Gastrointestinal System Flashcards
(122 cards)
1
Q
What is the digestive system (DS) also referred to as?
A
Digestive tract, gastrointestinal tract and alimentary canal
2
Q
What does the DS consist of?
A
1) Oral cavity (mouth)
2) Pharynx
3) Oesophagus
4) Stomach
5) Small intestine
6) Large intestine
3
Q
What do the accessory organs and glands of the DS include?
A
1) Teeth
2) Tongue
3) Salivary glands
4) Liver
5) Gall Bladder
6) Pancreas
4
Q
What is the daily energy requirement of the human body at rest?
A
Around 30kcal/kg of body weight
5
Q
What are the sub-units that can be assimilated and utilised by our cells for?
A
1) For energy generation (ATP)
2) Cell growth and repair
6
Q
What are the processes of the DS?
A
1) Ingestion
2) Propulsion
3) Mechanical digestion
4) Chemical digestion
5) Secretion
6) Absorption
7
Q
What do the processes of the DS allow for?
A
Eliminates indigestible waste material by defecation/excretion
8
Q
What does ingestion involve?
A
Introducing food and liquid nutrients into the digestive tract via the OC
9
Q
What is propulsion?
A
Moves food through the DS at a rate that permits optimal digestion and absorption along the DS
Includes deglutition (swallowing food)
10
Q
What is peristalsis?
A
Mechanism of transporting food along the DS
Involuntary process
Consists of successive waves of contraction and relaxation of smooth muscle layers in gut wall
11
Q
What is mechanical digestion in the oral cavity?
A
Solid food is process by chewing (mastication) and shearing action of teeth mixed with saliva by the tongue forming food boluses
12
Q
Why is mechanical digestion of ingested food important for chemical digestion?
A
Increases SA of food, facilitating subsequent chemical digestion by enzymes
13
Q
What other mechanical processing are there in the DS?
A
Churning of food in stomach
In the SI segmentation movements of gut wall ensure food is mixed well with digestive enzymes
14
Q
What is secretion?
A
Release of H2O, acids, enzymes, buffer by gut epithelium and accessory glands to aid chemical digestion of food
Secretions produced along DS may have digestive/protective functions
15
Q
What is absorption?
A
Movement of breakdown products of digestion (e.g., aa, fas, H2O and inorganic ions) across intestinal epithelium into interstitial fluid of gut epithelium
Then into lymph vessels/circulatory for distribution to cells
16
Q
What is defecation?
A
1) Eliminates faecal material containing indigestible residues (e.g., cellulose)
2) Faecal material includes colonic bacteria and metabolic waste products
3) Excretory products include heavy metals such as Fe2+, organic anion and cationic drugs excreted in bile
17
Q
What are the 4 major layers of the gut wall?
A
1) Mucosa
2) Submucosa
3) Muscularis externa
4) Serosa/Adventitia
18
Q
What are the 3 sub-layers in the mucosa?
A
1) Epithelium
2) Lamina propria
3) Muscularis mucosae
19
Q
What are the 2 division for the muscularis externa?
A
1) Longitudinal muscle
2) Circular muscle
20
Q
What are the 2 divisions within the intrinsic nerve plexus?
A
1) Myenteric nerve plexus
2) Submucosal nerve plexus
21
Q
What are the 2 division in serosa?
A
1) Epithelium
2) Connective tissue
22
Q
What are the properties of the mucosa?
A
1) Epithelium may be simple/stratified
2) Stratified squamous epithelium - protective
3) Lamina propria is highly vascular loose connective (aerola) tissue, rich in lymph vessels (mast cells part of mucosa-associated lymphoid tissue (MALT)), mucous secreting cells
23
Q
What does the muscularis mucosae of the mucosa contain?
A
Elastic fibres, inner circular layer of smooth muscle cells (SMC) concentric with lumen of DS and an outer longitudinal layer of SMC
24
Q
What are the properties of the submucosa?
A
1) Thick irregular layer of connective tissue
2) Rich in large blood vessels - extend to mucosal layer
3) Contains lymph vessels, glands and MALT tissue
4) Intrinsic Innervation by Enteric Nervous System - Submucosal plexus
25
What are the properties of the muscularis externa (ME)?
