Answer
Chemicals that can raise or lower the heart rate are often referred to as "chronotropic" agents. Chronotropy refers to the influence of these agents on the heart's rate of contraction. Agents that increase heart rate are called "positive chronotropic" agents, while those that decrease heart rate are known as "negative chronotropic" agents. Here are examples of each:
**Positive Chronotropic Agents (Increase Heart Rate):**
1. **Epinephrine (Adrenaline):** This hormone is released by the adrenal glands during the "fight or flight" response. It increases heart rate by binding to beta-adrenergic receptors on the heart, promoting a faster rate of electrical impulses and contractions.
2. **Norepinephrine:** Similar to epinephrine, norepinephrine is released during stress or excitement. It has a stimulating effect on the heart rate and contractility.
3. **Thyroid Hormones (Thyroxine):** Thyroid hormones regulate metabolism and also influence heart rate. Excessive levels of thyroid hormones (hyperthyroidism) can lead to an increased heart rate.
4. **Certain Medications (e.g., Beta-Adrenergic Agonists):** Drugs that activate beta-adrenergic receptors, such as certain asthma medications, can increase heart rate as a side effect.
**Negative Chronotropic Agents (Decrease Heart Rate):**
1. **Acetylcholine:** Acetylcholine is a neurotransmitter that, when released, binds to muscarinic receptors on the heart. Activation of these receptors slows down the heart rate by inhibiting the generation of electrical impulses.
2. **Beta-Blockers:** These medications block the effects of epinephrine and norepinephrine on beta-adrenergic receptors. As a result, they decrease heart rate and can be used to treat conditions like high blood pressure, arrhythmias, and certain heart diseases.
3. **Calcium Channel Blockers:** These drugs block the entry of calcium ions into heart muscle cells, leading to a reduced force of contraction and a slower heart rate.
4. **Digitalis (Digoxin):** This medication, derived from the foxglove plant, increases the force of contraction of the heart while also slowing down the heart rate. It's used to treat heart failure and certain arrhythmias.
It's important to note that the effects of these chemicals can vary depending on individual factors and circumstances. Some of these agents have multiple effects on the cardiovascular system beyond heart rate regulation, and their use should be under the supervision of a healthcare professional.
Work Step by Step
Chemicals that can raise or lower the heart rate are often referred to as "chronotropic" agents. Chronotropy refers to the influence of these agents on the heart's rate of contraction. Agents that increase heart rate are called "positive chronotropic" agents, while those that decrease heart rate are known as "negative chronotropic" agents. Here are examples of each:
**Positive Chronotropic Agents (Increase Heart Rate):**
1. **Epinephrine (Adrenaline):** This hormone is released by the adrenal glands during the "fight or flight" response. It increases heart rate by binding to beta-adrenergic receptors on the heart, promoting a faster rate of electrical impulses and contractions.
2. **Norepinephrine:** Similar to epinephrine, norepinephrine is released during stress or excitement. It has a stimulating effect on the heart rate and contractility.
3. **Thyroid Hormones (Thyroxine):** Thyroid hormones regulate metabolism and also influence heart rate. Excessive levels of thyroid hormones (hyperthyroidism) can lead to an increased heart rate.
4. **Certain Medications (e.g., Beta-Adrenergic Agonists):** Drugs that activate beta-adrenergic receptors, such as certain asthma medications, can increase heart rate as a side effect.
**Negative Chronotropic Agents (Decrease Heart Rate):**
1. **Acetylcholine:** Acetylcholine is a neurotransmitter that, when released, binds to muscarinic receptors on the heart. Activation of these receptors slows down the heart rate by inhibiting the generation of electrical impulses.
2. **Beta-Blockers:** These medications block the effects of epinephrine and norepinephrine on beta-adrenergic receptors. As a result, they decrease heart rate and can be used to treat conditions like high blood pressure, arrhythmias, and certain heart diseases.
3. **Calcium Channel Blockers:** These drugs block the entry of calcium ions into heart muscle cells, leading to a reduced force of contraction and a slower heart rate.
4. **Digitalis (Digoxin):** This medication, derived from the foxglove plant, increases the force of contraction of the heart while also slowing down the heart rate. It's used to treat heart failure and certain arrhythmias.
It's important to note that the effects of these chemicals can vary depending on individual factors and circumstances. Some of these agents have multiple effects on the cardiovascular system beyond heart rate regulation, and their use should be under the supervision of a healthcare professional.
