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G.I. > Physiology > Flashcards

Physiology Flashcards

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
Q

Short reflexes bring about

A

local distension activates sensory neurones exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas)

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26
Q

Long reflex

A

increase in gastric activity causes increased propulsive activity in the terminal ileum)

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27
Q

Peristalsis

A

Wave of relaxation followed by contraction

Contraction behind food
Relaxation in front

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28
Q

Contraction of circular muscle and longitudinal muscle…

A

Release of ACh and substance P from excitatory motorneurone

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29
Q

Relaxation of circular muscle and longitudinal muscle

A

Due to release of vasoactive intestinal peptide (VIP) and NO from inhibitory motorneurone

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30
Q

Segmentation

what is it
where does it occur?

A

Mixing, churning movements

Rhythmic contraction of circular muscle layer that mix and divide luminal contents

Occurs in small intestine

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31
Q

Colonic mass movement

A

sweeping contraction that forces faeces into the rectum

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32
Q

Migrating motor complex

A

sweeping contraction from stomach to terminal ileum

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33
Q

Tonic contractions

A

sustained contractions

Low pressure - stomach (storage function)

High pressure - sphincters

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34
Q

Sphincters of GI tract

A

6 (excluding the sphincter of Oddi)

One way valves

UOS (skeletal, not voluntary)
LOS
Pyloric sphincter
Ileocaecal valve
Internal anal (smooth)
External anal (skeletal)
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35
Q

Swallowing

phases

A

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
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36
Q

Alpha amylase

A

Breaks down linear INTERNAL alpha-1,4 linkages but NOT terminal linkages

Products are linear glucose oligomers (maltose, maltotriose)

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37
Q

Oligosaccharides

A

Integral membrane proteins

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38
Q

Lactose Intolerance

A

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

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39
Q

Overall process of digestion and absorption is known as?

A

Assimilation

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40
Q

Where are the final products of carbohydrate digested?

A

Duodenum and jejunum

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41
Q

What are glucose and galactose absorbed by?

Fructose

A

Secondary active transport - SGLT1

Fructose - facilitated diffusion mediated by GLUT5

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42
Q

EXIT for ALL monosaccharides?

A

Facilitated diffusion by GLUT2

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43
Q

SGLT1 operation

A

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
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44
Q

All dietary carbohydrate must be converted to?

A

Monosaccharides in order to be absorbed

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45
Q

How many pathways of protein digestion?

A

4

End product is amino acid in the blood.

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46
Q

Pepsin is an…

A

Endopeptidase

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47
Q

Enzymes in duodenum

A

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.

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48
Q

Amino acid absorption

A

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

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49
Q

How are Di-, tri- and tetra-peptides transported?

A

Via H+ dependent mechanisms (PepT1) at brush border

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50
Q

What does PepT1 do?

A

Transports Oligopeptides

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51
Q

Satiation

A

Sensatiion of fullness generated during a meal

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52
Q

Satiety

A

Period of time between termination of one meal and initiation of the next

53
Q

Satiation signals

A

CCK (cholecystokinin)

Peptide YY

Glucagon-like peptide 1

Oxyntomodulin

Obestatin

54
Q

Ghrelin

A

“Hunger signal”

Secreted by oxyntic cells

Increase before meals
Decrease after meals

Stimulates food intake (hypothalamus)

Help control fat metabolism

55
Q

CCK (Cholecystokinin)

A

Satiation signal

Secreted from enteroendocrine cells in duodenum and jejunum.

Stimulates hindbrain directly
Nucleus tractus solitarus

56
Q

Peptide YY

A

Satiation signal

Secreted from endocrine mucosal L cells

Signals travel to hypothalamus

57
Q

Glucagon-like peptide

A

Satiation signal

Released from L cells
Inhibits gastric emptying
reduces food intake

acts upon Hypothalamus and Nucleus Tractus Solitarus

58
Q

Oxyntomodulin

A

Suppresses appetite

59
Q

Obestatin

A

Satiation signal

Reduce food intake

60
Q

Which hormones report fat status back to the brain?

