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Category: 10th Class

Coordination and Control Part 1

The tissues and organs in the bodies of multicellular organisms do not work independently of each other. They work together performing their many tasks as the needs of the whole body. This means that these activities are coordinated. Coordination also enables the organism to respond to happenings in the world around it.
One familiar example of coordination is the way in which muscles work together during movement. When a boy runs to catch a ball, he uses hundreds of muscles to move his arms, legs and back. His nervous system uses information from his sense organs and coordinates these muscles. Due to this coordination, the muscles contract in the correct sequence, power and length of time. But that is not all. Such activities involve many other kinds of coordination. For example breathing and heartbeat rates are increased blood pressure is adjusted, and extra heat is removed fast from the body.
How does it happen? Life activities are controlled and coordinated i.e. body works as one unit, in which its different organs and systems cooperate and work in harmony with each other.

When we are writing something, our hands and fingers work in collaboration with our muscles, eyes, thoughts etc. and then very intricate movements result.

Types Of Coordination:

There are two types of coordination in organisms:

  1.  Nervous coordination brought about by nervous system and
  2. Chemical coordination brought about by endocrine system.
    Animals have both the nervous and chemical coordination systems in their bodies while plants and
    other organisms have only chemical coordination.

Coordinated Action:

A coordinated action has five components;

i- Stimuli:

What happens when we touch a snail? We might have seen the flowers of sunflower plant moving towards the sun. What could be the reason for all this? Touch, light etc. are factors that can bring about certain responses in living organisms. These factors are called stimuli. We can define a stimulus as any change in environment (external and internal), which can provoke a response in organism. More examples of stimuli are heat, cold, pressure, sound waves, presence of chemicals, microbial infections etc.

ii- Receptors:

Stimuli are detected by special organs, tissues or cells of body. For example sound waves are detected by ears, light is detected by eyes, chemicals in air are detected by nose and so on. The organs, tissues or cells which are specifically built to detect particular type of stimuli are called receptors


iii- Coordinators:

These are the organs that receive information from receptors and send messages to particular organs for proper action. In nervous coordination, brain and spinal cord are coordinators. They receive information and send messages through neurons in the form of nerve impulses. On the other hand, in chemical coordination, various endocrine glands play the role of coordinators. They receive information in the form of various chemicals and send messages by secreting particular hormones in blood.

iv- Effectors:

These are the parts of body which receive messages from coordinators and produce particular
responses. In nervous coordination, neurons carry messages from coordinators (brain and
spinal cord) to muscles and glands, which act as effectors. In chemical coordination, particular
hormones carry messages from coordinators (endocrine glands) to particular target tissues,
which act as effectors. For some hormones, nephrons act as effectors. Similarly, bones and liver
act as effectors for many hormones.

v- Response

On receiving the message from coordinators, the effector performs action. This action is called response. For example, pulling our hand away from something very hot and the movement of the flower of sunflower towards light are responses. Usually, nervous coordination produces immediate but short-living responses while chemical coordination produces slow but long-living responses.

Human Nervous System:

We have understood the basic model of the working of nervous system. The nervous system in man and in other higher animals is composed of two major components i.e. central nervous system and peripheral nervous system.

Central nervous system comprises of coordinators i.e. brain and spinal cord while peripheral nervous system consists of nerves that arise from central nervous system and spread in different parts of body. All these components are made of neurons. Now we will first examine the structure and types of neuron and then we will go to the divisions of nervous system.

Nerve cell or Neuron:

Nerve cell or neuron is the unit of the nervous system. The human nervous system consists of billions of neurons plus supporting (neuroglial) cells. Neurons are specialized cells that are able to conduct nerve impulses from receptors to coordinators and from coordinators to effectors. In this way they communicate with each other and with other types of body cells. The nucleus and most of the cytoplasm of a neuron is located in its cell body. Different processes extend out from cell body. These are called dendrites and axons. Dendrites conduct impulses toward cell body and axons conduct impulses away from cell body.

