Human physiology

Insulin: Maintaining glucose homeostasis

Insulin is a hormone produced by the beta cells of the pancreas. This hormone is primarily responsible for maintaining glucose homoeostasis in the human body.

The human body depends on glucose for most of its energy needs. In fact, glucose is the primary source of energy for all living cells. However, most human tissues cannot utilise glucose in the absence of insulin. The brain is an exception. The brain can use glucose even in the absence of insulin.

Let us briefly discuss human digestion. The food we eat consists of carbohydrates, proteins and fats. The amylase present in saliva starts the digestion of carbohydrates in food. The pancreatic amylase completes the process of digestion of carbohydrates in the small intestine. The pancreatic amylase completely breaks down the carbohydrates into glucose and fructose. Glucose and fructose are six carbon molecules that are the simplest of the sugars. Glucose enters the bloodstream after absorption from the small intestine.?

Blood then supplies glucose to tissues, and the excess glucose is converted into glycogen in the liver. Glycogen is the energy reserve of the body. When the body is fasting, glycogen is degraded into glucose and utilised by the cells.

As soon as glucose enters the bloodstream, it stimulates the release of insulin from the beta cells of the pancreas.Amino acids also stimulate the release of this hormone from the pancreas (in fact, amino acids are a more potent stimulus).

The insulin acts primarily on the liver, muscle and adipose tissues. Other tissues are not dependent?on this hormone to utilise glucose.


Insulin is a peptide hormone consisting of two polypeptide chains- A & B. A disulphide bond links the two chains. It is first synthesised as a single polypeptide chain- preproinsulin. This polypeptide chain is processed by the endoplasmic reticulum to produce a 39 amino acid residue. During this process, a polypeptide chain called C-peptide is released. We can check the functioning of the pancreas by checking the level of C-peptide in the blood.

The synthesis and release of this hormone are regulated at several levels- transcription of the gene, translation and post-translational modifications.


Insulin is an anabolic hormone. It induces the synthesis of many substances. It also regulates growth. The following effects are known:-

  1. Glycogen synthesis- The cells of the liver and the muscles are the primary targets of insulin. Insulin promotes uptake of glucose by the hepatocytes and myocytes. It also promotes synthesis of glycogen in the liver and muscle. When the body is fasting, the blood level of insulin decreases and this promotes degradation of glycogen. The degradation of glycogen maintains blood glucose at a constant level.

  2. Lipid synthesis- This hormone acts on the adipocytes or fat cells and promotes synthesis of triglycerides and fatty acids. Treatment with insulin leads to weight gain due to increased production of fat by adipose tissue (apart fro fluid retention). It also promotes esterification of fatty acids.

  3. Decreases the degradation of proteins

  4. Decreased degradation of fats

  5. Decreases production of glucose- Apart from degradation of glycogen, the human body has mechanisms to produce glucose (gluconeogenesis) from amino acids. Gluconeogenesis helps maintain blood glucose levels when the body is fasting, and the glycogen stores are depleted.?

  6. Increases uptake of amino acids. Also promotes the production of proteins.

  7. Increased potassium uptake by cells- Insulin promotes uptake of potassium by the cells. Therefore, serum potassium levels can fall following treatment with insulin. The ability to reduce serum potassium levels is harnessed therapeutically to reduce elevated serum potassium. This hormone increases uptake of potassium by increasing the concentration of Na-K ATAase on the cell surface by translocation of the receptors from the cytosol to the cell membrane.

  8. Effect on arterial muscles ? Has a significant impact on the arterial muscles. This hormone causes relaxation of the arterial muscles, thus, reducing arterial tone. The reduction in the arterial tone improves microcirculation.

  9. Increases secretion of hydrochloric acid in the stomach

  10. Reduces sodium excretion by the kidneys. Therefore, treatment with insulin can lead to fluid retention.

Disorders due to over or underproduction of insulin

Insulin plays a critical role in glucose homoeostasis. Therefore, over or underproduction can result in many disorders. Diabetes Mellitus is a disorder caused by underproduction. Lack of insulin leads to impaired utilisation of glucose by body tissues. Therefore, blood glucose levels rise and result in some problems- kidney damage, damage to blood vessels and nerves, etc.?

Until the development of injectable insulin, diabetes was a disease with high morbidity and mortality. In 1920. Scientists Banting and Best purified insulin and postulated that injections can be used to treat diabetes. Use of insulin to treat diabetes has revolutionised the management of this chronic disorder. For their work, Banting and Best were awarded the Nobel Prize in Physiology in 1923.

