The Digestive and Excretory System Flashcards
What enzyme is responsible for the chemical breakdown of food in the mouth? What does it break down?
Alpha-Amylase: breaks down starch into polysaccharides. Only carbohydrates break down chemically in the mouth. Everything else is broken down physically
What is a sphincter?
A ring of muscle that remains contracted so that there is no opening in the center. The stomach normally remains closed unless cardiac (entrance to the stomach) pyloric sphincter (entrance to the small intestines) opens.
What is the pH inside the stomach?
2
What are the gastric pits?
Deep pits in the stomach with exocrine glands embedded composed of various major stomach cells. Where the four major cell types in the stomach are found and releases the gastric juices
What are the chief cells?
Releases pepsinogen through the exocrine gland in the stomach which is activated due to the acidic environment of the stomach
What is pepsin?
Digestive enzyme in the stomach that breaks down proteins
What are parietal cells? What is distinctive about their form due to their function?
One of the major cells in the stomach that releases HCl through the exocrine gland. Also releases intrinsic factor which helps the ileum absorb the vitamin B12.
Because it takes a lot of energy to transport HCl into the lumen, parietal cells have lots of mitochondria.
How is the HCl transported into the lumen of the stomach? What happens as a result?
Through active transport which requires a lot of energy. Carbonic acid is made inside the cell. H+ goes into the stomach while biocarbonate ion is released to the interstitial side. The net result is that the pH of the stomach is lowered while the blood is raised.
What are the G-cells?
Releases gastrin which cause parietal cells to release HCl
What chemical results in the secretion of cell types in the stomach?
Acetylcholine
Where does the 90% of the digestion and absorption occur?
The small intestine
In the small intestine, where does the most digestion occur and where does the most absorption occur?
Most digestion occurs in the duodenum and the most absorption occurs in the jejunum and ileum.
How is the small intestine well-suited for absorption?
Villi and microvilli. The surface of the villi cells are called enterocytes. These enterocytes have small finger-like projections called microvilli that increase the SA for absorption. The microvilli appear as a fuzzy covering, called the brush border.
What digestive enzymes do brush border covering contain?
Carbohydrate, protein, and nucleotide-digesting enzymes
Dextrinase, maltase, sucrase, lactase, peptidase, nucleosidases
The small intestine is well-suited for absorption. How is the digestion takes place in the small intestine?
Pancreas
How is it that the fluid inside the duodenum is pH 6 while the stomach is pH 2?
Acids from the stomach is neutralized by the bicarbonate ions from the pancreas
The acinar cells of the pancreas release digestive enzymes to the main pancreatic duct which is released into what part of the small intestine?
Duodenum
What are the major pancreatic digestive enzymes released into the small intestine?
trypsin, chymotrypsin, pancreatic amylase, lipase, ribonuclease, and deoxyribonuclease
T/F: All pancreatic digestive enzymes are released as zymogens
True
How is trypsin activated? What does the activated trypsin do?
Activated by enterokinase in the brush border. Activated trypsin activates all other zymogens released from the pancreas
Function of trypsin and chymotrypsin
Degrade proteins into small polypeptides
Function of carboxypolypeptidase
cleaves amino acids from the sides of the peptides broken down by trypsin and chymotrypsin
Function of pancreatic amylase
Very powerful. Degrades proteins into disaccharides and trisaccharides. The brush border enzymes reduce them into monosaccharides to be absorbed.
Main nerve responsible for digestion
Vagus nerve from the parasympathetic nervous system