Whales do not possess the typical nose structure found on land mammals. Instead, they breathe through a highly modified nasal opening called the blowhole, which is positioned on the top surface of the head. This single or double opening is the sole point of gas exchange for these air-breathing marine mammals. The blowhole allows the whale to quickly exhale and inhale with minimal effort at the ocean’s surface.
The Blowhole: Whale Anatomy and Function
The blowhole is essentially a muscularized version of the nostril, engineered to function in an aquatic environment. A powerful, fibrous plug or muscular flap controls the external opening, keeping it tightly sealed when the whale is submerged. This closure is maintained by muscle relaxation, meaning the animal must actively contract muscles to open the blowhole for a breath, making whale breathing a conscious act.
When a whale surfaces, it first forcibly expels stale, warm air at a high velocity, which causes the characteristic “blow” or spout. This visible plume is not water but a combination of condensed water vapor, mucus, and oils from the respiratory tract. The rapid exhalation is immediately followed by a fast, deep inhalation of fresh air, often completed in less than two seconds for large species.
A crucial internal adaptation is the functional separation of the respiratory tract from the digestive tract. Unlike humans, a whale’s larynx extends upward to form a specialized structure called the “goosebeak.” This goosebeak locks into the nasal passage, creating a continuous airway from the blowhole directly to the lungs. This anatomical arrangement ensures that the whale can open its mouth to feed underwater without any risk of water entering the lungs.
The Evolutionary Journey of the Nostril
The placement of the blowhole on the head traces back to the whale’s terrestrial ancestors more than 50 million years ago. Early cetaceans, such as the Pakicetus, were land mammals with nostrils located at the tip of the snout, similar to most other mammals. As these ancestors began spending more time in the water, the nasal opening gradually migrated backward along the skull.
This evolutionary shift, often referred to as “telescoping” of the skull, moved the nostril from the front of the face to the crown of the head. The change allowed whales to breathe by barely breaking the water surface, a distinct advantage for an animal needing to maintain a streamlined body while swimming. The embryonic development of modern whales still reflects this history, as the nasal passage initially forms parallel to the palate before shifting to its final, angled position.
Variations in Blowhole Structure
The structure of the blowhole differs between the two main suborders of whales, reflecting distinct evolutionary paths. The Odontocetes, or toothed whales, which include dolphins, porpoises, and sperm whales, possess a single blowhole opening. This single external opening is the result of one of the two ancestral nostrils having functionally closed.
In contrast, the Mysticetes, or baleen whales, retain two distinct blowholes. These two openings are positioned side-by-side on the crown of the head, often forming a characteristic V-shape when viewed from above. Having two openings provides a larger cross-sectional area for air exchange, which is beneficial for these larger whales.
Respiratory Adaptations for Deep Diving
A whale’s respiratory system is internally fine-tuned for extended periods underwater. Whales demonstrate high efficiency in gas exchange, capable of refreshing approximately 80 to 90 percent of the air in their lungs with a single breath. This is significantly higher than the 10 to 20 percent air exchange typical in human respiration.
To support long dives, a whale’s blood and muscle tissue contain high concentrations of oxygen-storing proteins, like myoglobin, which hold oxygen reserves. When deep diving, the flexible rib cage and elastic lungs allow for a controlled collapse of the air sacs, or alveoli, under immense pressure. This alveolar collapse forces any remaining air into the rigid upper airways where gas exchange cannot occur. By preventing nitrogen from dissolving into the tissues at high pressure, this mechanism protects the whale from decompression sickness.