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Flashcards in Digestive System Deck (28):

4 basic processes

1. digestion: mechanical and chemical breakdown of food into smaller pieces
2. motility: SMOOTH MUSCLE movement of food down the digestive tract. Peristalsis. Mixing. Churning and segmentation.
3. secretion: digestive juice to the lumen
4. absorption: enterocytes of the intestinal wall absorb materials then into blood or lymph.



salivary glands
- moisten food to shape the food into a bolus.
- prevents cavities (lysozyme and antibodies)
- PSNS thin saliva with amylase rich
- SNS thick mucus rich saliva



mechanical: chewing into smaller pieces

1. carbs: polysach--> salivary amylase --> oligo and disach
2. fats: triglycerides --> lingual lipase --> monoglyc and FA



some drugs such as nitroglycerine (angina) --> vasodilator



3 phases
1. Buccal phase: voluntary, where we swallow the bolus
2. pharyngeal phase: involuntary, food triggers signals to the swallowing centre (medulla) and stimulates the swallowing reflex
3. esophageal phase: food goes down via peristalsis 1/3 somatic NS skel muscle
2/3 mix of both
3/3 PSNS smooth muscle

food cant enter...
1. mouth: because tongue on hard palette.
2. nasopharynx: because soft palette and uvula is raised
3. trachea: because epiglottis and glottis is down. respiration stops



mechanical: churning

1. carbs --> salivary amylase until ph is below 7
2. fats --> lingual lipase and gastric lipase (chief cells) until ph <5-6
3. proteins --> HCL (parietal cells) denatures it and activates pepsinogen (chief cells)
pepsinogen --> HCL --> pepsin + FB
proteins --> pepsin --> aa and peptides



little if any, vinegar, bile, aspirin, alcohol (penetrates mucus --> alkaline and from mucus cells)


Small Intestine DIGESTION

mechanical: segmentation

chemical 3 steps
1. neutralize alkaline fluid
-presence of acid in the duodenum leads to the secretion of secretin (hormone) which causes the pancreatic and gallbladder ducts to secrete HCO3- and causes a decrease in gastric acid secretion (parietal cells)

2. pancreatic enzyme release (pancreatic acinar cells)
1. carbs polysac --> pancreatic amylase --> oligo and disach
2. lipids triglycerides --> pancreatic lipase w/ bile salts --> monoglic and FA
3. proteins
trypsinogen --> enterpeptidase --> trypsin
trypsinogen --> trypsin --> trypsin + FB
chymotrypsinogen --> trypsin --> chymotryp
procarboxypeptidase --> trypsin --> carboxpeptidase
proteins --> proteases --> aa and peptides

3. intestinal wall (enterocytes using microvilli)
1. carbs: oligosach and disach --> oligosaccdases disachdases --> monosach.
sucrose --> sucrase --> gluc + fruct
lactose ---> lactase --> gluc + galact
maltose --> maltase --> gluc + gluc
2. proteins: peptides --> aminopeptidases + dipeptidases --> smaller peptides and aa
3. lipids --> none, no lipase on intestinal wall


REGULATION of Pancreatic Enzyme Secretion

presence of aa and fatty acids in the duodenum
-release of CCK
1. increases gallbladder rel. of bile.
2. decreases gastric secretion and motility.
3. increases pancreatic enzyme rel.



1. carbs: none olgosach and disach too big
2. lipids: yes FA and Monoglycerides
3. proteins: yes to aa no to peptides


Lactase Deficiency

lactose intolerance, bacteria fermentation, gas and diarrhea, no lactose digestion


celiac disease

gluten damages villi and decrease SA, bacteria fermentation, gas and diarrhea


Small Intestine ABSORPTION

where most absorption occurs
to enterocyte and out of enterocyte to blood or lymph.

gluctose and galactose --> 2 AT --> fac. trans
fructose --> fac trans --> fac trans
aa --> 2 AT --> fac trans
di + tri peptides --> endocytosis --> aa --> 2 AT --> fac trans
Monoglyc, FA >12C, fat sol vita, cholesterol --> simp diff --> exocytosis and diff into lymph lacteal
FA <12C --> simp diff --> diff blood
H20 --> osmosis --> osmosis(blood and lymph)


water Abs in SI

9000 ml/day enters the SI. 7000 ml from secretions and 2000 from diet. 500 goes to the LI. where 100 lost in the feces


where do the nutrients go from the SI

hepatic portal vein in the liver
lacteal --> thoracic ducts --> left subclavian vein


