Heart Flashcards
Components of the cardiovascular system:
Heart, blood vessels, and lymphatic vessels
How many circuits distribute blood in the body?
2 circulations - pulmonary and systemic
Describe pulmonary circulation:
Deoxygenated blood is pumped from the heart to the lungs via the pulmonary ARTERY. Oxygenated blood returns to the heart via the pulmonary VEIN
Describe systemic circulation:
Oxygenated blood is pumped from the heart to other tissues via arteries. Nutrient exchange occurs in capillaries. Deoxygenated blood returns from the tissue to the heart via veins
What are the layers of the heart analogous to?
Vessel tunics
Tunica initima:
Innermost layer, contacts the blood. It is a single layer of squamous epithelial cells - endothelium, subendothelial layer, internal elastic lamina
Tunica media:
Middle layer of blood vessel wall - circumferentially arranged Smooth muscle cells, fibroelastic CT, elastic lamellae, external elastic lamina. The smoot h muscle cells produce the extracellular molecules of the t. media
Tunica adventitia:
Outermost layer, Collagenous CT, fibroblasts, longitudinally arranged elastic fibers, smooth muscle cells, vaso vasorum, and nervi vascularis
Where is the heart located?
In the middle mediastinum and it is surrounded by the pericardial sac
The pericardial sac (pericardium) has 2 layers:
- Fibrous pericardium
- Serous pericardium
a. Parietal layer
b. Visceral layer
Describe the fibrous pericardium:
AKA external fibrous layer, it is dense fibroelastic CT that blends in with the surrounding loose CT
Describe the parietal layer of the serous pericardium:
Loose CT plus a layer of squamous epithelium (mesothelium)
Describe the visceral layer of the serous pericardium:
Loose CT plus layer of squamous epithelium (mesothelium). This layer is also called the epicardium of the heart wall
Are the parietal and visceral layers continuous or discontinuous?
They are continuous. They meet at the reflexion at the base of the heart, which forms the sac. In between the parietal and visceral layers of the serous pericardium is the pericardial cavity
Describe the pericardial cavity:
It is a potential space that is lubricated by a thin film of pericardial fluid. This space contains only several milliliters of pericardial fluid and functions to help lubricate the heart to prevent friction during beating.
What does pericarditis result from?
It is an inflammation of the pericardium that can cause friction between the layers and restrict the beating of the heart. IT can result in a pericardial effusion, an abnormal collection of fluid in the pericardial cavity. This interferes with normal heart contraction and decreases the ability of the heart to pump blood effectively.
Trace the path of blood flow in the heart:
Deoxygenated blood returns from the body tissues via the IVC or SVC –> to the right atrium –> passes from right atrium to right ventricle via the tricuspid valve –> blood is then pumped thru the pulmonary semilunar valve –> to pulmonary artery –> delivers the blood to the lungs, where it is oxygenated –> oxygenated blood returns to the left atrium of the heart via the pulmonary vein –> blood passes thru the mitral or bicuspid valve to fill the left ventricle –> oxygenated blood flows from left ventricle –> thru the aortic semilunar valve –> into aorta and arterial tree. Cycle will begin again
The atria are separated by:
The interatrial septum
The ventricles are separated by:
The interventricular septum
The 2 atria and ventricles are separated by:
the cardiac skeleton
What is the cardiac skeleton?
It is the central supporting structure of the heart to which some of the cardiac muscle fibers are attached and with which the valves are supported.
Structures of the cardiac skeleton are composed of::
Dense irregular CT
Components of the Cardiac skeleton:
- Annuli fibrosi
- Trigona fibrosi
- Septum membranaceum
What is the annuli fibrosi?
It surrounds each of the 4 cardiac valves to stabilize them. The core of the valve cusps (leaflets) arise from this connective tissue as well
What is the trigona fibrosi?
There are right and left fibrous trigones, they are triangular islands of CT that serve to strengthen the annuli fibrosi
What is the septum membranaceum?
This is an extension of the cardiac skeleton into the interventricular septum
What are the functions of the cardiac skeleton? (5)
- Separates the atrial musculature from the ventricular musculature
- Functions as sites of origin (points of insertion) or cardiac muscle
- Localizes and stabilizes valves
- Limits the diameter of valves
- Prevents spread of electrical impulses except via the conducting system
The wall of the atria and ventricles is composed of 3 layers:
- Epicardium
- Myocardium
- Endocardium
What is the epicardium?
It is the external layer of the heart wall, AKA the visceral reflection (layer) of the serous pericardium.
The epicardium is analogous to _______ of blood vessel walls.
Tunica adventitia
The epicardium consists of:
- A layer of simple squamous epithelium (mesothelium) and its associated basal lamina
- Epicardial CT
The epicardial connective tissue contains:
Fat, collagen fibers, elastic fibers, arteries, veins, and nerves. The portion of this tissue connecting to the myocardium is referred to as subepicardium
What is located in the connective tissue of the heart?
The coronary arteries, cardiac veins, and nerves that supply the heart - this is typically surrounded by adipose tissue
Where is fat stored in the heart?
