CIRCULATORY

SYSTEM

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Lector:

Associate professor, Kononenko A.G.2019 year

National University of Pharmacy

Department of Human Physiology and Anatomy

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PLAN

1. Circulatory system. Functions.

2. Circles of blood circulation. The factors causing the movement of

blood through the vessels.

3. The structure of the blood vessels. Classification by function.

4. Patterns of blood movement. The basic law of hemodynamics.

5. Blood flow characteristics: linear rate, circulatory time, etc.

6. The movement of blood through the veins. Factors contributing to it.

7. Arterial pressure. Types, factors. Measurement methods.

8. Arterial pulse. Properties, characteristics.

9. Regulation of vascular tone. Vasodomotor center: autoregulation,

nervous, humoral and reflex regulation.

10. Microcirculation.

Questions for individual work:

1. Physiological features of the blood flow (waves of the first,

second and third order).

2. Coronary blood circulation.

3. Portal circulation.

4. Microcirculation. Transcapillary exchange.

5. Types of blood capillaries, their structure.

6. Lymphatic system.

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Hemodynamics is a section of hydrodynamics that studies

the patterns of blood flow through vessels

Functions of the blood

circulation system

continuous blood flow through a

closed system of blood vessels

providing organ and body

systems with nutrients, oxygen and

BAS

HEMODYNAMICS

Systemic hemodynamics - the movement

of blood in the heart and trunk vessels

Regional or organ hemodynamics - blood

supply to organs

Microcirculation or tissue hemodynamics

- blood supply to tissues, movement of

blood in smallest vessels

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The cardio-vascular system

Heart Vessels

Blood Lymphatic

BIG CIRCLE CIRCULATIONS (CORPORAL).Begins an aorta which departs from a leftventricle. The aorta gives rise to large, average andfine arteries. Arteries pass in arterioles which cometo an end with capillaries. Capillaries pass in thevenules which blood collects in fine, average andlarge veins. Blood from the top part of a trunkarrives in the top vena cava, from inferior - in theinferior vena cava. Both these veins run into theright atrium in which the big circle of a circulationcomes to an end.

The blood circulating on the big circle of acirculation, provides all cells of an organism withoxygen and nutrients and carries away from themmetabolic products.

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CIRCLES OF CIRCULATION

Blood locomotion in an organism descends on two closed systems of the pots

bridged to heart, - to the big and small circle of a circulation.

SMALL CIRCLE CIRCULATIONS

(PULMONARY).

Begins a pulmonary trunk which departs from a

right ventricle and carries in lungs a venous

blood. The pulmonary fulcrum branches on two

branches going to the left and right lung. In

lungs pulmonary arteries share on finer arteries,

arterioles and capillaries. Pulmonary capillaries

pass in venules which then form veins. On four

pulmonary veins the arterial blood arrives in the

left atrium.

The role of a small circle of a circulation consists

that in lungs restoration (neogenesis) of gas

structure of blood is carried out.

CIRCLES OF CIRCULATION

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Classification of blood vessels

1. Arteries

2. Arterioles

3. Capillaries

4. Venules

5. Veins

Functions of blood vesselsProvide movement on an organism of a blood and the lymph,

containing:

1. Nutrients

2. BAS

3. Gases (О2 and СО2)

4. Metabolites

Types of arteries

and arterioles

Elastic

Muscular

Muscular-elastic

Types of capillaries

Continuous

Fenestrated

Sinusoids

Types of venules

Postcapillary

Collective

Muscular

Types of veinsSuperficial

Deep

Classification of blood vessels

GENERALIZED STRUCTURE OF

BLOOD VESSELS

Arteries and veins are composed of three tunics – tunica interna,

tunica media, and tunica externa

Lumen – central blood-containing space surrounded by tunics

Capillaries consist of the endothelial layer surrounded by a basement

membrane with occasional smooth muscle fibers.

