chapter19cardio

Base

Cardiovascular system

Pulmonary circuit and systemic circuit

Pulmonary circut

Systemic circuit (includes parts of lung and wall of the heart)

Pulmonary

Systemic

Apex

A. 9 cm

• Pericardium Fibrous layer of dense irregular ct and adeep thin serous layer
• pericardium sac is anchored by legaments to the diaphragm below the sternum anterior and more loosely anchored by fibrous ct to mediastinal tissue dorsal to the heart.

Visceral pericardium (epicardium) covers the heart surface.

• Pericardial cavity and contains pericardial fluid exuded by the serous pericardium.
• Pericardial fluid lubricates the membrane and allows the heart to beat almost with out friction.

• thin Epicardium covering surface
• Thick muscular Myocardium (middle)
• Thin Endocardium lining the interior of the chambers

is the serous memberane on the heart surface. Simple squamous epithelium overlying thin layer of areolar tissue. (some areas thick er adipose other area fat free and translucent some underlying myocardium shows thru.)

Epicardium

lines the interior of the heart chambers. simple squamous endothelium overlying athin areolar tissue layer; it has no adipose tissue. also covers valve surfaces and is continuous with the endothelium of the blood vessels.

Myocardium is composed of cardiac muscle. Thickest layer and performs the work of the heart. Muscle spirals around the heart so when the ventricles contract they exhibit a twisting motion. (cardiac myocytes or cardiocytes)

Fibrous skeleton found in the walls (septa) betwee nthe heart chambers and in fibrous rings around the opening of the heart valves and in sheets of tissue that interconnect these rings.

• 1. provides structural support for the heart around valves and openings of the great vessels, it holds the valve orifices open and prevents them from excessively streching when blood suges thru them.
• 2.It anchors the myocytes and gives them something to pull against.
• 3.nonconductor of electricity insulator betweeen atria and ventricles
• 4.?recoil of the fibrous skeleton may aid in refilling of heart?

Conducting arteries expand during ventricular systole to receive blood, and recoil during diastole. Their expansion takes some of the pressure off the blood so that smaller arteries downstream are subjected to less systolic stress. Their recoil between heartbeats prevents the blood pressure from dropping too low while the heart is relaxing and refilling.

Continuous capillaries found in most skeletal muscle. Endothelial cells, held together by tight junctions, form an uninterrupted tube. A thin protein-carbohydrate layer the basal lamina sounds the endothelium and spearates it from the adjacent connective tissues. The endothelial cells are separated by narrow intercellular clefts. Small solutes like glucose can passs thru these clefts, but hold back fromed elements of the blood and plasma protein, other large molecules. (blood brain barrier)protect and help maintain permiablity

Blood moves in the arteries under pressure, which strech the arteries. Elastic tissue makes sure it returns to normal size. this helps smooth out blood flow.

• Lymph nodes is an organ containing different types of cell. Part of the lymphatic system. Most numberous. Two functions:
• To cleanse the lymph
• Act as a site of T and B cell activation.

• The heart is enclosed in a double walled sac this is called pericardium.
• Outer wall called parietal pericardum made of two layers fibrous and serous layer.
• Serous layers turns and forms visceral pericardium or epicardium
• The sac is anchored by legaments to the diaphragm below the strenum anterior to it and more loosley anchorded by fibrous connective tissue to mediastinal tissue dorsal to the heart.
• Between the parietal and visceral is the pericadial cavity and contains pericardial fluid exuded by the serous pericardium.
• Wall of the heart consists of three layers:
• Epicardium external surface (visceral pericardium simple squamous epithelium overlying a thin layer of areolar tissue.
• Myocardium is cardiac muscle thickest layer perfroms the most work.
• endocardium lines the interior of the heart chambers. It is simle squamous endothelium overlying a thin areolar tissue no adipose overs valve surfaces and is continuous with the endothelium of the blood vessels.

