lecture 1 Flashcards

1
Q

4 tunics:

A

deep - superficial: mucosa, submucosa, muscularis, serosa

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2
Q

GI tract=

A

more neurons than spinal cord
largest lymphoid organ
harbors largest genome
largest endocrine organ in body

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3
Q

mucosa:

A

ole: absorption and secretion; villi increase absorptive area. Hosts specialized EE, goblet cells.
contains:
* lamina propria = layer of connective tissue under the epithelium, containing blood vessels, nerves
and lymphatic vessels (Peyer’s patches). Rich in immune cells; role in host defense.
* muscularis mucosae: thin layer of smooth muscles; provides villus movement.

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4
Q

submucosa role:

A

thick, highly vascular layer of connective elastic tissue where absorbed molecules enter blood and lymphatic vessels. Contains glands and submucosal plexus (Meissner’s plexus) that carries ANS activity to muscularis mucosae of small and large intestines.

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5
Q

serosa role:

A

role: binds and protects. Connective tissue continuing through the
mesenteries (a thin membrane rich in blood and lymphatic capillaries) and the peritoneum (a double
layer membrane surrounding the abdominal organs)

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6
Q

Muscularis externa:

A

radial (inner) and longitudinal (outer) smooth muscles + Auerbach plexus (in
contact with Meissner’s). Myenteric plexus lies in between. Controls segmental and peristaltic
movements along GI. Includes both sympathetic and parasympathetic nerve fibers and ganglia

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7
Q

Different Muscle for Different GI Functions

A
  • Longitudinal smooth muscle has very few electrical junctions; contracts in response to excitatory
    innervation. It contracts for intestinal
    shortening.
  • Circular smooth muscle has many
    electrical junctions and contracts
    spontaneously unless inhibited by
    its innervation. Reduces diameter
    of the lumen when it contracts.
  • Esophagus –largely striated
    muscle with both longitudinal
    and circular muscle.
  • Proximal Stomach – lacks
    distinct layering; smooth
    muscle lacks action
    potentials; slow changes in
    tone in proportion to changes
    in Vm.
  • Distal Stomach (antrum) –
    rhythmically active;
    contraction triggered by
    regular action potentials.
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8
Q

sphincters (GI)

A

control of urine
they are always contracting
* Most under involuntary control, no conscious input (ONE
exception) = external anal sphincter
* Autonomous of CNS, controlled by ENS.
* Retain content in specific sites for optimal digestion&absorption

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9
Q

GI sphincters: (pressure)

A
  • resting state (pressure) > adjacent segments = inhibits movement entre segments
  • relaxation = adjacent segments
    allows forward flow
  • constriction&raquo_space; adjacent segments
    prevents retrograde flow
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10
Q

main functions of GI tube:

A

ingestion
digestion
absorption (diffusion&active transport)
storage
elimination (Temporary storage and
subsequent elimination of
indigestible components of
food (but also cholesterol,
steroids, drug metabolites)
immune barrier (* Includes physical barrier formed by tight junctions
between cells of small intestine
* Cells of the immune system
that reside in connective tissue just below epithelium
* Commensal bacteria)
this all = via motility + secretion

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11
Q

Motility actions:

A
  • digestion ((motility, pH changes, biological detergents, enzymes), mastication, deglutition, peristalsis ( contractions that make food move through GI
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12
Q

secretion actions:

A

release of exocrine and endocrine products into GIT
- exocrine secretions: HCI, H2O, HCO2, bile, lipase, pepsin, amylase, trypsin, elastase, histamine
- endocrine secretions: hormones secreted into stomach + small intestin that help regulate GIT functions;

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13
Q

Oral cavity and esophagus process:

A

mastication: lubrication, food bolus, salivary amylase in saliva
catalyzes partial digestion of
starch.
medulla oblongata is important for swallowing
deglutition: begins as
voluntary activity
* Based on pressure gradient

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14
Q

role of peristalsis =

A

move food from mouth to stomach
fct = independant of gravity

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15
Q

GI sphincter: (LES)

A

constricts after food passes into stomach, relaxes on swallowing, tonically active under neural control, AcH contracts, NO VIP relaxes, prevents backflow/reflux (GERD)

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16
Q

stomach:

A

fct = reservoir
controls rate of meal delivery
partial digestion (proteins + sterilization), low pH kills pathogens
stomach contains gastric pits that increases surface area
exocrine glands = cells secrete gastric juice (goblet cells=secrete mucus, parietal cells= HCI + intrinsic factor (B12 absorption in intestine) (Children born to women who have low blood levels of vitamin B12 shortly before and after conception have an increased risk of neural tube defects such as spina bifida)
Contractions – churns chyme mixing it with gastric secretions
Eventually propelling food into small intestine
!! RECEPTIVE RELAXATION!!—controls pressure, accommodates volume
NOT essential to digestion – allows resections!!
chief cells = secrete pepsinogen, enterochromaffin = histamine + serotonin
G cells = gastrin
D cells = somatostatin

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17
Q

stomach divisions:

A
  • Divided anatomically into:
  • Cardia (secretes mucus and bicarbonate
    to protect)
  • Fundus (specialized secretory cells)
  • Body
  • Antrum (pyloric zone, motility, mixing
    grinding)
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18
Q

SI:

A
  • duodenum: after pyloric sphincter: has chemo + mechanosensitive nerve endings + EE cells, regulates digestion + absorption, receives pancreas + gallbladder secretions, coordinates food intake.
  • jejunum = abundant w villi
  • ileum: contains fewer folds, empties into large intestine, can be called for absorption if duodenum can’t do it.
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19
Q

SI functions:

A
  • foldings and projections: plicae circulares: large folds
    villi: fingerlike folds of mucosa, 15x more surface area
    microvilli: apical hair-like projection, 300x more surface area
    folds, villi, microvilli = increase surface area for exchange
    epithelial cells of GI mucosa are continuously replaced (billionth/day)
    they’re the ones that breakdown food when it comes
    microvilli = Brush border enzymes – attached to microvilli but not secreted into
    the lumen
    o Enzyme active sites are exposed to chyme in the lumen helping
    to complete digestion of food molecules
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20
Q

LI

A

fcts: reservoir for waste storage + indigestible material, reabsorption of fluid, solutes biles and salts
bacterial metabolism, production + absorption of vitamins ?
has no villi
does not express absorptive transporters for conventional nutrients
descending colon = primary fecal waste reservoir
contains large population of microflora
ferment indigestible food to produce short chain fatty acids
produce folic acid + vitaminK
reduce ability of pathogenic bacteria to invade
antibiotics can neg affect commensals
individuaal microbiome: role in obesity?
◦ Absorbs 90% of the remaining
water coming from the small
intestine
◦ Begins with osmotic gradient set up
by Na+
/K+ pumps
Water follows by osmosis
* Digestive secretions are mostly water.
* Only 100 ml are excreted in feces, so
the mechanisms for water absorption
are efficient

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21
Q

colon fluid and electrolyte absorption:

A

absorbs 90% of water from SI
water follows by osmosis

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22
Q

splanchnic circulation:

A

 Blood flows from the intestine first
to the liver via portal vein
 Fasting state: 65 % of blood flows
to the liver.
 Post-prandial period: 5x increase
in perfusion and 85% to the liver.
 Ensures detoxification, if needed
 Can reduce oral drug
bioavailability (“first pass”)
 Most lipids enter the lymphatic
drainage of the gut, packaged as
chylomicrons. Thereafter is
emptied into the thoracic duct.

    1. Blood supply to the
      gastrointestinal tract is under
      sympathetic control.
      1. Sympathetic activation triggers
        constriction of arteries and
        large veins, shunting blood to
        systemic circulation.
      2. Local blood flow is primarily
        under local control by GI
        hormones and
        neurotransmitters. For
        example CCK, gastrin and
        substance P all increase gastric
        and intestinal blood flow.
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23
Q

neurotransmitter system =

A

ensures motility (controls time available for digestion and absorption)
control of contraction and relaxation of muscle layers
motility patter: can be hormonal or nervous, nervous = soit extrinsinc (sympathetic), intrinsic (myentric plexus)
sympathetic stimulation = provides a tonic inhibitory influence over mucosal secretion
!! EXTRINSIC MOTOR NEURONS INCREASE OR
DECREASE ENTERIC REFLEX ACTIVITIES !!

24
Q

NE:

A

released by sympathetic system + decreases most GI activity

25
Q

AcH:

A

released by parasympathetic = increases GI activity

26
Q

neuro-humoral regulation:

A

nutrients activate: smell, taste + specific sensory nerve endings within the wall of the gut
◦ Responses conveyed via
autonomic nervous (uninvolontary control)
system and enteric (for the gut)
nervous system.
 Results in changes in
secretion and motility.