Structure of the blood vessel wall

Structural and functional organization of the vessel wall

Layer Characteristic

Tunica intima

(endothelium)

The inner, smooth surface of the vessels, consisting of a single

layer of flat cells, the main membrane and the inner elastic plate

Tunica media Consists of several interpenetrating muscle layers between the

inner and outer elastic plates

Elastic fibers Located in the inner, middle and outer layers and form a relatively

dense network, easily stretch and create elastic tension

Collagen fibers They are located in the middle and outer layers, form a network

that provides the tensile strength of the vessel with much more

resistance than elastic fibers, but, having a folded structure, they

counteract the blood flow only if the vessel is stretched to a

certain extent.

Smooth muscle

cells

They form the middle layer, are connected with each other and

with elastic and collagen fibers, create active tension of the

vascular wall (vascular tone)

Tunica externa

(adventitia)

The outer layer of the vessel consists of loose connective tissue,

fibroblasts, mast cells, nerve endings, and in large vessels also

includes small blood and lymphatic capillaries, depending on the

type of vessels has different thickness, density and permeability

TYPES OF ARTERIES

Elastic arteries. Thick-walled arteries near the heart – the aorta and its major

branches. Contain a high percentage of elastic fibers in all three of their tunics.

Their abundant elastic fibers allow them to expand, as blood pumped from the

ventricles passes through them, and then to recoil after the surge has passed.

Muscular arteries – distal to elastic arteries; deliver blood to body organs. Have

thick tunica media. Elastic fibers in an artery’s tunica intima decreases and the

amount of smooth muscle in its tunica media increases. Active in vasoconstriction.

Arteriole is a very small artery that leads to a capillary. Arterioles have the same

three tunics as the larger vessels, but the thickness of each is greatly diminished.

The critical endothelial lining of the tunica intima is intact. The tunica media is

restricted to one or two smooth muscle cell layers in thickness. The tunica externa

remains but is very thin.

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CAPILLARIES

A capillary is a microscopic channel that supplies blood to the tissues

themselves, a process called perfusion.

The wall of a capillary consists of the endothelial layer surrounded by a

basement membrane with occasional smooth muscle fibers. There is

some variation in wall structure: In a large capillary, several endothelial

cells bordering each other may line the lumen; in a small capillary,

there may be only a single cell layer that wraps around to contact itself.

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TYPES OF CAPILLARIES

Continuous – is found in almost all vascularized tissues. Continuous

capillaries are characterized by a complete endothelial lining with tight

junctions between endothelial cells.

Substances that can pass between cells include metabolic products,

such as glucose, water, and small hydrophobic molecules like gases and

hormones, as well as various leukocytes.

This is found in skin and muscle, sort of like a standard issue capillary.

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Fenestrated capillary is one that has pores (or fenestrations) in addition to

tight junctions in the endothelial lining. These make the capillary permeable

to larger molecules. The number of fenestrations and their degree of

permeability vary, however, according to their location.

Fenestrated capillaries are common in the small intestine, kidneys. They are

also found in the choroid plexus of the brain and many endocrine structures,

including the hypothalamus, pituitary, pineal, and thyroid glands.

TYPES OF CAPILLARIES

Sinusoid capillary (or sinusoid) is the least common type of capillary.

Sinusoid capillaries are flattened, and they have extensive intercellular gaps

and incomplete basement membranes, in addition to intercellular clefts and

fenestrations. This gives them an appearance not unlike Swiss cheese.

These very large openings allow for the passage of the largest molecules,

including plasma proteins and even cells.

Sinusoids are found in the liver and spleen, bone marrow, lymph nodes

(where they carry lymph, not blood), and many endocrine glands including

the pituitary and adrenal glands.

TYPES OF CAPILLARIES

CAPILLARY BED

Capillary beds – networks of capillaries serving the cells of a tissue. The

capillary beds branch off of a Metarteriole, which is a tiny arteriole that

connects a terminal arteriole with a venule. The venous end of the

metarteriole is called a Thoroughfare Channel. The capillaries branch off

of the arterial end of the metarteriole, then remerge into the thoroughfare

channel, to enter the venule. At the metarteriole end, there are precapillary

sphincters (muscular valves) leading to each capillary. If these sphincters

are closed, much blood will bypass the capillary bed and go straight to the

venule.

