Cardiovascular system

CARDIOVASCULAR SYSTEM

1. THE CARDIOVASCULAR SYSTEM

Definition and Functions

Cardiovascular system: A closed system of the heart and blood vessels.

The heart pumps blood.
The blood vessels allow blood to circulate to all parts of the body.
The system transports oxygen, nutrients, cell wastes, and hormones to and from cells.

The Heart: Location, Size, and Orientation

The heart is about the size of a human fist and weighs less than a pound.
It is in the thoracic cavity, between the lungs, in the inferior mediastinum.
The apex left hip
The base right shoulder.
The point of maximal intensity (PMI) - loudest heartbeat

Coverings of the Heart

Pericardium: A double-walled sac that covers the heart.

Fibrous pericardium: Loose, superficial outer covering.
Serous pericardium: Deep to the fibrous pericardium; composed of two layers.
Parietal pericardium: Outer serous layer lining the inner surface of the fibrous pericardium.
Visceral pericardium: Layer next to the heart; also called the epicardium.
Pericardial cavity: Space between the serous pericardial layers.
Serous fluid: Fluid in the pericardial cavity that helps reduce friction as the heart moves.

Layers of the Heart Wall

Epicardium: Outside layer; the visceral pericardium.
Myocardium: Middle layer, made mostly of cardiac muscle; responsible for contraction.
Endocardium: Inner layer, known as endothelium.

Memory aid: E–M–E, from outside to inside = Epicardium, Myocardium, Endocardium.

2. CHAMBERS, SEPTA, GREAT VESSELS, AND BLOOD FLOW

Four Chambers

Right atrium - receives oxygen- poor blood from the body
Right ventricle - pumps blood to the lungs
Left atrium - receives oxygen-rich blood from the lungs
Left ventricle - pumps blood to the body and it has the thickest walls

Septa

Interatrial septum: Separates the right and left atria longitudinally.
Interventricular septum: Separates the right and left ventricles longitudinally.

Major Vessels Connected to the Heart

Superior vena cava (SVC): Returns oxygen-poor blood from the upper body to the right atrium.
Inferior vena cava (IVC): Returns oxygen-poor blood from the lower body to the right atrium.
Pulmonary trunk: Leaves the right ventricle and divides into pulmonary arteries.
Pulmonary arteries: Carry oxygen-poor blood from the heart to the lungs.
Pulmonary veins: Return oxygen-rich blood from the lungs to the left atrium.
Aorta: Carries oxygen-rich blood from the left ventricle into systemic circulation.

The Heart Is a Double Pump

Right side = pulmonary circuit pump: Sends oxygen-poor blood to the lungs.
Left side = systemic circuit pump: Sends oxygen-rich blood to body tissues.
Arteries: Carry blood away from the heart.
Veins: Carry blood toward the heart.

Pulmonary Circulation

Blood flows from the right side of the heart to the lungs and back to the left side of the heart.

Pathway:

Right ventricle → Pulmonary trunk → Pulmonary arteries → Lung capillaries (gas exchange) → Pulmonary veins → Left atrium

Systemic Circulation

Oxygen-rich blood returned to the left side of the heart is pumped into the aorta, travels through systemic arteries to body tissues, and returns as oxygen-poor blood through systemic veins.

Pathway:

Left ventricle → Aorta → Systemic arteries → Tissue capillaries → Systemic veins → Superior vena cava and/or inferior vena cava → Right atrium

Why is the left ventricle thicker?

It has a thicker wall because it must pump blood through the systemic circuit to the whole body.

3. HEART VALVES

Function: Heart valves allow blood to flow in only one direction and prevent backflow.

Atrioventricular (AV) Valves

Right AV valve = tricuspid valve: Between the right atrium and right ventricle.
Left AV valve = bicuspid (mitral) valve: Between the left atrium and left ventricle.
Chordae tendineae: Anchor AV valve cusps to the walls of the ventricles and prevent the cusps from everting into the atria during ventricular contraction.
AV valves: Open during heart relaxation/filling and close during ventricular contraction.

