Topic 4Blood vessels & Hemodynamics

Joanna Komorowski, PH.D.

Lecture objectivesMarieb Chapter 19: pages 706- 721

• Express blood pressure in terms of cardiac output and peripheral resistance

• Describe the short-term neural and chemical mechanisms for the regulation of blood pressure

• Describe the role of the kidneys in the long-term regulation of blood pressure

• Define and explain the mechanisms of autoregulation with regard to local blood flow

• Explain the forces that act to influence capillary exchange• Identify the principal arteries and veins of the cardiovascular system:

You will be responsible for arteries and veins up to the level of the wrist and ankle, to each organ and to the brain (to and including the circle of Willis). If you begin early and review often, then you will find it is not as daunting as it looks. However, there will be little “learning time” during the lectures, so it will be up to you to put in the time.

Regulation of blood pressure

• Central regulation (CVC)• Autorgulaion (local factors)

Cardiovascular Control Center (CVC)The neural center that oversees changes in blood

vessels diameter is the vasomotor center

Vasomotor center in medulla

Pressor area - increases BPvia vasoconstriction

Depressor area - decreases BPby inhibiting nerves causing

vasoconstriction

Cardioaccleration center -Increases HR (is activated whenthe pressor area is stimulated)

Cardioinhibitory center - depresses heart activity(is

associated with vagus nerve)

Local factors: blood levels of H+, O2, CO2

Body temperature

Baroreceptors (pressure- sensitive mechanoreceptors) monitor chronic and acute BP changes; respond to arterial

BP changes, stretch,mechanicaldeformation

Vasomotor activity is regulated mainly by:

Baroreceptors -located in carotid sinus and aortic arch and in the walls of arteries, veins, and right atrium

Regulation of blood pressure

Regulation of Blood Pressure and Tissue Circulation

Neural control centers

Local tissue metabolism

Muscle afferents

Hormonal control

Regulation of blood pressure

Short term regulation1.Neural controls – changes in peripheral

resistance2.Hormonal controls – changes in peripheral

resistance

Long term regulation1.Hormonal control – changes in blood volume 2.Renal control – changes in blood volume

Neural control – 2 main goals:1)Maintaining adequate MAP by regulating blood vessel

diameter

2)Altering blood distribution to respond to specific

demandsof various organs

Most of neural control operates via: •baroreceptors and associated afferent fibres•the vasomotor center of the

medulla •vasomotor fibres innervate

vascular smooth muscle,

(mainly smooth muscles of the arterioles are controlled)

Short-term mechanism:Neural controls

Moment-to momentBP regulation

CO

BP = CO x TPR

TPR

Neural Control

Blood flow is tightly coupled to oxygen demand

Sympathetic stimuli result in: • Vasodilation of blood vessels in the heart and

skeletal muscles, thus, increased blood flow to these organs

• Vasoconstriction of blood vessels in the skin and abdominal organs

• Vasoconstriction of veins

Neural regulation of contraction• Different autonomic nerves serving smooth

muscle release different neurotransmitters

The effect of a specific neurotransmitter depends on the type of receptors

Some smooth muscle cells do not have nerve supply!!!!

They respond to other stimuli such as hypoxia, low pH, etc.

• Most postganglionic sympathetic neurons release norepinephrine (noradrenaline) which combines with -adrenergic receptors on smooth muscle in blood vessel walls, causing vasoconstriction

What would this do to blood pressure?What would this do to blood pressure?

• Blood vessels of the heart and skeletal muscle contain -adrenergic receptors; sympathetic stimulation of these receptors causes vasodilation

• This control system ensures that the heart and the active skeletal muscles receive adequate blood flow during stress

Neural Control of Blood Flow

Parasympathetic stimuli • Cause vasodilation of blood vessels in the digestive

tract and reproductive organs, by releasing acetylcholine, which inhibits smooth muscle contraction

Some sympathetic neurons are cholinergic (release acetylcholine) and cause vasodilation of blood vessels in skeletal muscle

Figure 19.8 top

Barororeceptor reflexes that help maintain BP

Figure 19.8 bottom

Barororeceptor reflexes that help maintain BP

The Autonomic Nervous System and Cardiovascular Function

Sympathetic HR (1 receptors)

