HL Reproduction in Biology

Examines 11.4.1 to 11.4.15

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Testis tissue: 11.4.1

Photo below...

  • Must be able to annotate light micrograph of testis tissue
  • Show wall of seminiferous tubule, fluid inside sem. tube, blood vessel, Sertoli and Leydig cells

FUNCTIONS

*Seminiferous tubule: production of sperm (spermatogenesis) occurs here. Made of cells, outer layer of these cells is the germinal epithelium.

*Cells w/ developed tails are spermatozoa

*Blood vessel: supply blood

*Leydig cells: secrete testosterone

*Sertoli cells: a 'nurse' cell of the testes that is part of a seminiferous tubule. It is activated by follicle-stimulating hormone. Main function is to nurture the developing sperm. In the wall of the tubule

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Spermatogenesis: 11.4.2

11.4.2 Processes involved in spermatogenesis

  • An outer layer cell called germinal epithelium divides endlessly by mitosis to produce diploid cells
  • Diploid cells grow larger and => primary spermatocytes
  • Each primary spermatocyte carries out the first division of meiosis to produce two secondary spermatocytes
  • Each secondary spermatocyte carries out the second division of meiosis to produce two spermatids
  • Spermatids become assoc. w/ Sertoli cells (help spermatids to develop into spermatozoa) = cell differentiation
  • Sperm detach from sertoli cells...eventually carried out of testis by fluid in center of tubule
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11.4.3 - 11.4.4

11.4.3 Role of LH, testosterone and FSH in spermatogenesis

Hormone Source Role

FSH: Pituitary gland: Stimulates primary spermatocytes to undergo 1st div. meiosis, to form secondary spermatocytes

Testosterone: Interstitial cells: testis Stim. develop. 2ndary spermato => mature sperm

LH: Pituitary gland: Stim. secretion of testosterone by the testis

11.4.4 is a DIAGRAM: draw this yourself and insert after this card!

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Oogenesis and prodn of semen: 11.4.5

11.4.5 Outline processes in oogenesis w/in ovary

  • In ovaries of female fetus, germinal epithelium cells divide by mitosis => diploid cells
  • Diploid cells grow into larger cells called primary oocytes
  • Primary oocytes start 1st meiosis but stop in prophase 1. PO + single layer of follicle cells form primary follicle
  • Baby girl is born, ovaries contain 400 000 primary follicles
  • Every menstrual cycle, a few primary follicles start to develop. PO completes 1st meiosis forming 2 haploid nuclei. Cytoplasm of PO is divided unequally forming a large secondary oocyte and small polar cell
  • Secondary oocyte starts 2nd meiosis but stops in prophase II. Follicle cells proliferating, follicular fluid forming
  • When mature follicle bursts at ovulation, egg released is still a secondary oocyte
  • After fertilization, secondary oocyte completes 2nd meiosis to form an ovum (w/ sperm nucleus inside) and second polar cell. 1st and 2ndpolar cells do not develop and eventually degenerate
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Fertilization 11.4.9

1. Arrival of sperm: Sperm are attracted by a chemical signal and swim up the oviduct to reach the egg. Fertilization only successful if many sperm reach the egg.

2. Binding: First sperm to break through layers of follicle cells binds to zona pellucida (triggers acrosome reaction).

3. Acrosome reaction: Contents of acrosome released by separation of the acrosomal cap from the sperm. Proteases from the acrosome digest a route for the sperm through zona pellucida, allowing sperm to reach plasma mem. of egg.

4. Fusion: Plasma mem. of sperm and egg fuse, sperm nucleus joins egg nucleus. Fusion causes cortical reaction.

5. Cortical reaction: Small vesicles (cortical granules) move to plasma mem. of egg and fuse w/ it, releasing contents by exocytosis. Enzymes from CG cause X-linking of glyco-proteins in zona p, making it hard + preventing more sperm entry.

6. Mitosis: Nuclei from the sperm and egg carry out mitosis using same centrioles and spindle of microtubules. A two-cell embryo is produced.

