• O   = UNIVERSAL DONOR
• AB = UNIVERSAL RECEIPIENT

Rh factors 

• The Rh factor is a type of blood protein, which was found for the first time in the blood of the rhesus monkey. If the factor is present in the blood, the blood is called Rh positive. If absent then it is Rh negative. If the mother is Rh -ve and the father Rh +ve and the baby is Rh +ve, the Rh +ve factor goes from the body of the baby to he circulation of the mother and causes formation of antibodies against Rh +ve factor. The anti Rh +ve protein enters the baby’s blood which coagulates resulting in the death of the baby. This disease is called erythroblastosis feotalis.

Blood related diseases 

• Leukemia: Leukemia is a very serious disorder of the body. This is a form of blood cancer and is characterized by an uncontrolled increase in the number of leucocytes with the appearance of immature forms in the blood stream. Leukemia is accompanied by anemia and is eventually fatal because the bone marrow cell that normally produce erythrocytes are displaced by leukemia cells.
• Hemopoiesis: Hemopoiesis is the formation of the formed elements (RBC. WBC.  and blood platelets). The mammals it takes place in the bone marrow the Kupffer cells of the liver (Intralobular capillaries), splenic sinuses, and lymph nodes. These together are referred to as the reticulo-endothelial system of the various hemopoietic centres. The bone marrow produces all the three types of blood cells.
• Anaemia: Anaemia is described as a condition in which the RBC count or the amount of hemoglobin per cell is less than normal. Loss of blood from the body due to hemorrhage, excessive bleeding during menstrual cycle, injury etc. causes Hemorrhagic anemia. A dietary deficiency of iron can also cause a characteristic anemia known as Hypochromic anemia. Other nutritional factors also adversely affect the formation of hemoglobin and normal development of the RBC. These factors are certain vitamins such as folic acid, ascorbic acid, riboflavin, and vitamin B12, and leads to pernicious anemia. Another form of Anemia, called sickle-cell anemia is linked with heredity.
• It is prevalent in people of Negroid origin. It is caused by abnormal hemoglobin known as hemoglobin S (HbS) that is formed under the influence of a particular pair of abnormal genes.
• Hemophilia: Hemophilia is characterized by severe hemorrhage even after relatively minor injuries by bleeding in the joints. The times of clotting which is usually 3-6 minutes in normal individuals may extent up to several hours in case of hemophilia patients. Hemophilia is a sex-linked disease and appears exclusively in males. It is carried by the absence of factor VIII (Antihemophilic globulin AHG). The gene for hemophilia is carried by X-chromosome and in the female its action is countered by the presence of the other heterochromosome X. As such hemophilia does not appear in the female but she can transmit it, she is called the carrier. In male the action of hemophilia gene is not counteracted and the individual exhibits hemophilia. The often-quoted example of sex-linked hemophilia patients is the descendants of Queen Victoria of England.

ENDOCRINE SYSTEM  

• There are many glands in the body system, which release secretions through ducts associated with the glands. These are exorine glands (or duct glands), eg. Salivary and sweat glands; other glands in the body release substnaces (hormones directly into the blood circulation, these are endocrine glands or (ductless glands).
• Chemically there are three kinds of hormones. These are:
  (1)   Protein hormones: Are those produced by the hypothalamus, pituitary, thyroid, parathyroid, pancreas and one of the hormones of ovary (relaxin and one of the placenta (human chrionic gonadotropin).
  (2)   Steroid hormones: Are produced by the adrenal, cortex ovaries and testes.
  (3)   Biogenic amines: Are produced by the pineal gland and the adrenal medulla.

HORMONAL DISEASES

• Name of Disease   Endocrine Gland          Effects and symptoms

REPRODUCTION

• Reproduction is the inherent property of the living organisms to continue their race by producing offsprings.
• Reproduction is of following two types:
• Asexual reproduction
• Sexual reproduction

Asexual reproduction 

• The development of new individuals without the fusion of the male and female gametes is known as asexual reproduction. The asexual reproduction usually includes mitotic division of the body (somatic) cells. Therefore it is also known as somatogenic reproduction. The asexual reproduction is common only in lower plants and animals and it is of following types: Binary fission, Budding, Gemmule formation, Spore formation, Vegetative reproduction, Regeneration
• Binary fission: In the binary fission, the body splits in such a way that two equal and indentical halves are produced. It is most common in protozoans, bacteria and some lower metazoans. First of all the nucleus divides by amitotic or mitotic division and the division of the nucleus is followed by the division of the cytoplasm. It is of following types-

  (a)   Simple type of binary fission, eg. Amoeba.

