Download Unit 3-4 Circulatory System Notes File

Cardiovascular system – The Heart and blood vessesls
Overview of Blood Circulation
Blood leaves the heart via arteries that branch repeatedly until they become
capillaries
Oxygen (O2) and nutrients diffuse across capillary walls and enter tissues
Carbon dioxide (CO2) and wastes move from tissues into the blood
Oxygen-deficient blood leaves the capillaries and flows in veins to the heart
This blood flows to the lungs where it releases CO2 and picks up O2
The oxygen-rich blood returns to the heart
Pathway of Blood Through the Heart and Lungs
1. Right atrium  tricuspid valve  right ventricle
2. Right ventricle  pulmonary semilunar valve 
pulmonary arteries  lungs
3. Lungs  pulmonary veins  left atrium
4. Left atrium  bicuspid valve (mitral)  left ventricle
5. Left ventricle  aortic semilunar valve  aorta
6. Aorta  systemic circulation
Coronary Circulation
Coronary circulation is the functional
blood supply to the heart muscle itself
Atria of the Heart
•Function: Atria are the receiving chambers of the heart
•Blood enters right atria from superior and inferior
venae cavae and coronary sinus
•Blood enters left atria from pulmonary veins
Ventricles of the Heart
•Function: Ventricles are the discharging chambers
(pumps) of the heart
•Right ventricle pumps blood into the pulmonary trunk
•Left ventricle pumps blood into the aorta
Vessels returning blood to the heart include:
Right and left pulmonary veins (from lungs)
Superior and inferior venae cavae (from the
rest of the body)
Vessels conveying blood away from the heart include:
Aorta
Right and left pulmonary arteries
Superior vena cava
Right pulmonary vein
Left pulmonary Vein
Mitral Valve
Pulmonary Valve
Tricuspid Valve
Inferior vena cava
Aortic Valve
Heart Valves
•Heart valves ensure unidirectional blood flow through the heart
Atrioventricular Valve Function
•Atrioventricular (AV) valves lie between the atria and the ventricles
•AV valves prevent backflow into the atria when ventricles contract
•Chordae tendineae anchor AV valves to papillary muscles
Semilunar Valve Function
Aortic Valve - Aortic semilunar valve lies between the left ventricle and the aorta
Coronary Valve - Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk
Heart sounds (lub-dup) are associated with closing of heart valves
First sound occurs as AV valves close and signifies beginning of systole
Second sound occurs when SL valves close at the beginning of ventricular diastole
Microscopic Anatomy of Heart Muscle
•Cardiac muscle is striated, short, fat, branched, and
interconnected
•The connective tissue endomysium acts as both
tendon and insertion
•Intercalated discs anchor cardiac cells together and
allow free passage of ions
•Heart muscle behaves as a functional syncytium
(like a single unit)
Heart muscle:
•Is stimulated by nerves and is self-excitable
(automaticity)
•Contracts as a unit
•Has a long (250 ms) absolute refractory period
Cardiac muscle contraction is similar to skeletal muscle
contraction
Heart Physiology: Intrinsic Conduction System
Specialized cells with rythmic changing membrane potential
Autorhythmic cells: sinoatrial node & atrioventricular node
Initiate action potentials
Have unstable resting potentials called pacemaker potentials
Use calcium influx (rather than sodium) for rising phase of the action potential
Pacemaker and Action Potentials
of the Heart
1.
2.
3.
Hyperpolarization opens Na+ channels (Na+ influx, depolarization)
Depolarization causes Ca2+ channels to open (Ca2+ influx, big depolarization)
Ca2+ and Na+ channels close K+ channels open (Ca2+ outflow, repolarization then
hyperpolarization)
Depolarization of autorythmic cells is spread to rest of cardiac muscle through gap junctions. There,
normal excitation-contraction coupling occurs.
Signal does not spread from atria to ventricles because there is no gap junction between the two
regions of heart.
