differentiation and development
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Differentiation and development. Development involves: 1) Cell division and differentiation Differentiation is the creation of different types of cells 2) Changes in anatomical structures Anatomical changes include g radual modification of physical and physiological characteristics - PowerPoint PPT PresentationTRANSCRIPT
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PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Embryology Lecture 5
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Development involves:1) Cell division and differentiation
Differentiation is the creation of different types of cells2) Changes in anatomical structures
Anatomical changes include gradual modification of physical and physiological characteristics
Development begins at fertilization
Differentiation and development
Development can be divided into: Prenatal and postnatal development
Prenatal development begins at fertilization and ends with birth Prenatal development includes:
Embryological development Changes occurring during the first two months after
fertilization Fetal development
Begins at the start of the ninth week and continues until birth
Postnatal development Commences at birth and continues to maturity
Stages of development
Fertilization is fusion of two haploid gametes (egg and sperm) each with 23 chromosome to produce a zygote that contains 46 chromosomes
Fertilization occurs in the uterine tubes Within a day of ovulation
Spermatozoa cannot fertilize an ovum until after capacitation
Fertilization (conception)
Fertilization Steps
• Step 1 Ovulation• At ovulation the oocyte is in metaphase
of meiosis II• Both the occyte and the polar body is
surrounded by corona radiate• Step 2 Fertilization
• Oocyte is surrounded by the sperms• Acrosomal enzyme from several sperms
creates gaps in corona radiata• One sperm makes contact with the
oocyte membrane• Sperm and oocyte fused • The process of meiosis will
complete
Fertilization
The first trimester is the period of embryological and early fetal development
Four processes occur during the first trimeter1) Cleavage2) Implantation 3) Placentation 4) Embryogenesis
The First Trimester
Cleavage - cleavage is the first cell division The first cleavage occurs at 32 hours Second cleavage occurs at 60 hour Third cleavage occurs at 72 hours Several divisions later the embryo becomes a solid mass of cells
known as morula Molurla becomes a blastocyst (also known as blastula) Blastocyte includes:
Trophoblast – outer layer of cells that give rise to the chorion and placenta
Inner cell mass – cluster of cells at one end of blastocyst Blastocoel – hallow fluid-filled inner cavity
The First Trimester
Cleavage
Cleavage and Blastocyst Formation
Implantation Attachment of blastocyst into the uterine
endometrium The uterus is prepared for implantation by the hormone
progesterone (see reproductive and endocrine lectures)Occurs about 7 days after fertilization
Placentation Blood vessels form around blastocyst and
placenta developsThe placenta is a complex organ that permits
exchange between the maternal and embryonic circulatory systems
The First Trimester
Implantation and Placentation
GastrulationAfter implantation, cell migration transforms
blastula (single cell layer) to gastrula (3 layered structure)
Gastrulation is the generation of 3 distinct germ (cell) layers
EndodermMesodermEctoderm
The First Trimester
The Inner Cell Mass and Gastrulation
Gastrulation By day 12 surface cells move toward the primitive streak A third germ layer forms
The three germ layers are: Ectoderm – superficial cells that did not migrate
Will become integument (epidermis, hair, nail, epithelium, nose, mouth and anal canal), lense of eye, ear and nervous system
Endoderm – cells facing the blastocoele Will become liver, pancreas, thyroid, bladder, lungs, epithelium of
digestive and respiratory systems. Mesoderm – migrating cells between ectoderm and endoderm
Will become musculskeletal system, circulatory system, excretory system, gonads, connective tissue of digestive and respiratory systems, smooth and cardiac muscle.
Germ layers
Germ layers
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Germ layers
Organs and glands are consist of or include more than one germ layerAdrenal cortex is derived from mesodermAdrenal medulla is derived from ectoderm
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NeurulationBy the end of gastrulation, regions of the germ
layers begin to develop into a rudimentary nervous system
Neurulation is the process of rudimentary nervous system formation Notochord – a rod of mesodermal cells that
develop along the axis. Notochord cause ectoderm to bend inward and
form a groove Ectoderms grow on either side of the groove and then
fuse together to form a neural tube Neural tube becomes central nervous system (Brain and
spinal cord)
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Fetal Respiration Growing fetus receives oxygen and eliminates carbon
dioxide through a specialized circulatory system The two components of this system are:
Placenta Umbilical cord
Placenta and umbilical cord are outgrowths of the 4 extra-embryonic membrane (Amnion, Chorion, Allantois and yolk sac) that are formed during the development Chorion extends villi into uterine wall and these villi become
closely associated with endometrial cells Chorionic villi forms intricate branching network for maternal
blood Umbilical cord connects fetus to placenta
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Four extraembryonic membranes:Yolk sac AmnionAllantoisChorion
Extraembryonic Membranes
Extraembryonic Membranes and Placenta Formation
Extraembryonic Membranes and Placenta Formation
Extraembryonic Membranes and Placenta Formation
Yolk sac Important site of blood cell formation
Amnion Encloses fluid that surrounds and cushions developing
embryo Allantois
Eventually becomes bladder Chorion
Placenta formation begins for chorion Chorion is a membrane that completely surrounds
amnion
Embryo Anatomy
A Three-Dimensional View of Placental Structure
Trophoblast secretes hormones to maintain pregnancy Human chorionic gonadotropin (hCG) – Prevents disintegration of corpus
luteum At the ovaries corpus luteum produce progesterone
Estrogens – in addition to having role in secondary sexual characteristics it is involved in the thickening of the endometrium
Progesterone - enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus
Human Placental Lactogen (hPL) - decreases maternal insulin sensitivity, and therefore raises maternal blood glucose levels, whilst decreasing maternal glucose utilization, which helps ensure adequate fetal nutrition
Placental prolactin- stimulates the mammary glands to produce milk Increased serum concentrations of prolactin during pregnancy cause enlargement of
the mammary glands of the breasts and increases the production of milk. However, the high levels of progesterone during pregnancy stop ejection of milk.
After childbirth progesterone decreases and milk ejection initiates. Relaxin
Hormones of the placenta
Second trimesterOrgan systems increase in complexity
Third trimesterMany organ systems become fully functionalFetus undergoes largest weight changeAt end of gestation fetus and uterus push
maternal organs out of position
Second and Third Trimesters
The Second and Third Trimesters
Growth of the Uterus and Fetus
Growth of the Uterus and Fetus
Developing fetus totally dependent on maternal organsMaternal adaptations include increased
Respiratory rateTidal volumeBlood volumeNutrient and vitamin uptakeGlomerular filtration rate
Structural and Functional Changes in the UterusProgesterone inhibits uterine muscle
contraction Opposed by estrogens, oxytocin and
prostaglandinsMultiple factors interact to produce labor
contractions in uterine wall
Factors Involved in the Initiation of Labor and Delivery
Labor and Delivery
Stages of laborDilation
The cervix dilates and fetus moves toward cervical canal
Expulsion The cervix completes dilation and fetus emerges
Placental Ejection of the placenta
Goal of labor is parturition