Semilunar Valves

Pulmonary semilunar valve: Between the right ventricle and pulmonary trunk.
Aortic semilunar valve: Between the left ventricle and aorta.
Semilunar valves: Closed during heart relaxation and open during ventricular contraction.

Valve Action in Sequence

Valves open and close in response to pressure changes in the heart.

When atrial pressure is greater than ventricular pressure, AV valves open and blood fills the ventricles.
When ventricles contract and ventricular pressure rises above atrial pressure, AV valves close.
When ventricular pressure rises above pressure in the pulmonary trunk and aorta, semilunar valves open and blood is ejected.
When ventricles relax and their pressure falls below arterial pressure, blood briefly flows back against the semilunar cusps, forcing the valves to close.

4. CARDIAC CIRCULATION

Blood in the heart chambers does not directly nourish the myocardium. The heart has its own nourishing circulatory system.

Coronary arteries: Branch from the aorta and supply the heart muscle with oxygenated blood.
Cardiac veins: Drain blood from the myocardium.
Coronary sinus: A large vein on the posterior heart that receives blood from cardiac veins; blood empties into the right atrium through the coronary sinus.

5. PHYSIOLOGY AND ELECTRICAL CONDUCTION OF THE HEART

Intrinsic Conduction System

Cardiac muscle can contract spontaneously and independently of nerve impulses.
Spontaneous contractions occur in a regular and continuous way.
atrial cells beat about 60 per minute
ventricular cells beat about 20–40 per minute
Intrinsic conduction system, also called the nodal system: Sets the heart rhythm.
It consists of specialized conducting tissue and ensures depolarization proceeds in one direction: from atria to ventricles.
heart rate of about 75 beats per minute.
Cardiac length is 0.8 seconds

Two systems regulate heart activity:
1.the autonomic nervous system (ANS)
2.the intrinsic conduction system.

Parts of the Conduction System

Sinoatrial (SA) node: Located in the right atrium; the heart’s pacemaker; starts each heartbeat.
Atrioventricular (AV) node: At the junction of the atria and ventricles; briefly delays the impulse.
AV bundle (bundle of His): Conducts the impulse from the AV node into the interventricular septum.
Bundle branches: Carry the impulse down the interventricular septum.
Purkinje fibers: Spread within the ventricular wall muscles.

Conduction Pathway — Memorize in Order

SA node → Impulse spreads through atria → AV node (brief delay) → AV bundle/bundle of His → Bundle branches → Purkinje fibers → Ventricles contract and eject blood

Heart-Rate Terms

Tachycardia: Rapid heart rate, over 100 beats per minute.
Bradycardia: Slow heart rate, less than 60 beats per minute.

6. CARDIAC CYCLE AND HEART SOUNDS

Cardiac cycle: One complete heartbeat in which both atria and ventricles contract and then relax.

Systole = contraction.
Diastole = relaxation.
Average heart rate in the lecture: approximately 75 beats per minute.
Normal cardiac cycle length in the lecture: 0.8 second.

Phases of the Cardiac Cycle

1. Atrial Diastole (Ventricular Filling)

The heart is relaxed and pressure in the heart is low.
AV valves are open; semilunar valves are closed.
Blood flows passively into the atria and then into the ventricles.

2. Atrial Systole

The atria contract while the ventricles remain in diastole.
Blood is forced into the ventricles to complete ventricular filling.

3. Isovolumetric Contraction

Atrial systole ends and ventricular systole begins.
Intraventricular pressure rises.
AV valves close; for a moment, the ventricles are completely closed chambers.

4. Ventricular Systole (Ejection Phase)

Ventricles continue to contract.
Intraventricular pressure exceeds pressure in the major arteries leaving the heart.
Semilunar valves open and blood is ejected from the ventricles.
The atria are relaxed and filling with blood.

5. Isovolumetric Relaxation

Ventricular diastole begins and ventricular pressure falls below pressure in the major arteries.
Semilunar valves close; for a moment, the ventricles are completely closed chambers.
When atrial pressure rises above intraventricular pressure, the AV valves open.

