Git Flashcards
1
Q
functions of GIT
A
transfer digested organic nutrients, minerals, and water from the external environment into the internal environment
- involves digestion and absorption, excretion, host defense
2
Q
function of digestion
A
form absorbable molecules from food through git motility, ph changes, and biologic detergents and enzymes
3
Q
function of absorption
A
movement of digestive food from the intestine into the blood or the lymphatic system
4
Q
function of excretion
A
non-absorbable components of food, bacteria, intestinal cells, and hydrophobic molecules (drugs), cholesterol and steroids are excreted
5
Q
host defense
A
lumen of git is considered to be outside of the body
git forms a barrier with the outside environment and contains a highly developed immune system
can inactivate harmful bacteria or other microorganisms
6
Q
components of the git
A
mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine
7
Q
3 accessory organs of the git
A
pancreas, liver, gallbladder
8
Q
structure of the git
A
a long muscular tube stretching from the mouth to the anus
- top third of esophagus is made of skeletal muscle, rest is smooth muscle
9
Q
lumen
A
- inside of tube of intestine
- contains many folds and processes to increase the surface area
- circular fold is where the entire inner surface folds in on itself
- contains villi
10
Q
4 layers of the git
A
- mucosa
- submucosa
- muscularis externa
- serosal layer
11
Q
3 layers of mucosa
A
- epithelium
- lamina propria
- muscularis mucosa
12
Q
muscularis externa
A
outer muscular layer of git
circular muscle, myenteric nerve plexus (regulate muscle function of git), longitudinal muscle (lengthen and shortens tube)
13
Q
serosal layer
A
connective tissue layer of git that encases the intestine and forms connections with the intestine and the abdominal wall
14
Q
function of epithelial layer
A
selective uptake of nutrients, electrolytes and water
prevent the passage of harmful substances
- surface is amplified by villi and crypts
- stem cells within crypts
15
Q
apical surface of epithelial layer
A
inserts the inside of the tube or the lumen of the tube
16
Q
basolateral surface of the epithelial layer
A
closest to the blood surface, facing away from the tube
17
Q
2 pathways that chemicals or molecules can use to get across an epithelial layer
A
- paracellular pathways
- transcellular pathway
18
Q
paracellular pathway
A
chemicals move between cells across the cell junctions; limited by tight junctions between cells, so only water and small ions can actually diffuse through the tight junctions; not many substances can get through this way in a healthy intestine
19
Q
transcellular pathway
A
cross the cell and therefore require transport protiens
20
Q
lamina propria
A
layer of the mucosa
- includes everything above the muscle layer
- connective tissue, blood vessels, nerve fibers, lymphatic vessels, immune and inflammatory cells for immune protection
21
Q
muscularis mucosa
A
layer of mucosa
- thin layer of smooth muscle
- not involved in contraction of the git and may function in moving the villi
22
Q
submucosa
A
beneath the mucosa layer
- contains blood vessels, lymphatic vessels, submucosal nerve plexus, connective tissues
23
Q
submucosal nerve plexus
A
network of nerves that relay info to and away from the mucosa
24
Q
portal circulation
A
circulation that carries the blood from the intestinal tract to the liver
- nutrient rich blood
- important for liver removing harmful substances and processing of nutrients
25
hepatic artery
contains fully oxygenated blood that perfuses the liver
26
hepatic portal vein
carries blood to the liver that has already perfused the stomach, pancreas and si and li
27
reflexes regulating gi processes are initiated by (3)
1. distension of the git wall by the volume of luminal contents
2 osmolarity of the contents ph of the contents
3. the conc of the specific digestion contents, such as monosaccharides, fatty acids, peptides, amino acids
28
mechanoreceptors activated by
mechanical stimuli (pressure and stretch)
29
osmoreceptors activated by
change is osmolarity
30
chemoreceptors activated by
specific chemicals
31
intrinsic neural regulation
contained wholly within the organ
- occurs through nerve plexi located in the git wall itself
32
enteric nervous system
intrinsic nerve regulation
- controls the activity of the secretomotor neurons which play a role in secretion and motility
