Blood Vessels Cardiovascular System - Linn–Benton...

3/27/2016

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Blood Vessels

Cardiovascular System

Blood Vessels

• Delivery system of dynamic structures

• Closed system

– Arteries

• Carry blood away from the heart

– Capillaries

• Contact tissue cells and directly serve cellular needs

– Veins

• Carry blood toward the heart

Figure 19.2

Large veins(capacitancevessels)

Largelymphaticvessels

Arteriovenousanastomosis

Lymphaticcapillary

Postcapillaryvenule

Sinusoid

Metarteriole

Terminal arteriole

Arterioles(resistance vessels)

Muscular arteries(distributingvessels)

Elastic arteries(conductingvessels)

Small veins(capacitancevessels)

Lymphnode

Capillaries(exchange vessels)

Precapillary sphincterThoroughfarechannel

Lymphaticsystem

Venous system Arterial system

Heart

Figure 19.20

Azygos

system

Venous

drainage

Arterial

blood

Thoracic

aorta

Inferior

vena

cava

Abdominal

aorta

Inferior

vena

cava

Superior

vena cava

Common

carotid arteries

to head and

subclavian

arteries to

upper limbs

Aortic

arch

Aorta

RA

RV LV

LA

Capillary beds of

head and

upper limbs

Capillary beds of

mediastinal structures

and thorax walls

Diaphragm

Capillary beds of

digestive viscera,

spleen, pancreas,

kidneys

Capillary beds of gonads,

pelvis, and lower limbs

Blood Vessel Structure

• Tissue layers

– Tunica intima

– Tunica media

– Tunica externa

Tunica

intima

Tunica

media

Tunica

externa

ValveValve

Endothelial

Cell

Figure 19.1b

Tunica media(smooth muscle andelastic fibers)

Tunica externa

(collagen fibers)

Lumen

Artery

Lumen

Vein

Internal elastic lamina

External elastic lamina

Valve

(b)

Endothelial cellsBasement membrane

Capillary

network

Capillary

Tunica intima

• Endothelium• Subendothelial layer

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Blood Vessel Structure Blood Vessel Structure

Vasa vasorum nourishes outer layers of large vessels

Figure 19.21b

Internal carotid artery

Common carotid arteries

Subclavian artery

Subclavian artery

Aortic arch

Ascending aorta

Coronary artery

Thoracic aorta (abovediaphragm)

Renal artery

Superficial palmar arch

Radial artery

Ulnar artery

Internal iliac artery

Deep palmar arch

Vertebral artery

Brachiocephalic trunk

Axillary artery

Brachial artery

Abdominal aorta

Superior mesenteric artery

Gonadal artery

Common iliac artery

External iliac artery

Digital arteries

Femoral arteryPopliteal arteryAnterior tibial arteryPosterior tibial artery

Arcuate artery(b) Illustration, anterior

view

Inferior mesenteric artery

Celiac trunk

External carotid artery

Arteries of the head and trunk

Arteries that supply the upper limb

Arteries that supply the lower limb

Arteries

• Transport blood from left ventricle to body

tissues

– High pressure

• Three groups

– Elastic (conducting)

– Muscular (distributing)

– Arterioles (resistance)

Table 19.1 (1 of 2)

Arteries

• Elastic arteries

– Near the heart

• Aorta and major branches

– Conducting arteries

• Conduct blood from the heart to medium-sized arteries

– Large and thick-walled

– Large lumen = low resistance

– Highly elastic

• Expand during systole & recoil during diastole

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Arteries

• Muscular arteries

– Distributing arteries

• Distal to elastic arteries

• Deliver blood to body organs

– Thick tunica media with more smooth muscle

– Active in vasoconstriction

– Examples

• Radial, femoral, brachial

Arteries

• Resistance arteries

– Smallest arterial vessels (arterioles)

