Action Potential in Cardiomyocytes Quiz

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Questions and Answers

What type of shock is caused by a decrease in blood volume due to hemorrhage?

Obstructive shock

Cardiogenic shock

Low-resistance shock

Hypovolemic shock (correct)

Hemostasis is the body’s natural reaction to an injury that inhibits bleeding and repairs tissue.

True

What is the primary process involved in stopping bleeding during hemostasis?

Vasoconstriction

The natural response to a bleeding injury is called ______.

Hemostasis Signup and view all the answers

Match the type of shock with its cause:

Hypovolemic shock = Decrease in blood volume Low-resistance shock = Excessive vasodilators release Cardiogenic shock = Extreme decrease in cardiac output Obstructive shock = Physical obstruction in circulation Signup and view all the answers

What is the term used to describe the transient period when the TMP exceeds 0 mV?

Overshoot Signup and view all the answers

During the plateau phase, there is a significant outflow of Ca2+ ions.

False Signup and view all the answers

What are the three pumps involved in restoring normal transmembrane ionic concentration gradients?

Na+-Ca2+ exchanger, Ca2+-ATPase, Na+-K+-ATPase Signup and view all the answers

Flow Rate is equal to the __________ difference divided by resistance.

pressure Signup and view all the answers

Match the following phases of action potential with their descriptions:

Phase 1 = Early repolarization with some K+ channels opening. Phase 2 = Plateau phase with balanced Ca2+ influx and K+ efflux. Phase 3 = Repolarization where outflow of K+ exceeds Ca2+ influx. Refractory Period = A period preventing the initiation of a new action potential. Signup and view all the answers

What is the primary function of aldosterone in the kidneys?

Promotes salt and water retention Signup and view all the answers

An increase in blood volume always increases arterial pressure regardless of cardiac output.

False Signup and view all the answers

What is the gravitational effect on blood pressure in mmHg/cm?

0.77 mmHg/cm Signup and view all the answers

The reflex that increases heart rate and peripheral resistance due to falling arterial pressure is triggered by the __________.

baroreceptors Signup and view all the answers

During standing, what happens to mean arterial pressure in vessels below the heart?

It increases significantly Signup and view all the answers

What physiological change is triggered due to a rapid loss of blood volume into the legs when standing?

Decrease in cardiac preload and venous return Signup and view all the answers

Match the following terms with their descriptions:

Baroreceptors = Sensory receptors that detect changes in blood pressure Aldosterone = Hormone that promotes salt and water retention Gravity = The force that affects blood pressure in relation to body position Shock = Condition resulting from a sudden decrease in blood flow to organs Signup and view all the answers

The circulatory system regulates the __________ and amount of blood in the vessels.

velocity Signup and view all the answers

What is the primary cause of a myocardial infarction?

Occlusive thrombosis at the site of plaque rupture Signup and view all the answers

An ECG shows ST segment depression and T wave inversion during a myocardial infarction.

True Signup and view all the answers

What device is implanted to control irregular heartbeats?

Pacemaker Signup and view all the answers

A heart rate of more than 100 beats per minute is known as _____ .

Tachycardia Signup and view all the answers

Match the following terms to their definitions:

Tachycardia = Slower than normal heartbeat Bradycardia = Faster than normal heartbeat Premature heartbeats = Irregular heartbeat Arrhythmia = Abnormal heart rhythms Signup and view all the answers

Which of the following is considered a common disease of the circulatory system?

Hypertension Signup and view all the answers

A myocardial infarction is a condition characterized by the heart muscle receiving too much blood.

False Signup and view all the answers

What can happen if myocardial ischemia is not treated in time?

Myocardial infarction or heart attack Signup and view all the answers

An abdominal aortic aneurysm (AAA) is an abnormal ____ of the aortic wall.

dilatation Signup and view all the answers

Which of the following treatments is NOT commonly associated with coronary artery disease (CAD)?

Heart transplant Signup and view all the answers

Match the following conditions to their descriptions:

Myocardial Ischaemia = Insufficient blood supply to the heart muscle Abdominal Aortic Aneurysm = Weak spot in aorta at risk of rupture Coronary Artery Disease = Blockage due to plaque buildup Arrhythmia = Abnormal heart rhythms Signup and view all the answers

Stable ischemic heart disease is characterized by sudden symptoms and emergency treatment.

False Signup and view all the answers

A common symptom of an abdominal aortic aneurysm may include awareness of ____ or abdominal pain.

pulsation Signup and view all the answers

What factor is primarily responsible for platelet adherence during the initial formation of a platelet plug?

