Functions of blood:
- Transport of digested food(glucose, amino acids, etc.)
- Transport of oxygen from lungs to tissues
- Transport of carbon dioxide from tissues to lungs
- Transport of excretory material
- Distribution of hormones
- Distribution of heat
- Clotting/Coagulation
- Prevent further blood loss
- Prevent entry of disease-causing germs
- Engulfing harmful bacteria
- Production of antitoxins and antibodies
Composition of blood:
40% cellular elements(RBC, WBC, platelets)
60% plasma(fluid)
Plasma – fibrinogen = serum
RBCs:
Structure: minute, biconcave, disc-like, flat in centre and thick and rounded a periphery
Size: approx. 7 micron
Small siza and concaviies increase surface area, making them very efficient in absorbing oxygen
Small size allows movemen through fine capillaries
Haemoglobin: chemical constituent of RBCs
- Contained in spongy body stroma
- Is a respiratory pigment
- Responsible for red colour of blood
- Contains iron(haemin) and protein(globin)
- Unstable compound formed with oxygen: oxyhaemoglobin
- Unsable compound formed wih carbon dioxide: carbaminohaemoglobin
- Stable compound formed with carbon monoxide: carboxyhaemoglobin
Note: in unstable compounds, the haemoglobin can deposit the oxygen/carbon dioxide at the tissues/lungs, but in unstable compounds, it cannot do that. So, the number of RBCs in the blood stream capable of exchanging respiratory gases reduces, leading to fatal problems like asphyxiation that may result in death.
Site of production of RBCs: bone marrow, long bones(ribs, bread bone, etc.)
Site of production of RBCs in embryos: spleen, liver
Mature RBCs are enucleated
Average lifespan of RBC : 120 days(Destroyed in spleen, liver and bone marrow)
Abnormally increased no of RBCs: Polycythaemia
Abnormally decreased no of RBCs: Erythropenia
WBCs:
- Have nuclei
- Don’ contain haemoglobin(which is why they aren’t red)
Structure: Amoeboid, move using pseudopodia
Diapedesis: squeezing through capillary walls into blood streams and tissues
Produced in bone marrow
Lifespan: 2 weeks(neutrophils only live for a few hours, and are rapidly replaced)
Leukemia: cancer; increase in no. of WBCs at cost or RBCs
Leukopenia: abnormal decrease in no. of WBCs
Functions:
- Phagocytosis(neutrophils engulfing bacteria)
- Inflammation(to localise invasion of germs)
- Local heat, swelling, redness, pain
- Pus: dead WBCs and destroyed tissue cells
- Formation of antibodies(by lymphocytes)
- Vaccination
TYPES OF WBCs:
Granular:
- Neutrophils: phagocytosis
- 3-4 lobes
- Neutral dyes
- Type of WBC prevalent in blood
- Eosinophils: Secrete antitoxins(associated with allergy)
- 2 lobes
- Stained red with eosin(Acid dye)
- Basophils: inflammation(dilate blood vessels)
- Indistinctly lobed nucleus
- Basic dyes(e.g. Methylene blue)
Agranular:
- Lymphocytes: Produce antibodies
- Smallest of WBCs
- Monocytes: Ingest germs
- Largest of WBCs
- Transform into macrophages at site of infection
Disease causing germs release poisonous toxins in blood
Lymphocytes produce chemical antibodies that are specific to the toxins for which they are produced
Antibodies act as antioxidants that detoxify the poisonous toxins
BLOOD PLATELETS:
Structure: minute, oval/round, non-nucleated
- 200000 - 400000 per cubic mm
- Derived from megakaryocyte
- Each platelet is surrounded with membrane
- Destroyed: spleen
- Lifespan: 3-5 days
Coagulation:
- Injured tissue releases thrombokinase/thromboplastin/factor X/Stuart Factor
- Thrombokinase acts as an enzyme and along with calcium ions, converts prothrombin(inactive) to thrombin(Active). Vitamin K(Fat soluble vitamin) is essential for production of prothrombin
- Thrombin in the presence of Calcium ions converts soluble fibrinogen into insoluble fibrin.
- Microscopic threads of fibrin form mesh over wound
- Mesh shrinks and squeezes out the rest of the plasma as serum(plasma - fibrinogen = serum). The mass left behind is clot(thrombus)
Clotting does not require air. Clotting can also happen due to cholesterol deposit inside blood vessel
Haemophilia: genetic disorder in which blood doesn’t clot properly due to lack of clotting proteins
Haemorrhage: very slow clotting of blood due to low platelet count
Blood grouping: discovered by Karl Landsteiner
Antigens: proteins on surface of RBCs (two types, A and B)
Antibodies: proteins in plasma complimentary to antigens (two types, A and B)
Blood groups:
A: Antigen A, Antibody B
B: Antigen B, Antibody A
AB: both Antigens, no Antibody
O: neither Antigen, both Antibodies
O - universal donor
AB - universal recipient
Rhesus positive(Rh+) - Rh factor present in blood
Rhesus negative(Rh-) - Rh factor absent in blood
Sensitivity of Rh+ to Rh- results in fatal reaction(agglutination)
Heart
Location: between both lungs, above diaphragm
- Feels like it’s in the left due to triangular end pointing towards left
Pericardium: double walled membranous covering around the heart
- Contains pericardial fluid, which reduces friction during heartbeat and protects it from mechanical injuries
Chambers of heart:
- Right auricle/atrium
- Left auricle/atrium
- Right Ventricle
- Left Ventricle
Atria/auricles: upper chambers
Ventricles: lower chambers
Auricles have thinner walls than ventricles because they pour the blood down into the ventricles, aided by the force of gravity. Ventricles push blood upwards, against the force of gravity, requiring more force and thicker, more muscular walls.
