Circulatory Sy Tm

Norfazlina Baharuddin

Asasi UiTM

Objectives

By the end of this chapter student should be able to:

1. Describe the function of the circulatory system

2. State and describe the composition and function of the blood

3. Differentiate between organisms without any circulatory system, organism with open and closed circulatory system

4. Differentiate between single and double circulation

5. Explain the structure of the heart, arteries and veins.

6. Explain the physiology of the heart and blood circulation

7. Describe the lymphatic system

Introduction

Circulatory system/ Cardiovascular system

Greek:

*Kardia means heart

*vas means vessel.

It consists of heart, blood, and blood vessels.

There are two different types of the circulatory system: open circulatory system and closed circulatory system.

Most of vertebrates have a closed circulatory system, whereas most invertebrate have an open circulatory

system.

Circulatory system function

The vertebrate circulatory system

performs several

function:

1.Transport nutrient

from the digestive

system and from

storage depots to

each cell


2.Transport oxygen and CO2

3. Transport metabolic waste from each cell to

organs that excrete them

4. Transport hormones from endocrine glands to

target tissues.


5. Helps maintain fluid balance (homeostasis)

6. Defends the body against invading organism

7.It helps maintain body temperature by

transporting heat (particularly important for

endothermic animals birds,mammals

8. Helps stabilize the pH

Blood composition and function

The circulatory system of human contains 4-6

liters of blood.

Blood consists of cells (45%) suspended in

plasma (55%) where

both can be separated

by spinning a blood

sample in a centrifuge.

Plasma

(55%)

Water (90%)

Substances (10%)

Salts

Plasma Protein

Nutrients

Waste product

Respiratory gases

Hormone


Inorganic salts (electrolytes)

Function:

i. Maintaining the osmotic balance between the

blood and the interstitial fluid

ii. Keeping the pH of the blood at 7.4 (pH buffer)

iii. Regulate the permeability of cell membranes


Plasma protein function:

Albumin : Help maintain osmotic balance and pH

Fibrinogen : Blood clotting

Immunoglobulin : Body defense

Blood

Red blood cell

ErythrocytesWhite blood cell

Leukocytes

Basophil Neutrophil Monocytes Eosinophil Lymphocytes

Platelet


Red Blood Cell

RBC lack nuclei and mitochondria

Are biconcave disks shaped, thinner in the center than on the sides. (provides for more surface area for gas

exchange).

Formed in the bone marrow


RBC circulated in the blood for three to four months before they get worn-out

Worn-out RBC are broken down at the liver where enzymes digest the amino acids to make

other proteins

Iron is returned to the bone marrow to make more RBC


White blood cell (WBC)/Leukocytes-body defense

Most spend their time in the interstitial fluid fighting against infection. They are synthesize in

the bone marrow.


i. Basophils

Helps fight infection by releasing the chemical

histamine.

Histamine dilates blood vessels and allow other

white blood cells to move out of the capillaries to

the tissues


ii. Neutrophils and Monocyte - are phagocytes

Fight bacteria, foreign proteins that enter body through wound and help the tissue heal by removing cellular debris (dead cells) Monocyte

Neutrophils


iii. Eosinophil - is a phagocyte that fights by parasitic protozoans and worms. They also

reduce allergy attacks


iv. Lymphocyte - key

cell in immunity which

defends the body by

producing antibodies

which are proteins that

react against foreign

substances. Other

lymphocytes fight

viruses and cancer

cells.


Platelets

Help in blood clotting together with the plasma protein fibrinogen.

Blood composition and functionBlood clotting (3 phases):

Constriction of blood vessels at site which slows blood loss.

Platelets becomes sticky and formed a plug to seal the site temporarily

Fibrin clot trap blood cells


Clotting factors (platelets and damaged

cells) activates the prothrombin protein to

convert it into the

thrombin protein.

