Stem cells, implantation, embryonic development Flashcards
What is a stem cell?
Cell from which all other cells with specialized functions are generated
Types:
-embryonic (pluri and toti potent)
-adult (multipotent)
-placental/cord blood
What are the some characteristics of stem cells?
-can replicate itself indefinitely
-provide unlimited sources of cells for repair of tissues e.g. bone, skin, muscle, etc
-can differentiate/produce specialised cells
What is the difference between stem and specialised cells?
When they mitotically divide;
new stem cells = proliferation
new specialised cells = differentiation
Define differentiation
Process by which dividing cells change their functional or phenotypical type
-differentiate into specialised cells
Define differentiation
Process by which dividing cells change their functional or phenotypical type
-differentiate into specialised cells
What are the two signals triggering differentiation?
-external: involving chem secretions of neighbouring cells+physical contact with neighbouring cells within microenvironment
-internal: controlled by genes
Define potency
The potential capacity of a stem cell to differentiate into different specialized cell types
What is totipotent?
Stem cells capable of developing into a new organism
-have the ability to form embryo+membranes that surround, support, nourish the embryo
What is pluripotent?
Stem cells with potential of developing into any cell/tissue founds in adults
What is multipotent?
stems cells with potential of developing into only a few cell types
-usually those found in the organ from which they derived=have a specific function
What are embryonic stem cells?
Undifferentiated cells taken from the inner cell mass of a 3-7 day old embryo
-totipotent or pluripotent as they have potential to become a wide variety of specialised cell types
What is implantation? How does it occur?
Process that enables the blastocyst to gain nourishment
-occurs after cyst has been in uterus 2-3days
-blastocyst sinks into the soft endometrium
-then absorbs nutrients from glands/blood vessels of uterine lining
Define blastocyst
A hollow cluster of dividing cells made by a fertilized egg
What are the 3 germ layers?
Endoderm
Ectoderm
Mesoderm
What is the ectoderm (outer most layer)
-epidermis
outer layer of body, skin, hair, mammary glands, nervous system
What is the mesoderm (middle layer)
Forms skeleton, muscles, connective tissue, heart, blood, urogenital tract
+stomach and intestines
What is the endoderm? (inner layer)
Forms lining of digestive system, lungs, thyroid
What occurs following implantation? (hormone production)
-blastocyst continues to develop if endometrium is maintained
-needs high levels of oestrogen+progestrone to be produced
hormones stop break down of endometrium/menstrual cycle
-corpus luteum produces oestrogen+progestrone required for support
Define corpus luteum
Cells remaining in ovary from follicle once oocyte is released
What are the embryonic membranes (2 most important)
-amnion—Surrounds the embryo, enclosing a cavity into which it secretes amniotic fluid
-chorion—Formed from the outer cells of the blastocyst and a layer of mesodermal cells
-yolk sac
-allantois
What is fertilisation?
begins following ejaculation
occurs when a sperm fuses with the egg that gets implanted in uterus of the female (becomes a zygote)
sperm travels through the fallopian tube and penetrates the zona pellucida layer of the ovum (female egg) and fuses with it which forms zygote (fertilized egg).
What is the placenta?
An organ that forms form maternal and foetal tissues during the first three months of gestation (embryo development)
Placenta functions
Immune-transports antibodies from mother into foetal blood supply so foetus has immunity to some infectious diseases
Respiratory-transports oxygen form mother to foetus and C02 from foetus to mother
Endocrine-secretes many hormones (oestrogen, progesterone, HCG) for pregnancy maintenance
Nutritional- transports nutrients (glucose, amino acids, fatty acids, vitamins, minerals, from mother’s blood to foetal blood
Excretory- transports nitrogenous wastes such as urea, uric acid, ammonia and creatinine from foetal blood to mother for excretion by kidney
Ways hormones aid pregnancy (3 main types)
HCG- Human chorionic gonadotropin helps thicken a person’s uterine lining to support a growing embryo and tells the body to stop menstruation
Oestrogen- allows the uterus and placenta to create new blood vessels and transfer nutrients to your baby.
Progesterone- helps the uterus (womb) grow during pregnancy and keeps it from having contractions.
How is a blastocyst formed and what is it?
A hollow ball of cells that surround a cavity filled with fluid.
Made following fertilisation when the original zygote has reached the uterus and has developed.
Define gonads
Primary reproductive organs that produce gametes
What is colostrum? Where is it produced?
A watery yellowish white fluid, with a high content of the mothers anti bodies, that are secreted from the breast at the time of child birth.
What are fimbriae and their function?
Finger like projection that will bring the ovum to the fallopian tube from the ovaries.
Why do maternal and foetal blood not mix?
Foetal blood circulates in the chorionic villi of the placenta whereas the mother’s blood pools in the spaces around the chorionic villi, bathing the villi in maternal blood.
The villi act as a barrier, as they are comprised of a few layers of cells however, an exchange of materials can occur via diffusion between the two blood supplies.
What is the ovarian cycle? and it’s process?
Series of events that take place within the ovaries
1. primary follicle -which begins to enlarge and divide, creating a layer of cells around the developing egg influenced by FSH
2. secondary follicle -cavity forms and production of oestrogen
3. mature follicle -secretions of these cells create a fluid filled space that gradually forces the egg to the edge of the follicle
4. when the mature follicle bursts it expels the egg (ovulation)
5. influenced by LH
What is the menstrual cycle? and it’s process?
Events occurring in the endometrium
1. ruptured follicle collapses into the corpus luteum
2. secretion of progesterone and oestrogen by corpus luteum
3. oestrogen and progesterone maintain the endometrium lining
-if fertilisation occurs: LH maintains corpus luteum for 3 months (then placenta takes over endocrine function)
-no fertilisation: scar tissue (corpus albicans) forms; hormone secretion ceases
