Ch13 - Vascular System - Franklin University

Essentials of Anatomy and Physiology, Seventh Edition
Valerie C. Scanlon and Tina Sanders
Copyright © F.A. Davis Company 2015
Chapter 13
The Vascular System

The vascular system consists of arteries, capillaries,
and veins.
General functions:
The blood vessels transport blood throughout the body
and return it to the heart.
The tissues of the vessels contribute to the maintenance
of blood pressure.

Arteries—carry blood from the heart to capillaries;
three layers in their walls
Inner layer (tunica intima)—simple squamous
epithelium (the endothelium)
Functions:
Middle layer (tunica media)—smooth muscle and elastic
connective tissue
Function:
Constriction or dilation—

Arteries (continued)
Outer layer (tunica externa)—fibrous connective tissue
Function:
Smaller arteries—arterioles:

Veins—carry blood from the capillaries to the heart;
three layers in their walls
Inner layer—folded into valves
Function:
Middle layer—thinner than in arteries, less smooth muscle
Reason:
Outer layer—thinner than in arteries, less fibrous
connective tissue
Reason:
Small veins—venules

Anastomoses—connections between vessels of the
same type
General function—to provide alternate pathways for
blood flow if a vessel is blocked
Arterial anastomoses—
Venous anastomoses—

Capillaries—carry blood from arterioles to venules
Capillary walls are one cell thick (simple squamous
epithelium).
Purpose:
Capillary exchanges:
Oxygen and carbon dioxide—
Blood pressure in capillaries creates filtration—
Albumin in the blood creates colloid osmotic pressure, a
pulling pressure—

Capillaries (continued)
Precapillary sphincters—smooth muscle cells at the
beginning of each capillary network
Function:
Tissues without capillaries:
Sinusoids—large, very permeable capillaries in the liver,
spleen, red bone marrow, and pituitary gland.
Function:

Pathways of Circulation
Three major pathways: Pulmonary:
Systemic:
Hepatic portal:
Fetal circulation—the pathway before birth that includes the
placenta
Questions: Where does pulmonary circulation begin? Systemic circulation?

Answers
Pulmonary circulation begins at the right ventricle of the heart.
Systemic circulation begins at the left ventricle.

Pulmonary Circulation
Right ventricle  pulmonary artery  right and left
pulmonary arteries  pulmonary capillaries  pulmonary
veins  left atrium
Questions: Where, in this pathway, does gas exchange take place?
By what process are gases exchanged?
Describe the movement of oxygen and of CO2.

Answers
Gas exchange takes place in the pulmonary capillaries.
Gases are exchanged by the process of diffusion.
Oxygen moves from the air in the alveoli to the blood in the
pulmonary capillaries.
CO2 moves from the blood in the pulmonary capillaries to
the air in the alveoli.

Systemic Circulation
Left ventricle  aorta  systemic arteries  capillaries
in body tissues  systemic veins  superior and
inferior caval veins  right atrium
(See Table 13–1 for the major systemic arteries and Table 13–2 for
the major systemic veins.)

Hepatic Portal Circulation
Blood from the digestive organs and the spleen flows into the
portal vein and through the liver before returning to the heart.
Purposes:
Questions: What is the term for the large, permeable capillaries of the liver?
Name the veins that carry blood from the liver to the inferior vena cava.

Answers
The large, permeable capillaries of the liver are sinusoids.
The veins that take blood from the liver to the inferior vena
cava are the hepatic veins.

Fetal Circulation—the fetus depends on the mother for
oxygen and nutrients and removal of waste products.
Placenta—site of exchanges between fetus and mother
Umbilical arteries—carry blood from the fetus to the placenta:
Umbilical vein—carries blood from the placenta to the fetus:
Ductus venosus—from the umbilical vein to the inferior
vena cava:

Fetal Circulation (continued)
Fetal heart: the foramen ovale in the interatrial septum permits
blood to flow from the right atrium to the left atrium—
The ductus arteriosus permits blood to flow from the
pulmonary artery to the aorta—
After birth—

