Respiratory System

The Respiratory System supplies the body with oxygen, Air is inhaled through the nose or mouth. It then travels into the pharynx, passes through the larynx, and down the trachea. The trachea branch and air reaches the lungs where it will diffuse into the blood via the alveoli.

 Respiration is the Act of Breathing:

• Inhaling (Inspiration)--taking in oxygen
• Exhaling (Expiration)--giving off carbon dioxide

The Respiratory System is made up of the organs involved in the interchanges of gases, and consists of the:

• Nose
• Mouth (Oral Cavity)
• Pharynx (Throat)
• Larynx (Voice Box)
• Trachea (Windpipe)
• Bronchi
• Lungs 

The Upper Respiratory Tract includes the:

• Nose
• Nasal cavity
• Ethmoidal air cells
• Frontal sinuses
• Maxillary sinus
• Sphenoidal sinus
• Larynx
• Trachea

The Lower Respiratory Tract includes the:

• Lungs
• Airways (Bronchi and Bronchioles) 
• Air sacs (Alveoli)

Nose and Pharynx

The respiratory system of humans begins with the nose, where air is conditioned by warming and moistening. Bone partitions separate the nasal cavity into chambers, where air swirls about in currents. Hairs and hairlike cilia trap dust particles and purify the air.

The nasal chambers open into a cavity at the rear of the mouth called the pharynx(throat). From the pharynx, two tubes called Eustachian tubes open to the middle ear to equalize air pressure there. The pharynx also contains tonsils and adenoids, which are pockets of lymphatic tissue used to trap and filter microorganisms.

Larynx

The Larynx (plural larynges), commonly called the voice box, is an organ in the neck of mammals involved in protecting the trachea and sound production. It manipulates pitch and volume. The larynx houses the vocal folds, which are an essential component of phonation. The vocal folds are situated just below where the tract of the pharynx splits into the trachea and the oesophagus.

Trachea

After passing through the pharynx, air passes into the windpipe, or trachea. The trachea has a framework of smooth muscle with about 16 to 20 open rings of cartilage shaped like a C. These rings give rigidity to the trachea and ensure that it remains open.

The opening to the trachea is a slit like structure called the glottis. A thin flap of tissue called the epiglottis folds over the opening during swallowing and prevents food from entering the trachea. At the upper end of the trachea, several folds of cartilage form the larynx, or voice box. In the larynx, flap like pairs of tissues called vocal cords vibrate when a person exhales and produce sounds.

Bronchi

At its lower end, the trachea branches into two large bronchi (singular, bronchus). These tubes also have smooth muscle and cartilage rings. The bronchi branch into smaller bronchioles, forming a bronchial “tree.” The bronchioles terminate in the air sacs known as alveoli. No gas exchange takes place in bronchi.
 

Lungs

Human lungs are composed of approximately 300 million alveoli, which are cup-shaped sacs surrounded by a capillary network. Red blood cells pass through the capillaries in single file, and oxygen from each alveolus enters the red blood cells and binds to the hemoglobin. In addition, carbon dioxide contained in the plasma and red blood cells leaves the capillaries and enters the alveoli when a breath is taken. Most carbon dioxide reaches the alveoli as bicarbonate ions, and about 25 percent of it is bound loosely to hemoglobin.

When a person inhales, the rib muscles and diaphragm contract, thereby increasing the volume of the chest cavity. This increase leads to reduced air pressure in the chest cavity, and air rushes into the alveoli, forcing them to expand and fill. The lungs passively obtain air from the environment by this process. During exhalation, the rib muscles and diaphragm relax, the chest cavity area diminishes, and the internal air pressure increases. The compressed air forces the alveoli to close, and air flows out.

The nerve activity that controls breathing arises from impulses transported by nerve fibers passing into the chest cavity and terminating at the rib muscles and diaphragm. These impulses are regulated by the amount of carbon dioxide in the blood: A high carbon-dioxide concentration leads to an increased number of nerve impulses and a higher breathing rate.

Diaphragm

In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm (Ancient Greek: diáphragma "partition"), is a sheet of internal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity (heart, lungs & ribs) from the abdominal cavity and performs an important function in respiration. A diaphragm in anatomy can refer to other flat structures such as the urogenital diaphragm or pelvic diaphragm, but "the diaphragm" generally refers to the thoracic diaphragm. Other vertebrates such as amphibians and reptiles have diaphragms or diaphragm-like structures, but important details of the anatomy vary, such as the position of lungs in the abdominal cavity.

The Ethmoid Sinus

Is each of the two paranasal sinuses within theethmoid bone, comprising the ethmoidal air cells and filled with air. These are divided into anterior, middle and posterior group. The ethmoidal air cells consist of numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, andpalatine bones. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony laminae.

Breathing

In mammals, the diaphragm divides the body cavity into the

• Abdominal Cavity, which contains the viscera (e.g., stomach and intestines) and the
• Thoracic Cavity, which contains the heart and lungs.

The inner surface of the thoracic cavity and the outer surface of the lungs are lined with pleural membranes which adhere to each other. If air is introduced between them, the adhesion is broken and the natural elasticity of the lung causes it to collapse. This can occur from trauma. And it is sometimes induced deliberately to allow the lung to rest. In either case, reinflation occurs as the air is gradually absorbed by the tissues.

Because of this adhesion, any action that increases the volume of the thoracic cavity causes the lungs to expand, drawing air into them.

• During Inspiration (inhaling)

1. The external intercostal muscles contract, lifting the ribs up and out.
2. The diaphragm contracts, drawing it down .

• During Expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breath 15–18 times a minute exchanging about 500 ml of air.
• In more Vigorous Expiration,

1. The internal intercostal muscles draw the ribs down and inward
2. The wall of the abdomen contracts pushing the stomach and liver upward.

Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each breath. This is called the vital capacity. Even with maximum expiration, about 1200 ml of residual air remain.