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Development of circulation system
Aorta
Ostium
Hemocoel
Heart
Dorsal blood vessel
Two of five
hearts
Ventral blood
vessels
Gut
cavity
Circulatory systems can be divided into two broad
categories: open and closed.
Open circulatory system: blood pumped by the heart
empties via an artery into an open, fluid-filled space, the
hemocoel. Pressure are low. Some invertebrates
Closed circulatory system: blood flows in a continuous
circuit of tubes from arteries to veins through capillaries.
All vertebrates and some invertebrates.
Plasma = 55% of whole blood
Platelets
“Buffy coat”
<1%
White blood cells
Packed cell
volume, or
hematocrit
Red blood cells =
45% of whole blood
Fig. 9-3, p.361
Movement of blood results from any or all of the
following mechanism
1. Forces imparted by rhythmic contractions of the heart
(vertebrate)
2. Elastic recoil of arteries following filling by the action
of heart (vertebrate)
3. Squeezing of blood vessels during body movement
(arthropods)
4. Peristaltic contractions of smooth muscle surrounding
blood vessels (giant earth worm).
Functions of the Circulatory System
• Transportation:
– Respiratory:
• Transport 02 and C02.
– Nutritive:
• Carry absorbed digestion products to liver and to
tissues.
– Excretory:
• Carry metabolic wastes to kidneys to be excreted in
the urine.
Functions of the Circulatory System
• Regulation:
– Hormonal:
• Carry hormones to target tissues to produce
their effects.
– Temperature:
• Divert blood to cool or warm the body.
Functions of the Circulatory System
• Protection:
– Clotting:
• Prevents blood loss.
– Immune:
• Leukocytes (antibodies and T cells),
cytokines and complement fixation protect
against pathogens.
Components of Circulatory System
Circulatory system consists of 4 basic parts:
1. A main propulsive organ, heart, force blood through body
2. An arterial system: distribute blood, pressure reservoir
3. Capillaries: transfer material between blood and tissues
4. A venous system: blood storage, returning blood to the
heart
Pulmonary and Systemic
Circulations
• Pulmonary circulation:
-Path of blood from right
ventricle through the lungs
and back to the heart.
• Systemic circulation:
– Oxygen-rich blood pumped
to all organ systems to
supply nutrients.
desmosome
Sarcoplasmic
reticulum
Gap junction
T-tube
Intercalated
disc
Carduac
myofubril
Intrinsic Conduction System
SA Node
Internodal Pathway
AV Node
AV Bundle
Bundle Branches
Purkinje Fibers
Conduction of Impulse
• AP from SA node spread quickly at rate of 0.8 1.0 m/sec.
• Time delay occurs as impulses pass through AV
node.
– Slow conduction of 0.03 – 0.05 m/sec.
• Impulse conduction increases as spread to
Purkinje fibers at a velocity of 5.0 m/sec.
• Ventricular contraction begins 0.1 – 0.2 sec. After
contraction of the atria.
Electrocardiogram (ECG): A record of electrical events
associated with contractions of the heart; typically obtained with
electrodes placed on the surface of the body.
Cardiac action potential
Electrical Activity of the Heart
• Automaticity: automatic nature of the heartbeat.
• SA node:
–
–
–
–
Demonstrates spontaneous depolarization.
Functions as the pacemaker.
Does not maintain a stable resting membrane potential.
Membrane depolarizes from –60 to –40 mV.
Depolarization
• Depolarization:
– VG fast Ca++ channels open.
– Ca++ diffuses inward.
– Opening of VG Na+ channels may also
contribute to the upshoot phase of the AP.
• Repolarization:
– VG K+ channels open.
– K+ diffuses outward.
Cardiac Muscle AP
• Resting membrane potential of –90 mV.
• SA node AP spreads to myocardial cells.
• When myocardial cell reaches threshold, the
cell depolarizes.
• Rapid upshoot occurs:
– VG Na+ channels open.
– Inward diffusion of Na+.
Cardiac Muscle AP
• Plateau phase:
– Rapid reversal in membrane polarity to –15
mV.
– VG Ca++ channels open.
– Slow inward flow of Ca++ balances outflow of
K+.
• Rapid repolarization:
– VG K+ channels open.
– Rapid outward diffusion of K+.
A. Initiation of action potential in autorhythmic cells:
1. Pacemaker Potential due to influx of sodium and reduced
efflux of potassium.
2. Depolarization and reversal of the membrane potential due to
influx of calcium.
3. Repolarization due to efflux of potassium.
B. .Initiation of action potential in contractile cells:
1. Opening of voltage-regulated fast sodium channels triggered
by entry of positive ions from adjacent cell: Depolarization due
to rapid influx of sodium
2. Plateau produced by calcium influx balancing potassium
efflux.
3. Repolarization due to efflux of potassium.
Pacemaker Potential
• - 40 mV is threshold for producing AP.
• Spontaneous diffusion caused by diffusion
of Na+ through slow Na++ channels.
• Lack of a stable resting potential
• Multiple array of channels
• Parasympathetic stimulation decrease rate
• Sympathetic stimulation increase rate
Refractory Periods
• Heart contracts as
on single unit.
• Contraction lasts
almost 300 msec.
• Refractory periods
last almost as long
as contraction.
• Summation cannot
occur.
Summary
1. The intrinsic conduction system of the heart initiates
depolarization impulses.
2. Action potentials spread throughout the heart, causing
coordinated heart contraction.
3. An ECG wave tracing records the electrical activity of
the heart.
Cardiac Cycle
• Refers to the repeating pattern of
contraction and relaxation of the heart.
• Systole:
– Phase of contraction.
• Diastole:
– Phase of relaxation.
The Cardiac
Cycle
Cardiac output
Cardiac output: volume
of blood pumped per
unit time from a
ventricle
Stroke volume: volume
of blood ejected from a
ventricle by each beat of
heart
Exercise increase heart
rates, not the stroke
volume