Human Respiratory System

Human Respiratory System

Human respiratory system consis of following parts:  

External nares: These are a pair of openings situated just above mouth.the two nostrils are separeted by nasal septum.

Nasal chambers: The external nares lead into two nasal chambers.these lie above the soft palate and are lined by mucous epithelium.the hairs of nasal chamber filters dust and germs.

Internal nares: Nasal chamber posteriorly opens into internal nares.

pharynx: Internal nares opens into naso pharynx. pharynx can be divided into naso,oral and laryngeal.pharynx is crossing of both food and air.the laryngopharynx opens into trachea through glottis ,situated jusst below the floor of pharynx.glottis is protected by cartilagenous flap of skin called epiglottis.

Larynx: The glottis opens into the larynx.it is the anterior modified part of trachea.it is an organ of sound production.the walls of the larynx are supported by four cartilages attached to each other by ligaments and membranes.they are c-shaped thyroid cartilage,ring shaped cricoid cartilade and a pair of pyramid shaped arytenoid cartilages.between thyroid and arytenoid cartilages lies the vocal cords.vocal cord produces sound when air is forcely passed through it.

Trachea: the larynx continues posteriorly into a long tube called trachea.it runs along with oesophagus.it is 11cm long and 3 cm thick.trachea on entering the thoracic cavity divides into left and right bronchi.

Bronchi: Trachea divides to form two bronchi. Each bronchi divides to form secondary and tertiary bronchi and finally into bronchioles ending up in very thin terminal bronchioles. the trachea and bronchi are internally lined by ciliated mucuous epithelium. the wall of bronchi is supported by 20 cartilagenous rings.Each terminal bronchiole gives rise to numerous thin, irregular walled and highly vascular sac like structure called alveoli.

Lungs: The two lungs of human are large,pinkish,soft,spongy and highly vascular organs.these are the actual site of gaseous exchange.they lie each on the either side of heart on pleural cavity of thorax.the lungs being important organs are externally covered by peritoneum.the right ling is larger and broader than left lungs. internally,each lobe of lungs bears numerous small alvioli which are thin walled and highly vascular.gaseous exchange takes place in alvioly by the process of diffusion.

Conducting Part of Respiratory System: all organs starting from external nares to terminal bronchioles are conducting parts.
Exchanging Part of Respiratory System: The alveoli and their ducts are the exchanging parts.


Mechanism of respiration

Breathing:

Breathing involves two process ,inspiration during which air is drawn in to lungs and expiration by which the alveolar air is released out from lungs. The movement of air into and out of the lungs is carried out by developing a pressure gradient between lungs and atmosphere. Inspiration occur if the intra pulmonary pressure is less than the atmospheric pressure because of which net pressure acts toward the lungs.Similarly, expiration takes place when the intra pulmonary pressure is greater than atmospheric pressure.
The diaphragm and a specialised muscles i.e external and internal intercostals between the ribs, help in generation of pressure gradient. Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic cavity . The contraction of external inter-costal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber . The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra pulmonary pressure to less than atmospheric pressure that forces the atmospheric air to move inside the lungs,i.e inspiration.
Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic volume and so the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure which removes the air from lungs into atmosphere.a human also can increase the rate of inspiration and expiration by the help of abdominal muscles.

Gaseous exchange : 

Gaseous exchange takes place in alvioli of lungs.as the alviolar membrane is extremly thin,the blood comes in contact with the air and exchange of gases takes place by diffusion.the diffusion occurs along the concentration gradient.the blood (venous blood) at alviolar contact have lower partial pressure (p.o2) and higher partial pressure(p.co2) than the partial pressure of o2 and co2 in gas at alvioli.as a result o2 is absorped and co2 is released off.

Transportation of gas:
1-3 per. oxygen is transported by blood plasma in soluble form.
97-99 per. oxygen is transported by haemoglobin in the form of oxyhaemoglobin.
7 per. of co2 is transported by blood as carbonic acid.
70 per. of co2 is transported as bicarbonate of alkali metals.
23 per. co2 is transported as carb-amino-haemoglobin.

Release of gases: 
In the tissue and cell where the partial pressure of o2 is less, oxyhaemoglobin releases o2 there and convert into haemoglobin.
carbonic acids,bicarbonates and carb-amino-haemoglobin reduces into co2 in blood.