Breathing  :

Breathing is the process that moves air in and out of the lungs, or oxygen through other respiratory organs such as gills. For organisms with lungs, breathing is also called ventilation, which includes both inhalation and exhalation.

Breathing is the process that moves air in and out of the lungs, or oxygen through other respiratory organs such as gills. For organisms with lungs, breathing is also called ventilation, which includes both inhalation and exhalation.

Respiration :



In physiology, respiration is defined as the movement of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction.

HUMAN RESPIRATORY SYSTEM :

NOISTRILS ( EXTERNAL NARES ) :
This is a pair of holes and hlep in filteration of air is known as nostrils .

NASAL CAVITIES :
These cavities are seperated from each other by by a thin cartilaginous medium verticle partition called nasal septum .

INTERNAL NARES : this is a posterior openings of nasal cavities . that lead into the nasopharynx .

PHARYNX :
it is a common opening of food and air . The pharynx is divided in three parts :
1. Nasopharynx ( part of nasal cavity )
2. Oropharynx ( part of oral cavity )
3. Laryngopharynx ( part of larynx )

LARYNX ( VOICE BOX ) :
The larynx /(plural larynges; from the Greek λάρυγξ lárynx), commonly called the voice box, is an organ in the neck of amphibians, reptiles, and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume. The larynx houses the vocal folds (vocal cords), which are essential for phonation. The vocal folds are situated just below where the tract of the pharynx splits into the trachea and the oesophagus .

GLOTTIS :
 the pharynx opens into larynx by a slit like structure is called glottis .

PRODUCTION OF SOUND : 

Sound is generated in the larynx, and that is where pitch and volume are manipulated. The strength of expiration from the lungs also contributes to loudness.

Manipulation of the larynx is used to generate a source sound with a particular fundamental frequency, or pitch. This source sound is altered as it travels through the vocal tract, configured differently based on the position of the tongue, lips, mouth, and pharynx. The process of altering a source sound as it passes through the filter of the vocal tract creates the many different vowel and consonant sounds of the world's languages as well as tone, certain realizations of stress and other types of linguistic prosody. The larynx also has a similar function to the lungs in creating pressure differences required for sound production; a constricted larynx can be raised or lowered affecting the volume of the oral cavity as necessary in glottalic consonants.

The vocal folds can be held close together (by adducting the arytenoid cartilages) so that they vibrate (see phonation). The muscles attached to the arytenoid cartilages control the degree of opening. Vocal fold length and tension can be controlled by rocking the thyroid cartilage forward and backward on the cricoid cartilage (either directly by contracting the cricothyroids or indirectly by changing the vertical position of the larynx), by manipulating the tension of the muscles within the vocal folds, and by moving the arytenoids forward or backward. This causes the pitch produced during phonation to rise or fall. In most males the vocal folds are longer and with a greater mass than most females' vocal folds, producing a lower pitch.

PATHWAY OF AIR :
Air enters the nostrils
passes through the nasopharynx,
oral pharynx
through the glottis
into the trachea
into the right and left bronchi, which branches and rebranches into
bronchioles, each of which terminates in a cluster of
alveoli
The alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 .
Breathing starts at the nose and mouth. You inhale air into your nose or mouth, and it travels down the back of your throat and into your windpipe, or trachea. Your trachea then divides into air passages called bronchial tubes.
For your lungs to perform their best, these airways need to be open during inhalation and exhalation and free from inflammation or swelling and excess or abnormal amounts of mucus.

The Diaphragm's Role in Breathing :

Inhalation and exhalation are the processes by which the body brings in oxygen and expels carbon dioxide. The breathing process is aided by a large dome-shaped muscle under the lungs called the diaphragm.
When you breathe in, the diaphragm contracts downward, creating a vacuum that causes a rush of fresh air into the lungs.
The opposite occurs with exhalation, where the diaphragm relaxes upwards, pushing on the lungs, allowing them to deflate.
The respiratory system has built-in methods to prevent harmful substances in the air from entering the lungs.

