Download Chapter 12—Cardiovascular and Lymphatic Systems. I. Overview of

Chapter 12—Cardiovascular and Lymphatic Systems.
I.
II.
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Overview of the cardiovascular system. Fig. 12.1.
a. The cardiovascular system rapidly transports oxygen, nutrients, secretions, and waste products
from one place to another, via the blood.
b. Cardiovascular system components:
i. Blood.
ii. Heart—a muscular pump that propels the blood through the body.
iii. Blood vessels—tubes through which the blood flows.
c. General flow of blood—the heart pumps blood into arteries, which branch to eventually become
arterioles, which become capillaries (where gas exchange occurs), which give rise to venules,
which merge to form veins, which return blood to the heart.
d. Heart rate and blood vessel diameter are constantly monitored and controlled via the nervous and
endocrine systems.
e. As the heart pumps, it puts pressure on the blood within the vessels.
i. This pressure causes some liquid and proteins of the blood to be forced out of the
capillaries and into the interstitial space, to become interstitial fluid.
f. Interstitial fluid is drained by lymphatic vessels, which eventually discharge into the venous
return.
Heart. Fig. 12.7.
a. Beats about 2.5 billion times in a 70 year lifespan.
b. Is composed mostly of cardiac muscle = myocardium.
c. Is surrounded by a tough, fibrous sac = parietal pericardium.
d. Adhering tightly to the surface of the heart is the visceral pericardium.
e. Between the parietal and visceral pericardium, there is a narrow space filled with serous fluid.
f. [Discuss heart anatomy].
Blood circulation. Fig. 12.9.
a. The heart is a "double pump."
b. The R atrium & R ventricle pump blood through the pulmonary circuit.
i. Flow of blood in the pulmonary circuit: R atrium  R atrioventricular (AV) valve =
tricuspid valve  R ventricle  Pulmonary semilunar valve  Pulmonary trunk 
Pulmonary arteries  Pulmonary arterioles  Pulmonary (alveolar) capillaries (gas
exchange in lungs)  Pulmonary venules  Pulmonary veins  L atrium.
ii. Pulmonary circuit.
1. Receives de-oxygenated blood (high carbon dioxide and low oxygen
concentrations) from the body's tissues, and circulates it through the lungs for gas
exchange in the alveolar capillaries.
c. The L atrium & L ventricle pump blood through the systemic circuit.
i. Flow of blood in the systemic circuit: L atrium  L AV (bicuspid = mitral) valve  L
ventricle  Aortic semilunar valve  Aorta  “systemic arteries and arterioles to body
organs/tissues”  Systemic capillaries (gas exchange in body tissues)  Systemic
venules and veins  Inferior or superior vena cava  R atrium.
ii. Systemic circuit.
1. Carries oxygenated blood from the heart to the tissues where gas exchange occurs
in capillaries. De-oxygenated blood then returns to the heart to enter the
pulmonary circuit.
d. Capillaries—site of gas exchange; simple squamous epithelium where the gasses diffuse down
their concentration gradients.
e. Each circuit has its own arteries, arterioles, capillaries, venules, and veins.
f. Coronary circulation. Fig. 12.10.
i. The heart has its own set of arteries and veins that service the myocardium.
Cardiac cycle. Fig. 12.11.
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b.
c.
d.
e.
V.
VI.
VII.
VIII.
A heartbeat is one sequence of contraction and relaxation of the heart chambers.
Contraction is simultaneous in both sides of the heart.
Systole = contraction phase.
Diastole = relaxation phase. [Talk about contraction, pressure changes, and movement of blood].
Heart sounds—lub-dup.
i. Lub = AV valves closing as the ventricles contract.
ii. Dup = semilunar valves closing as the ventricles relax.
How the heart contracts. Fig. 12.12.
a. Cardiac conduction system—the heart contains specialized cells that spontaneously produce and
conduct electrical impulses (action potentials) which stimulate cardiac muscle to contract.
i. Pacemaker cells. The heart can be cut off from all other nervous stimulation and still
keep beating.
ii. Excitation of cardiac muscle begins at the sinoatrial (SA) node.
1. Generates 70-80 action potentials per minute.
2. Each action potential spreads over the atria, causing them to contract.
3. The action potential then reaches the atrioventricular (AV) node within the
interatrial septum, where it slows, then passes into the bundle fibers and Purkinje
fibers.
4. Branches of the Purkinje fibers then make contact with the cardiac muscle cells
within the ventricles, which cause them to contract. [Talk about intercalated
disks].
iii. Electrocardiogram. Fig. 12.13.
1. Recording of the electrical events that occur in the heart, detected by electrodes
placed on the body surface.
2. Shape and duration of the electrical waves can be used to ascertain certain aspects
of heart health.
Neural controls over heart rate.
a. Nervous system innervation of the heart only adjusts the rate and strength of cardiac muscle
contraction.
i. Stimulation of sympathetic innervation increases the force and rate of contraction.
ii. Stimulation of parasympathetic innervation decreases the force and rate of contraction.
iii. Cardiac neural control centers are found in the spinal cord, medulla oblongata, and some
other areas.