Overproduction leads to dropping in blood glucose levels. When blood glucose level drops (hypoglycaemia) below a specified threshold symptoms like weakness, dizziness, palpitations, sweating and seizures can occur. Overproduction is the hallmark?of a disorder?called insulinoma.

Sense of smell: Dogs Vs. Humans

The sense of smell is one of the five senses. The sense of smell is an essential feeling and without it life would be difficult for humans. Can you think of what would happen if humans lost the sense of smell?

What happens when your nose is blocked due to cold? You lose the feeling of smell. Loss of sense of smell also leads to altered taste. Food that used to feel good to you no longer feels as good! So, the feeling of smell is necessary for the sense of taste as well.

So, which animal has the best sense of smell?

I am sure you have heard this phrase before- sniff like a bloodhound. Dogs have been used for many centuries as a hunting aid. Dogs are used to sniff out drugs, explosives and humans. So, what is so special about dogs that make them suitable for these duties?

Dogs have an incredible sense of smell. A dog has over 220 million smells receptors. In contrast, humans only have five million olfactory receptors. The bloodhound has as many as three hundred million receptors for smell.

The dog’s olfactory comprises of two nares, nasal cavity, a specialised layer of olfactory epithelium and a specialised organ- the vomeronasal organ.?

sense of smell

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Air enters through the nares. Odours in the inspired air are ascertained by the olfactory receptors in the specialised olfactory epithelium lining the nasal cavity. Each olfactory receptor stimulates an olfactory nerve. The odours then reach the olfactory lobe by travelling through the olfactory nerve.

The vomeronasal organ is a pair of elongated fluid-filled sac that opens into the mouth or the nose. The olfactory receptors in the vomeronasal organ are different from those in the nasal cavity. The olfactory neurones in the nasal cavity have cilia while those (Neurones) in the vomeronasal cavity usually have microvilli. Also, the neurones in the vomeronasal organ are specialised structures that are necessary for detection of pheromones. The vomeronasal organ is connected to the hypothalamus in the dog’s brain. The hypothalamus regulates many sexual and social behaviours.

So, have you seen a dog sniff? Sniffing is a technique that dogs use to maximise the detection of odours. Sniffing is a series of rapid inhalation and exhalation that is a disruption of the normal breathing pattern. Sniffing creates a pocket within the nasal cavity. This pocket allows accumulation of odour molecules and improves recognition of odours.

Difference between human and canine olfaction

There are many differences between humans and dogs when it comes to the sense of smell. As discussed before, the number of olfactory receptors is huge in dogs when compared to humans. Dogs are also more proficient in detecting pheromones.

Also, dogs have a very well developed olfactory lobe that helps with recognition of smells.

Therefore, your dog is far more proficient in recognising smells than you. However, recent research suggests that human sense of smell is better than we imagined. Although the number of olfactory receptors is lesser than that of a dog, we humans have a greater variety in terms of olfactory receptors. Recent studies suggest that there are over four hundred types of smell receptors in the humans. These (receptor) acting in various permutations and combinations can detect as many as one trillion smells (Nature.?doi:10.1038/nature.2014.14904 ).

Mitochondria- The powerhouse of the cell

Mitochondria are cellular structures that generate the energy required by cells for life processes. These organelles are mostly found in Eukaryotic cells. Their name comes from the Greek word- ????? (mitos or thread) and ???????? (chondrion or granular).

The number of mitochondria can vary from a few hundred to more than 2000/per cell (hepatocytes). The number and distribution of mitochondria are proportional to the energy requirement of the cells. Cells like red muscles that do sustained work are abundant in mitochondria. Similarly, the liver has high energy demand. Therefore, each hepatocyte can have in excess of 2000 . On the other hand, the white muscles have a small number of these organelles despite consuming a large amount of energy. Most of the energy used by the white muscles comes from anaerobic metabolism of glycogen. Therefore, the number of mitochondria is also small. Some cells like the red blood cells do not contain any mitochondria.

We have previously learned about aerobic and anaerobic metabolism. Mitochondria are exclusively involved in aerobic metabolism.

These organelles are 0.5 to 1.0 micrometres in size. They have a double layer of lipid membrane and the proteins and enzymes of the mitochondrial electron transport system are embedded within the two layers of the mitochondrial membrane.


