The Cardiovascular SystemA closed system of heart and blood vessels; functions to deliver oxygen and nutrients and to remove carbon dioxide and other waste products

The Heart

Coverings:

Pericardium – a double serous membrane

Visceral pericardium - Next to heart

Parietal pericardium - Outside layer

Serous fluid fills the space between the layers of pericardium

The Heart: Heart Wall· Three layers· Epicardium - Outside layer= visceral

pericardium; Connective tissue layer· Myocardium - Middle layer; Mostly

cardiac muscle· Endocardium - Inner layer of

endothelium

The Heart: Chambers - Right and left side act as separate pumps

· Four chambers: Right atrium, Left atrium; Right ventricle, Left ventricle

The Heart: Associated Great Vessels· Aorta - Leaves left ventricle· Pulmonary arteries - Leave right

ventricle· Vena cava - Enters right atrium· Pulmonary veins (four) - Enter left

atrium

Heart Contractions· Contraction is initiated by the sinoatrial node

· Sequential stimulation occurs at other autorhythmic cells

**Pacemaker

The Heart: Cardiac Cycle (.8 sec = 70 beats/min)

1. Atria contract simultaneously 2. Atria relax, then ventricles contract

Systole = contraction Diastole = relaxation

· Cardiac cycle – events of one complete heart beat

-Mid-to-late diastole – blood flows into ventricles

-Ventricular systole – blood pressure builds before ventricle contracts, pushing out blood

-Early diastole – atria finish re-filling, ventricular pressure is low --- Heart Sounds: lub - dub

Lub = closing of A-V valves and contarctions of ventricles

Dub = closing of semilunar valves

Heart murmurs - defect in valves (narrow/stenosis or leak)

The Heart: Cardiac Output· Cardiac output (CO) = Amount of blood pumped by each side

of the heart in one minute

CO = (heart rate [HR]) x (stroke volume [SV])

· Stroke volume = Volume of blood pumped by each ventricle in one contraction (80 ml)

The Heart: Valves· Allow blood to flow in only one direction· Four valves· Atrioventricular valves – between atria and ventricles:

Bicuspid valve (left); Tricuspid valve (right) · Semilunar valves between ventricle and artery:

Pulmonary semilunar valve; Aortic semilunar valve

*Valves open as blood is pumped through; Held in place by chordae tendineae (“heart strings”);

Close to prevent backflow

Coronary CirculationBlood in the heart chambers does not nourish the myocardium; The heart has its own nourishing circulatory

system:

· Coronary arteries; Cardiac veins; Blood empties into the right atrium via the coronary sinus

The Heart: Conduction System & EKG· Intrinsic conduction system (nodal system); Heart muscle cells contract, without nerve impulses, in a

regular, continuous way;slow (spontaneous) and fast (respond to changes) Na and Ca channels· Special tissue sets the pace

· Sinoatrial node = Pacemaker

· Atrioventricular node (depolarize and delay .1 sec to allow atria to empty)

· Atrioventricular bundle

· Bundle branches; Purkinje fibers (contraction proceeds upward from bottom)

The Heart: Regulation of Heart Rate· Stroke volume usually remains relatively constant

Starling’s law of the heart – the more that the cardiac muscle is stretched, the stronger the contraction

Heart as suction pump - 1. blood forced out of aorta, heart moves down due to Newton’s Law, heart recoils up providing suction of blood 2. After systole, elastic elements of heart expand, creating negative pressure--> sucks blood in

Changing heart rate is the most common way to change cardiac output· Increased heart rate:

· Sympathetic nervous system: hypothalamus, medulla cardiac acceleratory centers· Hormones: Epinephrine, Thyroxine· Exercise· Decreased blood volume

· Decreased heart rate:

· Parasympathetic nervous system: hypothalamus, medulla cardioinhibitory centers

· High blood pressure or blood volume

· Dereased venous return

Reflexes:

Baroreceptor reflex

Right atrial reflex - increase venous pressure (esp. exercise) --> increase HR

Aortic reflex, carotid sinus reflex - increase pressure in aorta or carotid sinus --> decrease HR

Chemoreceptors in aorta, carotid sinus - decrease pH (exercise --> increase CO2) or O2 --> increase HR

Blood Vessels: The Vascular System·Taking blood to the tissues and back

· Arteries· Arterioles· Capillaries· Venules· Veins

Blood Vessels: Anatomy·Three layers (tunics)

· Tunic intima - Endothelium· Tunic media- Smooth muscle; **arterioles - controlled by sympathetic nervous system

-->vasoconstriction / dilation --> determines BP, distribution of blood to different organs· Tunic externa - Mostly fibrous connective tissue; arteries - collagen, elastic fibers--

>expand/contract as heart beats

Differences Between Blood Vessel Types:

*Walls of arteries are the thickest*Lumens of veins are larger

*Skeletal muscle “milks” blood in veins toward the heart

*Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue

Movement of Blood Through Vessels·Most arterial blood is pumped by the heart

·Veins use the milking action of muscles to help move blood, valves prevent backflow due to gravity

Capillary Beds·Capillary beds consist of two types of vessels:

· Vascular shunt – directly connects an arteriole to a venule

· True capillaries – exchange vessels: Substances exchanged due to concentration gradients-