Heart Sounds

“Lub” (S1): Longer, louder sound caused by closure of the AV valves.
“Dup” (S2): Short, sharp sound caused by closure of the semilunar valves at the end of ventricular systole.

Memory aid:

“Lub” = AV valves close.
“Dup” = Semilunar valves close.

7. CARDIAC OUTPUT, STROKE VOLUME, AND HEART RATE

Cardiac output (CO): Amount of blood pumped by each side (ventricle) of the heart in one minute.
Stroke volume (SV): Volume of blood pumped by each ventricle in one contraction/heartbeat.
Heart rate (HR): Number of heartbeats per minute.

Formula:

CO = HR × SV

Lecture Example

HR = 75 beats/min
SV = 70 mL/beat

CO = 75 beats/min × 70 mL/beat
CO = 5,250 mL/min = 5.25 L/min

Regulation of Stroke Volume

The lecture states that about 60% of the blood in the ventricles (about 70 mL) is pumped with each heartbeat.
Starling’s law of the heart: The critical factor controlling stroke volume is how much cardiac muscle is stretched.
The more the cardiac muscle is stretched, the stronger the contraction.
Venous return is an important factor influencing the stretch of heart muscle.

Factors Modifying Basic Heart Rate

Sympathetic nervous system: Speeds up heart rate.
Parasympathetic nervous system: Primarily through vagus nerve fibers, slows and steadies heart rate.
Hormones: Epinephrine and thyroxine speed up heart rate.
Ions: Excess or lack of calcium, sodium, and potassium ions can modify heart activity.
Physical factors: Age, gender, exercise, and body temperature influence heart rate.

8. BLOOD VESSELS: TYPES AND WALL STRUCTURE

Main Vessel Types

Arteries and arterioles: Carry blood away from the heart.
Capillary beds: Main sites of exchange between blood and tissues.
Venules and veins: Return blood toward the heart.

Three Tunics (Layers) of Blood Vessels

Most blood vessels have three layers, except capillaries.

Tunica intima: Inner, friction-reducing lining; includes endothelium.
Tunica media: Middle layer of smooth muscle and elastic tissue; controlled by the sympathetic nervous system.
Tunica externa: Outermost protective covering, mostly fibrous connective tissue; supports and protects the vessel.

Arteries vs. Veins vs. Capillaries

Arteries: Have a heavier, stronger, stretchier tunica media than veins to withstand pressure changes.
Veins: Have a thinner tunica media and operate under lower pressure. Their lumen is larger than that of arteries, and they contain valves to prevent backflow.
Skeletal muscle pump: Contracting skeletal muscles compress veins and help “milk” blood toward the heart; valves keep blood moving in the correct direction.
Capillaries: Have only one cell layer (tunica intima), allowing exchange between blood and tissues.

Capillary Beds and Microcirculation

Capillary beds: Form networks consisting of a vascular shunt and true capillaries.
Microcirculation: Blood flow through a capillary bed.
True capillaries: Branch from a terminal arteriole and empty directly into a postcapillary venule.
Precapillary sphincters: Guard the entrances to capillary beds.
When precapillary sphincters are open, blood flows through true capillaries; when closed, blood flows through the vascular shunt.

9. MAJOR ARTERIES OF SYSTEMIC CIRCULATION

Aorta and Its Regions

Aorta: The largest artery in the body; leaves the left ventricle.

Ascending aorta: Leaves the left ventricle.
Aortic arch: Curves to the left.
Thoracic aorta: Descends through the thorax.
Abdominal aorta: Passes through the diaphragm into the abdominopelvic cavity.

Branches of the Ascending Aorta

The right and left coronary arteries supply the heart.

Branches of the Aortic Arch and Upper Limb

Brachiocephalic trunk: Divides into the right common carotid artery and right subclavian artery.
Left common carotid artery: Divides into left internal and external carotid arteries.
Left subclavian artery: Gives rise to the vertebral artery.

