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Physiology > GI System > Flashcards

GI System Flashcards

1
Q

How does food go through the body?

A
  1. mouth
  2. pharynx
  3. esophagus
  4. stomach
  5. duodenum -> jejunum -> ileum
  6. ascending -> transverse -> descending -> sigmoid colon
  7. rectum
  8. anus
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2
Q

4 associated glandular organs that are located outside the GI tract:

A
  • salivary glands
  • liver
  • gall bladder
  • pancreas
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3
Q

What are the 4 basic layers of the GI tract?

A
  • mucosa: innermost layer
  • submucosa
  • muscularis externa
  • serosa
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4
Q

T/F: mucosa is not intensely folded

A

F, it is intensely folded to increase SA

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5
Q

What makes up the mucosa?

A
  • epithelium
  • lamina propria
  • muscularis mucosa
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6
Q

Epithelium of the mucosa is a single…

A

layer of simple columnar cells

- aka enterocytes

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7
Q

What do the epithelium of mucosa in the esophagus and anus look like?

A

stratified squamous

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8
Q

Function of the lamina propria in the mucosa:

A

CT support for endothelium

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9
Q

Description of muscularis mucosa:

A

thin layer of smooth muscle that produces folds and ridges of mucosa

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10
Q

Submucosa of the GI tract is made up of…

A
  • mainly loose CT (collagen and elastin)
  • highly vascular
  • submucosal plexus of enteric nervous system
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11
Q

Some regions of the submucosa in the GI contain…

A

glands

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12
Q

Submucosal plexus is also known as…

A

Meissner’s plexus

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13
Q

What are the three parts of muscularis externa?

A
  • inner (thicker) circular smooth muscle layer
  • outer longitudinal smooth muscle layer
  • myenteric plexus of enteric nervous system (between layers)
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14
Q

Myenteric plexus is also known as…

A

Auerbach’s plexus

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15
Q

Serosa is also known as…

A

adventitia

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16
Q

Serosa is the…

A

outermost layer and mainly CT

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17
Q

What is the percentage of cardiac output to the GI at rest?

A

25%

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18
Q

All venous drainage occurs via…

A

hepatic portal system to the liver lymphatic drainage extensive

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19
Q

Venous drainage is important for…

A
  • transport of lipid soluble substances

- immunological screening

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20
Q

What are the two ways the GI tract can be innervated?

A
  • enteric nervous system

- reflexes

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21
Q

Is the enteric nervous system intrinsic or extrinsic?

A

intrinsic b/c neurons are located completely w/in GI wall

  • network of interconnected neurons w/in GI wall
  • integrates motor and secretory activity
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22
Q

What are the two major plexuses of the enteric nervous system?

A
  • myenteric (between circular and longitudinal muscle layers)
  • submucosal (between submucosa and circular muscle)
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23
Q

Myenteric plexus innervates…

A

muscle layers

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24
Q

Submucosal plexus innervates…

A

mucosa

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25
Q

Both plexuses are regulated by…

A

intrinsic and extrinsic reflexes

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26
Q

Examples of intrinsic and extrinsic reflexes:

A
  • sensory neurons
  • interneurons
  • motor neurons
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27
Q

Sensory neurons respond to what kinds of stimuli?

A
  • mechanical
  • chemical
  • pain
  • temperature
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28
Q

Sensory neurons can mediate both…

A

local and central reflex arcs

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29
Q

Interneurons in plexi form…

A

reflex arcs

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30
Q

Motor neurons release…

A

ach onto muscarinic receptors of smooth muscle and secretory cells

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31
Q

Enteric nervous system uses neurotransmitters such as…

A
  • Ach
  • serotonin (5HT)
  • ATP
  • NO
  • gastrin inhibitory peptide (GIP)
  • vasoactive intestinal peptide (VIP)
  • somatostatin
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32
Q

Examples of excitatory neurotransmitters:

A
  • Ach
  • Substance P
  • 5HT4 serotonin by stimulating Ach
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33
Q

Examples of inhibitory neurotransmitters:

A
  • VIP
  • NO
  • ATP
  • 5HT3 serotonin
  • GIP
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34
Q

VIP is what type of inhibitor?

A

non-adrenergic/non-cholinergic

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35
Q

How does NO act as an inhibitor?

A

via protein kinase G

- reduces intracellular Ca2+

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36
Q

How does ATP act as an inhibitor?

A

inhibits adenylate cyclase

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37
Q

How does 5HT3 act as an inhibitor?

A

inhibits Ach

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38
Q

Many of the drugs that affect lower GI function work by…

A

modulating the enteric nervous system

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39
Q

Drugs that affect lower GI function affect levels of…

A

Ach, 5HT (serotonin), dopamine, enkephalins, motilin and somatostatin (hormones)

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40
Q

Short local reflexes are what kind of reflexes?

A

intrinsic

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41
Q

Where do short local reflexes originate and end?

A

in the ENS

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42
Q

For short local reflexes, the submucosal plexus controls…

A

secretion and blood flow

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43
Q

For short local reflexes, the myenteric plexus influences…

A

motility

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44
Q

ANS short and long reflexes are what kind of reflexes?

