Muscle Anatomy and Diseases Overview

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Questions and Answers

What is the primary consequence of cardiomyopathy?

Inadequate muscle contraction (correct)

Increased muscle strength

Reduced heart size

Enhanced blood circulation

Which statement is true regarding the control of cardiac muscle?

Cardiac muscle contractions are initiated by nerve impulses.

Cardiac muscle is under voluntary control.

Cardiac muscle does not contain actin and myosin filaments.

Cardiac muscle is myogenic in nature. (correct)

Which category does muscular dystrophy belong to?

Joint disorders

Neurogenic muscular atrophies

Muscle fiber disorders (correct)

Disturbances of the neuromuscular junctions

What is a key feature of Duchenne's muscular dystrophy (DMD)?

Deletion in the dystrophin gene Signup and view all the answers

What is the primary cause of ischemic heart disease?

Atherosclerosis leading to blocked arteries. Signup and view all the answers

Which type of muscle is characterized by elongated, non-striated cells?

Smooth muscle Signup and view all the answers

Which of the following is NOT a characteristic of an ideal cardiac marker for myocardial injury?

Released late after injury Signup and view all the answers

What is the relationship between unstable angina and myocardial infarction?

Unstable angina involves reversible myocardial injury. Signup and view all the answers

How do cardiac biomarkers enter the blood circulation?

From necrotic cardiac myocytes Signup and view all the answers

In the context of congestive heart failure (CHF), what does left ventricular dysfunction refer to?

Decreased ability to pump blood. Signup and view all the answers

What condition is primarily characterized by weakness and degeneration of skeletal muscle with no evidence of neural degeneration?

Muscular dystrophy Signup and view all the answers

Which biomarker is commonly used in the treatment of congestive heart failure?

Angiotensin-converting enzyme (ACE) inhibitors. Signup and view all the answers

What is generally elevated even before symptoms develop in individuals with Duchenne's muscular dystrophy?

Creatine kinase (CK) enzyme Signup and view all the answers

Which of the following is a requirement for the measurement of a cardiac marker?

It must be minimally invasive Signup and view all the answers

What structural feature differentiates skeletal muscle from cardiac muscle?

Presence of intercalated discs. Signup and view all the answers

Which of the following conditions is not classified as acute coronary syndrome (ACS)?

Stable angina. Signup and view all the answers

What biomarker is considered the cornerstone for the detection of myocardial infarction (MI)?

cTnT and cTnI Signup and view all the answers

At what time frame do CK-MB or troponin levels typically become elevated after the onset of chest pain?

4 to 6 hours Signup and view all the answers

Which statement about CK-MB is true?

CK-MB is a heterodimer comprising muscle and brain subunits. Signup and view all the answers

What is the recommended time interval for obtaining blood samples to diagnose MI effectively?

2 to 4 hours, 6 to 8 hours, and 12 hours Signup and view all the answers

How do troponins compare to CK-MB in terms of sensitivity and specificity for cardiac injury?

Troponins are substantially more sensitive and specific. Signup and view all the answers

What does an elevated CK-MB and normal total CK indicate during the early stages of an MI?

Uncomplicated myocardial infarction Signup and view all the answers

How is the temporal pattern of CK-MB changes utilized in MI diagnosis?

To distinguish between uncomplicated MI and extension or reinfarction Signup and view all the answers

Which of the following is NOT true regarding myocardial infarction diagnosis?

Clinical history is irrelevant. Signup and view all the answers

What is the primary advantage of measuring cardiac troponins over CK-MB in the context of myocardial infarction?

Troponins remain elevated longer and have better specificity. Signup and view all the answers

Which statement about cardiac troponin T (cTnT) is accurate in the context of its timing after myocardial infarction?

cTnT levels plateau between 1 to 6 days after MI. Signup and view all the answers

How does the diagnostic sensitivity of cardiac troponin I (cTnI) compare to CK-MB within the first 72 hours after myocardial infarction?

cTnI and CK-MB have comparable sensitivity. Signup and view all the answers

Which condition would NOT cause an elevation in cardiac troponin I (cTnI)?

