Download Physiology Ch 11

Chapter 11
The Cardiovascular System
Anatomy of the Heart
cardiovascular system
- uses blood to transport oxygen, nutrients, cell wastes, hormones, etc. to and from the cells
- the heart provides the force to move the blood
heart
- approximately the size of a fist
- flanked by the lungs
apex
- end of the heart
- points down and to the left
- rests on diaphragm
base
- top of the heart
- great vessels emerge here
pericardium
- double sac (serous membrane) surrounding the heart
epicardium
- visceral pericardium
- hugs external surface of heart
- part of heart wall
parietal pericardium
- outer layer of pericardium
fibrous pericardium
- fibrous layer which reinforces parietal pericardium
- protects and anchors heart
serous fluid
pericarditis
3
- slippery fluid between pericardial layers
- reduces friction as heart beats
- inflammation of pericardium
- can reduce serous fluid causing pericardial layers to stick (adhesions)
Layers of Heart Wall
epicardium
- visceral pericardium
myocardium
- bundles of cardiac muscle
endocardium
- thin sheet of endothelium lining heart chambers
chambers of the heart
atria
- 2 of them  left atrium and right atrium (LA and RA)
- superior to ventricles
- receiving chambers (collect blood)
ventricles
- 2 of them  left ventricle and right ventricle (LV and RV)
- thick-walled
- discharging chambers (contract and pump blood into circulation)
septum - tissue that divides heart into right and left sides (interventricular or interatrial septum)
heart
- acts as a double pump
- right side pumps blood to lungs to pick up O2
- left side pumps blood to rest of body to deliver O2
pulmonary circulation
- involves right side of heart
- RA receives O2-poor blood from superior vena cava and inferior vena cava
- blood flows to RV which pumps blood to lungs through pulmonary trunk
- pulmonary trunk divides into right pulmonary artery & left pulmonary artery which bring blood to lungs
- O2 is picked up and CO2 is unloaded
- blood flows back to left side of heart (LA) through pulmonary veins
systemic circulation
- involves left side of heart
- O2-rich blood flows from LA to LV
- LV pumps blood through the aorta from which systemic arteries branch to supply all body tissues (LV is
thicker chamber than RV)
- O2-poor blood flows through systemic veins to superior or inferior vena cava and then to RA
valves - allow blood to flow in only 1 direction through heart
atrioventricular (AV) valves
bicuspid or mitral valve
tricuspid valve
semilunar valves
pulmonary valve
aortic valve
atrioventricular (AV) valves
bicuspid or mitral valve
tricuspid valve
chordae tendineae
semilunar valves
pulmonary valve
aortic valve
- between atria & ventricles
- prevent backflow into atria when ventricles contract
- open during ventricular relaxation
- closed during ventricular contraction
- left AV valve
- 2 flaps of endocardium
- right AV valve
- 3 flaps of endocardium
- tiny white cords anchoring flaps to ventricle walls
- between ventricles & 2 large vessels leaving the ventricles
- prevent arterial blood from reentering heart
- open during ventricular contraction
- closed during ventricular relaxation
- between RV and pulmonary trunk
- between LV and aorta
coronary circulation
coronary arteries
cardiac veins
- right and left coronary arteries branch off of the aorta
- bring blood to nourish the myocardium
- drain the myocardium
- empty into a vessel on back of heart (coronary sinus) which then empties into RA
angina pectoris - crushing chest pain which occurs when myocardium is deprived of O2
myocardial infarction
- death of heart cells deprived of oxygen
- AKA heart attack
Physiology of the Heart
intrinsic conduction system
sinoatrial (SA) node
- AKA nodal system
- regulates heart activity
- causes muscle contraction to occur in 1 direction (from atria to ventricles)
- causes heart to beat about 75 times per minute
- in RA
- starts each heartbeat, sets pace for the heart
- often called the pacemaker
- impulse then spreads through atria to atrioventricular (AV) node, through AV
bundle, through the bundle branches (in interventricular septum), and finally
through the Purkinje fibers (in ventricle walls)
SA node  AV node AV bundle bundle branches Purkinje fibers
tachycardia
bradycardia
- rapid heart rate (>100 beats per minute)
- slower heart rate than normal (<60 beats per minute)
systole - ventricular contraction
diastole - ventricular relaxation
cardiac cycle - events of 1 complete heartbeat
a) mid-to-late diastole
- heart completely relaxed
- pressure in heart is low
- blood flows into ventricles from atria
- AV valves are open; semilunar valves are closed
- then atria contract forcing rest of blood into ventricles
b) ventricular systole
- ventricles contract (atria are relaxed & fill with blood)
- pressure in ventricles increases rapidly
- AV valves are forced closed, semilunar valves open
- blood leaves ventricles
c) early diastole
- ventricles relax
- semilunar valves close
- pressure in ventricles drops
- AV valves open
- ventricles fill with blood again
heart sounds - “lub-dup”
first sound (lub)
second sound (dup)
 AV valves closing
 semilunar valves closing
heart murmurs - abnormal heart sounds
- often indicate valve problems
- if a valve doesn’t close tightly, a swishing sound is heard when the valve closes due to backflow
of blood
stroke volume - amount of blood pumped out by a ventricle with each heartbeat
- about 70 ml/beat
cardiac output - amount of blood pumped out by each side of the heart in 1 minute
- product of heart rate (HR) and stroke volume (SV)