Thrombin then converts fibrinogen into

a threadlike protein

called fibrin

Circulatory System

Some invertebrates have no circulatory system, some have an open circulatory system and

some have a closed circulatory system.

Many small and aquatic invertebrates have no

circulatory system

These are for cases of animals whose body cells are not arranged in numerous layers.

To them, a gastrovascular cavity provides adequate internal transportation.

Circulatory system

In cnidarians, their gastrovascular cavity

serves as the circulatory

system as well as a

digestive organ.

The animals tentacles capture prey and deliver

it through the mouth and

into the cavity, where

digestion occurs.

Circulatory system

The digested nutrients will diffuse across the cell lining to the cells at the outer layer.

As they stretches and contracts, movements in the body will stir up the contents of the

gastrovascular cavity and help distribute

nutrients.

Therefore, circulation is aided by contractions of muscles of the body wall.

Circulatory system

For flatworms e.g. the planaria, circulation is not necessary because their flattened body permits

effective gas exchange via diffusion.

Their branched intestine also brings nutrients close to all cells.

Circulatory system For pseudocoelomate (false cavity)

Animals such as nematodes, fluid in the body cavity helps circulate materials.

Contain complete digestive tract with mouth and anus (the tube-within-a-tube plan), no blood vascular system or

specialized respiratory organs

Coelomates (also known as eucoelomates "true coelom") have a fluid filled body cavity called a coelom

with a complete lining called peritoneum derived from

mesoderm.

Pseudocoelomate animals have a pseudocoel(literally false cavity), which is a fully functional body cavity. Tissue derived from mesoderm only partly lines

the fluid filled body cavity of these animals

Circulatory system Many invertebrates have an open circulatory system

such as arthropods and mollusks.

An open circulatory system is a system in which the heart pumps blood into vessels that have open

ends.

Instead of capillaries, blood vessels join directly with open sinuses (body cavity), where it actually baths the

internal organs.

In the system, blood and interstitial fluid are not distinguishable, which is known as hemolymph.

Circulatory system

Circulatory system

In mollusk, the heart has three chambers (2 atria, 1 ventricle).

The two atria receive hemolymph from the gills. The single ventricle pumps oxygen-rich hemolymph into blood

vessels that conduct it into the large sinuses (spaces) in

the hemocoel.

After bathing the body cells, the hemolymph passes into vessels that leads back to the gills where oxygen will be

reloaded.

* mollusk=Invertebrate having a soft unsegmented body usually

enclosed in a shell

A hemocoel is a series of spaces

between the organs of organisms with

open circulatory systems, like most

arthropods and molluscs. A combination of

blood, lymph, and interstitial fluid called

hemolymph circulates through the

hemocoel.

Circulatory system

Some arthropods have a pigment called hemocyaninthat turns blue when oxygenated.

Arthropods (insects) have a tubular heart.

In grasshoppers for instance, pumping of the tubularheart drives the hemolymph to move and brings the

nutrients directly into the body cells.

When the heart relaxes the hemolymph will go throughtiny openings (ostia) to the heart. The ostia have valves

to prevent backflow.

The rate of hemolymph circulation increase duringmovement of insects to provide more nutrients for cell

fuel.

Circulatory system

Some invertebrates and vertebrates have a closed circulatory system. In this system, the blood is

confined to the vessels, which keep it distinct from the

interstitial fluid.

Earthworm, an invertebrate has a closed circulatory system. Two main blood vessels extend throughout the

body. They are the dorsal and ventral blood vessels.

Circulatory system

In the anterior part of the

worm, five pairs of

contractile blood vessels,

which sometimes referred

as hearts connect dorsal

and ventral heart vessels.

Contraction of these

vessels, as well as the

contraction of muscles of

the body wall helps

circulate the blood.

Vertebrate circulation system

Generally, vertebrates heart have one or two atria (the chamber that receives blood returning to the heart) and

one or two ventricles (the chamber that pump blood out

of the heart)

Animals with higher metabolic rates have more complex circulation system

The vertebrate cardiovascular system became modified in the course of evolution, as the site of gas exchange

shifted from gills to lungs.

