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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 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

blood is unique it is the only flueid tissue in the body
this is fascinating
for real
what is blood
sujon Reply
lol. the red substance in your body. that circulates food nutrients and oxygen
Blood is composed of plasma and formed elements. The plasma is about 55% of blood and is about 80-90% water usually. The other 20-10% accounts for solutes such as ions, nutrients, gases, and hormones.
Blood is a fluid type of connective tissue and it's formed elements (cells) include RBC, WBC, and plalets.
what is sasamoid bone?
hafeez Reply
how many types of bone on the base of shape
i want join the conversation
juwar Reply
feel free to do so
where are you from ?
hi what's up
well hello
Im from kashmir,but I'm studying in punjab
I'm studying pharmacy at JUST University in jordan
so am i emad 😅
I am Javed Ali
hello i am hafeez from gilgit
explain the mechanism(release and control) of hormonal interplay for fluid and electrolyte.
Cassie Reply
There are three main ways in which hormones may be released. Humoral stimulus - occurs when their is an inbalance in electrolytes in the body. Neural stimulus - occurs when autonomic nerve fibers stimulate glands to release hormones.
Hormonal stimulus - occurs when a hormone causes another hormone to be released from another gland.
what are the main pumps found in the cell membrane
pauline Reply
sodium potassium pump
Differences between ligaments and catilage
joy Reply
differences between catilage and ligaments
Both are different types of connective tissues. Second difference is that cartilage contains chondroblasts rather than fibroblasts. Their is also slight differences on their extracrullar matrix. For ex, cartilages tend to contain more collagen than tendons and ligaments.
Both types of connective tissue also function differently. Ligaments connect bone to bone, while cartilage have a variety of function like cushioning bones and giving structural support like on the nose and ears.
explain the causes of the refractory period of a nerve fiber
Sophia Reply
Refractory period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation. Brief pause in stimulus or excitation.
To add on, the brief pause is produced because of the event of establishing a resting membrane potential that needs to be produced before depolarization (another action potential) can occur again.
The refractory period also gives a chance for neurotransmitters to be replenished on the axon terminal.
what is hypoxia
Akas Reply
I guess it's low supply the oxygen to the tissues
A condition in which tissues (especially the blood) are deprived of an adequate supply of oxygen
hanifa pia uko hapa
Hypoxia is the lack of oxygen concentration in the blood. Therefore, tissues will receive a low concentration of oxygen. Usually our bodies respond to Hypoxia by stimulating erythropoiesis in red bone marrow.
hypoxia is the lack of oxygen in blood absolutely.
hypoxia: is a condition in wich the concentration of oxygen goes down in tissue or all over the body but the low concentration of oxygen in blood is called hypoxiemia.
where is present Glenoid Cavity ?
A- Reply
what is the muscular tissue
Md Reply
muscular tissue is a type of tissue that provide to help in cotraction to aur body.
What's the difference in epithelial, connective, muscular and muscle tissue
and it's similarities
what is limb bone
Akshu Reply
this are bone attaching or joining to the axial bone.axial bone including skull,vertebrate and ribcage
how many bones make up the skull?
22 bones
where is present Glenoid cavity ?
how many bone in skull
almost there are 8 bones in skull
Explain the stages of mitosis and cell division
Bella Reply
Bella, this is a very long process to detail by text. However, to keep it brief, mitosis has four phases in order: prophase, metaphase, anaphase, and telophase which sometimes followed by cytokinesis. Note that some cells do not always do the cytokinesis phase.
As a result, some of the cells in the body are multinuclear (osteoclasts for ex).
explain further
difference between mitosis and meosis
In mitosis, two genetically exact daughter cells (somatic cells) are produced and they are diploid. In meiosis, four genetically unique cells (gametes) are produced and they are haploid.
Meiosis only occurs in reproductive organs. Mitosis is a type of asexual reproduction and is involved in tissue growth and regeneration(repair).
mitosis > Diploid to Diploid meiosis > Diploid to Haploid
systems of human body
Udezue Reply
define lymphatic system And give the composition of lymphatic fluid
sakshi Reply
the network of vessels through which lymphatic drains From the tissue into blood.lymph contain variety of substance like salts, glucose, proteins and fatsand water, white blood cells

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