Three Definitions of “High-Density Lipoprotein”

Introduction: The goal of this assignment is to understand the importance of definitions and to learn how their granularity and content are depended on the audience and purpose. I will provide three types of definitions for “high-density lipoprotein” – parenthetical, sentence, and extended (with at least four expansions) – for a non-technical audience.

Reading situation: A brochure explaining the role of high-density lipoprotein in relation to cardiovascular health.

Parenthetical definition: This test will determine the amount of high-density lipoprotein (the “good” cholesterol) in your blood plasma.

Sentence definition: High-density lipoprotein (HDL) is a type of lipoprotein, which is a complex of lipids (fats) and protein that is used to transport cholesterol and other types of lipids in the bloodstream (Britannica, 2019). Higher amounts of HDL in blood are associated with better cardiovascular health (Centers for Disease Control and Prevention, 2020).

Expanded definition:

What is high-density lipoprotein?

High-density lipoprotein (HDL) is a type of lipoprotein, which is a complex of lipids (fats) and protein that is used to transport cholesterol and fats in the bloodstream (Britannica, 2019). Since fats and cholesterol are not soluble in water, they cannot travel freely in blood and must be “packaged” to be transported (Britannica, 2019). The “high-density” in high-density lipoprotein comes from the fact that its density is higher than of other types of lipoproteins (Feingold, 2021).

What is it composed of?

High-density lipoprotein are particles of about 5-12 nm in size (one nanometer is one-billionth of a meter) (Feingold, 2021). The particles consist of an outer layer and a core (see Figure 1) (Feingold, 2021). The outer layer is made of phospholipids, which are the same biological compounds that make up membranes in human cells . In addition, the layer contains cholesterol, and lipoprotein-specific proteins. The core contains what is commonly known as fats, which are triglycerides and modified cholesterol.

Figure 1. Structure of a lipoprotein (Feingold, 2021)

How is it different from other lipoproteins?

Besides being higher in density than other lipoproteins, HDL also has different functions and effects on the body. For example, while low-density lipoprotein transports cholesterol from the liver to the tissues, HDL transports cholesterol from the tissues back to the liver, where cholesterol is broken down and consequently excreted from the body (Centers for Disease Control and Prevention, 2020).

How it affects cardiovascular health?

Higher amounts of HDL in blood are associated with higher cardiovascular health (Centers for Disease Control and Prevention, 2020). For this reason, HDL is commonly known as the “good” cholesterol. Low-density cholesterol, or the “bad” cholesterol, is responsible for forming fatty deposits in arteries called “plaques”. In contrast, HDL may slow plaque formation as it absorbs cholesterol from the body and directs it for excretion. Consequently, people with lower levels of HDL than usual are advised to speak with a doctor about lifestyle changes that can help increase it (Centers for Disease Control and Prevention, 2020).

References

Britannica, T. Editors of Encyclopaedia (2019, July 11). lipoprotein. Encyclopedia Britannica. https://www.britannica.com/science/lipoprotein

Feingold KR. Introduction to Lipids and Lipoproteins. (2021, January 19). Introduction to Lipids and Lipoproteins. (Feingold KR, Anawalt B, Boyce A, et al., Ed.). Endotext [Internet]. Retrieved June 8, 2022, from https://www.ncbi.nlm.nih.gov/books/NBK305896/

Centers for Disease Control and Prevention. (2020, January 31). LDL & HDL: Good & Bad Cholesterol. Centers for Disease Control and Prevention. Retrieved June 8, 2022, from https://www.cdc.gov/cholesterol/ldl_hdl.htm