making egg and sperm & development and birth Flashcards
Mitosis
- 4 stages (+ interphase)
- somatic cells
- produces 2 diploid daughters
- gen. var. does not change
- no. of chromosomes stay the same
Meiosis
- 8 stages (+ interphase)
- germ/sex cells
- produces 4 haploid daughter cells
- gen. var. increases
- no. of chromosomes is halved
Female reproductive system
- Ovaries open into peritoneal cavity
- Fimbriae direct ovum in uterine tube/fallopian tube/oviduct
- Successful fertilisation normally occurs in the first third of the uterine tube
- Vagina
Male reproductive system
Testis and scrotum
Epididymis
Vas deferens or ductus deferens
Urethra
Seminal vesicles
- Prostaglandin, stimulate motility of sperm
- Fructose, nutrient source for the sperm
- Clotting agents (different from blood), coagulates semen after ejaculation
Prostate gland
- Citric acid, used by sperm in ATP production (energy)
- Proteolytic enzymes, eventually breakdown clotting agents
Bulbourethral (Cowper’s) glands
- Mucous (released pre-ejaculation), lubricate urethra and end of penis to prevent damage to sperm
- Alkaline fluid, neutralise acidity of urethra
Vagina
channel connecting to the cervix
Spermatogenesis
the process of sperm cell formation that occurs in the seminiferous tubules of the testes in males
seminiferous tubules
coiled tubes, the walls of which contain cells that produce sperm
Sperm. Proliferative phase:
- Undifferentiated germ cells (spermatogonia) undergo mitotic divisions to increase their numbers.
- As a result, some of the spermatogonia become primary spermatocytes, which enter the meiotic phase.
Sperm. Meiotic phase:
- primary spermatocytes undergo two successive meiotic divisions to produce four haploid cells called spermatids.
- Each spermatid contains half the genetic material of the original primary spermatocyte.
Spermatid differentiation
the process by which immature, haploid cells called spermatids transform into mature, highly specialised sperm cells during the final phase of spermatogenesis
1.Formation of the acrosome:
- Acrosome: specialised organelle that covers the head of the mature sperm and contains enzymes needed for fertilisation.
- During spermatid differentiation, a vesicle derived from the Golgi apparatus fuses with the nuclear envelope to form the acrosome.
2.Elongation and condensation of the nucleus:
The spermatid nucleus becomes highly condensed and elongated to form the head of the mature sperm.
3.Formation of the flagellum:
- Flagellum: long, whip-like structure that propels the sperm.
- During spermatid differentiation, a centriole at the base of the cell elongates and forms the axoneme, the core of the flagellum.
4.Shedding of excess cytoplasm:
- Immature spermatids contain a large amount of excess cytoplasm, which is removed during spermatid differentiation to create a streamlined shape for easier movement.
Oogenesis
- process of egg cell formation in females.
- It occurs in the ovaries and begins during foetal development, but most of the process occurs after puberty and continues until menopause.
Ovaries
- Suspended by ligaments
- Ovarian follicle containing - Oocyte, blood vessels, lymphatic vessels and nerves
Oog. Proliferative Phase:
- Begins during foetal development when the primordial germ cells divide and differentiate into oogonia, which are the precursor cells of eggs.
- Oogonia undergo mitotic divisions to increase their numbers and form primary oocytes.
Oog. Meiotic Phase:
- Paused at prophase I of meiosis until puberty.
- At puberty, a small number of primary oocytes are stimulated to resume meiosis I.
- One of these primary oocytes is released from the ovary during each menstrual cycle and begins meiosis II, which is only completed if the egg is fertilised.
- Meiosis results in the production of one mature egg and three nonfunctional polar bodies.
Oog. Differentiation Phase:
- Occurs after fertilisation or after the primary oocyte has completed meiosis II to produce a mature egg.
- The egg undergoes further differentiation, during which it acquires the necessary organelles and molecular machinery to support early embryonic development.