  (b)   Transverse binary fission e.g. Paramecium.

  (c)   Strobilation, eg. Aurelia

  (2)   Budding: In certain multicellular animals, eg. hydra and fungi and body gives out a small outgrowth known as the bud, the bud is supported by the parent body and it ultimately develops into a new individual.

  (3)   Gemmule formation: In certain metazoan animals, eg. fresh water sponges and in some bryophytes such as Marchantia, the asexual reproduction is carried on by  certain peculiar asexual bodies known as gemmules, which is composed of a group of undifferentiated cells which contain stored food material.

  (4)   Spore formation: In many unicellular plants, fungi etc. the asexual reproduction by spore formation is very common under unfavourable conditions. In this process the condensation of protoplasm due to reduction in the water content results. These spores under favourable conditions absorb water and germinate to form a new plant.

  (5)   Vegetative reproduction: A fragment or part of the plan grows to produce new plants. Fragmentation is very common in algae and fungi. In higher plants the vegetative propagation takes place under the following ways:

• Sucker stem as in mint banana, which run horizontally under ground, can be separated and grown individually and each is able to develop into separate plant. The vegetative multiplication in the certain storage fleshy leaf like Bryophyllum has also been found very useful. If Bryophyllum leaf is cut and put on the surface of soil numerous new plant come out within few weeks from different fragments of original leaf.
  (6)   Regeneration: In the life of an organism the loss of many kinds of cells and other structure occurs. These lost parts have to be restored if the organism has to lead a normal life. There is an inherent capacity in all organisms, to replace damaged on lost parts of tissues. This inherent capacity of regaining the lost part is known as regeneration. It can be defined as replacement, repair or restoration of the lost or damaged structures or reconstitution of a whole body from the small fragment of it during the post embryonic life of an organism.

Sexual reproduction in Plants 

• This is very common type of reproduction in the angios permic plants. In these plants the vegetative branch at some stage (at maturity or vegetative phase) changes to the reproductive phase i.e. flower. The period and time of bearing flower varies from species to species. Flowers may be bisexual or unisexual. Meiosis (reduction division) occurs in the male and female parts of a flower to form male (pollen grains) and female (ovum) geametes. In order to produce seeds (to reproduce) male and female gametes fuse together to form zygote that divides mitotically and develops into a seed. The male gamete (pollen grains) is motile and reaches up to the ovum for fertilization. This process of transference of pollen grains from the anther of a flower to the stigma of the same or of different flower is called pollination. It is of two types-
  (1)   Self-pollination: It the pollen grains are transferred to the stigma of the same flower or between two flowers borne by the same parent then it is self pollination or autogamy.
  (2)   Cross-pollination: If the pollen-grains are transferred to the stigma of a different flower borne by a different plant then it is called cross - pollination or allogamy.

Reproduction in Mammals 

• The development of new individual takes place by the fusion of the sex cells or male and female gametes. Gametes grow and mature inside the testes and ovaries, which are specialized organs to produce sperms in the males and ova in the females. Sexes in human beings are separate, that is male organ, the testes are found in male individuals and female organ, and the ovaries are found in female body. Once the egg (ovum) is fertilized it movies to uterus and gets implanted. Fertilization is internal.

ANIMAL HUSBANDRY

•  Animal husbandry is the study of rearing, feeding, management, production and utilization of all the economically important animals.
•  India is an agriculture-based country. Thirty percent of the total land holdings are held by 70 per cent of small and marginal farmers. They held 80 percent of the total livestock in the country. Crop agriculture in India depends mainly on bullocks, which contribute approximately 40,000 MW power to agricultural operations. The main aims of animal husbandry are
  1.    To provide animal power for agricultural operations.
  2.    To use the land which are not useful for agriculture.
  3.    To change the agricultural & industrial product in animal protein.
  4.    Employment for a large population.
  5.    To reduce extra load from agriculture by producing meat, milk etc.
  6.         To get FYM (Farm Yard Manure) from their urine & dung

Animal Breeding 

• Breeding is to improve the inferior stock by meeting with outstanding and improved type of animal so that they can render better service to man.
• Inbreeding: It involves the mating of related individuals for 4.5 generations.
• Close breeding: The mating of (a) full sister to full brother (b) sire to his daughter or dam to her son. Undesirable recessive genes may be discovered by this system but the progeny become more susceptible to diseases. Homogeneity increases in this system.
• Line breeding: The mating of animals of wider degrees of relationship than those selected for close breeding. Uniformity increases but the real individual merit is ignored in this system.

