II.

Bodies of Whales

Whales are enormous in size compared to all other animals. The blue whale is one of the largest animals that has ever lived, reaching a length of over 24 m (80 ft) and a weight of 150 metric tons. Its heart is as big as a Volkswagen Beetle, and its body is almost as large and about as heavy as that of the largest known dinosaur.

Whales have a streamlined, rounded body tapering in the rear to a pair of broad horizontal tail flukes that provide the main propulsive thrust for swimming. They have paddle-shaped flippers that help stabilize and steer the whale while swimming. The bones of the flippers resemble the jointed limbs and digits of land mammals. Many whales have a dorsal fin located at or behind the center of the back.

A.

Skin

A whale’s skin feels much like smooth, wet rubber to the touch. The skin has no sweat glands or oil glands, and it is nearly devoid of hair. Beneath the skin is a thick layer of fat called blubber that aids in buoyancy, serves as a source of stored energy, and helps preserve body heat. Blubber permits whales to stay warm even in near-freezing waters.

B.

Blowhole and Lungs

Whales do not breathe through their mouths, but rather through a nostril, or blowhole, located on the top of the head. Toothed whales have only a single blowhole; baleen whales have two blowholes. The blowhole opens by a slight muscular contraction and closes automatically when the muscle relaxes. As a whale surfaces it exhales through the blowhole, creating a loud sound and characteristic cloud of mist known as the spout. The spout is caused by condensation from the exhaled warm, moist air, not from seawater trapped in the blowhole, as was once believed.

Air taken in through the blowhole travels through the trachea (windpipe) to the lungs. Unlike for most land animals, the trachea does not connect to the throat. So when the whale opens its mouth underwater to feed, water does not rush into the lungs as it would in land animals. This structural arrangement enables the whale to breathe air and swallow food at the same time.

The lungs transfer oxygen to the blood while removing the blood’s carbon dioxide. Relative to body size, whale lungs are proportionally somewhat smaller than human lungs. But whale lungs are far more efficient: While human lungs exchange about 15 to 20 percent of their contents with each breath, whale lungs exchange about 90 percent with each breath. This means that whales can take up oxygen and dispose of carbon dioxide much faster than humans, enabling them to hold their breath underwater for long periods.

C.

Digestive System

When whales swallow food, it travels through the esophagus to a multichambered stomach that resembles the stomachs of ruminant hoofed animals such as cattle, sheep, and deer. In the first stomach chamber, a saclike extension of the esophagus, food is crushed. In the second chamber, digestive juices further break down food. Most cetaceans have a third stomach chamber, which regularly contracts to mash and thoroughly mix food with digestive juices. The stomach capacity of a large whale can reach 760 liters (200 gallons).

From the stomach food moves through the intestine, where nutrients pass through the intestinal wall and are absorbed into the blood. Remaining waste materials are eliminated through the anus into the ocean. Cetaceans lack two internal organs found in most land mammals: the gallbladder and appendix.

D.

Sense Organs

The eyes of most whales are well adapted for life underwater. Strong muscles surrounding each eye change the shape of the eye’s lens. This enables whales to focus their vision both underwater and above water. Whale eyes can withstand high pressure when the animal dives to great depths, and the tear ducts shed oily tears that enhance underwater vision and protect the eyes from the effects of salt water.

The streamlined bodies of whales do not have the external ear structures called pinnae that land mammals use to gather airborne sound. But whales still have excellent hearing and can perceive a wide range of sounds, many of which are not audible to humans. For toothed whales that commonly hunt for food in the dark depths of the ocean, hearing is often enhanced by echolocation, in which the animals emit clicking sounds that bounce off objects. The returning echo is used as a sonar image of the underwater surroundings. Toothed whales share this ability with bats, shrews, and a few kinds of birds.

Baleen whales have a poor sense of smell, and toothed whales lack smell entirely. Some whales, such as dolphins, can taste different chemicals in water to differentiate between sweet, sour, bitter, and salty, but in general the sense of taste in whales is limited.