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BIO 265 – Human A&P II. Chapter 19 Blood Vessels. Blood Vessels. Amazing fact about blood vessels: 60,000 miles in an adult! Earth’s circumference is 24,902 miles What are the different types of blood vessels? Arteries - elastic, muscular, and arterioles Capillaries

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Bio 265 human a p ii

BIO 265 – Human A&P II

Chapter 19

Blood Vessels

Blood vessels
Blood Vessels

  • Amazing fact about blood vessels:

    • 60,000 miles in an adult!

    • Earth’s circumference is 24,902 miles

  • What are the different types of blood vessels?

    • Arteries - elastic, muscular, and arterioles

    • Capillaries

    • Veins – venules and veins

  • Figures 19.1 and 19.2 and Table 19.1

Blood vessels1
Blood Vessels

  • The inside of a blood vessel is called the lumen

  • All blood vessels have an internal lining called endothelium (it lines the lumen)

    • Simple squamous epithelium

    • This layer is continuous with the endocardium

  • Capillaries:

    • Composed of endothelium with a basement membrane

    • Figure 19.3 and others

Structure of arteries and veins
Structure of Arteries and Veins

  • Three tunics or layers:

    • Tunica intima – primarily endothelium

    • Tunica media – location of circular smooth muscle and elastin

      • Functions?

    • Tunica adventitia – layer of connective tissue

      • Merges with other connective tissue around the vessel

      • Also contains the vasa vasorum

    • Figure 19.1 and other figure

Structure of arteries and veins1
Structure of Arteries and Veins

  • Veins have valves that only allow blood to flow toward the heart

    • The valve structure and function is very similar to the semilunar valves in the heart

  • Figure 19.1 and other figure

Structure of arteries and veins2
Structure of Arteries and Veins

  • The valves in the veins are critical for returning blood to the heart because there is almost no blood pressure in the veins

    • Blood is pumped through the veins by respiration (breathing) and by skeletal muscle contractions

  • Figure 19.6

Structure of arteries and veins3
Structure of Arteries and Veins

  • Varicose veins result from these valves not functioning properly

    • Pot-bellies, pregnancy, standing, hemorrhoids

    • Figure 19.6


  • What is the function of capillaries?

    • Capillary Exchange

      • gases, nutrients, wastes, etc.

    • Capillary exchange is driven by 2 things:

      • Concentration gradients (diffusion)

        • Most solutes move this way

      • Fluid movement (primarily moves water to the tissues)

        • Tissue swelling and the lymphatic system

    • Figures 19.14, 19.15, 19.2 and others


  • Capillaries are organized into networks called capillary beds

    • Figure 19.4


  • The structure of the capillary beds allows the regulation of blood flow through the tissues

    • This involves the precapillary sphincters

    • Figure 19.4

Control of blood flow
Control of Blood Flow

  • Blood flow through tissues (tissue perfusion) is tightly controlled

    • It is related to the metabolic rate and function of the tissue (muscle, liver, kidney, etc.)

    • O2 (and other nutrients) are the key

      • They are required for smooth muscle contraction

    • Figure 19.4

Control of blood flow1
Control of Blood Flow

  • Long-term control involves the number of blood vessels and capillaries

    • Muscle and heart attack examples

  • The growth of new blood vessels is called angiogenesis

  • The density of capillaries primarily depends upon O2 concentration

Aging of arteries
Aging of Arteries

  • Changes in arteries:

    • Arteriosclerosis – loss of elasticity in the arteries

      • What effects does this have?

    • Atherosclerosis – deposition of material in the arterial walls to form plaques

      • Effect?

      • Figure from other text

Blood pressure regulation
Blood Pressure Regulation

  • Blood Pressure depends on 3 primary factors:

    • Cardiac output

    • Peripheral resistance (this is determined by blood vessel diameter)

    • Blood volume

Blood pressure regulation1
Blood Pressure Regulation

  • There are two types of regulation:

    • Short-term and Long-term

  • Short-term

    • Baroreceptors – get with a partner and discuss how this mechanism could affect blood pressure.

      • They affect the cardiovascular center in the medulla

      • This can change heart rate and peripheral resistance to raise and lower BP!

      • Figure 19.8

Blood pressure regulation2
Blood Pressure Regulation

  • Chemoreceptor Reflexes

    • When oxygen, pH, or carbon dioxide levels change dramatically, the cardiovascular center can increase blood pressure.

  • Adrenal Medulla Hormones

    • What hormones are produced here?

    • These affect heart rate and peripheral resistance

      • Increase heart rate

      • Vasodilation in cardiac vessels

      • Vasoconstriction in vessels to the skin and viscera

Blood pressure regulation3
Blood Pressure Regulation

  • Atrial Natriuretic Peptide (ANP)

    • Released when atria are stretched

    • Increases Na+ loss in the urine

    • Also causes vasodilation

    • Effect?

  • ADH (vasopressin) – at very high levels causes vasoconstriction

  • Angiotensin II – vasoconstriction

  • Inflammatory chemicals (like histamine) cause vasodilation

  • Alcohol – inhibits ADH and causes vasodilation

Blood pressure regulation4
Blood Pressure Regulation

  • Long-Term Regulation (these alter blood volume):

  • Direct renal filtering

    • High BP causes more fluid to get filtered and lost

    • Low BP slows filtration and loss down

  • Atrial Natriuretic Peptide – effect?

  • Renin-Angiotensin-Aldosterone Mechanism

    • When BP decreases, the kidneys secrete renin

    • Renin activates a plasma protein called angiotensin II

    • Active angiotensin II causes vasoconstriction and the release of aldosterone from the adrenal cortex

Blood pressure regulation5
Blood Pressure Regulation

  • Aldosterone increases Na+ and Cl- absorption by the kidney which increases water retention

  • Angiotensin can also stimulate the release of ADH

  • This mechanism is very important for daily regulation of BP and in countering circulatory shock

  • ADH – effect?

  • Alterations in blood pressure
    Alterations in Blood Pressure

    • Hypotension (BP below 100 mm Hg) – usually no problem

    • Hypertension (BP over 140/90 mm Hg)

      • Temporary high BP can be normal

      • Strains the heart

      • Contributes to atherosclerosis

      • Can lead to heart failure

      • Cause is usually unknown

    Circulatory shock
    Circulatory Shock

    • Shock is a condition where blood flow is not adequate to meet the body’s needs

      • (Low blood pressure)

      • Hypovolemic shock – blood loss, dehydration, extensive burns

      • Vascular shock – extreme vasodilation

        • Anaphylactic shock

        • Septic shock – bacterial toxins