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Human Physiology II > CH16 - Digestion > Flashcards

CH16 - Digestion Flashcards

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1
Q

Digestion is one part of what 4 main processes?

A

1) Digestion (the actual breaking up of molecules)
-mechanical: physical break-up (ex. in mouth w/ teeth)
-chemical: enzymes break the bonds within molecules

2) Motility (movement of food through the digestive tract)
-bolus (solid lump of food, relatively undigested) to chyme (liquidy, more digested — stomach acids, enzymes, saliva, food, etc.)

3) Secretion
-lots of secretion, happens every step of the way
-anything from: digestive enzymes that help breakdown food or activate other enzymes by breaking them down, to saliva and acid

4) Absorption (last thing that happens — later in digestive tract)
-nutrients from digestive tract into the blood
-mostly in small intestine

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2
Q

What are the 3 phases of digestion?

A

1) Cephalic (head): sensory inputs (smell/see/remember eating + actually eating)
-feed forward mechanisms (even before you eat, your body prepares itself — ex. salivating)
-lasts till you hit stomach
-bolus

2) Gastric (stomach): anything and everything that happens in the stomach
-a bit of feedback for itself
-bolus —> chyme

3) Intestinal (intestines): chyme
-feedback mechanisms (communicates w/ stomach — ex. sends signal to stomach sending chyme when overloaded)

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3
Q

Where does the info move through the sensory inputs?

A

vagus nerve —> CNS’ direct connection to the ENS
-don’t need inputs outside of ENS, but often still get it

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4
Q

What are the accessory portions of the digestive tract?

A

gall bladder, liver, pancreas
-secretion
-processing

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5
Q

Function of sphincters/valves?

A

on either end of stomach
-control how fast we move things
-prevent stomach acid from backflowing

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6
Q

What is GERD?

A

gastroesophangeal reflux disease
-top sphincter that connects back to esophagus does NOT close properly
-gases in stomach can bubble up into your esophagus (acid reflux — heart burn)

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7
Q

Does the stomach absorb nutrients?

A

NO
-storage of food
-lots of chemical/mechanical digestion to prepare food for SI

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8
Q

Where are the majority of nutrients/vitamins absorbed?

A

small intestine

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9
Q

Where does water absorption occur?

A

large intestine
-draw out water, get ready to become feces

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10
Q

What is the central opening of the GI tract?

A

lumen
-4 layers surround it

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11
Q

Explain the mucosa layer of the GI tract.

A

-closest to lumen
-most direct contact w/ food
-large surface area allows for lots of cells that make different secretions (enzymes) —> ex. in stomach (in SI, large surface area helps w/ absorption)
-few blood vessels

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12
Q

Explain the submucosa layer of the GI tract.

A

-connective tissue that wraps around mucosa layer to hold it together
-has a nerve layer from the ENS
-has blood vessels within it to provide blood flow to mucosa layer

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13
Q

What is the ENS?

A

enteric nervous system
-lives entirely in digestive tract
-works largely on its own, doesn’t need input from brain to work (separate nervous system — a lot of the processes are automatic)

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14
Q

Explain the mucularis externa layer of the GI tract.

A

-lots of musculature (to move things around digestive tract) —> smooth muscle (involuntary, automatic control)
-has nerve layer to control the smooth muscle
-outer/inner muscle layers run in 2 different directions (different movement allows for mixing)
-inner: can change diameter of tube of muscle — constrict/dilate to move things forward
-outer: other layer runs length of the tube to allow shortening/lengthening of the tube — contract/relax whole selection
-has layer of blood also

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15
Q

Explain the serosa layer of the GI tract.

A

-furthest from lumen, closest to body wall
-connective tissue that helps keep whole tube connected, all wrapped around the outside (keeps the layers together)
-helps reinforce/attach the organs to the body wall

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16
Q

What happens in the mouth — where bolus moves?