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CAPILLARY EXCHANGE

Only occurs across capillary walls

between blood and surrounding tissues

3 routes across endothelial cells

intercellular clefts

fenestrations

through cytoplasm

Mechanisms involved diffusion,

transcytosis, filtration and reabsorption

VENOUS SYSTEM: VENULES

Venule is an extremely small vein, generally 8–

100 micrometers in diameter. Postcapillary

venules join multiple capillaries exiting from a

capillary bed.

The walls of venules consist of endothelium, a

thin middle layer with a few muscle cells and

elastic fibers, plus an outer layer of connective

tissue fibers that constitute a very thin tunica

externa.

Venules are the primary sites of emigration or

diapedesis.

Large venules have one or two layers of smooth

muscle (tunica media)

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VENOUS SYSTEM: VEINS

Veins are formed when venules converge.

Composed of three tunics, with a thin tunica

media and a thick tunica externa consisting of

collagen fibers and elastic networks

Capacitance vessels (blood reservoirs) that

contain 65% of the blood supply

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Comparison of tunics in arteries and veins

Arteries Veins

General

appearance

Thick walls with small lumens;

Generally appear rounded

Thin walls with large lumens;

Generally appear flattened

Tunica

intima

Endothelium usually appears wavy due

to constriction of smooth muscle;

Internal elastic membrane present in

larger vessels

Endothelium appears smooth;

Internal elastic membrane absent

Tunica

media

Normally the thickest layer in arteries;

Smooth muscle cells and elastic fibers

predominate (the proportions of these

vary with distance from the heart);

External elastic membrane present in

larger vessels

Normally thinner than the tunica

externa; Smooth muscle cells and

collagenous fibers predominate;

Nervi vasorum and vasa vasorum

present; External elastic membrane

absent

Tunica

externa

Normally thinner than the tunica media

in all but the largest arteries;

Collagenous and elastic fibers; Nervi

vasorum and vasa vasorum present

Normally the thickest layer in veins;

Collagenous and smooth fibers

predominate; Some smooth muscle

fibers; Nervi vasorum and vasa

vasorum present

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Comparison of tunics in the blood vessels

Comparison of tunics in the blood vessels

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BLOOD VESSELS FUNCTIONS

Artery functions:

Transport and distribution of blood throughout the body

Maintaining blood pressure to ensure blood flow through the

capillaries

The volume of blood that fills the arterial system does not exceed

10-15% of the total circulating blood

Veins functions: return of blood from the tissues to the heart

Veins hold 70-80% of all circulating blood.

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Capillary functions:

the exchange of nutrients, gases, metabolic productsbetween blood and tissue cells;

delivery of water, minerals, nutrients, oxygen from thedigestive system, respiratory system to the organs andtissues of the body;

Removal of end products of metabolism from organs andtissues to excretory systems;

heat distribution in the body;

BLOOD VESSELS FUNCTIONS

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FUNCTIONAL TYPES OF VESSELS

1. Magistral (aorta, pulmonary arteries) – the transformation

of a pulsating blood flow into a uniform

2. Resistive (arterioles, end arteries) – change the diameter

and create resistance to blood flow due to the layer of muscle

fibers

3. Sphincters (precapillary arterioles) – limit or increase the

area of the exchange surface of the capillaries

4. Metabolic (capillaries) – thin walls provide transcapillary

exchange

5. Capacictance (veins) – high stretch provides the ability to

store or throw out large amounts of blood

6. Arterio-venous anastomoses – provide the transition of

blood from arterioles to venules, bypassing the capillaries

CIRCULATION ROUTES: ANASTOMOSES

Arterio-venous shunt: blood flows

from artery directly to vein. Located in

fingers, toes, ears; heat loss, allows

blood to bypass exposed areas during

cold

Venous anastomosis: more common;

alternate drainage of organs

Arterial anastomosis: collateral

circulation

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Blood flow in vessels

R depends on:

R

PPQ 21

Q – quantity of a blood;

P1 – P2 – pressure in the beginning and in the end of a vessel;

R – resistance to flow.

