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Other factors influencing heart rate

Using a combination of autorhythmicity and innervation, the cardiovascular center is able to provide relatively precise control over HR. However, there are a number of other factors that have an impact on HR as well, including epinephrine, NE, and thyroid hormones; levels of various ions including calcium, potassium, and sodium; body temperature; hypoxia; and pH balance ( [link] and [link] ). After reading this section, the importance of maintaining homeostasis should become even more apparent.

Major Factors Increasing Heart Rate and Force of Contraction
Factor Effect
Cardioaccelerator nerves Release of norepinephrine
Proprioreceptors Increased rates of firing during exercise
Chemoreceptors Decreased levels of O 2 ; increased levels of H + , CO 2 , and lactic acid
Baroreceptors Decreased rates of firing, indicating falling blood volume/pressure
Limbic system Anticipation of physical exercise or strong emotions
Catecholamines Increased epinephrine and norepinephrine
Thyroid hormones Increased T 3 and T 4
Calcium Increased Ca 2+
Potassium Decreased K +
Sodium Decreased Na +
Body temperature Increased body temperature
Nicotine and caffeine Stimulants, increasing heart rate
Factors Decreasing Heart Rate and Force of Contraction
Factor Effect
Cardioinhibitor nerves (vagus) Release of acetylcholine
Proprioreceptors Decreased rates of firing following exercise
Chemoreceptors Increased levels of O 2 ; decreased levels of H + and CO 2
Baroreceptors Increased rates of firing, indicating higher blood volume/pressure
Limbic system Anticipation of relaxation
Catecholamines Decreased epinephrine and norepinephrine
Thyroid hormones Decreased T 3 and T 4
Calcium Decreased Ca 2+
Potassium Increased K +
Sodium Increased Na +
Body temperature Decrease in body temperature

Epinephrine and norepinephrine

The catecholamines, epinephrine and NE, secreted by the adrenal medulla form one component of the extended fight-or-flight mechanism. The other component is sympathetic stimulation. Epinephrine and NE have similar effects: binding to the beta-1 receptors, and opening sodium and calcium ion chemical- or ligand-gated channels. The rate of depolarization is increased by this additional influx of positively charged ions, so the threshold is reached more quickly and the period of repolarization is shortened. However, massive releases of these hormones coupled with sympathetic stimulation may actually lead to arrhythmias. There is no parasympathetic stimulation to the adrenal medulla.

Thyroid hormones

In general, increased levels of thyroid hormone, or thyroxin, increase cardiac rate and contractility. The impact of thyroid hormone is typically of a much longer duration than that of the catecholamines. The physiologically active form of thyroid hormone, T 3 or triiodothyronine, has been shown to directly enter cardiomyocytes and alter activity at the level of the genome. It also impacts the beta adrenergic response similar to epinephrine and NE described above. Excessive levels of thyroxin may trigger tachycardia.

Calcium

Calcium ion levels have great impacts upon both HR and contractility; as the levels of calcium ions increase, so do HR and contractility. High levels of calcium ions (hypercalcemia) may be implicated in a short QT interval and a widened T wave in the ECG. The QT interval represents the time from the start of depolarization to repolarization of the ventricles, and includes the period of ventricular systole. Extremely high levels of calcium may induce cardiac arrest. Drugs known as calcium channel blockers slow HR by binding to these channels and blocking or slowing the inward movement of calcium ions.

Questions & Answers

what should be the nature of cell
Kashish Reply
Cells die and reproduce
Nejat
knuckle of the middle finger
James Reply
because of the gases (nitrogen, oxygen)
Nejat
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Joshua Reply
To prevent collision with the lungs, lubricates the heart, protects the heart from infection in the event a peripheral organ is effected, and stabilizes the heart within the mediastinum.
Jeremiah
This app should be updated too much as there is very little information for some topics.I hope you will consider my information....
aman Reply
adenohypophysis is made up of what type of cells and what is the name of those cells?
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motor root of the trigeminal nerve
Vandana
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Joshua
what passes through foramen ovale?
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what are the organelles of a cell
Amina Reply
muscular system
Vandana
nucleus ribosome Golgi body call membrane cytoplasm
Sabina
these are the cellular components that functions to provide energy,remove waste and cell division
Waziri
Organelles of the cell are: Mitochondria,Ribosome,golgi apparatus, nucleus, secretory granules, nuclear e t c
Khadijah
what are local hormones
Richard
Local hormones are hormones that effect the cell that released them or cells near the releasing cell and they do not circulate within the blood stream.
Jeremiah
the trachea bifurcated into how many branches on the right lung
barbie
three lobes
Richard
Explain the normal flow of blood.
Shikha
how can we maintain the internal living things
Choolwe Reply
how many seconds does a human will stop if you sneeze
Kharl Reply
idk
Erika
1 sec not specific
Jane
1_3seconds
Mannu
physiology of vision
Sudipta Reply
Can pure water become gel like?
ovie Reply
No
Abdulazeez
what is Homeostasis
Laura Reply
It is the ability of an organism to co ordinate it's internal environment so as to achieve balance in all areas
ovie
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Sandra Reply
what is physiology
Sandra
The study of how the body works
Joseph
the branch of biology dealing with the functions and activities of leaving organisms and their parts including all physical and chemical processes
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the study of human body . phicically and chemically it's called anotomy physiology
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the branch of biology dealing with the functions and activities of living organisms
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it is the scientific study of the body structure
Choolwe
What Choolwe Muselitata said is the definition of anatomy
KWAKU
Physiology can also be described as the way in which a living organism or bodily part functions
KWAKU
Anotomy is the science which we humen body of structure and function know as the anotomy
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study of the body funtion and structure
Kaoum
functional study of the body
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it is the study about the functions of body organs
Mannu
What is the meaning of incision and drainage
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jeniffer Reply
You start the TPR then BP after explaining the procedure to the patient and your requirements ready.
Dauda
which type of vein to you inject to give infusions?
Belinda
*do
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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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