Severe skeletal muscle injury. Signup and view all the answers

What is a significant limitation of myoglobin as a biomarker for myocardial infarction?

Myoglobin lacks specificity due to presence in skeletal muscle. Signup and view all the answers

What can be inferred about the release kinetics of cardiac troponins compared to CK-MB after myocardial infarction?

Troponins and CK-MB have similar release kinetics. Signup and view all the answers

What is a distinguishing feature of troponins compared to creatine kinase (CK) in the context of acute myocardial injuries?

Troponins demonstrate cardiac specificity, unlike CK. Signup and view all the answers

What time frame indicates when cardiac troponin I (cTnI) remains elevated after an acute myocardial infarction?

4 to 10 days. Signup and view all the answers

Study Notes

Cardiac & Skeletal Muscle Disease and Muscle Biomarkers

The presentation covers cardiac and skeletal muscle diseases and associated muscle biomarkers.
The date of the presentation is 17-18/12/2024.

Muscle Anatomy and Function

There are three types of muscle: skeletal, cardiac, and smooth.
Skeletal muscles are made up of unbranched, cylindrical muscle cells arranged in parallel bundles.
Skeletal muscle fibers are neurogenic, meaning their contraction is initiated by nerve impulses.
Skeletal muscle can be divided into fast-twitch and slow-twitch types, which differ in their biochemical nature.
Cardiac muscle is found exclusively in the heart.
Like skeletal muscle, cardiac muscle contains actin and myosin filaments.
Cardiac muscle contraction is involuntary, termed myogenic.
Smooth muscle is composed of elongated, non-striated cells.
Smooth muscle cells have a single, centrally located nucleus and are not under voluntary control.
SMC is found in walls of tubes and sacs like blood vessels, the uterus, bladder, and intestines.

Pathological Conditions

Ischemia is a condition where an organ has an insufficient blood supply to maintain essential functions.
Atherosclerosis is the most common cause of ischemia.
In atherosclerosis, cholesterol deposits in arterial walls, potentially occluding the arteries.
Ischemic heart diseases range from unstable angina to frank myocardial infarction (with large areas of necrosis).
Acute Coronary Syndrome (ACS) is a group of conditions that suddenly obstruct or severely limit blood flow to the heart muscle.
Congestive Heart Failure (CHF) involves a decreased capacity to pump blood.
CHF represents a spectrum of diseases, ranging from left ventricular dysfunction to end-stage overt CHF.
An important therapy for CHF is treatment with angiotensin-converting enzyme (ACE) inhibitors.
Cardiomyopathy is characterized by inadequate muscle contraction caused by direct damage to myocardial cells, typically resulting in heart failure.
Cardiomyopathy often manifests as an enlargement of all four chambers of the heart.

Diseases of Skeletal Muscle

Diseases of skeletal muscle are characterized by motor function impairment, such as muscular weakness.
The three major categories of muscle disorders include neurogenic muscular atrophies, muscle fiber disorders (myopathies), and disturbances of the neuromuscular junctions.
Muscular dystrophy is a general term for a group of genetic, chronic muscle diseases.
General characteristics include progressive weakness and skeletal muscle degeneration without neural degeneration.
These genetic diseases have varying inheritance patterns.
- Disease progression, onset age, and fiber type effects differ among the various types of muscular dystrophy.

Disorders of Muscle Fibers: Muscular Dystrophies

Pseudohypertrophic muscular dystrophy (Duchenne's muscular dystrophy – DMD) is the most common type.
Most people with DMD have a deletion in the dystrophin gene and a defective dystrophin protein.
Serum creatine kinase (CK) enzyme is often elevated even before symptoms appear.
No effective treatment currently exists for DMD, though gene therapy is a promising avenue.

Changes of Analytes in Disease

Myocardial damage causes necrotic cardiac myocytes to release intracellular components.
These released molecules are detectable in the peripheral circulation and called cardiac biomarkers.
An ideal cardiac biomarker should be abundant and present in myocytes but low in blood.
It should be released early after injury and absent in non-myocardial tissues.
It must show a direct relationship between plasma level and myocardial injury.
It should persist in the blood for sufficient diagnostic time.
Measurement of the biomarker should be easy, inexpensive, and rapid.
Myocardial Infarction (MI) is a damaging process in which ischemic injury is irreversible, leading to cell death and necrosis.
AMI diagnostic relies on patient history, ECG interpretation, and serum cardiac biomarker levels.

