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Atrioventricular (av) node

The atrioventricular (AV) node    is a second clump of specialized myocardial conductive cells, located in the inferior portion of the right atrium within the atrioventricular septum. The septum prevents the impulse from spreading directly to the ventricles without passing through the AV node. There is a critical pause before the AV node depolarizes and transmits the impulse to the atrioventricular bundle (see [link] , step 3). This delay in transmission is partially attributable to the small diameter of the cells of the node, which slow the impulse. Also, conduction between nodal cells is less efficient than between conducting cells. These factors mean that it takes the impulse approximately 100 ms to pass through the node. This pause is critical to heart function, as it allows the atrial cardiomyocytes to complete their contraction that pumps blood into the ventricles before the impulse is transmitted to the cells of the ventricle itself. With extreme stimulation by the SA node, the AV node can transmit impulses maximally at 220 per minute. This establishes the typical maximum heart rate in a healthy young individual. Damaged hearts or those stimulated by drugs can contract at higher rates, but at these rates, the heart can no longer effectively pump blood.

Atrioventricular bundle (bundle of his), bundle branches, and purkinje fibers

Arising from the AV node, the atrioventricular bundle    , or bundle of His    , proceeds through the interventricular septum before dividing into two atrioventricular bundle branches    , commonly called the left and right bundle branches. The left bundle branch has two fascicles. The left bundle branch supplies the left ventricle, and the right bundle branch the right ventricle. Since the left ventricle is much larger than the right, the left bundle branch is also considerably larger than the right. Portions of the right bundle branch are found in the moderator band and supply the right papillary muscles. Because of this connection, each papillary muscle receives the impulse at approximately the same time, so they begin to contract simultaneously just prior to the remainder of the myocardial contractile cells of the ventricles. This is believed to allow tension to develop on the chordae tendineae prior to right ventricular contraction. There is no corresponding moderator band on the left. Both bundle branches descend and reach the apex of the heart where they connect with the Purkinje fibers (see [link] , step 4). This passage takes approximately 25 ms.

The Purkinje fibers    are additional myocardial conductive fibers that spread the impulse to the myocardial contractile cells in the ventricles. They extend throughout the myocardium from the apex of the heart toward the atrioventricular septum and the base of the heart. The Purkinje fibers have a fast inherent conduction rate, and the electrical impulse reaches all of the ventricular muscle cells in about 75 ms (see [link] , step 5). Since the electrical stimulus begins at the apex, the contraction also begins at the apex and travels toward the base of the heart, similar to squeezing a tube of toothpaste from the bottom. This allows the blood to be pumped out of the ventricles and into the aorta and pulmonary trunk. The total time elapsed from the initiation of the impulse in the SA node until depolarization of the ventricles is approximately 225 ms.