A

1) chewing
-mechanical digestion: tearing apart of food — teeth
-chemical digestion: through hydrolysis to breakdown pieces

2) salivation
-chemical digestion of carbs in mouth via amylase (in saliva)

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17
Q

What are the 2 sources of amylase?

A

1) mouth saliva
2) pancreas

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18
Q

What is in saliva?

A

-amylase
-water-based compounds that soften food
-mucus helps lubricate things + move along better

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19
Q

Where does food enter from?

A

pharynx (behind nose + mouth)
-shared compartment in respiration + digestion

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20
Q

What compartment is exclusive to digestion?

A

esophagus (narrower tube behind trachea)

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21
Q

What is the esophagus’ main secretion?

A

mucus

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22
Q

What is the main role of the esophagus?

A

to move food from the mouth to the stomach

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23
Q

What is the epiglottis and its purpose?

A

-cartilage flap
-closes off the trachea everytime you swallow (stop breathing for split second), so food doesn’t go down the wrong tube

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24
Q

What force is involved in swallowing?

A

peristalsis
-large force generated by muscle to move bolus forward (gravity NOT largely involved in moving food)

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25
What are the functions of the stomach?
-storage of food -production of secretions -chemical/mechanical digestion -NOT absorption
26
What are some purposes of the folds in the stomach wall?
-can stretch out if you eat a lot (can store more food) -increase surface area so you can have lots of enzymes for chemical digestions
27
What is the pyloric sphincter?
opening that controls how you allot food from stomach to small intestine (regulates flow)
28
What is the beginning of the small intestine called?
duodenum
29
What is gastric emptying?
the process of moving stuff (chyme) from stomach to small intestine -upper part of stomach = peristalsis -as mixing happens, contraction of muscles force pyloric sphincter more open (can send more chyme) -have to neutralize chyme -chyme into SI comes in little bits (don't want a lot, otherwise SI can't do its job)
30
What is gastric mixing?
things go back and forth (musculature of stomach changes as you move through stomach) -preparing things for SI -strong contraction closes pyloric sphincter completely, chyme gets pushed back/around to prepare — churning
31
What is an acidic stomach protection from?
bacteria/virus (acidity gets rid of them)
32
What factors is gastric mixing/emptying influenced by?
1) factors within the stomach -receptors (sensory processes like stretch — tells how much food is in stomach by how stretched it is + adjust how fast things are moving) -[chyme] —> too concentrated = SI can't deal with it (slow gastric emptying) 2) factors within the duodenum -[chyme] -info about presence of fat and acid (SI can't deal with it — gastric emptying would slow down) -stretch detectors (too stretched, want to slow things down) 3) neural or hormonal responses -from ENS or brain (PNS = rest and digest) -hormones in blood circulate around stomach/intestines
33
Explain secretin and its functions.
-made in SI (works in stomach/pancreas) -released when high [acid] released into SI -closes pyloric sphincter completely and stops gastric emptying -increases secretion of HCO3- from pancreas (goes into SI to neutralize acid)
34
What is in the gastric juice?
1) gastric acid (HCl): breaks down enzymes from inactive to active -parietal cells 2) pepsinogen —> pepsin (active): breaks down proteins -chief cells 3) gastric lipase: breaks down fat -co-secreted with pepsin 4) somatostatin -D cells 5) histamine -ECL cells 6) gastrin -G cells -all cells in mucosa layer
35
What signals control/regulate the production of acid?
-somatostatin (negative feedback — inhibits acid) -histamine (stimulates acid production) -gastrin (hormone that comes from stomach lining — helps breakdown protein, directly+indirectly stimulates acid production)
