Human Respiratory Organs

 Human respiratory organs:

Are nostrils, nasal Chambers, pharynx, lanynx, trachea, bronchus, bronchioles, lungs and diaphragm.

* Nostrils: Are two Small openings above the mouth through which air passes in and out during breathing. (Dirhynous having 2 nostrils)

* Nasal Chambers: Each nostril opens into a small Chamber called nasal chamber. Two nasal chambers remain separated with each other by nasal septum Cartilaginous ( hyaline Cartilage) towards lower/anterior side while bony ( Ethmoid and vomer bone @ EV) towards upper / posterior side.

Each nasal Chamber remains differentiated into 3 regions:

⇒ Vestibular region: is Anterior wider region and remains lined by keratinised stratified epithelium with hairs. The hairs filter air.

⇒ Respiratory part: is middle part and remains lined by pseudo stratified ciliated Columnar epithelium with mucus Cells i.e. respiratory epithelium.

⇒ Olfactory region: is the Posterior region and remains lined by Olfactory epithelium or schnederian membrane. it is pseudostratified Ciliated columnar epithelium with endings of Olfactory nerves. this part identifies Smell. The Bowman's gland is present in this area which produces mucus like fluid which Keeps Olfactory surface moist and dissolves odour molecules so can be detected by Olfactory receptors.

Each nasal Chamber has 3 bony elevations ( processes) on its lateral wall called nasal conchae (turbinate) which are  maxilloturbinate, Ethmoturbinate  and nasoturbinate. They increase the surface area of nasal Chamber.

 when air passes through Nasal Chamber, the hairs filter the air, mucus traps dust particles, lysozyme present in mucus sterilize the air by killing the microorganisms like bacteria and the temperature of air is brought around 1 of body temperature ie. air Conditioning is done. thus, nasal breathing is better than oral breathing.

 * The nasal bleeding is Called epistaxis. It generally takes place at lower or anterior end of Nasal septum Called Little's area where plexus (network) of capillaries Called Kiesselbach's plexus is present.

 * Paranasal sinuses: The air filled spaces around nasal Chamber are Called paranasal sinuses. There are 4 Paranasal sinuses @ FrEMS

⇒ Frontal PNS

⇒ Ethmoid PNS

⇒ Maxillary PNS : largest

⇒ Sphenoid PNS:

Inflamation of sinuses is Called sinusitis which normally takes place in maxillary sinus.

*Pharynx:The nasal Chamber opens into pharynx by internal nostrils. It is vertical tubular Cavity of about 12cm. and is common passage for food and air. It Consists of 3-parts: Nasopharynx, oropharynx and Laryngopharynx.

* Naso-pharynx: is upper part and its roof contains a pair of openings of internal nostrils. A pair of openings of eustachian tube are present each on either side of

naso-pharynx. It remains lined by pseudostratified Ciliated

Columnar epithelium.

A pair of pharyngeal tonsils are found on the roof of naso-pharynx each around each opening of internal nostrils.

Tubal tonsils are found around the openings of eustachian tube.

Only air passes through it.

* oro-pharynx: is middle part lying behind buccal Cavity. Both food and air passes through it. The part where food and air cross each other is Called pharyngeal Chaisma. The palatine tonsils are present in it. It remains lined by non-keratinised stratified squamous epithelium.

* Laryngo-pharynx: is lower part and remains lined by non-keratinised stratified squamous epithelium. It Consists of two openings on its floor ; glottis in front and gullet in back.The gullet Continues into oesophagus. The glottis opens into larynx.

 A cartilaginous flap is present in front of glottis Called epiglottis. This epiglottis closes glottis at the time of swallowing to prevent entry of food into glottis.

* Larynx: It is Small , wide, thin walled tubular Chamber and is anterior modified part of trachea. It lies infront of oesophagus at the level of C3 to C6. It remains lined by pseudostratified ciliated columnar epithelium. The Cilia beat outward to eject out unwanted substances.

Its wall remains supported by  9 cartilages of which 3 are unpaired and 3 are paired.

The unpaired cartilages are @ ETC ;

Epiglottis, Thyroid and Cricoid.

The Paired cartilages are @ ACC;

Arytenoid, Cuneiform and corniculate(cartilage of Santorini).

The thyroid, Cricoid and anytenoid are made up of hyaline Cartilage while others are made up of elastic cartilage.

⇒ Epiglottis : is flattened, leaf like.

⇒ Thyroid: is C-Shaped & is largest.

⇒ Cricoid: is ring like.

⇒ Arytenoid: is pyramid Shaped.

⇒ cuniform: is club or wedge shaped.

⇒ Corniculate: is horn shaped.

  In the Cavity of larynx 2 pairs of vocal cords are present ;

1 Pair true vocal Cords and 1 Pair false vocal Cords. The true vocal cords are fibrous elastic bands and help in sound production. The space between two vocal Cords is Called Rima glottidis. The vibration of these vocal Cords produces sound.

Until puberty, the larynx of male and female are similar. However, after puberty, It grows faster in male due to the effect of androgens. Thus, in adult larynx is larger in male. The enlarged larynx in male is called as Adam's apple (Rudraghanti).

 The Sound has pitch, loudness and quality.

The pitch of sound depends upon length and tightness of vocal cords. In aduIt males, vocal Cords are longer. Thus, male voice has low Pitch.

