What is bile ? What is its composition and function ?

Question 14:What is bile ? What is its composition and function ?
Answer: Bile is a yellowish green liquid having a bitter taste, it is secreted by liver (contains 98 % of water) and is stored in gall bladder.
Bile consists of 4 types of chemicals. They are inorganic salts like Na, K, Ca, biocarbonates, Bile salts sodium glycocholate and sodium taurocholate bile pigments such as biliverdin, bilirubin and fatty substances such as cholesterol and phospholipids. Bile is alkaline. It contains no digestive enzymes. Still, has some digestive function such as (i) it neutralises the acidity of chyme and enables the action ofpancreatic and intestinal enzymes, (ii) activates pancreatic lipase and augment the action of other pancreatic enzymes, (iii) emulsifies fat and promotes fat digestion, (iv) helps the absorption of fatty acids and vitamins D, E and K, (v) stimulates the peristaltic movements of intestinal wall.
Question 15:Citing examples, explain open and closed circulatory system ? In human heart there is no mixing up of impure and pure blood - why ?
Answer: Open circulatory system is one in which blood flow through open spaces like lacunae and sinuses for bathing the living cells directly.
eg. In arthropods and molluscs.
Closed circulatory system is one in which' blood flows through closed tubes called blood vessels.
e.g. :- In chordates and some annelids (eg. earthworm)
Human heart is four chambered with two auricles (left and right) and two ventricles (left and right). The two auricles are separated from each other by a longitudinal interauricular septum. Similarly two ventricles are also separated from each other by an interventricular septum. The right auricle communicates with the right ventricle only and the left auricle communicates with the left ventricle only. So deoxygenated blood entering the heart in right auricle passes into right ventricle which pumps it into pulmonary arteries. Oxygenated blood enter left auricle and reaches left ventricle. The left ventricle pumps it into aorta for distribution. So there is no mixing of deoxygenated and oxygenated blood in the human heart.