III. The Respiratory System

A. Requirements for Gas Exchange1. Membrane must be moist2. Large Surface Area3. System of Transport4. Respiratory Pigment (must combine

reversibly with oxygen)a) Hemoglobin -amino acid chains with a

central porphyrin or heme group of ironb) Hemocyanins -contain copper. Found in

mollusks and arthropodsc) Chlorocruorins and hemerythrins

5. Air Vs Water

a) Air contains more oxygen

b) Water loss is a problem with air breathers

c) Aquatic organisms must also maintain water balance and ion balance

5. Air Vs WaterB. Adaptations for Gas Exchange

1. Tracheal Tubes System of branching tubes that run from the openings in the exoskeleton of arthropods called the spiracles to all the tissues of the body

a) Diffusion of oxygen and carbon dioxide is through the cell membranes

b) Muscle movement aids in the pumping of oxygen

c) Arthropod circulatory and respiratory systems are usually not related

2. Gills -out growths of aquatic animals that are divided and subdivided to provide surface area for diffusion a)Need water flowing

across them to stay open. They collapse and lose surface area

b)Gills dry out on land

c)Counter Current Exchange system -blood entering gill is oxygen poor ,while water entering the gill is oxygen rich. This allows for efficient diffusion

3. Lungs -in growths of the body surface that provide surface area for diffusion of oxygen

C. Human Gas Exchange

1. Structures in the Head

1. Structures in the Heada) External Nares -hair covered openings into

nasal cavityb) Nasal Cavity -paired openings separated by

cartilage with three projections called chonchae which provide surface area for warming and moistening air entering lungs

c) Olfactory Epithelium -the organ of smell is located on the roof of the nasal cavity

d) Sinuses -small cavities in the bones of the skull. The lining of the sinuses produce mucus and dilate during infection producing more mucus

2. Structures in the Throat

a) Pharynx -air leaving nasal cavity enters the pharynx which branches into the exophagus and larynx

b) Larynx -voice box. Muscles raise the larynx during swallowing. This moves a flap of tissue, the epiglottis, over to block food from entering the trachea

c) Trachea -as air passes the larynx it enters the trachea which branches into the bronchi in the lungs

3. Structures in the Lungs

3. Structures in the Lungsa) Bronchi enter the lungs and branch into

smaller structures called bronchiolesb) Bronchioles branch repeatedly until they

reach small air sacs called alveolic) Alveoli are sacs only one cell thick with

capillaries running along their outsided) The pleural cavity encloses the lungs and

keeps the tissue moiste) The total surface area of the alveoli is

about the size of a tennis court

D. Mechanisms of Breathing

1. Inhalation -(inspiration), taking air into the lungs

a) Rib muscles contract

b) Diaphragm contracts increasing the size of the pleural cavity forcing the lungs to expand to equalize pressure

2. Exhalation -(expiration), rib muscles and diaphragm relax forcing air out of the lungs

E. Gas Exchange

1. Once air has enter the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses into the alveoli

2. The rate at which the diffusion occurs is dependent upon the pressure of the gases

40 mm Hg 100 mm Hg

P O2 = 160

mmHg

3. Partial Pressure of Oxygena) Partial pressure of oxygen entering the

lungs 21% O2 in Air X 760 mmHg (barometric pressure of air at seal level) = 160 mm Hg

b) Because the P O2 of venous blood in 40 mm Hg and the inhaled air’s P O2 is 160mm Hg, Oxygen diffuses into the blood

c) The blood is moving to fast for equilibrium to occur, so the arterial blood P O2 = 100mm Hg

4. Oxygen Transport

a) Only 3% of oxygen dissolves into the plasma, 97% of the oxygen is carried by hemoglobin.

b) Hemoglobin forms loose reversible bonds with oxygen

c) Oxygen-Hemoglobin Dissociation Curve -as oxygen concentration increases there is a progressive increase in the amount of hemoglobin combined with oxygen

d) Oxyhemoglobin dissociation is also influenced by carbon dioxide

1) Carbon dioxide combines with water in the plasma to form carbonic acid which dissociates freeing H+ ions resulting in greater acidity of the blood

2) Lactate released from active muscles also lower blood pH

3) Oxyhemoglobin dissociation increases at a faster rate under the condition of low pH. This is called the Bohr effect

Carbon dioxide Transport

5. Carbon dioxide Transport

a) Only a small amount of carbon dioxide dissolves in the plasma (7%). Most (70%)enters RBCs where an enzyme, carbonic anhydrase, assists rapid inter-conversion of carbon dioxide and water into carbonic acid, protons and bicarbonate ions.

b) 23% of carbon dioxide combines directly with the hemoglobin

F. Regulation of Breathing1. Respiratory center -controls breathing by

monitoring the amount of CO2 in the blooda) Pneumotaxis center -located in the medulla and

pons are a group of cells which regulate the rate of breathing

b) Inspiratory and Expiratory Centers -control inhalation and exhalation respectively

c) Inhalation occurs when CO2 levels stimulate the inspiratory center

d) Exhalation in triggered by the inhibiting of the message to the inspiratory center

2. Chemoreceptors in the aorta and carotid arteries monitor the P O2 levels. If P O2 levels are low, increased breathing occurs

G. Gas Exchange Under Stress

1. Hyperventilation -reduces CO2 levels in the blood. May result in dizziness or unconsciousness because normal blood pressure drops.

2. High Flyinga) Barometric pressure decreases with altitude

b) A person will suffer from Hypoxia, lack of oxygen if P O2 drops below 40-50% Hb saturation.

3. Low Diving

a) Diving under water pressure increases 1 atmosphere per 10 meters

b) Decompression sickness -can occur if a diver comes up to quickly. Dissolved blood gases will come out of solution producing bubbles which can blood blood vessels causing pain, dizziness, paralysis, unconsciousness & death