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Physiology Semester 2 > GI Structure/ Innervation > Flashcards

GI Structure/ Innervation Flashcards

1
Q

Wall of the GI Tract Surfaces:

A

Mucosal Surface: Faces the lumen

Serosal Surface: Faces the blood

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2
Q

Transit Amplifying Cells of the Intestinal Epithelium

A
  • Proliferating intestinal stem cells that will differentiate
  • Later function depends on where they move
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3
Q

Why is the “duodenal cluster” called a cluster?

A

The components have the same progenitor cells during embryogenesis

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4
Q

Components of the Autonomic Nervous System

Innervating the GI Tract

A

Extrinsic Component:

  • Sympathetic and Parasympathetic Innervation

Intrinsic Component:

  • Enteric Nervous System
  • Contained within the submucosal and myenteric plexsuses in the GI wall
  • Has extensive communication with the parasympathetic and sympathetic branches
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5
Q

2 Levels of Control of the GI Tract:

A
  • Central Nervous System
  • Enteric Nervous System
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6
Q

Function & components of the duodenal cluster unit:

A
  • Duodenum - Pancreas - Biliary system Critical regulator of digestion and absorption
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7
Q

Function of mucosal plicae, villi, and microvilli

A
  • Dramatically increase intestinal surface area - Energy efficiency - Excessive capacity of digestion and absorption, esp when food is scarce
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8
Q

Enterocytes of the Villi of the Intestine

A

Mature and differentiated intestinal epithelial cells

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9
Q

Histology of the GI Wall:

A

Mucosal Layer:

  • Epithelial Cells = specialized to carry out absorptive and secretory functions
  • Lamina proprina = connective tissue (primary) blood and lymph vessels
  • Muscularis mucosa = smooth muscle cells
    • Contraction changes the shape and surface area of the epithelial cell layer
  • Layer closest to the lumen is the mucosal layer

Submucosal Layer:

  • Collagen, elastin, glands, and blood vessels
  • Submucosal plexus
    • Controls secretion

Muscularis Layer:

  • Circle muscle layer
  • Myenteric plexus
    • Controls motility of the GI tract
  • Longitudinal muscle layer
    • thin, with few nerve fibers
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10
Q

Mucosal layer of the GI Wall

A
  • Most internal layer, closest to the lumen - Lined by a single layer of intestinal epithelial cells - Contains the lamina proprina
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11
Q

The Intestinal Epithelium (Cell Types)

A
  • Intestinal Stem Cells
  • Paneth Cells
  • Transit Amplifying Cells
  • Goblet Cells
  • Enteroendocrine Cells
  • Enterocytes
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12
Q

Myenteric Plexus of the ENS:

A
  • Located between the longitudinal and circular muscle layers
  • Primary function = controls motility
  • Provides motor innervation to the 2 muscle layers and secreto-motor innervation to the mucosa
  • Extends the entire length of the gut
  • Present in the striated-muscle portion of the esophagus
    • Innervates motor-end plates
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13
Q

Intestinal Villi

A
  • Projections from mucosal plica
  • Lined by intestinal epithelial cells
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14
Q

Functions of the Stomach

A
  • Reservoir that conducts some digestion and partially sterilizes a meal - Pepsin secretion for protein digestion - Gastric Acid secretion for sterilizing the meal
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15
Q

Function of the Esophagus

A
  • Transfer bolus from mouth to stomach
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16
Q

Integration of GI Nervous System

(Short-Loop Reflex)

A

GI Epithelium, Chemoreceptors & Mechanoreceptors –> Sense

Intrinsic Sensory Afferent Neurons of the ENS –> Synapse

Enteric Nervous System (Myenteric Plexus and Submucosal Plexus) –>

Intrinsic Efferent Neurons –>

Effectors (Smooth muscle, secretory cells, endocrine cells and Blood Vessels)

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17
Q

Functions of the Myenteric Plexus:

A
  • Control of tonic contractions
    • Sphincter area
      • Maintain pressure around the sphincter
  • Control of the intensity of rhythmic contractions
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18
Q

Ileocecal valve

A
  • Retains the majority of GI bacteria within the colon - Permits the residues of digested material, water and other cellular debris to enter the colon - Movement from small intestine –> large intestine only
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19
Q

Structure of the Wall of the GI Tract

A
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20
Q

Functions of the Submucosal Plexus:

A
  • Secretory Activity
  • Endocrine Activity
  • Blood Flow
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21
Q

Lamina Proprina

A
  • Underlies the intestinal epithelial cell layer of a villus
  • Contains lymphatic vessels and blood vessels
  • Purpose is nutrient transport
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22
Q

Sympathetic Innervation

(Extrinsic Nervous System):

A
  • Short preganglionic fibers that synapse in the ganglia outside the GI wall
  • Fibers originate from the thoracolumbar spinal cord
  • Preganglionic fibers synapse in the prevertebral ganglia
  • Postganglionic fibers synapse on the ganglia in the ENS OR directly innervate smooth muscle, endocrine, and secretory cells
  • Post-ganglionic nerve fibers are adrenergic (release NE)
    • Synapse on ganglia in ENS plexuses or directly innervate smooth muscle, endocrine or secretory cells

** Innervation via post-ganglionic fibers**

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23
Q

Parasympathetic Innervation:

(Extrinsic Nervous System)

A
  • Innervation supplied by the vagus nerve (cranial nerve X) & pelvic nerve
  • Long preganglionic fibers that synapse in ganglia in or near the target organs
  • Post-ganglionic neurons are cholinergenic or peptidergic

** Fibers synapse in the ganglia inside the GI wall**

  • Ganglia are located in the walls of the organs within the myenteric and submucosal plexuses
  • Information relay from parasympathetic nervous system - coordinated with plexuses –> relayed to smooth muscle, endocrine, and secretory cells

** Innervation of the GI tract via preganglionic fibers**

** Fibers originate in the brainstem or spinal cord**

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24
Q

Microcircuits of the Enteric Nervous System:

A

Sensory (afferent) neurons

  • Receive sensory input
  • Mechanoreceptors: Monitor the distension of the gut wall
  • Chemoreceptors: Monitor the chemical conditions in the lumen

Interneurons

  • Relay information through the myenteric plexus along the GI tract

Motor Efferent Neurons:

  • May be stimulatory or inhibitory- depending on the NT’s
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25
Q

Sympathetic fibers that innervate the GI tract are ________ and synapse on _______ or ________.

A
  • Post-ganglionic
  • Enteric nervous system ganglia
    • Myenteric and Submucosal Plexus
  • Directly on target cells
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26
Q

Vagus Nerve (Cranial Nerve X)

(Mixed Nerve):

A
  • 75% of fibers are afferent
    • delivery of sensory info from mechanoreceptors and chemoreceptors in the wall of the GI tract to CNS
  • 25% of fibers are efferent
    • deliver motor info from CNS to target tissues in periphery
      • Smooth muscle
      • Secretory cells
      • Endocrine cells
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27
Q

Goblet cells of the Intestinal Epithelium

A
  • Mucus secretion and lubrication
  • Prevents entry of harmful organisms from intestinal lumen directly into the vilus
  • No direct contact with bacteria
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28
Q

Vago-Vagal Reflexes:

A
  • Mechanoreceptors and chemoreceptors in GI mucosa relay afferent info to the CNS via the vagus nerve
  • Reflexes triggered
    • Efferent limb is also the vagus nerve

** Afferent and Efferent Limbs are containg in the Vagus Nerve**

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29
Q

Enteric Nervous System Cell Bodies:

A
  • Arranged in 2 systems of ganglia

Myenteric Plexus:

  • Apical surface of the esophagus

Submucosal Plexus:

  • Well developed area in the duodenum and moving along
  • Absorption and secretion
30
Q

Function & components of the biliary system:

A
  • Organs and ducts ( bile duct, gallbladder and liver ducts) that are involved in the production and transport of bile - Biliary system drains into the duodenum
31
Q

Upper and lower esophageal sphincters

A
  • Control swallow and reflux
  • Prevent reflux from stomach back to oral cavity
32
Q

Sphincters of the GI Tract:

A
  • Control valves - Selective retention of meal movement - Upper and lower esophageal sphincters - Pyloric sphincter - Sphincter of Oddi - Ileocecal valve - Internal and external sphincter
33
Q

Enteric Nervous System (ENS):

A
  • Part of the intrinsic branch of the autonomic nervous system
  • Specific to the GI wall
  • Localized within the Submucosal Plexus (Meissner’s Plexus) & Myenteric Plexus
  • Can direct all functions of the GI in the absence of extrinsic innervation
  • Located in the ganglia in them myenteric and submucosal plexuses
  • Controls the contractile, secretory and endocrine functions
34
Q

Location of the Myenteric Plexus:

A
  • Lies between the circular muscle layer & the longitudinal muscle layer of the GI wall
35
Q

Ileum General Function

A
  • Less of a function in absorption than the jejunum
  • Major site of bile acid recycling and back-up absorption
36
Q

Internal and external anal sphincters

A
  • Control defecation
37
Q

Intestinal Stem Cells of the Intestinal Epithelium

A
  • Regenerate new intestinal epithelial cells inside the villus
38
Q

Segments of the GI Tract

A
  • Oral Cavity - Esophagus - Stomach
39
Q

Vagus Nerve (Cranial Nerve X)

Innervation:

A
  • Parasympathetic innervation
  • Innervates the upper GI tract
  • Striated muscles of the upper 1/3 of the esophagus
  • Wall of the stomach
  • Small intestine
  • Ascending colon
  • Portion of the transverse colon

** Innervates from distal esophagus to the proximal large intestine**

40
Q

Sphincter of Oddi:

A
  • Controls the outflow of bile and pancreatic secretion into the lumen of duodenum
  • Acts like a gate
41
Q

Mucosal Plica

A
  • Folds (invaginations) on the internal layer (luminal surface) of the small intestine
  • Project into the lumen
  • Contain villi

** Excessive capacity for digestion and absorption especially when food is scarce**

** Energy efficiency due to increase in surface area**

42
Q

Enteroendocrine Cells of the Intestinal Epithelium

A
  • Produce hormones
    *
43
Q

Pelvic Nerve Innervation:

A
  • Parasympathetic nervous system
  • Innervates the lower GI tract
  • Walls of the transverse, descending, and sigmoid colon

** Innervates the rectum and colon **

44
Q

Paneth Cells of the Intestinal Epithelium

A

Secrete anti-microbial peptides

45
Q

Pyloric Sphincter:

A
  • Controls the outflow from the stomach
  • Controls the delivery rate of food to the duodenum
  • Functions to ensure the duodenum’s capacity for digestion is not exceeded
46
Q

The parasympathetic fibers that innervate the GI tract are primairly ______ and integrate with ________

A
  • Pre-ganglionic
  • Enteric nervous system ganglia
47
Q

Layers of the GI Wall

A
  • Mucosa
    • Most internal layer
    • Closest to the Lumen
    • Lined by a single layer of epithelial cells
  • Submucosa
    • Glands
    • Nerve plexus
      • Submucosal plexus
  • Muscularis
    • 2 muscle layers with myenteric plexus in between
      • Circular muscle layer (more interior)
      • Longitudial muscle layer (more exterior)
  • Serosa
48
Q

Submucosal (Meissner’s Plexus) of ENS:

A
  • Located within the submucosa
  • Best developed in the small intestine
    • Plays important role in the secretory control
    • Abundant in the proximal duodenum
49
Q

Function of the Oral Cavity

A
  • Initial intake of food - Shaping and lubricating a smooth bolus of ingested food for swallowing - Reduce microbial contamination by salivary secretions
50
Q

