- Blood circulates through arteries, veins, and capillaries in a closed system.
- Tissue fluid fills the spaces between cells and facilitates exchange between blood and cells.
- Lymph is transported through lymph vessels and supports immune function.
- Arteries carry oxygenated blood (bright red), while veins carry deoxygenated blood (dark red), although veins may appear blue from the outside.
- Non-circulating fluids, like synovial fluid and vitreous humour, are confined to specific organs and do not move through a circulatory system.
Definitions [12]
Definition: Closed Blood Circulatory System
A closed blood circulatory system is one in which blood flows entirely within blood vessels, as seen in humans and other vertebrates.
Definition: Open Blood Circulatory System
An open blood circulatory system is found in animals like insects, where blood flows freely through body cavities without confined blood vessels.
Define the following term:
Blood
Blood is a fluid that circulates in the heart, arteries, capillaries, and veins of vertebrate animals. It transports nutrients and oxygen throughout the body and removes waste.
Definition: Serum
The plasma from which the protein fibrinogen has been removed is called serum.
Define the Circulatory system.
The circulatory system is a transport system moving substances throughout our body with the help of blood.
Define the Veins.
Veins are the blood vessels that carry deoxygenated (impure) blood from the body cells to the heart.
Define the Arteries.
Arteries are the blood vessels in which oxygenated blood is going away from the heart to all parts of the body.
Definition: Cardiac Cycle
The complete sequence of events that occurs during one heartbeat, including contraction and relaxation of the atria and ventricles, is called the cardiac cycle.
Definition: Double Circulation
Double circulation is the process in which blood passes through the heart twice during one complete cycle—once for pulmonary circulation (to and from the lungs) and once for systemic circulation (to and from the body).
Definition: Hepatic Vein
The hepatic vein is the blood vessel that carries blood away from the liver and drains it into the posterior vena cava, completing the hepatic portal system.
Definition: Pulse
Pulse is the rhythmic expansion and elastic recoil of an artery caused by the contraction of the heart during ventricular systole.
Definition: Tissue Fluid
As the blood flows in the capillaries of the tissues, the plasma and the leukocytes "leak out" through their walls. This fluid bathes the cells and is called the tissue fluid or the intercellular or extracellular fluid.
Key Points
Key Points: Need for Transport Inside the Body
- Nutrients from the digestive system are transported to all body cells.
- Oxygen from the lungs is delivered to tissues, while carbon dioxide is carried back for exhalation.
- Excess water, salts, and nitrogenous wastes like urea are transported to excretory organs.
- Hormones from endocrine glands are circulated to target organs via the blood.
- Blood and lymph not only transport substances but also perform other essential functions in the body.
Key Points: Fluids in Our Body
Key Points: Blood Vessels Entering and Leaving the Heart
- The right atrium receives deoxygenated blood through two veins: the anterior vena cava (from the upper body) and the posterior vena cava (from the lower body).
- The left atrium receives oxygenated blood through four pulmonary veins, two from each lung.
- The pulmonary artery arises from the right ventricle and carries deoxygenated blood to the lungs for oxygenation.
- The aorta arises from the left ventricle and distributes oxygenated blood to all parts of the body.
- The coronary arteries, branching from the base of the aorta, supply blood to the heart muscles; their blockage can cause myocardial infarction (heart attack) or angina pectoris due to reduced blood supply.
Key Points: Valves of the Heart
- The tricuspid valve (right atrio-ventricular valve) is located between the right atrium and right ventricle; it has three cusps held by chordae tendineae attached to papillary muscles.
- The bicuspid or mitral valve (left atrio-ventricular valve) lies between the left atrium and left ventricle and has two cusps.
- The pulmonary semilunar valve is located at the opening of the pulmonary artery from the right ventricle; it has three pocket-shaped cusps.
- The aortic semilunar valve is found at the origin of the aorta from the left ventricle and also has three pocket-shaped cusps.
Key Points: Circulation of Blood in the Heart
- The cycle begins with atrial contraction (atrial systole) while the ventricles are relaxed; blood flows easily from atria into ventricles through open cuspid valves.
- As ventricles contract (ventricular systole) and atria relax, pressure closes the cuspid valves, preventing blood from flowing back into the atria.
- Chordae tendinae, attached to papillary muscles, hold the cuspid valve flaps in place and prevent their inversion during ventricular contraction.
- Blood is pushed out of the ventricles into the pulmonary artery and aorta through semilunar valves, which open under pressure from below.
- When ventricles relax again, blood tends to return, but the semilunar valves fill and close, preventing backflow into the heart.
Key Points: Heart Beat
- One heartbeat lasts about 0.85 seconds and includes atrial contraction, ventricular contraction, and relaxation of all chambers.
- The first sound "LUBB" is caused by the closure of tricuspid and bicuspid valves at the start of ventricular contraction.
- The second sound "DUP" is due to the closure of semilunar valves at the start of ventricular relaxation.
- Smaller animals and newborns have faster heart rates because of higher metabolism and heat loss.
