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PHGY216 > Module 6 > Flashcards

Module 6 Flashcards

1
Q

What is the role of the digestive system

A
  • primary - take nutrients from water and the foods we eat
  • harvest electrolytes

Ingestion
* physically eating food

Digestion
* Breakdown of food into small molecules that can be absorbed

Absorbtopm
* nutrients to the circulatory system

Distribution
* movement in the circulatory system and delivery to the tissues

Usage
* Movement of nurteints into cells for usage

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2
Q

What is digestive motility

A
  • musclar contractions that mix and move food and propel the content
  • smiliar to smooth muscle contractions in the cirulatory system
  • propulsive movements move the food and the speed depends on the segment of the digestive system
  • the speed is optimized for optimal digestion
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3
Q

Which organs use skeletal muscle rather than smooth muscle to move materials

A
  • Top of esophagus
  • Mouth
  • External anal spinchter
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4
Q

What is digestive secretion

A
  • secretion of digetsive juices by the exocrine glands
  • all contain water
  • secrete a mix of enzymes with bile salts
  • functionality depends on the area and region of the tratc
  • secretetory cells of glands get water and raw materials from plasma
  • Upon endocrine signal they release their contents and are usually completely reabsorebd once their function has been completed
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5
Q

What is chemical digestion

A
  • enzymatic breakdown of foods
  • compelx to simple molecules
    Carbs
  • mostly come from plants as starch or glycogen
  • polysaccjarides that are broken down into monosaccharides
  • not all mono can be absorbed

fats
* usually come as tryglycerides
* broken down by release two fatty acids and leaving a monosachharide
* glycerol molecule with one fatty acid molecule
* all these materials can be reabsorbed

Proteins
* come from meat, legumes, eggs and dairy products
* broken down into a single amino acid and maybe a peptide that can be reabsorbed

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6
Q

What is the process of absoreption

A
  • Mostly occurs in the small intestine
  • where digetsion is completed
  • small absrobale units, water, electrolutes go from the tradct lumen into the blood and lymph
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7
Q

What are the digestive tract walls

A
  • Mucosa
  • Submucosa
  • Muscularis externa
  • serosa
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8
Q

What is mucosa

A
  • innermost layer
  • has microvilli
  • esophagus has the lowest amount of folding and the small intestine has the largest amount
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9
Q

What is submucosa

A
  • thick layer of CT
  • supports mucosa
  • provides distensibility and elasticioty
  • larger blood nad lympth vessels that send branches
  • to mucosa and the outer layers
  • contains the submucosal plexus which is a network of veins
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10
Q

What is the muscularis externa

A
  • Smooth muscle layer that covser the sub mucosa
  • Made of 2 muscles
  • circular inner later
  • outer longitudinal layer
  • contractions in the layer decrease the lumen diameter
  • between two muscle layers there is another layer in the nerve network
  • the myentric plexus along with hormones are local chemical mediators
  • help regulate gut activity
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11
Q

What is the serosa

A
  • outer CT layer
  • covers the digestive tract
  • suspends the tract in the cavity and allows for contractions
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12
Q

How is the digetsive tract regulated

A
  • 4 factors
  • intrinsic nerve plexus
  • extrinsic nerve plexus
  • GI hormones
  • autonomic smooth muscle functions
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13
Q

WHat is the intrinsic nerve plexus

A
  • ENS enteric nervous system
  • found in submucosa layer
  • primary purpose is to self regulate - recieves input from the autonimic nervous system
  • ENS is involved in all aspects of digestion
  • Sensory neurons that recieve info on regional stimuli
  • Other nevres will innervate smooth muscle cells and exocrine glands
  • the CNS and ENS is connected by intraneurons
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14
Q

What is the extrinsic nervous system

A
  • sympathetic nervous system and the parasympathetic system
  • modify motility and secretion by changing the activity of the ENS
  • regulate the release of some GI hormones and also sometimes directly innervate specific muscles
  • SYmpathetic system slows digestion
  • parasympathetic increases it and the secretion of digestive jyices
  • Unique to the parasympathetic system, the postganglionic fibers actually part oft he intrinct nervous systems
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15
Q

What are Gi hormones

A
  • in mucosa and parts of the digestive system, endocrine glands rleease their hormones into the blood where they are carrued to different parts of the digestive system
  • They have excitatory or inhibityory effects on the motility and exocrine gland secretions
  • some GI hormones are found outside of the digestive tract
  • The ones in the brain function as neurotransmitters and neuromodulators
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16
Q

