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Transport in Mammals Chapter 8

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Lesson Objectives(a) State the functions of blood(b) List the different ABO blood groups & all possible combinations for the donor& recipient in blood transfusions.(c) Identify the main blood vessels to & from the heart, lungs, liver & kidney.(d) Relate the structure of arteries, veins & capillaries to their functions.(e) Describe the transfer of materials between capillaries & tissue fluid.(f) Describe the structure& function of the heart in terms of muscular contraction and the working of valves.(f) Outline the cardiac cycle in terms of what happens during systole and diastole. (Histology of the heart muscle, names of nerves and transmitter substances are not required).(h) Describe coronary heart disease in terms of the occlusion of coronary arteries and list the possible causes, such as diet, stress and smoking, stating the possible preventative measures.

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Transport in Mammals

Introduction

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Q. CAN WE DEPEND ON ONLY DIFFUSION AND OSMOSIS FOR THE UPTAKE OF USEFUL SUBSTANCES AND THE REMOVAL OF WASTE PRODUCTS?

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Think about this…

Are all blood RED?

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7

8

Skink

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Haemoglobin, Hemocyanin & HemovanabinHaemoglobin Hemocyanin Hemovanabin

Colour Deoxygenated blood = darker shade of red;Carboxyhemoglobin= bright redcyanide poisoning increased redness all over body because body can’t use oxygen

colorless when deoxygenated and dark blue when oxygenated

vanabins turn a mustard yellow with oxygen

Who? Veterbrates Squid;Snails;Centipede; horseshoe crab etc…

Sea squirts and sea cucumbers

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Are monkeys (our closest

relative) blood cells the

same as

ours?

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• Animals and bacteria have cell surface antigens referred to as a blood type

• Antigens from the human ABO blood group system are also found in apes such as chimpanzees, bonobos and gorillas.

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Why do athletes

train in high altitude places?

Think about this . . . A leech feeds on blood of other animals without

causing blood clots. Why?

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Think about this . . .

Why Draculas are able to live for thousands of years?

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Transport in Mammals

Components of Transport System

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Task: Create a flowchart of components of transport in mammals

• Pair work• Blank papers provided• Write your name, class, date• Write Title: I used to think…

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Q. What kind of transport systems have mammals developed?

Blood Circulatory System Lymphatic System

Blood/ Fluid

Blood vessels Heart Not in ‘O’ levels syllabus

Learning Objectives (a) & (e)

Learning Objectives

(b) – (d)

Objective (f) – (h)

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Transport in Mammals

Components of Blood

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Study of Haemotology

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1. Can you identify the following blood disorder?

Sickle Cell Anaemia

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2. Can you identify the following blood disorder?

Haemophilia

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3. Can you identify the following blood disorder?

Leukemia

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4. Can you identify the following blood disorder?

Thalassemia

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A. Components of Blood

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A.1 What is blood made up of?

• Plasma (55%)• Red Blood cells• White blood cells• Platelets

45%

A.1. State the functions of bloodComponents of Transport System

Component Plasma Red blood cells

White blood cells

Platelets

Function - Transports blood cells, ions, soluble food substances, hormones, carbon dioxide,urea, vitamins, plasma proteins

- Contains haemoglo-bin & oxygen transport

-Performs phagocyto-sis, antibody formation & causes tissue rejection

-For blood clotting.- Platelets adhere to damaged areas, combine with fibrinogen to form fibrin.

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A.2 Think about this . . . .

• Is blood a tissue?– Yes, it is fluid tissue– Consists of blood cells and platelets

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A.3 Plasma

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A.3 How does plasma look like?

• Straw coloured liquid• 90% water

A.4 What are the functions of plasma?

• Water– Solvent for transporting substances– Maintain constant body temperature

• Proteins – Fibrinogen, prothrombin– Involved in blood clotting

• Hormones– Transported from endocrine glands to target organs

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A.4 What are the functions of plasma? (II)

• Urea– Metabolic waste– Transported from liver to kidney for excretion

• Carbon dioxide– From all tissues to lungs– Present as bicarbonate ions

• Dissolved nutrients – From small intestine to all tissues

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A.5 Red blood cells

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A.5 How does a red blood cell / erythrocyte look like?

A.5 What is the function of red blood cells?

• Contains haemoglobin (Hb) that transports oxygen

Haemoglobin (purplish red)

+ Oxygen

Oxyhaemoglobin

(bright red) (unstable compound)

LungsTissue

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A.5 How are RBC adapted for their function?