“ADIPOSITY SIGNALS”

A

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

61
Q

Leptin roles

A

Food intake/energy expenditure/fat deposition

Peripheral glucose homeostasis/insulin sensitivity

Maintenance of immune system

Maintenance of reproductive system

Angiogenesis

Tumourigenesis

Bone formation

62
Q

Insulin

A

Circulates in proportion to body adiposity

High levels of insulin receptors in hypothalamus

63
Q

Dopamine

A

Hedonistic pathway

Food addiction

Chocolate, sugar & fat

64
Q

Human obesity

A

High levels of leptin levels

Corresponds to High fat level

65
Q

Diet induced obesity leads to

A

Leptin resistance

1) Defective leptin transport
2) Altered signal transduction following leptin binding to its receptor

66
Q

Therapy for obesity

A

Bariatric surgery

Gastric by pass surgery

Induces high level of complete resolution of TIIDM

Restricts calorie intake.

67
Q

Adaptive thermogenesis

A

> 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
Q

What 3 glands is saliva secreted from?

which nerves innervate them?

A

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
Q

Largest saliva gland?

A

Parotid

70
Q

What are the functional units of the salivary gland?

A

Salivons

71
Q

Serous cells (within salivon)

A

Watery secretion rich in α-amylase; contain small, dense, secretory granules

72
Q

Mucous cells (within salivon)

A

Produce a thick mucous rich secretion.

73
Q

What pH is salvia normally?

What does this help with?

A

Alkaline, hypotonic

Helps buffer acids in foods

74
Q

Which electrolytes are found in HIGHER concentrations than that in the plasma?

A

K+ & HCO3-

75
Q

Secretions of glands.

Composition

A

Parotid - watery, alpha-amylase rich

Submandibular - mixed serous and mucous cells, more viscous

Sublingual - thick solution rich in mucous

76
Q

HCO3- concentration… with increased flow rate of saliva?

A

Increases

as does pH

77
Q

K+ concentration… with rate?

A

Decreases

78
Q

Formation of saliva - stages

A
  1. Primary secretion by acinus cells

2. Secondary modification by duct cells -

79
Q

Secondary modification of saliva

A

By striated, intercalated and excretory ducts.

Removes Na+ and Cl-

Adds K+ and HCO3-

Diluting effect.

Saliva becomes alkaline

80
Q

Salivary control

A

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
Q

Normal salvia production is dominated by what kind of stimulation?

A

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
Q

What do muscarinic receptor antagonists cause/ antidepressants cause?

A

Dry mouth

83
Q

Sympathetic stimulation of saliva glands

A

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
Q

What causes relaxation in the stomach (nerve)?

A

Vagus CNX

85
Q

Emptying of stomach.

Rate of emptying proportional to:

A

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
Q

Duodenum has to be ready to receive chyme. Can delay emptying of stomach by:

A

Enterogastric reflex (neuronal)//

decreases astral peristaltic activity

Hormonal response//

release of enterogastrones (secretin and CCK) - inhibits stomach contraction

87
Q

What stimuli in the duodenum drive the neuronal and hormonal responses?

A

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
Q

What cells are present in the funds and body of the stomach?

A

Oxyntic mucosa

> Chief cells - pepsinogen
Enterochromaffin - histamine
Parietal cell - HCL, Intrinsic factor

89
Q

What cells are present tin the antrum?

A

pyloric gland area

D cells - somatostatin
G cells - gastrin

90
Q

What does intrinsic factor do?

A

Binds vitamin B12

allows absorption in terminal ileum.

91
Q

What does histamine do?

A

Stimulates HCl secretion

92
Q

Gastrin - function in stomach

A

Stimulates HCl secretion

93
Q

Somatostatin - function in stomach

A

INHIBITS HCL secretion

94
Q

HCl - function in stomach

A

Activates pepsinogen –> pepsin

Denatures proteins

Kills many micr organisms

95
Q

Pepsinogen

A

Inactive precursor

Pepsin, once formed (by HCl), activates pepsinogen

POSITIVE FEEDBACK LOOP

96
Q

What enzyme does H+ and Cl- secretion depend on?