Vertebrate circulation system -fish

In fishes blood flows in a single circuit only.

The fish heart contains one atrium and one ventricle.

Each chamber has an additional structure in a form of chambers:

sinus venosus with the atrium - are collection chambers

ventricle and conus arteriosus - are pumping chambers.

Vertebrate circulation system-fish

The sinus venosus isthe first chamber to

contract, followed by the

atrium, ventricle, and

conus arteriosus.

This series ofcontraction pumps blood

into a single circuit of

blood vessels.


Blood is oxygenated as it passes through capillaries of the gills.

In gills, fresh oxygen will diffuse in through the countercurrent exchange system. As blood circulates

through the gills, pressure is low, so blood passes slowly

to other organs.

Fish swimming movements facilitate the circulation.

The oxygenated blood that has passed the capillary beds of organs returned to the atrium of the two-

chambered heart of fishes


The obvious limitation is that as blood passed through the capillaries in the gills; the blood loses much pressure

developed by the contraction of the heart, making the

circulation from the gills to the rest of the body quite

sluggish.

This feature limits the rate of oxygen delivery to the rest of the body.

This one-way circuit which only pumps deoxygenated blood is adequate for fishes, but will not be enough for

the more active life styles of vertebrates.

Vertebrate circulation system-Amphibian

As evolution occurs on the land vertebrates, their heart became partitioned into partly right and left halves.

But although it is partially partitioned, it is enough to direct blood flow through two partially separated circuits.

This causes the amphibian to possess double circulation system.

In this double circulation system, the ventricles pumped blood into a forked artery that leads to pulmocutaneous

and systemic circulation. In this way, oxygenated and

deoxygenated blood is kept separate

Vertebrate circulation system- Amphibian

The frog has two atria and one ventricle. The right atrium receives deoxygenated

blood from the systemic circulation and

the left atrium receives oxygenated

blood from the lungs.

Oxygenated blood is received by the

left atrium and then enters into the frog's

single ventricle

Because they only have a single ventricle, both atria pump into a single

ventricle.

However, deoxygenated blood is pumped out of the heart before oxygenated blood

is pumped in.

Vertebrate circulation system- Amphibian

Much of the deoxygenated blood is directed into the pulmonary circulation that delivers it to the lungs and

skin where it is recharged with oxygen.

The systematic circulation delivers oxygenated blood into arteries that conduct to various tissues of the body.

One advantage for amphibian is that inside water they can obtain additional oxygen through diffusion at their

skin.

Vertebrate circulation system-Reptiles

In reptiles like crocodiles, the walls between the ventricles are separated by a septum that partially

subdivides the ventricle.

Lizards have a muscular septum which partially divides the ventricle.

This prevents mixing of the two bloods.

Vertebrate circulation system- Reptiles

The left half of the ventricle pumps oxygenated blood

(received from the left atrium)

to the body.

The right half pumps deoxygenated blood (received

from the right atrium) to the

lungs.

Vertebrate circulation system-

mammals and birds

In all mammals and birds, the septum is

complete.

Complete separation requires blood to pass

into the heart twice each

time it tours the body.

Variation of Circulatory system

Heart structure

Human heart is not much bigger than a fist and weighs

less than a pound, yet it is a

remarkable organ that is well

adapted for pumping blood.

It is located in the chest cavity directly under the

breastbone.

Heart structure

The heart is enclosed by a double sac of serous membrane called the pericardium

A slippery lubricating fluid (serous fluid) is produced by the serous pericardial membranes.

This fluid eliminates friction that happens during

the beating of the heart

Heart structure

This fibrous layer helps protect the heart and anchors it to the surrounding structures, such as

the diaphragm and the sternum.

