GI physiology Flashcards
What are the extrinsic salivary glands
Parotid gland
Sub lingual
Sub mandibular
Account for 90% of saliva secreted
What are the intrinsic salivary glands
Labial
buccal
palatine
secrete saliva at a constant rate
accounts for 10% of saliva secretion
Where does the parotid gland secrete saliva
Via parotid duct into 2nd maxillary molar
Where does the submandibular gland secrete saliva
via Wharton’s duct into the lingual frenulum
Where does the sublingual gland secrete saliva
10-20 sublingual ducts
into floor of oral cavity
What cells make up salivary glands
serous cells
mucous cells
cells making up parotid gland
serous cells
cells making up submandibular gland
serous and mucous cells
cells making up sublingual gland
mucous cells do contain a small amount of serous cells
Intrinsic salivary glands are made up of what kind of cells?
Mucous
What cranial nerves supplies the sublingual and submandibular gland
CN7 Facial nerve (parasympathetic)
Deep petrosal nerve (symp)
What cranial nerves supplies the parotid gland
CN9 Glossopharyngeal nerve (parasymp)
Deep petrosal nerve )symp
What receptors can stimulate salivation, what else?
Chemoreceptors (acidic)
Mechanoreceptors (chewing)
Sight of food
Smell of food
Thought of food
Difference in saliva produces in parasymp and symp nervous system
Parasymp: volume of saliva increases: water and electrolyte-rich
Symp: Saliva that is protein-rich, thicker viscous saliva
What is found in saliva (ions etc)
Ions: Na+ K+ Cl- HCO3-
H20
IgA
Cystatin
Proline-Rich proteins
Lysozymes
How does water enter and leave acinus
Acinar cells contain:
Aquaporin 3+5
Pericellular transport
How does water enter acinus
peri cellular transport
Oral cavity boundaries
Anterior: Oral vestibule
Posterior: Palatoglossal arch
Purpose of mastication and salivation
Increase SA for chemical digestion
Decrease abrasion of G.I lining
What muscles are involved in elevation of tongue?
Extrinsic muscles of tongue
What muscles are involved in forming central trough?
Intrinsic muscles of tongue
Mandibular depression
Lateral pterygoid (CNV3)
Digastric (anterior belly) (CNV3)
Mylohyoid (CNV3)
Geniohyoid (C1) (Cervical plexus)
Let’s Dance Monkey Grooves
Mandibular elevator
Masseter
Temporalis
Medial pterygoid
CNV3
Move more trees
Oral phase
Oral cavity boundaries:
A: Oral vestibule
O: Palatoglossal arch
Mastication process:
Lat & Med pterygoid
Masseter
Temporalis
ALL INNERVATED BY CNV3
Salivation
chemical digestion
soften food
The downward slope of the tongue
Intrinsic & Extrinsic muscles of the tongue (CN XII)
Pharyngeal phase
Prevent bolus from going into the nasopharynx
Prevents bolus from going into the larynx
Prevents bolus from going into the pharynx
The upper oesophageal sphincter relaxes (Cricopharyngeus)
Prevent bolus from going into the nasopharynx how?
Uvula elevates
Levator Veli palatial contract
Tensor Veli palatini contract
Lifts soft palate
Prevents bolus from going into the larynx how?
- Approximate vocal cords adducts
- Retroversion of epiglottis
Prevents bolus from going into the pharynx HOW?
- Outer longitudinal layer - elevates pharynx and larynx
- Inner longitudinal layer - pharyngeal peristalsis
- Suprahyoid muscle - larynx elevated and moved anteriorly
Oesophageal phase
Primary peristalsis is a continuation of pharyngeal peristalsis (Lower oesophageal sphincter relaxes)
Secondary Peristalsis (Local reflexes). If the bolus is stuck
Is stage 1 of swallowing voluntary or involuntary?
Voluntary.
What happens in stage 1 of swallowing?
Food is compressed against the roof of the mouth and is pushed to the oropharynx by the tongue.
Is stage 2 of swallowing voluntary or involuntary?
