Chapter 7. Circulation

8/4/2019 Chapter 7. Circulation

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Introduction

• Movement of body fluids inside the body of

animals to transport materials from the region offormation to the region of utilization or disposalis known as CIRCULATION.

• System of vessels and heart through whichblood flows in an animal is called CirculatorySystem

• William Harvey (1628) who discovered bloodcirculation including pumping activity of the

heart.



Parts of Circulatory System

• Blood: It consisting of fluid plasma and freecells or blood corpuscles.

• Heart: Attached with muscular walls thatcontract periodically to pump the blood through

the body.• Arteries and Veins: A system of blood vessels

and capillaries through which the fluid bloodmoves.



Medical Terms related to Circulation

• Angio-logy: Study of Blood Vascular

System including Arteries, Veins, andHeart.

• Cardio-logy: Study of heart and itsfunctioning.

• Hemato-logy: Study of formation,

composition, functions and diseases ofblood.



Types of Circulatory System

• 1). Open Circulatory System:

– it is seen in many invertebrates (leeches, ARTHROPODS:

cockroaches, insects spiders butterflies, MOLLUSCS: jelly fish,snails, slugs and ascidians).

– Blood is pumped by the heart into a vessel which opens into

the open fluid spaces called SINUSES so that the tissues are

bathed by the blood which is known as HAEMO-LYMPH.

– From the sinus the blood is carried by the veins to the heart.

– There are no inter connecting vessels or capillaries between

the arteries and the veins, as the blood comes out of blood

vessels.

– Such system is called OPEN CIRCULATORY SYSTEM.



Characteristics of Open Circulatory System

• 1) The blood flows at a very low velocity & at

low pressure due to the absence of smoothmuscles.

• 2) There is direct exchange of materials

between the cells & the blood because of the

direct contact between them.

• 3) The respiratory pigment, when present, is

dissolved in the plasma of the blood and

there are no red corpuscles.



Figure of Circulatory System



• 2). Closed Circulatory System:

– Such type of circulatory system is seen in annelids,

Cephalopods, holothurians and in all Vertebrates includingman.

– Blood is carried through a system of elastic tubes-arteries,

capillaries and veins. – The blood remains inside the blood vessels and does not

come out.

– The blood returns to the heart without actually leaving thissystem of blood vessels.

– Since blood remains in this closed system it is known asCLOSED CIRCULATORY SYSTEM.

– There are 3 types of closed circulatory system: 2 chamberedheart (fish) / 3 chambered heart (amphibians & reptiles) / 4chambered heart (man)



Characteristics of Closed Circulatory

System• 1) The speed of circulation is more rapid due to the

presence of muscular and contractile blood

vessels.

• 2) The supply and removal of materials to and

from the tissues by the blood is enhanced, therebyincreasing the efficiency of circulation.

• 3) The volume of blood flowing through a tissue or

organ is regulated by the contraction and

relaxation of the muscles of the blood vessels.



Functions of Blood• 1). Transportation:

– Transport O2 & CO2 between respiratory organs and tissues.

– Transport H2O & digested food from the digestive tract to other organs.

– Transport stored food from one organ / tissue to other target tissue ororgan.

– Transport metabolic wastes, excess minerals in solution and excess waterto the excretory organs.

– Transport hormones from the glands where they are produced to theplaces of use in the body.

– Transport antibodies for immunity or defense against foreign bodies, tomaintain normal health and protection from infection.

• 2). Regulation: It regulates the pH of the tissues by means of buffers.

• 3). Maintenance: It maintains the H2O balance between the tissues andexcretory system.

– It serves to maintain the temperature of the entire body within closelimits.



Structure of Heart

• The heart is about the size of a fist & lies in the thoracic cavity.• The human heart has a mass of between 250 - 350 grams .

• It is a muscular organ covered by a tough fibrous membranethe pericardium.

• The pericardium consists of an outer, tough fibrouspericardium, which attaches to the diaphragm & also to thegreat vessels of the heart & an inner, delicate serouspericardium which is double membrane composed of an outerparietal layer & an inner visceral layer.

• Between this 2 layers is pericardial cavity filled with serousfluid or pericardial fluid which acts as lubricant & shockabsorber & protects the heart from being damage.