Heart Physiology: Sequence of Excitation
Sinoatrial (SA) node generates impulses about 75 times/minute
Atrioventricular (AV) node delays the impulse approximately 0.1 second
Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)
AV bundle splits into two pathways in the interventricular septum (bundle branches)
Bundle branches carry the impulse toward the apex of the heart
Purkinje fibers carry the impulse to the heart apex and ventricular walls
Heart Excitation - Electrocardiography (ECG or EKG)
•Electrical activity is recorded by electrocardiogram (ECG)
•P wave corresponds to depolarization of SA node
•QRS complex corresponds to ventricular depolarization
•T wave corresponds to ventricular repolarization
•Atrial repolarization record is masked by the larger QRS complex
AP for cardiac muscle has extra SLOW voltage-gated Ca2+-channel
(slow = opens after faster)
Ca2+
K+
Membrane potential
Na+
2. Na+ Influx
1. Fast volt-gated Na+-ch opens
2. Na+ Influx
3. volt-gated Na+-ch closes
time
++ +
1. volt-gated
Na+-ch opens
+ +
+
SLOW volt-gated Ca2+-ch opens
3. v-g Na+-ch closes
v-g Ca2+-ch opens
v-g K+-ch opens
volt-gated K+-ch opens
4. Ca2+ Influx
K+ Outflux
4. Ca2+ Influx
K+ Outflux
+ in  depol
Cancel each other out
5. volt-gated Ca2+-ch closes
6. only K+ outflux + out  repol
+
5. v-g Ca2+-ch closes
+
6. only K+ Outflux
Regulation of Heart Rate
Autonomic Nervous System
•Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise
•Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS
•PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone
Chemical Regulation of the Heart
•The hormones epinephrine and thyroxine increase heart rate
•Intra- and extracellular ion concentrations must be maintained for normal heart function
Tachycardia – abnormally fast heart rate – over 100bpm
Bradycardia – slow heart rate – under 60 bpm
(good in athletes who have higher stroke volume (SV)
Normal
sec
Bradycardia, Sinus Rhythm
Normal P, QRS, T, rate < 60
sec
Tachycardia, Sinus Rhythm
Normal P, QRS, T, rate > 100
sec
Ventricular Tachycardia (VTAC)
Bizarre, wide QRS, no Pwav, rate > 100
sec
Hypercalcemia
Short/absent ST segment
sec
Ventricular Fibrillation (VFIB)
Chaotic waves
sec
Asystole
Flatline
http://www.gwc.maricopa.edu/class/bio202/cyberheart/ekgqzr0.htm
Blood Flow
Actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given period:
Is measured in ml per min.
Is equivalent to cardiac output (CO), considering the entire vascular system
Is relatively constant when at rest
Varies widely through individual organs
Blood Pressure (BP)
Force per unit area exerted on the wall of a blood vessel by its contained blood
Expressed in millimeters of mercury (mm Hg)
Measured in reference to systemic arterial BP in large arteries near the heart
The differences in BP within the vascular system provide the driving force that keeps blood moving
from higher to lower pressure areas
Resistance – opposition to flow
•Measure of the amount of friction blood encounters
•Generally encountered in the systemic circulation
•Referred to as peripheral resistance (PR)
The three important sources of resistance are
1. blood viscosity – “stickiness” of the blood
2. total blood vessel length – longer = more resistance
3. blood vessel diameter
Changes in diameter are frequent and significantly alter resistance
Resistance varies inversely with the fourth power of vessel radius
For example, if the radius is doubled, the resistance is 1/16 as much
Blood Flow, Blood Pressure, and Resistance
Blood flow (F) is directly proportional to the difference in blood pressure (P) between two points
If P increases, blood flow speeds up; if P decreases, blood flow declines
Blood flow is inversely proportional to resistance (R)
If R increases, blood flow decreases
R is more important than P in influencing local blood pressure
Systemic Blood Pressure
The pumping action of the heart generates blood flow through the vessels along a pressure
gradient, always moving from higher- to lower-pressure areas
Pressure results when flow is opposed by resistance
•Is highest in the aorta
•Declines throughout the length of the pathway
•Is 0 mm Hg in the right atrium
steepest change in blood pressure at arterioles
Arterial Blood Pressure
Arterial BP reflects two factors of the arteries close to the heart
Their elasticity (compliance or distensibility)
The amount of blood forced into them at any given time
Blood pressure in elastic arteries near the heart is pulsatile (BP rises and falls)
Systolic pressure – pressure exerted on arterial walls during ventricular contraction
Diastolic pressure – lowest level of arterial pressure during a ventricular cycle
Pulse pressure – the difference between systolic and diastolic pressure
Mean arterial pressure (MAP) – pressure that propels the blood to the tissues
MAP = diastolic pressure + 1/3 pulse pressure
Capillary Blood Pressure
Capillary BP ranges from 20 to 40 mm Hg
Low capillary pressure is desirable because high BP would rupture fragile, thin-walled capillaries
Low BP is sufficient to force filtrate out into interstitial space and distribute nutrients, gases, and
hormones between blood and tissues
Venous Blood Pressure
Venous BP is steady and changes little during the cardiac cycle
The pressure gradient in the venous system is only about 20 mm Hg
A cut vein has even blood flow; a lacerated artery flows in spurts
Factors Aiding Venous Return
Venous BP alone is too low to promote adequate blood return and is
aided by the:
Respiratory “pump” – pressure changes created during
breathing suck blood toward the heart by squeezing local
