Concept of the Circulatory System

TRANSPORT

CONCEPT OF THE CIRCULATORY SYSTEM

• In complex animals, including humans, the circulatory system includes the medium, vessels and pump.

• Medium: the fluid that flows in the circulatory system i.e: blood in animals, haemolymph in some invertebrates

• Vessels: a system of large and small vessels i.e: arteries, veins and capillaries

• Pump: muscular heart

COMPOSITION OF HUMAN BLOOD

Human Blood

Cellular components (45%) Plasma (55%)

erythrocytes leucocytes platelets

Granulocytes Agranulocytes

Eosinophils Neutrophils Basophils

Lymphocytes Monocytes

Water (90-92%) Soluble solutes

ERYTHROCYTES

• There are five millions of erytrocytes in every mililitre of blood

• Shape: small, biconcave discs, diameter of 8 um and thickness of 2 um.

• This shape serves to increase the surface area for gaseous exchange through the thin cell membrane.

• Erythrocytes have no nucleus. So, there is space for great quantities of haemoglobin.

ERYTHROCYTES

• Haemoglobin (Hb), is the site of oxygen attachment, contains iron

• Hb combines with oxygen to form oxyhaemoglobin.

• Erythrocytes are produced in the bone marrow at the rate of 2 million cells per second.

• They circulate in the body for 120 days.

ERYTHROCYTES

LEUCOCYTES

• Also known as the white blood cell • Responsible for the defence of organisms against

diseases.• Less numerous than erythrocytes (6000 to 10 000 in

every mm of blood)• Have nuclei, do not have haemoglobin, larger and do not

have fixed shapes.• Phagocytic leucocytes can move by changing body

shape.• Manufactured in the bone marrow but nay migrate to the

thymus gland or lymph nodes for their growth and development stages.

LEUCOCYTES - GRANULOCYTES

• Have granular cytoplasm and lobed nuclei.• 3 types: neutrophils, eosinophils and

basophils• Neutrophils: phagocytes, engulf foreign

materials by phagocytosis• Eosinophils help to control allergic

response• Basophils: secrete heparin to prevent

blood from clotting

LEUCOCYTES - GRANULOCYTES

Neutrophil Eosinophils Basophil

LEUCOCYTES: AGRANULOCYTES

• Have relatively clear cytoplasm, nuclei are not lobed

• Two types: monocytes and lymphocytes• Monocytes: The largest leucocytes, live a days

in the blood and then move into the tissues. In the tissues, they are known as macrophages.

• Lymphocytes: the smallest leucocytes. Produce antibodies to aid in the destruction of pathogens and neutralise toxins.

LEUCOCYTES: AGRANULOCYTES

Monocyte Lymphocyte

PLATELETS

• Small, irregularly shaped fragments of large cells in the bone marrow

• Important in the process of blood clotting

• Each mililitre of blood contains about 250000 platelets.

PLATELETS

PLASMA

• Pale, yellow liquid• Made up of 90% water and 10% dissolved

solutes.• Dissolved solutes consist of digested

nutrients, dissolved gases, minerals, hormones, plasma proteins and excretory wastes

• Blood serum: same as blood plasma but without clotting factors.

FUNCTION OF BLOOD IN TRANSPORT

• Transport of oxygen: Oxygen combines with Hb in the erythrocytes to form oxyhaemoglobin. The erythrocytes are carried by the circulating blood to other part of the body.

• Transport of carbon dioxide: Carbon dioxide diffuses into the surrounding blood capillaries. It then combines with water to form carbonic acid. This reaction is catalysed by an enzyme in the erythrocytes (carbonic anhydrase).


• Carbon dioxide: The carbonic acid then ionises to form hydrogen ions and hydrogen carbonate ions

• Hydrogen carbonate ions then leave the erythrocytes and remain in the plasma

• 70% of carbon dioxide is transported in the form of hydrogen carbonate ions.

• Another 23% combines with the Hb to form carbaminohaemoglobin.

• 7% dissolves directly in the blood plasma.