Feature FunctionCircular, flattened, biconcave in shape

Increase cell’s SA : VolEnables rapid diffusion of O2 into and out of cell

Absence of nucleus Pack in more Hb

Elastic cell membrane Pass through small blood capillaries

Presence of haemoglobin

Pigment combines reversibly with oxygen

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Q. Where are RBC formed?

Bone Marrow (Ribs)

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Q. How are bone marrow biopsy done?

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A.5. What are some characteristics of RBC?

• Life span ~ 120 days

• Once dead, broken down in spleen and liver

• Replacement rate ~ 2 500 000 RBC / s

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A.5 Think about this . . . .

• Male ~ 5.4 million RBC per mm3 of blood

• Female ~ 4.8 million RBC per mm3 of blood • Why does an average male have more RBC per

mm3 of blood?

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Think about this . . . .

• What is carbon monoxide poisoning?

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Q. What is carbon monoxide poisoning?

Haemoglobin + Carbon Monoxide

Carboxyhaemoglobin

(very stable compound)

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A.6 White blood cells

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A.6 How does a white blood cell / leucocyte look like?

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A.6 What is the function of white blood cells?

• Defend body against diseases

A.6 How are WBC adapted for their function?Types of WBC Feature Function

Lymphocyte Produce antibodies

• Agglutination of bacteria

• Neutralize toxins• Remain in body

after infection

Phagocyte Phagocytosis Actively seek, engulf and ingest bacteria

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A.6 Where are lymphocytes formed?

• Lymph nodes

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A.6 What is the difference between lymphocytes and phagocytes?

White Blood Cells

Lymphocyte

Phagocyte

Monocyte Polymorph

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Think about this . . . .

• The white blood cell count of someone who has a fever is higher than that of a normal person. Why?

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A.7 Platelets

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A.7 How do platelets look like?

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A.7 What is the function of platelets?

• Involved in the formation of blood clots– Form a temporary plug at cut or wound– Prevent excessive loss of blood– Prevent entry of bacteria

A.7 How are blood clots formed?

Damaged tissues release thrombokinase

Prothrombin Thrombin

Thrombokinase + Calcium ions

Fibrinogen

Insoluble fibrin

threads

Thrombin + Vitamin K

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Think about this . . . .

• Why doesn’t the blood in your body clot even though platelets are present?

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A.7 Why doesn’t the blood in your body clot even though platelets are present?

• Heparin – an anticoagulant• Produced in liver• Present in

undamaged cells

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A.7 Think about this . . .

• A leech feeds on blood of other animals without causing blood clots. Why?

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A.7 What is leech therapy?

• What is leech therapy?

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A.7 Think about this . . . .

• In the case of organ transplants, it is very important that the recipient’s body accepts the donor’s organ. How do doctors reduce the risk of tissue rejection during organ transplants?

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A.7 Think about this . . . .

• In Singapore, TV actress Andrea de Cruz narrowly escaped death after taking diet pills called Slim 10. She underwent an emergency liver transplant in May 2002, after her boyfriend, actor Pierre Png, donated half his own liver. Is it possible to have successful organ transplants even though the donor and recipient may not be genetically related?

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IN SUMMARY…

BLOOD

A.7 What are the functions of blood?

Function Feature of blood that enables this function

1) Transport

Plasma transports oxygen, carbon dioxide, soluble food substances, hormones, antibodies, urea

2) Protection

Lymphocytes – Agglutination, – Neutralisation of toxinsPhagocytes – PhagocytosisPlatelets – Blood-clotting 63

A. What are the differences between RBC, WBC and platelets?

RBC WBC Platelet

Appearance

Biconcave, circular

Irregular shape Irregular shape

Site of production

Bone Marrow Lymphocytes – Lymph nodesPhagocytes – Bone marrow

Bone marrow

Life span 120 days 1 day or less 6 days

Presence of Hb and nucleus

No nucleusHb present

NucleatedHb absent

No nucleusHb absent

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B. Blood group classification

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B.1 Blood group classification

• ABO blood groups–A, B, AB, O blood groups

• Rhesus / Rh factor classification–Rh positive or Rh negative

Q. Why are blood groups named as ‘A’, ‘B’, ‘AB’ or ‘O’?

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Human Blood Groups

Blood group Antibody present in PLASMA

Antigen present on RED BLOOD CELL

A Anti-b A

B Anti-a B

AB None A and B

O Anti-aAnti-b

None68

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B.2 Blood tranfusions

• Recipient’s plasma must not contain antibodies that will react with antigen donor’s blood cells

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Q. What happens when an A+ donates blood to a B+?

