G.I. > Physiology > Flashcards

Physiology Flashcards

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1
Q

Gastro-intestinal motility is mostly due to the activity of what kind of muscle?

A

Smooth muscle

Circular, longitudinal and muscular mucosae

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2
Q

Where in the GI tract is there skeletal muscle?

A

Mouth, pharynx, upper third of oesophagus.

External anal sphincter

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3
Q

What skeletal muscle is not under voluntary control in the GI tract?

A

Upper oesophageal skeletal muscle.

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4
Q

Contraction of circular muscle does what to the lumen>

A

Narrower and longer

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5
Q

Longitudinal muscle makes the intestine

A

shorter and fatter

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6
Q

Adjacent smooth muscle cells are coupled by?

forming a functional…?

A

Gap junctions.

Forming a functional syncytium

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7
Q

How does electrical activity in the small and large intestine occur?

A

As slow waves

Synchronous muscle cell contractions

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8
Q

What are the slow waves driven by (pacemaker)?

A

Interstitial cells of Cajal

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9
Q

When does contraction occur? (in terms of slow waves)

A

Contraction only occurs if the slow wave amplitude is sufficient to trigger SMC action potentials

A threshold must be reached

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10
Q

Up- stroke of GI AP?

A

Voltage activated Ca2+ channels

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11
Q

Downstroke by?

A

Voltage activated K+ channels.

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12
Q

Where are the interstitial cells of cajal located?

A

Between the longitudinal and circular muscle layers

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13
Q

More action potentials =

A

stronger contraction

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14
Q

Enteric Nervous system

A

Intrinsic to GI tissue

Can operate independently

Hormones and extrinsic nerves exert a strong influence

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15
Q

Basal electric rhythm of stomach, S.I. and L.I.

A

Stomach = 3 slow waves/min

S.I. = 12 waves/min in duodenum

8/min in terminal ileum

L.I. = 8/min in proximal colon

16/min in sigmoid colon
favouring retention of luminal contents

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16
Q

Myenteric Plexus (Auerbach’s)

A

Regulates motility and sphincters.

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17
Q

Submucous (Meissner’s) plexus

A

Modulates epithelia and blood vessels

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18
Q

How is muscular, secretive and absorptive activities coordinated?

A

> Sensory neurones
Interneurones
Effector neurones

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19
Q

What do the pelvic splanchnic nerves innervate?

A

The distal 1/3rd of the transverse colon

Sigmoid colon

Rectum

S2,3,4 keeps the shit of the floor

PARASYMPATHETIC

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20
Q

What does the vagus nerve innervate?

A

The proximal 2/3 of the transverse colon and the rest of the proximal GI tract (stomach, S.I.)

PARASYMPATHETIC

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21
Q

What does the parasympathetic nerves in GI do?

A

Excitatory - increase gastric, pancreatic and S.I. secretion, blood flow and SM contraction

Inhibitory - relaxation of some sphincters

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22
Q

Sympathetic innervation of the GI tract

A

Superior cervical ganglion - oesophagus

  1. Celiac
  2. Superior mesenteric
  3. Inferior mesenteric

correspond to their arterial counterparts

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23
Q

Function of sympathetic innervation

A

Increased sphincter tone.

Decreased motility, secretion and blood flow.

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24
Q

Nerve reflexes in GI tract

  • 3 types
  • Intrinsic and extrinsic reflexes
A

Local reflex - peristalsis (intrinsic reflex)

Short reflex - intestino-intesitnal inhibitory reflex (extrinsic reflex)

Long reflex - gastroileal reflex (extrinsic reflex) – these go to the medulla oblongata

