phospholipids and ketone bodies

1. Overview

• Phospholipids:

  • Amphipathic molecules with hydrophilic (polar) heads and hydrophobic (non-polar) tails.

  • Essential in cell membrane structure and function, including signaling and as lung surfactant.

• Ketone Bodies:

  • Water-soluble compounds (acetone, acetoacetate, and β-hydroxybutyrate) produced in the liver during fatty acid oxidation.

  • Serve as alternative energy sources during fasting or glucose deprivation.

2. Phospholipids

• Structure:

  • Two main types:

    1. Glycerophospholipids: Contain glycerol as the backbone.

    2. Sphingophospholipids: Contain sphingosine, predominant in nerve tissue (e.g., sphingomyelin).

• Functions:

  • Structural components of cell membranes.

  • Reservoirs for intracellular messengers.

  • Essential in bile and lung surfactant production.

• Degradation:

  • Phospholipases hydrolyze phosphodiester bonds, releasing molecules like arachidonic acid.

  • Remodeling of membrane-bound phospholipids involves replacing fatty acids.

• Clinical Relevance:

  • Niemann-Pick Disease:

    • Caused by defective sphingomyelin degradation due to sphingomyelinase deficiency.

    • Type A: Rapid neurodegeneration.

    • Type B: Affects visceral organs, leading to chronic disease.

3. Glycolipids and Prostaglandins

• Glycolipids:

  • Found in all membranes but most abundant in nerve tissue.

  • Involved in cellular interactions, growth, and development.

• Prostaglandins:

  • Potent, hormone-like compounds produced in small amounts in nearly all tissues.

  • Act locally with a short half-life, regulating inflammation and other processes.

4. Ketone Bodies

• Production:

  • Synthesized in the liver during fasting or carbohydrate restriction from fatty acid oxidation.

  • Steps include conversion of acetyl-CoA to acetoacetate, β-hydroxybutyrate, and acetone.

• Usage:

  • Transported in the blood to peripheral tissues (muscles, brain), where they are reconverted to acetyl-CoA for energy production via the TCA cycle.

• Excessive Production:

  • Leads to ketonemia and ketonuria in conditions like uncontrolled diabetes and prolonged fasting.

  • Diabetic ketoacidosis (DKA): Results in acidemia due to the loss of protons from circulating ketones, causing severe dehydration and acidosis.