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FHB - GI/Metabolism - Exam 3 > Lecture 1 & 2: (44/45) GI Regulation & Anatomy > Flashcards

Lecture 1 & 2: (44/45) GI Regulation & Anatomy Flashcards

1
Q

What are the overall functions of the GI tract?

A
  1. Absorb nutrients/water into circulation
  2. Participate in excretion of waste substances

Motility

Secretion

Digestion

Absorption

+ excretion

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2
Q

What are the different regulatory mechanisms in the GI tract?

A
  1. Endocrine
  2. Paracrine
  3. Neural
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3
Q

What is the only voluntary aspect of eating?

A

Swallowing

  • the rest of MOTILITY is based on contractions of smooth muscle to reduce size of food and mix food with enzymes before it is propelled from the mouth to the rectum
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4
Q

What is secretion?

A

is the release of enzymes, biological detergents, mucus, ions and water in the GI lumen by the:

GI epithelia and
associated glands

(salivary, pancreas, liver, gall bladder)

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5
Q

What is the stomach’s defense mechanism to protect it from the acidic environment?

A
  1. Mucosal Lining (mucus protects)

2. High pH (bicarbonate secreted to neutralize the HCl)

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6
Q

What is the function of the liver?

A

Does NOT provide enzymes, but adds BILE which is important for digestion of lipids

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7
Q

What is digestion?

A

Macromolecules are converted to smaller absorbable molecules (glucose, maltose, etc)

  • physical & CHEMICAL modification into carbs, amino acids, and lipids
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8
Q

What is absorption?

A

Process by which nutrients, electrolytes and water are absorbed from the GI lumen into the bloodstream.

  1. source of energy
  2. Components of biological structures
  3. Essential metabolic pathways
  4. Restore physiological activities
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9
Q

What is excretion? What gets excreted from the liver?

A

Excretion:

The GI tract :
stores and excretes waste substances from ingested food materials

Liver :
Cholesterol
Steroids
Drug metabolites

Colon STORES the fecal material and prevents it from backing up into the GI system since it is mixed with bacteria

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10
Q

What is the largest immune organ of the body?

A

GI tract

  • open to external environment and vulnerable to infectious microorganisms
  • many complex immune cells
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11
Q

Where are most enzymes found?

A

Duodenum

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12
Q

What are the associated GLANDULAR organs? Which of these is the only one NOT innervated by Vagas ?

A
  1. Salivary
  2. Pancreas
  3. Liver
  4. Gall Bladder
  5. Endocrine Glands or Cells

Salivary glands –> innervated by 9 and 10

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13
Q

What are the 6 sphincters of the GI system?

Which prevents the food from entering the airway? Which regulates the gastric reflux when abdominal pressure increases (ex: pregnancy)

A
  1. Upper Esophageal - (between pharynx and esophagus)
  2. Lower Esophageal - (between esophagus and stomach)
  3. Pyloric
  4. Sphincter of Oddi
  5. Ileocecal
  6. Internal and
  7. external anal

Upper Eso. = protects airway

Lower Eso. = regulates gastric reflux

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14
Q

What are the 3 major arteries supplying the abdominal organs and which organs specifically?

A

Splanchnic circulation = 25% of C.O.

  1. Celiac artery: supplies the liver, spleen and stomach.
  2. Superior mesenteric artery:

supplies the pancreas, small intestine, and proximal colon.

  1. Inferior mesenteric artery: supplies the distal colon.
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15
Q

Where does the venous drainage from the GI tract return to?

A

PORTAL VEIN!

  • portal circulation to liver first, then hepatic veins into the Inferior Vena Cava
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16
Q

What is the purpose of Lymphatic Drainage in the gut?

A

This is important for the transport of lipids and lipid-soluble molecules (including some vitamins and drugs)

  • too large for capillaries
  • drained via thoracic duct to systemic circulation
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17
Q

What are the 4 layers of the gut wall?

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa
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18
Q

What is the innermost layer of the lumen of the GI tract called?

A

MUCOSA

made of

  1. Epithelium (tight junctions)
  2. Lamina Propria
  3. Muscularis Mucosae
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19
Q

What are the 4 specialized cells within the epithelial layer of the MUCOSA?

