Topic 22-24: Reproduction & Development Flashcards
1
Q
Describe the components of female reproductive system
A
- Ovary/ovaries: site of oogenesis
+ located in the peritoneal cavity, near the lower abdomen
+ suspended by suspensory ligament
+ not directly connected to oviduct - Fimbriae: extensions of uterine tube/oviduct/fallopian tube
+ like ribbons going over ovaries
+ cillia: hair-like structures on surface
+ like ribbons going over ovaries, eggs released by ovaries (ovulation) are captured and sweep by the cillia into the oviduct - Vagina:
+ channel connecting to the cervix and leading to the uterus
+ outer muscular layer: able to expand in child birth and intercourse
+ inner mucous layer: secretions to protect vagina and internal organs as well as facilitating copulation - External genitalia:
+ vestibule: opening entry to vagina, has 2 folds of skin around
+ has glands secreting substances for protection
2
Q
Where does successful fertilization normally occurs at?
A
Successful fertilization normally occurs at the 1st third of uterine tube
3
Q
Describe the components of male reproductive system and also incorporate the flow of sperm
A
- Testis: site of spermagenesis
- Epididymus: a tube attached to testis
+ sperm move here from testis via tubules and ductules for further maturation - Vas/Ductus deferens: if ejaculation occurs, sperm move into here
+ lots of blood vessels and nerves
+ peristalsis –> facilitate sperm to travel for a long way - Seminal vesicle: produce secretions
+ sugar fructose and nutrients (needed for the sperm to move)
+ proteins and enzymes
+ prostagladin (stimulate motality of sperm)
+ clotting agents (coagulate semen after ejaculation) - Prostate gland: 2 parts (gladular and msucular tissues)
+ citric acid (used in ATP production, needed for sperm to swim)
+ neutralizes (protect sperm from acidic vagina)
+ proteolytic enzymes (protection, breaking down clotting agents) - Bulbourethral glands:
+ mucous secretions (neutralize, lubricate urethra –> easier for sperm to travel) - Urethra: 3 regions: prostatic, membranous, penile
4
Q
Describe the process of oogenesis
A
- Ovarian follicles contain oocytes within themselves which go through different stages.
- Before birth, there are primordal germ cells differentiating into oogonia, most immature stage, which stay in the ovaries. There are around 5 million oogonia before birth but only 400,000 at birth.
- Oogonia go through mitotic division and some enlarge to become primary oocytes.
- Primary oocytes go through meiosis I, but pause at prophase I, and then stay in ovaries. Now the primary oocytes are surrounded with granulosa cells, making primordial follicles.
- When puberty come, primordial follicles become primary follicles which contain
+ primary oocytes
+ thicker layers of granulosa cells
+ zona pellucida, which is a layer between oocyte and granulosa cells - Primary follicles then become secondary follicles which contain the same as primary follicles but more:
+ antrum (cavity filled with fluid from granulosa cells)
+ outer most layer - theca - When secondary follicle mature, they become mature/Graffican follicle. When lutenising hormone (LH) peaks, the primary oocyte get released, complete meiosis I to become secondary oocyte (n) which move into uterine tube.
- If sperm is present, the secondary oocyte will finish meiosis II and become a zygote.
- The leftover granulosa cells form Corpus lutetum, which produce progesterone and some oestrogen to stimulate uterus to thicken. If no embryo implanted, the corpus lutetum is degenerated.
5
Q
What hormones are involved in regulation of reproduction in males and females?
A
- Gonadotropin releasing hormone (GnRH): from hypothalamus, promoting production of LH and FSH
- Lutenizing hormone (LH): from anterior pituitary gland, when peak resulting in ovulation
- Follicle stimulating hormone (FSH): from anterior pituitary gland
6
Q
Describe the process of spermatogenesis
A
There are seminiferous tubules in testes with germ cells which develop into spermatocytes and Sertoli cells which nourish developing germ cells.
- Spermatogonia go through mitotic division to produce more of them which happens throughout a male’s life, not before birth like in oogenesis.
- These cells will differentiate into primary spermatocytes, then via meiotic division to become secondary spermatocytes.
