REPRODUCTION

IB HLCORE

Asexual Reproduction

• Asexual reproduction involves only a single animal. The animal produces offspring through repeated mitosis of cells in some part of its body.

• The offspring are, genetically identical to the parent.

Sexual Reproduction

• It requires the production of haploid gametes through meiosis.

• During fertilization, two gametes usually from separate parents fuse and give rise to a diploid individual.

• Since the offspring receives genes from each of its two parents, its genome is not identical to that of either parent.

Types OfAsexual reproduction

• Budding• Fragmentation• Regeneration• Parthenogenesis

Male Reproductive System

Female Reproductive System

Label the Parts

Female Reproductive system

Structure of female reproductive system:

• Ovaries are a pair of compact bodies located in the abdominal cavity attached to the dorsal body wall by a fold of peritoneum.

• It has been estimated that after birth, each ovary contains about 300,000 ova. But only a few reach maturity.

• The ovaries of the sexually matured female contain ova at various stages of development. The final stage is a structure called corpus luteum.

• Fallopian tube: Close to each ovary is a funnel shaped structure called Fallopian tunnel. It receives the ova as they are sent out of the ovary. The Fallopian funnel leads to a narrow tube called Fallopian tube.

• The two Fallopian tubes open behind the uterus.

Contd..

• Uterus: It is a hollow, thick walled muscular organ situated in the pelvic cavity between the bladder and the rectum. The inner lining is the mucus membrane the endometrium.

• The main function of the uterus is to prepare the endometrium to receive the fertilized ovum.

• Vagina: This is a muscular tube lined with mucus membrane connecting the cervix at the upper end and with external genitalia at the lower end. Vagina serves as a birth canal.

Ovulation

Role of hormones on the female reproductive system

• The pituitary gland produces FSH (Follicle stimulating hormone) and LH (Luteinizing hormone). These two hormones affect processes in the ovary.

• FSH stimulates the development of follicles –fluid filled sacs that contain an egg cell.

• LH stimulates follicles to become mature, release their egg (ovulation) and then develop into a structure called the corpus luteum.

• The ovary produces estrogen and progesterone.• These two hormones stimulate the development of female

secondary sexual characteristics during puberty.• They also stimulate the development of the uterus lining that is

needed during pregnancy.

THE MENSTRUAL CYCLE

• Starting at the age of puberty, human females begin a hormonal cycle known as the menstrual cycle.

• Each cycle lasts on an average, 28 days.• The purpose of this cycle is to time the release of an egg or an

ovum (ovulation) for possible fertilization and later implantation into the inner lining of the uterus. This implantation must occur when the uterine lining (the endometrium ) is rich with blood vessels.

• The highly vascular endometrium is not maintained if there is no implantation.

• The breakdown of the blood vessels leads to the menstrual bleeding.

Hormones controlling menstrual cycle:

• Hypothalamus is the regulatory centre of the menstrual cycle.

• The hypothalamus produces a hormone known as gonadotropin releasing hormone (GnRH).

• The target tissue of this hormone is the near by pituitary gland and it results in the pituitary gland producing two hormones into the blood stream- follicle stimulating hormone and luteinizing hormone. The target tissues for these two hormones are the ovaries.

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• Effects of hormones (FSH , LH, Progesterone, estrogen)on the ovaries:

• One of the effects of FSH and LH on the ovaries is to increase the production and secretion of another reproductive hormone by the follicle cells of ovaries.

• The hormone is estrogen. Estrogen enters the blood stream. It’s target tissue is the endometrium of the uterus. The result is the highly vascularized endometrium.

• Another effect of FSH and LH is the production of structures within the ovaries called the Graffian follicles.

----• A spike in the level of FSH and LH leads to ovulation. (release of

oocyte from the Graffian follicle) This enters the fallopian tube soon after ovulation.

• The outer ring of follicle cells remains within the ovary. The cells of this outer ring begins to divide and fill in the area left by ovulation and this forms a glandular structure known as corpus luteum.

• Corpus luteum is hormonally active and produces a hormone-progesterone. Progesterone is a hormone that maintains the thickened, highly vascular endometrium and the embryo will be able to implant.

• Estrogen levels rise to a peak and stimulate LH secretion by the pituitary gland.