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11.4.6 - 11.4.7

11.4.6 is a DIAGRAM: draw this yourself and insert after this card!

11.4.7 Roles of parts in prodn of semen

Sperm from testis arrive in epididymis, unable to swim. Undergo maturing process while stored in epididymis (can now swim)

2 seminal vesicles and prostate produce and store fluids released in ***********. Fluid mixes w/ sperm and incr. vol of ejaculate. Fluid from seminal vesicles has nutrients for sperm incl. fructose. It also contains mucus which protects sperm in ******. The fluid from the prostate gland contains mineral ions and is alkaline = protects sperm from acidic conditions.

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Role of HCG: 11.4.10

11.4.10 Role of HCG in early pregnancy

After implanting in uterus wall, embryo starts to secrete HCG (human chorionic gonadotrophin). HCG prevents degeneration of corpus luteum which would happen at end of menstrual cycle. HCG stim. corpus luteum to grow and to cont. secretion of estrogen and progesterone. This is essential to allow pregnancy to continue.

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Embryo development and placenta structure: 11.4.11

11.4.11 Outline early embryo development up to implantation of blastocyst

The zygote produced by fertilization in the oviduct is a new human individual. It starts to divide by mitosis to form a 2-cell embryo, then a 4-cell embryo and so on until a hollow ball of cells called a blastocyst is formed.While these early stages in the development of the embryo are happening, the embryo is transported down the oviduct to the uterus. When it is about 7 days old, the embryo implants itself into the wall of the uterus where it cont. to grow and develop.

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Placenta structure 11.4.12-11.2.14

11.4.12 Structure and function of placenta maintain pregnancy

  • Placenta: disc-shaped structure, 185mm in diameter and 20mm thick when fully grown.
  • Placental villi: small projections that give large SA (14m2) for gas exchange and exchange of other materials. Fetal blood flows through caps of villi.
  • Inter-villous spaces: maternal blood flows thru spaces, brought by uterine arteries and carried away by u veins.
  • Endometrium: lining of uterus into which placenta grows.
  • Myometrium: muscular wall of uterus, used during childbirth.
  • Deoxygenated fetal blood: flows from the fetus to the placenta along two umbilical arteries.
  • Oxygenated feta blood: flows back to fetus from placenta along umbilical vein.

11.4.13 State that fetus is supported/protected by amniotic sac and amniotic fluid.

11.4.14 State that materials are exchanged b/w the maternal and fetal blood in the placenta.

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Compare spermatogenesis and oogenesis: 11.4.8

Many similarities between formation of sperm and eggs

  • Both start w/ proliferation of cells by mitosis
  • Both involve cell growth before meiosis
  • Both involve the two divisions of meiosis

Spermatogenesis

Millions produced daily, released during ***********, sperm formation starts in puberty, sperm prodn. continues throughout adult life, 4 sperm are produced per meiosis.

Oogenesis

One produced every 28 days, released ~day 14 of cycle by ovulation, early stages egg prodn. start in fetal development, egg prodn. becomes irregular, then stops:menopause, only one egg is produced per meiosis

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11.4.15 Process of birth and hormonal control

Through the 9 months of pregnancy, progesterone ensures that the uterus develops and sustains the growing fetus. The level of progesterone in the mother becomes increasingly high. The end of pregnancy is signalled by a fall in progesterone level. This allows the mother's body to secrete another hormone - oxytocin.

Oxytocin causes the muscle in the uterus wall to contract. Uterine contractions stimulate the secretion of ore oxytocin. The uterine contractions therefore become stronger - an example of positive feedback.

While the muscle in the wall of the uterus is contracting, the cervix relaxes and becomes wider. The amniotic sac bursts and the amniotic fluid is released. Finally, often after many hours of contractions, the baby is pushed out through the cervix and the ******. The umbilical cord is cut and the baby begins its independent life. Contractions continue for a time until the placenta is expelled.

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