Glucose, the principal source of energy for the cell is degraded in the cytosol by anaerobic metabolism to produce pyruvate. The pyruvate is taken up by the mitochondrial membrane by an active process and this (pyruvate) is further degraded by the enzymes in the mitochondrial matrix. The process of degradation of pyruvate results in the production of water, carbon dioxide and energy. The energy released by the breakdown of glucose is captured in the phosphate bonds of Adenosine triphosphate (ATP). ATP is used by the cell for its energy requirements. As oxygen is required for this process, this (breakdown of glucose) is called as aerobic metabolism or respiration.

Mitochondria are unique in many aspects. They can replicate, i.e. it can divide and reproduce in response to increasing energy demand. They also contain DNA, the genetic code of life. Defects or problems in the mitochondrial DNA can cause many diseases- mitochondrial disease. The musculoskeletal system is commonly involved by disorders of the mitochondria. These disorders are called mitochondrial myopathies. The pattern of inheritance of mitochondrial disorders is also unique. As the zygote (the fertilised ovum) receives all its mitochondria from the mother, all mitochondrial disorders are transferred from the mother to the offspring.

In addition to generating energy, these organelles also regulate many cellular functions like cell signalling, differentiation, control of cell cycle and apoptosis.

In conclusion, mitochondria are vital organelles that generate energy for maintenance of life processes.

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The human eye

The human eye is one of the five sense organs. It perceives the meaning of light. It is because of the human eye that we can see the varied and beautiful world around us. There are two eyes, located within a bony socket called the orbit. The bones of the skull and face form the boundaries of the orbital cavity. Within the orbital cavity, lies the eye, the extra-ocular muscles, loose connective tissue, blood vessels, nerves and the optic nerve.

The outermost covering of the human eyes is sclera, a thick, fibrous sheath. It functions to protect the eyeball from injury. The white colour of the eye is because of the sclera.

The cornea is the transparent portion of the eye that light to enter the eye. ?In previous chapters, we have learned about refraction. The cornea can be considered to be a refractive medium that brings the light rays to focus. Most of the refraction occurs at the out surface of the cornea.

human eye

Human eye: A cross-section.

The Iris, a muscular diaphragm, controls the entry of light into the human eye. How does the Iris monitor the entry of light into the human eye? Iris does so by controlling the size of the pupil, a small aperture. Have you noted what happens when you shine a torch into the eye? The pupil constricts, thus reducing the amount of light entering the human eye.

Immediately behind the Iris, lies the lens. The lens is flattened towards the front and it is suspended in the eye by muscles called the ciliary muscles. These muscles help with the process of adaptation. The ciliary muscles can increase or decrease the focal length of the lens to enable the eye to focus on objects across a broad range of focal lengths.

The light from a source is refracted by the cornea and the lens and is brought to focus on the light sensitive layer of the human eye- the retina.The retina contains two types light sensitive cells- the rods and cones. The rods, numbering 120 million are more numerous and are more sensitive to light. On the other hand, cones, numbering 6-7 million sense colour. The cones are concentrated around the centre of the retina, an area called the optic disc. Within the optic disc lies the fovea. Cones are present in the highest concentration in the fovea. Therefore, colour perception is best at the fovea.

The light that is refracted by the cornea and the lens forms an inverted real image over the retina. The image is transmitted to the occipital lobe of the brain by the visual pathways comprising the two optic nerves, optic tracts and their projections. The human brain processes the signals. Therefore, we only see the erect images.

Thus, the human eye behaves like a camera for all purposes. There is one difference though- the human eye can appreciate the depth of field, which a camera sorely lacks.

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Neurons: The building blocks of the nervous system

Neurons are the cells of the nervous system. In the previous article, we had learned about the organization of the human nervous system. In this article, we shall learn about the basic building block of the nervous system- the neurons.

The human brain and the spinal cord themselves contain a hundred billion neurons. The neuron is a long cell with three parts- the cell body, the axon, and the nerve endings. The cell body contains the nucleus and the bulk of the cytoplasm of the neuron. The cell body is metabolically active and hence contains mitochondria and storage structures like the endoplasmic reticulum and Golgi bodies. The cell body also has multiple projections called dendrites. The nerve ending of one neuron interacts with the dendrite of another neuron the synapse.

How are messages carried through the neurons?

Neurons use a combination of chemical and electrical signals to disseminate messages. These compounds are called as neurotransmitters. The common neurotransmitters in the human brain include acetylcholine, dopamine, serotonin, GABA, and glutamate. These compounds are synthesized in the cell body and transported to the nerve endings where they get stored.