• Absorbed food materials: Soluble digested food (simple sugars, amino acids, vitamin B and C and mineral salts are absorbed into the capillaries of the villi in the small intestine. They are transported by hepatic portal vein to the liver and then to the heart.

• Fatty acids, glycerol and vitamins A, D, E and K are absorbed into the lacteals. Then transported by the lymph into the blood circulatory system via the left subclavian vein.


• Excretory waste: deamination of excess amino acids occurs in the liver

• Amino group is removed from the amino acid and is converted to urea

• Urea is transported by blood to the kidneys to be excreted.


• Heat: blood helps to regulate body temperature by distributing heat from heat-producing sites such as the skeletal muscles to areas of heat loss such as the skin.

• Hormones: transports hormones such as insulin and glucagon to the target organs.

FUNCTION OF HAEMOLYMPH IN TRANSPORT

• Haemolymph is a circulating blood-like fluid found in some invertebrates with open circulatory systems

• Haemolymph is not confined to vessels only• Haemolymph in insects is pumped into fluid-filled spaces

called the haemocoel.• Haemolymph bathes the tissues and internal organs

directly.• Nutrients and hormone diffuse from haemolymph into

cells.• Waste products diffuse out from cells into the

surrounding haemolymph.

STRUCTURE OF HUMAN BLOOD VESSELS

• Arteries: Blood vessels that carry the blood away from the heart.

• Arteries branch out into smaller vessels called arterioles.

• Arterioles branch out into tiny vessels called capillaries

• Capillaries join with one another to form venules. Venules join together to form veins.

• Veins transport blood back to the heart.

DIFFERENCES BETWEEN ARTERIES, CAPILLARIES AND VEINS

CHARACTERISTICSARTERIESCAPILLARIESVEINS

FUNCTIONTransport blood away from the heart

Connect arterioles to venules

Transport blood to the heart

Transport oxygenated blood (except the pulmonary artery)

Act as the sites for exchange of substances with the cells

Transport of deoxygenated blood (except for pulmonary vein)

MUSCULAR WALLThick muscular muscle

Thinnest wall (one cell thick)

Thinner wall

PRESENCE OF VALVESNo valves except semilunar valves at the base of aorta and pulmonary artery

No valvesHave valves to prevent back flow of blood.

PRESSUREBlood flows in pulses under high pressure

No pulse. Pressure lower than arteries but higher than veins

NO pulse. Blood flows under lower pressure than arteries.

LOCATION OF THE HEART

THE HEART- FRONT VIEW

THE HEART – REAR VIEW

CROSS SECTION OF HUMAN HEART

THE HEART

• A dark, cone shaped muscular organ found in the thoracic cavity

• Size of clenched fist, weighs from 350 to 450 grams in average adult

• Located between the lungs with its apex slightly orientated to the left.

• Consists of for chambers: 2 upper thin-walled atria and two lower thick-walled ventricles.

• The septum separates the right chambers from the left chambers.

THE HEART- VALVES

• Bicuspid valve: Between left atrium and left ventricle.

• Tricuspid valve: Between right atrium and right ventricle is tricuspid valve

• Semilunar valves: at the base of the aorta and pulmonary artery

HEART-NODES

• Sino-atrial node: a group of specialised cells located in the right atrial wall (near the entrance of the anterior vena cava). Acts as pacemaker which initiates the heartbeat. SA node generates a wave of excitatory impulses which spread to the two atria causing them to contract simultaneously.

HEART-NODES

• Atrio-ventricular node (AVN): lies at the base of atrium.

• Impulses from AVN are conducted by specialised muscle fibres (bundle of His and Purkinje fibres)to the ventricular walls.

• This causes the contraction of both ventricles to pump the blood out of the heart.

THE HEART

• The right ventricle pumps the blood into the pulmonary artery that carries the blood to the lungs.

• The left ventricle which is thicker and more muscular pumps the blood into the aorta to be distributed to different parts of the body.

