The document discusses three key aspects of the digestive system: 1) Absorption is the process by which digested nutrients pass from the gastrointestinal tract into the bloodstream and lymph systems to be distributed to cells. This occurs mainly through diffusion, facilitated diffusion, osmosis, and active transport. 2) In the large intestine, sluggish movements and occasional mass movements help move waste toward the rectum while allowing for nutrient absorption. 3) Defecation involves the relaxation of the internal anal sphincter and contraction of the external anal sphincter in a reflex triggered by the presence of waste in the rectum, allowing for the voluntary elimination of solid and liquid waste from the anus.

1. THE DIGESTIVE SYSTEM
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2. The Absorption Process
Absorption is the passage of digested food from the gastrointestinal
tract into the cardiovascular and lymph systems for distribution to cells.
Sugars and amino acids go through capillaries; glycerol/fatty acids go to
lymphatic system. Absorption occurs by:
• Diffusion – the process by which molecules move from an area of
high concentration to an area of lower concentration.
• Facilitated diffusion and Osmosis
• Active Transport – movement of molecules from an area of low
concentration to an area of higher concentration; (requires energy)
STATION 20: let’s break it down!

3. Propulsion in the Large Intestine
• Sluggish peristalsis allows time for the diffusion of nutrients into the
bloodstream and waste into the rectum
• Mass movements
• Slow, powerful movements
• Occur three to four times per day
• Presence of feces in the rectum causes a
defecation reflex
STATION 20: let’s break it down!

4. The Defecation Process
• Defecation is the final act of digestion, by which
organisms eliminate solid, semisolid, or liquid waste
material from the digestive tract via the anus.
• The anus has an involuntary internal and a
voluntary external anal sphincter.
• The defecation reflex occurs when the internal anal
sphincter relaxes and the external anal sphincter
contracts. The voluntary control of the external
sphincter muscle allows you to “hold it in” until you
are ready to defecate and relax the sphincter.
STATION 20: let’s break it down!