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The Circulatory System Blood Vessels. Anatomy & Physiology II Chapter 15. The Vascular System. Closed system Blood vessels Four heart chambers. Blood Vessels. Delivery system of dynamic structures that begins and ends at the heart

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the circulatory system blood vessels

The Circulatory SystemBlood Vessels

Anatomy & Physiology II

Chapter 15

the vascular system
The Vascular System
  • Closed system
  • Blood vessels
  • Four heart chambers
blood vessels
Blood Vessels
  • Delivery system of dynamic structures that begins and ends at the heart
    • Arteries: carry blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of a fetus
    • Capillaries: contact tissue cells and directly serve cellular needs
    • Veins: carry blood toward the heart
blood vessels4
Blood Vessels

Five types of blood vessels

  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
blood circuits
Blood Circuits

Two groups of blood vessels

  • The pulmonary circuit
    • Pulmonary artery and its branches
    • Capillaries in lungs
    • Pulmonary veins
  • The systemic circuit
    • Aorta
    • Systemic capillaries
    • Systemic veins

Blood flow in a closed system of vessels

Oxygen content changes as blood flows through the capillaries. 

Zooming In •

Judging from color coding, which vessels pick up oxygen? Which vessels release oxygen?

vessel structure
Vessel Structure

Three tunics (coats) of arteries and veins

  • Inner (endothelium)
  • Middle (smooth [voluntary] muscle)
    • Controlled by autonomic nervous system
    • Thinner in veins
  • Outer (supporting connective tissue)

Sections of small blood vessels

Drawings show the thick wall of an artery, the thin wall of a vein, and the single-layered wall of a capillary.

A venous valve also is shown. The arrow indicates the direction of blood flow.  

Zooming In: Which vessels have valves that control blood flow?

systemic arteries
Systemic Arteries

The aorta

  • Largest artery
  • Receives blood from left ventricle
  • Branches to all organs
the aorta and its parts
The Aorta and Its Parts
  • Ascending aorta
  • Aortic arch
  • Thoracic aorta
  • Abdominal aorta

The aorta and its branches

Zooming In:

How many brachiocephalic arteries are there?


Principal systemic arteries

Zooming In: How many brachiocephalic arteries are there?

branches of the ascending aorta and aortic arch
Branches of the Ascending Aorta and Aortic Arch
  • Ascending aorta
    • Left and right coronary arteries
  • Aortic arch
    • Brachiocephalic artery
      • Right subclavian artery
      • Right common carotid artery
    • Left common carotid artery
    • Left subclavian artery
branches of the thoracic aorta
Branches of the Thoracic Aorta
  • Branches to chest wall, esophagus, and bronchi
  • Intercostal arteries
branches of the abdominal aorta
Branches of the Abdominal Aorta
  • Celiac trunk
    • Left gastric artery
    • Splenic artery
    • Hepatic artery
  • Superior mesenteric artery
  • Inferior mesenteric artery
  • Paired lateral branches
    • Phrenic arteries
    • Suprarenal arteries
    • Renal arteries
    • Ovarian and testicular arteries
    • Lumbar arteries
the iliac arteries and their subdivisions
The Iliac Arteries and Their Subdivisions
  • Internal iliac arteries
  • External iliac arteries
    • Femoral artery
      • Popliteal artery
        • Tibial arteries
        • Dorsalis pedis
arteries that branch to the arm and head
Arteries That Branch to the Arm and Head
  • External carotid artery
  • Internal carotid artery
  • Subclavian artery
    • Vertebral artery
    • Axillary artery
      • Brachial artery
        • Radial artery
        • Ulnar artery

Communication between two vessels

  • Circle of Willis
  • Superficial palmar arch
  • Mesenteric arches
  • Arterial arches

Arteries that supply the brain

The bracket at right groups the arteries that make up the circle of Willis.

  • Smallest arteries
  • Lead to capillary beds
  • Control flow into capillary beds via vasodilation and vasoconstriction
systemic veins
Systemic Veins
  • Superficial veins
    • Cephalic, basilic, median cubital veins
    • Saphenous veins
  • Deep veins
    • Femoral and iliac vessels
    • Brachial, axillary, subclavian vessels
    • Jugular veins
    • Brachiocephalic vein
the venae cavae and their tributaries
The VenaeCavae and Their Tributaries
  • Superior vena cava
    • Head, neck, upper extremities
  • Azygos vein
    • Chest wall
  • Inferior vena cava
    • Right, left veins from paired parts, organs
    • Unpaired veins from spleen, digestive tract

Principal systemic veins

Zooming In:How many brachiocephalic veins are there?

venous sinuses
Venous Sinuses
  • Coronary sinus
  • Cranial venous sinuses
    • Cavernous sinuses
      • Petrosal sinuses
    • Superior sagittal sinus
      • Confluence of sinuses
    • Transverse sinuses (lateral sinuses)

Cranial venous sinuses

The inset shows the paired transverse sinuses, which carry blood from the brain to the jugular veins.

the hepatic portal system
The Hepatic Portal System

Carries blood from abdominal organs to liver

  • Superior mesenteric vein
  • Splenic vein
  • Gastric, pancreatic, inferior mesenteric veins
  • Sinusoids

Hepatic portal system

Veins from the abdominal organs carry blood to the hepatic portal vein leading to the liver. Arrows show the direction of blood flow. 

