Introduction
We see with the help of eyes . When light enters the eye, it passes through the cornea, iris and lens before reaching the retina. In the retina, millions of light sensitive cells called rods and cones react to the light. This results in a series of complex chemical reactions. The se reactions form electrical impulses in the optic nerve, which sends them to the brain. The brain interprets these signals as an image.
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| Human Eye |
Size
The eyes are small in size. Each eye is about 2.5 cm wide, 2.5 cm deep and 2.3 cm tall.
Socket and Lid
The eye socket is a bony cavity which contains the eyeball. The front part of the eye is protected by the eyelid, which keeps the eyes moist and clean.
Macula
Macula is a region of the retina. It is responsible for providing sharp vision and fine details that are required for reading and driving.
Lens
The eye lens is a biconvex lens with a diameter of about 1 cm. The lens is used to fine-tune vision.
Introduction
We move our eyes with the help of six muscles. The medial rectus muscle moves the eyes towards the nose. The lateral rectus muscle over the eyes towards the nose. The superior and inferior rectus muscles are responsible for upward and downward motion of the eyes. The superior and inferior oblique muscles help us to rotate the eyes.
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| Human Eye |
Sclera
Sclera is the white part of the eyeball. Sclera is the outer covering and gives shape to the eyes. It has several blood vessels that provide blood.
Iris
Iris lies behind the cornea and gives colour to the eyes. Iris can change its shape with the help of several muscles attached to it.
Pupil
Pupil circle at the centre of the iris. The pupil allows light to pass into the eye.
Retina
Retina is the innermost layer of the eye. It provides vision by sensing light with the help of rod and cone cells. Rod cells are responsible for vision in low light and cone cells are responsible for colour vision and detail.
Introduction
Kidneys filter blood through the tiny filters, called nephrons. Nephrons are basic functional and structural units of kidneys. Each kidney has about one million nephrons. Nephrons have a tiny blood vessel called glomerulus interlinked with collecting tubule for urine. In the glomerulus, chemical exchange take s place where urea, mineral salts, and toxins are filtered out from blood. This waste fluid is released from the body in the form of urine.
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| Kidney |
Kidneys
Kidneys are bean-shaped organs located near the middle of back just below the rib cage. Kidneys are the main organs of the urinary system that filters blood.
Other organs
Other urinary organs are ureter, urinary bladder, and urethra, Urethra carries urine from kidneys to bladder. Urethra passes urine out of the body.
Urinary System
The urinary system is also responsible for maintaining normal blood pressure and controlling production of red blood cells.
Blood
Kidneys filter about 200 quarts of blood every day and produce 2 quarts of waste products and extra water that flows into the bladder.
