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Phys 210 > GI tract > Flashcards

GI tract Flashcards

(110 cards)

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1
Q

Functions of the GI tract

A
  1. Digestion
    - chemical alteration of food into absorbable molecules
  2. Absorption
    - movement of digested food from the intestines into blood
  3. Excretion
  4. Host defense
    - highly developed immune system
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2
Q

Components

A

mouth, pharnyx, esophagus, stomach, small intestine (duodenum, jejunum, illeum), large intestine, accessory organs (pancreas, liver, gallbladder)

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3
Q

Layers of GIT

A
  1. Mucosa
  2. submucosa
  3. muscularis externa
  4. serosa
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4
Q

Muscosa layers - epithelial

A

a. epithelial layer
- layer of cells that lines all body cavities and surfaces
- apical surface = faces lumen
- basolateral = faces blood stream
- tight junctions confine transport proteins to specific regions
-provides selective uptake
- surface area is amplified by villi and crypts

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5
Q

paracellular pathway

A

limited by tight junction seal
water and small ions can diffuse through tight junctions

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6
Q

transcellular pathway

A

two step process which requires a transport protein on the apical and basolateral surfaces of cell

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7
Q

Mucosa layers - lamina propria

A

b. lamina propria
- connective tissue
- small blood vessels
- nerve fibres
- lymphatic vessels

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8
Q

mucosa layers - muscularis mucosa

A

c. muscularis mucosa
- thin layer of smooth muscle (not involved in contractiom of GIT)

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9
Q
  1. Submucosa
A

plexus of nerve cell bodies
- relays info to and away from mucosa
blood and lymphatic vessesls

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10
Q
  1. muscualris externa
A

thin layer of circular muscle
- narrowing of lumen
myenteric nerve plexus
- network of nerve cells regulate muscle function
thinner outer layer of longitudinal muscle
- shortens the tube

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11
Q
  1. serosa
A

thin layer of connective tissue
- forms connections so intestines do not freely float

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12
Q

Blood supply to the liver

A

portal circulation (series circulation)
- blood is taken from digestive tract and empties directly into liver
- allows liver to remove harmful substances (like a filter)
-liver also receives systemic oxygenated blood (10%) (parallel blood flow)

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13
Q

Regulation of GI processes

A

reflexes initiated by:
distension of wall by volume of luminal contents
osmolarity of contents
pH of contents
conc. of specific digestion contents

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14
Q

intrinsic neural regulation of GI processes
(short reflexes)

A

enteric nervous system ( contained within GI tract)
- controls activity of secretomotor neurons
- contained within walls of GIT
- can function independantly of CNS
1. myenteric plexus
2. submucosal plexus

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15
Q

myenteric plexus

A

influences smooth muscle

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16
Q

submucosal plexus

A

influences secretion (closer to the lumen)

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17
Q

Intrinsic vs extrinsic

A

Intrinsic → contained wholly within the organ
Occurs through nerve plexi located in the GIT wall itself Nerve plexi = branching networks of intersecting nerves
Extrinsic - regulation is through systems outside of the organ/ GI tract
Through the parasympathetic and sympathetic nervous system

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18
Q

Extrinsic regulation of GI processes
(long reflexes)

A

done by autonomic nervous system
-parasympathetic
stimulates flow of saliva, stimulates peristalsis and secretion, stimulates release of bile

-sympathetic
stimulates flow of saliva, inhibits peristalsis and secretion

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19
Q

Neurocine

A

a nerve cell produces a electrical signal resuting in a neurotransmitter to be released which travels across to synapse onto another nerve cell or effector cell

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20
Q

Endocrine

A

a chemical messenger passes from cell which produced it into blood and is carried by blood to its distant target

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21
Q

Paracrine

A

chemical messenger diffuses through interstitial fluid to nearby cells

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22
Q

Autocrine

A

chemical messenger acts on cells which produced it

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23
Q

CCK

A

a GI hormone
- fatty acids and amino acids in the small intestine trigger CCK secretion from cells in small intestine into blood

  • CCK stimulates:
    pancreas to increase digestive enzyme secretion
    gall bladder contraction - release of bile acids for fat breakdown!!
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24
Q

Secretin

A

GI hormone
released from S cells in small intestine
acid stimuli’s release
lowers HCl and stomach motility
increases bicarbonate/ H2O from pancreas and bile

