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
Ileum
Wait… 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.
Adaptations
Of the small intestine for absorption
Terms to remember
Ingestion
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
The Digestive System
Absorption of Digested Food
About 90% of the digested food is absorbed in the small intestine.
liver
gall
bladder
hepatic
portal vein
pancreas
bile duct
pancreatic
duct
duodenum
Absorption
• The process whereby digested food
materials are taken into body cells
Adaptations of small intestine
Increase 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
Absorption of Digested Food
hepatic vein
to heart
posterior
vena cava
liver
stomach
hepatic
portal vein
intestinal vein
gastric vein
small intestine
Blood is carried directly from the stomach and the intestine
to the liver via the hepatic portal vein.
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?