Physiology - The Digestive System

What is the digestive system?

a network of organs that mediate the ingestion and digestion of food, as well as absorption of nutrients and elimination of wastes.

What is the alimentary canal?

organs that transport food and act as digestion, absorption, and elimination

• oral cavity

• pharynx

• small intestine

• rectum

• esophagus

• stomach

• large intestine

What are accessory organs?

organs that aid in digestion and absorption

direct contact with food

• teeth

• tongue

indirect contact w/ food

• salivary glands

• liver

• gall bladder

• pancreas

What is mechanical digestion?

digestion by tearing, grinding, crushing

• ex. chewing by teeth and tongue

What is chemical digestion?

digestion by chemicals (acids, enzymes, etc) secreted by accessory organs

• ex. secretion of zymes in saliva

How does digestion in the oral cavity occur?

mechanical: mastication (teeth and tongue)

chemical: mediated by saliva (hypotonic solution w/ 99% water and 1% dissolved elements)

• lubricates food to facilitate swallowing

• delivers enzymes to breakdown fats and carbs

What is bolus

food after being digested in the oral cavity

What do acinar cells do?

create and secrete saliva in response to external stimuli. salivation regulated by the nervous system.

parasympathetic stimulation and salivation

stimulates salivation

• ion section into the duct lumen

• H2O diffusion into the lumen

• ion reabsorption to maintain hypotonicity

(cells secrete ions, water follows bc osmosis, ions are then removed)

sympathetic stimualtion and salivation

inhibits salivation

What is peristalisis?

“wave like” movement of smooth muscle contractions and relaxations.

• ex. stomach grumbling, swalling, fecal matter movement

What are circular muscles (peristalsis)?

form upper and lower estophageal sphincters; contract behind bolus to move it forward (think of pulling drawstring on bag)

What are longitudial muscles (peristalisis)

contract to stablize esophagus

(think of pulling sides of a slinky)

what is chemical digestion in the stomach mediated by?

gastric juice, composed of HCL and digestive enzymes

What is pepsinogen? (chemical digestion: stomach)

protease precursor secreted by chief cells

inactive form of pepsin

What is HCL? (chemical digestion: stomach)

secreted by parietal cells that

• weaken hydrogen bonds

• mediates conversion of pepsinogen to pepsin

What are goblet cells? (chemical digestion: stomach)

secretes mucus that protects stomach lining

What are parietal cells (chemical digestion: stomach)

secretes gastric acid (HCL hydrochloric acid)

What are chief cells? (chemical digestion: stomach)

secretes pepsinogen which is a protease (enzyme that breaks down proteins) precursor

What are D cells? (chemical digestion: stomach)

secretes somatostatin which inhibits acids secretion

What are G cells? (chemical digestion: stomach)

secretes gastrin which stimulates acid secretion

What is chyme? (chemical digestion: stomach)

food/bolus after being mixed w/ gastric juice