Human Embryo Development

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Human Embryo Development Extended Study Learning Objectives List the sequence of development of an embryo Explain the term fertilized egg Explain the term blastocyst ...
Title: Human Embryo Development 1 Human Embryo Development
  • Extended Study
  • 2 Learning Objectives
  • List the sequence of development of an embryo
  • Explain the term fertilized egg
  • Explain the term blastocyst
  • Explain the term amnion
  • Explain how the placenta is formed
  • Explain how the embryo develops up to the third month of gestation
  • 3 Sequence of development from fertilised egg
  • Early stages
  • 4 Sequence of development from fertilised egg
  • The zygote contains 46 chromosomes, twenty three from the egg and 23 from the sperm
  • 5 It divides rapidly by mitosis to produce 2 cells, then 4, then 8, 16 etc. and continues to divide 6
  • At this point the developing individual is referred to as the morula
  • 7
  • Around 5 days after fertilisation the morula forms a hollow ball of cells called the blastocyst
  • 8
  • The outer layer of the blastocyst forms the trophoblast. This will later develop into the layer of membranes that surround the embryo (placenta and amnion)
  • Trophoblast 9
  • The inner cells (called the inner cell mass) of the blastocyst will eventually form the embryo. These cells are not yet specialised. They have a phenomenal ability to differentiate divide to give rise to many different types of tissue
  • Inner cell mass 10 Stem cells
  • Huge research potential to renew or repair damaged body parts.
  • 11 Learning check
  • How many chromosomes in a fertilised egg?
  • Is a fertilised egg haploid or diploid?
  • What is the developing individual referred to when it is made up of 8 cells?
  • What is it referred to after a number of days?
  • What is unusual about the cells of the inner cell mass?
  • 12 The morula/blastocyst is pushed along the fallopian tube until it enters the uterus 13
  • Here it will implant into the uterus wall. The endometrium now provides nourishment for the developing blastocyst
  • Connections with the mother will begin to form (placenta and umbilical cord)
  • 14 This point marks the beginning of pregnancy 15 Sequence of development from fertilised egg
  • Development of the embryo
  • 16
  • About 10 days after fertilisation the inner cell mass forms the embryonic disc
  • This usually consists of three layers called germ layers
  • Ectoderm (outside)
  • Mesoderm (middle)
  • Endoderm (inside)
  • 17
  • Each of these layers gives rise to specific structures in the developing embryo
  • In humans the mesoderm is split by a layer called the Coelom
  • This allows space for more complex organs such as heart, lungs and kidneys to develop
  • 18 Ectoderm skin, nervous system Coelom heart, lungs Mesoderm muscles, skeleton Endoderm inner lining of digestive system 19 The Amnion 20 The Amnion
  • When first formed the amnion is in contact with the embryo, but at about the fourth or fifth week fluid begins to accumulate within it (amniotic fluid)
  • The primary function of the amnion and amniotic fluid is the protection of the embryo for its future development
  • 21 Four to five weeks after fertilisation
  • The heart forms and starts to beat
  • The brain also develops
  • The limbs have started to form
  • 22 (No Transcript) 23 By the 6th week
  • Eyes are visible
  • The mouth, nose and ears are forming
  • The skeleton is at the early stages of development
  • 24 By the 8th week
  • the major body organs are formed
  • Sex glands have developed into testes or ovaries
  • Bone is beginning to replace cartilage
  • 25 By the 8th week
  • At this stage the embryo has taken on a recognisably human from.
  • From this point it is referred to as a foetus
  • The foetus continues to grow. No new organs are formed from this point
  • 26 By the 12th week (3 months)
  • The nerves and muscle become co-ordinated allowing the arms and legs to move
  • The feotus sucks its thumb, urinates and even releases feaces into the amniotic fluid
  • 27 By the 12th week (3 months)
  • The gender of the foetus can be seen in scans
  • 28
  • The time from fertilisation to birth (the gestation period) lasts about 38 weeks (9 months)
  • 29 Learning Check
  • What are germ layers?
  • Name them
  • What features have already appeared by the fifth week?
  • At what stage is the developing individual referred to as a feotus?
  • 30 Placenta formation 31 Placenta formation 32 Placenta formation
  • The placenta forms from a combination of the tissues of the uterus and the embryo
  • Soon after implantation a membrane called the chorion completely surrounds the amnion and embryo
  • 33 (No Transcript) 34
  • The chorionic villi emerge from the chorion and invade the endometrium allowing the transfer of nutrients from maternal blood to fetal blood
  • 35
  • This combination of the chorionic villi and the endometrium will eventually form the placenta which becomes fully operational about three months into the pregnancy
  • 36 The Placenta Chorion Embryo Placenta Mothers blood Mother Nutrients, Oxygen, antibodies Wastes, Carbon Dioxide, Water Amnion Amniotic fluid Umbilical cord Embryos blood Embryo 37
  • Placenta allows gases, nutrients, waste, antibodies, some drugs, hormones and micro-organisms to be exchanged between mother and baby
  • Placenta also produces hormones
  • 38
  • Blood supplies of mother and embryo do not mix
  • Blood types may not be compatible
  • Mothers blood pressure might damage embryo
  • 39
  • Umbilical cord connects the embryo with the placenta
  • it takes blood from the embryo to the placenta and back again
  • It must be cut at birth to separate mother and baby
  • 40 45 seconds after birth! 41 Syllabus 42 Learning check
  • Name the structures that move into the endometrium and eventually become part of the placenta
  • At what point does the placenta become fully operational?
  • Why is it important that the blood of the mother and baby do not mix?
  • 43 Depth of treatment
  • Sequence of development from fertilised egg, morula, blastocyst, existence of amnion, placenta formation from embroyonic and uterine tissue.
  • Development of embryo up to third month.
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