Upper limb pathway:

Subclavian → Axillary → Brachial → Radial and ulnar arteries → Deep and superficial palmar arches → Digital arteries

Branches of the Thoracic Aorta

Intercostal arteries: Supply muscles of the thoracic wall.
Bronchial arteries: Supply the lungs.
Esophageal arteries: Supply the esophagus.
Phrenic arteries: Supply the diaphragm.

Branches of the Abdominal Aorta

Celiac trunk: First branch of the abdominal aorta. Its three branches are:
1. Left gastric artery — stomach.
2. Splenic artery — spleen.
3. Common hepatic artery — liver.
Superior mesenteric artery: Supplies most of the small intestine and the first half of the large intestine.
Renal arteries: Supply the kidneys.
Gonadal arteries: Ovarian arteries supply the ovaries; testicular arteries supply the testes.
Lumbar arteries: Supply muscles of the abdomen and trunk.
Inferior mesenteric artery: Supplies the second half of the large intestine.
Common iliac arteries: Final branches of the aorta.
Internal iliac arteries: Supply pelvic organs.

Lower limb pathway:

External iliac → Femoral → Popliteal → Anterior and posterior tibial arteries

The dorsalis pedis and arcuate arteries are also labeled in the lecture.

Important Arteries of the Head and Trunk

Common carotid, internal carotid, external carotid, and vertebral arteries supply the head/brain regions.
Subclavian arteries supply the upper limbs through the axillary and brachial arteries.
Coronary arteries supply the heart muscle.

10. MAJOR VEINS OF SYSTEMIC CIRCULATION

Superior and Inferior Vena Cava

Superior vena cava: Enters the right atrium and drains the head and arms/upper body.
Inferior vena cava: Enters the right atrium and drains the lower body.

Veins Draining the Upper Limb and Head

Radial and ulnar veins → Brachial vein → Axillary vein.
Cephalic vein: Drains the lateral aspect of the arm and empties into the axillary vein.
Basilic vein: Drains the medial aspect of the arm and empties into the brachial vein.
Median cubital vein: Joins the cephalic and basilic veins in the elbow area.
Subclavian vein: Receives venous blood from the arm via the axillary vein and from skin/muscles via the external jugular vein.
Vertebral vein: Drains the posterior part of the head.
Internal jugular vein: Drains the dural venous sinuses of the brain.
Right and left brachiocephalic veins: Receive blood from subclavian, vertebral, and internal jugular veins; join to form the superior vena cava, which empties into the right atrium.
Azygos vein: Drains the thorax.

Veins Draining the Lower Limb and Abdomen

Anterior and posterior tibial veins and fibular veins drain the legs. The lecture slide spells “fibial.”
Lower limb pathway: Posterior tibial vein → Popliteal vein → Femoral vein → External iliac vein.
Great saphenous veins: Longest veins of the body; receive superficial drainage of the legs.
Each common iliac vein is formed by the union of the internal and external iliac veins on its side.
Right gonadal vein: Drains the right ovary in females or right testicle in males.
Left gonadal vein: Empties into the left renal vein.
Renal veins: Drain the kidneys.
Hepatic veins: Drain the liver.

Hepatic Portal Circulation

The hepatic portal circulation is formed by veins draining digestive organs, which empty into the hepatic portal vein.

The hepatic portal vein carries blood from digestive organs, the spleen, and pancreas to the liver, where nutrients and other absorbed substances are processed before the blood returns to systemic circulation.

Key point: The hepatic portal vein takes blood to the liver first; the inferior vena cava is not part of the hepatic portal system itself.

Arterial Supply of the Brain and Circle of Willis

Internal carotid arteries divide into anterior and middle cerebral arteries; these supply most of the cerebrum.
Vertebral arteries join within the skull to form the basilar artery.
The basilar artery serves the brain stem and cerebellum.
Posterior cerebral arteries branch from the basilar artery and supply the posterior cerebrum.
Small communicating arterial branches unite anterior and posterior blood supplies to form the cerebral arterial circle (circle of Willis).
The lecture labels the anterior communicating, anterior cerebral, posterior communicating, and posterior cerebral arteries as parts of this circle.

