Digestive System Flashcards
Lec 30, 31, & 32
1
Q
What body parts are involved in digestion?
A
- digestive tract - mouth to anus 2. accessory organs - salivary glands, pancreas, liver, teeth, etc.
2
Q
What are the 4 basic processes of digestion? (list)
A
- digestion a. mechanical b. chemical 2. absorption 3. motility 4. secretion
3
Q
What is digestion (simple)?
A
breakdown of large food pieces into small mols. mechanical - motility. chemical - enzymes with acid
4
Q
What is absorption?
A
nutrients in lumen are transported into enterocytes, cells that line the villi of the small intestine, then are transported from the enterocytes into the blood or lymph.
5
Q
What is motility?
A
smooth mm contractions in tract. mix food/chyme - segmentation and churning. move food/chyme - peristalsis
6
Q
What is secretion?
A
digestive juices into lumen. secrete undigestible matter.
7
Q
How does the mouth digest food (methods)?
A
mechanically breaking down food by chewing which increases surface area. chemical breakdown with enzymes in saliva.
8
Q
What is the fxn of salivary glands?
A
secrete saliva that moistens for speech, food manipulation, tase. prevents caries bc contains lysozyme and antibodies.
9
Q
What is the innervation of salivary glands?
A
PSNS - stimulates secretion of saliva that is thin and enzyme rich. SNS - stimulates secretion of saliva that is mucus rich.
10
Q
What are the processes occurring in the mouth?
A
- digestion: mechanical - chewing to break food into smaller pieces and mix with saliva. chemical - carbs –salivary amylase–> disaccharides and oligosaccharides. triglycerides –lingual lipase–> monoglycerides and FAs. 2. absorption - no food, some drugs like nitroglycerin for pain in chest.
11
Q
At which parts of the body does mechanical digestion/motility occur?
A
mouth (chewing), esophagus (peristalsis), stomach (churning), small intestine (segmentation and peristalsis), large intestine* (just motility*).
12
Q
At which parts of the body does chemical digestion occur?
A
mouth (salivary amylase, lingual lipase), stomach (HCl denature prot, gastric acid, pepsin breakdown prot), small intestine (step 1, 2 - pancreatic, and 3 - intestinal wall).
13
Q
At which parts of the body does absorption occur?
A
kind of the mouth (some drugs), stomach (little food, some drugs), small intestine (lipids, proteins, carbs), large intestine (H2O, drugs, some fermentation products).
14
Q
What is the purpose of the pharynx and esophagus?
A
transports food from mouth to stomach via swallowing and peristalsis.
15
Q
What are the 3 phases of deglutition? (list)
A
- buccal phase 2. pharyngeal phase 3. esophageal phase
16
Q
What happens during the buccal phase?
A
voluntary. food is compacted into a bolus by the tongue, which moves to the pharynx by the tongue pressing on the hard palate.
17
Q
What happens during the pharyngeal phase?
A
involuntary/reflexive. swallowing centre (medulla) initiates swallowing reflex.
18
Q
What happens during the esophageal phase?
A
involuntary/reflexive. food moves down esophagus via peristalsis (wav-like contractions of smooth mm). upper 1/3 is skel mm innervated by somatic motor neurons. middle 1/3 is skel mm and smooth mm innervated by somatic motor neurons and PSNS vagus nerve. lower 1/3 is smooth mm innervated by PSNS vagus nerve.
19
Q
Why cant food re-enter the mouth after buccal phase?
A
bc tongue is pressed against the hard palate, blocking the way.
20
Q
Why can’t food enter the nasopharynx?
A
bc the uvula and soft palate are elevated, closing off the nasopharynx.
21
Q
Why can’t food enter the trachea?
A
bc the glottis and epiglottis are closed during swallowing (so breathing temporarily stops when we swallow).
22
Q
What is the purpose of the stomach?
A
mechanically churns food, chemically breaks down proteins with gastric acid and enzymes, and regulates controlled release of chyme (partially digested food) into the small intestine.
23
Q
What processes occur in the stomach? (list)
A
mechanical (motility) and chemical digestion, absorption.
24
Q
What is the mechanical digestion done in the stomach?
A
churning (motility) which mixes food with gastric acid and enzymes.
25
What is the chemical digestion done in the stomach?