1) Comprised of visceral SMC
2) Arranged into inner circular and outer longitudinal layer of SMC
3) Role in mechanical digestion and peristaltic movements of food along DS
4) Responsible for gut mobility
26
How is the ME regulated?
By the ENS - large myenteric nerve plexus lies between 2 muscle layers
Motility of SMC in each layer is coordinated by enteric sensory neurons, interneurons and motor neurons in plexus
27
What is the role of pacesetter cells (PC)?
1)Rhythmic contractions (peristalsis) of SMC is set by PC located in the MM and ME
2) PCs have resting membrane potential of -60/-50mV and undergo spontaneous depolarisation
3) Are electrically coupled to adjacent SMC by gap junctions
4) Depolarisation spreads through adjacent cells inducing wave of contraction in entire muscle layer
28
What does innervation of the gut wall of the DS consist of?
1) Intrinsic and extrinsic components
2) Intrinsic innervation is enteric nervous system (ENS)
3) Enteric neurons derived from neural crest cells
4) Both components allow for precise control of digestive processes as regulation of gut motility and secretory activity during digestive periods
29
What are the properties of the enteric nervous system (ENS)?
1) Consists of approx. 100mil neurons derived from neural crest cells
2) Consists of complete neural reflex circuits regulating gut motility and secretory processes of DS
3) Can work autonomously without instructions from brain (e.g., in control of peristalsis)
4) Extrinsically innervated
30
What is the process of local sensory-motor reflex circuits?
1) Sensory neurons monitor gut lumen activity (e.g., distension of gut wall)
2) Internuerons activated by sensory neurons relay action potentials that activate enteric motor (effector) neurons
3) Motor neurons stimulate/inhibit a wide range of effector cells including PCs of the ME, secretory cells, submucosal blood vessels
31
What are the properties of the serosa/adventitia?
1) Thin layer connective tissues
2) Contains blood and lymph vessels
3) Adipose tissue
4) Covered by simple squamous epithelium - mesothelium
32
What is the oral/buccal cavity comprised of?
1) Lips - anterior boundary
2) Cheeks - lateral boundary
3) Palate - superior boundary
4) Tongue - inferior boundary
5) Mostly lined by stratified squamous epithelium
6) Regions exposed to significant friction (e.g., gums - gingiva) covered by protective layer of keratinised epithelial cells
33
What is the palate?
1) anterior part of palate is termed hard palate, posterior - soft palate
2) Cleft palates - common congenital disorder resulting in malformation of hard palate
34
How does the palatine shelves of the hard palate develop?
During 6th week of embryonic development, palatine shelves form on each side of tongue as downward oblique outgrowths from maxillary processes
The nasal cavity is open it oral cavity
35
What happens to the palatine shelves during the 7th week of embryonic development?
1) Tongue moves downward in OC
2) Palatine shelves elevate to occupy horizonal positions relative to tongue
3) Fusion of palatine shelves with primary palate separates oral from nasal cavity
4) Enables hard palate to perform digestive function effectively
36
What is the lnp, mnp and mx?
1) Lnp - lateral nasal prominence
2) Mnp - medial nasal prominence
3) Mx - maxillary
37
What causes clefting abnormalities?
Defects in the coordinate fusion of the lnps, mnp and mx processes
38
What is folic acid used for during development?
Prevents FA deficiency during pregnancy
39
What is the structure of the hard palate?
1) Separates oral and nasal cavities
2) Has thick ridge (raphe) runs along midline of hard palate
3) Mucosa on each side of raphe is corrugated
40
What is the function of the hard palate?
Facilitates deglutition providing a surface against the tongue, applying force on food propelling it onwards down GI tract
41
What is the soft palate?
1) Flexible flap of skeletal tissue
2) Finger-like structure, uvula dangles from free edge of soft palate
3) Is attached to tongue and pharyngeal wall by 2 pairs of lateral muscular arches
42
What is the uvula involved in?
Deglutition and helps prevent food from entering pharynx prematurely
43
What are the 2 arches in the soft palate?
1) Anterior arch - palatoglossal arch
2) Posterior arch - palatopharyngeal arch
44
What are the accessory organs and glands of the OC?
