Why does hair not grow on scars?

Why does hair not grow on scars?

Skin consists of two principal layers — epidermis and dermis. The epidermis is a continuously self renewing layer. Keratinocyte (a cell producing a protein found in tissues like hair, nails, scales and skin.) is the chief cell in this layer. It also consists of melanocyte — the pigment forming cell.

Deeper to the epidermis, is the dermis, which is composed of collagenous (Greek; Kolla: glue) and elastic fibre network in an amorphous ground substance. It accommodates nerves, blood vessels and pilo-sebaceous unit.

A pilo-sebaceous unit consists of hair and its follicle, associated muscle and a secretory gland called sebaceous gland. An injury to the skin results in a scar.

A scar (Greek; eschara: a hearth, fire place, scab) is defined as a mark consisting of fibrous material formed in the healing process of a wound.

The scar forms in three overlapping phases — an immediate response to the injury, when the hemostasis (arrest of bleeding) is achieved and the germs are engulfed, followed by formation of new blood vessels and new cells required for the regeneration of epidermis and finally replacement of these newly formed blood vessels and cells by fibres, i.e., the scar.

The scar contains few cells and blood vessels and no pilo-sebaceous unit and nerves as they never regenerate, hence no hair growth.

Experimentally, addition of dermal papillae fibroblasts to a wound can induce hair follicle formation. Scars bleed despite a few blood vessels, because they lack the elastic and contracting properties of normal skin.

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

Why does the colour of urine vary from light to bright yellow when we do not drink water for a long time?

Why does the colour of urine vary from light to bright yellow when we do not drink water for a long time?

Urine is composed of water, certain electrolytes, and various nitrogenous wastes and urobilins. The yellow colour in the urine is due to the chemicals called urobilins. Urochrome was the original name given to that pigment thought to give urine its colour. It is now known that several related pigments are responsible, and therefore the original name has been dropped. These are the breakdown products of the blood's haemoglobin of red blood cells. 

The basic functional unit of the kidney is the nephron. There are more than a million nephrons in each kidney. These nephrons form urine by three precisely regulated processes. They are filtration, re-absorption and secretion. The total amount of water and other dissolved wastes removed from the blood each day by the kidneys is about 180 litres for a person of 70 kg. We neither drink this much water nor excrete it out in urine form. Large amounts of water are re-absorbed into the blood stream from the proximal tubules through the process of passive re-absorption. The nutrient glucose, which is the blood sugar, is entirely re-absorbed into the blood stream from proximal tubules. None of the nutrient is wasted in the urine. Sodium and other ions are only partially re-absorbed from the renal tubules back into the blood. Urobilins are not re-absorbed. Drinking large amount of water dilutes urobilin content of urine and makes it look clear. 

Drinking very little water, concentrates the urobilin content of the urine and it looks dark yellow as the body tries to maintain a constant amount of water within the body system. Any rise or drop in blood osmotic pressure due to a lack or excess of water is detected by the hypothalamus, which notifies the pituitary gland via negative feedback. 

When a person has not taken water for a long time, a lack of water causes the posterior pituitary gland to secrete antidiuretic hormone (ADH), which results in water re-absorption and an increase in urobilin concentration of urine making it dark yellow. Therefore it is the marker of dehydration and the need for water intake.

When a person drinks a lot of water, he must eliminate excess water from the body in order to maintain the water content. So, when the water content of the body is more, the production of antidiuretic hormone (ADH) is decreased and the collecting tubule becomes less permeable to water, rendering urine dilute and abundant and the urobilins and other nitrogenous wastes get diluted.

Source: thehindu.com

Why does a place which has been urinated upon smell even after the urine has dried up?

Why does a place which has been urinated upon smell even after the urine has dried up?

Urine has the end products of metabolism and foreign substances and their breakdown products. These include substances like urea, uric acid, creatinine and a large number of drugs and their metabolic end-products. Normal urine itself has a faint aromatic type of odour. Though the constituents of urine which are responsible for this odour are not clearly known, it is claimed by some investigators that at least in part, it is due to the presence of small amounts of certain volatile organic acids present in urine. This odour, to some extent, depends upon the nature of the food and drug intake also.

Normal urine is acidic in nature. Once the urine is passed, it undergoes decomposition and gives rise to an unpleasant ammoniacal odour as in the case of alkaline fermentation in nature under atmospheric conditions. Bacteria act on the urine and the effect on urea is to convert it into ammonium carbonate. Bacteria and yeast can act on glucose also as in the case of diabetic urine. If the urine is alkaline or becomes alkaline under the atmospheric conditions, phosphates are precipitated. On standing, uric acid and urates are deposited. 

Urobilinogenis oxidised to urobilin and ascorbic acid is also oxidised. Proteinuria, urine that contains proteins, as such has a typical smell and undergoes decomposition easily. When the urine is passed, and the place dries up when left uncleaned, only the water and the volatile components present in the urine evaporate, but the other above mentioned components and the products of their chemical changes remain in the place and impart an odour to the place itself.

Source: thehindu.com

Irritation develops when dust particles fall in the eye. But the irritation is felt only when the eye is in an open condition and not when closed. Why?

