- 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 [7]
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.
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.
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.
Define the Circulatory system.
The circulatory system is a transport system moving substances throughout our body with the help of blood.
Define portal vein.
A portal vein is one that starts with capillaries and also ends in capillaries.
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: Fluids in Our Body
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: 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.