1) Teeth
2) Tongue
3) Salivary glands
45
What are the structures of the tongue?
1) Consists of intercalating bundles of intrinsic and extrinsic skeletal muscle fibres
2) Attached to the floor of the OC by thing mucosal tissue - lingual frenulum
3) Lingual frenulum limits excessive posterior movements of tongue
4) Superior surface and lateral edges are covered with papillae
46
What is the function of the tongue?
1) Manipulates food between teeth for mechanical processing
2) Mixes food with saliva to form food boluses
47
What are the 3 types of papillae in the dorsum of the tongue?
1) Filiform (thread-like) projections arranged in parallel rows in anterior 2/3rd of tongue - contain sensory receptors for touch
2) Fungiform (mushroom-like) - extensions of tongue's lamina propria, more numerous at tip of tongue, contain gustatory receptors
3) Circumvallate Papillae - arranged in upside-down V array in posterior surface of dorsum, all contain gustatory receptors
48
Where are minor salivary glands located in mucous membrane?
1) Cheeks - buccal glands
2) Lips - labial glands
3) Palate - palatal glands
4) Tongue - lingual glands
All produce small quantities of saliva
49
Where are the major salivary glands located?
1) Parotid gland
2) Submandibular gland
3) Sublingual gland
50
How do major salivary glands deliver their secretions into OC?
1) Branching system of ducts to deliver secretory products into OC
2) Each gland divided into lobules containing structural and functional secretory units - acinus + intercalated duct
3) Acinus contains 15-100 acinar cells that synthesise and secrete protein products into intercalated ducts for delivery
51
What are the structures of major salivary glands?
1) Paired compound exocrine glands
2) Are specialised secretory organs
3) Polarised epithelial cells
4) Specialised for production of large amounts of proteins - have well developed RER
52
What are the 2 salivary acinar cell populations and what do they produce?
1) Mucous secreting acinar cells - secrete mucins (HMW, heavily glycosylated proteins)
2) Serous secreting acinar cells - produce watery secretion containing a-amylase, proline-rich proteins and ions
53
Where are acinar cell populations found?
1) Parotid gland - only secrete serous
2) Submandibular gland - secretes both mucin and serous
3) Sublingual gland - only secrete mucin
54
What solutes are found in saliva?
1) Na+, K+, Cl-, HCO3-, phosphate
2) Cl- required for activation of salivary amylase, HCO3- and phosphate buffer ingested acidic foods
3) Thiocynate ions
55
What is the compostion of saliva?
Approx. 99.5% H2O and 0.5% solutes, pH is approx. 6.75-7
56
What proteins other from principal protein products are found in saliva?
1) Lysosyme
2) Proline-rich proteins (accounts for 1/3rd of total aa content)
3) Immunoglobulins IgA
4) Defensins
5) Nucleases, lipase, GFs (e.g., nerve GFs), peroxidases
57
What are the digestive functions of saliva?
1) Provide lubrication for food bolus formation, mastication and deglutition
2) Provide enzymes and optimal pH for carbohydrate and lipid digestion
3) H2O content of saliva is solvent for dissolving food so tastants can be tasted and digested
58
What are the protective oral hygiene functions of saliva?
1) Prevent dehydration of oral mucosa
2) Wash away microbes and food particles
59
What are the factors of saliva that destroy bacteria?
1) Thiocyanate ions (bactericidal)
2) Lysosyme attack bacteria allow thiocyanate ions to enter + destroy bacteria
3) Lysosymes digest food particles that support bacterial growth
4) Immunoglobulins IgA destroy bacteria
5) Proline-rich proteins - antimicrobial
6) Defensins - antimicrobial
60
How do functions of the OC help drug administration?
1) Mucosa beneath tongue is sufficiently thin and vascular for absorption into blood stream of lipid-soluble drugs (e.g., nitroglycerin - treatment for angina)
2) Some drugs can be administered via buccal route (e.g., rescue medication for epilepsy 'status epilepticus', midazolam)
61
What is the structure of the pharynx?
