for class XII

Human ear
Ear is stato acoustic organ. It is responsible for sensations of equilibrium and hearing. It is sensitive to frequencies of sound waves and to change in relation with gravity. There are two ears and are situated one on either side of head.

Each ear consists of three main parts.
 External ear
 Middle ear
 Internal ear

External ear -- it consists of pinna, auditory canal and tympanic membrane or ear drum. It is air filled cavity. It receives or collects sound waves and directs he sound waves to middle ear.
Pinnae-- these are flap of tissue supported by cartilages. These are found one on either side of head. these are immovable. Thee is presence of small opening that leads into auditory canal. It collects the sound waves and sends it to auditory canal.
Autitory canal -- it is also known as ear tube or external auditory meatus. It is lined by skin which has hairs for protection. Glands are preset to secret brown wax. If more and more wax is collected, it may cause deafness. It ends in eardrum.

Tympanic membrane-- it is also known as ear drum. It is thin sheet of tissue. it is delicate, membranous structure. It vibrates in response to the sound waves. It transmits sound waves to middle ear.

Middle ear - - it is also air filled cavity. It consist of three tiny bones called ear ossicles . thjey are malleus, incus and stapes, ear ossicles move forward and backward in resplonse to vibrations of ear drum.

Malllleus -- it is hammer shaped and articulate with incus on the other side.
Incus-- it is anvil like structure articulating with malleus on one side and stapes on other side.
Stapes -- it is stirrup like. Its foot plate or base is attached to oval window called fenestra ovalis or fenestra vestibule. These three ear ossicles are arranged in lever like action. They magnify and transfer the vibrations from ear drum to cochlea of inner ear through oval window.

Eustachian tube – it is a tube that leads from pharynx to middle ear. It helps in equalizing air pressure on both sides of ear drum. When air pressure is unequal, the ear drum becomes more stretched and can cause pain.

Inner ear -- it is fluid filled chamber it consists of complex system of canals and cavities. It basically consists of cochlea (associated with hearing) and vestibular apparatus( associated with balance)





Cochlea -- it is a highly coiled tube about 35 mm in length. It has got three canals inside, the vestibular canal, middle canal and tympanic canal. The reissner’s membrane separates the vestibular and middle canal. Similarly basilar membrane separates middle and tympanic canal. Both vestibular and tympanic canal are filled with fluid called perilymph. The vestibular canal is connected to oval window on the other side of which stapes is attached. The tympanic canal is connected to round window. The middle canal is filled with endolymph. There is basilar membrane on one side. The sensory hair cells rest on this basilar membrane. These cells are in contact with tectorial membrane above . the tectorial membrane, sensory hair cells and basilar membrane together form the organ of corti. The organ of corti can generate the sound impulse and send it to brain through auditory nerve.

Mechanism of hearing

As the sound waves enter the external ear, they pass through canal and strike the ear drum. The vibrations of ear drum are transmitted to three ear ossicles which magnify them 20 to 25 times. As stapes fits into the oval window, when it vibrates, the fluid perilymph in the vestibular canal vibrates. These vibrations cause the movement of the basilar membranes which in turn moves the sensory hair cells attached to it creating the nerve impulse. The sound waves transmitted to nerve impulse travel through auditory nerve to auditory cortex in brain. If the vibrations in perilymph are more than needed to stimulate the sensory hair cells, then they can be dissipated through round window into the middle ear and into the pharynx. The variations in the intensity and pitch are determined by the amplitude by which the basilar membrane vibrates and region of the organ of corti that gets stimulated.

Mechanism of balance

The vestibular apparatus of inner ear consist of utriculus, sacculus and semicircular canals. All of them are filled with endolymph. The three semicircular canals are at right angle to each other. Each one has a swelling at one end called ampulla. The semicircular canals open into utriculus where it is connected to the sacculus. The balance receptors are present in the utriculus, sacculus and the ampullae of the semicircular canals. These receptors contain the sensory hair cells which are very sensitive to the position of head with respect to gravity. The three semicircular canals are so arranged that the movement in any plane can be detected by these cells and generate impulse. The impulses are passed on to brain through the auditory nerves. Then we know that the body is not in balance and keep it in balance.






