- 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 the circulatory system.
Definitions [3]
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 portal vein.
A portal vein is one that starts with capillaries and also ends in capillaries.
Key Points
Key Points: Fluids in Our Body
Key Points: Circulatory Pathways
- Two types of circulatory pathways - Open (arthropods & molluscs, blood into body cavities, less regulated) and Closed (annelids & chordates, a closed network of vessels, more precise).
- All vertebrates have a muscular chambered heart - Fish = 2-chambered, Amphibians & Reptiles (except crocodiles) = 3-chambered, Crocodiles, Birds & Mammals = 4-chambered.
- In fish, the heart pumps deoxygenated blood, which is oxygenated by the gills.
- Amphibians and reptiles have incomplete double circulation - oxygenated and deoxygenated blood mix in a single ventricle.
- Birds and mammals have complete double circulation - separate pathways for oxygenated and deoxygenated blood.
- Open system = simple, less energy-intensive; Closed system = more efficient, precise regulation.
Key Points: Human Circulatory System
- Arteries carry oxygenated blood from the heart to tissues, while veins bring deoxygenated blood back; capillaries connect them.
- Exception: Pulmonary artery carries deoxygenated blood, and pulmonary vein carries oxygenated blood.
- The heart is fist-sized, located in the thorax between the lungs, and protected by the pericardium.
- The heart has four chambers separated by septa, with valves (tricuspid, bicuspid/mitral, semilunar) ensuring one-way blood flow.
- Heart sounds: “Lub” is due to closure of the tricuspid and bicuspid valves, and “Dub” is due to closure of the semilunar valves.
- The SA node (pacemaker) generates impulses (70–75/min) and controls the heartbeat through the AV node and the bundle of His.
Key Points: Regulation of Cardiac Activity
- The heart is myogenic - its activities are intrinsically regulated by nodal tissue (SAN and AVN), meaning it generates its own impulse.
- A neural centre in the medulla oblongata moderates cardiac function through the ANS.
- Sympathetic nerves (ANS) increase heart rate, ventricular contraction strength and cardiac output.
- Parasympathetic nerves (ANS) decrease heart rate, slow conduction speed and reduce cardiac output. (AIPMT 2007)
- Adrenal medullary hormones also increase cardiac output.
Key Points: Disorders of Circulatory System
- Hypertension (high BP) is when blood pressure is above 120/80 mm Hg; ≥140/90 mm Hg is serious and can damage the heart, brain, and kidneys.
- Coronary Artery Disease (CAD) or atherosclerosis occurs due to fat, cholesterol, and calcium deposits, narrowing the arteries supplying the heart.
- Angina (angina pectoris) is chest pain caused by reduced oxygen supply to the heart muscles due to restricted blood flow.
- Heart failure is when the heart cannot pump enough blood to meet the body's needs; it is different from a heart attack and cardiac arrest.
- Coronary thrombosis is the formation of a blood clot in the coronary arteries, often in the left anterior descending artery.
- These disorders mainly affect blood flow and oxygen supply, leading to serious cardiovascular problems.