36
What does gastrin stimulate, and how?
acid production -stimulates parietal cells (direct HCl production) -stimulates ECL cells (indirect — produce histamine, which then stimulates HCl production AND parietal cells)
37
How does acid production cause a feedback loop?
acid from parietal cells stimulate: -chief cells (produce pepsinogen) -D cells (produce somatostatin —inhibits HCl production, and BLOCK G cells and parietal cells)
38
How does stomach acid affect enzymes in the stomach?
activator of enzymes -HCl cleaves off inactive component example: pepsinogen —> pepsin -if pepsin always active in stomach, would start breaking down stomach itself
39
Why doesn't the stomach digest itself?
1) inactive enzymes 2) mucus: forms (neutral) layer that rides on top of cells -pepsin inhibited by mucosa, thus inactive near cells 3) bicarbonate: neutralizing protons from stomach acid
40
How can one form gastric ulcers?
hole in mucosa layer (get digestion of stomach)
41
What is gastric bypass?
reduction of size of stomach -take top of SI and attach to top of stomach (thus, can't eat a lot — stretch receptors triggered faster) -missing most of gastric phase (pyloric sphincter) -less processing that normally would exist
42
What are some side effects of gastric bypass?
1) diarrhea -greater [chyme] in SI, draws water 2) nutrient deficiencies -lacking processing —> food entering intestinal phase really early 3) B12 deficiency -need intrinsic factors released by parietal cells to create B12 -less gastric phase = less intrinsic factor
43
What are the accessory organs?
1) Gall-bladder -storage of bile that's made in the Liver 2) Liver -produces bile -"gland" -exocrine + endocrine function 3) Pancreas -"gland" -exocrine (secreted onto surface of tissue) -endocrine (hormones into blood) -secretions enter in top of SI (duodenum) -come together in common duct (between stomach and SI)
44
Describe the Pancreas' exocrine function/secretions.
exocrine: on/in lumen, on top of mucosal layer to interact with food -HCO3- (convert from acidic stomach to basic SI) -enzymes for each nutrient type: 1) carbs => pancreatic amylase (+ lactase, maltase, sucrase) 2) proteins => trypsinogen (inactive) 3) fats => pancreatic lipase
45
Describe the Pancreas' endocrine function/secretions.
endocrine: maintain homeostatic range of blood sugar levels -insulin (present in high concentration in fed state — just after eating, tells body to take up blood sugar => store or use it) -glucagon (more common in fasted state — haven't ate in a while => trigger body to use glucose stores, break them down to increase blood sugar) -insulin + glucagon = antagonistic
46
Describe some functions of the Liver.
-helps metabolize food (enzymes, secretions, etc.) -helps to detox blood (once absorbed nutrients, go directly to Liver first => break down foreign materials/detoxify them — then go to main blood supply) -makes plasma proteins (help carry things that need to move around in blood, but don't mix well w/ water => ex. cholesterol) -helps with fat metabolism (BILE — liquid secretion)
47
What is the hepatic portal system?
allows blood flow to come out of digestive tract, into the Liver -secretions from Liver go to digestive tract -absorbed material goes to Liver first 1) SI absorbs products of digestion 2) Nutrients travel in hepatic portal vein to Liver => filtered, detoxed, checked for microbes 3) Liver monitors blood content 4) Blood enters general circulation by way of hepatic vein
48
Describe bile salt structure.
have a: -negatively charged water soluble part -lipid/fat soluble part
49
Describe the process of bile salts and fat digestion.
-emulsification => makes fats more digestible -big fat bubble broken down into smaller pieces attached to bile salts (into small fat droplets — keeps water soluble parts away from lipid soluble) -smaller pieces get arranged in a matrix
50
What are some things that can slow down gastric emptying?
-too much fat -high [chyme] -high [acid] -SI stretched too much
51
How does segmentation in the SI help with mixing?
-smooth muscle in submucosa + muscularis externa layer => change diameter of tube => alternate contraction (mixing) -contract on one side (moves material away), contract on other side (brings material back to other side) -everything becomes mixed up