Schwann cells are special neuroglial cells located at regular intervals along axons. In some neurons, Schwann cells secrete a fatty layer called myelin sheath, over axons. Between the areas of myelin on an axon, there are nonmyelinated points, called the nodes of Ranvier. Myelin sheath is an insulator so the membrane coated with this sheath does not conduct nerve impulse. In such impulses are called saltatory (‘jumping’) impulses. This increases the speed of nerve impulse.

On the basis of their functions, neurons are of three types;

1. Sensory neurons conduct sensory information (nerve impulse) from receptors towards the CNS. Sensory neurons
have one dendrite and one axon.
2. Interneurons form brain and spinal cord. They receive information, interpret them and stimulate motor neurons.
They have many dendrites and axons.
3. Motor neurons carry information from interneurons to muscle or glands (effectors). They have many dendrites but only one axon.


A nerve means the union of several axons that are enveloped by a covering made of lipid. Based on the property of axons, the nerves are classified into three types.

  1. Sensory nerves contain the axons of sensory neurons only.
  2. Motor nerves contain the axons of motor neurons only.
  3.  Mixed nerves contain the axons of both i.e sensory and motor neurons.

Divisions of the Nervous System:

The details of the central and peripheral nervous systems are given below.

Central nervous system:

The central nervous system consists of brain and spinal cord.

A- Brain

In animals, all life activities are under the control of brain. The structure of brain is suitable to perform this function. Brain is situated inside a bony cranium (part of skull). Inside cranium, brain is covered by three layers called meninges. Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries.
The brain contains fluid-filled ventricles that are continuous with the central canal of spinal cord. Fluid within ventricles and central canal is called cerebrospinal fluid (CSF).

The Divisions of Brain

There are three major regions in the brain of human and other vertebrates. These are forebrain, midbrain and hindbrain. Important parts of each of these regions are described below:


Forebrain is the largest area of brain. It is most highly developed in humans. Following are the important
parts of this region.

  1. Thalamus lies just below cerebrum. It serves as a relay centre between various parts of brain and spinal cord. It also receives and modifies sensory impulses (except from nose) before they travel to cerebrum. Thalamus is also involved in pain perception and consciousness (sleep and awakening).
  2. Hypothalamus lies above midbrain and just below thalamus. In humans, it is roughly the size of an almond. One of the most important functions of hypothalamus is to link nervous system and endocrine system. It controls the secretions of pituitary gland. It also controls feelings such as rage, pain, pleasure and sorrow.
  3. Cerebrum is the largest part of forebrain. It controls skeletal muscles, thinking, intelligence and emotions. It is divided into two cerebral hemispheres. The anterior parts of cerebral hemispheres are called olfactory bulbs which receive impulses from olfactory nerves and create the sensation of smell. The upper layer of cerebral hemispheres i.e. cerebral cortex consists of grey matter. The grey matter of nervous system consists of cell bodies and non-myelinated axons. Beneath this layer is present the white matter. The white matter of nervous system consists of myelinated axons. Cerebral cortex has a large surface area and is folded in order to fit in skull. It is divided into four lobes.

Midbrain lies between hindbrain and forebrain and connects the two. It receives sensory information and sends it to the appropriate part of forebrain. Midbrain also controls some auditory reflexes and posture.


Hindbrain consists of three major parts.

  1. Medulla oblongata lies on the top of spinal cord. It controls breathing, heart rate and blood pressure. It also controls many reflexes such as vomiting, coughing, sneezing etc. Information that passes between spinal cord and the rest of brain pass through medulla.
  2. Cerebellum is behind medulla. It coordinates muscle movements.
  3. Pons is present on top of medulla. It assists medulla in controlling breathing. It also serves as a connection between cerebellum and spinal cord.
B- Spinal Cord:

The spinal cord is in fact a tubular bundle of nerves. It starts from brain stem and extends to lower back. Like brain, spinal cord is also covered by meninges. The vertebral column surrounds and protects spinal cord.

The outer region of spinal cord is made of white matter (containing myelinated axons). The central
region is butterfly shaped that surrounds the central canal. It is made of grey matter (containing neuron cell bodies).

31 pairs of spinal nerves arise along spinal cord. These are “mixed” nerves because each contains axons of both sensory and motor neurons.

At the point where a spinal nerve arises from spinal cord, there are two roots of spinal nerve.
Both roots unite and form one mixed spinal nerve.

