11.4-Sexual Reproduction Flashcards
Oogenesis
Oogonium → Oogonia → Primary Oocyte [stopped in prophase I] → (loses 1st polar body) Secondary Oocyte [stopped in metaphase II]→ (loses 2nd polar body after its fertilised) Ovum
Spermatogenesis
Spermatonium → spermatogonia → primary spermatocyte → secondary spermatocyte → spermatid → spermatozoa
Sertoli Cells
Helps the spermatids to develop into spermatozoas
→ gives them nutrients and nurse them
→ can also detect cells that aren’t developing properly = can cancel them and digest
Epididymis
** Where the sperm is stored**
+ Testicle fluid = removed
+ Sperm mature here and dev. ability to swim
Where is sperm made?
In seminifourous tubules
Which cells produce testosterone to initiate spermatogenesis?
Leydig cells
Seminal Vesicles
+ adds nutrients that include fructose for respiration
+ Mucus to protect sperm
Prostate gland
+ Adds fluids that neutralise the vaginal acids and mineral ions
+ Prostoglandins = switch sperm cells on to start swimming
What happens when the spermatozoas are ready to be released?
+ The muscular contractions squeeze the epididymis to release the sperm cells into the Vas Deferens to go up!
+ It also squeezes the glands to provide nutrients and protection for the cells
Zona Pellucida
Layer of gel composed by glycoproteins
Corona Radiata
Layer of follicle cells
Acrosome vesicle
Contain enzymes required to digest its way through the ovum wall
Microtubules in the Flagellum are in what arrangement?
9+2 arrangement
Function of Protein fibres in the spermatozoa
To strengthen tail = add longitudinal rigidity and provide mechanism for propulsion
Helicle mitochondrion in spermatozoa
Synthesise ATP to provide energy for movement of tail structure
Fertilisation makes a?
Zygote
Polyspermy is?
When multiple cells enter the egg
Preventing Polyspermy Step 1: Acrosome reaction
+ The sperm must penetrate the thick cumulus mass to reach the Zona Pellucida
+ The contact betw/ the Zona Pellucida and proteins in the sperm cell membrane = trigger acrosome reaction
+ Acrosome vesicle fuse w. sperm plasma membrane and releases enzymes that digest a pathway through the Zona Pellucida
Preventing Polyspermy Step 2: Penetration of Egg Membrane
+ The acrosome reaction exposes an area of membrane on tip of the sperm that has proteins that can bind to egg membrane
+ The 1st sperm that gets through the Zona Pellucida → binds to the membrane = sperm and egg fuse
+ Sperm nucleus enters the egg cell = fertilisation!
+ Ca2+ released from egg endoplasmic reticulum
Preventing Polyspermy Step 3: The Cortical Reaction
+ Sperm causes the activation of the egg
+ Cortical Granules (vesicle located near egg membrane)
→ When egg activated = their contents released from egg by exocytosis
+ In mammals = Cortical vesicle enzymes = digest the binding proteins → no further sperm can bind
+ Enzyme also results in general hardening of Zona Pellucida
+ Release of Ca2+ ions = activates meiosis and prepare cell for completion of meiosis II and cell division
External fertilisation
+ Aquatic animals often release their gametes directly into the water
→ animals have behaviours that bring eggs in close proximity w/ sperm
What are the risks of External fertilisation (5)
\+ predation \+ Susceptibility to environmental variation \+ Temp. \+ pH fluctuations \+ pollution
Internal fertilisation
+ Terrestrial animals → or else gametes will dry out
+ Ensures sperm and ova = placed in prolonged close proximity to e.o
+ Once egg fertilised → developing embryos can be protected inside female
What happens to ovum after it is fertilised?
+ Divides by mitosis to form 2 diploid nuclei and cytoplasm = divides equally forming 2-cell embryo
+ 2-cell embryo → replicate DNA → carry out mitosis → divide again → form 4-cell embryo
= abt 48hrs
What happens to the 4-cell embryo after 48hrs?
+ Further cell division happens BUT it is unequal
→ leads to migration of cells = embryo shaped like a hollow ball
→ BLASTOCYST = not even recognisable as anything (ball of stem cells!)