Cardiac contractility (1 receptors)

• Vasodilation of coronary arteries (2

receptors) and skeletal muscle arteries• Mild vasodilation of pulmonary vessels

(2)• Vasoconstriction in abdomen, kidneys

and skin blood vessels muscle ()• Vasodilation in muscle and skin

(cholinergic)

SymbolsSymbols

- vasoconstriction

2 - vasodilation

1- vasoconstiction

The Autonomic Nervous System and Cardiovascular Function

Parasympathetic

HR

strength of atrial contraction (vagal innervation of atria but not ventricles)

• modest vasodilation of coronary arteries

Chemoreceptors (chemical sensors)

• Located close to aortic and carotid barorecepetors in aortic and carotid bodies

• Monitor blood-borne substances (O2, CO2, [H+])

• Increase respiration in order to increase CO2 output and O2 intake

• Increase BP by sending afferent signals via glossopharyngeal (IX) and vagus (X) nerves to the cardiovascular acceleratory center in response to [O2] or [CO2] or [H+]

Regulation of blood pressure

Short term regulation1.Neural controls – changes in peripheral

resistance2.Hormonal controls – changes in peripheral

resistance

Long term regulation1.Hormonal control – changes in blood volume 2.Renal control – changes in blood volume

Short-term mechanism: Hormonal Controls

Vasoconstrictors:Vasoconstrictors:• Catecholamines (norepinephrine and epinephrine) - from

adrenal medulla -vasoconstriction at -adrenergic receptors

• Vasopressin (ADH) - produced by hypothalamus, stored in

posterior pituitary

• Renin - Angiotensin II system angiotensin II

• Serotonin, released in response to blood vessel injury, causes arteriolar constriction

Short-term mechanism: Hormonal Control of BP

Vasodilators:Vasodilators:• Histamine, released by eosinophils and mast

cells in most tissues• Atrial Naturetic Peptide (ANP) produced by

the heart• Bradykinin, vasodilator in tissues such as

blood• Catecholamines, vasodilators at 2-adrenergic

receptors• Prostacyclin, vasodilator in several vascular

beds

Long term regulation of BPHormonal Control

Left atrial volume receptors and hypothalamic osmoreceptors:

• Help regulate salt and water balance• Control BP through blood volume

Hormones:• Renin-angiotensin system aldosterone• Vasopressin (ADH) • Epinephrine and norepinephrine from the adrenal

medulla ( CO but not volume per se) • ANF (Atrial Naturetic Factor) = ANP (peptide)

Table 19.2

Renin

Angiotensinogen

Angiotensin I

Angiotensin II

ACE*

* ACE - angiotensin convertingenzymes

Thirst

Sites of Thirst and ADH Release in Hypothalamus

Small changes in plasma osmolality are more effective

than small changes in blood pressure and volume in stimulating

ADH release

Thirst = the conscious desire for water

The release of AVP occurs beforethe sensation of thirst!!!

ADH involvement in BP Control: volume effect

The Role of ANP in the Regulation of Blood Pressure

RAP = Right Atrial Pressure

HCT =Hematocrit

UNaV = Urine sodium Excretion (Natriuresis)

UV = Urine volume(Diuresis)

ANP: •generalized vasodilation•antagonizes aldosterone and ADH actions• antagonizes epinephrine• sodium and water loss from the body

Figure 19.9

Long-term mechanism:Renal regulation of Blood Pressure

An increase in blood volume is followed by a rise in BP and stimulateskidneys to eliminate water via:• direct mechanism – independent of hormones

• indirect mechanism – hormone-dependent

Figure 19.11

Activity ofmuscularpump andrespiratory

pump

Releaseof ANP

Fluid loss fromhemorrhage,

excessivesweating

Crisis stressors:exercise, trauma,

bodytemperature

Bloodbornechemicals:

epinephrine,NE, ADH,

angiotensin II; ANP release

Body size

Conservationof Na+ and

water by kidney

Blood volumeBlood pressure

Blood pH, O2, CO2

Dehydration,high hematocrit

Bloodvolume

Baroreceptors Chemoreceptors

Venousreturn

Activation of vasomotor and cardiacacceleration centers in brain stem

Heartrate

Strokevolume

Diameter ofblood vessels

Cardiac output

Initial stimulus

Result

Physiological response

Mean systemic arterial blood pressure

Bloodviscosity

Peripheral resistance

Blood vessellength

Measuring Pulse Rate and Arterial BP

Arterial Pulse• Produced when the left ventricle forces blood against the

wall of the aorta. The impact creates a pressure wave along the branches of the aorta and the rest of the arterial walls

