14: Digestion and Absorption Flashcards
What are the end results of digesting carbohydrates, fats, and proteins?
Carbs: poly or disaccharides converted to monosaccharides
Fats: triglycerides split into 3 FAs and a glycerol
Proteins: amino acids
What is sucrose and what it it split into? What enzyme is used?
A disaccharide cane sugar
Split into glucose and fructose via sucrase in the intestine.
What is lactose and what is it split into? What enzyme is used?
Disaccharide milk sugar.
Split into glucose and galactose via lactase in the intestine.
What are starches and what are they broken into? What enzymes are used and where are they found?
Large polysaccharides frmo non-animal sources such as potatoes and grains.
Broken into maltose and 3-9 glucose polymers via Pytalin in saliva and pancreatic amylase.
Then made into glucose via maltase and dextrinase in the intestine.
What is the function of pepsin? What percentage of protein digestion is this? What is needed?
Breaks down collagen, the connective tissue in meats.
10-20%
Pepsin is activated at low pH (2-3)
What pancreatic secretions are involved in protein digestion?
Trypsin and chymotrypsin break proteins into smaller peptides.
Carboxypolypeptidase cleaves ends of polypeptides to amino acids.
Elastase digests the elastin fibers that hold meat together.
Where are peptidases found and what is their function?
Found on brush border of duodenum and jejunum.
Break polypeptides and amino acids into amino acids.
What are most fats ingested as? How are they digested?
Triglycerides.
Lingual lipase (10%)
Emulsification
Where does emulsification begin and what is the purpose?
Begins with agitation in the stomach.
Bile salts and lecithin in bile reduce reduce tension and allow for fragmentation in the sm. intestine.
Increases surface area up to 1000 fold so pancreatic lipase can act.
What happens once fat is emulsified?
Pancreatic lipase acts to break it into fatty acids and 2-monoglycerides.
Bile salts incorporate them into micelles for transport to the brush border for absorption.
Why is the formation of micelles so important?
It keeps the parts of TG’s apart so they don’t come back together.
Allows them to be in an aqueous environment and aids in our bodies ability to absorb them.
What is steatorrhea? What is it caused by?
A clinical condition in which stool floats due to fat in it.
This occurs when you don’t form micelles; Can be caused by chronic pancreatitis when pts can’t make lipase and thus can’t digest fats.
What are the folds of the small intestine called? What nerves are involved in absorption here?
The valvulae conniventes, which are covered in vili for increased SA.
Meissner’s plexus.
Describe water absorption with hypoosmotic chyme and hyperosmotic chyme?
Hypoosmotic chyme: water diffuses into cells (out of tube) by osmosis
Hyperosmotic chyme: water moves from plasma into chyme (tube)
Describe the concentration of sodium in the intestinal lumen compared to the interstitial fluid?
Intestinal lumen: ~140
Interstitial fluid: ~50
How are Na levels in the intestinal lumen and interstitial fluid maintained?
Na moves down its gradient (140 and 50) out of the cell and into the lumen.
Na is then pumped out via the Na/K ATPase and more needs to be continually moving into the cell to maintain the levels around 50.
Describe chloride absorption?
It follows the movement of sodium in the duodenum and jejunum.
Describe bicarbonate absorption?
Occurs in the duodenum and jejunum.
Bicarb from secretin on pancreatic and biliary epithelium combines with H to form carbonic acid.
H2CO3 dissociates into H2O and CO2. CO2 is expelled and water is absorped.
Where are calcium and iron absorbed?
The duodenum
Where are potassium, magnesium, and phosphate reabsorbed?
Throughout the small intestine.
Where are bile salts and vitamin B12 absorbed?
Ileum
What clinical measurement would you look at to determine which type of anemia a patient has? What are the three types based on this measurement?
Mean corpuscle volume (size of RBC)
Can be microcytic, normalcytic, or macrocytic.
What is the most common cause of microcytic anemia?
Iron deficiency
What is a common cause of macrocytic anemia?
Folate deficiency and vitamin B12 deficiency
What are the two ways that carbohydrates are absorbed and what percentage does each make up?
80% absorbed as glucose
20% as galactose and fructose.
How are glucose, galactose, and fructose absorbed?
Glucose and galactose are co-transported with sodium by active transport.
Fructose does not utilize the sodium transport mechanism.
How are the majority of proteins absorbed?
By co-transport with sodium.
What is the process by which fats are absorbed?
Micelles move to cell surface, monoglycerides and FAs diffuse out of the micelle into the interior of the cell where they’re converted to TGs and absorbed via lymphatics.
Ultimately get into the blood as chylomicrons.
What happens to a small amount of short and medium chain fatty acids?
They are directly absorbed without conversion to triglycerides.
How much fluid enters the colon? How much it typically excreted as stool?
~1500 mL enters colon and 100-200 mL is excreted as stool.
What is absorbed in the large intestine? What does this result in?
Sodium and chloride are actively absorbed in the proximal large intestine; this is enhanced by aldosterone.
This causes a gradient that results in the absorption of water.
What is secreted in the large intestine? What function does this have?
Bicarbonate is secreted in exchange for chloride.
Bicarb buffers neutralizes bacterial acidic waste products.