Effects of Inbreeding

• Decrease in growth rate, reduction in the reproductive efficiency, higher death rates, more occurrences of hereditary abnormalities and lethal factors.
• Out breeding: Breeding of unrelated individuals.
• Out crossing: Mating of unrelated (up to 4-6 generations) pure breed animals within the same breed. Additive effects are obtained in this system for milk production, growth rate etc.
• Cross breeding: Mating of animals of different breeds.

  (a)   Criss crossing: The two breeds are crossed alternatively to utilise heterosis in both dams and progeny.

  (b)   Triple crossing: Three breeds are crossed rotationally.

  (c)   Back crossing: Mating of crossbred animal with one of the pure parent races.

Artificial Insemination (AI)

• Deposition of semen artificially (manually) in the genitalia of the female at proper time of the reproductive cycle is called as Artificial Insemination (A1). The technique is important in the prevention of sexually transmitted diseases (STD) the same quantity of semen can serve 50 to 100 more females, and the superior quality semen can be 50 to 100 more females, and the imported from foreign countries for A1.

Age of attaining sexual maturity

Fertility

EXCRETORY SYSTEM

• Excretion is the process by which the metabolic waste products formed as a result of anabolism and catabolism are eliminated from the body. Some of these waste products may become toxic i they accumulate beyond a certain concentration An important requisite for the continuation of life therefore is the removal of metabolic waste products such as ammonia  [??] organs concerned with this function are called excretory organs. In addition to the kidney, the skin, lung, intestine and liver also eliminate metabolic waste products directly or indirectly. The removal of carbon dioxide from the lungs is also an e excretory process. Nitrogenous wastes i.e. ammonia, urea and uric acid are derived from catabolism of dietary proteins.

Kidney

• Kidney, one of a pair of glands, whose function is the elaboration and excretion of the urine.
• In humans, kidneys are situated in the region of the loins, one on each side of the spine, and are embedded in fatty tissue. They are bean-shaped, possessing a convex outer border and a concave inner border. The inner border presents an indentation, the hilum, at which the blood vessels enter and leave. In front is the renal vein carrying blood from the kidney; behind it lies the renal artery carrying blood to the kidney. Most posterior is the ureter, a tube that conveys urine to the bladder. The hilum arises from a deeper indentation, the sinus of the kidney, in which the ureter dilates to form a small sac, the pelvis. The kidney also embodies glomeruli, aggregations or loops of capillaries enclosed within thin envelopes of endothelial lining called Bowman’s capsules, located at the blind beginning ends of the renal tubules. The functions of lidney are :
   (1) The kidney not only removes the waste products from the body but also plays a very important role in maintained a constant composition of the blood transprative of the nature of the food or mild intake.
  (2)   Urine is acidic in nature, the kidneys perform an important function in selectively filtering out the acidic substances from the blood into the urine and maintain the correct pH balance.
  (3)   The kidneys also regulate the loss of excess water from the body.

Diseases of the Kidney

• Nephritis : The infection is caused by the bacteria (streptococci) which results in inflammation of kidney
• Pyelonephritis :  Inflammation of the tissues of Kidneys and the Ureters in the pelvic region.
• Polyuria : Amount of urine passed out more.
• Uraemia : The concentration of urea is increased in the blood.
• Alkaptonuria : It is a genetic disease in which homogentistic acid’s excreted with urea.
• Anuria : Failure of kidney to form urine (as in the case of hepatitis B).
• Gout : High level of uric acid in the blood.
• Dysuria : Painful Urination

Other organs of Excretion in Man

(a)   Skin: The skin acts as an organ of excretion with the help of the sweat glands present in it. These glands remove water, urea and some salts from blood and excrete them on the surface of the skin.

