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My Article no 3

                                                                                COORDINATION AND CONTROL

The tissues and organs in the bodies of multicellular organisms don 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.

Our familiar example of coordination the way in which muscles work together during movement. When a boy runs to catch 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 system cooperate and work in harmony with each other.

TYPES OF COORDINAITON

There are two types of coordination in organisms;

1.       Nervous coordination brought about by nervous system and

2.       Chemical coordination brought about endocrine system

Animals have both the nervous and chemical coordination system in their bodies while plants and other organisms have only chemical coordination.

Coordination Action

A coordinated action has five components.

1.       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.

2.       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.

My Article no 2

                                                                HOMEOSTASIS 

Homeostasis may be defined as the maintenance of the internal conditions of body equilibrium, despite changes in the external  environment. For example, the core temperature of human body remains at about 37 Centigrade 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 examples 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 the processes of diffusion and osmosis, which ar

e essential for the functioning of cells.

Thermoregulation: the maintenance of internal body temperature is called thermoregulation. The enzymes of body work best at particular temperatures are 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: Excretion is also process of homeostasis. In this process, the metabolic wastes are eliminated from body to maintain the internal conditions at equilibrium.

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 mesophyll 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.

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 lady finger) etc.

Osmotic Adjustments in Plants

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

·         Hydrophytes 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.

·         Xerophytes 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.

·         Halophytes 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. 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.

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.

·         The kidney filters excess water, salts, urea, uric acid etc. form the blood and forms urine.

Skin

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.

Lungs

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 human 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 form 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 27 grams. They are placed against the back wall of abdominal cavity just below diaphragm, on eon either side of vertebral column. They are protected by the last 2ribs. 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 duct. 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. Is 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.

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 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 Stones

When urine becomes concentrated, crystals of many salts e.g. calcium oxalate, calcium and ammonium phosphate, uric acid etc. are formed in it. Such large crystals cannot pass in urine and form hard deposits called kidney stones. Most stones start in kidney. Some may travel to ureter or urinary bladder.

The major causes of kidney stones are age, diet (containing more green vegetables, salts, vitamins C and D), recurring urinary tract infections, less intake of water, and alcohol consumption. The symptoms of kidney stones include severe pain in kidney or in lower abdomen, vomiting, frequent urination and foul-smelling urine with blood and pus.

About 90% of all kidney stones can pass through the urinary system by drinking plenty of water. In surgical treatment, the affected area is opened and stones are removed. Lithotripsy is another method for the removal of kidney stones. In this method, non-electrical shock waves from outside are bombarded on the stones in the urinary system. Waves hit the dense stones and break them. Stones become sand-like and are passed through urine.

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 and face and shortness of breath.

The kidney failure is treated with dialysis and kidney transplant.

a.       Dialysis

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

1.       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.

2.       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. 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 three times per week.

b.      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-stag kidney failure is kidney transplantation. Is is the replacement of patient’s damaged kidney with a donor a healthy kidney.   

My Articles no 1

                                                Gaseous Exchange

Cellular respiration is the process in which the C-H bonds in food are broken by oxidation reduction reaction 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.

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 water.

Gases Exchange in Human

In human 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.

The nasal cavity opens into the pharynx by means of two small openings called internal nostrils. Pharynx is a muscular passage and is common to both food and air. It extends to the opening called internal nostrils. Pharynx is a muscular passage and is common to both food and air. It extends to the opening of the oesophagus and the larynx. The air goes from the pharynx into the larynx. We know that glottis is a narrow opening at the floor of pharynx which leads into larynx.

The larynx is a box, made of cartilage. It is present between pharynx and trachea. It is also called the voice box. Two pairs of fibrous bands called vocal cords are stretched across the larynx. The vocal cords vibrate when the air passes through them. This vibration produces sounds.

Larynx continues to the trachea, which is also called the windpipe. It is about 12 cm long tube which lies in front of the oesophagus. There are C-shaped cartilaginous rings in the wall of trachea. The cartilages keep the trachea from collapsing even when there is no air in it.

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 lungs of its side and then divides into smaller branches.

The bronchi continue dividing in the lungs until they make several fine tubes called bronchioles. The bronchioles progressively lose cartilages as they become narrower. The bronchioles 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 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 intercostal muscles. A thick muscular structure, called diaphragm, is present below the lungs.

The left lungs are slightly smaller and have 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.

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.

1.       Inspiration or In halation

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.

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 irs 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.

Human 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 carryout cellular respiration at 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.

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 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 infections affects both lungs then, it is called double pneumonia. The most common cause of pneumonia is a bacterium, streptococcus pneumonia. 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 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. pneumonia. Antibiotics are used in the treatment of this type of pneumonia.

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 tightnesss.

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 tumours. 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.

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 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 government 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 chemical s, 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.

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.

Smoking als 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 in 3 times higher in smokers than in non-smokers.