Unit 11: Cardiovascular System

Cardiovascular system

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

Heart anatomy

size of a human fist, weighing less than a pound; located in the thoracic cavity between the lungs in the inferior mediastinum (medial section of the thoracic cavity)

Apex

pointed region; directed toward left hip and rests on the diaphragm

Base

area where great vessels emerge; points toward right shoulder

Pericardium

double walled sac; serous membrane is deep to the fibrous pericardium and composed of parietal and visceral pericardium; serous fluid fills the space between the layers of pericardium called the pericardial cavity

Parietal pericardium

outside layer that lines the inner surface of the fibrous pericardium

Visceral pericardium

next to heart and also called the epicardium

Myocardium

middle layer composed mostly of cardiac muscle

Endocardium

inner layer know as endothelium

Atria

right and left; superior receiving chambers; assist with filling the ventricles; blood enters under low pressure from veins of the body

Ventricles

right and left; inferior discharging chambers; thick-walled pumps of the heart; during contraction, blood is propelled into circulation

Interatrial septum

separates the two atria longitudinally

Interventricular septum

separates the two ventricles longitudinally

Double pump

arteries carry blood away from the heart and veins carry blood toward the heart; right side works as the pulmonary circuit pump and left side work as the systemic circuit pump

Pulmonary circulation

blood flows from the right side of the heart to the lungs and back to the left side of the heart; blood is pumped out of right side through pulmonary trunk which splits into pulmonary arteries and takes oxygen-poor blood to lungs; oxygen-rich blood returns to the heart from the lungs via pulmonary veins

Systemic circulation

oxygen-rich blood returned to the left side of the heart is pumped out into the aorta; blood circulates to systemic arteries and to all body tissues; left ventricle has thicker walls because it pumps blood to the body; oxygen-poor blood returns to the right atrium via systemic veins which empty blood into the superior or inferior vena cava

Heart valves

allow blood to flow in only one direction to prevent backflow

Atrioventricular valves (AV)

between atria and ventricles; bicuspid (mitral) valve - left; tricuspid valve - right; chordae tendineae anchor the cusps to the walls of the ventricles; open during heart relaxation, when blood passively fills the chambers; closed during ventricular contraction

Semilunar valves

between ventricle and artery; pulmonary semilunar and aortic semilunar valves; closed during heart relaxation; open during ventricular contraction

Cardiac circulation

blood in the heart chambers doesn’t nourish the myocardium and instead the heart has its own nourishing circulatory system; coronary arteries, cardiac veins, and coronary sinus

Coronary arteries

branch from the aorta to supply the heart muscle with oxygenated blood; on left, anterior interventricular artery and circumflex artery; on right, posterior interventricular artery and marginal artery

Cardiac veins

drain the myocardium of blood

Coronary sinus

large vein on the posterior of the heart; receives blood from cardiac veins; blood empties into the right atrium via this

Physiology of heart

cardiac muscle contracts spontaneously and can occur independently of nerve impulses; contractions occur in a regular and continuous way; atrial cells beat 60 times/minute; ventricular cells beat 20-40 times/minute; need unifying control system

Intrinsic conduction system

nodal system; sets the heart rhythm, composed of special nervous tissue, ensures heart muscle depolarization in one direction only (atria to ventricles); enforces a heart rate of 75 beats per minute

Steps of intrinsic conduction system

sinoatrial node (SA node) starts each heartbeat; impulse spreads through the atria to the AV node; atria contract; at the AV node, impulse is briefly delayed; impulse travels through the AV bundle, bundle branches, and Purkinje fibers; ventricles contract and blood is ejected from the heart

Tachycardia

rapid heart rate, over 100 beats/minute

Bradycardia

slow heart rate, less that 60 beats/minute

Cardiac cycle

refers to one complete heartbeat; both atria and ventricles contract then relax; systole = contraction; diastole = relaxation; length normally 0.8 second

Atrial diastole

ventricular filling; heart is relaxed; pressure in heart is low; AV valves are open; blood flows passively into the atria and ventricles; semilunar valves are closed

Atrial systole

ventricles remain in diastole; atria contract; blood is forced into the ventricles to complete ventricular filling

Isovolumetric contraction

atrial systole ends and ventricular systole begins; intraventricular pressure rises; AV valves close to prevent blood backflow into atria; ventricles completely close chambers for a moment

Ventricular systole

ejection phase; ventricles continue to contract; intraventricular pressure now surpasses the pressure in the major arteries leaving the heart; semilunar valves open; blood ejected from the ventricles; atria are relaxed and filling with blood

Isovolumetric relaxation

ventricular diastole begins; pressure in ventricles falls below that in the major arteries; semilunar valves close to prevent blood backflow into the ventricles; for another moment ventricles are completely closed chambers; when atrial pressure increases above intraventricular pressure, AV valves open

Lub

longer, louder heart sound caused by the closing of the AV valves

Dup

short, sharp heart sound caused by the closing of the semilunar valves at the end of ventricular systole

Cardiac output (CO)

amount of blood pumped by each side (ventricle) of the heart in 1 minute; product of stroke volume and heart rate

Stroke volume (SV)

volume of blood pumped by each ventricle in one contraction (each heartbeat); about 70 ml of blood is pumped out of the left ventricle with each heartbeat

Starling’s law of the heart

critical factor controlling SV is how much cardiac muscle is stretched called preload; more the cardiac muscle is stretched, the stronger the contraction; venous return is the important factor influencing the stretch of heart muscle

Two factors influence preload

amount of venous return (volume of blood returning to the heart) and the length of time the ventricles are relaxed and filling (determined by heart rate)

Contractility

ability of cardiac muscle tissue to generate tension

Afterload

amount of pressure the ventricles must overcome to eject blood

Neural (ANS) controls

sympathetic nervous system speeds heart rate; parasympathetic nervous system primarily vagus nerve fibers slow and steady the heart rate