Involuntary.
What happens in stage 2 of swallowing?
The nasopharynx closes off due to soft palate elevation. The trachea is closed off by the epiglottis. Elevation of the hyoid bone shortens and widens the pharynx.
Is stage 3 of swallowing voluntary or involuntary?
Involuntary.
What happens in stage 3 of swallowing?
The pharyngeal constrictor muscles sequentially contract to produce peristaltic waves. This propels the bolus of food down the Oesophagus. This is followed by depression of the hyoid bone.
Name 6 muscles/groups of muscles that are involved in swallowing.
- Buccinator.
- Suprahyoids.
- Muscles of the palate.
- Muscles of the floor of the mouth.
- Infrahyoids.
- Pharyngeal constrictor muscles.
B SIMMP
Which muscle(s) manipulate food in chewing. Elevate the hyoid bone and flatten the floor of the mouth?
Buccinator and Suprahyoids.
What is the function of the muscles of the soft palate in swallowing?
They act to tense and elevate the soft palate.
What is the function of the muscles of the floor of the mouth in swallowing?
They raise the hyoid bone and larynx.
What is the function of the infrahyoids?
To depress the hyoid bone and larynx.
What is the function of the pharyngeal constrictor muscles?
They contract sequentially producing peristaltic waves which drive food into the oesophagus.
Do parotid glands have mainly serous or mainly mucous acini?
Mainly serous acini.
What is serous acini secretion composed of?
alpha amylase - this is needed for starch digestion.
Do sublingual glands have mainly serous or mainly mucous acini?
Mainly mucous acini.
What is mucous acini secretion composed of?
Mucin - needed for lubrication.
Do submandibular glands have mainly serous or mainly mucous acini?
They have serous and mucus acini.
Which of the main salivary glands is constantly active?
Submandibular.
What is the function of saliva?
It acts as a lubricant for chewing, swallowing and speech. It is important in oral hygiene; has a role in immunity, wash and it can also act as a buffer.
What is the optimum oral pH?
7.2
What is the pH range of saliva?
6.2 - 7.4
Name 4 factors that can affect the composition of saliva.
- Stimulus.
- Age.
- Gender.
- Drugs.
Are serous acini dark staining or pale staining on a histological slide?
Dark staining.
(Mucus acini = pale staining).
What is the epithelium lining of intercalated ducts?
Simple cuboidal epithelium.
What is the function of intercalated ducts?
They connect acini to larger striated ducts.
What ions are reabsorbed at striated ducts?
Na+ and Cl-
Is saliva hypotonic or hypertonic?
Hypotonic - water reabsorption and ion secretion.
What is the importance of the striated duct basal membrane being highly folded?
It is folded into microvilli for the active transport of HCO3- against its concentration gradient.
What organelle is abundant in striated ducts and why?
Mitochondria. For the active transport of ions.
Name 2 ions that striated ducts secrete.
K+ and HCO3-
Name 2 ions that striated ducts reabsorb.
Na+ and Cl-
What ducts do striated ducts lead on to?
Interlobular (excretory) ducts.
What is the epithelium lining of interlobular ducts?
Simple columnar epithelium.
What is the parasympathetic innervation of the Parotid gland?
Cn 9 - glossopharyngeal.
What is the parasympathetic innervation of the Sublingual gland?
Cn 7 - facial.
What is the parasympathetic innervation of the Submandibular gland?
Cn 7 - facial
What nerve passes through the parotid gland but does not innervate it?
The facial nerve (Cn 7) gives rise to its 5 terminal branches in the parotid gland.
What artery ascends through the parotid gland?
The external carotid artery.
Does parasympathetic innervation stimulate or inhibit salivary secretion?
Stimulates.
What stimulates the cephalic phase of gastric secretions?
Sight of food
thought of food
smell of food
taste of food
Cephalic phase what happens (para)
Stimulus stimulates structures within the cerebral cortex to the hypothalamus
Stimulus sent to the vagus nerve to the stomach to trigger the secretion of HCl and pepsin, more is produced
What inhibits the cephalic phase of gastric secretions?
