Transcript The Heart - Sign in to SCH Academy

The Cardiovascular System
A 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 Circulation
Blood 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!
atherosclerosis
aldosterone
arteriosclerosis
ADH
Renin-Angiotensin
- aldosterone
RAAS
baroreceptors
Alcohol
hypothalamus
Histamine
nicotine
saturated/polyunsaturated/monounsaturated fatty
acids
HDL / LDL
Atherosclerosis /
inflammation
genes ??
vasoconstriction --->
increased blood pressure
estrogen linked to
reduced heart disease
Disorders
Atherosclerosis - 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