Chapter 11.4 Flashcards
Gametogenesis
What is gametogenesis
Process by which diploid precursor cells undergo meiotic division to become haploid gametes
Gametogenesis
What is gametogenesis in males and what does it produce?
Spermatogenesis and produce spermatozoa
Gametogenesis
What is gametogenesis in females and what does it produce?
Oogenesis and produce ova
Gametogenesis
Where does the process of gametogenesis occur?
Gonads
Gametogenesis
What are the steps of gametogenesis?
-Multiple mitotic divisions and cell growth of precursor germ cells
-Two meiotic divisions (meiosis I and II) to produce haploid daughter cells
-Differentiation of the haploid daughter cells to produce functional gametes
Spermatogenesis
Where does spermatogenesis occur?
In the seminiferous tubules of the testes
Spermatogenesis
When does spermatogenesis occur?
Occurs at puberty where the germ line epithelium undergoes mitotic divisions to form spermatogonia
Spermatogenesis
What happens to spermatogonia after they have undergone mitosis?
They undergo cell growth to produce spermatocytes
Spermatogenesis
What happens to spermatocytes after the cell growth period?
Spermatocytes undergo two meiotic divisions to form four haploid daughter cells, spermatids
Spermatogenesis
What happens to the spermatids after the meiotic divisions?
Spermatids then undertake a process of differentiation in order to become functional sperm cells, spermatozoa
Oogensis
Where does oogenesis occur?
In the ovaries
Oogensis
When does oogenesis occur?
Begins during fetal development, when a large number of oogonia are formed by mitosis
Oogensis
What happens to the oogonia after they have undergone mitosis?
Undergo cell growth until they are large enough to undergo meiosis becoming primary oocytes
Oogensis
What happens to the primary oocytes during meiosis?
They are arrested in prophase 1 where granulosa cells surround the cells forming follicles
Oogensis
Till when are the primary oocytes stuck in prophase 1?
Until the girl hits puberty
Oogensis
What happens after the girl hits puberty?
Each month, hormones (FSH) will trigger the continued division of some of the primary oocytes
Oogensis
What would be the result of the first meiotic division?
Two cells of unequal size, one cell retains the entirety of the cytoplasm to form a secondary oocyte, while the other cell forms a polar body
Oogensis
What happens to the secondary oocyte after it has been produced by the primary oocyte?
It will start to undergo the second meiotic division and will be arrested in metaphase 2
Oogensis
What happens to the secondary oocyte after it has been trapped in metaphase 2?
Released from the ovary (ovulation) and enters into the oviduct (or fallopian tube)
Oogensis
What are the follicles formed around secondary oocyte and what do they serve?
It is a corona radiata that forms and works to nourish the seconadry oocyte
Oogensis
How will the secondary oocyte complete its second meiotic division?
If the oocyte is fertilized by a sperm, where another polar body is formed
Oogensis
What happens at the end of meiosis 2?
Mature egg form ovum, before the ovum is fused with sperm to form zygote
Differences between oogenesis and spermatogenesis
How is number of cells produced different in spermatogenesis and oogenesis?
-In spermatogenesis, the cells divide equally during meiosis to produce four functional gametes
-In oogenesis, the cells do not divide equally and as a result only one functional gamete is formed (plus 2 – 3 polar bodies)
Differences between oogenesis and spermatogenesis
How is the size of cells produced different in spermatogenesis and oogensis?
-In spermatogenesis, the cells that are formed following differentiation are all of equal size with equal amounts of cytoplasm
-In oogenesis, one daughter cell (the ovum) retains all of the cytoplasm, while the other daughter cells form polar bodies
Differences between oogenesis and spermatogenesis
How does the timing of the processes of spermatogenesis and oogensis differ?
-In spermatogenesis, the production of gametes is a continuous process that begins at puberty and continues until death
-In oogenesis, It begins before birth (prenatally) with the formation of a fixed number of primary oocytes (~40,000). It continues with the onset of puberty according to a monthly menstrual cycle. It ends when hormonal changes prevent the further continuance of the menstrual cycle (menopause)
Seminiferous Tubule
What is the role of seminiferous tubule?
The production of sperm
Seminiferous Tubule
What surrounds the tubules?
A basement membraned lined with a germline epithelium
Seminifiroues Tubule
What nourishes the matured sperm?