Anything that stimulates the sympathetic nervous system
Stress, emotional upset e.t.c
cephalic phase sympathetic
Nerve impulses travel down splanchnic nerve to inhibit the secretion of HCL + pepsin
what happens when the gastric phase is stimulated due to gastric distension
Activates stretch receptors go through either vago vagal reflex or enteric reflex
What cells are within the gastric glands of the antrum that either stimulate/inhibit gastric phase secretion
enteroendocrine G cells
What do enteroendocrine G cells release
Gastrin
What is gastrin responsible for
Binds to chief cells receptors and secretes pepsinogen which gets converted to pesin
Binds to parietal cell receptors and secretes HCL
What pH is necessary for pepsinogen to be converted to pepsin
1.8-3.5
What inhibits/stimulates gastric phase
Stimulates:
Distension
Partially digested protein-pH related
Inhibits:
S.N.S
Somatostatin
What can inhibit/stimulate the parietal cell
Stimulates:
Gastrin
Ach
Histamine
Inhibits
prostaglandin
somatostatin
PPS HAG
What can inhibit/stimulate the chief cell
Stimulates
Ach
Secretin
Histamine
Inhibits
Gastrin
CASH G
What does the enterochromaffin cell secrete
Histamine
(Stim: Ach, Gastrin)
(Inhibit: Somatostatin)
What is the purpose of the mucosal barrier?
Prevents corrosive damage by HCl + pepsin
Where do the most powerful contractions in the stomach take place?
Pylorus
What happens when the pylorus contract
Retropulsion (chyme back up stomach)
Chyme pumped into duodenum
What do S cells secrete
Secretin
What does secretin stimulate/inhibit
Stimulates the liver to turn cholesterol into bile synthesis
Inhibits G cells to secrete Gastrin
Stimulate ductal epithelial cells of the pancreas to secrete HCO3-
What do I cells secrete
Cholecystokinin
what does Cholecystokinin stimulate
Stimulates the liver to break down cholesterol into bile
Stimulates the gallbladder to secrete conc bile
Binds to the sphincter of Oddi to relax
Binds to pancreatic acinar cells to excrete pancreatic digestive enzymes contents via exocytosis
Pyloric sphincter purpose
Lets small amounts of chyme into duodenum, the ensures that H+ doesn’t get too high and damage duodenum
What is the mucosal barrier made-up of
Gel layer (Top): H2O, Phospholipid, High amount of mucins: HCO3-)
HCO3- layer
What converts pepsin into pepsinogen
HCO3-
If pepsin wants to escape the gel layer of the mucosal barrier then it reacts with HCO3- of the mucosal barrier
H+ + HCO3- —> H20 + CO2
Diff between tonic and rhythmic contractions
Tonic is a sustained contraction
Rhythmic is alternating contractions
What are the interstitial cells of Kajal
Pacemaker cells
They spontaneously depolarise that cause other smooth muscle of GI tract to contract
Explain spike potential
Every time a wave is produced above the subthreshold it generates spike potential. The bigger the wave above subthreshold the more spike potential is formed. This means that a bigger force of contraction will be produced.
Fundamentals of motility
Segmentation (Rhythmic)
- mix chyme with digestive juices
- increases absorption of nutrients
Propulsion/Peristalsis (Rhythmic)
-move G.I content along the G.I tract
Resovoir functions (storage functions)(Tonic) -Sphincter
What is peristalsis
alternating wave of contraction and relaxation
Zenkers diverticulum
Outpouching just above UES
Dysphagia
Cough/Regurgitation
Halitosis
Primary function of oesophagus in G.I motility
Peristalsis
What is receptive relaxation
It is when the vagus nerve relaxes the fundus of the stomach as its getting ready to receive the food prior to food being in the stomach
What do receptive & adaptive relaxation play a role in
Gastric accommodation
What is gastric accommodation
When the bolus is in the stomach the intra-gastric volume increases
But the intragastric pressure stays the same as long as it’s not above 1.5l
What stimulus plays and important role in segmentation/peristalsis
distension
PSNS
SNS
Irritants
Segmentation in small intestine
-Sluggish short-lived contractions
-mixing chyme + BILE+ pancreatic enzymes + intestinal/pancreatic fluid ( HCO3- & mucous)
Mixing chyme enhances absorption
-anterograde (->anal) and retrograde (-> oral)
-Increases contact time with the chyme and mucosal surfaces to stimulate absorption
Role of stomach?