Heart structure

The heart walls are composed of three layers the outer epicardium, the myocardium and the inner most

endocardium

Heart structure

Each half of the heart has two chambers; an

atrium and a ventricle

The left and the right side of the heart are

divided by a septum.

Between each atrium and a ventricle is an AV

(atrioventricular)

valve.

Heart structure

On the right side, it is usually referred as

tricuspid valve

wherelse on the left side

is usually referred as the

bicuspid valve (mitral

valve).

Between each ventricle and the artery is a

semilunar valve.

Heart structure

The valves function is to regulate the direction of blood flow.

They did this by automatically closing after a blood flow and preventing the blood from flowing backward

Heart structure

The atrium is thin-walled because its function is only to

collect blood returning to the

heart and pump it in a short

distance to the ventricles

The ventricles are thick walled

because it needs to pump

blood to all of the bodys organs.

Heart circulation- pulmonary system

The pulmonary circuit

- connects the hearts

and the lungs only.

Heart circulation- pulmonary system The right atrium will receive

deoxygenated blood from

inferior vena cava, which

carries blood from lower

parts of the body, and

superior vena cava, which

carries blood from the upper

parts of the body.

From the right atrium, blood is pumped to the right

ventricle, which exits out

from the heart through two

pulmonary arteries, one

going to each lung.

Heart circulation

At the lungs, CO2 will diffuse to the alveolus tobe exhaled out of the body.

Oxygen will be loaded to the blood and becarried into the heart by the pulmonary veins.

Heart circulation

This circuit leads from the hearts right half to the capillary beds in

both lungs and then

to the hearts left half.

Therefore, this cycle is only a short loop one.

Heart circulation-Systemic system

The systemic circuit

is a longer loop that

starts at the hearts left

half and ends at the

hearts right half.

Oxygenated blood is

pumped in from the

pulmonary veins into

the left atrium and the

left ventricle.

Heart circulation-systemic system

Blood is then pumped by the left ventricle into

the aorta, the largest

artery. Arteries that

branch off from the

aorta conduct blood to

all regions of the body.

Heart circulation-systemic system

Oxygenated blood will flow

through the arterioles and

capillary beds in all

regions.

Oxygen will diffuse

out of the blood and

carbon dioxide wastes diffuse

into the blood, and later

carried in the veins to

the hearts left half to enter

the pulmonary circuit.

Cardiac cycle

In a healthy heart, the atria contract simultaneously.

After the contraction, the atrium relaxes and the ventricles start to contract.

Systole and diastole means heart contraction and heart relaxation respectively.

The term cardiac cycle refers to the events of one complete heartbeat, during which both atria and

ventricles contract and relax.

Since the heart beat at approximately 75 times per minute, the length of the cardiac cycle is normally

0.8 second.

Cardiac cycle

i. Atrial and ventricular diastole - At this point, the

pressure of the heart is low and blood is flowing

passively into the atria and ventricles. The AV valves

are open and semilunar valves closed.

ii. Atrial systole, ventricular diastole - The atria starts to

contract and forced the remaining blood to the

ventricles. When the ventricular pressure is higher

than arteries, blood rushes out of ventricles

iii. Ventricular systole, atrial diastole- Blood is pushed

out of the system. The ventricles are completely

closed chambers

When using a stethoscope, you can hear two distinct sounds during cardiac cycle.

The first lup sound is caused by the closing of the artrioventriculur valves.

The second heart sound, dup sound occurs when the semilunar valves are closed.

Cardiac cycle

Cardiac output (CO)

Cardiac output is the amount of blood pumped out by each ventricle in one minute.

It is the product of the heart rate (HR) and the stroke volume (SV)

Stroke volume is the volume of blood pumped out by each ventricle with each heartbeat.

If we use the normal resting heart rate (75beats/min) and stroke volume (70 ml/beat) the average cardiac

output is about 5 liter/min.

Cardiac output

i) Regulation of stroke volume

Depends on venous return that effects the stretching of the cardiac muscle cells.

Venous return is the amount of blood entering the heart.