. Blood transfusions

• Who can receive blood from whom?

OAB, A, B, Oa and bnoneO

AB, A, B, OABnoneA and BAB

B and OB and ABaBB

A and OA and ABbAA

Can receive blood from

Can give blood toAntibodiesAntigensBlood group

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B.3 Universal Donor vs Universal Recipient

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B.4 What is meant by the Rhesus Factor?

• Protein found on surface of RBC– Presence of protein Rh positive– Absence of protein Rh negative

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C. Major Blood Vessels

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Pulmonary artery Pulmonary vein

Vena cava Aorta

Hepatic vein

Hepatic artery

Renal arteryRenal vein

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C. Types of Blood Vessels

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Q. What are Blood vessels?

• System of tubes through which blood flows in the body

• Three types of blood vessels :1. Arteries2. Capillaries3. Veins

• Total length of blood vessels 160 000 km

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Types of Blood Vessels

3.5,

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C.1 ARTERY

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Artery

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Artery

Endothelium

Wavy elastic band

Lumen

Connective Tissue

Smooth muscle

Characteristics Artery Reason

Size of wall Thick Arteries receive blood directly from the heart. Blood is at high pressure. Thick walls required to withstand high blood pressure in the arteries.

Layer of elastic

and muscle tissues

Thick Enables the artery wall to stretch and recoil. Pushes the blood along in spurts. Creates the pulse.

Direction of blood flow

Heart to organs Arteries carry blood AWAY from the heart

Oxygen content

Oxygenated blood, except

pulmonary artery

Arteries carry blood away from the heart, hence they carry oxygenated blood. Pulmonary artery carry blood away from heart to lungs, it carries deoxygenated blood.

Colour Red Arteries carry oxygenated blood. Oxy-haemoglobin appears red.

Location Deep muscle Usually large vessels, within deep muscles for protection.

Valves Absent except in

pulmonary artery

Blood pressure is high, blood does not backflow. No valves required. In pulmonary artery, valves (semi-lunar valves) present to prevent backflow of blood into ventricles.

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C.2 VEIN

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Vein

Endothelium

Lumen

Connective Tissue

Smooth muscle

Characteristics Vein Reason

Size of wall Thin Veins receive blood from the capillary network. Blood is at low pressure. Blood flow is slow and smooth. Thick walls are not required.

Layer ofelastic and

muscle tissues

Thin(Less elastic tissue)

The veins do not need to stretch or recoil. The blood is at low pressure.

Direction of blood flow

Organs to heart Veins carry blood BACK to the heart.

Oxygen content

Deoxygenated blood, except

pulmonary vein

Veins carry blood back to the heart, from the capillary network. Hence, they carry deoxygenated blood. Pulmonary vein carry blood from the lungs back to the heart, hence they carry oxygenated blood.

Colour Bluish-red Veins carry deoxygenated blood. Deoxy-haemoglobin appears bluish.

Location Nearer to body surface

Near to the capillary network which is found in all tissues.

Valves Present Blood flow is slow and at low pressure. Valves are required to prevent backflow of blood.

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Valves

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Exercising helps blood to flow!

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C.3 Capillary

Capillary• Where exchange of materials

take place between blood and tissues/cells

• Branch repeatedly and found between cells of almost all tissues (why?)

• Consists if a thin layer of flattened (why?) endothelial cells which are selectively permeable

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Capillary

Capillary Characteristics Capillary Reason

Size of wall One-cell thick For efficient exchange of materials between the blood and the tissue cells.

Layer of elastic and muscle tissues

Absent -

Direction of blood flow Arteriole to venule

Blood flows from artery to vein.

Oxygen content Oxygenated blood at the

arteriole end.

Deoxygenated blood at the venule end.

Oxygen diffuses from the blood cells into the tissue cells in the capillary network. Hence, the blood at the venous end of the capillary is deoxygenated.

Colour Bluish-red Capillary carry deoxygenated blood. Deoxy-haemoglobin appears bluish.

Location Inside all tissues

Exchange of materials happen between capillaries and all body tissue.

Valves Absent -92

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Differences between Blood Vessels

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How are the 3 blood vessels linked?

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E. TRANSFER OF MATERIALS BETWEEN CAPILLARIES AND FLUID

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Q. What is the relationship between capillaries, cells and lymph vessels?

