EK B2 Ch5 Digestive System Flashcards
Digestive system
- Breaks down food and absorbs constituents
- Can be thought of as a “tube within a tube”
- Digestive tract begins at mouth and ends at anus
- Digestive system is specialized (cows can digest plant cellulose, humans can’t)
Three classes of organisms classified by diet
- Carnivore = meat eating
- Herbivore = plant eating
- Omnivore = meat and plant eating
digestive tract
- Digestive tract and liver are contained in the peritoneal cavity
- Digestive tract has several tissue layers
- Mucosa secretes mucus and enzymes, is the epithelium that lines inside of tract
- Submucosa surrounds mucosa, contains blood vessels, lymph vessels, and nerves
- Inner muscle layer (circular muscle) surrounds submucosa
- Outer muscle layer (longitudinal muscle) surrounds inner muscle
- Serosa and peritoneum surround muscle
GI motility and peristalsis
- Smooth muscle contraction in GI enables food movement and mixing
- Peristalsis is wavelike smooth muscle contraction that propels food forward
- Peristalsis functions throughout digestive tract
Mouth and ingestion
- Food is ingested and tasted in the mouth
- Mechanical digestion by teeth and tongue
- Lubricate food with saliva and chew to smaller bits
- Chemical digestion of carbohydrates
- Salivary amylase breaks down starch → smaller sugars
- Chewed food is shaped into a bolus
- Tongue moves bolus to back of mouth, swallowing moves bolus into pharynx
pharynx
Pharynx and esophagus do not digest food
• Pharynx is entrance to digestive and respiratory systems
pharynx and esophagus
- Pharynx and esophagus do not digest food
- Pharynx is entrance to digestive and respiratory systems
- Esophagus leads to digestive system
- Trachea leads to respiratory system
- Epiglottis is a flap that covers the trachea during swallowing
- Peristalsis moves bolus through pharynx to esophagus
- Lower esophageal (cardiac) sphincter controls entry of bolus to stomach
- Sphincter = smooth muscle ring
sphincter
= smooth muscle ring
trachea
leads to respiratory system
Esophagus
Esophagus leads to digestive system
stomach 2
- Mechanical digestion from churning (smooth muscle contractions)
- Chemical digestion of protein
- Little absorption in stomach (only water, alcohol, a few drugs)
- Stomach is elastic, folds (rugae) expand to accommodate food
Secretions include alkaline mucus, hydrochloric acid, and pepsinogen zymogen
- Secretions controlled by hormones and nervous system
- Acid environment (pH ~ 2)
- Acidity inactivates bacterial and viral pathogens, denatures proteins
- Acidity inactivates salivary amylase, activates pepsinogen → pepsin
- Mucus and tight junctions protect stomach lining
- Lack of mucus or failure of junctions → ulcer (sore)
pepsin
- Acidity inactivates salivary amylase, activates pepsinogen → pepsin
- Pepsin hydrolyzes proteins into shorter polypeptides
Chyme
- Chyme = soupy, partially digested food mixture
- Chyme exits stomach through the pyloric sphincter
stomach cell types
- Chief cells secrete pepsinogen
- Parietal cells secrete hydrochloric acid (pump H+ and Cl–)
small intestine
- Chemical digestion of carbohydrate, protein, and lipid
- Absorption of most nutrients
- Longest part of the digestive tract
- Three regions of small intestine: duodenum, jejunum, ileum
- Most digestion takes place in duodenum
- Most absorption takes place in jejunum, ileum
- Acidic chyme is neutralized by sodium bicarbonate (from pancreas)
- Ileocecal valve controls exit to large intestine
small intestine enzymes and secretions
- Key digestive substances in small intestine are made in the pancreas and liver
- Small intestine secretes a hormone called cholecystokinin (CCK)
- CCK stimulates release of bile from gallbladder and enzymes from pancreas
Cholecystokinin is a peptide hormone - Bile is made in the liver and stored in the gallbladder
- Proteases, lipases, amylase, DNAse, RNAse from pancreas
- Small intestine makes some of its own enzymes to hydrolyze protein and carbohydrates
Bile
- is made in the liver and stored in the gallbladder
- Bile emulsifies fats (mechanical digestion increases fat surface area, then lipases perform chemical breakdown)
CCK
- Small intestine secretes a hormone called cholecystokinin (CCK)
* Cholecystokinin is a peptide hormone - CCK stimulates release of bile from gallbladder and enzymes from pancreas
Aminopeptidase
Aminopeptidase cuts protein from N terminus
Small intestine makes some of its own enzymes to hydrolyze protein and carbohydrates: aminopeptidase is one of them
Maltase
Maltase hydrolyzes maltose → glucose and glucose enzyme of small intestine!