Anything that increases the volume or speed of venous return increases stroke volume and force of contraction.

Exercise speeds venous return caused by the enhanced squeezing action of active skeletal muscle.

Low venous return might result from severe blood loss.

Cardiac outputii) Regulation of heart rate

Electrical pulses in the heart are controlled by special groups of cells called nodes.

During times of physical and emotional stress, the nerves of the sympathetic division stimulate SA

(sinoatrial) and AV (atrioventricular) nodes to increase

the heart beat.

The SA (sinoatrial) node generates an electrical signal that causes the upper heart chambers (atria) to contract;

the signal then passes through the AV (atrioventricular)

node to the lower heart chambers (ventricles), causing

them to contract, or pump.

Cardiac output

Parasympathetic nerves slow and steady the heart rate.

Various hormones and ions can also have a dramatic effect on the heart activity

Epinephrine and thyroxine increases heart rate whereas reduced number of ions such as sodium

and potassium decrease the heart rate.

A number of other physical factors such as age, gender, exercise and body temperature also

affects the heart rate.

Cardiac output

Cardiac muscle need not to be stimulated by nerve impulses before their contraction, they can contract

spontaneously and independently.

Conduction system of the heart

Two types of controlling systems act to regulate heart activity.

i. The autonomic nervous system The nerves from this system act to slow down or accelerate the heart rate

depending on which division is activated.

ii. Nodal system (Intrinsic conduction system) A specialized tissue that functions as if it is a combination

of muscle and nervous tissue.


This conduction system depends on the action made

by the SA (sinoatrial node)

and AV node

(atrioventricular node)

The SA node is located on the right atrium. The SA

node is often called the

pacemaker because it starts

each heartbeat.

Conduction system the heart

From the SA node, the impulse spreads through the atria

causing it to contract.

And later spread to the AV node.

The AV node is located at the junction of the atria and

ventricles. This branches to the

bundle of His, left and right

bundle branches and Purkinje

fibers which spread within the

muscles of the ventricle walls.


At the AV node, the impulse is delayed briefly to give the atria

time to finish contracting. The

impulse then passes to the

bundle of His, the bundle

branches and Purkinje fibers

causing the ventricles to

contract.

This contraction ejects blood superiorly into the large arteries

of the heart.

Electrocardiogram (ECG)

An electrocardiogram is a recording of the electrical changes that occur in myocardium (the middle

muscular layer of the heart wall) during a cardiac cycle.

Body fluids contain ions that conduct electrical currents, and therefore the electrical changes in myocardium can

be detected at the skins surface.

When an electrocardiogram is being taken, electrodes placed on the skin are connected by wires to an

instrument that detects the myocardium electrical

changes.

Electrocardiogram (ECG)

When the SA node triggers an impulse, the atrial fibers produce an electrical change that is called the P wave.

The P wave indicates the atria are about to contract.

After that the QRS complex signals that ventricles are about to contract.

The electrical changes that occur as the ventricular muscle fibers recover produce the T wave.

Blood Vessel

Blood vessels The vertebrate circulatory system includes three main

types of blood vessels, which are arteries, capillaries

and veins.

An artery carries blood away from the heart chamber toward other tissues.

When an artery enters an organ, it divides into many smaller branches called arterioles.

The arterioles deliver blood into the microscopic capillaries.

Blood vessels

Materials are only

exchanged between the

blood and the interstitial

fluid bathing the cells

through the capillary

walls, which are only

one cell thick, which is

the endothelium.

Blood vessel

From the capillaries at capillary beds, the deoxygenated blood flow will combine

through venules and back to veins.

The thick walls of arteries and vein prevent gases and nutrients from passing through.

Blood vessels

Histologically, blood vessels

consist of concentric

layers or "tunics"

i. The tunica intima is the

inner lining, consisting of

endothelium and a

relatively thin layer of

supporting connective tissue.