1. carbohydrates - salivary amylase remains active in the stomach until pH drops below 7. 2. lipids - lingual lipase and added gastric lipase remains active in the stomach until pH drops below 5-6. 3. proteins - HCl from parietal cells denatures proteins and acts on pepsinogen (an iactive enzyme secreted by chief cells) to create the active enzyme pepsin. pepsin then breaks down proteins into peptides and aas.
26
What is the pepsinogen pathway?
pepsinogen --HCl, then pepsin--> pepsin. proteins --pepsin--> peptides, aas.
27
How is the stomach protected?
protected from its own acidity causing self-digestion by alkaline mucous (mucous cells).
28
What absorption happens in the stomach?
very little food, some drugs like alcohol and aspirin which penetrate the mucous.
29
What is the purpose of the small intestine?
the primary site for digestion and absorption of nutrients.
30
What processes occur in the small intestine? (list)
1. digestion - mechanical and chemical 2. absorption
31
What is the mechanical digestion done in the small intestine?
segmentation and peristalsis (motility).
32
What does chemical digestion in the small intestine involve secretions from?
1. pancreas - pancreatic juice 2. gall bladder - bile 3. intestinal wall - enzymes
33
what are the steps in chemical digestion in the small intestine (list)?
1. neutralize acid 2. pancreatic enzymes 3. intestinal wall enzymes
34
What happens during step 1 of chemical digestion in the small intestine?
chyme from the stomach has a low pH (acidic) that would damage the intestinal wall, so need to neutralize. when acidic chyme is released into the duodenum it triggers secretion of secretin hormone from cells in the intestinal wall. secretin stimulates duct cells of the pancreas and gall bladder to secrete an alkaline fluid (HCO3-) that will neutralize the acid in chyme. secretin also acts on parietal cells of the gastric glands in the stomach to reduce acid secretion.
35
What decreases gastric acid secretion?
Secretin hormone from cells of intestinal wall - act on parietal cells of gastric glands. CCK from enteroendocrine cells.
36
What happens during step 2 of chemical digestion in the small intestine?
pancreatic enzymes are secreted into the intestinal lumen from pancreatic acinar cells to continue chemical digestion. carbohydrates - polysacc --pancreatic amylase--> disacc and oligosacc. lipids - triglycerides --lipase and bile salts--> FAs and monoglycerides. proteins - trypsinogen --enteropeptidase--> trypsin. trypsinogen --trypsin--> trypsin. chymotrypsinogen --trypsin--> chymotrypsin. procarboxypeptidase --trypsin--> carboxypeptidase. dietary and secreted proteins --proteases--> peptides and aas.
37
What are the pancreatic enzymes released?
pancreatic lipase, pancreatic amylase, enteropeptidase, trypsin, proteases.
38
How is pancreatic enzyme secretion regulated?
presence of FAs and aas in the duodenum stimulates the secretion of the hormone cholecystokinin CCK from enteroendocrine cells of the small intestine.
39
What are the effects of CCK?
1. stimulates/increases pancreatic enzyme secretion 2. stimulates gall bladder contractions - release bile into duodenum 3. decreases gastric motility and decreases gastric secretions.
40
What happens during step 3 of chemical digestion in the small intestine?
enzymes on the surface of microvilli of enterocytes further breakdown nutrients so that they are small enough to be absorbed. carbohydrates - disacc and oligosacc --dissacharidases and oligosaccharidases--> monosacc. ex. sucrose --sucrase--> glucose and fructose. ex. maltose --maltase--> glucose and glucose. ex. lactose --lactase--> glucose and galactose. proteins - peptides --aminopeptidase and dipeptidase--> smaller peptides and aas. lipids - no further digestion (no lipase).
41
What are the intestinal enzymes secreted?
disaccharidases (sucrase, maltase, lactase), oligosaccharidases, aminopeptidases, and dipeptidases.
42
What does a lactase deficiency cause?
lactose intolerance bc lactose isnt broken down by lactase, so it remains undigested and passes into the large intestine where it ferments from bacteria, resulting in gas and diarrhea.
43
What is the process of absorption in the small intestine?
transport of nutrients from the lumen of the small intestine into enterocytes then into blood or lymph.
44
Why is the small intestine the main site of absorption?
1. large surface area - due to folds, villi, microvilli 2. nutrients are digested into molecules small enough to be absorbed
45
What is the pathway of absorption for carbohydrates?
