physiology of circulation system

7/31/2019 Physiology of Circulation System

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PHYSIOLOGY OF CIRCULATIONSYSTEM

Dr. Dini Sri Damayanti,MKes


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The Blood Vessels

The cardiovascular system has three typesof blood vessels:

Arteries (and arterioles) carry blood awayfrom the heart

Capillaries where nutrient and gas

exchange occur Veins (and venules) carry blood toward the

heart.


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Blood vessels


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The Arteries

Arteries and arterioles take blood awayfrom the heart.

The largest artery is the aorta.

The middle layer of an artery wallconsists ofsmooth muscle that canconstrict to regulate blood flow and

blood pressure. Arterioles can constrict or dilate,

changing blood pressure.


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The Capillaries

Capillaries have walls only one cell thick to allowexchange of gases and nutrients with tissuefluid.

Capillary beds are present in all regions of thebody but not all capillary beds are open at thesame time.

Contraction of a sphinctermuscle closes off a

bed and blood can flow through an arteriovenousshuntthat bypasses the capillary bed.


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Anatomy of a capillary bed


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The Veins

Venulesdrain blood from capillaries,then join to form veins that take bloodto the heart.

Veins have much less smooth muscle

and connective tissue than arteries. Veins often have valves that prevent the

backward flow of blood when closed.

Veins carry about 70% of the bodysblood and act as a reservoirduringhemorrhage.


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The Vascular Pathways

The cardiovascular system includes twocircuits:

1) Pulmonary circuitwhich circulates

blood through the lungs, and

2) Systemic circuitwhich circulates blood

to the rest of the body.3) Both circuits are vital to homeostasis.


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Cardiovascular system diagram


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The Pulmonary Circuit

Thepulmonary circuitbegins with thepulmonary trunkfrom the right ventriclewhich branches into twopulmonaryarteries that take oxygen-poor blood to the

lungs. In the lungs, oxygen diffuses into the

blood, and carbon dioxide diffuses out of

the blood to be expelled by the lungs. Fourpulmonary veins return oxygen-rich

blood to the left atrium.


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The Systemic Circuit

The systemic circuitstarts with the aortacarrying O2-rich blood from the left

ventricle.

The aorta branches with an artery going toeach specific organ.

Generally, an artery divides into arterioles

and capillaries which then lead to venules.


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The vein that takes blood to the vena cava oftenhas the same name as the artery that deliveredblood to the organ.

In the adult systemic circuit, arteries carry bloodthat is relatively high in oxygen and relatively

low in carbon dioxide, and veins carry blood thatis relatively low in oxygen and relatively high incarbon dioxide.

This is the reverse of the pulmonary circuit.


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Blood Flow

The beating of the heart is necessary tohomeostasis because it creates pressure

that propels blood in arteries and the

arterioles. Arterioles lead to the capillaries where

nutrient and gas exchange with tissue

fluid takes place.


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Blood Flow in Arteries

Blood pressure due to the pumping of theheart accounts for the flow of blood in thearteries.

Systolic pressure is high when the heart

expels the blood. Diastolic pressure occurs when the heart

ventricles are relaxing.

Both pressures decrease with distance fromthe left ventricle because blood entersmore and more arterioles and arteries.


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Cross-sectional area as it

relates to blood pressure and

velocity


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Blood Flow in

Capillaries

Blood moves slowly in capillariesbecause there are more capillaries thanarterioles.

This allows time for substances to beexchanged between the blood and

tissues.


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Blood Flow in Veins

Venous blood flow is dependent upon:

1) skeletal muscle contraction,

2) presence of valves in veins, and3) respiratory movements.

Compression of veins causes blood to

move forward past a valve that thenprevents it from returning backward.


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Blood Flow in Veins

Venous blood flow is dependent upon:

1) skeletal muscle contraction,

2) presence of valves in veins, and3) respiratory movements.

Compression of veins causes blood to

move forward past a valve that thenprevents it from returning backward.


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Changes in thoracic and abdominal pressurethat occur with breathing also assist in thereturn of blood.

Varicose veins develop when the valves of veinsbecome weak.

Hemorrhoids (piles) are due to varicose veins inthe rectum.

Phlebitis is inflammation of a vein and can leadto a blood clot and possible death if the clot isdislodged and is carried to a pulmonary vessel.


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Blood pressure (BP)

A constant flow of blood is necessary totransport oxygen to the cells of the body

The arteries maintain an average bloodpressure of around 90 mmHg

This helps push the blood from the arteries

into the capillaries In the capillaries, oxygen transfers from the

blood to the cells


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Systole and Diastole

The arteries fluctuate between a state ofsystole and diastole

In systole, the pressure in the arteriesincreases as the heart pumps blood into thearterial system

As the pressure increases, the elastic walls ofthe arteries stretch

This can be felt as a pulse in certain arteries


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Systole and Diastole

In diastole, the recoil of the elastic arteriesforces blood out of the arterial system intothe capillaries

The pressure in the arteries falls as bloodleaves the system

Minimum diastolic pressure is typically 70-80

mmHg

Maximum systolic pressure is typically 110-120 mmHg


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Factors affecting ABP:

Sex M > F due to hormones/ equal at menopause.

Age Elderly > children due to atherosclerosis.

Emotions due to secretion of adrenaline &noradrenaline.

