Blood: Plasma and its Components

• All living cells require nutrients and oxygen, and waste must be removed for healthy tissues.
• Efficient mechanisms are essential for moving substances to and from cells.
• Different animal groups have developed various transport methods for this purpose.
• Sponges and coelenterates circulate water through body cavities for cell exchange.
• Complex organisms use special fluids like blood to transport materials.
• Lymph is another body fluid that aids in substance transport.

Blood

• A connective tissue consisting of a fluid matrix, plasma, and formed elements.

Plasma

• A straw-colored, viscous fluid which is around 55% of the blood's volume
• Water makes up 90-92% of plasma, and proteins account for 6-8%.
• Fibrinogen, globulins, and albumins are major proteins in plasma.
• The fibrinogens are needed for blood clotting or coagulation.
• Globulins primarily function in the body's defense mechanisms.
• Albumins help maintain osmotic balance.
• Plasma contains small amounts of minerals like sodium, calcium, and magnesium, and substances like glucose, amino acids, and lipids.
• Clotting factors are present in plasma in an inactive form.
• Serum is plasma without the clotting factors.

Formed Elements

• Erythrocytes, leukocytes, and platelets form around 45% of blood
• Erythrocytes, also known as red blood cells (RBCs), are the most abundant cells in the blood.
• A healthy adult man has around 5 to 5.5 million RBCs per cubic millimeter of blood.
• RBCs are formed in the red bone marrow in adults.
• Most mammals have RBCs without a nucleus and are biconcave-shaped.
• Hemoglobin, an iron-containing complex protein, gives RBCs their red color and transports respiratory gases.
• A healthy individual has 12-16 grams of hemoglobin in every 100 ml of blood.
• RBCs have an average lifespan of 120 days and are destroyed in the spleen.
• Leukocytes, also known as white blood cells (WBCs), are colorless due to the lack of hemoglobin.
• WBC counts average 6000-8000 per cubic millimeter of blood.
• Granulocytes and agranulocytes are the two main categories of WBCs
  • Neutrophils, eosinophils, and basophils are granulocytes.
  • Lymphocytes and monocytes are agranulocytes.
• Neutrophils are the most abundant WBCs at 60-65%.
• Basophils are the least abundant WBCs at 0.5-1%.
• Neutrophils and monocytes (6-8%) are phagocytic cells destroy foreign organisms entering the body.
• Basophils secrete histamine, serotonin, and heparin and are involved in inflammatory reactions.
• Eosinophils (2-3%) resist infections and are associated with allergic reactions.
• Lymphocytes (20-25%) are B and T cells, responsible for immune responses.
• Platelets, or thrombocytes, are cell fragments produced from megakaryocytes in the bone marrow.
• Blood contains 150,000-350,000 platelets per cubic millimeter.
• Platelets release substances involved in coagulation or blood clotting.
• A reduction in platelet number can lead to clotting disorders and excessive blood loss.

Blood Groups

• Human blood differs in certain aspects, leading to blood grouping.
• The ABO and Rh groupings are widely used.

ABO Grouping

• Based on the presence or absence of two surface antigens (A and B) on RBCs
• Individual plasma contains natural antibodies in response to these antigens.
• Blood groups are A, B, AB, and O.
• Blood type of a donor must be matched with potential recipients due to transfusion requirements
• Group 'O' blood can be donated to persons with any other blood group; therefore, individuals are called 'universal donors'.
• Persons with 'AB' group can accept blood from persons with AB as well as the other groups of blood,Therefore, such persons are called 'universal recipients'.

Rh Grouping

• The Rh antigen, similar to that present in Rhesus monkeys, is observed on the surface of RBCs in about 80% of humans.
• Individuals with the Rh antigen are Rh positive (Rh+ve), and those without it are Rh negative (Rh-ve).
• Rh-ve people exposed to Rh+ve blood form specific antibodies.
• Rh group should also be matched before transfusions.
• A special case of Rh incompatibility is observed in Rh-ve pregnant women with an Rh+ve fetus.
• During the first pregnancy, Rh antigens of the fetus are not exposed to the Rh-ve blood of the mother due to placental separation.
• During delivery of the first child, maternal blood may be exposed to small amounts of Rh+ve blood from the fetus, causing production of anti-Rh antibodies on mothers side.
• In subsequent pregnancies, Rh antibodies from the mother (Rh-ve) can damage the RBCs of the fetus (Rh+ve)
• Erythroblastosis fetalis can cause fatal anaemia and jaundice
• Administration of anti-Rh antibodies to the mother immediately after the delivery of the first child avoids Erythroblastosis foetalis

Coagulation of Blood

• Blood stops flowing after injury due to coagulation or clotting to prevent excessive blood loss.
• A cut or injury site forms a reddish-brown scum.
• Blood clots are formed of fibrins trapped in formed elements
• Fibrins are formed from inactive fibrinogens by the enzyme thrombin
• Thrombins, in turn are formed from inactive prothrombin in the plasma
• Thrombokinase is required for this reaction.
• This complex, formed by a series of linked enzymic reactions (cascade process) involving many factors, is necessary for this reaction
• Injury stimulates platelets to release factors
• Tissue factors at the injury site initiate coagulation, and calcium ions play a vital role in clotting.

Lymph (Tissue Fluid)

• As blood passes through capillaries in tissues, blood gets dispersed along with water and dissolved substances.
• This fluid, lacking larger proteins and formed elements left behind is called the interstitial fluid or tissue fluid.
• Interstitial fluid shares the same mineral distribution as plasma.
• The exchange of nutrients and gases between the blood and cells occurs through this lymph.
• The lymphatic system collects the lymph through an elaborate network of vessels and drains the fluid back into the major veins.
• Lymph is a specialized colourless fluid containing lymphocytes for immune responses.
• It acts also as an important carrier for nutrients and hormones etc
• It also absorbs fats through lacteals in the intestinal villi.

