Human development in-utero Flashcards
What is a zygote?
Fusion of gametes to 16 cells.
What is a morula?
Day 3- clump of cells undergoing mitosis.
What is a blastocyst?
Day 4/5-20- inner cell mass to bilaminar disc
What is an embryo?
21- 56- from somites to organogenesis.
What is a foetus?
Week 9- birth.
What is the outer layer of the ovum?
Corona radiata.
What is the middle layer of the ovum?
Zona pellucida.
What is the inner layer of the ovum?
Cortical granule.
Why is the acrosome part of the sperm important?
Secretes enzyme that attacks the corona radiata.
Can 1 sperm penetrate the corona radiata?
No, takes many sperm to release enough enzyme to penetrate.
What is the process of fertilisation?
-after penetrating corona radiata, binds plasma membrane of ovum and enters cell
-depolarisation of cell membrane and release of Ca2+ ions prevent polyspermy
-genetic info of sperm fuses with ovum to complete fertilisation
What kind of cells are sperm and egg cells?
Haploid cells.
What kind of the cell is the newly formed zygote?
Diploid cell.
What is the meaning of cleavage?
Mitotic divison (1 cell to 2 cells etc).
What is the process of cleavage?
-2-3 hrs after = 2 cells
-1 day after= 4 cells
-2 days after= 8 cells
-3 days after= 16 cells (morula)
What are some features of the morula?
Remains with the zone pellucida (prevents implantation in fallopian tubes due to smooth surface).
What are the 3 layers of the blastocyst?
-outer layer (trophoblast)
-inner cell mass
-blastocystic cavity
What does the inner cell mass differentiate into?
Epiblast and hypoblast (form bilaminar disc).
What does the bilaminar disc differentiate into?
Endoderm, mesoderm and ectoderm (primary germ layers).
Where does the blastocyst embed into?
Upper posterior wall of the uterus.
What is decidualisation?
Process of the endometrium getting ready for implantation (growth factor).
What firstly supplies the blastocyst with nutrients?
Endometrial glands- accumulate glycogen, growth factor proteins.
What initially makes contact with endometrium?
The trophoblast cells.
How do you make sure the blastocyst is properly implanted?
Cytotrophoblast and syncitiotrophoblast (blastocyst then enveloped by folds of endometrium and the trophoblast cells proliferate).
What is the trophoblast?
The outer surface of the blastocyst (becomes the fatal part of the placenta).
What does the inner cell mass of the blastocyst become?
The foetus.
What is the decidua basalis?
Maternal part of the placenta is formed from the endometrium where implantation occurred.
What is produced by the trophoblast cells to maintain the corpus luteum?
The hCG hormone.
What is gastrulation?
Where the cells in the embryo begin to fold back on themselves to create a cavity.
The amnion (inner membrane surrounding the foetus) begins to develop.
When is gastrulation complete?
When the 3 germ layers are present (formed from the bilaminar disc).
What does the ectoderm become?
The brain, spinal cord and skin (mammary glands, pituitary glands, enamel)
What does the mesoderm become?
The skeleton, muscle kidneys and heart (cartilage, gonads, spleen).
What does the endoderm become?
The GI tract and lungs (resp system).
Where does the primitive axis of the body come from?
The notochord (any problems with the cord will happen here).
What is neuralation?
Neural tube and neural crest form from the primitive streak.
Why is folic acid supplement suggested for women trying to get pregnant?
This helps with the neural tube development.
What else happens during gastrulation?
Secondary and tertiary chorionic villi begin to form (important for the placenta).
What is the chorion?
Part of the placenta and facilitates exchange of gases, nutrients and waste.
What does the amnion contain?
Fluid that cushions and protects the embryo.
What does the extra-embryonic membrane consist of?
Chorion, blood cells in yolk sac, blood vessels in allantois, amnion.
What is the allantois?
Temporary respiratory organ and store for foetal excretions.
How do nutrients reach the embryo?
Are passed across the placenta (4 layers of cells so blood will never meet).
What happens to the embryo from day 21 onwards?
-organogenesis
-heart is the 1st organ to function
-neural tube closes
-somite development (muscle and vertebrae).