- It provides a smooth

surface that minimizes

resistance to the flow of blood.

Blood vessels

ii. The tunica mediais the middle

muscular and/or

elastic layer,

containing smooth

muscle and elastic

tissue in varying

proportions.

Blood vessels

iii. The tunica adventitia

is the outer, fibrous

connective tissue

layer.

- This elastic fibers

allow the blood vessel

to stretch and recoil

Blood vessels

Nervous tissue is

generally inconspicuous

in blood vessels but

serves to regulate

smooth muscle function

and to mediate pain

sensation

The smooth muscle

allows arteries and

some veins to regulate

blood flow by constricting.

Blood vessels

Capillaries lack two

outer layers present in

veins and arteries.

This allows exchange of

blood between the

blood and interstitial

fluid

Blood vessels

Arteries have thicker middle and outer vessel

layer as compared to veins to withstand high pressure

and velocity of blood pressure from the heart.

The veins do not have to deal with high pressure and velocity because blood that flows through them are

returning from the long journey to the heart.

They have valves to prevent backflow of blood returning to the heart in low pressure

Physiology of circulation - Blood flow

velocity

The velocity of blood in the blood vessel follows the law of continuity, which describes the blood flow through a

pipe.

A fluid flows through narrower segments faster than through wider segments

However, total cross sectional area of the blood capillaries slows down the flow of blood in vast numbers

of blood capillaries.

The slow progress of blood flow arterioles capilaries

venules is important as it allows the exchange of substances between blood and interstitial fluid.

Physiology of circulation Arterialpulse

A good indication of a persons circulatory system can be obtained by taking arterial pulse

and blood pressure measurement

Arterial pulse

The surge of blood entering the arteries that caused the walls to stretch and recoil can be felt

as a pulse in any artery that runs close to the

bodys surface.

Physiology of

circulation - Pulse We can feel the pulse by placing

several fingers on the radial

artery which lies near the outer

border of the palm side of a

wrist.

A carotid artery is another alternative for feeling the pulse.

It is located on the either side of

the trachea of the neck.

The pulse rate indicates the rate of the heart beat because the

arterial walls pulse whenever the

left ventricle contracts.

Physiology of circulation Blood pressure

Blood pressure is the pressure of blood against the wall of a blood vessel.

A sphygmomanometer can be used to measure blood pressure, usually in the brachial artery of the

arm.

Physiology of circulation

The blood pressure cuff is wrapped around the elbow and inflated until the cuff pressure exceeded the systolic

blood pressure.

At this point, blood flow in the arm is stopped and a brachial pulse cannot be heard.

The pressure in the cuff is gradually reduced.

The systolic pressure is recorded as the first tapping sound is heard.

As the pressure is reduced further, the sounds become louder and later disappeared when the artery is no

longer constricted and blood flows freely. The diastolic

pressure is recorded as the sound disappears.

Blood pressure

When the ventricles contract, they force blood into large, thick walled elastic arteries that

expand as the blood is pushed into them.

Continual blood flow depends on the stretchiness of the arteries.

Because the heart continuously contracts and relaxes, the off-and-on flow of blood into the

arteries causes the heart pressure to rise and

fall during each beat.

Blood pressure

Thus, two arterial blood pressure measurements are made, systolic (the pressure in the arteries at

the peak of ventricular contraction) and diastolic

pressure (the pressure in the arteries when the

ventricles are relaxing).

Blood pressures are reported in millimeters of mercury (mmHg) with the systolic pressure written

first. For example 120/80.

The high pressure forces the blood to continually move into the arterioles, capillaries, venules and

veins.

Blood pressure

In the venules and veins, blood pressure is very minimal. Therefore, instead of blood pressure,

venous return depends on:

i. Skeletal muscle contraction

ii. The presence of valves in the veins

iii. Respiratory movements

Blood velocity increases in the venous vessels due to reduction in cross sectional area as small

venules join to form veins.