• Lead to capillary beds

• Control valves to capillary beds

– Site of most vasodilation and vasoconstriction

ArterioleVenule

Metarteriole

Capillaries

• Exchange vessels

• Exceedingly thin walls – just a tunica intima

• Capillary beds

– Microcirculation

between arterioles

and venules

Capillaries

• Two types

1. Continuous

• Open junctions between adjacent endothelial cells

• Most common

• In skin & muscles

2. Fenestrated

• Pores = permeable

• Intestines, endocrine organs, kidneys

Capillaries Capillaries

• Precapillary sphincters

– Cuff of smooth muscle fibers

– Acts as a valve to control blood flow into the

capillary

– Responds to local chemical conditions

– Vasomotor nerves (sympathetic)

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Figure 19.4

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

(b) Sphincters closed—blood flows through metarteriole

thoroughfare channel and bypasses true capillaries.

Precapillary

sphincters Metarteriole

Vascular shunt

Terminal arteriole Postcapillary venule

Terminal arteriole Postcapillary venule

Thoroughfare channel

True capillaries

Capillaries

• Tissue capillary bed may be flooded with blood

or nearly completely empty

• Examples: GI tract after a meal; skeletal muscle

during exercise

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

• Continuous capillaries of the brain

– Tight junctions are complete, forming the blood-

brain barrier

– Carrier-mediated transport

Figure 19.3a

Red blood

cell in lumen

Intercellular

cleft

Endothelial

cell

Endothelial

nucleus

Tight junction Pinocytotic

vesicles

Pericyte

Basement

membrane

(a) Continuous capillary. Least permeable, and

most common (e.g., skin, muscle).

Figure 19.3b

Red blood

cell in lumen

Intercellular

cleft

Fenestrations

(pores)

Endothelial

cell

Endothelialnucleus

Basement membrane

Tight junction

Pinocytotic

vesicles

(b) Fenestrated capillary. Large fenestrations

(pores) increase permeability. Occurs in special

locations (e.g., kidney, small intestine).

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Figure 19.3c

Nucleus of

endothelial

cell

Red blood

cell in lumen

Endothelial

cell

Tight junction

Incomplete

basement

membrane

Large

intercellular

cleft

(c) Sinusoidal capillary. Most permeable. Occurs in

special locations (e.g., liver, bone marrow, spleen).

This is not in the Study Guide, just FYI

Capillaries

• Functions

– Exchange area for blood and interstitial fluid

compartment

– Diffusion

• O2 and nutrients from the blood to tissues

• CO2 and metabolic wastes from tissues to the blood

Veins

• Functions

– Collect blood from capillary beds

– “drain” organs and tissues of blood

• Become larger as they come closer to the heart

Figure 19.26b

Renal vein

Splenic vein

Basilic vein

Brachial vein

Cephalic vein

Dural venous sinuses

External jugular vein

Vertebral vein

Internal jugular vein

Superior vena cava

Right and left

brachiocephalic veins

Axillary vein

Great cardiac vein

Hepatic veins

Hepatic portal vein

Superior mesenteric

vein

Inferior vena cava

Ulnar vein

Radial vein

Common iliac vein

External iliac vein

Internal iliac vein

Digital veins

Femoral vein

Great saphenous vein

Popliteal vein

Posterior tibial vein

Anterior tibial vein

Small saphenous vein

Dorsal venous arch

(b) Illustration, anterior

view. The vessels of the

pulmonary circulation

are not shown. Dorsal metatarsal veins

Inferior mesenteric vein

Median cubital vein

Subclavian vein

Veins of the head and trunk Veins that drain

the upper limb

Veins that drain

the lower limb

Copyright © 2010 Pearson Education, Inc.

