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epidermis
epiderme m

Skin. The outer protective layer of cells in animals or plants. The epidermis in many multicellular invertebrates is one cell thick and often covered with a cuticle. In most vertebrates, the epidermis is the outer layer of skin, and in terrestrial vertebrates it may be composed of several layers of dead cells. In plants, the epidermis is one cell thick, and may have a scale on the aerial structures. See leaf, root, and stem.


epiglottis
Epiglotte f

Reed . Washer. A shutter of cartilage and membrane found at the base of the tongue on the inner wall of the pharynx. The epiglottis closes the trachea (windpipe) during swallowing. See digestion.


epithelium
epithelium m

Epithelium. Endothelial tissue in vertebrates consists of stacked layers of cells that cover internal and external surfaces, such as: the skin and the linings of the respiratory and digestive organs and the urinary and reproductive organs. Epithelia may also contain specialized structures, as in cilia and goblet cells.


erythrocyte
erythrocyte m

Red blood cell See red blood cell.


eustachian tube
trompe f d'Eustache

Eustachian tube. A tube that connects the middle ear to the pharynx in humans and tetrapods, and is important in equalizing the air pressure on both sides of the eardrum. See ear


evolution
evolution f

The evolution of complex organisms from simpler ancestors over successive generations, see natural selection.

excretion
execution f

Empty. Eliminate waste. Living organisms get rid of waste products resulting from metabolism.
The main products offered are: water, carbon dioxide, and nitrogenous compounds such as urea. In simple organisms, excretion occurs through the cell membrane or epidermis, while in higher plants it occurs through leaves, while most animals have specialized excretory organs. For example: In humans, the lungs excrete water and carbon dioxide, and the kidneys excrete urine. See kidney.


exoskeleton (or external skeleton)
exosquelette m

External skeleton A skeleton found outside the body of some invertebrates, such as the cuticle of insects and the shell of crabs. Some organisms periodically shed and renew their exoskeletons to allow growth, a process known as moulting.
. endoskeleton compare with


eye
oeil m

Eye A sensory organ that responds to light, and ranges from very simple structures in invertebrates to complex organs in insects (compound eye - com) (pound eve) and vertebrates. The drawing shows a vertical cross-section of the human eye.

Choroid. Vitreous mixture, retina (rods and cones), sclera, fovea, optic nerve, blind spot, aqueous humor, iris, cornea, pupil lens, conjunctiva, suspension ligament.

The eye muscles enable the eye itself to move up, down, and sideways, and the sclerotic layer is a tough, protective layer that forms on the front side of the eye, the transparent cornea.

The choroid is a black-pigmented layer under the sclera, and it is rich in blood vessels that supply the eye with food and oxygen.

The retina is a layer of nerve cells that are sensitive to light. There are two types of cells in the retina, each named according to its shape.

(a) Rods, which are highly sensitive to low-intensity light and are particularly concentrated in the eyes of nocturnal animals.

(b) Cones, which are sensitive to bright light. There are different types of them that are stimulated by different wavelengths of light, and thus they are responsible for color vision. Animals whose retinas lack cones are color blind, while color blindness in humans results from a defect in the cones.

The fovea is a yellow spot, a small area of ​​the retina that contains only cones in high concentration, which gives the highest degrees of detail and color.

The blind spot is the part of the retina from which nerve fibers connected to the rods and cones leave the eye to enter the optic nerve, which leads to the brain. Since there are no light-sensitive cells at this point, the brain does not register the image that forms on the blind spot.

The lens is a transparent, convex structure that can change curvature and is mainly responsible for scattering light on the retina.

A direct image on the retina
Light coming from an object

The lens is kept in place by suspen sory ligaments connected to the ciliary muscles, whose contraction or relaxation changes the shape of the lens, allowing sharp focusing of both distant and near objects. This is called accommodation.

The iris is the colored part of the eye, and it contains muscles that change the size of the pupil, that is, the hole through which light enters the eye. When the light is weak, the pupil opens wide (dilates) to increase the brightness of the image, and in bright light the pupil shrinks, protecting the retina from possible damage. This mechanism constitutes an example of reflex action.

Constricted pupil (accommodation to light)
Pupil - iris
Dilated pupil (adaptation to darkness)

Because the pupil is small, light rays enter the eye in such a way that the image on the retina becomes upside down (inverted), and the brain corrects this reversal of the image.

The image is mirrored and smaller than the object

The aqueous and vitreous humours are two liquids that fill the eye chambers and help maintain their shape, focus light, and allow nutrients, oxygen, and wastes to spread to and from the eye cells.