Digestion and Absorbtion - 6.1 Flashcards
Where does protein digestion begin?
The Stomach (w/ pepsin & pepsinogen)
Outline the roles of hydrochloric acid in the stomach.
- It denatures proteins by lowering the pH ~2
- Supplies H+, which activates pepsinogen into pepsin
- Pepsin then breaks down proteins into amino acids / peptides
- Kills bacteria
Outline the hormonal and nervous mechanisms that control the secretion, content, and volume of gastric juice.
- Sight/smell of food triggers medulla to send signal to stomach to secrete gastric juice (via vagus nerve)
- Impulses from stretch receptors send signals to brain which sends signals to stomach to trigger production of gastrin
- Gastrin causes sustained release of gastric juices (HCL)
Where does most chemical digestion happen?
The small intestine
Explain the role of the pancreas in digestion.
As an exocrine gland(secretes enzymes from lumen of small intestine - stimulated by secretin)
- Breaks down fats / starches / sugars
- Excretes amylase, lipase, trypsin, & nuclease
What is amylase?
Secreted by pancreas & salivary glands, hydrolyzes starch(substrate) into maltose (product).
What is lipase?
Pancreatic enzyme, hydrolyzes triglycerides into monoglycerides / fatty acids / glycerol.
What is trypsin / endopeptidase?
Pancreatic enzyme, hydrolyzes proteins into amino acids and polypeptides.
What is nuclease?
Pancreatic enzyme, hydrolyzes nucleic acids into nucleosides.
What is the general function of the villi?
Villi absorb monomers formed by digestion as well as mineral ions and vitamins.
Structure of cells of the epithelium of the villi is adapted for the absorption of food.
How is the structure of a villus related to its function?
Epithelial cells - surround each villus (decreases diffusion distance for nutrients into bloodstream)
Rich Capillary Network - large concentration gradient (between blood and the fluid in the small intestine) allows for rapid absorption of nutrients
Lacteals - Absorb lipids (into lymphatic system – transports fats, drains tissues of excess fluids)
Intestinal crypts - release juices that act as ‘carrier fluids’ for nutrients
Label the Structures of a Villus.
List and explain the different forms of transport used by the small intestine to absorb different nutrients.
Diffusion - fatty acids absorbed through conc. gradient
Facilitated Diffusion - fructose pumped through protein channels in the epithelial cell membrane
Active transport (uses ATP) - glucose/amino acids pumped through protein channels against conc. gradient
Endocytosis - cholesterol in lipoprotein particles transported by means of vesicles.
Outline the role of the large intestine.
- Absorbs water / minerals / vitamins / ions
- Peristalsis (contraction of muscles) to move food undigested food
- Secretes mucous (lubrication)
Explain why cellulose and lignin are not digested in humans.
Because humans do not posses the enzymes necessary to break them down.
State the other substances that are also egested (excreted) by the body.
BELCH
- Bile pigments
- Epithelial Cells
- Lignin
- Cellulose
- Human Microflora / bacteria
Outline the roles of fiber in the diet.
- More fiber = faster rate of material movement through the intestine
- Decreases hunger (prevents obesity)
- Absorbs water to keep faces soft to pass (reduces constipation)
- “Works out” microflora
Outline the cause for stomach ulcers.
- Helicobacter pylori.
- Secretes urease to increase pH and to
neutralize gastric acids to allow survival - Secretes mucinase which degrades the mucous lining of stomach wall
- Stomach wall is then digested by stomach acid(HCL)
Consequences / Treatments for stomach ulcers.
- Inflammation
- Digestion of stomach lining by HCL & pepsin
- Treated by Proton Pump Inhibitors cuz they reduce stomach acid production
- Allows ulcers to heal
- Or antibiotics