Venules

• Formed when capillary beds unite

• Very porous

– Allow fluids and WBC’s into tissues

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Figure 19.5

Heart 8%

Capillaries 5%

Systemic arteries

and arterioles 15%

Pulmonary blood

vessels 12%

Systemic veins

and venules 60%

Veins

• Thinner walls, larger lumens than arteries

• Blood pressure is lower than in arteries

• Thin tunica media and a thick tunica externa

• Capacitance vessels (blood reservoirs)

– Contain up to 60% of the blood supply

Blood Vessel Matching

1. Pump

2. Resistance vessels, site of most vasodilation and vasoconstriction

3. Exchange sites

4. Pressure reservoirs, conducting vessels

5. Blood reservoirs

6. Distributing vessels

a. Veins

b. Arterioles

c. Capillaries

d. Heart

e. Elastic arteries

f. Muscular arteries

Venous Blood Pressure

• Low pressure

– Due to cumulative effects of peripheral resistance

• Working against gravity

– Valves

– Skeletal muscle action

– Thoracic pressure changes

Venous Valves

Figure 19.7

Valve (open)

Contracted

skeletal

muscle

Valve (closed)

Vein

Direction of

blood flow

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Varicose Veins

• Incompetent valves

– Pregnancy

– Obesity

– Long periods of standing

– Hemorrhoids

Blood Flow

• Blood flow is involved in

– O2 delivery

– Removal of wastes

– Gas exchange (lungs)

– Absorption of nutrients (digestive tract)

– Urine formation (kidneys)

• Perfusion– Rate of blood flow per given volume of tissue

• Blood flow (F)– Volume of blood flowing through a vessel, an organ, or tissue

in a given period• Measured as ml/min• Varies widely through individual organs

– Based on needs

Blood Flow Blood Flow

• F= Δ P

R

o F = Blood flow

o ΔP = Difference in pressure between two points

o R = Resistance

Blood Flow

� F= Δ P

R

• Relationship between blood flow, blood pressure, and resistance

– If ∆P increases, blood flow speeds up

– If R increases, blood flow decreases

• R is more important in influencing local blood flow

– Changed by altering blood vessel diameter

Blood Pressure

• Blood pressure (BP)

– Force per unit area exerted on the wall blood vessel by the blood

– Expressed as the height of a column of mercury (mmHg)

– P = H x D

• P = pressure

• H = height of column

• D = density of material in the column

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Blood Pressure

• Factors influencing blood pressure

– Cardiac output (CO)

– Peripheral resistance (PR)

– Blood volume

Blood Pressure

• Systolic pressure

– Pressure exerted during ventricular contraction

– Top number

• Diastolic pressure

– Lowest level of arterial pressure

– Bottom number

• Average value = 120/80

• Pulse pressure

– Difference between systolic and diastolic pressure

Figure 19.6

Systolic pressure

Mean pressure

Diastolic

pressure

Blood Pressure

• Basic concepts

– The pumping action of the heart generates blood

flow

– Pressure results when flow is opposed by resistance

• Systemic pressure

– Highest in the aorta

– Declines throughout the pathway

– Is close to 0 mmHg in the right atrium

• The steepest drop occurs in arterioles

Arterial Blood Pressure

• Reflects two factors of the arteries close to the

heart

– Elasticity

– Volume of blood forced into them at any time

• Blood pressure near the heart is pulsatile

Arterial Blood Pressure

� Mean arterial blood pressure (MABP)

�Pressure that propels blood to tissues

�Represents average blood pressure

MABP = diastolic pressure + 1/3 pulse pressure

Pulse pressure and MABP both decline

with increasing distance from the heart

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Hypertension

• “Silent Killer”