The loudness of sound depends upon the force of vibration ; greater the force , Sound will be louder.

The quality of sound depends upon shape of mouth, position of lips, tongue & teeth and air sinuses of face and Skull.

•      sound Producing organ in birds is syrinx located at the base of trachea.

•      Sound produced by Rabbit is called Quaking.

* Trachea (wind pipe): is a tubular structure of length (10-12) Cm and width about 2.5 cm. and lies in neck infront of oesophagus. It remains supported by (16-20) C-shaped Cartilages which are incomplete dorsally towards oesophagus. It extends up to fourth thoracic vertebrae (T4). It remains lined by Pseudostratified Ciliated Columnar epithelium with goblet Cells. the Cilia beat outward to expell out dust, food particles, microorganisms etc.

The point of bifurcation of trachea is Called Carina.

The muscles in posterior (back) Wall of trachea is called trachealis.

* Bronchus and bronchioles: At the border of 4th and 5th thoracic vertebrae the trachea divides into Rt. bronchus and It. bronchus.

The Rt. bronchus is wide, more vertical and short ( 2.5 Cm in length) @ Wives. Thus, inhaled foreign particles more frequently enter into Rt. bronchus.

The Rt. primary bronchus enters inside Rt. lungs while Lt. primary bronchus enters inside It. Lungs.

After entering inside Rt. lungs , the Rt. bronchus divides into 3-branches while the Lt. bronchus inside It. lungs divide into 2 branches. These branches are Called secondary bronchioles. These secondary bronchioles divide into tertiary bronchioles. About 10 tertiary bronchioles are present inside Rt. lungs while 8 inside the Lt. lungs. These bronchioles remain supported by ring like Cartilage. these tertiary bronchioles further divide into bronchioles of diameter about 1mm and are Without Cartilaginous support. All these remain lined by Ciliated Columnar epithelium with mucus cells.

These bronchioles further divides into terminal bronchioles about 0.5 mm in diameter and remains lined by non_ glandular ciliated Columnar epithelium. These terminal bronchioles further divide into respiratory bronchioles and these respiratory bronchioles further divide into alveolar bronchioles or ducts. Each alveolar duct ends into alveolar sac. An alveolar Sac is formed of Central passage and 6 to 8 pocket like out growths Called alveolie or air sacs of diameter about 0.1mm.

About 300 to 7oo million alveolie are present inside lungs and their surface area is about(70-100) m . The surface area of Skin is about 1.7 square meter.

The alveolie are structural and physiological unit of lungs. They Provide surface area for gaseous exchange. They remain lined by simple squamous epithelium Called pneumocytes. The pneumocytes are of two types; Type-I and Type -II.

Type- I Cells are more numerous and for gaseous exchange. They also produce Angiotensinogen Converting enzyme (ACE).

Type-II Cells are  few in number secrete surfacant which is Composed of lecithin (Phospholipid) and Proteins which prevent Collapsing of alveolie during expiration.

The alveolar wall also Contains alveolar macrophages Called dust cells which are phagocytic in nature.

A number of Smaller pores are present in wall of alveolie Called Pore of Kohn which make the Process of diffusion faster.

During exchange of gases, gases pass through respiratory membrane which Consists of

- Squamous epithelial lining of alveolie,

- endothelial lining of Capillaries and

- Basement membrane between these two.

 * Lungs: A Pair of soft, spongy and elastic organs in thoracic cavity each on either side of heart.

The thoracic Cage Consists of 37 bones; sternum-1, thoracic vertebrae - 12 and 12 pairs of Ribs.

They lie inside pleura which is thin, transparent, double layered Peritoneal sac. Its outer layer is called Parietal pleuron while inner layer is called visceral pleuron. the space between these two layers is called pleural Cavity which remains filled with pleural fluid which

- allows free frictionless movement of lungs,

- protects the lungs from mechanical shock & injuries and

- provides space for the expansion of lungs.

Each lung is conical in shape with narrow upper end and broader base. Its anterior narrower end is Called apex, lower broad semilunar region is called diaphragmatic region, outer

Convex surface is Called Coastal region and inner Concave surface is called mediastinal surface. The mediastinal surface has triangular depressed area called hilum through which bronchus, blood vessels and nerves enter inside lungs. The space between two lungs is Called mediastinum.

Each lung is lobulated structure and externally divided into lobes. The Rt. lung is comparatively larger than It. lung. The Rt. lung has 3 lobes; superior lobe, middle lobe and inferior lobe while It. lung has 2 lobes superior lobe and inferior lobe. The It. lung has depressed area called Cardiac notch in mediastinal surface to accomodate heart.

 * Diaphragm: is dome Shaped musculotendinous structure which forms floor of thoracic cavity and separates thoracic cavity with abdominal Cavity.

It is Characteristics of mammal. However, is also present in some reptiles like crocodile, Alligator and Gharial @ CAG.

It's peripheral portion is muscular while Central part is of tendon.

During inspiration it Contracts and become flat while during expiration it relaxes and becomes dome shaped.

Three important structures pierce the diaphragm Which are venacava (T8), Oesophagus (T10) and Aorta (T12).

phrenic is latin word for diaphragm. The phrenic artery supply blood to diaphragm while phrenic vein Collects blood from it. the phrenic nerve is present in diaphragm.