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Blood Flow and the Control of Blood Pressure. 15. Overview: Cardiovascular System. Arteries take blood away from the heart and veins return it. Arteries connect to arterioles, that connect to capillaries, that connect to venules, that connect to veins

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Blood flow and the control of blood pressure

Blood Flow and the Control of Blood Pressure

15


Overview cardiovascular system
Overview: Cardiovascular System

Arteries take blood away from the heart and veins return it.

Arteries connect to arterioles, that connect to capillaries, that connect to venules, that connect to veins

Two portal systems shown here have two sets of capillaries connected

Figure 14-1


Functional model of the cardiovascular system
Functional Model of the Cardiovascular System

Systemic Arteries maintain pressure during ventricular relaxation by changing vessel diameter

Arteries and veins are for travel and capillaries for exchange

Figure 15-1


Blood vessel structure
Blood Vessel Structure

Blood vessels vary in diameter and wall thickness.

Veins have a larger diameter and thinner walls than arteries.

Capillaries are thin enough to allow for diffusion and narrow to restrict RBC to flow in single file

Figure 15-2


Metarterioles
Metarterioles

Capillaries lack smooth muscle and elastic tissue reinforcement which facilitates exchange

The walls are thin enough to allow WBC and plasma to scape. Plasma that leaves the capillaries and bathes the tissues will be called lymph and will be collected by lymphatic capillaries.

Figure 15-3



Capillaries exchange
Capillaries: Exchange

  • Plasma and cells exchange materials across thin capillary wall

  • Capillary density is related to metabolic activity of cells

  • Capillaries have the thinnest walls

    • Single layer of flattened endothelial cells

    • Supported by basal lamina

  • Bone marrow, liver and spleen do not have typical capillaries but sinusoids


Two Types of Capillaries

Continous Capillary Fenestrated Capillary

Sinusoidal Capillary


Angiogenesis
Angiogenesis

  • New blood vessel development-after birth, happens to accommodate tissue growth like when one gains weight

  • Necessary for normal development-growth needed during childhood

  • Wound healing and uterine lining growth-blood vessel formation needed in adulhood

  • Controlled by cytokines-chemical signal that induce mitosis

    • Mitogens: VEGF and FGF-vascular endothelial growth factor and fibroblast growth factor

    • Inhibit: angiostatin and endostatin- these natural occuring chemicals are being used to treat cancer and coronary disease

  • Coronary heart disease

    • Collateral circulation- natural formation of additional blood vessels to supplement flow of blocked vessels


Velocity of blood flow
Velocity of Blood Flow

Velocity of flow depends on total cross-sectional area of the vessels. The greater the total cross-sectional area the slower the velocity. Velocity is slowest at the capillaries. Although the diameter of a capillary is smaller than any other vessel its total cross-sectional area is greater than any other.

Figure 15-17


Review of blood flow
Review of Blood Flow

Flow is inversely proportional to resistance. Resistance is influenced by vessel diameter. The larger the diameter the slower the speed as long as the flow rate is constant.


Pressure differences in static and flowing fluids
Pressure Differences in Static and Flowing Fluids

Pressure falls over distance as energy is lost because of friction. In circulation the further away the blood is from the heart the lower the pressure. Pressure is lower is veins than in arteries

Figure 14-3a


Fluid flow through a tube
Fluid Flow through a Tube

Flow  ∆P

Pressure gradient cause a fluid to flow . Blood vessels create pressure gradients by altering diameter size

Figure 14-4


The role of radius in determining resistance to flow
The Role of Radius in Determining Resistance to Flow

A small change in diameter can use a great change in resistance and flow. Thus blood vessels can dramatically alter blood flow when they vasoconstrict or vasodialate

Figure 14-5


Fluid rate versus velocity of flow
Fluid Rate Versus Velocity of Flow

The velocity of flow is influenced by cross-sectional area. Although a large cross-sectional area may allow more fluid to pass at one time, it also causes it to slow down. Don’t think of cross-sectional area as the diameter of the blood vessel.

Figure 14-6


Pressure throughout the systemic circulation
Pressure throughout the Systemic Circulation

Blood pressure is highest in the arteries and decreases continuously as it flows through the circulatory system.

Systolic pressure is exerted on vessel walls when the heart contracts

Diastolic pressure is pressure during heart relaxation.

Pulse pressure measures strength of pressure wave systolic P – diastolic P

Mean arterial pressure measures driving pressure diastole P + 1/3 pulse pressure.

Figure 15-5


Elastic recoil in arteries
Elastic Recoil in Arteries

(a)

Ventricular contraction

Arterioles

1

2

3

1

2

Ventricle contracts.

Semilunar valve opens.

Aorta and arteries expand

and store pressure in

elastic walls.

3

This process explains how pressure is transferred to blood vessels when the heart contracts

Figure 15-4a


Elastic recoil in arteries1
Elastic Recoil in Arteries

(b)

Ventricular relaxation

1

2

3

Semilunar valve shuts,

preventing flow back

into ventricle.

1

Isovolumic ventricular

relaxation occurs.

2

Elastic recoil of arteries

sends blood forward into

rest of circulatory system.

3

This process explains how pressure is maintained in blood vessels while the heart relaxes

Figure 15-4b


Measurement of arterial blood pressure
Measurement of Arterial Blood Pressure

Pulse Pressure = systolic P – diastolic P

Valves ensure one-way flow in veins

MAP = diastolic P + 1/3(systolic P – diastolic P)

Figure 15-7


Pressure change
Pressure Change

  • Pressure created by contracting muscles of the heart and blood vessels is transferred to blood

  • Driving pressure is created by the ventricle. Thus usually blood pressure reading focus on left ventricular systole and diastole and arterial pressure not venous pressure.

