Respiration takes place only through the lungs in mammal. Lungs are situated in the pleural cavities found in the thorax.

The respiratory channel is separated from the food channel by the presence of palate. The respiratory system of rabbit comprises nasal chambers, larynx, trachea, bronchi and lungs.

Respiratory Organ and its Related Parts:

1. Nasal chamber:

The air passes through the external nares into two large respiratory passages, which are hollow cavities present above the plate. The respiratory passage is divided in to right and left halves by the mesethm bone. Each side, the respiratory passages is divided in to two regions.

An anterior nasal chamber.

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A posterior respiratory tube.

The nasal chamber is bounded dorsally by nasal bone and ventrally by hard palate. The turbinals, very much folded scroll kike bones, are present within the nasal chambers. The turbinals are covered by richly vascular, glandular and ciliated epithelium. One respiratory tube opens behind the soft palate through the internal nares into the pharynx directly and that too very close to the glottis.

Function:

The nasal chambers serve as very efficient filters, i.e. it removes fine and coarse dust particles, germs etc. through mucous covering the turbinals.

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It helps to warm up the air before it is to be inhaled and enters the lungs.

Due to the covering of sensory epithelium, it helps in the detection of smell.

2. Larynx.

The pharynx opens into a larynx or sound blood through the glottis. The larynx lends in to a trachea. This is the anterior end of the windpipe or trachea.

Structure:

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The larynx is a cylindrical box like structure. Its wall is supported by following four cartilages.

( i ) The thyroid, cartilage, forming an incomplete ring around the larynx. Dorsally, it is incomplete but ventrally it is complete and broad.

(ii) The cricoid cartilage is a complete ring around the base of larynx and it lies at the base of thyroid dorsally.

Two small cartilages, called arytenoids, articulate with the cricoids. They are present above the thyroid and in front of the cricoids. A small Knob-like structure, called cartilage of Santorin, is present at the anterior end of each arytenoid.

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From the ventral edge of the thyroid and in front of glottis, arises an elastic cartilaginous epiglottis which serves to prevent food, entering the glottis (that to larynx, trachea etc.).

Inside the larynx, there is a cavity known as laryngeal chamber, which contains vocal cords. Vocal cords are two pairs of elastic membranes. Pair of true vocal cords is present in front of the true vocal cords. These vocal cords can be set into vibration by the passage of air over them to produce the ‘voice’ – in rabbits mainly a squeak. These membranes close the glottis except for a slit between their free edges. It is through the gap that air enters during respiratory movements.

Trachea:

After larynx, the trachea is a long respiratory tube is a long respiratory tube extending through the neck into the thoracic cavity. It is lined internally by ciliated cartilaginous rings which are incomplete on the dorsal side. These ‘c’ shaped cartilaginous rings help to prevent the collapse of trachea and to keep it expanded allowing free passage of air to and from the lungs. The mucous glands present in the wall of trachea help (i) in keeping its inner surface moist and shmy, (ii) in holding dust particles and bacteria. Thus only the clear air is allowed to pass into the lungs. The dust particles are swept towards the pharynx by cilia.

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Bronchi:

In the thorax, the trachea divides into left and right bronchi (sing bronchus) which enter the lungs. The bronchi possess the similar structure as the trachea. After entering in to the lungs, each bronchus divides into many thinner branches, called bronchioles.

Which again divide into finer bronches of less diameter known as respiratory bronchioles. Each respiratory bronchiole divides again into many finer branches, called alveolar ducts or infundibulum. The alveolar ducts end in small hollow air sacs, known as alveolar sacs. Each alveolar sac is formed of many small thin walled hollow alveoli or air cells.

The respiratory bronchiole alveolar duct, alveolar sac and alveoli are devoid of cartilaginous rings but their walls possess ciia. There is a network of capillaries of pulmonary artery and pulmonary vein around each alveolus. This complicated branching increases the total respiratory surface and allows the air to penetrate into every portion of the lungs.

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Lungs:

The lungs are soft compact and spongy mass of tissues lying in the pleural cavity within the thorax. Each lung is covered by a fold of coelomic epithelium, which is in contact with the organ (visceral pleura). Each lung is divided into lobes. The right lung has four lobes.

(i) Anterior azygos.

(ii) Right anterior lobe.

Right posterior lobe.

Posterior azygos. But left lung has got two lobes.

Left anterior lobe.

A left posterior lobe.

The left posterior lobe is three times larger than the left anterior lobe.