Unlike other muscles that get tired and sore after working out for sometime, how come the muscles of the heart never get tired even after beating continuously?

Unlike other muscles that get tired and sore after working out for sometime, how come the muscles of the heart never get tired even after beating continuously?

Even though it seems as if the heart is beating without a break, the heart does rest for a very short time in between two beats. The human heart has four chambers — the left and right atria on top, which drain, into two corresponding ventricles below, through valves. The atria receive blood from the entire body through veins. This blood flows through the connecting valves into the ventricles, and the ventricles contract and push blood out into arteries, which branch and supply to the whole body. 

The heart beats in 'cycles' and each cycle consist of a systole and a diastole. Taking the average heart rate to be 75 beats per minute each cycle lasts just 0.8 seconds. In the systole, which lasts about 0.27 seconds, the ventricles contract pumping blood out into the arteries and in the diastole, which lasts around 0.53 seconds, the ventricles receive blood from the atria. It is during diastole that the heart muscle rests. Also, if we were to plot the contraction of a single heart muscle fibre on a graph it can be seen that there is a refractory period for the fibre during which it will not contract on applying a second stimulus. This prevents the heart muscles from developing tetanus.

Source: thehindu.com

Does the permanent tooth form only after the milk tooth falls down or is it formed already?

Does the permanent tooth form only after the milk tooth falls down or is it formed already?

The permanent tooth is not formed after the loss of primary tooth. Normally there are tooth buds in the developing foetus itself. These tooth buds, sometimes called the tooth germs, are an aggregation of cells, which eventually form the tooth. A whole lot of processes happen inside the tooth bud to form a tooth. This phenomenon is generally referred to as calcification and this calcification of primary teeth takes place between 13 and 16 months of postnatal life. There are ten sets of primary tooth buds in both the jaws. After complete calcification the primary dentition takes two to three years to emerge into the oral cavity.

The transition from primary to permanent teeth begins at about 6 years of age. The permanent tooth buds stay beneath the primary teeth. The calcification process starts in the permanent tooth too. For the permanent teeth there are 16 sets of tooth buds, each forming at different years of age. The crown portion of the permanent teeth starts to form and this crown portion is formed by enamel. There are four centres for formation of each tooth. All these centres coalesce to form a lobe, which forms the crown of the tooth. After the crown is formed, root formation begins. At the cervix of the crown, cemetum accumulates for the root to be formed. Once root development takes place in the permanent teeth underneath the primary teeth, this initiates resorption or eroding of the roots of the primary teeth by cells called osteoclasts. This resorption of primary teeth roots causes exfoliation of the primary teeth, which is normally referred to as tooth shake. Once the primary tooth falls off, the permanent tooth starts to emerge through the gingival or the gums. The first permanent tooth that erupts is the lower first molar at the age of 6 years. Gradually all primary teeth begin to exfoliate and permanent teeth emerge into the oral cavity.

Source: The Hindu

Why does sweat not emit a foul odour in small children, unlike in adults?

Why does sweat not emit a foul odour in small children, unlike in adults?

Sweating, a thermoregulatory function of the body, allows cooling by evaporation of sweat produced by the eccrine and apocrine sweat glands. The human body has about four million sweat glands. About three million of these, the eccrine sweat glands, distributed all over the body, are found in great numbers over the soles of the feet, forehead, palms and cheeks. They produce a clear, odourless fluid consisting of water and salts mainly sodium and potassium. If allowed to evaporate, it does not usually cause a bad odour or bromhidrosis. 

The million apocrine glands that form the rest of the sweat glands are located in the axilla and the urogenital region. These glands produce a colourless fluid that has proteins and fats. The bacteria present in the skin, especially in the hairy flexures like the armpit, act upon the sweat of the apocrine glands breaking it down into end products with a characteristic odour. Unlike the eccrine glands, the apocrine glands develop and function only around puberty under the influence of the sex hormones. Therefore the sweat of children is generally odourless. However, there are a few conditions when the child's sweat may be offensive. Sometimes children attain precocious puberty when the apocrine glands become active under the influence of the prematurely circulating sex hormones. 

In a rare genetic condition known as 'Fish Odour Syndrome' the lack of a particular hormone interferes with protein metabolism and results in the accumulation of trimethylamine, a compound with an offensive fishy smell, rather like Caliban, the social outcast in Shakespeare's Tempest.If a child's sweat has a persistently offensive odour despite reasonable standards of personal hygiene it might be advisable to seek medical advice and further investigation.

Source: thehindu.com

Can cancer occur in the heart?

Can cancer occur in the heart?

Answer 1: 

Image source: en.wikipedia.org

Yes, cancer can occur in the heart but it is very rare. Cancer or Neoplasia is a disease of the organs with actively dividing cells, wherein the cell proliferation/division process goes out of control due to viral infection or changes in the DNA sequence. For example, skin, intestine, bone marrow and the like, have high populations of dividing cells and are more often prone to cancer.The heart muscle cells are essentially non-dividing and hence are not very susceptible to cancer. Cancer of the heart muscle called angiosarcoma does occur but is rare and occurs more often in children and in the right side of the heart. Cancers like melanoma are known to spread to the heart and most of these tumours are benign.

