The circulatory system transports blood, nutrients, gases, hormones, and metabolic wastes throughout the body. In vertebrates, the closed circulatory system includes the heart, blood vessels, and blood. The heart pumps blood which contains erythrocytes, leukocytes, platelets, and plasma. Erythrocytes transport oxygen and carbon dioxide while leukocytes help fight infection. Platelets assist in blood clotting to prevent blood loss from injuries. The circulatory system regulates temperature, pH, and homeostasis.

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CHAPTER 3 : CIRCULATORY SYSTEM
Functions :
Transport ;
1. Metabolic wastes
2. Oxygen
3. Hormones
4. Nutrients
Helps ;
1. Regulate body temperature
2. Stablize pH
3. Defends against invading microorganism
4. Maintains homeostatic balance
Composition and functions of blood
- 45% cellular elements
- 55% plasma
Cellular elements
Components Functions
Erythrocytes (RBC) Transport oxygen and carbon dioxide (respiratory
gases)
Leukocytes (WBC) Helps in immunity and defense
Platelets Blood clotting
Plasma
Water Solvent
Ions (electrolytes) - Osmotic balance between blood and
- interstitial fluid
- pH buffer
- regulation of membrane permeability
Plasma proteins; consist of
Components Functions
Albumin Osmotic balance
Fibrinogen Blood clotting
Immunoglobin Body defense
Substances transport by blood ( nutrients, respiratory gases, hormones) 10%
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Erythrocytes
- Lack nuclei and mitochondria Provide high TSA for
- Biconcave gases exchange
- Thinner centre
- Formed in bone marrow
Composition ;
- 4 polypeptides chains
- 4 heme groups (organic compound)
Heme group has iron to bind with oxygen
RBC ;
- Circulate in blood for 3 to 4 months
- Worn out RBC broken down at liver with the helps of enzymes
- Iron from the RBC back to bone marrow : to make other RBC
Leukocytes (WBC)
monocytes
agranulocyte
lymphocytes
leukocytes
neutrophil
granulocytes basophil
eosinophil
!
Usually, granulocytes names, end with ‘phil’
While agranulocytes names end eith ‘cytes’
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Basophil
Adaptations
- Irregular shape
- Nucleus constricted into two lobes
- Cytoplasm contain granules ; bluish black
Functions Histamine
- dilates blood vessels
- Helps fight against infections
- Allow other WBC to go to tissues
- Release histamine
Neutrophil
- Phagocytes which fight bacteria
- Phagocytic action causes
 formation of phagosome
 Secretion of hydrolitic enzymes
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Eosinophil
- Phagocyte
- Fights parasitic protozoans and worms
- Reduce allergy attacks
Monocytes
- Phagocytes
- Fight bacteria which enter the body through wound
- Help heal tissue by removing debris (dead cells)
Phagocytic actions :
- Use intermediary (opsonising)
Pattern recognition receptors
- Intermediaries are antibodies and complement - Recognize pathogens
- Bind to the microbe via pattern recognition
Lymphocytes
- Key cell in immunity
- Defends body
- Produce antibodies (protein)
- Fight viruses and cancer cells
Platelets
- Functions in blood clotting together with the plasma protein fibrinogen
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BLOOD CLOTTING MECHANISM :
Clotting factors in
plasma Clumped platelets Damaged cells
form
Activators
thromboplastin
Calcium ions, Ca2+ Vitamin K
Prothrombin (inactive Thrombin (active plasma
plasma protein) protein which act as enzyme)
Fibrinogen Fibrin(insoluble)
(soluble)
Fibrin form a mesh of fibres across the wound, sealing
wound and preventing further loss of blood
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Circulatory system (CS)
Invertebrate Vertebrate
- Some don’t have CS (small and aquatic) - Closed CS
- Have open CS
- Have closed CS
Those without CS, has Gastrovascular cavity (GvC)
In Cnidarians, GvC acts as CS digestive organs
Circulation helped by contractions of muscles of the body wall
Flatworms
- No need circulation
- Flattned body allows effective diffusion of gases
- Have branched intestine to spread nutrients to cell
Open and closed CS have 3 components:
- Fluid (blood/lymph)
- Tubes (blood vessels)
- Muscular pump (heart)
OpenCS
Open CS
- Heart pumps blood into vessels that have open ends
- Blood contained in body cavity
- Cannot differentiate blood and lymph so it is named as haemolymph
Open CS in mollusc
- Heart has 3 chambers
Two atria - Receive haemolymph from the gills
Ventricle - Pump haemolymph rich in oxygen into blood vessels
- Vessels conduct haemolymph into large sinuses in haemocoel.