---• High levels of estrogen and progesterone are a negative feedback

signal to the hypothalamus. The hypothalamus does not produce GnRH when these hormone levels are high. So FSH and LH remain at a level not conducive to the production of another Graffian Follicle during this time.

• IF there is no pregnancy, the corpus luteum begins to break down and then there is a decline in both progesterone and estrogen levels. As both of these levels fall, the highly vascular endometrium can no longer be maintained. The capillaries and small blood vessels begin to rupture and menstruation begins.

• The drop in progesterone and estrogen levels also signals the hypothalamus to begin secreting GnRH and thus normal menstrual cycle begins.

Hypothalamus

anterior lobe of Pituitary gland

Ovaries estrogen Progesterone

Endometrium of uterus Increased vascular tissue

Menstrual cycle• Anterior Pituitary Hormones: • Follicle Stimulating hormone (FSH)• Stimulates the development of a primary follicles (oocytes).• Increases the number of follicular cells which in turn produce oestrogens. • Produces follicular fluids.• Develops the oocyte in the follicle. • Lateinising Hormone (LH):• surges in mid cycle (12 days) to bring about ovulation. • high LH is associated with a resumption of meiosis in the oocyte. Meiosis

has been arrested in Prophase I since the embryonic stage. Only at the point of fertilisation does meiosis complete.

• stimulates the development of the corpus luteum.• Click 4 biology

• Ovarian Hormones• Oestrogen:• Stimulates the development of the endometrium (lining of the uterus)

and it associated blood supply.• During the first half of the cycle there is positive feedback through

increased sensitivity of the follicle cells to FSH (Up-regulation of receptors on the follicular cell plasma membrane).

• During the second half of the cycle (high oestrogen) there is negative feedback on FSH and LH.

• • Progesterone:• maintains the lining of the endometrium• negative feedback on FSH and LH

Menstrual cycle and Ferility• a) Follicle Stimulating Hormone (FSH) is secreted by the pituitary gland of the brain and stimulates the

development of a primary follicle.• (b) Primary follicle cells secrete oestrogen which in turn increase the secretion of FSH in a positive

feedback.• (c) The oestrogen thickens the lining of the uterus in preparation for a fertilised egg.• (d) The peak of oestrogen secretion at day 12 causes the pituitary to release a surge of LH. This loosens

the now mature egg which is released in ovulation• LH reduces the secretion of Oestrogen • LH stimulates the empty follicle to develop into the corpus luteum • • e) Progesterone and oestrogen together stop any more LH and FSH being secreted from the pituitary.

(negative feedback)• This prevents further follicle development or ovulation. • (f) Progesterone maintains the lining of the thickened endometrium in preparation for the implantation

of a fertilised egg.• (g) If implantation does not take place then the Corpus luteum degenerates and fails.• The progesterone production stops. • The endometrium breaks down and the 'menstrual period' begins • The inhibition of FSH and LH by ovarian hormones has been removed and so they begin their secretions

again of FSH. • A new cycle has begun. • .

Male Reproductive System

Male Reproductive Ssytem• It consists of a pair of testes, seminal tracts and related glands.• Testes: Testes are paired, ovoid organs lying one in each scrotal sac. The

testes are concerned with the formation of the male gamete known as spermatozoa. Each testes consists of large number of seminiferous tubules. The interstitial cells (Leydig cells) lie between the seminiferous tubules and secrete the hormone testosterone.

Male Reproductive System

• Epididymis:• The seminiferous tubules unite to form a long tubular

and highly coiled structure called epididymis which lies on the outside of each testis and attached to it. It is the main store house of sperms and becomes motile here.

• Vas deferens:• The epididymis, after arising from the testis

differentiates into a muscular tube called the vas deferens. It ascends and reaches via abdominal cavity into the pelvis opening into the urethra.

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• Seminal vesicle: These are paired tubular glands situated behind the neck of the bladder. Each seminal vesicle by its duct joins with the vas deferens of that side.

• Urethra: After leaving the urinary bladder, urethra passes through the prostrate galnd, where it is known as prostatic urethra. Urethra serves as a common passage for both urine and semen.

• Seminal vesicle, prostate gland and bulbourethral gland secrete semen.

Roles of testosterone

. determines the development of male genitalia(reproductive organs) during embryonic development.

• ensures development of secondary sexual characteristics during puberty.

• maintains the sex drive of males throughout their lifetime.

