Option D2 Digestion Flashcards
Exocrine glands produce and secrete…
substances via a duct onto an epithelial surface – either the surface of the body or the lumen of the digestive tract/ gut
Examples of digestive glands
Gastric glands
Salivary glands
Pancreatic glands
Intestinal glands
Gastric secretions - nervous mechanism
- Immediate response to the sight or smell of food through secretion of gastric juices by the stomach pre-ingestion
- Food entering the stomach causes distention, which is detected by stretch receptors in the stomach lining
- Signals are sent to the brain, where sustained gastric simulation is triggered by the release of digestive hormones
Gastric secretions - hormonal mechanism
- Gastrin is secreted by the stomach and simulates the release of stomach acids
- If stomach pH drops too low, secretion is inhibited by gut hormones
- When digested food passes the small intestines, the duodenum also releases digestive hormones
3a. Secretion and CCK simulate the pancreas and liver to release digestive juices
3b. Pancreatic juices contain bicarbonate ions which neutralise stomach acids, while the liver produces bile to emulsify fats
Normal pH of the stomach
Gastric glands that line the stomach wall secrete and acidic solution that creates a 1.5-2.0 pH which is optimum for hydrolysis reactions by stomach enzymes
Function of acidic condition in the stomach
- assists in digestion of food
- activates stomach proteases (pepsin)
- prevents pathogenic infections
Pancreas releases…
bicarbonate ions into the duodenum which neutralizes the stomach pH (intestinal pH~7.0-8.0)
How is the low pH environment in the stomach maintained?
Proton pumps in the parietal cells of the gastric pits secrete H+ ions (active transport) which combine with Cl- ions to form hydrochloric acid
Proton pump inhibitors (PPI)
drugs that irreversibly bind to proton pumps and prevents H+ production. This will raise the pH in the stomach however could cause increased susceptibility to gastric infections due to lower acidity
The inner epithelial lining of the small intestine is…
highly folded finger-like projections called villi
Features of Villi
M - Microvilli – Ruffling of epithelial membrane further increases surface area
R - Rich blood supply – Dense capillary network rapidly transports absorbed products
S - Single layer epithelium – Minimises diffusion distance between lumen and blood
L - Lacteals – Absorbs lipids from the intestine into the lymphatic system
I - Intestinal glands – Exocrine pits (crypts of Lieberkuhn) release digestive juices
M - Membrane proteins – Facilitates transport of digested materials into epithelial cells
Structural features in the epithelial lining of villi
Tight Junctions: creating an impermeable membrane, they keep digestive fluids separate from tissues and maintain a one-way movement concentration gradient
Microvilli: it borders the villi and greatly increases the surface area allowing for more absorption
Mitochondria: epithelial cells of intestinal villi will possess large numbers of mitochondria to produce ATP for various transport mechanisms
Summary of egested materials
B - Bile pigments E - Epithelial cells L - Lignin C - Cellulose H - Human flora (bacteria)
Dietary fiber
indigestible portion of food derived principally from plants and fungi. Humans lack enzymes to break down certain plant matter
Health benefits of a rich fiber diet
- reduction of constipation frequency
- lowers blood cholesterol and regulates blood sugar levels
- it aids in weight management
