In this video, we will study about the respiratory system. The human respiratory system is one of the most vital organ systems of the body. We breathe about 16,000 to 24,000 times per day which exchanges about 11,000 liters of air with the atmosphere. In this process, the oxygen of the atmospheric air is delivered to the human body which is then utilized by all the tissues. and the carbon dioxide which is produced by the human body is exported to the lungs and then exchanged with the atmospheric air.
In this video we will first talk about the brief anatomy and physiology of the human respiratory system then we will discuss how the gas transport to the alveoli occurs we will talk about how the human respiratory system works together with circulatory system and then we will talk about how the gas exchange happens in the alveoli So first coming to the anatomy and physiology of the human respiratory system The vocal cords present in the larynx divide the respiratory tract into the upper respiratory tract and the lower respiratory tract The upper respiratory tract contains structures like the nasal cavity, the pharynx and the part of the larynx above the vocal cords. The lower respiratory tract starts with the part of the larynx below the vocal folds, trachea, bronchi, bronchioles as well as the alveoli. So let's first talk about the brief anatomy of the nose and the nasal cavity. Now if we take a look at this diagram in a bit detail, we can see that the nasal cavity is made up of a roof which is in turn made up of the bones forming the base of the skull. It also consists of a floor which is made up of the palatine bones.
The main job of the nose and the nasal cavity in the respiratory tract is the filtration of air. This is made possible by small minute hair-like structures present in the nasal cavity called cilia. The filtration of air is also facilitated by the mucus which is secreted by the nasal walls.
This traps dust, pollens as well as other pollutants present in the atmospheric air. The other job that the nozzle cavity performs is warming and humidification of the air which prevents the dryness in the respiratory membranes. Oral cavity also serves as a secondary opening for the respiratory tract.
The downside of this is that there is no filtration, no humidification and no temperature regulation through the oral cavity. But there is a plus side also which is that the oral cavity has a wider opening so it facilitates greater intake of air during exercise. So till now we have studied the air that we inhale passes through our nasal cavity or the oral cavity into the pharynx. So coming to the next important structure in the human respiratory tract which is the pharynx.
Pharynx is basically a muscular tube which lies behind the nose, the mouth as well as the larynx. And it connects the oral and the nasal cavity to the larynx as well as the oesophagus. Now the part in the blue you see is the part which is called the nasopharynx.
This is the part which lies behind the nasal cavity. The second part of the pharynx is called the oropharynx which is the part in the green which lies behind the oral cavity and the third is called the laryngopharynx which lies behind the larynx. So the air that we inhale through our nose or through our oral cavity passes back into the pharynx. When the air reaches the pharynx, it has two important structures where it can go forward. The first is the trachea which lies in the front and second is the esophagus which lies at the back.
Normally the air enters in the trachea because esophagus at normal conditions is a collapsed structure. One important structure to note here is the epiglottis. The epiglottis is basically a cartilaginous structure which closes the entry of the trachea and prevents the entry of food.
It is an elastic cartilage which closes the laryngeal inlet and prevents entry of food into the trachea and further the lungs. The next important structure in the respiratory tract is the larynx. The larynx is located right here and it is also known as the voice box as well as the Adam's apple. The larynx is made up of many cartilages and the larynx contains the vocal cords.
The main function of the larynx in the human respiratory system is that it connects the pharynx to the trachea and the second important structure is the production of sound or speech. The next important structure is the trachea. So the trachea is basically a tube-like structure which connects the larynx to the bronchi and the bronchi in turn connect to the lungs. If we take a closer look at the section of the trachea, we can see that the trachea is basically made up of 20 C-shaped cartilages from above to below.
These cartilages basically prevent the collapse of the trachea because there is a negative pressure in trachea as well as the lungs during inhalation. If you see closely, these tracheal rings are basically C-shaped. These are not completely circular because esophagus lies behind the trachea and if these rings were circular, they would have compressed the esophagus during swallowing and this could have led to choking.
The trachea then divides into the primary bronchi. Now this is called the primary bronchi because it is the first division of the trachea. The primary bronchi then divides into secondary bronchioles and then the secondary bronchioles divide into the tertiary bronchioles.
Now what happens next is that these tertiary bronchioles again divide for about 20 divisions to form the conducting bronchioles. So you can see the tertiary bronchioles divide many times to form very small sac like structures. The tertiary bronchioles lead into the conducting bronchioles.
