4.1 STRUCTURAL AND FUNCTIONAL ORGANIZATION OF THE CARDIOVASCULAR SYSTEM Flashcards
DESCRIBE the structure of the heart
a. The heart is the central organ of the cardiovascular system.
(1) Located in the thoracic cavity between the two lungs.
(2) 2/3 of its mass lies to the left of the midline.
(3) The base of the heart is formed by the atria (upper chambers of the heart).
(4) The apex of the heart is the pointed end of the heart, formed by the tip of the left ventricle (lower chamber of the heart).
b. The heart is surrounded by the pericardium, which protects and holds the heart in place.
c. Two parts of the pericardium:
(1) Fibrous pericardium: tough, inelastic and outer connective tissue*
(2) Pericardium functions to protect the heart by:
(a) Anchoring in place ( attached to the diaphragm)*
(b) Prevents it from over stretching*
(3) Serous pericardium: thinner, delicate and forms double layer around heart*
(a) Parietal layer: fused to the fibrous pericardium.*
(b) Visceral layer (epicardium): adheres tightly to the heart.*
(c) Between the two layers is the pericardial cavity filled with fluid.
(d) Lubricating fluid - preventing friction between membranes
d. Made up of three layers:
(1) Epicardium (to include the visceral layer of the serous pericardium)*
(2) Myocardium*
(a) Forms two separate networks via gap junctions and intercalated disks: Atrial and ventricular.
(b) Each network contracts as a unit.
(3) Endocardium
(a) Lines inside of myocardium and covers valves.
e. The heart is composed of four chambers: two atria and two ventricles.
(1) They are separated by a interatrial or interventricular septum.
(2) Wall thickness depends on the work load.
(3) Atria are the thinnest because they empty their contents into the ventricles.
Ventricles are thicker because they have to move blood out of the heart.
(4) The right ventricle is thinner than the left because it pumps blood to the lungs
while the left ventricle pumps blood to the entire body.
(5) There are four valves in the heart, designed to prevent back flow in response to two separate mechanisms.
(6) The two Atrioventricular (AV): located between atria and ventricles.
(a) Tricuspid Valve (3 cusps)
(b) Bicuspid (also known as Mitral) Valve (2 cusps)
(7) Chordae tendineae connect to papillary muscles (located on ventricle side)
(a) Prevent valve cusps from pushing up into the atria when ventricles contract
(8) The Semilunar (SL) Valves, close secondary to a pressure change.
(a) Aortic Valve
(b) Pulmonic Valve
IDENTIFY the major blood vessels that enter and exit the heart
a. Superior and Inferior Vena Cava
(1) Both drain deoxygenated blood from the upper and lower body into the right
atrium.
b. Coronary Sinus
(1) Drains deoxygenated blood from the coronary veins into the right atrium.
c. Pulmonary trunk and Pulmonary artery
(1) Blood is pumped from the right ventricle into the pulmonary trunk which then branches into the pulmonary arteries that then carry this deoxygenated blood into the lungs to be oxygenated.
d. Pulmonary veins
(1) Carries oxygenated blood from the lungs and transports it to the left atrium.
(a) Left atrium empties into the left ventricle which then pumps blood into the
aorta.
e. Aorta
(1) Carries oxygenated blood to the entire body from the left ventricle.
DESCRIBE how blood flows through the heart
a. Deoxygenated blood enters the heart via the superior and inferior vena cava or coronary sinuses, drains into the right atrium, empties into the right ventricle, then pumped to the lungs via the pulmonary trunk and left and right pulmonary arteries to be oxygenated.
b. After oxygenation, blood is pumped to the heart by the pulmonary vein into the left atrium, which empties into left ventricle and is pumped through the body via the aorta.
c. A constant, uninterrupted blood supply is essential for the heart’s function.
d. Blood flow through the myocardium is known as coronary circulation.
(1) There are two principal coronary vessels:
(a) Right coronary artery
(b) Left coronary artery
(2) Both are branches from the aorta and supply the heart with O2 rich blood.
(3) The coronary sinus collects the heart’s deoxygenated blood and returns it to the right atrium.
DESCRIBE the electrical structure of the heart.
a. Cardiac excitation normally begins in the sinoatrial (SA) node, and is then conducted through:
(1) The atria (via Bachmann’s bundle) causing contraction
(2) Atrioventricular (AV) node
(3) AV bundle branches (known as the bundle of his)
(4) Right and left bundle branches
(5) Purkinje fibers
b. How a wave form is created on electrocardiogram?
