1.2 The Circulatory System

LEARNING OUTCOMES

•       To state what a circulatory system is,

•       To state the three components of circulatory system in humans & animals

•       To state the medium of transport humans & animals

•       To state the composition of human blood

•       Explain the function of blood & haemolymph in transport

CIRCULATORY SYSTEM

•       The mass flow of fluid through the tissues & organ of the organism.

•       The bodily system consisting of the heart, blood vessels, and blood that circulates blood throughout the body, delivers nutrients and other essential materials to cells, and removes waste products

•       Allows for the transport & exchange of nutrients, oxygen & waste products.

•       Also protecting the body against infection.

•       3 main components : a medium (blood), vessels (arteries, capillaries & veins) & a pump (heart).

Blood & Haemolymph

•      Blood – medium of transport in human & animals

•      Transport O2, CO2, nutrients, hormones & waste products.

•      Regulate the pH of body fluid, the body temperature & the water content of cells.

•      Protects the body against diseases, blood clots to protect the body against excessive blood loss following an injury.

•      Haemolymph – in many arthropods (such as insects) and certain molluscs, fills in the entire body cavity (haemocoel).

•      A circulating blood-like fluid with an open circulatory system

•      Transport water, inorganic salts & organic compounds

•      The haemolymph bathes the tissues & internal organ directly.

COMPOSITION OF HUMAN BLOOD

2 main components of human blood:

RED BLOOD CELLS

•       Contain 5 million RBC in every millilitre of human blood

•       Erythrocytes  is shaped like a biconcave disc (thinner at the centre than at its edge)à large TSA/V ratio for gaseous exchange

•       7.5-8.0 µm in diameter

•       Has a thin plasma membrane

•       Small biconcave shape + thin flexible plasma membrane enable the RBC to squeeze through the narrow blood capillaries.

•       Mature RBC have no nucleus à more space to pack in haemoglobin (respiratory protein containing iron).

•        Haemoglobin contains haem groups which gives the erythrocytes its red colour.

•        The haem group contains an iron atom & is the site of O2 binding.

•       Each blood cells contains about 250 million haemoglobin molecules. Each haemoglobin can combine with 4 O2 molecules à oxyhaemoglobin

•       Lifespan of an erythrocytes is only 120 days à destroyed by the phagocytes in the liver & spleen.

•       Continuously produced by the bone marrow of the long bones, ribs, skull & vertebrae.

•       More than 2 million RBC are destroyed & replaced every second in the human body

•        

LEUCOCYTE

Ø  Colourless & have a nucleus, not contain haemoglobin

Ø  Larger than RBC

Ø  Classified as either granular or granular

Ø  6000 – 10000 WBC in every millilitre of blood.

Ø  Do not have fix shape, can move by changing body shape

Ø  Produced in the bone marrow, some migrate to the thymus gland & others to lymph nodes during their growth & development stages.

Granulocytes	Have granular cytoplasm & a lobed nucleus •          produced in bone marrow •          72% leukocytes are granulocytes	Basophils : Secrete heparin to prevent blood clotting
		Eosinophils : Help to control allergic responses
		Neutrophils : Phagocytes granulocytes. They engulf foreign material (bacteria) by phagocytosis & destroy them.
Agranulocytes	•         relatively clear cytoplasm & nucleus is not lobed.	Monocytes : The largest of the leucocytes. Circulate in the bloodstream for a few days à body tissues to become phagocytic macrophage
		Lymphocytes : The smallest leucocytes. Important in the body’s defence against pathogens. Some produce antibodies to aid in the destruction of pathogens or neutralise the toxins

PLATLETS

•      Small irregular shaped cell fragments produced in the bone marrow

•      Play an important role in blood clotting to reduce blood loss & to prevent the entry of pathogens through the wounds into the body.