What is autonimic smooth muscle function

A
  • Some smooth muscle cells ahve pacemaker like rhythmic cells
  • sponteanous changes in membrane poyential
  • this type of electrical reaction is called slow wave contractions
  • located in the boundary of the circulatoryu and longitudinal muscle layers
  • slow wave contractions are not action poentials, in that they cannot produce contractions

Control of them
* Associate between closer and furyher to threshold
* if waves reach threshold, they will depoalrize and cause a contraction
* sincet he cells are connected by gap junctions, one contractoon will cause all the cells to ciontract as entire unti and allows it to function as one big contraction

What determines whether action poentials are intiated
* Mechanical, neuroal, and hormonal factors modulate the slow wave
* if starting membrane poential is closer to threshold, peak of the ossilations can trigger and action potential
* This is what happens when food is in the digestive tract so there is increased muscle activity for mixing product

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17
Q

What is tge cephalic phase of digestion

A
  • Begins before food has entered the mouth
  • thought, sight, or smell of food stims the cerebral cortex
  • actives the parasympathetic system via the vagus nerve and is sent to the the stomach to start secretions
  • Main purpose is to prepare for the arrival of food
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18
Q

What is the oral phase of digestion

A
  • Palate
  • Roof of the oral cavity
  • Permits breathing while chewing
    Tongue
  • floor of the oral cacity
  • controleld by skeletal muscle ocntractions of the tongue
  • important for chewing, swallowing, and speech
  • taste buds are located on the tongue

Pharynx
* Cavity behind the nose and mouth
* Connects both these things to the esophagus
* COmmon for both digestive system and the repsirtaory system

Teeth
* External bones embedded in the jaw that are used for mastification of food and mixing it with saliva

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19
Q

What is saliva

A
  • Secreted from the salivary galnds
  • Located outside the oral cavity
  • 1-1.5L of saliva secreted daily
  • 0.5% of electrolytes, exynesu,es and otehr proteins
  • amylase and mucus and lyzyme are the main proteins

Functions
* Amylase begins breaking down carbohydrates within the mouth
* braks down polysaccharides into disacchairdes with maltose
* mucus moistens thf food to faciliyaye swallowing
* lysozume is an antibacyerial
* saliva is important role in speech by lubricating tongue nad lips
* COntains bicarbonate buffer to neutralize acids form bonds and bacteria in the mouth

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20
Q

What is the autonomi control of salivation

A
  • Sympathetic and parasympathetic systems do not work against each other
  • They work together to increase secretion
  • para produces fast flow watery saliva rich in enzymes
  • Sympathetic stims smaller volumer whihc are more dry. This is better for stressful activities
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21
Q

What is the simple salivary secretion reflex

A
  • occurs when chemoreceptors and mechanoreceptors respond to oral presewnce of food
  • activates and sends info to the salivary center in the brainste,
  • sent via extreinsic autonomic nerves
  • to salivary glands
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22
Q

What is conditional salivary reflex

A
  • mouth watering reflex
  • happens when thinking see or smelling
  • learned response ot the pleasure of eating things that stims the cerebral coryex
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23
Q

Explain the swalloing reflex

A
  • Considered all or none
  • included in both esophageal and oral phase of digestion
  • volunatrily intiiated
  • bolus present and puts pressure on pharynx causes an involunatry response of 25 muscles to response
  • pressure sensor in pahrynx sends afferent signals to the swalloing center
  • Located in the medulla of the brain stem
  • efferent from swalling activate the muscles
  • cannot be stopped once started
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24
Q

What is the oropharyngeal phase of swallowing

A
  • occurs in 2 phases
  • oropharynheal is the first- rapid 1s
    Mouth
  • once swalling is initiated
  • tongue postions against the palate to keep food from entering

Nasal passage
* Uvula elevates and blocks the nasal passage

Respiratory passages
* respiratory center in the brain stem is inhibited so there is no movement of air into the larynx
* elevates and vocal folds tighten to prevent food from entering the trachea

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25
Q

What is the esophageal phase

A
  • Bolus is forced ahead of the peristalic wave down into the stomach
  • if bolus does not make it with the primary peristalic wave the distension of the esophagus initiates this secondary wave is not limited by swalloing center
  • secondary wave is not initiated by the swallowing center
  • comes from t he intrinsic nerve plexus
  • persitalic waves relax lower esophageal sphincter to allow bolus into stomach
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26
Q

Describe the end of the esophageal phase

A
  • mucus is used as lube throughout the esophagus for easy movement
  • protective layer from gastirc juices
  • with exception of swalling, LES remains tightly contracted to prevent the reflex acidic stomach contents from getting into the esophague
  • known as the gastric relfex
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27
Q

