NTD Nutrisi Ternak Dasar - Pencernaan dan Metabolisme … · These protein-coated lipid droplets...
Transcript of NTD Nutrisi Ternak Dasar - Pencernaan dan Metabolisme … · These protein-coated lipid droplets...
11/4/15
1
Lipid Diges.on
3.1 CLASSIFICATION OF LIPID
LIPID
GLYCEROL BASED NON-‐GLYCEROL BASED SIMPLE COMPOUND GLYCOLIPID PHOSPHOGLYCERIDES
SPHINGOMYELINS CEREBROSIDES WAXES STEROIDS TERPENES
FATS GLUCOLIPIDS GALACTOLIPIDS LECITHINS CEPHALINS
11/4/15
2
3.2. FATS
• FATS AND OILS ARE CONSTITUENTS OF BOTH PLANTS AND ANIMALS
• BOTH HAVE THE SAME GENERAL STRUCTURE BUT HAVE DIFFERENT PHYSICAL AND CHEMICAL PROPERTIES.
• ESSENTIAL FATTY ACIDS = LINOLEIC, ARACHIDONIC, LINOLENIC
• PROPERTIES OF FATS = – HYDROLISIS (SAPONIFICATION), – OXIDATION, – ANTIOXIDANTS, – HYDROGENATION
3.3 Glycolipids • In these compounds two of the alcohol groups of the glycerol are
esterified by faVy acids and the other is linked to a sugar residue.
CH2OH
11/4/15
3
3.4. STEROIDS • STEROLS
These have eight to ten carbon atoms in the side chain, an alcohol group at carbon atom 3, but no carbonyl or carboxyl groups. They may be classified into: q The phytosterols of plant origin, q The mycosterols of fungal origin, q The zoosterols of animal origin.
• CHOLESTEROL HDL, LDL
• ERGOSTEROL
This phytosterol is widely distributed in brown algae, bacteria and higher plants. • BILE ACID • STEROID HORMONES
OESTROGENS AND PROGESTERONE
Monogastric Diges.on
• Challenges – Lipids are not water soluble – Triglycerides too large to be absorbed
• Diges.ve solu.on – Triglycerides mix with bile and pancrea.c secre.ons
• Emulsifica.on and diges.on
11/4/15
4
Bile • Produced in liver, stored in gallbladder
– Except horse • Alkaline solu.on composed of:
– Bile salts – Cholesterol – Lecithin – Bilirubin
• Responsible for fat emulsifica.on – Detergent ac.on
Mixed micelle formed by bile salts, triacylglycerols and pancreaMc lipase.
11/4/15
5
Diges.on of Lipid
• Bile salts emulsify lipids • Pancrea.c lipase acts on triglycerides
– Triglycerides sn-‐2 monoglyceride + 2 faVy acids
• Pancrea.c (co) lipase – Ac.vated by trypsin – Interacts with triglyceride and pancrea.c lipase
• Displaces bile to allow recycling • Improves ac.vity of pancrea.c lipase
Pancrea.c Colipase
• Secreted from pancreas as procolipase – Ac.vated (cleaved) by trypsin
• Anchors lipase to the micelle – One colipase to one lipase (i.e., 1:1 ra.o)
11/4/15
6
Dietary Fat (large TG droplet)
Bile Salts
Lipid emulsion
Lipase 2-Monoglyceride
+ 2 FFA
Emulsifica.on
• Produces small lipid spheres – Greater surface area
• Lipases aVack TG at 1 and 3 posi.ons Gl
ycerol
Fatty Acid1
Fatty Acid2
Fatty Acid3
Lipase
Gl
ycerol
Fatty Acid3
Fatty Acid1 Fatty Acid2
Triglyceride 2-Monoglyceride
+
2 Free Fatty Acids
2 H20
11/4/15
7
Diges.on of Lipid
• Phospholipase A1 and A2 – Hydrolyzes faVy acids from phospholipids
• Cholesterol esterase – Hydrolyzes faVy acids from cholesterol esters
Micelle Forma.on
• Complex of lipid materials soluble in water • Contains bile salts, phospholipids & cholesterol
• Combines with 2-‐monoglycerides, free faVy acids and fat-‐soluble vitamins to form mixed micelles
11/4/15
8
Micelle Forma.on
Lipid Absorp.on
• Mixed micelles move to intes.nal mucosal cells (enterocytes) and release contents near cell
• The bile salts are re-‐absorbed further down the gastrointes.nal tract (in the ileum), transported to the liver, and finally recycled and secreted back into the diges.ve tract
11/4/15
9
Nutrient Absorp.on -‐ Lipids
• FaVy acids, 2-‐monoglycerides, cholesterol, and cholesterol esters move down concentra.on gradient (passive diffusion)
• Repackaged in intes.nal cell for transport to liver – Some is reformed into triglycerides – Chylomicrons
