Flashcards in Digestive system lecture Deck (141):
What biomolecule is digested in the stomach?
Primarily proteins, a little bit of fat
Technical term for the chemical breakdown of molecules into smaller biomolecules
Process of taking biomolecules (usually) in their smallest form and moving it either into the blood or the lymph?
What is taken into the lymph?
Fat is taken into the lymph
Most of the digestion takes place in the?
small intestine, also where absorption takes place
Process of moving certain substances i.e. signal molecules, enzyme, or hydrochloric acid from a cell into the lumen of the GI tract?
pH of gastric juice?
What else is in there besides hydrochloric acid?
What protects the stomach from the strong acid?
Mucus layer that contains bicarbonate which protects the cells of stomach from extreme pH of gastric juice
What is secreted into the stomach?
Zymogens, brush border enzymes
Enzymes built into the microvilli
Brush border enzymes
Which type of muscle activity would cause squeezing and mixing
Segmental contractions, also called segmentation
Which cells secrete hydrochloric acid in the stomach?
Which cells secrete enzymes in the stomach?
In the stomach which cells secrete paracrines?
Enterochromaffin-like (ECL) cells secrete histamine. D-cells secrete somatostatin
Pepsin breaks peptide bonds but is secreted....
In its inactive form called pepsinogen
Breaks down fat a little bit in the stomach
What is motility
It is more than movement of peristalsis and segmental contractions, even chewing your food, putting food in your mouth
Swallowing, putting food into the esophagus
Different kinds of secretion
When you think of the muscle layer lining the GI tract there are two arrangements of the smooth muscle
1) Some muscle fibers are called longitudinal, they run the length of the tract. They shorten and lengthen
2) Others are called circular, when they contract they squeeze, these push behind the bolus & mixes the food
They coordinated together to move the bolus forward
Smallest component of triglyceride.
In the GI tract you end up with a?
Monoglyceride & fatty acids to get it out of the GI tract then it forms chylomicron
We get glycogen from?
We get starch from
We want to convert galactose & fructose into?
Total fluid input into digestive system.
Total fluid removed from digestive system
9 liters into lumen
9 liters removed from lumen
Motility in the mouth?
Yes. Ingestion, mastication, deglutition begins here, segmentation
Secretions in the mouth.
Salivary amylase in saliva
Digestion in the mouth
Mechanically & chemically by the action of salivary amylase which acts on starch which breaks down into individual glucose molecules and that is when we can absorb it. Very little digestion actually takes place in the mouth
Do we absorb anything in the mouth?
Not a lot but certain substances can be absorbed under the tongue (sublingual delivery) like certain medications, even a tiny bit of glucose. The benefit of this is it doesn't have to face digestive processes further along
Oral cavity & esophagus: Motility
Motility- Swallowing, chewing
Motility- Peristaltic mixing and propulsion
Small intestine motility
Motility- Mixing & propulsion primarily by segmentation
Large intestine motility
Segmental mixing; mass movement for propulsion
Do we have motility in the esophagus?
Do we have digestion in the esophagus?
Does the esophagus contribute to digestion?
Yes digestion does take place a little bit because after you swallow food it takes about 10 seconds to pass down the esophagus which gives time for salivary amylase to break it down
No the esophagus does not contribute to digestion, digestion just continues
Motility in the stomach
Yes lots of muscle activity there to mix the food & direct the chyme into the small intestine
Which branch of the nervous system is housed completely within and around the GI tract?
Another branch involved in regulating digestion.
Does histamine enter the stomach?
No it acts as a signal molecule & binds to neighboring cells
These cells of the stomach secrete enzymes.
What is digested based on these enzymes?
Proteins & fats
This helps to unwind tertiary structures (bending and folding) which is held by ionic contractions, repulsions, hydrogen bonds, disulfide bonds
Gastric acid (hydrochloric acid)
What happens when you bombard proteins with hydrogen ions which is what happens in the stomach
It starts to unravel and enzymes can go in and start breaking bonds
What type of bond do you find between two adjacent amino acids?
What enzyme in present in the stomach to break these bonds?
A peptide bond
Why does only 10% of fat digestion take place in the stomach?
