THE RESPIRATORY SYSTEM: STRUCTURE, ORGANS, & FUNCTIONS

February 18, 2025February 15, 2022 by chitasmita.com

Contents hide

1 WHAT IS THE RESPIRATORY SYSTEM

2 THE ORGANS OF THE RESPIRATORY SYSTEM RESPIRATION: BREATHING, AND EXCHANGE OF GASES

2.1 NOSE AND NASAL CAVITY

2.1.1 FUNCTIONS OF THE NOSE IN THE RESPIRATORY SYSTEM

2.1.1.1 OLFACTORY FUNCTION OF THE NOSE

3 PHARYNX

3.1 FUNCTIONS OF PHARYNX

3.2 LARYNX

3.2.1 FUNCTIONS OF LARYNX

3.3 TRACHEA

3.3.1 FUNCTIONS OF TRACHEA

3.4 Related

WHAT IS THE RESPIRATORY SYSTEM

The cells of the body need energy for all their metabolic activities. Most of this energy is derived from chemical reactions, which can only take place in the presence of oxygen. The main waste product of these reactions is carbon dioxide. The respiratory system provides the route by which the supply of oxygen present in the atmospheric air enters the body, and it provides the route of excretion for carbon dioxide.

The condition of the atmospheric air entering the body varies considerably according to the external environment, e.g. it may be dry, cold, and contain dust particles or it may be moist and hot. As the air breathed in moves through the air passages to reach the lungs, it is warmed or cooled to body temperature, moistened to become saturated with water vapor, and ‘cleaned’ as particles of dust stick to the mucus that coats the lining membrane. Blood provides the transport system for these gases between the lungs and the cells of the body. The exchange of gases between the blood and the lungs is called external respiration, and that between the blood and the cells is internal respiration.

THE ORGANS OF THE RESPIRATORY SYSTEM RESPIRATION: BREATHING, AND EXCHANGE OF GASES

The organs of the respiratory system are

Nose
Pharynx
Larynx
Trachea
Two bronchi (one bronchus to each lung)
Bronchioles and smaller air passages
Two lungs and their coverings, the pleura
Muscles of breathing- the intercostal muscles and the diaphragm

NOSE AND NASAL CAVITY

The nasal cavity is the main route of air entry and consists of a large irregular cavity divided into two equal passages by a septum. The posterior bony part of the septum is performed by the perpendicular plate of the ethmoid bone and the vomer. Anteriorly, it consists of hyaline cartilage. The nasal cavity is a part of the respiratory system.

LINING OF THE NOSE

The nose is lined with very vascular ciliated columnar epithelium (ciliated mucous membrane) which contains mucus-secreting goblet cells. At the anterior nares, this blends with the skin and posteriorly it extends into the nasal part of the pharynx.

FUNCTIONS OF THE NOSE IN THE RESPIRATORY SYSTEM

The nose is the first of the respiratory passages through which the inspired air passes. However, The function of the nose is to begin the process by which the air is warmed, moistened, and filtered.

The CONCHAE increases the surface area and causes turbulence, spreading inspired air over the whole nasal surface. The large surface area maximizes warming, humidification, and filtering.

FIRSTLY, WARMING:- This is due to the immense vascularity of the mucosa. This explains the large blood loss when a nosebleed (epistaxis) occurs.

SECONDLY, FILTERING AND CLEANING:- This occurs as hairs at the anterior nares trap larger particles. Smaller particles such as dust and microbes settle and adhere to the mucus. The mucus protects the underlying epithelium from irritation and prevents drying. The synchronous beating of the cilia wafts the mucus toward the throat where it is swallowed or coughed up (expectorated).

THIRDLY, HUMIDIFICATION:– As air travels over the moist mucosa, it becomes saturated with water vapor. Irritation of the nasal mucosa results in sneezing, a reflex action that forcibly expels an irritant.

OLFACTORY FUNCTION OF THE NOSE

The nose is the organ of the sense of smell. Nerve endings that detect smell are located in the roof of the nose in the area of the cribriform plate of the ethmoid bones and the superior conchae. These nerve endings are stimulated by airborne odors. The resultant nerve impulses are conveyed by the olfactory nerves to the brain where the sensation of smell is perceived.

PHARYNX

The pharynx is a tube 12 to 14cm long that extends from the base of the skull to the level of the 6th cervical vertebra. It lies behind the nose, mouth, and larynx and is wider at its upper end.

The pharynx is divided into three parts-

NASOPHARYNX
OROPHARYNX
LARYNGOPHARYNX

THE NASOPHARYNX

The nasal part of the pharynx lies behind the nose above the level of the soft palate. On its lateral walls are the two openings of the auditory tubes, one leading to each middle ear. On the posterior wall are the pharyngeal tonsils(adenoids), consisting of lymphoid tissue. They are most prominent in children up to approximately 7 years of age. After that, they gradually atrophy.