- After haemolymph bath the body cells, it passed to vessels which lead back to the gills to
receive oxygen again.
Haemolymph consist of
Haemocoel - Blood
- Lymph
- Space between the organs with the open CS - Interstitial fluid
- Contained haemolymph
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Open CS in arthropods
- Some arthropods have haemocyanin (piment)
- Haemocyanin turns blue when oxygenated
- Arthropod has tubular heart
In grasshopper,
- When tubular heart pump(contract),
haemolymph to move into body cells
- Haemolymph brings along nutrients
- When heart relaxes, haemolymph return back to heart through tiny pores called ostia
- Ostia has valves to prevent backflow
- more haemolymph circulate during movement : provide nutrients for cell energy
Closed SC
- blood in vessels, does not mixes with interstitial fluid
invertebrate : earthworm
- has two main blood vessels
- Dorsal and ventral blood vessels
Dorsal and ventral blood vessels connect via the 5 pairs of contractile blood vessels (heart)
Contraction of these vessels and body muscle helps circulation of blood.
Vertebrate
Fish
- Single circulation of blood
- Heart has one atrium and one ventricle
- Each chamber has its own chamber
Atria has sinus venous
- Collection chambers
Ventricle has conus arterious
- Pumping chambers
Flow of contraction
sinus conus
atrium ventricle
venous arterious
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1. Blood in the heart is deoxygenated
2. When blood pump out of conus arterious, the blood is oxygenated (respiratory capillaries)
3. Blood then travel to body cells
4. Body cells used up oxygen
5. Blood enter systemic capillaries
6. Deoxygenated blood enters the heart again
G
B Respiratory
Systemic atrium
capillaries I
O caplillaries
L
D
L
Y
Sinus venosus Conus arteriosus S
ventricle
However, there is a problem in the circulation
- Blood lose pressure from the heart while travel through the gills
- Making the circulation from gills a bit slow
- Rate of oxygen transfer to the body is limited/slow
Conclusion : single circulation suitable for fish but not to other active vertebrates
Closed CS (Double Circulation)
 Separate circulation of oxygenated blood and deoxygentaed blood
 To supply blood with oxygen, blood in mamals and reptiles have to pass pulmonary circuit
 Blood in amphibians have to pass pulmocutaneous circuit
 blood then pass oxygen to cells of mammals, reptiles and amphibian through systemic circuit
 double circulation : higher pressure then single circulation
Mammals, reptiles Amphibians
Blood receives oxygen from
Pulmonary circuit Pulmocutaneous circuit
Delivers oxygenated blood through
Systemic circulation
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Amphibian circulatory system
- Two partially partitions heart
- Right and left
- Ventricles pumped into forked artery which leads to
pulmocutaneous and systemic circuit
- Oxygenated blood and deoxygenated blood is not mixed
1) Deoygenated blood pumped out of heart first
2) Followed by oxygenated blood
• Much deoxy. Blood send to pulmonary circuit. Pulmonary circuit deliver blood to lung and
skin.
• At the lungs and skin, oxygen is recharged
• The systematic circulation delivers oxygenated blood into arteries that conduct to various
tissues of the body.
Advantage : oxygen can diffuse into skin when inside the water
Reptile
- Heart separated by septum
- But partially subdivide ventricle
- Prevent mixing of blood
Mammals and birds
- Septum complete
- Blood pass heart two times for each cycle
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