– Resting systolic >140 mmHg and/or diastolic >90 mmHg

• Causes

– Loss of flexibility in vessel walls

• Results

– Heart failure

– Renal failure

– Stroke

– Increased risk of aneurysm

Capillary Blood Pressure

• Not pulsatile

• 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

Peripheral Resistance

• The opposition to blood flow exerted by vessel walls– The result of friction

• Influenced by 3 factors– Blood viscosity

– Blood vessel length

– Blood vessel radius


• Viscosity = a fluid’s resistance to flow

• Blood viscosity influenced by…

– Albumin

– Erythrocytes


• Vessel length

– The farther fluid travels = more cumulative friction


• Vessel radius

– Most significant factor

– Vasoconstriction and vasodilation

– Flow is proportional to fourth power of radius

• Alteration of radius profoundly affects blood flow

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Poiseuille’s Law

• Formula representing the factors influencing flow

F = ΔPπr4

8 nL

F= flow

ΔP = pressure gradient

r4 = vessel radius

n = viscosity

L = vessel length

Poiseuille’s Law

• Blood flow is directly proportional to pressure

gradient and vessel radius

F = ΔPπr4

8 nL

Poiseuille’s Law

• Blood flow is inversely proportional to vessel

length and blood viscosity

F = ΔPπr4

8 nL

Regulation of Peripheral Resistance

• Local control

– Arterioles vary diameters = autoregulation

• A response to the chemical composition of the blood

– Faster flow = faster removal of wastes


� Local controlLocalized hypoxia

Metabolites (CO2, lactic acid, adenosine)

Acidic pH

Inhibit smooth muscle

Vasodilation

Increased blood flow


• Local control

– Precapillary sphincters

• Respond to local stimuli and vasoactive hormones

– Endothelial cells & platelets

• Vasodilators

– NO, prostacyclin

• Vasoconstrictors

– Endothelians, seratonin, thromboxane A2

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Figure 19.15

Metabolic

controls

pH Sympathetic

αααα Receptors

ββββ ReceptorsEpinephrine,

norepinephrine

Angiotensin II

Antidiuretic

hormone (ADH)

Atrial

natriuretic

peptide (ANP)

Dilates

Constricts

Prostaglandins

Adenosine

Nitric oxide

Endothelins

Stretch

O2

CO2

K+

Amounts of:

Amounts of:

Nerves

Hormones

Myogenic

controls

Intrinsic mechanisms(autoregulation)

• Distribute blood flow to individual

organs and tissues as needed

Extrinsic mechanisms

• Maintain mean arterial pressure (MAP)

• Redistribute blood during exercise and

thermoregulation


• Example of autoregulation

– Blood flow to skeletal muscles

• During muscle activity, blood flow increases in direct

proportion to the metabolic activity

• Blood flow can increase 10× or more during physical activity

Figure 19.13

Brain

Heart

Skeletal

muscles

Skin

Kidney

Abdomen

Other

Total blood flow during strenuous

exercise 17,500 ml/min

Total blood

flow at rest

5800 ml/min


• Neural control

– Directed by ANS via sympathetic innervation

• Vascular smooth muscle lacks parasympathetic input


� Neural control

�Vasomotor center in medulla = primary control center

�Integrates input from 3 ANS reflex circuits

�Baroreflex

�Chemoreflex

�Ischemic reflex


• Baroreflex

– Baroreceptors (pressure receptors) in

• Carotid sinuses

• Aortic arch

– Example: Blood pressure increases

• Inhibitory signals are sent to the

vasomotor center

• Stimulatory signals are sent to

the cardioinhibitory center (which acts

through which nerve?)

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Baroreceptors

in carotid sinuses

and aortic arch

are stimulated.

Impulses from baroreceptors

stimulate cardioinhibitory center

and inhibit vasomotor

center.

Rate of

vasomotor impulses

allows vasodilation,

causing R

Sympathetic

impulses to heart

cause HR,

contractility, and

CO.

Stimulus:

Blood pressure

(arterial blood

pressure rises above

normal range).

3

2

1

Homeostasis: Blood pressure in normal range

4b

5

4a

CO and R

return blood

pressure to

homeostatic range.

Baroreceptors

in carotid sinuses

and aortic arch

are inhibited.

Impulses from baroreceptors stimulate

cardioacceleratory center and stimulate vasomotor center.

