Final answer:
Heart rate and contraction force are controlled by hormones such as adrenaline, norepinephrine, and thyroid hormones, along with the autonomic nervous system. Environmental factors and ions like calcium, potassium, and sodium also influence heart function. All these components together maintain homeostasis in the cardiovascular system.
Step-by-step explanation:
The hormones that control heart rate (HR) and contraction force primarily involve the autonomic nervous system and the endocrine system. The control of cardiac muscle contractions, or heartbeats, is a sophisticated process that involves specialized pacemaker cells in the heart. These cells are directly responsible for setting the pace of the heartbeat without conscious control and are influenced by signals from the autonomic nervous system to either increase or decrease heart rate.
One of the main hormones that influence HR and contraction force is adrenaline (or epinephrine), which is released during the body's fight-or-flight response. When adrenaline is introduced to the bloodstream, it causes the heart rate to increase, which in turn increases blood pressure and prepares the body for a quick response to a perceived threat. Along with adrenaline, norepinephrine (NE) and thyroid hormones also play a role in modulating heart function.
Certain ions, such as calcium, potassium, and sodium, are vital for the proper electrical functioning of the heart and can affect HR and contraction strength. Environmental factors including body temperature, hypoxia, and pH balance also have an impact. These all must be precisely regulated to maintain homeostasis and optimum cardiovascular function.
Beyond HR, hormones and other factors can influence stroke volume (SV), which is the volume of blood pumped from the heart with each beat. SV depends on preload, contractility, and afterload, all key factors in determining how much blood the heart pumps and how forcefully it does so. The same hormones that affect HR also affect these components, thus impacting overall cardiac function.