The epicardium
What is the middle layer of the heart wall containing cardiac muscle cells called?
The myocardium
The myocardium is analogous to the _______ of blood vessel walls
Tunica media
What are some defining characteristics of cardiac muscle cells?
Cardiac msucle is composed of cardiac muscle cells (myocytes). Cardiac muscle cells contain 1 or 2 nuclei, are packed with myofibrils and large mitochondria, and connect to each other via intercalated discs
What do intercalated discs consist of?
- Fascia adherens
- Desmosomes
- Gap junctions
What is the function of fascia adherens?
It connects two cardiac muscle cells via a junction binding to ACTIN thin filaments in each cell
What is the function of desmosomes in intercalated discs?
They connect the two cells via DESMIN and VIMENTIN intermediate filaments
What is the function of gap junctions in intercalated discs?
They provide for ionic communication and coupling
What are the differences in myocardial thickness?
- The atrial myocardium is thinner than the ventricular myocardium
- The myocardium of the left ventricle is 3x thicker than the myocardium of the right ventricle
How are cardiac muscle cells of the atrium and ventricle different?
Atrial myocardial cells are smaller, have a less elaborate t-tubule system, and have more gap junctions
What is atrial natriuretic factor?
Atrial cardiac muscle cells produce, store, and secrete a polypeptide called ANF
ANF is stored in:
Electron dense granules
ANF is released into:
The surrounding capillaries
The receptors for ANF are found in:
Cells in the adrenal cortex, kidney, and vascular smooth muscle
What does ANF stimulate and what does it do?
It stimulates the kidney to excrete sodium in the urine and functions in regulating fluid balance, in regulating electrolyte balance (sodium levels) and in regulating blood pressure
ANF ________ blood pressure.
Decreases
In the ventricular wall, muscle is arranged in complex spiral and helical patterns called:
Trabeculae carnea
Fingerlike muscular projections from the ventricular wall into the lumen of the ventricle are known as:
Papillary muscles
In the atrial wall, the innermost bundles of muscle fibers are arranged as a latticework that gives a ridged appearance known as the:
Pectinate musculature
What is the internal layer of the heart wall?
The endocardium
What does the endocardium line?
Cardiac valves and papillary muscles, as well as the inner walls of the atria and ventricles
The endocardium is analogous to the _______ of blood vessels
Tunica intima
The endocardium consists of:
- Endothelium (simple squamous) with associated basal lamina
- Endocardial CT - contains fibroblasts, collagen fibers, elastic fibers, and some smooth muscle cells (the deeper layer of this CT, where it connects to the myocardium is called subendocardial layer)
What is the impulse conduction system of the heart?
Consists of specialized cardiac muscle fibers that initiate and conduct electrochemical impulses resulting in the coordinated contraction and relaxation of the heart
What controls contractions of the heart?
Cardiac muscle is capable of contracting without any stimulus from the nervous system, although the autonomic nervous system modulates HR
Stimulation of sympathetic nerves:
Accelerates the heart rate
Stimulation of parasympathetic nerves:
Slows the heart rate
Describe the path of the conduction system:
Impulse initiated in the sinoatrial node (SA) –> impulse travels thru the atrial muscle –> results in atrial contraction –> impulse conducted to the atrioventricular node (AV) via specialized internodal fibers –> at AV node, the signal is delayed –> from AV node, impulse passes to the Bundle of His and the left and right bundle branches where it travels rapidly –> impulse is then conducted to the Purkinje fibers (4 m/s) –> delivers the impulse to a subset of ventricular cardiac muscles –> stimulated ventricular cardiac muscle cells conduct the impulse to other ventricular cardiac muscle cells via gap junctions –> ventricular contraction
Electrocardiogram:
The conduction of the electrical contraction impulses thru the heart is responsible for the production of the voltage trace recorded as the EKG
Where is the SA node located?
In the wall of the right atrium close to the orifice of the superior vena cava
What does the SA node often surround?
A branch of the coronary artery
Describe SA nodal cells:
They are modified cardiac muscle cells that are spindle-shaped and smaller than normal cardiac muscle cells. The myofibrils are fewer in number and less organized than normal cardiac muscle cells (exhibit a paler staining appearance in H&E/trichrome). SA nodal cells are joined by intercalated discs that are less well-developed than in normal cardiac muscle cells
What is the SA node referred to as the pacemaker?
Contraction of the heart is initiated at the SA node. It initiates an impulse that spreads along tracts of modified cardiac muscle fibers (internodal fibers) to the AV node
Where is the AV node located?
In the floor of the right atrium just above the tricuspid valve
Describe the cells of the AV node:
AV nodal cells appear as a mass of small, pale-staining cells isolated by CT (similar in appearance to SA nodal cells), cells are roughly spindle shaped and in some areas form a reticular meshwork. The intercalated discs connect the cells but are poorly developed
What happens to the impulse in the AV node?
It is delayed to allow for filling of the ventricles. Then the impulse passes into the Bundle of His
