Respiration involves 3 processes:
 1) breathing - moving air in and out of the lungs
 2) transportation of gases by the circulatory system
 3) exchanging carbon dioxide for oxygen in the body tissues

Animals exchange oxygen and carbon dioxide through moist body surfaces.
   - some simple animals do this through their outer skin (ex. earthworm)
   - some aquatic animals do this by filtering oxygen from water with gills (ex. fish)
   - some small animals use openings (tracheae) to exchange gases (ex. insects)
   - air-breathing vertebrates use a trachea to bring air in/out to internal lungs (ex. humans)

Gills
   - the amount of oxygen in water is only 3-5% of what it is in air
   - warmer and/or saltier water holds less oxygen
   - the gills are ventilated by drawing in water to pass over the gills so that oxygen can be absorbed into the bloodstream
   - as the water moves over the blood vessels, the blood is moving in the opposite direction to help in transferring oxygen into the blood (countercurrent exchange)

Tracheae
   - insects use tubes (tracheae) around their body that are open to the outside and take in air
   - as they extend deeper into the insect's body and become smaller, the tracheoles (smallest tubes) end up at a dark blue fluid in the body tissue and gases are exchanged
   - there are some air sacs in areas of the body that require larger amounts of oxygen

Human Respiratory Structures
Nose

• provides an airway
• warms, moistens and cleans the air
• houses the olfactory receptors
• the external nose is made of bone and cartilage
• internally, the nose is divided by the nasal septum
• paranasal sinuses and nasolacrimal ducts drain into the nasal cavity

Pharynx

• from the base of the skull to the sixth cervical vertebrae
• nasopharynx: behind the nasal cavity; an air conduit
• oropharynx: behind the oral cavity; passageway for food and air
• laryngopharynx: in the throat; passageway for food and air
• pairs of tonsils are found in the oropharynx and nasopharynx

Larynx

• “voice box”
• contains the vocal cords
• serves as an airway
• serves as a switching mechanism to route food and air into the proper channels
• the epiglottis prevents food/liquids from entering the trachea

Trachea

• extends from the larynx to the primary bronchi
• it is reinforced by C-shaped cartilage rings that keep it open
• its mucuso (mucus membrane lining) is ciliated

Bronchi and bronchioles

• there are 2 bronchi, one that goes to the left lung and one that goes to the right lung
• the 2 bronchi branch off into smaller and smaller bronchioles
• the terminal bronchioles lead into the respiratory zone

Alveoli - air sacs at the end of the bronchioles; air exchange occurs across the respiratory membrane of the alveoli
 

Breathing
       - average amount of one breath - 500 mL
       - max. volume of air - 4800 mL (males), 3400 mL (females)
       - our breathing rate is controlled by breathing control centers in the pons and medulla of the brain stem
       - as the carbon dioxide level increases, the brain stem increases our breathing rate
       - when you take in many large breaths (hyperventilate), it gets rid of so much carbon dioxide the brain tells the lungs to stop working for a while

Transport of respiratory gases

• Oxygen is carried in the blood bound to the hemoglobin of red blood cells.
• The hemoglobin turns most of the carbon dioxide into a bicarbonate ion.

Hypoxia - occurs when the body doesn’t get enough oxygen to its tissues
Acidosis - the accumulation of too much carbon dioxide

Smoking
   - kills about 430,000 people in the US every year
   - results in increased risk of lung cancer, emphysema, cardiovascular disease, etc.
   - cigarette smoke contains over 4000 chemicals, many of which are detrimental to your health

Fetal respiration
   - a fetus exchanges gases through its umbilical cord (which leads to the placenta)
   - gases flow back and forth across the placental-uterine boundary
   - fetal hemoglobin attracts oxygen more than the mother's hemoglobin, so oxygen is taken from the mother's blood and transported to the fetus

Major respiratory disorders:

• emphysema - the lungs lose their elasticity and alveoli become brittle and rupture
• chronic bronchitis - excessive mucus production in the lower respiratory passageways
• tuberculosis - caused by a bacteria
• lung cancer - aggressive; spreads rapidly; usually caused by smoking
• asthma - the bronchioles constrict