Transcript Circulatory System

Circulatory System
Topic 6.3
6.2
6.2
• Basic human heart facts
– Resting heart beat is about 60 beats per minute with
each beat ejecting 75 ml of blood
– Maximal heart rate can be greater than 200 bpm each
with a volume of 120+ ml
– Coronary arteries supply the heart with oxygen and
nutrients
– The heart is asymmetrical with the left side being
slightly larger than the right
– Over time aerobic exercise can increase all of the
above
6.2
• Parts of the heart
– Atria = collecting chambers
• collect blood that is pumped into them by the
veins
– Ventricles = pumping chambers
• Pump blood into arteries at high pressure
– Valves prevent blood from flowing in the wrong
direction
– Veins carry blood towards the heart
– Arteries carry blood away from the heart
6.2
• Flow of blood through the heart
– Deoxygenated blood flows from the superior vena cava
(vein carrying blood from the body) into the right atrium
– At the same time, oxygenated blood is flowing from the
Pulmonary veins, which come from the lungs, into the left
atrium
– The walls of the atria contract and blood is pushed into the
ventricles
– During this the atrioventricular are open and the semilunar valves are closed
6.2
– After the ventricles have filled with blood, the
atrioventricular valves close and the semi-lunar
valves
– The walls of the ventricles contract
– Blood is pushed from the right ventricle into the
Pulmonary Artery (carries blood to the lungs)
– Blood is pushed from the left ventricle into the
Aorta (carries blood to the body)
6.2
– Once the ventricles
are emptied the
semi-lunar valves
close, preventing
backflow of blood
from the arteries
– The whole process
begins again as
another heartbeat
6.2
• Control of the heartbeat
– Myogenic muscle contraction
• Signal for heartbeat comes from the heart itself
and not from the brain
• Signal originates in the Sinoatrial Node
• SAN is a specialized set of cardiac cells that
generate an electric impulse
• The impuse spreads across the atria at a speed
of approx 1m per sec., causing the atria to
contract
6.2
• The impulse is “insulated” from the ventricular
muscle so only the atria contract
• The atrioventricular node picks up and
conducts the impulse
• The impulse is carried by muscle fibers down
the center of the heart (fibers are located in the
septum that separates the left and right
ventricles)
• Once the impulse reaches the end of these
fibers (very bottem of the heart) the ventricles
will contract
6.2
• The heart is now in full systole (contraction)
• The pressure increase closes the
atrioventricular valves and closes the semilunar valves
• The contraction stops and the heart is now in
full diastole (relaxation)
• Pressure in the ventricles falls and the backflow
of blood in the arteries closes the semi-lunar
valves
6.2
– Control of the heartbeat
• The myogenic rythym of the heart can be
controlled by signals to the heart from either
the brain or hormones
• These signals will increase or decrease the
heartrate depending on the demand for oxygen
• There are nerves that come from the brainstem
(medulla) which have involuntary control over
heart rate
6.2
• The adrenal glands produce the hormone adrenalin
• The target tissue for adrenalin is the AV node
• Adrenalin travels through the blood from the adrenal
glands (located just above the kidney) to the SAN
• The adrenalin stimulates the node to increase its
electrical output, which therefore results in an increase
in heart rate
• Adrenalin is usually produced in response to stressful
situations, which might often require extra oxygen (e.g.
“fight or flight” response)
Blood Vessels
6.2
• Structure and function of blood vessels
– Arteries
• Thick outer layer of longitudinal collagen and elastic
fibers to avoid bulges and leaks
• Thick wall to withstand high pressure (bp is at its
highest just after leaving the heart)
• Thick layers of circular elastic muscle fibers to help
pump blood on after each heart beat
• Narrow lumen (empty inner space that blood flows
through) to help maintain high pressures
– High pressure is needed to help get blood through
the body
6.2
– Veins
• Thin wall with little collagen and elastic fibers
– Blood is at a much lower pressure after it has
passed through the body tissues (little danger of
bursting)
– Thin wall allows for muscle fibers to squeeze it in
order to help move blood back to the heart
• Wide lumen
– Needed to accumulate the slow flowing blood
• Have valves to prevent backflow of blood
6.2
– Capillaries
• Wall consists of a single layer of thin cells
– Allows for the distance for diffusion in or out to the
surrounding tissues to be small
– Pores between cells in the wall allow some of the plasma
(fluid portion of blood) to leak out and form tissue fluid
– Very narrow lumen
• Only about 20 micrometers across
• Allows capillaries to fit into tight spaces
• Many small capillaries together will have a larger
surface area than fewer wider ones
6.2
6.2
• Blood
– Components
• Plasma (fluid portion)
– Composed of salts (e.g. sodium and chloride), gases
(oxygen and carbon dioxide), proteins (e.g. albumin
and fibrinogen), nutrients (e.g. glucose) and waste
(e.g. urea)
• Erythrocytes (red blood cells)
– transport oxygen
• Leucocytes (white blood cells)
– Two types: phagocytes and lymphocytes
– Fight disease
• Platelets (cells without nucleus)
– help with blood clotting
6.2
6.2
– Blood transports:
• Nutrients
– Glucose, amino acids
• Gases
– Carbon dioxide, oxygen
• Hormones
• Antibodies
• Urea
• Heat