What is the stomach and what are its parts

A
  • J shaped chamber
  • divided into 3 areas
  • seperated by internal barrier called the pyloric sphincter

Fundus
* lies above the esophageal opening

Body
* main part of the stomach

antrum
very musclar lower section
barrier between the stomach and the small intestine in the pyloric spinchter

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28
Q

What are the 4 stages of gastric motility

A
  • FIlling
  • storage
  • mixing
  • emptying
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29
Q

Describe gastric filling

A
  • stomahc volume is 50mL
  • expands to 1000mL
  • even 4000mL
  • deep folds that get smaller and flatten out as it expands allows for expansion without increase in tension or pressure
  • occirs by the vagally mediated process called receptive relaxation
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30
Q

Describe gastric storage

A
  • pacemaker cells in the fundus generate slow wave potentials travel down the length of the stomahc
  • they do not necessarily reach threshold
  • depends onm the level of smooth muscle excitability when the threshold is reached
  • persiatlic wave sweeps over the funcus down towards the pyloric sphincter
  • food is stored in the body of the stomach and gradually moved into the muscular antrum where mixing occurs
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31
Q

What is gastric mixing

A
  • With each peristalic wabe
  • chyme is pushed towards the pyloric spinchter
  • usually in an almost closed position
  • cannot pass through it
  • Chyme folds back upon itself only tobe propelled forward and folded back over and over
  • process is called retropulsation
  • ensures chyme is thrououghly muxed until the particles are small enough for emptying
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32
Q

What is gastric emptying

A
  • with each wave chyme is pushed through the spinchter
  • the antrium is 30mL
  • very strong wave occurs a a greater volume of chyme will pass before the sphincter closes again
  • intensity of the peristalic wave is under the influence of various signals within the stomach
  • Main factor influencing the strength of contract is the amount of chyme in the stomach and its fluidity
  • Greater volume of chyme
  • more ditension and therefore more contractions
  • faster chyme becomes a liquid the faster it will pass through
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33
Q

Describe gastric emptying in terms of factors

A
  • duodenum also unfluences the rate
  • Sends signals to reduce gastric emptying
  • neural responses are mediated by the intrinsic nerve plexus and autonomic nerves
  • called the enterogastric reflex
  • hormones are released from the duodenal mucosa
  • Two important homrones are secretun and cholecystokinin
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34
Q

What is gastric emptying in terms of fat

A
  • Most potent stim for inhibiting gastric emptying
  • Takes long time for fat to be digested and absorbed
  • fat reduces gastric emptying to allow more time to process
  • high fat meals remain in stomahc for 6 hours
  • high protein can empty in 3 hours
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35
Q

What is gastric empyting in terms of acid

A
  • stoamch secretes HCl mixed with chyme
  • duodenum neutrakizes it to prevent damage
  • secretions from the pancreas does this
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36
Q

Describe hypertonicity in gastric emptying

A
  • Proteins and carbs are broken down into smaller molecules
  • can have a dramatic increase in osmoarlity
  • water moves freely
  • Moves into the lumen by osmosis
  • if digestion is faster than absorption
  • increase the osmaorlity will bring enough water to distend the duodenum and potentially decrease plasma volume
  • Increased osmoalrity in the duodenum reflexively inhibit gastric emptying
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37
Q

Describe distention in the case of gastric emptying

A
  • More the duodenum is distended slower the rate of gastric emptying
38
Q

What do gastric secretions do

A
  • Luminal surface of stomach has pockets
  • formed by infolding of the gastric mucosa called gastric pits
  • at the bottom lie gastric glands
  • 3 types of secretory cells whos exocrine secretions are collectively known as gastric juices
39
Q

What are mucous cells and chief cells

A
  • CHief cells
  • more numerous cells in the gastric gland and secrete pepsinogen

Mucous cells
* Line the pits and entrance to the glands to secerete a watery mucus

40
Q

What is hydrocholirc acid and what does it do

A

Parietal cells actiovely secrete HCl into the gastric pits
empty into the lumen of the stomach and can decrease the pH to as low as 2
Functions
* activates pepsinogen to active form of pepsin
* Breaks down CT and muscle fibers
* Denatures proteins
* kills microogranisms ingested with food

41
Q

How is HCl made

A
  • in parietal cells h2o is broken into H and OH
  • HCO3 that is brought into the parietal cell leaks back into the lumen
  • generated OH conbimes with H to form H2CO3 to make H2O sibce parietal cells ahve large carbonic anhydrase
  • h2o combines with co3 to form h2co3 which partially disassociates in h and hco3 rengerating secreted H
  • HCO is moved into the plasma by Cl HCO3 exchanger
  • exchanger creates a buildup of Cl within parietal cells
  • Then moves through channels down its electrochemical gradient into the gastric lumen
42
Q

