11.4: reproduction

11.4: Reproduction

11.4.1

Germinal epithelium cells (spermatogonium)

Sertoli cell

Developing spermatozoa

spermatids

Leydig cell

Each time a spermatogonium divides it may either undergo mitosis, to maintain the number of spermatogonia, or spermatogenesis.

Spermatogenesis is the production of spermatids by the process of meiosis.

Spermatogenesis begins with meiosis I to produce two haploid cells.

Each haploid cell divides again during meiosis II to produce a total of 4 spermatids.

Spermatids undergo major rearrangements of their cellular components as they differentiate into sperm.

Sertoli cells regulate the process of spermatogenesis and nourish the developing sperm.

As the spermatids develop they migrate from the outer edge of the seminiferous tubule to the lumen, the central cavity of the tubule.

Once mature, sperm are released into the lumen (at a rate of several million per day) and pushed to the epididymis where they acquire motility.

LH (secreted by pituitary gland): Stimulates the secretion of testosterone by the testes

FSH (secreted by pituitary gland): Stimulates the first division of meiosis

Testosterone (secreted by Leydig cell): Stimulates the second division of meiosis and cells to develop into sperm

Spermatogensis:

11.4.3

Secondary oocyte

Mature follicle

Secondary oocyte

Germinal epuithelium

Primary follicle

Secondary oocyte inside mature follicle

Primary follicles

Polar bodies

Gametogenesis

Spermatogenesis Oogenesis

Gametogenesis

Spermatogenesis• Mitosis in germinal

epithelium cells (spermatogonium cells)

Oogenesis• Mitosis in germinal

epithelium cells(oogonium cells)

Gametogenesis


epithelium cells (spermatogonium cells)• Some cells remain as

germinal epithelium cells and some undergo meiosis



• Some cells remain as germinal epithelium cells and some undergo meiosis

Gametogenesis




• Cell growth before meiosis




• Cell growth before meiosis

Gametogenesis




• Cell growth before meiosis• 2 divisions of meiosis to

produce spermatids [n] (not differentiated into

spermatozoa yet)

Oogenesis• Mitosis in germinal epithelium

cells(oogonium cells)


• Cell growth before meiosis• 2 divisions of meiosis to

produce eggs [n]

Gametogenesis

Spermatogenesis• Commences at puberty• Meiosis is continuous

Oogenesis• Commencing in fetal

development , a girl is born with approx 400,000 developing egg cells arrested in Prophase I (meiosis is not continuous) surrounded by a layer of follicle cells forming the primary follicle.

Gametogenesis

Spermatogenesis• Meiosis is continuous

Oogenesis• Meiosis is not continuous.• During puberty, once a month,

6-12 primary follicles develop forming two haploid nuclei [n]. Meiosis is arrested in Prophase II. Now the developing egg cell is called a secondary oocyte. As follicle grows it develops a large fluid filled cavity, now it is called a mature follice. Only one mature follicle develops per month.

Gametogenesis

Spermatogenesis• Four viable spermatids

produced per meiosis

Oogenesis• One viable egg produced

per meiosis and three polar bodies.

Gametogenesis



• Equal division of cytoplasm



• Unequal division of cytoplasm

Gametogenesis



• Equal division of cytoplasm

• Millions produced daily



• Unequal division of cytoplasm

• One egg cell on average every 28 days

Gametogenesis

Spermatogenesis• Released during ejaculation

Oogenesis• Released on about day 14 of

the menstrual cycle

11.4.6

Corona radiata

Zona pellucida

nucleus

Polar bodyCortical granules

Polar body in orange

11.4.7

Epididymis:*testicle fluids are removed and the sperm concentrated *sperm mature here and develop the ability to swim

Seminal vesicles:*adds nutrients that include fructose sugar for respiration*mucus to protect sperm in the cell