Lipid Absorp.on
• Once in enterocyte – Glycerol and short chain faVy acids directly enter mesenteric blood
– 2-‐monoglycerides and longer-‐chain free faVy acids reformed into triglycerides, and then packaged with protein to form chylomicrons
– Phospholipids hydrolyzed to free faVy acids
11/4/15
10
Lipid Absorp.on
Short and medium chain fatty acids
simple diffusion exocytosis
Lipid Absorp.on (Chylomicrons) • Chylomicrons absorbed from enterocytes into lacteals (lymph vessels) – Ul.mately enter blood via thoracic duct
• Most long chain faVy acids absorbed into lympha.c system
– Excep.on is poultry
• Blood lipids transported as lipoproteins
11/4/15
11
Lipid Absorp.on (Direct Transfer) • Alternate route is for free faVy acids to enter circula.on directly – Free faVy acids (FFA) also called non-‐esterified faVy acids (NEFA)
– Mostly less than 12 C (short and medium chain faVy acids)
• Non-‐esterified faVy acids enter the liver via the portal vein
Overview of FaVy Acid Uptake • Short-‐ and medium-‐chain faVy acids
– Enter portal blood directly from enterocytes – Bound to albumin in blood
• Albumin–FFA complex – Oxidized in liver or elongated and used for triglyceride forma.on
• Long-‐chain faVy acids – Form chylomicrons – Drain into the lympha.cs via the lacteal in mammals (no lacteal in avian small intes.nal villi)
– Enter bloodstream at the thoracic duct • Upstream from liver • Slow entry into the blood
11/4/15
12
In the Enterocyte... • Newly formed triglycerides accumulate as ‘lipid droplets’ at the endoplasmic re.culum – Coated with a protein layer
• Stabilizes lipids for transport in lymph and blood (aqueous environment)
• At the Golgi apparatus, carbohydrates are aVached to the protein coat
• The glycoproteins act as signaling molecules
These protein-coated lipid droplets are called chylomicrons
Overview of Lipid Digestion in Mammals
11/4/15
13
Overview of Lipid Diges.on and Absorp.on in Avians
Portal blood*
*Lymph in mammals
FaVy acid
bind
ing protein
Lipid Diges.on -‐ Ruminants
• Microbes rapidly modify lipids: • Lipolysis
Triglycerides Glycerol + 3 free faVy acids
• Biohydrogena.on – Addi.on of H to unsaturated faVy acids
• Satura.on – If carried to comple.on, all double bonds become single bonds
11/4/15
14
Biohydrogena.on
Weight percent of fatty acids
Fatty acid Diet Abomasal digesta
16:0 (palmitic) 18:0 (stearic) 18:2 (linoleic) 18:3 (linolenic)
26 6 17 31
29 45 4 6
Sheep fed alfalfa hay
Biohydrogena.on
• Reduc.on of double bonds • Result: faVy acids that are more saturated with hydrogen
Saturated
Unsaturated
11/4/15
15
Biohydrogena.on of Linoleic Acid
Linoleic acid (18:2)
cis-9, trans-11 CLA
trans-11 18:1
Stearic acid (18:0)
isomerase
reductase
reductase
Intermediate fa-y acids are conjugated linoleic acids
Lipid Diges.on and Synthesis by Microbes
• Rumen microbes – Produce “trans” configured double bonds – Alter chain length – Change posi.on of double bonds – Produce odd-‐chain and branched-‐chain FA
• Rumen adipose .ssue varies greatly from dietary fat – Dietary fat must be rumen protected to affect animal
11/4/15
16
Effect of Lipid on Rumen Fermenta.on
• Excess amounts of unsaturated faVy acids and triglycerides – Decrease methane produc.on – Impair fiber diges.on – Form soaps – Alter rumen metabolism towards propionate produc.on – less acetate
• Decrease milk fat – Produce trans faVy acids
• Inhibit lipid synthesis in mammary gland – Decrease milk fat
Lipid Diges.on -‐ Ruminant
• Diges.on and absorp.on of lipids is similar to monogastrics except – Fat enters small intes.ne in different form than was presented to animal in diet
– Lipids absorbed more slowly – More transported as VLDL