Beyond Ingestion…. Digestive system (2)

Review: Parts of Digestion Ingestion – taking in of nutrients Digestion – breakdown of complex molecules into smaller components by enzymes Absorption- transport of digested nutrients to the tissue of the body Egestion – removal of waste food material from the body

Review: Food has been: mechanically chewed by the teeth moistened and partially digested by saliva Saliva contains the enzyme AMYLASE that breaks down starch into simple sugars The bolus is swallowed and………

And digestion is beginning……. The bolus goes through the pharynx, closes the epiglottis (so food doesn’t enter the trachea) and enters the esophagus…

Esophagus Food and fluids move through the esophagus NOT because of gravity but because peristalsis. Peristalsis = rhythmic, wavelike muscle contractions http://www.walgreens.com/adamHtml/animation/200000.htm

Peristalsis is why we can drink while standing on our head!

Sphincters Is a ring-shaped muscle that relaxes or tightens to open or close a passage or opening in the body. Examples are the anal sphincter (around the opening of the anus) and the pyloric sphincter (at the lower opening of the stomach).

There is a sphincter at the top and the bottom of the esophagus.

“do not try this at home”!!

So, the food has now passed through the esophagus, thru the lower esophageal sphincter and into the stomach…

Functions of the stomach Bulk storage (capacity of approx 1.5L) of undigested food Mechanical breakdown of food (muscular contractions of the stomach) Disruption of chemical bonds via acids and enzymes

Structure of stomach Millions of cells line the inner wall of the stomach These cells secrete gastric fluids

Gastric Juices: Mucus: protects stomach against digestion and corrosion HCl: hydrochloric acid kills harmful substances ingested with food Pepsinogen: is activated to pepsin in the presence of HCl, the enzyme pepsin digests protein

Problems: ulcers and heartburn http://www.walgreens.com/adamHtml/animation/200000.htm

Endoscopy:

So far, chemical digestion Part Enzyme Digests Example Mouth Amylase Carbs Bread Stomach Pepsin Proteins Meat HCl (hydrochloric acid) allows pepsin to do its digestion and kills pathogens that come into the stomach.

Mechanical digestion Mouth Teeth Stomach Muscular contractions Physically breaking food into smaller pieces so there is more surface area for chemical digestion. Mouth Teeth Stomach Muscular contractions

Next stop on the digestive bus: thru the pyloric sphincter to the small intestine… Just something to look forward to……