The Digestive System

The mysterious process uncovered!

FUNCTION

► Take in food ► digests food ► absorbs nutrients and water so they can get to cells ► excrete wastes STRUCTURE ► Essentially a long tube with two openings, one for in and one for out ► Movement of material is one way

The Pathway

►

MOUTH:



physical digestion (chewing)



chemical (saliva) digestion

► Pharynx (i.e. throat)

Epiglottis

is a flap that closes when the act of swallowing occurs to prevent food from going down the trachea (breathing tube) ►  

Esophagus

Connects the pharynx and the stomach. wave-like contractions of the smooth (i.e. involuntary) muscles push food down toward the stomach.

    

Stomach

Holds food (stores up to 2 liters) Physical digestion (muscles “churn” food) Chemical digestion (hydrochloric acid and enzymes help break down food and kill harmful microbes or parasites) J-shaped has inner folds to increase surface area

Stomach Photo

Small Intestine

► ► ► ► Performs chemical digestion Nutrients diffuse through the intestine walls and into blood stream About 7 meters/23 feet in length!!!

lined with small finger-like projections called Villi (increased surface area increases diffusion)

Villi

► ►

Large Intestine (or Colon)

Absorbs water/forms feces Around 1.5 m/4.5 feet (shorter than small intestine, but has larger diameter)

Rectum/Anus

► Rectum: storage of feces ► Anus: controls expulsion of feces

Accessory Organs

► Help with food digestion by adding digestive enzymes that help break down food ► Food does not pass through these organs ► Liver (produces bile which filters and breaks down fat), pancreas (produces insulin which balances sugar levels in the blood), gall bladder (stores bile)

► Why do you think the digestive system is such a long tube?

Now, who’s hungry?

► Digestion Transit Times:  Mouth: ► one minute  Esophagus: ► 4-8 seconds    Stomach: ► 2-4 hours Small Intestine: ► 1-4 hours Large Intestine: ► 10 hours to several days!

Homework/Activity

► Puzzle of the digestive system      Cut out the pieces, glue them together on the chart paper and label them Colour the organs food pass through directly one colour Colour the accessory organs a different colour Draw the outline of the liver and label it Complete the chart to summarize the functions of the different parts of the digestive system ► Read over section 3.3, pages 80-82 ► Answer questions 2,4,5 on page 82