The Respiratory

System

Chapter 10

Organs of the Respiratory System

• Nose• Pharynx• Larynx• Trachea• Bronchi• Lungs

Accessory Structures

• Thorax• Diaphragm

The Nose

The Nose (naso or rhino)

• Acts as entrance for air and exit for carbon dioxide

• Lined with a ciliated epithelial mucus membrane

• Filters dust and foreign material• Warms & moistens entering air• Has olfactory receptors

Nostrils (Nares)

• Paired openings that vary in pliability and expandability to accommodate an increased need for oxygen.

• The horse has pliable and expandable nostrils because mouth breathing is not characteristic.

Pharynx (Throat)• A musculomembranous saclike structure• Upper portion is attached to the base of the

skull and the lower portion with the esophagus

• Connects with the nasal chambers, mouth, larynx and eustachian tubes

The pharynx is divided into three parts:•Nasopharynx – opens into the Eustachian tubes•Oropharynx – opens into the mouth•Laryngopharynx – opens into the larynx & esophagus

The pharynx is used as passageway for both air and

food. Depending on the species it may also have a role in

vocalization.

Larynx (Voice Box)

• Located just below the pharynx• Serves as a passage for air• The epiglottis is a lid-like

structure that prevents food from entering the airway during swallowing

The larynx plays an important role in creating sound. Air passes through the

glottis during expiration causing a vibration, and producing a sound.

Trachea (Windpipe)

• A tube formed of smooth muscle with numerous C shaped rings of cartilage embedded in the tissue

• These rings prevent collapse of the structure.

The end of the trachea separates

into smaller airways called

the primary bronchi.

The Bronchi

• Lined with a ciliated mucous membrane & C-shaped cartilage rings, which become complete as the bronchi enter the lungs

• They then divide into smaller secondary branches, then bronchioles, then alveolar ducts

The Bronchi

The alveolar ducts terminate into alveolar sacs:

Small, squamous epithelium lined spaces that allow the lungs to achieve the primary function of oxygen and carbon dioxide

exchange.

As the bronchioles get smaller, the cartilage rings begin to

disappear. There are no rings in the alveolar ducts, sacs or

alveoli.

The Lungs

• The primary structures of the respiratory system

• Occupy almost the entire thoracic space

• Each contains millions of alveoli and capillaries

Membranes in the Lungs

• Visceral pleura - Serous membrane that encases the lungs

• Parietal pleura – Lines the thoracic cavity

These membranes reduce friction during respiration.

The space between these membranes is called the pleural

cavity or potential space.

Thorax (Chest Cavity)

Lined with a membrane similar to the covering of the lungs, that lubricates both surfaces during respiration

The pleural membrane divides the chest into 3 parts:•Right pleural cavity•Left pleural cavity•Mediastinum

The mediastinum contains the heart, thymus, esophagus, trachea, bronchi, nerves, arteries,

veins and lymphatic vessels.

• A dome-shaped musculomembranous partition separating the thoracic and abdominal cavity

• Attaches to the lumbar and abdominal cavities at the lumbar vertebra, lower ribs and sternum

The Diaphragm

Normal feline chest

Diaphragmatic Hernia

The diaphragm is the primary muscle of respiration.

•Inspiration: Contracts, flattens and lowers, increasing thoracic capacity.•Expiration: Relaxes and returns to its normal position

Respiratory Process

The respiratory cycle is divided into three parts:•Inspiration•Expiration•Rest

Respiration• Involves the

exchange of oxygen and carbon dioxide wastes

• Tissue does not store oxygen and takes in only the oxygen it needs.

During exercise the oxygen requirement can more than double. Flow of air in and out of the lungs

depends on changes in the thoracic cavity. Inspiration and expiration are in accordance with pressure differences between the atmosphere and

air in the lungs

Tidal volume (TV):The amount of air inhaled during

ordinary respiration

Inspiratory reserve volume (IRV):The amount of air that can be

forcibly inhaled beyond the normal amount

Expiratory reserve volume (ERV):The volume of air that can be

forcibly expelled beyond normal expiration

Some air will always be trapped in the alveoli no matter how forcibly

an animal exhales due to intrathoracic pressure.

Residual Volume (RV):Air remaining in the lungs after

forced expiration

Minimal volume:Air remaining in the alveoli of a

collapsed lung

Vital capacity (VC):The largest amount of air that can be moved in and out of the lungs.The sum of the total of inspiratory

and expiratory reserve volumes plus tidal volume

There are several nerves from the brain that pass down the chest wall and diaphragm to control

respiration…

Vagus nerve:Originates in the brain and sends

branches to the larynx, heart, bronchi, esophagus, stomach, liver

and abdomen.

Phrenic nerve:Originates in the cervical spine

and passes to the diaphragm

Thoracic nerve:Originates in the thoracic spinal cord, these are the nerves of the

muscles of the thorax

Next up…

The GI Tract