A
  1. Absorptive Enterocytes
    - majority
    - digestion/absorption
  2. Enteroendorcrine cells
    - regulatory peptides released to regulate GI fx.
  3. Gastric Mucosal Cells –> produce protons (parietal cells produce acid)
  4. Mucin - Producing Cells –> glycoprotein production
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20
Q

Which epithelium has no absorptive function:

  1. Esophogeal
  2. Intestinal

What type of cells make up both?

A

no absorptive = ESOPHOGEAL

  • transports swallowed food
  • SQUAMOS

Intestinal

  • columnar type
  • absorption/uptake
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21
Q

What is the surface area of small intestinal epithelium?

What is unique about these?

A

Villi and Crypts

  • continuously renewed via programmed cell death (3-5 days)
  • proliferative cells in the zone of intestinal stem cells
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22
Q

What is the function of villi? (named for this)

What extensions do they have?

What is a clinical correlate associated with Reduced Surface Area of the Villi?

A
  1. Unit of REABSORPTION
  2. Microvilli or BRUSH BORDER
  3. Celiac Disease:
    - malabsorption
    - flattened = less surface area and malnutrition due to malabsorption
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23
Q

What layer of the Mucosa is find immediately below the epithelium?

What is it composed of?

What is the next layer?

A
  1. Lamina Propria
    - connective tissue, collagen, elastin
    - glands, nodes, capillaries, nerve fibers
  2. Muscularis Mucosae
    - thin layer of SMOOTH muscle
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24
Q

What is the next layer after Muscular Mucosa?

What is the name for the dense network of nerve cells here? often referred to as the Little Brain in the Gut! (2 names)

TEST!!!

A
  1. Submucosa
    - connective, collagen, elastin
    - glands
    - nerve trunks, blood vessels, lymph
  2. SUBMUCOSAL PLEXUS OR

MEISNER’s Plexus**
of the enteric nervous system

  • integrates motor & secretory activities
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25
Q

What is the function of the muscular externa/propria?

What 2 layers does it consist of (which is first off of the luminal side)

What lies between these 2 layers?

A
  1. Contractions help mixing and propelling contents of the GI tract
  2. Inner Circular Muscle layer
  3. Outer Longitudinal Layer

MYENTERIC PLEXUS in between
(Auerbach’s plexus) –> the other part of little brain in the gut

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26
Q

What is the outermost layer of the GI tract?

What cells does it consist of?

What is its function?

A
  1. Serosa
  2. Squamous Epithelial
  3. Keeps organs suspended in cavity
  4. Viscous secretions to lubricate the abdominal organs and REDUCE FRICTION
27
Q

Which is GI most active?

intermeal period or the post-prandial period

A
  1. POST - PRANDIAL
    - Intense activity

Relative Quiscence = intermeal

28
Q

What secretions are completely neural and do not require endocrine or paracrine mechanisms?

A

SALIVARY secretions

CN 9 and 7

29
Q

What are the sensor cells of the GI system?

What happens when their receptors are activated?

A

Enteroendocrine cells

(EEC’s)

  • respond to stimulus by secreting regulatory peptide or hormone
  • signal transduction cascade occurs!

(can be stimulated w/ a meal & WITHOUT neural input

30
Q

Endocrine regulation requires that what occurs? (2)

A
  1. EEC hormones bind to membrane receptor in target cell to trigger a SIGNAL TRANSDUCTION cascade
  2. Enters the circulation!
    ex: Gastrin (hormone) is released by G cells in the distal part of stomach – stimulates acid secretion by the ECL and parietal cells (gastric corpus or body).
31
Q

What is paracrine regulation?

How is it different from endocrine regulation?

A
  1. Where a chemical messenger or regulatory peptide released from a sensing cell (often EECs) - acts on a nearby target cell by DIFFUSION through the interstitial space
  2. not transported via circulation!!
32
Q

The following are regulated via paracrine or endocrine mechanisms?

  1. Histamine
  2. Seratonin
  3. Cholecystokinin
A
  1. Histamine - PARACRINE
  2. Seratonin - PARACRINE
  3. Cholecystokinin
    - BOTH

it is released from the duodenum in response to dietary protein, lipid- acts locally on nerve terminals (paracrine effect) and on pancreas (endocrine effect).

33
Q

Besides protecting the cells in the GI system from bacteria, what else do the immune cells release?