Cardiac Biomarkers in MI

CK-MB is one of three isoenzymes derived from total creatine kinase (CK).
Total CK is a dimeric enzyme with two subunits, "M" (muscle) and "B" (brain).
CK-MB is the first cardiac biomarker to meet most criteria.
Myocardium is the only tissue with a substantial amount of CK-MB.
MI diagnosis requires analyzing blood samples taken at specific intervals.
Guidelines recommend collecting samples at 2-4 hours, 6-8 hours and 12 hours after suspected MI.
The time frame can be adjusted based on previous results or high suspicion of MI.
During the initial MI course, elevated CK-MB but normal total CK can be present.
CK levels sometimes may not exceed the limit.
Troponin (T) levels are more sensitive and specific for cardiac injury than CK-MB.
Troponin is the preferred biomarker for cardiac disease.

Diagnostic Use of Cardiac Troponins

Troponin is crucial for MI diagnosis and risk assessment in ACS.
The release kinetics of cTnI and cTnT are similar to CK-MB after MI.
Troponin remains elevated in blood for 4 to 10 days after MI.
Very low troponin values in patients without cardiac disease facilitate lower ranges for MI determination.
Troponin's specificity helps differentiate events from skeletal muscle injury, reducing uncertainty caused by increased CK-MB.

Cardiac Troponin I (cTnI)

cTnI, despite a smaller molecular weight than cTnT, has similar release kinetics and use in early MI detection to cTnT and CK-MB.
cTnI offers the same advantages over CK-MB in major clinical applications.
cTnI remains elevated for 3 to 7 days after acute MI.
cTnI and CK-MB display comparable diagnostic sensitivity.
cTnI maintains improved sensitivity 72 hours after MI to 96 hours compared to CK-MB.
Unlike CK-MB, cTnI is not elevated in extreme skeletal muscle injury cases, including marathon running or muscular dystrophy.

Cardiac Troponin T (cTnT)

After an MI, cTnT increases in the serum after 4 hours.
cTnT reaches a peak or plateau between 1 and 6 days.
A subsequent peak may arise from a secondary pool of "bound fraction."
According to WHO, cTnT and CK-MB present similar sensitivities for the first 48 hours after chest pain onset.
cTnT's extended serum life may provide more comprehensive information on recent myocardial dysfunction.

Sensitivity and Specificity of Muscle Biomarkers

(Detailed table provided of sensitivity and specificity of various biomarkers for detecting myocyte necrosis).

Myoglobin

Myoglobin is found in both cardiac and skeletal muscles, thereby limiting its diagnostic specificity for MI.
Myoglobin appears as the earliest marker for MI.
A rise in blood myoglobin is often detectable within 1 to 2 hours of symptom onset.
Myoglobin presence is not specific to cardiac tissue, and patients with renal failure, injuries, or skeletal muscle diseases can also show abnormal myoglobin concentrations.
Myoglobinuria presence can be used to determine massive muscle cell damage.

CK & CK Isoenzymes in Non-MI Conditions

In conditions other than MI, the isoenzyme pattern does not usually follow the typical rise-and-fall pattern.
Instead, it's often chronically elevated in various skeletal muscle diseases.
Conditions like Duchenne's muscular dystrophy, polymyositis, and rhabdomyositis often exhibit markedly elevated CK-MB in serum.
The high level of total CK in skeletal muscle (5 to 10 times that of cardiac) leads to dramatically higher CK levels in skeletal muscle disorders. (More details on specific CK value increases for different muscle pathologies given in a table).

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Description

This quiz explores the intricacies of cardiac and skeletal muscle diseases, as well as the relevant muscle biomarkers associated with these conditions. Gain a deeper understanding of muscle anatomy, function, and the differences between muscle types, including their contraction mechanisms. Ideal for those interested in anatomy and physiology.