(b)   Lungs: The lungs are the chief organs or respiration; they absorb oxygen and eliminate CO2.

(c)   Intestine: The intestine plays a minor of epithelial cells. These cells excrete certain salts for example those of calcium and iron.

(d)   Liver: It may be considered as an accessory excretory organ because it plays only a minor role in excreting waster products directly from the body. Urea the chief introgenous waste material in the human body is formed in the liver.

NERVOUS SYSTEM 

• In mammals all body activities are either directly or indirectly under the control of the nervous system. Direct control is exercised by supplying nerves to the various organs and tissues, while indirect control is exercised through the endocrine glands and the circulatory system. The nervous system receives a variety of stimuli from the various parts of the body. Depending on the nature of the stimuli, it sends out appropriate orders to the concerned organs. Both exterior (e.g. pressure, pain, heat etc which are caused due to changes in the external conditions and proprioceptive sensations (sensations which concern the physical state of the body, e.g. functioning of the internal organs) are brought to the brain and spinal cord through sensory nerves. Orders, which are carried out in response to these sensations, are conveyed to the appropriate organs through motor nerves.
• The nervous system of all vertebrates including that of men is divisible into two parts (i) the central nervous system (ii) the peripheral nervous system. The central nervous system includes the brain and the spinal cord. The peripheral nervous system consists of different nerves that arise from the brain (cranial nerves) and the spinal cord (spinal nerves).

Brain

• Portion of the central nervous system contained within the skull. The brain is the control center for movement, sleep, hunger, thirst, and virtually every other vital activity necessary to survival. All human emotions—including love, hate, fear, anger, elation, and sadness—are controlled by the brain. It also receives and interprets the countless signals that are sent to it from other parts of the body and from the external environment. The brain makes us conscious, emotional, and intelligent.
• The adult human brain is a 1.3-kg (3-lb) mass of pinkish-gray jellylike tissue made up of approximately 100 billion nerve cells, or neurons; neuroglia (supporting-tissue) cells; and vascular (blood-carrying) and other tissues.
• Between the brain and the cranium—the part of the skull that directly covers the brain—are three protective membranes, or meninges. The outermost membrane, the dura mater, is the toughest and thickest. Below the dura mater is a middle membrane, called the arachnoid layer. The innermost membrane, the pia mater, consists mainly of small blood vessels and follows the contours of the surface of the brain.
• A clear liquid, the cerebrospinal fluid, bathes the entire brain and fills a series of four cavities, called ventricles, near the center of the brain. The cerebrospinal fluid protects the internal portion of the brain from varying pressures and transports chemical substances within the nervous system.
• From the outside, the brain appears as three distinct but connected parts: the cerebrum (the Latin word for brain)—two large, almost symmetrical hemispheres; the cerebellum (“little brain”)—two smaller hemispheres located at the back of the cerebrum; and the brain stem—a central core that gradually becomes the spinal cord, exiting the skull through an opening at its base called the foramen magnum. Two other major parts of the brain, the thalamus and the hypothalamus, lie in the midline above the brain stem underneath the cerebellum.
• The brain and the spinal cord together make up the central nervous system, which communicates with the rest of the body through the peripheral nervous system. The peripheral nervous system consists of 12 pairs of cranial nerves extending from the cerebrum and brain stem; a system of other nerves branching throughout the body from the spinal cord; and the autonomic nervous system, which regulates vital functions not under conscious control, such as the activity of the heart muscle, smooth muscle (involuntary muscle found in the skin, blood vessels, and internal organs), and glands.

Cerebrum

• Most high-level brain functions take place in the cerebrum. Its two large hemispheres make up approximately 85 percent of the brain’s weight. The exterior surface of the cerebrum, the cerebral cortex, is a convoluted, or folded, grayish layer of cell bodies known as the gray matter. The gray matter covers an underlying mass of fibers called the white matter.
• The cerebrum receives information from all the sense organs and sends motor commands (signals that result in activity in the muscles or glands) to other parts of the brain and the rest of the body.

Cerebellum

• The cerebellum coordinates body movements. The cerebellum coordinates voluntary movements by fine-tuning commands from the motor cortex in the cerebrum. The cerebellum also maintains posture and balance by controlling muscle tone and sensing the position of the limbs. All motor activity, from hitting a baseball to fingering a violin, depends on the cerebellum.