What is mucus

A
  • Mucus acts as a lubricant and protects the gastric mucosa against mechanical injurt
  • protects the stomach from the acidic environment
  • even though the lumen in the stomach has pH of 2 mucus layer has a pH of around 7
  • protects stomahc from self-dogestion because it is more alkaline than the stomach lumen
  • Any pepsin that comes near the stomahc in inactivated
43
Q

What are intrinsic factors

A
  • Secreted by parietal cells and is important for the absorption of b!2
  • essentia; for normal body function of RBC
  • \Can only be asbrobed in combining intrinsic factors with a receptor in the latter part of the samll intetsine
  • causiong it to undergo receptor mediated endocytosis
44
Q

What are the other secretory cells

A

G cells
* endocrine cells in the pyloric area
* secrete hormone gastrin
* released by stim of protein in the stomach and AcH from the intrinsic nerve plexus
* only in blood and travels to stomach and fundus where it stims chief and parietal cells to increase secretions

Electrochromaffin like cells
* found in cheif and parietal cells
* in oxyntic mucosa
* secrete histamine
* acts as a paracrine to increase HCl secretion
* Histamine is stimmed by gastrin and AcH

D cells
* Found near the pylorus
* in response to acid they secrete somatostasin acts as a paracrine inhibit the secretions of parietal cells and dECL cells

45
Q

What is gastric digestion

A
  • in stomach food stays semi solid
  • as the perisyalic contractions are not strong enough for mixing

Protein
* Not mixed with gastric juices
* very little protein digestion occurs until the food moves into the antrum
* where it is mixed with gastric juices

**Carbohydrates **
* Food is mixed with salivary amylase
* acid inhibits amylase activity
* interior of food mass is not exposed to acid

46
Q

what is gastric absorption

A
  • No food or water is absorbed through the wall of the stomach into the blood

Alcohol
* Ethanol is somewhat lipid soluble
* diffuses through the cell wall
* absrobed faster in intestinal wall where there is greater surface area
* delyaing alchol absorption can be achieved by eating high fat foods
* consuming alchol slows down gastric empotying and slows absorption

aspirin
* Weak acids such as acetylsalicylic acid are completely unionized in the acidic environment of the stomach
* unionized form they are lipid soluble
* and can cross the plasma membrane of the epithelial linning of the stomach

47
Q

What are the pancreas an biliary secretions

A
  • pancreatic secretions and biliary secretions as they are essential for digestion and are added to the samll intestibe lumen adnd mixed with chyme right after it leaves the stomach
48
Q

What is the exocrine pancreas

A
  • pancreas secretes gastric juices
  • a mixture of pancreatic enzymes and aqueous alkaline secretions
49
Q

What are the pancreatic enzyme types

A
  • Exocrine part is the grape like clusters of secretory cells
  • that empty into the duodenum
  • pancreatic acinar cells secrete 3 different types of pancreatic enzymes
  • proteolytic enzymes
  • pancreatic amylase
  • pancreatic lipase
50
Q

What are the proteolytic enzymes

A
  • everything secreted here is done in its inactive form
    Trypsinogen
  • Converted to the active trypsin by enterokindase
  • embedded into luminal border cells linning duodenal mucosa within secretory vessels
  • trypsin is inhibitor to procest pancrease in case trysinogen is accidentally activated

Chymotrypsinogen
* converted to chymotrypsin by trypsin

procarboxypeptidase
* Converted to carboxypeptidase by trypsin

51
Q

What is pancreatic amylase

A
  • simialr to salivary amylase
  • converts polysaccharides into disaccharide maltose
  • hydrolyzes starches
  • glycogen and most other carbohydrates
  • exception is cellulose
52
Q

What is pancreatic lipase

A
  • only enzyme within entire digestive system that can digest fats
  • hydroluzes triglycerides into monoglycerides and free fatty acids
  • both can be absorbed
53
Q

What is the control of exocrine secretions

A
  • During the cephallic phase
  • small amount of parasympathethic mediated paracrine secretion and during the gasyric phase of digestion
  • further small increased secretion from gastrin
  • bulk of pancreatic secretions under homronal control
  • presence of chyme in the duodenum causes release of secretin and CCK
54
Q

What is secretin

A
  • presence of acid cause the duodenal and judenal mucosa to release secretin into the blood
  • then travels to the pancreas where it stims the duct cells to increase their secretions of the NAHCO3 rich fluids
  • amount of secretin released is propertional to the amount of acid that enter the duodenum
55
Q

