Question

Explain how the sympathetic nervous system (and endocrine system) act directly to regulate heart rate and thus cardiac output. Include a detailed description of the mechanism (include the target cells, the proteins, signaling molecules, ions, and changes in membrane pontial where appropriate) and explain how the mechanism operates to alter heart rate.Explain how the parasympathetic nervous system acts to directly regulate cardiac output (1 mechanism). Discuss each mechanism separately including a detailed description of each mechanism (include the target cells, the proteins, signaling molecules, ions, and changes in membrane pontial where appropriate). Make clear how each affects cardiac output. This shoul require about half a page.Explain in detail the Frank-Starling law of the heart. Be sure to define what it is, and describe how it operates (the mechanism). Explain why it is an important way that cardiac output is regulated. Demonstrate your understanding by describing a particular scenario when it would operate and its significance.

Answer 1

Sympathetic nervous system:The sympathetic nervous system directs the body's rapid involuntary response to dangerous or stressful situations. A flash flood of hormones boosts the body's alertness and heart rate, sending extra blood to the muscles.The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate. ... The reduced heart rate results from an increase in activity of the parasympathetic nervous system, and perhaps from a decrease in activity of the sympathetic nervous system.

The types of sympathetic or adrenergic receptors are alpha, beta 1 and beta 2. Alpha-receptors are located on the arteries. When the alpha receptor is stimulated by epinephrine or norepinephrine, the arteries constrict. This increases the blood pressure and the blood flow returning to the heart.Damage to the vagus nerves, providing the parasympathetic innervation of the heart, will affect the ability to decrease the heart rate, leading to tachycardia. Similarly, damage to the sympathetic fibres contributing to the cardiac plexus can reduce the ability to increase heart rate, causing bradycardia.The sympathetic nervous system releases norepinephrine (NE) while the parasympathetic nervous system releases acetylcholine (ACh). Sympathetic stimulation increases heart rate and myocardial contractility.

Mechanism:The sympathetic nervous system (SNS) has a wide variety of cardiovascular effects, including heart-rate acceleration, increased cardiac contractility, reduced venous capacitance, and peripheral vasoconstriction.Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including many of those in the skin, the digestive tract, and the kidneys. This occurs as a result of activation of alpha-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons.There are three parts to your autonomic nervous system: 1 The sympathetic system is responsible for your body's 'fight or flight' reaction. 2 The parasympathetic system looks after the workings of your body during rest and recuperation. It also controls your heart rate and body temperature under normal conditions.For example, the sympathetic nervous system can accelerate heart rate, widen bronchial passages, decrease motility of the large intestine, constrict blood vessels, increase peristalsis in the esophagus, cause pupillary dilation, piloerection (goose bumps) and perspiration (sweating), and raise blood pressure.

The sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. The parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.

Parasympathetic nervous system: The parasympathetic nervous system is one of three divisions of the autonomic nervous system. Sometimes called the rest and digest system, the parasympathetic system conserves energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract.

Mechanism:The parasympathetic nervous system (PNS) controls homeostasis and the body at rest and is responsible for the body's "rest and digest" function. The parasympathetic nervous system is responsible for the body's rest and digestion response when the body is relaxed, resting, or feeding. It basically undoes the work of sympathetic division after a stressful situation. The parasympathetic nervous system decreases respiration and heart rate and increases digestion.When the parasympathetic nervous system is activated, it produces a calm and relaxed feeling in the mind and body. ... There are many techniques that a person can use to strengthen and activate their parasympathetic nervous system, causing a relaxation response in their body. For example: Spend time in nature.The autonomic nervous system is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.

Frank -Starling law of Heart: The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction (the end diastolic volume), when all other factors remain constant.

The Frank-Starling Law is the description of cardiac hemodynamics as it relates to myocyte stretch and contractility. The Frank-Starling Law states that the stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction.

Significance:The Frank–Starling law of the heart indicates that the increased filling pressure of the right heart results in increased cardiac output. Any increase in output of the right heart is quickly communicated to the left heart as an increased filling pressure

As impaired myocyte contractility results in depression of ventricular stroke volume and cardiac output, the Frank-Starling mechanism has compensatory effects. As the elevated ventricular diastolic volume increases the stretch on the myocardial fibers, there will be a subsequent increase in stroke volume.

The Frank–Starling law of the heart represents the relationship between stroke volume and end diastolic volume. The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant.

The Frank-Starling mechanism allows the cardiac output to be synchronized with the venous return, arterial blood supply and humoral length, without depending upon external regulation to make alterations. The physiological importance of the mechanism lies mainly in maintaining left and right ventricular output equality.