Prostate:*adds fluids that neutralise the vaginal acids

http://click4biology.info/c4b/11/prostate.htm

Spermatogenesis

Oogenesis

Location Testes Ovaries

Onset Production begins at puberty Production begins in a female fetus

Duration Meiosis 1 and 2 are continuous Meiosis stops for many years

Final products (1 diploid cell and) 4 sperm cells (1 diploid cell ànd) 1 egg 3 polar bodies

Quantity Several million sperm per day One egg per month

Mobility Self-propelling/ have flagellum Do not have flagellum

Size Sperm is much smaller than egg Egg is much larger than sperm

11.4.8

11.4.91. Attracted by a chemical signal, sperm swim up the uterus and into the oviduct.

11.4.9

2. Sperm wriggle through corona radiata cells

11.4.9

2. When the first sperm contacts the zona pellucida it triggers the acrosome reaction, in which the contents of the acrosome are released.

11.4.9

3. Proteases from the acrosome digest the zona pellucida enabling the sperm to reach the plasma membrane of the egg.

11.4.9

4. When 1 sperm finally contacts the egg, the cell membranes of egg and sperm fuse, and the sperm head is drawn into the cytoplasm of the egg.

11.4.95. As the sperm enters it triggers two changes to the egg. First, it triggers the cortical reaction which causes vesicles near the surface of the egg to harden the zona pellucida thereby preventing additional sperm from entering.

6. Second, it causes the egg to undergo a second meiotic division, producing a haploid gamete and a second polar body.

11.4.10

11.4.111. Fertilisation occurs in the oviduct. After fertilisation, the egg continues its passage along the oviduct, where the first cell divisions (mitosis) take place.

11.4.112. The first division occurs about 36 hours after fertilisation. About 24 hours later, the 2 cells divide to form 4 cells.

11.4.113. At 4 days a solid ball of cells called the morula has formed: it is no larger than the original egg.

11.4.11 4. By about 7 days there are more than 100 cells arranged around a central cavity; a stage called the blastocyst.

11.4.11

5. When the blastocyst reaches the uterus it becomes implanted in the endometrial lining, where it absorbs nutrients and thickens.

11.4.11

6. The developing embryo extends fingerlike projections into the uterus that develop into part of the placenta.

11.4.121. After an embryo implants in the uterine wall, tissues of the uterus and fetus form the placenta.

11.4.122. The placenta has 2 major functions: 1) production of estrogen & progesterone, and 2) exchange of molecules between maternal & fetal blood.Progesterone and estrogen are needed to prevent menstruation and build up the wall of the uterus.

3. The placenta begins to form when the fetus develops a villus, a finger-like growth into the uterus.

Blastocyst implanting

11.4.124. The number of villi increases steadily to meet the needs of the growing fetus.Maternal blood flows out of capillaries into inter-villous spaces surrounding each villus.Fetal capillaries are very close to the surface of each villus (within 5 µm of the maternal blood).

11.4.125. The cells separating fetal and maternal blood form a selectively permeable barrier known as the placental barrier.Microvilli project from each villus to increase surface area, which allows rapid diffusion of molecules.

11.4.126. Nutrients and O2 diffuse from maternal blood to fetal blood, and carbon dioxide diffuses from fetal blood to maternal blood.

7. Fetal blood flows toward the placenta in the umbilical artery, and away from the placenta in the umbilical vein.

11.3.4

Materials are exchanged between the maternal and fetal blood in the placents

11.4.13The fetus is supported by and protected by the amniotic fluid and amniotic sac

11.4.15 End of pregnancy

1. End of gestation: progesterone levels fall.

2. With fall of progesterone, the pituitary gland secretes the hormone oxytocin.

3. The oxytocin causes the smooth muscle in the walls of the uterus to contract and labour has begun

3. This in turn further stimulates the pituitary of the mother to release more oxytocin. POSITIVE FEEDBACK

4. The strength and frequency of the myometrial contractions is further increased.

5. The strength and frequency of the myometrial contractions is further increased.

6. In turn this further stimulates more oxytocin production

7. The process builds with stronger and stronger contractions final the child passes though the cervix and vagina to be born.Contractions continue for a further period until the placenta is delivered (after birth).

11.4: reproduction

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