Sympathetic Nervous System PDF

# Sympathetic nervous system ## By Dr Eman Elmohamady Lecturer of Pharmacology Faculty of Medicine ## The sympathetic nervous system The sympathetic nervous system is a part of the autonomic nervous system (ANS), which is responsible for regulating involuntary bodily functions. The sympathetic...

# Sympathetic nervous system ## By Dr Eman Elmohamady Lecturer of Pharmacology Faculty of Medicine ## The sympathetic nervous system The sympathetic nervous system is a part of the autonomic nervous system (ANS), which is responsible for regulating involuntary bodily functions. The sympathetic nervous system is responsible for the "fight or flight" response, which is a set of physiological changes that prepare the body for a stressful situation. - The sympathetic nervous system plays an important role in regulating **heart rate, blood pressure,** and **breathing**, as well as **digestion** and **metabolism**, **pupils** and **glands**. ### The ANS - The ANS is a network of nerves that control the body's internal organs and glands. It is divided into two branches: the **sympathetic nervous system** and the **parasympathetic nervous system**. - **Sympathetic nervous system:** The sympathetic nervous system is responsible for the "fight or flight" response. It is activated when the body is under stress. - **Parasympathetic nervous system:** The parasympathetic nervous system is responsible for the "rest and digest" response. It is activated when the body is at rest. ### Sympathetic vs Parasympathetic - The sympathetic and parasympathetic nervous systems often have **opposite effects** on the body's organs. For example, the sympathetic nervous system increases heart rate, while the parasympathetic nervous system decreases heart rate. - The sympathetic nervous system is responsible for the **"fight or flight" response**, which prepares the body for action in a dangerous situation. - The **"rest and digest" response**, which is controlled by the parasympathetic nervous system, helps the body to relax and conserve energy. ## Sympathomimetic drugs - Sympathomimetic drugs are drugs that **mimic the effects** of the sympathetic nervous system. They are used to treat a variety of conditions, such as asthma, low blood pressure, and nasal congestion. - Sympathomimetic drugs work by **stimulating** the **adrenergic receptors** in the body. - These receptors are found on the surface of cells throughout the body. ### Adrenaline - Adrenaline is the **most well-known sympathomimetic drug.** It is produced by the adrenal glands and is released into the bloodstream when the body is under stress. - Adrenaline works by **stimulating all types of adrenergic receptors,** which are found throughout the body. - The effects of adrenaline include: - Increased heart rate and blood pressure, Bronchodilation, Vasoconstriction, Sweating, Pupil dilation. ### Adrenergic receptors - There are several different types of adrenergic receptors which can be divided into: - **Alpha receptors:** alpha 1 and alpha 2 receptors, are responsible for vasoconstriction, pupillary dilation, and contractions of the urinary and pyloric sphincters. - **Beta receptors:** beta 1, beta 2 and beta 3 receptors, are responsible for increased heart rate and contractility, bronchodilation, smooth muscle relaxation, glycogenolysis, lipolysis, and thermogenesis. #### Alpha 1 receptors - The alpha 1 receptor is coupled to the Gq protein, which activates phospholipase C (PLC). - PLC catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) into diacylglycerol (DAG) and inositol triphosphate (IP3). - DAG activates protein kinase C (PKC), while IP3 releases calcium ions from intracellular stores. - The increase in calcium ions leads to contraction of smooth muscle. #### Beta 1 receptors - The beta 1 receptor is coupled to the Gs protein, which activates adenylyl cyclase (AC). - AC catalyzes the conversion of ATP to cAMP. - cAMP activates protein kinase A (PKA). - PKA phosphorylates various proteins, leading to increased heart rate and contractility. #### Beta 2 receptors - The beta 2 receptor is also coupled to the Gs protein, which activates adenylyl cyclase (AC). - AC catalyzes the conversion of ATP to cAMP. - cAMP activates protein kinase A (PKA). - PKA phosphorylates various proteins, leading to bronchodilation and smooth muscle relaxation. ### Actions of adrenaline - **Heart:** Adrenaline stimulates the **beta 1 receptors in the heart**, which increases heart rate and force of contraction. This leads to increased cardiac output. - **Blood vessels:** Adrenaline causes **vasoconstriction of blood vessels**. This is due to the stimulation of the **alpha 1 receptors in blood vessels**. However, it is found that adrenaline also stimulates a2 receptors that are often found on the smooth muscle of blood vessels, which may lead to vasodilation in the skeletal muscle. - **Lungs:** Adrenaline causes **bronchodilation**. This is due to the stimulation of **beta 2 receptors in the lungs**. - **G.I.T:** Adrenaline causes **relaxation of the smooth muscles of the G.I.T**, thus slowing down the digestion process. - **Urinary bladder:** Adrenaline causes **constriction of the bladder sphincter**. This is due to the stimulation of **alpha 1 receptors in the bladder**. - **Sweat glands:** Adrenaline stimulates the **sweat glands**, which causes sweating. - **Hair follicles:** Adrenaline causes **hair erection**. This is due to the stimulation of the **alpha 1 receptors in the hair follicles**. ### Therapeutic uses of adrenaline - Adrenaline is used to treat a variety of conditions, including: - **Anaphylaxis:** Adrenaline is the first-line treatment for anaphylaxis, a severe allergic reaction. It is given by injection to reverse the effects of the allergic reaction and prevent death. - **Asthma:** Adrenaline can be used to treat the symptoms of asthma. Adrenaline is often used to treat acute asthma attacks. It works by relaxing the smooth muscles in the airways, which makes it easier to breathe. - **Cardiac arrest:** Adrenaline is used to treat cardiac arrest, a condition in which the heart stops beating. It is given by injection to stimulate the heart to beat again. ### Contraindications to adrenaline - Adrenaline should not be used in people with: - **Hypertension:** Adrenaline can cause a rapid increase in blood pressure. - **Heart disease:** Adrenaline can worsen heart disease. - **Diabetes:** Adrenaline can increase blood sugar levels. ### Beta blockers - **Beta blockers** are a class of drugs that block the effects of the sympathetic nervous system. - Beta blockers work by blocking the beta receptors in the body. - They are used to treat a variety of conditions, such as hypertension (high blood pressure), angina (chest pain), and heart failure. ### Types of beta-blockers - Beta-blockers can be classified into following types: - **Non-selective beta-blockers:** Block both beta 1 and beta 2 receptors. - **Selective beta-blockers:** Block only beta 1 receptors. ### Therapeutic uses of beta blockers - Beta blockers are used to treat a variety of conditions, including: - **Hypertension:** Beta blockers are often used as first-line therapy for hypertension. They work by reducing heart rate and blood pressure. - **Angina:** Beta blockers are used to treat angina, a condition in which the heart does not receive enough blood. They work by reducing heart rate and oxygen demand. - **Heart failure:** Beta blockers are used to treat heart failure. They work by reducing heart rate and workload, which can help to improve heart function. ### Side effects of beta-blockers - Beta blockers can cause a number of side effects, including: - **Bradycardia:** Beta-blockers can slow the heart rate. - **Fatigue:** Beta-blockers can cause tiredness. - **Cough:** Beta-blockers can cause a dry cough. ### Contraindications to beta blockers - Beta blockers should not be used in people with: - **Asthma:** Beta blockers can worsen asthma symptoms. - **Bradycardia:** Beta blockers can make bradycardia worse. - **Heart block:** Beta blockers can block the conduction of electrical signals through the heart. ### MCQs 1. **Adrenaline is added to local anesthetics to:** - a- Delay its absorption - b- Prolong its duration - c- Decrease its toxicity - **d- All of the above** 2. **Adrenaline is the physiological antagonist of:** - a- Atropine - b- Dopamine - **c- Histamine** - d- Acetylcholine 3. **Beta blockers can be used in the following disease:** - a- Bronchial asthma - **b- Hypertension** - c- Hypoglycemia - d- Heart block 4. **Which one of the following is FALSE about uses of beta blockers?** - a- Arrhythmia - b- Heart block - **c- Hypertension** - d- Angina 5. **Which one of the following is FALSE about contraindications of beta blockers?** - **a- pregnancy** - b- Heart block - c- Hypertension - d- Diabetes mellitus 6. **True or false:** - 1- Adrenaline is absorbed well when given orally. **False** - 2- Adrenaline can be used in treatment of hypertension and arrhythmia. **False** 7. **Enumerate 4 uses of adrenaline?** - **Anaphylaxis** - **Asthma** - **Cardiac arrest** - **Local anesthetics** 8. **Mention 4 benefits of addition of adrenaline to local anesthesia?** - **Prolongs the duration of action** - **Reduces bleeding** - **Decreases systemic toxicity** - **Decreases local absorption** 9. **Enumerate 4 uses of beta blockers?** - **Hypertension** - **Angina** - **Heart failure** - **Arrhythmias** ### The Bottom Line The sympathetic nervous system plays an important role in the "fight or flight" response. Sympathomimetic drugs, such as adrenaline, mimic the effects of the sympathetic nervous system. Beta blockers block the effects of the sympathetic nervous system. - Sympathomimetic drugs are used to treat a variety of conditions, such as asthma, low blood pressure, and nasal congestion. - Beta blockers are used to treat a variety of conditions, such as hypertension, angina, and heart failure.