21.1 - 21.7
I. Transport in Invertebrates
A. Invertebrates use an open or a closed circulatory system, and use hemolymph or blood as
the circulatory fluid.
B. Invertebrates with an Open or a Closed System Circulatory System
II. Transport in Vertebrates
1. Vertebrates have a closed circulatory system called a cardiovascular system.
a. The atria are the chambers of the heart that receive blood.
b. The ventricles pump blood into arteries.
2. There are three kinds of blood vessels: arteries carry the blood away from the heart,
capillaries are where the exchange with tissue fluid takes place, and veins return the
blood to the heart.
III. Transport in Humans
A. The Human Heart
1. Endocardium is the inner lining.
2. The myocardium is a major portion of the heart consisting mostly of cardiac muscle;
its muscle fibers are branched and tightly joined together.
3. The heart lies within the pericardium, a sac that secretes a lubricating fluid.
4. The heart has two upper, thin-walled atria and two lower, thick-walled ventricles.
5. Heart valves direct the flow of blood and prevent any backward movement.
a. Valves are supported by strong fibrous tendons (chordae tendineae) which
support the valves and prevent them from inverting when the heart contracts.
b. Atrioventricular valves between the atria and ventricles prevent any back flow
from the ventricle to the atrium.
c. Semilunar valves are located between the ventricles and their attached vessels.
1) The pulmonary semilunar valve lies between the right ventricle and the
pulmonary trunk.
2) The aortic semilunar valve lies between the left ventricle and the aorta.
B. Path of Blood Through the Heart
1. The route of blood through the heart is as follows:
a. Oxygen-poor blood enters the right atrium from both the superior vena cava and
the inferior vena cava.
b. The right atrium sends blood through the right atrioventricular (tricuspid) valve to
the right ventricle.
c. The right ventricle sends blood through the pulmonary semilunar valve into the
pulmonary trunk and arteries to the lungs.
d. Oxygen-rich blood returns from the lungs through pulmonary veins and is
delivered to the left atrium.
e. The left atrium sends blood through the left atrioventricular (bicuspid or mitral)
valve to the left ventricle.
f. The left ventricle sends blood through the aortic semilunar valve into the aorta
and on to the body proper.
The heart is therefore a double pump serving the lungs and body circulations
simultaneously; O2-poor blood and O2-rich blood never mix.
Since the left ventricle has the harder job of pumping blood throughout the body, its
walls are thicker; accordingly, blood pressure is greatest in the aorta.
Blood pressure decreases as the cross-sectional area of the arteries and arterioles
Skeletal muscle contraction is responsible for the blood movement in veins.
C. The Heartbeat
1. The human heart contracts (beats) about 70 times a minute (2.5 billion times in a
2. The heartbeat or cardiac cycle consists of phases.
3. The atria contract first while the ventricles relax (0.15 sec.), then the ventricles
contract while atria relax (0.30 sec.), and then all chambers rest (0.40 sec.).
4. Systole refers to the contraction of heart chambers and diastole refers to the
relaxation of the heart chambers.
5. The volume of blood that the left ventricle pumps per minute into the systemic circuit
is called the cardiac output.
6. When the heart beats, the familiar lub-dub sound is heard as the valves of the heart
7. Rhythmic contraction of the heart is due to the cardiac conduction system.
a. The sinoatrial (SA) node is the “pacemaker”.
b. The atrioventricular (AV) node
c. Although the beat of the heart is intrinsic, it is regulated by the sympathetic and
parasympathetic nervous system.
8. An electrocardiogram (ECG) is used as a diagnostic tool.
D. Vascular Pathways
1. The Pulmonary Circuit circulates oxygen-poor blood to the lungs and return
oxygen-rich blood from the lungs
2. The Systemic Circuit
4. The portal system is a pathway of blood flow that begins and ends in capillaries.
E. Blood Pressure
1. Systolic pressure results from blood being forced into the arteries during ventricular
2. Diastolic pressure is the pressure in arteries during ventricular diastole.
F. Capillary Exchange
1. Two forces control the movement of fluid through the capillary walls.
a. Osmotic pressure tends to cause water to move from tissue fluid to the blood.
b. Blood pressure tends to cause water to move from the blood to tissues.
IV. Blood
A. Red Blood Cells
1. Red blood cells (erythrocytes) are small biconcave disks.
2. When mature, RBCs lack a nucleus and contain hemoglobin.
3. There are 6 million RBCs per mm3 of whole blood.
4. Each RBC contains about 250 million hemoglobin molecules.
B. White Blood Cells
1. White blood cells (leukocytes) differ from RBCs in being larger and in having a
2. Function is fighting infections.
C. Platelets are for blood glotting.
Review Qs:
1. The Greek root words for "heart" and "vessels": __________
2. The four chambers of human heart: ____________________________.
3. Blood flow directions in arteries and veins: ______________________.
4. Which kind of blood, O2 and CO2 blood, in systemic and pulmonary arteries and veins?
5. A heart murmur is a distortion of the heartbeat due to blood flowing back through a valve
that should be closed. If the heart sound is lub-dub-ssshhh, the most likely cause is a failure
of the ________________ valves.
6. The vessels in our circulatory system that allow molecules to diffuse across to tissues are
7. Sequences of blood passing through heart: _________________________________.
8. The Latin root word for "of the lungs" indicates ________________.
9. The coronary circulation serves the ______________.
10. Normal blood pressure in a 25-year-old person would likely be close to ______ mm Hg.
11. Features of RBC: (See summary)
12. Endocardium, myocardium and pericardium, what are they?
13. The structure that absorbs nutrients from the small intestines and delivers the nutrients in the
blood to the liver is the __________________.
14. The pacemaker of the cardiac conduction system is the _____________________.
15. The major primary function of the pulmonary circulatory circuit is _______________.
16. Veins primarily depend upon which of the following forces to return blood to the heart?
_______________, __________________________, __________________________
17. The leading cause of preventable death in the United States is cardiovascular disease.
Preventive measures? ___________, ________________, _______________
18. List 4 major cardiovascular disorders.
True or false:
19. All capillary beds have blood running to them at all times.
20. Calcium ions are needed for proper blood clotting.
21. The circulatory system is the only way by which an animal can supply oxygen and nutrients
to its cells, or remove waste materials from the cells.
22. The major portion of the heart is the myocardium, made up mainly of cardiac muscle.
23. Sphincter muscles regulate the opening and closing of the capillary beds, directing the flow
of blood to different areas of the body depending on the body's needs.
24. Heart contractions arise in the nodal tissue of the right atrium, and can occur without nerve
impulse activation.
25. A portal system is a part of the circulatory system that begins and ends with a capillary bed.
26. A portal system carries blood from one organ to another without passing through the heart.
27. The sound of the heartbeat is made when the ventricles contract to pump blood out of the
28. From the baroreceptor and chemoreceptor reflex that keeps the blood pressure (BP)
homeostasis shown bellow, able to predict a drug as mimicker OR blocker of sympathetic OR
parasympathetic agent.
BP level lowered
Blood O2 level lowered
(E.g. bleeding or suddenly, standing up from supine position)
Baroreceptor (pressure receptor)
Nerve pathway to the brain (afferent)
Sympathetic and
Parasympathetic centers in the brain
Neuronal and hormonal efferent pathways
Sympathetic tone
Parasympathetic tone
BP level increases back to normal
Blood O2 level increases to normal