Nutrition in Man

Let’s Recap!

•What are the 3 parts of the small intestine?•What are the 3 secretions found in the

duodenum?• Are you able to recall what enzymes are

involved?•What about bile? How does bile aid in fats

digestion?

Lesson Objectives

Lesson Objectives

• What are the things you want to know to about the ileum ?

• In your pairs, share what you want to know about the ileum and write it on your whiteboard

• 3 minutes

Lesson Objectives

• Describe the functions of ileum in terms of absorption of carbohydrates, proteins and fats

• To state the adaptation of small intestines

in absorption of nutrients , closely relating to the structures : villi and microvilli

IleumWait… What about jejunum?

Structure

•Highly coiled tube; inner walls contains numerous folds, villi and microvilli

Functions

•Mainly for absorption

•Walls have numerous folds to provide a large surface area for absorption of digested food

Functions

• Epithelial cells of the villi are one-cell thick to allow for quick diffusion.

• Richly supplied with blood capillaries and lymphatic capillaries to carry away absorbed food substances to maintain a concentration gradient.

AdaptationsOf the small intestine for absorption

Terms to rememberIngestion

Mechanical digestion

Chemical digestion

Absorption

Assimilation

Recall diffusion…•What factors affect the rate of diffusion of

molecules across a partially permeable membrane?• Temperature• Surface area• Concentration gradient• Thickness of the membrane

Rate of absorption

• The rate of absorption of digested food substances depends on:

• The length of the small intestine

• The thin epithelial wall that lies between the food substances and the blood capillaries

• The concentration gradient across the intestinal wall

Absorption of Digested FoodAbout 90% of the digested food is absorbed in the small intestine.

The Digestive System

duodenum

bile duct

hepatic portal vein

pancreas

pancreatic duct

liver

gall bladder

Absorption

• The process whereby digested food materials are taken into body cells

Adaptations of small intestineIncrease surface area to volume ratio

1) The small intestine is long and have inner walls with

numerous transverse folds

2) The presence of minute finger-like projection called

villi

3) The presence of finger like projection called

microvilli on each villus

Villi and microvilli

Small Intestine Lining of small intestine

Section of a villus Microvilli

Circular folds, villi, microvilli

Villi and microvilli

• The villi of the small intestine increases the surface area ratio to volume by approximately 100-folds!

• Do you know how big that is?

Demonstration

Adaptations of small intestine

Other adaptations

1) Villi have thin walls and membranes to facilitate

diffusion

• Epithelial wall of the villi is only one cell thick

2) Intestinal wall and villi richly supplied with blood vessels

and lymphatic vessels

• Carry away absorbed food

Villi

• Absorbed by villi of small intestine• Simple sugars• Amino acids• Fatty acids and Glycerol

How does absorption take place in the intestines?

Glucose and amino acids:

Diffusion

• Transport of substances away from the intestines maintains the concentration gradient for diffusion of new substances across the intestinal walls

How does absorption take place in the intestines?

Glucose and amino acids:

Diffusion

• Transport of substances away from the intestines maintains the concentration gradient for diffusion of new substances across the intestinal walls

How does absorption take place in the intestines?

Fatty acid and glycerol:

• Each villus has a lymphatic capillary (lacteal)

which transports fats

Transport of nutrients…

• Lead into small venules joined together

forming hepatic portal vein

• Carries blood directly to liver

Blood is carried directly from the stomach and the intestine to the liver via the hepatic portal vein.

posterior vena cava

stomach

gastric vein

small intestine

to heart

intestinal vein

hepatic portal vein

liver

hepatic vein

Absorption of Digested Food

Summary

Summary

• What is absorption?

• What are the three adaptations of small intestine to increase surface area ratio to volume?

• What are some of the other ways to facilitate the absorption of nutrients?

• How are the nutrients being absorbed?

Muddiest Point

•Any Question?