Vasomotor

fibers stimulate

vasoconstriction,

causing R

Sympathetic

impulses to heart

cause HR,

contractility, and

CO.

5

4a

4b

3

2

CO and R

return blood pressure

to homeostatic range.


• Chemoreflex

– Excitatory or inhibitory signals to vasomotor

center

– Chemorecetors detect low blood pH, O2 levels

and high CO2 levels

– Chemoreceptors are located in the

• Carotid bifurcation

• Aortic arch

• Large arteries of the neck


• Medullary Ischemic Reflex

– Triggered by low perfusion of the medulla

Hypoxia and hypercapnia (high blood CO2) of the brain

Vasoconstriction in extremities

Blood flow directed to head and upper body


• Hormonal controls

– Angiotensin II

• Generated by kidney release of renin

• Causes vasoconstriction

– Atrial natriuretic peptide/factor

• Causes blood volume and blood pressure to decline

• Causes generalized vasodilation


• Hormonal controls cont.

– Antidiuretic hormone (ADH, vasopressin)

• Causes intense vasoconstriction in cases of extremely low

BP

– Epinephrine

• Causes generalized vasoconstriction and increases cardiac

output

Figure 19.11

Activity ofmuscularpump andrespiratory

pump

Release

of ANP

Fluid loss from

hemorrhage,

excessive

sweating

Crisis stressors:

exercise, trauma,

body

temperature

Bloodborne

chemicals:

epinephrine,

NE, ADH,

angiotensin II;

ANP release

Body size

Conservation

of Na+ and

water by kidney

Blood volume

Blood pressure

Blood pH, O2,

CO2

Dehydration,

high hematocrit

Blood

volume

Baroreceptors Chemoreceptors

Venous

returnActivation of vasomotor and cardiac

acceleration centers in brain stem

Heart

rate

Stroke

volume

Diameter of

blood vessels

Cardiac output

Initial stimulus

Result

Physiological response

Mean systemic arterial blood pressure

Blood

viscosity

Peripheral resistance

Blood vessel

length

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Fluid Shifts Between Capillaries and

Tissue

• Capillaries allow plasma and solutes to pass into interstitial space �

interstitial or extracellular fluid (ECF)

– Facilitates exchange of resources & wastes between

cells & plasma

– Dynamic equilibrium

– Imbalances?

– Exceptions?

Figure 19.2




Lymphaticcapillary

Postcapillaryvenule

Sinusoid

Metarteriole

Terminal arteriole





Lymphnode



Lymphaticsystem


Heart

Regulation of ECF Movement

• Hydrostatic and osmotic pressure

– Hydrostatic “pushes” and osmotic “sucks”

– 4 types

Capillary hydrostatic pressure

Interstitial osmotic pressure

Interstitial hydrostatic pressure

Capillary osmotic pressure

Move water out of

the vascular system

Move water into

the vascular system

Figure 19.17

HP = hydrostatic pressure• Due to fluid pressing against a wall

• “Pushes”

• In capillary (HPc)• Pushes fluid out of capillary

• 35 mm Hg at arterial end and

17 mm Hg at venous end of

capillary in this example

• In interstitial fluid (HPif)• Pushes fluid into capillary

• 0 mm Hg in this example

OP = osmotic pressure• Due to presence of nondiffusiblesolutes (e.g., plasma proteins)• “Sucks”• In capillary (OPc)

• Pulls fluid into capillary• 26 mm Hg in this example

• In interstitial fluid (OPif)• Pulls fluid out of capillary• 1 mm Hg in this example

Arteriole

Capillary

Interstitial fluid

Net HP—Net OP

(35—0)—(26—1)

Net HP—Net OP

(17—0)—(26—1)

Venule

NFP (net filtration pressure)is 10 mm Hg; fluid moves out

NFP is ~8 mm Hg;fluid moves in

Net

HP

35

mm

Net

OP

25

mm

Net

HP

17

mm

Net

OP

25

mm


• Hydrostatic

– Capillary hydrostatic pressure (HPc)