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25
Gastrin
GI hormone released from G cells in stomach antrum - peptides/amino acids in stomach cause release increases HCl and stomach/ileum motility
26
Peristalsis
Circular and longitudinal muscle contraction of two outer smooth layers of the GIT - propels contents of lumen towards the anus
27
Segmentation
mixing - contraction and relaxation of the intestinal segments with little net movement to allow mixing of contents and enzymes, and slows down food movement for absorption
28
Basic electrical rhythm
GIT has pacemaker cells throughout the smooth muscle that are constantly undergoing spontaneous depolarization-repolarization cycles These slow waves are the basic electrical rhythm - do not cause muscle contractions on their own!! excitatory hormones/NTs further depolarize to bring to threshold and contract
29
Phases of gastrointestinal control
1. cephalic 2. gastric 3. intestinal
30
control of food intake
hypothalamus - feeding centre in lateral region - satiety centre in ventromedial region
31
activation of feeding centre in lateral region increases what?
hunger
32
acitvation of satiety centre in ventromedial region does what?
makes you feel full
33
Leptin
inhibits neuropeptide Y - neurotransmitter that stimulates hunger
34
regulation of water intake stimualtion
1. Increased plasma osmolarity (osmoreceptors) 2. Decreased plasma volume (baroreceptors) 3. Dry mouth and throat 4. Prevention of over-hydration by GI tract
35
three main salivary glands
1. parotid - watery (serous) secretion 2. submandibular - serous/mucous secretion 3. sublingual - mucous secretion
36
components of saliva
mostly water - hypotnic + alkaline contains digestive enzymes - amylase + lipase
37
functions of saliva
Moistens and lubricates food Initiates digestion Dissolves a small amount of food which effects appetite and food intake Prevents microbial colonization
38
cells of salivary glands
1. Acinar 2. ductal 3. myoepithelial
39
Acinar
proteins (amylase mucin) - released by exocytosis water, and electrolyte (Cl-,Na+) secretion = primary secretion (isotonic)
40
ductal
lets HCO3 (bicarbonate) in and Na+ and Cl- out = secondary modification so its alkaline and hypotonic
41
myoepithelial cells
contract and expel formed saliva from acinus into ducts
42
Saliva regulation
NO HORMONE REGULATION primarily parasympathetic + sympathetic
43
Role of saliva in digestion
starch digestion is initiated in the mouth by amylase (cleaves inernal a-1,4 linkages) - creates maltose, maltotriose and a-limit dextrin
44
how is swallowing initiated?
complex reflex initiated by pressure receptors in the wall of the pharnyx - stimulated by food/ liquid entering pharnyx
45
steps of swallowing
a. tongue pushes food bolus to the back of the pharnyx b. soft palate elevates to prevent food entering the nasal passages - swallowing centre inhibits respiration, raise the larynx, and close the glottis c. epiglottis covers glottis to prevent food or liquid entering the trachea d. food descends into the esophagus
46
esophageal sphincter
upper esophageal sphincter - ring of skeletal muscle just below pharnyx lower esophgeal sphincter - ring of smooth muscle at stomach
47
functions of the stomach
+ storage of food + mechanical breakdown of food + chemical breakdown of food - secretes pepsinogen (digests proteins) - secretes HCl (dissolves food, partially digests macromolecules) + controls the rate food enters the small intestine +secretes intrinsic factor - critical for absorption of B12
48
What are the names of the different regions of the stomach?
1. Fundus 2. Body - both are thin layer of smooth muscle - secretes mucus, pepsinogen, Hcl 3. antrum - thicker smooth muscle layer - secretes mucus, pepsinogen, gastrin
49
Mucous cell
secretes mucous to protect stomach lining from acid
50
parietal cell
secretes intrinsic factor and HCl - not found in antrum
51
Chief cell
secretes pepsinogen (precursor to pepsin- which digests proteins)
52
Enteroendocrine cells/ G cells
secrete gastrin (hormone that stimulates HCL production by parietal cell and stimulates GI motility) - mostly in antrum
53
zymogen
means that it is a precursor for a protein/enzyme
54
Enterochromaffin-like (ECL) cells
- gastric glands - secretes histamine (stimulates HCl release)
55
D-cells
-secretes somatostatin (negative regulator of HCL secretion!!)