11. PULSE AND VITAL SIGNS

Vital signs: Measurements of arterial pulse, blood pressure, respiratory rate, and body temperature.

Arterial pulse: Alternate expansion and recoil of a blood vessel wall (a pressure wave) that occurs as the heart beats.

Pulse is monitored at pressure points in superficial arteries where it can be easily palpated.
The lecture gives an average resting pulse of 70–76 beats per minute in a healthy person.

Pulse Points Labeled in the Lecture

Superficial temporal artery
Facial artery
Common carotid artery
Brachial artery
Radial artery
Femoral artery
Popliteal artery
Posterior tibial artery
Dorsalis pedis artery

12. BLOOD PRESSURE

Definition and Pressure Gradient

Blood pressure (BP): The pressure blood exerts against the inner walls of blood vessels. It is the force that causes blood to continue flowing through vessels.

When ventricles contract, blood is forced into elastic arteries near the heart.
Blood flows along a descending pressure gradient: pressure decreases as distance from the heart increases.
Pressure is highest in arteries, lower in capillaries, and lowest in veins.

Systolic and Diastolic Pressure

Systolic pressure: Pressure in the arteries at the peak of ventricular contraction.
Diastolic pressure: Pressure when the ventricles relax.
Blood pressure is expressed as systolic over diastolic in millimeters of mercury (mm Hg), for example, 120/80 mm Hg.

Auscultatory Method of Measuring Blood Pressure

The indirect method most often measures systemic arterial pressure at the brachial artery.
The cuff is wrapped snugly around the arm above the elbow and inflated until its pressure exceeds systolic pressure; blood flow is stopped and no sounds are heard.
The cuff pressure is gradually lowered while listening with a stethoscope.
The first soft tapping sounds heard indicate the systolic pressure.
When the artery is no longer constricted and sounds disappear, the pressure is recorded as the diastolic pressure.

Formula and Factors That Affect BP

BP = CO × PR

BP: Blood pressure.
CO: Cardiac output, or the amount of blood pumped out of the left ventricle per minute.
PR: Peripheral resistance, or the friction blood encounters as it flows through vessels.

Autonomic Nervous System

Parasympathetic activity has little to no effect on BP.
Sympathetic activity promotes vasoconstriction and increases BP.

Kidneys

Kidneys regulate BP by changing blood volume.
If BP is too high, kidneys release more water in urine.
If BP is too low, kidneys release renin, triggering formation of angiotensin II, a vasoconstrictor.

Angiotensin II

Stimulates aldosterone release.

Aldosterone

Enhances sodium and water reabsorption by the kidneys.

Temperature

Heat causes vasodilation.
Cold causes vasoconstriction.

Chemicals

Various substances can raise or lower BP; epinephrine increases heart rate and BP.

Diet

The lecture notes that a diet low in salt, saturated fats, and cholesterol is commonly believed to help prevent hypertension.

Factors Increasing BP Listed in the Lecture

Exercise
Postural changes
Chemicals (renin, nicotine, and others)
Increased blood viscosity
Kidney conservation of water and salt
Increased stroke volume
Increased heart rate
Vasoconstriction
Increased cardiac output
Increased peripheral resistance

Ranges and Terms Stated in the Lecture

Normal range stated in the lecture: Systolic pressure 110–140 mm Hg and diastolic pressure 70–80 mm Hg.
Hypotension: Low blood pressure; the lecture specifies low systolic pressure below 100 mm Hg. It is often associated with illness; acute hypotension is a warning sign for circulatory shock.
Hypertension: Sustained elevated arterial pressure of 140/90 mm Hg in the lecture; it warns of increased peripheral resistance.

Exam note: Learn these ranges as stated in your lecture slides. Clinical cutoffs may differ across current guidelines and patient situations.