What is CCK

A
  • in response to the presence of fats and duodenum
  • in a lesser extend protein in the duodenal mucosa releases CCK into blood
  • travels to the pancreas and stims the pancreayic acinar cells to increase digestive enzyme secretion
  • presence of carbohydrates in the duodenym does not stim the release of CCK
  • since all 3 classes of pancreatic enzymes are syored together
  • high protein meal does not preferntially release proteolytic enzumes
56
Q

What is the liver and fuck does it do

A
  • important for producing bile salts
  • important for fat digestion
    Other functions
  • metabolic processing of fats, carbs, proteins after absorption
  • detoxificaiton and degredation of body wastes, hormonal drugs and foreign compounds
  • synth plasma proteins
  • storage of glycogenm, fats, uron, copper and vitamin
  • Involved in the activation of vitamin D
  • removal of old red blood cells and bacteria
  • excreting cholesterol and bilrubin
57
Q

What is liver blood flow

A
  • Each liver hepatocyte performs the same tasks
  • Perform these tasls each hepatocyte has to be in contact with both arterial blood and venous blood coming from the digestive tract
  • each minute, about 1L of veous blood flows from the digestige system through the hepatic portal vein into the liver to deliver anything that was absorbed

Hepatic artery
* Supplies 250mL of arterial blood to deliver O2 and blood born metabokites

58
Q

What are the lobules

A
  • functional unit of the liver is called lobules
  • hexagonal arrangement surrounding a central vein at each of the 6 corners
  • brain of the hepatic portal vein and bile duct
  • bile ducts converge to form the common bile duct
  • transports bile from the liver to duodeum
59
Q

What is the wedge of the lobe

A
  • Blood from the hepatic portal vein flow from the periphery into the lobule through the capillary like structures call sinosoids
  • run between rows of liver cells towards central vein
  • kupfer cells are macrophagses that line sinosoids and remove old blood cells and bacteria
  • central vein of all lobules converge to create thehepatic vein
  • lowcated between hepatic cells are thin bile arrying channel called the bile canaliculus
  • hepatocytes are constantly secreting bile into the caiculus which carries the bilke from the center of the lobule to the periphery and into the bile duct
  • each hepatocyte is in conatct with a sunosoid on one side and a bile canaliculus on the other
60
Q

What is bile

A
  • Constantly produced
  • does not enter the duodeum duct is guarded by the sphcinter of Oddi that is closed until bile is needed
  • when closed secreted bile is diverted back up to the common bile duct and into the gall bladder for storage

gall bladder can store 50mL of bile and 250mL of the bile that are produced each day
* Composed of manily bile salts
* cholesterol lecithin and bilrubin in an queous fkuid similar to the pancreatic NaHCO3 secretion
* bile salts are derivates of chilesterol and are important for fat digestion and absorption

61
Q

What is enteropatic circulation

A
  • all bile sals are reabsorbed into the iuluem and transported back through the hepatic portal sustem in the liver where they are recycled by secretuin back into the bile
  • receycling between the small intestine and the liver is called neterhepatic circulation

Steps
* Secreted buke salts consist of 9% old, recycled and 5% newly synethsized bile salts
* 95% of bile salts are reabsorbed by terminal iluem
* reabsorbed bile salts are recycled by enterhepatic circulation
* 5% are lost in feces

62
Q

What are the structures of bile salts

A
  • have a detergent like effects on fats
  • convert fat globules in chyme into lipid emulsion of numerous small fats
  • droplets each less than 1mm of diameter
  • effectively increase surface are of the luminal fats for pancreatic lipase
  • bile salts have lipid soluble part
  • interatcs with the surface of fat droplets and a negative charged water soluble end allows the bile salts to decrease the surface tension of lipid droplets and break them into smaller droplets
63
Q

How is fat digested and absorbed

A
  • Polar ends of the bile salts repel each other and prevent the small droplets from coming back together
  • lipi droplets are dispered as emulsification
  • lipase alone cannot penetratde the layer of bule salts surrounding the lipid droplet
  • along with lipase, the pancrease secreted solipase which binds to lipase and the bile salts to hold the lipase at the site of action so it can break down tryglycerides
64
Q

what are micelles

A
  • structure of lipid soluble compounds surrounded by water soluble bile salts are called micells
  • along with lethicin which also has lipid soluble and water soluble ends and cholesterol bile salts form clusters with outer lipophobic shell while maintaining lipophillic core
  • cholesterole is found within this core along with any digested fats and other lipid soluble compounds
  • micellular formation allows lipid solluble substances to be transported within the chyme to the site of absorption
65
Q