Exercise due to venous return.

Hormones(e.g. Adrenaline, noradrenaline, thyroid H).

Gravity Lower limbs > upper limbs. Race Orientals > Westerns ? dietry factors, or weather.

Sleep due to venous return.

Pregnancy due to metabolism.


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Factors determining ABP:

Blood Pressure = Cardiac Output X Peripheral Resistance

(BP) (CO)Flow

(PR)Diameter of

arterioles BP depends on:

1. Cardiac outputCO = SV X HR.2. Peripheral resistance.3. Blood volume.


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More cells constriction of bloodvessel walls


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Regulation of ABP:

Maintaining B.P. is important to ensure a steady blood

flow (perfusion) to tissues.

B.P. is regulated neurally through centers in medulla

oblongata:

1. Vasomotor Center (V.M.C.), or (pressor area):

Sympathetic fibers.

2. Cardiac Inhibitory Center (C.I.C.), or (depressor area):

Parasympathetic fibers (vagus).


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Regulation of ABP(continued)

cardiac control centers in medulla oblongata

1. Cardiacacceleratorcenter(V.M.C)

2. Cardiacinhibitorycenter(C.I.C)

Sympathetic n. fibers Parasympathetic n. fibers

Regulatory mechanisms depend on:a. Fast acting reflexes:

Concerned by controlling CO (SV, HR), & PR.

b. Long-term mechanism:

Concerned mainly by regulating the blood volume.


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Regulation of CO:

A fast acting mechanism.

CO regulation depends on the regulation of:

a. Stroke volume, &

b. Heart rate


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Regulation Of COP

COP = SV X HR

HR : Sympatic /parasympatic SV : Venous return, Contractility


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Regulation of Peripheral

Resistance (PR):

A fast acting mechanism. Controlled by 3 mechanisms:

1. Intrinsic.

2. Extrinsic.

3. Paracrine.

Extrinsic mechanism is controlled through several

reflex mechanisms, most important:1. Baroreceptors reflex.

2. Chemoreceptors reflex.


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Baroreceptors

How does the body know that there has beena fall in blood pressure?

Baroreceptors on the aorta and carotid artery

respond to falls in BP

They send signals to the cardiovascularcentre in the brain stem medulla

The medulla sends signals along thesympathetic nerves to the arterioles andheart, increasing SVR and cardiac output


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1. Baroreceptors reflex:

Baroreceptors are receptors found in carotid sinus &

aortic arch.

Are stimulated by changes in BP.

BP

+ Baroreceptors

= V.M.C ++ C.I.C

= Sympathetic

Vasodilatation & TPR

+ Parasympathetic

Slowing of SA node ( HR)

&

CO


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2. Chemoreceptors reflex:

Chemoreceptors are receptors found in carotid &

aortic bodies.

Are stimulated by chemical changes in blood mainly

hypoxia (

O2), hypercapnia (

CO2), & pH changes. BP

+ Chemoreceptors

++ V.M.C = C.I.C

+ Sympathetic

Vasoconstriction

& TPR

= Parasympathetic

HR

Haemorrhage

Hypoxia

+ Adrenalmedulla


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3. Other Vasomotor Reflexes:

1. Atrial stretch receptor reflex:

Venous Return ++ atrial stretch receptors reflex

vasodilatation &

BP.2. Thermoreceptors: (in skin/or hypothalamus)

Exposure to heat vasodilatation.

Exposure to cold vasoconstriction.

3. Pulmonary receptors:

Lung inflation vasoconstriction.


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4. Hormonal Agents:

NA vasoconstriction.

A vasoconstriction (except in sk. ms.).

Angiotensin II vasoconstriction. Vasopressin vasoconstriction.


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REGULATION OF ARTERIAL BLOODPRESSUREB. Regulation of Blood Volume


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Regulation of Blood Volume:

A long-term regulatory mechanism.

Mainly renal:

1. Renin-Angiotensin System.2. Anti-diuretic hormone (ADH), or vasopressin.

3. Low-pressure volume receptors.


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1. Renin-Angiotensin System:

Most important mechanism for Na+ retention in

order to maintain the blood volume.

Any drop of renal blood flow &/or Na+, willstimulate volume receptors found in juxtaglomerular

apparatus of the kidneys to secrete Renin which will

act on the Angiotensin System leading toproduction

ofaldosterone.


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Renin

Aldosterone

Adrenalcortex

Corticosterone

Angiotensinogen

(Lungs)

renal blood flow &/or Na+

++ Juxtaglomerular apparatus of kidneys(considered volume receptors)

Angiotensin I

Convertingenzymes

Angiotensin II

(powerfulvasoconstrictor)

Angiotensin III

(powerfulvasoconstrictor)

Renin-Angiotensin System:

N.B. Aldosterone is the main regulator of Na+ retention.


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2. Anti-diuretic hormone (ADH), or

vasopressin:

Hypovolemia & dehydration will stimulate the

osmoreceptors in the hypothalamus, which will lead

to release of ADH from posterior pituitary gland.

ADH will cause water reabsorption at kidney tubules.


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3. Low-pressure volume receptors:

Atrial natriuritic peptide (ANP) hormone, is secreted

from the wall of right atrium to regulate Na+ excretion

in order to maintain blood volume.


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physiology of circulation system

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