11.4 Sexual reproduction (HL) Flashcards
Define gametogenesis
Process by which diploid precursor cells undergo meiotic division to become haploid gametes
What is a haploid gamete?
Sex cell
What is gametogenesis in females called?
Oogenesis
What is gametogenesis in males called?
Spermatogenesis
Where are spermatoza produced?
Seminiferous tubules of the testes
When does spermatogenesis occur?
Begins at puberty
What are the steps to spermatogenesis?
Germline epithelium cells divide mitotically to produce spermatogonia
These grow into spermatocytes which undergo mitosis and differentiation to become sperms
What is the name given to a primary spermatocyte after meiosis 1?
Secondary spermatocyte
What is the name given to undifferentiated products of meiosis in spermatogenesis?
Spermatids
When does oogenesis occur?
Begins during foetal development but is not completed until after puberty
Describe the process of oogenesis and when each step occurs
Pre-natal
Oogonia undergo growth to become primary oocytes
They begin to undertake meiosis but are arrested in Prophase I and granulosa cells surround them to form follicles
Each month after puberty
FSH triggers the continued division of some cells which will complete meiosis I to form to unequally sized cells (one polar and one with more cytoplasm)
The polar body is trapped in the follicle until it degenerates and meiosis II begins but is arrested at metaphase II
The secondary oocyte is released into the oviduct where, if fertilised, meiosis II will be completed and the mature ovum will fuse it’s nucleus with that of the sperm
What is a zygote?
An ovum with a sperm cell inside where both nuclei have fused
How many gametes are produced by spermatogenesis?
4
How many gametes are produced by oogenesis?
1 (plus 2/3 polar bodies)
In which part of the seminiferous tubules do spermatogonia grow?
Top layer of cells
What nourished spermatozoa?
Sertoli cells in the seminiferous tubules
What type of follicles are primary oocytes arrested in?
Primordial follicles
What type of follicle is the dominant follicle which ruptures to give a secondary oocyte?
Graafian follicle
What happens to the follicle after the release of a secondary oocyte?
Becomes a short-lived corpus luteum which secretes ovarian hormones and eventually degenerates to a corpus albicans
Which cells produce testosterone?
Leydig cells (interstitial cells)
What are the components of a human egg cell?
Nucleus
Cytoplasm
Cortical granule
Zona pellucida (jelly coat)
Corona radiata (follicular cells) - outside the egg
What are the components of a human sperm?
Head -
Acrosome
Nucleus
Centriole
Mid piece -
Mitochondria
Tail -
Axoneme
Describe external fertilisation
Fusion of gametes outside the parental bodies
What are the three steps to human fertilisation?
Capacitation
Acrosome reaction
Cortisol reaction
What occurs during capacitation (as a step of human fertilisation)?
Chemicals in the uterus dissolve the sperm cholesterol coat to improve hyperactivity
The acrosome cap is also destabilised
What occurs during the acrosome reaction (as a step of human fertilisation)?
The sperm pushes through the corona radiata and the acrosome vesicles fuse with the jelly coat and release digestive enzymes to soften this and push through and bind to the now exposed docking proteins
The egg membrane and sperm fuse and the nucleus (and centriole) of the sperm enter the egg
What occurs during the cortical reaction (as a step of human fertilisation)?
Cortical granules in the egg cytoplasm release enzymes into the zona pellucida which thicken and harden the jelly coat to prevent polyspermy
What causes meiosis II to be completed in the ova after sperm and egg fusion?
An influx of Ca2+
Define morula
A solid ball of cells created after a zygote undergos several miotic divisions
Define bastocyst
A morula which has continued to divide and undergone differentiation and cavitation
What are the 3 distinct parts of a blastocyst?
Inner cell mass (will become an embryo)
Trophoblast (will develop into the placenta)
Blastocoele (fluid filled cavity)
When does implantation occur?
6-8 days after fertilisation the blastocyst is implanted in the endometrium where the embryo will gain oxygen and nutrients from the endometrial tissue
What is secreted by the endometrial lining after implantation of a bastocyst?
hCG
(human chorionic gonadotrophin)
What does hCG do to the corpus luteum?
Promotes its survival so it continues to secrete oestrogen and progesterone
What is the function of oestrogen in early pregnancy?
Inhibits FSH and LH production by the pituitary glands
What is the function of progesterone in early pregnancy?
Maintains the endometrium and thickens the cervix
How long are hCG levels maintained and what takes over afterwards?
8-10 weeks while the placenta develops and becomes responsible for progesterone secretion and the corpus luteum degenerates
Describe the structure of the placenta
Umbilical cord with foetal veins and arteries which branch into chorionic villus
There is then an intervillous space across which materials can diffuse
On the outside of the intervillous space are the maternal veins and arteries
What materials does the mother exchange towards the foetus?
Nutrients, oxygen, antibodies, vitamins, water
What materials does the foetus exchange back with the mother?
CO2, urea, hormones
What is the positive feedback loop involved in pregnancy?
Baby pushed cervix causing stretch -> Stretching sends a signal to the bran to release oxytocin -> Oxytocin causes contractions so that the baby pushes
What two hormones are released just before birth?
Oxytocin
Estirol
What is the function of estirol?
Inhibits progesterone which was inhibiting uterine contractions and increases muscular sensitivity to oxytocin
What hormone does the foetus release during the birthing process?
Prostaglandin
What causes longer gestation periods?
Larger animal size/mass and level of development at birth
What are the two levels of mammalian development at birth?
Altricial
Precocial
What are altricial mammals?
Generally helpless, undeveloped offspring at birth
What are precocial mammals?
More developed offspring which are mobile and generally independent