DIRECTION OF BLOOD FLOW

CARDIAC CYCLE

• Is the series of events that occur during one complete heartbeat. It includes systole (contraction) and diastole (relaxation) of both the atria and the ventricles.

• Normal blood pressure cannot exceed 140/90 mm Hg. 140 (systolic reading), 90 (diastolic reading).

• The average heart rate is about 72 heartbeats per minute.

MOVEMENT OF BLOOD IN VEIN

• Pressure from the heart is decreasing as the blood reaches veins. It is not sufficient to force blood back into the heart.

• Blood in the vein has to move against gravitational pull.

• When body moves, the skeletal muscles around the veins contract and press on the vein that causes the valves to open. When the muscles relax, the valve will be closed. This prevents the back flow of blood.

• The opened valves force blood to move toward the heart.

DISCUSSION

• List out the factors that may caused the elevation in the rate of heart beat.

• Explain how such factors can affect the rate of heart beat.

a. In fight and flight situation (adrenaline)b. When a person gets excitedc. An increase in the partial pressure of

carbon dioxide.d. When body temperature is elevated

REGULATORY MECHANISM OF BLOOD PRESSURE

• Baroreceptors a stretch-sensitive receptor located in the walls of the aorta and carotid arteries.

• Increase in blood pressure: Baroreceptors are stretched, impulses are sent to the cardiovascular control centre in the medulla oblongata of the brain. From there impulses are sent via parasympathetic nerve to the heart and slow down the blood pressure

REGULATORY MECHANISM OF BLOOD PRESSURE

• Decrease in blood pressure: Increases the simulation of SAN by sympathetic nerve. The contraction of the cardiac muscles of the heart and the smooth muscles of the arteries will also increase. Blood pressure will return to its normal level.

• A person’s blood pressure can be measured by sphygmomanometer.

CIRCULATORY SYSTEMS IN FISH, AMPHIBIANS AND HUMANS

FISH• A fish has single closed

circulatory system.• Fish has a heart consisting of

two separates chambers, atrium and ventricle.

• Deoxygenated blood enters the atrium and then ventricle

• Ventricle pumps blood to the capillaries of the gills where gaseous exchange occurs

• Oxygenated blood then flows directly to the body tissues.

AMPHIBIANS• Gaseous exchange occurs

through lungs and skins• Double closed circulatory

system (pulmonary and systemic)

• The heart has three chambers (two atria, one ventricle)

• Oxygenated blood is mixed with deoxygenated blood in the ventricle.

• Blood contains lower levels of oxygen but sufficient to meet the requirements of amphibians.

MAMMALS• Have double closed circulatory

system (pulmonary and systemic)• Mammals have 4 chambers of

heart.• Acts as two separated pumps.• Oxygenated blood is separated

from deoxygenated blood.• Supplies oxygen and nutrient-rich

blood rapidly to the body tissues.• Separation of right and left

chambers prevent the high blood pressure from damaging the fine capillaries.

BLOOD CLOTTING MECHANISM



BLOOD CLOTTING

FORMATION OF THE INTERSTITIAL FLUID

• Formed by higher hydrostatic pressure at the arterial end of the capillaries.

• The high pressure forces some fluid out through the capillary walls into the intercellular spaces between the cells.

• Once the fluid leaves the capillary walls, it is called interstitial or tissue fluid

• Composition of the interstitial fluid is similar to the blood plasma except for it has no erythrocytes, platelets or large protein molecules.

IMPORTANCE OF INTERSTITIAL FLUID

• Forms the internal environment• Bathes the cells and supplies oxygen and

nutrients through diffusion• Carbon dioxide and waste products such

as urea diffuse from the cells into the interstitial fluid

• Homeostatic processes help in keeping the internal environment within the normal range.

FATE OF THE INTERSTITIAL FLUID

• 90% flows back into the venous end of the capillary system where the hydrostatic pressure is low. The remaining 10% of the interstitial fluid enters the lymphatic capillaries and is called lymph.

• Excess of interstitial fluid caused oedema – tissue swelling

FORMATION OF INTERSTITIAL FLUID

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Concept of the Circulatory System