CO = HR x SV
example:
CO =
75 beats
minute
x
70 mL = 5250 mL/min
beat
- varies with demands of the body
- increases when HR or SV increase, and drops when HR or SV decrease
physical factors affecting heart rate
age
- HR decreases with age
gender
- HR faster in females; 72-80 vs. 64-72 in males
body temperature
- heat increases HR by increasing metabolic rate of heart cells
- cold decreases HR
exercise
- HR increases (nervous system triggers and also muscles generate heat)
congestive heart failure - decreases pumping efficiency of heart
- often caused by weakening of heart due to coronary atherosclerosis (fatty buildup in
coronary arteries), high blood pressure, or multiple heart attacks
pulmonary edema
- due to failure of left side of the heart
- blood backs up into lungs causing blood vessels to swell
- fluid leaks from vessels into lung tissue
peripheral congestion - due to failure of the right side of the heart
- blood backs up in systemic circulation
- edema (swelling) occurs  most noticeable in feet, ankles, fingers
Blood Vessels
vascular system
arteries
arterioles
capillaries
venules
veins
- closed transport system made up of blood vessels
- blood vessels leaving the heart (carry blood away from heart)
- branch into smaller and smaller arteries
- smallest arteries
- branch into capillaries
- smallest blood vessels
- form capillary beds in tissues
- exchange of materials occurs between tissue cells and blood
- drained by venules
- smallest veins
- join to form veins
-drain tissues and return blood to heart
- empty into vena cavae which enter the heart
walls of arteries and veins have 3 layers:
tunica intima
- thin inner layer of endothelium
- lines interior of vessels
tunica media
- middle layer
- mostly smooth muscle and elastic tissue
- vessels constrict or dilate to increase or decrease blood pressure
tunica externa - outer layer
- mostly fibrous connective tissue
- supports & protects vessels
arteries
- thickest walls of all the blood vessels (especially tunica media)
veins
- thinner walls
- blood often flows against gravity
- larger veins have valves to prevent backflow
- contraction of skeletal muscles also helps blood return to heart
capillaries
- walls 1 cell layer thick (only tunica intima)
- exchanges made between blood and tissue cells
- form networks called capillary beds
microcirculation - circulation through a capillary bed
varicose veins - common in people who stand for long periods, in obese people, and pregnant women
- blood pools in legs due to insufficient venous return of blood
- veins become twisted and dilated
aorta
- largest artery of the body (about size of garden hose)
- ascending aorta
- part of aorta rising upward from LV
aortic arch
- ascending aorta arches to the left
thoracic aorta
- aorta plunges downward through thorax
abdominal aorta - aorta passes through diaphragm into abdominopelvic cavity
iliac arteries
- final branches of abdominal aorta
- 1 supplies each leg
a few more arteries:
carotid arteries
axillary arteries
radial arteries
femoral arteries
popliteal arteries
dorsalis pedis artery
-supply head
- run through armpits
- supply forearm
- supply thighs
- run through back of knee
- supplies dorsum of foot
superior vena cava
- veins draining head and arms empty here
inferior vena cava
- veins draining lower body empty here
Physiology of Circulation
pulse - pressure waves caused by the expansion and recoil of an artery with each beat of the LV
- equal to heart rate
- averages 70 – 76 beats/min in a resting person
pressure points - areas where arteries are close to surface
- pulses can be palpated here
- also pressure can be applied here to stop blood flow to distal tissues during hemorrhage
blood pressure - pressure blood exerted against the inner walls of blood vessels
- highest in large arteries and drops throughout the circulatory pathway
- reaches zero at the vena cava
- if a vein is cut  blood flows evenly from the wound
- if an artery is cut  blood leaves in rapid spurts
systolic blood pressure
- pressure in the arteries at the peak of ventricular contraction
diastolic blood pressure
- pressure when ventricles are relaxing
blood pressure - given in millimeters of mercury (mm Hg)
- systolic pressure given before diastolic (example: 120/80)
peripheral resistance
- amount of friction encountered by blood as it flows through blood vessels
- may be increased by narrowing of blood vessels by nervous system or atherosclerosis,
by increased blood volume, or by increased blood thickness
rise in blood pressure
- may be caused by anything that increases cardiac output or peripheral resistance
- examples:
age
weight
time of day
exercise
body position
emotional state
drugs
hypertension
- high blood pressure
- chronic hypertension strains heart and damages arteries
- myocardium may enlarge as heart pumps against increased resistance
- when strained too much, heart weakens and becomes “flabby”
- damage to blood vessels speeds up atherosclerosis
primary (essential) hypertension
- no specific cause found (90% of cases)
factors thought to be involved in hypertension:
hypotension
diet (high cholesterol, saturated fat, sodium)
obesity
heredity
race
stress
- low blood pressure
- usually systolic pressure below 100 mm Hg
- usually no cause for concern
coronary artery disease
- filling of blood vessels with calcified fatty deposits
- diet is most important contributing factor
- risk is lowered if people eat less animal fat, cholesterol, and salt
- other preventative measures:
avoid stress
don’t smoke
exercise