1) Consists of 3 distinct regions - nasopharynx, oropharynx and laryngopharynx
2) Food boluses pass from OC to oropharynx then to laryngopharynx
3) Oropharynx and laryngopharynx lined by stratified squamous epithelium
4) Lamina propria has rich supply of mucus-secreting glands
62
What is the process of deglutition?
1) Initiated voluntarily but then proceeds automatically
2) Involves multiple sets of skeletal muscles that control activity of tongue, soft palate, oropharynx, laryngopharynx and oesophagus
3) Coordinated contraction of these sets of muscles results in deglutition, each must receive motor command to contract at correct time
63
What happens in the process of deglutition in the voluntary (buccal) phase?
1) Begins with ingestion of food
2) Ends shortly after tongue compresses a food bolus against hard palate, retracts and propels bolus towards oropharynx
64
When food boluses are propelled toward the oropharynx what mechanoreceptors do they stimulate in the buccal phase?
1) Uvula
2) Palatoglossal arch
3) Palatopharyngeal
4) Posterior pharyngeal wall
65
What happens in the pharyngeal-oesophageal phase?
1) Stimulation of mechanoreceptors activates sensory afferent neurons in cranial nerve IX
2) APs sent from cranial sensory neurons to swallowing centre in nucleus tractus solitarius (NTS) located in medulla and lower pons
3) Sensory input processed in NTS
4) NTS activates adjacent motor nucleus ambiguous (NA)
5) NA contains cell bodies of motor neurons that innervate skeletal muscles involved in deglutition
66
What is the motor output from NA in the pharyngeal-oesophageal phase?
Motor commands (APs) sent from NA via cranial nerves 1X + X to skeletal muscles involved in deglutition
67
What are the involuntary phase events in pharyngeal-oesophageal phase?
1) Respiratory centres in CNS are inhibited - breathing stops momentarily
2) Contraction of superior pharyngeal constrictor muscles initiates this
3) Soft palate and uvula rise to close off nasopharynx
4) Larynx raised and epiglottis folds over opening in larynx to respiratory tract
5) All routes in pharynx except digestive tract sealed off
6) Food moves through pharynx towards oesophagus via contractions of pharyngeal constrictor muscles
7) Upper oesophageal sphincter is relaxed
8) Bolus moves through oesophagus via peristalsis, distension of oesophageal wall due to approaching food bolus near stomach triggers opening of lower oesophageal sphincter
68
What is dysphagia?
Common complication of neurological disorders (e.g., amyotrophic lateral sclerosis, ALS)
Characterised by selective death of motor neurons (Mns) in brain cortex, brain stem (NA) and spinal cord (e.g., somatic NS)
69
What are some of the symptoms of dysphagia?
1) Impaired speech
2) Laboured breathing
3) Death usually occurs within 2-5yrs of disease onset
70
What is the structure of the oesophagus?
1) Muscular tube extending from laryngopharynx to stomach
2) Resting muscle tone of circular muscle layer of proximal oesophagus prevents air from entering oesophagus - region is termed upper oesophageal sphincter (UOS)
3) Comparable region in distal oesophagus termed lower oesophageal sphincter (LOS)
4) LOS normally constantly contracted, prevents reflux of food material from stomach to oesophagus
71
What are the regional specialisations of the oesophagus?
1) Specialised for transport of food and liquids from upper digestive tract to stomach
2) Has 4 layers of typical gut wall - mucosa comprised of stratified squamous epithelium
72
What is the function of mucus-producing oesophageal glands?
1) As food bolus moves through oesophagus, glands secrete mucus that lubricates oesophageal wall
2) They become more complex near oesophago-gastric junction (LOS)
73
Food is propelled by what 2 types of peristaltic movements in the oesophagus?
1) Primary peristaltic waves
2) Secondary peristaltic waves
74
What are the general functions of the stomach?
1) Temporary storage of ingested food
2) Mechanical digestion of food boluses
3) Chemical digestion of food boluses by acids + enzymes
4) Production of intrinsic factor
75
What is the structure of the gastric cardia?
1) Surrounds lower oesophageal sphincter
2) Has rich supply of mucous secreting glands
3) Mucous protects cardia and oesophageal mucosa from gastric acid and digestive enzyme
76
What is the structure of the fundus in the stomach?