Sucrase
Sucrase hydrolyzes sucrose → glucose and fructose small intestine enzyme
Lactase
Lactase hydrolyzes lactose → glucose and galactose small intestine enzyme
small intestine microscopic structure
- Small intestine surface has “brush-border” appearance
- Surface is covered with villi (finger-like protrusions)
- Each villus is a single layer of cells
- Each cell has many microvilli
- Villi and microvilli vastly increase surface area
- Large surface area aids absorption and digestion
nutrient absorption in the small intestine
- Nutrient absorption occurs by diffusion, passive, and active transport
- Two key routes for nutrient absorption: blood and lymph
- Each villus has capillaries and a lacteal (lymph vessel) • Amino acids and glucose → capillaries → blood
- Blood flows directly to liver via hepatic portal vein
- Fatty acids and glycerol → packaged as chylomicrons → lacteal → lymph
chylomicrons
- Chylomicrons are protein-coated fat droplets
- Chylomicrons are made from glycerol and fatty acids in small intestine epithelial cells
large intestine
- Large intestine is also called the colon
- Cecum, ascending colon, transverse colon, descending colon, sigmoid colon
- Sigmoid colon leads to rectum and anus
- Appendix is at end of cecum
- Colon absorbs H2O and salt from chyme
- As water is absorbed, residual undigested food is converted to feces
- Colon has more bacteria than any other part of digestive tract
- Mutualistic bacteria digest some food and provide vitamin B and K
large intestine chyme
- If chyme moves too quickly, water is not absorbed, stool is watery: diarrhea
- If chyme moves too slowly, too much water absorbed, stool is hard: constipation
pancreas
- Produces sodium bicarbonate to neutralize chyme in small intestine
- Secretes digestive enzymes (exocrine) into small intestine
- Trypsin (from trypsinogen) hydrolyzes peptides
- Chymotrypsin (from chymotrypsinogen) hydrolyzes peptides
- Carboxypeptidase (from procarboxypeptidase) hydrolyzes peptides from C terminus
- Pancreatic amylase breaks down carbohydrates
- Pancreatic lipase breaks down fats into fatty acids and glycerol
- RNAse and DNAse digest nucleic acids
Chymotrypsin
• Chymotrypsin (from chymotrypsinogen) hydrolyzes peptides
Trypsin
Trypsin (from trypsinogen) hydrolyzes peptides
Carboxypeptidase
Carboxypeptidase (from procarboxypeptidase) hydrolyzes peptides from C terminus
Pancreatic amylase
Pancreatic amylase breaks down carbohydrates
Pancreatic lipase
• Pancreatic lipase breaks down fats into fatty acids and glycerol
Liver
- Key metabolic center
- Makes bile (stored in gall bladder)
- Common bile duct conveys bile to small intestine
- Nutrients from digestion flow through hepatic portal vein to liver → circulation
- Stores iron and fat soluble vitamins: A, D, E, K
- Detoxifies drugs and alcohol
- Converts glucose → glycogen
- Converts precursors, including pyruvate, oxaloacetate, glycerol and amino acids → glucose (gluconeogenesis)
- Converts ammonia → urea
- β-oxidation of fats
- Deamination of proteins
- Control fat metabolism and makes cholesterol
- Liver can regenerate itself from 1/4 of original size
Small intestine 3 parts:
3 sections=Duodenum, jejunum, ileum
Duodenum= first one third of small intesntine is where most chemical digestion takes place in body! Ton of chemical breakdown of food at this point, then the much more chopped up stuff is much smaller pieces of everything moves onto jejunum and ileum where most ABSORPTION takes place, where little molecules at that point down to monomers and amino acid, where stuff is absorbed and passes out of digestive tract into the rest of the body!!