• The wall of the heart has 3 layers: the outer EPI-CARDIUM, themiddle MYO-CARDIUM & the inner ENDO-CARDIUM.



External Structure of Heart



External Structure

• Divided into 4 chambers: upper 2 auricles / atria &lower 2 ventricles

• 2 left chambers are separated from the 2 right by a

partition fibrous in nature called atrial partition /inter-atrial septum

• Partition separating 2 ventricles is known as inter-

ventricular septum, its upper ¼ part is fibrous andlower ¾ part is muscular

• The Aorta arises from the left ventricle carryingoxygenated blood to the tissues

• The pulmonary trunk arises from the rightventricle which is less muscular than left carryingdeoxygenated blood to the lungs.



- The 3 veins (inferior + superior vena cava and coronary

sinus) open into the right atrium bringing venous blood ordeoxygenated blood from the lungs.

- The 4 chambers of the heart perform 4 different functions.

- The left ventricles pumps oxygenated blood to the tissues.

- In tissues, oxygen in the blood is used up and the blood

becomes deoxygenated.

- The deoxygenated blood is brought back to the heart

through veins which open into the right atrium.- It is then pumped into right ventricle, then into the lungs

through pulmonary trunk

- Blood inside the lungs becomes re-oxygenated and isreturned to the left atrium through the pulmonary veins

- From it then enters the left ventricle to be pumped out in

the circulation again.





Internal structure of Heart





Internal Structure

• Left and right auricles / atria are separated by inter-atrial / inter-auricular septum

• A depression on this septum is called Fossa Ovalis

• An opening called Foramen Ovale is present in thisarea during foetal stage

•Right auricle receives deoxygenated blood from1). Superior Vena Cava which brings blood from the

upper part of body,2). Inferior Vena Cava which brings blood from middle

part and lower part3). Coronary Sinus which brings blood from heartwalls.



• Opening of the coronary sinus is regulated by

Thebasius valve and the opening of inferior vena cava

is regulated by Eustachius valve

• Left Auricles receives oxygenated blood from lungs

through 4 pulmonary veins• L. + R. ventricles are separated by an Inter-Ventricular

Septum

• L. ventricle is larger with extra thick walls as comparedto R. ventricle as it pumps blood to all part of body

• The inner walls of ventricles possess a network of

small & large muscular projections called Columnae

Carneae & Musculie Papillares / Pappilary Muscles



• The wall of R. Ventricle contains a Moderator Band that extends between upper papillary muscles andinter-ventricular septum

• Auricles opens into Ventricles through Artio-Ventricular apertures controlled by valves

• The aperture between R. Auricle and R. Ventricle is

guarded by TRICUSPID valve having 3 flaps• The aperture between L. Auricle and L. Ventricle isguarded by BICUSPID valve / MITRAL valve having 2flaps

• These valve’s flaps are kept in position by inelasticChordae Tendinae connected to Papillary Muscles• L. Ventricle opens into the aorta by an opening

guarded by a ring of 3 semilunar valves.

• Similarly, R. Ventricle opens into pulmonary andthrough an opening guarded by a rising of semilunarvalves



Miscellaneous

• Average heart beat in adult human is 72 perminute.

• SA node / SAN (Sinu-Auricular Node): it issituated on the right wall of R. Auricle abovethe opening of Superior Vena Cava. It is alsocalled the PACE-MAKER because Cardiacimpulse originates here.

• AV-node / Auriculo-Ventricular Node): It issituated between the R. Auricle and R. Ventriclenear inter-Atrial Septum. AV-node is connectedto Bundle of His / AV bundle. It is also calledPACE-SETTER.

• Purkinje Fibres: It originate from the bundle ofHis and enter into the walls of ventricle.



Neurogenic

HeartMyogenic

Heart

Impulse for the heartbeat comes from a nervefrom a nearby ganglion.