Irritation develops when dust particles fall in the eye. But the irritation is felt only when the eye is in an open condition and not when closed. Why?

When a small foreign body falls in the eye and causes irritation it is usually situated either on the cornea or stuck on the inner surface of the upper eyelid. When the eyes are kept open we tend to blink at least 15 to 20 times a minute.

Image Source: wikihow.com

Every time the eyelid moves over the cornea, both the lid and the cornea get irritated and the discomfort is quite severe. If the eye is kept closed, there is no movement of the eyelid or cornea and the irritation is much lesser.

The cornea (black part of the eye) is the most sensitive part of the external eye and is very rich in nerve fibres. When the foreign body is either on the cornea or on the eyelid, the corneal nerve fibres are irritated and the resultant discomfort is very severe. On the other hand, if the foreign body is lodged in the conjunctiva (white part of the eye) the irritation is much less severe because compared with the cornea, the conjunctiva is less sensitive. Rubbing the eye vigorously when a foreign body is present in the eye can cause damage to the delicate epithelium of the cornea.

A very small foreign body lodged in the cornea can, under rare conditions, be covered by the epithelium of the cornea. In such cases, there will be no irritation at all. For this to occur, the foreign body should be very small, it should be inert, and should be smooth. Under these conditions, the corneal epithelium can grow over it.

Source: thehindu.com

Why does orally taken polio vaccine not get destroyed in the stomach's digestive system?

Why does orally taken polio vaccine not get destroyed in the stomach's digestive system?

Polio virus is an enterovirus which means that the route of entry of this virus is through the gastrointestinal system. It is an RNA virus. Viruses can be classified into two types. Some viruses are enveloped in a lipid layer that can be destroyed by the lipolytic agents present in the digestive system. The lipid layer cannot withstand the stomach's digestive system as it is sensitive to alcohol, acid and other enzymes in the digestive system. Examples are influenza and HIV viruses. On the other hand, there are other types of viruses, which are non enveloped, called naked viruses, like the polio virus, which cannot be destroyed by acid (pH 3), ether, chloroform, bile or other proteolytic enzymes present in the digestive tract. Therefore the polio vaccine that contains attenuated strains of live polio virus, when given orally, cannot be destroyed by the digestive acids and enzymes and survives in the intestinal tract and induces local immunity in the intestinal tract.The dead virus used in the vaccine administered through injections, like the attenuated oral polio vaccine, would not be destroyed by the stomach's digestive system when taken orally.

Source: thehindu.com

Why do we sometimes see spherical or cylindrical structures moving in front of our eyes during normal vision?

Why do we sometimes see spherical or cylindrical structures moving in front of our eyes during normal vision?

Image source: taurangaeyespecialists.co.nz

Most of us can see squiggly floating images in our visual field. These floaters are called vitreous floaters and are largely innocuous. The inside of the eye is filled with a jelly like material called vitreous. This jelly like substance tends to undergo liquifaction with age. This process of liquifaction can occur in the early teens or in the late fifties and sixties. When liquifaction of the vitreous occurs a few unliquified particles remain and move around with movement of the eye. Though these particles are usually microscopic in size they are clearly visible to the individual as they are very close to the retina. These vitreous floats are more clearly visible against a clear background, for example, against the sky, a white wall or white paper. Vitreous floaters may increase or decrease slightly with time. These physiological floaters are not a sign of disease. However, sudden appearance off multiple floaters associated with flashes of light or appearance of a very large number of floaters, may be a sign of retinal disorder and should be investigated.

Source: thehindu.com

Why do players consume bananas and not other fruits during tennis matches?

Why do players consume bananas and not other fruits during tennis matches?

Image Source: en.wikipedia.org

Athletic and sport activities like tennis demand lot of energy. While there are many sugar containing energy sources such as fruits or raw glucose itself, a good energy source will need to provide sustained energy as well as other benefits. Banana is the most preferred energy source of athletes.It contains different types of sugars and is also a very good source of Potassium. Tennis players also get dehydrated a lot and lose salts in the body. The sodium-potassium balance in the body is very important to maintain constant blood supply, which in turn determines energy supply to active parts of the body. Banana provides enough potassium, and sustained energy from various sugars. Banana is also available all over the world almost all times of the year. Last, but not least, unlike many other fruits, bananas come in their own hygienic natural `packing', which can just be peeled off and eaten safely.

Source: thehindu.com

Is It Necessary To Warm Up Before Playing Physically?

Is It Necessary To Warm Up Before Playing Physically?

Warming of body raises temperature from 1 degree to 2 degree F, in order to reduce the viscosity of muscle to have better mobility, range of motion, stretch reflexes for better power in muscle and cardiorespiratory adjustment of supply of blood, oxygen & glucose as per demands of effort during playing.

The warm-up exercises include rolling, stretching, flexing and agilitic movements to develop coordinated complex movements of neuromuscular function (mechanism of reciprocal stimulation and inhibition).

This thereby, prevents incidence of injury of musculo-skeletal structures, improve efficiency of muscular effort (ergonomics). Lack of adequate warming up before playing develops bodily and psychological problems.

Published in The Hindu on Nov 22, 2001.