A

Carbonic anhydrase

HCO3- ions exchanged for Cl- ions

Proton (H+) pump with K+

97
Q

What receptor does gastrin bind to?

A

CCK2 receptors

98
Q

What is the STRONGEST agonist of hydrogeen ion secretion?

A

HISTAMINE

99
Q

Secratagogues (histamine, gastrin, ACh) cause…

A

Trafficking of H+/K+ ATPase

Moves the ATPase from cytoplasm to apical membrane/ extended microvilli.

100
Q

What do D cells do?

A

Secrete somatostatin

101
Q

What are the 3 phases of gastric secretion?

A

Cephalic phase
Gastric phase
Intestinal phase

Half the acid produced during cephalic stage

102
Q

Cephalic stage

A

Prepares stomach to receive food.

103
Q

Gastric phase

A

Mechanical and chemical factors augment secretion.

Distension –> increased HCl via ACh receptor

Protein digestion products –> stimulate G cels –> Gastrin –> HCl release

104
Q

G cells secrete?

A

Gastrin

105
Q

Enterochromaffin-like cells secrete?

A

Histamine

106
Q

Intestinal Phase - factors originating from S.I. that switch off acid secretion.

A

↓ gastric motility –> ↓ gastric secretion

As stomach empties, the stimuli for secretion become less intense.

Secretion of somatostatin resumes

large inhibitory

107
Q

What do PPIs block?

A

K+/H+ ATPase membrane inserted

do not bock tubulovesicles

108
Q

NSAIDs block?

A

COX
thereby reducing Prostaglandins whihc inhibit secretion

leading to increased acid secretion.

–> Peptic ulcers & bleeding

109
Q

What protects the mucosa?

A

Locally produced prostaglandins (PGE2 and PGI2)

> Reduce acid secretion
Increase mucous and bicarb secretion
Increase mucosal blood flow

110
Q

H. pylori

A

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
Q

Zollinger-Ellison syndrome

A

Rare

gastrin-producing tumour

112
Q

Salivary gland composition

A

External capsule
Septa separating lobes and lobules
Lobules composed of salivons

113
Q

Each salivon consists of

A

Secretory acinus
Intercalated duct
striated duct

114
Q

Striated ducts unite to form

A

Interlobular ducts

Excretory cells

115
Q

Salivon

A

• 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
Q

Functions of saliva (4)

A

> Lubrication
Protection
— against bacteria and their metabolic products

> Digestion
— alpha amylase

> Other

117
Q

What pH is saliva?

A

Alkaline so to buffer foods

118
Q

Why is the overall effect of the secondary modification of saliva diluting?

A

Because H20 cannot pass through the duct walls (intercalated, excretory and striated)

119
Q

What exchanges Cl- for HCO3- across the apical membrane?

What is it regulated by?

A

HCO3-/CL- antiporter

Regulated by the cystic fibrosis transmembrane conductance regulator (CFTR)

120
Q

What empties from the stomach more quickly?

A

Liquids

121
Q

Stomach distension increases… what?

A

Motility due to stretch of smooth muscle

Activity of intrinsic nerve plexuses

Vagus nerve activity

Gastrin release

122
Q

Roll of mucous in oxyntic mucosa?

A

Protective

123
Q

What do parietal cells do in the stomach?

A

Secrete HCl

Intrinsic factor

124
Q

What occurs in pernicious anaemia?

A

Autoimmune disease

Targets parietal cells and intrinsic factor

Does not allow absorption of vitamin b12

–> b12 deficiency

125
Q

How can gastric damage die to long term NSAID treatment be prevented?

A

By using a stable PGE1 analogue

— inhibits basal and food stimulated gastric acid production

— maintains (or increases) secretion and mucous and bicarbonate

126
Q

Cushing’s ulcer

A

Heightened vagal tone leading to acid hypersecretion

127
Q

Sucralfate

A

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
Q

Bismuth chealate

A

Mucosal strengthener

aluminium

toxic towards H pylori

G.I. (20 decks)

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