•      Each millilitre of blood contains about 250000 platelets., do not have a nucleus

PLASMA

•       The pale yellow liquid part of the blood

CONTENT	DESCRIPTION
Water	•         90% of plasma content.
Plasma protein	•          Albumin •         Globulin – type of antibody •         Fibrinogen- helps blood clotting
Mineral ions	•          sodium, potassium & chloride
Absorbed food substances	•          glucose, amino acids, cholesterol & other lipids
Waste products	Urea, CO2, uric acid, creatinine and a little ammonium ion.
Dissolved gases	O2, CO2 & Nitrogen
Hormones & enzymes	Insulin, adrenaline, ADH

•         Blood serum – plasma from which fibrinogen & other clotting factors have been removed

The Concept of Circulatory System

LEARNING OUTCOME

• Describe the structure of human blood vessels

STRUCTURE OF HUMAN BLOOD VESSELS

•       Tubes that transport blood from one part to another in the human body

HUMAN BLOOD VESSELS

3 types of human blood vessels

Artery: thick walled carrying blood at high pressure

 Transport blood away from the heart

•         Carry blood away from the heart

•         Branch into smaller vessels à arterioles à capillaries

•         To transport blood quickly & at high pressure to the tissues.

•         Arteries walls consist of epithelial tissue, smooth muscle & connective tissue

•         The muscle tissue enables the artery to constrict & dilate.

Vein: thin walled carrying blood at low pressure.

Transport blood to the heart.

•         Transport blood back to the heart

•         Consist of epithelial tissue surrounded by smooth muscle (thinner than arteries) & connective tissue

•         Blood flows under low pressure

•         Have large lumens & valves that maintain the one-way flow of blood

Capillary: very small, the walls may be just one-cell thick

     Connect arterioles to venules

•      The sites for the exchange of nutrients, respiratory gases & waste products.

•      Thin-walled blood vessels which allow rapid gaseous exchange to occur, only one-cell thick.

•      Capillaries à venules à veins

 

Differences between arteries, capillaries & veins

Arteries	Capillaries	Veins
Transport 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 deoxygenated blood (except the pulmonary vein)
Thick muscular wall	Thinnest wall, one cell in thickness	Thinner wall
No valves except semi-lunar valves at the base of the aorta & pulmonary artery	No valves	Valves present to prevent back flow of blood
Blood flows in pulse under high pressure	No pulses; pressure lower than arteries but higher than veins	No pulses; blood flows under lower pressure than arteries

THE HUMAN HEART

LEARNING OUTCOMES

•         Explain how blood is propelled through the human circulatory system,

•         Explain briefly how blood pressure is regulated,

•         Compare & contrast the circulatory systems in the following humans, fish & amphibians.

•         Conceptualise the circulatory system in humans.

                

•       The valves in the heart ensure that blood flows only in one direction

•       Tricuspid valve – right atrium & right ventricle

•       Bicuspid valve – left atrium & left ventricle

•       Semi-lunar valve – at the base of aorta & pulmonary artery

•       The heart is made up of cardiac muscle which is myogenic (it contracts & relaxes automatically throughout life)

•       The rhythmic contractions are generated within the cardiac muscle itself & are not initiated by nerves.

•       The heart functions like two pumps with different pressure systems.

•       Right pump à deoxygenated blood à lungs

•       Left pump à oxygenated blood à body

•       Sinoatrial (SA) node (specialised cardiac muscle cell) located in the right atrial wall, near the entrance of the superior vena cava.

•       Function like a pacemaker à causing the atria to contract simultaneously à force blood into ventricles

•       Left ventricle is thicker & more muscular than the right ventricles à generate a greater pressure to pump blood through aorta & to other arteries in the body.

How does the blood in the veins flow back to the heart?

•       Normal movement à contraction of skeletal muscles squeezes the veins, increased pressure pushes open the valves in the veins to force the flow of blood towards the heart.

•       The valves in the veins prevent back flow of the blood

•       The residual heart pressure

•       Inhalation à the inspiratory movements lower the thoracic pressure & helps to draw the blood along the main veins towards the heart.

•       Gravity helps to return blood in those veins above the heart.