THE OROPHARYNX

The oral part of the pharynx lies behind the mouth, extending from below the level of the soft palate to the level of the upper part of the body of the 3rd cervical vertebra. The lateral walls of the pharynx blend with the soft palate to form two folds on each side. Between each pair of folds is a collection of lymphoid tissue called the palatine tonsil.

During swallowing, the nasal and oral parts are separated by the soft palate and the uvula.

THE LARYNGOPHARYNX

The laryngeal part of the pharynx extends from the oropharynx above and continues as the esophagus below, I.e. from the level of the 3rd to the 6th cervical vertebrae.

FUNCTIONS OF PHARYNX

firstly, The passageway for the air and food pharynx is an organ involved in both the respiratory and the digestive systems. Air passes through the nasal and oral sections and food through the oral and laryngeal sections.

secondly, Warming and humidifying– By the same methods as in the nose, the air is further warmed and moistened as it passes through the pharynx.

Thirdly, Taste– There are olfactory nerve endings for the sense of taste in the epithelium of the oral and pharyngeal parts.

Fourthly, Hearing– The auditory tube, extending from the nasopharynx to each middle ear, allows air to enter the middle ear. Satisfactory hearing depends on the presence of air at atmospheric pressure on each side of the tympanic membrane.

Fifthly, Protection– The lymphatic tissue of the pharyngeal and laryngeal tonsils produces antibodies in response to antigens, e.g. microbes. The tonsils are longer in children and tend to atrophy in adults.

sixthly– Speech– The pharynx functions in speech; by acting as a resonating chamber for sound ascending from the larynx, it helps (together with the sinuses) to give the voice its characteristics.

LARYNX

The larynx or ‘voice box ‘ extends from the root of the tongue and the hyoid bone to the trachea. It lies in front of the laryngopharynx at the level of the 3rd, 4th, 5th, and 6th cervical vertebrae. there is a little difference in the size of the larynx between the sexes. Thereafter it grows larger in the male, which explains the prominence of the ‘Adam’s apple and the generally deeper voice.

Structures associated with the larynx

Superiorly- The hyoid bone and the root of the tongue.

Interiorly- It is continuous with the trachea.

Anteriorly- The muscles attached to the hyoid bone and the neck muscles.

Posteriorly- The laryngopharynx and 3rd to 6th cervical vertebrae.

Laterally- The lobes of the thyroid gland.

FUNCTIONS OF LARYNX

Production of sound. sound has the properties of pitch, volume, and resonance.

The Pitch of the voice depends upon the length and tightness of the cords. At puberty, the male vocal cords begin to grow longer, hence the lower pitch of the adult male voice.
The volume of the voice depends upon the force with which the cords vibrate. The greater the force of air, the more the cords vibrate and the louder the sound emitted.
Resonance, or tone, is dangling upon the shape of the mouth, the position of the tongue and lips’ position, facial muscles, and the air in the paranasal sinuses.

Speech. This occurs during expiration when the sounds produced by the vocal cords are manipulated by the tongue, cheeks, and lips.

Protection of the lower respiratory tract. During swallowing (deglutition) the larynx moves upwards, occluding the opening into it from the pharynx and the hinged epiglottis closes over the larynx. This ensures that food passes into the esophagus and not into the lower respiratory passages.

Passageway for air. This is between the pharynx and the trachea.

Humidifying, filtering, and warming. These processes continue as inspired air travels through the larynx.

TRACHEA

The trachea or windpipe is a continuation of the larynx and extends downwards to about the level of the 5th thoracic vertebra where it divides at the carina into the right and left primary bronchi, with one bronchus going to each lung. It is approximately 10 to 11 cm long and lies mainly in the medium plane in front of the esophagus.

FUNCTIONS OF TRACHEA

Firstly- Support and patency. The arrangement of cartilage and elastic tissue prevents kinking and obstruction of the airway as the head and neck move. The absence of cartilage posteriorly allows the trachea to dilate and constrict in response to nerve stimulation, and for indention as the esophagus distends during swallowing. The cartilages prevent the collapse of the trachea.

Secondly- mucociliary escalator. This is the synchronous and regular beating of the cilia of the mucus membrane lining that wafts mucus with adherent particles upwards toward the larynx where it is either swallowed or coughed up.

Thirdly- Cough reflex. Nerve endings in the larynx, trachea, and bronchi are sensitive to irritation, which generates nerve impulses conducted by the vagus nerves to the respiratory center in the brain stem.

Fourthly- Warming, humidifying, and filtering. These continue as in the nose, although air is normally saturated and at body temperature when it reaches the trachea.