Lesson 4 - Digestion in the Small and Large Intestine

Question 1

Absorption in the Small Intestine

Answer 1

Vitamins, minerals, and water are also absorbed in the small intestine through passive or active transport

Passive transport is the movement of materials
across a cell membrane without the use of energy from the cell (e.g. simple diffusion, osmosis, facilitated diffusion)

Diffusion follows the concentration gradient, from an area of higher concentration to an area of lower concentration

Amino acids diffuse directly into the bloodstream

Osmosis is the diffusion of water molecules across a selectively permeable membrane, from an area of higher concentration (of water molecules) to an area of lower concentration

Facilitated diffusion is the diffusion of molecules across a membrane through transport proteins embedded in the cell membrane.

Each transport protein has a unique size and shape that allows only certain substances to pass through. Transport proteins increase the rate of diffusion of specific nutrient molecules

Active transport: materials are moved
across a cell membrane, from an area of
lower concentration in an area of higher
concentration, using energy provided by the
cell

Active transport is used to transport
molecules that are too large to diffuse
through the cell membrane or that have a
strong/ uneven electrical charge that
prevents diffusion

Question 2

What Happen in the Large Intestine

Answer 2

The large intestine is approximately 1.5
m in length and 7.6 cm in diameter.

Digestion (and most absorption) is
complete by the time the digested
material reaches the large intestine

There is still a significant quantity of
undigested and indigestible material,
such as cellulose, that cannot be broken
down by humans and must be expelled.

Cecum:
- Receives the processed material from the small
intestine

Colon:
- Water is absorbed via osmosis (~20L daily!)
- Vitamin (B and K) and Mineral (sodium Na+ and chloride Cl- ions) are absorbed

Rectum:
- The last 20 cm of the large intestine
- Holds the waste products of digestion

Anus:
- Eliminates waste through an external opening

Question 3

What is Egestion?

Answer 3

Egestion: the removal of waste food materials
from the body

The absorption of water in the large intestine changes the liquid material in the colon into a
soft solid called feces.

Nerves in the wall of the large intestine detect
the movement of feces into the rectum. This
initiates the defecation reflex, which causes the
urge to have a bowel movement