- contained completely within the walls of the git
- brain of the gut
- can function independently of the cns
- critical for involuntary functions
33
myenteric plexus
found between the two muscle layers, the circular muscle and the longitudinal muscle, or the muscularis externa responsible for influencing and regulating the smooth muscle
34
submucosal plexus
found in the submucosa
predominately influences secretion
35
extrinsic neural regulation
outside of the git wall
- occurs through ans
36
long reflex =
extrinsic pathway
37
short reflex =
intrinsic pathway
38
4 categories of chemical messenger regulation
- endocrine regulation
- neurocrine regulation
- paracrine regulation
- autocrine regulation
39
endocrine regulation
a hormone secreting gland cell releases a hormone across its basolateral surface into the blood; the hormone enters the blood and travels to its target cells in one or more distant places in the body
40
neurocrine regulation
a nerve cell produces a electrical signal resulting in the release of neurotransmitter which travels across a synapse and acts on a post-synaptic target cell (either a neuron or an effector cell)
41
paracrine regulation
a local cell releases a paracrine substance which diffuses through the interstitial fluid to act on target cells in close proximity to the site of release of the paracrine substance; this would occur across the apical surface of the cell into the lumen of the gland
42
autocrine regulation
a local cell releases a substance which acts on the cell that released it
43
endocrine cells
produce hormones
found in the epithelium of the stomach and the small intestine
44
3 main gi hormones
secretin, cholecystokinin (CCK), gastrin
- all peptide hormones
- participates in feedback control system
45
cck
- release stimulated by the presence of fatty acids and amino acids in the si
- released into blood
- stimulates the pancreas to increase digestive enzyme secretion and causes contraction of the gallbladder (releases bile acids for fat breakdown)
- absorption of fats and amino acids stop release of cck (negative feedback control system)
46
interstitial motility
stimulated by contraction and relaxation of the two muscle layers in the outer portion of the git
- peristalsis
47
segmentation
important for mixing of the food
- mostly occurs in si
- functions are to allow mixing of contents with digestive enzymes, slows the transit time to allow for absorption of nutrients and water
48
pacemaker cells
cells in the git that are distributed throughout the smooth muscle cells
constantly under spontaneous depolarization-repolarization cycles called slow waves (propagated through the circular and longitudinal muscle layers through gap junctions)
49
3 phases on gastrointestinal system
cephalic phase: head
gastric phase: stomach
intestinal phase: intestine
50
cephalic phase
head
- initiated through stimulation of receptors in the head by sight, smell, taste, and chewing of food and the emotional state
- reflexes regulated by parasympathetic fibers that activate neurons in the git nerve plexuses
- vagal nuclei in the brain cause the parasympathetic nerve to release ach at the parietal cell; results in the stimulation of acid production
51
gastric phase
stomach
- receptors in the stomach are stimulate by distension, or stretching of stomach, acidity, amino acids and peptides
- the responses to these stimuli are mediated by both short (gastrin) and long (ach) neural reflexes
52
intestinal phase
intestine
- receptors in intestine are stimulated by distension, acidity, osmolarity, and digestive products
- mediated by short and long neural reflexes and by hormones (secretin, cck, gip - secreted by endocrine cells in the small intestine)
53
role of hypothalamus in food intake
important for maintaining homeostasis
- command centre for neural and endocrine control coordination and for control of behaviour
contains a feeding centre in the lateral region (hunger)
contains a satiety center in the ventromedial region (full)
54
orexigenic factors
increase intake
- neuropeptide Y - in hypothalamus, stimulates hunger
- ghrelin - from endocrine cells in stomach during fasting, released into blood, travels to hypothalamus, stimulates release of neuropeptide Y
55
anorexigenic factors
decrease intake
- leptin - produced by adipose or fat tissue
- insulin - produces by the pancreas, stimulates reduction in food intake