Because the fat is a giant glob and the enzymes don't have a lot of time to break it down
Does the stomach contribute to the breakdown of carbohydrates?
Will hydrochloric acid break down carbohydrates?
No, onces it gets to the stomach salivary amylase will not break down carbohydrates any more. Enzymes only work within its optimum pH and the pH of the stomach is too acidic for it.
Hydrochloric acids don't break covalent bonds
Presence of protein
Secretes hydrochloric acid
Proton pump inhibitor would work here
Who takes a proton pump inhibitor?
Someone who has excess secretion of hydrogen chloride in the stomach
Where does the stomach get its hydrogen ions?
When carbon dioxide diffuses into the cell the enzyme carbonic anhydrase catalyzes a reaction between the carbon dioxide and water to form carbonic acid. Carbonic acid then dissociates into bicarbonate ion and hydrogen ion
The layer of the wall of the digestive tract that contains blood vessels, small glands, and a nerve plexus is the
The largest pair of salivary glands is the
Which of these cells in the lining of the duodenum produce digestive enzymes?
In which phase of stomach secretion does the greatest amount of secretion take place?
Gastrin secretion is stimulated by
duodenal pH greater than 3
The ______ secretes peptidases and disaccharidases, whereas the _______ secretes trypsin, chymotrypsin, amylase, lipase, and nuclease
small intestine, pancreas
Initial chemical digestion of proteins occurs in the ______ by the digestive secretion _______.
Defecation is stimulated by
parasympathetic reflexes & local reflexes
Carbon dioxide plus water gives you?
Type of transporter for the chloride shift
Why does chloride follow hydrogen in the parietal cell?
Chloride accumulates in the cells so it moves by diffusion out to the lumen of the stomach
Do our cells secrete hydrochloric acid?
No, they secrete hydrogen and chloride
What do proton pump inhibitors do?
They block hydrogen-potassium pump
Remember what H+ is...
A proton, so this is where a proton pump inhibitor would work, wherever there is a hydrogen pump
What is a proton pump inhibitor?
A class of drugs for example; Prilosec, Nexium, Protonix, etc.
Does bicarbonate mix with the gastric juice?
No it stays in/mixed with the mucus otherwise you will neutralize the acid and it won't be able to digest anything
Small intestine secretions come from
The pancreas & the cells of the duodenum & gallbladder
What is digested in the small intestine?
Biomolecules: carbohydrates, fats, & proteins
Function of pancreatic amylase in the small intestine does what?`
Goes after complex carbohydrates
Disacchridases enzymes in the small intestine do what?
Break down disaccharides; sucrose, maltose, lactose
Sucrose will be broken down to glucose & fructose
Maltose will be broken down to glucose & glucose
Lactose will be broken down to galactose & glucose
All of these can be absorbed from the GI tract into the blood, they'll go to the liver for processing
Explain fat digestion in the small intestine
First thing you want to do is expose it to bile, & the bile salts will cause this fat to emulsify (break apart) then lipase can get in and start breaking triglycerides down
Who breaks covalent bonds?
What does the small intestine absorb?
1) Amino acids
2) Monosaccharides l Fat
Chyme is entering from the stomach with a pH of 2. The enzymes in the small intestine have an optimum pH of around 7. So the chyme gets exposed to bicarbonate which?
Will neutralize it and bring it to a normal pH range. Mucus is also secreted from the intestinal goblet cells, bile produced & secreted by the liver; temporarily stored & secreted by the gallbladder
Pacreatic enzymes of the small intestine
Inactivated zymogens are activated once they get into the small intestine
Why do we have zymogens?
Because the goal of all the enzymes is to break down biomolecules into their monomers. So the reason they are inactive is because we are made up of biomolecules and if they were always activated we wouldn't be able to survive, they would destroy the cells that produce them and all the cells they come into contact with
When are zymogens activated?
Only when they are in a location where there are molecules that you want broken down
What happens when trypsinogen becomes activated?
Called trypsin & activates zymogens to their activated enzyme form
Must have activated trypsin present in order to activate?
All the zymogens
How do you activate trypsin?
It comes out as a zymogen, an inactive enzyme. enteropeptidase in brush border activates trypsin
Another name for enteropeptidase
Why wouldn't you want phospholipase to come out in its active form?