Eye
Eye is photoreceptor organ. Two eyes are situated at the front in the orbital fossae of skull. Eyes are very much important, so they are protected by eye brows and eye lids. Eyes can be moved within the orbit in different directions. The movement of eyes is due to six sets of muscles attached to outer surface of eye ball. They are superior, inferior , medial and lateral rectal muscles and superior and inferior oblique muscles. Eye lashes protect eyes from entering dust particles and germs.

There are presence of glands like meiobomian and lachrymal or tear gland. Meiobomian gland is found at upper inner corner of eye. It secretes oily secretion. This oil holds little tear for lubrication. Lachrymal glands are found at outer corner of eye. Lachrymal glands secrete watery fluid called tear. Tear is salty fluid which keeps conjunctiva moist. Tear is drained into nose through nasolacrimal duct at inner corner of conjunctiva.

Eyes are spherical structure. The diameter is about 2.5 cm. Eyes consist of tissues arranged in three concentric layers.
o Outer layer consists of sclerotic or sclera and cornea
o Middle layer consists of choroids, ciliary body and iris
o Inner layer consists of retina

Sclerotic layer -- it is made up of tough connective tissue. it is white in color and opaque. It forms about 5/6 part of eye ball. Most of its part lies at back. It provides surface for attachment of muscles. It maintains shape and protects inner part.
Cornea -- it is elevated part at the front. It is thin and transparent. It forms about 1/5 part of eye ball. It allows light to pass into eye. Due to curvature, it helps in focusing a real inverted image on retina.
Conjunctiva -- it is very much thin transparent membrane covering the cornea and sclera. It is having blood supply. If injured, it gives red color to the eye.

Choroids-- it is vascularised and pigmented layer. So it provides nourishment to retina. Due to pigmentation, it reduces the reflection of light inside eye.
Ciliary body – it is found at the junction of sclera and cornea. It is also vascularised. There are presence of ciliary muscles. These muscles change shape of lens. Contraction results in more spherical shape and relaxation results in flattened shape. From ciliary body, there arises suspensory ligaments. Suspensory ligaments hold lens in position.
Iris -- it is separated from cornea and forms muscular diaphragm just in front of lens. It is also vascularised. It gives color to eye like black, brown, blue etc.
Pupil -- iris is perforated and the opening is called pupil. The dilated muscle present in iris can control the size of pupil. It controls the amount of light entering the eye. In the bright light the size of pupil becomes smaller and in dim light it becomes larger.




Retina -- it consists of two sub layers, outer pigmented and inner photoreceptor layer. In the photoreceptor layer, there are two types of photosensitive cells, cones and rods. The cones are for discrimination of color hence gives sharp vision. The rods are for formation of image at dim light. Three types of cones are there. One type is stimulated by red end of spectrum, the second one by middle green region and third one by blue violet end. The normal color blind is inability to distinguish between red and green.

Fovea -- it is also known as yellow spot. It is slightly depressed area at middle part of retina. It contains only cones. It forms sharpest image.
Blind spot—at the back of eye, from where the optic nerve enters into the eye is called blind spot. It does not contain cones and rods. If image is formed at blind spot, it can not be seen. No image is formed here.

Lens – it is transparent, biconvex structure held in position by suspensory ligaments. It focuses light on the retina for image formation.
Aqueous chamber -- it is space behind cornea and in front of lens. It is filled with watery fluid called aqueous humour. It nourishes cornea and support lens by its pressure. Behind the lens is large space called vitreous chamber filled with jelly like space called vitreous humour. It supports lens and retina.
Working of eye -- light rays fall on cornea. The light rays pass through pupil, lens. The rays are converged by cornea, aqueous humour lens and vitreous humour. They focus the rays at retina. So a small inverted image of object is formed. The convexity of lens can be changed to bring a sharp focus on retina. The eyes are able to focus distant object as well as near by objects. It is known as accommodation. The eyes are suited for viewing distant objects. To see nearer objects, the lens becomes thicker by contraction of ciliary muscles.
Defects of eyes
Defects of eyes are due to curvature of cornea, change in curvature of lens, size of eye ball and opacity of lens etc.
Normal vision is called emmetropia
Myopia or near sightedness
Nearer objects can be seen clearly but objects at about the distance of 6 meters can not be seen clearly. It is due to large eye ball or high curvature of lens. The rays coming fro distant object are focused in front of retina. It can be corrected by biconcave lens.