1) Number of vessels

2) Blood viscosity

3) Vessel length: pressure and flow decline with distance

4) Vessel radius – very powerful influence over flow; most

adjustable variable, controls resistance quickly (vasomotion:

change in vessel radius)

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BASIC HEMODINAMICS LAW

R

PPQ 21

The amount of blood flowing per unit

of time through the circulatory

system is the greater, the higher the

pressure difference in its arterial and

venous ends and the less resistance to

blood flow from the vessels

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CHARACTERISTICS OF HEMODYNAMICS

Volume rate of a blood flow

Linear rate of a blood flow

Pulse wave propagation speed (Vп):

in vessels of an elastic type = 7-10 m/sec

in vessels of a muscle type = 5-8 m/sec

Time of blood circulation: 27 systoles or 20-23 sec

in a small circle: 1/5 of the time

In a large circle: 4/5 total time

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Volume rate of a blood flow is quantity of a blood (in ml),

proceeding through cross section of vessels per 1 minute.

V – volume rate of a blood flow;

P – a difference of average pressure;

R – hydrodynamic resistance.

R

P=Q

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Linear rate of blood flow (V) – is rate of flowing

of a blood along a vessel, depends on volume rates of

a blood flow (Q), divided on the area of section of a

blood vessel.

2r

QV

Linear rate depends on:

1) type

2) size

vessels

Different departments are different:

arteries – 20-25 cm/sec

capillaries – 0.03-0.05 cm/sec

venules – 0.07 cm/sec

veins – 1.3 cm/sec

vena cava – 20-33 cm/sec

Laminar blood flow – the movement of blood by cylindrical

layers.

Blood cells are formed in the central, axial flow, in which red

blood cells are located in the center, and the plasma moves

near the vascular wall. The smaller the vessel diameter, the

closer the formed elements are to the vascular wall and the

more inhibited the movement of blood.

Turbulent blood flow is motion with

characteristic twists. Such movement of

blood occurs in places of branching or

narrowing of the arteries, in areas of the

bends of blood vessels. This creates

additional resistance for the movement of

blood in the vessels.

GEOMETRICAL AND HYDRODYNAMIC

CHARACTERISTICS OF VASCULAR TONE

VesselDiameter,

cm

General

number in

the organism

Length,

cm

Speed of blood

flow,

cm/sec

Aorta 1,6-3,2 1 80 ~50

Large arteries 0,6-0,1 103 40-20 13

Small arteries,

arterioles

0,1-0,02 108 5-0,2 6-8

Capillaries 0,0005-0,001 109 0,1 0,3

Venules, small

veins

0,02-0,2 108 0,2-1,0 0,07-1,3

Large veins 0,5-1,0 103 10-30 3,6

Vena cava 2,0 2 50 33

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1. Stretching of an aorta and large arteries;

2. Formation of the elastic chamber;

3. Transition of kinetic energy in energy of elastic resistance.

Properties of an arterial vessel wall provide

transformation of a pulsing blood flow to

the constant:

Blood pressure is the pressure of circulating

blood on the walls of blood vessels

Provides:

• Blood circulation

• Optimal blood supply to organs and tissues

• Formation of tissue fluid in the capillaries

• Secretion and excretion processes

Depending on the type of vessel distinguish pressure:

Arterial

Venous

Capillary

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1. Working of heart during

a systole, and a diastole.

Arterial pressure is the pressure of blood on the

walls of arteries.

Factors

define influence

2. Resistance of vessels

depends on:

- Elasticity,

- Conditions of a smooth

muscular tissue.

1. Sex

2. Age

3. Kind of activity

4. Atmospheric pressure

5. Weight, ect.

3. Volume of a blood.

4. Viscosity of a blood.

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Methods of measuring

of arterial pressure

The direct

(bloody)

The indirect

(Bloodless,

Korotkov's method)

The indirect method is called so because we

are measured of a AP on resistance which is

produced by a wall of an arterial vessel to

pressure which is produced in a rubber cuff.

MEASURING BLOOD PRESSURE

Systemic arterial BP is measuredindirectly with the auscultatory method.

