Biology Lecture 6
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What is the single most major rxn in digestion?
Where does Carbohydrate Digestion begin? Where else does it occur?
- 1st = in the mouth (α-amylase)
- also occurs in the pancreas (pancreatic amylase)
Where does Protein Digestion begin? Where else does it occur?
- 1st = in the stomach (pepsin ---- precursor = pepsinogen)
- also occurs in the pancreas (trypsin and chymotrypsin)
Where does Fat Digestion begin? Where else does it occur?
1st & only = pancreas (lipase --- with the help of bile)
What helps a food bolus to move down the esophagus?
Peristallic Action (smooth muscle contraction)
What is the primary purpose of the stomach?
It reduces food to chyme and begins the process of protein digestion through pepsin and its low pH
What are the cell types found in the stomach?
- 1) Chief Cells: secrete pepsinogen deep in the exocrine glands (needs to be activated by the low pH of the stomach to activate into pepsin)
- 2) Mucous Cells: secrete mucous to protect the epithelial cells from acid erosion
- 3) Parietal Cells: secretes HCl (lowers the pH of the stomach and increases the pH of the blood)
- 4) G-Cells: secretes gastrin (stimulates parietal cells to secrete HCl)
What are the major hormones that affect stomach juice secretion?
- Acetylcholine - affects all
- Gastrin - affects mainly HCl
- Histamine - affects mainly HCl
What absorbs nutrients in the stomach?
No absorption occurs in the stomach.
What are the parts of the small intestine?
- Duodenum - the first and largest section, most absorption occurs here
- Jejunum - the middle section, medium sized and medium absorption
- Ilium - the last and smallest section with the least amount of absorption happening here
Where are villi located?
The small intestine
What do villi do?
- they increase the surface area of the absorption
- within each villus is a capillary network and lymph vessel (AKA lacteal)
- microvilli constitute the brush boarder - it contains membrane bound digestive enzymes (between villi intestinal exocrine glands secrete juices to regulate the pH to 7.6 and lysozyme which regulates bacteria)
What is the function of the pancreas?
- the pancreas secretes bicarbonate ion which lowers the pH of the pancreas to 6
- it also secretes major enzymes that aid in the further digestion of macromolecules
What are the major enzymes secreted by the pancreas?
- 1) Trypsin & Chymotrypsin: degrades proteins
- 2) Pancreatic Amylase degrades carbohydrates via hydrolysis into glucose polymers
- 3) Lipase: degrades fat with the help of bile
- 4) Ribonuclease: breaks down RNA
- 5) Deoxyribonuclease: breaks down DNA
What happens to bile after it has aided in the degradation of fat molecules?
Most of it is reabsorbed by the small intestine
What is the primary function of the large intestine?
- Water and electrolyte absorption
- Recognize that when this fails - diarrhea is the result
How is glucose absorbed?
It is dragged into enterocytes by Na+ via secondary active transport down the Na+ concentration gradient
How is galactose absorbed?
Similarly to glucose: it is dragged into enterocytes by Na+ via secondary active transport down the Na+ concentration gradient
- These cells are involved in absorption
- epithelial like cells found in the small intestine and colon
How is fructose absorbed?
- Via facilitated diffusion
- much of it is converted to glucose in the enterocyte
How is glucose transported?
- glucose is transported from high concentration to low concentration via facilitated diffusion (except for in enterocyte and liver cells)
- all crabs are absorbed into the blood and transported to the liver (glycogenesis for storage)
- all cells can produce and store some glycogen but muscle and liver cells store a lot
- when all glycogen stores are full, glucose is converted to fat for long term storage
How is protein absorbed?
- Protein degradation results in amino acids
- many of them are absorbed down the Na+ concentration gradient and some are absorbed via facilitated diffusion
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