The dendrites of neurons and the neuromuscular junction contain receptors for neurotransmitters. The receptors change their shape on binding with the neurotransmitters?and many downstream reactions like the influx of sodium and efflux of potassium occur. An electrical current originates because of the ionic difference, and this current reaches the nerve ending through the axon. When this current reaches the nerve ending, the stored neurotransmitters are released.

There are two kinds of neurons- myelinated and unmyelinated.

The myelinated neurons have a layer of myelin, a lipid, over them. The myelin serves to insulate the axon. Some areas of the axon, known as nodes of Ranvier, are devoid of this coating. The myelin does not cover the nodes of Ranvier. Therefore, electrical impulses have to jump from one node to another. Therefore, the speed of transmission is high in the myelinated neurons. The motor neurons are myelinated neurons.

In contrast, the unmyelinated neurons do not have the insulating layer of myelin around them. In these cells, the electrical impulse will have to travel along the full length of the axon. Therefore, the speed of transmission of impulses is slower in the unmyelinated neurons. The neurons of the pain system are unmyelinated.

Neuromuscular junction

The nerve endings terminate either on another neuron or a neuromuscular junction. The neuromuscular junction is a highly evolved structure that translates the electrical signals from the neurons into action by the muscles. The primary neurotransmitter in the neuromuscular junction is acetylcholine. Have you heard of a disease called Myasthenia Gravis? This disease causes muscular weakness because of damage to the neuromuscular junction.

So, in this article, we have learned that neurons are the basic building blocks of the human nervous system. They interact with other neurons, ranging from simple one synapse reflex arc to multisynaptic complex networks. We shall discuss the reflex arc in the next article.

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An overview of the human nervous system

The human nervous system is an organised collection of neurons that controls and coordinates, not only movements but most other life processes. In our previous articles on the musculoskeletal system, we learnt about the muscles and bone. If the musculoskeletal system is the wheel of a car, then the human nervous system performs the function of the brakes and the accelerator.

The central nervous system (CNS), the peripheral nervous system and the enteric nervous system are the three components of the human nervous system.

The CNS consists of the brain, the cranial nerves and the spinal cord. The human brain is the most evolved amongst all living beings. It is the seat of all thinking and action. It is a highly sophisticated and organised structure with different regions of the brain subserving various functions. The brain consists of three anatomical regions- forebrain, midbrain and the hindbrain.

The forebrain, comprising of the cerebrum is the area where all higher mental functions like speech, thinking, planning, execution, comprehension, etc. are carried out. The midbrain and hindbrain are more involved with maintaining vital life processes like breathing, circulation, etc. The cerebellum is a part of the hindbrain; it serves the function of coordination of movements.

The spinal cord carries the messages from the brain to the respective muscles and organs. ?Have you ever seen a telephone or a fibre optic cable? ?Within the cable are millions of slender optical fibres that transmit signals. The spinal cord also looks similar. The axons of the neurones in the brain run through the spinal cord and exit the spinal cord at different levels.

The nerves exiting the spinal cord from the peripheral nervous system. The peripheral nervous system is the final pathway for all the impulses that originate from the brain. The nerves of the peripheral nervous system terminate on the muscles and other organs and control their function.

The enteric nervous system is that part of the human nervous system that handles the control and coordination of the gastrointestinal system. The enteric nervous system is a network of neurones within the digestive tract. The enteric nervous system senses changes within the GI tract and it also receives impulses from the CNS through the Vagus nerve.

How many of you have seen a person afflicted with Polio or someone with partial paralysis of one side of the body? In both cases, the muscles are unable to move as the nerves that control them have died due to some reason. Therefore, the movement would not be possible without the human nervous system.

So how does the human nervous system send signals to the muscles? What kind of messages are sent? We will learn more about this in the next article on the structure and function of neurones.

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How do humans move: The musculoskeletal system?

Humans have a highly developed system to perform the task of movement- the musculoskeletal system. The musculoskeletal system consists of the bones that form the skeleton and specialised connective tissue- muscles that carry out the function of movement. The muscles are attached to the bones at both their ends (some muscles like the tongue are appended to a bone at only one end). The muscles are attached to bone using ligaments. Ligaments are very sturdy structures formed of collagen and other connective tissue. The muscles are excitable, elastic, and they extend and contract by the action of their contractile units, also called as sarcomeres.

A sarcomere is the basic unit (contractile) of the muscle. Actin and myosin are the essential components of a sarcomere. The actin and myosin filaments are made up of a contractile protein called myoglobin. The two filaments interdigitate and when they slide over each other, movements of the musculoskeletal system is seen.