• Capillary blood pressure

• Tends to force fluids through the capillary walls

• Is greater at the arterial end (35 mm Hg) of a bed than at the venous end (17 mm Hg)

– Interstitial hydrostatic pressure (HPif)

• Pressure of fluid within intercellular spaces

• Constantly enters lymphatic drainage

• Averages 0 mmHg


• Osmotic

– Interstitial fluid osmotic pressure (OPif)

• The osmotic pressure force created by interstitial solutes

• Low (~1 mm Hg), due to low protein content

– Capillary colloid osmotic pressure (OPc)

• Created by non-diffusible plasma proteins, which draw

water toward themselves

• ~26 mm Hg

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• The movement of fluid between the

extracellular compartments is driven by a

pressure gradient

– Most influenced by capillary hydrostatic pressure


• Net Filtration Pressure (NFP)

– Comprises all the forces acting on a capillary bed

NFP = (HPc - HPif) - (Opc - OPif)


• Arterial NFP– Arterial end of a capillary bed = hydrostatic forces

dominate• Fluid moves out

• NFP = (35-0) – (26-1) = 10 mm Hg

• Venous NFP– Venous end of a capillary bed = osmotic forces dominate

• Fluid moves in

• NFP = (17-0) – (26-1) = -8 mm Hg

• Excess fluid– Returned to the blood via the lymphatic system

Figure 19.17

HP = hydrostatic pressure

• Due to fluid pressing against a wall• “Pushes”• In capillary (HPc)

• Pushes fluid out of capillary• 35 mm Hg at arterial end and

17 mm Hg at venous end ofcapillary in this example

• In interstitial fluid (HPif)• Pushes fluid into capillary• 0 mm Hg in this example

OP = osmotic pressure• Due to presence of nondiffusiblesolutes (e.g., plasma proteins)• “Sucks”• In capillary (OPc)

• Pulls fluid into capillary• 26 mm Hg in this example

• In interstitial fluid (OPif)• Pulls fluid out of capillary• 1 mm Hg in this example

Arteriole

Capillary

Interstitial fluid

Net HP—Net OP

(35—0)—(26—1)

Net HP—Net OP

(17—0)—(26—1)

Venule

NFP (net filtration pressure)is 10 mm Hg; fluid moves out

NFP is -8 mm Hg;fluid moves in

NetHP35mm

NetOP25mm

NetHP17mm

NetOP25mm

Filtration=fluid moves out

Reabsorption=fluid moves in

Figure 19.2




Lymphaticcapillary

Postcapillaryvenule

Sinusoid

Metarteriole

Terminal arteriole





Lymphnode



Lymphaticsystem


Heart Edema

• Occurs when filtration greatly exceeds

reabsorption

– Abnormal increase in interstitial fluid volume

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Venous Blood Pressure

• Changes little during the cardiac cycle

• Low pressure due to cumulative effects of

peripheral resistance

• Central venous pressure

– Pressure at the point where vena cava enter heart

– Average = 4.6 mm Hg

Venous Return

• Venous hydrostatic pressure relatively low

• Returning blood to heart requires adaptations

Mechanisms of Venous Return

1. Thoracic pump

• Pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand

2. Cardiac Suction

• During atrial systole, movement of AV valves enlarges atria = lower pressure = increasing pressure gradient between vena cava

3. Muscular pump

• Contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow

4. Gravity

• Helps with return of blood from superior regions

21_09

Mechanisms of Venous Return

• Circulatory shock

– Definition = CO is insufficient to meet the metabolic demands of the tissues

– Cardiogenic shock

• Heart’s ability to pump blood is impaired

– Other types of shock

• Due to low venous return (LVR)