Hypermetropia
In this distant objects can be seen but near objects are not seen clearly. It is either due to small eye ball, or low convexity of lens. The rays coming from near objects are focused beyond the retina. Use of biconvex lens can correct it.

Presbyopia
It is also long sightedness. It is developed after the age of 40. It is due to loss of flexibility of lens. It is corrected by use of convex lens.

Astigmatism
The vertical and horizontal bars can not be focused at the same time. It is due to uneven curvature of cornea. For correction, cylindrical lens is used.

Cataract
It is developed after about the age of 60. The lens becomes less transparent. Light rays can not pass and person losses ability to see. No treatment for this, the lens should be removed surgically. The artificial lens should be implanted or spectacles with convex lens should be used.

Glaucoma
If the aqueous humour is secreted more, the intra ocular pressure increases which can cause blindness. If it is detected in time it can be cured.

Night blindness
It is due to deficiency of vitamin A in diet. Vitamin A forms Rhodopsin. It is needed for working of rods in the retina.

Color blindness
It takes place due to absence of certain cone cells. The normal colorblindness is that in which red and green can not be differentiated.


Human reproductive system

The reproductive system in and are distinctly different both in structure and fuction. There are some common terms applied to both.
Primary sex organs or gonads
Testis in
Ovaries in
These organs under go number of changes during development and perform basic functions
1. produce gametes testis -sperms
ovaries -ova
2. as ductless glands secrete hormones
testis - testosterone
ovary - estrogen and progesterone
the development of both of these organs is under the control of gonadotropins FSH and LH from anterior pituitary gland

secondary sex organs
in male, prostate gland, seminal vesicle, vas deferens and penis etc
in female, fallopian tubes, uterus, vagina and mammary glands etc

These organs perform important functions but do not produce gametes. These are associated with primary sex organs. The development growth maintenance is under the control of sex hormones produced by ovaries and testis. Sex hormones responsible for sexual behavior and drives influence development of many other organs and tissues of body.

Accessory or external sex characters
They do not play any direct role in reproduction but are distinct and help to distinguish both sexes.
In male, low pitch voice and distribution of pattern of body hair
In female, high pitch voice and distribution pattern of body hair.


Male reproductive system

The male reproductive system consists of testis, epididymus, duct system and accessory glands.

Testis
These are paired gonads. They produce male gametes sperms and secrete male sex hormones testosterone. These are present or enclosed in a loose fold of skin called scrotum. They are found out side the abdominal cavity, where temp remains 2- 3 C below body temperature that is essential for sperm formation. Each testis is enclosed in a tough capsule known as tunica albugenia and testis consists of large no. of seminiferous tubules. In between the tubules there are specialized cells known as Leydig cells. Seminiferous tubules open into a space inside the testis called rete testis. From this space a no. of small, very fine tubules called vasa efferentia arise. These vasa efferentia fuse in the head of epididymus.



Epididymus
Single highly coiled tube about 5 meters long. Sperms formed in the seminiferous tubules pass through vasa efferentia and they are stored in the epididymus. Sperms get concentrated and maturity and mobility in epididymus. Epididymus leads into vas deferens.

Vas deferens
It is short straight tube. It ascends into abdominal cavity. It loops over the urinary bladder and opens into common urethra. Urethra passes through penis and opens at tip of penis.

Penis
It is made up of spongy muscular tissue. This tissue when filled with blood causes erection and enlargement of the organ. The tip of penis (glans) is highly sensitive. Sexual excitement can cause the erection of penis. Vessels are dilated to collect blood in spongy tissue. As tissue become distended, it compresses the vein so as to inhibit flow of blood out of tissue. With continued stimulation the penis and underlying bulb become hard and enlarged.
The penis consists of 3 columns of spongy tissue, 2 columns of corpora cavernosa above and 1 column of corpus spongiosum below. Corpus spongiosum includes the urethra. The tip of glans is slightly enlarge. It is covered by fold of skin called prepuce. The function of penis is to deposit semen in the genital tract of female.


Female reproductive system

Consists of ovary, oviducts, uterus, vagina, vulva and accessory glands.

Ovary -- paired structure, dark coloured and held in position by ligaments( mesovarium. Situated in abdominal cavity, one on either side of vertebral coloumn behind kidneys.

