Biology 2402 A&P Exam 3 Cardiovascular System - Heart
Ch. 13
The cardiovascular system is composed of a pump (heart) and a series of tubes (blood
vessels) that carry the blood and materials throughout body.
The heart - a hollow organ in the pericardial cavity (lower mediastinum in thoracic
cavity) just above diaphragm. Describe (draw and label) each of the following:
pericardial sac (fibrous pericardium)Fig 13.2, 13.4
pericardial cavity with pericardial fluid parietal pericardium ( a serous membrane)visceral pericardium (a serous membrane)tissues of the heart:
endocardium myocardium epicardium *Cardiac tamponade is a serious problem when the pericardial cavity fills with pericardial
fluid (heart can not expand). What does this say about the elasticity of the pericardial sac?
*How can the heart beat vigorously and not be damaged by friction?
*What is the difference between the visceral pericardium and the parietal pericardium?
Structure of the heart:
Double pump with complete separation between the two Fig 13.1, 13.7
right side pumps through pulmonary circuit to lungs
left side pumps through systemic circuit to all body tissues
Each pump (left and right) consist of a thin wall receiving chamber (atria) and a
thick wall power chamber (ventricle)
Fig 13.5-.6
Therefore the heart is composed of four chambers - left and right atria contract
together pumping blood into the left and right ventricles - the ventricles
contract together pumping blood through the pulmonary and systemic circuits.
*What are the interatrial and interventricular septa and where are they located?
*The left ventricle is much larger than the right ventricle and the left has a much thicker
myocardium. Sooooo.. which pumps the most blood, the left or right ventricle?
Valves are made of fibrous connective tissue and are passive (what does passive mean?)
- Atrioventricular valves are between atria and ventricle; composed of cusps, which
are attached to chordae tendinae and papillary muscles in walls of ventricles.
- right AV valve between right atria and right ventricle (= tricuspid valve)
- left AV valve between left atria and left ventricle (=bicuspid, mitral valve).
- AV valves prevent blood flow backwards into atria from ventricles.
- Semilunar valves are at base of arteries carrying blood from heart, prevent blood
flow backwards from arteries into ventricle when ventricles relax.
- pulmonary semilunar valve is between pulmonary artery and right ventricle,
- aortic semilunar valve is between aorta and left ventricle.
*Follow the flow of blood from the right atrium through the heart and circuits back to the
right atrium. List all of the chambers, valves and circuits in the correct sequence.
Cardiac cycle - one heart beat
13.3, Fig 13.10
(blood flows from high to low pressure, cardiac valves are passive)
R. and L. atria contract together (atrial systole) and relax together (atrial diastole)
R. and L. ventricles contract together (ventricular systole) and relax together
(ventricular diastole)
Chambers relax and fill passively during diastole, contract and pump actively
during systole
Cardiac cycle: atrial systole - ventricular systole - relaxation 70 cycles/minute
Heart sounds are due to fluid turbulence as valves close:“lubb-dupp...lubb-dupp..”
“lubb” - av valves closing as ventricles contract
“dupp” - semilunar valves close as ventricles relax
Heart murmurs due to valve insufficiency or stenosis (leaky backflow).
Cardiac conduction - Electrical conduction in the heart
Fig 13.11-.15
Cardiac muscle cells have several unique traits:
long refractory period autorhythmicity gap junctions in intercalated discs - this forms atrial network and ventricular network (functional syncytium) separated by
dense connective tissue that forms framework of heart
*What are gap junctions and why are they important to the working of the heart?
*What nonconductor separates the atrial network and the ventricular network?
*What is tetanus, why is it dangerous and how does the heart prevent it?
Specialized cardiac muscle cells that work as a conduction system:
sinoatrial node (SA node) - “pacemaker”
atrioventricular node (AV node) atrioventricular bundle (AV bundle, bundle of His) left and right bundle branches Purkinje fibers Stimulation starts at SA node (these cells have the shortest autorhythmicity and are
effected by the autonomic nervous system and hormones) which stimulates the muscle
cells of the atria from cell to cell as a wave. The wave dies out at the AV septum which is
made of non-conducting connective tissue, except at the AV node.
The AV node delays then sends the electrical impulse down the AV bundle which divides
into a right and left branch. The bundle branches connect to Purkinje fibers that spread
into the muscle cells of the inferior ventricles. The stimulation then travels upward
through the muscle cells of the ventricles cell to cell to the AV septum where it dies out.
Muscle cells contract when stimulated so the muscle contractions follow the electrical
stimulation as waves - top of atria to AV node, bottom of ventricles to AV septum.
*Make a drawing of the heart and include the location of the conducting system (label).
*Describe the pattern of electrical activity in the heart and explain why this particular
pattern is important.
Electrocardiogram (ECG or EKG) - recording of electrical activity of heart
P wave Fig 13.14-.15
QRS complex T wave *Draw a typical ECG and label each of the waves listed above.
*What event in the heart causes each of these waves?
