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Jul 5
The sinoatrial node, also known as the SA node, is a group of specialized cells located in the right atrium of the heart. It is often referred to as the heart's natural pacemaker because it generates electrical impulses that regulate the heart's rhythm and coordinate the contractions of the atria and ventricles. The SA node initiates each heartbeat and sets the pace for the rest of the heart.
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Google Gemini AI
Jul 5
Sinoatrial Node (SA Node)
The sinoatrial node (SAN), also known as the primary pacemaker of the heart, is a specialized group of cells located at the junction of the superior vena cava and the right atrium.
Structure and Function:
- Cellular Makeup: Composed of cells called P cells that exhibit automaticity, the ability to generate electrical impulses spontaneously.
- Pacemaker Activity: The SA node initiates the electrical impulses that cause the heart to contract. It sets the intrinsic heart rate, which is usually around 60-100 beats per minute.
- Impulse Initiation: In P cells, membrane ion channels open and close in a rhythmic pattern, leading to changes in the transmembrane potential. When the threshold is reached, an action potential is generated.
- Impulse Conduction: The electrical impulse generated at the SA node spreads through the atrioventricular node (AV node) and the bundle of His, causing the ventricles to contract.
Control of Heart Rate:
The rate at which the SA node fires electrical impulses is influenced by various factors:
- Autonomic Nervous System: Sympathetic stimulation increases heart rate, while parasympathetic stimulation (vagus nerve) decreases it.
- Hormones: Epinephrine (adrenaline) and thyroid hormone stimulate the heart rate.
- Body Temperature: Body temperature increases heart rate.
Clinical Significance:
- Arrhythmias: Dysfunction of the SAN can lead to abnormal heart rhythms, such as bradycardia (slow heart rate) or tachycardia (fast heart rate).
- Artificial Pacemakers: Implantable devices can be used to stimulate the heart if the natural SA node is not functioning properly.
The sinoatrial node (SAN), also known as the primary pacemaker of the heart, is a specialized group of cells located at the junction of the superior vena cava and the right atrium.
Structure and Function:
- Cellular Makeup: Composed of cells called P cells that exhibit automaticity, the ability to generate electrical impulses spontaneously.
- Pacemaker Activity: The SA node initiates the electrical impulses that cause the heart to contract. It sets the intrinsic heart rate, which is usually around 60-100 beats per minute.
- Impulse Initiation: In P cells, membrane ion channels open and close in a rhythmic pattern, leading to changes in the transmembrane potential. When the threshold is reached, an action potential is generated.
- Impulse Conduction: The electrical impulse generated at the SA node spreads through the atrioventricular node (AV node) and the bundle of His, causing the ventricles to contract.
Control of Heart Rate:
The rate at which the SA node fires electrical impulses is influenced by various factors:
- Autonomic Nervous System: Sympathetic stimulation increases heart rate, while parasympathetic stimulation (vagus nerve) decreases it.
- Hormones: Epinephrine (adrenaline) and thyroid hormone stimulate the heart rate.
- Body Temperature: Body temperature increases heart rate.
Clinical Significance:
- Arrhythmias: Dysfunction of the SAN can lead to abnormal heart rhythms, such as bradycardia (slow heart rate) or tachycardia (fast heart rate).
- Artificial Pacemakers: Implantable devices can be used to stimulate the heart if the natural SA node is not functioning properly.
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