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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 1 | HUMAN EMBRYOLOGY.

 
HUMAN       EMBRYOLOGY.
 Type of HUMAN oocyte/ovum is:    secondary  OLIGOlecithal   ISOlecithal
HUMAN  oocyte/ovum has 3 tunics and contains in ooplasm 2 types of granules:  
        1) YOLK granules,     2) CORTICAL granules (it contain GAGs and lytic enzymes).    
                            3 TUNICS,  surrounding  human OOCYTE/OVUM: 
   1) OOLEMMA (plasma membrane),  2) ZONA PELLUCIDA (contains:GAGs, including 
                                hyaluronic acid,  and  glycoproteins  ZP1-, ZP2-, ZP3-fractions). 
     3) CORONA RADIATA.  It is composed of cells of follicular epithelium..
       Abbrev. “GAGs”  means:  “GlycosAminoGlycans”  (groop of compound carbohydrates).
     FERTILIZATION in human happens in upper 1/3 of fallopian tube  after  OVULATION.
OVULATION is releasing of SECONDARY OOCYTE  from ovary into fallopian tube. 
Fertilisation  includes  3 phases: 1) DISTANT interaction of gamets with    CAPACITATION (sperm becomes is able to recognize ZPs of zona pellucida). 2) CONTACT interaction of gamets with ACROSOME reaction  and CORTICAL reaction, resulting in formation of  nonpermeable FERTILISATION MEMBRANE. It prevents polyspermia (entrance of more than 1 spermatozoon).
    3) FUSION of sperm and ovum  nuclei, diploid set of chromosomes is restored, resulting in 
       ZYGOTE formation.              Zygote undergoes to CLEAVAGE  (mitotic division).
 Type of cleavage in human is: HOLOBLASTIC UNEQUAL. It result is formation of BLASTOCYST (human blastula).        Wall of  BLASTOCYST is composed 2 cellular masses:  
        a) inner cell mass, or EMBRYOBLAST,   and      b) outer cell mass, or TROPHOBLAST.
   Outer layer of trophoblast is  syncytiotrophoblast.  During 1st to 4th days embryo locates in fallopian tube. During days 5th to 6th blastocyst locates in uterus lumen.  Day 7th  is accompanied by 2 events: 
                     1st is  - IMPLANTATION,      2nd is - beginning of DELAMINATION.
 Implantation – is embedding of blastocyst into endometrium. Endometrium – is tunica mucosa of uterus. Syncytiotrophoblast secrets LYTIC enzymes. It  locally destroy endometrium and blastocyst is embedded into this pit.  Trophoblast, surrounding blastocyst, differentiates into  CHORIONIC  VILLI.. 
 Delamination  (or  early phase of  gastrulation,  happens since 7th  till 14th day) –  is division of EMBRYOBLAST on 2 layers:  EPIBLAST ( or primary ectoderm)   and   HYPOBLAST ( or primary endoderm).           Thus, after delamination  embryo becomes  bilaminar.
 Immigration (or late phase of gastrulation, happens since 15th till 23rd day)- is movement of epiblast cells, resulting in formation of 2 intermediate structures : primitive streak and primitive node. Primitive STREAK differentiates into MESODERM.      Primitive NODE differentiates into NOTOCHORD.
  Thus,  after immigration embryo becomes trilaminar  and    has       3 AXIAL organs.
    ECTOderm   gives rise to :1) NEURAL TUBE ,   2)  neural CREST,     3) SURFACE ectoderm.
  Middle layer of neural tube, or mantle  zone, contains neuroblasts, differentiating into:-- neurons of CNS   (of  brain and spinal cord),   --rods and cons of retina.    Neural crest   contains neuroblasts, differentiating into:   -  neurons  of PNS (of ganglia),   -- pigment cells of skin (melanocytes),  
  --chromaffin cells of suprarenal gland MEDULLA. 
    Surface  ECTOderm  differentiates into :  --epidermis (skin epithelium),   --tooth enamel, 
   --epithelium of oral cavity   and  of  rectal anus.
   Embryonic MESODERM is composed of: 1) SOMITES (mesodermal segments), 2) SPLANCHNIC mesoderm,    4) Intermediate mesoderm,       5) MESENCHYME,         6) Paramesonephric duct.
  Somite is composed of 3 parts: A) DERMAtome of somite.  It diff.into skin connective tissue (or dermis).   B) MYOtome of somite.   It differentiates into striated skeletal muscle tissue.
   C) SCLEROtome of somite.  It diff. into   bone tiss. and   cartilage tissue. 
  Splanchnic mesoderm diff. into: -- suprarenal gland CORTEX,  -- into striated cardiac  muscle tiss.
  Mesenchyme diff. into :-loose connective tiss.,  -smooth muscle tiss.,  -blood cells,  -  blood vessels.
  Embryonic endoderm lines gut from inside. Gut has 3 parts: a) foregut, b) midgut, c) hindgut.
   Endoderm of foregut diff. into:  - epithelium of stomach and of duodenum,  -- epithelium of liver,
       --epithelium of pancreas,              - epithelium of bronchi and of pulmonary alveoli,
                        - - follicular cells of thyroid gland,  parathyroid glands.
 Paramesonephric duct (or Muller duct) diff. into epithelium of  fallopian tubes and of uterus.
 
Составитель – доцент В.В. Бондаренко.
 
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