· Oxygen and nutrients leave the blood

· Carbon dioxide and other wastes leave the cells

Capillary Exchange: Mechanisms ( increased surface area --> decrease rate of blood flow--> better exchange):·Direct diffusion across plasma membranes·Endocytosis or exocytosis·Some capillaries have gaps (intercellular clefts)- Plasma membrane not joined by tight junctions·Fenestrations (pores) of some capillaries

Measuring Arterial Blood Pressure

Blood Pressure· Measurements by health professionals are

made on the pressure in large arteries

· Systolic – pressure at the peak of ventricular contraction

· Diastolic – pressure when ventricles relax

Factors Determining Blood Pressure

Variations in Blood Pressure· Normal= 140–90 mm Hg systolic; 90–60 mm Hg diastolic

· Hypotension - Low systolic (below 110 mm HG); Often associated with illness

· Hypertension- High systolic (above 140 mm HG)

*Pressure in blood vessels decreases as the distance away from the heart increases

Blood Pressure: Effects of Factors· Neural factors: Autonomic nervous system adjustments (sympathetic division)

· Ex. Baroreceptor reflex· Renal factors: Regulation by altering blood volume; Renin – hormonal control

***RAAS -Renin /Angiotensin/Aldosterone System: Decrease blood pressure to kidneys --> renin--> +ACE -->-->angiotensins -->vasoconstriction ; angiotensins-->adrenals secrete aldosterone-->incr Na/water reabsorption--> increase blood volume--> incr BP

· Temperature: Heat has a vasodilation effect; Cold has a vasoconstricting effect

· Chemicals: Various substances can cause increases or decreases

· Diet

PUTTING IT ALL TOGETHER!

baroreceptors

atherosclerosis

arteriosclerosisADH

aldosterone

hypothalamus

Renin-Angiotensin - aldosterone

RAAS

Alcohol

Histamine

nicotine

vasoconstriction ---> increased blood pressure

saturated/poly- unsaturated/mono-unsaturated fatty acids

HDL / LDLAtherosclerosis / inflammation

genes ??

estrogen linked to reduced heart disease

DisordersAtherosclerosis - growing plaque gradually narrow artery (stenosis) --> reduced blood flow, esp. during “stress” --> angina pectoris. Can relieve with nitroglycerine = vasodilator. If plaque grows large enough, can lead to heart attack (15%); mainly(85%) cap covering plaque ruptures, promoting clot formation over break, stopping blood flow there or wherever clot then lodges. OR - Artery may go through a series of plaque rupture, repairs (clot cleared naturally, cap repaired with scar tissue), until heart attack/stroke occurs.

*explains why angioplasty (balloon/catheter inserted in femoral artery --> coronary arteries, open balloon and clear plaque) and stents (metal framework inserted in narrowed artery using angioplasty) may not work long term, because they trigger inflammatory response!http://www.youtube.com/watch?v=EQVEdFSlUGU&feature=channel

Hypertension - “high blood pressure”: essential (primary) - cause unknown = 90% cases; secondary - due to other disorders in body.

contributing factors: smoking, diet, stress, lack exercise, weight, genetics

effects: atherosclerosis/arteriosclerosis; heart attack/disease; stroke; kidney failure

treatment: lose weight, decrease stress, diet(esp. salt), exercise; diuretics, beta blockers, angiotensin inhibitors

Heart Attack (myocardial infarction) -- 1.5 million/year; 500,000 immediate deaths

Coronary By-pass surgery

Congestive Heart Failure: heart not able to supply oxygen demands of body; caused by coronary artery disease, hypertension, previous heart attacks, etc.; Surviving cells expand but less efficient; heart pumps faster, body retains fluids, blood vessels constrict in futile attempt to increase blood flow. L. Ventricles fails --> blood backs up in lungs, pulmonary edema, respiratory distress

R. Ventricle fails first --> blood backs up in systemic vessels --> edema in extremities

Arrhythmias -400,000 sudden deaths/year; irregular rhythm --> heart beats too rapidly to pump blood effectively; due to scar tissue on heart from previous heart attack, congenital

Treatment: drugs, surgery or catheter to remove scar tissue, implanted defribillators, pacemakers

Valves - stenosis (narrowing) or incompetency (do no shut fully): surgery / artificial valve

Drugs: clot busters - t-PA

anti-hypertensives: vasodilators, diuretics, B-blockers, angiotensin inhibitors, calcium channel blockers (decrease myocardium contraction)

Heart Transplants and Alternatives: 400,000 people per year w/ heart failure, 45,000 need the 2,500 hearts available for transplants

Heart transplant - human, genetically modified pig (experimental), cell transplant (experimental)

LVAD

Artificial Heart

Other

Recommended fat levels:

LDL < 130 mg/dL; HDL > 40 mg/dL;

total cholesterol / HDL <4.5

Saturated fatty acids (no double bonds in tail). ---> raise HDL, raise LDL

Unsaturated fatty acids (double bond(s) in tail)

Monounsaturated fats - one double bond ---> raise HDL, lower LDL

Polyunsaturated fats - > one double bond ---> lower HDL, lower LDL

Partially hydrogenated (trans) fatty acids -----> lower HDL, raise LDL

**Damage to endothelium lining from hypertension, chemicals(CO, etc.), pathogens

Major Arteries of Systemic Circulation

Major Veins of Systemic Circulation

Circulation to the Fetus

Figure 11.15

Comparison of Blood Pressures in Different Vessels