Role of Testosterone• 1. Week 7 of embryonic development, testosterone initiates the

development of male genitalia.• 2. Around mid teens, testosterone initiates the development of

secondary sexual characteristics• increase in muscle mass• increase in the length of the long bones (height)• increase in the length of the vocal cords (voice deepens)• spermatogenesis• growth of the penis and testis • 3. Post puberty testosterone maintains the production of sperm

cells and the male sex drive. • Click 4 biology

In-vitro fertilization (IVF)

• http://www.truveo.com/Medical-animation-of-egg-fertilization/id/598695294

• • http://

www.taumed.com/video/viewvideo.jsp?vid=179&cid=22050000

• Natural fertilization occurs in one of a female’s Fallopian tubes 24-48 hours after ovulation. The resulting zygote begins to divide by mitosis and takes several more days to travel down the Fallopian tube to the endometrium of the uterus. When the embryo reaches the endometrium, it has already mitotically divided many times. The embryo will then implant in the highly vascular tissue of the endometrium.

Infertility • Some couples do not achieve fertilization and pregnancy when

they wish to. This is called infertility. It maybe temporary, because the causes can be resolved, or permanent. The causes may be

• Males with low sperm counts. This can be rectified by concentrating the male sperm before being placed into the uterus of the female using a catheter.

• Males with impotence.• Females who cannot ovulate normally.• Females with blocked Fallopian tube.• stenosis (blockage) of the cervix which again can be overcome by

simple procedures and the mechanical introduction of sperm through this passage (as above).

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• Approximately one in six couples have some experience of temporary or permanent infertility. Many of these couples can be helped to have a child by in-vitro fertilization –IVF. For example blocked oviducts in a woman prevents conception, but IVF can overcome this problem. Other problems like low sperm count cannot be resolved.

• IVF. First performed by Sir Robert Winston in 1978 Oldham England. Louise Brown was the first of millions of 'test tube babies'.

Steps involved in IVF

• A drug is injected once a day for three weeks, to stop the woman’s normal menstrual cycle.

• Large doses of FSH are injected once a day or 10-12 days to stimulate the ovaries to develop many follicles. (week-4)

• HCG (human chorionic gonadotropin) is injected 36 hours before egg collection, to loosen the egg in the follicles and to make them mature.(week-5).

• The man provides semen by ejaculating into a jar. The sperms are processed to concentrate the healthiest ones. (week-5)

• The eggs are extracted from the follicles using a device inserted through the walls of the vagina.

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• Each egg is mixed with sperm in a shallow dish. The dishes are kept overnight in an incubator.

• The dishes are checked to see if fertilization has worked.• Two or three embryos are selected and placed, via a long

plastic tube, into the uterus. Any healthy embryos from culturing that are not implanted can be frozen and used later if another implantation procedure is needed. (week-7)

• A pregnancy test is done to see if any embryos have implanted. (week-7/8)

• A scan is done to see if the pregnancy is continuing normally. The heart should be visible beating. (week-9)

Steps Involved in IVF

Ethical issues concerning IVF

• Arguments for IVF:• It enables couples who would otherwise be unable to have a

children to have a family.• Embryos that are visibly not healthy in early stages of

development can be eliminated from consideration for implantation.

• Genetic screening is possible on embryos before implantation to eliminate the chance of passing on some genetic diseases.

• Any embryos that are killed during IVF are unable to feel pain or suffer, because their nervous system has not developed.

• Infertility brings great unhappiness to parents who want to have children, which in some cases can be overcome by IVF.

Ethical arguments against IVF• Embryos that are produced during culturing, but are not implanted are either

frozen or destroyed.• More embryos are produced than are needed and the spare embryos are

sometimes killed, denying them the chance of life.• IVF is an unnatural process carried out in laboratories in contrast to natural

conception occurring as a result of an act of love. Infertility should be accepted as a will of God and it is wrong to try to circumvent it by using IVF to have a child.

• There are complex legal issues concerning the use of these frozen embryos when couples split up.

• Genetic screening of embryos could lead to society choosing desirable characteristics.

• Some reproductive problems of an individual are genetically passed on and IVF bypass nature’s way of decreasing the genetic frequency of that reproductive problem.

• Multiple births and problems associated with multiple births are more likely with IVF than with natural conception.