Downing: Heart Histology Flashcards
What are the components of the circulatory system?
- Cardiovascular system- carries blood between tissues and the heart in both directions
- Lymphatic vascular system- collects lymph, the excess extracellular fluid and delivers it back to the CVS
What are the components of the CVS?
Heart pulmonary circuit (blood to and from lungs) systemic circuit (blood to body) arteries capillaries veins
What are the three layers of the vessel tunics?
- Tunica intima (analogous to the endocardium of the heart)
- Tunica media (myocardium)
- tunica adventitia (epicardium)
How do the three layers of the vessel tunics differ?
- Tunica intima- simple sqaumous epithelial lining, subendothelial connective tissue layer
- media- smooth muscle cells arranged cocentrically around the lumen
- adventitia- fibroelastic connective tissue arranged longitudinally
What are the three layers of the heart?
Endocardium, myocardium, epicardium
What is the endocardium?
The inner lining of the heart that is continuous with the tunica intima of the blood vessels entering and leaving the heart.
What are the 4 layers of the endocardium?
Just remember that it’s made up of subendothelial connective tissue
Which layer of the endocardium contains the purkinje fibers?
subendocardial layer
What is the myocardium?
The middle and thickest layer of the heart
Where is the myocardium the thickest?
Ventricles
What is the myocardium comprised of?
Sheets of cardiac muscle cells that are joined together by intercalated disks forming a contractile network
How is the arrangement of cardiac muscle cells important to the mechanics of the heart.
The cardiac muscle cells are arranged in complex spirals around the heart chambers that allow blood to be “wrung” out of the ventricles.
What is endomysium?
Fine CT found between adjacent cells that contains capillaries and lymphatics.
Where are the roles of specialized cardiac muscle cells?
- Some attach myocardium to fibrous skeleton of the heart
- specialized for endocrine secretions (atronatrouretic polypeptide put out by atrial cells)
- specialized for impulse generation/impulse control (at interface of endo and myo)
What are the two layers of the epicardium?
Inner fibrous layer and the outer serous layer (= visceral layer of the pericardium)
What is found in the inner fibrous layer of the epicardium?
Loose CT, numerous fat cells, bundlesl of nerve fibers, arteries and veins.
What is the outer serous layer composed of?
Simple squamous epithelium
Where does the visceral layer of the pericardium lie?
At the roots of the major vessels entering and leaving the heart, the visceral layer is reflected back to become continuous with the parietal layer of the pericardium.
What is formed between the two layers of the pericardium (visceral and parietal) and what does it contain?
A sac containing lubricating fluid.
What is pericarditis?
Infections within the pericardial sac; can restrict proper beating of the heart d/t adhesions between the two layers of the pericardial sac.
What type of cells compose the impulse conducting system and what do they do?
Modified cardiac muscle cells that coordinate the heart beat.
Where is the SA node?
In the wall of the SVC adjacent to its junction with the right atrium
Does the SA node have it’s own blood supplpy?
yes
What happens when nodal cells spontaneously depolarize?
Starts a wave of depolarization that is conducted via gap junctions across the atria and along internodal atrial pathways that eventually lead the atria to contract.
Where does the AV node lie?
In the interarterial septum near the opening of the coronary sinus
Does the AV node have it’s own artery and autonomic nerve supply?
YES
What does the AV node do?
It delays the impulse from the SA node momentarily than conducts it to the ventricles via the AV bundle of His
What is the AV bundle of HIS?
A conduction path from the AV node through the fibrous CT separating the atrial and ventricular muscle masses to enter the interventricular septum.
What happens to the AV bundle of HIS w/in the interventricular septum?
The AV bundle divides into right and left branches, which become typical purkinje fibers halfway down the septum.
What are purkinje fibers?
Specialized cardiac muscle cells found in the deepest layer of the endocardium. They extend down to the interventricular septum and up the lateral walls of the ventricles.
What makes purkinje fibers unique?
They have a large diameter, more sarcoplasm, more glycogen and fewer myofibrils
What muscles do the purkinje fibers supply?
The papillary muscles of the heart.
Depolarizaton of the purkinje fibers leads to contraction of what muscles?
The papillary muscles and entricular contractions that begin at the apex of the heart and spread up the lateral walls.
What is the cardiac skeleton?
It’s essentially four valve rings joined together, that is made up of a tough, dense, CT base on which the cardiac muscle and valves insert
What are attached to the superior surface of the fibrous skeleton?
Atria and arterial trunks
What is attached to the interior aspect of the cardiac skeleton?
Ventricles and atrioventricular valve leaflets
What forms the valves?
- Endocardium covered by endothelium
2. Core of dense fibro-elastic connective tissue