(1) Waves on an ECG are created by placing electrodes on the skin to pick up the electrical current generated by the heart.
(2) When reviewing an ECG recording three discernible waves will be noted:
(a) P wave: representing atrial depolarization
(b) QRS Complex: representing ventricular depolarization (masks atrial
repolarization due to size)
(c) T wave: representing ventricular repolarization
c. The phases of the cardiac cycle.
(1) A cardiac cycle represents everything associated with one heartbeat, typically
lasting 0.8 seconds.
(2) Three phases in a cardiac cycle:
(a) Relaxation period; the ventricles start to relax and repolarize (repolarization is indicated as the T wave on an EKG); all four chambers of the heart, including
the atria enter into a period of diastole (dilation), during diastole, the ventricles
are filled to 75%.
(b) In atrial systole (contraction) both atria depolarize (noted as the P wave). After depolarization the last 25% of blood is ejected from the atria to the ventricles.
(c) Ventricular systole (contraction) is indicated by the QRS complex. The
ventricles depolarize then contract ejecting the blood into either the pulmonary trunk (right ventricle) or the aorta (left ventricle).
1) Approximately 70ml of blood is ejected into systemic circulation per
ventricular contraction.
d. Cardiac Output.
(1) Cardiac output (CO) - the amount of blood ejected from the left ventricle into the aorta per minute.
(2) NOTE: the same is ejected from the right ventricle, during ventricular contraction.
(3) CO formula = stroke volume x heart rate
= 70 ml/beat x 75 beats/min
= 5250 ml/min or 5.25 L/min
- DESCRIBE the structure of arteries and veins
a. There are five main types of blood vessels found throughout the human body. Each type has a specific role in carrying out its function to circulate blood throughout the body.
b. Arteries: thick, triple layered vessels that carry blood away from the heart.
c. Arterioles: thin vessels formed by arteries branching down in size.
d. Capillaries: hair-like microscopic vessels found throughout the body. Capillaries are also known as exchange vessels, which connect arterioles to venules.
e. Venules: very thin vessels formed when capillaries reunite.
f. Veins: designated vessels that return deoxygenated blood to the heart to be
oxygenated.
(1) Veins are structurally similar to arteries possessing three individual layers
(2) Their middle and inner layers are thinner and the lumen is generally larger than the corresponding artery
(3) This is because veins and venules contain about 64% of the total volume of blood. Because veins contain so much of the blood, certain veins function as blood
reservoirs (liver, spleen and skin)
g. Capillaries:
(1) Very small lumens which cause blood to move through them very slowly,
(2) Allows them to move nutrients and other substances in and out efficiently,
(3) Capillary filling is controlled by small arterioles and pre-capillary sphincters via
auto-regulation, (constrict or dilate), which is the ability of local tissues to blood
flow into the area according to metabolic demands.
(a) Autoregulation: the ability of local tissues to adjust blood flow (constrict or
dilate) into the area according to metabolic demands via vasodilators and
vasoconstrictors.
(4) Slowest rate of blood flow takes place within the capillaries allowing time for exchange through walls
(5) Balance of BP and osmosis determines amount of fluid in circulation
(a) Excess fluid lost is returned to the circulatory system via the lymphatic system
(b) Local signals can adjust capillary flow (autoregulation)
DESCRIBE how blood flows through blood vessels
a. Blood pressure is defined as pressure exerted on the walls of the vessels as the
ventricles contract.
(1) Highest in the aorta and the large systemic arteries.
(2) Dependent on the volume of blood in the cardiovascular system, normally 5 liters or 5.3 quarts.
(3) Anything that increases blood volume, i.e. water retention will increase blood pressure.
(4) Volume or blood loss more than 10% is potentially life threatening.
(5) Cardiac output is defined as Heart Rate multiplied by Stroke Volume.
(6) Vascular resistance is the opposition to flow (lumen size).
b. Factors that regulate blood flow and BP
(1) Blood volume and ventricular contraction: cardiac output
(2) Vascular resistance: opposition to flow, which depends on:
(a) Smaller lumen (with vasoconstriction) results in greater resistance
(b) Greater vessel length (weight gain) results in greater resistance
(c) Higher viscosity (as with high hematocrit) results in greater resistance
c. Blood flow to the body is regulated by the brain. The medulla oblongata, controlled by neural and hormonal feedback from 3 main types of receptors.