Contraction of  skeletal muscle around veins

FACTORS MODIFYING THE HEART RATE

•        SA node can initiate heartbeat on its own. The heart rate may be modified by certain other factors.

•        (a) the sympathetic nerve carrying impulses to the heart can increase the heart rate

            (b) the parasympathetic nerve carrying impulses to the heart slows down the heart

rate.

•       When excited à an increased secretion of the hormone adrenaline @ epinephrine which causes the heart  to beat faster

            (a) an increase in the partial pressure of CO2 in the blood or a decrease in pH increase the heart rate

            (b) a fall in partial pressure of CO2 in blood decreases the heart rate.

•        Heart rate also increase when body temperature is elevated @ when there is a decrease in blood pressure

Regulatory Mechanism of blood pressure

•       Blood pressure – the force of the blood exerted by the pumping heart on the walls of the arterial blood vessels.

•       Arterial blood pressure is highest during contraction of the ventricles (ventricular systole) & lowest during diastole.

•       Normal human blood pressure – 120/80 mm Hg

•       Can be measured by using a sphygmomanometer

•       Blood pressure is regulated by a negative feedback mechanism.

•       Stretch-sensitive receptors @ baroreceptors – located in the arch walls of the aorta & carotid arteries (supply blood to the brain).

•       Monitor the pressure of blood flowing to the brain & to the body.

•       An increase in blood pressure stretches the baroreceptors à impulses are sent to the cardiovascular centre in medulla oblongata to help regulate blood pressure.

•       Impulses sent via parasymphatetic nerve to the heart à slow down the heartbeat à smooth muscles of arteries relax, decrease the resistance of blood flow in the blood vessels à blood pressure decrease

•       The widening of blood vessels = vasodilation

•       The weaker cardiac muscle contraction & lower resistance of blood flow in blood vessels à blood pressure ¯, back to normal value

•       If blood pressure low (in a state of shock) à baroreceptors less stimulated à send nerve impulses at a slower rate to the cardiovascular centre à stimulation of SA node by the sympathetic nerve à stronger cardiac muscle contraction as well as the smooth muscles in the walls of arteries à increase the resistance of blood flow in the blood vessels.

•       Narrowing of blood vessel à vasoconstriction

CIRCULATORY SYSTEM IN FISH, AMPHIBIANS & HUMANS

CIRCULATORY IN HUMANS, FISH &AMPHIBIANS

CIRCULATORY SYSTEM IN FISH

•        Single circulatory system – blood flows through the heart only once for each circulation.

•        Heart à Deoxygenated blood à gills àoxygenated blood à  body à heart

•        Blood pressure drops à collected in sinuses (large spaces) à atrium

CIRCULATORY SYSTEM IN HUMANS

•        Double circulatory system – blood flows through the heart only twice for each circulation.

•        The pulmonary circulation & systemic circulation.

•        Pulmonary circulation – right ventricle à deoxygenated blood à  lungs (via pulmonary arteries) à pulmonary veins à left atrium

•        Systemic circulation – left ventricle à oxygenated blood à  body (via aorta) à superior & inferior vena cava à right atrium.

•        Complete double circulatory system à heart being divided into two à right pump (to lungs) & left pump (to body parts).

•        Advantages : oxygenated blood returns to heart to be pumped again à increases the pressure of the blood à speeding up the delivery.

CIRCULATORY SYSTEM IN AMPHIBIANS

•        Double circulatory system – blood flows through the heart only twice for each circulation.

•        The pulmonary circulation & systemic circulation.

•        Three-chambered heart à two atria & one ventricle.

•        Some mixing of oxygenated & deoxygenated blood in ventricle à enter the systemic circulation (incomplete double circulatory system) à less efficient.