The musculoskeletal system is divided in skeletal muscles, smooth muscles and cardiac muscle (based on the function). The skeletal muscles are attached to the bones at both their ends. The skeletal muscles handle all visible movement of humans, and they are under voluntary control. Smooth muscles are present in the gastrointestinal tract. These muscles are not under voluntary control. Cardiac muscle is a specialised form of smooth muscle. The cardiac muscle is comprised of many different cells, that functionally behave as one cell. The cells are connected to each other through structures called as a syncytium.

The musculoskeletal system can also be classified based on the pace of contractility- red and white muscles. The red muscles effect sustained activity. Therefore, they contain many mitochondria and myoglobin. In the chapter on life processes and respiration, we learnt that mitochondria are the power plants of the cell. Mitochondria produce energy in the form of ATP. ATP is then used by the actin and myosin filaments to effect movements of the musculoskeletal system. The red muscles contain many mitochondria and hence use aerobic respiration for producing energy. In contrast, the white muscles are used for short bursts of intense activity. The white muscles contain few mitochondria. Hence, they depend on anaerobic respiration for energy. Anaerobic respiration can provide power quickly, but there is an accumulation of lactic acid, which leads to fatigue. Therefore, the white muscles are primarily developed in those areas where short; quick, intense activity is required- for example the muscles of the eye.

The musculoskeletal system by itself cannot produce movement. The different parts of the musculoskeletal system need to be coordinated. The nervous system serves the function of control and coordination of the musculoskeletal system. We shall learn more about the human nervous system in the next article.

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Life processes: Human excretory system

In our previous article, we had discussed the process of excretion in general. In this article, we shall discuss the human excretory system in detail. We have previously learnt that carbon dioxide, urea and other solutes are the primary waste products of metabolism. Lungs are the primary organs responsible for the excretion of carbon dioxide while the kidneys are the main organs that excrete urea and other nitrogenous waste products from the body.

The human excretory system comprises of two kidneys, the ureters, the urinary bladder and the urethra. The kidneys are two bean-shaped organs that occupy a place over the loins. The kidneys receive nearly 25% of the cardiac output. The kidneys are made up of small filtering units called nephrons. Each kidney contains nearly a million nephrons. Each nephron has an artery that brings blood into it and another which takes blood out of it. The ?former is called as the afferent arteriole, and the latter is called as the efferent arteriole. The afferent arteriole, inside the nephron, leads to a network of fine tubes with a single layer of cells lining the inside of the tubes. This tuft of tubes is called the glomerulus. Blood enters the glomerulus under pressure, and the plasma is filtered out into the space between the glomerulus and the wall of the nephron. This plasma then flows through a series of tubes, where glucose, amino acids and other essential substances are reabsorbed. Within these tubules, the urine is concentrated and finally delivered to a structure called as the renal pelvis. From the renal pelvis, the urine flows through two long tubes called ureters (one for each kidney).

The ureters join the urinary bladder, a storage organ of the human excretory system. The urinary bladder is a hollow muscular organ that holds urine till it is voided outside through the urethra. The internal and external sphincters are two circular muscles that control the voiding of urine.

As the bladder fills up with urine, it sends signals through nerves to neurons within the spinal cord. A micturition reflex is set up; that is characterised by contraction of the urinary bladder and relaxation of the internal sphincter. This process is involuntary, yet we can hold urine as the external sphincter is under voluntary control.

The human excretory system is similar in both males and females up to the bladder. In men, the urethra merges with the genital tract to form the urogenital tract, while, in women, the urethra and the genital tract remain separate, although nearby.

The human excretory can function adequately, even when a part or one whole kidney is damaged. It is for this reason that diseases of the kidney are typically found late in the course?after substantial damage has occurred to the kidneys. It is therefore, important that we take adequate precautions to safeguard our kidneys. A minimum urine output of 1200 ml/day is required for the proper health of the kidneys. One of the easiest ways to improve the functioning of the kidneys is to drink plenty of water. We should drink at least eight glasses of water every day.

To conclude, the human excretory system, cComprising two kidneys, ureters, urinary bladder and urethra?is the primary mode of excretion of nitrogenous waste substance.The human excretory system produces urine, the final waste product. The urine consists urea, salts, solutes and other nitrogenous waste products dissolved in water. This urine is then voided out through the urethra.

