Sharks have a ventral mouth opening with serrated teeth that can operate simultaneously or be gradually replaced. Their gastrointestinal tract includes a stomach and spiral intestine, and they lack salivary glands but have a well-developed liver and pancreas. Sharks have 5-7 pairs of gill slits on the sides of their pharynx and large olfactory lobes and cerebellum in their brain. Their skin has sensory buttons and taste buds in their oral cavity. Sharks have two-chambered hearts and use their gills to breathe by taking in water and releasing it, exchanging oxygen and carbon dioxide in their blood which is then distributed throughout their body.

1. Shark’s body structure
The mouth opening is ventral to the head and consists of a transverse slit. This provided with jaws,
formed by the palatocuadrado and jaw, which carry several sets of serrated teeth, conical or flat
pavementous. They can operate simultaneously several sets of teeth, or can operate a single, gradually
replaced by new series rearwards. Other small teeth can be distributed throughout the oral cavity.
Gastrointestinal tract comprises, in addition to respiratory function pharynx a saclike stomach and
intestine valve rectilinear spiral, the end portion thereof is provided rectal gland. They have no salivary
glands, the liver is well developed, and also have pancreas. Do not have a swim bladder. At the sides of
the pharynx opened five, six or seven rarely, clefts pairs, on whose walls are sheets of the same name.
These slits separately lead to the outside, to the sides of the back of the head.
The brain has particularly developed olfactory lobes, the cerebellum is large. On the body surface are
distributed sensitive buttons, and in the oral cavity taste buds. The lateral line organs, located in the side
channel also extend into the channel head and suborbitarios supra, and mandible. On the head are also
the ampullae of Lorenzini, which are electroreceptor’s. The fosillas olfactory covered nasal valves are
located in front of the mouth opening to the underside of the head. The eyes are protected by eyelids
and sometimes by phone nictitating membrane.
Aquatic
The urethras empty into the intestine forming a sewer. Always separate the sexes. The ovaries, even or
odd, are generally provided with oviducts, which flow into the sewer, together or separately, sometimes
accompanied by nidamentarias glands. In males there is a urogenital union; also drain into the sewer
deferens. Often the middle part of the ventral fins of the male has a copulatory organ shape.
In the circulatory system of man are the arteries that carry blood from the heart to the body and veins,
since blood vessels throughout the body, the heart. The movement of sharks is different. To start has
only two chambers (unlike humans possess four ), there have lungs , veins carry blood to the atrium and
ventricle then passes from there the arteries leading to the gills where oxygenate from there distributed
to the rest of body.
Shark blood has a hematocrit varied depending on the activity and characteristics of the species. Benthic
species have a percentage lower than 20%, with hemoglobin fairly low (less than 6 g per 100 ml of
blood).
Sharks use their gills to "breathe”. Unlike humans, sharks have separated from the respiratory tract.
To swimming, forcing leave their mouth open water inlet, which is conducted to the sides of the
gastrointestinal tract, thus passes through the gills taking oxygen from the water while releasing the
carbon dioxide. From this point, the blood is distributed throughout the body and in step releases
oxygen and absorbs carbon dioxide from muscles and organs.
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