Heart dynamics - movement of blood through heart to match supply of oxygen to tissues
with oxygen demand by tissues
- stroke volume is amount of blood pumped from heart in one beat
- heart rate is cardiac cycles (beats) per minute
Cardiac Output = stroke volume X heart rate = blood pumped per minute
72 beats/min X 70 ml/beat = 5040 ml/min
Cardiac reserve = CO maximun / CO resting = about 5
range from 0 (sick) to 6-7 (trained athlete)
*What is your cardiac reserve? How can you increase this value?
*What is cardiac output? What changes to increase the cardiac output?
Blood Vessels
Vascular = closed system of vessels averaging about 62,000 miles ,
different types with different characteristics:
heart ---> arteries ---> arterioles ---> capillary bed ---> venules ---> veins ---> heart
Vessel walls made of three layers:
Fig 13.17
tunica interna - inner layer made of epithelial cells, called endothelium, which
forms smooth lining to aid blood flow
tunica media - middle layer made of smooth muscle and fibrous framework with
varying amount of elastic fibers - contraction of muscle changes diameter
of vessel (vasoconstriction when contracted, vasodilation when relaxed)
tunica externa - connective tissue sheath around vessel attaches vessel to
surrounding tissue
Arteries - carry blood away from heart; contain blood under high pressure with high flow
rate; no exchange of material with surrounding tissue; walls are thicker than othervessels.
- elastic (conducting) arteries - largest, close to the heart, pressure highest
tunica media composed mostly on elastic fibers, little smooth muscle.
- muscular (distribution) arteries - medium size, branch to all body regions
tunica media composed mostly of smooth muscle, little elastic fibers.
- arteriole - smallest arteries, branch to form capillary beds
tunica media composed of several layers of smooth muscle; last smooth muscle of
arteriole at beginning of capillary bed forms precapillary sphincter
*The endothelium forms a very smooth lining of arteries. Why is this important?
*Which layer (tunica) can change the diameter of an artery?
*What is the value of elastic arteries having mostly elastic fibers in their tunica media?
*What is the value of the tunica media of arterioles and muscular arteries containing
mostly smooth muscle?
Capillaries - area of vascular system where material are exchanged between blood and
tissues; very small vessels but branch to form extensive network = capillary bed.
- very thin walls - only tunica interna (endothelium).
- small gaps between endothelial cells allow diffusion of molecules.
-constriction and dilation of precapillary sphincters controls flow of blood into
capillary bed to match metabolic demands
- capillary beds have a very large cross sectional area that provides a drop in
blood pressure, a very large surface area for exchange and a lower flow
rate of blood.
Fig 13.18-.20
*Why does the blood pressure drop in capillaries and why is this important?
*What is the primary function of capillaries?
Capillary exchange
Fig. 13.21
also see 3.3 pp60-64
- water and small molecules diffuse through the endothelial cells or through spaces
between the endothelial cells
- normally proteins are too large to leave the capillary and are not lipid soluble so
they can not pass through the cell membranes
- small molecules diffuse from high concentration to low concentration
- the movement of water and small molecules out of and into the capillaries (bulk
flow) is determined by two forces, hydrostatic pressure and osmotic pressure
- hydrostatic pressure, which is blood pressure, is highest at the arteriole end (35
mm Hg), drops throughout the length of the capillary to the venule (16 mm Hg)
- osmotic pressure, due to osmosis, is constant through the length of the capillary at
about 24 mmHg (plasma proteins cause this and usually stay in capillaries)
- osmosis is the movement of water through a selectively permeable membrane from
an area of high solute concentration to an area of low solute concentration.
Dissolved protein molecules that are in the blood but can not pass through
the capillary walls play a major roll in osmosis. The proteins make the
blood more solute concentrated, so, therefore, osmosis is into the blood
from the tissue.
- at the arteriole end the blood pressure pushing fluids out is higher than the
osmotic pressure pulling fluids in. The net flow is out.
- at the venule end the blood pressure pushing fluids out is lower than the osmotic
pressure pulling fluids in. The net flow is in.
- the flow in is almost equal to the flow out, but fluid accumulates in the tissues.
- the excess tissue fluid is removed by the lymphatic system and returned to the
blood.
- edema is an abnormally high accumulation of intercellular fluid.
*What is the role of plasma proteins in capillary exchange and why is the balance upset if
plasma proteins escape into the tissues from the blood?
*What is the role of the lymphatic system in maintaining tissue fluid balance?
*Describe the forces that cause fluid exchange in the capillaries.
*Why does the velocity of the blood (flow rate) drop in the capillary bed?
*How does this affect the exchange of materials between the blood and tissues?
Veins - vessels that return blood to heart
Fig 13.17, 13.22
- blood under low pressure with low flow rate, but large volume (60% of blood)
- no exchange of materials between blood and tissues
- three layers present but thinner than in arteries, tunica externa thickest
- valves in walls maintain flow toward heart, prevent backflow
Fig 13.23
- blood moved by pressure produced when veins are squeezed between contracting
skeletal muscles and by negative pressure in thoracic cavity due to breathing
*Why are valves found in veins, but cannot be in arteries?
