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Anatomia człowieka (886)

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! EN_90227064_0001 SCI
PHOTO: EAST NEWS/SCIENCE PHOTO LIBRARY Illustration based on a scanning electron micrograph of macrophages fixed to the surface of alveoli (air sacs) in the human lung. Macrophages are monocytes (white cells) which have migrated from the blood to tissues, notably in the lymphatic system & lungs. They act as scavengers, engulfing foreign particulate matter by the process of phagocytosis. In addition, the macrophage deals with foreign (antigenic) substances during the initial phase of immune response. Antigens are presented on the surface of the macrophage so that they can be recognized & ultimately eliminated by specific lymphocytes.
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! EN_90227078_0001 SCI
PHOTO: EAST NEWS/SCIENCE PHOTO LIBRARY Illustration showing the role of an oligodendrocyte in the myelination of nerve fibres (axons) in the central nervous system (CNS - the brain & spinal cord). Oligodendrocytes belong to a group of cells called neuroglia ('nerve glue') which comprise all non-neural cells in the CNS. The dendritic processes from the cytoplasm of the oligodendrocyte give rise to the spiral-wrapped sandwich of cytoplasmic membrane that comprises the myelin sheath. A single oligodendrocyte may serve up to 50 nerve axons; 4 are visible here. Myelination effectively increases diameter of axon & hence velocity of impulse conduction.
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! EN_90227008_0001 SCI
PHOTO: EAST NEWS/SCIENCE PHOTO LIBRARY Illustration of the layers of nerve cells comprising the mammalian retina, the light- sensitive layer of the eye. At bottom, the outermost layer of pigmented cells supports a number of rod- & cone-type photosensitive cells. The rods outnumber cones by about 20:1 - hence only cones are shown here. The cell bodies above the rods & cones layer form the integrating bipolar cell layer; a single cell body may be seen to serve several rod receptors via numerous synapses (junctions). The upper ganglion layer of cell bodies belong to fibres comprising the optic nerve (top).
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! EN_90226995_0001 SCI
PHOTO: EAST NEWS/SCIENCE PHOTO LIBRARY Illustration depicting the human nervous reflex arc, showing the components involved in the muscular response of the arm to the stimulation caused by the heat of a candle flame against the hand. The pain impulse passes via a sensory nerve from the hand to synapses (junctions) in the white matter of the spinal cord (top right) which connect with two motor nerves that supply the biceps (right) and triceps muscles in the upper arm. Thus the sensation of pain caused by the heat of the flame provokes an upward jerk of the hand.
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! EN_90226909_0001 SCI
PHOTO: EAST NEWS/SCIENCE PHOTO LIBRARY Illustration based on a scanning electron micrograph of a single T-lymphocyte, a class of white blood cell. The T-cell develops in the thymus & is a key component of the immune system involved in cell-mediated response to invasion of body by foreign organisms or particles, notably viruses and some bacteria, which are protected from direct attack from antibodies (produced by B- lymphocytes) by their host cells. Unlike B-cells, T-cells do not produce antibodies; instead they recognize selective surface antigens on infected cells and certain types ('killer' T-cells) proceed to destroy infected cells by direct contact.
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! EN_90241030_0001 SCI
PHOTO: EAST NEWS/SCIENCE PHOTO LIBRARY Blood cells. Artwork (based on a scanning electron micrograph) showing various blood cells escaping from a sectioned small vein (top right). Red blood cells (erythrocytes) appear as biconcave discs; the knobbly red cells have become crenated (this occurs in high plasma concentrations). Red blood cells contain the oxygen-transporting pigment haemoglobin that circulates oxygen around the body. White cells (leucocytes) appear white; some (known as B-lymphocytes) have numerous microvilli projecting from their surfaces. The smaller branched structures (brown) are blood platelets.
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