A

extrinsic

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45
Q

Extrinsic innervations of the ANS short and long reflexes alter the activity of…

A

enteric (intrinsic) neurons

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46
Q

Extrinsic innervations of the ANS short and long reflexes coordinate the activity of…

A

regions located farther from each other than local reflexes

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47
Q

Feedforward reflexes of ANS short/long are based on current status prepare…

A

forward regions for what is coming

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48
Q

Examples of feedforward reflexes:

A
  • cephalic reflexes

- gastrocolic reflex

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49
Q

Function of cephalic reflexes:

A

increases secretion and motility in response to smell/thought of food

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50
Q

Function of gastrocolic reflex:

A

increases activity in stomach coupled with motor and secretory activity in colon
- it’s a central reflex arc

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51
Q

SNS terminates on…

A

enteric neurons, blood vessels, and sphincters

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52
Q

Post-ganglionic adrenergic fibers of the SNS release…

A

norepi, which inhibits activity of muscularis externa

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53
Q

What happens when SNS is stimulated?

A
  • digestion inhibited
  • decreases slow intrinsic activity, which produces muscle relaxation
  • induces contraction of some sphincters and muscularis mucosa
  • inhibits GI secretion and alpha 2
  • vasoconstriction to redirect blood flow away from GI
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54
Q

PNS travels from…

A

vagus nerve from lower esophagus to transverse colon -> pelvic nerves to colon -> rectum -> anus

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55
Q

Post-ganglionic cholinergic neurons are located where and release what?

A
  • in plexi

- release Ach onto muscarinic receptors

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56
Q

What happens when PNS is stimulated?

A
  • increases amplitude of slow intrinsic waves, which produces muscle contraction
  • stimulates GI secretions
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57
Q

Pre-ganglionic neurons in the PNS release…

A

Ach to intrinsic neurons

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58
Q

GI peptides can regulate…

A

secretion and motility

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59
Q

GI peptides are secreted within the..

A

GI tract

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60
Q

Examples of GI peptides:

A
  • hormones
  • neuropeptides
  • cytokines
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61
Q

T/F: GI peptides can’t have action on the CNS

A

F

  • CCK affects satiety
  • grehlin affects hunger
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62
Q

GI hormone facilitates…

A
  • gastrin family
  • secretin family
  • motilin and others family
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63
Q

How does the gastrin family function?

A

gastrin and CCK bind to CCKB receptors

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64
Q

How does the secretin family function?

A

secretin, VIP, GIP, GLP-1 all decrease gastric emptying

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65
Q

How does the motilin and others family function?

A

motilin stimulates migrating motor complex

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66
Q

Major functions of the GI:

A
  • ingestion
  • digestion
  • absorption
  • secretion
  • movement
  • excretion
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67
Q

Ingestion is the…

A

entry of food into tract through the mouth

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68
Q

Digestion is the…

A

breakdown of food into absorbable pieces

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69
Q

Digestion can occur two ways:

A
  • mechanical: w/ teeth

- chemical: via digestive enzymes

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70
Q

For chemical digestion, there are separate…

A

enzymes for each major nutrient groups

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71
Q

Chemical digestion is regulated by…

A

hormones

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72
Q

Absorption is when…

A

small nutrient molecules move across GI wall into the vascular system

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73
Q

What gets secreted during secretion?

A
  • enzymes
  • pH regulating substances
  • regulatory hormones
  • mucus
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74
Q

Movement of food through the GI tract uses the…

A

longitudinal and inner circular layers of smooth muscle

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75
Q

Excretion is the…

A

elimination of wastes

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76
Q

GI system regulates…

A

secretion and motility

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77
Q

Problems GI tract has to overcome to do its job:

A
  • avoiding autodigestion to prevent digestion of body cells
  • mass balance of GI fluids
  • immune defense exposure to toxins/pathogens as food travels through GI tract
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78
Q

What is secreted to protect the GI tract?

A

mucus

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79
Q

Failure of avoiding autodigestion results in…

A

ulceration

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80
Q

GI has to absorb fluid mass equivalent to…

A

what it secretes but what is also lost in feces and urine

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81
Q

Failure of mass balance of the GI occurs when…

A

one vomits or diarrhea

- results in dehydration

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82
Q

Immune defense of the GI tract is reinforced by…

A
  • mucus
  • digestive enzymes
  • acidity of stomach
  • gut associated lymphoid tissue (GALT)
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83
Q

Failure of immune defense of the GI tract results in…

A

food poisoning/infections

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84
Q

What is a major contributor to RMP of GI smooth muscle?

A

Na+/K+ ATPase

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85
Q

What are tonic contractions?

A

sustained contractions seen in sphincters

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86
Q

What are phasic contractions?

A

pattern of depolarization/repolarization seen in the stomach and small intestine

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87
Q

GI smooth muscle has what type of waves?