Because it breaks apart phospholipids of cell membranes
Activates Trypsin (Trypsinogen --> Trypsin)
Trypsin activates other pancreatic enzymes such as?
Where is the last chance to take water back (reabsorption)
Absorption of electrolytes that include Vitamin B, K
Where is vitamin folic acid and vitamin k produced?
Formed by microflora in the gut
Breakdown of carbohydrates is going from the more complex polysaccharide to?
Describe the breakdown of carbohydrates in the mouth
1) Starts in the mouth by salivary amylase which breaks down starch into its smallest components
2) Action continues until amylase is exposed to extreme pH in the stomach
No more digestion of carbohydrates until you get to the small intestine
Describe the breakdown of carbohydrates in the small intestine
1) Once in the small intestine pancreatic amylase continues digestion of starch into di-, tri- and oligosaccharides
2) Brush border disaccharidases: Maltase breaks down maltose into 2 glucose, sucrase breaks down sucrose into fructose & glucose, lactase breaks down lactose into glucose & galactose
Which form of carbohydrates are absorbed?
Only monosaccharides which is the smallest unit
Which transporter is moving fructose out of the lumen of the GI tract? And exits on?
Exits on GLUT 2
Carbohydrate absorption: Glucose & Galactose move by?
Sodium moving down its gradient
Cotransport with Na+
Secondary active transport
• Active transport of Na+ maintains concentration gradient
Where do monosaccharides go after the small intestine?
1) Into blood
2) Hepatic portal vein to
Describe fructose & galactose absorption
1) Converted into glucose in the liver
2) Fructose can be converted to fat by adipocytes
Describe glucose absorption
1) Stored as glycogen in liver or muscle (or as fat in adipocytes) OR
2) Delivered to other cells for immediate use
Carbohydrate absorption (brief)
1) Initially broken down by salivary amylase in the mouth
2) Continues down esophagus, gets to the stomach
3) NO MORE carbohydrate digestion in the stomach
4) Once in small intestine pancreatic amylase breaks it down
5) Then the disaccharidases
6) Then it can be absorbed
Who breaks the proteins quaternary & tertiary structure?
Hydrochloric acid being secreted into the GI tract in the stomach by parietal cells
First step of protein digestion
We want to first unravel it and then start breaking it down. HCl is responsible for unraveling it.
Does protein digestion take place in the mouth or esophagus?
No because there is no enzyme in the mouth or esophagus to break it down
Enzymes that breakdown proteins are called?
Proteases or peptidases which are not in the saliva but are in the stomach
Destroys tertiary structure, exposes peptide bonds
Hydrochloric acid (HCl)
Breaks peptide bonds, larger into smaller peptides
Pepsin activated by hydrochloric acid (low pH)
Pancreatic enzymes in the small intestine that digest proteins
• Internal peptide bonds (endopeptidase)
• Internal peptide bonds
• Carboxyl-end amino acids (exopeptidase)
Can break up amino acids only from the carboxyl-end
Brush border enzymes of small intestine
• Breaks down di- and tri-peptides into free amino acids
• Cleaves amino-end peptide bonds (exopeptidase)
• Activates trypsin
Brush border enzyme that takes from the amine end of proteins
Pepsin in the stomach, trypsin and chymotrypsin in the small intestine
Internal peptide bonds
Terminal peptide bonds to release amino acids
Aminopeptidase is found
In the brush border
Carboxypeptidase is found
What is a di-peptide made up of?
Two amino acids
For protein absorption free amino acids co-transportout of lumen with?
How do the di-and tripeptides get absorbed?
1) Via transporter molecules
-secondary active transport with H + into epithelial cells
2) Once inside the epithelial cells there are di- and tri-peptidases which hydrolyzed into free AAs
3) Free amino acids leave cell via Na+ antiport
4) Remaining Di- and tri-peptides leave cell via H+ exchanger
5) AAs & di- & tri-peptides enter hepatic portal vein and then get delivered to liver
Enzymatic fat digestion is carried out by?
Lipases, enzymes that remove two fatty acids from each triglyceride molecule. The result is one monoglyceride & two free fatty acids
In the digestive tract in the gut in the presence of lipase, triglyceride is broken down into?
