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FHB > GI 01 & 02: GROSS ANATOMY AND BASIC PHYSIOLOGY > Flashcards

GI 01 & 02: GROSS ANATOMY AND BASIC PHYSIOLOGY Flashcards

1
Q

What are the 4 main functions of the GI tract (and what is the fifth that textbooks often leave out)?

A

Motility, digestion, absorption, secretion, and excretion

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2
Q

What causes motility?

A

Contractions of smooth muscle in the gut lining

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3
Q

With regard to food particle size, what does motility contribute?

A

Helps reduce the size of the particles (helps in the breakdown process of food size). This allows for increased contact of area of food with chemicals and the mixing of those chemicals with food

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4
Q

With regard to motility, what do we think of as its main main function

A

Propels food in the caudad direction

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5
Q

Is the rate of mobility important?

A

Yes, it is going to happen at a rate that is best for full breakdown (digestion) and absorption of ingested food (ex. apples down to fructose)

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6
Q

What is secretion

A

The release of enzymes from cells in the GI lumen

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7
Q

What kinds of cells participate in secretion?

A

Epithelial cells lining the GI tract and associated glandular organs

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8
Q

What are the major associated glandular organs that participate in secretion

A

Gall bladder, pancreas, salivary glands, liver

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9
Q

What is the digestion process?

A

The process by which large macromolecules are broken down into smaller micromolecules

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10
Q

Why is digestion critical?

A

A whole apple isn’t useful to us but individual fructose is- therefore digestion is required to get things to absorbable levels of size

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11
Q

What are the two aspects of digestion?

A

Physical and chemical breakdown (mixing via strong muscles and enzymes)

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12
Q

What is the process of absorption?

A

Nutrients and water are moved from GI lumen into the blood

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13
Q

What are the reasons we need to absorb nutrients

A

Energy
Building blocks for other shit
parts of metabolic pathways
Regulation of all physiological activitie

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14
Q

What is the process of excretion

A

Waste –> bye bye
This includes storage and excretion of ingested food that goes through, but also products from the liver such as steroids, drug metabolites, and cholesterol

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15
Q

Why is it important that the GI tract has an immunocological function?

A

It’s exposed to the external environment - we can consider the GI tract the largest immune organ in the body

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16
Q

Connection between gut microbiome and immunity

A

They’re linked (as gut microbiome increases so does immunity and this tracks with age)

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17
Q

What are the major functional segments of the GI tract

A
  • mouth and pharynx
  • esophagus
  • stomach
  • small intestine (duodenum, jejunum, ileum)
  • large intestine (colons)
  • rectum
  • anus
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18
Q

Associated glandular organs of Gi tract

A
  • salivary glands
  • pancreas
  • liver
  • gall bladder
  • associated endocrine glands in gastric walls
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19
Q

What are sphincters

A

specialized circular smooth muscle

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20
Q

What are the sphincters of the GI tract

A
  • Upper esophageal
  • lower esophageal
  • Pyloric
  • sphincter of oddi (the one at the GB/pancreas/small intestine junction)
  • ileocecal
  • internal (involuntary) and external (voluntary) anal sphincter
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21
Q

Layers of gut wall

A
  • mucosa
  • submucosa
  • muscularis externa
  • serosa
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22
Q

What is the mucosa

A

Innermost layer of gut wall, made of epithelium, lamina propria, and muscularis mucosae

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23
Q

What is gut epithelium?

A

Single layer of continuous cells linked by tight junctions - can consist of many specialized groups

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24
Q

absorptive enterocytes

A

Most abundant epithelial cell in gut, play vital role in digestion and absorption

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25
Q

Enteroendocrine cells

A

Release regulatory peptides, amines - regulate GI function

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26
Q

Gastric mucosal cells

A

Produce protons (important for stomach acid)

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27
Q

Mucin producing cells

A

Produce a glycoprotein that protect the GI wall

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28
Q

Esophageal epithelium

A

Hellps in transportation of swallowed food (no absorption) -thus they are squamous and simple

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29
Q

Intestinal epithelium

A

Helps in absorption and selectiveuptake of ions, nutrients, and water - they have a big job and are therefore big themselves (columnar)

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30
Q

the surface area and small intestine epithelium consist of (large structure, and the places in between those structures) to increase surface area

A

Villi and crypts

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31
Q

Lifespan of Gi cells

A

3-5 days

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32
Q

Where are the proliferative cells in the Small intestine?

A

Crypts (these are called intestinal stem cells)

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33
Q

What exactly are villi and crypts

A

Fingerlike projections of the small intestine (they are units of absorption)- crypts are the invaginations/folds

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34
Q

What does every villus have?

