1. THE RESPIRATORY SYSTEM

2. involves breathing transport of gases with tissue cells
Overview: Gas exchange in an animal with lungs
involves breathing transport of gases with tissue
cells
Interchange between an organism and its environment
Provides oxygen for cellular respiration and removes
carbon dioxide as a byproduct
Gas exchange involves breathing, transport of gases,
exchange of gases among body cells

3. Animals exchange O2 and CO2
 Moist Surface
 Lots of surface area
 Capillaries close to surface for gas exchange
 Gas exchange takes place by diffusion

4. Four Types of Respiratory Organs
 Respiratory Surface- use their entire outer skin as a gas exchange organ; there are no specialized gas exchange surfaces/organs; ex: earthworms- small size or flatness provides a high ratio of respiratory surface to body volume for sufficient gas exchange
 Gills- extensions, or outfoldings, of the body surface specialized for gas exchange ex: fish- O2 diffuses across the gills into capillaries and CO2 diffuses in the opposite direction into the environment
 Tracheal System- is an extensive system of branching internal tubes through out the body with the respiratory surfaces at their tips. ex: insects-gas exchange in insects requires no assistance from the circulatory system
 Lungs- internal sacs lined with moist epithelium and extensive branching forming a large respiratory surface; ex: animals (terrestrial vertebrates)- gases are carried between the lungs and the body cells by the circulatory system

6. Gills are adapted for gas exchange in aquatic environments
Many aquatic organisms use gills as extensions of their body (increasing respiratory surface) to absorb the O2 from their H2O environment efficiently
Structure of fish gills:
 Gas exchanged is enhanced by ventilation to increase the flow of the surrounding water or air over the respiratory surface
 As fish swim water flows over the gills while they also pump water across the gills by coordinating the opening and closing of its mouth and operculum.
 Ventilating gills takes a lot of energy
Countercurrent Exchange:
 Countercurrent exchange is the transfer of a substance from a fluid moving in one direction to another fluid moving in the opposite direction (counter one another)
 Blood flows opposite the movement of water past the gills making in possible to transfer oxygen to the blood.

8. The tracheal system of insects provides direct exchange between the air and body cells
 This system is designed in insects to transport O2 directly to body cells through a network of finely branched tubes, tracheoles, and the largest tube the trachea.
 With respiratory surfaces at the tips of the tiny branching tubes, the rate of water loss is greatly reduced
 The trachea for a small insect generates enough O2 and removes enough CO2 to support cellular respiration. While larger insects may need to ventilate their tracheal system.

9. In the human respiratory system, branching tubes convey air to lungs located in the chest cavity
 Air enters the nostrils where it is warmed, humidified, filtered and sampled for odors
 Passes the pharynx and larynx (voice box)
 To the trachea which is reinforced by cartilage rings
 To the bronchi which branch into each lung
 To the bronchioles (smaller branches)
All branches of the respiratory system are covered in mucus and cilia. The mucus traps foreign particles and the cilia beats it up to the pharynx where it can be swallowed or spit out.
 To the alveoli which are covered in capillaries for gas exchange.

10. Smoking – An assault on the Respiratory System
 Although the lungs are protected by mucus and cilia, smoking can destroy these protections.
 One puff on a cigarette can expose a person to more than 4,000 chemicals.
 Tobacco smoke irritates cells, inhibiting or destroying cilia.
 Smoking can lead to many diseases such as lung cancer, heart disease, and emphysema.
 Fifteen years after quitting, a former smoker’s risk of lung cancer and heart disease is similar to that of people who have never smoked.

11. Negative Pressure Breathing Ventilates Lungs
Lungs are ventilated by negative pressure breathing.
 The diaphragm and muscles within the rib cage contract. This increases volume decreasing pressure, forcing air from outside into the lungs.
 The contraction of rib muscles and diaphragm expands the chest cavity and reduces air pressure in the alveoli, this is known as negative pressure
 Vital capacity is the maximum volume of air that can be inhaled and exhaled, but the lungs still hold a residual volume so they don’t collapse.

12. Breathing is Automatically Controlled
 Breathing is usually automatic and controlled subconsciously by the respiratory center at the base of the brain. Breathing continues during sleep and usually even when a person is unconscious.
 Sensory organs in the brain and in the aorta and carotid arteries monitor the blood and sense O2 and CO2 levels.
 Normally, an increased concentration of CO2 is the strongest stimulus to breathe more deeply and frequently. Conversely, when the CO2 concentration in the blood is low, the brain decreases the frequency and depth of breaths.
 During breathing at rest, the average adult inhales and exhales about 15 times a minute.

13. Blood transports respiratory gases
Circulation in the heart pumps oxygen-poor blood to the lungs, where it picks up O2 and drops off CO2.
 Then the heart pumps oxygen-rich blood to body cells, where it drops off O2 and picks up CO2.
 O2 is carried on respiratory pigments. In humans, this pigment is hemoglobin. The pigments have binding sites (heme groups) that can pick up or drop off gasses based on partial pressures

14. Hemoglobin carries O2 helps transport CO2 , and buffers the blood
 Hemoglobin in red blood cells transports oxygen, helps buffer the blood, and carries some CO2.
CO2 is carried on hemoglobin, dissolved in blood or as bicarbonate ions.
 H2O + CO2  H2CO3  H+ + HCO3- (most H is bound by hemoglobin to keep pH stable)

15. The human fetus exchanges gases with the mother’s bloodstream
A human fetus exchanges gases with maternal blood in the placenta.
A network of capillaries exchanges O2 and CO2 with maternal blood that carries gases to and from the mother’s lungs
 Fetal hemoglobin enhances oxygen transfer from maternal blood.
 At birth, rising CO2 in fetal blood stimulates the breathing control centers to initiate breathing.