The hormones in males (before puberty)
Testosterone and Inhibin inhibit:
* GnRH (secreted by immature hypothalamus) and,
* Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) secretion by the anterior pituitary gland
The hormones in males (puberty)
- Begins 12-14yrs old
- Hypothalamus maturation reduces sensitivity to testosterone and inhibin
- GnRH secretion that increases Luteinizing hormone (LH) and follicle stimulating hormone (FSH)
- Enlargement of reproductive organs and development of secondary male characteristics
The hormones in females (before puberty)
- Oestrogen and progesterone (ovaries) negative-feedback
- Low GnRH (immature hypothalamus), low LH and FSH (anterior pituitary)
The hormones in females (puberty)
- Begins 11-13yrs old
- Maturation of hypothalamus: high GnRH, high LH and FSH
- decrease negative-feedback of oestrogen and progesterone
- oestrogen production increased by developing follicle
- Enlargement of reproductive organs and development of secondary female characteristics
Menses
(4-5 days)
removal of superficial layer of endometrium
Day 1 of cycle – first full day bleeding
Proliferative Stage (menstrual)
- Sustained increase in oestrogen stimulates GnRH secretion by hypothalamus
- GnRH triggers LH and FSH secretion from anterior pituitary
- FSH stimulates oestrogen prod. by develop. follicles, results in positive feedback
- Large increase in LH triggers ovulation (approx.day 14) which is the start of the secretory stage
Secretory Stage, Corpus luteum
- Secretes progesterone and small amounts of oestrogen
- Progesterone thickens endometrium and causes fluid secretion (nutrients for embryo)
- Progesterone and oestrogen inhibit hypothalamus and anterior pituitary and hence LH and FSH secretion decline after ovulation
If fertilisation…
(7-8 days after ovulation)
* Endometrium becomes fully developed
* Human chorionic gonadotropin (HCG) production by the trophoblasts during implantation of the embryo which maintains corpus luteum
If no fertilisation…
(menses)
* Endometrium sloughed
* Corpus luteum degenerates, reducing progesterone
* Increase FSH
Fertilisation Day 0
- Preventing polyspermy
Two mechanisms prevent more than one sperm:
- Fast block (Na+) diffuses into oocyte from extracellular space, and
- Slow block (Ca2+) release by ER, initiate cell division (complete meiosis) and trigger cortical reaction
Zygote
Formed when pronuclei of sperm and egg fuse
Cleavage Day 1 to 6
repeated mitotic division as the embryo migrates down the oviduct to the uterus
Implantation Day 7 to 10
The developing embryo attaches to the lining of the uterus and begins to receive nutrients and oxygen from the mother’s blood supply.
Gastrulation Day 12
- The inner cell mass of the blastocyst undergoes complex cellular and molecular changes that result in the formation of the three germ layers: the endoderm, mesoderm, and ectoderm.
- These germ layers will give rise to all the different tissues and organs of the body.
Neurulation Day 18
- Ectoderm differentiates into the neural plate, which will eventually give rise to the central nervous system (CNS)
-
Folding of neural tube determines position of:
Grey matter (unmyelinated neurons and cell bodies) and
White matter (myelinated neurons) in CNS
Organogenesis begins around 3 to 8 weeks and continues until birth
Depends on the development of different organs
Brain: week 3
Heart: week 3, the 4 chambers formed in week 7
Kidneys: week 9
* From fertilisation to week 7 a developing human is referred to as an embryo.
* From week 8 to birth, the developing human is called a foetus
Gestation 280 Days
… 40 weeks or 9 months (3 trimesters)
Parturition
- Dilation of the cervix (contractions of the uterine muscles)
- Descent and expulsion of the baby through the birth canal
- Delivery of the placenta.
Developmental origins of health and disease
the exposure to environmental factors during gestation (prenatal) and the first year after birth (perinatal) will determine the development of human diseases in adulthood
Which of the following best describes the feedback mechanism between the gonads and the hypothalamus/pituitary gland in females?
It is sometimes positive feedback and sometimes negative feedback
Gonads
glands that produce hormones that are involved in reproduction and other functions of the body
chimera
a single organism composed of cells with more than one distinct genotype
embyonic development
- Production of a polar body through meiosis II
- Mitosis
- Leaving the zona pellucida
- Implantation
The stages of embryonic development
Zygote > Morula > Blastocyst > Gastrula
The largest number of oocytes are produced in the ovaries during which period of life:
birth
Which is the first developmental stage when all three cell layers are present?
gastrula