  • If blood vessels constrict, blood pressure increases because the diameter decreases and the muscle exerts more pressure on the blood.

  • If blood vessels dilate, blood pressure decreases because the opposite happens.

  • Blood volume changes are major factors for blood pressure in CVS. Drinking a lot of fluid increases blood volume, blood loss and dehydration decreases blood volume. The kidneys try to regulate blood volume via fluid loss or retention. The CV system cause changes in diameter to help compensate when posible.


Blood pressure
Blood Pressure

Blood pressure control involves both the cardiovascular system and the renal system

Increase or decrease in blood volume is compensated by CV and kidney changes

Figure 15-9


Stroke volume and cardiac output
Stroke Volume and Cardiac Output

  • Stroke volume

    • Amount of blood expelled by one ventricle during a contraction

    • EDV – ESV = stroke volume

  • Force of contraction

    • Stroke volume increases of decreases based on contraction force

    • Affected by length of muscle fiber and contractility of heart

  • Frank-Starling law

    • Stroke volume increase as EDV increases

  • EDV determined by venous return

    • Skeletal muscle pump

    • Respiratory pump

    • Sympathetic innervation

  • Cardiac output

    • Volume of blood pumped by one ventricle in a given period of time

    • CO = HR  SV (heart rate times stroke volume)

    • Average = 5 L/min



Blood pressure1
Blood Pressure

Mean arterial pressure is a function of cardiac output and resistance in the arterioles= the volume produced by the heart times vessel radius (vasodilation/vasoconstriction)

Figure 15-8


Arteriolar resistance vasoconstriction
Arteriolar Resistance (vasoconstriction)

  • Sympathetic reflexes- control blood distribution as needed to maintian homeostasis such as body temperature

  • Local control of arteriolar resistance- based on metabolism of tissue and tissue needs for blood flow, can override CNS control in heart and muscle

  • Hormones- those that bind to kidney cells and control salt and water levels.

  • Myogenic autoregulation- increased blood flow causes increase pressure that stretches the walls. The smooth muscle responds by contracting thus increasing resistance and reducing flow. Therefore, no neural input is needed

  • Paracrines –secreted by endothelium, allows for local control

    • Active hyperemia- increase blood flow accompanies increased metabolic activity. As more paracrines accumulate, they call for more blood.

    • Reactive hyperemia- increase blood flow after a state of abnormally low metabolic rate due local hypoxia. Nitric oxide is made for vasodilation

  • Sympathetic control

    • SNS: norepinephrine; tonic release maintains myogenic tone, increase release causes vasoconstriction

    • Adrenal medulla: epinephrine: heart, liver, and skeletal muscle vasodilate


Hyperemia
Hyperemia

Figure 15-11a


Norepinephrine
Norepinephrine

Tonic control of arteriolar diameter

Figure 15-12



Blood pressure2
Blood Pressure

KEY

Medullary

cardiovascular

control

center

Stimulus

Sensor/receptor

Integrating center

Efferent pathway

Change in

blood

pressure

Effector

Carotid and aortic

baroreceptors

Components of the baroreceptor reflex

Figure 15-21


Blood pressure3
Blood Pressure

KEY

Medullary

cardiovascular

control

center

Stimulus

Sensor/receptor

Integrating center

Efferent pathway

Change in

blood

pressure

Effector

Parasympathetic

neurons

Carotid and aortic

baroreceptors

Sympathetic

neurons

Figure 15-21 (5 of 10)


Blood pressure4
Blood Pressure

KEY

Medullary

cardiovascular

control

center

Stimulus

Sensor/receptor

Integrating center

Efferent pathway

Change in

blood

pressure

Effector

Parasympathetic

neurons

Carotid and aortic

baroreceptors

Sympathetic

neurons

SA node

Ventricles

Figure 15-21 (8 of 10)


Blood pressure5
Blood Pressure

KEY

Medullary

cardiovascular

control

center

Stimulus

Sensor/receptor

Integrating center

Efferent pathway

Change in

blood

pressure

Effector

Parasympathetic

neurons

Carotid and aortic

baroreceptors

Sympathetic

neurons

SA node

Ventricles

Veins

Arterioles

Figure 15-21 (10 of 10)


Blood pressure6
Blood Pressure

The baroreceptor reflex: the response to increased blood pressure

Figure 15-22


Blood pressure7
Blood Pressure

The baroreceptor reflex: the response to orthostatic hypotension

PLAY

Figure 15-23

Animation: Cardiovascular System: Blood Pressure Regulation


Distribution of blood
Distribution of Blood

Distribution of blood in the body at rest

Figure 15-13


Cardiovascular disease cvd risk factors
Cardiovascular disease (CVD): Risk Factors

  • Risk factors that are not controllable

    • Gender

    • Age

    • Family History

  • Risk factors that are controllable

    • Smoking

    • Obesity

    • Sedentary lifestyle

    • Untreated hypertension

  • Uncontrollable genetic but modifiable lifestyle

    • Blood lipids

      • Leads to atherosclerosis

      • HDL-C versus LDL-C

    • Diabetes mellitus

      • Metabolic disorder contributes to development of atherosclerosis


Ldl and plaque
LDL and Plaque

The development of atherosclerotic plaques

Figure 15-24


Hypertension
Hypertension

Graph shows the relationship between blood pressure and the risk of developing cardiovascular disease

Essential hypertension has no clear cause other than hereditary

  • Carotid and aortic baroreceptors adapt

  • Risk factor for atherosclerosis

  • Heart muscle hypertrophies

    • Pulmonary edema

    • Congestive heart failure

  • Treatment

    • Calcium channel blockers, diuretics, beta-blocking drugs, and ACE inhibitors

Figure 15-25


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