*Blood pressure in veins is very low. What forces move blood back to the heart?
Cardiovascular regulation
13.25, 13.26, 13.16
blood flow to a tissue must meet oxygen and nutrient demand - homeostasis
two major factors affect blood flow: blood pressure and resistance
blood flow = blood pressure / resistance
BF = BP/R
Each of these major factors is affected by secondary factors:
I. blood pressure - (systolic and diastolic) - directly proportional to BF
A. cardiac output
(Frank Starling law of the heart)
1. stroke volume - volume of blood returning to ventricles
- length of ventricular diastole (time to fill)
- venous pressure
- force of contraction of heart muscle
- pressure in arteries
2. heart rate
B. blood volume
1. retention or loss of water in kidneys, tissues
2. blood loss
II. resistance (peripheral resistance - friction with blood vessels)- inversely
proportional to BF
A. blood viscosity (proportion of blood that is fluid or cells)
B. total length of blood vessel length
C. turbulence
D. blood vessel diameter (slight vasoconstriction or vasodilation has large
effect = systemic vascular resistance = peripheral resistance)
Blood flow maintained through several methods, neural, hormonal and autoregulation.
Neural (nervous system - this involves sensory receptors, integration and effectors):
baroreceptor measure blood pressure in key locations (carotid sinus, aortic sinus
and rt. atria)
chemoreceptors measure the level of key chemicals in the blood (carbon dioxide,
hydrogen protons and oxygen - CO2 , H+ , O2 ) in carotid and aortic bodies.
Integration occurs in several centers in the medulla oblongata:
cardioacceleratory center increases heart rate and strength of contraction
via the sympathetic nervous system
cardioinhibitory center decreases heart rate and strength of contraction via
the parasympathetic nervous system
vasomotor center controls the diameter of blood vessels (mostly arterioles)
higher brain centers give input about other factors such as emotional state
or anticipated physical activity
Hormonal:
antidiuretic hormone - released from post. pituitary in response to osmotic
concentration of blood in hypothalamus - increases water retention in
kidneys, increases volume of blood and blood viscosity
aldosterone - released from adrenal cortex via stimulation from hypothalamus increases sodium and water retention from kidneys, increases volume of blood
epinephrine and norepinephrine - from adrenal medulla, increases heart rate and
strength of contraction and vasoconstriction
Autoregulation:
precapillary sphincter can contract or relax to precisely regulate the flow of blood
through an individual capillary bed to match blood flow with the oxygen demand
of the cells. Precapillary sphincter relaxes in response to metabolic waste products
of cells.
*Describe the baroreceptor reflex when the blood pressure increases in the carotid sinus.
*Describe the baroreceptor reflex when the blood pressure increases in the rt. atria.
*Which three factors that affect blood flow does the nervous system primarily affect to
maintain the appropriate flow of blood in the short term?
*How does physical activity increase blood flow?
*Which factor that affects blood flow do hormones affect primarily on a long-term basis?
*Describe the precapillary sphincters- what type cells are they and where are they
located?
*How are precapillary sphincters involved in the regulation of blood flow?
*Which factor that affects blood flow is affected by precapillary sphincters?
*Anaphylactic shock is the result of precapillary sphincters throughout the body being
blocked so that they relax. How does this affect peripheral resistance.
*What structures are primarily responsible for changing peripheral resistance?
*What is the function of arterial anastamoses, such as around the knee and the brain?
*The venous system contains a large volume of blood, about 60% of blood in body while
the arterial system contains only about 15% of the blood volume. Obviously the same
amount of blood has to has to move through the arteries and the veins. Explain how they
can have such different volumes, and why this is important to maintaining blood flow.
Some vessel details:
Arteries carry blood away from the heart. Veins bring blood to the heart.
The pulmonary circuit carries blood from the right ventricle to the lungs and back
to the left atria (leaving deoxygenated, returning oxygenated).
The systemic circuit carries blood from the left ventricle to all tissues in the body
and back to the right atria (leaving oxygenated, returning deoxygenated).
The only portion of the vascular system where materials are exchanged between
the blood and the tissues is the capillary beds.
Usually blood passes through only one capillary bed as it flows through either
circuit. Portal systems are the second capillary bed in a route.
Arterial anastomoses are alternate routes that allow blood to bypass a constriction.
Identify the following vessels on a diagram of a human:
pulmonary arteries
pulmonary veins
systemic arteries
ascending aorta
aortic arch
descending aorta
brachiocephalic
left and right subclavian
l. and r. common carotid
axillary
brachial
radial
ulnar
celiac trunk
superior mesenteric
renal
gonadal
inferior mesenteric
common iliac
external iliac
femoral
popliteal
systemic veins
superior vena cava
brachiocephalic
subclavian
external jugular
inferior vena cava
hepatic
renal
common iliac
external iliac
femoral
great saphenous
hepatic portal
Fig 13.27 - 13.35