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Phsyiology 210 B > Gastrointestinal Tract 1 - general intro > Flashcards

Gastrointestinal Tract 1 - general intro Flashcards

1
Q

Digestion

A
  • Chemical alteration of food into absorbable molecules

- GI motility, pH changes, biological detergents and enzymes.

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2
Q

Absorption

A

Movement of digested food from the intestine into the blood or lymphatic system

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3
Q

Does the GI tract have an immune system?

A

YES

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4
Q

Components of the GIT

A

— Mouth

  • Pharynx
  • Esophagus
  • Stomach

Small intestine

  • Duodenum
  • jejunum
  • Ileum

Large intestine

Accessory organs

  • Pancreas
  • Liver
  • Gall bladder
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5
Q

Structure of the GIT

A
  • Long muscular tube stretching from mouth to anus.

- Composition is similar from mid-esophagus to anus

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6
Q

Layers of the GIT

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa
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7
Q

Layers of mucosa

A

a) Epithelium
b) Lamina propria
c) Muscularis mucosa

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8
Q

Layers of mucosa

a) Epithelial layer

A
  • layer of cells that lines all body cavities and surfaces.

“Polarized” = different at one surface compared to the other

  • Basolateral and apical arrangement, each with different transport proteins
  • Tight junctions confine transport proteins to specific membrane regions
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9
Q

Which layer of the mucosa contains the villi and the crypts? And if so what do they do?

A

Epithelium layer.

Increase SA, stem cells from crypts divide and migrate upwards.

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10
Q

Selective Transport of Nutrients Across the Epithelium

A

Paracellular pathway is limited by tight junction seal
- Water and small ions can diffuse through tight junctions

Transcellular pathway is a two step process and requires a transport protein on the apical and basolateral surface of the cell

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11
Q

Layers of the mucosa

b) Lamina propria

A
  • connectivetissue
  • smallbloodvessels
  • nervefibres(slide16)
  • lymphaticvessels
  • immune and inflammatory cells
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12
Q

Layers of the mucosa

C) Muscularis mucosa

A

Thin layer of smooth muscle

  • Not involved in contraction of the GIT
  • May be important in villi movement
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13
Q
  1. Submucosa
A
  • Plexus of nerve cell bodies
  • Relay information to and away from the mucosa
  • Also composed of connective tissue, blood and lymphatic vessels
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14
Q
  1. Muscularis Externa
A

Thick inner layer of circular muscle
- Fibres oriented to cause narrowing of lumen

Myenteric nerve plexus
- Network of nerve cells, regulate muscle function

Thinner outerlayer of longitudinal muscle
- Fibres oriented to shorten tube

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15
Q
  1. Serosa
A

Connective tissue, encases intestine and forms connection point to the abdominal wall

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16
Q

Blood supply to the GIT

A

Blood perfuses intestine and then flows to liver via the portal vein

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17
Q

Portal circulation

A
  • The portal vein drains blood from the digestive tract and empties directly into the liver.

Purpose: allow the liver to:

  • Remove harmful substances (filter)
  • process nutrients
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18
Q

circulation of nutrient-rich blood between the gut and liver is called the

A

portal circulation

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19
Q

Liver is an unusual organ because it receives blood from both

A

venous (portal) and arterial circulation

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20
Q

Liver receives less

A

oxygenated blood, more nutrient rich blood than other organs.

21
Q

Regulation of GIT is governed by

A

volume and composition of lumen contents

22
Q

Reflexes in the lumen initiated by

A
  • Distension of wall by volume of luminal contents
  • Osmolarity of contents
  • pH of contents
  • Concentrations of specific digestion contents
    (Monosaccharides, fatty acids, peptides, and amino acids)
23
Q

The reflexes in the GIT are reproduced by

A
  • Mechanoreceptors-activated by mechanical stimuli such as pressure and stretch
  • Osmoreceptors -activated by changes in osmolarity
  • Chemorecpetors - activated by binding of certain chemicals
24
Q

Intrinsic Neural Regulation of GI Processes via

A

Enteric nervous system

25
Q

Enteric nervous system

A

Controls the activity of the secretomotor neurons
(motility and secretary funct.)

  • contained within walls of GIT
  • independent of CNS
26
Q

The two nerve networks that compose the Enteric nervous system, and what they each do?

A
  • Myenteric plexus-influences smooth muscle

- Submucosal plexus- influences secretion

27
Q

Extrinsic Neuronal Regulation of GI Processes

A

Regulation is through the autonomic nervous system

  • Parasympathetic
  • Sympathetic

Influences the motility and secretion of the GIT

  • Hunger
  • Sight/smell of food
  • Emotional state
28
Q

Parasympathetic does what to the GIT?