• Capillaries contain blood• Spaces between cells contain tissue fluid• Lymph vessels contain lymph

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NOT IN NOTES-Describe the transfer of substances between capillaries and tissue

fluid

• Read TB pages 164-165Questions to discuss1. What is interstitial fluid?2. How is tissue fluid formed?3. Why is the interstitial fluid needed?4. What is carried at the arterial end of the capillary?5. What does the venous end of the capillary contain?Look at the picture given. 6. What is the difference between the net pressure at the

arterial and venous end? Why is this important?

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Q. What are the differences between blood plasma, tissue fluid and lymph

• Blood plasma– Appearance : Straw coloured liquid– Location : Liquid part of blood in blood vessels– Composition : Plasma, plasma proteins

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Q. What are the differences between blood plasma, tissue fluid and lymph

• Tissue fluid– Appearance : Colourless, watery liquid– Location : Surrounds all cells of body and fills

the spaces between them– Composition : Same as blood plasma but no

plasma proteins

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Q. What are the differences between blood plasma, tissue fluid and lymph

• Lymph– Appearance : Colourless, watery liquid– Location : Lymphatic capillaries– Composition : More waste products and less

food substances than tissue fluid

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Transport in Mammals (II)

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F. STRUCTURE OF HEART

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Lesson Objectives(f) Describe the structure& function of the heart in terms of muscular contraction and the working of valves.(g) Outline the cardiac cycle in terms of what happens during systole and diastole. (Histology of the heart muscle, names of nerves and transmitter substances are not required).(h) Describe coronary heart disease in terms of the occlusion of coronary arteries and list the possible causes, such as diet, stress and smoking, stating the possible preventative measures.

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Q. What is the function of the heart?

• Pumps oxygenated blood to all parts of the body

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Q. Where is your heart located?

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Q. How does the heart look like?

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Q. How is the heart protected?

• Muscles of chest walls• Rib cage• Sternum• Diaphragm• Pericardium

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Q. Can the heart develop outside the body?

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F.1 EXTERNAL STRUCTURE OF THE MAMMALIAN HEART

3) Left Atrium

5) Right Ventricle

2) Left Ventricle

1) Apex

4) Right Atrium

6) Vena cava

8) Aortic Arch

7) Pulmonary artery

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F.2 Internal Structure of the Mammalian Heart

5) Septum

1) Left ventricle

3) Right atrium

4) Right ventricle

2) Left atrium

6) Superior vena cava

7)Inferior vena cava

8) Pulmonary artery

9) Pulmonary vein

10) Aorta

11) Tricuspid valve

13) Semi-lunar valves

12) Bicuspid valve

1

1

2

3

5

4

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7

8

9

10

11

11

6

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F.3 Flow of blood in the heart

All parts of the body

OrganLungs

AortaBlood vesselPulmonary artery

Semilunar valveValveSemilunar valve

Left ventricleChamberRight ventricle

Bicuspid valveValveTricuspid valve

Left atriumChamberRight atrium

Pulmonary veinBlood vesselSuperior and Inferior Vena Cava

LungsOrganAll parts of the body

Left side of the heart

Right side of the heart

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Q. In one complete circulation, how many times does blood pass through the heart?

• Pulmonary circulation– Blood circulation to and from the lungs

• Systemic circulation– Blood circulation to and from all other parts of the

body

DOUBLE CIRCULATION in birds and mammals

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2) Deoxygenated blood at high pressure

3) Oxygenated blood at low pressure

1) Deoxygenated blood at low pressure

4) Oxygenated blood at high pressure

Pu

lom

on

ar

y

Cir

cu

lati

on

Syste

mic

C

ircu

lati

on

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F.4 What is the function of the atria?

• Right atrium– Receives deoxygenated blood from the vena cava

• Left atrium– Receives oxygenated blood from the lungs via the

pulmonary vein

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F.4 What is the function of the ventricles?

• Right ventricle– Pumps blood to the lungs via pulmonary artery

• Left ventricle– Pumps blood to all parts of the body (except the

lungs) via the aorta

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Q. HOW DO THE ATRIA WALLS DIFFER FROM VENTRICLE WALLS?

Why is there a need for this difference?

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F.4 What is the function of the vena cava?

• Superior vena cava– Returns deoxygenated blood from the head and

upper limbs to the heart

• Inferior vena cava– Returns deoxygenated blood from the lower

limbs and organs to the heart

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F.4 What is the function of the pulmonary artery/vein?

• Pulmonary artery– Carries deoxygenated blood to the lungs

• Pulmonary vein– Carries oxygenated blood from the lungs to the

left atrium of the heart

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F.4 What is the function of the aorta?