Modified musculartissue or nodular tissuein heart muscles

initiates the electro-chemical impulse tocontrol heart beat.

e.g. Most Arthropodsand some Annelids

e.g. Molluscs andVertebrates



Patterns of Circulation

• 2 patterns – 1). Systemic Circulation: it begins in the L. Ventricle & ends in R.Auricle

– 2). Pulmonary Circulation: It starts in the R. Ventricle & ends in

the L. Auricle• The right half of the heart is concerned with pumping

deoxygenated blood

• The left half of the heart is concerned with pumping of

oxygenated blood.• 2 sets of valves which regulate the flow of blood through the

heart which prevents the back flow of blood

– 1). Antrio-ventricular valves: It separates the cavities of Auricle &Ventricle

– 2). Semilunar valves: They are present where the PulmonaryArtery leaves the R. Ventricle and the Aorta leaves the L.Ventricle.





HEART BEAT:

The heart beat is the rhythmic contraction &

relaxation of all the muscles of heart• 1). Systole: the contraction of the heart is called

Systole• 2). Diastole: the relaxation of the heart is called

Diastole

• The heart rests only during the short intervalbetween contractions.

• The heart has an inbuilt capacity to contractrhythmically without any external stimulus.



Cardiac Cycle- Event that occurs in

the heart during one

beat, is called heart

beat.

- One cardiac cycle

includes auricular

systole, ventricular

systole and complete

diastole.









Heart Sound

• Each heart beat has 2 sounds, Lubb and Dubb• The first heart sound marks the beginning of ventricular

systole (contraction), a sound due to closure of

Auriculo-Ventricular valve (AV-valve)• The second indicates the end of ventricular contraction

and is due to closure of semilunar valve.

• One heart beat is completed in about 0.8 second(onecardiac cycle)

• Tachycardia: It is a condition when there is an

abnormally rapid heart.

• Bradycardia: Slowing of heart beat than the normal iscalled Bradycardia.



Origin of Heart Beat• In all vertebrates, heart beat is

originated by the muscles (myogenicheart) called Sinu-Auricular Node

(SA-Node) or “pace maker”



Arteries / Veins

A t i



Arteries

•The artery wall consists of three layers:

• Tunica Adventitia –

– the strong outer covering

– composed of connective tissue, collagen & elastic fibres.

– These fibres allow it to stretch to prevent overexpansion due tothe pressure that is exerted on the walls by blood flow.

• Tunica Media –

– the middle layer of the walls of arteries & veins. – composed of smooth muscle & elastic fibres.

– This layer is thicker in arteries than in veins.

• Tunica Intima – – the inner layer of arteries & veins.

– composed of an elastic membrane lining & smooth endothelium(epithelial tissue) that is covered by elastic tissues.







Veins



Veins• The vein wall consists of three layers:

• Tunica Adventitia – – the strong outer covering.

– composed of connective tissue collagen & elastic fibers.

– These fibers allow it to stretch to prevent overexpansion due to thepressure that is exerted on the walls by blood flow.

• Tunica Media – – the middle layer of the walls of arteries and veins.

– It is composed of smooth muscle & elastic fibers.

– This layer is thicker in arteries than in veins.

• Tunica Intima – – the inner layer of arteries and veins.

– It is composed of an elastic membrane lining & smooth endothelium(epithelial tissue) that is covered by elastic tissues.

– Veins do not contain the elastic membrane lining that is found inarteries. In some veins the tunica intima layer also contains valves tokeep blood flowing in a single direction.





Capillaries



• Capillaries have very thin walls comprised only of

endothelial cells, which allows substances tomove through the wall with ease.

• Capillaries are very small, measuring 5-10

micrometres in width.

• However, the cross-sectional area of capillaries

within an average size muscle would be largerthan that of the Aorta.

• This allows a fast and efficient transfer of

oxygen-carrying red blood cells to the site wherethey are needed.



Vasa Vasorum

• They are the vessels which

supply blood to the wall of

artery and veins.



Blood

• Blood is the fluid Connective Tissue.

•Red in colour because of the presence of

Hb (heame = iron).

• Human body contains 5-6 lits of blood.

• It is composed of 2 components Plasma

and Blood cells / corpuscles / formed

elements.

Blood Plasma



Blood Plasma

• It is the fluid part of the blood.

• Out of 5 lits, 3.5 lits is the plasma.

• It consists of 90% of H2O, 7.3% proteins(albumin, globulin, fibrinogen and prothrombin)

and 3% is glucose, nitrogeneous wastes,

minerals, enzyme and hormones.

• Plasma transport gases and other minerals,

maintains blood pH, body immunity, body heatregulation, and regulates the osmotic pressure

of the blood.

