Small and Large Intestine Flashcards
What are the three sections of the small intestine, and what are their primary functions?
The small intestine is divided into the duodenum (most digestion), the jejunum (most absorption), and the ileum (important absorption).
What organs secrete into the small intestine, and what are their secretions?
The stomach delivers chyme and HCL, the liver and gallblader secrete bile, and the pancreas secretes bicarbonate and various enzymes (amylase, lipase, trypsinogen, chymotrypsinogen).
Describe the structure of the brush border in the small intestine.
The endothelium has many folds (villi), which themselves have many smaller projections (microvilli). These serve to increase the surface area. The projections are lined with enzymes (brush border peptidase and lactase).
How are proteins digested?
1) Brush border peptidase
2) Trypsin: secreted from the pancreas as trypsinogen and activated by enteropeptidase.
3) Chymotrypsin: secreted from the panreas as chymotrypsinogen and activated by trypsin.
The proteins are broken down into individual amino acids by hydrolyzing peptide bonds.
How are carbohydrates digested?
The disaccharides and polysaccharides are broken down into monosaccharides by cleaving glycosidic bonds.
1) Brush border enzymes, such as lactase.
2) Amylase, secreted by the pancreas.
How are nucleotides digested?
Brush border nucleosidases break nucleotides into pentose phosphate and bases.
How is fat digested?
Bile from the liver and gallbladder organize the globs of fat into smaller micelles. This increases surface area for pancreatic lipase to break the tiglycerides into triglycerol heads and free fatty acids.
How are amino acids and nucleotides absorbed?
Enterocytes use primary active transport, using a molecule of ATP to transport the AA or nucleotide component into the enterocyte. From there it exits (not clear how) the enterocyte and enters capillaries into the bloodstream.
How are monosaccharides absorbed?
Via secondary active transport. The enterocyte uses ATP to establish a sodium ion gradient (low Na concentration in the cell), and then uses a cotransporter to take up the sugars. They leave the cell using a sodium ion antiporter, which also uses the sodium gradient. They wind up in capillaries.
How are fats absorbed?
Due to their hydrophobic tail, fatty acids may freely diffuse into the enterocytes. From there, they are organized into chylomicrons. Being too large to enter capillaries, they are absorbed by lacteals, broken into smaller molecules, and deposited into veins.
Describe the divisions of the colon, starting with the end of the ileum.
1) Ileo-cecal valve: sits between the ileum and the cecum
2) Cecum: the pouch that sits at the beginning of the colon. The appendix hangs off of this.
3) Ascending colon, 4) Transverse colon, 5) Descending colon, 6) Sigmoid colon
What are the functions of the colon, and what symptoms arise from their malfunction?
1) Absorption of water: too much absorption -> constipation, too little -> diarrhea.
2) Absorption of inorganic ions such as sodium.
3) Contains many microorganisms to aid in digestion.
What is the purpose of the bacteria in our colon?
The bacteria aid in digestion, as they are able to process nutrients that we cannot. Mainly, specific carbs, the result of which is methane and hydrogen sulfide.
What is the purpose of the rectum?
Storage of fecal matter
Describe the composition of the anus.
The anus is comprised of two sphincters: the internal anal sphincter, comprised of smooth muscle, and the external anal sphincter, comprised of skeletal muscle.