Von Willebrand factor Signup and view all the answers

The conversion of fibrinogen to fibrin results in the formation of long, insoluble threads that help stabilize the platelet plug.

True Signup and view all the answers

What substance stimulates the conversion of prothrombin into thrombin?

Prothrombin activator Signup and view all the answers

The reactive process that forms a temporary plug in response to injury is called _______.

primary hemostasis Signup and view all the answers

Match the following terms with their descriptions:

Thromboxane = Stimulates platelets to clump together Fibrinogen = Soluble plasma protein converted to fibrin Von Willebrand factor = Promotes platelet adherence Prothrombin = Plasma protein converted to thrombin Signup and view all the answers

What effect does standing have on mean arterial pressure (MAP) in an artery below the heart?

MAP decreases due to gravitational effects Signup and view all the answers

An increase in blood volume always leads to a decrease in arterial pressure.

False Signup and view all the answers

What immediate physiological response occurs when a person stands up and experiences falling arterial pressure?

Increased heart rate and peripheral resistance due to sympathetic discharge Signup and view all the answers

A sudden decrease in blood flow to organs and tissues is referred to as ______.

shock Signup and view all the answers

Match the following factors with their effects on arterial pressure:

Increased cardiac output = Decreases blood volume Increased blood volume = Increases arterial pressure Effect of gravity = Decreases pressure in vessels above the heart Sympathetic discharge = Increases heart rate and peripheral resistance Signup and view all the answers

What is the main role of fibrin during the coagulation process?

To stabilize the platelet plug Signup and view all the answers

Fibrinolysis is the process of forming a temporary clot after injury.

False Signup and view all the answers

What substance is generated during fibrinolysis that competes with thrombin?

Fibrin degradation products (FDPs) Signup and view all the answers

The condition of having too much clotting due to abnormal hemostasis is called _____ .

Thrombophilia Signup and view all the answers

Match the conditions with their associated risks:

Thrombophilia = Deep Vein Thrombosis (DVT) Hypocoagulability = Internal bleeding from minor injuries Heart Attack = Inadequate blood supply to the heart Stroke = Interruption of blood supply to the brain Signup and view all the answers

Which of the following processes is involved in converting plasminogen to its active form?

Urokinase Signup and view all the answers

Hypocoagulability can lead to excessive blood clotting.

False Signup and view all the answers

What role does tissue plasminogen activator (t-PA) play in hemostasis?

Activates plasminogen Signup and view all the answers

Fibrinolysis primarily occurs after _____ (when the bleeding has stopped).

a few days Signup and view all the answers

Which medication type is commonly used to prevent excessive clotting?

Anticoagulants Signup and view all the answers

Study Notes

Action Potential in Cardiomyocytes

Phase 1 - Early Repolarization: Na+ leaks into the cell, increasing the transmembrane potential (TMP) to -70mV. The TMP rapidly depolarizes to 0mV and slightly above, creating a "overshoot". Some K+ channels open, allowing an outward flow of K+, returning the TMP to approximately 0mV.
Phase 2 - The Plateau Phase: Ca2+ channels open when the TMP is greater than -40mV, allowing a small but steady influx of Ca2+ down its concentration gradient. This influx is significant for excitation-contraction coupling. Meanwhile, K+ continues to leak out through delayed rectifier K+ channels. These two countercurrents balance, maintaining the TMP at a plateau just below 0mV throughout phase 2.
Phase 3 - Repolarization: Ca2+ channels gradually inactivate. The persistent outflow of K+, now exceeding Ca2+ inflow, brings the TMP back towards the resting potential of -90mV, preparing the cell for a new cycle of depolarization.
Phase 4 - Resting Potential: Normal transmembrane ionic concentration gradients are restored by returning Na+ and Ca2+ ions to the extracellular environment, and K+ ions to the cell interior. Pumps involved include the sarcolemmal Na+-Ca2+ exchanger, Ca2+-ATPase and Na+-K+-ATPase.

Cardiac Cycle Refractory Period

The refractory period is the time during which a muscle cell is unable to respond to a stimulus. It is important in the cardiac cycle to prevent tetanus (sustained contraction) and ensure coordinated heart rhythms.

Flow Rate

Flow rate is directly proportional to the pressure difference between two points and inversely proportional to the resistance. This can be represented by the equation: Flow Rate = Pressure Difference / Resistance.

