Lipid digestion, absorption and transport Flashcards
name the structural components of lipids and lipid classification
- COOH (carboxyl group)
- Steroids - ring structure that doesn’t contain enough hydroxyl groups to make them water soluble
- phospholipids
- triglyceride
- fatty acids
why are lipids hydrophobic?
- are made up of ring structure - steroids which do not contain enough hydroxyl groups to make them water soluble
what are phospholipids
- made up of 2 fatty acids and a phosphate group
- major component of the cell membrane
what is the main dietary neutral fat
triglyceride/ treacly glycerols (TAG)
- made up of 3 carbon backbone and 3 fatty acids
what are the major components of all types of fats
fatty acids
what are 3 types of fatty acids
saturated
monounsaturated
polyunsaturated
what is a saturated fatty acid
has maximum possible number of hydrogen atoms attached to every carbon atom
- ‘saturated’ with hydrogen atoms and all of the carbons are attached to each other with single bonds
what are unsaturated fatty acids
- a pair of hydrogen atoms in the middle of a chain is missing creating a gap that leaves two carbon atoms connected by a double bond rather then a single bond
- chain has fewer hydrogen atoms- unsaturation
what is a monounsaturated fatty acid
a fatty acid with one double bond because it has one gap
what are polyunsaturated fatty acids
fatty acids having more than one gap are called polyunsaturated
what type of fatty acids are present usually in foods of animal and plant origin
in animal origin- a large proportion of fatty aces are saturated
in plant origin and some seafood- large proportion of fatty acids are monounsaturated and polyunsaturated
which types of food are saturated fats found in
- butter, cheese,while milk, ice cream, lard and fatty meats
- found in some vegetable producs such as coconut, palm and palm kernel oil
- saturated fats are solid at room temperature
- raise your cholesterol
where do monounsaturated fats come from
seeds or nuts such as avocado, olive, peanut and canola oils
- may reduce total cholesterol and LDL cholesterol
- liquid at room temperature
where do polyunsaturated fats come form?
vegetables, seeds or nuts such as corn safflower,sunflower,soybean, cotton seed and sesame seed oils
- lower cholesterol
- use them in place of saturated fats
- ;liquid at room temperature
how are trans fats made?
- vegetable oils are processed or hydrogenated into shortening and stick margarine
- sources of trans fats include snack foods, baked foods and fired foods made with ‘ partially hydrogenated vegetable oil’
what are the 7 functions of lipids?
- fat is one of the body fuels for energy, it serves as a source of energy once calories form carbohydrates are used up
- fat helps the body absorb important fat-soluble vitamins (Vitamins, A,D,E,and K)
- fat supports key body processes such as acting as biosynthetic precursors (steroid hormones form cholesterol)
- fat cushions internal organs and protects them from being damaged (kidneys are shielded with fat in fed state)
- the fat layer below the skin also insulates the body from heat loss
- fat plays a vital role in maintaining healthy skin and hair
- Fat (phophsolipids) form part of the myelin sheath around nerve and nervous tissue including brain and spinal cord
how many calories does each gram of fat provide
9 calories
describe lipid digestion
- oral cavity : lingual lipase and chewing
- stomach - lingual lipase and gastric lipase split triglyceride into diglycerides and fatty acids , only 30% break down occurs after 2-4 Hours in stomach
- lingual lipases and gastric lipases are also known the acidic lipases as their activity is stimulated and increased by an acidic environment
- Small intestine - acid chyme stimulates mucosa cells to release a hormone (choleocytsokinin) which stimulate gall bladder and pacreas to release bile and digestive enzymes respectively
how does emulsification of lipids occur?
Bile salts/ acids are secreted from the gall bladder and contain cholesterol
- bile salts/acids have hydrophobic and hydrophilic side
- the hydrophobic side attaches itself to the lipid and emulsifies it increasing the surface area that can be acted upon by pancreatic lipase
name the different enzymic digestions of lipids in small intestine
- triglyceride uses pancreatic lipase to break down to 2 FA and 2-monoacylglycerol
(2 FA from carbon 1&3 are removed leaving 1 FA attached to carbon 2 of the glycerol) - cholesterol ester is broken down by cholesterol ester hydrolase to cholesterol and fatty acid
- phospholipids is broken down by phospholipase A2 to lysophospholipid + fatty acid which uses lysophosplipase to form glcyerolphosphoryl base + fatty acid
how are lipids absorbed
- as fatty acids are released from TAGs by digestion, they retain their association with bile acid and complex with other lipid to form structures called micelle.
- this will make them have a water soluble coat that will aid their transport into the mucosal lining of the intestines
- the ingest containing the micelles approach the brush border of the intestinal lining cells the lipid,monoglycerides and micelles are taken up by the epithelaila cells enterocytes
what is steatorrhea
- fats not absorbed properly
- result from diseases that affect absorption such as Crohn’s disease and cystic fibrosis
- higher solubility
- enter brush border by simple diffusion
what to chylomicrons do
- help transport lipids into lymph vessels n the intestine Calle the central lacteal, they are transported through the lymph vessels and enter the blood circulation via the thoracic duct
determine the classes of lipoproteins
Chylomicrons formed in intestine
Glycoproteins - mixture of lipids and proteins
Classified according to the density
High density- high protein density
describe the composition of the different lipoproteins
where are chylomicrons synthesised and secreted by
chylomicrons are synthesised by absorptive cells of the intestinal lining and are secreted by these cells into the lymphatic system which joins the blood circulation at the subclavian or by the jugular vein.
