11- Digestion and Absorption of Nutrients II – Fats (Lipids)

A set of vocabulary-style flashcards covering fats: digestion, absorption, transport, and the roles of lipids and fat-soluble vitamins, plus clinical relevance like malabsorption.

Lipids

A broad group of nonpolar biomolecules including fats; dietary fat is mostly triglycerides and varies in chain length and saturation.

Triglycerides

Glycerol backbone esterified with three fatty acids; the main form of dietary fat.

Fatty acids

Building blocks of lipids; can be saturated or unsaturated; essential fatty acids cannot be made endogenously; linoleic (18:2 ω6) and linolenic (18:3 ω3) are essential.

Essential fatty acids

Fatty acids required from diet (e.g., linoleic and linolenic acids) because the body cannot synthesize them.

Linoleic acid (18:2 ω6)

An essential fatty acid of the ω6 family; precursor to other signaling lipids.

Linolenic acid (18:3 ω3)

An essential fatty acid of the ω3 family; precursor to longer ω3 fats.

Arachidonic acid

A long-chain fatty acid produced from linoleic acid; its synthesis is dependent on having sufficient linoleic acid.

Phospholipids

Lipids like triglycerides but with two fatty acids and a phosphate-containing head group; examples include phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS).

Sphingolipids

Membrane lipids with serine as the backbone (not glycerol); examples include ceramide; important in skin and other membranes.

Ceramide

A core sphingolipid molecule; a building block for more complex sphingolipids and present in skin.

Fatty acids (essential vs non-essential)

Essential fatty acids must be obtained from the diet; non-essential fatty acids can be synthesized.

Gastric lipase

Lipase produced by chief cells in the stomach; initiates fat digestion; optimum activity at low pH.

Lingual lipase

Lipase secreted from the tongue; starts digestion in the mouth and is active at low pH.

Pancreatic lipase

Main fat-digesting enzyme in the small intestine; secreted by pancreatic acinar cells.

Colipase

Pancreatic cofactor that anchors lipase to the fat droplet and counters bile salt inhibition.

Bile salts

Produced by the liver; emulsify fats to form a large surface area for lipases; recycled via enterohepatic circulation.

Emulsification

Process by which bile salts break fat droplets into smaller droplets to increase lipase access.

Micelles

Small, mixed lipid aggregates formed in the intestine that transport fatty acids and 2-monoacylglycerol to enterocytes.

2-Monoacylglycerol

A digestion product of triglycerides; combines with fatty acids in micelles for absorption.

Chylomicrons

Lipid-protein particles formed in enterocytes to transport dietary triglycerides via the lymphatic system.

VLDL (Very Low-Density Lipoprotein)

Lipoprotein produced in enterocytes and liver; transports triglycerides and other lipids; released into blood.

Lipoprotein lipase

Enzyme on endothelial surfaces that hydrolyzes triglycerides in chylomicrons to fatty acids and glycerol.

Enterohepatic recirculation

Recycling of bile acids from the intestine back to the liver for reuse.

Short- and medium-chain fatty acids

Absorbed directly into portal blood, are water-soluble, and do not require micelles.

Long-chain fatty acids

Absorbed via mixed micelles; re-esterified to triglycerides in the smooth endoplasmic reticulum and packed with apoproteins into chylomicrons.

Chylomicrons and lymphatics

Chylomicrons exit enterocytes into the lymphatic system (lacteals) before reaching the bloodstream.

Enterocytes and lipid processing (overview)

In enterocytes, CIC: re-esterification to TGs in SER; apo-proteins added in rough ER; chylomicrons/VLDL assembled and transported to Golgi and then to lymphatics.

Fat-soluble vitamins

A, D, E, and K; solubilized in micelles and absorbed with dietary fats.

Vitamin A (retinol and beta-carotene)

Fat-soluble vitamin; deficiency causes night blindness; essential for rhodopsin in the eye.

Vitamin D

Fat-soluble vitamin produced in skin via sunlight; deficiency causes rickets in children and osteomalacia in adults.

Vitamin E (alpha-tocopherol)

Fat-soluble antioxidant; protects against oxidative damage; deficiency is rare.

Vitamin K

Fat-soluble vitamin involved in gamma-carboxylation of glutamate residues; crucial for blood coagulation, bone metabolism, and vascular health.

Fat malabsorption

Inadequate fat digestion/absorption due to liver/gallbladder, pancreatic, or intestinal disease; symptoms include steatorrhea and fat-soluble vitamin deficiencies.

Steatorrhea

Excess fat in feces; a common sign of fat malabsorption.