Thalamus and Hypothalamus

• The thalamus and the hypothalamus lie underneath the cerebrum and connect it to the brain stem. The thalamus is the main relay station for incoming sensory signals to the cerebral cortex and for outgoing motor signals from it. All sensory input to the brain, except that of the sense of smell, connects to individual nuclei of the thalamus.
• The hypothalamus lies beneath the thalamus on the midline at the base of the brain. It regulates or is involved directly in the control of many of the body’s vital drives and activities, such as eating, drinking, temperature regulation, sleep, emotional behavior, and sexual activity. It also controls the function of internal body organs by means of the autonomic nervous system, interacts closely with the pituitary gland, and helps coordinate activities of the brain stem.

Brain Stem

• The brain stem is evolutionarily the most primitive part of the brain and is responsible for sustaining the basic functions of life, such as breathing and blood pressure. It includes three main structures lying between and below the two cerebral hemispheres—the midbrain, pons, and medulla oblongata.

Midbrain 

• The topmost structure of the brain stem is the midbrain. It contains major relay stations for neurons transmitting signals to the cerebral cortex, as well as many reflex centers—pathways carrying sensory (input) information and motor (output) commands. Relay and reflex centers for visual and auditory (hearing) functions are located in the top portion of the midbrain. A pair of nuclei called the superior colliculus control reflex actions of the eye, such as blinking, opening and closing the pupil, and focusing the lens. A second pair of nuclei, called the inferior colliculus, control auditory reflexes, such as adjusting the ear to the volume of sound. At the bottom of the midbrain are reflex and relay centers relating to pain, temperature, and touch, as well as several regions associated with the control of movement, such as the red nucleus and the substantia nigra.

Pons

• Continuous with and below the midbrain and directly in front of the cerebellum is a prominent bulge in the brain stem called the pons. The pons consists of large bundles of nerve fibers that connect the two halves of the cerebellum and also connect each side of the cerebellum with the opposite-side cerebral hemisphere. The pons serves mainly as a relay station linking the cerebral cortex and the medulla oblongata.

Medulla Oblongata

• The long, stalklike lowermost portion of the brain stem is called the medulla oblongata. At the top, it is continuous with the pons and the midbrain; at the bottom, it makes a gradual transition into the spinal cord at the foramen magnum. Sensory and motor nerve fibers connecting the brain and the rest of the body cross over to the opposite side as they pass through the medulla. Thus, the left half of the brain communicates with the right half of the body, and the right half of the brain with the left half of the body.

Brain Cells

• There are two main types of brain cells: neurons and neuroglia. Neurons are responsible for the transmission and analysis of all electrochemical communication within the brain and other parts of the nervous system. Each neuron is composed of a cell body called a soma, a major fiber called an axon, and a system of branches called dendrites.
• Neuroglial cells are twice as numerous as neurons and account for half of the brain’s weight. Neuroglia (from glia, Greek for “glue”) provide structural support to the neurons. Neuroglial cells also form myelin, guide developing neurons, take up chemicals involved in cell-to-cell communication, and contribute to the maintenance of the environment around neurons.

Cranial Nerves

• Twelve pairs of cranial nerves arise symmetrically from the base of the brain and are numbered, from front to back, in the order in which they arise. They connect mainly with structures of the head and neck, such as the eyes, ears, nose, mouth, tongue, and throat. Some are motor nerves, controlling muscle movement; some are sensory nerves, conveying information from the sense organs; and others contain fibers for both sensory and motor impulses. The first and second pairs of cranial nerves—the olfactory (smell) nerve and the optic (vision) nerve—carry sensory information from the nose and eyes, respectively, to the undersurface of the cerebral hemispheres. The other ten pairs of cranial nerves originate in or end in the brain stem.

