Physiology
Cardiovascular
Sympathetic stimulation causes all of the following cardiovascular effects, EXCEPT for:
Answer:
Sympathetic stimulation increases heart rate and cardiac contractility. Activation of sympathetic nerves also causes arterial and venous vasoconstriction. Arterial vasoconstriction increases total peripheral resistance (TPR) and thus reduces flow, so downstream pressure and venous return will fall. Venoconstriction does not significantly impede flow because venous resistance is low compared to arteries, but it reduces their compliance and hence capacity. Thus vasoconstriction has the same effect as increasing blood volume, and increases CVP. Sympathetic stimulation thus increases cardiac output by increasing heart rate, contractility and CVP, and increases blood pressure by increasing TPR and cardiac output.Autonomic Effects on Heart
Physiology / Cardiovascular / Cardiac Output
Last Updated: 1st June 2023
Both the heart rate and contractility can be modulated by the autonomic nervous system.
Sympathetic Stimulation
Sympathetic stimulation increases heart rate and cardiac contractility. Activation of sympathetic nerves also causes arterial and venous vasoconstriction. Arterial vasoconstriction increases total peripheral resistance (TPR) and thus reduces flow, so downstream pressure and venous return will fall. Venoconstriction does not significantly impede flow because venous resistance is low compared to arteries, but it reduces their compliance and hence capacity. Thus vasoconstriction has the same effect as increasing blood volume, and increases CVP. Sympathetic stimulation thus increases cardiac output by increasing heart rate, contractility and CVP, and increases blood pressure by increasing TPR and cardiac output.
Parasympathetic Stimulation
Parasympathetic stimulation causes a marked decrease in heart rate (negative chronotropic effect) but only a slight decrease in heart muscle contractility (negative inotropic effect) as parasympathetic ventricular innervation is sparse.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