- peptide YY - released from the intestine to reduce food intake
- melanocortin - released directly from the hypothalamus, acts to reduce intake of food
56
water intake stimulated by (4)
1 increased plasma osmolarity- stimulates osmoreceptors (sensory receptors in the thirst center of the hypothalamus) 2 decreased plasma volume
3 dry mouth and throat
4 prevention of over-hydration
57
3 main pairs of large salivary glands
parotid
submandibular
sublingial
58
composition of saliva
water, electrolytes, digestive enzymes, glycoproteins, antimicrobial factors (lysozyme, lactoferrin
59
functions of saliva
- moistens and lubricates food
- initiates digestion with digestive enzymes (amylase and lipase)
- dissolves small amounts to diffuse into taste buds
- prevents microbial colonization due to the presence of antimicrobial factors
- aids in speech
- buffers (bicarbonate helps regulated acid from food or acid reflux)
60
what are salivary glands made of
many microscopic ducts that branch out from grossly visible ducts
61
what 3 cells are salivary glands made of
acinar cells, ductal cells, myoepithelial cells
62
acinar vells
secrete initial saliva
63
ductal cells
create the alkaline and hypotonic nature of saliva
64
myoepythelial cells
have characteristics of both smooth muscle (can contract) and epithelial cells
65
primary secretions of saliva
from acinar cells, not yet alkaline or hypotonic, it is isotonic
- contains sodium, potassium, chloride, bicarbonate and water
- enzymes and mucous are added through exocytosis
66
what modifies the saliva
myoepithelial cells contract to push saliva into ductal cell region
ductal cells modify saliva to form the hypotonic and alkaline saliva - loss of sodium and chloride, gain of potassium and bicarbonate
67
what regulates saliva production
parasympathetic and sympathetic pathways
68
amylase
found in saliva
enzyme that can breakdown starches
inhibited by acidic ph in stomach once swallowed
69
amylose
a straight chain of glucose molecules with alpha-1,4 linkages
breakdown leads to formation of maltose and maltotiose
70
amylopectin
chain of glucose molecules with alpha-1,4 linkages as well as alpha-1,6 linkages
breakdown leads to formation of maltose, maltotriose, and alpha-limit dextrin
71
amylase
can only cleave the internal alpha-1,4 linkages
72
lingual lipase
found in saliva
stable in acid - can remain active in stomach
73
sjorgrens syndrome
autoimmune disease; the immune system destroys the salivary glands
74
xerostomia
dry mouth
75
consequences impairment to salivary secretion
dry mouth
decreased oral ph - tooth decay, esophageal erosions
difficulty in lubricating and swallowing food
76
treatment of xerostomia
frequent sips of water and fluoride treatment to combat the microbial populations which flourish in the absence of saliva
77
what is swallowing initiated by
pressure receptors in the wall of the pharynx
78
pharynx
the passage at the back of your throat that is common to air and food
79
stratified squamous epithelium
layers of flattened cells, or stratified cells
- protect the underlying regions of the esophagus from food
80
upper esophageal sphincter
just below the pharynx
- ring of skeletal muscle
81
lower esophageal sphincter
located where the esophagus joins the stomach
- ring of smooth muscle
82
heartburn occurs when
the lower esophageal sphincter does not close properly, after a big meal, during pregnancy
83
stomach functions
storage of food
mechanical breakdown of food
chemical breakdown of food
- secretes pepsinogen (cleaved to form pepsin - initiates protein digestion)
- secretes hydrochloric acid
controls rate at which food enters si
- secretes intrinsic factor (absorption of VB12)
84
components of the stomach
fundus, body, antrum
85
fundus and body
upper part of stomach
both have thin layer of smooth muscle
mucus, pepsinogen, and hcl are secreted
86
antrum
lower region of stomach
thicker smooth muscle layer
physical breakdown, mixing and grinding
mucus, pepsinogen, and gastrin are secreted
87
pyloric sphincter
controls emptying of the stomach
88
exocrine
a chemical messenger secreted into ducts and then onto an epithelial surface without passing into the blood
89
major exocrine secretions
mucus, hydrochloric acid, pepsinogen
90
mucus
protects the stomach epithelium from acid and digestive enzymes, predominately pepson
- helps avoid self-digestion
