1. Delivery of nutrients to cells
Chapter 22

2. Preparation for absorption
Digestive enzymes act as food is moved along alimentary canal
Small intestine has a structure suited to absorption
- large surface area
- villi & microvilli
- Very thin lining
- Dense network of vessels (capillaries & lacteals)

3. Nutrient absorption
Glucose & amino acids into capillaries via epithelium
- direct to bloodstream
Lipids into lacteals
- lymphatic system
Other nutrients absorbed into capillaries
E.g. calcium, iron, vitamins
Bile salts act as an emulsifier of lipids
-ve heads repel each other
- bile salts made in liver, stored in gall bladder
- with lipase, speeds up lipid digestion

4. Lipid absorption Lipase digests fat into 2 products
Products + Bile Salts = Micelles
Micelles are water soluble particles
They move to epithelium surface of intestine wall
Monoglyceride + Fatty acids diffuse through into epithelial cells
Once through the Smooth ER - built back into triglycerides
Coated with lipoprotein and exit by exocytosis
Enter lacteals – lymphatic system

5. Liver Blood Supply Hepatic artery in (oxygenated)
Hepatic vein away (deoxygenated)
Hepatic portal vein (deoxygenated from the gut)
– part of the portal system
- allows liver to process digestion products
Liver regulates nutrient & urea concentrations
Hepatic artery – normal conc of nutrients & urea
Hepatic portal vein – normal urea, high conc of digestion products
Hepatic vein – normal nutrient conc., high conc of urea

6. Role of liver in metabolism
Glucose:
In excess – insulin converts glucose to glycogen
Further excess converted into fat
Low levels – glucagon converts glycogen to glucose
Lipids:
Dietary lipids removed from circulation
- make cholesterol (hormones), lipoproteins etc
Protein:
Make plasma proteins – albumins, globulins, fibrinogen
Amino acid conversions – transaminase enzymes
- amino acids converted

7. Fate of absorbed materials
Carbohydrate:
Absorbed by cells for energy
Stored as glycogen or fat
Lipids:
Circulated in lipoproteins
Glycerol & Fatty acids absorbed by cells for energy
Excess FA’s & Glycerol stored in adipose tissue
Proteins:
Absorbed by cells for protein synthesis
Energy source to cells (following deamination)
Vitamins & Minerals:
Metal ions e.g iron – enzyme activators (co-factors)
Vitamins (organic, non-proteins) – co-enzymes