What is bilrubin

A
  • not involved in digestion but instead waste producted secreted from bile salts
  • comes from the degredation of hemoglobin in RBC
  • yellowis in colour
  • once in digestive tract bacterial enzymes mainly found uin the large intestine modify its colour to the brown colour associtaed with feces
  • in absence of bile secretions the feces would be greyish white
  • most bilrubin excreted in the feces but some is reabsorbed in small intestine hwere it evebtually excreted in the urine which is why urine has yellow colour to it
66
Q

How is bile secretion regulated

A

Chemical
* most potent chemical signal is bile salts themself
* when the salts are reabsorbed they stim the release in the liver via the enterhepatic system and stim the further release

Hormonal
* Secretin stims the secretion of aqueous alkaline component of bile salts but does not stim the release of bile salts

Neural
* During the cephalic phase
* Vagal stim of the liver promotes the release of bile salts before food reaches the stomach or intestine

67
Q

How is bile stored in the gall bladder

A
  • secreted by the liver but cannot entert he duodenum because of the spinchter of oddi is closed
  • Backs up the gall bladder for storage
  • active transport of salt out of the gall bladder
  • with water osmotically following it concentated the bile 5 to 10 times
  • during digestion when chyme reaches the small intestine
  • presence of fat in the duodenum triggers the release of cck
  • CCK both causes the gall bladder to contract and cause the spinchter of oddi to relax allowing the bile to flow into the duodeum

–
* Gall bladder concentrated bile
* they precipitaet and form gallstones
* it can be removed with no negative effets on digestions
* bile is still produced but it will not be stored in the bladder but in the common bile duct where it dillates

68
Q

What is a basic overview of the small intestine

A
  • where majority absorption occurs
  • in 3 parts
  • duodenum
  • jejum
  • iluem
69
Q

What is intestinal motility

A
  • segmentation which both mixes and slowly propels chyme
  • movement is not peristalic

Steps
* occurs localized concentric contractions occur ever few centimeters, trapping chyme in the relaxed areas
* after a brief period of time the contracted areas relax and and ring like contraction appear in the priviously relaxed areas
* Chyme is moved back and fourth for thourough mixing and is slowly moved forward

70
Q

What is intestinal segmentation

A
  • in the empty iluem caused by gastrin
  • secreted due to presence of chyme in the stomach
  • gastroileal reflext, segmentation ihjtiated by the pacemaker cells that generate a basic electrical rhythm BER
  • similar to be seen in the stomach
  • BER brings circular smooth muscle ot threshold then contratcions occur within the duodeum and jejum.
  • BER if 12 minytes while 9 minute in the terminal iluem
  • hormone gastrin and exterinsic nerv activity
  • segmentation is absent between meals
71
Q

What is the migrating motility complex

A
  • Most of the meal is absorbed through the segmentation contractions end and are replaced by migrating motility complex
  • motility consist of weak peristalic waves that are sustained for only short distances before dying out
  • They start at the stomach and slowly move their way down the intestine
  • Purpose is to move any remnant of the pervious meals, any mucosal debris and any bacteria forward towards the colon
  • WHen peristalic waves reach the end of the iluem they start again at the beginning od the duodenum
72
Q

What are the secretions and digestion of the small intestine

A
  • mucosa has exocrine glands secrete 1.5L a day to provide lube and protections
  • provides lots of H2O for hydrolytic reactions carried by the enzymes
  • no intestinal enzymes are secreted into the small intestine lumen
  • digestion is the reuslt of pancreatic enzymes
  • some intestinal enzumes are membrane bound and not secreted into lumen
  • Luminal furface of small intestine has smaller hair like projections called microvilli that brush the border which aid in the process of absorption
  • the brush also contains membrane boudn enzymes which are categorized into 3 classes

Enterokinases
* Convert pancreatic trypsinogen to trypsin

Disaccharides
* Complete carb digestion by hydrolyzing disaccharides maltose sucrose lcatose into monosaccharides

Amino peptidases
* Hydrolyze small peptide fragments into indiividual amino acids

73
Q

How does absorption work in the small intestine

A
  • Primary function of the small intestine
  • all carbs, proteins, fat electrlyeys vitamins as the majoritu of water are absroebd in this part of the digestive system
  • All absorbotption occurs in the duodenum and jejum
  • iluem is vital for absorption of things like vitamin b12 and bile salts
  • on a daily basis 200g or more carbs 100g or 50g or more of amino acids and 7-8L of water are absorbed
  • the absorptive capapcity of the snall intestine is much greater
  • anything ingested will be absorbed of some compouinds such as Ca and Fe regulated with excess being excreted in feces
  • Mucosa linning the small intestine is highly adapted for absorption as it has very large surface area and has a variety of specialized transport mechanisms
74
Q

