Digestion Unit Flashcards
Digestion involves 4 main processes:
- Ingestion: taking in of food
- Digestion: mechanical and chemical breakdown of food
- Absorption: transport of food, salt, and water molecules across the gut lining
- Elimination: removal of undigested solid waste from the body
Animals are
Heterotrophs
The different digestive tracts
Alimentary canal, from mouth to anus. Or tract that goes mechanical digestion to chemical digestion.
Small intestine size
Over 6m long and 2.5 cm in diameter
Large intestine size
About 1.5m long and 5 cm in diameter
Mechanical digestion is important because
it increases the surface area of the food for digestion by enzymes and makes it easier to swallow
How does food from one organ to the next?
Peristalsis
At the junction of the esophagus and stomach?
A ring like muscle called the lower esophageal sphincter, closing the passage between the two organs
Purpose of esophageal sphincter
To prevent hydrochloric acid from splashing up into the esophagus. If the ES is not closing properly gastroesophageal reflux disorder (heart burn) may result
Stomach has 3 mechanical tasks:
- Stores swallowed food and liquid.
- To mix food and liquid and digestive juices produced by the stomach. Churning.
- Empty it’s contents slowly into small intestine.
Order of what stays in stomach the longest
carbohydrates, proteins, then fats
Stomach main four areas
Cardia, fondus, body, and pylorus
Movement of Food Out of the Stomach:
- After 1-2 hours of mixing and churning the food, peristaltic contractions of the stomach move the contents (chyme) towards the pyloric sphincter
- Each contraction moves about 3mL of chyme through the pyloric sphincter and into the duodenum
Movement in the Small Intestine:
- After moving into the small intestine, chyme is moved along by peristalsis
- Circular muscle contracts behind the food and expands in front of it, producing a traveling wave like contraction
- Most nutritional material has been removed from the food by the time it reaches the large intestine
Movement in the Large Intestine (Colon):
- Fecal matter moves more slowly through the large intestine than through the small intestine
- This enables up to 2L of water to be reabsorbed per day
- Movements along the large intestine include segmentation; peristalsis and mass movements
Movement of feces
Segmentation alternate sections of muscle contract moving feces back and forth, causing mixing. Peristalsis moved the forces towards the rectum. Extra peristaltic eaves called mass movements move faces from transverse colon into the rectum. Occurs 2-3 times a day
Chemical digestion in the mouth
Chemical digestion begins in mouth where salivary glands will secrete salivary amylase
What is salivary amylase?
A carbohydrate splitting enzyme that begins the hydrolysis of plant and animal starches.
Amylase breaks down large carbohydrates into double sugars. Will continue to break down until reaches stomach.
Deactivated by acidic environment in stomach.
The stomach secretes gastric juice, which includes
Hydrochloric acid (HCl)
Pepsin (enzyme)
Mucus
Intrinisc Factor
Hydrochloric Acid (HCl)
- secreted from parietal cells
- pH of 1 (extremely acidic)
- kills bacteria
- activates pepsinogen
Pepsin (enzyme)
- secreted from mucus and chief cells
- pepsinogen is activated by HCl to create pepsin
- pepsin is an enzyme that breaks down/ digests proteins
Mucus
- secreted by mucus cells
- mucus is “bicarbonate rich” (anti-acid) this allows it to coat and lubricate the stomach surface
- protects the stomach lining from HCl and bacteria that may cause ulcers
Intrinisc factor
- secreted from parietal cells
- vital for vitamin B12 absorption
No food…
No food is absorbed in the stomach. However, some medications and alcohol are absorbed here.