A

PARACRINE FACTORS

34
Q

Is Celiac’s Disease a dysfunction in paracrine or endocrine regulation?

What is the main pathology of Celiac Disease?

A
  1. PARACRINE
  2. Allergic response to GLIADIN in gluten
    - causes inflammation in small intestine and reduces density & length of microvilli

= causes malabsorption of nutrients

35
Q

Is CCK paracrine or endocrine regulated?

What does it do to the following:

  1. Gastric Emptying
  2. H+ secretion
  3. Food intake
  4. Pancreatic Enzyme secretion
  5. Contraction of gallbladder
A

BOTH!

DECREASES:
Gastric emptying and
H+ secretion;
- Food intake;

INCREASE:
Pancreatic enzyme
secretion;
Contraction of gallbladder;

36
Q

What is the action of Peptide YY (PYY)? Is this paracrine or endocrine?

A

BOTH!

Decreases:
1. Gastric Emptying
& H+ secretion

  1. Pancreatic Enzyme secretion
  2. Intestinal Motility
  3. Food intake
37
Q

What are the two sets of nerves innervating the gut?

How do each relate to the cell body of the gut wall?

Which is autonomic?

A

Intrinsic & Extrinsic

  1. Intrinsic = cell body is INSIDE gut wall
    - submucosal plexus (little brain of gut)
    - myenteric plexus
  2. Extrinsic = cell body is OUTSIDE gut wall
    - AUTONOMIC
38
Q

What are the 2 parasympathetic subdivisions of the Extrinsic Neural System?

A
  1. Vagal
    - esophogus, stomach, gallbladder, pancreas, 1st part of intestine, colon (proximal)
  2. Pelvic
    - distal part of colon & anorectal
39
Q

Parasympathetic post-ganglionic cells secrete what? What type of neurons are these?

A
  1. Cholinergic & Peptidergic
    - release acetylcholine or peptides (substance P, vasoactive intestinal peptide VIP)

long fingers, short arms
- long preganglionic fibers synapse in ganglia in the walls of the organ

40
Q

Vagovagal reflexes are only efferent.

True or False

A

False

  • mixed afferent (75%) and efferent (25%)
41
Q

What brings information to the afferent fibers before they synapse with interneurons and stimulate the Efferent fibers?

A

SENSORY information from periphery

  1. Mechanoreceptors
  2. Chemoreceptors
42
Q

What is the main function of the sympathetic nervous system in relation to the GI tract?

What are the exceptions?

A

INHIBITS GI tract

  • exception:
    GI sphincter muscles are activated by sympathetic innervation to constrict the muscles
    = TONIC STIMULATION

post-ganglionic fibers are adrenergic and release epinephrine

43
Q

What is the percentage of afferent to efferent in parasympathetic and sympathetic innervation?

A

parasympathetic
75 - afferent
25 - efferent

Sympatheitc
50 afferent
50 efferent

44
Q

Which system
communicates with the following: (synapses in these areas)

  1. Longitudinal Muscle
  2. Circular Muscle
  3. Mucosa
  4. Myenteric Plexus
  5. Submucosal plexus (Meissner’s plexus - little brain)
A

Parasympathetic = muscle

Sympathetic:
myenterix plexus
& submucosal plexus

45
Q

The majority of the gut activity is regulated by what neural system?

A

ENTERIC Nervous System (ENS –> Intrinsic)

  1. Myenteric Plexus
  2. Submucosal plexus

The myenteric plexus - between the longitudinal and circular muscle layers.

The submucosal plexus - in the submucosa.
Neurons in the two plexuses are linked by interganglionic strands.

46
Q

What is released by the neurons of ENS?

Can the ENS act autonomously?

A

Neurotransmitters & neuromodulators

YES! Autonomic activity also called “little brain in the gut”

  • receive input from extrinsic (parasympathetic & sympathetic) neurons which modulate their activity
47
Q

Sympathetic & Parasympathetic

Synapses of the ENS (Intrinsic) are mostly where?

A

Submucosal & Myenteric Plexus

  • they communicate with secretory cells, endocrine cells, and mechanoreceptors and chemoreceptors

as well as circular muscle, longitudinal muscle, and mucosa

48
Q

What are the effectors of the Enteric Nervous system?