  • The dorsal root contains sensory axons and a ganglion where cell bodies are located.
  •  The ventral root contains axons of motor neurons.

Spinal cord performs two main functions:

  1.  It serves as a link between body parts and brain. Spinal cord transmits nerve impulses from body parts to brain and from brain to body parts.
  2. Spinal cord also acts as a coordinator, responsible for some simple reflexes

Previous Lectures:

Gaseous Exchange



Homeostasis may be defined as the maintenance of the internal conditions of body at equilibrium, despite changes in the external environment. For example, the core temperature of human body remains at about 37°C despite fluctuations in the surrounding air temperature. Similarly, the blood glucose level remains about 1g per litre despite eating a meal rich in carbohydrates. Body cells need the internal environment in which conditions do not change much. Stable internal conditions are important for the efficient functioning of enzymes. The following are some process of homeostasis. Osmoregulation: It is maintenance of the amounts of water and salts in body fluids (i.e. blood and tissue fluids). We know that the relative amounts of water and salts in body fluids and inside cells control by the processes of diffusion and osmosis, which are essential for the functioning of cells
(Recall “the concept of tonicity” from Grade IX Biology). Thermoregulation: The maintenance of internal body temperature is called thermoregulation. The enzymes of body work best at particular temperatures (optimum temperature). Any change in body temperature may affect the functioning of enzymes. Excretion is also a process of homeostasis. In this process, the metabolic wastes are eliminated from body to maintain the internal conditions at equilibrium.

Metabolic waste means any material that is produced during body metabolism and that may harm the body

Homeostasis In Plants:

Plants respond to environmental changes and keep their internal conditions constant i.e. homeostasis. They apply different mechanisms for the homeostasis of water and other chemicals (oxygen, carbon dioxide, nitrogenous materials etc)

Removal of Extra Carbon dioxide and Oxygen:

In daytime, the carbon dioxide produced during cellular respiration is utilized in photosynthesis and hence it is not a waste product. At night, it is surplus because there is no utilization of carbon dioxide. It is removed from the tissue cells by diffusion. In leaves and young stems, carbon dioxide escapes out through stomata. In young roots, carbon dioxide diffuses through the general root surface, especially through root hairs. Oxygen is produced in mesophyll cells only during daytime, as a by-product of photosynthesis. After its utilization in cellular respiration, the leaf cells remove the extra amount of oxygen through stomata.

Removal of Extra Water:

We know that plants obtain water from soil and it is also produced in the body during cellular
respiration. Plants store large amount of water in their cells for turgidity. Extra water is removed from plant body by transpiration. At night, transpiration usually does not occur because most plants have their stomata closed. If there is a high water content in soil, water enters the roots and is accumulated in xylem vessels. Some plants such as grasses force this water through special pores, present at leaf tips or edges, and form drops. The appearance of drops of water on the tips or edges of leaves is called guttation.

Removal of Other Metabolic Wastes:

Plants deposit many metabolic wastes in their bodies as harmless insoluble materials. For example, calcium oxalate is deposited in the form of crystals in the leaves and stems of many plants e.g. in tomato

The removal of excretory products is a secondary function of leaf fall. If the leaves are not shed, the calcium oxalate just remains as harmless crystals in the leaves

In trees which shed their leaves yearly, the excretory products are removed from body during leaf fall. Other waste materials that are removed by some plants are resins (by coniferous trees), gums (by keekar), latex (by rubber plant) and mucilage (by carnivorous plants and ladyfinger) etc.

Osmotic Adjustments in Plants:

On the basis of the available amount of water and salts, plants are divided into three groups.


Are the plants which live completely or partially submerged in freshwater. Such plants do not face the problem of water shortage. They have developed mechanisms for the removal of extra water from their cells. Hydrophytes have broad leaves with a large number of stomata on their upper surfaces. This characteristic helps them to remove the extra amount of water. The most common example of such plants is water lily.


Live in dry environments. They possess thick, waxy cuticle over their epidermis to reduce water loss from internal tissues. They have less number of stomata to reduce the rate of transpiration. Such plants have deep roots to absorb maximum water from soil. Some xerophytes have special parenchyma cells in stems or roots in which they store large quantities of water. This makes their stems or roots wet and juicy, called succulent organs. Cacti (Singular
Cactus) are the common examples of such plants.