• Aorta– Carries oxygenated blood to all parts of the body

except the lungs

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F.5 What is the function of the atrioventricular valves?

• Tricuspid valve (Right)– Prevents backflow of blood to the right atrium

when the right ventricle contracts

• Bicuspid valve (Left)– Prevents backflow of blood to the left atrium

when the left ventricle contracts

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F.5 What is the function of the semilunar valves?

• Pulmonary valve– Prevent backflow of blood from the pulmonary

artery into the right ventricle when the right ventricle relaxes

• Aortic valve– Prevent backflow of oxygenated blood from the

aorta into the left ventricle when the left ventricle relaxes

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F.5 How do heart valves look like?

126

x

127

F.5 Where are the heart valves located?

128

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Q. Have you heard of “tugging at one’s heart strings”?

• Chordae tendineae– Attached to walls of ventricles– Prevent flaps of valve from being flapping back

into the atrium when ventricles contract

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F.6 HOW DOES THE CHORDAE TENDINEAE LOOK LIKE?

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F. Cardiac Cycle

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Cardiac Cycle Overview

pulmonary vein1

3

vena cava

right ventricle

left atrium

right atrium

2

1

• Both atria and ventricles are relaxed.

• Right atrium receives blood from the vena cava (both superior and inferior vena cava)

• Left atrium receives blood from the pulmonary vein.

left ventricle

135

2

1 3

right ventricle

left ventricle

2

Cardiac Cycle• Atria fill up

with blood.

• Atria contract, blood is pumped into the ventricles

• Tricuspid and bicuspid valves are forced open.

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3

21

aortic arch

3

pulmonary arch

bicuspid valve

tricuspid valve

Cardiac Cycle Ventricular Systole

· Ventricles filled with blood.

· Ventricles contract.(blood pressure increases)

· Tricuspid and bicuspid valves close, producing LOUD ‘lub’ sound.(prevents backflow of blood into atria)

· Aortic and pulmonary semi-lunar valves open.

· Blood flows from ventricles into pulmonary artery and aorta.

137

4pulmonary vein

3

2

4

vena cava

right ventricle

left ventricle

left atrium

right atrium

Cardiac Cycle Ventricular Diastole

· Ventricles relax.(blood pressure decreases)

· Aortic and pulmonary semi-lunar valves close, producing SOFT ‘dub’ sound(prevent backflow of blood into ventricles)

· Tricuspid and bicuspid valves open.

WHOLE CYCLE (1-4) REPEATS!

Heart sounds…

• Lub dub …. Lub dub

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F.1 What causes heart sounds?

• Opening and closing of valves

• ‘Lub’ Sound– Closing of bicuspid and tricuspid valves

• ‘Dub’ Sound– Closing of semilunar valves

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F.2 What happens when your valves don’t function properly?

• Heart murmurs

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F. Blood Pressure

142

Q. What is blood pressure?

• Force that blood exerts on walls of blood vessels as a result of the contraction and relaxation of the heart

• Highest in the aorta, lowest in the veins• Higher during ventricular contraction and

lower during relaxation

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Q. How is blood pressure measured?

• Measured using a sphygmomanometer• Reading 120/80 (120-systole, 80-diastole)

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Q. What happens if a person has high blood pressure?

• Pressures above 140/90• Causes the walls of the arterioles to thicken,

narrowing the lumen and reducing supply of oxygen to the tissues

• Higher risk of arteriole ballooning out and possibly bursting

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Blood pressure graph

Vena cava

Small arteries

Large arteries

Capillaries

Arterioles

Large veins

Small veins

Venules

Aorta

Ao

rta

Ven

a ca

va

Sm

all

arte

ries

Lar

ge

arte

ries

Cap

illa

ries

Art

erio

les

Lar

ge

vein

s

Sm

all

vein

s

Ven

ule

s

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Heart pressure graph

Refer to your worksheet …

147

Function:

•Comparing the pressure of the aorta, right ventricle and right atrium.

•Predict the sequence of events in the heart.

Pre Point 1

•Both atrium pressure and ventricle pressure are low.

•When Atria P > Ventricle P

•Atrial Systole occurs: Tricuspid / Bicuspid valves open to allow blood flow from atria ventricles • Ventricle pressure rises

above atrium pressure.

