrinsic factor
What do chief cells secrete in the stomach?
- pepsin
- gastric lipase
What do G cells secrete in the stomach?
Gastrin
What do D cells secrete in the stomach? Where are they found?
Secrete: somatostatin
Found: in antrum (close to pyloric valve)
What is the function of hydrochloric acid in the stomach?
- kills pathogens/bacteria
- initiates digestion
- produces pepsin from pepsinogen precursor
What is the function of mucus in the stomach?
Protects mucosal surface from damage caused by HCl
What is the function of pepsinogen in the stomach?
Precursor of the endopeptidase pepsin
What is the function of intrinsic factor in the stomach?
- Important in the absorption of B12 (in the gut)
- important in erythropoeisis
What is the function of gastrin in the stomach?
Stimulates gastric acid production for digestion
What is the function of somatostatin in the stomach?
Inhibits release of gastrin
What is an endopeptidase? Function?
An enzyme that hydrolyses the inner bonds between amino acids (rather than the terminal/end bonds) = shortens amino acid chains
Stimulation of which nerve increases pepsinogen secretion in the stomach?
Vagus nerve
(CN X)
Which neurotransmitter acts to increase pepsinogen secretion via CN X ?
Acetylcholine
Which chemicals act as stimulants for the secretion of hydrochloric acid (HCl) in the stomach?
- acetylcholine (via vagal input)
- gastrin (from G cells)
- histamine (from enterochromaffin cells)
- other hormones
Stimulation of which nerve can increase secretion of HCl in the stomach?
Vagus nerve
(CN X)
What are the factors/chemicals that inhibit gastric acid secretion?
- somatostatin
- secretin
- gastric inhibitory peptide (acts on parietal cells)
What are the 3 phases of gastric acid secretion called?
- Cephalic phase (40%)
- Gastric phase (50%)
- Intestinal phase (10%)
Roughly what % of gastric acid secretion occurs in the cephalic phase?
40%
Roughly what % of gastric acid secretion occurs in the gastric phase?
50%
Roughly what % of gastric acid secretion occurs in the intestinal phase?
10%
Which phase(s) of gastric acid secretion is/are vagally (CN X) mediated ?
Cephalic phase
Gastric phase
What factors trigger the Cephalic phase of gastric acid secretion?
Thought, smell, sight and taste of food
How does the Cephalic phase result in gastric acid secretion?
- Thought/sight/taste/smell of food releases Acetylcholine (via vagus nerve)
- ACh stimulates parental cells and G cells to release gastrin
How does the gastric phase result in gastric acid secretion?
- Distension, reflex activation of enteric neurones and vagal outflow stimulates parietal cells and G cells to secrete gastrin + gastric acid
- digested proteins in stomach stimulate G cells too
How does the intestinal phase result in gastric acid secretion?
Amino acids in the blood (from protein digestion) directly stimulate parietal cells to produce gastric acid
What are the 2 mechanisms that inhibit gastric acid secretion ?
- Gastric mechanism
- Duodenal mechanism
How does the gastric mechanism of inhibiting gastric acid secretion work?
- if proteins are in the stomach they create a buffer to keep lumen pH > 3 (normal)
- as stomach empties, lumen pH falls below pH 3
- stimulates D cells to release somatostatin to inhibit gastrin release
How does the duodenal mechanism of inhibiting gastric acid secretion work?
as stomach empties into duodenum lumen pH falls
- acidification of duodenal lumen stimulates secretin release (inhibits gastrin secretion)
- acidification of duodenal lumen + presence of fatty acids and salt release gastric inhibitory peptide which acts on parietal cells to inhibit HCL secretion
List the 6 major GI hormones and where they’re produced…
- Gastrin // G cells in antrum of stomach
- Motilin // duodenum
- Gastric inhibitory peptide (GIP) // small intestine
- Cholecystokinin (CCK) // small intestine
- Secretin // small intestine
- Vasoactive intestinal peptide (VIP) // glands and nerves
