F4 Biology teaching notes Ch 6: NE 27

6.4  Absorption (Book 1A, p. 6-20)

Ø   Absorption of food molecules mainly takes place in

the (1) small intestine, only small amounts

take place in the stomach and the large intestine.                                  

A  How is the small intestine adapted for absorption? (Book 1A, p. 6-20)

Feature	Adaptation for absorption
Ileum is very long	n Increase the surface area for absorption n Increase the time for absorption
n Inner wall is highly-(2)folded (摺疊) n with numerous (3) villi (絨毛) n Numerous (4) microvilli on the epithelial cells of villi) (brush border刷狀緣)	Increase the (5) surface area for absorption èFig10: Inner wall of ileum, villi and epithelium èFig11: Photomicrograph of villus and its epithelium èFig12: Villi, epithelium and microvilli
Thin (6) epithelium (上皮) (one-cell think)	Reduces the (7) diffusion distance for diffusion of food molecules into the blood
Present of associated transport system: n a network of (8) blood capillaries n (9) lacteal (乳縻管)	n Rapidly carry away the absorbed food molecules, thus n keeping a steep concentration gradient of food molecules across the wall of the small intestine to increase the rate of (10) ____________________________
Movement of the villi caused by (11) peristalsis	n Keep villi contact with newly digested food molecules n Keeps a steep (12) concentration gradient of food molecules across the wall of the small intestine to increase the rate of diffusion

http://www.youtube.com/watch?v=XSUalboGM0A&feature=related (youtube: 小腸)

http://www.youtube.com/watch?v=iK8MOA32vAY&feature=related

B  How is digested food absorbed? (Book 1A, p. 6-21)

http://bcs.whfreeman.com/thelifewire/content/chp50/5002001.html (動畫: 脂肪的吸收)              

1      Absorption into the blood

n  Water-soluble food molecules, e.g. monosaccharides, amino acids, minerals and water- soluble

vitamins, can be absorbed into the capillaries by (13) diffusion and (14) active transport.

n  As the absorption of digest food into the blood (15) increases / decreases the water potential of the content in the small intestine, water is drawn into the blood by (16) osmosis.

2      Absorption into the lymph (淋巴)

n  Fatty acids and glycerol enter the epithelium of the villi by (17) diffusion.

n  In the epithelial cells, they recombine into fine (18) lipid droplet, which then enter the (19) lacteal of the lymphatic system (淋巴系統).

n  (20) Lipid-soluble vitamins are also absorbed into the lacteals.

n  The lipids and lipid-soluble vitamins in the lacteals are transported to the main (21) lymph vessel (淋巴管), and eventually to the bloodstream near the neck region.

	Water-soluble substances	Lipid-soluble substances
Example	l monosaccharides, amino acid l minerals and water soluble vitamins	l Fatty acid and glycerol l Lipid-soluble vitamins
Ways of absorption	l  Food substances are absorbed by diffusion and active transport l  Water is absorbed by osmosis	Diffusion
Transport	microvilli à epithelium à capillary network in villi à hepatic portal vein (肝門靜脈) à Liver à hepatic vein (肝靜脈) à heart à different parts of body	epithelium à reform lipid à lacteals (乳糜管)   à lymph vessels (淋巴管) à heart à different parts of body

Ø  Over 90% of water are absorbed in stomach and small intestine by (22) osmosis.

Ø  Only small amounts water and minerals are absorbed in (23) large intestine.