Live in sea waters and are adapted to salty environments. Salts enter in the bodies of such plants due to their higher concentration in sea water. On the other hand, water tends to move out of their cells into the hypertonic sea water. When salts enter into cells, plants carry out active transport to move and hold large amount of salts in vacuoles. Salts are not allowed to move out through the semi- permeable membranes of vacuoles. So the sap of vacuoles remains even more hypertonic than sea water. In this way, water does not move out of cells. Many sea grasses are included in this group of plants.

Osmosis is the movement of water from hypotonic solutions (less solute concentration) to hypertonic solutions (higher solute concentration), through semipermeable membrane.

Homeostasis In Humans:

Like other complex animals, humans have highly developed systems for homeostasis. The following are the main organs which work for homeostasis:

  • Lungs remove excess carbon dioxide and keep it in balance.
  •  Skin performs role in the maintenance of body temperature and also removes excess water and salts.
  •  The kidney filters excess water, salts, urea, uric acid etc. from the blood and forms urine.


We know that our skin consists of two layers. Epidermis is the outer protective layer without blood vessels while dermis is the inner layer containing blood vessels, sensory nerve endings, sweat and oil glands, hairs and fat cells. Skin performs important role in the regulation of body temperature. The thin layer of fat cells in the dermis insulates the body. Contraction of small muscles attached to hairs forms ‘Goosebumps’. It creates an insulating blanket of warm air.

Similarly, skin helps in providing cooling effect when sweat is produced by sweat glands and excess body heat escapes through evaporation. Metabolic wastes such as excess water, salts, urea and uric acid are also removed in sweat.


In the previous chapter we have learned how lungs maintain the concentration of carbon dioxide
in the blood. Our cells produce carbon dioxide when they perform cellular respiration. From cells,
carbon dioxide diffuses into tissue fluid and from there into blood. Blood carries carbon dioxide to
lungs from where it is removed in air.

The Urinary System Of Humans:

The excretory system of humans is also called the urinary system. It is formed of one pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Kidneys filter blood to produce urine and the ureters carry urine from kidneys to urinary bladder. The bladder temporarily stores urine until it is released from body. Urethra is the tube that carries urine from urinary bladder to the outside of body.

Structure of Kidney:

Kidneys are dark-red, bean shaped organs. Each kidney is 10 cm long, 5 cm wide and 4 cm thick and weighs about 120 grams. They are placed against the back wall of abdominal cavity just below diaphragm, one on either side of vertebral column. They are protected by the last 2 ribs. The left kidney is a little higher than the right. The concave side of kidney faces vertebral column. There is a depression, called hilus, near the centre of the concave area of kidney. This is the area of kidney through which ureter leaves kidney and other structures including blood vessels, lymphatic vessels and nerves enter and leave kidney.

The longitudinal section of the kidney shows two regions. Renal cortex is the outer part of kidney and it is dark red in color. Renal medulla is the inner part of kidney and is pale red in color. Renal medulla consists of several cone shaped areas called renal pyramids. Renal pyramids project into a funnel-shaped cavity called renal pelvis, which is the base of ureter.

The functional unit of the kidneys is called nephron. There are over one million nephrons in each kidney. There are two parts of a nephron i.e. renal corpuscle and renal tubule . The renal


corpuscle is not tubular and has two parts i.e. glomerulus and Bowman’s capsule. Glomerulus is a network of capillaries while Bowman’s capsule is a cup-shaped structure that encloses glomerulus. The renal tubule is the part of nephron which starts after Bowman’s capsule. Its first portion is called the proximal convoluted tubule. Next portion is U-shaped and is called the Loop of Henle. The last portion of renal tubule is the distal convoluted tubule. The distal convoluted tubules of many nephrons open in a single collecting ducts. Many collecting ducts join together to form several hundred papillary ducts which drain into renal pelvis.