27
Q

endocrine control of alimentary function by gut peptides:

A

1- specific stimulus secretion of peptide space-
2- peptide enters hepatic portal venous drainage, puis enters systemic venous return to right heart
3- Peptide carried to target site(s) by
systemic arterial circulation

28
Q

control of pancreatic water and bicarbonate secretion

A

by hormonal secretin
(Secretin Release
from Duodenal Mucosa, Pancreatic Bicarbonate Secretion into Duodenal
Lumen)
- when acid goes inside duodenum, secretin = released from mucosa, goes into pancreas and then pancreatic bicarbonate is secreted into duodenal lumen.

29
Q

CONTROL OF PANCREATIC ENZYME
SECRETION & GALLBLADDER EMPTYING
BY HORMONAL CHOLECYSTOKININ (CCK)
Gallbladder Contraction

A

CCK = released from duodenal mucosa, et secretion of pancreatic enzyme into duodenal lumen, then the gallbladder contracts.

30
Q

CCK hormone, fct:

A
  • control of pancreatic enzyme secretion (into duodenal lumen)+ gallbladder emptying (contraction)
  • is released from duodenal mucosa
  • acts in the sphincter of oddi in order to contract and release bile
    OR
  • Source: duodenum, jejunum, illeum (I cells),
    nerve terminals, brain
  • Stimuli: free fatty acids, aa
  • Action: pancreatic secretion (enzymes and HCO3 secretion), gallbladder contraction and
    sphincter of Oddi relaxation, inhibition of pylorus and gastric emptying; controls food intake.
31
Q

lipids stay longer in:

A

intestine = emptying = slow, digestion takes longer

32
Q

control of gastric acid secretion by Gastrin

A

distention/ protein in antrum triggers secretion, gastrin triggers acid

33
Q

Gastrin:

A

◦ Source: antrum (G cells) and duodenum
◦ Target: ECL, parietal gastric corpus
◦ Action: stimulation gastric emptying, acid&pepsin secretion
◦ Stimuli: luminal Aa, peptides, vagal, distension
◦ Inhibitor: H+, , somatostatin

34
Q

secretin

A

◦ Source: duodenum (S cells)
◦ Target: vagal afferent, pancreatic acinar cells
◦ Action: Neutralizing acid (stimulating pancreatic and bile HCO3
-
secretion), inhibiting gastric acid secretion and gastric emptying
◦ Stimuli: luminal H+, pH<4.5
◦ Inhibitor: increased pH

35
Q

motilin

A

◦ Source: EEC stomach, duodenum, jejunum, colon
◦ Target: enteric neurons
◦ Action: stimulates gastric and intestinal motility , major regulator of
MMCs Controls GI between meals.
◦ Stimuli: cyclic neural stimulation during fasting, fatty acids and acids in
the duodenum
◦ Inhibitor: meal ingestion

36
Q

peptide yyy

A
  • Source: intestine L cells
  • Stimuli: FFA, glucose, hydrolyzed protein
  • Action: inhibition gastric emptying, pancreatic secretion, gastric
    acid, motility
37
Q

somatotastin:

A
  • Source: pancreatic and GI D cells
  • Stimuli: acid in lumen
  • Inhibits secretion of gastrin, VIP, GIP, secretin and motilin
38
Q

GIP

A
  • Source: duodenum, jejunum (K cells)
  • Stimuli: Glucose, amino acids, fatty acids
  • Action: inhibits gastric secretion and motility;
    stimulates insulin secretion; lowers glucose
39
Q

VIP

A
  • Source: GI nerves, blood
  • Stimulates electrolyte secretion,
    relaxation smooth muscles, dilation
    blood vessels, inhibits gastric acid
    secretion
40
Q

GLP-I

A
  • Source: GI nerves, blood
  • Stimulates electrolyte secretion,
    relaxation smooth muscles, dilation
    blood vessels, inhibits gastric acid
    secretion
41
Q

ghrelin

A
  • Source: O/X gastric cells
  • Increases food intake
  • Increases intestinal motility
  • Stimulates GH secretion
42
Q

CONTROL OF PANCREATIC ENZYME
SECRETION & GALLBLADDER EMPTYING BY HORMONAL CHOLECYSTOKININ (CCK)

A
  • CCK Release from Duodenal Mucosa
  • Pancreatic Enzyme Secretion into Duodenal Lumen + Gallbladder Contraction
43
Q