Each ovary is lined by germinal epithelium. The inner mass of fibrous connective tissue is called stroma. Stroma contains blood capillaries and nerve fibers and ovarian follicles etc. ovarian follicles develop from germinal epithelial cells. A marured follicle is called Graafian follicle. Outer membrane of Graafian follicle is membrane granulose. There is fluid filled cavity called antrum. In this cavity there lies ovum. The ovum is surrounded by Zona pellucida or zona radiata

The Graafian follicle finally ruptures to release mature egg into surrounding peritoneal cavity. It is picked up by fimbriated opening of fallopian tube. The follicle cells with blood clot forms corpus luteum.

The duct system-- consists of 2 fallopian tubes, uterus and vagina.
Fallopian tubes or oviducts. These ducts have a funnel shaped fimbriated opening to receive eggs as they mature. The ciliated funnel leads distally into a long narrow and convoluted tubule called fallopian tube. It has infundibulum which is fimbriated, ampulla, wide part where fertilization takes place, isthimus, narrow and straight part. Its walls are contractile and lined internally with ciliated epithelium. These cilia help egg to move towards uterus.

Uterus – 2, fallopian tube open into a thick walled muscular organ called uterus. The inner wall of uterus is called endometrium. Endometrium is richly supplied with blood vessels and glands. Upper dome shaped part is Fundus, broad above and narrow below is body, The lower tip of uterus is called cervix where there is opening internal os and opening below external os opens to vagina

Vagina -- it is a large fibromuscular chamber ( tube) that runs from uterus to outside. The fibro muscular chamber is lined by stratified epithelium. It opens outside by vulva.
Females have separate urethral and vaginal openings unlike males. At vaginal orifice, partially covered membrane in vergin called hymen. Epithelial cells produce glycogen, anaerobic oxidation of which produce lactic acid for protection from infection.

Vulva is guarded by two folds of tissue labia majora and labia minora.

Clitoris present analogous to penis in male.

Glands
bertholin’s gland one pair,similar to cowper’s gland
The secretion of bertholin’s gland is viscid fluid that makes the vaginal passage slippery needed at the time of intercourse.
Mammary gland one pair, located at chest region. The development of mammary gland is influenced by female sex hormone. The production of milk is due to another hormone called prolactin. The release of milk is due to oxytocin hormone soon after the birth of child.



Process of fertilization
During the sexual intercourse, ejaculation takes place in which semen is deposited in the vagina of female called orgasm. Due to the contraction of vaginal passage, sperms move up into the uterus and fallopian tube. If they find the ovum, the wall of ovum dissolved by the sperm lysine of large no. of sperms. Then one sperm pierces the ovum and fuses with the ovum. It results into the formation of zygote. It is implanted into the wall of uterus known as endometrium.




Menstrual cycle

Cyclic changes occur with periodicity of 28 days. Starts about the age of 9- 10, continues to about the age of 50. No cycle during pregnancy. Starts again after few months of child birth. Stoppage of cycle at old age menopause, which shows incapability of woman of reproduction.

Menstrual phase
o lasts for about first 3- 5 days.
o Breaking down of endometrium , epithelium lining, connective tissue blood vessels slashed off and discharge as menstruation.
o Estrogen and progesterone very low.
o Weeping of uterus

Proliferative phase
o it remains for 5th to 14th day, it lasts for about 9 or 10 days till ovulation.
o Begins with repair of damaged endometrium
o Induced by FSH, also follicular phase – one egg matures in each cycle.
o Primary oocyte undergoes first meiotic div, and changed into sec oocyte forms Graafian follicle.
o Estrogen secreted by Graafian follicle, its level increases, becomes maximum about 3 days before ovulation.
o Estrogen causes thickening of endometrium and develop blood vessels in it.
o Uterine movement increase due to contraction of uterine muscles.

Ovulation phase
o One matured egg is released from the Graafian follicle on the 14th day.
o Corpus luteum is formed by ruptured follicle also called yellow body.

Secretory phase
o Lasts for 12 -14 days, from 15th to 28th day.
o Induced by LH also called Luteal phase.
o Corpus luteum releases Progesterone, causes further thickenings of endometrium for implantation.
o Under its influence, tubular glands secrete mucus, uterus becomes fluid filled and glandular.
o Uterine movement decrease considerably.
o Progesterone inhibits further maturation of any follicle or ovulation from ovary.
o If ovum is not fertilized, corpus luteum degenerates, level of both estrogen and progesterone decrease at about 28th day.