Functioning of Kidney:

The main function of kidney is urine formation, which takes place in three steps . The first
step is pressure filtration. When blood enters the kidney via the renal artery, it goes to many arterioles, and then to the glomerulus. The pressure of blood is very high and so most of the water, salts, glucose and urea of blood is forced out of glomerular capillaries. This material passes into the Bowman’s capsule and is now called glomerular filtrate.

The second step is the selective re-absorption. In this step about 99% of the glomerular filtrate is reabsorbed into the blood capillaries surrounding renal tubule. It occurs through osmosis, diffusion and active transport. Some water and most of the glucose is reabsorbed from the proximal convoluted tubule. Here, salts are reabsorbed by active transport and then water follows by osmosis. The descending limb of loop of Henle allows the reabsorption of water while the ascending limb of Loop of Henle allows the reabsorption of salts. The distal convoluted tubule again allows the reabsorption of water into the blood. The third step is the tubular secretion. Different ions, creatinine, urea etc. are secreted from blood into the filtrate in renal tubule. This is done to maintain blood at a normal pH (7.35 to 7.45).

After the above mentioned steps, the filtrate present in renal tubules is known as urine. It moves into collecting ducts and then into pelvis.

Osmoregulatory Function of Kidney:

Osmoregulation is defined as the regulation of the concentration of water and salts in blood and other body fluids. Kidneys play important role in osmoregulation by regulating the water contents of blood. It is an important process as excessive loss of water concentrates the body fluids whereas excess intake of water dilutes them.

When there is excess water in body fluids, kidneys form dilute (hypotonic) urine. For this purpose, kidneys filter more water from glomerular capillaries into Bowman’s capsule. Similarly less water is reabsorbed and abundant dilute urine is produced. It brings down the volume of body fluids to normal. When there is shortage of water in body fluids, kidneys filter less water from glomerular capillaries and the rate of reabsorption of water is increased. Less filtration and more reabsorption produce small amount of concentrated (hypertonic) urine. It increases the volume of body fluids to normal. This whole process is under hormonal control.

Disorders Of Kidney:

There are many different kidney disorders.

Kidney (Renal) failure:

Kidney failure means a complete or partial failure of kidneys to function. Diabetes mellitus and hypertension are the leading causes of kidney failure. In certain cases, sudden interruption in the blood supply to kidney and drug overdoses may also result in kidney failure. The main symptom of kidney failure is the high level of urea and other wastes in blood, which can result in vomiting, nausea, weight loss, frequent urination and blood in urine. Excess fluids in body may also cause swelling of legs, feet face and shortness of breath. The kidney failure is treated with dialysis and kidney transplant.

1 Dialysis:

Dialysis means the cleaning of blood by artificial ways. There are two methods of dialysis.

 A. Peritoneal Dialysis:

In this type of dialysis, the dialysis fluid is pumped for a time into the peritoneal cavity which is the space around gut . This cavity is lined by peritoneum. Peritoneum contains blood vessels. When we place dialysis fluid in peritoneal cavity, waste materials from peritoneal blood vessels diffuse into the dialysis fluid, which is then drained out. This type of dialysis can be performed at home, but must be done every day.

B. Haemodialysis:

In haemodialysis, patient’s blood is pumped through an apparatus called dialyzer. The dialyzer contains long tubes, the walls of which act as semi-permeable membranes (Fig. 11.12). Blood flows through the tubes while the dialysis fluid flows around the tubes. Extra water and wastes move from blood into the dialysis fluid. The cleansed blood is then returned back to body. The haemodialysis treatments are typically given in dialysis centres.

2. Kidney Transplant:

We know that dialysis needs to be repeated after every few days and is unpleasant for patients and
attendants. Another treatment for the end-stage kidney failure is kidney transplantation. It is the replacement of patient’s damaged kidney with a donor healthy kidney. Kidney may be donated by a deceased-donor or living-donor. The donor may or may not be a relative of the patient. Before transplant, the tissue proteins of donor and patient are matched. The donor’s kidney is transplanted in patient’s body and is connected to the patient’s blood and urinary system. The average lifetime for a donated kidney is ten to fifteen years. When a transplant fails, the patient may be given a second kidney transplant. In this situation, the patient is treated through dialysis for some intermediary time. Problems after a transplant may include transplant rejection, infections, imbalances in body salts which can lead to bone problems and ulcers.

