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Melanin functions Melanin is the brown black, non-haemoglobin-derived pigment normally present in the hair, skin choroid of the eye, meninges and adrenal medulla. It is synthesized in the melanocytes and dendritic cells, both of which are present in the basal cells of the epidermis. Melanin is stored in the form of cytoplasmic granules in the phagocytic cells called the melanophore, present in the under lying dermis. Melanocytes possess the enzyme tyrosinase necessary for the synthesis of melanin from the amino acid called tyrosine Tyrosine tyrosinase Melanin Various disorders of melanin pigmentation cause generalized and localized hyperpigmentation and hypopigmentation. Generalized hyperpigmentation a) In Addison’s disease, there is generalized hyperpigmentation of the skin, especially in areas exposed to light and buccal mucosa. b) Hyper pigmentation on skin of face, nipples and genitalia during pregnancy under the influence of oestrogen. c) In chronic arsenical poisoning, there is c...

Skin The skin is a major organ of the body forming 8% of its total mass and having an area between 1.1-2.2m2. It is the major interface between the body and the environment and covers the entire surface. It is continuous with mucosae at the various orifices and with lining tissue of organs like eyes and ears Various structures including sebaceous glands, sweat glands, hair follicles and nails are formed by modifications of epidermis. Sebaceous glands secrete an oily substance called sebum and open on the sides of the hair follicles. Sweat glands are of two types, Merocrine and Apocrine. Merocrine glands are found throughout the body opening on the surface and secreting a clear watery fluid. Apocrine glands are found in the regions like axilla, areola, pubis, scrotum and perianal regions. Their ducts may open on the surface or into the hair follicle. Dermis is made up of connective tissue consisting of matrix in which is embedded elastic and collagen fibres to give strength and elastici...

Hearing Aid – Noise pollution Hearing Aid Patients with a conductive defect which does not respond fully to treatment may be helped with a hearing aid. A hearing aid is an electronic, battery-operated device that amplifies and changes sound to allow for improved communication. Hearing aids receive sound through a tiny microphone, which then converts the sound waves to electrical signals. The amplifier increases the loudness of the signals and then sends the sound to the ear through a speaker in an ear piece which fits into an outer ear canal. The electric signals are converted back to sound waves. A volume control on the aid usually operated by turning a tiny wheel enables the level of incoming sound to be adjusted. More powerful aids that amplify sound to a greater degree are available. In these aids the microphone, amplifier and battery are contained in a larger case worn on the body; the currents is carried to the ear piece by a thin wire. Some people with conductive deafness e...

Defects of the ear Several defects of the ear lead to hearing loss or even deafness. Hearing loss, or hearing impairment, happens when there is a problem with one or more parts of the ear or ears. Types of Hearing Loss There are a few different types of hearing loss: conductive, sensory, mixed (conductive and sensory combined), and neural. Conductive hearing loss:- This happens when there is a problem with a part of the outer or middle ear. Most kids with conductive hearing loss have a mild hearing loss and it is usually temporary because in most cases medical treatment can help. (Defects of the ear) Sensory hearing loss This happens when the cochlea is not working correctly because the tiny hair cells are damaged or destroyed. Depending on the loss, a person may be able to hear most sounds (although they would be muffled); only some sounds; or no sounds at all. Sensory hearing impairment is almost always permanent and the ability to talk normally may be affected. (Defects of the ear) ...

Mechanism of hearing Functions of External Ear Sound waves enter the external auditory meatus, pass along the external eustachian canal and fall on the tympanic membrane (TM). This causes the TM to vibrate. (Mechanism of hearing) Functions of Middle Ear  The middle ear is an air filled cavity in the temporal bone which opens via the eustachian tube into the nasopharynx. The auditory tube opens during chewing, swallowing and yawning thus keeping the pressures on both sides of the tympanic membrane equal. The three auditory ossicles are localised in the middle ear. Of these, the malleus is attached to the TM, and the stapes to the membranous oval window on the medial wall. Incus articulates with these two bones. Thus vibrations of the TM are transmitted to the oval window. As the TM has an area of 90mm2 and the foot plate of the stapes 3.2mm2 and the lever system formed by the ossicles multiplies the force 1.3 times. (Mechanism of hearing) The vibrations of the oval window generate press...

EARS Our ears provide us with two vital but very different senses : hearing and balance. Sound detected by the ears provides essential information about our external sourounding and allow us to communicate. In addition our ears contribute to our sense of balance to maintain upright posture and move without falling over. Sound is the sensation produced by longitudinal vibrations in the external environment. Loudness of sound is correlated with amplitude of sound wave and pitch with frequency (No.of waves / unit time). Audible frequencies to humans is in the range 20 – 20,000 cycles per second (cps, Hz). Only the young people are able to hear this full range. Sound perception depends on the loudness as well as frequency. The human ear is most sensitive to 50 – 5000 Hz range. But most sounds we normally hear fall within 500 – 5000 Hz. Since the human ear can differentiate a wide range of sound energy (the loudest noise perceived is approximately 1012 times more intense th...

Eye Infections and Eye Care Eye Infections 1. Stye A stye is an acute infection of the glands located at the eyelid margin. There is swelling, pain, itching and redness in a small area at the lid margin. Treatment consists of using frequent warm compresses on the eye. (Eye Infections) 2. Conjunctivitis: Infection in the conjuctiva is called conjunctivitis. Due to the infection the invisible blood vessels within the conjunctiva become engorged. Inflammation of the conjuctiva causes redness, discomfort and a discharge from the affected eye. The most common causes for conjunctivitis are infections (in children) and allergy (in adults). (Eye Infections) 2a. Infective conjunctivitis : Most conjunctival infection are caused by bacteria (e.g staphylococci) and are spread by hand-to-eye contact or by viruses associated with a cold, sore throat, or illness such as measles, viral conjunctivitis sometimes occurs in epidemics, spreading rapidly through schools and other groups. (Eye Infections) 2b...