D3.1 Reproduction

How does sexual or asexual reproduction exemplify themes of change or continuity? What changes within organisms are required for reproduction?

asexual reproduction

reproduction not involving gametes and fertilization, all offspring are genetically identical

sexual reproduction

reproduction involving the production and fusion of gametes involving two stages:

1. meiosis-special division that makes gametes with half the number of chromosomes

2. fertilization- fusion of female and male gametes to form a zygote

gamete

• haploid male or female sex cell that is able to unite with another of the other sex to form a zygote

• have unique sequence of alleles due to random assortment and crossing over

fertilization

random fusion of haploid male and female gametes to form a zygote with diploid number of chromosomes

meiosis 706

• nuclear division with daughter cells (gametes) containing half the number of chromosomes of the parent cell

• halves the normal chromosome number forming haploid cells

cytokinesis

splitting of cytoplasm in parent cell between daughter cells, following the division of the nucleus

diploid

cells with nuclei containing two sets of chromosomes

haploid

cells with nuclei containing one set of chromosomes

differences between sperm and egg

• sperm travels to egg so it is smaller and has fewer energy reserves

• many sperms must be produced so they are small

male reproductive system

• two testes situates in scrotum hanging outside the main body cavity (form optimum temp)- producing sperm and testosterone

• epididymis stores sperm and sperm ducts carry them in seminal fluid outside the body

• seminal vesicles and prostate gland

• penis containing spongy erectile tissue that can fill with blood for erection

testis

site of spermatozoa- sperm production and production of hormone testosterone

sperm

motile male gamete

sperm duct

tube carrying sperm from the epididymis to the urethra

seminal fluid (semen)

male reproductive fluid, containing spermatozoa in a liquid that supports the sperm

prostate gland

releases alkaline secretion that neutralizes and urine left in the urethra and aids sperm mobility

urethra

tube that runs from bladder to outside of the body, in males also conveys semen

penis

external male organ used for urination and sexual intercourse

female reproductive system

• ovaries near the base of abdominal cavity secrete hormones oestradiol and progesterone

• pair of oviducts that extend from uterus and open as funnels close to ovaries- they transport egg cells and are a site of fertilization

• uterus- size and shape of inverted pear has thick muscular wall and inner lining- endometrium which builds up every month for embryo

• vagina- muscular tume that can enlarge to allow entry of penis and exit of baby. it is connecsted to uerus at cervix and opens to the exterior at the vulva

oestradiol

oestrogen

ovary

female reproductive organ in which the female gametes are formed; gland which secretes oestradiol and progesterone

oviduct

tube connecting ovary to uterus; site of fertilization

uterus

the organ in which the embryo develops in female mammals

endometrium

the lining of the uterus

menstruation

shedding of the endometrium from the uterus

vagina

muscular canal leading from uterus to outside of the body

cervix

ring of muscles at neck of uterus

hormones in female reproductive system

• cyclical secretion of oestradiol and progesterone

• menstrual cycle in which concentrations of FSH and LH and oestradiol and progesterone change

• menstrual cycle consists of two cycles- ovarian and uterine

follicle-stimulating hormone FSH

hormone secreted by pituitary gland that stimulates the development of egg cell into mature ovarian folicle in the ovary

luteinizing hormone (LH)

hormone produced by pituitary gland that stimulates ovulation and corpus luteum formation

menstrual cycle

monthly cycle of ovulation and menstruation in females

ovarian cycle

monthly changes that occur to ovarian folicles leading to ovulation and formation of corpus luteum.

uterine cycle

cycle of changes to the uterus lining (approx 28 days)

hypothalamus

part of the forebrain that controls the release of FSH and LH by the anterior pituitary gland

hormone regulation in menstual cycle

1. secretion of FSH

2. growth of follicle and secretion of oestradiol

3. release of LH leading to ovulation

4. corpus luteum secretes progesterone

5. falling levels of LH and FSH allow corpus luteum to degenerate

osetradiol inhibits FSH

progesterone inhibits LH

changing levels of hormones in menstrual cycle

1. FSH secretion that stimulates development of ovarian follicle

2. developing follicle secretes oestradiol

3. oestradiol reaches peak mid cycle and inhibits further secretion of FSH, this prevents probablility that other follicles will develop (negative feedback)

4. high levels of oestradiol stimulate secretion of LH, which stimulates ovulation on day 14, ovarian follicle releases egg, LH stimulates conversion of the vacant follicle into corpus luteum

5. corpus luteum secretes progesterone and a little oestradiol

6. levels of FSH and LH decrease and allow corpus luteum to degenerate- levels of progesterone and oestradiol also fall- endometrium brakes down and is lost through vagina- falling levels of progesterone cause secretion of FSH

7. new cycle beigins

8. if the egg is fertilized then the developming embryo becomes endocrine gland and secretes a hormone thet maintains corpus luteum as an eendocrine gland- corpus luteum brakes down placenta takes over as endocrine gland and secretes osetradiol and progesterone

oestradiol

• ovarian folicle secretes it

• in uterus it stimulates build-up of endometrium for embryo

• leads to increase in FSH receptors increasing oestradiol production (positive feedback)

• reaches peak mid cycle and inhibits further secretion of FSH, this prevents probablility that other follicles will develop(negative feedback)

ovulation

release of oocyte from ovary

ovarian follicle

fluid-filled spherical sac that contains and nourishes and immature egg or oocyte

progesterone

• secreted by corpus luteum

• in uterus it continues build up of endometrium

• in pituitary gland it inhibits secretion of LH (negative feedback)

corpus luteum

a hormone-secreting structure that develops from an ovarian follicle after an oocyte has beed discharged. It degenerates after few days unless pregnancy has begun.

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