1001NSC Lecture Notes - Lecture 11: Inner Cell Mass, Acrosome, Syncytiotrophoblast
20 Jun 2018
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Embryonic Development
Three stages in embryonic development:
Growth
Differentiation
Morphogenesis
Ovum must be fertilised within 12-24 hours
Sperm
300 million sperm in one ejaculation, only 2000 actually make it to ovum
Other are lost by leakage, killed by acidic vaginal environment, fail to penetrate, destroyed
by WBC’s in uterus
50% of sperm enter wrong fallopian tube
Sperm Capacitation
Freshly ejaculated sperm are unable or limited to fertilise the ovum as the must first
undergo a series of changes
Associated with: removal of adherent seminal plasma proteins, reorganisation of cell
membrane lipids and proteins, influx of extracellular calcium
Capacitatio:
Prior to ejaculation, membrane of sperm head contains much cholesterol
Cholesterol toughens and prevents pre-mature release of acrosomal digestive enzymes
Acidic vaginal fluid washes away cholesterol
Sperm head becomes more permeable to Ca2+ ions
Sperm mobility increases and it swims toward the ovum
Acrosomal reaction:
Release of digestive enzymes from the acrosome of sperm cell
Blocks to Polyspermy
Humans are monospermic, one sperm to fertilise one ovum
Fast block and slow block ensure monospermy
Fast block: once a sperm enters cell membrane of ovum, Na+ ions rush into ovum, ovum
becomes depolarised
Slow block: Sperm enters ovum, Ca2+ ions release into ovum, cortical granules release enzymes
which washed away other sperm
Cleavage (at 2 days):
First stage after fertilisation
First 4 cell divisions, no increase in size
Rapid cell divisions following fertilisation produce multi-cellular morula
Morula (at 3 days):
at three days, undergoes surface smoothing
Compaction:
Expression of first cell adhesion molecules, surface of embryo becomes smoother
Differentiation (at 4 days):
Separates again
Blastula (at 6 days):
Consists of outer later of cells that eventually form placenta, and inner cell mass which
forms embryo
Implantation (at 6 days):
Attachment to uterine wall
Syncytiotrophoblast grows roots and digests its way into endometrium
Gastrulation (at 2 weeks):
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Document Summary
300 million sperm in one ejaculation, only 2000 actually make it to ovum. Other are lost by leakage, killed by acidic vaginal environment, fail to penetrate, destroyed by wbc"s in uterus. Freshly ejaculated sperm are unable or limited to fertilise the ovum as the must rst undergo a series of changes. Associated with: removal of adherent seminal plasma proteins, reorganisation of cell membrane lipids and proteins, in ux of extracellular calcium. Prior to ejaculation, membrane of sperm head contains much cholesterol. Cholesterol toughens and prevents pre-mature release of acrosomal digestive enzymes. Sperm head becomes more permeable to ca2+ ions. Sperm mobility increases and it swims toward the ovum. Release of digestive enzymes from the acrosome of sperm cell. Humans are monospermic, one sperm to fertilise one ovum. Fast block: once a sperm enters cell membrane of ovum, na+ ions rush into ovum, ovum becomes depolarised.
