Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure

Figure 19.2

Large veins(capacitancevessels)

Largelymphaticvessels

Arteriovenousanastomosis

Lymphaticcapillary

Postcapillaryvenule

Sinusoid

MetarterioleTerminal arteriole

Arterioles(resistance vessels)

Muscular arteries(distributingvessels)

Elastic arteries(conductingvessels)

Small veins(capacitancevessels)

Lymphnode

Capillaries(exchange vessels)

Precapillary sphincterThoroughfarechannel

Lymphaticsystem

Venous system Arterial systemHeart

Blood Vessels: The Vascular System

Layers of Blood Vessels

Figure 19.1b

Tunica media(smooth muscle under control of symp. n.s. andelastic fibers)

Tunica externa(fibrous connective: collagen fibers)

LumenArtery

LumenVein

Internal elastic lamina

External elastic lamina

Valve

(b)

Endothelial cellsBasement membrane

Capillarynetwork

Capillary

Tunica intima• Endothelium• Subendothelial layer

Differences Between Blood Vessel Types Walls of arteries are the

thickest, while lumen is smaller in diameter

Walls of veins are thinner, while lumens of veins are larger

Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue

Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure

Table 19.1 (1 of 2)

Elastic Arteries

Large thick-walled arteries with elastin in all three tunics

Aorta and its major branches

Large lumen offers low-resistance

Act as pressure reservoirs—expand and recoil as blood is ejected from the heart

Muscular Arteries

Distal to elastic arteries; deliver blood to body organs

Have thick tunica media with more smooth muscle

Active in vasoconstriction

Arterioles

Smallest arteries

Lead to capillary beds

Control flow into capillary beds via vasodilation and vasoconstriction

Arteries, Compared

Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure

Large veins(capacitancevessels)

Largelymphaticvessels

Arteriovenousanastomosis

Lymphaticcapillary

Postcapillaryvenule

Sinusoid

MetarterioleTerminal arteriole

Arterioles(resistance vessels)

Muscular arteries(distributingvessels)

Elastic arteries(conductingvessels)

Small veins(capacitancevessels)

Lymphnode

Capillaries(exchange vessels)

Precapillary sphincterThoroughfarechannel

Lymphaticsystem

Venous system Arterial systemHeart

Capillaries and Capillary Beds

Figure 19.2

Capillaries Found in all tissues except for cartilage,

epithelia, cornea and lens of eye

Three structural types

1. Continuous capillaries

2. Fenestrated capillaries

3. Sinusoidal capillaries (sinusoids)

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

Figure 19.3a

Red bloodcell in lumen

IntercellularcleftEndothelialcell

Endothelialnucleus

Tight junction Pinocytoticvesicles

Pericyte

Basementmembrane

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

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)

Figure 19.3b

Red bloodcell in lumen

Intercellularcleft

Fenestrations(pores)

Endothelialcell

EndothelialnucleusBasement membrane

Tight junction

Pinocytoticvesicles

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

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

Figure 19.3c

Nucleus ofendothelialcell

Red bloodcell in lumen

Endothelialcell

Tight junction

Incompletebasementmembrane

Largeintercellularcleft

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

Capillary Beds Interwoven networks of capillaries form the

microcirculation between arterioles and venules

Consist of two types of vessels

1. Vascular shunt (metarteriole—thoroughfare channel):

o Directly connects the terminal arteriole and a postcapillary venule

2. True capillaries

o 10 to 100 exchange vessels per capillary bed

o Branch off the metarteriole or terminal arteriole

Figure 19.4

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

Precapillarysphincters Metarteriole

Vascular shunt

Terminal arteriole Postcapillary venule

Thoroughfare channel

True capillaries

Postcapillary venuleTerminal arteriole

(b) Sphincters closed—blood flows through metarteriole thoroughfare channel and bypasses true capillaries.