Diseases of Nervous System

• Stroke : A condition due to the lack of oxygen O₂  to the brain which may lead to reversible or irreversible damage. The damage to a group of nerve cells in the brain is often due to interrupted blood flow, caused by a blood clot or blood vessel brusting. Depending upon the area of the brain that is damaged, a stroke can cause Coma, Paralysis, Speech problem and Dementia (lack of sleeping).
• Hydrocephaly:  An increased quantity of C.S.F. inside the brain that can result in increased pressure.
• Meningitis : Refers to infection or inflammation of meninges resulting in severe headache, vomiting, pain and stiffiness of neck. It is due to Streptococcus Pneumoniae, Neisseria Meningitis and Haemophilis influnzae.
• Horner’s Syndrome : Results from damage of sympathetic trunk of one side.
• Celebral Plasy : A developmental defect that happens to the brain during birth. It causes spostic paralysis in coordination, speech impearement. People having Cerebral Plasy can have a normal I.Q. or higher.
• Encephalitis : This disease is the inflammation of the brain. Its symptoms include lethargy (fatigue) and drowsiness.
• Epilepsy :  It happens when the electrical activity in the brain is not normal.
• Coma : A state of unconsciousness where the person does not respond to stimuli. One’s patient recovers from Coma may experience amnesia (loss of memory) 

Brain Imaging

• Several commonly used diagnostic methods give images of the brain without invading the skull. Some portray anatomy—that is, the structure of the brain—whereas others measure brain function. Two or more methods may be used to complement each other, together providing a more complete picture than would be possible by one method alone.
• Magnetic resonance imaging (MRI), introduced in the early 1980s, beams high-frequency radio waves into the brain in a highly magnetized field that causes the protons that form the nuclei of hydrogen atoms in the brain to reemit the radio waves. The reemitted radio waves are analyzed by computer to create thin cross-sectional images of the brain. MRI provides the most detailed images of the brain and is safer than imaging methods that use X rays. However, MRI is a lengthy process and also cannot be used with people who have pacemakers or metal implants, both of which are adversely affected by the magnetic field.
• Computed tomography (CT), also known as CT scans, developed in the early 1970s. This imaging method X-rays the brain from many different angles, feeding the information into a computer that produces a series of cross-sectional images. CT is particularly useful for diagnosing blood clots and brain tumors. It is a much quicker process than magnetic resonance imaging and is therefore advantageous in certain situations—for example, with people who are extremely ill.
• Changes in brain function due to brain disorders can be visualized in several ways. Magnetic resonance spectroscopy measures the concentration of specific chemical compounds in the brain that may change during specific behaviors. Functional magnetic resonance imaging (fMRI) maps changes in oxygen concentration that correspond to nerve cell activity.
• Positron emission tomography (PET), developed in the mid-1970s, uses computed tomography to visualize radioactive tracers radioactive substances introduced into the brain intravenously or by inhalation. PET can measure such brain functions as cerebral metabolism, blood flow and volume, oxygen use, and the formation of neurotransmitters. Single photon emission computed tomography (SPECT), developed in the 1950s and 1960s, uses radioactive tracers to visualize the circulation and volume of blood in the brain.
• Brain-imaging studies have provided new insights into sensory, motor, language, and memory processes, as well as brain disorders such as epilepsy; cerebrovascular disease; Alzheimer’s, Parkinson’s, and Huntington’s diseases; and various mental disorders, such as schizophrenia.

EYE

• Light-sensitive organ of vision in animals. The eyes of various species vary from simple structures that are capable only of differentiating between light and dark to complex organs, such as those of humans and other mammals, that can distinguish minute variations of shape, color, brightness, and distance. The actual process of seeing is performed by the brain rather than by the eye. The function of the eye is to translate the electromagnetic vibrations of light into patterns of nerve impulses that are transmitted to the brain.

