MBBS: Phospholipids and Respiratory Distress Syndromes

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of pulmonary surfactant in the alveoli?

It enhances the thickness of the alveolar walls.

It promotes the absorption of oxygen into the bloodstream.

It reduces the surface tension of the fluid lining the alveoli. (correct)

It increases the surface tension of alveolar fluid.

Which enzyme hydrolyzes sphingomyelins to ceramide and phosphorylcholine in the lysosomes?

Sphingomyelinase (correct)

Lecithinase

Phospholipase A1

Phospholipase C

What significant role does arachidonic acid play when released from membrane phospholipids?

It promotes the synthesis of sphingomyelin.

It functions as a structural component of cell membranes.

It increases the surface tension in the alveoli.

It acts as a precursor for bioactive lipid mediators. (correct)

How does Niemann-Pick disease affect sphingomyelin metabolism?

It leads to accumulation of sphingomyelin due to enzyme deficiency. Signup and view all the answers

What is the relationship between surface tension and the radius of the alveoli, according to the law of Laplace?

Collapsing pressure is inversely related to the radius of the alveoli. Signup and view all the answers

Which of the following correctly classifies the subgroups of Glycerophospholipids?

Sphingomyelin and Phosphatidylserine Signup and view all the answers

What is the main role of lecithin in the human body?

Maintenance of surface tension in the lungs Signup and view all the answers

Which of the following phospholipids is most abundant in cell membranes?

Phosphatidylcholine Signup and view all the answers

In the context of the synthesis of surfactant, what is the main phospholipid component that helps reduce surface tension in the alveoli?

Phosphatidylcholine Signup and view all the answers

Which condition is most closely associated with a deficiency in surfactant in neonatal infants?

Neonatal respiratory distress syndrome Signup and view all the answers

What enzyme is primarily responsible for the degradation of phospholipids in the human body?

Phospholipase Signup and view all the answers

Which of the following best describes the Law of Laplace as it relates to alveolar function?

States that larger alveoli have lower pressure due to decreased surface tension Signup and view all the answers

Which of the following is NOT a nitrogenous base found in phospholipids?

Threonine Signup and view all the answers

Which of the following statements accurately describes the classification of phospholipids?

Phospholipids are categorized into two groups based on the type of fatty alcohol present. Signup and view all the answers

What is the primary function of pulmonary surfactant in the lungs?

To stabilize the alveoli by reducing surface tension on the fluid lining. Signup and view all the answers

Which enzyme is responsible for the hydrolysis of sphingomyelins in lysosomes?

Sphingomyelinase Signup and view all the answers

What is a consequence of elevated surface tension in the alveoli?

Increased likelihood of alveolar collapse. Signup and view all the answers

What is the primary site for the synthesis of glycerophospholipids in the body?

Liver Signup and view all the answers

Niemann-Pick disease is primarily caused by the deficiency of which enzyme?

Sphingomyelinase Signup and view all the answers

What forces resist lung distension, contributing to surface tension effects in alveoli?

Attractive forces among water molecules. Signup and view all the answers

Which component is NOT part of the biosynthesis pathway for pulmonary surfactant?

Bronchial epithelial cells Signup and view all the answers

Study Notes

Objectives for MBBS Students

Students should be able to discuss phospholipids, including classification of glycerophospholipids and sphingophospholipids, synthesis and degradation.
Students should also be able to discuss surfactant, its biosynthesis and function.
Topics include the Law of Laplace, Respiratory Distress syndrome (RDS), neonatal respiratory distress syndrome, and adult respiratory distress syndrome.

Case of Neonatal Respiratory Distress Syndrome

A 30-year-old pregnant woman (G3P2) gave birth to a 1.5 kg baby girl at 30 weeks gestation via Cesarean section.
The mother received a dose of betamethasone 10 hours before delivery.
The baby was resuscitated, intubated, and given surfactant within 15 minutes of delivery.
Apgar scores were 2, 5, and 6 at 1, 5, and 10 minutes, respectively.
The baby was mechanically ventilated due to severe respiratory distress syndrome (RDS).

Phospholipids

Phospholipids (or phosphatides) are a type of compound lipid containing a phosphate group.
Phospholipids are composed of fatty acids (saturated and unsaturated), a nitrogenous base (choline, serine, threonine, or ethanolamine), phosphoric acid, and fatty alcohols (glycerol, inositol, or sphingosine).

Glycerophospholipids

Type 2 Lecithin (phosphatidylcholine) is the most abundant phospholipid in cell membranes.
It's crucial for body choline storage (methyl group donor in methylation reactions).
It's involved in nerve impulse transmission (choline-acetylcholine).
Lysolecithin removes fatty acids from lecithin.
Lecithin maintains surface tension and adherence of inner lung surface.
Deficiency causes Respiratory Distress Syndrome (RDS) in infants.