How is foetal circulation different?
Blood is exchange between the atria through the foramen ovale (when born, this closes and becomes fossa ovalis).
What day is blood in embryo?
18.
What day does basic blood circulation happen in the embryo?
25.
How is the heart formed in the mesoderm?
Intraembryonic coelom (horseshoe shape) formed. Then separates into 2 layers.
-1 endocardial tube on each side and develop blood islands
-tubes meet, grow and twist (communications between them).
How do the lungs develop?
-28= tracheo-oesphageal fold
-budding to develop bronchi
-weeks 5-17= glands
-weeks 16-25= growth of capillary networks
-week 24- birth terminal sac
How is the gut developed?
-day 28- tube from mouth to anus and bulges start to form (stomach)
-day 40- proliferation and series of rotations
-liver and gall bladder develops from buds.
What happens weeks 9-12 for foetal development?
-eyelids meet, fingernails, gut develops
-fetal CRL
-uterus still pelvic organ
Weeks 13-16 for foetal development?
-bones harden, start growing hair, uterus now abdominal organ (less morning sickness).
Weeks 17-20 for foetal development?
-sebaceous glands present (vernix- absorbed into skin, covers and protects whilst in utero)
-myelination of spinal cord (allow nerve impulses to travel)
-screening offered for congenital heart defects.
Weeks 21-25 for foetal development?
-viability week 24 (lungs not fully developed)
Weeks 26-29 for foetal development?
-eyes open, scalp hair, testes in scrotum, skin thickens.
Week 30 onwards for foetal development?
Growth
-brain myelination, lungs fully developed, fat stores established (keep warm until feeding).
What is the purpose of surfactant in the lungs?
Prevent alveoli from collapsing.
What is zygote nourished by until placenta established?
Uterine secretions.
What is the purpose of the placenta secreting progesterone?
Prevents uterine contractions.
Which hormones promote these uterine contractions after week 40?
Oestrogen and oxytocin (progesterone secretion stops).
What is the placenta made up of?
Embryonic tissue and uterine wall.
What is the purpose of the chorionic villi of the chorion?
Facilitate exchange between foetus and mother.
What is the purpose of the umbilical cord?
Carry fetal blood to and from the placenta (fetal and maternal blood do not mix). However, some viruses can cross the placenta.
What is the purpose of the placenta?
-allow diffusion of o2, nutrients and waste
-remove waste
-protective barrier against microorganisms
-produce hormones
What does FSH do?
-stimulate maturation of follicle
-stimulates production of oestrogen.
What does LH do?
-stimulate maturation of follicle, ovulation
-production of oestrogen and progesterone
What does Oestrogen do?
-growth of reproductive organs
-promotes proliferative of cycle
-growth of uterus and mammary glands
-female libido
What does progesterone do?
-growth of breasts
-promotes secretary phase
-quiets the myometrium
-enhances mammary glands to produce milk
-increases body temp
What does hCG do?
-maintain corpus luteum
What does prolactin do?
-milk production
-inhibits FSH release
What does relaxin?
Flexibility of tissues.
What does oxytocin do?
Uterine contractions during labour.
What is the 1st stage of labour?
-regular painful contractions until cervix reaches full dilation.
What is the 2nd stage of labour?
-from full dilation until explosion of foetus.
What is the 3rd stage of labour?
-from expulsion of foetus until placenta and membranes are delivered.
Where does fertilisation occur?
Vagina.
What is fast block to polyspermy?
Depolarise.
What is slow block to polyspermy?
Release of Ca2+.
What do cytotrophoblast cells contribute to the formation of?
The placenta.
What does the lucunar stage mark the start of?
The uteroplacental circulation (allows passage of material blood and secretions from surrounding uterine glands).
What is the notochord?
This is the tube of cells that begin to form within the mesoderm layer.
What does the head, trunk and limbs develop from?
The paraxial mesoderm.
What ruptures to form the urogenital and anal openings?
The oropharyngeal membrane.
What is a teratogen?
Chemical or environmental agents that can induce abnormalities to development to foetus.
Which weeks is a teratogen most likely to induce abnormalities?
3-5 weeks.
