Explain your answer in terms of the exogenous, endogenous and reverse cholesterol blood lipid transport pathways.

Sure, let's break down the cholesterol transport pathways:

1. Exogenous pathway: This pathway involves the absorption of dietary cholesterol from the intestines. Lipids from the diet are packaged into chylomicrons, which are then released into the bloodstream. Lipoprotein lipase (LPL) breaks down the chylomicrons, releasing fatty acids and cholesterol. The cholesterol is then taken up by the liver. A high total cholesterol:HDL ratio could indicate that there is a lot of dietary cholesterol being absorbed and not enough being transported away by HDL.

2. Endogenous pathway: This pathway involves the production of cholesterol by the liver. The liver packages cholesterol into very low-density lipoproteins (VLDLs). These VLDLs are broken down into LDL, which can be taken up by cells throughout the body. If there is too much LDL and not enough HDL to transport it away, this could result in a high total cholesterol:HDL ratio.

3. Reverse cholesterol transport pathway: This pathway involves the transport of cholesterol from the body's tissues back to the liver. HDL plays a key role in this process. It picks up excess cholesterol from the cells and transports it back to the liver, where it can be excreted. A high HDL level (and therefore a low total cholesterol:HDL ratio) is beneficial because it means more cholesterol is being removed from the body's cells.

In summary, a lower total cholesterol:HDL ratio is generally better because it indicates that there is a good balance between the cholesterol being absorbed and produced by the body, and the cholesterol being transported away by HDL.