Rabbit: respiratory and circulatory systems
Air reaches the rabbit's lungs through the nostrils, larynx, trachea and bronchi; the diaphragm helps breathing. A four-chambered heart keeps oxygenated and deoxygenated blood apart.
Path of air
The **larynx** is the voice box. The **epiglottis** is a flap that covers the glottis during swallowing, so food does not enter the windpipe.
Lungs and breathing
- Two spongy, pink lungs lie in the thoracic cavity, each covered by a double membrane, the pleura.
- Each lung has a very large number of tiny air sacs, the alveoli, wrapped in blood capillaries. Oxygen diffuses into the blood; CO₂ diffuses out.
- Breathing in (inspiration): the diaphragm contracts and flattens, and the intercostal muscles lift the ribs. The chest cavity grows, and air rushes in.
- Breathing out (expiration): the diaphragm and intercostal muscles relax. The chest cavity shrinks, and air is pushed out.
The heart and its main vessels
| Part | Feature |
|---|---|
| Position | In the thoracic cavity between the lungs, inside a double membrane, the pericardium |
| Right auricle | Receives deoxygenated blood from the body through two precavals (from the front) and one postcaval (from the hind part) |
| Left auricle | Receives oxygenated blood from the lungs through the pulmonary veins |
| Valves between auricles and ventricles | Tricuspid on the right, bicuspid (mitral) on the left; they stop blood flowing back |
| Right ventricle | Pumps deoxygenated blood to the lungs through the pulmonary artery |
| Left ventricle | Thickest wall; pumps oxygenated blood to the body through the aorta (left systemic arch) |
| Semilunar valves | At the bases of the pulmonary artery and the aorta |
Blood and double circulation
The rabbit has a closed circulatory system: blood always flows inside vessels. Blood has plasma with red blood cells (round, biconcave and without a nucleus), white blood cells and platelets. Blood passes through the heart twice in one round of the body. Pulmonary circulation goes from the heart to the lungs and back; systemic circulation goes from the heart to the body and back. This double circulation never lets oxygenated and deoxygenated blood mix.
How to draw the respiratory system of a rabbit
- 1Draw a narrow tube down the middle of the page: the trachea. Mark C-shaped cartilage rings across it, and draw a small box at the top: the larynx.
- 2At the bottom, split the tube into two: the right bronchus and the left bronchus.
- 3Draw a large, spongy lung around each bronchus, with branching lines for bronchioles. At one tip, draw a small bunch of grapes for the alveoli.
- 4Draw a curved dome below both lungs: the diaphragm. Label the space around the lungs thoracic cavity and the lining pleura.
Like the rabbit, you breathe with a diaphragm; a hiccup is a sudden jerk of this muscle. Many forms of pranayama in yoga train slow, deep breathing with the diaphragm.
2 marks: “What is the role of the diaphragm in the rabbit?” It separates the thoracic and abdominal cavities; its contraction and relaxation help in breathing in and out.
4 marks: “Describe the structure of the heart of the rabbit.” Four chambers; right auricle receives blood from two precavals and one postcaval; left auricle from pulmonary veins; tricuspid, bicuspid and semilunar valves; pulmonary artery and aorta; pericardium; double circulation.
7 marks: “Explain the respiratory system of the rabbit with a labelled diagram.” Labelled diagram; path of air from nostrils to alveoli; lungs and pleura; gas exchange; breathing in and out with the diaphragm and intercostal muscles.
The rabbit's right auricle gets '2 + 1': two precavals and one postcaval. 'Try Right': Tricuspid on the Right.