Circulatory System

The circulatory system consists of two circulations (pulmonary and systemic) to provide adequate blood flow throughout the body.
Aldosterone promotes salt and water retention by increasing water absorption in the kidney.
Angiotensin-converting enzyme (ACE) breaks down bradykinin, a potent vasodilator, thus increasing blood pressure.

Regulation of Arterial Blood Pressure

Causal relationships between arterial pressure and blood volume:
- An increase in arterial pressure due to increased cardiac output induces a decrease in blood volume by promoting fluid excretion by the kidneys. This restores blood volume to its original value.
- An increase in blood volume due to increased fluid ingestion induces an increase in arterial pressure. This restores arterial pressure to its original value by promoting fluid excretion by the kidneys.
- Blood volume is a major determinant of arterial pressure.
Effect of Gravity on Blood Pressure:
- Pressure increases in any vessel below the level of the heart, while it decreases in any vessel above the level of the heart due to gravity.
- Gravitational effect = 0.77 mmHg/cm at the density of normal blood.
  - In an adult in an upright position, if the mean arterial pressure (MAP) at heart level is 100mmHg, the MAP in an artery at the height above the heart is: 100 - (0.77 x 50) = 62mmHg.
- Cardiac output (CO) falls during standing because the rapid loss of blood volume into the legs reduces cardiac preload and venous return, leading to lower stroke volume (SV).
- CO increases during exercise because both heart rate (HR) and SV increase, as well as venous return, until the heart rate approaches its maximum.

Baroreceptors Reflex Mechanism during changes in body posture

Immediately upon standing, arterial pressure in the head and upper part of the body tends to fall, which can lead to loss of consciousness.
The falling pressure at the baroreceptors triggers an immediate reflex, leading to strong sympathetic discharge throughout the body. This minimizes the decrease in pressure in the head and upper part of the body by increasing heart rate and peripheral resistance.

Circulatory System

The circulatory system controls the velocity and amount of blood in the vessel to ensure adequate blood supply throughout the body.
The heart and blood vessels control the amount of blood flow to body parts.
Blood vessels regulate blood flow by contraction and relaxation, along with valves to prevent backflow of blood. This maintains blood pressure upon changes in body posture.

Shock

Shock is a life-threatening medical emergency characterized by a sudden decrease in blood flow to organs and tissues, potentially damaging them.
Lack of blood flow deprives cells and tissues of oxygen and nutrients, impairing function.
Arterial pressure is usually decreased in shock.
Any damage to the heart can be irreversible after prolonged shock.
Types of shock:
- Hypovolemic shock: Caused by a decrease in blood volume due to hemorrhage or loss of fluid.
- Low-resistance shock: Caused by excessive release of vasodilators, as in allergy or infection, leading to a decrease in total peripheral resistance.
- Cardiogenic shock: Caused by factors such as heart attack, leading to an extreme decrease in cardiac output.

Hemostasis

Hemostasis is the body's natural reaction to injury that stops bleeding and repairs damage.
Hemostasis involves a series of processes that occur simultaneously to form a blood clot and stop bleeding.
- Vasoconstriction: The wall of the blood vessel "shrinks" to reduce the size of the area the blood flows through.
- Primary hemostasis (platelet clotting): Platelets adhere to the vessel wall and form a platelet plug.
- Secondary hemostasis (coagulation cascade): A series of enzymatic reactions lead to the formation of a fibrin clot.
- Fibrin clot remodeling (fibrinolysis): The clot is gradually broken down by enzymes.

Vascular Diseases

Vascular diseases encompass any condition that affects the heart or blood vessels.
May come on suddenly or develop gradually over years.
Some examples include:
- Myocardial ischemia
- Abdominal aortic aneurysm (AAA)
- Hypertension
- Coronary artery disease (CAD)
- Myocardial infarction (heart attack)
- Arrhythmia (abnormal heart rhythms)

Prevention of Heart Disease

A healthy lifestyle can significantly reduce the risk of heart disease. This includes:
- Maintaining a healthy weight
- Eating a balanced diet
- Engaging in regular physical activity
- Avoiding smoking and excessive alcohol consumption
- Managing stress levels.

Myocardial Ischemia

Myocardial ischemia (or cardiac ischemia) means the heart muscle is not getting enough blood.
If the lack of blood is severe or lasts more than a few minutes, it can damage the heart muscle.
Treatments include medications and procedures to improve blood flow to the heart muscle depending on the cause.