56
acidification of stomach lumen
1. H+/K+ ATPase - pumps H+ into lumen in exchange for K+ into cells - ACTIVE transport (uses atp) 2. Carbonic anydrase (CA) -catalyses formation of H2CO3 from H2O and CO2 - H2CO3 dissociates H+ (for lumen secretion) and HCO3- 3. Cl-/HCO3- exchanger - excess HO- is taken out of cell INTO BLOOD as HCO3- in exchnage for Cl- 4. K+ channels K+ diffuses back into stomach lumen - loss of positive charge (compensated when Cl- leaves cell too) 5. Cl- channels - Cl- leaks back into stomach lumen through diffusion
57
4 chemical messengers that regulate acid secretion
- gastrin (gastric hormone) - acetlycholine (NT) -histamine (paracrine) - somatostatine (paracrine) from D-cells
58
what activates pepsinogen?
-released from chief cells -activated by acidic pH in stomach lumen
59
factors that increase acid secretion?
Acetylcholine, gastrin and histamine all directly increase acid secretion
60
factors that inhibit acid secretion?
Somatostatin directly inhibits acid secretion by parietal cells
61
Different GI phases
1.cephalic - stimulation in the brain - sight , smell, taste etc causes exciatiry stimuli via vagus nuclei 2. Gastric phase - occurs when food reaches the stomach Major phase, regulates gastric production 3. Intestinal phase - occurs when food that has been partially broken down by the stomach enters the SI (duodenum) Mainly inhibitory, wants to slow down food for the intestine to absorb/digest - Mediated by secretion and CCK
62
Gastric motility
Waves of contraction is set by the basic electrical rhythm, but strength of contraction is determined by stimulatory input.
63
What causes vomiting?
Motion sickness/inner ear infection Alcohol/toxins Pressure on CNS GIT disturbances (i.e infection) sight /smells etc
64
The pancreas, exocrine gland
Exocrine gland = releases substances into a duct that drain onto epithelial surfaces Source for majority of enzymes required for digestion Carbohydrate, protein, aft, nucleic acid !!!!!secretes HCO3- which is critical for enzyme function
65
The pancreas, endocrine gland
= secretes products directly into blood stream Produces hormones that regulate the entire body i.e insulin
66
Pancreatic ducts
Duct cells secrete H2O and HCO3- Acinar cells produce and secrete digestive enzymes through exocytosis
67
Pancreatic juices
isotonic, alkaline contains electrolytes - high HCO3-, low Cl- contains digestive enzymes ( secreted by acinar cells)
68
production of HCO3- by pancreatic duct cells
1. CFTR opens - allows diffusion of Cl- into duct lumen 2. Cl- in lumen is exchanged for HCO3- in cell (Cl- goes back into the cell) 3. H2O and Na+ follow paracellulary in response to electrochemical gradient across epithelium 4. Neutral pH pf cytosol is maintained by exchange of H+ (exported) and Na+ (imported) - this is dependant on the chemical gradient generated by Na+/K+-ATPase
69
Alkaline tide
after a big meal, when the parietal cells are producing lots of acid in stomach - lots of HCO3- is pumped into the blood tide = moving into blood
70
Acid tide
after a big meal, duct cells in pancreas are producing and secreting HCO3-, so large amounts of H+ are pumped across the basolateral surface into the blood stream
71
acinar cells in pancreas
synthesize and package pro-enzymes into zymogen granules
72
proteases
digest proteins into peptides and amino acids
73
amylolytic enzymes
digest starch into sugars
74
lipases
digest triglycerides into free fatty acids and monoglycerides
75
nucleases
digest nucleic acids into free nucleotides
76
how to activate enzymes
enterokinase turns trypsinogen into trypsin which then activates enzymes
77
Major proteases secreted by the pancreas
trypisinogen (activated by enterokinase to form trypsin) chymotrypsinogen (activated by trypsin to form chymotrypsin) Pro-elastase (activated by trypsin to form elastase) all of them hydrolyze interior peptide bonds of proteins and polypeptides
78
Regulation of Pancreatic juice secretion
Acid in duodenum stimulates Scells - secrete secretin - leads to more HCO3- production (duct cells) Digested fat/protein in small intestine stimulates I cells - secrete CCK - stimulates production of Enzymes (from acinus cells)
79
Secretin and CCK both
inhibit gastrin secretion - reduced stomach motility - reduced acid secretion
80
The hepatic and lobule structure