Erythrocytes (Red Blood Corpuscles)



Erythrocytes (Red Blood Corpuscles)• Erythros = Red, Cyton = cell

• Non-nucleated, biconcave, 7.4 um in diameter, 2 um thickness,volume is 90 um3, each RBC contains 30 ug of Hb.

• Avg normal RBC in Male = 5.0 - 5.5 millions and in Female = 4.5 –

5.0 millions, in Infant = 6.7 millions and in Feotus = 7.8 millionsper cc.

• RBC develops in Red bone marrow of large bones hence namedas Erythropoietic Organs.

• Life span of a RBC is about 120 days.• Spleen is considered the graveyard of RBC.

• Abnormal rise in the total count of RBC is called polycythemia.

• Smallest RBC is found in Traguls (Musk Deer).

• Largest RBC is found in Amphiuma.• Functions

– Transport of respiratory gases (O2 and CO2)

– Hb is an excellent acid – base buffer, which maintains the pH of blood.



Blood platelets

• Oval to spherical in shape, 2 – 3 u in

diameter.

• Nucleus is absent, no. of platelets / cmm of

blood ranges from 200,000 – 450, 000.

• These are produced by the mega-karyocytesin the bone marrow and are destroyed in the

spleen.

• These initiate blood coagulation and repair

capillary endothelium.

Blood Groups



Blood Groups

• Discovered by Landsteiner.

• Human Blood contains certain specific substances

called Antigens and Antibodies.• On the basis of these, human blood can be

distinguished into blood group A, B, AB and O.

• AB blood group is considered the universal

recipient and blood group O is the universal donor.

• On the basis of Rh antigen blood can bedistinguished into Rh+ and Rh- blood groups.

Principal Arteries



Principal Arteries

• The L. Ventricle pumps oxygenated blood into a 3 cm thickvessel, called AORTA.

• The pulmonary aorta carries the blood from R. Ventricle toLungs

• Following arteries arise from the aorta: – 1). Coronary Artery to Heart wall.

– 2). Brachiocephalic to Head and Fore Arms.

– 3). Phrenic to Diaphragm. – 4). Coeliac to Alimentary Canal

• Gastric to Stomach

• Common Hepatic to Liver

• Splenic to Spleen• 5). Renal Artery to Kidney

• 6). Genital Artery to Male and Female Gonads

• 7). Common Iliac to Hind limb

Principal Veins



Principal Veins

• The blood for anterior parts of the body is

brought into SVC (superior vena cava)

• Similarly blood from posterior part of thebody is received by PVC (posterior vena cava)

or IVC (inferior vena cava)• Renal vein receives blood from kidneys and

carries it to IVC.

Hepatic Portal System



Hepatic Portal System

• Portal System is a part of various system in whichvein divides twice into capillaries before they join

posterior or anterior vena cava.

• Hepatic portal system collects the nutrients from

intestine by means of capillaries.

• Excess amount of nutrients are removed by liver,capillaries rejoin and form veins, which open into

inferior vena cava.

Blood Clotting



Blood Clotting

• Coagulation of blood occurs when blood oozes out from injured or cutblood vessels.

• Thrombokinase or thromboplastin enzyme released by blood plateletsinitiates the process of blood clotting.

• Prothrombin in the blood is present as inactive globulin.

• It is activated to from thrombin before coagulation of blood takes place.

• Coagulation initiating substances known as thromboplastins are releasedfrom clumped platelets and damaged tissues into blood.

• Thromoplastins speed up the formation of enzyme prothrombinase.

• These enzyme acts upon prothrombin and hydrolyzes it to thrombin tostart the process of coagulation.

• Ca++ ions accelerate the thrombin formation and activate it forcoagulation.

• After clotting of blood the transparent fluid left is know as serum.• Average clotting time ranges from 3 - 5 minutes.









Miscellaneous



Miscellaneous

• Heparin: It is an anticoagulant present in blood

prevents activation of Prothrombin.

• Antithrombin: It is present in blood inhibits

thrombin, if formed in blood.

• These factors check the coagulation of blood insideblood vessels, so blood usually does not coagulates

during normal circulation.

• In human beings suffering from hemophilia clotting

is delayed or fails.

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Chapter 7. Circulation

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