CIRCULATORY SYSTEMS

ORGANISMS	CIRCULATORY SYSTEM	CHARACTERISTICS
HUMANS	COMPLETE DOUBLE CLOSED CIRCULATORY SYSTEM	•         The blood enters the heart twice during one complete cycle. •         The oxygenated & deoxygenated blood not mixing together
FISH	SINGLE CLOSED CIRCULATORY SYSTEM	•         An atrium & a ventricle •         The deoxygenated blood enters the atrium & then the ventricle •         The blood enters the heart once
AMPHIBIANS	INCOMPLETE DOUBLE CLOSED CIRCULATORY SYSTEM	•         Two atria, one ventricle •         Mixing of oxygenated blood & deoxygenated blood in the single ventricle.
INSECTS	OPENED CIRCULATORY SYSTEM	•         Blood flow in haemocoel

EXERCISE 1.2

1. The walls of the left side of the heart are generally thicker than those of the right side of the heart, and the wall of the ventricles are thicker than those of the atria. Suggest reasons for these differences.

2. Describe the similarities and differences between the arteries and veins.

1.1 The Importance of Having a Transport System in Some Multicellular Organisms

•         LEARNING OUTCOMES :

•         To identify the problem that could be faced by multicellular organisms in obtaining their cellular requirements & getting rid of their waste products

•         To suggest how the problem is overcome in multicellular organisms

•      All living organisms need to constantly exchange substances between cells & their external environment (food, waste & gases).

•      All this process is performed by a transport system.

       

•         Small organisms have a large total surface area to volume (TSA/V) ratio. So, diffusion of substances occurs rapidly (short distance only).

•         Some simple organisms such as flatworms have thin flatten bodies à provide a large surface area

•         In Hydra, water enters through the mouth into the body cavity. As the body wall is only two cell layers thick, substances can move rapidly into or out of the body cells.

•         Do not require a specialised internal transport system

•      Larger organisms, increased need for more nutrients & oxygen to be supplied to the larger number of cells. Need to excrete more waste products.

•      The size increases, TSA/V ratio decreases.

•      Many of the body cells are too far away from the external surface or between different parts of the body.

•      Simple diffusion occurs at too slow a rate to sustain cellular activities.

•      Larger multicellular organisms have adapted by developing specialised structures to increase the surface area for exchange of substances.

•      Have developed an internal transport system of vessels or tubes.

•      In human & more complex animals, there is development of a blood circulation system to carry the substances.

•      In plants, transport of substances is carried out by the vascular system (xylem & phloem).

EXPERIMENT 1.1 : Determining the relationship between total surface area to volume ratio & its effect on the rate of diffusion

•      AIM : To determine the relationship between TSA/V ratio & its effect on the rate of diffusion

•      PROBLEM STATEMENT : What is the effect of TSA/V ratio on the rate of diffusion of substances?

•      HYPOTHESIS : the larger the size of the object, the smaller the total surface area to volume ratio & the lower the rate of diffusion

•      VARIABLES : Manipulated – size of potato cubes, Responding – Area stained relative to total surface area of cut surface, Fixed – red ink solution, potato

•      MATERIAL : potatoes,  coloured solution

•      APPARATUS : 400 ml beaker, white tile, knife, ruler & forcep.

•      PROCEDURE :

–     A knife is used to cut 3 potato cubes with the dimensions 1cm x 1cm x 1cm, 2cm x 2cm x 2cm, 4cm x 4cm x4cm

–     The 3 potato cubes are immersed in coloured solution for 30 minutes

–     The potato cubes are removed from the beaker. Each potato is cut in half.

–     The region stained by the colour solution are observed.

·         RESULT :

	A	B	C
Original length (cm)	1	2	4
Original width (cm)	1	2	4
Original height (cm)	1	2	4
Total surface area (cm2)
Volume (cm3)
TSA/V ratio
Relative rate of diffusion

•      DISCUSSION :

•      CONCLUSION :

–     Make your own conclusion

EXERCISE 1.1

1. State two problems faced by multicellular organisms in obtaining their cellular requirements & removing waste product.

2. State how these problems are overcome in multicellular organisms.

3. Explain why unicellular organisms do not face the problems listed in (Q1).