– Hypovolemic shock

– Vascular shock

» Neurogenic shock

» Septic shock

» Anaphylactic shock

Types and Causes of LVR Shock

1. Hypovolemic shock

– Most common form of shock

– Result of blood loss

• Direct losses: hemorrhage, trauma, burns, bleeding ulcers

• Indirect losses: fluids other than blood lost

– Burns and dehydration

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Types and Causes of LVR Shock

2. Vascular shock

– Body retains normal blood volume but blood accumulates in extremities

a) Neurogenic shock

• Usually follows spinal cord trauma � widespread vasodilation

b) Septic shock

• Bacterial endotoxin simulates vasodilation

c) Anaphylactic shock

• Following allergic reaction

• Sudden release of histamine � massive vasodilation and permeability changes

Figure 19.18

Signs and symptoms

Acute bleeding (or other events that cause

blood volume loss) leads to:

1. Inadequate tissue perfusionresulting in ↓ O2 and nutrients to cells

2. Anaerobic metabolism by cells, so lactic

acid accumulates3. Movement of interstitial fluid into blood,

so tissues dehydrate

Initial stimulus

Result

Physiological response

Chemoreceptors activated(by ↓ in blood pH)

Baroreceptor firing reduced(by ↓ blood volume and pressure)

Hypothalamus activated(by ↓ pH and ↓ blood pressure)

Major effect Minor effect

Brain

Activation of

respiratory centers

Cardioacceleratory and

vasomotor centers activatedSympathetic nervous

system activated

ADH

released

Neurons

depressedby ↓ pH

Intense vasoconstriction

(only heart and brain spared)↑Heart rate Central

nervous systemdepressed

Adrenalcortex

Kidney

Renin released

↓ Renal blood flow

Aldosterone

released

Kidneys retain

salt and water

Angiotensin II

produced in blood

Water

retention

↓ Urine output↑ Rate and

depth ofbreathing

Tachycardia,

weak, threadypulse

Skin becomes

cold, clammy,and cyanotic

Thirst Restlessness

(early sign)

Coma

(late sign)

CO2 blown

off; bloodpH rises

Blood pressure maintained;

if fluid volume continues todecrease, BP ultimately

drops. ↓ BP is a late sign.

Pathways of Blood Circulation

• Complete circuits begin and end at heart

• A double pump with 2 pathways

– Pulmonary circulation

– Systemic circulation

Systemic Circulation

• Carries oxygen rich blood to all parts of the body

• Subdivisions

– Coronary circulation

• Supplies myocardium

– Hepatic-portal circulation

• Directs blood from spleen, stomach, pancreas, gallbladder, and intestines to the liver via portal vein

– Organs of digestion and recycling – materials are substantially metabolized in the liver before reaching general circulation

– Jaundice

• Portal systems

– 2 capillary beds

Copyright © 2010 Pearson Education, Inc.

(c) The hepatic portal circulation.

Hepatic veins

Liver

Spleen

Gastric veins

Inferior vena cava

Inferior vena cava(not part of hepaticportal system)

Splenic vein

Right gastroepiploicvein

Inferiormesenteric vein

Superiormesenteric vein

Large intestine

Hepatic portal vein

Small intestine

Rectum

Pulmonary Circulation

• Carries oxygen poor blood from heart to

alveolar surface of lungs and oxygen rich blood

back to the heart

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Fetal Circulation

• Oxygen and nutrients obtained from maternal

blood

– Respiratory and digestive systems not yet functional

– Blood oxygenated in placenta

• Attached to uterine wall by cotyledons (contain placental

villi)

• Waste carried from fetus by umbilical arteries

– Extensions of the internal iliac arteries

• Nutrient rich blood enters fetal circulation by umbilical

vein

Fetal Circulation

• Ductus venosus

– Continuation of the umbilical

vein under liver

– Drains into inferior vena cava

– Allows blood to bypass the liver

– Functionally closes minutes

after birth

– Structurally closes in term

infants in 3-7 days

Fetal Circulation

• Foramen ovale

– Opening between right and left atria � bypasses fetal

lungs

– Blood routed to aorta

Fetal Circulation

• Foramen ovale

– First breath after birth decreases pulmonary pressure

– Left atrial pressure exceeds right and forces foramen

ovale closed

– May remain open

• Patent foramen ovale or ASD

• “Hole in the heart”