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The human circulatory system

The human circulatory systems consist of the heart, arteries, and veins. The lungs also form an important component of the circulatory system. It has been discussed previously in our article on human respiration.

The heart, a muscular organ is the centre of the human circulatory system. The heart is located in the chest, towards the left side. It contains four chambers- the right atrium, the right ventricle, the left atrium and left ventricle. The left atrium and ventricle are connected in series and form the left side of the heart. The left heart receives blood (oxygenated) from the lungs and pumps it to various parts of the body. The pulmonary veins, four in number, ?bring oxygenated blood from the lungs to the left atrium. The outflow from the left heart goes into a large blood vessel (in fact, the biggest blood vessel in the body) – the aorta. The aorta has many branches at different levels that supply blood to the various organs.

The right side of the human circulatory system consists of the right atrium and ventricle that are connected in series. The right heart receives deoxygenated blood from the various parts of the body and pumps it through the pulmonary artery into the lungs. Within the lungs, by the process of simple diffusion, oxygen is taken in by the haemoglobin present in red cells, and the carbon dioxide is excreted out into the air. This entire process is called respiration.

The heart pumps blood through the body continuously. In never stops during a person?s lifetime. The pumping action of the heart is finely co-ordinated. The atria relax to receive the blood. Once it is filled up, the atria contract, pushing the blood into the ventricles. During this process, the ventricles are in a relaxed state. Once the ventricles fill up with blood, they contract, pumping the blood into the blood vessels. The pumping action of the heart is noticeable in many ways. We can feel the heart pumping if we put our hands over the left side of the chest. The heart produces sounds while pumping blood. The heart sounds are of two types- lub and dub. These sounds are heard by placing a stethoscope on our chest. A doctor is trying to listen to the heart sounds when (s) he is listening to your chest.

The function of the heart can also be felt by feeling the pulse. When the heart pumps blood, it does so in waves. These waves are palpable be putting our finger on any artery. The commonest way to palpate a pulse is by placing a finger on the wrist where the radial artery is palpable.

Thus, to summarise, the human circulatory system is a system consisting of a central pump (the heart) that is connected to a network of tubes (the blood vessels). It functions to transport nutrients, oxygen and waste products through the body.

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Life processes: Human circulation

The human circulation is a specialised system that performs the task of transport of nutrients, oxygen and waste products of life various life processes in the human body. The human circulation is similar in many ways to transportation in plants. There are many distinguishing features as well.

The human circulation also has a well-developed system of tubes to transport various substance across the body. These tubes are called arteries and veins. A series of small tubes called capillaries, connect the arteries and veins. Blood, a liquid connective tissue, flows within this network of tubes. Plasma is the aqueous component of the blood. Plasma is mostly water in which salts, proteins and cells are dissolved or suspended.

The cells that are suspended are mainly red blood cells, white blood cells and platelets.

The red blood cells (RBC?s), as their name denotes, are red in colour. The red cells are the predominant cells in the blood. The RBC?s contain a pigment-haemoglobin. Haemoglobin is the oxygen-carrying molecule in the blood. As the human body is a complex structure, its energy requirements are high. Simple diffusion is insufficient for this purpose. Therefore, the human circulation contains haemoglobin, which can bind to 4 molecules of oxygen, thus greatly enhancing the efficiency of oxygen transport.

We all have seen how plumbing works in our houses. There is a tank that is used to store water. A network of tubes then conveys this water to our houses. A pump fills the tank with water. ?Will water flow in the taps if there is no pump? No. Similarly, the human circulation also requires a pump to circulate blood through the body. The heart pumps blood into the circulatory system. The heart is a muscular organ about the size of one?s fist and is made up of 4 chambers.

This system of chambers separates the human circulation into two closed, parallel systems- the arterial system or arteries for transporting oxygenated blood and the venous system or veins for carrying de-oxygenated blood.

Also to carrying oxygen, human circulation also plays other roles. The blood circulates to the intestines from where it absorbs the products of digestion. It takes waste products of life processes from cells to the kidneys and lungs for excretion. It also serves to transport some signals that modulate growth, development and metabolism, i.e. hormones.

Now that we have learnt about the human circulation, what will happen if one part of the system dysfunctions? The pump can get damaged, the tubes can get damaged, there could be a block in the plumbing, and there could be an abnormal leak. All these can cause problems with the functioning of human body and can lead to diseases like heart attack, thrombosis, bleeding, etc.

Thus, to summarise, the human circulation is the process that transports nutrients, oxygen and waste matter through the human body.

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