A

slow waves (basic electrical rhythm)

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88
Q

Slow waves originate from…

A

pacemaker cells

  • interstitial cells of Cajal (modified smooth muscle cells)
  • between smooth muscle layers and nerve plexus
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89
Q

Because adjacent cells are coupled by gap junctions, the muscle behaves as a…

A

functional syncitium

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90
Q

Amplitude and frequency of slow waves can be modified by…

A
  • activity of extrinsic and intrinsic nerves, hormones, and paracrine substances
  • reflexes
  • inflammatory mediators
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91
Q

Inflammatory mediators are involved in…

A

GI disorders

  • Celiac’s
  • inflammatory bowel
  • Crohn’s disease
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92
Q

Three major patterns of motility…

A
  • peristalsis
  • rhythmic segmentation
  • migrating motor complex (MMC)
  • tonic contractions
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93
Q

What is peristalsis?

A

propulsive movements forward

- progressive waves of movement

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94
Q

Peristalsis is generated by…

A

slow waves

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95
Q

Peristalsis is altered through…

A

reflex actions

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96
Q

What is rhythmic segmentation?

A

mixing movements

  • breaks food into smaller particles facilitating digestion
  • isolated to short segments of tract
  • alternating segmental contractions
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97
Q

What is the migrating motor complex (MMC)?

A

movements between meals

- begins in stomach and sweeps through GI

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98
Q

MMC clears GI of…

A

food remnants and bacteria between meals

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99
Q

What is an example of tonic contraction in the GI?

A

sphincter contraction

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100
Q

Tonic contraction limits…

A

movement into the next segment of GI

- prevents backflow

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101
Q

Chemical and mechanical digestion begins in the…

A

mouth

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102
Q

Saliva is secreted by…

A

acinar cells of parotid, sublingual, and submandibular glands

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103
Q

Function of saliva:

A
  • softens and moistens food

- dissolves food so it can be tasted

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104
Q

Saliva contains…

A
  • amylases, which breaks starch into smaller polysaccharides

- lysozymes (antibacterial enzyme)

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105
Q

What is a bolus?

A

mass of smaller particles mixed with salivary enzymes

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106
Q

What is another word for swallowing?

A

degluttation

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107
Q

Swallowing moves the bolus down…

A

pharynx and into the esophagus

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108
Q

Swallowing is initiated voluntarily by…

A

the tongue pushing bolus against soft palate

- remainder is under reflex control

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109
Q

Where is the swallowing reflex center located?

A

medulla

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110
Q

Why does nasopharynx close when one swallows?

A

prevents movement of food into nasal passages

- under reflex control

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111
Q

Why does the epiglottis close when one swallows?

A

inhibits respiration to prevent inhalation of food

- under reflex control

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112
Q

What relaxes to let food enter the esophagus?

A

upper esophageal sphincter

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113
Q

What do long swallowing reflexes do?

A

prep stomach for incoming food

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114
Q

Steps of movement of food through esophagus by peristalsis:

A
  • peristaltic wave initiated (contracts above bolus, relaxes below bolus)
  • wave travels to pharynx
  • relaxation of lower esophageal sphincter allows food to enter into stomach
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115
Q

How does food enter into the stomach?

A

by relaxation of lower esophageal sphincter and lowering of pressure to allow food to flow down esophagus

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116
Q

Lower esophageal sphincter is normally under…

A

tonic contraction by extrinsic and intrinsic nerves to prevent gastric contents from entering the esophagus

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117
Q

What happens if the lower esophageal sphincter doesn’t stay contracted?

A

GERD/heartburn

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118
Q

What is the vomiting reflex?

A

reverse peristalsis

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119
Q

Where is the vomiting center located?

A

medulla

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120
Q

What counts as a strong stimulus for the vomiting reflex?

A

distention of stomach and duodenum

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121
Q

Stomach motility is responsible for…

A
  • storage of food
  • mixing of food
  • slow emptying of chyme into duodenum
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122
Q

What makes up the proximal stomach?

A
  • cardia
  • fundus
  • superior 1/3 of body
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123
Q

When does proximal stomach relax?

A
  • in response to swallowing (under parasympathetic control)

- in response to food (vagovagal reflex)

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124
Q

How does the vagovagal reflex work?

A
  • swallowing and food in stomach picked up by vagal afferents
  • signal travels to dorsal vagal complex in brain
  • vagal efferents cause receptive relaxation (allows stomach to relax and take in more food)
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125
Q

What makes up the distal stomach?

A
  • inferior 2/3 of body
  • antrum
  • pylorus
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126
Q

When is the distal stomach at rest?

A

in between meals

- there are periodic contractions to clear stomach

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127
Q

What kind of contractions occur in the distal stomach?

A
  • phasic contractions which begin in the body of the stomach
  • ends with slow waves
  • sometimes intense peristaltic waves
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128
Q

What happens during phasic contractions in the distal stomach?

A
  • food is mechanically broken down
  • gastric phase: secretions initiated by food
  • results in chyme
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129
Q

Phasic contractions in the distal stomach are regulated by…

A
  • hormones
  • gastrin (+ g cells)
  • histamine (+ECF cells)
  • somatostatin (-D cells)
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130
Q

How do slow waves function in the distal stomach?

