The Respiratory System

ATS Unit 6

Learning Goals

• Describe the functions of the respiratory system.

• Identify the major structures of the respiratory system and their function.

• Discuss the physiological process of external respiration.

Functions of the Respiratory System

1. Provide oxygen for cellular respiration. 2. Dispose of Carbon Dioxide, a waste product

of cellular respiration. 3. Production of sounds.

External Respiration

• This is the gas exchange that occurs in the alveoli of the lungs, between inhales air and the blood in the alveolar capillaries.

Structures of the Respiratory System

• From superior to inferior: – Nasal Cavity– Pharynx– Larynx– Trachea– Lungs and Pleura– Bronchi and Bronchioles– Alveoli– Diaphragm

The Nasal Cavity

• Opening are called nostrils or nares. – Divided by a septum. – Further divided into cavities called

turbinate's which creates three narrow passages ways in the cavity (crates movement in inhaled air).

– The cavity is lined with epithelium that is ciliated and produces mucous (to clean and moisten inhaled air).

Sinuses and the Sense of Smell• Sinuses are cavities located in the

various bones of the skull with outlets into the nasal cavity. – These are also lined with mucous

membranes.– They help to make the skill lighter. – They give resonance to the voice.

The olfactory nerves are in the superior surfaces of the nasal cavity and lead to the olfactory nerve in the brain. We will talk more on this later (unit 8).

The Pharynx

• This is commonly called the throat and is a common passage for both air and food. – Three portions: Nasopharynx,

Oropharynx, Laryngopharynx– Connects to the Eustachian tubes

which drain the inner ear. – Extends down to the epiglottis.

The Epiglottis

• This is a flap made of cartilage found behind the tongue at the bottom of the laryngopharynx. – At rest, it stands upright to allow air to pass into

the larynx. – It closes during swallowing to prevent food from

entering the lungs.

The Larynx• AKA the Voice Box

– This a made of several plates for cords of fibrocartilage.

– The opening in called the glottis (epiglottis means?)

– As air leaves the lungs, muscles tighten the cords to allow vibration to occur that create sound.

– Sounds are refined by movements in the mouth, tongue and lips.

The Trachea

• This tube extends from the Larynx to the point where it divides into the Bronchi. – It is constructed of membranes supported by

string but flexible hyaline cartilage rings. This makes it very hard to collapse.

– It runs in front of the esophagus. – Continues to be lined by the ciliated, mucous

producing epithelium found in other parts of the respiratory tract.

The Bronchi and Bronchioles

• These tubes, very similar in structure to the trachea, extend first to the left and right Bronchi and then into increasingly smaller branches into all lobes of the lungs.

Alveoli

• At the end of each small bronchiole, there is a collection of alveoli. – An Alveolus is a small sack made of thin

epithelium, surrounded by capillaries. – On inhale, they fill with air that can then

be diffused across the membrane of the alveolar sack and into the capillaries full of deoxygenate blood from the heart.

– A substance in the alveoli called surfactant keeps them from collapsing on exhale.

The Lungs and Pleura

• All od the bronchi, bronchioles and alveoli are housed in two soft organs called the lungs. – The left has two lobes and the right has three. – They are housed in the thorax, above the

diaphragm and are separated from the heart by the membranes of the mediastinum.

– They have their own two layer membrane (with lubricating fluid in-between) called the pleura.

The Diaphragm

• This is a dome shaped muscle that sits below the lungs in the thorax. – It divides the thorax from the abdominal contents. – It is necessary for the physical process of

breathing. – It is stimulated by the phrenic nerves to contract. – It is a skeletal muscle but works both voluntarily

and involuntarily.

The Mechanics of Breathing: Inhale (Inspiration)

• This is the active part of the cycle. – The intercostal (rib muscles) pull the rib cage up

and out. The diaphragm expands down (contracting).

– This expansion of the chest cavity creates lower pressure inside than out, causing air to rush in.

– Outwardly, we see the chest rise and expand, and the abdomen distend slightly as the contents are pushed down by the diaphragm.

Mechanics of Breathing: Exhale (Expiration)

• This is the passive part of the cycle. – All respiratory muscles relax to original shape and

position. Rib cage descends and collapses slightly.– As this occurs, the pressure in the outside of the

body becomes lower than inside the chest cavity and air is forced out.

– Outwardly, the shoulders and chest descend, the abdomen flattens.

Things that keep you breathing…

• The Pleura: – Without the air tight chest cavity created by the

pleura around the lungs, expansion would not be possible, because air could pass freely through the chest wall.

• The Elasticity of the Lungs– They need to be able to expand and contract as they

fill and empty. – In some diseases, the lungs become scarred and

fibrotic and cannot expand and collapse adequately.