Complex Lipid Metabolism and Surfactants

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Questions and Answers

What is the primary structural characteristic of phospholipids?

They are solely composed of fatty acids.

They have only hydrophobic tails.

They are amphipathic, having both hydrophilic and hydrophobic regions. (correct)

They are entirely hydrophilic in nature.

What role does phosphatidylcholine (PC) play in lung surfactant?

It increases surface tension in the alveoli.

It enhances the rigidity of cell membranes.

It serves solely as an intracellular messenger.

It is a major lipid component that decreases surface tension. (correct)

Which statement best describes the function of nonmembrane-bound phospholipids in the body?

They are involved in lung surfactant and bile formation. (correct)

They are exclusively involved in signaling pathways.

They only function in energy storage.

They act as enzymes for metabolic reactions.

What is the consequence of insufficient surfactant production in preterm infants?

Elevated risk of respiratory distress syndrome (RDS). Signup and view all the answers

What does the L/S ratio indicate regarding fetal lung maturity?

It assesses the amount of DPPC compared to sphingomyelin. Signup and view all the answers

What is the major lipid component of lung surfactant?

Dipalmitoyl-phosphatidylcholine (DPPC). Signup and view all the answers

Which cellular structure is primarily involved in the production of DPPC for lung surfactant?

Type II pneumocytes. Signup and view all the answers

How do phospholipids contribute to the structure of cell membranes?

They serve as the predominant membrane lipids, associating with nonpolar constituents. Signup and view all the answers

What does a ratio of two or above indicate in terms of pneumocyte maturation?

It is evidence of maturity related to surfactant production. Signup and view all the answers

How can lung maturation be accelerated in pregnant women?

By administering glucocorticoids before delivery. Signup and view all the answers

What is the primary site of glycosphingolipid abundance in the body?

Nerve tissue Signup and view all the answers

Which role do glycosphingolipids NOT fulfill in biological systems?

Regulating enzyme activity within mitochondria. Signup and view all the answers

What causes sphingolipidoses?

Deficiency of certain lysosomal hydrolases. Signup and view all the answers

What symptom may result from a deficiency of a sphingolipid degrading enzyme?

Neurological deterioration. Signup and view all the answers

Which diagnostic method is NOT typically used for identifying sphingolipidoses?

MRI imaging of brain structures. Signup and view all the answers

What treatment is used for sphingolipidoses?

Recombinant human enzyme replacement therapy. Signup and view all the answers

Study Notes

Complex Lipid Metabolism

Phospholipids are amphipathic molecules, meaning they have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.
The hydrophilic head of a phospholipid interacts with the intracellular or extracellular aqueous environment.
The hydrophobic tail interacts with the nonpolar portions of other membrane constituents like glycolipids, proteins, and cholesterol.
Phospholipids are the predominant lipids in cell membranes.
Phospholipids also function as a reservoir for intracellular messengers and anchor for some proteins.
Nonmembrane-bound phospholipids serve additional functions, including components of lung surfactant and bile.

Role of Phosphatidylcholine (PC) in Lung Surfactant

Di-palmitoyl phosphatidylcholine (DPPC) is a major component of lung surfactant.
DPPC is made and secreted by Type II pneumocytes.
Lung surfactant is an extracellular fluid layer lining the alveoli.
Surfactant decreases surface tension of this fluid layer, reducing the pressure needed to maintain flat alveoli, thereby preventing alveolar collapse (atelectasis).

Respiratory Distress Syndrome (RDS)

RDS in preterm infants is associated with insufficient surfactant production and/or secretion.
RDS is a significant cause of neonatal deaths in Western countries.
Lung maturity of the fetus can be gauged by determining the ratio of DPPC to sphingo-myelin (usually written as the L/S ratio) in amniotic fluid.
A ratio of two or above indicates lung maturity, reflecting the major shift from sphingomyelin to DPPC synthesis in pneumocytes at approximately 32 weeks of gestation.
Lung maturation can be accelerated by giving the mother glucocorticoids shortly before delivery.
Administration of natural or synthetic surfactant can be used in the prevention and treatment of infant RDS.
RDS can also occur in adults due to insufficient surfactant production in damaged or destroyed surfactant-producing pneumocytes (e.g., from infection or trauma).

Overview of Glycolipids

Glycolipids are molecules containing both carbohydrate and lipid components.
Glycolipids are also called glycosphingolipids.
Glycosphingolipids are essential components of all membranes, but found in greatest amounts in nerve tissue.
Glycosphingolipids are located in the outer leaflet of the plasma membrane, interacting with the extracellular environment.

Sphingolipidoses

In a normal individual, the synthesis and degradation of glycosphingolipids are balanced.
If a specific lysosomal hydrolase required for degradation is missing, a sphingolipid accumulates.
Lysosomal lipid storage diseases caused by these deficiencies are called sphingolipidoses.
The result of a specific hydrolase deficiency can dramatically affect nerve tissue, leading to neurological deterioration and potentially early death.

Diagnosis and Treatment

Sphingolipidoses can be diagnosed measuring enzyme activity in cultured fibroblasts or peripheral leukocytes, or analyzing DNA.
Histologic examination of the affected tissue is also useful.
Recombinant human enzyme replacement therapy is a treatment option.

Reference

Champa, Harvey, and Ferrier (2005), Lippincott's Illustrated Reviews: Biochemistry. (5th/6th edition)

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Description

Explore the fascinating world of complex lipid metabolism, focusing on phospholipids and their crucial roles in cell membranes and lung surfactant. Learn about the properties of amphipathic molecules and the specific functions of phosphatidylcholine (PC) in respiratory health.