A
  • begins at gastric pacemaker
  • force and velocity increase as chyme approaches gastroduodenal junction
  • moves food through open pyloric sphincter
  • if sphincter is closed, bolus is forced back into stomach (retropulsion)
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131
Q

What kind of contractions are responsible to emptying the distal stomach?

A

intense peristaltic waves (pyloric pump)

132
Q

Describe the pyloric sphincter

A

circular smooth muscle with 2 ring-like thickenings

133
Q

Opening of the pylorus is controlled intramurally by…

A

contractions in the antrum

134
Q

The pyloric sphincter prevents…

A

regurgitation of duodenal contents back into stomach

135
Q

The pyloric sphincter has what kind of reflex?

A

enterogastric reflex (extrinsic)

136
Q

Enterogastric reflex decreases…

A

emptying rate of gastric contents into duodenum to prevent overwhelming the duodenum
- inhibits antral contractions and stimulates pyloric sphincter to close

137
Q

Enterogastric reflex is activated through…

A

duodenal mucosal receptors in response to:

  • hyperosmotic solution of chyme/nutrients/enzymes
  • duodenal pH < 4.5
  • fatty acids and monoglycerides
138
Q

Hyperosmotic solution of chyme/nutrients/enzymes work via…

A

osmoreceptors to inhibit further gastric emptying

139
Q

How does duodenal pH activate enterogastric reflex?

A
  • excess gastric acid gets dumped into duodenum
  • sensed by duodenal chemoreceptors
  • S-cells of duodenum release secretin
  • secretin activates enterogastric reflex
140
Q

What does secretin stimulate?

A
  • release of bicarb from pancreas

- enterogastric reflex

141
Q

How do fatty acids and monoglycerides activate enterogastric reflex?

A
  • presence of excess fats in duodenum stimulates I cells of duodenum to release hormone cholecystokinin (CCK)
  • gastric emptying is slowed, so fat entry doesn’t exceed the rate of fat breaking down
142
Q

What is stimulated when CCK is released?

A
  • contraction of pyloric sphincter and gallbladder smooth muscle
  • duodenal neurons that initiate vagovagal reflex
  • relaxes sphincter of Oddi
143
Q

What is decreased when CCK is released?

A

rate of stomach emptying

144
Q

When contraction of gallbladder smooth muscle and sphincter of Oddi is relaxed, what happens?

A

pancreatic juices and bile are able to enter into the duodenum

145
Q

While food is in the small intestine, the majority of _____ and _____ are completed

A

digestion and absorption

146
Q

What participates in digestion and absorption in the small intestine?

A
  • bicarb from pancreatic duct
  • digestive enzymes from intestinal epithelium and exocrine pancreas
  • bile from liver via gallbladder
  • mucus from intestinal goblet cells
147
Q

Function of bicarb:

A

neutralize chyme

148
Q

Function of bile from liver:

A

facilitates emulsification of fats

149
Q

Function of mucus from intestinal goblet cells:

A

prevents autodigestion

150
Q

Contractility and secretions of the small intestine are regulated by…

A

neuronal and hormonal clues

151
Q

Chyme in the small intestine activates…

A

the enteric nervous system

  • decreases gastric motility and secretion
  • specific nutrients in the chyme can stimulate release of hormones and mechanisms to stimulate release of insulin
152
Q

What type of movement is the most frequent in the small intestine?

A

segmental contractions

  • closely spaced contractions and relaxations of circular muscle
  • exposes fresh materials to absorptive surfaces
153
Q

Aside from segmental contractions, what other movement does small intestine have?

A
  • short peristaltic contractions

- long peristaltic contractions (migrating myoelectric complex)

154
Q

Frequency of short peristaltic contractions of the small intestine:

A
  • regular when there is food

- few between meals

155
Q

What do long peristaltic contractions of the small intestine do?

A

empty stomach and small intestine between meals

156
Q

What stimulates long peristaltic contractions of the small intestine?

157
Q

When is motilin produced?

A

when there is fat and protein by M cells

158
Q

What inhibits long peristaltic contractions of the small intestine?

A
  • presence of food in stomach
  • gastrin
  • CCK
159
Q

What is the intestinointestinal reflex of the small intestine?

A

over-distension of one area leads to the relaxation of the rest of the small intestine

160
Q

What regulates the emptying of the small intestine?

A

ileocecal valve/sphincter

161
Q

The ileocecal valve/sphincter is normally…

A

closed

  • distention of cecum leads to cecal enteric reflex, which prevents retrograde flow
  • distension of ileum promotes relaxation of sphincter
162
Q

The ileocecal valve/sphincter has a reflex called…

A

gastroileal reflex or gastrocolic reflex

- same thing, just different name

163
Q

Gastrocolic reflex is initiated by…

A
  • stretch in stomach
  • increased motility of stomach
  • byproducts of digestion in duodenum
164
Q

Function of gastrocolic reflex:

A
  • increases movement of material through ileocecal sphincter

- helps make room for more food

165
Q

Motility of the colon is relatively…

A

slow

  • contents can stay here for many hours
  • decreased motility causes greater absorption and constipation
166
Q

Colon has an inner band of…

A

longitudinal smooth muscle, aka taenea coli

167
Q

Contractions of taenea coli causes wall of colon to…

A

form haustrations (pockets)

168
Q

What occurs within haustrations?