• Corresponds to the beating of the heart• All arteries have a pulse, but you can palpate a pulse at

certain landmarks better than others• The radial artery is the most common site to take a pulse -

use the middle fingers!!!!

• Pressure wave due to alternating expansion & recoil of elastic arteries

• Pressure points (push surface artery against firm tissue, usually radial artery)

Fig. 19.11

sln.fi.edu/biosci2/ monitor/inline/pulse.gif

Taking a pulse

The Procedure of Taking the Radial Pulse (a) and the Carotid Pulse (b)

• Tachycardia - pulse rate > 100 bpm• Bradycardia - pulse rate < 60 bpm• Pulse rate after severe blood loss, exercise, or eating----

WHY?

Venous PulseVenous Pulse• Only occurs in the largest veins• It is a reflected pulse produced by the changes in pressure

that accompany atrial contractions

Systolic BPThe highest force with which blood pushes against arterial walls as a result of ventricular contraction

Systolic pressure reflects the force of ventricular contraction

Diastolic BPThe lowest force with which blood pushes against arterial walls as a result of ventricular relaxation

Provides information about systemic vascular resistance

Blood pressure is expressed as systolic/diastolic

(in mmHg

Measuring BP• Auscultatory method using sphygmomanometer (brachial artery)

• Cuff fully inflated (artery fully collapsed »» no flow)

•Cuff pressure lowered to < peak systolic pressure (momentary high velocity spurt) »» record cuff pressure as systolic BP

•Cuff pressure lowered to < diastolic pressure (continuous flow - sounds disappear) »» record cuff pressure as diastolic pressure

i

Measurement of Arterial BP

Blood Pressure mm Hg

• Normal BP = 120/80 mm Hg• High normal = 130-139/85-89• Mild hypertension (high BP) = 140-159/90-99• Moderate hypertension = 160-179/100-109• Severe hypertension = 180-209/110-119• Very severe (morbid) hypertension = >209/120• Hypotension <90/40• Shock <80/40• Prevalence of hypertension increases with age(4% at 18-20 y, 44% at 50-59y, 65% at 80+ y)

Factors influencing BP

BP is influenced by age, gender, weight, race, stress, nutrition, mood, posture, fitness level, etc..

Blood Pressure During Exercise• Systemic BP is affected mostly by increased CO• There is a linear in systolic BP with levels of

exercise (Max systolic BP should not > 260 mm Hg)• Diastolic BP either remains unchanged or slightly*• Pulse pressure usually with the intensity of exercise• BP reaches a steady-state during sub-maximal steady-

state exercise• With prolonged exercise systolic BP will start

decreasing, diastolic will remain constant ( in systolic BP reflects dilation of vessels)

• Resistance exercise BP, it may temporarily reach 480/350 mm Hg!!!!!

Figure 19.12

Distribution of blood flow during exercise

Autoregulation: Local regulation of blood flow

Autoregulation = Local adjustment of blood flow to a given tissue metabolism due primarily to chemical (metabolic) and physical factors in that area

Local factors causing vasodilation include:• Decreases in O2 or nutrient levels• Increases in CO2 levels in that area• Decrease in pH• Increases in adenosine, lactic acid, cAMP, cGMP,

K+, heat, inflammatory chemicals and nitric oxide (NO)

Autoregulation: Local regulation of blood flow cont.