A

The epithelial cell on the suraface has numerous cytoplasmic extensions that create a “brush border” / microvilli to increase the surface area even more

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35
Q

What can happen if you have destruction of villi and microvilli?

A

Malabsorption and malnutrition - happens in celiac disease

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36
Q

Lamina propria

A

Immediately below epithelium, consists of connective tissue (collagen, elastin). This is rich in glands, and contains lymph vessels and nodes, capillaries, and nerve fibers

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37
Q

Muscularis mucosae

A

Thin layer of smooth muscle cells in a folding configuration caused by contractions

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38
Q

Submucosa

A

Consists of connective tissues (collagen, elastin). Also has glands, nerves that can sense stretch, blood vessels, and has a dense nerve plexus called the “submucosal plexus” (pt 1 of gut brain). Overall this helps with the integration of motor and secretory activities

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39
Q

What is the meissner’s plexus

A

This is the submucosal plexus in the submucosal layer and is pt 1 of gut brain

40
Q

Muscularis externa / muscularis propria

A

Contractions in this layer help in mixing and propelling GI tract contents; there are two layers of smooth muscle (inner circular, outer longitudinal). Between the two layers is the second part of the gut brain, the myenteric plexus

41
Q

What is auerbach’s plexus

A

Myenteric plexus, pt 2 of gut brain (this is the plexus impt in coordinating peristalsis

42
Q

Serosa

A

Outermost layer of Gi tract; consists of squamous mesothelial cells and lines surface of abdominal wall to keep organs suspened. Also, secretions are viscous and lubricates abdominal organs - this is important to reduce friction between ab organs during contractions and relaxation of GI tract

43
Q

Portal circulation

A

Venous blood arising from abdominal organs flows to liver first via portal vein (portal circulation). Blood from liver is transported via hepatic veins to inferior vena cava, and then pumped by the heart which will supply the rest of the tissues.

44
Q

Importance of portal vein going to liver

A

The liver is going to detoxify from any bad shit that might have gotten absorbed - it also will keep some nutrients for itself

45
Q

Splanchnic Circulation

A

This is the circulation that actually supplies the GI tract - it has a HUGE blood flow (25% of CO), and a large reservoir function as well as a huge diversity of organs it perfuses.

46
Q

3 major arteries of splanchnic circulation

A

Celiac, superior mesenteric artery, inferior mesenteric artery

47
Q

What does the celiac artery supply

A

liver, spleen, stomach

48
Q

what does the superior mesenteric artery supply

A

pancreas, SI, proximal colon

49
Q

What does the inferior mesenteric artery supply

A

Distal colon

50
Q

Lymphatic circulation purpose

A

Helps return fluids, FA molecules, white cells to the blood - this is crucial for the absorption of lipids and lipid soluble molecules , as well as some vitamins and drugs. It also plays a role in immune fxn and filtering (ex, bacteria enter capillaries and pass into lymph vessels, eventually getting to nodes where there are many immune cells). They also pick up interstitial fluid to carry them back to circulation

51
Q

Is fatty acid absorbed directly into blood

A

no it must go through lymphatic system

52
Q

GI activity overall

A

GI goes through relative quiescence and intense activity which can vary through food intake, as well as communication between segments

53
Q

How do we regulate GI function

A

Endocrine, paracrine, and neural siganling

54
Q

Sensor cells (for endocrine fxn in GI tract) aka enteroendocrine cells

A

respond to stimulus by secreting a regulatory peptide or homrone that will travel endocrine style to a target cell at a distant location

55
Q

are enteroendocrine cells / sensor cells typically open or closed type and are there exceptions?

A

Open (apex of cell is in contact with GI lumen for sensing, and base releases hormone that diffuses into local capillaries)
But some are closed - these do not have contact with Gi luminal surface (ECL cells of gastric epithelium are like this)

56
Q

Paracrine signaling

A

A chemical messenger or regulatory peptide released from a signaling cell diffuses to nearby cell - it is not transported in circulation (targets are generally smooth muscle, absorptive enterocytes, secretory cells in glands, and other EECs)

57
Q

Histamine

A

Paracrine signaler released by enterohromaffin-like cells in stomach, diffuses through Interstitial space and binds to neighboring parietal cells that then secrete HCl

58
Q

Cholecystekinin

A

Paracrine or endocrine signaler, it is released from duodenum in response to dietary protein, lipids - acts locally on nerve terminals, but also goes into bloodstream to affect pancreas (paracrine; endocrine respectively)

59
Q

What is another major system in Gi tract that relies on paracrine signaling

A

Immune system

60
Q

Celiac disease

A

Response to Giladin in wheats that leads to destruction of microvilli

61
Q

The gut is innervated by 2 sets of nerves. What are they (basically)?