A
  • stimulates peristalsis and secretion in stomach
  • stimulates release of bile in liver
  • stimulates saliva flow
29
Q

sympathetic does what to the GIT?

A
  • inhibits peristalsis and secretion in stomach
  • conversion of glycogen to glucose in liver
  • stimulates saliva flow
30
Q

Four categories of chemical messengers

A
  • Endocrine: chemical messenger passes from cell which produced it into blood and is carried by blood to its (relatively distant) target
  • Neurocrine: chemical messenger is released from a nerve, travels across a synapse and acts on a post-synaptic target cell
  • Paracrine: chemical messenger diffuses through intestinal fluid to nearby cells
  • Autocrine: chemical messenger acts on the cell which produced it
31
Q

Endocrine cells are scattered throughout the

A

epithelium of the stomach and small intestine.

32
Q

One surface of each endocrine cell exposed to the GI lumen, meaning ?

A
  • Chemical substances in lumen stimulate cell to release hormones across opposite surface of cell into blood vessels in lamina propria
  • Hormones travel through blood to target cells
33
Q

Four best understood GI hormones are

A
  • secretin
  • cholecystokinin (CCK)
  • gastrin
  • glucose dependent insulinotropic peptide (GIP)

(ALL PEPTIDES)

34
Q
  • secretin
  • cholecystokinin (CCK)
  • gastrin
  • glucose dependent insulinotropic peptide (GIP)

Do what?

A
  • Each participates in a feedback control system that regulates some aspect of the GI lumen
  • Most GI hormones affect more than one type of target cell
35
Q

Fatty acids and amino acids in the small intestine triggers

A

CCK

secretion from cells in small intestine into blood.

36
Q

Circulating CCK stimulates:

A
  • pancreas to increase digestive enzyme secretion
  • gall bladder contraction
    (release bile acids = fat breakdown
37
Q

Fats and amino acids are absorbed and stimulation of CCK release is stopped-due to their removal, therefore it is a

A

Negative feedback control system

38
Q

Gastrin

A
  • Stomach antrum (G cells)
  • Stimuli for release: Peptides/amino acids in stomach, parasymp nerves
  • HCl increases
  • motility increases (stomach, ileum, lrg intestine)
39
Q

Secretin

A
  • small intestine (S cells)
  • Stimuli for release: acid in small intestine (pH<4.5)
  • HCl decreases
  • motility decreases (stomach, ileum, lrg intestine)
  • HCO3 / H20 increase from pancreas and in bile
40
Q

CCK *

A
  • small intestine (I cells)
  • Stimuli for release: digested fat/protein in small intestine
  • HCl decreases
  • motility decreases (stomach, ileum, lrg intestine)
  • enzyme from pancreas increase
  • bile expulsion increase
41
Q

GIP*

A
  • Stomach antrum (K cells)
  • Stimuli for release: glucose or fat in small intestine
  • increase insulin
42
Q

What allows for the movement of contents form one site to another in the GIT

A

Contraction and relaxation of the two outer smooth muscle layers

43
Q

Peristalsis (propulsion)

A
  • Circular muscle contracts on the oral side of a bolus of food (longitudinal
    layer relaxes).
  • Circular muscle contracted moves toward the anus, propelling the contents of the lumen in that direction,
  • as the ring moves, the circular muscle on the other side of the distended area relaxes (longitudinal muscle contracts), facilitating smooth passage of the bolus
44
Q

Segmentation (mixing)

A
  • Contraction and relaxation of intestinal segments (not towards LI)
  • Mostly in small intestine
  • Allows mixing with digestive enzymes
  • Slows transit time to allow absorption of nutrients and water
45
Q

GIT has pacemaker cells throughout

A

smooth muscle cells

46
Q

The pacemaker cells are Constantly undergoing spontaneous depolarization-repolarization cycles, these cycles are called

A

slow waves: basic electrical rhythm

47
Q

Slow waves propagated through the

A

circular and longitudinal muscle layer through gap junctions

48
Q

In the absence of neural/hormonal input spontaneous slow waves

A

don’t result in significant contractions

  • Excitatory hormones/neurotransmitters further depolarize the membrane and bring it close to threshold
49
Q

number of AP and the force of contraction relationship

A
  • # of action potentials fired = to force of contraction
  • frequency of contraction maintained by the basic electrical rhythm
  • force of contraction mediated by neuronal and hormonal input

Phsyiology 210 B (24 decks)

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