How is surface area maximized in the small intestine

A
  • inside of the epyhelial linning is not smooth
  • inenr surface has many circular folds
  • there are projections called villi which increase the surface area 10 fold
  • the epithelail cells of the villi also have projections called microvilli
  • the brush the border with increase the surface area 20 fold
75
Q

How is water absorbed in the small intestine

A
  • Absorbed passivelu and actively
  • chloride follows sodium from the electrical graident
  • and water follows Na from the osmotic gradient

Passive
* in appropriate eletrochem graident
* moves down the gradient into the intersitial fluid
* moving between the intestinal epithelial cells through leaky tight junctions

Active
* Movement of sodium through cells required active transport
* passively cross luminal membrane through Na channels or cotransported with glucose or amino acids
* once inside and epithelial cells, Na is pumped out acorss the basolateral membrane and into the intersitial fluid where it diffuses into the capilalries

76
Q

How is protein absorbed in the small intestine

A
  • 3 sources of exogenous proteins need to be digested and absorbed
  • they account for up to 40g
  • they need to be broken down into amino aicds and small peptides
  • absorbed by secdonary active transport similar to glucose and galactose
  • small peptides have different carruer and are broken down both by the brush and the brush border
  • amino peptides as well as intracellular peptidases. Amino acids move out across the basolateral membrane and into the blood

Steps
* digestive enzymes are all proteins and need to be absorbed
* proteins from the epithelial mucosal cells that have been sloughed off
* plasma proteins that normally leak from the cpaillary into the digestive tract lumen

77
Q

How are carbohydrates absirbed in the small intestine

A
  • All carbohydrayes are absorbed as monolsaccharides through active transport
  • transported either by sodium onosaccharides cotransport of sodium independent facillitated diffusion
  • also important to note there are preferences for monosaccharide absorption

Galactose
* transported first and can be absorbed by secondary active transport
* Basolateral NAK pumps require energy and bring NA into the epiethlial cells
* Na is then used by cotransport
* Carries to bring glucose and galactose into the epithelial cell
* Once concentrated inside
* galactose moves down its concentration graident across the basolateral membrane and into blood

Glucose
* transported second and very similar to galactose
* absorbed by secondary active transport
* basolateral Na K pumps require energy and bring Na into the epithelial cells
* this Na is then used by cotransport carrier to bring glucose and galactose into the epithelial cell
* Once concentrated inside glucose moves down its concentration graident acorss the basolateral membrane and into the blood

Fructose
* Transported las and is transported by facilitated diffusion

78
Q

How are fats aborbed in the samll intestine

A
  • Bile salts emulsify fats and that pancreatic lipase digest the truglyceride into monoglyceride and fatty acids within the fat droplets
  • when micelles reach lum,inal membrane of epithelial cells
  • monoglycerides and fatty acids can diffuse from miccels into the epithelial cells
  • micells then reyurn to the chyme to pick up more triglycerides
  • repeated alonh the length of small intestine
  • terminal iluem bile salts are reabsorbed by active transport
  • Once inside the epithelial cells
  • monoglycerides are free fatty acids converted back into tryglycerides
  • tryglyericde are attracted to each other and form lipid droplets and they coated with a layer of lipoprotein to make fat droplests water soluble in this form they are called chylomicrons
  • they leave endothelial cells by exocytosis
  • capilalries have a bsement membrane
  • chylomircrons cannot directly enter them
  • instead they are taken into the lympathetic sustem before being delivered to the blood
79
Q

How are minerals such as iron absorbed in the small intestine

A
  • Essential for hemoglobin
  • 15-20mg a day is dietary intake, men are 0.5-1mg
  • women need more iron for menstrual flow

Steps
* amoynt dpends on its state. Ferrous iron is more readily absorbed than ferric iron. Only a portion of ingested iron is in the right form to be absorbed
* dietary ironis absorbed into samll intestine eputhelial cells and is imemdtaely needed for RBC. IS transffered into the blood
* once inside the epithelial cell has 2 fates
* if not immediately needed for RBC - delivered to blood where its bound to transferrin for bone marrow delivery
* if not immediately used it is stored within the epithelial cell in granular form called ferritin
* any ferritin is also dumped into the lumen when the epithelial cell is sloughed off within 3 days. All excess iron is excreted in feces