Sertoli cells which are found on tubule lining
Seminiferous Tubules
What resided outside of the tubules?
Leydig cells that produce testosterone
Ovary
What happens to the follicles within the ovary?
Primordial follicles will mature to form primary follicles, then secondary follicles then a dominant or Graafian follicle, which will rupture and release seconadry oocyte. The ruptured follicle will develop into corpus lutuem which will produce ovarian hormones
Sperm
What are the differnet sections of a spermatozoa?
Head, mid-piece and tail
Sperm
What is the head piece composed of?
Haploid nucleus which hold genetic information, an acrosome cap which contains hydrolytic enzymes that will penetrate jelly coat and paired centrioles which are used in order to divide
Sperm
What is the function of the midpiece?
Contains high numbers of mitochondria which provide the energy (ATP) needed for the tail to move
Egg
What are the layers surrounding the egg?
The zone pellucida (jelly coat) and corona radiata
Sperm
What is the function of the tail?
The tail (flagellum) is composed of a microtubule structure called the axoneme, which bends to facilitate movement
Egg
What is the zona pellucida?
The zona pellucida is a glycoprotein matrix which acts as a barrier to sperm entry
Egg
What is the corona radiata?
The corona radiata is an external layer of follicular cells which provide support and nourishment to the egg cell
Sperm
What is the function of the cortical granules?
Release their contents upon fertilisation to prevent polyspermy
Animal Fertilization
What is external fertilization?
Involves the fusion of gametes (egg and sperm) outside of the body of a parent
External Fertilization
Which type of animals undergo this type of fertilization?
Aquatic animals, as there environmment allows the gametes to travel. In addition, the environment is susceptible to environmental factors such as predators and pH changes. So they produce large quantity of gametes
Animal Fertilization
What is internal fertilization?
Involves the fusion of gametes (egg and sperm) inside of the body of a parent
Internal Fertilization
Which type of animals undergo this type of fertilization?
Terrestrial animals typically use internal fertilization so as to prevent exposure and desiccation of gametes or embryos, but at a potential survival cost to the parent
Human Ferilization
What are the steps of human fertilization?
Capacitation, Acrosome reaction, Cortical reaction
Capacitation
When does capacitation occur?
Capacitation occurs after ejaculation, when chemicals released by the uterus dissolve the sperm’s cholesterol coat, This improves sperm motility and destabilises the acrosome cap
Acrosome Reaction
What is the acrosome reaction?
When the sperm reaches an egg, the acrosome reaction allows the sperm to break through the surrounding jelly coat
Acrosome Reaction
How does the acrosome reaction happen?
The sperm pushes through the follicular cells of the corona radiata and binds to the zona pellucida. The acrosome vesicle fuses with the jelly coat and releases digestive enzymes which soften the glycoprotein matrix. The sperm then pushes its way through the softened jelly coat and binds to exposed docking proteins on the egg membrane. The membrane of the egg and sperm then fuse and the sperm nucleus (and centriole) enters the egg
Cortical Reaction
When does the cortical reaction occur?
The cortical reaction occurs once a sperm has successfully penetrated an egg in order to prevent polyspermy
Cortical Reaction
How does the cortical reaction happen?
Cortical granules within the egg’s cytoplasm release enzymes (via exocytosis) into the zona pellucida (jelly coat). These enzymes destroy sperm binding sites and also thicken and harden the glycoprotein matrix of the jelly coat. This prevents other sperm from being able to penetrate the egg (polyspermy), ensuring the zygote formed is diploid .
Blastocyst Formation
What happens after fertilization?
Influx of Ca2+ into the ova prompts the completion of meiosis II, where the egg and sperm nucleus fuse to form a zygote
Blastocyst Formation
What will happen to zygote if it undergoes mitotic divisions?
Form a solid ball of cells called a morula
Blastocyst Formation
What will occur to morula when it undergoes differentitaion and cavitation?
Formation of a blastocyst
Blastocyst Formation
What is the structure of the blastocyst?
An inner cell mass, A surrounding outer layer called the trophoblast, A fluid filled cavity called the blastocoele
Implantation of Blastocyst
How is the implantation of the blastocyst done?
Blastocyst breaches the jelly coat that was surrounding it and preventing its attachment to the endometrium. Digestive enzymes are released which degrade the endometrial lining, while autocrine hormones released from the blastocyst trigger its implantation into the uterine wall
**Implantation of Blastocyst **
How will the process of embryogenesis persist?