The conducting bronchioles then form a 4-5 division series of respiratory bronchioles. These respiratory bronchioles are in turn connected to the alveoli. The alveoli are sac-like structures in which the actual gas exchange happens.
The conducting bronchioles are called conducting bronchioles because no gas exchange happens in them since they have large or thick walls. But respiratory bronchioles have very thin walls and some amount of gas exchange can happen in these respiratory bronchioles. But majority of the gas exchange happens in the alveoli because of their close proximity to the blood vessels.
The division of the bronchioles to such an extent increases the effective surface area of the lungs. So the air that we inhale finally reaches into the alveoli. Now let's look at this diagram to understand how the respiratory system of our body works in conjunction with the circulatory system to provide gas exchange.
In this diagram you can see the lungs, the heart as well as the circulation pool of the body showing the deoxygenated blood in blue color as well as the oxygenated blood in the pink color. The heart receives all the deoxygenated blood from the body through the superior as well as the inferior vena cava. This blood has a low concentration of oxygen and this is then pumped to the lungs through the pulmonary arteries.
In the lungs, this deoxygenated blood is subjected to gas exchange which converts it into oxygenated blood which is pumped back to the heart. The heart then pumps this oxygenated blood to the body which utilizes the oxygen present in this blood. And again this blood is converted into deoxygenated blood which is pumped back to the heart. The heart pumps all the deoxygenated blood to the lungs through two main arteries, the right and left pulmonary artery.
Just as we saw with the previous branching pattern, that a single bronchus almost divides 20-25 times before the formation of alveoli. The similar phenomena happens with the large blood vessels that enter into the lungs. These blood vessels also divide several times which leads to formation of small capillaries that are in extremely close contact with the alveoli.
Due to this, the cardiac output that comes in large vessels divides into many small streams of blood. This leads to exposure of the 5 liters of blood coming through the heart to almost 250-300 million alveoli per minute. Due to this, a rapid gaseous exchange happens between the alveolar air and the blood that is exposed to the alveoli. Now let's try to understand how the actual gas transport happens inside a single alveoli.
So the air that we inhale passes through our respiratory tract deep into our body into a bunch of structures called alveoli. Well, this is important to create a very less distance between the alveolar air and the blood. Now to understand this, take a closer look at this section of an alveoli which are attached to the end of a respiratory bronchiol.
You can see that a bunch of alveoli are surrounded closely by blood vessels. If we take a single alveoli out of this bunch and magnify it under a microscope, We can see that the alveoli is completely surrounded by a single capillary. But in reality they are surrounded by multiple capillaries to have very close contact with the blood.
In these capillaries, the deoxygenated blood enters from one side, it exchanges the gases with the alveolar air and finally oxygenated blood is released from the other side. If we take a closer look at the junction between the alveoli and the capillary wall, you can With the green side represents the space inside the alveoli. The cells in the sky blue represent the alveolar epithelium.
On the other side, we have the blood vessels which contain the RBCs. and the wall of the blood vessel is the endothelium. In between them is the basement membrane which separates these two cell layers.
So you can see clearly that the air that we inhale in the alveoli is a very close proximity which is approximately few micrometers from the blood vessel. Here comes the role of difference in the concentration of gases on either side. Most of you know that the diffusion occurs due to the difference in concentration of a substance on either side. So if we take a look at the concentration difference of the alveolar air and the blood of carbon dioxide and oxygen, we can see that the alveolar air has a low concentration of carbon dioxide as compared to the blood which has a higher concentration.
Whereas Opposite of that is true in case of oxygen where high concentration of oxygen is present in alveolar air as compared to low concentration of oxygen in the blood. Due to this, the high concentration of carbon dioxide is exchanged with the alveolar air and the carbon dioxide is released outside in the atmosphere. Whereas the fresh oxygen that is coming through the alveolar air is transported to the blood and the blood is made oxygenated.
So the blood coming on one side of the capillary which is a deoxygenated blood. is converted into oxygenated blood on the other side. This oxygenated blood is then sent to the heart and the heart then pumps this oxygenated blood to whole of the body which is then utilized.
So this was a brief description of the human respiratory system. I hope you found this video helpful. Make sure to help our channel by subscribing to our youtube channel and also make sure to like our page for all the flashcards, mnemonics and upcoming stuff. Thank you so much for watching.