80
Q

What is diarrhoea

A
  • 2nd major loss of water
  • disrupts acid base balance
  • beneficial for rapid emptying
  • for removal of potentialy harmful materials
  • excessive prolongation causes dehydration and metabolic loss of HCO3. There are 3 main cuases of siarrhoea

Excessive samll intestine motility
* Arises from the local irritation or emotional stress
* increased motility does not allow sufficent time for water absorption

Excess of osmotically active particles
* undigested lactose exerted as osmotic effect to draw water into the intestines

Toxins from the cholera and other microoragnisms
* These toxin promote excessive fluid secretion by the intestinal mucosa

81
Q

What is the large intestine

A
  • made of cecum, appendix and colon
  • 500-1500mL of chyme enters here
  • this chyme consist of indigestible food elements such as cellulose, unabsorbed bilary secretions and some fluids
  • upper half of yhe colon extracts a little more Na and water but the majorutt of it moves to the lower half for storage before it is eliminated
82
Q

What are haustral contractions

A
  • large intestine has circular and longitudinal smooth muscle layers
  • longtitudal layers do not completely surround the inestine
  • they are organized into 3 distinct bands
  • taenia coli
  • its length is shorter than underlying smooth muscle in the mucosal layer
  • if these layers were to be stretched out they would bunch up and form sacs called haustra
  • they are not in a fixed position and can change location as a reuslt of the contraction
83
Q

How does the large intestines motility work

A
  • mainly haustral contractions
  • slow and non propulsive
  • they are generally autonomous
  • rhythmicity of colonic smooth muscle cells are analogous to segmentation
  • frequency it a lot lower
  • in the duodeum segmentation occurs ever y12 minute. Haustral contractions can be as few as 2/hour
  • they care controlled by localled mediated reflexes including the intrinsic nerve plexus
84
Q

What are large intetsinal mass movements

A
  • usually follow meals
  • marked increase in the haustral contractions
  • These are cakked nass movements and are driven by gastrocolic reflex
  • mediated from the stomach by the release of gastrin and by the extrinsic autonomic nerves
  • when a new meal enters the stomach, the gastroileal reflex moves the contents of the small intestine to the large intestine
  • gastrocolic reflex moves the contents of the large intestine to the rectim and trigger the defecation reflex
85
Q

What are the defecation reflex

A
  • Fecal matter fills the rectum
  • ## stretch receptors send impulses to the spinal cord which send reflex signals via parasympathetic system to the distal colon
  • ## causes the internal anal spinchter (smooth muscle involuntary) to relax and cause contractions in the signoidal colon and rectum
  • if the external anal spinchter (skeletal muscle voluntary) is relaxes then defecation will occur. If the timing is appripate volunatry control of the externa anal spinchter keep it closed

-
* When defecation occurs
* contractions of the abdominal muscles and a forcible expiration against the closed glottis
* increase the abdominal presusre and aid in expelling the feces
* rectum gradually calms its activity and the urge to defecate subsides
* at the next mass movement, more feces enters the rectum and the defecation reflex repeats

86
Q

What are the secretions of the large intestine

A
  • no enzymes in this bitch
  • secretions here are alkaline nigga
  • mucus to lubricate and protect the colon by neurtalizing acids produced from bacterial fermentation
  • in contrast to the other digestive organs
  • colon does not secrete anti bacterial agents
  • slow motility actually favours bacterial growth
  • any bacteria that doesnt reach the colon can thrive
  • 10k dif species of bacteria that comrpsie the microbiome in the colon and are beneficial
87
Q

What are the roles of the gut microbiome

A
  • enhance intestinal immunity by competing with potentially pathogenic microbes for nutrients and space
  • promoye colonic motility
  • make nutrional contributions as a result of their metabolism
  • helps maintain the integrity of the colon mucosa
88
Q

What is the gut microbiome

A
  • largest number of bacteria
  • by age 2 gut flora has been established
  • same with intestinal epithelum and the intestibal mucosal barrier secreted by the epithelum
  • have co developed in a way which not only provides a barrier to pathogenic organisms but also supportibe of the gut flora
  • research on the topic of the microboime has dramatically reshaped our understanding of human biology
  • Findings from this research has suggested that the compisition of our microbiome may mediate digestion as well as diseases processes
89
Q

What is large intestine absorption

A
  • luminal surface is relatively smooth so low SA for absorption
  • lacks specialized transported found in the small inestine
  • so only really absorbs salta nd water

Large intestine is not a major route of elimination for the body

90
Q

Irritable bowel syndrome

A
  • no severe signs or symptoms
  • symptoms are
  • cramping
  • abdominal pain
  • bloayin
  • diarrhea
  • constipation or both
  • it is chronic

PHGY216 (6 decks)

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