Chapter 21The Cardiovascular System: Blood

Vessels and Hemodynamics• Structure and function of

blood vessels

• Forces involved in circulating blood

• Major types of circulation to be studied in lab

Basic circulatory route

Heart Arteries

ArteriolesCapillaries

Tissues

Venules

Veins

Structure of Vessels

•Comparison of Arteries and Veins

•Blood flows away from heart in ________arteries

•Blood flows toward heart in ______

•Arteries are thicker than veins

veins

•Veins have regularly spaced valves

•Which vessels have the highest pressure?

•Which vessels carry about 64% of the blood?

Distribution of Blood

------------Tunica ExternaCollagen & Elastic Fibers

---------------Tunica MediaSmooth Muscle & Elastic Fibers

-----------------Tunica InternaEndothelium, Basement

Membrane & Elastic Fibers

Vessel Structure

•Elastic Arteries•Less muscle and more elastic tissue•Larger arteries such as aorta•Why do the larger arteries have more elastic tissue? What purpose do they serve?

Types of Arteries

• Muscular Arteries•Less elastic tissue and more muscle

•Medium size to smaller arteries

Types of Arteries

•Capable of greater vasoconstriction and vasodilation to adjust rate of flow

Smaller Vessels• Arterioles

-Smallest arteries

- Deliver blood to capillaries

- Smallest ones lose tunica externa

- Called resistance blood vessels because their vasoconstriction increases resistance, and their vasodilation (relaxation) decreases resistance to blood flow

Capillaries•Microscopic vessels – form microcirculation

•Tubes of endothelium and basement membrane

•Connect arterioles to venules

•Function in exchange of substances with tissues

•Interconnect like a net to form capillary beds

Types of Capillaries • Continuous

-Adjacent endothelial cells form tight fit

-Least permeable

-In muscle, brain, connective tissue and lungs

- Pores (holes) in endothelial cells

- Quite permeable - In kidneys, intestines and endocrine (hormone) glands

• Fenestrated

Types of Capillaries•Sinusoids

-Largest capillaries

-Large fenestrations and large gaps between endothelial cells- Scant basement membranes

- Most permeable

- In liver, some endocrine glands and bone marrow

•Fenestrated Capillary

•Sinusoid

Types of Capillaries

•Continuous Capillary

Venules

•Small veins that collect blood from capillaries

•Tunica media contains only a few smooth muscle cells & scattered fibroblasts

•Rather porous endothelium

MicrocirculationArterioles, Capillaries and Venules

---------------Arteriole

----------Capillary

---Venule

-------------------------Metarteriole

--------------Thoroughfare channel

Anastomoses

• Union of two or more arteries supplying the same body region– blockage of only one pathway has no effect

• circle of willis underneath brain

• coronary circulation of heart

• Collateral Circulation:

-Alternate route of blood flow through an anastomosis.

- can occur in veins and venules as well

Physiology of Circulation-Blood Pressure

•Blood pressure (BP) is the force the blood exerts against vessel walls

•Difference in blood pressure (pressure gradient) along vessels causes blood to flow

•Blood flows from higher to lower pressure

•Pressure is highest in the aorta and lowest in the vena cavae

Blood Flow

•Amount of blood flowing through vessels per unit of time (mL per minute)

Resistance (R) to blood flow

•Produced as the blood encounters friction and turbulence against the vessel and heart walls

•Increased resistance decreases blood flow

•For blood to flow, BP must overcome R

•Greatest R is in arterioles-called peripheral resistance (PR)

Blood Pressure Formula

•Blood pressure = Flow X Resistance

Flow causes BP, Flow causes BP

R causes BP, R causes BP

Factors in Flow and Resistance

•Factors in Flow•Cardiac Output (CO)

= Amount of blood ejected by left ventricle in one minute

•Blood volume= Total amount of blood in body•More than 10% drop causes drop in BP

•Diameter of vessels, especially arterioles

•Length of vessels

•Viscosity of blood

vasoconstriction

Has BP increased or decreased?

•Factors in Resistance

Measurements of Arterial blood pressure

•Systolic pressure(SP) and diastolic pressure (DP)

•Systolic pressure(SP) •Pressure in arteries when left ventricle is contracting

•High number on blood pressure reading

•Diastolic pressure(DP) •Pressure in arteries when left ventricle is relaxing

•Low number on blood pressure reading

Measuring Arterial BP

•BP measured in millimeters of mercury (mm Hg)

•Use a manometer

•Usually taken in upper arm

•High number is systolic pressure

•Low number is diastolic pressure•Typical reading is 120 mmHg/80 mmHg

•140/90 or above considered high

Sphygmomanometer

•Pulse pressure (PP) •Difference in Systolic and diastolic pressures or PP=SP-DP

Other Pressures

•High during exercise, anxiety, influence of certain drugs and with hardening of arteries

•Mean Arterial Blood Pressure (MABP or MAP)•Single measure of arterial BP

•Formula:MAP = Diastolic Pressure + Pulse Pressure/3

Pressure Gradients Different Vessels•Arterial Pressure Gradient =

•Averages about 60 mmHg•Difference in arterial pressure from Aorta to capillaries

•Capillary Pressure Gradient•Difference in pressure from arteriole to venule side of capillary bed•Averages about 20 mmHg

•Venous Pressure Gradient•Difference in pressure from venules to Vena cavae•Averages about 16 mmHg