The fetal and adult cardiovascular systems exhibit significant differences, reflecting different sources of respiratory and nutritional support. Most strikingly, the embryonic lungs are collapsed and nonfunctional, and the digestive tract has nothing to digest. The nutritional and respiratory needs of the fetus are provided by the diffusion across the placenta. Although the interatrial and interventricular septa develop early in fetal life, the interatrial partition remains functionally incomplete until birth. The foramen ovale, or interatrial opeing, is associated with a long flap that acts as a valve. Blood can flow freely from the right atrium to the left atrium, but any backflow will close the valve and isolate the two chambers from one another. Thus, blood entering the heart at the right atrium can bypass the pulmonary circuit. A second short-circuit exists between the pulmonary and aortic trunks. This connection, the ductus arteriosus, consists of a short, muscular vessel. With the lungs collapses, the capillaries are compressed and little blood flows through the lungs. During diastole, blood enteres the right atrium and flows into the right ventricle, but it also passes into the left atrium through the foramen ovale. Avout 25 percent of the blood arriving at the risght atrium bypasses the pulmonary circuit in thie way. In addition, more than 90 prcent of the blood leaving the right ventricle passes through the ducus arteriosus and enters the systemic circuit rather than continuing to the lungs.

One thing that distinguishes the heart from other muscles is that the heart muscle is a "syncytium," meaning a meshwork of muscle cells interconnected by contiguous cytoplasmic bridges. Thus, an electrical excitation occurring in one cell can spread to neighboring cells. Another defining characteristic is the presence of pacemaker cells. These are specialized muscle cells that can generate action potentials rhythmically.

• 1. blood enters right atrium from superior and inferior venae cavae
• 2. blood in right atrium flows thru right av valve into right ventricle
• 3. contraction of right ventricle forces pulmonary valve open
• 4. blood flows thru pulmonary valve into pulmonary trunk
• 5. blood is distributed by right and left pulmonary arteries to the lungs, where it unloads co2 and loads o2
• 6. blood returns from lungs via pulmonary veins to left atrium
• 7. blood in left atrium flows thru left av valve into left ventricle
• 8. contraction of left ventricle (same time with step 3) forces aortic valve open
• 9. blood flows thru aortic valve into ascending aorta
• 10.blood in aorta is distributed to every organ in the body, where it unloads O2 and load co2
• 11.blood returns to heart via venae cavae

• Cusps or leaflets are covered with endothelium and consists of two or three fibrous flaps of tissue.
• The atrioventricular AV valves regulate the opening between the atria and ventricles. Tricuspid valve as three cusps and the bicuspid as two or mitral valve. String like tendons chordae tendineae connect to papillary muscles on the floor of the ventricle.
• Semilunar valves pulmonary and aortic valves regulate the flow of blood from the ventricles into the great arteries. the pulmonary valve controls the opening from the right ventricle into the pulmonary trunk, and the aortic valve controls the opening from the left ventricle into the aorta. The three cusps shaped like a shirt pocket. No cords. Opening and closing is the result of pressure gradients.
• Pathologies: Valvular insufficency any failure of a valve to prevent reflux the backwards flow of blood.
• Valvular stenosis is a form of insufficiency in which the cusp are stiffened and opening is constricted by scar tissue. Heart murmur regurgitation of blood through the incompetent valves creates turbulence .
• Mitral valve prolapse MVP is an insufficency in which one or both mitral valve cusps bulge into the atrium during ventricular contraction

Listening to sounds made by the body is called auscultation. Cardiac cycle generates two or three sounds that are audible with a stehoscope. First and second heart sounds S1 S2 described as lub dupp. S1 is lounder and longer. S2 is a little softer and sharper. In children and adolescents it is normal to hear a third sound S3. The heart valves themselves operate silently but S1 and S2 occur in conjuction with the closing of the valves as a result of turbulence in the blood stream and movement of the heart wall. S1 occurs at the beginning of the av valves close as ventricular blood surges back against the cusps. S2 occurs as blood rebounds from the closed semilunar valves and the ventricles expand. Isovolumetric phase because the semilunar valves are closed the av valves have not yet opened and the ventricles are therefore taking in no blood. Heart sound S3 occurs from the result from the transition from expansion of the empty ventricles to their sudden filling with blood.

Pressure gradient pressure difference between two points. point a and b, a is higher in pressure then b. Assuming nothing blocks its way a fluid will flow from a to b down the gradient. pressure at a will fall and b will rise until two are equal.There will be no pressure gradient between a and b flow will cease. flow will also cease if something blocks it way a point of obvious is the opening and closing of heart valves. If the av valve is open the blood flows in the ventricle from the atrium. When the ventricles contracts its internal pressure rises. When the aortic valve opens blood is ejected from the ventricle into the arota. There is always a prositive blood pressure in the arota, and if it is greater than the pressure in the ventricle it holds the aortic valve closed and prvents the expulsion of blood.