(1) Proprioceptors: Monitor movements of joints and muscles.
(2) Baroreceptors: Pressure receptors in the aorta and carotid arteries.
(3) Chemoreceptors: located in the arch of the aorta and carotid bodies that stimulate sympathetic and parasympathetic response to chemical changes in thebody.
d. Two main circulation pathways of blood through the body:
(1) Systemic circulation: arteries and arterioles that carry oxygen and nutrient rich blood throughout the body, veins and venules that carry carbon dioxide and
waste to the right atrium.
(a) All systemic arteries branch off the aorta.
(b) All systemic veins empty into superior vena cava, inferior vena cava, or the coronary sinus.
(2) Deoxygenated blood returns to heart via the above vessels and goes into the right atrium to be oxygenated
(3) Pulmonary circulation: blood pumped by the right ventricle to the lungs, picks up oxygen and returns via pulmonary veins to the left atria.
(4) Pulmonary capillaries: where gas exchange takes place to re-oxygenate the blood.
IDENTIFY the principal vessels of the arterial circulation.
a. Four principal branches of the aorta:
(1) The Ascending Aorta
(2) Arch of the Aorta
(3) Thoracic Descending Aorta
(4) Abdominal Descending Aorta
b. Arteries that branch from the arch of the aorta.
(1) Ascending Aorta - both the left and right coronary arteries branch off the
ascending aorta.
(2) Arch of the Aorta
(a) Right Brachiocephalic trunk, which then branches into
1) Right common carotid artery: Right side of head and neck
a) External carotid: external structures of skull
b) Internal carotid: internal structures of scull (eyeball, ear, brain)
2) Right subclavian artery: Right upper limb
(b) Left common carotid artery: Left side of head and neck
1) External carotid: external structures of skull
2) Internal carotid: internal structures of scull (eyeball, ear, brain)
(c) Left subclavian artery: Left upper limb
1) External carotid: external structures of skull
2) Internal carotid: internal structures of scull (eyeball, ear, brain)
(d) Subclavian arteries continue to branch further into:
1) Axillary artery: Supplies shoulder
2) Brachial artery: supplies upper arm
3) Radial artery: supplies lateral portion of forearm, wrist and hand
4) Ulnar artery: supplies medial portion of forearm, wrist and hand
(3) Thoracic Aorta
(a) Bronchial arteries: Bronchi of lungs
(b) Esophageal arteries: Esophagus
(c) Posterior intercostal arteries: Intercostal and chest muscles
(d) Superior phrenic arteries: Superior and posterior surfaces of diaphragm
(4) Abdominal Aorta
(a) Celiac trunk which, further branches into:
1) Inferior phrenic arteries: Inferior surface of diaphragm
2) Common hepatic artery: Liver, stomach, duodenum, and pancreas
3) Left gastric artery: Stomach and esophagus
4) Splenic artery: Spleen, pancreas, and stomach
(b) Superior mesenteric artery: small intestine, cecum, ascending and transverse colons, and pancreas
(c) Suprarenal arteries: Adrenal glands
(d) Renal arteries: Kidneys
(e) Gonadal arteries which, branches into:
1) Testicular arteries OR
2) Ovarian arteries
(f) Inferior mesenteric artery: Supplies the large intestine, part of the rectum,
descending colon.
(g) Common iliac arteries, branching to form the abdominal aorta
1) External iliac arteries: supply lower limbs, and further branch into:
a) Femoral arteries: lower abdominal wall, groin, external genitals, thigh
b) Popliteal arteries: supplies muscles and skin on posterior portion of
legs, calf muscles, knee joint, femur, patella and fibula
c) Anterior tibial arteries: supply the knee joints, anterior muscles and
skin of the legs, and ankle joints.
d) Posterior tibial arteries: distribute to the muscles, bones, and joints of the leg and foot.
e) Medial and lateral plantar arteries: supply muscles and skin of the feet and toes.
2) Internal iliac arteries: Supplies pelvis
IDENTIFY the principal vessels of the venous circulation.
a. Veins transport blood back to the heart via pressure generated by:
(1) Contractions of the heart
(a) The pressure generated by the contraction of heart creates a pressure
difference in the circulatory system.