• Ventricle P > Atria P

• Ventricular Systole occurs & resulting in 2 events:

(1)At Point 1: Tricuspid & Biscuspid closes

(2) At Point 2: Semi-lunar valves open 148

Aortic semi-lunar valves openTri/Biscuspid closes

To prevent backflow from ventricle back into atrium

To allow blood flow into aorta & pulmonary artery

Point 1 & 2

150

At Point 3:

•Ventricle pressure falls below aorta pressure

•Aorta P > Ventricle P

•Blood backflows from Aorta / pulmonary artery ventricles

•Aortic SL valves close

•Ventricle pressure falls sharply

•Ventricle undergoing ventricular DIASTOLE

Aortic SL valves close

151

At Point 4:

•Ventricle pressure falls below atrium pressure.

• Atria P > Ventricle P

•Blood flows from

Atrium ventricle

•Bicuspid valves open

WHOLE CYCLE REPEATS!

Bicuspid valves open

152

2. Aortic semi-lunar valves open

1. T

ri/Bi

scus

pid

clos

es

1. To prevent backflow from ventricle back into atrium

2. To allow blood flow into aorta & pulmonary artery

3. Aortic SL valves close

4. Bicuspid valves open

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H. HEART DISEASES

Coronary Heart Disease (CHD)

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155

Coronary arteries supply blood to the heart.

Blocked Coronary Arteries

HEART ATTACK

156

AtherosclerosisAtherosclerosis is the deposition of fatty substances on the

INNER surfaces of the coronary arteries.

Lumen

Blood pressure

157

Thrombosis

Blood clots form easily in the narrow lumen.

The blood clot is known as a thrombosis.

Coronary Heart Disease• Arteriosclerosis

Hardened / thickened artery wallsFat depositsBlood clots can occur

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Preventing CHD

1. Proper diet2. Proper Stress Management3. No smoking

• Nicotine increases blood pressure and the risk of blood clotting in the coronary arteries

• Carbon monoxide increases fatty deposits

4. Exercise

159

Summary

Q. What have we learned?

Lesson Objectives(a) State the functions of blood(b) List the different ABO blood groups & all possible combinations for the donor& recipient in blood transfusions.(c) Identify the main blood vessels to & from the heart, lungs, liver & kidney.(d) Relate the structure of arteries, veins & capillaries to their functions.(e) Describe the transfer of materials between capillaries & tissue fluid.(f) Describe the structure& function of the heart in terms of muscular contraction and the working of valves.(f) Outline the cardiac cycle in terms of what happens during systole and diastole. (Histology of the heart muscle, names of nerves and transmitter substances are not required).(h) Describe coronary heart disease in terms of the occlusion of coronary arteries and list the possible causes, such as diet, stress and smoking, stating the possible preventative measures. 161

Arteries

Blood

TRANSPORT SYSTEM IN MAMMALS

Lymphatic System

consists of

consists of

is divided into chambers

VenulesCapillariesArterioles

Ventricles

pumps deoxygenated blood into the lungs

Atria

Consists of: • Red blood cells • White blood cells • Platelets • Plasma

join up to formbranch into

Heart

right left

pumps oxygenated blood to the rest of the body

receives deoxygenated blood from the rest of the body

receives oxygenated blood from the lungs

Circulates from: • Heart to lungs and back (pulmonary circulation) • Heart to the rest of the body and back (systemic circulation)

Blood Circulatory System

Blood vessels

Veins

right left

branch into join up to form

162

Failure/

malfuction

Heart diseases

Damaged tissue and platelets

Prothrombin (inactive)

Insoluble fibrin threads form a mesh to trap blood cellsFibrinogen

thrombin

produceThrombokinase (enzyme)

Thrombin (active)thrombokinase

and calcium ions

The clotting process can be summarised in the three reactions shown below:

1

3

2

Mechanism of Blood Clotting

The Cardiac Cycle

4

4. The ventricles then relax. This is ventricular diastole. • The drop in pressure in the ventricles causes the semi-lunar valves in the two arches to close. This produces a soft ‘dub’ sound.This prevents the backflow of blood into the ventricles.• The drop in pressure in the ventricles also causes the bicuspid valves to open. • The whole cycle (1-4) then repeats.

pulmonary vein

aortic arch

1

3

2

pulmonary arch bicuspid

valvetricuspid valve

vena cava

right ventricle

left ventricle

left atrium

right atrium

right ventricle

left ventricle

1. Both the atria and the ventricles are relaxed.• The right atrium receives blood from the venae cavae while the left atrium receives blood from the pulmonary veins.

2. • The atria contract, forcing blood into the ventricles.

3. • After a short pause, the ventricles contract. This is called ventricular systole.