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Human Physiology II > CH16 - Digestion > Flashcards

CH16 - Digestion Flashcards

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
Q

What are the functions of the stomach?

A

-storage of food
-production of secretions
-chemical/mechanical digestion
-NOT absorption

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26
Q

What are some purposes of the folds in the stomach wall?

A

-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
Q

What is the pyloric sphincter?

A

opening that controls how you allot food from stomach to small intestine (regulates flow)

28
Q

What is the beginning of the small intestine called?

A

duodenum

29
Q

What is gastric emptying?

A

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
Q

What is gastric mixing?

A

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
Q

What is an acidic stomach protection from?

A

bacteria/virus (acidity gets rid of them)

32
Q

What factors is gastric mixing/emptying influenced by?

A

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
Q

Explain secretin and its functions.

A

-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
Q

What is in the gastric juice?

A

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
Q

What signals control/regulate the production of acid?

A

-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
Q

What does gastrin stimulate, and how?

A

acid production
-stimulates parietal cells (direct HCl production)
-stimulates ECL cells (indirect — produce histamine, which then stimulates HCl production AND parietal cells)

37
Q

How does acid production cause a feedback loop?

A

acid from parietal cells stimulate:
-chief cells (produce pepsinogen)
-D cells (produce somatostatin —inhibits HCl production, and BLOCK G cells and parietal cells)

38
Q

How does stomach acid affect enzymes in the stomach?

A

activator of enzymes
-HCl cleaves off inactive component

example: pepsinogen —> pepsin
-if pepsin always active in stomach, would start breaking down stomach itself

39
Q

Why doesn’t the stomach digest itself?

A

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
Q

How can one form gastric ulcers?

A

hole in mucosa layer (get digestion of stomach)

41
Q

What is gastric bypass?

A

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
Q

What are some side effects of gastric bypass?

A

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
Q

What are the accessory organs?

A

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
Q

Describe the Pancreas’ exocrine function/secretions.

A

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
Q

Describe the Pancreas’ endocrine function/secretions.

A

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
Q

Describe some functions of the Liver.

A

-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
Q

What is the hepatic portal system?

A

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
Q

Describe bile salt structure.

A

have a:
-negatively charged water soluble part
-lipid/fat soluble part

49
Q

Describe the process of bile salts and fat digestion.

A

-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
Q

What are some things that can slow down gastric emptying?

A

-too much fat
-high [chyme]
-high [acid]
-SI stretched too much

51
Q

How does segmentation in the SI help with mixing?

A

-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
Q

What are some enzymatic secretions in the SI?

A

-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
Q

What are villi and microvilli? What do they form?

A

-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
Q

What macromolecule is easiest to digest? Which is hardest?

A

-carbs = easiest (digest earliest too through salivary amylase)
-fats = hardest (but some small fats can dissolve through lipid bilayer)

55
Q

Walk through carb digestion/absorption in the SI.

A

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
Q

What is lactose intolerance?

A

-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
Q

Walk through protein absorption/digestion in the SI.

A

-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
Q

Where does protein digestion start?

A

stomach

chemical:
-HCl denatures the 3D structure
-pepsin breaks it down more (still complex)

mechanical:
-peristalsis (upper part of stomach)
-gastric mixing

59
Q

Walk through fat absorption/digestion in the SI.

A

-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
Q

How is diarrhea a protective mechanism?

A

trying to get out foreign material (e.g., E.coli)

61
Q

What is secretory diarrhea?

A

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
Q

What is osmotic diarrhea?

A

extra [solute] in intestines that draws water in
-eating too much food
-digestive disorder, not properly breaking things down or absorbing

63
Q

What is diarrhea “created” in?

A

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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