Previous Lectures:

Gaseous Exchange



Gaseous Exchange

In Grade IX, we have studied how cells generate ATPs from food. Cellular respiration is the process in which the C-H bonds in food are broken by oxidation reduction reactions and the energy is transformed into ATP. In aerobic respiration, oxygen is used and there is complete oxidation of the food material. Carbon dioxide and water are also produced in this process. Organisms get the oxygen, needed for cellular respiration, from their environment and provide it to their cells. The carbon dioxide produced during cellular respiration is taken out of the cells and ultimately from the body. Taking in oxygen and giving out of carbon dioxide is termed as gaseous exchange.
The term breathing is used for the process through which animals take air in their bodies to get oxygen from it and then give out the air for getting rid of carbon dioxide. Thus breathing and respiration are not synonymous. Respiration involves the mechanical and the bio-chemical processes whereas breathing is only the mechanical or physical process of exchange of gases.
In this chapter we will go through the mechanisms of gaseous exchange in plants and
in humans.

Gaseous Exchange In Plants:

Plants have no organs or systems for the exchange of gases with the environment. Every cell of the plant body exchanges gases with the environment by its own. The leaves and young stems have stomata in their epidermis. The gaseous exchange occurs through these stomata. The inner cells of leaves (mesophyll) and stems also
have air spaces among them, which help in the exchange of gases.

Leaf cells face two situations. During the daytime when the mesophyll cells of leaves are carrying out photosynthesis and respiration side by side, the oxygen produced in photosynthesis is utilized in cellular respiration. Similarly the carbon dioxide produced during cellular respiration is utilized in photosynthesis. However, during night when there is no photosynthesis occurring, the leaf cells get oxygen from the environment and release carbon dioxide through stomata.

In woody stems and mature roots, the entire surface is covered by bark which is impervious to gases or water. However, there are certain pores in the layer of bark. These are called the lenticels. The lenticels allow air to pass through them. Gases diffuse in and out of the general surface of the young roots. The gases are found in the soil surrounding the roots. The aquatic plants get the oxygen dissolved in water and release carbon dioxide in the

Gaseous Exchange In Humans:

In humans and other higher animals the exchange of gases is carried out by the respiratory system. We can divide the respiratory system in two parts i.e. the air passageway and the lungs.

  • The Air Passageway:

The air passageway consists of the parts through which the outside air comes in the lungs and after the exchange of gases it goes out. This passage of air consists of the following parts. The nose encloses the nasal cavity. It opens to the outside through the openings called the nostrils. The nasal cavity is divided into two portions by a wall. Each portion is lined by fine hairs and mucous which filter the dust particles from the air. The mucous also moistens and warms the incoming air and keeps its temperature nearly equal to that of the body.
On entering the chest cavity, the trachea divides into two smaller tubes called bronchi (Singular: bronchus). The bronchi also have cartilaginous plates in their walls. Each bronchus enters into the lung of its side and then divides into smaller branches. The bronchi continue dividing in the lungs until they make several fine tubes called bronchi-oles. The bronchi-oles progressively lose the cartilages as they become narrower. The bronchi-oles end as fine tubules called the alveolar ducts. Each alveolar duct opens into a cluster of pouches called alveoli. The alveoli form the respiratory surface in human body. Each alveolus is a sac-like structure lined by a single layer of epithelial cells. It is bound on the outside by a network of capillaries. The pulmonary artery from the heart containing deoxygenated blood enters the lungs and branches into arterioles and then into capillaries which surround the alveoli. These then join together to form the venules which form pulmonary vein. The pulmonary vein carries the oxygenated blood back to the heart.

The vibrations in vocal cords and the movements of lips, cheeks, tongue and jaws produce
specific sounds which result in speech. Speech is an ability that only humans are gifted with and
this is one of the characteristics which has put human beings superior to all.

  • The Lungs:

All the alveoli on one side constitute a lung. There is a pair of lungs in the thoracic cavity. The chest wall is made up of 12 pairs of ribs and the rib muscles called intercoastal muscles. A thick muscular structure, called diaphragm, is present below the lungs.