Hexagonal structure with central vein running through the centre Portal triads at each corner Has hepatic artery, portal vein and bile duct
81
What does the liver do?
- filter the blood - forms and secretes bile into a duct (exocrine gland)
82
blood flow to the liver
receives blood from systemic (25%) and portal circulation (75%)
83
what is bile made out of
1. bile acids 2. cholesterol 3. salts (Na+, K+, HCO3-) 4. phospholipids 5. bile pigments 6. trace metals
84
How does bile help in fat digestion
pancreatic lipase can only work at the surface of lipid molecules - larger droplets need to be emulsified into smaller ones for lipase - emulsifying agents prevent aggregation of droplets - ampipathic bile acids and phospholipids
85
biile acids also form mixed micelles with ?
phospholipids and products od lipase ( free fatty acids + monoglycerides) = micelle
86
what do micelles do?
keep monoglycerides and fatty acids in small soluble aggregates like a "holding station" for small insoluble lipids until they free form and diffuse across the small intestine epithelium
87
what produces bile?
hepatocytes produce and secrete bile
88
how much bile is recovered? enterohepatic circulation
95% - occurs through enterohepatic circulation - reabsorbed across the small intestine into portal circulation then they are transported back into hepatocytes
89
Regulation of bile
CCK Increases contraction of gallbladder and relaxes the sphincter of oddi Secretin Increases HCO3- secretion by the bile duct cells (+ pancreas)
90
sections of small intestines
1. duodenum 2. jejunum 3. illeum
91
illeum
digestion and absorption - bile acids - vitamin B12
92
jejnumun
digestion and absorption
93
duodenum
mixing of pancreatic digestive enzymes and bile with food absorption of nutrients,iron, and calcium
94
how is surface area increased
intestinal villi, crypt, and micro villi
95
Cell types of the small intestine
1. absorptive cell - brush border enzymes 2. goblet cell - secretion of mucus 3. enteroendocrine cell - release of hormones - I or S cells 4. paneth cell - secrete antibacterial proteins
96
what are brush border enzymes
enzymes anchored to the brush border with catalytic activity in the lumen - break down carbohydrates and peptides into sugars and amino acids
97
digestion of carbohydrates
starch is broken down into maltose, maltriose and a limit dextrins by salivary and pancreatic amylases then they are broken down into monosacchardies glucose by brush border enzymes sucrose = glucose + fructose lactose = glucose + galactose
98
how to absorb glucose/galactose
by SGLT transporter
99
how to absorb fructose
by GLUT5
100
protein digestion
proteins are broekn down by pepsin in the stomach and in the small intestine by pancreatic proteases then they are broken down further into free amino acids by pancreatic proteases and brush border enzymes
101
fat digestion
lipid droplets are emulsified by bile acids and phospholipids and allow pancreatic lipase to release free fatty acids and monoglycerides
102
Absorption of Iron
stored by ferritin (a protein) in enterocyte iron that is not stored is released on blood side of enterocyte and transported through the blood attached to the plasma protein transferrin
103
where is the majority of water/fluid reabsorbed
by the small intestine
104
where does absorption and secretion of water
water absorption at the villi secretion of the crypts
105
absorption of water in small intestine
predominantly depends on Na+ gradients generated during secondary active nutrient uptake water follows Na+ into the cell
106
secretion of water in the small intestine
predominately depends on Cl- gradients generated by secondary active Na+/K+/2Cl- transporter H2O follows the Cl- out of the cell
107
Regions of the large intestine
- cecum/appendix No apparent function in humans Ascending/transverse/descending/sigmoidal colon - re absorption of water - Reservoir for storage of wastes and indigestible materials prior to elimination by defecation Rectum - Reservoir for feces Anus - Two sphincters that control defecation
108
does large intestine contain villi
NO! only crypts (smaller surface area)
109
cells of large intestine
1. absoprtive cells/ enterocytes Similar to small intestine but no brush border enzyme 2. Golblet cells Secrete mucin to create protective mucus layer
110

Phys 210 (2 decks)

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