Respiratory System

Blood Circulation

• Remember, all cells need oxygen in order to make ATP– Oxygen is only carried by red

blood cells via hemoglobin, so it runs out quickest

• Additionally, carbon dioxide is produced as a waste product and so must be released from the blood constantly– CO2 mixes with water to make

acid so it has to be balanced

Respiratory System

• The respiratory system consists of the lungs and the air passages that allow air to reach the lungs– The lungs themselves have capillaries

that allow gas exchange• The respiratory system also

includes the diaphragm, the sheet of muscle that drives quiet breathing– Pulls down when contracting, like

pulling a syringe plunger

Respiratory System

Air Passages

• The conducting zone is all of the respiratory system that allows air to flow– Mouth and nose– Nasal Passages– Throat (pharynx)– Larynx– Trachea– Bronchi– Bronchioles

Nasal Passages

• The nasal passages leading from the nose to the pharynx have a number of key features:– Mucous membranes that trap

particles– Cilia (tiny moving hairs) that

move mucus to the pharynx– Olfactory epithelium for smelling– Auditory tube for equalizing

pressure of middle ear

Pharynx and Larynx

• The pharynx carries both food and air to the trachea and esophagus

• The top of the trachea is the larynx (voice box) which produces speech– A flap of cartilage called the

epiglottis folds over the larynx when swallowing to prevent inhaling food

Trachea

• The trachea is the passage for air to the lungs– Anterior to the esophagus

• Held open by C-shaped rings of cartilage– The trachealis muscle can

squeeze the back ends of the ring together, which happens when you cough

Bronchi and Bronchioles

• The bronchi (singular bronchus) are the branches of the trachea– Branch further to make secondary

and tertiary bronchi inside the lungs

– Reinforced with cartilage• The bronchi branch further to

make bronchioles– Not reinforced with cartilage, but

covered in smooth muscle• Can dilate and constrict

Alveoli

• The bronchioles eventually become respiratory bronchioles, part of the respiratory zone of the lungs

• The bronchioles end in air sacs called alveoli (singular alveolus) covered in capillaries– This is where gas exchange

occurs

Alveolus Structure

• Alveoli are composed of simple squamous epithelium

• Lubricated by an alveolar fluid that includes a surfactant– Allows air to pass by water

with less friction– Premature babies do not yet

produce surfactant so breathing is very difficult for them!

Gas Exchange

• Oxygen diffuses into the blood in the lungs and carbon dioxide diffuses out– The lungs keep a large storage of CO2 to maintain pH

balance (CO2 + H2O = acid)– This is why breathing excessively fast

(hyperventilation) can cause you to pass out, since your blood is becoming too alkaline too fast

Gas Exchange System

Obligatory Smoking References• Breathing particulate matter

(smoke) in is bad for your lungs!– Can damage alveoli and obstruct

bronchioles• Tobacco plants produce a

particularly unpleasant mix of chemicals including tar and mutation-causing chemicals– But on the other hand, nicotine

makes you feel really good (and is also addictive because it taps into your dopamine circuits)