Circulatory Pathways

• Two types of circulatory patterns exist: open and closed.
• Arthropods and molluscs have an Open circulatory system, where blood is pumped by heart into open spaces called sinuses.
• Annelids and chordates have a closed circulatory system, pumping blood through a closed network of vessels.
• A closed system can be regulated, thus more advantageous.
• All vertebrates have a muscular chambered heart
  • Fishes have a 2-chambered heart (one atrium and one ventricle).
  • Amphibians and most reptiles have a 3-chambered heart (two atria and one ventricle).
  • Crocodiles, birds, and mammals possess a 4-chambered heart (two atria and two ventricles).
• In fish, the heart pumps out deoxygenated blood, which is then oxygenated by the gills.
• Reptiles and amphibians, receive oxygenated blood from the gills/lungs/skin and deoxygenated blood from other areas via left/right atriums respectively.
• Circulation gets mixed in the single ventricle which results in incomplete circulation
• Birds and mammals have complete double circulation with ventricles pumping out blood to each vessel, where atria receive blood from diff vessel.

Human Circulatory System

• Consist of chambered heart, a fluid-filled blood vascular network, and blood
• Heart is located in the thoracic cavity between lungs, protected by the pericardium
• Our heart has four chambers: two small atria and two large ventricles
• The inter-atrial septum separates the right and left atria.
• The inter-ventricular septum separates the left and right ventricles.
• Thick fibrous tissue Atrio-ventricular septum is in each ventricle
• The right atrium and right ventricle opening is guarded by the tricuspid valve, whereas a bicuspid/mitral valve guards the left side.
• Semilunar valves are provided within the blood vessels.
• Valves aid only one direction of flow- from the atria to the ventricles, and from the ventricles to the pulmonary artery or aorta; therefore preventing backward flow.
• The heart is a cardiac muscular organ where the ventricular walls are much harder than atria.
• Nodal tissue can be observed across the heart.
• Sino-atrial node (SAN) can be spotted around the right atrium above the corner and the atrio-ventricular node (AVN) can be found in the left corner, near the atrio-ventricular septum.
• The bundle of His which continues on the inter-ventricular septum then splits into left and right bundles and later forms purkinje fibres.
• Nodal musculature produces action potentials with any external stimulation and is autoexcitable.
• SAN generates the maximum number of action potential at 70-75 min and act as a rhythmic contraction for activity and is the pacemaker of the heart.

Cardiac Cycle

• The cardiac cycle begins with all four heart chambers in diastole (relaxed state.)
• Tricuspid and bicuspid are opened as blood from pulmonary veins and vena cava flows into ventricles through chambers.
• SAN stimulates atria in systole which increases blood flow by 30%
• AVN and AV bundle transmits signals to bundle of His for ventricular muscle contraction
• Atria undergoes diastole with ventricular systole that closes tricuspid and bicuspid valves due to high pressure of blood into atria
• Ventricular pressure increases and semilunar valves protecting the blood flow outward in ventricles, where ventricles undergo diastole and close bloods vessels due lack of blood.
• Joint diastole where blood flows through ventricles by pressure and SAN allows events to happen in correct sequence for process
• Each ventricle pumps 70ml of blood during systole.
• A cardiac cycle is systole and diastole of heart valves running in sync and happens 72 times.
• Total blood pumped out for heart is stroke beat volume.

Electrocardiograph (ECG)

• Graphically represents the electrical activity of the heart during the cardiac cycle.
• A patient is connected to the machine that records voltage and shows ECG where three electrical leads (one for wrists and left ankle) is required to track activity of heart.
• Multiple leads can attached to chest region for detailed function
• Identified letters such as P to T showcases activity of heart
• P= contraction of atria

Three electrical leads

• QRS complex- contraction of ventricles
• T Wave= ventricles are normal for systole
• By tracking certain events, the heart rate can be determined across all individuals.

Double Circulation

• Blood is pumped by artery and veins where vessels include:
  • an inner lining that is tunica intima (lining of squamous endothelium)
  • tunica media around tunica intima
  • Tunica externa is the elastic fibres -Tunica media is thinner in veins
• Right ventricle pumps blood to pulmonary artery whereas, left oxygenated blood into aorta, and then the pulmonary artery takes deoxygenated blood into the left atrium
• Pulmonary circulation transfers oxygenated blood into the left atrium; however, systemic circulation is taking to venules and right atrium.
• Hepatic portal system sends blood from intestine to liver to be delivered at the systemic and then connects to cardiac.

Regulation of Cardiac Activity

• Heart is known for myogenic activity (auto regulated)
• Medulla oblangata has neural center that cardiac system through ANS (autonomic nervous system), sympathetic or parasympathetic activity.
• Sympathetic increases heart rate, ventricular contraction, cardiac output.
• Parasympathetic decrease heart rate and speed, causing the action potential.
• Adrenal causes increase in output.

Disorders of Circulatory System

• Systolic and pumping is higher due hypertension.
• Normal is 120:80 mm Hg

Greater than 140: 90

• Leads to heart and organ failure.
• Coronary Artery Disease (CAD or atherosclerosis)- narrowing via muscular tissue where calcium, cholesterol, and fat causes heart.
• Angina (angina pectoris) and indicates symptom via chest pain when not enough blood is received.
• Heart Attack is commonly seen across middle-age that means less blood is pumped effectively, also referred to as congestive heart failure due lack of oxygen
• Common main for heart failure is heart attack of cardiac arrest.