1. glucose and galactose enters enterocyte via secondary AT, then leaves enterocyte and enters blood by carrier mediated facilitated diffusion. 2. fructose enters enterocyte by carrier mediated facilitated diffusion, then leaves enterocyte to enter blood by carrier mediated facilitated diffusion.
46
What is the pathway of absorption for proteins?
1. aas enters enterocyte via secondary AT, then leaves enterocyte via carrier mediated facilitated diffusion 2. di and tripeptides enter enterocyte via secondary AT. in enterocyte, enzymes breakdown into aas and then leave the enterocyte by carrier mediated facilitated diffusion.
47
What is the pathway of absorption for lipids?
1. MGs and FAs that are long chain, fat soluble vitamins enter enterocyte via simple diffusion and leave enterocyte via exocytosis and then diffusion into the lymph lacteal. 2. FA short chain enters enterocyte via simple diffusion and leaves enterocyte by diffusion.
48
What is the pathway of water absorption?
enters enterocyte via osmosis and leaves it by osmosis into blood and lymph.
49
How much water is absorbed and used and from where?
around 8500 mL a day absorbed by small intestine assuming; water is ingested in food and drink - around 2000ml. get water from secretions - around 7000ml. so 9000ml taken in and 500ml a day lost to large intestine.
50
Where do absorbed nutrients go?
1. to the liver via the hepatic portal vein (blood) 2. into lacteals (lymph) and are carried through lymphatic circulation through thoracic duct to the left subclavian vein where they enter the blood (lacteal --> thoracic duct --> left subclavian vein --> blood)
51
Where do we get bile from?
1. liver (bile synthesis) 2. gall bladder (stores)
52
What is the composition of bile?
water, bile salts (derived from cholesterol), bile pigments (bilirubin form rbc breakdown), ions (HCO3-), and detoxified/inactivated drugs.
53
What is the fxn of bile salts?
1. emulsification of fats. breaks up larger fat globules into small fat droplets to increase surface area for enzyme digestion. 2. micelle formation - keeps products of fat digestion in solution.
54
What is a micelle?
vesicle like structure formed from bile salts and phospholipids thats filled with MGs and FAs. interior is hydrophobic and exterior is hydrophilic.
55
How do micelles affect pathway of lipid absorption?
in lumen of small intestine lipids emulsified by bile salts and then digested by pancreatic lipase to form FAs and MGs which are packaged into micelles. micelles transport fat digestion products to the surface of the enterocytes that line the lumen of small intestine. FA and MGs then able to diffuse into the enterocyte.
56
What happens to fat digestion products when they get into the enterocyte?
FAs and MGs undergo reassembly in the smooth ER by enzymes to become diglycerides and FAs and then again enzymes make it become triglycerides. then in the golgi apparatus the triglycerides are packaged with cholesterol, proteins, and phospholipidsto form the chylomicron. chylomicrons then packaged into vesicles and exocytosed into ISF. chylomicrons diffuse into lymph lacteal
57
What are the 3 regulatory phases of gastric motility/secretion (list)?
1. cephalic phase 2. gastric phase 3. intestinal phase.
58
What happens during the cephalic phase?
prepares stomach for food by triggering though sight smell taste of food. PSNS vagus nerve and the enteric NS coordinate secretions and motor responses in the stomach. Enteric NS and PSNS --> increases enzymes pepsinogen and lipase. --> increases gastrin hormone. --> increases acid secretion. increases smooth mm motility.
59
What happens during the gastric phase?
food in stomach causes distension which activates stretch receptors --> signal enteric NS and PSNS --> increase enzyme secretion pepsinogen. --> increase gastrin secretion. --> increase acid secretion. --> increase smooth mm motility. Ca, aa, peptides, alcohol and caffeine act on gastrin secretion.
60
How does the pH of the stomach change with food?
food is a buffer, so pH decreases slowly, and reached 3 when stomach is nearly empty.
61
What happens in the stomach when the pH is less than 3?
shuts down enteric NS which decreases acid. decreases gastrin and therefore decreases acid (bc gastrin acts in acid secretion and enzyme secretion)
62
What happens during the intestinal phase?
controls the rate of chyme entry into the duodenum. 1. initially (while eating) get increased gastric secretion - duodenal gastrin release due to duodenal stretch. 2. then inhibitory signals cause: a. decreased gastric motility (slows emptying) due to; 1. CCK - released due to presence of FAs and aas. 2. enterogastric reflex - enteric neural reflex that inhibits gastric motility to allow time for digestion and absorption in the small intestine. b. decreased gastric secretion (acid and enzyme) due to: 1. secretin released due to acid 2. CCk released in response to presence of aas and FAs in the duodenum 3. enterogastric reflex increased SNS sinaling decreases secretions.