What happens to the Blastocyst at 7 days after fertilisation?
+ consists of abt 125 cells
+ been moved by the cilia of cells in oviduct wall → down the oviduct
+ reached the uterus
+ Zona Pellucida = broken down → blastocyst has used up the reserves of egg = needs external food supply
Implantation
+ Blastocyst sinks into the endometrium
+ Outer layer of Blastocyst = develops finger like projections = allowing it to penetrate the endometrium
+ Also exchange materials w/ mother’s bl. = absorbing food and O2
After 8 weeks what is the embryo now called?
Fetus
→ recognisable as human and sex can be determined soon
What does pregnancy depend on?
The maintenance of the endometrium
→ which depends on the continual production of progesterone and oestrogen
In early pregnancy what hormone does the embryo produce? and what does it do?
hCG
→ stimulates the corpus luteum to continue to secrete progesterone and oestrogen
What does the placenta do?
Facilitates the exchange of materials betw/ mother and embryo
→ needed cuz the body surface area to vol. ratio = becomes smaller as fetus grows larger
What is the placenta made of?
Fetus tissues, in contact w/ maternal tissues in uterus wall
+ Fetus dev. membrane that forms amniotic sac that contains amniotic fluid → to support and protect the fetus
What is the basic functional unit of the placenta?
Placental Villus
→ increase in # during pregnancy = to cope w/ the increase demands of foetus for exchange of materials w/ mother
Where does the maternal blood flow?
In the intervillous space around the villi
Where does the foetus blood circulate?
in blood capillaries close to the surgace of each villus
How big is the distance betw/ the foetal and maternal blood?
V. small = 5μm approx.
What is the placental barrier?
Cells that separate maternal and foetal blood
→ MUST be selectively permeable = allowing some substances to pass BUT not others!
What is the chorion?
The foetal part of the placenta
Is blood in the umbilical vein oxygenated or deoxygenated?
Oxygenated
Is blood in the umbilical arteries oxygenated or deoxygenated?
Deoxygenated
By 9 weeks of the pregnancy what does the placenta secrete?
Oestrogen and Progesterone in LARGE quantities to sustain the pregnancy!
→ The Corpus Luteum is no longer needed
→ There is danger of miscarriage IF the switch fails
How does O2 and CO2 move in and out of the foetal blood past the placental barrier?
Diffusion
How does glucose move into the foetus blood past the placental barrier?
Facilitated diffusion
How do antibodies move into the foetal blood past the placental barrier?
Endocytosis
How does water move in and out of the foetal blood past the placental barrier?
Osmosis
Parturition?
Child birth
What is birth mediated by?
Positive feedback involving oestrogen and oxytocin
During pregnancy which hormone does progesterone inhibit?
Oxytocin by the pituitary gland = inhibits the contractions of muscular outer wall of the uterus (Myometrium)
At the end of pregnancy what happens to the different hormone levels?
+ Hormones produced by the foetus = signal to the placenta to STOP secreting pregesterone and therefore Oxytocin is produced.
What does oxytocin stimulate?
The contraction of muscle fibres in the Myometrium
Positive feedback mechanism of oxytocin
The contractions stimulated by oxytocin = detected by stretch-receptors = signal to pituitary gland (posterior) to secrete more oxytocin
+ Oxytocin makes contractions more freq. and more vigorous which stimulates increase secretion of more oxytocin
What does the freq. increase in contraction cause?
Gradual increase in the myometrial contractions = allowing baby to be born w/ min intensity of contractions
What causes the cervix to dilate?
Relaxation of muscle fibres
What bursts the amniotic sac?
Uterine contraction → causes amniotic fluid to pass out
What finally happens to push the baby out?
Further uterine contractions (over hrs)
Altricial species
Give birth to relatively helpless, incompletely developed young/ offspring
Precocial species
Offspring hv. open eyes, hair = immediately mobile and somewhat able to defend themselves against predators
+ Mammals w/ large body size = more likely to be precocial → correlate w/ long gestation period