Small intestine needs a TON of help, as a reminder liver and pancreas and gall bladder which works with liver are all sending stuff over to small intestine
So helping really sending stuff to duodenum first part of small intestine, where so much chemical digestion is taking place
We have the acid coming from stomach with a pH of 2, small intestine does not have stuff to protect itself so acid chyme, first role of business for duodenum is to neutralize that aciditiy, so small intestine shouts out to pancreas to send over something to neutralize the aciditiy, pacnreas sends sodium bicarbonate solution
From gen chem this is basic and what alters pH of all this material gushing in small intestine so doesn’t burn a hole in the wall, so pancreas also does a whoel lot more than that, so first to know pancreas sends sodium bicardboante and a lot of other stuff to neutralize chyme in duodenum but then TONS of digestive enzyme for every macromolecule
Pancreatic juice
trypsin another proteases and chymotrypsin hydrolyzes pepsides
carboxypeptidase, another thing that breaks down peptides
pancreatic amylase to break down carbs and prancreatic lipase to break down fats into fatty acids and glycerol= all of this is sometimes referred to as pancreatic juice, pancreas just sends over big stew of enzymes plus sodium bicarcboante*
endocrine secretions are hromones secretd from cells diretly into blood stream, exocrine secretons are secreted mostly digstive enzymes when mention exocrine secreton! Those are secreted from cells but don’t go into blood stream secreted by ducts!
The fact that all of the pancreatic juice goes through that little tube into the small intestine, that makes all of these enzymes exocrine secertions becuas ethey are going through ducts!
Pancreas is famous for being what kind of organ?
Pancreas is famous for being an exocrine organ and endocrine organ, in sense that it secretes all of these enzymes so it is exocrine, but also secretes hromones= insulin and glucagon** so it is endocrine!
Different cells in pancreas that do different thing but pancreas can wear an exocrine and endocrine hat, usually both!
exocrine secretions are secreted mostly digstive enzymes when mention exocrine secretion; all of these enzymes are exocrine secertions becuase they are going through ducts!
Bile
Fat- trickier for digestive system to handle, harder to solubilize its hydrophobic, if you have a big chunk of butter or something its harder to process in aqueous environment, so mention bile!
BILE= main thing in auxillary organs liver connected closely to digestive tract, liver produces bile and then stored in gallbladder
Gallbladder is the little pocket that sits on bottom of liver, liver makes bile, bile is stored in gallbladder and when food enters small intestine–> bile sent over to first part of small intestine we are talking about
Role of bile acts as emulsifier or detergent= what it is doing is physically breaking up bigger chunks of fat into smaller chunks of fat, same way soap or detergent would, gets in there and helps to solibuilize chunks of fat, physical not a chemical purpose then once the big chunks of fat are broken into smaller chunks of fat then enzyme lipase, on our list of enzymes from pancreas, lipase can get in there and have enough access to do chemistry hydrolyze bonds in triglcyerides*
So then material all chopped up, have a lot of smaller monomers at this point, smaller peptides and aa, triglycerides chopped down to fatty acids and glycerol, sugar broken down to smaller sguars glucose fructose, lactroses, picture smaller monomers moving onto jejunum and ileum where absorption occurs once chopped up everything into smaller parts!
What goes into the blood stream right to the liver?
The lining example of up and down, up and down surface, top of the lumen, interior of tube, and the finger like projections project up into lumen!
Notice that inside of this there is a capillary and lacteal! The green thing is lacteal or lymph vessel! The break down products of carbs and proteins simple sugars and amino acids, small peptides, will be absorbed directly across epilethial layer of cells into capillarys, look at red arrows in picture, glucose goes straight across epitheial cells into blood/ amino acids right into blood!