91
hcl
important for hydrolysis (breakdown) of proteins into their component amino acids, dissolving food, digesting macromolecules and sterilization of food
92
pepsinogen
precursor to the enzyme pepsin which is important for protein digestion
93
minor secretions of the stomach
intrinsic factor - for VB12 absorption
gastrin (endocrine) - stimulates hcl production and increasing stomach motility
histamine (paracrine) - stimulates hcl production
somatostatin (paracrine) inhibits hcl production
94
generalized gastic gland
some of the cell types are not found in all regions of the stomach
- mucous cell, parietal cell, chief cell, enteroendocrine cell, ECL cell, D cell
95
mucous cell
at luminal end of gland
produce mucus to protect the stomach lining from cell digestion
96
parietal cell
secretes intrinsic factor and hcl found mostly in gastric glands of the body and fundus of the stomach (not in antrum) modified surface with canaliculi (inc sa of cells to maximize the secretion of acid and if into lumen of stomach) - when activated canaliculi become more defined
97
chief cells
found in gastric glands in all regions of the stomach
- secretes pepsinogen
98
enteroendocrine cell
found in gastric glands in the antrum
known as G cells
- secretes gastrin
99
enterochromaffin-like cells (ECL cell)
found in gastric glands in all regions of the stomach
- secretes histamine (stimulates hcl production)
100
d cell
found in gastric glands in all regions, but more found in antrum
- secretes somatostatin (regulator that negatively regulates hcl production)
101
acidification of the stomach lumen
parietal cell
- apical surface faces the stomach lumen
- Na/K ATPase
- H/K ATPase
- carbonic anhydrase
- Cl/HCO3 exchanger
- K channels
- Cl channels
- HCl
102
role of Na/K ATPase in acidification of stomach lumen
pumps 3 Na out of the cell and pumps two K into the cell for every molecule of ATP hydrolyzed
establishes electrochemical gradients with high K, low Na on inside of cell
103
role of H/K ATPase in acidification of stomach lumen
apical/luminal membrane of the parietal cell
pumps out a proton from the parietal cell into the stomach lumen
- primary active transport pathway (ATP hydrolyzed)
acid is leaving, cell becomes more basic
104
role of carbonic anhydrase in acidification of stomach lumen
parietal cell gets rid of base by removing bicarbonate (base) catalyzes the formation of h2co3 from h2o and co2
h2co3 dissociates into h and hco3-
105
role of Cl/HCO3- exchanger in acidification of stomach lumen
hco3- is pumped out in exchange for a chloride ion (secondary active transport)
106
role of K channels in acidification of stomach lumen
as protons are pumped out through the apical primary active transporter, K levels increase in the cytosol; K channels in the apical surface open and allow K to leave the cell down its conc gradient
- diffusion through channels
- loss of positive charge with K, compensated with loss of Cl
107
role of Cl channels in acidification of stomach lumen
apical membrane
Cl lost into lumen of stomach as diffuses through Cl channels
108
4 chemical messengers that regulate insertion
gastrin
ach
histamine
somatostatin
109
chemical messengers regulate
the insertion of H/K ATPase into the plasma membrane of the parietal cell
110
role of gastrin
hormone released by G cells
stimulates insertion of the H/K ATPase into the membrane, stimulating HCl secretion
111
role of ach
neurotransmitter
increased parasympathetic activity causes the release of ach
increases insertion of H/K ATPase into the membrane, stimulating acid secretion
112
role of histamine
paracrine released from ECL cells
stimulates insertion of H/K ATPase into the membrane, stimulating acid secretion
113
role of somatostatin
paracrine released from D cells
inhibits the released of HCl, gastrin, and histamine
114
pepsinoegn
secreted by chief cells as an inactive precursor
release is stimulated by the enteric nervous system
parallels the release of HCl
115
gastric motility
a peristaltic wave in the body of the stomach and a stronger force of contraction in the antrum will result in the pyloric sphincter closing
important for breaking down food
huge capacity to stretch
116
where is the pacemaker cells located
stomach in smooth muscle layer
117
causes of vomiting
psychogenic, gastrointestinal disturbances, inner ear infections, chemoreceptors in the brain and git detecting toxins, pressure in the cns
