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Medical Academy named after S.I. Georgievsky
of Vernadsky CFU


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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 2 | EYE

EYE .(organ of vision).
CORNEA (=CO). NO blood VESSELs in CO. Thus, after transplantation of cornea rejection of it does NOT happen On cross section CO has 5 layers:
  1. Anterior EPITHELIUM. It is – stratified squamous NONkeratinized,
  2. Bowmans membrane,
  3. Substantia proria (or corneal STROMA). It is occupied 90% of cornea. It is composed of CONNECTIVE tissue LAMELLAE (or PLATES). One LAMELLA is composed of: a) parallelly arranged COLLAGEN fibrills, b) chondroitin sulfate, c) fibroblasts.
  4. Descemets membrane,
  5. Posterior EPITHELIUM. It is – simple  squamous.
VITREOUS BODY. It is composed of: a) cells (hyalocytes), b) ground substance (too much of HYALURONIC acid), c) TRANSPARENT protein vitrein.
NO blood VESSELS in lens. After transplantation of lens rejection of it does NOT happen. Main tissue type in LENS is – EPITHELIUM.
It is presented by cells, named lens fibres. It are: a) long (1 cm), narrow  epithelial cs, b) without nucleus, c)It cytoplasm contains TRANSPARENT protein crystalline.
Main tissue type – is NERVE tissue. Additionally – is pigment EPITHELIUM.
Nerve tissue is presented by TRIneuronal reflex arch:
1st neuron in arch- is PHOTORECEPTOR cell.
2nd neuron – is BIPOLAR neuron.
3rd  neuron – is MULTIPOLAR neuron. It axons  leave retina and form fibres of optic nerve.
There are 2 types of photoreceptor cells: 1) RODs and 2) CONs.
Common plan of both structure is same: Rod and con are composed of 3 portions:
1) MODIFIED dendrite, 2) Perikaryon, 3) Axon.
Dendrite is composed of 3 portions: a) OUTER segment, b) connecting stalk, c) inner segment.
If OUTER segment of dendrite is CYLINDER-shaped and contains 1000 complete membrane DISCs, so cell type – is ROD. Discs contain visual pigment. RHODOPSIN.
Funct.of RODs: it are receptors of TWIGH LIGHT (dim light, NONcolour) vision.
If OUTER segment of dendrite is CONICAL-shaped and is composed of INcomplete membrane semidiscs, so cell type – is CON. Photopigment IODOPSIN is located in outer segment.
Funct. of CONs: it are receptors of COLOUR (bright light) vision. Pathology of cons- is hereditary desease DALTONISM (colour blindness).
Commonly, rods and cons transform energy of incoming photons into nerve impulse with participation of photopigment molecules.
Outer segments of dendrites contact with pigment epithelium. Funct.: pigment epithelial cs make PHAGOCYTOSIS of membrane discs and semidiscs of outer segments, providing every day RENEWAL of outer segments.
Embryonic origins: 1) for neurons of retina – is INNER layer of optic CUP, 2) for pigment epithelium – is outer layer of optic CUP. Optic CUP- is double-layered outgrowth of NEURAL TUBE, 3) for epithelium of LENS – is lens placode (derivative of surface ECTODERM). 4) for corneal stroma, vitreous body, sclera, tunica vasculosa (including iris) – is mesenchyme.
Organ of taste – is TASTE BUD (=TB).
TB – is oval-shaped association of epithelial sensory cells in epithelium, covering  lingual papillae.
TB contains 3 types of epithelial cells: 1) DARK sensory cs, 2) LIGHT sensory cs. Both types – are tall columnar cs with apical MICROVILLI, protruding into taste pore. Funct.: is taste perception.
Basal surface of both types forms synaptic junction with afferent nerve fibres. 3) BASAL cs – are short cs. Funct.: is origin for regeneration of dark and light cs after it death.
Составитель – доцент В.В. Бондаренко.
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