A sphygmomanometer is placed on thearm superior to the elbow

Pressure is increased in the cuff until it isgreater than systolic pressure in thebrachial artery

Pressure is released slowly and theexaminer listens with a stethoscope

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The first heard sound is recorded as

the systolic pressure

The pressure when sound disappears

is recorded as the diastolic pressureThe tonometer consists of:

1. An aerotonometer;

2. A rubber pear;

3. Rubber cuff;

4. A stethoscope.

TYPES OF ARTERIAL PRESSURE

1. Systolic (maximum) pressure – pressure exerted on

arterial walls during ventricular contraction

110-125 mm Hg

2. Diastolic (minimum) pressure – lowest level of arterial

pressure during a ventricular cycle

60-80 mm Hg

3. Pulse pressure – a difference between systolic and diastolic

pressure

35-50 mm Hg

4. Mean arterial pressure (MAP) – pressure that propels

the blood to the tissues

MAP=Diastolic pressure + 1/3Pulse pressure

90-95 mm Hg

CAPILLARY BLOOD PRESSURE

Capillary BP ranges from 20 to 40 mm Hg

Low capillary pressure is desirable because high BP would rupture

fragile, thin-walled capillaries

Low BP is sufficient to force filtrate out into interstitial space and

distribute nutrients, gases, and hormones between blood and tissues

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VENOUS BLOOD PRESSURE

Venous BP is steady and changes little during the cardiac cycle

The pressure gradient in the venous system is only about 20 mm Hg

A cut vein has even blood flow; a lacerated artery flows in spurts

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Arterial pulse – rhythmic fluctuations of a wall the arteries

caused by rising of pressure in a systole of a left ventricle.

Graphic registration of pulse fluctuations is

measured on a sphygmometer.

A - anacrote;

C - catacrote

DN - dicrotic notch.

Anacrote –A – rising part: AP is increased;

Stretching of a wall of an artery.

Catacrote – C – descending part: Pressure is

decreased in the end of a ventricle systole.

Dicrotic notch – stroke of blood on the semilunar

valves on the curve

А

C

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Pulse are measured by a palpation on a radial artery.

MEASURING OF PULSE

PULSE PROPERTIES

1. Frequency (normal or frequent) – the number of beats

per minute (normal about 70)

2. Rhythmicity (rhythmic or arrhythmic) – correctness of

alternation of pulse attacks

3. Filling – the degree of change in artery volume, which

is determined by the power of pulse attack

4. Tension (hard or soft) – the force to be applied to

arrhythmic artery to the complete disappearance of the

pulse (solid or soft)

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Blood movement in veins

The factors defining movement of a blood on venous vessels:

1. Heart function (provides pressure difference in arteries

and right atrium)

2. Valves of the endothelium of the veins (ensure the

movement of blood in one direction - to the heart)

3. The suction of the chest

4. Contraction of skeletal muscles – movement of blood to

the heart, relaxation – transfer of blood from the arterial

system to the venous

Venous Valves

• Venous valves are hinge-like flaps formed from folds of the tunica

intima.

• Venous valves are most abundant in the veins of the limbs, where

upward flow of blood is opposed by gravity.

• The one-way valves prevent backflow as blood travels toward the heart.

Muscular Pump

• In the muscular pump, contracting skeletal muscles press against veins,

forcing blood through one-way valves. Gravity drains blood from head

and neck

Respiratory Pump

• Pressure changes occurring in the ventral body cavity during breathing

create the respiratory pump that sucks blood upward towards the heart.

• As we inhale, pressure in the thoracic cavity decreases. Meanwhile

pressure increases in the abdominal cavity, squeezing abdominal veins.

These create an sucking effect that pulls blood toward the heart.47

MECHANISMS OF VENOUS RETURN

SKELETAL MUSCLE PUMP

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CONTROL OF BLOOD PRESSURE AND

BLOOD FLOW

Neural control

Hormonal control

Local control (autoregulation)

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NEURAL CONTROL

1. Sympathetic division influences the diameter of arteries; parasympathetic fibers do

not innervate the smooth muscle of vessels. Vasomotor tone refers to the fact that

sympathetic fibers are always "active" at vessels. Under "normal" conditions, the diameter

of a vessel is about half its total possible diameter, because of input by sympathetic fibers.

Most sympathetic postganglionic fibers secrete NE. Most blood vessels’ smooth

muscle contain alpha-1 adrenergic receptors, which respond to NE and E by

constricting.

Some blood vessels serving skeletal muscle contain beta-2 adrenergic receptors,

which respond to NE and E by relaxing.