The Human Eye

• The entire eye, often called the eyeball, is a spherical structure approximately 2.5 cm (about 1 in) in diameter with a pronounced bulge on its forward surface. The outer part of the eye is composed of three layers of tissue. The outside layer is the sclera, a protective coating. It covers about five-sixths of the surface of the eye. At the front of the eyeball, it is continuous with the bulging, transparent cornea. The middle layer of the coating of the eye is the choroid, a vascular layer lining the posterior three-fifths of the eyeball. The choroid is continuous with the ciliary body and with the iris, which lies at the front of the eye. The innermost layer is the light-sensitive retina.
• The cornea is a tough, five-layered membrane through which light is admitted to the interior of the eye. Behind the cornea is a chamber filled with clear, watery fluid, the aqueous humor, which separates the cornea from the crystalline lens. The lens itself is a flattened sphere constructed of a large number of transparent fibers arranged in layers. It is connected by ligaments to a ringlike muscle, called the ciliary muscle, which surrounds it. The ciliary muscle and its surrounding tissues form the ciliary body. This muscle, by flattening the lens or making it more nearly spherical, changes its focal length.
• The pigmented iris hangs behind the cornea in front of the lens, and has a circular opening in its center. The size of its opening, the pupil, is controlled by a muscle around its edge. This muscle contracts or relaxes, making the pupil larger or smaller, to control the amount of light admitted to the eye.
• Behind the lens the main body of the eye is filled with a transparent, jellylike substance, the vitreous humor, enclosed in a thin sac, the hyaloid membrane. The pressure of the vitreous humor keeps the eyeball distended.
• The retina is a complex layer, composed largely of nerve cells. The light-sensitive receptor cells lie on the outer surface of the retina in front of a pigmented tissue layer. These cells take the form of rods or cones packed closely together like matches in a box. Directly behind the pupil is a small yellow-pigmented spot, the macula lutea, in the center of which is the fovea centralis, the area of greatest visual acuity of the eye. At the center of the fovea, the sensory layer is composed entirely of cone-shaped cells. Around the fovea both rod-shaped and cone-shaped cells are present, with the cone-shaped cells becoming fewer toward the periphery of the sensitive area. At the outer edges are only rod-shaped cells.
• Where the optic nerve enters the eyeball, below and slightly to the inner side of the fovea, a small round area of the retina exists that has no light-sensitive cells. This optic disk forms the blind spot of the eye.

Eye Diseases

• Eye disorders may be classified according to the part of the eye in which the disorders occur.
• The most common disease of the eyelids is hordeolum, known commonly as a sty, which is an infection of the follicles of the eyelashes, usually caused by infection by staphylococci. Internal sties that occur inside the eyelid and not on its edge are similar infections of the lubricating Meibomian glands. Abscesses of the eyelids are sometimes the result of penetrating wounds. Several congenital defects of the eyelids occasionally occur, including coloboma, or cleft eyelid, and ptosis, a drooping of the upper lid. Among acquired defects are symblepharon, an adhesion of the inner surface of the eyelid to the eyeball, which is most frequently the result of burns. Entropion, the turning of the eyelid inward toward the cornea, and ectropion, the turning of the eyelid outward, can be caused by scars or by spasmodic muscular contractions resulting from chronic irritation. The eyelids also are subject to several diseases of the skin such as eczema and acne, and to both benign and malignant tumors. Another eye disease is infection of the conjunctiva, the mucous membranes covering the inside of the eyelids and the outside of the eyeball.
• Disorders of the cornea, which may result in a loss of transparency and impaired sight, are usually the result of injury but may also occur as a secondary result of disease; for example, edema, or swelling, of the cornea sometimes accompanies glaucoma.
• The choroid, or middle coat of the eyeball, contains most of the blood vessels of the eye; it is often the site of secondary infections from toxic conditions and bacterial infections such as tuberculosis and syphilis. Cancer may develop in the choroidal tissues or may be carried to the eye from malignancies elsewhere in the body. The light-sensitive retina, which lies just beneath the choroid, also is subject to the same type of infections. The cause of retrolental fibroplasia, however—a disease of premature infants that causes retinal detachment and partial blindness—is unknown. Retinal detachment may also follow cataract surgery. Laser beams are sometimes used to weld detached retinas back onto the eye. Another retinal disease, called macular degeneration, which affects the central retina, is a frequent cause of loss of vision in some older persons.
• The optic nerve contains the retinal nerve fibers, which carry visual impulses to the brain. The retinal circulation is carried by the central artery and vein, which lie in the optic nerve. The sheath of the optic nerve communicates with the cerebral lymph spaces. Inflammation of that part of the optic nerve situated within the eye is known as optic neuritis, or papillitis; when inflammation occurs in the part of the optic nerve behind the eye, the disease is called retrobulbar neuritis. When the pressure in the skull is elevated, or increased in intracranial pressure, as in brain tumors, edema and swelling of the optic disk occur where the nerve enters the eyeball, a condition known as papilledema, or chocked disk.