13. CAPILLARY EXCHANGE AND FLUID MOVEMENT

Exchange of Gases, Nutrients, and Wastes

Interstitial fluid (tissue fluid): Fluid found between cells.
Substances move between blood and tissue cells through capillary walls because of concentration gradients.
Oxygen and nutrients leave blood and move into tissue cells.
Carbon dioxide and other wastes leave tissue cells and enter the blood.

Routes Across Capillary Walls

Direct diffusion through membranes.
Diffusion through intercellular clefts (gaps between cells in the capillary wall).
Diffusion through pores of fenestrated capillaries.
Transport via vesicles.

Fluid Movement at Capillary Beds

Blood pressure: Forces fluid and solutes out of capillaries.
Osmotic pressure: Draws fluid into capillaries.
At the arterial end, blood pressure is higher than osmotic pressure, so fluid moves out of the capillary into interstitial fluid.
At the venous/venule end, blood pressure is lower than osmotic pressure, so fluid moves from interstitial fluid back into the capillary.

Memory aid: Arterial end = fluid OUT; venous end = fluid IN, as presented in the lecture.

14. DEVELOPMENTAL ASPECTS OF THE CARDIOVASCULAR SYSTEM

Embryonic Development

In an embryo, the heart develops as a simple tube and pumps blood by week 4 of pregnancy.
Over the next 3 weeks, the heart becomes a four-chambered organ capable of acting as a double pump.

Umbilical Cord

The umbilical cord carries nutrients and oxygen from maternal blood to fetal blood.
Fetal wastes move from fetal blood to maternal blood.
One umbilical vein: Carries nutrient- and oxygen-rich blood to the fetus.
Two umbilical arteries: Carry wastes and carbon dioxide-rich blood from the fetus to the placenta.

Fetal Shunts

Shunts allow fetal blood to bypass the lungs and liver before birth.

Ductus venosus: Allows blood to bypass the liver and enter the inferior vena cava, then the right atrium.
Foramen ovale: Shunts blood from the right atrium directly to the left atrium; becomes the fossa ovalis at or after birth.
Ductus arteriosus: Connects the pulmonary trunk and aorta; becomes the ligamentum arteriosum at birth.

Age-Related Cardiovascular Problems

Weakening of venous valves.
Varicose veins.
Progressive arteriosclerosis.
Hypertension resulting from loss of vessel elasticity.
Coronary artery disease resulting from fatty, calcified deposits in the vessels.

15. HIGH-YIELD COMPARISON TABLE

Artery

Carries blood away from the heart.
Generally has a thicker, stronger, stretchier wall.

Vein

Carries blood toward the heart.
Has lower pressure, a larger lumen, and valves that prevent backflow.

Capillary

Has a one-cell-layer wall.
Exchanges gases, nutrients, and wastes with tissues.

Pulmonary circuit

Right heart → Lungs → Left heart.

Systemic circuit

Left heart → Body tissues → Right heart.

AV valves

Tricuspid on the right.
Bicuspid/mitral on the left.
Close at the start of ventricular contraction.

Semilunar valves

Pulmonary and aortic.
Open during ventricular contraction.
Close as ventricles relax.

Systole

Contraction.

Diastole

Relaxation.

Tachycardia

Heart rate over 100 beats/min in the lecture.

Bradycardia

Heart rate below 60 beats/min in the lecture.

16. FORMULAS AND NUMBERS TO MEMORIZE

Cardiac output: CO = HR × SV
Lecture example: 75 beats/min × 70 mL/beat = 5,250 mL/min = 5.25 L/min.
Blood pressure: BP = CO × PR
Average heart rate in lecture: Approximately 75 beats/min.
Cardiac cycle length in lecture: 0.8 second.
Tachycardia: Over 100 beats/min.
Bradycardia: Less than 60 beats/min.
Lecture pulse average: 70–76 beats/min at rest in a healthy person.
Lecture BP ranges: Systolic 110–140 mm Hg; diastolic 70–80 mm Hg.
Lecture hypotension value: Systolic below 100 mm Hg.
Lecture hypertension value: Sustained 140/90 mm Hg.