Cardiovascular system 2

Name the chambers of the heart in the Diagram

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Calculate cardiac output per minute when the heart rate is 84 beats per minute and stroke volume is 80ml.

80ml x 84 = 6,720 mls/min (6.72 litres)

Describe the effect upon cardiac function of the following: Decreased core body temperature

Reduced excitability of the sinoatrial node leads to... Reduced rate of impulse generation Muscle contraction becomes weaker Heart rate and stroke volume falls

Describe the stages of the cardiac cycle and the order of contraction of the chambers of the heart.

Right and left atrial systole - Right and left ventricular systole - Relaxation period (atrial and ventricular diastole)

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.

The resting heart rate is approximately 72 beats per minute at rest because parasympathetic activity is predominating, so acetylcholine is being released onto the SA node, and the effect is to inhibit impulse generation so that the heart is beating more slowly than it would if left to its own devices!

What is the sinoatrial node? What is the function?

The sinoatrial (SA) node is a section of nodal tissue that is located in the upper wall of the right atrium. The SA node is also referred to as the pacemaker of the heart. Function: Sets the rate of contraction for the heart. Spontaneously contracts and generates nerve impulses that travel throughout the heart wall causing both atria to contract.

Describe the two divisions of the ANS and explain the acronym SLUDD, and what the four 'E' situations are...

The sympathetic system coordinates the stress response and activities associated with being alert, watchful and able to respond to risks/danger. It is responsible for the physiological reactions involved with the four 'E's - exercise, excitement, emergency and embarrassment. The parasympathetic system, when active, promotes physiological processes involved with rest and restoration/maintenance of body tissues,. 'SLUDD' stands for salivation, lachrymation, urination, digestion and defeacation. When awake and active, the sympathetic system tends to predominate, whereas the parasympathetic is more active when sleeping and at rest. The two systems work in conjunction, generally when one is active, the other is suppressed and its activity inhibited. The relative balance depends upon a variety of incoming information - from other brain areas, from sensory receptors in the body (muscles, joints, skin), and from chemical signals in the bloodstream.

How is cardiac output calculated?

Stroke volume (mls/beat) x heart rate (beats/min) = cardiac output (mls/min)

What neurotransmitter is released by the Vagus nerve and what is its effect?

As a parasympathetic nerve, the vagus nerve releases acetylcholine onto the SA node. This has the opposite effect ,of inhibiting the SA node, so that it generates fewer impulses and the heart's rate of contraction slows.

What neurotransmitter is released onto the sino-atrial node by the cardiac accelerator nerve, and what is its effect?

As a sympathetic nerve, the CAN releases adrenaline and nor-adrenaline (epinephrine and norepinephrine). The effect is to increase the excitability of the SA node so that it generates more impulses and so increases the rate of contraction of the heart (it also sends fibres into the ventricular myocardium, in which the release of adrenaline increases the force of contraction of the muscle, so increasing stroke volume).

Outline the functions of the autonomic nervous system (ANS)

This is the part of the nervous system that controls and regulates involuntary (those things that happen automatically and are not under conscious control) activity in the body tissues. The hypothalamus is the 'control centre' for many autonomic functions, including growth and maturation, reproduction, food and water intake (hunger, satiety and thirst) sleep, temperature control. It has two divisions - Sympathetic Parasympathetic It acts on body tissues through a network of nerves that stimulate or inhibit cell activity, and through the release of hormones