A

localized segmental contractions similar to segmentation

  • mixing function
  • compaction of feces
169
Q

T/F: In the colon, peristaltic propulsion occurs in a single direction

A

F, occurs in both directions

170
Q

T/F: retrograde speeds up progress through colon

A

F, it slows it down

171
Q

Peristaltic propulsion in the colon is primarily regulated by…

A

intrinsic enteric reflexes caused by filling and distention

172
Q

What is mass movement in the colon?

A

wave of contractions that occur 1-3x day

173
Q

How does mass movement in the colon occur?

A
  • large part of internal circular muscle contracts powerfully and propels food distally
  • contents get pushed along a significant length of colon, which is mediated through the gastrocolic reflex and/or orthocolic response
174
Q

Colon has what kind of reflex?

A

defecation reflex: emptying of lower colon initiated by filling of rectum

175
Q

What happens when colon is distended?

A
  • internal anal sphincter is relaxed
  • external anal sphincter is constricted
  • induces urge to defecate
176
Q

External anal sphincter is under…

A

voluntary regulation and modulated by higher centers

177
Q

Defecation is aided by…

A

conscious abdominal contractions against a closed glottis (Valsalva maneuver)

178
Q

What are the major nutrient groups?

A
  • carbohydrates
  • proteins
  • fats
179
Q

Carbohydrates are ingested as…

A
  • polysaccharides
  • disaccharides
  • monosaccharides
180
Q

Function of polysaccharides:

A

storage reservoir for glucose

- basically large chains of glucose

181
Q

Glycogen is a major…

A

animal polysaccharide

182
Q

Starch is a polysaccharide that can be found where?

183
Q

What is a major source of carbs for humans?

184
Q

Starch also has cellulose which is the…

A

indigestible plant carb, which is a major component of dietary fiber

185
Q

Disaccharides are made up of…

A

two monosaccharides

186
Q

Examples of disaccharides:

A
  • sucrose
  • lactose
  • maltose
187
Q

Sucrose is made up of…

A

glucose and fructose

188
Q

Lactose is made up of…

A

glucose and galactose

189
Q

Maltose is made up of…

A

glucose and glucose

190
Q

Examples of monosaccharides:

A
  • glucose
  • fructose
  • galactose
191
Q

Chemical digestion of carbs begins in the…

A

mouth w/

  • enzyme salivary alpha-amylase (ptyalin)
  • ductal cells of salivary glands
192
Q

Salivary alpha-amylase (ptyalin) is made by…

A

acinar cells of the salivary glands

  • parotid
  • submandibular
  • sublingual
193
Q

What stimulates salivary alpha-amylase (ptyalin)?

A

PNS (Ach) in response to smell, taste or presence of food in mouth
- aka cephalic phase of digestive regulation

194
Q

What is the optimum pH for salivary alpha-amylase (ptyalin)?

195
Q

At what pH is salivary alpha-amylase (ptyalin) inactivated?

196
Q

Function of salivary alpha-amylase (ptyalin):

A

break down starch to oligosaccharides

197
Q

Ductal cells of salivary glands modify…

A

electrolytes in secretions reabsorbing Na+ and Cl- while secreting K+ into saliva

198
Q

Chemical digestion of carbs stops in the…

199
Q

Why does chemical digestion of carbs stop in the stomach?

A

when alpha amylase gets mixed with gastric acid, the salivary enzymes are inactivated

200
Q

When does chemical digestion of carbs resume after being stopped in the stomach?

A

small intestine

201
Q

Initial duodenal digestion of carbs occurs because of…

A

secretions from the exocrine pancreas

202
Q

Pancreas is organized into…

A

lobes that have acinar and ductal cells

203
Q

Pancreatic ductal cells contain…

A

carbonic anhydrase and secretes HCO3-, which neutralizes acid chyme

204
Q

Pancreatic ductal cells are stimulated by…

A

secretin, which is released by S cells of the duodenum in response to pH <4.5

205
Q

Pancreatic acinar cells are stimulated by…

A
  • Ach
  • long vagovago reflexes
  • CCK (cholecystokinin)
206
Q

Ach stimulates pancreatic acinar cells in response to…

A

thinking about food, smell, taste or presence of food in mouth
- this is the cephalic phase of pancreatic secretion

207
Q

Long vagovago reflexes stimulate pancreatic acinar cells in response to what?

A

presence of food in stomach

- this is the gastric phase of pancreatic secretion

208
Q

CCK stimulates pancreatic acinar cells in response to what?

