Topic 13: Gas Exchange Ch. 42. Gas Exchange pp Gas Exchange. Gas Exchange in Fish pp Gas Exchange in Fish

Size: px

Start display at page:

Download "Topic 13: Gas Exchange Ch. 42. Gas Exchange pp Gas Exchange. Gas Exchange in Fish pp Gas Exchange in Fish"

Theresa Norris
5 years ago
Views:

Topic 13: Gas Exchange Ch. 42 Fig. 42.24 Gas Exchange pp.979-989 Gas exchange involves the uptake of oxygen and the discharge of carbon dioxide (i.e. respiration or breathing).

1 Topic 13: Gas Exchange Ch. 42 Fig Gas Exchange pp Gas exchange involves the uptake of oxygen and the discharge of carbon dioxide (i.e. respiration or breathing). It is necessary for cellular respiration. Respiratory medium - The source of oxygen; either air (~21%) or water (~0.5%). Respiratory surface - The part of the animal where O 2 diffuses in and CO 2 diffuses out. Gas Exchange Gas exchange surfaces have four characteristics in common: 1. Wet because gases can only be exchanged when dissolved in water. 2. Thin and permeable. 3. Have a large O 2 gradient. 4. Have a large surface area. Gas Exchange in Fish pp Fish live in water, so keeping their respiratory surface wet is not a problem. They are covered in think scales so they can not easily exchange gases through them, instead they use gills. Gills - Out-foldings of the body surface specialized for gas exchange. Oxygen level in the water is low so to maintain efficient gas exchange, fish use a countercurrent exchange system. Gas Exchange in Fish Fig Gills are composed of: Archs - Supporting structure of the gill containing blood vessels. Each arch has two rows of filaments. Filaments - Composed of flattened plates called lamellae. Lamellae - Composed of capillaries. It is where water flows over the capillaries and O 2 is picked up and CO 2 eliminated. 1

2 Gas Exchange in Fish To help increase water flow over the gills (ventilation), boney fish have opercula. Operculum - Hard but flexible cover that protects the gills and aids in the pumping of water over the gills. Ventilation of the gills: 1. Water enters the mouth. 2. Moves through slits in the pharynx. 3. Flows over the gills between the lamellae. 4. Operculum pumps water outside. pp Grasshoppers breath air which has a high concentration of oxygen but is dry. To keep their exchange surface wet it is internalized. To increase the surface area, it is composed of highly branched trachea. Trachea - Air tubes that branch throughout the entire body of an insect. The tracheal system also include air sacs which store air and spiracles. Spiracles - Openings to the outside of the tracheal system which can be closed, usually to prevent water loss. The abdomen can be compressed and expanded to increase air flow (ventilation). Fig Trachea are highly branched into smaller tracheoles which deliver O 2 and remove CO 2 directly from cells. This system therefore does not need to rely on the circulatory system to exchange gasses. This system is highly efficient for small organisms but can not exchange enough gas to support large organisms. pp Mammals have lungs. Lungs are not in direct contact with all other parts of the body, therefore the circulatory system is needed for transport of gases. The lung is lined with a thin moist epithelium which is supplied with a dense net of capillaries for exchange. Pathway of air in the lungs: 1. Air enters the mouth or nostrils which filter air and sample for odors. 2. It then enters the pharynx which is shared by respiratory and digestive systems. 3. Then through the larynx (voice box). To prevent food entering the respiratory system the larynx can be closed by the epiglottis, a flap of cartilage. 4. The trachea (windpipe) connects the pharynx with lungs. It has rings of cartilage to maintain shape. 2

5. The trachea branches into two bronchi, one leading to each lung. 6. The bronchi further branch into smaller bronchioles. 7. At the end of the bronchioles are alveoli.

- Air is moved into and out of the lungs though negative pressure breathing which creates a vacuum that sucks air in. - The diaphragm is a thin muscle that separates the thorax from the abdomen.

3 5. The trachea branches into two bronchi, one leading to each lung. 6. The bronchi further branch into smaller bronchioles. 7. At the end of the bronchioles are alveoli. These are air sacs connected to blood capillaries. Gas exchange occurs here. Fig Note: Air enters, turns around and leaves. It is two-way flow. - Air is moved into and out of the lungs though negative pressure breathing which creates a vacuum that sucks air in. - The diaphragm is a thin muscle that separates the thorax from the abdomen. - It is curved when relaxed and flat when contracted. - Contracting the diaphragm makes the thoracic cavity larger, creating a vacuum. - To compensate, air rushes into the lungs to fill the void. - To exhale, the diaphragm is relaxed, making the thoracic cavity smaller, forcing air out. - When more oxygen is needed (i.e. during exercise), the rib cage also expands and contracts to increase the size of the thoracic cavity. Fig Gas Exchange in Frogs - Frogs have lungs but use positive pressure breathing. Positive pressure involves forcing air into elastic lungs which then contract and force air back out. There is no diaphragm. 3

4 Gas Exchange in Birds p.984 Birds have the most efficient gas exchange system of vertebrates. They have two lungs and 8-9 air sacs. Air sacs Specialized regions of the respiratory system that act like bellows. Contraction and relaxation ventilate the lungs. Gas exchange does not occur here. Air sacs also decrease density of bird which enhances ability to fly. Birds have parabronchi instead of alveoli. Gas Exchange in Birds Parabronchi Straight tubes that keep air moving in one direction in the lungs. They are the site of gas exchange. How birds ventilate their lungs: 1. Inhalation - All air sacs expand. Posterior sacs contain fresh air. Anterior sacs contain stale air. 2. Exhalation - All air sacs deflate. Air is forced from the posterior air sacs into lungs. Exchange occurs across the parabronchi. Air from anterior sacs forced out of the body. Fig Gas Exchange in Birds Results: 1. Air is always passing through the lungs in the same direction. Gases are exchanged during inhalation and exhalation. 2. One way flow creates a higher O 2, gradient, allowing for more exchange. 3. Lungs are smaller and lighter. Control of Breathing in Humans pp Breathing in humans is regulated by negative feedback. When we inhale, the lungs expand. When the lungs stretch, a signal is sent to the medulla oblongata. The medulla oblongata then sends a signal back to exhale which prevents the lungs from expanding too much. Control of Breathing in Humans The stimulus to inhale is caused by the medulla oblongata detecting a lowering of the ph of cerebrospinal fluid that surrounds the brain. CO 2 produced by the cells of the brain enters the cerebrospinal fluid by diffusion and changes to carbonic acid, lowering ph. The medulla oblongata then sends a signal to the diaphragm to expand the lungs to take in O 2 and remove CO 2. 4

5 Control of Breathing in Humans The amount of O 2 in the blood is not used to regulate breathing unless it becomes very low. In that case, sensors in the aorta and carotid arteries send signals to the medulla oblongata to increase breathing rate. Fig

Pop Quiz. What produces mucus, HCl and pepsinogen in the stomach? List a water soluable vitamin What is a ruminant stomach?

Pop Quiz. What produces mucus, HCl and pepsinogen in the stomach? List a water soluable vitamin What is a ruminant stomach? Pop Quiz What produces mucus, HCl and pepsinogen in the stomach? List a water soluable vitamin What is a ruminant stomach? Respiratory System Review Cellular respiration: obtain glucose and oxygen, get