** all go to medulla oblongata**
118
benefits of vomiting
remove harmful substances before they are taken into your body
nausea and feeling bad associated with vomiting are a negative conditioning, prevent you from consuming noxious substances again
119
negative consequences of vomiting
dehydration
electrolyte imbalance
metabolic alkalosis (condition in which the ph of a tissue is elevated beyond normal, due to the loss of acid from stomach)
acid erosion of tooth enamel
120
peptic ulcers
damage to or erosion of the git mucosa
occurs in regions which are acidic such as esophagus, stomach, or duodenum
121
what causes an ulcer
imbalance of aggressive factors (acid and pepsin) and protective factors (mucus and bicarbonate)
- infection from the bacterium helicobacter pylori, inflammation of the lining and irritation and eventually chronic inflammation and erosion
- non-steroidal anti-inflammatory drugs which reduce prostaglandin production, smoking, excessive alcohol, gastrinomas
122
treatment of ulcers
antibiotics to get rid of H. pylori infection
H/K pump inhibitors
histamine receptor antagonists prostaglandin-type drugs
123
is the stomach essential for life
no, but problems can occur without it
124
what problem would occur if you had a very small stomach or a stomach removed
VB12 deficiency
more bacteria in system (HCl sterilizes food)
no regulation of food entering si
125
exocrine pancreas
important for digestion
produces secretions that go into the git
source of majority of enzymes required for digestion of carbs, proteins, fats, and nucleic acids
problems not noticed till <10%
secretes bicarbonate into duodenum for neutralization of stomach acid (digestive enzymes completely inactive under acidic ph, stomach acid must be neutralized)
126
endocrine pancreas
not involved in digestion but it is important for producing hormones that regulate the entire body (insulin)
127
functional anatomy of pancreas
- main pancreatic duct drains the exocrine secretions into the si
- sphincter of oddi regulates release of liver and pancreas contents into si
- exocrine pancreas secretes substances into ducts that drain onto the epithelial surface (apical) and converge into the pancreatic duct
- endocrine pancreas secretion occurs across the epithelial basolateral surface for diffusion into blood
128
acinar cells
produce and secrete digestive enzymes
pancreatic ducts have acinar cells at the end portion of the duct
129
ductal cells
secrete bicarbonate for neutralization of acid
water also secreted
130
pancreatic juices contain
isotonic and alkaline (bicarbonate)
electrolytes (high in HCO3, low in Cl)
digestive enzymes
131
how do the ductal cells of the pancreas produce the alkaline, watery solution
1 cl channels on apical surface of the ductal epithelium, CFTR (cystic fibrosis transmembrane conductance regulator) allows Cl to diffuse out of the duct cell into the lumen
2 cl that has diffused out is exchanged for HCO3-
3 neutral ph of cytosol is maintained by exchange of h for na (Na/H exchanger)
4 cl gradient into the duct lumen draws na and water paracellularly, or between cells
132
alkaline tide
in the stomach a large amount of bicarbonate is pumped across the basolateral surface into the blood; after a meal
133
acid tide
large amount of acid is pumped across the basolateral surface into the blood
134
proteases
enzymes that digest proteins into peptides and amino acids
135
amylolytic enzymes
digest starches into sugars
136
lipases
digest triglycerides into free fatty acids and monoglycerides
137
nucleases
digest nucleic acids into free nucleotides
138
zymogens
proenzymes or inactive precursor enzymes
139
enterokinase
cleaves trypsinogen into trypsin
- activated into the duodenum
140
why does the pancreas produce and store proenzymes
to prevent autodigestion
- proenzymes not activated until the si
141
trypsinogen
activated by enterokinase in the duodenum to trypsin (important for activating other enzymes)
142
chymotrypsinogen
activated by trypsin to the active enzyme chymotrypsin
143
pro-elastase
activated by trypsin to the active enzyme elastase
144
pro-carboxypeptidase A and B
activated by trypsin to the active enzyme carboxypeptidase A and B
145
lipase
hydrolyzes triglycerides into free fatty acids and monoglycerides
146
phopholipase A2
hydrolyzes phospholipids into free fatty acids and lysophospholipids