Questions & Answers

yellow marrow has been identified as
Raychelle Reply
Which of the following accurately describe external resipration
Gwendolyn Reply
from the heart to the lungs
Phee
I think it's not outside organ of respiratory all respiratory organ are inside of human body
Moha
diffusion of CO2 and oxygen at a pulmonary capillary surrounding an alveolar sac.
Jeremiah
In other words, from the external environment to the lungs (alveoli) then to the pulmonary capillary then to the heart. So this is a stage of inhalation. inhale = external respiration.
Jeremiah
What kind of discussion
horyaal Reply
what is the function of the placenta
Nchimunya Reply
The placenta acts to provide oxygen and nutrientsto the fetus, whilst removing carbon dioxide and other waste products.
Moha
Also it's the barrier through which the mother is connected to the fetus.
Samuel
I want to discuss... atherosclerosis.., everything about it, about to treatment n prevention at age 50 +
Doctors
Please participate in discussion
Doctors
ok let's discuss now
Moha
first define the word artherosclerosis
Moha
a disease of the arteries characterized by the deposition of fatty material on their inner walls.
tabe
hardening of the arteries, due to fats..
jenelyn
Q = which type of fat utilized for this.., I.e LDL, HDL, TG, VLDL...?
Doctors
Atherosclerosis is a condition of deposition of plaque inside the artries
Arvind
Plaque include such as fat, chalestrol, calcium etc
Arvind
Thank you kumar...., is there any way that we can protect these plaques without any medicines., I. e exercises n food stuffs
Doctors
go to the gym
Moha
what is chylomicrons?
Moha
how can plaque buildup in The angina or vessels ?
Moha
Atherosclerosis is a condition of deposition of plaque inside the artries
Doctors
atherosclerosis can also be caused by tortuousness of arteries with old age as contributing factor.
edward
You tube Prof Fink...he is an amazing lecturer and does a brilliant job on arteriosclerosis
Jacqueline
what are cell
Chigozie Reply
The basic structural and functional unit of any living thing. Each cell is a small container of chemicals and water wrapped in a membrane. 
Yusuf
cell is the structural and functional basic unit of life
Zaid
So every living thing was Created From a Cell
Anthony
from a fusion of two cells , the sperm and the egg
Shikoh
What is the only bone that doesn't have any articulation?
Jimmy
that magical fusion of cells
OBED
why body immune system attack and destroy the body own cell during type 1 diabetes?
Sanamacha Reply
It's an autoimmune disease... targeting the pancreas
Claudia
what are the three genetic defects of pregnancy?
Belinda Reply
structure of fallopian tubes
Akash Reply
what z the role played by the transport system
zinitha Reply
how fats are digested in the human body
Nabukwasi Reply
Fat digestion begins in the stomach but some argue in that it starts in the mouth. Reason is because the sublingual gland secretes an enzyme called lingual lipase. However, this enzyme is not activated until it comes into contact with gastric fluids (HCl). In the stomach, HCl breaks down the lipid..
Jeremiah
due to body heat
Mule
into smaller molecules. Going from a triglyceride and a fatty acid to a monoglyceride and a a fatty acid no longer bound to one another. This is known as lipolysis.
Jeremiah
After lipolysis in the stomach from gastric and lingual lipase, an acidic chyme is produced after stomach churning the bolus. The chyme exits the stomach at the pyloric sphincter and enters the first section of the small intestine known as the duodenum.
Jeremiah
in the duodenum. An alkaline mucus from goblet cells neutralizes the acidic chyme to prevent acid burns. After that, the pancreas and gallbladder secrete a number of enzymes to continue lipolysis. Bile from the gallbladder enters the duodenum via common bile duct. The acinar cells in the pancreas...
Jeremiah
secretes pancreatic lipase after enteroendocrine cells in the duodenum secrete a stimulator hormone called CCK. Cck stimulates bile synthesis and secretion as well as pancreatic lipase.
Jeremiah
Bile emuslifies the lipid, allowing the lipases to continue lipolysis
Jeremiah
this breakdown continues until it reaches the jejunum of the small intestines. At this point, the lipid has been broken down small enough to absorbed into the blood stream. So villi in the jejunum, absorb the contents.
Jeremiah
ileum, the last small intestine region, absorbs anything that wasn't absorbed previously. Like minerals, vitamins, bile salts, water soluble material. Villi here complete that task. Fatty acid and glycerol however, are absorbed by lacteals. small lymph vessels. And are transported to the liver.
Jeremiah
That concludes lipid digestion. Anything else that remains is deficated after it travels through the large intestines.
Jeremiah
parents with blood group AB & 0,,,what will b the blood group of their offspring
imran
what are the different branches of anatomy
Nabukwasi
hopefully that helped.
Jeremiah
which ion is low of blood level?
Ezra Reply
what is coagulation?
feng Reply
liquid turning to solid... blood clots.
Kristy
coagulation : liquid blood into blood clots caused with a coagulant.
jaime
when the blood turn from liquid form to solid
June
it said to coagulate by the action of active plasma protein called *fibrin*
Hassan
I.e liquid inform of blood when to solid
Hassan
it is the process by which blood becomes more viscous or becomes thick
CHRISTOPHER
cloting of blood cells
Kabange
clot of blood
Moses
the process of forming semi solid lumps in a liquid
rida
conversion of blood to solid state
Ezra
semi solid., rather than solid form
Doctors
what is pivot functioned
Ever
to less thefriction
Hirsi
how to calculate the micrograph
Ampong Reply
it can be used to knw the disease condition
Akbar Reply
which gland secret tears
Opoku
lacrimal glands
Diego
explain the blood supply to the brain
Brenda Reply
There are two paired arteries which are responsible for the blood supply to the brain; the vertebral arteries, and the internal carotid arteries. These arteries arise in the neck, and ascend to the cranium.
Sabrina
two arteries main vertebral arteries & internal carotid artery
Akbar

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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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