developement and ageing Flashcards
Fertilisation
the union of haploid genetic material to form a single diploid nucleus
- peristaltic contraction and wave-like motion of cilia transport the oocyte down the uterine tube towards the uterus.
- sperm swim up the female reproductive tract into the uterine tube by the flagella tails
capacitation of sperm
the physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg.
capacitation of ejaculated sperm
- leak from the vagina
- destroyed by the acidity
- fail to pass through the cervix
why does sperm require capacitation in the oviduct?
- normally inactive
- lower membrane fluidity via loss of cholesterol
- protein and carbohydratesremovals = allows interaction with ovum membrane
-altered membrane potential - allows ca2+ entry for acrosomal entry
-
how does sperm migrate through the reproductive tract
chemotaxis
can only pass through cervical mucous at late follicular stage
For fertilisation to occur?
- sperm must penetrate approaching oocyte
- penetrate corona radiata
- cross zona pellucida
- cross oocyte membrane
Acrosomal reaction
release of digestive enzymes = allows sperm to cross zp and for sperms nucleus to enter oocyte.
cortisol reaction
prevents polyspermy = rapid activation of cortical granules to release hydrolytic enzymes, preventing further sperm entry
zygote
- from fertilisation to the end of the second week
- cell division creates a blastocyst that migrates along the oviduct to the uterus
- implantation
embryo
- weeks 3-8
- all principal adults organs, body cavities, limbs and facial development begins
- period of organogenesis (formation of organs)
foetus
- weeks 9 to birth
- placenta becomes fully functional
- major period of growth
formation of zygote
- sperm must penetrate the outer layers of the oocyte
- when sperm bind to zona pellucida acrosome contents are released (acrosomal reaction)
- sperm fuses with secondary oocyte
cortical reaction - granules release chemicals to change ZP preventing other sperm from entering
oocyte complexes meiosis (expulsion of polar body).
events of fertilisation
- oocyte at ovulation
- fertilisation and oocyte activation
- pronucleus formation begins
- spindle formation and cleavage preparation
- amphimixis occurs and cleavage begins
- cytokenesis begins
early rapid mitotic cell division of a zygote
cleavage
morula
successive cleavages produce solid mass of cells
- as the number of morula increases, it moves from the site of fertilisation down the uterine tube towards the uterus and enters the uterine cavity.
Blastocyst
morula develops into a blastocyst
At the end of the zygote
- embryonic disc has formed
- yolk sac and chorion are seen
- implantation is complete
- lacunae have started forming in the endometrium
Embyro
- weeks 3-8
- major period of organeogenesis
- sexual differentiation initiated
- placenta fully developed
- cell proliferation, differentiation, migration and programmed cell death
What happens at a week 3?
- allontois begins to forms (from yolk sac, grows towards all of blastocyst)
- chrorion formation
mesoderm surrounds blastocyst - starts too see cellular differentiation
- gastrulation occurs (folding of embyronic cells)
ectoderm
bran, spinal chord, hair, nails
mesoderm
intermediate layer
endoderm
epithelial lining
What is the allantois
extends into umbilical stalk and forms part of urinary bladder
Amnion
- thin membrane which surrounds the embyro
- fills with fluid - filtrate of maternal of maternal blood and foetal urine
- shock development, temperature regulation, prevents adhesions
yolk sac
- transfer nutrients to the embryo - needed before the placenta and the umbilical cord have formed.
- site of early blood protection
- develops into gonadal stem cells which migrate into embryo
Chorion
- develops into placenta
- secretes hcg
- will develop to contain blood vessels
- blood vessels anastomose with umical cord vessels
Allontois
- participates in gas exchange and waste removal early in pregnancy
How does embryo sexual differentiates?
- all embryos starts female
- initially have Mullerian ducts and wolferian ducts
- At 10 weeks (females) wolfian ducts degenerates (begins oogenesis)
- At week 8 in males - sky gene activates.
The release of anti-mullerian hormone initiates degeneration of Mullerian ducts.
Release of DHT = development of male reproductive structures
Foetus stage
- week 9 to birth
- major period of growth
- teratogens harms the development
change in chorion in hormone
- from day 8 until 4 months secretes hcg
- hcg maintains corpus luteum
- corpus luteum produces progesterone and oestrogen, preventing menstruation and ovulation
- progesterone suppresses myometrium contractions
change in hormone production in the placenta?
- by 4 months produces progesterone and oestrogen, corpus luteum is no longer necessary
- becomes a major endocrine organ
maternal changes during pregnancy?
- weight gain
- increase heart rate
- increase blood volume
- increase cardiac output
- increased ventilation
- GI tract compressed causing heartburn and constipation
Paturition (labour)
Labour begins when progesterone’s inhibition is overcome by an increase in oestrogen levels
- progesterone inhibits uterine interaction
- progesterone secretion plateaus
- late in pregnancy = placenta produces large amounts of oestrogen
- oestrogen overcome progesterone and labour begins
positive feedback during labour
- uterine contractions force the foetal head into cervix
- stretch receptors send nerve impulses to the hypothalamus causing the release of oxytocin
- oxytocin = more contractions producing more stretch of cervix
stages of birth
- Dilation
- Expulsion
- Placental stage
post-partum period
the period following delivery of the baby and the placenta
- reproductive organs return to normal state
- uterus decreases in size
- uterine discharge of blood for 2-4 weeks
Milk let down reflex
milk production stimulated by prolactin, release in response to oxytocin and inhibition of production by progesterone.
role of oxytocin
causes release of milk into mammary glands
stages of life
- neonatal
- infancy
- childhood
- adolescence
- adulthood
- senescence
senescence
decline in function in most systems
menopause
loss of menstrual cycle - exhausted follicle supply and loss of oestrogen production
andropause
reduced testestrone
programed ageing
cell has a limited amount of divisions.
- telomeres shorten to prevent chromosomal damage
- once telomeres are ‘used’ genetic material is degraded
- telomeres repairs telomeres in young
non-programmed ageing
- cells and DNA are damaged overtime
due to cells divisions and environmental factors e.g. UV damage