Zooming In: What vessel do the hepatic veins drain into?

circulation physiology
Circulation Physiology
  • Blood exchanges oxygen, carbon dioxide, other substances generated by cells
  • Tissue fluid (interstitial fluid) is exchange medium

Connection between small blood vessels through capillaries

The blood delivers oxygen (O2) to the tissues and picks up carbon dioxide (CO2) for transport to the lungs.

Note the lymphatic capillaries, which aid in tissue drainage.

  • Microscopic blood vessels
  • Walls of thin tunica intima, one cell thick
  • Pericytes help stabilize their walls and control permeability
  • Size allows only a single RBC to pass at a time
  • In all tissues except for cartilage, epithelia, cornea and lens of eye
  • Functions: exchange of gases, nutrients, wastes, hormones, etc.
  • Three structural types
    • Continuous capillaries
    • Fenestrated capillaries
    • Sinusoidal capillaries (sinusoids)
continuous capillaries
Continuous Capillaries
  • Abundant in the skin and muscles
    • Tight junctions connect endothelial cells
    • Intercellular clefts allow the passage of fluids and small solutes
  • Continuous capillaries of the brain
    • Tight junctions are complete, forming the blood-brain barrier


Red blood

cell in lumen







Tight junction





Continuous capillary:

Least permeable, and most common (e.g., skin, muscle).

fenestrated capillaries
Fenestrated Capillaries
  • Some endothelial cells contain pores (fenestrations)
  • More permeable than continuous capillaries
  • Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)



Red blood

cell in lumen







Basement membrane



Tight junction

Fenestrated capillary: Large fenestrations (pores) increase permeability. Occurs in special locations (e.g., kidney, small intestine).

sinusoidal capillaries
Sinusoidal Capillaries
  • Fewer tight junctions, larger intercellular clefts, large lumens
  • Usually fenestrated
  • Allow large molecules and blood cells to pass between the blood and surrounding tissues
  • Found in the liver, bone marrow, spleen



Red blood

cell in lumen




Tight junction

Nucleus of






Sinusoidal capillary: Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen).

blood flow through capillary beds
Blood Flow Through Capillary Beds
  • Precapillary sphincters regulate blood flow into true capillaries
  • Regulated by local chemical conditions and vasomotor nerves

Vascular shunt



Thoroughfare channel


True capillaries

Terminal arteriole

Postcapillary venule

(a) Sphincters open—blood flows through true capillaries.

Terminal arteriole

Postcapillary venule

(b) Sphincters closed—blood flows through metarteriole

thoroughfare channel and bypasses true capillaries.

capillary exchange
Capillary Exchange

How substances move between cells and capillary blood

  • Diffusion
    • Main process
  • Blood pressure
    • Moves material into tissue fluid
  • Osmotic pressure
    • Moves material into capillaries
factors aiding venous return
Factors Aiding Venous Return
  • Respiratory “pump”: pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand
  • Muscular “pump”: contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow
  • Vasoconstriction of veins under sympathetic control
the dynamics of blood flow
The Dynamics of Blood Flow

Vasomotor center in medulla regulates vasomotor activities

  • Vasodilation
  • Vasoconstriction
  • Precapillary sphincter
return of blood to the heart
Return of Blood to the Heart
  • Mechanisms that promote blood’s return to heart
  • Contraction of skeletal muscles
  • Valves
  • Breathing

Role of skeletal muscles and valves in blood return.

Role of skeletal muscles and valves in blood return. (A) Contracting skeletal muscle compresses the vein and drives blood forward, opening the proximal valve, while the distal valve closes to prevent backflow of blood. (B) When the muscle relaxes again, the distal valve opens, and the proximal valve closes until blood moving in the vein forces it open again.

the pulse
The Pulse
  • Ventricular contraction
  • Wave of increased pressure
  • Begins at heart and travels to arteries
  • Influenced by various factors
    • Body size
    • Gender
    • Age
    • Muscular activity
    • Emotion
    • Body temperature
    • Thyroid secretion
blood pressure
Blood Pressure
  • Force exerted by blood against vessel walls
  • Determined by heart’s output and resistance to blood flow
systemic blood pressure
Systemic Blood Pressure
  • The pumping action of the heart generates blood flow
  • Pressure results when flow is opposed by resistance
  • Systemic pressure
    • Is highest in the aorta
    • Declines throughout the pathway
    • Is 0 mm Hg in the right atrium
  • The steepest drop occurs in arterioles
arterial blood pressure
Arterial Blood Pressure
  • Systolic pressure: pressure exerted during ventricular contraction
  • Diastolic pressure: lowest level of arterial pressure
  • Pulse pressure = difference between systolic and diastolic pressure
systemic blood pressure50
Systemic Blood Pressure