Bile is made of...

bile salts
bile pigments from bilirubin (RBC breakdown)
ions (HCO3)
detoxified inactivated drugs, toxins, hormones


function of bile salts

emulsify fats into smaller droplets
create a micelle keeps fats in the solution (bile salts and phospholipids)
- hydrophobic inner
- hydrophillic outer

micelle diffuses to enterocyte --> FA and MGS diffuse into the enterocyte


@ the enterocyte

FAs and MG --> FA DIGLYC (in SER) -TRIGLYC --> proteins, cholesterol, and phospholipids added in Golgi --> cholymicron (watersol) --> exocytosis --> lymph


Gastric motility/secretion

3 regulatory phases
1. cephalic phase: preparing stomach for food
- smell, thought, sight, taste.
PSNS + enteric (mostly PSNS)
- increase in gastric acid, gastric enzymes, motility, and gastrin secretion

2. gastric phase
food in stomach, activates stretch receptors
same thing as before except mostly enteric
- aa and FA trigger presence of food
- Ca, alcohol, caffeine, aa, peptides may increase digestion too

stops when pH is below 3

3. Intestinal Phase
- controls rate of which chyme (bolus + gastric juice) enters the SI.
1. stop ovewhelming the SI with tonicity
2. proper reabs.
3. acid can be neutralized

- intially, duodenal stretch causes an increase in gastric acid for a short time.

- inhibitory signals cause
1. decrease in gastric motil by...
CCK rel
enterogastric reflex (enteric NS): triggered by aa/peptides, acid, duodenal stretch, hypertonicity
--> done directly or via CNS to SNS.
2. decrease in gastric secretion
Secretin and CCK



Gastrin (stomach and duodenum): increase gastric acid and enzyme secretion

secretin: (duodenum) decrease gastrin secretion and increase HCO3 secretion

CCK: (duodenum) due to aa and fa. increase gallbladder contraction, pancreatic enzyme secretion, decrease gastric motil and secretion.


Large intestine MOTILITY

haustral contractions: weak and slow allow reabs of salts and water and mixing,

mass movements: due to food in stomach, power waves from the gastrocolic reflex pushing food from the tranverse colon to the rectum.

fecal mass in rectum cause the urge to poop.


Rectal defecation reflex

stim: feces in rectum
CNS: sacral segment of spinal cord PSNS
effector: smooth muscle of the rectal walls,
internal sphincter relaxes
external sphincter contracts (skel m. voluntary) not part of reflex


Large Intestine DIGESTION

none, fermentation or creation of vitamins (b5,b6,k,folate,biotin)


Large Intestine ABSORPTION

400, 100 lost in feces.
Na via active transport
some fermentation products (gases, vitamins)
drugs, rectally (anaesthetics)


Large Intestine SECRETION

HCO3 and K


Fate of absorbed nutrients

1. Glucose: blood to body cells via insulin.
glycogen in skel m. 75% and liver 25% (1% of entire energy stores)

2. Lipids
cholesterol --> cell membrane, bile salts, steroids
triglycerides --> 3 FA and Glycerol by lipase on endothelial cells
---> oxidized for ATP
---> storage as TG in adipose tissue 99% storage
---> membranes and myelin

3. Amino Acids
- enter cell via 2 ATP or Fac trans
- GH increases entry of this into cells
- insulin increases this to skel muscle
- for protein synthesis
- not stored, excess converted to fat
- can be used as energy when glucose is low.


Metabolic rate

body's rate of energy use. sum of all mechanical and chemical reactions.

factors affects MR
1. SNS increases MR
2. hormones (TH, EPI) increase
3. body temp (1 degree increase MR 10%)
4. exercise increase
5. food ingestion increases
6. sleep decreases


Basal metabolic rate

energy body needs for essential activities