Abdominal Aortic Aneurysm (AAA)

Abdominal aortic aneurysm (AAA) is a potentially life-threatening condition involving abnormal dilatation of the aortic wall, which supplies blood to the belly, pelvis, and legs.
It represents a weak spot in the blood vessel wall that is at risk for rupturing and causing internal bleeding.
AAA is sometimes referred to as a stomach aneurysm.
Symptoms may include abdominal or back pain, awareness of pulsation, or no symptoms until the aneurysm ruptures.
Treatment includes open surgery or medication to lower blood pressure if the size is not critical.

Coronary Artery Disease (CAD)

Coronary artery disease (CAD) is a narrowing or blockage of the coronary arteries due to plaque buildup.
Plaque buildup limits the blood supply of oxygen-rich blood to the heart.
It is considered a "silent killer" because it can be asymptomatic.
There are two main forms:
- Stable ischemic heart disease: Chronic, coronary arteries gradually narrow over years, and the heart receives less oxygen-rich blood but individuals live with the condition day to day.
- Acute coronary syndrome: Emergency, sudden rupture and formation of blood clots in the coronary artery which block blood flow to the heart.
Treatment often includes lifestyle changes, risk factor management, and medications.

Myocardial Infarction (Heart Attack)

Myocardial infarction (heart attack) is always due to the formation of an occlusive thrombosis at the site of rupture or erosion of the atheromatous plaque in a coronary artery.
This is an extremely dangerous condition caused by a lack of blood flow to the heart muscle.
Without blood flow, the affected heart muscle will begin to die.
If blood flow isn't restored quickly, a heart attack can cause permanent heart damage and even death.
Diagnosis involves ECG; repolarization and depolarization become abnormal relative to the surrounding myocardium.
ECG may show ST segment depression and/or T wave inversion in myocardial infarction.

Arrhythmia (Abnormal Heart Rhythms)

Arrhythmia is an irregular heartbeat, faster or slower than normal.
Different types of arrhythmias are induced from the lower chambers of the heart or slower heart rhythms caused by disease in the conduction system.
Treatment may involve anti-arrhythmic drugs, heart rate control drugs, anticoagulants, or anti-platelet drugs depending on the cause.

Types of Arrhythmia

Tachycardia: Beating fast (>100 beats/m)
- Examples include atrial fibrillation and ventricular fibrillation.
Bradycardia: Beating slow (< 60 beats/m)
- Examples include sick sinus syndrome and conduction block.
Premature heartbeats: Beat irregularly.

Pacemaker

In cases of heart problems with irregular heartbeat, a small battery-operated device (pacemaker) can be implanted under the skin to help regulate the heart rhythm.
The pacemaker consists of:
- The generator: Contains the battery and information to control the heartbeat.
- The leads: Are wires that connect the heart to the generator and carry electrical messages to the heart.

Regulation of Arterial Blood Pressure

An increase in arterial pressure due to an increased cardiac output causes a decrease in blood volume by promoting fluid excretion by the kidneys. This restores arterial pressure to its original value.
An increase in blood volume due to increased fluid ingestion causes an increase in arterial pressure. This tends to restore blood volume to its original value by promoting fluid excretion by the kidneys.
Blood volume is a major determinant of arterial pressure.

Effect of Gravity on Blood Pressure

Pressure increases in any vessel below the level of the heart and decreases in any vessel above.
Gravitational effect = 0.77 mmHg/cm at the density of normal blood.
In an adult in an upright position, if the mean arterial pressure (MAP) at heart level is 100mmHg, MAP in an artery at the height above the heart = 100 - ( 0.77 x 50) = 62mmHg.
Cardiac output (CO) falls during standing because the rapid loss of blood volume into the legs reduces cardiac preload and venous return, leading to a lower stroke volume (SV).
CO increases normally during exercise because heart rate (HR) and SV increase greater and venous return is greater until the heart rate is close to the maximal.

Baroreceptors Reflex Mechanism during changes in body posture

Immediately on standing, arterial pressure in the head and upper body tends to fall, which can lead to loss of consciousness.
Falling pressure at the baroreceptors elicits an immediate reflex, resulting in strong sympathetic discharge throughout the body.
This minimizes the decrease in pressure in the head and upper body by increasing heart rate and peripheral resistance.

Circulatory System

The circulatory system controls the velocity (flow rate) and amount of blood in the vessel to provide enough blood supply throughout the body.
The heart and blood vessels control the amount of blood flow to the body parts to provide adequate blood flow.
Blood vessels control the amount of blood flow by contraction and relaxation to regulate blood flow.
Valves in the blood vessels prevent backflow of blood, so the blood pressure can be maintained upon change of body posture.