veins
Muscular “pump” – contraction of skeletal muscles “milk”
blood toward the heart
Valves prevent backflow during venous return
Monitoring Circulatory Efficiency
Efficiency of the circulation assessed by taking pulse and blood pressure
Vital signs – pulse and blood pressure, along with respiratory rate and body temperature
Pulse – pressure wave caused by the expansion and recoil of elastic arteries
Radial pulse (taken on the radial artery at the wrist) is routinely used
Varies with health, body position, and activity
Measuring Blood Pressure
Systemic arterial BP is measured indirectly with the auscultatory method
1.A sphygmomanometer (blood pressure cuff) is placed on the arm superior to the elbow
2.Pressure is increased in the cuff until it is greater than systolic pressure in the brachial artery
3.Pressure is released slowly and the examiner listens with a stethoscope
4.The first sound heard is recorded as the systolic pressure
5.The pressure when sound disappears is recorded as the diastolic pressure
Blood Flow Through Tissues
Blood flow, or tissue perfusion, is involved in:
Delivery of oxygen and nutrients to, and removal of wastes from, tissue cells
Gas exchange in the lungs
Absorption of nutrients from the digestive tract
Urine formation by the kidneys
Blood flow is precisely the right amount to provide proper tissue function
Velocity of Blood Flow
Blood velocity:
Changes as it travels through the systemic circulation
Is inversely proportional to the cross-sectional area
Slow capillary flow allows adequate time for exchange between blood and tissues
Blood Vessels
Blood is carried in a closed system of vessels that begins and ends at the heart
The three major types of vessels are arteries, capillaries, and veins
Arteries carry blood away from the heart, veins carry blood toward the heart
Capillaries contact tissue cells and directly serve cellular needs
Blood Vessels Structure
Endothelium, Smooth Muscle & Connective Tissue
•
•
•
Arteries
– have thicker walls  protect against blood pressure that are necessary for blood flow
– Increased smooth muscle for more control
Capillaries
– Very thin(only endothelium) best for exchange
– Susceptible to higher pressures
– Allow only a single RBC to pass at a time
– There are three structural types of capillaries: continuous, fenestrated, and sinusoids
Veins
– Flexible walls: can store blood
– Low pressure, muscles milk for return flow
Regulation of Blood Pressure
• Blood pressure is determined by cardiac output and peripheral resistance due to constriction of
arterioles
• Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure
• Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall
Regulation of blood flow / microcirculation (capillaries) = tissue perfusion
•
Two mechanisms regulate distribution of blood in capillary beds:
– Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel
– Precapillary sphincters control flow of blood between arterioles and venules
Terminal arteriole
Precapillary
sphincters
Postcapillary venule
Regulation of Blood Flow and Pressure
• Heart
– Neural: Autonomic Nervous sytstem, ANS
• Parasympathetic – Acetylcholine – decreases H.R.
• Sympathetic – norepinephrine – increases H.R. & Strength
– Hormonal
• Epindephrine (adrenal medulla) increase H.R. & Strength
• Blood Vessels
– Neural – sympathetic (norepindephrine)
• Vasoconstriction or vasodilation
At Capillaries Diffusion is sufficient
Net outward flow
Fluid Return by the Lymphatic System
• The lymphatic system returns fluid that leaks out in the capillary beds
• This system aids in body defense
• Fluid, called lymph, reenters the circulation directly at the venous end of the capillary bed
and indirectly through the lymphatic system
• The lymphatic system drains into veins in the neck
Circulatory Systems
• While diffusion gets nutrients into and out of the blood. Transport system for mass blood
movement (circulation) is required to connect organs
• In small and/or thin animals, cells can exchange materials directly with the surrounding medium
• Most complex animals have internal transport systems that circulate fluid
Diffusion Rates
Distance (µm)
1
0.5 msec
10
50 msec
100
5 seconds
1,000 (1mm)
8.3 minutes
10,000 (1cm)
14 hours
Open and Closed Circulatory Systems
•
•
More complex animals have either open or closed circulatory systems
Both systems have three basic components:
– A circulatory fluid (blood or hemolymph)
– A set of tubes (blood vessels)
– A muscular pump (the heart)
Both need to come near surface of body for nutrient exchange
Open Circulatory system:
(insects, mollusks & arthropods)
• hemolymph = general body fluid (blood and interstitial fluid
combined)
• bathes the organs
a) Hemolymph is pumped out through open-ended vessels &
flows out among the cells
b) muscle contractions move hemolymph toward tail &
around  when the heart relaxes the fluid returns
through several pores
Time required
Closed Circulatory system
vertebrates, earthworms, octopus
• blood confined to vessels - cardiovascular system
• heart pumps the blood
 through larger vessels (arteries)
 to smaller ones (capillaries)
 then back through larger vessels (veins) again to heart
Single Circulation
• Vertebrate hearts contain two or more
chambers
• Blood enters atrium and is pumped out through
a ventricle
single circulation with a two-chambered heart
• blood leaving the heart passes through two capillary
beds before returning
Double Circulation
• Amphibian, reptiles, and mammals
• Oxygen-poor and oxygen-rich blood are pumped separately from the right and left
sides of the heart