Biology Lecture 6

Hydrolysis

• 1st = in the mouth (α-amylase)
• also occurs in the pancreas (pancreatic amylase)

• 1st = in the stomach (pepsin ---- precursor = pepsinogen)
• also occurs in the pancreas (trypsin and chymotrypsin)

1st & only = pancreas (lipase --- with the help of bile)

Peristallic Action (smooth muscle contraction)

It reduces food to chyme and begins the process of protein digestion through pepsin and its low pH

• 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)

• Acetylcholine - affects all
• Gastrin - affects mainly HCl
• Histamine - affects mainly HCl

No absorption occurs in the stomach.

• 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

The small intestine

• 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)

• 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

• 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

Most of it is reabsorbed by the small intestine

• Water and electrolyte absorption
• Recognize that when this fails - diarrhea is the result

It is dragged into enterocytes by Na⁺ via secondary active transport down the Na⁺ concentration gradient

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

• Via facilitated diffusion
• much of it is converted to glucose in the enterocyte

• 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

• Protein degradation results in amino acids
• many of them are absorbed down the Na⁺ concentration gradient and some are absorbed via facilitated diffusion