- The full sequence of contraction and relaxation in a heartbeat is called the cardiac cycle.
Key Points: Pacemaker
- The pacemaker is the sino-atrial node (SAN) located in the wall of the right atrium near the opening of the superior vena cava.
- The SAN generates electrical impulses that initiate the heartbeat and regulate its rhythm.
- The impulse from the SAN is passed to the atrioventricular node (AVN) located near the inter-atrial septum and tricuspid valve.
- From the AVN, the impulse travels through the Bundle of HIS, which extends along the interventricular septum.
- The Bundle of HIS branches into Purkinje fibres that spread throughout the ventricles and cause them to contract.
- This entire system ensures coordinated contraction of atria and ventricles during each heartbeat.
- If the natural pacemaker fails, an artificial pacemaker can be implanted to maintain proper heart rhythm.
Key Points: Double Circulation
- Pulmonary circulation begins in the right ventricle and sends deoxygenated blood to the lungs via the pulmonary artery.
- The pulmonary veins return oxygenated blood from the lungs to the left atrium.
- Systemic circulation starts in the left ventricle, sending oxygenated blood to all body parts through the aorta.
- The aorta gives rise to branches that supply various body organs and tissues.
- Deoxygenated blood from the body returns to the right atrium through the anterior and posterior vena cava.
Key Points: Hepatic Portal System
- Veins from the stomach and intestines first carry blood to the liver through the hepatic portal vein, not directly to the heart.
- In the liver, the hepatic portal vein breaks into capillaries, allowing processing of absorbed nutrients before blood enters general circulation.
- The hepatic vein collects blood from the liver and drains it into the posterior vena cava.
- The liver performs glycogenesis, deamination, and detoxification of absorbed substances.
- The hepatic portal system ensures that digested food and harmful substances are filtered and processed before entering the bloodstream.
Key Points: Spleen
- The spleen stores blood and releases it during emergencies like haemorrhage or stress.
- It produces lymphocytes to help in immune defence.
- The spleen helps destroy old or damaged red blood cells, along with the liver.
- In the embryo, the spleen functions as a site for RBC production.
Important Questions [25]
- What are the functions of blood?
- Give biological reasons for the following statements: The left ventricle of the heart has a thicker wall than the right ventricle.
- The diagram given below represents a section of the human heart. Answer the questions that follow :
- State the exact location of the Chordae tendinae
- Differentiate Between Lubb and Dup (Names of the Valves Whose Closure Produce the Sound)
- The Biological/Technical Term for the Vein Which Drains the Blood from the Intestine to the Liver.
- the Biological/technical term for Blood vessels carrying blood to the left atrium.
- The Vein that Carries Oxygenated Blood.
- Fill in the Blanks with Suitable Functions: Eustachian Tube and ______
- The Diagram Below Represents the Human Heart in One Phase of Its Function. Study The Diagram Carefully and Answer the Questions that Follow
- Explain Pulse
- The exact location of the tricuspid valve
- The Diagram Below Represents the Simplified Pathway of the Circulation of Blood. Study the Same and Answer the Questions Which Follow
- Explain Diapedesis.
- Give Technical Terms For The Protective Covering of the Heart
- Name the Following: the Blood Vessel Which Supplies Blood to the Liver.
- Blood in the Pulmonary Artery Or Pulmonary Vein (Which One Contains Less Oxyhaemoglobin ?)
- Mention the exact location of the Pulmonary semilunar valve
- Give Appropriate Biological Or Technical Terms for the Following : the Complex Consisting of a Dna Strand and a Core of Histones
- Give Appropriate Biological Or Technical Terms for the Following the Relaxation Phase of the Heart.
- Given Below is a Diagram of a Human Blood Smear. Study the Diagram and Answer the Questions that Follow: Name the Components Numbered ‘1’ to ‘4’ and Mention Two Structural Differences Between the Parts ‘1’ and ‘2’. and Name the Soluble Protein Found in Part ‘4’ Which Forms Insoluble Threads During Clotting of Blood
- Match the Items Given in Column a with the Most Appropriate Ones in Column B and Rewrite the Correct Matching Pairs :
- Aqueous humour, Vitreous humour, lris, Central canal
- The exact location of the Bicuspid value
- The heart sound 'Dub' is produced when ______.
Concepts [18]
- Need for Transport in the Body
- Fluids in Our Body
- Blood
- Functions of Blood
- Plasma (The Liquid Portion of Blood)
- Erythrocytes vs Leukocytes vs Thrombocytes – A Comparative Overview
- Blood Circulatory System
- Blood Vessels Entering and Leaving The Heart
- Valves of the Heart
- Circulation of Blood in the Heart (Functioning of Heart)
- Heart Beat
- Pacemaker
- Arteries Vs Veins
- Pulmonary and Systemic Circulation (Double Circulation)
- Hepatic Portal System
- The Pulse
- Tissue Fluid (Or Intercellular Fluid)
- The Spleen
