A&P Cardiovascular System PowerPoint (nursing)

Essentials of Anatomy and Physiology, Sixth EditionValerie C. Scanlon and Tina SandersEssentials of Anatomy and Physiology, Sixth EditionValerie C. Scanlon and Tina Sanders

Copyright © 2011. F.A. Davis Company

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 – 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. 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 systemic arteries and Table 13–2 for 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:



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 mmHg

Systolic pressure: during ventricular contraction

Diastolic pressure:

Normal range of systemic BP: 90 to 120/60 to 80 mmHg.

In the arterioles, systolic and diastolic pressures merge.

Capillary BP is 30 to 35 at the arterial end, 12 to 15 mmHg at the venous end.

Importance:



Blood pressure (continued)

In the veins, BP decreases.

Caval veins –

Pulmonary BP – always low: 20 to 25/8 to 10 mmHg.

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)

Questions: What nervous system regulatory mechanism (that is, for what organ) contributes to the regulation of blood pressure?

What part of the brain contains the centers for nervous regulation of blood pressure?



Answers

The nervous mechanism for regulation of heart rate and force of contraction contributes to the regulation of blood pressure.

The medulla of the brain contains the centers for nervous regulation of blood pressure.




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 –




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

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A&P Cardiovascular System PowerPoint (nursing)