A

Motility
Secretion
Blood Flow

49
Q

What is the function of the following:

  1. Acetylcholine
  2. NE
  3. VIP

In terms of :

  1. Smooth muscle (relaxed or contracted)
  2. Salivary and gastric/pancreatic secretions
A
  1. Acetylcholine
    - contraction of smooth muscles in wall
    - increase salivary, gastric, and pancreatic secretions
  2. NE
    - relax smooth muscles in wall (opposite)
    - contract sphincters
    - increase salivary secretion
  3. VIP
    - relax smooth muscle
    - increase intestinal & pancreatic secretion
50
Q

What is the function of the following:

  1. Neuropeptide Y
  2. Substance P
A
  1. Neuropeptide Y
    - relax smooth muscle
    - decrease intestinal secretion
  2. Substance P
    - contract smooth muscle
    - increase salivary secretion
51
Q

What permits the rapid cell-to cell spread of action potentials in the GAP JUNCTIONS of smooth muscles of the GI tract?

A

Interstitial Cells of Cajal!

low resistance gap junctions!

(test)

52
Q

What is phasic contraction of the GI tract?

A

periodic contractions followed by relaxation – found in esophagus, gastric antrum, small intestine – involved in mixing and propulsion

53
Q

What is tonic contraction of the GI tract?

A

a constant level of contraction or tone WITHOUT REGULAR PERIODS OF RELAXATION

– found in orad (upper) region of stomach and lower esophagheal, ileocecal and internal anal sphincters.

( no state of relaxation to prevent chyme from moving backwards)

54
Q

When does contraction occur during an action potential?

A

At the end once the actin potentials have summated

55
Q

What are unique features of GI smooth muscle electrical activity?

Do these elicit action potentials?

A
  1. SLOW WAVES
    - oscillating depolarization and depolarization of the membrane potential
    - NOT large enough to elicit an Action Potential
    - if at the peak of the slow wave the membrane potential is depolarized up to threshold, the AP occurs on “top of” the slow wave
56
Q

Where do slow waves originate?

Often called the “pacemaker cells for GI smooth muscle”

(Test)

A

Interstitial Cells of Cajal

  • between longitudinal and circular layer of muscular external

** PACEMAKER CELLS for GI smooth muscle**

57
Q

What do sub-threshold slow waves produce?

What about when AP’s occur on top of the slow waves?

A
  1. TONIC contractions (w/o action potentials)
  2. Phasic contraction
    - when AP occurs on top of the slow waves
58
Q

How are skeletal muscles different from smooth muscle?

A

Individual action potentials in the smooth muscle are NOT followed by separate twitches

  • summate into one LONG CONTRACTION
59
Q

The frequency and amplitude of the slow wave are controlled by what 3 influences?

A
  1. Neural
  2. Hormonal
  3. Paracrine
60
Q

What are the 2 patterns of GI motility?

A
  1. Segmentation

2. Peristaltic

61
Q

Where do Segmentation contractions occur primarily?

What is their main function?

Is there forward movement?

A
  1. Small & Large intestine
  2. MIXING of luminal contents w/ GI tract secretions & increase exposure to mucosal surfaces for absorption
  3. NO FORWARD movement
    - allows chyme to merge & mix
62
Q

Where do Peristaltic contractions occur primarily?

What is their main function?

Is there forward movement?

A
  1. Pharynx, esophogus, gastric antrum, small & large intestine also*
  2. PROPEL the chyme forward along the GI tract
  3. Contraction at the ORAD (behind) to the bolus, and relaxation in the CAUDAD (forward)
    - chyme propelled toward CAUDAD directon
63
Q

What neurotransmitters are involved in ORAD contractions? (behind)

In CAUDAD? (front)

2 for each

A
  1. ORAD
    - ACh & Substance P
  2. CAUDAD:
    - VIP and Nitric Oxide
64
Q

What is the function of the following:

  1. GRP (gastrin Releasing Peptide) /Bombesin
  2. Enkephalins (Opiates)

In terms of:
Gastric Secretion & Smooth Muscle contraction/relaxation

A
  1. GRP (gastrin Releasing Peptide) /Bombesin
    * INCREASE gastric secretion
  2. Enkephalins (Opiates)
    - CONTRACT smooth muscles
    - decrease intestinal secretion

FHB - GI/Metabolism - Exam 3 (21 decks)

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