RESPIRATORY SYSTEMS Skin- unicellular and small animals Trachea- in arthropoda Gills- Fish Parabronchus-Birds Lung-many vertebrates except fish

The respiratory gases that animals must exchange are oxygen (O2) and carbon dioxide (CO2). Diffusion is the only means by which respiratory gases are exchanged between the internal body fluids of an animal and the outside medium (air or water).

Many anatomical adaptations maximize the specialized body surface area (A) over which respiratory gases can diffuse.

Invertebrate respiratory system Respiratory gases can diffuse through air most of the way to and from every cell of an insect’s body. This diffusion is achieved through a system of air tubes, or tracheae, that communicate with the outside environment through gated openings called spiracles. Insect body fluid never carries respiratory gases. Crustaceans have internal gills. Arachnids have specialized folded tracheae

Fish Gills The internal gills of fish are supported by gill arches that lie between the mouth cavity and the protective opercular flaps. Water flows unidirectionally into the fish’s mouth, over the gills, and out. The gills have an enormous surface area for gas exchange because they are so highly divided. Each gill consists of hundreds of leaf-shaped gill filaments.

Blood flows through the lamellae in the direction opposite to the flow of water over the lamellae. This countercurrent flow optimizes the gas exchange.

Vertebrate respiratory system Amphibia Reptiles, mammal The surface area(alveoli) of the respiratory organs increases from amphibia to mammals. Birds don’t have alveoli instead they have parabronchus.They don’t have a diaphragm.

Bird lung The structure of bird lungs allows air to flow unidirectionally through the lungs, rather than having to flow in and out. Thus there is little dead space in bird lungs, and the fresh incoming air is not mixed with stale air. In this way, a high PO2 gradient is maintained. In addition to lungs, birds have air sacs at several locations in their bodies. The air sacs are interconnected with the lungs and with air spaces in some of the bones. The air sacs receive inhaled air, but they are not gas exchange surfaces. In bird lungs, the bronchi divide into tubelike parabronchi that run parallel to one another through the lungs The air sacs keep fresh air flowing unidirectionally and continuously over the gas exchange surfaces. Thus, the bird can supply its gas exchange surfaces with a continuous flow of fresh air

HUMAN RESPIRATORY SYSTEM Air enters the lungs through the oral cavity or nasal passage, which join together in the pharynx. a single trachea leads to the lungs. At the beginning of this airway is the larynx, or voice box, which houses the vocal cords. The trachea is about 2 cm in diameter. Its thin walls are prevented from collapsing by Cshaped bands of cartilage that support them as air pressure changes during the breathing cycle. The alveoli are the sites of gas exchange. The total number of alveoli in human lungs is about 300 million. Even though each alveolus is very small, their combined surface area for diffusion of respiratory gases is about 70 m2

Inhalation is initiated by contraction of the muscular diaphragm. As the diaphragm contracts, it expands the thoracic cavity, pulls on the pleural membranes, and increases the negative pressure in the pleural cavity. Exhalation begins when the contraction of the diaphragm ceases. The diaphragm relaxes and moves up, and the elastic recoil of the lung tissues pushes air out through the airways. When a person is at rest, inhalation is an active process and exhalation is a passive process

When we are at rest, the amount of air that moves in and out per breath is called the tidal volume (about 500 ml for an average human adult). The combined tidal volume, inspiratory reserve volume, and expiratory reserve volume is the vital capacity. The lungs and airways cannot be collapsed completely; they always contain a residual volume. The total lung capacity is the sum of the residual volume and the vital capacity.

Blood Transport of Respiratory Gases The liquid part of the blood, the blood plasma, carries some O2 in solution, but its ability to transport O2 is quite limited. To increase its O2 transport capacity, the blood of most animals, vertebrate and invertebrate, also contains molecules that can bind reversibly to O2 depending on its partial pressure. Hemoglobin increases the capacity of blood to transport O2 by about 60-fold. Each molecule of hemoglobin can bind to four molecules of O2. Muscle cells have their own oxygen-binding molecule, myoglobin.

External respiration: between alveoli and blood. Internal respiration: between blood and tissue cells. Cellular respiration: breakdown of glucose

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Oxygen transport Oxygen exchange depends on the partial pressure of the oxygen. The partial pressure in alveoli is 104. But it is 40 mmHg at pulmonary artery. Thus oxygen passes to blood. And is carried as oxyhemoglobin. Hb + O2 HbO2 (in alveoli) (in alveoli) HbO2 Hb+O2 ( in tissues) ( in tissues) The oxygen partial pressure in aorta decreases to 40 in tissues. And oxygen passes from blood to tissues.

Carbondioxide transport Carbondioxide passes to blood according to the partial pressure. –CO2 is carried as a soluble gas in plasma –Some is carried as carboxyhemoglobin. –Some is carried in the carbonic acid form When CO 2 diffuses from tissues to the blood, with the help of the carbonic anhydrase enzyme water reacts with CO2 and forms carbonic acid. Then carbonic acid ionizes and form H and bicarbonate ions HCO 3. H ions bind with Hb. HCO 3 ions diffuses from erythrocytes to plasma and transported to lungs. In tissues: H CO 2 + H 2 O H 2 CO 3 HCO 3 HCO3, binds with Na, to form NaHCO3.

In lungs NaHCO3 ions ionizes to HCO3 and diffuses to erythrocytes. Then HCO3 binds with H and form carbonic acid. Carbonic acid ionizes to CO 2 and water with the help of enzyme. CO 2 is thrown out to alveoli. In alveoli: HCO 3 H 2 CO 3 CO 2 + H 2 O H

Control of respiration Breathing is an autonomic function of the nervous system. The autonomic nervous system maintains breathing and modifies its depth and frequency to meet the demands of the body for O2 supply and CO2 elimination. The breathing rhythm is an autonomic function generated by neurons in the medulla(brain stem) and modulated by higher brain centers. The most important feedback stimulus for breathing is the level of CO2 in the blood(decrease in pH). The breathing rhythm is sensitive to feedback from chemoreceptors on the ventral surface of the medulla and in the carotid and aortic bodies on the large vessels leaving the heart hill.com/sites/ /student_view0/chapter44/animations.html hill.com/sites/ /student_view0/chapter44/animations.html