Exam 4 Review:  Chapter 24:  Lipid Metabolism

ketone bodies - Any of a class of organic compounds, such as acetone, having a carbonyl group linked to a carbon atom in each of two hydrocarbon radicals and having the general formula R(CO)R, where R may be the same as R ; in general they are colorless volatile liquids having a pungent odor; in lipid metabolism, three of the byproducts of fatty acid catabolism (acetone, acetoacetate, and beta-hydroxybutyrate).  aka - ketones

ketogenesis - The metabolic production of ketone bodies (acetone, acetoacetate, and beta-hydroxybutyrate) which are byproducts of fatty acid catabolism; they may accumulate in excess in the blood and urine of uncontrolled or out-of-control diabetics because the majority of cells in their bodies are unable to utilize glucose for fuel despite its presence.

ketosis = ketoacidosis. - An acidosis (an abnormal increase in the acidity, i.e., hydrogen ion concentration, in the body fluids) with an accumulation of ketone bodies (acetone, acetoacetate, and beta-hydroxybutyrate); it occurs primarily in untreated or out-of-control diabetes mellitus or in starvation as a byproduct of increased fatty acid catabolism.

acidosis - Any abnormal increase in the acidity of the body's fluids (with a corresponding drop in the pH), caused either by the accumulation of acids (increase in hydrogen ions) or by depletion of bicarbonate ions which serve as buffers; there are a variety of specific causes which fall into two main groups, respiratory and metabolic.

cholesterol - A multiple (4-membered) carbon-ring lipid molecule which serves as a minor structural component in cell membranes and is also the precursor for synthesis of estrogen, testosterone, and related steroid hormones.

lipoproteins - Any of the series of soluble lipid-protein complexes which are transported in the blood; each aggregate particle consists of a spherical hydrophobic core containing triglycerides and cholesterol esters surrounded by an amphipathic monolayer of phopholipids, cholesterol and apolipoproteins; classes of lipoproteins include chylomicrons, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

chylomicrons - The class of largest diameter soluble lipid-protein complexes which the lowest in density (mass to volume ratio); their composition is ~2% apolipoproteins, ~5% cholesterol, and ~93% triglycerides and phospholipids; their normal role is to be synthesized by the intestinal mucosal cells to transport dietary (exogenous) triglycerides and other lipids from the intestines via the lacteals and lymphatic system to the systemic circulation to the adipose tissue and liver for storage and use; they are only present in the blood in significant quantities after the digestion of a meal.

high-density lipoproteins (HDL) - The class of small diameter soluble lipid-protein complexes which the highest in density (mass to volume ratio); their composition is ~45% apolipoproteins, ~25% cholesterol, and ~30% triglycerides and phospholipids; their normal role is to transport cholesterol and other lipids from the tissues to the liver for disposal; elevated levels of HDL are associated with decreased risk of cardiovascular disease.

low-density lipoproteins (LDL) - The class of large diameter soluble lipid-protein complexes which the fourth lowest in density (mass to volume ratio); their composition is ~25% apolipoproteins, ~45% cholesterol, and ~30% triglycerides and phospholipids; their normal role is to transport cholesterol and other lipids from the liver and intestines to the tissues for use; elevated levels of LDL are associated with increased risk of cardiovascular disease.  nickname - bad cholesterol

List:

 8.  4 types of lipoproteins and their functions.

Lipoprotein	Function
chylomicrons	transport lipids absorbed from a meal from the intestines to the adipose tissue and, to a lesser degree, to the liver, for storage
very low-density lipoproteins (VLDL)	transport lipids, particularly neutral fats (triglycerides) and cholesterol, from the the liver to most somatic tissue cells for their various metabolic purposes
intermediate-density lipoproteins (IDL)	transport lipids, neutral fats (triglycerides) and cholesterol, from the the liver to most somatic tissue cells for their various metabolic purposes
low-density lipoproteins (LDL)	transport lipids, particularly cholesterol, and neutral fats (triglycerides), from the the liver to most somatic tissue cells for their various metabolic purposes
high-density lipoproteins (HDL)	transport lipids, particularly cholesterol, and neutral fats (triglycerides), to the the liver for catabolism and elimination
[Note:]	[all lipoproteins transport smaller quantities of phospholipids which may be delivered to various cells  for their various metabolic purposes, as well as serving, along with apolipoproteins, as the external emulsifiers of the lipoprotein droplets]

Sketch and Label:

1. a simplified diagram of the structure of a lipoprotein.

Below is a "simplified" diagram of the structure of a lipoprotein, in this case, an LDL.  To the right is a slightly more complex drawing which can be generalized to any of the classes of lipoproteins.  The main points to note for the exam are these:  (1)  Any lipoprotein consists of an inner hydrophobic core and an outer layer of amphipathic molecules, one molecule thick, which serves to emulsify the lipoprotein droplet in the water of the body fluids; (2) the outer layer consists primarily of phospholipids and free cholesterol molecules and a smaller number of characteristic proteins called apolipoproteins; (3) the inner core consists of large quantities of hydrophobic lipids, neutral fats = triglycerides and cholesterol esters; (4) the differences among the different classes of lipoproteins consist primarily of differences in the proportions of lipids in the core as well as some differences in the apolipoproteins present in the outer layer.

The Diagram below summarizes the interrelationships between the various lipoproteins and their functions and the organs and tissues with which they interact.  You will not be expected to reproduce or discuss this figure on the exam, but it does contain useful background information of clinical significance which you will meet again in clinical courses.