The Cardiovascular System



The Cardiovascular System

The major parts of the cardiovascular system include:

•the heart – the blood “pumper”; has 4 chambers

•arteries- carry blood away from the heart

•veins- carry blood to the heart

•capillaries- connections between the arteries and the veins; found in

peripheral parts such as the organs and skin

Function of the CVS:

-pumps blood with oxygen, carbon dioxide and nutrients throughout the body

The role of blood in the CVS:

-red blood cells carry the oxygen and carbon dioxide

-white blood cells fight infection

- nutrients are carried to the body

Anatomy of the heart:

Coverings: pericardium- encloses the heart and the proximal ends of the large blood vessels

Structure of Cardiac Muscle:

Blood flow through the heart and body:

Body

inf. and sup. vena cavae

rt. atrium

rt. ventricle

pulmonary artery

lungs

pulmonary vein

lf. atrium

lf. ventricle

aorta

Fetal Circulation: respiratory, excretory and digestive systems aren’t working

Maternal blood supply- remember, the baby’s organs don’t need to work yet, so we don’t need to get a lot of blood to them

umbilical vein- take O2 and nutrients to the fetus

½ of the blood goes to the liver to keep it developing

½ of the blood goes to the ductus venosus (a by-pass of the liver)

( inferior vena cava (oxygenated and deoxygenated blood mix)

( right atrium ** a little blood goes to the pulmonary trunk

( blood that does get to the right ventricle will go out the pulmonary trunk and will be shunted to the aorta through the ductus arteriosus (at birth, this will stop functioning and become the ligamentum arteriosum

( foramen ovale (opening in the atrial septum) ( left atrium

( left ventricle ( aorta ( umbilical arteries

( waste is then carried to the umbilical cord ( mom

Blood Pressure

-the force that blood exerts against the inner walls of blood vessels (typically refers to pressure in the arteries)

Blood pressure changes in response to the phases of the cardiac cycle:

ventricular systole- period when the ventricles squeeze blood out into the pulmonary trunk (from the right ventricle) and the aorta (from the left ventricle)

--maximum pressure

----> measured as the systolic pressure

ventricular diastole- period when the ventricles relax

--lowest pressure

----> measured as the diastolic pressure

Blood pressure is stated as systolic pressure eg, 120

diastolic pressure 60

****Each contraction of the ventricles can be felt as the pulse

Factors that influence arterial blood pressure:

1. Heart Action- the contraction of the heart determines how much blood will enter the arterial system

=stroke volume (70 ml in an average adult male)

Cardiac output = stroke volume x heart rate

2. Blood Volume- sum of the formed elements (WBC’s, RBC’s, platelets) and the plasma ( 5 liters (or about 8% of body weight)

-volume varies with age, sex, body size

3. Peripheral Resistance- caused by the friction between blood and the walls of the blood vessels

-hinders blood flow; BP must increase to overcome the resistance (makes the heart work harder, increases muscle mass)

4. Blood Viscosity- the “thinness” of the blood; the ease with which blood’s molecules move past each other

The Heart’s electrical conduction system:

-cardiac muscle cells will contract spontaneously even without stimulation from the nervous system

-to be efficient, the heart has to have a control system. There are 2 parts to this system:

1. Autonomic nerves- will act to speed up or slow down your heart beat depending on your physical and emotional state

- in times of stress, the sympathetic division of the ANS speeds up the heart in order to get more oxygen to the parts of the body that need it

-when you calm down, the parasympathetic division of the ANS slow the heart rate

2. The Intrinsic Conduction System (nodal system)- is built right into the heart muscle

Parts:

Sinoatrial node (SA node)- located in the right atrium

- a tiny cell mass that has the highest rate of depolarization

-is the pacemaker of the heart; gets the beat going

Atrioventricular node (AV node)- also in the right atrium

- the impulse that started in the SA node temporarily stops here to allow the atria time to stop contracting

AV bundle, bundle branches and Purkinje fibers- the impulse is conducted along these pathways to complete the beat of the heart

The Cardiac Cycle: the events of one complete heartbeat. Both atria and ventricles contract and then relax.

The Electrocardiogram (EKG or ECG)- a recording of the electrical changes in the myocardium during a cardiac cycle.

-the electrical changes are caused by the depolarization of the heart muscle.

-depolarization occurs when ions flow across the muscle cell membrane

Each wave in the EKG represents the depolarization or repolarization of the heart muscle:

P-wave- depolarization of the atrial fibers (atria contract)

QRS complex- depolarization of the ventricles (ventricles contract)

T-wave- repolarization of the ventricles (ventricles relax)

**the EKG does not show the repolarization of the atrial muscle because it happens when the ventricles contract and is therefore “covered up” by the QRS complex

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tricuspid valve

pulmonary semilunar valve

bicuspid valve

aortic semilunar valve

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