● When a finger is cut, the wound does not continue to `color{violet}("bleed")` for a long time; usually the `color{violet}("blood stops")` flowing after sometime.

● `color{violet}("Blood")` exhibits `color{brown}("coagulation or clotting")` in response to an`color{violet}(" injury or trauma.")`

● This is a mechanism to prevent excessive loss of `color{violet}("blood")` from the `color{violet}("body.")`

● One can observed a `color{violet}("dark reddish brown scum")` formed at the site of a cut or an injury over a period of time.

● It is a clot or coagulam formed mainly of a network of threads called `color{brown}("fibrins")` in which `color{violet}("dead and damaged")` formed elements of blood are trapped.

● `color{violet}("Fibrins")` are formed by the conversion of `color{brown}("inactive fibrinogens")` in the plasma by the enzyme `color{brown}("thrombin.")`

● `color{violet}("Thrombins")`, in turn are formed from another inactive substance present in the plasma called `color{brown}("prothrombin.")`

● An `color{violet}("enzyme complex")` , `color{brown}("thrombokinase,")` is required for the above reaction.

● This complex is formed by a series of linked `color{violet}("enzymic reactions")` ( `color{brown}("cascade process")`) involving a number of factors present in the plasma in an inactive state.

● An injury or a `color{violet}("trauma")` stimulates the `color{brown}("platelets")` in the blood to release certain factors which activate the mechanism of `color{violet}("coagulation.")`

● Certain factors released by the tissues at the `color{brown}("site of injury")` also can initiate coagulation.

● `color{brown}("Calcium ions")` play a very important role in `color{violet}("clotting.")`

● As the `color{violet}("blood passes")` through the `color{violet}("capillaries in tissues")`, some water along with many small water soluble substances move out into the spaces between the `color{violet}("cells of tissues")` leaving the larger proteins and most of the
formed elements in the `color{violet}("blood vessels.")`

● This fluid released out is called the `color{brown}("interstitial fluid or tissue fluid.")`

● It has the same `color{violet}("mineral distribution")` as that in `color{violet}("plasma.")`

● Exchange of `color{violet}("nutrients, gases")`, etc., between the `color{violet}("blood")` and the `color{violet}("cells")` always occur through this fluid.

● An elaborate network of vessels called the `color{brown}("lymphatic system")` collects this fluid and drains it back to the major veins.

● The fluid present in the `color{violet}("lymphatic system")` is called the `color{brown}("lymph.")`

● `color{violet}("Lymph")` is a colourless fluid containing `color{brown}("specialised lymphocytes")` which are responsible for the immune responses of the body.

● `color{violet}("Lymph")` is also an important carrier for `color{violet}("nutrients, hormones")`, etc.

● `color{brown}("Fats")` are absorbed through `color{violet}("lymph")` in the `color{brown}("lacteals")` present in the `color{violet}("intestinal villi")`

● The circulatory patterns are of two types – `color{brown}("open or closed.")`

● `color{brown}("Open circulatory system")` is present in arthropods and `color{violet}("molluscs")` in which `color{violet}("blood pumped")` by the heart passes through large vessels into open spaces or body cavities called `color{brown}("sinuses.")`

● Annelids and chordates have a `color{brown}("closed circulatory system")` in which the `color{violet}("blood pumped")` by the `color{violet}("heart")` is always circulated through a closed network of `color{brown}("blood vessels.")`

● This pattern is considered to be more advantageous as the `color{violet}("flow of fluid")` can be more precisely regulated.