Dome-shaped region beneath diaphragm
77
What is the structure of the corpus (body) of the stomach?
1) Mid-portion of stomach
2) Largest part of stomach
3) Acts as mixing tank for food bolus and stomach secretions
4) Specialised for mechanical digestion of food boluses
78
What is the structure of pyloric antrum in the stomach?
1) Corpus narrows to form pyloric canal that empties into duodenum
2) Pyloric sphincter regulates emptying of chyme (highly-acidic partially digested food)
79
How is the gastric muscularis externa adapted for mechanical digestion?
1) Rugae - longitudinal folds of mucosa and submucosa of relaxed stomach
2) Muscularis mucosae - extra outer circular smooth muscle layer
3) Muscularis externa - additional layer of smooth muscle cells
80
What is the structure of the stomach?
1) Lined by simple columnar epithelium
2) Epithelium has goblet cells that produce protective HCO3- ions and mucus
3) Mucous surface layer traps bicarbonate-rich fluid beneath - protective alkaline mucous layer
4) Deep depressions in surface epithelium of gastric mucosa are gastric pits
5) These lead into gastric glands that extend deep into lamina propria of stomach wall
81
What are the different cell types in the proximal stomach compared to the distal?
1) Mucous neck cells
2) Parietal (oxyntic) cells
3) Chief (peptic) cells
4) Enteroendocrine cells release hormones (e.g., gastrin directly into lamina propria)
82
What is gastic juice?
Combined secretions of parietal (HCl) and chief (enzymes) cells - about 1.5L can be produced per day
83
What is the role of parietal cells (PCs) in the gastric gland of the proximal stomach?
1) Large triangular shaped secretory cells located in proximal region of each cell
2) Secrete copious volumes of HCL
3) Secrete intrinsic factor
4) Innervated by vagus nerve
84
What is the role of chief cells (peptic)?
1) Smaller in size that parietal cells
2) Located close to the base of each gland
3) Secrete zymogen pepsinogen
4) At pH <3, pepsinogen hydrolysed to pepsin - active enzymatic form
5) Gastric acid secretion (GAS) and pepsinogen secretion occur mainly in fundus and corpus of stomach
85
What are the other cell types in the gastric gland of the proximal tube?
1) Mucous secreting neck cells
2) Enteroendocrine cells (such as histamine secreting enterochromaffin-like (ECL), Somatostatin secreting enteroendocrine cells (D cells)
86
What are the secretions of the gastric glands of the distal stomach?
There is no secretion of HCL/intrinsic factor/pepsinogen in pyloric antrum as pyloric glands lack parietal and chief cells
87
What do pyloric glands contain?
1) Endocrine (enteroendocrine) cells
2) D cells
88
What do the endocrine cells in the pyloric glands do?
1) Secrete the hormone gastrin
2) Exists in several forms - little gastrin (17aa peptide), big gastrin (34aa peptide)
3) Both forms equally bioactive + present in equal amounts during digestive periods
4) Stimulate acid secretion
5) Stimulate release of histamine from ECL cells
6) Promotes mucosal growth in corpus and small/large intestines
89
What do D cells do in the pyloric glands?
1) Secrete somatostatin
2) Peptide hormone inhibits gastrin secretion
3) Blocks acid secretion from parietal cells
90
How do parietal cells secrete HCl as they do not produce it in their cytoplasm?
1) Carbonic anhydrase converts CO2 and H2O to carbonic acid (H2CO3)
2) H2CO3 dissociates to HCO3- and H+ ions
3) HCO3- released into extracellular fluid by HCO3-/Cl- antiporter that exchanges intracellular HCO3- for extracellular Cl-
4) Cl- diffuse passively across cell through open chloride channels in apical membrane of parietal cells and into lumen of gastric glands
91
How are H+ ions transported to the gastric glands?
1) Actively transported by H+/K+ ATPase pump
2) Changes intracellular H+ ions for luminal K+ ions
92
What is the source of luminal K+ ions in GAS?
1) Extrusion of H+ ions into lumen of gastric gland exchanges for K+ ions
2) H+/K+ ATPase pump provides energy for this
93
What are the specialisations of the PC apical membrane for GAS?