The left lung is slightly smaller and has two lobes and the right lung is bigger with three lobes. They are spongy and elastic organs. The lungs also have blood vessels that are the branches of the pulmonary arteries and veins. Each lung is enclosed by two membranes called the outer pleural membrane and the inner pleural membrane. The membranes enclose a fluid which provides lubrication for the free expanding and contracting of the lungs.

Photo by Robina Weermeijer on Unsplash

  • The Mechanism of Breathing:

The physical movements associated with the gaseous exchange are called breathing. There are two phases of breathing i.e. inhalation and exhalation.


Photo by Elijah Hiett on Unsplash

1. Inspiration or Inhalation:

During inspiration, the rib muscles contract and ribs are raised. At the same time the dome-shaped diaphragm contracts and is lowered. These movements increase the area of the thoracic cavity, which reduces the pressure on lungs. As a result, the lungs expand and the air pressure within them also decreases. The air from outside rushes
into the lungs to equalize the pressure on both sides.

The breathing movements are involuntary to a large extent. However, we can control the
rate of breathing but not for a long time.

2. Expiration or Exhalation:

After the gaseous exchange in the lungs, the impure air is expelled out in exhalation. The rib muscles relax bringing the ribs back to the original position. The diaphragm muscles also relax and it gets its raised dome shape. This reduces the space in the chest cavity and increases the pressure on lungs. The lungs contract and the air is expelled out of them. Humans breathe 16 -20 times per minute in normal circumstances i.e. at rest. The rate of breathing is controlled by the respiratory centre in the brain. The respiratory centre is sensitive to the concentration of carbon dioxide in the blood. When we do exercise or some hard job our muscle cells carry out cellular respiration at a greater rate. It results in the production of more carbon dioxide which is released in the blood. This greater than normal concentration of carbon dioxide stimulates the respiratory centre of brain. The respiratory centre sends messages to the rib muscles and diaphragm to increase the rate of breathing so that the excess carbon dioxide present in blood can be removed out of body. During exercise or other hard physical works the breathing rate may increase up to 30-40 times per minute.

Comparison between the inspired and expired air

Feature Inspired Air Expired Air
Amount of oxygen 21% 16%
Amount of carbon dioxide 0.04% 4%
Amount of nitrogen 79% 79%
Amount of water vapors Variable Saturated
Amount of dust particles Variable Almost None
Temperature Variable Almost equal to body temperature

Respiratory Disorders:

There are a number of respiratory disorders which affect people. The percentage of such disorders is particularly high in Pakistan. It is due to the more concentration of air pollutants not only in the urban but also in the rural atmosphere. Some of the important respiratory disorders are described next.

1. Bronchitis:

Bronchitis is the inflammation of the bronchi or bronchioles. It results in excessive secretions of mucus into the tubes, leading to the swelling of tubular walls and narrowing of tubes . It is caused by viruses, bacteria or exposure to chemical irritants (e.g. tobacco smoke).

There are two major types of bronchitis i.e. acute and chronic. The acute bronchitis usually lasts about two weeks and patients recover with no permanent damage to the bronchi or bronchioles. In chronic bronchitis, the bronchi develop chronic inflammation. It usually lasts for three months to two years.


Symptoms of bronchitis include a cough, mild wheezing, fever, chills and shortness of breath (especially when doing hard job).

2. Emphysema:

Emphysema is the destruction of the walls of the alveoli. It results in larger sacs but with less surface area for gaseous exchange . As lung tissue breaks down, the lungs do not come back to their original shape after exhalation. So air cannot be pushed out and is trapped in the lungs.

The majority of people diagnosed with chronic bronchitis are 45 years of age or older.

The symptoms of emphysema include shortness of breadth, fatigue, recurrent respiratory infections and weight loss. By the time the symptoms of emphysema appear, the patient has usually lost 50% to 70% of his / her lung tissue. The level of oxygen in blood may get so low that it causes serious complications.

3. Pneumonia

Pneumonia is an infection of lungs. If this infection affects both lungs then, it is called double pneumonia. The most common cause of pneumonia is a bacterium, Streptococcus pneumoniae.