Left ventricle has thicker walls than the right ventricle because the left ventricle pumps the blood only up to the lungs, while the left ventricle pumps it out to all the parts of the body.
Blood vessels entering the heart:
- Anterior Vena Cava/Superior Vena Cava/Precaval
- Carries deoxygenated blood from upper regions of body to right atrium
- Posterior Vena Cava/Inferior Vena Cava/Postcaval
- Carries deoxygenated blood from lower regions of body to right atrium
- Pulmonary veins
- Four pulmonary veins enter the left atrium from the lungs, carrying oxygenated blood
Blood vessels leaving the heart:
- Pulmonary artery: arises from the right ventricle, carries deoxygenated blood to lungs
- Aorta: arises from left ventricle, carries oxygenated blood to all parts of body
Coronary arteries:
- Arise from base of aorta
- Supply blood heart muscles
- Blockage in coronary artery: deadening of heart, myocardial infarction(heart attack)
Angina pectoris: chest pain due to insufficient supply of blood to heart muscle
Valves regulating blood flow:
- Right atrio-ventricular/tricuspid valve
- Located between right auricle and right ventricle
- Three flaps
- Apices of flaps held in position by chordae tendineae arising from papillary muscles(muscular projections of ventricle walls)
- Left atrio-ventricular/bicuspid/mitral valve
- Located between left auricle and left ventricle
- Two flaps
- Pulmonary semilunar valve
- Located at opening of right ventricle into pulmonary artery
- Three in number
- Aortic semilunar valve
- Located at point of origin of aorta from left ventricle
- Three in number
Circulation
- Contraction of auricles, dilation of ventricles (auricular systole/ventricular diastole), blood flows from auricles to ventricles
- Ventricles contract, auricles dilate (ventricular systole, auricular diastole)
- Flaps of valves tighten, preventing backflow of blood into auricles
- Blood enters into pulmonary artery from right ventricle and aorta from left ventricles
- Blood flowing through pulmonary arteries get oxidised in lungs and flow to left auricle via pulmonary veins
- Oxygenated blood is distributed throughout the body by the aorta. The subsequent deoxygenated blood is collected by the vena cavae and poured back into the right auricle.
- When ventricles and auricles dilate, blood from aorta and pulmonary artery return
Total duration of single human heartbeat: 0.85 seconds
- Auricular systole : 0.15 sec
- Ventricular systole: 0.30 sec
- Joint diastole: 0.40 sec
LUBB: closing of tricuspid and bicuspid(atrio-ventricular) valves
DUBB: closing of semilunar(aortic and pulmonary) valve
Smaller the size of the organism, more the heart rate
Pacemaker/Sino-Atrial Node(SAN):
- Creates the impulse/command that starts the heartbeat
- Located in walls of right auricle near the opening of the superior vena cava
- Impulse is relayed to ventricles by special conducting fibres
Atrio-Ventricular Node(AVN)
- Found near interauricular septum(separates both auricles) near the tricuspid valve
- connects the heart's auricles and ventricles to coordinate beating
- Bundle of HIS(muscle fibres) originate in AVN, extend to interventricular septum
- Purkinje fibres: branched fibres of bundle of HIS running along ventricular walls
BLOOD VESSELS:
Artery: carries blood away from heart toward organ
- Thick muscular walls
- Narrow lumen(central canal)
- Blood flows in spurts
- Carries oxygenated blood(exception: pulmonary artery)
Vein: carries blood away from organs towards heart
- Thin muscular walls
- Wider lumen
- Blood flows uniformly
- Contains thin pocket-shaped valves to prevent backflow of blood
- Carried deoxygenated blood(exception: pulmonary vein)
Arteriole: smallest/final branch of artery
Venule: smallest blood vessel formed after rejoining of capillaries
Capillaries:
- Narrow tube
- Made of single layer of squamous epithelium
- No muscles
Functions:
- Outward diffusion of oxygen into intercellular fluid
- Inward diffusion of carbon dioxide from intercellular fluid
- Diffusion of glucose, amino acids, urea, hormones, etc.
- Allow diapedesis
- Can dilate(vasodilation) and constrict(vasoconstriction), controlling extent of blood flow
Heightened temperature: vasodilation → increased blood flow
Cold surroundings: vasoconstriction → decreased blood flow
Layers of blood vessels(other than capillaries):
- Connective tissue layer
- Muscular layer
- Endothelium
Differences between arteries and veins
Arteries | Veins |
Carry blood away from hear towards organ | Carry blood towards heart away from organ |
Progressively branch, decreasing size | Progressive, unite, increasing size |
Smallest artery breaks into arterioles | Smallest vein arises from venules |
Walls are thick and highly muscular | Walls are thin and not so muscular |
Elastic walls | Non-elastic walls |
Narrower lumen | Wider lumen |
No valves | Contain pocket shaped valves |
Can constrict/dilate and control blood flow | Cannot control blood flow |
Placed deeper in the body | Placed closer to the skin |
Do not collapse when empty | Collapse when empty |
Carry oxygenated blood(with the exception of pulmonary artery) | Carry deoxygenated blood(with the exception of pulmonary vein) |
Double circulation
- Pulmonary Circulation(Pulmonary artery → lungs → pulmonary veins → left auricle)
- Systemic Circulation(aorta → body parts/tissues → vena cava → right auricle)
Portal vein: vein that starts and ends in capillaries