1) Tubulovesicles (TVs) present in apical region of parietal cells at rest
2) TVs express H+/K+ ATPase pumps, K+ and Cl- ion channels
3) When stimulated, cytoskeleton re-organisation allows TVs to fuse with apical membrane and form canaliculi
4) This increases SA (50-100%) of apical membrane for acid secretion
94
What happens at maximal rates of HCl secretion?
1) Huge luminal [HCL acid] gradient towards epithelium potentially corrosive to epithelial cells
2) Digestive enzymes (e.g., pepsin) could digest cells of stomach walls
95
What are the protective mechanisms of the gastric mucosa?
1) Mucosal gel layer (MGL), made of mucin, phospholipids, electrolyes and H2O
2) HCO3- ions secreted by surface epithelial cells
96
How does mucin protect the gastric mucosa?
1) Is a tetrameric protein
2) Consists of 4 identical peptides linked by strong disulphide bonds
3) Extremely viscous, consequently forms mucous gel with other components
4) Secreted by epithelial goblet cells and mucous neck cells
97
How does secreting HCO3- protect the gastric mucosa?
1) HCO3- become trapped between epithelial cells and unstirred overlying MGL
2) Local pH of 7 is maintained in vicinity of apical membrane of epithelial cells
3) Na/HCO3- cotransporter may mediate uptake of HCO3- across basolateral membrane of surface epithelial cells
98
What are the other protective mechanisms of the gastric mucosa (not HCO3- or MGL)?
1) Tight junctions between epithelial cells exclude gastric juice from deep layers of gastric walls (e.g., lamina propria and MM sublayers)
2) Apical membranes of deep glandular cells are impermeable to HCl
3) Rapid replacement of damaged epithelial cells by stem cells located between gastric pits and gastric glands
99
What are the 3 main phases of GAS during a digestive period?
1) Cephalic
2) Gastric
3) Intestinal
100
What is the cephalic phase of GAS regulation?
1) Prepares stomach for digestive functions
2) Sight, smell, taste, thought of food trigger APs in higher brain centres
3) APs relayed to dorsal motor nucleus (DMN) of vagus nerve (DMNV) in medulla
101
What happens in the cephalic phase during GAS regulation by the vagus nerve?
1) DMN contain cell bodies of parasympathetic, vagal, pre-ganglionic efferent motorneurons
2) Their axon run through CNX
3) APs from higher brain centres activate these neurons
4) APs sent via vagus nerves to stomach
5) APs initiate 4 distinct physiological processes that increase GAS during cephalic phase
102
What are the 4 physiological processes that increase GAS during the cephalic phase?
1) In gastric glands of fundus and corpus - vagal post-ganglionic motorneurons release ACh in muscarinic (M3) ACh receptors in basolateral membrane of PCs. ACh binds to M3 receptors and stimulates H+ secretion into lumen of gastric glands
2) ACh released from axon collaterals of cholinergic vagal postganglionic neurons diffuses through lamina propria to adjacent ECL cells - release histamine, binding to H2 receptors on basolateral membrane of PCs stimulating H+ secretion into lumen of gastric glands
3) In gastric glands of antrum - peptidergic postganglionic vagal efferent motorneurons release Gastrin Releasing Peptide(GRP) near basolateral of G cells. G cells release gastrin (big and little) - then stimulates acid secretion directly through gastrin receptors (CCK2R) on basolateral membrane of PCs and indirectly through histamine release from ECL cells
4) In corpus and antrum of stomach - as luminal pH decreases, stimulates somatostatin release from D cells, inhibiting gastrin release from G cells (in antrum) and histamine release from ECL cells (in corpus) reducing GAS
103
How does the vagus nerve counteract the reduction of GAS?
1) Inhibits release of somatostatin from D cells
2) Reduces inhibition of gastrin release from G cells and histamine release from ECL cells by somatostatin
3) Prevents inhibition of cephalic phase by somatostatin
104
What is Zollinger-Ellison syndrome (ZE)?
1) Over-production of gastrin
2) Non-beta cell tumours of pancreatic islets continuously secrete excessive amounts of gastrin
3) Therefore, gastrin secretion not under physiological control
105
How can unregulated gastrin secretion lead to chronic hypersecretion of HCl from PCs?