Diseases of eyes 

EAR 

• Organ of hearing and equilibrium. It is composed of three divisions—external, middle, and internal—the greater part of which is enclosed within the temporal bone.
• The external ear is that portion of the auditory apparatus lateral to the eardrum, or tympanic membrane. It comprises the auricle, or pinna (the external flap of the ear), and the external auditory canal, which is 3 cm (1.25 in) in length.
• The middle ear, on the inner side of the eardrum, embodies the mechanism for the conduction of sound waves to the internal ear. It is a narrow passage, or cleft, that extends vertically for about 15 mm (about 0.6 in) and for about the same distance horizontally. The middle ear is in direct communication with the back of the nose and throat by way of the eustachian tube, which allows for passage of air into and out of the middle ear. Traversing the middle ear is a chain of three small, movable bones called the ossicles: the malleus, or hammer handle; the incus, or anvil; and the stapes, or stirrup. The ossicles connect the eardrum acoustically to the internal ear.
• The internal ear, or labyrinth, is the part of the temporal bone containing the organs of hearing and equilibrium to which the filaments of the auditory nerve are distributed. It is separated from the middle ear by the fenestra ovalis, or oval window. The internal ear consists of membranous canals housed in a dense portion of the temporal bone and is divided into the cochlea (Greek, “snail shell”), the vestibule, and three semicircular canals. All these canals communicate with one another and are filled with a gelatinous fluid called endolymph.

Hearing

• Sound waves are carried through the external auditory canal to the eardrum, causing it to vibrate. These vibrations are communicated by the ossicular chain in the middle ear through the oval window to the fluid in the inner ear. The movement of the endolymph stimulates in the cochlea a set of fine hairlike projections called hair cells. Collectively these projections are called the organ of Corti. The hair cells transmit signals directly to the auditory nerve, which carries information to the brain. The overall pattern of response of the hair cells to vibrations of the endolymph encodes information about sound in a way that is interpretable by the brain’s auditory centers. The range of hearing, like that of vision, varies in different persons.

Disorder of Ear

• Balance disorder: A disturbance that causes an individual to feel unsteady, giddy, woozy or have a sensation of movement, spinning or floating. An organ in our ear (inner), the labyrinth, is an important part of our vestibular (balance) system.
• Labyrinthitis:  An infection or inflammation of the inner ear causing dizziness and loss of balance.
• Menicre’s disease: An inner ear fluid balance disorder that causes episodes of vestigo, fluctuating hearing loss, tinnitus ( a ringing or roaring in the ear), and sensation of fullness in the ear.
• Otitis Media: An infection of Middle ear.
• Otalagia :  Ear ache
• Salpingitis : Inflammation of Eustachian tube (fallopian canal)

NOSE

• Organ of smell, and also part of the apparatus of respiration and voice. Considered anatomically, it may be divided into an external portion—the visible projection portion, to which the term nose is popularly restricted—and an internal portion, consisting of two principal cavities, or nasal fossae, separated from each other by a vertical septum, and subdivided by spongy or turbinated bones that project from the outer wall into three passages, or meatuses, with which various sinuses in the ethmoid, sphenoid, frontal, and superior maxillary bones communicate by narrow apertures.
• The margins of the nostrils are usually lined with a number of stiff hairs (vibrissae) that project across the openings and serve to arrest the passage of foreign substances, such as dust and small insects, which might otherwise be drawn up with the current of air intended for respiration. The skeleton, or framework, of the nose is partly composed of the bones forming the top and sides of the bridge, and partly of cartilages. On either side are an upper lateral and a lower lateral cartilage, to the latter of which are attached three or four small cartilaginous plates, termed sesamoid cartilages. The cartilage of the septum separates the nostrils and, in association posteriorly with the perpendicular plate of the ethmoid and with the vomer, forms a complete partition between the right and left nasal fossae.
• The nasal fossae, which constitute the internal part of the nose, are lofty and of considerable depth. They open in front through the nostrils and behind end in a vertical slit on either side of the upper pharynx, above the soft palate, and near the orifices of the Eustachian tubes, leading to the tympanic cavity of the ear.
• In the olfactory region of the nose the mucous membrane is very thick and colored by a brown pigment. The olfactory nerve, or nerve of smell, terminates in the nasal cavity in several small branches; these ramify in the soft mucous membrane and end in tiny varicose fibers that in turn terminate in elongated epithelial cells projecting into the free surface of the nose.