A

Extrinsic and intrinsic

62
Q

extrinsic NS of the gut

A

Nerves that innervate gut with cell bodies located outside of gut ; these are part of the autonomic nervous system

63
Q

Intrinsic (enteric) nervous system

A

Cell bodies are inside of the gut wall; made of myenteric and submucosal plexi

64
Q

Can intrinsic and extrinsic nervous systems communicate

A

YES

65
Q

Extrinsic innervation is primarily through what branch of ANS

A

Parasympathetic (although sympathetic does happen)

66
Q

How does parasympathetic innervation occur (via what nerves)

A

vagal and pelvic , primarily vagal

67
Q

Vagus nerve innervates:

A

Esophagus, stomach, gallbladder, pancreas, 1st part of intetine, cecum, proximal colon

68
Q

pelvic nerve innervates:

A

distal part of the colon and anorectal region

69
Q

What does PSNS innervation of the gut result in

A

OVerall, activates GI function

70
Q

Where does PSNS innervation of gut originate

A

Brain stem (medulla) for vagus nerve, and sacral spinal cord for pelvic nerve

71
Q

What are the neurotransmitters for PSNS innervation of gut

A

Ach, substance P, VIP

72
Q

What kind of nerve is the vagus nerve and how does that play into how it functions in the GI tract

A

mixed - 75% afferent (to brain) and 25% efferent (to gut from brain)

73
Q

What are the afferent fibers of the vagus nerve telling the brain (what receptor types)

A

sensory information - mechanoreceptors and chemoreceptors

74
Q

what is a vagovagal reflex

A

A vagus response due to vagal input

75
Q

Generally how does SNS activity impact gut and what is the exception

A

inhibition of GI smooth muscle - exception is GI sphincters, which are activated (closed)

76
Q

What are the SNS ganglia that serve Gi tract

A

celiac, superior mesenteric, inferior mesenteric

77
Q

What do the SNS fibers release

A

NE

78
Q

with regard to SNS innervtion how much is afferent and how much is efferent

A

50/50

79
Q

Main fxn of myenteric plexus

A

regulate mobility

80
Q

main fxn of submucosal plexus

A

modulate overall activity of cells (esp endocrine cells)

81
Q

Can enteric nervous system function without CNS

A

yes

82
Q

Long neural reflex

A

Sensory afference to medulla (ex. vagal), then efference back to motor to GI

83
Q

Short neural reflex

A

Loop that stays entirely in enteric nervous system

84
Q

What kind of neural reflex is a vagovagal reflex

A

Long (to cns and back)

85
Q

What muscles are voluntary for sphincters, what kind of muscle do they have

A

Pharynx, upper 1/3 of esohagus, external anal sphincter

86
Q

Two kinds of contractions of smooth muscle in GI tract

A

Phasic, tonic

87
Q

Phasic contractions

A

Periods of contraction followed by relaxation - found in esophagus, gastric antrum, small intestine (involved in mixing and propulsion)

88
Q

Tonic contractions

A

Constant level of contraction / tone withtout periods of relaxatio regulalry - found in orad (upper) region of stomach and lower esophgeal region, ileocecal and internal rectal sphincters

89
Q

What are slow waves?

A

Slow electrical waves of oscilating de and re polarization of membrane potential that are not large enough to elicit an action potential or contraction. If, at the plateau/peak of slow wave, membrane is further depolarized to threshold then you get a full AP (strong contraction

90
Q

Is slow wave frequency constant along Gi tract, or does it vary?

A

Frequency of waves varies based on area, has to do with function

91
Q

Where do slow waves originate from?

A

Interstitial cells of Cajal (ICCs) - these are “GI pacemaker cells”

92
Q

Segmental contraction

A

Predminantly in Small and large intestine - this is when you contract in the middle of the food bolus / chyme to break it up and then the chyme comes back together again - important for mixing but produces no forward movement

93
Q

Peristaltic contraction

A

Contraction in orad direction and relaxation in caudal direction to result in net forward propulsion of food

94
Q

NT’s associated with contraction

A

Ach and Substance P

95
Q

NT’s associated with relaxation

A

NO and VIP

96
Q

Which set of neurons, ascending or descending, go in the orad direction?

A

Ascending (will release Ach and Substance P to contract circular smooth muscle and will release NO and VIP to relax longitudinal muscle)

Reverse is true for descending in caudal direction

FHB (54 decks)

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