(b) This pressure difference helps to push the blood in one direction to empty it
into the right atrium.
(2) The skeletal muscle pump
(a) Contracting skeletal muscles (especially in lower limbs) squeeze veins pushing their contents upwards.
(b) Because of venous (one-way) valves, the blood only flows in one direction – to the heart.
(3) The respiratory pump
(a) Inhalation decreases thoracic pressure and increases abdominal pressure, enhancing blood to flow heart
(b) Exhalation allows refilling of abdominal veins, which is then pumped to the thoracic veins and to the heart
(c) Pressure generated pushes blood in one direction, to the right atrium where the pressure is approximately O mm Hg.
b. Three systematic veins carry deoxygenated blood to the heart:
(1) The coronary sinus - Main vein to drain the heart
(2) Superior vena cava - Empties blood drained from the head, neck, chest and upper limbs into the superior portion of the right atria.
(3) Inferior vena cava - Largest vein in the body, drains the abdomen, pelvis and
lower extremities into the inferior portion of the right atria.
c. The three main veins that drain blood away from the head:
(1) The internal jugular- cranial bones, meninges, and brain
(2) External jugular- scalp and face
(3) Vertebral veins- cervical vertebrae, cervical spinal cord, neck muscles
d. The principal veins that drain the upper body are the:
(1) Superficial Veins
(a) Cephalic veins: drains the lateral aspect of upper limb
(b) Basilic veins: drain medial aspect of upper limb
(c) Median antecubital veins: drain palms and forearms
(2) Deep Veins
(a) Radial veins: drain lateral aspect of forearm
(b) Ulnar veins: drain medial aspect of forearm
(c) Brachial veins: drain forearms, elbow joints, and arms
(d) Axillary veins: drain arms, axillae, and upper part of chest wall
(e) Subclavian veins: drain arms, neck, and thoracic wall
e. The principal veins that drain the abdomen:
(1) Hepatic portal circulation
(a) Blood drains from the gastrointestinal tract and spleen into hepatic portal vein
(b) Is then delivered to the liver to be process and absorb substances from the GI tract
(c) Blood returns to systemic circulation through the hepatic vein
f. The principal veins that drain the lower body are:
(1) Superficial Veins
(a) Consists of the great saphenous veins: drain leg and thigh, groin, external genitals, and abdominal wall
(b) Small saphenous veins: drain the foot and leg
(2) Deep Veins
(a) Posterior tibial veins: drain foot and posterior leg muscles
(b) Anterior tibial veins: drain ankle joint, knee joint, tibiofibular joint, and
anterior leg
(c) Popliteal veins: drain skin and muscles and bones of the knee
(d) Femoral veins: drain muscles of the thigh, femurs, external genitalia, and
superficial lymph nodes.
g. How pulse and blood pressure are measured.
(1) Pulse is assessed by holding pressure on common arteries for one minute.
(2) Common arteries used:
(a) radial artery
(b) carotid artery
(c) brachial artery
(d) popliteal artery
(3) Pulse rate same as heart rate, normally around 75 beats per minute (BPM).
(a) Below 60 BPM – bradycardic
(b) Above 100 BPM – tachycardic
(4) Instrument used to measure blood pressure: Sphygmomanometer, also known as a BP cuff.
(5) Normal Findings
(a) Systolic (top/first value less than 120 mm Hg)
(b) Diastolic (bottom/last value less than 80 mm Hg)
h. Aging of the Heart
(1) As we age stiffening of the aorta occurs.
(2) There is a loss of cardiac muscle strength causing reduced CO and increased systolic pressure.
(a) Increasing the risk of CAD, CHF and atherosclerosis.
DESCRIBE the relationship between exercise and the heart
a. Regular exercise, at least 20 minutes 3-5 times weekly, is essential to improve overall cardiovascular health. Examples of activities recommended:
(1) Brisk walking
(2) Running cross-country
b. Benefits of exercise:
(1) Maintaining low resting heart rate about 40-60 beats per minute.
(2) Better control of blood pressure.
(3) Decreases anxiety and depression.
(4) Controls weight.
(5) Increases our body’s ability to dissolve blood clots by increasing fibrinolytic
activity.