CONTROL OF GASTRIC ACID SECRETION
BY HORMONAL GASTRIN

A
  • Distension or Protein in Antrum
    Triggers Gastrin Secretion
  • Gastrin Triggers Acid
    Secretion from Fundus
44
Q

The enteric nervous system:

A
  • can act independently of CNS
  • “little brain”
  • The myenteric plexus
    (Auerbach’s plexus): between the
    outer longitudinal and middle
    circular muscle layers (esophagus
    to rectum). It promotes
    communication with the
    pacemaker cells of the intestine.
  • Along the entire GI tract
  • The submucous plexus
    (Meissner’s plexus): located
    within the mucosa between
    muscularis mucosae and circular
    muscle of muscularis externa.
  • More developed in small and
    large intestine
45
Q

Enteric neurons:

A

Intrinsic primary afferent neurons
(IPANs): Respond to mechanical and chemical stimuli Transmit info to other neurons
Interneurons: connect IPANS to motor neurons, Integrate info from IPANS and relay it to enteric motor neurons
Participate in local motility reflexes
Motor neurons: Excitatory or inhibitory
Innervate muscle layers, blood
vessels and glands.
Intestinofugal afferent neurons (IFANs)
(they’re actually efferent)
Carry efferent signals from the gut
Work as mechanoreceptors that
detect changes in gut volume
(+ voir page 57) + (64 pr paracrine)

46
Q

the peristaltic reflex

A

reflex response to stretch
affects all GI tract segments
contraction followed by relaxation
independant of extrinsic innervation
involves 5HT (activates myenteric)
substance P and AcH contract muscle
NO VIP, ATP cause relaxation ahead stimulus
(only moves forward)

46
Q

BER:

A

spontaneous rhythmic fluctuations in smooth muscle membrane
present in ALL segments, except esophagus and proximal stomach
initiated by cells of cajal (pacemaker, ICC)
coordinates peristalsis and other motor activities
contractions occur only during depolarization
rarely causes muscle contraction
spike potentials on BER waves increases muscle tension

46
Q

afferent VS efferent:

A

afferent = sensory
efferent = motor

47
Q

migrating motor complexes:

A

migrate from stomach to ileum
occur during fasting between periods of digestion
initiated by motilin
migrate aborally, occur every 90 min
gastric, pancreatic, bile secretion increases during MMC
clear the stomach + intestine of luminal contents for next meal
eating stops MMC, inhibits motilin, resumes periastalsis and BER

48
Q

longitudinal VS circular muscle:

A
49
Q

peristaltic reflex

A

longitudinal muscles relax and circular contract within the propulsive segments during peristalsis
ENS releases AcH to induce contraction above bolus, …
primary peristalsis = triggered by swallowing in esophagus, wave that moves down the esophagus is coordinated with LES opening.
secondary peristalsis = triggered by distention to clear esophagus. (triggered when smtg = lodged in esophagus, or which refluxes from stomach)

50
Q

LES relaxation:

A

= final component of esophageal motility
under resting conditions, the LES is tonically contracted
myogenic = contractile state of the muscle = independant of neural input.
increases intrinsically as stretched
tone of sphincter = can be increased by AcH contraction…

51
Q

fcts of stomach:

A

reservoir: for large volumes of food
homogenizer: fragmentation of food

52
Q

regulation non-peptidal neurocrines:

A

 Acetylcholine (Ach)
◦ Source: extrinsic, preganglionic efferent fibers, intrinsic (ENS)
interneurons ( excitatory nerves to muscle)
◦ Action:
Stimulates secretions. Acts on muscarinic receptors
 Directly stimulates parietal cell to secrete acids
 Mediates gastrin release
 Stimulates pancreatic enzymatic secretion
 Stimulates pepsinogen secretion
Stimulates muscle contraction
 Nitric oxide
◦ Source: intrinsic (ENS) interneurons (inhibitory nerves to muscle)
◦ Actions: inhibitory neurotransmitter
 5-hydroxytryptamine (serotonin)
◦ Source: intrinsic interneurons
◦ Action: stimulates intestinal contraction

53
Q

immune fct of GI system:

A

 Gut Associated Lymphoid Tissue (GALT),
including Peyer’s Patches in the lamina propria
of small intestine.
◦ Immune surveillance for potential pathogens in
the small intestine.
◦ Contains macrophages, dendritic cells, B
lymphocytes, and T lymphocytes.
◦ M Cells in the epithelium - antigen presenting
cells that encounter and present antigens to B
and T lymphocytes.

53
Q
A