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25
Short reflexes bring about
local distension activates sensory neurones exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas)
26
Long reflex
increase in gastric activity causes increased propulsive activity in the terminal ileum)
27
Peristalsis
Wave of relaxation followed by contraction Contraction behind food Relaxation in front
28
Contraction of circular muscle and longitudinal muscle...
Release of ACh and substance P from excitatory motorneurone
29
Relaxation of circular muscle and longitudinal muscle
Due to release of vasoactive intestinal peptide (VIP) and NO from inhibitory motorneurone
30
Segmentation what is it where does it occur?
Mixing, churning movements Rhythmic contraction of circular muscle layer that mix and divide luminal contents Occurs in small intestine
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Colonic mass movement
sweeping contraction that forces faeces into the rectum
32
Migrating motor complex
sweeping contraction from stomach to terminal ileum
33
Tonic contractions
sustained contractions Low pressure - stomach (storage function) High pressure - sphincters
34
Sphincters of GI tract
6 (excluding the sphincter of Oddi) One way valves ``` UOS (skeletal, not voluntary) LOS Pyloric sphincter Ileocaecal valve Internal anal (smooth) External anal (skeletal) ```
35
Swallowing phases
i) Oral/voluntary phase ii) Pharyngeal iii) Oesophageal 1. Close lips (orbicularis oris and CNVII) 2. The tongue (CN XII) pushes the blousy posteriorly towards oropharynx 3. Contract pharyngeal constrictor muscles (CNX) to push bolus inferiorly towards oesophagus 4. inner longitudinal layer of pharyngeal muscles (CN IX & X) contracts to raise the larynx, shortening the pharynx and closing off laryngeal inlet 5. Bolus reaches oesophagus
36
Alpha amylase
Breaks down linear INTERNAL alpha-1,4 linkages but NOT terminal linkages Products are linear glucose oligomers (maltose, maltotriose)
37
Oligosaccharides
Integral membrane proteins
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Lactose Intolerance
Caused by lactase insufficiency Primary lactase deficiency (primary hypolactasia) --- most common Secondary lactase deficiency - caused by damage/infection to proximal S.I. Congenital lactase deficiency - rare autosomal recessive disease
39
Overall process of digestion and absorption is known as?
Assimilation
40
Where are the final products of carbohydrate digested?
Duodenum and jejunum
41
What are glucose and galactose absorbed by? Fructose
Secondary active transport - SGLT1 Fructose - facilitated diffusion mediated by GLUT5
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EXIT for ALL monosaccharides?
Facilitated diffusion by GLUT2
43
SGLT1 operation
Sodium and glucose symport 1. 2 Na bind 2. Affinity for glucose increases and glucose binds 3. Na+ and glucose translocate 4. 2 Na+ dissociate 5. Glucose dissociates 6. repeat
44
All dietary carbohydrate must be converted to?
Monosaccharides in order to be absorbed
45
How many pathways of protein digestion?
4 End product is amino acid in the blood.
46
Pepsin is an...
Endopeptidase
47
Enzymes in duodenum
Endopeptidases// Trypsin Chymotrypsin Elastase Exopeptidases// Procarboxypeptidase A Procarboxypeptidase B All of these enzymes are secreted as proenzymes and are converted to active form in duodenum.
48
Amino acid absorption
7 different mechanisms at brush border// 5 Na+ dependent co transporters 2 Na+ independent 5 different mechanisms on basolateral membrane// 3 mediate efflux, Na+ independent 2 mediate influx, Na+ dependent BIDIRECTIONAL
49
How are Di-, tri- and tetra-peptides transported?
Via H+ dependent mechanisms (PepT1) at brush border
50
What does PepT1 do?
Transports Oligopeptides
51
Satiation
Sensatiion of fullness generated during a meal
52
Satiety
Period of time between termination of one meal and initiation of the next
53
Satiation signals
CCK (cholecystokinin) Peptide YY Glucagon-like peptide 1 Oxyntomodulin Obestatin
54
Ghrelin
"Hunger signal" Secreted by oxyntic cells Increase before meals Decrease after meals Stimulates food intake (hypothalamus) Help control fat metabolism
55
CCK (Cholecystokinin)
Satiation signal Secreted from enteroendocrine cells in duodenum and jejunum. Stimulates hindbrain directly Nucleus tractus solitarus
56
Peptide YY
Satiation signal Secreted from endocrine mucosal L cells Signals travel to hypothalamus
57
Glucagon-like peptide
Satiation signal Released from L cells Inhibits gastric emptying reduces food intake acts upon Hypothalamus and Nucleus Tractus Solitarus
58
Oxyntomodulin
Suppresses appetite
59
Obestatin
Satiation signal Reduce food intake
60
Which hormones report fat status back to the brain? "ADIPOSITY SIGNALS"