Hormones and ions

epinephrine and thyroxine speed heart rate; excess or lack of calcium, sodium, and potassium ions also modify heart activit

Physical factors

age, gender, exercise, and body temperature all influence heart rate

Blood vessels

form a closed vascular system that transports blood to tissues and back to the heart; made up of arteries, veins, and capillary beds

Arteries and arterioles

carry blood away from the heart; has a heavier, stronger, stretchier tunica media than veins to withstand changes in pressure

Capillary beds

vessels that play a role in exchanges between tissues and blood; only one cell layer thick (tunica intima); allow for exchanges between blood and tissue; blood flow through capillary bed is called microcirculation; blood flows from terminal arteriole →exchange vessels of capillary bed →postcapillary venule

Venules and veins

vessels that return blood toward the heart; has thinner tunica media than arteries and operate under low pressure; valves to prevent backflow of blood; lumen of veins larger than arteries; skeletal muscle “milks” blood toward heart

Tunica intima

innermost layer of blood vessels that forms a friction-reducing lining; endothelium

Tunica media

middle layer of blood vessels made up of smooth muscle and elastic tissue; controlled by sympathetic nervous system

Tunica externa

outermost layer of blood vessels made up mostly of fibrous connective tissue; supports and protects vessel

Precapillary sphincters

regulate blood flow through capillary blood; when open, blood flows through and exchanges with cells can occur; when close, blood flows through shunt and bypasses cells in that region

Vascular shunt

directly connects arteriole and venule at opposite ends of bed

Vital signs

measurements of arterial pulse, blood pressure, respiratory rate, and body temperature

Arterial pulse

alternate expansion and recoil of blood vessel wall (pressure wave) that occurs as the heart beats; monitored at pressure points in superficial arteries where pulse is palpated; pulse averages 70-76 bpm at rest in healthy person

Blood pressure

pressure blood exerts against inner walls of blood vessels; force that causes blood to continue to flow in the blood vessels

Blood pressure gradient

when ventricles contract, blood forced into elastic arterioles close to heart; high to low pressure; pressure decreases in blood vessels as distance from heart increases; pressure high in arteries, lower in capillaries, and lowest in veins

Measuring blood pressure

2 arterial blood pressures measured: systolic which is pressure in arteries at peak ventricular contraction and diastolic which is pressure when ventricles relax; expressed as systolic pressure over diastolic pressure in mm of mercury (Hg) - 120/80 mm Hg

Auscultatory method

indirect method of measuring systemic arterial blood pressure, most often in brachial artery

Peripheral resistance

amount of friction blood encounters as it flows through vessels; arterial bp directly related to cardiac output and peripheral resistance; BP = CO x PR

Neural factors on blood pressure

autonomic nervous system; parasympathetic has little to no effect on bp and sympathetic promotes vasoconstriction and increases bp

Renal factors on blood pressure

kidneys regulate bp by altering blood volume; if bp increases, the kidneys release water in urine; if bp decreases, kidneys release renin to trigger formation of angiotensin II (vasoconstricter); angiotensin II stimulates release of aldosterone which enhances sodium and water reabsorption by kidneys

Temperature factors on blood pressure

heat has a vasodilating effect and cold has a vasconstricting effect

Chemical factors on blood pressure

various substances cause increase or decrease in bp; epinephrine increases heart rate and bp

Diet factors on blood pressure

commonly believed that diet low in salt, saturated fats, and cholesterol prevents hypertension (increase bp)

Variations in blood pressure

variable; systolic pressure 110-140 mm Hg and diastolic pressure 70-80 mm Hg

Hypotension

low bp; low systolic (below 100), often associated with illness, acute hypotension is warning sign for circulatory shock

Hypertension

high bp; sustained elevated arterial pressure of 140/90 mm Hg; warns of increased peripheral resistance

Capillary exchange of gases and nutrients

interstitial fluid found between cells; substances move to and from blood and tissue cells through capillary walls; exchange due to concentration gradients; oxygen and nutrients leave blood and move into tissue cells; CO2 and other wastes exit tissue cells and enter blood

Substances take various routes entering and leaving blood

direct diffusion through membranes, diffusion through intercellular clefts (gaps between cells in capillary wall), diffusion through pores of fenestrated capillaries, transport via vesicles

Fluid movements of capillary beds

depends on difference between two pressures; blood pressure forces fluid and solutes out of capillaries; osmotic pressure draws fluid into capillaries; blood pressure is higher than osmotic pressure at arterial end of capillary bed; blood pressure is lower than osmotic pressure at venous end of capillary bed; fluid moves out of capillary at beginning of bed and reclaimed at opposite (venule) end

Cardiovascular developments in an embryo

heart develops as a simple tube and pumps blood by week four of pregnancy; heart becomes four chambered organ capable of acting as a double pump over next three weeks

Umbilical cord

carries nutrients and oxygen from maternal blood to fetal blood; fetal wastes move from fetal blood to maternal blood; houses one umbilical vein which carries nutrient and oxygen rich blood to fetus and two umbilical arteries which carry wastes and CO2 rich blood from fetus to placenta

Shunts bypassing lungs and liver present in fetus

blood flow bypasses liver through ductus venosus and enters inferior vena cava →right atrium; blood flow bypasses the lungs, blood entering right atrium is shunted directly into left atrium through foramen ovale (becomes fossa ovalis at or after birth); ductus arteriosus connects aorta and pulmonary trunk (becomes ligamentum arteriosum)

Age related problems

weakening of venous valves, varicose veins, progressive arteriosclerosis, hypertension resulting from loss of elasticity of vessels, coronary artery disease resulting from fatty, calcified deposits in vessels