A

presence of fat and protein in duodenum

- this is the intestinal phase of pancreatic secretion

209
Q

Acinar cells of the pancreas secrete…

A

pancreatic alpha amylases, which are released by exocytosis

210
Q

Function of pancreatic alpha amylases:

A

break polysaccharides into smaller oligosaccharides and disaccharides

211
Q

Examples of duodenal secretions:

A
  • sucrase
  • lactase
  • enterokinase
  • peptidase
212
Q

Function of sucrase:

A

cleaves sucrose into glucose and fructose

213
Q

Function of lactase:

A

cleaves lactose into glucose and galactose

214
Q

What causes lactose intolerance?

A

a deficiency of lactase

215
Q

Where does the greatest absorption of monosaccharides occur?

A

in brush border cells of the duodenum and jejunum

- they’re specialized for absorption

216
Q

Glucose and galactose compete for…

A

entry into epithelial enterocytes via apical SGLT1 (Na+ glucose transporter 1)
- basolateral Na+/K+ ATPase maintains the Na+ gradient needed for the secondary active transport

217
Q

Glucose and galactose move out of the duodenum and jejunum by…

A

facilitated diffusion into the ISF by basolateral GLUT 2 transporter

218
Q

Fructose moves in and out of cells via…

A

facilitated diffusion transporters

  • enters apical border on GLUT-5
  • exits basolateral by GLUT-2
219
Q

Proteins are…

A

long chains of amino acids

- aka polypeptides

220
Q

Proteins are obtained from…

A
  • ingested food
  • breakdown of digestive secretions
  • exfoliated epithelial cells
221
Q

Amino acids are _____ units

A

absorbable

222
Q

Chemical digestion of proteins begins in…

A

stomach due to secretions of gastric pit glands in mucosa

223
Q

Cardiac glands are located…

A

below lower esophageal sphincter

224
Q

Cardiac glands are made up of…

A

columnar epithelial cells that secrete mucus gel and alkaline fluid that has HCO3-

225
Q

Function of cardiac glands:

A

protect epithelium from mechanical and gastric acid injury

226
Q

How does aspirin and other NSAIDs affect cardiac glands?

A

inhibit mucus and HCO3- secretion

- prolonged use can result in gastritis or gastric ulcers

227
Q

What can helicobacter pylori affect the mucus gel layer?

A

can break it down and promote ulcers

228
Q

Oxyntic glands are the acid secreting region in…

A

fundus and body of stomach

229
Q

What cells make up the oxyntic glands?

A
  • surface mucus cells
  • mucous neck cells
  • chief cells
  • endocrine cells
  • parietal/oxyntic cells
230
Q

Surface mucus and mucous neck cells of oxyntic glands secrete…

A

mucus and bicarb

- protects stomach from autodigestion

231
Q

Where are chief cells located in oxyntic glands?

A

bottom of gland

232
Q

Chief cells of oxyntic glands are stimulated by…

A

acid secretion or Ach

233
Q

What do chief cells of oxyntic glands secrete?

A
  • gastric lipase for fat digestion

- pepsinogen, which is an inactive enzyme used for protein digestion

234
Q

What activates pepsinogen?

A

HCl and turns it into pepsin

235
Q

Function of pepsin:

A

convert about 15% of dietary protein to small peptides and amino acids

236
Q

Examples of endocrine cells:

A
  • ECL (enterochromaffin-like cells)

- gastrin

237
Q

Function of ECL cells:

A

secrete histamine

238
Q

ECL cells are triggered by…

A
  • gastrin

- Ach

239
Q

Gastrin is produced by…

A

G cells in response to presence of amino acid in stomach

240
Q

Stomach releases acid secretions in response to…

A
  • stomach distension
  • presence of amino acids and peptides
  • sight, smell, and taste of food
  • calcium
  • caffeine
  • alcohol
241
Q

How do somatostatin from D cells, prostaglandins, and epidermal growth factor inhibit HCl secretion?

A

inhibits adenylyl cyclase

242
Q

What happens during meals for digestion of proteins?

A
  1. increase in gastric lumen pH to 5/6
  2. decreased somatostatin released by D cells
  3. increased gastrin secretion
  4. increased HCl secretion
243
Q

What happens between meals for digestion of proteins?

A
  1. gastric lumen pH<2
  2. increased somatostatin release by D cells
  3. decreased gastrin secretion
  4. decreased HCl secretion
244
Q

What turns off gastrin production?

A

somatostatin from D cells

  • occurs when pH < 2
  • stops when pH > 5
245
Q

What can stimulate gastrin release?

A

coffee/caffeic acid

246
Q

Where are parietal/oxyntic cells located in oxyntic glands?

A

deeper and along the sides

247
Q

What is the intrinsic factor that is made in the parietal/oxyntic cells of oxyntic glands?

A

a glycoprotein that binds vitamin B12 and allows its absorption in small intestine

248
Q

Parietal/oxyntic cells contains…

A

carbonic anhydrase that’s used to produce HCl to lower pH of lumen

  • converts CO2 + H2O to carbonic acid
  • carbonic acid then dissociates to H+ and HCO3-
249
Q

What is located on the basolateral membrane of parietal/oxyntic cells of oxyntic glands?