Answer 2: 

Yes, though heart cancer is extremely rare. The vast majority of heart tumours are noncancerous (benign). Occasionally, cancer can spread to the heart from other parts of the body. Treatment of heart tumours involves surgical removal. Cancer can affect the heart in other ways, such as causing damage to the heart valves or stiffening of the heart muscle. Cancer treatments can also affect the heart. Certain chemotherapy drugs can damage the heart. Radiation therapy directed at or near the heart can also damage the heart muscle and increase the risk of coronary artery disease later in life.

Source: thehindu.com

What is brain mapping? How is it done and what are its uses?

What is brain mapping? How is it done and what are its uses?

In brain mapping the architectural details including the structure and function of the normal and abnormal (diseased state) human brain are generated. It uses a multidisciplinary approach involving brain imaging, neuropsychology, clinical neuroscience, computer science and bioinstrumentation, to integrate information on a scale ranging from whole brain structure to the microscopic level.

Image source: emaze.com

Modern brain scanning technique consists of electro encephalography (EEG), magneto encephalography (MEG), positron emission tomography (PET), magnetic resonance imaging (MRI and functional MRI), computed tomography (CT) and the like.A comprehensive brain map is generated using these various imaging techniques on healthy volunteers. To this DNA information can also be added with details like ethnicity, family and medical history and educational background. These are stored as digital brain atlas libraries to serve as base line data and any departure like in a diseased state can be easily recognised.

Human brain mapping is useful for diagnosing and treating several neurological disorders with precision like brain tumours, stroke, epilepsy, seizures, migraine, Alzheimer's disease and Parkinson's disease. It is also useful in several psychiatric disorders such as depression, anxiety, panic attacks, schizophrenia and the like. In addition, it is helpful in identifying areas of the brain involved in various cortical brain activities such as vision, memory, sleep, smell, taste, behaviour and the like.

Source: thehindu.com

Why do wrinkles develop in our fingers when they are immersed in water for a long time?

Why do wrinkles develop in our fingers when they are immersed in water for a long time?

Our skin has a protective top layer, called the stratum corneum. The primary function of this layer is to provide the much-needed protection to the underlying tissues from injury. With the primary reason being to provide protection, stratum corneum found in palms, fingers, soles and toes - areas that are more prone to mechanical abrasion - are much thicker compared with the layers found elsewhere. Stratum corneum, made of protein and fats, has a tendency to absorb water. And the absorption is seen to be maximum in these areas where the layer is the thickest. But with no room provided for the layer to expand on absorbing water, the most natural way to accommodate the expanded layer is to form wrinkles. It has been found that the time taken for wrinkles to form in these areas is influenced by the water composition.

Image source: youtube.com

Seawater, which has a high mineral content, tends to keep water from penetrating into the skin. On the other hand, river water and water available in households have relatively lesser mineral content and this plays a direct role in the ability of the layer soaking in more water and forming more wrinkles and more quickly when immersed in water. This can be easily seen by immersing one's hand in household bathing water and noting the time taken to see wrinkles developing and the time taken for wrinkles to develop when swimming in sea water. Again, a distinction has to be made on the level of salinity of seawater. It would probably take a relatively longer time for wrinkles to develop when swimming in the Dead Sea compared with the Arabian Sea or Bay of Bengal. However, the wrinkles formed are transient by nature. The skin returns to its normal state once it loses the absorbed water. Hence it is different from wrinkles seen in aged people. In this case, wrinkles are formed not due to absorption of water but due to a predominant loss of elastic tissue in the underlying dermal layer of the skin, two layers beneath the outermost stratum corneum.

Source: thehindu.com

Haemoglobin carries oxygen in humans, but in insects haemoglobin does not exist. Then how does the flow of oxygen happen?

Haemoglobin carries oxygen in humans, but in insects haemoglobin does not exist. Then how does the flow of oxygen happen?

Answer 1: 

Image source: en.wikipedia.org

Blood vascular system in insects is open type, consisting of a large cavity called Haemocoel. Haemocoel is filled with blood, in which all the organs bathe. The blood is white in colour due to the absence of the respiratory pigment `haemoglobin'. Its absence is compensated by a special system called `tracheal system'.Tracheal system consists of small white shining tubes called `trachea'. They open to the exterior through a pair of openings called `spiracles' in every segment of thorax and abdomen. These spiracles are valved. The trachea divides and re-divides to form fine tubules which end as `tracheole cell' near the tissues. Tracheole cell has distal tube like projections called the `tracholes', which innervate the tissues. Tracheole cell is filled with tracheolar fluid (mainly consisting of water) and plays a vital role in respiration.In insects the oxygen from environment is directly carried to tissues.Oxygen continuously enters the trachea passively through thoracic spiracles, but carbon-dioxide is pumped out actively at regular intervals through abdominal spiracles.

Answer 2: 

Water in equilibrium with atmospheric air at 37{+o}C dissolves about 0.46 volumes per cent of oxygen and this is adequate only for tissues with low rates of metabolism. In arthropods, to which insects belong, there are no small blood vessels or capillaries connecting the arteries with veins. Nets of minute sinuses are found. Hence the circulating fluids bathe the major organs and tissues. Tracheal system, characteristic of insects helps in exchange of gases. The air from outside enters the tracheal tubes by the stigmata and conveyed to the tissues directly. The alternate contraction and relaxation of the insect abdomen brings the ingress and egress of the air. Exchange of gases takes place directly without the involvement of blood or blood pigments.

Source: thehindu.com