Control of Heart Rate in Mammals
Control of Heart Rate in Mammals
Control of Heart Rate
- The heart rate in mammals is controlled by the autonomic nervous system which is self-governing and operates involuntarily. It has two main divisions: the sympathetic nervous system and the parasympathetic nervous system.
- The sympathetic nervous system is responsible for speeding up the heart rate during times of stress or exercise, known as the fight or flight response.
- The parasympathetic system returns the heart rate to normal after a stressful event has passed, and also maintains a slower heart rate during periods of rest or digestion.
Interplay of Hormones and Nervous System
- The hormone adrenaline plays a crucial role in regulating the heart rate. It is produced in the adrenal glands and released into the bloodstream in response to stress, fear, or physical activity.
- Adrenaline acts upon the sinoatrial node in the heart, which is the natural pacemaker of the heart, and causes it to fire at a faster rate, thereby increasing the heart rate and contractility of the heart muscles.
- Adrenaline acts in conjunction with the sympathetic nervous system to increase heart rate during the fight or flight response.
Role of Baroreceptors and Chemoreceptors
- Baroreceptors are nerve endings located in the aorta and carotid arteries that monitor blood pressure. When blood pressure falls, they send a signal to the brain to invoke the fight-or-flight response and increase heart rate.
- Chemoreceptors in the aorta and carotid arteries monitor the levels of oxygen and carbon dioxide in the blood. When oxygen levels are low or carbon dioxide levels are high, these receptors signal the brain to increase heart rate to boost circulation and gas exchange.
- These receptor-mediated responses are examples of negative feedback.
Impact of Age, Fitness, and Disease
- The average resting heart rate for a healthy adult is between 60 and 100 beats per minute. Factors such as age, physical fitness, and presence of cardiovascular disease can significantly impact heart rate.
- Endurance training can lead to a condition called athletic heart syndrome, where the heart’s resting rate is significantly lower than average due to efficiency, often below 60 beats per minute. This is a healthy adaptation to intense physical training.
- Disease conditions like heart disease, high blood pressure, and diabetes can affect the control of heart rate and lead to arrhythmias or irregular heart rhythms.
Understanding the complex regulation of heart rate is essential to many aspects of mammalian physiology and is linked to many other body systems like the respiratory and endocrine systems.