Some viral (influenza virus) and fungal infections may also lead to pneumonia. When the causative organisms enter the alveoli, they settle there and grow in number. They break the lung tissues and the area becomes filled with fluid and pus.


The symptoms of pneumonia include a cold that is followed by a high fever, shivering, and a cough with sputum production. Patient may become short of breath. The patient’s skin colour may change and become dusky or purplish. It is due to poor oxygenation of blood. Vaccines are available to prevent pneumonia caused by S. pneumoniae. Antibiotics are used in the treatment of this type of pneumonia.

Prior to the discovery of antibiotics, one-third of pneumonia patients died from the infection

4. Asthma

Asthma is a form of allergy, in which there is inflammation of the bronchi, more mucous production and narrowing of the airways. In asthma patients, the bronchi and bronchioles become sensitive to different allergens (allergy causing factors) e.g. dust, smoke, perfumes, pollens etc. When exposed to any of such allergens, the sensitive airways
show immediate and excessive response of constriction. In this condition, the patient feels difficulty in breathing.


The symptoms of asthma vary from person to person. The major symptoms include shortness of breath (especially with exertion or at night), wheezing (whistling sound when breathing out), cough and chest tightness. The chemicals with ability to dilate the bronchi and bronchioles are used in the treatment of asthma. Such medicine is given in the form of inhalers.

5. Lung Cancer:

Lung cancer is a disease of uncontrolled cell divisions in the tissues of the lung. The cells continue to divide without any control and form tumors. The cellular growth may also invade adjacent tissues beyond the lungs. The most common symptoms are shortness of breath, coughing (including coughing up blood) and weight loss.

Lung cancer is the most common cause of cancer-related deaths and is responsible for more than 1.3 million deaths worldwide annually

The main causes of any cancer include carcinogens (such as those in cigarette smoke), ionizing radiation and viral infection. Smoking is the main cause of lung cancer. This risk of lung cancer is significantly lower in non smokers. Cigarette smoke contains over 50 known carcinogens. Passive smoking (the inhalation of smoke from another’s smoking) is also a cause of lung cancer. The smoke from the burning end of a cigarette is more dangerous than the smoke from the filter end.

Eliminating tobacco smoking is a primary goal in the prevention of lung cancer. The World Health Organization has called for governments to stop tobacco advertising to prevent young people from taking up smoking.

Bad Effects of Smoking:

Smoking is harmful due to the chemicals in cigarettes and smoke. Tobacco smoke contains over 4,000 different chemicals, out of which at least 50 are carcinogens and many are poisonous. Many people think that lung cancer is the only smoking-related disease and it is the number one cause of death among smokers. But it is not right. Cigarette smoke affects the body from head to toe. Smokers have a much higher risk of developing a number of life threatening diseases.

If a person stops smoking, the chance to develop cancer decreases as damage to the lungs is repaired and contaminant particles are gradually removed.
Nicotine is a powerful poison and was widely used as an insecticide in the past. When inhaled through tobacco smoking, it reaches our circulatory system and not only hardens the walls of the arteries but also damages the brain tissues.
According to the WHO, the rates of smoking have declined in the developed world. In the developing world, however, it is rising by 3.4% per year as of 2002

Smoking may also lead to the cancers in kidneys, oral cavity, larynx, breast, bladder and pancreas etc. Many chemicals in tobacco smoke damage the air passageway, which leads to emphysema and other respiratory disorders.

The World No Tobacco Day is celebrated on the 31st of May every year

Smoking also has effects on the circulatory system. The carbon monoxide present in tobacco smoke lessens the oxygen-carrying capacity of haemoglobin. Many other chemicals in smoke increase the production of blood platelets. When platelets are more than the normal numbers, they make the blood viscous and it can lead to arteriosclerosis. Smokers are at greater risk of developing infections, particularly in the lungs. For example, smoking increases the risk of tuberculosis by two to four times, and of pneumonia by four times. Smoking is also responsible for weakening and staining the teeth. Tooth loss is 2 to 3 times higher in smokers than in non-smokers.

Non-smokers who are exposed to second-hand smoke (passive smoke) at home or work increase their heart disease risk by 25-30% and their lung cancer risk by 20-30%


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