- Secondary spermatocytes will become spermatid via meiosis. Spermatids will differentiate to produce sperm head, midpiece, tail and become a complete sperm.
- Sperms will be released into the lumen of seminiferous tubules to the epididymus for further maturation.
7
Q
Describe the regulation of reproduction by hypothamalic-pituitary-gonadal axis in males
A
- Before puberty: Testosterone and inhibin have negative feedback loop on hypothalamus and anterior pituitary gland, inhibiting the production of GnRH, LH and FSH.
- After puberty:
+ Hypothalamus and anterior pituitary gland are matured, less sensitive to testosterone and inhibin.
+ Hypothalamus produces GnRH, inducing production of LH and FSH in anterior pituitary gland.
+ LH and FSH act on cells in testes to trigger spermatogenesis as well as secondary male characteristics
8
Q
Describe the regulation of reproduction by hypothamalic-pituitary-gonadal axis in females
A
- Before puberty: Oestrogen and progesterone inhibit the production of GnRH, LH and FSH
- After puberty:
+ Hypothalamus and anterior pituitary gland are matured, less sensitive to oestrogen, progesterone and inhibin
+ Hypothalamus produces GnRH, inducing production of LH and FSH in anterior pituitary gland.
+ LH and FSH act on cells in ovaries to trigger oogenesis, menstrual cycle as well as secondary female characteristics.
+ Developing follicles release oestrogen which reduce production of GnRH –> reduced LH and FSH
+ Some follicles don’t have enough hormones to grow –> start to die off, leave 1 dominant one
+ This dominant follicle releases more oestrogen which continues to grow higher and higher until a point when it starts to have positive feedback on the anterior pituitary gland, making it more sensitive to GnRH.
+ More LH are produced. When LH peaks, ovulation occurs.
9
Q
Describe the steps of menstrual cycle
A
- Menses (4-5 days):
+ removal of superficial layer of endometrium (uterus lining from previous cycle)
+ Low level of progesterone and estrogen - Proliferative stage:
+ The follicles start developing –> increased level of oestrogen, inhibit production of GnRH, LH and FSH –> developing follicles die, leaving 1 dominant one –> increased oestrogen, go higher
+ Eventually, oestrogen makes pituitary gland more sensitive to GnRH, increased LH which promote further development and finally ovulation (around 14 days into the cycle) - Secretory stage: secondary oocyte get released
+ Remnants of corpus luteum forms (pause other steps)
+ Secretion of mostly
~ progesterone: thickens endometrium, prepare for implatation of embryo
~ some oestrogen: both reduce activity of hypothalamus and anterior pituitary
+ Increased progesterone inhibits hypothalamus-pituitary → suppressed LH and FSH - If fertilization occurs:
+ Fully developed endometrium, ready for embryo
+ Embedded embryo has outer tropoblast layer to establish connection with the endometrium
+ The tropoblast layer secretes human chorionic ganadotropin (HCG) which helps to maintain the corpus luteum to continue secreting progesterone in order to thicken endometrium and suspend menstruation. - If no fertilization:
+ Corpus luteum is degenerated
+ Reduced progesterone will allow hypothalamus and anterior pituitary gland to operate –> increased LS, FSH –> menses
10
Q
What process do sperms have to go through in the uterus?
A
Capacitation which involves enzymic reactions with uterus secretions to stabilize acrosomal head, ready for implantation, and increase tail motality.
11
Q
How does the ovum ensure monospermy?
A
- Fast Na+ diffusion into oocyte from extracellular space
- Slow Ca2+ release by ER, initiating cell division (complete meiosis II) and trigger cortical reaction (secreting proteins to remove any sperms entering after there is already 1)
These processes also thicken the Zona Pellucida.
12
Q
What is a zygote?
A
A zygote is formed when there is fusion of the pronuclei of sperm and egg.
13
Q
Describe IVF
A
In vitro fertilization (IVF) is a process of extracting eggs and sperm, fertilize in vitro, transfer the blastocyst back into the uterus. This happens in around 3-5 days.
14
Q
Indentify and describe different stages in the growth of the fetus
A
- Fertilisation
+ Capacitation: As the sperm approaches the egg, it undergoes a process called capacitation, which involves changes in the sperm membrane that enable it to penetrate the egg.
