Cardiovascular System Pt.3 - Excitability of the Heart & Blood Vessels Flashcards
How are the cardiac muscle able to cause the heart to contract?
Self-excitable cells; initiate signal telling heart to contract
What is the pathway of the signal propagated to cause the heart to contract
- Sinoatrial Node
- Atrioventricular Node
- Atrioventricular Bundle (Bundle of His)
- Right and left bundle branches
- Purkinje Fibres
Note: These places are where there are clumps of cardiac muscle
How does the Sinoatrial Node work?
Right near the top of the atria; “pacemaker of the heart” which makes it this modified cardiac muscle cell that generates own electrical signals causing contractions of the cardiac muscle atria
What is unique about the SA node?
- Generates it’s own signal
- Autonomic Nervous System can speed up/slow down that signal
- Parasympathetic signal slows RHR from 100bpm ==> 70bpm
- Sends signal to both atria to make them contract in unison
Vagal tone: Slows the RHR from 100 to 70
What is the AV node?
Located on the floor of the right atria; picks up signal from SA node and transfers it down to the AV Bundle
What is the AV bundle?
Modified cardiac muscle cells that carry the signal and splits into the right and left bundle branches
What is the right and left bundle branches?
Bundle branches that continue to carry that electrical signal; split into these right and left and run along the ventricle called purkinje fibres
What are the purkinje fibres?
- Responsible for delivering signal throughout ventricles
- Found in the “interventricular septum” of the ventricles
- Coordinated contraction of both ventricles and papilary muscle (Holds AV valve shut when ventricles contract)
What are the three classes of arteries and how are they different?
- Elastic artery
- Muscular artery
- Arteriole
- Based on elasticity and size
When blood leaves the heart where does it go?
Elastic arteries; very big and elastic arteries that need to take on the massive amount of pressure blood being pumped through them
As blood moves through the body the arteries branch off and become smaller. After the elastic artery where does blood go through?
- Muscular arteries; smaller and less elastic because no high amounts of pressure to withstand since it is all branched out
- After muscular arteries they go to arterioles; much smaller than muscular which then go to capillaries
What does the blood from the artery (arteriole specifically) difuse into?
Capillaries; oxygen diffuses into the capillaries and the arteriole blood picks up CO2
Capillaries have single cell wall
Where does blood go after diffusion occurs with the capillaries
Into the veins; specifically the venule which is the smallest type of veins
After the venule where does the blood go?
Medium-sized vein
After the medium sized-vein where does blood go?
Large veins and into the heart
Inferior vena cava is a large vein
How many layers of blood vessels are there and what are they?
3 layers
- Tunica Interna
- Tunica media
- Tunica Externa
What is the Tunica interna? What is it made of?
- Innermost layer of blood vessels made of simple squamous epithelial cells
- Within arteries and veins & capillaries
How many layers does the capillary have and what does it contain?
- One layer; Tunica Interna
- Simple squamous cells for gas exchange
What layer is superficial to the Tunica Interna but deep to the Tunica Externa
Tunica Media; muscular layer
* Thick on arteriole (Thickest layer of wall) side but not on venous side
* Made of smooth muscle cells
Why must the Tunica Media have a thick muscular layer?
So the arteries can control blood distribution
* If eating and trying to digest but a tiger runs in, your tunica media gets a sympathetic signal to constrict in the GI Tract and the blood goes to the leg muscles to run away
What is the Tunica Externa
Outermost layer only in arteries and veins
* Made mostly of aerioler connective tissue
What is unique to the Tunica Externa and the veins?
Thickest wall for veins
Purpose of Tunica Externa
More structural; anchor blood vessels to nearby structure
What is the purpose of valves in the venous system?
To help return blood to the heart because blood moves up against gravity plus not as much muscle on veins to push.
What ways does blood go through the veins to the heart?
- Moving of blood through the valves and closing them once it moves along
- Massaging action of muscles - Musculovenous Pump
* When muscles near the vein contract it pushes on vein to push blood up
Musculovenous Pump important in lower limbs and diaphragm
