Digestion and Absorption Quiz Flashcards
Pepsin/pepsinogen
Pepsin is an enzyme that is produced in the gastric glands, is acidic, and works in the stomach. It turns proteins into peptides.
Hydrochloric Acid
Pepsinogen is activated (into pepsin) in the stomach by HCl
Pepsin does NOT auto-digest stomach cells once it is activated (as a layer of mucus coats/ protects the cells lining the stomach wall). HCl creates the ideal acidity of about 2.
Gastic Juices
- Site/ smell of food triggers reflex response – brain (medulla) sends impulses (via vagus nerve) to gastric glands in stomach to secrete gastric juice (ensures gastric juice (pepsin(ogen) and HCl and mucous) presence in stomach by time food consumed/ when food arrives)
- Food enters stomach causing distention – detected by stretch receptors in stomach lining
- Impulses from stretch receptors sent to brain (to medulla oblongata) which sends signal to stomach through vagus nerve that triggers gastrin (hormone) secretion into bloodstream (from endocrine cells in stomach wall), and causes stomach to begin producing and secreting HCl (parietal cells) and pepsinogen (chief cells)
- Gastrin causes sustained release of gastric juices (particularly acid component - HCl)
Where does most chemical digestion happen?
small intestine
Role of Pancreas
The pancreas secretes enzymes into the lumen of the small intestine
Digestive enzymes are primarily produced and secreted by the pancreas (outside of salivary glands (salivary amylase) and the stomach (pepsin)).
Enzymes are secreted by the pancreas through a duct into the lumen of the small intestine (exocrine gland)
Each enzyme acts on a specific substrate
Note: Secretin (hormone from small intestine) stimulates the pancreas the release enzymes and bicarbonate ions as chyme passes into small intestine from stomach. Bicarbonate ions neutralize stomach acid and provide optimum pH for digestive enzymes in small intestine
Hormones from the pancreas
Amylase, Lipase, Protease, Nuclease
Function of Amylase
changes starch to maltose in the lumen
function of Lipase
changes triglycerides to monogylicerides in the lumen
function of Protease
changes lipids to amino acids in the lumen
function of Nuclease
changes nucleic acids to nucleosides in the lumen
function of villi
- Villi increase the surface area of epithelium over which absorption is carried out.
- Villi absorb monomers formed by digestion as well as mineral ions and vitamins
- the structure of cells of the epithelium of the villi is adapted to the absorption of food
microvilli
- increases surface area for absorbing
capillaries in villi
Capillary networks are close to the epithelial cells of the villus to minimize diffusion distance of nutrients
-Capillary networks maintain a large concentration gradient (between the fluid of the blood and the fluid within the small intestine) allowing for rapid absorption of nutrients
Lacteals
Lacteals absorb lipids (into the lymphatic system – transports fats, drains tissues of excess fluids, and immunity)
Fats are absorbed by the…
Lacteal
sugars are absorbed by the…
veins and arteries
role of large intestine
MAIN FUNCTION: Absorption of water (and minerals/ vitamins/ ions)
Highly folded – maximizes surface area for absorption of water into the blood
Secretes mucus
Lubricates passing faeces
Movement of undigested/ undigestable food products
Peristalsis
egested substances
Note: Cellulose and lignin are not digested because humans do NOT possess enzymes (cellulase) or gut bacteria to break them down
BELCH: bile pigments, epithelial cells, lignin, cellulose, human microflora/ bacteria - these are all egested
Causes, consequences, and treatments of stomach ulcers
Helicobacter pylori, the bacteria that leads to the formation of a stomach ulcer, survives the acidic conditions of stomach by penetrating mucus lining (mucosa). It then goes on to secrete urease to increase pH and to neutralize gastric acids to allow survival, and attachment to and infection of epithelial cells lining the stomach wall (underneath mucus lining). This causes inflammation (body’s immune response) which damages goblet cells in stomach lining (secrete mucus) and H. pylori also secretes mucinase which degrades the mucous lining of stomach wall. As mucus breaks down, stomach wall/ epithelial lining damaged/ digested by stomach acid/ HCl and pepsin (ulcers) - treated with antibiotics, anti-acidics, and PPI’s. Prolonged damage to stomach wall (and chronic H. pylori infection = 20+ years) may lead to stomach cancers
The role of fiber in the diet
the rate of material movement through the intestine is positively correlated with its fiber content. helps “clean out” old/ damaged intestinal cells and unabsorbed materials, it provides bulk to keep materials moving, it absorbs water to keep faeces soft and easy to pass, “works out” the body’s normal microflora, reduces frequency of constipation, lowers risk of colon and rectal cancers, lowers blood cholesterol, regulates blood sugar levels (slows absorption rate of glucose), and decreases hunger (aids in weight management/ prevention of obesity)