Blood Pressures in Various Vessels

Capillary Exchange •Passage of water and solutes between capillary plasma and interstitial fluid•Three Methods

1.Diffusion is movement of solute from ____ to ____ concentration

2.Transcytosis is movement of large molecules across capillary cells by ____________________________

high low

formation of pinocytotic vesicles

Capillary Exchange

3.Bulk Flow – Filtration and Reabsorption - Movement of fluid and solute from capillaries into interstitial fluid is _______filtration- Movement of fluid and solute from interstitial fluid into capillaries is __________reabsorption

•Two opposing pressures at work - Blood Hydrostatic Pressure (BHP) is the blood pressure that pushes fluid out of blood- Blood Colloidal Osmotic Pressure (BCOP) is a “suction” pressure that pulls fluid into blood

Capillary Exchange

•Mechanism of Filtration and Reabsorption

- On arteriole side of capillary, BHP BCOP – push pull

-On venule side of capillary, BCOP BHP – pull push

- Higher BHP on arteriole side pushes water and solute from capillary into interstitial fluid - filtration

- Higher BCOP on venule side pulls water and solute from interstitial fluid into capillary - reabsorption

Drawing of Filtration and Reabsorption

Venous pressure and venous return

• Venous pressure is very low and can not account for return of blood to heart

• Factors that aid in venous return

- Venous valves prevent backflow of blood once it is squeezed past them

- Contraction of skeletal muscles squeeze veins and push blood toward heart- Breathing squeeze pulmonary vessels

Illustration of Venous Return

Velocity of Blood Flow•Blood flows fastest in _______arteries•Blood flows slowest in _________capillaries

----Cross-sectional Area

----Velocity

Arteries & Arterioles Capillaries Venules & Veins

Blood Pressure Regulation

• Local regulation within tissues

• Central (neural) regulation by brain

Local Regulation to assure proper tissue perfusion

•Autoregulation of Blood Flow -Tissues regulate blood flow to meet their needs

•Local Vasodilators -↑CO2 or ↓O2

-↑acid

-↑NO -inflammatory chemicals such as histamine -↑body temperature

Central Control of Blood Pressure & Flow

• Role of Cardiovascular Centers - cardioaccelerator, cardioinhibitory & vasomotor centers of the medulla oblongata

- Help regulate heart rate & stroke volume

- Specific neurons regulate vessel diameter

- Regulate by input from sensory receptors and output to heart

Input to the Cardiovascular Center•Higher brain centers such as cerebral cortex, limbic system & hypothalamus- anticipation of competition- increase in body temperature

•Proprioceptors- input during physical activity

•Baroreceptors- changes in pressure within blood vessels

•Chemoreceptors- monitor concentration of chemicals in the blood

Output from the Cardiovascular Center•Heart

- Parasympathetic (vagus nerve) - decreased heart rate- Sympathetic (cardiac accelerator nerves) - increased contractility & rate

•Blood vessels- Sympathetic vasomotor nerves

•Decreased stimulation produces dilation & decreased BP•Increased stimulation produces constriction & increased BP•Continual stimulation keeps arterioles in tonic contraction called vasomotor tone

Input and Output

•Neural Regulation of Blood Pressure – Aortic/Carotid Reflexes

•Baroreceptor reflexes- Carotid sinus reflex

•Receptors in carotid artery wall

•Sensory input to cardiovascular center in medulla

•Maintains normal BP in the brain

- Aortic reflex•Receptors in wall of ascending aorta•Sensory input to cardiovascular center in medulla

•Maintains general systemic BP

Chemoreceptor Reflexes• Carotid bodies and aortic bodies

– Detect changes in blood levels of O2, CO2, and H+ (hypoxia, hypercapnia or acidosis )

– Causes stimulation of cardiovascular center– Increases sympathetic stimulation to heart &

vessels Cardiac output and increase in blood pressure

• Also change breathing rates

Diagram of Baroreceptor Reflexes

↓BP

Cardiovascular Center

Return to Homeostasis

Sympathetic

Cardiac Output and Vasoconstriction

BP

↓Stimulation of baroreceptors

Cardiovascular CenterStimulation of baroreceptors

↓Cardiac Output and Vasodilation↓Cardiac Output and Vasodilation

↓SympatheticParasympathetic

Parasympathetic

Homeostasis Disturbed, BP too high

Homeostasis Disturbed, BP too low

Innervation of the Heart

• Speed up the heart with sympathetic stimulation• Slow it down with parasympathetic stimulation (X)• Sensory information from baroreceptors (IX)

Hormonal Regulation of Blood Pressure• Renin-angiotensin-aldosterone system

– Decrease in BP or decreased blood flow to kidney

– Release of renin results in formation angiotensin II• Systemic vasoconstriction

• Causes release of aldosterone (H2O & Na+ reabsorption)

• Epinephrine & norepinephrine– Increases heart rate & force of contraction

– Causes vasoconstriction in skin & abdominal organs

– Vasodilation in cardiac & skeletal muscle

• Antidiuretic hormone (ADH) causes vasoconstriction and water retention

Clinical Terms

• Hypertension: Blood pressure above 140/90

• Aneurysm:

Localized abnormal dilatation of a blood

Vessel.

• Venous Claudication:

Lameness due to inadequate venous drainage.

Deep Venous Thrombosis:A blood clot in a deep vein.

• Phlebitis: Inflammation of a vein.

• Phlebotomist:A person who draws blood.

• Venipuncture:Puncture of a vein to obtain blood.