A

HCO3-/Cl- exchanger

  • moves HCO3- to ICF by facilitated diffusion, which causes “alkaline tide” (raises pH of blood leaving stomach)
  • Cl- enters cell from ECF
250
Q

What is located on the apical membrane of parietal/oxyntic cells of oxyntic glands?

A

H+/K+ ATPase (aka proton pump)

251
Q

How does the H+/K+ ATPase pump work?

A
  • pumps H+ into lumen and brings K+ into cell
  • K+ leaks back out via leak channels on apical border, which in turn increases number and activity of H+/K+ ATPases
  • Cl- enters lumen via diffusion
  • H+ combines with Cl-
252
Q

Function of HCl:

A
  • kills most ingested microorganisms
  • converts inactive pepsinogen to active pepsin
  • creates low pH of 1 for optimal action of pepsin
253
Q

HCl secretion is stimulated by…

A
  • Ach via M3 receptors
  • gastrin via CCK receptors
  • histamine from ECL cells via H2 receptors
  • caffeine on adenosine receptors -> cAMP
254
Q

Ach stimulates HCl secretion in response to…

A
  • sight, smell, and taste of food
255
Q

Pathway for Ach:

A
  1. G protein is activated and associated with phospholipase C (PLC)
  2. increases DAG, protein kinase C (PKC), IP3
  3. increases intracellular [Ca2+]
256
Q

Gastrin stimulates HCl secretion in response to…

A
  • distension of stomach

- presence of amino acids and peptides

257
Q

What does histamine activate?

A
  • G protein associated with adenylyl cyclase and increases cAMP
  • K+ channel on basolateral membrane
258
Q

Histamine is the paracrine agonist with the…

A

strongest effect compared to gastrin and Ach

259
Q

Effect of caffeine on the stomach:

A

increases acid production so it can cause ulcers, irritable bowel syndrome, and decrease calcium uptake

260
Q

HCl secretion is inhibited by…

A
  • somatostatin

- paracrines (prostaglandins (E&I) and epidermal growth factor (EGF))

261
Q

Somatostatin is released from…

A

D cells in response to pH < 2 in stomach

262
Q

How do paracrine hormones inhibit HCl secretion?

A

by inhibiting adenylyl cyclase

263
Q

Chemical digestion of proteins continues in the…

264
Q

T/F: small intestine has low capacity to process protein

A

F, has a high capacity and absence of stomach pepsin doesn’t impair protein digestion

265
Q

Initial duodenal protein digestion occurs due to…

A

pancreatic secretions, which are proteases (endopeptidases) secreted in inactive zymogen form

266
Q

Examples of pancreatic secretions:

A
  • trypsinogen (most potent)
  • chymotrypsinogen
  • proelastase
  • procarboxypeptidase
  • trypsin inhibitor
267
Q

Procarboxypeptidase is an…

A

exopeptidase that cleaves terminal amino acid

268
Q

Trypsin inhibitor is made by…

A

pancreatic acini to prevent premature activation of trypsinogen in pancreas

269
Q

Enterokinase is secreted by…

A

duodenal mucosa in response to presence of food

270
Q

Function of enterokinase:

A

convert trypsinogen into trypsin

  • trypsin activates chymotrypsin, carboxypeptidase, and elastase
  • then proteins are converted to oligopeptides
  • also has peptidases that converts oligopeptides to smaller peptides and amino acids
271
Q

50% of protein absorption occurs in the…

A

duodenum

- rest are in the jejunum and ileum

272
Q

For absorption of proteins, the apical membranes of the small intestines contain…

A

transporters for single amino acids and peptides

273
Q

Examples of transporters in the apical membranes of the small intestines:

A
  • single amino acid transporters
  • secondary active transport through Na+ driven symporters
  • facilitated diffusion at basolateral membranes (moves amino acids into ISF)
274
Q

For absorption of proteins, peptide transporters are what kind of transporters?

A
  • apical secondary active transport through H+ driven symporters
275
Q

Function of peptide transporters in absorption of proteins:

A
  • converts proteins to single amino acids by intracellular peptidases
  • helps with facilitated diffusion at basolateral membranes by moving amino acids into ISF
276
Q

During absorption of proteins, small peptides can be moved across the cell via…

A

transcytosis

277
Q

What are the primary lipids of a normal diet?

A

triglycerides/fat

278
Q

Chemical digestion of fats begin and end in the…

A

small intestine

279
Q

Before digestion of fats can occur, they must be…

A

emulsified by bile to increase SA

280
Q

Where is bile made and stored (two different places)?

A
  • made in liver by hepatocytes

- stored in gall bladder

281
Q

Bile salts are…

A

amphipathic, which means they have a hydrophobic area and a hydrophilic area
- can be reabsorbed and recycled

282
Q

Function of bile salts:

A
  • emulsify lipids to increase SA available for enzymatic action
  • solubilize cholesterol and phospholipids
283
Q

Digestion of fats occurs due to…

A

pancreatic secretions

- mainly pancreatic lipases aided by colipases

284
Q

Pancreatic lipases only have access to…

A

lipids on surface of fat droplets

285
Q

Function of pancreatic lipases:

A
  1. breaks fat into fatty acids and glycerol

2. fatty acids and glycerol form micelles of fat digestive products and fat soluble vitamins

286
Q

What is the benefit of having micelles of fat digestive products and fat soluble vitamins?