Blood pressure—the pressure exerted against blood vessel walls. Fig. 12.14.
a. BP is highest in the aorta, and falls more and more along the length of the systemic circuit.
b. BP is measured at rest.
c. Typical adult BP is 120/80 mm of Hg.
i. 120 = systolic pressure, when ventricular contraction causes the highest pressure within
the aorta.
ii. 80 = diastolic pressure, when the ventricle is relaxed and the pressure is lowest in the
aorta.
d. Blood flow is resisted by friction and the viscosity of the blood.
i. Resistance greatly increases as blood moves from the arteries to the arterioles. (Because
of the reduced size of the vessels).
ii. As a result, BP drops.
e. Resting BP is regulated by the medulla oblongata, which integrates sensory information from the
myocardium and from pressure receptors in the aorta and carotid arteries.
i. This information is used to coordinate the rate and strength of heartbeats with changes in
the diameter of arterioles and some veins.
Blood velocity. Fig. 12.5.
a. Blood entering the aorta is moving relatively fast.
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XI.
b. As the aorta branches, and the arteries branch, blood velocity decreases. This is because total
cross-sectional area has increased, and because of resistance.
c. At the capillary level, blood is moving at its slowest (allows for diffusion).
d. Velocity then gradually increases in the veins converging on the heart.
Vessel structure and blood pressure. Fig. 12.2.
a. Surges of pressure generated by each cardiac cycle can be felt at certain arteries near the body
surface = pulse. [Discuss elastic arteries & elastic recoil].
b. Arteries offer little resistance to blood flow.
c. Arterioles offer more resistance to blood flow than other vessels.
d. Capillaries, whose walls are one cell layer thick, are so narrow that individual RBC's must pass
in single file; capillaries offer high resistance individually, but the total cross-sectional area of a
capillary bed is greater than that of the arteriole leading into the bed. Therefore, the pressure
drop here isn't as great as in the arterioles. Fig. 12.5.
i. Precapillary sphincters regulate blood flow through capillary beds. Fig. 12.4.
e. Venules also cause additional resistance to blood movement, but less than arterioles and
capillaries.
f. Veins provide some resistance to blood flow, but less than arterioles, capillaries, and venules.
g. 50-60% of total blood volume can be found in the veins at any given time.
h. Pressure in veins is very low. Therefore, blood must have assistance in getting back to the heart.
Fig. 12.6.
i. The contractions of skeletal muscles "milk" blood through the veins back to the heart.
ii. Veins also have valves to prevent blood from back flowing.
iii. The act of breathing assists the movement of venous blood in the abdominal and thoracic
cavities.
i. Vessels that help control blood pressure:
i. Some arteries, all arterioles, and some veins have smooth muscle layers in their walls
(tunica media).
ii. Under the control of the endocrine and nervous systems, these smooth muscle layers can
be made to:
1. Relax = vasodilation.
2. Constrict = vasoconstriction. [Discuss significance].
Exchanges of fluid and solutes at capillaries. Fig. 12.3.
a. Capillaries perfuse tissues and come to within 0.01 mm of nearly every cell.
b. In addition to gases, ions, wastes, etc., fluids and solutes also move into and out of the capillaries
in response to:
i. Blood pressure (hydrostatic pressure)—forces some plasma components into the
interstitial space, forming the interstitial fluid.
ii. Osmotic pressure—water enters the capillaries due to the high concentration of solutes
within the blood.
iii. Proteins and other molecules can enter and leave the capillary walls by endocytosis and
exocytosis.
c. Overall, there is a net movement of fluid out of the capillaries. Some solutes follow this fluid
movement.
d. These movements help maintain proper fluid balance between the blood and surrounding tissues,
and in maintaining blood volume.
Lymphatic system. Fig. 12.17. (Fig. 12.17b is upside down).
a. Helps defend the body against attack and injury, and works closely with the immune system.
b. Is made up of lymphatic vessels, tissues, and organs.
c. Lymphatic vessels:
i. Return interstitial fluid to the blood.
ii. Transport fats absorbed from the digestive tract.
d.
e.
f.
g.
h.
i.
iii. Help defend against disease-causing organisms and transport foreign particles and cell
debris to lymph nodes, where they are destroyed.
Lymph (interstitial fluid) moves into lymph capillaries through overlapping valve-like structures.
Fig. 12.16.
Lymph capillaries merge with larger lymph vessels that have internal valves to prevent backflow.
Lymph vessels converge and empty into veins in the lower neck.
i. Movement of lymph through lymphatic vessels occurs via similar mechanisms as venous
blood flow back to the heart from the lower extremities.
ii. Blockage of lymphatic vessels causes severe swelling. Fig. 12.15.
Lymph nodes contain many WBCs and macrophages that destroy foreign particles and debris
found in the lymph. Fig. 12.17. (Fig. 12.17b is upside down).
The spleen stores macrophages and lymphocytes, and filters the blood.
The thymus is the location where lymphocytes multiply and differentiate into T cells, B cells,
and natural killer cells, which function in immunity. The thymus also produces hormones
(thymosins) that initiate lymphocyte differentiation.
Study suggestions for this chapter: In the textbook at the end of the chapter, the sections entitled 1)
Highlighting the Concepts, 2) Recognizing Key Terms, and 3) Reviewing the Concepts are all good for you to
gauge your comprehension and focus your study efforts.