Questions and Answers
What is the sinoatrial node and what is its function?
The sinoatrial (SA) node is a section of nodal tissue located in the upper wall of the right atrium; it sets the rate of contraction for the heart by generating nerve impulses that cause both atria to contract.
Name the chambers of the heart.
Right atrium, left atrium, right ventricle, left ventricle.
Describe the effect on cardiac function of decreased core body temperature.
Decreased core body temperature reduces excitability of the sinoatrial node, leading to a reduced rate of impulse generation, weaker muscle contraction, and a fall in heart rate and stroke volume.
Describe the stages of the cardiac cycle and the order of contraction of the chambers of the heart.
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How is cardiac output calculated?
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Calculate cardiac output per minute when the heart rate is 84 beats per minute and stroke volume is 80 ml.
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Outline the functions of the autonomic nervous system (ANS).
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Describe the two divisions of the ANS and explain the acronym SLUDD.
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What neurotransmitter is released onto the sinoatrial node by the cardiac accelerator nerve, and what is its effect?
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What neurotransmitter is released by the vagus nerve and what is its effect?
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Explain why the inherent rate of discharge of the S-A node is 100 impulses per minute, yet the resting heart rate of an adult is, on average, 72 beats/minute.
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Study Notes
Sinoatrial Node
- Located in the upper wall of the right atrium, the sinoatrial (SA) node is known as the heart's pacemaker.
- Functionally, it sets the heart's contraction rate by generating spontaneous nerve impulses that trigger atrial contraction.
Cardiac Function and Temperature
- Decreased core body temperature reduces the excitability of the SA node.
- This results in a lower rate of impulse generation and weaker muscle contractions.
- Ultimately, both heart rate and stroke volume decrease.
Cardiac Cycle
- The cardiac cycle consists of three main phases:
- Right and left atrial systole (contraction).
- Right and left ventricular systole (contraction).
- Relaxation period for both atria and ventricles (diastole).
Cardiac Output Calculation
- Cardiac output can be calculated using the formula: Stroke volume (mls/beat) x Heart rate (beats/min) = Cardiac output (mls/min).
Cardiac Output Example
- When the heart rate is 84 beats per minute and stroke volume is 80ml, the cardiac output is 6,720 mls/min (6.72 litres).
Autonomic Nervous System (ANS)
- The ANS regulates involuntary bodily functions, including growth, reproduction, and temperature control, mediated by the hypothalamus.
- It has two divisions:
- Sympathetic: coordinates stress responses.
- Parasympathetic: promotes rest and restoration.
Functions of the Two Divisions of ANS
- The sympathetic system is tied to the four 'E' situations: exercise, excitement, emergency, and embarrassment.
- 'SLUDD' (salivation, lachrymation, urination, digestion, defecation) represents functions of the parasympathetic system.
- Typically, when one division is active, the other is suppressed, adapting to information from sensory receptors and chemical signals.
Neurotransmitters and Cardiac Function
- The cardiac accelerator nerve releases adrenaline and nor-adrenaline, increasing SA node excitability and heart contraction rate, enhancing stroke volume.
- The vagus nerve releases acetylcholine, which inhibits the SA node, slowing the heart's rate of contraction.
Inherent Rate of SA Node vs. Resting Heart Rate
- The SA node has an inherent rate of 100 impulses per minute, but the average resting heart rate for adults is about 72 beats/minute due to predominant parasympathetic activity inhibiting impulse generation.
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Description
Explore key concepts about the cardiovascular system with these flashcards. Learn about the sinoatrial node, its definition, and its crucial function in regulating heart contractions. Perfect for students studying human anatomy and physiology.