Leptin - made and released from fat cells Insulin - made and released from pancreatic cells Inform brain to alter energy balance - eat less and increase energy burn MALFUNCTIONS in obese state
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Leptin roles
Food intake/energy expenditure/fat deposition Peripheral glucose homeostasis/insulin sensitivity Maintenance of immune system Maintenance of reproductive system Angiogenesis Tumourigenesis Bone formation
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Insulin
Circulates in proportion to body adiposity High levels of insulin receptors in hypothalamus
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Dopamine
Hedonistic pathway Food addiction Chocolate, sugar & fat
64
Human obesity
High levels of leptin levels Corresponds to High fat level
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Diet induced obesity leads to
Leptin resistance 1) Defective leptin transport 2) Altered signal transduction following leptin binding to its receptor
66
Therapy for obesity
Bariatric surgery Gastric by pass surgery Induces high level of complete resolution of TIIDM Restricts calorie intake.
67
Adaptive thermogenesis
> Adult humans have brown adipose tissue > Brown adipose tissue dissipates energy as heat Increase energy expenditure uncoupling of oxidative metabolism from ATP production Uncoupling protein 1 (UCP1) - fatty acid activated protein short circuits proton gradient in mitochondria - Produce heat
68
What 3 glands is saliva secreted from? which nerves innervate them?
Parotid - CN IX Submandibular - CN VII Sublingual - CNVII Parotid duct of Stensen (opposite second maxillary molar teeth) Submandibular - duct of Wharton --> sublingual caruncula Sublingual - medial to submandibular glands. Ducts of Rivinus --> connect with whartons
69
Largest saliva gland?
Parotid
70
What are the functional units of the salivary gland?
Salivons
71
Serous cells (within salivon)
Watery secretion rich in α-amylase; contain small, dense, secretory granules
72
Mucous cells (within salivon)
Produce a thick mucous rich secretion.
73
What pH is salvia normally? What does this help with?
Alkaline, hypotonic Helps buffer acids in foods
74
Which electrolytes are found in HIGHER concentrations than that in the plasma?
K+ & HCO3-
75
Secretions of glands. | Composition
Parotid - watery, alpha-amylase rich Submandibular - mixed serous and mucous cells, more viscous Sublingual - thick solution rich in mucous
76
HCO3- concentration... with increased flow rate of saliva?
Increases | as does pH
77
K+ concentration... with rate?
Decreases
78
Formation of saliva - stages
1. Primary secretion by acinus cells | 2. Secondary modification by duct cells -
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Secondary modification of saliva
By striated, intercalated and excretory ducts. Removes Na+ and Cl- Adds K+ and HCO3- Diluting effect. Saliva becomes alkaline
80
Salivary control
Simple (unconditioned)// Receptors in mouth activated in presence of food Acquired (conditioned, pavlov's dog)// - think about, see, smell, hear prep of food Impulses via afferent nerves.
81
Normal salvia production is dominated by what kind of stimulation?
Parasympathetic Glossopharyngeal (CNIX) Facial (CNVII) Muscarinic ACh receptors More blood to glands Increased synthesis and secretion of alpha amylase Increased fluid flow Contraction of myoepithelial cells Large volume, watery saliva
82
What do muscarinic receptor antagonists cause/ antidepressants cause?
Dry mouth
83
Sympathetic stimulation of saliva glands
Dominant at stressful times. Dry mouth Increased secretion of alpha amylase, K+ and HCO3- Increased contraction of myoepithelal cells Decreased blood flow to glands Thick mucous rich saliva
84
What causes relaxation in the stomach (nerve)?
Vagus CNX
85
Emptying of stomach. Rate of emptying proportional to:
Peristaltic action in direction of pylorus Contractions become stronger due to presence of food Supra-threshold gastric slow waves Pyloric sphincter open just enough to allow a wee squirt of chyme into duodenum Rate of emptying proportional to VOLUME and consistency of chyme in stomach.
86
Duodenum has to be ready to receive chyme. Can delay emptying of stomach by:
Enterogastric reflex (neuronal)// decreases astral peristaltic activity Hormonal response// release of enterogastrones (secretin and CCK) - inhibits stomach contraction
87
What stimuli in the duodenum drive the neuronal and hormonal responses?
FAT - delay required to digest and absorb in S.I. ACID - time required for neutralisation HYPERTONICITY - products of carbs are osmotically active and draw water into S.I.. Need for slowing down of digestion DISTENSION
88
What cells are present in the funds and body of the stomach?