Some sympathetic postganglionic fibers secrete Ach (specifically serving skeletal

muscle, brain and sweat glands). Blood vessels containing cholinergic receptors

respond by relaxing.

So, since most sympathetic fibers only release NE, and most blood vessels respond to

NE by constricting, general vasodilation reflects a decrease in sympathetic activity

while general vasoconstriction reflects an increase. However, since vessels that

service the brain and skeletal muscle are served by populations of sympathetic fibers

that release Ach, and since some vessels in these areas respond to NE by relaxing,

vasodilation in these areas reflects an increase in sympathetic activity.50

2. The control of sympathetic activity, as it relates to vessel diameter, involves

communication between the hypothalamus, the cardiovascular centers of the

medulla, and two types of sensory neurons (baroreceptors and chemoreceptors).

The cardiovascular (CV) centers are a cluster of neurons in the medulla that include

the cardiac centers and the vasomotor centers. The cardiac centers control ANS

preganglionic fibers to the heart. The vasomotor centers control ANS preganglionic

fibers to blood vessels.

Baroreceptors involved in blood pressure regulation are located in the Carotid Sinuses

(expansions of the carotid arteries to the brain), the Aortic Sinuses (expansions in the

aortic arch), and the right atrium.

When blood pressure rises in the aortic and carotid sinuses (the walls of the vessels are

stretched), the vasomotor centers are alerted and sympathetic activity is tuned down,

allowing vessels to dilate and pressure to decline. In addition, parasympathetic activity

to the HEART increases, reducing Heart Rate and Cardiac Output. The reverse is true

as well; when pressure declines, sympathetic activity steps up (vessels constrict), and

HR/CO increase

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NEURAL CONTROL

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Chemoreceptors involved in blood flow regulation are located in the

carotid bodies (near carotid sinuses) and aortic bodies (near aortic

arch). When O2 drops or CO2 rises, general sympathetic activity is

initiated, increasing HR and CO, constriction of vessels, and an

increase in respiratory rate. Another population of chemoreceptors is

located in the medulla at the 4th ventricle. These guys monitor pH of

the CSF and have a particularly strong effect on breathing rate. We

will consider the role of those chemoreceptors in more detail when we

get to Respiration.

NEURAL CONTROL

HUMORAL CONTROL

Vasoconstriction

adrenalin

norepinephrine

vasopressin

angiotensin

serotonin

Vasodilation

histamine

acetylcholine

kinins

prostaglandins

AUTOREGULATION

Autoregulation – local regulation of tissue perfusion. This is a mechanism

that allows each tissue to have some control over how much blood is

delivered to it.

a. In autoregulation, tissue perfusion is adjusted by altering the diameter (via

constriction/dilation) of terminal arterioles and precapillary sphincters, thus

adjusting the amount of blood allowed to flow through the capillary bed.

Each capillary bed can be affected separately.

b. Factors that cause dilation or constriction of terminal

arterioles/precapillary sphincters are chemicals that are biproducts of

metabolism, or are released by cells (recall the process of hemostasis, many

of the chemicals are the same).

Chemicals that cause dilation: CO2, organic acids, low O2,

inflammatory chemicals from cells (NO, histamine), elevated local

temperature/

Chemicals that cause constriction: primarily chemicals involved with

hemostasis, ex. prostaglandins54

AUTOREGULATION

RAAS SYSTEM

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DISTRIBUTION OF BLOOD FLOW

(AT THE REST)

The following list breaks down the blood flow throughout the body:

Systemic circulation 84%

o Systemic veins 64%

Large veins 18%

Large venous networks (liver, bone marrow, and integument) 21%

Venules and medium sized veins 25%

o Systemic arteries 13%

Arterioles 2%

Muscular arteries 5%

Elastic arteries 4%

Aorta 2%

o Systemic capillaries 7%

Pulmonary circulation 9%

o Pulmonary veins 4%

o Pulmonary arteries 3%

BLOOD FLOW IN RESPONSE TO NEEDS

Arterioles shift blood flow with changing priorities

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BLOOD FLOW COMPARISON

During exercise: perfusion of lungs, myocardium and skeletalmuscles; perfusion of kidneys and digestive tract

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