A monoglyceride with a glycerol and one fatty acid & the other two fatty acids are free. This is what happens to get it out of the lumen of the GI tract. The monoglyceride and the 3 fatty acids can then be taken across the cell membrane
Most fat digestion takes place in the?
1) First has to be exposed to bile which causes emulsification where its broken into droplets
2) Now lipase can go in and start breaking the covalent bonds & getting those fatty acids off of the complex structure
3) Lipase breaks the bonds where you end up with triglyceride
Phospholipids into free fatty acids
What does lipase do?
Breaks bonds between fatty acids and glycerol
• Triglyceride--->monoglyceride+2 free fatty acids
Intestinal hormone that regulates digestive function and may play a role in appetite
Digestive hormone cholecystokinin (CCK):
Stimulus for release:
Stimulus for release: Fatty acids and some amino acids
Primary targets: Gallbladder, pancreas, stomach
Primary effects: Stimulates gallbladder contraction & pancreatic enzyme secretion. Inhibits gastric emptying & acid secretion
Other info.: Promotes satiety (sense of being full). Some effects may be due to CCK as a neurotransmitter
Digestive hormone glucagon-like peptide-1 (GLP-1)
Stimulus for release:
Stimulus for release: Mixed meal that includes carbohydrates or fats in the lumen
Primary targets: Endocrine pancreas
Primary effects: Stimulates insulin release. Inhibits glucagon release & gastric function
Other info.: Promotes satiety (sense of being full)
5 steps for fat digestion & absorption
1) Bile salts from liver coat fat droplets
2) Pancreatic lipase & collapse break down fats into monoglycerides & fatty acids stored in micelles
3a) Monoglycerides & fatty acids move out of micelles and enter cells by diffusion
3b) Cholesterol is transported into cells
4) Absorbed fats combine with cholesterol & proteins in the intestinal cells to form chylomicrons
5) Chylomicrons are removed by the lymphatic system
Cephalic Phase is?
1) Stimuli & sensors in the head
-The thought of food, the smell or sight of food, food in the mouth
2) Signal processed in Medulla Oblongata
Efferent: Autonomic Nervous System: Parasympathetic
-Salivary glands, stomach, intestine, glandular organs
Gastric Phase is?
1) Stimuli & Sensors in the Stomach
- Distension of the stomach
- Presence of peptides/proteins/amino acids in stomach
2) Signals processed by Gastric mucosal cells
- Efferent: Paracrines, hormones
- Secretory cells & smooth muscle
Intestinal Phase is?
1) Stimuli & Sensors in the Intestines
- Entry of chyme into duodenum
2) Signals processed in Small Intestine
- Efferent: Enteric nervous system & other cells in intestine
• Feedback to stomach to slow motility & secretions
• Feed-forward to pancreas to secrete insulin when
carbohydrates are present
- Gastric mucosal cells, beta cells of pancreas
Increased gastric activity & Increases ileum motility
Gastroileal Reflex (gastro=stomach, ileal=last segment of small intestine)
Ileum distension & Decreased gastric motility means slow down the emptying of the stomach, can go in the other direction
Extreme distension of one segment & Increased relaxation of other segments
Segments of the small intestine
Secretion in the oral cavity & esophagus
Saliva (salivary glands) (only in the oral cavity)
Digestion in the oral cavity & esophagus
Carbohydrates, fats (minimal)
Absorption in the oral cavity & esophagus
1) HCl by parietal cells
2) Pepsinogen and gastric lipase by chief cells
3) Mucus and bicarbonate by surface mucus cells
4) Gastrin by G-cells
5) Histamine by ECL cells
Proteins & a little bit of fat
Lipid soluble substances such as alcohol & aspirin
Small intestine secretion
2) bicarbonate & enzymes by the pancreas
3) bile by the liver
4) mucus by goblet cells
5) hormones: CCK, secretin, GIP, & other hormones
Small intestine digestion
Carbohydrates, fats, polypeptides, nucleic acids
Small intestine absorption
Peptides by active transport; amino acids, glucose, & fructose by secondary active transport; fats by simple diffusion; water by osmosis; ions, minerals, & vitamins by active transport
Large intestine secretion
Mucus by goblet cells
Large intestine digestion
None, except by bacteria