+ Acrosome reaction: When the sperm reaches the egg, it binds to the zona pellucida, a layer of glycoproteins surrounding the egg. This triggers the acrosome reaction, in which enzymes are released from the acrosome of the sperm to digest a path through the zona pellucida.
+ Fusion of sperm and egg membranes: Once the sperm penetrates the zona pellucida, it comes into contact with the egg membrane. The membranes of the sperm and egg fuse, allowing the sperm to enter the egg.
+ Completion of meiosis: The fusion of the sperm and egg triggers the completion of meiosis in the egg, resulting in the formation of a mature ovum and the expulsion of the second polar body.
+ Formation of zygote: The nuclei of the sperm and egg fuse, resulting in the formation of a single, diploid cell called a zygote. - Cleavage
+ Cleavage: After fertilization, the zygote undergoes a series of rapid cell divisions called cleavage. These divisions do not increase the overall size of the embryo, but instead result in the formation of smaller cells called blastomeres.
+ Morula formation: As cleavage continues, the embryo develops into a solid ball of cells called a morula. The morula contains 16 to 32 blastomeres.
+ Blastocyst formation: As the morula continues to divide, a fluid-filled cavity called the blastocoel forms in the center of the embryo, creating a structure called a blastocyst. The blastocyst has an inner cell mass that will eventually develop into the embryo, and an outer layer of cells called the trophectoderm that will form the placenta.
+ Hatching: The blastocyst hatches out of the zona pellucida, which is no longer needed after blastocyst formation, and begins to prepare for implantation in the uterus.
Implantation
+ Adhesion: The trophectoderm cells of the blastocyst differentiate into two distinct cell types: the cytotrophoblast and the syncytiotrophoblast. The syncytiotrophoblast forms finger-like projections called villi, which burrow into the endometrium and establish a firm attachment to the maternal tissue.
+ Invasion: The syncytiotrophoblast continues to invade deeper into the endometrial lining, breaking down and absorbing maternal tissue as it goes. The cytotrophoblast cells also begin to differentiate and form cell columns, which help to anchor the syncytiotrophoblast to the endometrium. Also, human chorionic gonadotropin is released to maintain the progesterone and thickening of endometrium to support the fetal development.
+ Apposition: The blastocyst approaches the endometrium and loosely attaches to the surface of the endometrial lining.
+ Decidualization: The endometrial tissue surrounding the implanted blastocyst undergoes a process of differentiation called decidualization, which creates a nutrient-rich environment for the developing embryo. - Gastrulation
+ Formation of the primitive streak: The first sign of gastrulation is the formation of a groove-like structure called the primitive streak on the surface of the blastula.
+ Migration of cells: Cells at the edge of the blastula begin to migrate towards the primitive streak and move inward through the streak to form the three germ layers.
+ Formation of the endoderm: The first cells to migrate through the primitive streak form the endoderm, which gives rise to the lining of the digestive and respiratory systems.
+ Formation of the mesoderm: The next wave of cells to migrate through the primitive streak form the mesoderm, which gives rise to structures such as the muscles, bones, and circulatory system.
+ Formation of the ectoderm: The last cells to migrate through the primitive streak form the ectoderm, which gives rise to structures such as the skin, nervous system, and sense organs. - Neurulation
+ Formation of the neural plate: The first step in neurulation is the formation of the neural plate, which is a thickened region of ectodermal cells that lies above the notochord.
+ Folding of the neural plate: The neural plate then begins to fold inward along a central axis, forming a groove called the neural groove.
+ Formation of the neural tube: As the neural folds continue to grow and meet at the midline, they eventually fuse together to form the neural tube. The cells at the tip of the neural tube differentiate into the brain, while the cells further down the tube differentiate into the spinal cord.
+ Differentiation of neural crest cells: As the neural tube is forming, a group of cells breaks off from the ectoderm and migrates to other parts of the body. These cells are called neural crest cells and give rise to a variety of structures including the peripheral nervous system, the adrenal gland, and parts of the face and skull.
15
Q
What happens in 3 trimesters?
A
- 1st trimester: oragogenesis is completed
- 2nd, 3rd trimesters: growth and increase in size