Storage (reservoir)
Mixing
emptying
Peristalsis in small intestine
Propulsive action (oral –> anal)
Migrating mobility complex
Occurs between meals (Fasting State)
Peristalsis starts at stomach to ileum
2 hours typical duration
Pulls food residue, dead cells, undigested substances
stimulated by motilin
What opens the ileocecal valve as its always closed and what is the purpose of this
Increase in gastrin
Gastrocecal reflex
=relax ileocecal valve & contraction of distal ileum
Haustral contractions
segmentation
triggered by distension
occurs in ascending & descending colon
mainly driven by Teniae Coli
Absorption: electrolytes, water, complex B vitamins
Mass movement (Peristalsis) of large intestine
Propulsion of rectum
primarily occurs in transverse & descending colon
Primary stimulants: stretch, irritants, the gastrocolic reflex
Occurs 3-5 times per day
During meals or after
Contractions over 20cm of a portion of large intestine
Defaecation Reflex
- Stretch of sigmoid colon and rectum
- stimulates sensory fibres and travel to CNS
- Stimulates parasympathetic motor fibres
- Contraction of the sigmoid colon and rectum
5, Relax the internal anal sphincter - Relax the external anal sphincter (voluntarily)
What nerve innervates the external anal sphincter
pudendal nerve
What innervates the internal anal sphincter
Pelvic nerve
Describe the internal anal sphincter
smooth muscle involuntary reflex (muscle) innervated by the autonomic nervous system
Describe the external anal sphincter
Skeletal muscle
voluntary
innervated by the somatic nervous system
G.I Motility of oesophagus is primarily
Peristalsis
G.I Motility of small intestine is primarily
Peristalsis
Segmentation
Ileocecal valve plays a role as well
G.I Motility of large intestine is primarily
Haustral contractions (segmentation) Mass movement (peristalsis) Defaecation reflex
What enzyme digests carbohydrates secreted by salivary glands
salivary alpha-amylase
What enzyme digests carbohydrates secreted by pancreatic acinar cells
pancreatic amylase secreted in the duodenum
What enzymes are secreted in the aid of digesting lipids
Sublingual and parotid secreting lingual lipase
Chief cells in the stomach secreting gastric lipase
Pancreas secreting bile, pancreatic lipase, PLA2, Cholesterol Ester Hydrolyse
What is the volume of an empty stomach?
50ml
What is the maximum volume of the stomach?
1.5L
What is receptive relaxation?
Smooth muscle in the body and fundus of the stomach relaxes prior to the arrival of food, this allows the stomach volume to increase. There is afferent input from Cn 10. NO and serotonin also influence relaxation.
Where do peristaltic waves begin in the stomach?
In the gastric body.
Where in the stomach are peristaltic contractions the most powerful?
In the gastric antrum.
Why is the pyloric sphincter closed as the peristaltic wave reaches it?
This prevents chyme entering the duodenum and so the gastric contents are forced back and mixed together in the body of the stomach.
On average, how many peristaltic waves are there a minute?
3 (slow repol/depol cycles).
Name 2 factors that can increase the strength of peristaltic contractions.
- Gastrin.
- Gastric distension.
Name 5 factors that can decrease the strength of peristaltic contractions.
- Duodenal distension.
- Low pH in duodenum lumen.
- Increased duodenal osmolarity.
- Increased sympathetic action.
- Decreased parasympathetic action.
ID LID
What do parietal cells secrete?
H+ and intrinsic factor.
What cells secrete Gastrin?
Enteroendocrine cells / G cells.