Velocity of Blood Flow—inversely related to the
cross-sectional area of the vascular segment
Aorta—smallest cross-sectional area = most rapid flow (30
cm/sec)
Capillaries—in total have the largest cross-sectional area =
slowest flow (<0.1 cm/sec)
Veins—cross-sectional area decreases:
Importance of slow flow in capillaries—

Blood Pressure—the force exerted by the blood
against the walls of blood vessels; measured in mm Hg
Systolic pressure: during ventricular contraction
Diastolic pressure:
Normal range of systemic BP: 90 to 120/60 to 80 mm Hg
In the arterioles, systolic and diastolic pressures merge.
Capillary BP is 30 to 35 at the arterial end, 12 to 15 mm Hg at
the venous end.
Importance:

Blood Pressure (continued)
In the veins, BP decreases.
Caval veins—
Pulmonary BP is always low: 20 to 25/8 to 10 mm Hg.
Reason:
Importance:

Maintenance of Systemic Blood Pressure—
many mechanisms and factors contribute
1. Venous return—the amount of blood that returns to the heart.
If venous return decreases:
Maintaining venous return:
Constriction of veins—
Skeletal muscle pump—
Respiratory pump—

Maintenance of Systemic BP (continued)
2. Heart rate and force—
3. Peripheral resistance—resistance created by the
diameter of arteries and arterioles, which are usually
slightly constricted
Greater vasoconstriction—
Vasodilation—

4. Elasticity of the large arteries
Ventricular systole stretches the walls of these arteries,
which lowers systolic BP.
During ventricular diastole, the elastic walls recoil.
Question: How does arterial recoil affect diastolic blood pressure?

Answer
The recoil of elastic arteries raises diastolic blood pressure.

5. Viscosity of blood—viscosity is created by the presence
of RBCs and the plasma proteins, especially albumin.
Decreased viscosity as in severe anemia or liver disease:
6. Loss of blood—for small losses, compensation occurs
quickly:
Large losses:

7. Hormones
ADH—increases water reabsorption by the kidneys:
Aldosterone—increases reabsorption of Na+
ions by the
kidneys, and water follows:
ANP—increases excretion of Na+
ions and water by the
kidneys:
Norepinephrine—stimulates vasoconstriction:
Question: How does epinephrine affect blood pressure?

Answer
Epinephrine increases heart rate and force of contraction
(cardiac output), both of which raise blood pressure.

Distribution of Blood Flow
Metabolically active tissues require more oxygen and receive a
greater proportion of circulating blood.
Blood flow to a tissue or organ is increased by—
In less active tissues, blood flow is decreased (temporarily) by—

Regulation of BP—the two types of mechanisms
are intrinsic and nervous.
Intrinsic mechanisms:
1. The heart—responds to increased venous return:
2. The kidneys—decreased blood flow decreases filtration:
Decreased BP stimulates secretion of renin by the kidneys
to start the renin-angiotensin mechanism.
Angiotensin II—

Regulation of BP (continued)
Nervous mechanisms:
1. The heart—
2. Peripheral resistance—the vasomotor center in the medulla
consists of the vasoconstrictor area and the vasodilator area.
The vasoconstrictor area—
The vasodilator area—

Regulation of BP (continued)
The tissue in arteries, arterioles, and veins that receives
motor impulses—
To increase vasoconstriction (and BP):
To decrease vasoconstriction (and BP):

Wrap-Up Question
Name the part or aspect of the vascular system described.
1. The lining of vessels
2. Tissue that brings about vasoconstriction
3. BP when the LV is relaxed
4. Receptors in the carotid sinuses
5. Large vein to the liver
6. Prevent backflow in veins
7. Major artery of the trunk
8. CNS site of vasomotor center

Answers
1. The lining of vessels—endothelium
2. Tissue that brings vasoconstriction—smooth muscle
3. BP when the LV is relaxed—diastolic
4. Receptors in the carotid sinuses—pressoreceptors
5. Large vein to the liver—portal vein
6. Prevent backflow in veins—valves
7. Major artery of the trunk—aorta
8. CNS site of vasomotor center—medulla

Ch13 - Vascular System - Franklin University

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Ch13 - Vascular System - Franklin University