Common Glycerophospholipids

Phosphatidic acid: The simplest phospholipid with no specific functions.
Lecithin (phosphatidylcholine): Abundant in cell membranes, critical for structure and fluidity. In the lungs, dipalmitoylphosphatidylcholine (DPPC) is a key component of pulmonary surfactant, reducing surface tension.

Other Phospholipids

Phosphatidyl ethanolamine (cephalin): Similar to lecithin but replaces choline with ethanolamine. Important in blood clotting and membrane processes.
Phosphatidyl serine: Crucial for cell integrity, especially in the brain. Declines with age. Plays a role in cell signaling, including apoptosis (programmed cell death) where it signals phagocytosis.
Phosphatidyl inositol: A less common component of cell membranes. Involved in cell signaling.

Glycerophospholipid Synthesis

The liver synthesizes glycerophospholipids.
Synthesis requires ATP, glycerol kinase, fatty acyl CoA, thiokinase, and CTP.
It includes the activation of glycerol, fatty acids, choline, or ethanolamine, using ATP and coenzymes, then the assembly of the final phospholipid molecule.

Glycerophospholipid Degradation

Phospholipases (A1, A2, C, D) are enzymes involved in the breakdown processes of glycerophospholipids.
They act on different bonds within the phospholipid molecule to release components, such as fatty acids, glycerol, and phosphoryl base.

Sphingophospholipids

Sphingomyelin is a sphingolipid containing sphingosine, a fatty acid, phosphorylcholine (phosphate + choline), serving as a major component in the brain and nerve tissue.
Synthesis starts with palmitic acid, and its combination with serine then acyl-CoA, creating ceramide.
Ceramide then reacts with phosphatidylcholine to form sphingomyelin and diacylglycerol.

Sphingomyelin Degradation

Sphingomyelinase (an enzyme in lysosomes) breaks down sphingomyelin into ceramide and phosphocholine.
Ceramidase then degrades ceramide into sphingosine and fatty acids.

Niemann-Pick Disease

A genetic absence of sphingomyelinase causes Niemann-Pick disease.
Sphingomyelin builds up in the liver and spleen, enlarging these organs and causing problems.
It can also cause unsteady gait, speech difficulties, swallowing problems, widespread brain damage (dementia), and seizures.

Lysosomal Storage Disorders

They are genetic diseases related to the metabolism of sphingolipids or other complex molecules, resulting in their accumulation in lysosomes, causing dysfunction in various organs of the body.
This accumulation leads to many physical problems.

Pulmonary Surfactant

A complex mixture of lipids (90%) and proteins (10%).
Secreted by type II alveolar epithelial cells (pneumocytes).
Crucial for reducing surface tension in the alveoli to prevent collapse.

Surfactant Composition

Phospholipids (mostly phosphatidylcholine).
Neutral lipids.
Hydrophilic proteins (SP-A, SP-D).
Hydrophobic proteins (SP-B, SP-C).

Surfactant Function

Lowers alveolar surface tension.
Stabilizes alveoli, maintaining their size.
Prevents alveolar collapse, allowing easier breathing.
Maintains uniform alveolar size.

Alveolar Stability

Pulmonary surfactant, and alveolar interdependence are two factors that oppose the tendency of alveoli to collapse, allowing the lungs to operate effectively.

Law of Laplace

The relationship between pressure in the alveoli, surface tension, and radius of the alveoli.
Pressure is directly proportional to surface tension and inversely proportional to alveolar radius.
Implications for RDS in newborns: Smaller alveoli will experience greater pressure differentials.

Respiratory Distress Syndrome in Newborns

Premature infants may not produce enough surfactant due to underdeveloped lungs, leading to RDS issues.

Treatment for Respiratory Distress Syndrome

Surfactant replacement therapy is essential for managing RDS in premature infants.

Summary of Questions

Students have questions about phospholipid classifications, common types, synthesis steps, functions, lysosomal storage disorders, cells involved in surfactant secretion, surfactant components, functions, forces maintaining or collapsing alveoli, and more.

Fill in the Blanks

This section provides incomplete sentences related to phospholipids, surfactant, respiratory distress conditions, etc. for students to fill in based on previous information about the various topics discussed.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz focuses on key concepts related to phospholipids, including their classification and functions, particularly in the context of surfactant biosynthesis and respiratory distress syndromes. Students will explore clinical cases such as neonatal respiratory distress syndrome and understand the implications of phospholipid functions in health and disease.