Segments of the G.I. Tract:

A
  • Oral Cavity
  • Esophagus
  • Stomach
  • Duodenal Cluster Unit
  • Biliary System
  • Jejunum and Ileum
  • Colon
  • Rectum and Anus
51
Q

Function of the Oral Cavity

A
  • Initial intake of food
  • Shaping and lubricating a smooth bolus for swallowing
  • Reduction of microbial contamination by salivary secretions
52
Q

Esophagus:

A
  • Transfer of the bolus from the mouth to the stomach
  • Upper and Lower Esophageal Sphincters
    • Control Swallowing and reflux back to oral cavity
53
Q

Function of the Stomach:

A
  • Acts as a reservoir
  • Conducts some digestions
  • Partially sterilizes the meal
  • Pylorus
    • Controls the outflow from the stomach
  • Pepsin
    • Enzyme for protein digestion in the stomach
  • Gastric Acid
    • Sterilizes the meal
54
Q

Where is the food sterilized?

A

In the Stomach

HCL Secretion

55
Q

Components of the Duodenal Cluster Unit:

A
  • Duodenum
  • Pancreas
  • Biliary System: production and transport of bile
    • Liver
    • Gallbladder
    • Sphincter of Oddi

**Critical regulators of digestion and absorption **

56
Q

Function of the Jejunum:

A
  • Site of Absorption for the majority of nutrients
57
Q

Function of the Ileum:

A
  • Small role in nutrient absorption
  • Major site of bile acid recycling and back-up absorption
58
Q

Function of the Colon:

A
  • Absorbs water and electrolytes
  • Stores wastes
  • Stores indigestible ingesta
59
Q

Rectum and Anus:

A
  • Storage (temporary) and expulsion of feces
60
Q

General Function of Intestinal Epithelial Cells

A
  • Digestion and absorption
61
Q

Crypt Structure (Function)

A
  • Invaginations of the intestinal epithelial cell membrane that surround a vilus
  • Crypt Region Contains:
    • Transit Amplifying Cells
    • Intestinal Stem Cells
    • Paneth Cells
62
Q

Intestinal Stem Cells:

(Location & Function)

A
  • Localized in the crypt region
  • Purpose is to regenerate new intestinal epithelial cells inside the villus
63
Q

Villi of Intestinal Epithelium

A
  • Contain mature and differentiated intestinal epithelial cells (enterocytes)
64
Q

What is the primary control of the myenteric plexus?

A
  • Controls motility
65
Q

Enteroendocrine Cells:

A
  • Produce and secrete hormones
66
Q

How does the parasympathetic nervous system innervate the GI Tract?

A
  • Pre-ganglionic fibers (long)
  • Originate in brainstem and spinal cord
  • Vagus n.
    • Distal esophagus to proximal large intestine
  • Pelvic n.
    • Rectum
    • Colon
67
Q

Sympathetic Nervous System __________ fibers synapse on prevertebral ganglia

A

Preganglionic

68
Q

___________ fibers of the sympathetic nervous system synapse on ____ or ________

A
  • Post-ganglionic
  • ENS ganglia
    • Myenteric Plexus
    • Submucosal Plexus
  • Target Cells
    • Secretory
    • Endocrine
    • Smooth Muscle
69
Q

Primary function of the Submucosal Plexus:

A

Controls:

  • Secretion
  • Endocrine Function
  • Blood Flow
70
Q

Parasympathetic Preganglionic Neurons use _______ (NT)

A

Acetylcholine (ACh)

71
Q

Sympathetic Nervous System:

Preganglionic Neurons use _________

Postganglionic Neurons use ________

A
  • Acetylcholine (ACh)
  • Norepinephrine (NE)
72
Q

Central Nervous System:

Modifies Enteric Nervous System Activity to:

A
  • Optimal digestion
  • Optimal absorption
  • Host defesne

Physiology Semester 2 (7 decks)

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