• May be surgically closed

Fetal Circulation

• Ductus arteriosis

– Connects pulmonary artery with descending thoracic

aorta

– Also aids in bypassing lungs

Fetal Circulation

• Ductus arteriosis

– Failure to close at birth = patent ductus arteriosis

– Leads to pulmonary hypertension

and congestive heart failure

– NSAIDs are administered to

force closure

• Why NSAIDs MUST be

avoided in late pregnancy

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Figure 28.14a

Aortic archFetusSuperior vena cava

Ductus arteriosus

Ligamentum arteriosum

Lung

Pulmonary artery

Pulmonary veinsHeart

Foramen ovale

Fossa ovalis

LiverDuctus venosus

Ligamentum venosum

Ligamentum teres

Umbilical vein

Inferior vena cava

Hepatic portal vein

UmbilicusAbdominal aorta

Common iliac artery

Umbilical arteries

Medial umbilical ligaments

Urinary bladder

Umbilical cord

(a)

Placenta

High oxygenation

Moderate oxygenation

Low oxygenation

Very low oxygenation

Placenta

Umbilical vein

Ductus venosus

Inferior vena cava

Right atrium

Right ventricle

Pulmonary artery

Fetal Circulation

Left atrium

Aorta

Internal

iliac arteries

Umbilical

arteries

Placenta

Foramen ovale

Ductus arteriosis

Hypertension

• “Silent Killer”

– Produces few symptoms

• Major cause of heart failure, stroke & kidney

failure

• Resting systolic above?

• Resting diastolic above?

Blood Pressure Level (mmHg)

Category Systolic Diastolic

Normal < 120 and < 80

Prehypertension 120-139 or 80-89

High Blood Pressure

Stage 1 Hypertension

140–159 or 90–99

Stage 2 Hypertension

160 or 100

Categories for Blood Pressure

Levels in Adults

(Ages 18 Years and Older)

Hypertension

• Arteries are stretched

– Tears endothelium = exposes muscle = focal point

for atherosclerosis = worsens hypertension

• Remember atherosclerosis?

– Emboli may lodge in narrowed vessel

– Clots may form on roughened endothelium

– Long-standing belief that high lipid, high cholesterol

diets contribute are being called into question

Renal Hypertension

• Blood flow to kidneys is reduced

– Leads to thickening of arterioles � respond as

though BP were reduced � Angiotensin II produced

� aldosterone released

• Increases blood volume and BP

– Worsens existing hypertension �kidney failure may

result

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Hypertension

• Primary hypertension– 90% of hypertensive conditions

– Cause unknown

– Contributing factors include • Genetics

• Obesity» Adipose tissue extensively vascularized

» 10 miles per pound!!

» Means increased peripheral vascular resistance

• Smoking» Nicotine = coronary vasoconstrictor

• Diet» Salt = water retention � higher blood volume

» Mineral deficiencies (Mg, K, Ca)

Hypertension

• Secondary hypertension

– 10% of cases

– Due to identifiable disorders

• Kidney disease

• Atherosclerosis

• Endocrine disorders

– Hyperthyroidism

– Cushing’s disease

– Polycythemia

• Deep venous thrombosis (DVT)

• Affects mainly the veins in the lower leg and the thigh

• It involves the formation of a clot (thrombus) in the larger veins of the area

This picture shows a red and swollen thigh and leg caused by a

blood clot (thrombus) in the deep veins in the groin

which prevents normal return of blood from the leg to the heart.

• Can be caused by any condition that restricts venous return in the lower

extremities

• Cause in 1/3 of cases is unknown

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