Nostril hairs help in filteration of air :
Respiratory System Hairs in your nose help filter out large particles. Microscopic hairs, called cilia, are found along your air passages and move in a sweeping motion to keep the air passages clean. But if harmful substances, such as cigarette smoke, are inhaled, the cilia stop functioning properly, causing health problems like bronchitis.
Mucus produced by cells in the trachea and bronchial tubes keeps air passages moist and aids in stopping dust, bacteria and viruses, allergy-causing substances, and other substances from entering the lungs.
Impurities that do reach the deeper parts of the lungs can often be moved up via mucous and coughed out or swallowed.


Cartilages :

Posterior view of the larynx; disarticulated cartilages (left) and intrinsic muscles (right)
There are 6 cartilages, three unpaired and three paired, that support the mammalian larynx and form its skeleton.
Unpaired cartilages:
Thyroid cartilage: This forms the Adam's apple. It is usually larger in males than in females. The thyrohyoid membrane is a ligament associated with the thyroid cartilage that connects the thyroid cartilage with the hyoid bone.

Cricoid cartilage: A ring of hyaline cartilage that forms the inferior wall of the larynx. It is attached to the top of trachea. The median cricothyroid ligament connects the cricoid cartilage to the thyroid cartilage.
Epiglottis: A large, spoon-shaped piece of elastic cartilage. During swallowing, the pharynx and larynx rise. Elevation of the pharynx widens it to receive food and drink; elevation of the larynx causes the epiglottis to move down and form a lid over the glottis, closing it off.
Paired cartilages:
Arytenoid cartilages: Of the paired cartilages, the arytenoid cartilages are the most important because they influence the position and tension of the vocal folds. These are triangular pieces of mostly hyaline cartilage located at the posterosuperior border of the cricoid cartilage.
Corniculate cartilages: Horn-shaped pieces of elastic cartilage located at the apex of each arytenoid cartilage.
Cuneiform cartilages: Club-shaped pieces of elastic cartilage located anterior to the corniculate cartilages.

Muscles :
The muscles of the larynx are divided into intrinsic and extrinsic muscles.
The intrinsic muscles are divided into respiratory and the phonatory muscles (the muscles of phonation). The respiratory muscles move the vocal cords apart and serve breathing. The phonatory muscles move the vocal cords together and serve the production of voice. The extrinsic, passing between the larynx and parts around; and intrinsic, confined entirely. The main respiratory muscles are the posterior cricoarytenoid muscles. The phonatory muscles are divided into adductors (lateral cricoarytenoid muscles, arytenoid muscles) and tensors (cricothyroid muscles, thyroarytenoid muscles).


Intrinsic :
The intrinsic laryngeal muscles are responsible for controlling sound production.
Cricothyroid muscle lengthen and tense the vocal folds.
Posterior cricoarytenoid muscles abduct and externally rotate the arytenoid cartilages, resulting in abducted vocal folds.
Lateral cricoarytenoid muscles adduct and internally rotate the arytenoid cartilages, increase medial compression.
Transverse arytenoid muscle adduct the arytenoid cartilages, resulting in adducted vocal folds.
Oblique arytenoid muscles narrow the laryngeal inlet by constricting the distance between the arytenoid cartilages.
Thyroarytenoid muscles - sphincter of vestibule, narrowing the laryngeal inlet, shortening the vocal folds, and lowering voice pitch. The internal thyroarytenoid is the portion of the thyroarytenoid that vibrates to produce sound.
Notably, the only muscle capable of separating the vocal cords for normal breathing is the posterior cricoarytenoid. If this muscle is incapacitated on both sides, the inability to pull the vocal folds apart (abduct) will cause difficulty breathing. Bilateral injury to the recurrent laryngeal nerve would cause this condition. It is also worth noting that all muscles are innervated by the recurrent laryngeal branch of the vagus except the cricothyroid muscle, which is innervated by the external laryngeal branch of the superior laryngeal nerve (a branch of the vagus).