z:Physl 210A/B > GIT Lec 1: Intro > Flashcards

GIT Lec 1: Intro Flashcards

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1
Q

Function of GIT

A
  • transfer of nutrients, minerals, water from external to internal
    (digestion - absorption - excretion)
    -immune defense (host defense) - GIT is continuous with exterior
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2
Q

Digestion is

A

chemical changes of food to absorbable materials

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3
Q

Absorption is

A

transfer of digested food from intestine into blood and lymphatic vessels

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4
Q

Excretion is

A

removal of components not absorbed

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5
Q

Things that are excreted

A

bacteria, intestinal cells, drugs, cholesterol, steroids

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6
Q

Two parts of the GI system

A

tract and accessory organs

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7
Q

Tract in GIT is composed of

A

mouth, pharynx, esophagus, stomach, small intestine, large intestine

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8
Q

Accessory organs of GIT

A

pancreas, liver, gall bladder

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9
Q

composition of muscle from top of esophagus..

A

skeletal muscle

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10
Q

composition of muscle from mid-esophagus to anus..

A

smooth muscle

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11
Q

Layers of GIT (LUMEN TO EXTERIOR)

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa
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12
Q

Layers of Mucosa

A
  1. Epithelium
  2. Lamina propria
  3. Muscularis mucosa
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13
Q

Epithelial layer has..

A
  • polarized layer (basolateral and apical side)

- villi and microvilli (cellular level)

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14
Q

basolateral

A
  • also serosal, blood

- facing blood vessels

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15
Q

apical

A
  • luminal,mucosal

- facing lumen

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16
Q

SA of GIT increased by

A

villi (finger-like projection in epithelial layer), microvilli, crypts (invaginations in epithelial layer)

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17
Q

Epithelial layer performs…

A

selective uptake of nutrients, electrolytes, water

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18
Q

polarized layer of epithelium caused by

A

different transport proteins at apical and basolateral surface and tight junctions that prevent movement of transport proteins to membrane regions

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19
Q

Crypts in epithelial layer..

A

have stem cells that divide and migrate up the villus (rapid cells turnover)

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20
Q

paracellular pathway through epithelium (GIT)

A
  • between the cells
  • limited by tight junction seal
  • water, small ions pass through
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21
Q

transcellular pathway through epithelium (GIT)

A
  • through the cells

- 2 step (transport on apical side then basolateral)

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22
Q

Lamina propria

A
  • second layer of mucosa after epithelial layer

- connective tissue, small blood vessels, nerve fibers (end), lymphatic vessels, immune cells

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23
Q

Muscularis mucosa

A
  • third layer of mucosa after epithelial layer and lamina propria
  • thin layer of smooth muscle for villi movement not contraction of GIT
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24
Q