1) Enhances basal secretion of HCl
2) Chronic hypersecretion of HCl erodes mucosa of stomach wall leading to gastritis and gastric (peptic) ulcers
106
What are gastric acid secretagogues?
Molecules that stimulate gastric acid secretion from PCs through 2nd messenger systems - ACh, histamine and gastrin
107
How do gastric acid secretagogues affect HCl secretion from PCs?
1) HCl secretion is low if only 1 ligand binds to PCs
2) When all 3 secretagogues bind - volume produced is greater than sum of volumes produced by each secretagogue acting alone
107
What are pharmacological treatments for ZE?
1) Rantidine (H2 receptor antagonists) -disrupt potentiation effect of secretagogues on GAS from Pcs
2) Omeprazole - blocks H+/H+ ATPase pump blocker - example of proton pump inhibitor
108
What does the entry of food into the stomach trigger in the gastric phase?
1) Distension of gastric mucosa
2) Partially digested proteins in gastric gland of lumen
109
What happens in the distention of gastric mucosa of corpus and antrum?
1) Stimulates mechanoreceptors in gastric mucosa, then activates vagal afferent pathway from stomach to DMN
2) DMN integrates sensory inputs from stomach and transmits APs conveyed through vagal efferent pathway to stomach
3) Vagal afferent and vagal efferent pathways termed vago-vagal reflex
4) Vago-vagal reflex maintains GAS through 4 processes that mediated HCl secretion from PCs when vagus nerve activated during cephalic phase
5) Distention of gastric mucosa activates local ENS pathway (short myenteric reflex) releasing ACh into vicinity of PCs, ACh stimulates acid secretion from PCs
110
What do partially digested proteins (peptones) do in the antrum?
1) Indirect stimulator of acid secretion from PCs
2) Directly stimulate G cells to release gastrin - promoting acid secretion from PCs
3) Coffee, caffeine and ingredients in beer + wine stimulate acid secretion via same mechanism as peptones
111
What is the role of inhibitory components in the gastric phase in the regulation of GAS?
1) Low luminal gastric pH stimulates antral D cells to secrete somatostatin
2) Somatostatin inhibits gastrin secretion from G cells
3) This reduces acid secretion during this phase
112
What are the 2 components of the intestinal phase of GAS?
1) Excitatory
2) Inhibitory
113
What happens in the excitatory component of the intestinal phase?
1) Partially digested food in duodenum stimulate intestinal mucosal cells to release gastrin
2) Gastrin stimulates HCl acid secretion from PCs
114
What happens in the inhibitory component of the intestinal phase?
1) Enterogastric reflex initiated as intestine distends with chyme containing fats, H+ etc.
2) Inhibits dorsal motor nucleus in medulla
3) Inhibit local enteric reflexes
4) Activates sympathetic nerves that induce pyloric sphincter to contract further and prevent more chyme entering duodenum
5) Enterogastric reflex attenuates gastric activity and protects duodenum from excessive acidity
6) Fats stimulate enterogastrones, secretin, CCK, VIP and GIP released from intestinal mucosa - all inhibit GAS
115
What are the functions of the small intestine?
1) Completion of chemical digestion of food
2) Nutrient and water absorption from DS
116
What are the 3 sections of the small intestine?
1) Duodenum
2) Jejunum
3) Ileum
117
What are the specialisations of the small intestine?
1) Plicae circularis (Pcs)- permanent circular folds of mucosa and submucosa
2) Villi
3) Microvilli
4) These all increase SA for nutrient absorption
118
How does PC and villi maximise nutrient absorption?
Structure changes along the small intestine according to the role of each region in nutrient digestion and absorption
119
What is the function of the duodenum?
1) Has short leaf-like villi
2) Few Pcs
3) Receives and neutralises chyme - prevents damage to SI mucosa
120
What is the villi and Pcs of the jejunum like?
1) Most well-developed long villi
2) Prominent most well-developed Pcs
121
What is the ileum's villi and Pcs like?
1) Shorter villi
2) Decrease in size of Pcs towards mid-region of ileum