Oxyntic mucosa > Chief cells - pepsinogen > Enterochromaffin - histamine > Parietal cell - HCL, Intrinsic factor
89
What cells are present tin the antrum?
pyloric gland area D cells - somatostatin G cells - gastrin
90
What does intrinsic factor do?
Binds vitamin B12 allows absorption in terminal ileum.
91
What does histamine do?
Stimulates HCl secretion
92
Gastrin - function in stomach
Stimulates HCl secretion
93
Somatostatin - function in stomach
INHIBITS HCL secretion
94
HCl - function in stomach
Activates pepsinogen --> pepsin Denatures proteins Kills many micr organisms
95
Pepsinogen
Inactive precursor Pepsin, once formed (by HCl), activates pepsinogen POSITIVE FEEDBACK LOOP
96
What enzyme does H+ and Cl- secretion depend on?
Carbonic anhydrase HCO3- ions exchanged for Cl- ions Proton (H+) pump with K+
97
What receptor does gastrin bind to?
CCK2 receptors
98
What is the STRONGEST agonist of hydrogeen ion secretion?
HISTAMINE
99
Secratagogues (histamine, gastrin, ACh) cause...
Trafficking of H+/K+ ATPase Moves the ATPase from cytoplasm to apical membrane/ extended microvilli.
100
What do D cells do?
Secrete somatostatin
101
What are the 3 phases of gastric secretion?
Cephalic phase Gastric phase Intestinal phase Half the acid produced during cephalic stage
102
Cephalic stage
Prepares stomach to receive food.
103
Gastric phase
Mechanical and chemical factors augment secretion. Distension --> increased HCl via ACh receptor Protein digestion products --> stimulate G cels --> Gastrin --> HCl release
104
G cells secrete?
Gastrin
105
Enterochromaffin-like cells secrete?
Histamine
106
Intestinal Phase - factors originating from S.I. that switch off acid secretion.
↓ gastric motility --> ↓ gastric secretion As stomach empties, the stimuli for secretion become less intense. Secretion of somatostatin resumes large inhibitory
107
What do PPIs block?
K+/H+ ATPase membrane inserted | do not bock tubulovesicles
108
NSAIDs block?
COX thereby reducing Prostaglandins whihc inhibit secretion leading to increased acid secretion. --> Peptic ulcers & bleeding
109
What protects the mucosa?
Locally produced prostaglandins (PGE2 and PGI2) > Reduce acid secretion > Increase mucous and bicarb secretion > Increase mucosal blood flow
110
H. pylori
Protected in mucous gel. Secretes agents causing a persistent inflammation Wekanes mucosal barrier Breakdown of mucosal barrier damages the mucosal cell layer and leaves the submucosa subject to attack by HCl and Pepsin.
111
Zollinger-Ellison syndrome
Rare | gastrin-producing tumour
112
Salivary gland composition
External capsule Septa separating lobes and lobules Lobules composed of salivons
113
Each salivon consists of
Secretory acinus Intercalated duct striated duct
114
Striated ducts unite to form
Interlobular ducts | Excretory cells
115
Salivon
• ACINUS Formed from pyramidal shaped secretory acinar cells around a central lumen that are either - -- serous cells - -- mucous cells * Contractile myoepithelial cells that surround the acinus * Serous demesnes * Intercalated duct (cuboidal) * A striated duct (columnar)
116
Functions of saliva (4)
> Lubrication > Protection --- against bacteria and their metabolic products > Digestion --- alpha amylase > Other
117
What pH is saliva?
Alkaline so to buffer foods
118
Why is the overall effect of the secondary modification of saliva diluting?
Because H20 cannot pass through the duct walls (intercalated, excretory and striated)
119
What exchanges Cl- for HCO3- across the apical membrane? What is it regulated by?
HCO3-/CL- antiporter Regulated by the cystic fibrosis transmembrane conductance regulator (CFTR)
120
What empties from the stomach more quickly?
Liquids
121
Stomach distension increases... what?
Motility due to stretch of smooth muscle Activity of intrinsic nerve plexuses Vagus nerve activity Gastrin release
122
Roll of mucous in oxyntic mucosa?
Protective
123
What do parietal cells do in the stomach?
Secrete HCl | Intrinsic factor
124
What occurs in pernicious anaemia?
Autoimmune disease Targets parietal cells and intrinsic factor Does not allow absorption of vitamin b12 --> b12 deficiency
125
How can gastric damage die to long term NSAID treatment be prevented?
By using a stable PGE1 analogue --- inhibits basal and food stimulated gastric acid production --- maintains (or increases) secretion and mucous and bicarbonate
126
Cushing's ulcer
Heightened vagal tone leading to acid hypersecretion
127
Sucralfate
Mucosal strengthener Aluminium Binds to ulcer base ionically (aluminium is negative and ulcer base is positive) and forms a mucosal barrier against acid and pepsin
128
Bismuth chealate
Mucosal strengthener aluminium toxic towards H pylori
G.I.
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