52
What are some enzymatic secretions in the SI?
-peptidases (enzymes that break down peptides) -enteropeptidases (activate pancreatic enzymes, kinases that cleave off inactive component => e.g., trypsinogen —> trypsin) -pancreatic enzymes (arrive in either active or inactive form => e.g., pancreatic amylase)
53
What are villi and microvilli? What do they form?
-villi: in the mucosa layer of SI => finger-like extensions => increase SA so lots of room for enzymes, secretions, absorptions -microvilli are on the villi -form the BRUSH BORDER
54
What macromolecule is easiest to digest? Which is hardest?
-carbs = easiest (digest earliest too through salivary amylase) -fats = hardest (but some small fats can dissolve through lipid bilayer)
55
Walk through carb digestion/absorption in the SI.
whole process = ENERGY dependent (Na+/K+ ATPase pump) enter as polysaccharides: 1) starch (plant source) 2) glycogen (animal source) -salivary amylase (1st) + pancreatic amylase break these down into disaccharides (lactose, maltose, sucrose) BRUSH border: -broken down into monosaccharides by pancreatic enzymes (lactase, maltase, sucrase) -sodium + energy dependent (Na+/K+ ATPase pump) -to get across membrane have to be broken down into smallest unit possible to get through TRANSPORTER (specific => ex. fructose/glucose one different) leaving epithelial cell of villus into capillaries: -NOT energy dependent (just diffuses) -[high] due to buildup of sugars in cell => [low]
56
What is lactose intolerance?
-have none to little lactase (can't break down lactose) -high [lactose] in SI = draws in water -bacteria love to eat lactose, start fermentation
57
Walk through protein absorption/digestion in the SI.
-ENERGY dependent enter as: 1) exogenous protein = dietary protein (you ate) 2) endogenous protein = recycling/digesting old proteins/enzymes in your body (AA can be reused to build up new proteins) protein => peptides: -pepsin (little bit of pepsin from stomach travels into SI) -trypsin (pancreatic proteolytic enzymes) BRUSH border (peptides => AA): -some enzymes embedded here that breakdown peptides into AA as coming into cell -sodium+energy dependent (Na+/K+ pump) to get INTO cell INTRAcellular peptidases: -some small peptides absorbed into cell, enzymes (intracellular peptidases) within the cell then break them down into AA out of epithelial cell of villus into capillary: -PASSIVE (not energy dependent)
58
Where does protein digestion start?
stomach chemical: -HCl denatures the 3D structure -pepsin breaks it down more (still complex) mechanical: -peristalsis (upper part of stomach) -gastric mixing
59
Walk through fat absorption/digestion in the SI.
-PASSIVE entry (ACTIVE exit) start as: -big fat bubble (and leave as one => converted back) in LUMEN: 1) emulsification by bile salts (smaller, stay in stable shape, higher SA = can attach better to next enzyme) 2) pancreatic lipase -broken down into monoglycerides + free fatty acids => can just diffuse/dissolve across membrane (NO ENERGY) repackaging, leaving epithelial cell of villus: -start building back fat bubble (attach water soluble molecules, coat with lipoproteins — proteins from Liver) -TOO BIG, can't get through capillary ACTIVE transport out of cell towards blood: -instead go through lymph system (Lacteal = lymph vessels, wider than blood vessel) -lymph (contains NO RBCs) + blood get interchanged through body
60
How is diarrhea a protective mechanism?
trying to get out foreign material (e.g., E.coli)
61
What is secretory diarrhea?
something else has made you sick (bacteria/virus => secretes toxin or something that increases [chyme]) -water follows solute = flood of water in intestines, LI can't absorb all of it = loose stool
62
What is osmotic diarrhea?
extra [solute] in intestines that draws water in -eating too much food -digestive disorder, not properly breaking things down or absorbing
63
What is diarrhea "created" in?
created in SI, and passed on -e.g., moving chyme too quickly, not enough time to process = concentrated chyme (high [chyme])

Human Physiology II (3 decks)

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