Systolic pressure

Mean pressure



arterial blood pressure51
Arterial Blood Pressure
  • Reflects two factors of the arteries close to the heart
    • Elasticity (compliance or distensibility)
    • Volume of blood forced into them at any time
  • Blood pressure near the heart is pulsatile
capillary blood pressure
Capillary Blood Pressure
  • Ranges from 15 to 35 mm Hg
  • Low capillary pressure is desirable
    • High BP would rupture fragile, thin-walled capillaries
    • Most are very permeable, so low pressure forces filtrate into interstitial spaces
maintaining blood pressure
Maintaining Blood Pressure
  • Requires
    • Cooperation of the heart, blood vessels, and kidneys
    • Supervision by the brain
maintaining blood pressure54
Maintaining Blood Pressure
  • The main factors influencing blood pressure:
    • Cardiac output (CO)
    • Peripheral resistance (PR)
    • Blood volume
maintaining blood pressure55
Maintaining Blood Pressure
  • F = P/PR and CO = P/PR
  • Blood pressure = CO x PR (and CO depends on blood volume)
  • Blood pressure varies directly with CO, PR, and blood volume
  • Changes in one variable are quickly compensated for by changes in the other variables
cardiac output co
Cardiac Output (CO)
  • Determined by venous return and neural and hormonal controls
  • Resting heart rate is maintained by the cardioinhibitory center via the parasympathetic vagus nerves
  • Stroke volume is controlled by venous return (EDV)
cardiac output co57
Cardiac Output (CO)
  • During stress, the cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation
    • ESV decreases and MAP increases


BP activates cardiac centers in medulla



Activity of respiratory pump

(ventral body cavity pressure)

Sympathetic activity

Activity of muscular pump

(skeletal muscles)

Epinephrine in blood

Sympathetic venoconstriction

Venous return

Contractility of cardiac muscle



Stroke volume (SV)

Heart rate (HR)

Initial stimulus

Physiological response

Cardiac output (CO = SV x HR


Figure 19.8

control of blood pressure
Control of Blood Pressure
  • Short-term neural and hormonal controls
    • Counteract fluctuations in blood pressure by altering peripheral resistance
  • Long-term renal regulation
    • Counteracts fluctuations in blood pressure by altering blood volume
cardiac output
Cardiac Output
  • Volume of blood pumped out of each ventricle in
  • one minute
  • Heart rate
    • Beats per minute
  • Stroke volume
    • Controlled by force of contractions
resistance to blood flow
Resistance to Blood Flow

Peripheral resistance is affected by

  • Vasomotor changes
  • Baroreceptors in large arteries
  • Elasticity of blood vessels
  • Viscosity
  • Total blood volume
blood pressure measurement
Blood Pressure Measurement

Pressure is measured in the brachial arm artery using a sphygmomanometer

  • Systolic pressure
    • Occurs during heart contraction
    • Normal systolic: 120 mmHg
  • Diastolic pressure
    • Occurs during heart relaxation
    • Normal diastolic: 80 mmHg
abnormal blood pressure
Abnormal Blood Pressure
  • Hypotension
    • Lower than normal blood pressure
  • Hypertension
    • High blood pressure
  • Essential hypertension
    • No apparent medical cause
treatment of hypertension
Treatment of Hypertension
  • Stage 1
    • 140/90 mm Hg
    • Diet, exercise, weight loss
  • Stage 2
    • 160/100 mm Hg
    • Drugs added to treatment
arterial degeneration and other blood vessel disorders
Arterial Degeneration andOther Blood Vessel Disorders
  • Arteriosclerosis
    • Atherosclerosis
  • Clot formation
  • Leg cramps, pain, lameness
  • Cerebral artery sclerosis
  • Hypertension
  • Coronary artery arteriosclerosis
  • Renal artery damage
  • Ischemia, gangrene
treatment for arterial degeneration
Treatment for Arterial Degeneration
  • Balloon catheterization
  • Bypass grafts
  • Stents
  • Endarterectomy
  • Bulging sac in blood vessel wall
  • Swelling deranges other structures
  • Can burst, causing death
  • Surgery can replace damaged segment
  • Profuse escape of blood from vessels
  • Internal or external
  • Can be life-threatening
    • Apply pressure to wound
    • Elevate extremity above heart
    • Apply pressure to pressure point

Inadequate blood flow to tissues

  • Classified by type
    • Cardiogenic
    • Septic
    • Hypovolemic
    • Anaphylactic
  • Classified by severity (cause unknown)
    • Mild
    • Severe

Formation of blood clot in a vessel

  • Deep venous thrombosis (DVT)
  • Embolus
  • Pulmonary embolism
  • Phlebitis
  • Thrombophlebitis
varicose veins
Varicose Veins

Superficial veins that are swollen, distorted, and ineffective

  • Saphenous veins of lower extremities
  • Rectal veins (hemorrhoids)