Response to accumulation of local metobiltes: immediate vasodilation in “needy” tissues (relaxation of precapillary sphincters) active or reactive hyperemiaactive or reactive hyperemia

Long-Term Autoregulation:

• Eg: increases in number/ diameters of tissue blood vessels, e.g., when coronary vessels become occluded, in response to regular exercise or living at high altitude

Myogenic Controls (Local!):

• vascular smooth muscle responds to increased stretch with increased tone »» stretch is resisted »» vasoconstriction

• decreased stretch results in vasodilation

• result: tissue perfusion homeostasis so cells not deprived/capillaries not damaged

Fig. 19-10 (R&P)

Myogenic AutoregulationPhysical

Active Hyperemia - Chemical

Myogenic controlBoth physical (myogenic) and chemical(metabolic) factors determine final autoregulatory response in tissues

Figure 19.14

Summary of control of arteriolar smooth musclein the systemic circulation

DilateConstrict

Exchange of nutrients, wastes and gasses

Mechanisms for exchange

• Diffusion (a passive process)• Vesciular transport (endocytosis and

exocytosis) • Bulk flow (filtration and absorption) - a

movement of a fluid (liquid or gas) from region of higher pressure to one of lower pressure (a passive process)

Figure 19.15

Capillary transport mechanism

Routes of exchange:

• Diffusion or active transport of some small molecules through endothelial membranes

• Diffusion through intercellular clefts (pores);most substances including water, small hydrophilic molecules

• Passage of large molecules through endothelial fenestrations (little windows)

• Passage of some larger molecules through endothelial tissue via pinocytic vesicles

J. Carnegie, UofO

Capillary Exchange Mechanisms: examplesVesicle Transport:

• for relatively large, lipid-insoluble molecules (e.g., insulin)

• shuttling via endocytosis, then exocytosis

• also antibody molecules from maternal to fetal circulation

Diffusion:• primary mechanism for dissolved solutes & gases; eg: O2, CO2, glucose• follow gradients• heat moves via convection down a thermal gradient• water-filled pores (Na+. K+, Cl-, glucose) or through bilayer (O2, CO2, urea)• pores <1% capillary SA; lipid-soluble substances have 100X more SA

http://www.skcc.org/n_images/transcytosis.jpg

Fluid exchange

~ 20 L of fluid are filtered out of capillaries each day before returning to blood

Fluid exchangeAs blood flows through a capillary, the blood hydrostatic pressure (BHP = HP) tends to push fluid out through the capillary pores

The blood colloid osmotic pressure (BCOP = OP) tends to pull water from the interstitial fluid into the capillary

There is a very small interstitial fluid osmotic pressure (IFOP) that tends to move fluid out of the capillaries into the interstitial fluid

NEF = the difference between BHP and BCOP

Net filtration pressure (NFP) – shows direction of fluid movement

Fluid exchangeThe formula for calculating NFP:

NFP = [HPC – Hpif] – [OPC – OPif]Example: when HPC = 35 mmHg at the arterial end of capillary and 17 mmHg at the venous end;

OPC=26mmHg and OPif =1 mmHg; unlike HP, OP does not vary from one end of capillary to the other

Thus, net osmotic pressure that pulls fluid back to capillary is OPC – Opif =

= 26 mmHg – 1mmHg = 25 mmHg

NFP = (35 - 0) – (26 – 1) = 10 mmHg• The net force at the arterial end = 10 mm Hg forcing plasma out of capillary by a process called

filtration• The net force at the venous end is equal to (17-0)-(26-1) = -8 mmHg, pulling water back into the

capillary by osmosis• As a result of this exchange, a constant flow of interstitial fluid washes over the tissue cells, supplying O 2 and

nutrients and carrying away CO2 and wastes

Fluid flows at capillaries

HP = hydrostatic pressure OP = colloid osmotic pressure

NFP = Net Filtration Pressure

Figure 19.17

Paths of Circulation

A. Pulmonary Circuit = the vessels that carry blood from the right ventricle to the lungs, and the vessels that return blood to the right atrium

(i) pulmonary trunk(ii) Right and left pulmonary artery(iii) Capillaries in the lungs(iv) Right and left pulmonary veins

B. Systemic Circuit = the vessels that carry blood from the heart to body cells and back to the heart

1. Arterial System2. Venous System

The Coronary Arteries

Note the anastomoses between the coronary arteries. This is an interarterial anastomosis which provides collateral circulation to different parts of the myocardium. The fact that the coronary arteries fill during ventricular diastole allows them to overcome the resistance which would be too great during ventricular systole.