The breakdown products of fats take a little bit of a different path, but sticking with glucose and amino acids they go right into blood stream from lumen of small intestine, into a capillary inside one of these villi*
To really connect the dots, the blood in that capillary can come together into larger vessels and go into hepatic portal vein into liver, so blood flow from the digestive system, the blood rich in nutrients that have just been absorbed goes righ to the liver! Through the hepatic portal vein, v important when talking about metabolism, talking about how liver gets first crack and nutrients. The liver has glucokinase instead of hexokinase so can skim off excess glucose and store it as glycogen, can do glycogen making pathway by time the blood gets passed the liver, it should have a tightly regulated concentration of glucose, there shouldn’t be crazy high blood sugar anymore
How do fats get
From liver gets first crack and nutrients, has glucokinase instead of hexokinase so can skim off excess glucose and store as glycogen, can do glycogen making pathway, by time the blood gets passed the liver! Blood not as high in glucose anymore past liver!
Then blood continues to travel around the body, and insulin is necessary for getting glucose into the cells as blood goes through muscle cells need insulin, insulin helps the sugar get into cells and then the cells can do glycolysis and krebs cycle and make atp and then really connected to all metabolism stuff talking about
Fats get into small inestines, broken up physically by bile, then broken up chemically by lipase, then fatty acids and glycerol and other broken down lipids, but then they don’t pass directly into blood, instead they will go into lympathic system, into that lacteal green vessel can see inside villus!
Triglycerides broken down and fats broken by lipase to glycerol and fatty acid some monoglycerides as well smaller breakdown products, those smaller breakdown products go into tan colored epithetial cell then built up again
Triglycerides are reassembled inside the cell, and then they are further packaged with proteins and glycolesterol into these spheres called chylomircons* so in the epithetlial cells lining small intestine chylomicrons made and then go into green vessels called lacteals do not go directly into blood stream* so then everything in lacteal or lymp vessels circulates around and then eventually gets poured into regular veins and venus circulation, duct called thorasis duct near each shoudler, all this stuff gets emptied into regular blood circulation just doesn’t go there right away! Can talk a lot more detail about this lympathic system with immune system, second transport system picks up chylomicrons to around…….? liver uses this to make LDL and HDL good cholesterol versus bad cholesterol*
Classic MCAT question which of the following is not absorbed from small intestine=
Things like glucose are absorbed from small intestine into blood, but chyromicrons are produced in the cells that line the small intestine* made in the cells the lining of the small intestine, up in pink part is lumen fo small intestine, where all digestion taking place
chyromicrons not absorbed in lumen don’t exist in lumen produced in cell!
Liver facts
It converts ammonia to urea!
With proteins you can hydrolyze proteins to amino acids then clip off amino group because nitrogen needs to go off of the molecule for the moelcuel to fit into a lot of metabolic pathways we know about, so if cut an amino group off of an amino acid first thing get is ammonia= nh3!
Ammonia is pretty toxic do not want a lot of ammonia floating around in blood, can make blood too basic v toxic for many different reasons, send ammonia to liver to be converted to urea, urea form in which we keep / want our nitrogen based waste, want in urine, excrete nitrogen based waste as urea!!!
So liver responsible for this step taking ammonia comes from amino acid, turning into urea and then kidney gets rid of urea!
Cool crazy fact about liver is can regenerate itself from quarter of riginal size, certainly can’t do that with heart, can’t cut a donor heart in half and give to two different ppl but can do that with liver! A liver can regrow and regenerate itself pretty special among our organs
Our body has a method to safely package ammonia in a less toxic form to be excreted. This safer compound is urea, which is produced by the liver using 2 molecules of ammonia (NH3) and 1 molecule of carbon dioxide (CO2). Most urea is then secreted from the liver and incorporated into urine in the kidney to be excreted from the body, as shown below.