Submucosa

A

-second layer of GIT after mucosa

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25
Submucosa has
- nerve cell bodies, that relay info from mucosa | - connective tissue, blood, lymphatic vessels
26
Muscularis externa
-third layer of GIT, after mucosa, submucosa before serosa
27
Muscularis externa has..(layers)
- thick inner layer of circular muscle - myenteric nerve plexus - thin outer layer of longitudinal muscle
28
myenteric nerve plexus
plexus of nerves from the sympathetic and parasympathetic systems between the two layers of muscle in the small intestine
29
Thick inner layer of circular muscle in small intestine is responsible for the..
narrowing of lumen
30
Thin outer layer of longitudinal muscle is responsible for the..
shortening of tube
31
Serosa
- last layer of GIT | - connective tissue, encasing intestine, connection to abdominal wall
32
Blood moves in GIT through
intestine then liver through via portal vein
33
portal vein drains..
blood from digestive tract into the liver
34
blood in the portal vein is
nutrient rich but oxygen poor
35
blood circulation between gut and liver is called...
portal circulation
36
the purpose of portal circulation is..
to remove harmful materials and process nutrients
37
the unique aspect of blood supply to the liver is..
it has arterial and venous circulation via hepatic artery and portal vein
38
GI secretion and motility is controlled by..
-volume of type of contents
39
Reflexes of GIT caused by..
- distension of wall by luminal contents - osmolarity of contents - pH of contents - concentration of monosacc., fatty acids, peptides, a.a
40
Reflexes measured by..
- mechanoreceptors (pressure, stretch) - osmoreceptors (osmolarity) - chemoreceptors (binding of specific chemicals)
41
The enteric nervous system is...
- the intrinsic nervous system in GIT - "brain of the gut" - dense and complex network of neurons (10^8)
42
The enteric nervous system controls..
the activity of secretomotor neurons
43
Secretomotor neurons control
motility and secretory function
44
The enteric nervous system can function
independently of CNS which is crucial for involuntary function
45
The enteric nervous system has two nerve networks:
- submucosal plexus (innermost) | - myenteric plexus
46
Submucosal plexus influences
secretion
47
myenteric plexus influences
smooth muscle
48
Extrinsic regulation of GIT is by
autonomic nervous system (parasympathetic and sympathetic)
49
Autonomic nervous system influences..
motility and secretion of GIT
50
Extrinsic factors that influence motility and secretion of GIT
- hunger - sight/smell of food - emotional state
51
parasympathetic (rest/digest) system (GIT)
-simulates saliva, peristalsis, gallbladder, secretion
52
sympathetic (fight/flight) system (GIT)
- stimulates saliva | - inhibits peristalsis,gallbladder, secretion
53
Short reflexes in GIT:
stimulus => receptors => nerve plexus => smooth muscle/gland => response
54
Long reflexes in GIT:
stimulus => CNS => efferent autonomic neurons => nerve plexus
55
types of chemical messengers:
- endocrine - neurocrine - paracrine - autocrine
56
endocrine
hormone target cells by blood circulation in distant places in the body
57
neurocrine
neurotransmitter effects neuron/effector close by
58
paracrine
chemical messenger released by cell to effect nearby cells
59
autocrine
chemical messenger released by cell to act on itself
60
endocrine cells in GIT are (location)
on the epithelium of the stomach and small intestine
61
endocrine cells in GIT (lumen vs lamina propria)
substances in lumen stimulates hormone release on basolateral side into blood vessels in lamina propria
62
Four main GI hormones
- secretin - cholecystokinin (CCK) - gastrin - glucose dependent insulinotropic peptide (GIP)
63
Four main GI hormones generalized
- all peptides - feedback control system - target more `than one type of cell
64
gastrin released by
G cells in stomach antrum
65
stimuli for gastrin release
peptides/a.a in stomach, parasympathetic nerves
66
gastrin major actions
- increases HCl in stomach | - increases motility of stomach, ileum, large intestine
67
secretin released by
S cells in small intestine
68
stimuli for secretin release
acid in small intestine (pH<4.5)
69
secretin major actions
- decreases HCl - decreases stomach motility - increase bicarbonate and water from pancreas and in bile
70
CCK released by
I cells in small intestine
71
stimuli for CCK release
digested fat/protein in small intestine
72
CCK major actions
- decreases HCl - decreases stomach motility - increases enzymes from pancreas - increase bile expulsion
73
GIP released by
K cells in small intestine
74
stimuli for GIP release
glucose or fat in small intestine
75
GIP major actions
-increases insulin before sugar is absorbed into blood
76
Intestinal motlity
-contraction and relaxation of two outer smooth muscle layers of GIT allows movement of contents from one site to another
77
Two components of intestinal motility
peristalsis and segmentation
78
peristalsis (propulsion)
- first => oral side: circular muscle contracts and longitudinal relaxes - second => anus side: circular muscle releases and longitudinal contracts
79
segmentation (mixing)
- contraction and relaxation of intestinal segments | - little net movement towards large intestine
80
segmentation occurs in
small intestine for the mixing of contents with enzymes, absorption of nutrients and water
81
GIT pacemaker cells are in
smooth muscle
82
GIT pacemaker cells are (action)
constantly undergoing spont. depolarization and repolarization cycles known as slow waves
83
slow waves are
basic electrical rhythm of GIT (below threshold)
84
Frequency of contraction in GIT is set by
slow waves, basic electrical rhythm,
85
Slow waves are propagated
through circular + longitudinal muscle layer through gap junctions
86
neural + hormonal input and slow waves
depolarize membrane and bring it to threshold for contractions to occur
87
action potentials is proportional to
force of contraction which is mediated by neuronal/hormonal input
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