A
  • increased transport of lipid digestion products to brush border
  • enhanced absorption of lipid products by epithelial cells
287
Q

What are the fat soluble vitamins?

288
Q

What are the absorbable units of fats?

A
  • fatty acids

- glycerol

289
Q

Where do micelles diffuse?

A

in the brush borders of duodenum and jejunum

290
Q

Fatty acids will bind to ____ to prevent formation of oil droplets

A

proteins in the cytosol

291
Q

Fat soluble vitamins enter epithelial cells via…

292
Q

Cholesterol gets transported into cell on…

A

brush border transport proteins

- inhibited by ezetimibe

293
Q

Binding proteins transport lipid digestion products to…

A

smooth ER and golgi to process and package lipids into chylomicrons
- they then leave by exocytosis

294
Q

T/F: chylomicrons can enter gut capillaries

A

F, they’re too big

- enter lymphatic capillaries and are transported to veins via lymphatic vessels

295
Q

What stimulates bile production?

A

CCK in response to presence of fat in duodenum

296
Q

What happens after bile production is stimulated?

A
  1. bile gets emptied into biliary canaliculi that then empties into bile ducts
  2. bile gets released into common bile duct
  3. bile can then directly enter duodenum at sphincter of Oddi
297
Q

Sphincter of Oddi is usually…

A

closed and bile gets stored in gallbladder

298
Q

Function of gall bladder:

A
  • stores bile between meals

- concentrates bile 10-20 fold

299
Q

CCK can stimulate contraction of…

A

gallbladder smooth muscle, which empties bile into common bile duct

300
Q

Terminal end of the common bile duct empties into..

A

duodenum through sphincter of Oddi

301
Q

When is sphincter of Oddi is under high contractile tone?

A

between meals

- relaxed by CCK

302
Q

What is bilirubin?

A

bile pigment

  • product of degraded RBCs
  • makes bile yellow
303
Q

What is cholesterol’s only route for secretion?

304
Q

Too much cholesterol in bile can lead to…

A

gallstones

305
Q

What is the main site of absorption for micronutrients, water, and electrolytes?

A

small intestine

- jejunum is more active than ileum

306
Q

Water absorption in the small intestines depends on…

A

absorption of ions

- specifically Na+ and Cl-

307
Q

Na+ is absorbed along…

A

the entire length of intestine

  • moves into epithelial cells with gradient
  • Na+ driven transporters facilitate absorption of other substances
308
Q

Ca2+ is absorbed by…

A

all areas of intestine

  • moves into epi cells by passive diffusion w/ gradient through channels
  • binds to calbindin inside cell
309
Q

Ca2+ moves across what membrane in the intestine?

A

basolateral membrane into ISF by Ca2+ ATPase or Na+/Ca2+ exchanger

310
Q

What enhances absorption of Ca2+?

A

1,25 dihydroxy-vitamin D

311
Q

Vitamin B12 (cobalmin) is absorbed in…

A

ileum bound to intrinsic factor from stomach

312
Q

Iron is absorbed across…

A

apical border with H+ on divalent metal transporter 1 (DMTI1)

  • heme that got absorbed by apical transporter protein gets converted to Fe2+
  • all Fe2+ gets removed from colon cells by transporter ferroportin
313
Q

Transporter ferroportin is regulated by…

A

hormone hepcidin

- dependent on body iron levels

314
Q

Iron needs what kind of plasma transporter?

A

transferrin

315
Q

After absorption, iron travels to…

A

the liver for storage or carried to bone marrow for RBC production

316
Q

Vitamin C and most of vitamin B is absorbed by…

A

carrier mediated transport throughout the small intestine

317
Q

What are parts of the large intestine/colon?

A
  • ascending
  • transverse
  • descending
  • sigmoid
318
Q

Colon absorbs the remaining…

A

water and salt

319
Q

Na+ absorption in the colon is driven by…

A

a gradient created by Na+/K+ ATPase on basolateral membrane

  • are apical Na+ channels in colon
  • Na+ can also enter via cotransport with Cl- or Na+/H+ exchanger pump
320
Q

In the large intestine, Cl- follows which gradient?

A

Na+ electrical gradient into the ISF

  • can be cotransported with Na+ or exchanged with HCO3- on apical surface
  • also Cl- channels on basolateral surface
321
Q

Immune functions of the GI tract:

A
  • salivary lysozymes

- extensive lymphatic presence

322
Q

What is the first line of immune defense for the GI tract?

A

salivary lysozymes

323
Q

Why is there an extensive lymphatic presence in the GI tract?

A

b/c there is continuous exposure to the external environment

324
Q

Examples of lymphatic presence in the GI tract:

A
  • GALT tissue

- Peyer’s patches in mucosa (M cells here bind antigens)

325
Q

What happens if there is an over-activity of immune response in the GI tract?

A
  • inflammatory bowel disease

- Chron’s disease

Physiology (33 decks)

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