Blood Flow Through Capillary Beds

High O2, low pH,

nutrients, low CO2, cold

external temperatures, fight or

flight conditions

Low O2, high CO2, high pH,

low nutrients,

hot external

temperatures,

relaxation

Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure

Table 19.1 (2 of 2)

Venules

Formed when capillary beds unite

Very porous; allow fluids and WBCs into tissues

Postcapillary venules consist of endothelium and a few pericytes

Larger venules have one or two layers of smooth muscle cells

Veins

Formed when venules converge

Have thinner walls, larger lumens compared with corresponding arteries

Blood pressure is lower than in arteries

Thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks

Called capacitance vessels (blood reservoirs); contain up to 65% of the blood supply

Venules and Veins

Veins Adaptations that ensure

return of blood to the heart

1. Large-diameter lumens offer little resistance

2. Valves prevent backflow of blood

o Most abundant in veins of the limbs

Venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain)

One-way valves in veins prevent backflow where

positive pressure is at a mininum

Figure 19.5

Heart 8%

Capillaries 5%

Systemic arteriesand arterioles 15%

Pulmonary bloodvessels 12%

Systemic veinsand venules 60%

Most of the Blood is in Veins and Venules

Vascular Anastomoses Interconnections of blood vessels

Arterial anastomoses provide alternate pathways (collateral channels) to a given body region

• Common at joints, in abdominal organs, brain, and heart

Vascular shunts of capillaries are examples of arteriovenous anastomoses

Venous anastomoses are common

Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure

Pulse Pulse – pressure

wave of blood

Monitored at “pressure points” where pulse is easily palpated

Figure 11.16

Physiology of Circulation: Definition of Terms

Blood flow

• Volume of blood flowing through a vessel, an organ, or the entire circulation in a given period, measured in ml/min

Blood pressure (BP)

• Force per unit area exerted on the wall of a blood vessel by the blood, expressed in mm Hg

• Measured as systemic arterial BP in large arteries near heart

Peripheral Resistance

• Opposition to flow; a measure of the amount of friction blood encounters

• Generally encountered in the peripheral systemic circulation

• Three important sources of resistance

o Blood viscosity (relatively constant)

o Total blood vessel length (relatively constant)

o Blood vessel diameter (Resist. varies inversely with the fourth power of vessel radius (e.g., if the radius is doubled, the resistance is 1/16 as much)

Local Blood PressuresSystemic pressure

• Highest in the aorta, declines throughout the pathway; 0 mm Hg in the right atrium

Arterial 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

o Systolic pressure: pressure exerted during ventricular contraction

o Diastolic pressure: lowest level of arterial pressure

o Pulse pressure = difference between systolic and diastolic pressure

Mean arterial pressure (MAP): pressure that propels the blood to the tissues

MAP = diastolic pressure + 1/3 pulse pressure

Pulse pressure and MAP both decline with increasing distance from the heart

Capillary blood pressure

Low capillary pressure is desirable; low pressure forces filtrate into interstitial spaces

Venus blood pressure - near zero

Comparison of Blood PressuresDisease causing blood pressure

change

Arteriosclerosis: Hardening of the artery walls and decrease of elasticity, restricting flow and increasing blood pressure.

Atherosclerosis: A specific type of arterosclerosis where arteries are clogged by an accumulation of plaques: cholesterol particles (lipoproteins), fat, calcium, cellular waste and other substances.

Blood pressure results when flow is opposed by resistance

Factors Aiding Venous Return

1. Respiratory “pump”: pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand

2. Muscular “pump”: contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow

3. Vasoconstriction of veins under sympathetic control

Measuring Arterial Blood Pressure Measurements by health professionals

are made on the pressure in large arteries

• Systolic – pressure at the peak of ventricular contraction

• Diastolic – pressure when ventricles relax

Pressure in blood vessels decreases as the distance away from the heart increases

Blood pressure animation onlineNormal BP is

120/75-80Listen for the sounds of Kortokoff

Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure

Variations in Blood Pressure

Human normal range is variable

• Normal

o 110-140 mm Hg systolic or just 120/70

o 70-80 mm Hg diastolic

• Hypotension

o Low systolic (below 110 mm HG)

o Often associated with illness or physical conditioning

• Hypertension

o High systolic (above 140 mm HG)

o Can be dangerous if it is chronic

o Caused by many things, including a high saturated fat and/or salty diet, little exercise, & chronic stress

Cardio System II: Vasculature and Pressure

Blood Vessel Anatomy

• Arteries and arterioles

• Capillaries (3 types)

• Veins and venules

Pulse and Pressure Points

Blood Pressure

• Factors Regulating Blood Pressure