63
What is the enterogastric reflex?
triggered by presence of aas/peptides or acid in the duodenum, duodenal stretch, hypertonicity. sensory receptors such as stretch receptors and chemoreceptors are activated. signals are sent directly by enteric NS to the CNS to decrease PSNS activity and increase SNS activity. increased SNS signalling decreases motility.
64
Why is gastric emptying regulated?
so that; a. acid can be neutralized in the small intestine. b. tonicity does not overwhelm the small intestine c. time for digestion/absorption in small intestine.
65
In short what decreases gastric motility?
CCK and enterogastric reflex (increases SNS activity).
66
What are the digestive processes done in the large intestine? (list)
motility, absorption, secretion.
67
What is the different kinds of motility done in the large intestine?
1. haustral contractions - slow and weak that move material down the tube. allows mixing, absorption of salts and H2O. 2. mass mvmts - due to food in stomach via gastrocolic reflex = powerful waves of contractions from transverse colon to rectum. moves fecal mass to rectum - initiates urge to defecate.
68
What is the rectal/defecation reflex?
stimulus= feces in rectum receptor= stretch receptors in rectal wall CNS integration= sacral segment of SC (PSNS) effector= smooth mm of rectum contracts, while internal anal sphincter relaxes. the external anal sphincter is skeletal mm and is therefore controlled voluntarily and is not part of the reflex.
69
What digestion happens in the large intestine?
none, but bacterial fermentation of undigested nutrients occurs. bacteria synthesize some vitamins (B6, B5, K, folate, biotin).
70
What absorption happens in the large intestine?
H2O, around 400ml a day via osmosis where 100 ml a day is lost in feces. some fermentation products like gases and vitamins. drugs when administered rectally ie anaesthetics.
71
What secretion happens in the large intestine?
K+, HCO3-.
72
What is the fate of absorbed nutrient glucose?
from blood into body cells (via glucose transporters so carrier mediated facilitated diffusion). bc when blood glucose lvls increase, insulin increases glucose uptake into skel mm cells, fat cells, and liver cells. glucose then used in cells.
73
What is glucose used for in cells?
1. catabolism for atp production 2. anabolism for stored glucose as glycogen (75% in skel mm, 25% in liver), represents 1% of bodys energy stores.
74
What is the fate of absorbed nutrient lipids?
1. cholesterol - used to make steroid hormones, bile salts, cell membranes. 2. triglycerides. - in blood are delivered to tissues. lipase on endothelial cells of organs breaks TGs down into 3 FAs and glycerol. 3. FAs and glycerol - transported into tissue cells to be used.
75
What are FAs and glycerol used for in the cell?
1. used for atp production (except by neurons) 2. stored as TGs in adipose tissue (represents 99% of bodys stored energy). 3. used to synthesize cell parts ie membranes, myelin.
76
What is the fate of absorbed nutrients amino acids?
enter cells by secondary AT or facilitated diffusion. GH increases entry into most cells. insulin increases entry into skel mm cells. in cells, aas are used mainly for protein synthesis. aas are not stored - excess is converted to fat. can be used for nrg (atp synthesis) when glucose is low ie starvation.
77
What is metabolic rate?
bodys rate of energy use - the sum of all chemical reactions and mechanical work.
78
What are the factors that affect metabolic rate?
1. SNS - increases met rate. 2. hormones ie epi, thyroid hormone - increase met rate. 3. body temp - 1C rise = 10% increase i =n met rate. 4. exercise - increases met rate 5. food ingestion - increases met rate 6. sleep - decreases met rate.
79
What is basal metabolic rate?
the energy the body needs for essential activities like HR, kidney fxn, and breathing.
80
Digestion hormone summary from stomach to duodenum.
Gastrin - increases acid secretion, increases gastric enzyme secretion (lipase and pepsinogen). Secretin - increases alkaline fluid secretion (duct cells of pancreas and gallbladder), decreases gastric secretion. CCK - increases pancreatic enzyme secretion, increase gall bladder contraction, decreases gastric motility and gastric secretion.