Blood pressure

When the skeletal muscles contract, they compress the weak walls of veins. This causes

the blood to move past the next valve.

Once past the valves, blood cannot flow backwards.

During inhalation, the thoracic pressure falls and abdominal pressure rises as the chest expands.

This respiratory movement also allows blood in veins to return back to the heart.

Blood pressure

Fluid movements in capillary beds

The fluid movements across a capillary wall result from the two opposing forces blood pressure and osmotic pressure.

At the arteriole end, blood pressure exceeds osmotic pressure, therefore ultrafiltration happens

causing fluid to flow out of the capillaries, bringing

together nutrients and gases

Fluid movements in capillary beds

Lymphatic system

Water and solutes undergo ultrafiltration process caused by the pressure of the blood at the

capillary beds to form interstitial fluids.

The interstitial fluid will be returned to the blood by way of an open circulatory system called the

lymphatic system.

The lymphatic system consists of lymphatic capillaries, lymphatic vessels, lymph nodes and

lymphatic organs.

Lymphatic system

Lymphatic system

Excess fluid that is that is drained into blind-ended lymph capillaries is called the lymph.

The lymph starts at the capillary beds, where they enter the lymph capillaries and later merges with the lymph

vessels/lymph veins that are equipped with valves to

prevent backflow of fluid toward the capillaries

Lymphatic system

At strategic locations, lymph veins enter lymph

nodes, which are small, organized mass of lymph

tissue. Lymph nodes have two functions;

i. they filter the lymph as it slowly passes through

ii. they are battlegrounds where lymphocytes

and foreign agents are destroyed during an

infection.

Lymphatic system

Lymphatic system

Lymph nodes are most

numerous in the neck

region, under the arms,

in the groin region, in the

chest and abdomen.

In cases of infection,

lymph nodes enlarge

and may be felt as hard

little knots below the skin.

Lymphatic system

Lymph veins that leave the lymph nodes conduct lymph towards the shoulder region.

The lymphatic veins flow into one of two lymph ducts.

The right lymph duct drains from the right arm, shoulder area, and the right side of the head and neck.

The left lymph duct, or thoracic duct, drains from the legs, gastrointestinal tract and other abdominal organs,

thoracic organs, and the left side of the head and neck

and left arm and shoulder.

These ducts then drain into the subclavian veins on each side.

Lymphatic system

Lymphatic system

Consists of three important organs

tonsils, spleen and thymus

i) Tonsils are masses of lymph

tissue under the lining of the

oral cavity and throat. Tonsils

help protect the respiratory

system from infection by

destroying bacteria and other

foreign agents that enter the

body through the mouth and

the nose.

Lymphatic system

ii. The thymus is where

immature lymphocytes

differentiate into

Tlymphocytes.

iii. The spleen filters the blood and reacts immunologically to

bloodbone antigens. The

spleen functions in both

immune and hematopoietic

systems.

Mechanism of lymph flow

The lymphatic system preserves fluid balance

by collecting about 10% of the interstitial fluid and

the protein that accumulates in the fluid. The

lymph capillaries have no obvious entrance, water

and solutes moves into clefts between cells


Lymph capillaries merge into lymph vessels that have a larger diameter. Lymph vessel contain smooth

muscle in their wall.

Therefore, mechanism of backflow depends on:

i. Pressure gradient (hydrostatic pressure)

ii. Muscular and respiratory pumps push lymph

forward. Just like veins, besides having valves,

lymphatic vessels depend mainly on the movement of

skeletal muscles to squeeze the fluid along.

Lymphatic system-function

Have three obvious functions

i. Drainage

Collect water and that has leaked out of the blood in

capillary beds due to fluid pressure and returned it to the

bloodstream

ii. Disposal

Foreign cells and materials /cellular debris are brought to

the lymph nodes for disposal

iii. Delivery

Picked up fats that had been absorbed in the small intestine and delivers it into the bloodstream.

Circulatory Sy Tm

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