Shock

It denotes any situation in which a sudden decrease in blood flow to the organs and tissues damages them because lack of blood flow means the cells and tissues do not get enough oxygen and nutrients to function well.

Primary Hemostasis (platelet clotting)

When endothelial cells are damaged, revealing subendothelial collagen proteins from the extracellular matrix, thromboxane causes platelets to swell, grow filaments, and start clumping together, or aggregating.
Von Willebrand factor causes platelets to adhere to each other and the walls of the vessel.
This process results in a platelet plug that seals the injured area.
If the injury is small, the platelet plug may be able to form within several seconds.

Secondary Hemostasis (coagulation cascade)

When blood vessels are damaged, vessels and nearby platelets are stimulated to release prothrombin activator.
Prothrombin activator activates the conversion of prothrombin, a plasma protein, into thrombin. This reaction requires calcium ions.
Thrombin facilitates the conversion of fibrinogen into long, insoluble fibers of the protein, fibrin.
Fibrin threads wind around the platelet plug at the damaged area of the blood vessel, forming an interlocking network of fibers and a framework for the clot.
This net of fibers traps and helps hold platelets, blood cells, and other molecules tight to the site of injury, functioning as the clot.
This temporary fibrin clot can form in less than a minute and slows blood flow before platelets attach.

Fibrinolysis (Fibrin clot remodeling)

It is the last stage of hemostasis in the body.
It remodels the existing temporary clot into a fibrin clot (permanent).
It involves a process called fibrinolysis during which the body remodels the clot into the same kind of tissue that was there before the injury.
It involves plasminogen, which becomes entrapped within the clot when it formed.
It gives rise to production of fibrin degradation products (FDPs), which compete with thrombin, and thus slow down clot formation by preventing the conversion of fibrinogen to fibrin.

Potential Risk if Hemostasis Does Not Work

Thrombophilia (hypercoagulability or too much clotting): Blood clots too much or too easily, developing or getting stuck in different places in the body, resulting in severe, life-threatening problems. Most medications include antiplatelet, anticoagulant and fibrinolytic (fibrin-breaking or clot-busting) drugs. Common examples of diseases related to too much blood clotting:
- Deep Vein Thrombosis (DVT)
- Heart Attack
- Stroke
Hypocoagulability (not enough clotting): Without proper clotting, even minor injuries can lead to a lot of blood loss, including the risk of internal bleeding.

Vascular Diseases

Common diseases of the circulatory system affect the heart or blood vessels. These conditions may come on suddenly or develop gradually over years.

Examples of Vascular Disease

Myocardial Ischemia: The heart muscle is not getting enough blood (which contains oxygen and nutrients) to work as it should. If this lack of blood from the coronary arteries persists for more than a few minutes, it can damage the heart muscle.
Abdominal Aortic Aneurysm (AAA): An abnormal dilatation of the aortic wall that supplies blood to the belly, pelvis, and legs. This is a potentially life-threatening condition because a weak spot in the blood vessel wall is at risk for rupturing and causing hemorrhage if not treated.

Examples of Disease of the Heart

Hypertension: High blood pressure.
Coronary Artery Disease (CAD): A narrowing or blockage of the coronary arteries, usually due to plaque buildup. Plaque buildup limits the blood supply of oxygen-rich blood to the heart.
Myocardial Infarction (heart attack): Occurs when the flow of blood to a part of the heart muscle is blocked, usually by a blood clot.
Arrhythmia (abnormal heart rhythms): Irregular heartbeat.

Prevention of Circulatory System Problems

Some risk factors cannot be changed, but the following can help reduce risk:
- Physical activity daily
- Eat a heart-healthy diet
- Ease stress
- Sleep well
- Maintain a healthy weight
- Manage conditions such as diabetes, high blood pressure, and cholesterol
- Quit smoking

Risk Factors for Hypertension

Hereditary factors
Obesity
Lack of exercise
Diet high in salt
Heavy drinking
Kidney disease

Risk Factors for Vascular Defect

Cigarette smoking
High levels of saturated fat
High blood cholesterol
Diabetes
Certain drugs
Aging
Some types of stress

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Test your knowledge on the action potential phases in cardiomyocytes. This quiz covers the details of early repolarization, the plateau phase, repolarization, and resting potential. Understand the key ions involved and their roles in cardiac function.