Liver converting ammonia into urea
Ammonia is pretty toxic do not want a lot of ammonia floating around in blood, can make blood too basic v toxic for many different reasons, send ammonia to liver to be converted to urea, urea form in which we keep / want our nitrogen based waste, want in urine, excrete nitrogen based waste as urea!!!
So liver responsible for this step taking ammonia comes form amino acid, turning into urea and then kidney gets rid of urea!
Ammonia= NH3
Our body has a method to safely package ammonia in a less toxic form to be excreted. This safer compound is urea, which is produced by the liver using 2 molecules of ammonia (NH3) and 1 molecule of carbon dioxide (CO2). Most urea is then secreted from the liver and incorporated into urine in the kidney to be excreted from the body, as shown below.
Bile 2
Bile made in liver, stored in gall bladder and released from gall bladder
It is physiclally breaking down big blobs of fat into smaller blobs** the enzyme that will chemically digest fat after that is lipase
How is glucose broken down….
Glucose broken down and then reasborbed mostly in jejunum and ilenum, then goes through capillaries then hepatic portal vein
Lipase breaks down trigyclerides> free fatty acids go into epiphelial cells lining small intestine* but then they get build up again intro triglycerides and then built up even more through packages with proteins into chylomicrons
Chylomicrons don’t go directly into blood which go into lacteals part of lympathic system then everything in lympathic system dumps into regular system by way of thorsaic duct by shoulder
Under normal circumstances all glucose should be absorbed in proximal tube, if not shows up in urine and sign of diabetes or high blood sugar***
Fatty acid image
Q. 16. Which of the following is NOT absorbed from the intestinal lumen?
a. Chylomicrons
b. amino acids
c. Fatty acids
d. Glucose
Answer is a Chylomicrons
- chylomicrons from there go into green lacetal at hte bottom and from there they circulate in lymphatic system and then all that material in lympahtic system/ fluid in lacteals gets dumped through pores into thoracisc duct in shoulder and hten goes into veins
- chylmocirons never present in lumen of small intestine, only created inside of that epithelial cell, in tan*
- What is a lacetal:
a. absorb glucose from lumen
b. carry amino acids to the liver via the hepatic portal vein
c. transport chylomircons
d. are present within intestinal eptithelial cells
answer is c transport chylomicrons
small vessel that transports fluid through the lymphatic system, sometimes they refer to it as a lympth capillary*
chylomicrons pass from epithelial cells lining the small intestine and transported by lacetals**
- Cholera toxin (vibrio cholerae) stimulates the excessive secretion of chloride ion into the intestinal lumen. Na+ ions follow passively. Which of the following would you NOT expect as a result?
a. Diarrhea
b. Increased movement of water into the lumen
c. Subsequent increase in aldosterone levels
d. Constipation
d. constipation
the lumen of a tube would be like the inside of the tube, can tlak about the lumen of any enclosed thing but here the lumen of the intestine means* inside the tube*** also thinking lumen of ER for protein synthesis, again just means interior*
if we have a cholera toxin causing cl- extra inside of the lumen if think about balance of solute and water, H20 will stay in the lumen more becuase of more solute extra Cl- so all of this extra water that otherwise woud have been reabsorbed, but hanging around because we know water likes to follow solute so becuase of cholera all this excess Cl- so the water hangs out and then the whole thing moves merrily along and by the time all that waste material leaves the body it is much more watery then it would be otherwise*
Would water come in as well following Na+ from outside lumen into colon?- mainly all water already there just doesnt get absorbed because Na/cl-, lot of it is supposed to get absorbed and if it doesnt that is a huge amount of water loss
crazy statistics of ppl which cholera lose body water weigh 10% of water in hours, dramatic and often fatal lose of water* suddenly becasue of all of this* why for ppl who have prompt and good medical care you would not die of water loss you need to be rehydrated and body wait it out. if you do not have access to that you lose too much water fast, so fast and fatal amount of water loss nothing can do
Image of what cholera issues would look like:
What does deamination look like?
deamination of proteins happens in liver
Conversion of ammonia to urea looks like….
