Ibn al-Nafis

 Firstly describe the pulmonary circulation, coronary circulation, and capillary circulation with true anatomy of the heart which form the basis of the circulatory system. He wrote: “The lungs are composed of parts, one of which is the bronchi, the second the branches of the arteria venosa and the third the branches of the vena arteriosa, all of them connected by loose porous flesh. The blood from the right chamber of the heart must enter the left chamber, but there is no direct pathway between them. 

The thick septum of the heart is not perforated and does not have visible openings as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substance, be mingled with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart Arteries and the heart do not expand and contract at the same time, but rather the one contracts while the other expands” and vice versa. 

He also recognized that the purpose of the pulse is to help disperse the blood from the heart to the rest of the body. He completely rejected the Galenic theory of pulsation after his discovery of the pulmonary circulation. Furthermore, he developed his own Nevisian theory of pulsation after discovering that pulsation is a result of both natural and forced motions, and that the “Forced motion must be the contraction of the arteries caused by the expansion of the heart, and the natural motion must be the expansion of the arteries. 

The primary purpose of the expansion and contraction of the heart is to absorb the cool air and expel the wastes of the spirit and the warm air; however, the ventricle of the heart is wide. Moreover, when it expands it is not possible for it to absorb air until it is full, for that would then ruin the temperament of the spirit, its substance and texture, as well as the temperament of the heart. Thus, the heart is necessarily forced to complete its fill by absorbing the spirit

A White Great Shark

A great white shark attacks from A Seton and behind, taking its victim by surprise. To do this it has to come up fast and keep its quarry in sight. Its eves must react rapidly to the change in light if its hunt is to be successful. Like all other sharks, the great white relies on its array of senses to locate prey such as seals and sea lions. But its sight is crucial to pinpointing a victim at the surface. Silhouetted against the light just as a human, entering a brightly lit room from the darkness outside, can be briefly dazzled and take 2 few seconds to adjust to the change, so a shark, rising to the surface from the murky depths must cope with a rapid increase in light. It cannot afford to wait for its eves to adjust — a lost second and the prey could be gone.

The secret of this ability lies in the tapetum, a laver of mirror-like plates at the back of the eyeball. It is the tapetum that eerily lights up the cat’s eyes when it is caught in Car headlamps at night. By reflecting light back through the retina, it effectively doubles the amount of light for the eye to use. This is essential for night hunters, like the cat. if they are to see with clarity, especially in the faint moonlight. In the day, though, too much light can be a problem. The cat copes by narrowing its pupil, the gap that Jets in light, to 4 wafer-thin slits, using the muscles in the iris.

The great white shark's tapetum greatly enhances its vision in the murky depths, but it has no iris to protect its eyes when it surfaces rapidly. In order to compensate, it has developed a ‘curtain’ of cells containing pigment. As the shark moves into bright light, these automatically expand over each tapetal plate and then contract as it returns to the depths.

While it is swimming in shallow water, a shark needs to be able to see into the light above it and into the dark below. In this case, the tapetal curtain reacts differently in each half of the eye. The lower half-eye of a killer whale hunting deep in the ocean, a blue shark relies upon reflective plates behind its eyeballs to increase the amount of light striking the retina. of the tapetum, which reflects light from above, is covered to protect the retina. The upper half of the tapetum, which reflects light from below, is exposed to make the most of the light hitting the retina and so give as clear a picture as possible of the murky depths below.