Download Circulation Chapter 42 Circulation systems reflect phylogeny. 1

AP Biology
March 2008
Circulation
Chapter 42
Circulation systems reflect phylogeny.
1) Some animals with simple body plans possess a
gastrovascular cavity rather than a true circulatory system.
i) Cnidarians
ii) Hydras
iii) Planarians
iv) Other Flatworms
A gastrovascular cavity serves both in digestion and
distribution of substances throughout the body.
2) Both open and closed circulatory systems have:
a) Blood
b) Vessels
c) Heart
3) In open circulatory systems, blood bathes the organs
directly.
a) The blood and lymph combined are called
hemolymph.
i) Hemolymph is a circulatory fluid, a mixture of blood
and interstitial fluid.
4) In a closed circulatory system, the blood never leaves the
heart or the vessels.
5) A human circulatory system is called the cardiovascular
system.
a) The heart has:
i) The atrium: the chambers of the heart that receives
blood.
ii) The ventricles: pump blood into the arteries.
6) There are three kinds of blood vessels: arteries carry blood
away from the heart, capillaries are where exchange with
tissue fluid takes place, and veins return blood to the
heart.
a) Arteries
i) Have thick walls and are resilient
ii) Expand to accommodate the sudden increase in
blood volume that results after heart contraction.
iii) Divided into small arterioles
b) Arterioles
i) Constriction and dilation are regulated by the
nervous system to regulate blood pressure.
c) Capillaries
i) Microscopic blood vessels with a wall formed of one
layer of simple squamous cells.
ii) Capillary beds are so prevalent that, in humans, all
cells are within 60-80 µm of a capillary.
iii) Only 5% are open at one time; if the animal eats,
capillary beds of the digestive system open.
iv) Capillaries are so narrow that red blood cells must
pass through in a single file.
v) Gas, nutrient, and waste exchange occur across
thin walls.
d) Venules
i) Vessels that take blood from capillaries, and join to
form a vein.
e) Veins
i) Transport blood toward the heart
ii) Wall of a vein is much thinner than that of arteries;
there is low blood pressure.
iii) One way valves open in the direction of the heart;
close to prevent backflow
Transport in humans.
The heart pumps blood.
1) Pumping of heart keeps blood moving in arteries.
2) Skeletal muscle contraction is responsible for blood
movement in veins.
3) Heart is cone-shaped, muscular organ, ~~ the size of a fist.
4) It is located between the lungs directly behind the sternum
and is tilted so that apex is directed to the left.
5) Myocardium is major portion of the heart consisting mostly
of cardiac muscle; muscle fibers are branched and tightly
joined together.
6) The heart lies within a pericardium sac that contains
pericardial fluid, which provides cushioning.
7) Endocardium lines the inner surface of the heart; it consists
of connective tissues and endothelial tissue.
8) The internal wall called the septum separates the heart
into right and left halves.
9) The heart has two upper, thin-walled atria and two lower,
thick-walled ventricles.
a) The atria receive blood from the venous portion of the
cardiovascular system.
b) Atria are so much smaller and weaker than the
muscular ventricles, but they hold the same volume of
blood
c) Ventricles pump blood into the arterial portion of the
cardiovascular system.
10)Heart valves direct flow of blood and prevent backward
movement.
a) Valves are supported by strong fibrous tendons
(chordae tendineae) attached to muscular projections
of ventricular walls; they prevent valves from inverting.
b) Atrioventricular valves located between atria and
ventricles prevent back flow from ventricle to atrium.
c) Right atroventricular (tricuspid) valve on the right side
of the heart consists of three cusps or flaps.
d) Left atrioventricular (bicuspid or mitral) valve on the left
side consists of two cusps or flaps.
e) Semilunar valves resembling half-moons are located
between a ventricle and an artery that prevents back
flow from artery to ventricle.
i) The pulmonary semilunar valve lies between the
right ventricle and the pulmonary trunk.
ii) The aortic semilunar valve lies between the left
ventricle and the aorta.
Path of Blood Through the Heart
1) Deoxygenated blood enters the right atrium from both the
superior vena cava and the interior vena cava.
2) Right atrium sends blood through the right atrioventricular
valve to the right ventricle.
3) Right ventricle sends blood through the pulmonary
semilunar valve into the pulmonary trunk and arteries to
lungs.
4) Oxygenated blood returns from the lungs through the
pulmonary veins and is delivered to the left atrium.
5) The left atrium sends blood through the left atrioventricular
(bicuspid or mitral) valve to the left ventricle.
6) Left ventricle send blood through the aortic semilunar
valve into the aorta and to the body.
The heart is therefore a double pump serving the lungs and
body circulations simultaneously.
The Heartbeat
1) The heart contracts (beats) about 70 times/min
2) Heartbeat (cardial cycle) consists of phases:
a) Systole – contraction of heart chambers
b) Diastole – relaxation of heart chambers
3) The atria contract first when ventricles relax (0.15 sec),
then ventricles contract while atria relax (0.3 sec), then all
chambers rest (0.40 sec).
4) The heart is in diastole about 50% of the time.
5) The short systole of the atria is needed only to send blood
into ventricles.
6) The term “systole” refers to the left ventricle systole.
7) When the heart beats, the familiar “lub-dub” sound is
heart as the valves of the heart close.
a) Lub – vibrations of the heart when the atrioventricular
valves close.
b) Dub – vibrations due to the closing of the semilunar
valves.
8) Pulse is a wave effect that passes down walls of arterial
blood vessels when the aorta expands and then almost
immediately recoils following ventrical systole.
9) Since there is one arterial pulse per ventricular systole,
arterial pulse rate can be used to determine heart rate.
10)Heart contraction is intrinsic; heart will beat without any
stimulation from nervous system because it contains nodal
tissue with both muscular and nerve characteristics.
a) Sinoatrial (SA) node
i) “Pacemaker” found in upper dorsal wall of the right
atrium.
ii) Initiates heartbeat by sending out an excitatory
impulse every 0.85 sec to cause atria to contract
b) Atrioventricular (AV) node
i) Found in base of right atrium very near septum
ii) When stimulated by impulses from SA node, it sends
out impulses through septum to cause ventricles to
contract.
Physical principles govern blood circulation.
1) Blood pressure refers to the hydrostatic pressure that blood
exerts against the wall of a vessel and that propels the
blood.
a) It is measured and recorded as two numbers separated
by a dash.
i) The first number is the systolic pressure, when the
heart contracts.
ii) The second number is the diastolic pressure, when
the heart is relaxed.
2) The lymphatic system is responsible for returning lost fluid
and proteins to the blood in the form of lymph.
a) Along a lymph vessel are lymph nodes that filter lymph
and attack viruses and bacteria, playing an important
role in immunity.
Blood is a connective tissue with cells suspended in plasma.
1) Plasma is mostly water, but it also contains ions,
electrolytes, and plasma proteins.
a) It transports:
i) Nutrients
ii) Metabolic wastes
iii) Gases
iv) Hormones
b) It carries:
i) Red blood cells (erythrocytes)
(1) Transports oxygen via hemoglobin (an ironcontaining protein)
ii) White blood cells (leukocytes)
(1) Part of the immune system
iii) Platelets
(1) Fragments of cells responsible for blood clotting.
2) Blood contains a soluble plasma protein called fibrinogen.
a) This protein forms clots when it is converted to its active
form, fibrin.