Note the anastomoses between the coronary arteries. This is an interarterial anastomosis which provides collateral circulation to different parts of the myocardium. The fact that the coronary arteries fill during ventricular diastole allows them to overcome the resistance which would be too great during ventricular systole.

Coronary arteries originate behind aortic semilunar valve: fill during ventricular diastole

Interarterial anastomosis –a connection betweenarteries that providescollateral circulation todifferent areas of themyocardium

Fig. 19.4b

Major Arteries of the Systemic Circulation

Aortic arch

Descending aorta

Thoracic aorta

Bronchial arteryPericardial arteryEsophageal arteryMediastinal artery

Posterior intercostal artery

Abdominal aorta

Celiac arteryPhrenic arterySuperior mesentric arterySupra renal arteryRenal arteryGonadal arteryInferior mesenteric arteryLumbar arteryMiddle sacral arteryCommon iliac artery

Left side of head& left upper limb

right side of head& right upper limb

Arteries of the head, neck and brain

Fig 19.5d

The Circle of Willis

- provides collateral circulation to the brain

Arteries of the Upper limb and Thorax

Arteries of the Abdomeno

rgan

s o

f u

pp

er

dig

esti

ve t

ract

Arteries of the pelvis and lower limb

The Aorta and Its Principal Branches

Portion of Aorta Major Branch

General Regions/organs supplied

Ascending aorta

Arch of aorta

Rt & lt coronary artery

Heart

Brachiocephalic artery

rt upper limb,rt side of head

Lt common coratid artery

Lt side of the head

Lt subclavian artery

lt upper limb

Descending aortaThoracic aorta

Esophageal artery

Mediastinal artery

Posterior intercostal artery

Bronchial artery

Pericardial artery

Bronchi

Pericardium

Esophagus

Mediastinum

Thoracic wall

Portion of Aorta Major Branch

General Regions/organs supplied

Abdominal aorta

Celiac artery

Superior mesentric artery

Phrenic artery

Supra renal artery

Renal artery

Gonadal artery

Inferior mesenteric artery

Lumbar artery

Middle sacral artery

Common iliac artery

Organs of upper digestive tract

Diaphram

Portions of small & large intestine

Adrenal gland

kidney

Ovaries & testis

Lower portions of large intestine

Posterior abdominal wall

Sacrum and coccyx

Lower abdominal wall, pelvic organs & lower limbs

Venous System

Veins that return blood to the heart after gas, nutrient and waste exchange, usually follow pathways that are parallel to the arteries.

Some exceptions:(i) Jugular veins (head)-external jugular (face and scalp)-internal jugular (brain)

(ii) Median cubital vein (venipuncture site)

(iii) Subclavian vein + jugular = brachiocephalic veins on each side

(iv) Superior vena cava: union of brachiocephalic veins (head and upper limbs)

(v) Coronary sinus (cardiac veins)(vi) Cardiac veins (caps of the myocardium)

(vii) Hepatic Veins (drain the Hepatic Portal System)

(viii) Great Saphenous vein= longest vein in the body, extends from the medial ankle to the external iliac vein

(ix) Inferior vena cava (drain from the abdominal & lower limb)

All coronary veins empty into the coronary sinus, which enters the rightatrium directly, without going through either the inferior or superior venacave. This is the only systemic venous drainage which does this. Notethe anastomosis of these veins as well

All coronary veins empty into the coronary sinus, which enters the rightatrium directly, without going through either the inferior or superior venacave. This is the only systemic venous drainage which does this. Notethe anastomosis of these veins as well

To right atrium

The Coronary Veins

Major Veins of the Systemic Circulation

Veins of the head and Neck

Veins of the upper limb and thorax

Veins of the Abdomen

Large Intestine

Spleen

Small Intestine

Hepatic artery

Hepatic Portal Systemtakes blood from the spleen , stomach, small and large intestine to the liver before it enter general circulatiom

Hepatic Portal Systemtakes blood from the spleen , stomach, small and large intestine to the liver before it enter general circulatiom

Veins of the Pelvis and Lower Limbs