When blastocyst is implanted in uterine wall
hCG
What is hCG
Promotes the maintenance of the corpus luteum within the ovary and prevents its degeneration
hCG
From where is the hCG released?
From blastocyst once it has been implanted in uterine wall
hCG
What will happen when corpus luteum does not degenerate?
It will keep on producing estrogen and progesterone
**hCG **
What is the role of estrogen that is released from corpus luteum?
Inhibits FSH and LH production by the pituitary gland, preventing the release of more eggs from the ovaries
hCG
What is the role of progesterone that is released from corpus luteum?
Progesterone also functions to maintain the endometrium (which is nourishing the embryo) and thicken the cervix
Placenta
What is the placenta?
Functions as the life support system for the foetus
Placenta
What are the 2 key functions of placenta?
-It facilitates the exchange of materials between the mother and foetus
-It secretes hormones to maintain the pregnancy after the corpus luteum has degenerated
Structure of Placenta
What is the shape of the pacenta?
The placenta is a disc-shaped structure that nourishes the developing foetus
Structure of Placenta
From what is the placenta formed?
It is formed from the development of the trophoblast upon implantation and eventually invades the uterine wall
Structure of Placenta
What are lacunae?
Maternal blood pools via open ended arterioles into intervillous spaces within the placenta
Structure of Placenta
What are the function of the chronic villi?
Extend into lacunae and mediate the exchange of materials between the foetus and the mother
Structure of Placenta
What is the function of the umbilical cord?
Exchanged material is transported from the villi to the foetus, connects the foetus to the placenta
Material Exchange of Placenta
How does material exhange occur in the placenta?
The chorionic villi extend into the intervillous space (lacuna) and exchange materials between the mother and foetus
**Material Exchange of Placenta **
What are features that aid in the material exchange?
Chorionic villi are lined by microvilli to increase the available surface area for material exchange. Foetal capillaries within the chorionic villi lie close to the surface to minimise diffusion distance from blood in the lacunae
Material Exchange of Placenta
What materials will diffuse from lacunae to faoetal capillaries?
Oxygen, nutrients, vitamins, antibodies and water
Materila Exchange of Placenta
What materials will diffuse from lacuane into maternal blood vessels
Foetal waste (such as carbon dioxide, urea and hormones)
**Hormonal Role of Placenta **
What hormones does the placenta produce?
Estrogen and progestrone
**Hormonal Roles of Placenta **
What is the function of estrogen releases from placenta?
Estrogen stimulates the growth of uterine muscles (myometrium) and the development of the mammary glands
Hormonal Roles of Placenta
What is the function of progesterone that is released from placenta?
Progesterone maintains the endometrium, as well as reducing uterine contractions and potential maternal immune responses
Hormonal Roles of Placenta
What is the function of progesterone that is released from placenta?
Progesterone maintains the endometrium, as well as reducing uterine contractions and potential maternal immune responses
Birth Process
What is positive feedback?
Involves a response that reinforces the change detected
Birth Process
How does positive feedback used in the case of childbirth?
The detection of uterine wall stretching will lead to the release of oxytocin that induces uterine muscles to contract, reducing space in womb. This causes continous stretching until fetus is removed
**Hormonal Control in Birth Process **
What are the chemical regulators of the birth process?
Oxytocin, estriol, progesterone and prostaglandin
Hormonal Control in the Birth Process
How is estriol released?
Due to the stree induced resulting from stretches in uterine wall.
Hormonal Control in Birth Process
What is the role of estriol?
Prepares the smooth muscle of the uterus for hormonal stimulation by increasing its sensitivity to oxytocin. Inhibits progesterone, which was preventing uterine contractions from occurring while the foetus developed
Hormonal Control in Birth Process
When is oxytocin released by posterior pituitary?
When uterus is primed for childbirth
Hormonal Control of Birth Process
What is the role of oxytocin?
Stimulates the uterine muscles to contract, initiating the birthing process
Hormonal Control of Birth Process
When does the fetus release prostaglandins?
It responds to uterine contractions by releasing prostaglandins, which triggers further contractions
Hormonal Control of Birth Process
When will the contractions stop?
When labour is complete and the baby is birthed
