Reproduction

SL and HL – Papers 1 and 2

Introduction to Reproduction

• One of the six life functions is to reproduce• In humans, the reproductive systems and

urinary systems are arranged close to each other

• Gametes – sex cells• Gonads – glands which produce gametes– Male – testes– Females - ovaries

Male Reproductive System

• Urinary tract connected to reproductive tract, through urethra

• Parts of system

• External– Penis– Scrotum

Male Reproductive System

• Internal– Testes• Produce spermatozoa and testosterone• Made up of seminiferous tubules• Tubules end in the epididymis• Inside tubules are sperm cells called spermatogonia

– Vas Deferens or sperm duct– Urethra

Male Reproductive System

– Three glands• Seminal vesicle – Prostaglandins and fructose• Prostrate gland – Alkaline solution• Cowper’s gland – Mostly mucous

– Mixture of mature sperm and seminal fluid is called semen.

Male Reproductive System

Female Reproductive System

• Urinary system and reproductive system are separate

• Parts of system• External– Labia– Vulva

Female Reproductive System

• Internal– Ovaries• Secrete estrogen, initially progesterone and egg cells

called oogonia, that mature to ova

– Fallopian tubes or oviducts• Ends – fimbriae

– Connected to the uterus• Lined by endometrium

Female Reproductive System

– Cervix – opening to the uterus– Vagina

• Endometrium clears itself every 28 days, called the menstrual cycle.

Female Reproductive System

Secondary Sexual Characteristics• Female Secondary Sexual

Characteristics• Usually around age 13, but can be

younger• Maturation of the ovaries, and

enlargement of the vagina and uterus

• Development of breasts• Widening of the pelvis• Deposition of fat under the skin of

the buttocks and thighs• Growth of pubic hair and hair

under the arm• Monthly ovulation and

menstruation• Changes in behaviour associated

with sex drive

• Male Secondary Sexual Characteristics

• Usually around age 15, but can be younger

• Development and enlargement of the testes, scrotum, penis, and glands of the reproductive tract

• Increased skeletal muscle development

• Enlargement of the larynx, deepening of the voice

• Growth of pubic hair, underarm hair, and body hair

• Continuous production of sperm• Changes in behaviour associated

with sex drive

Spermatogenesis and Hormonal Control in Males

• The process of producing sperm cells is called Spermatogenesis.

• Done by the spermatogonia that line the seminiferous tubules

• Sertoli cells nourish the developing sperm• Sperm finish maturation in epididymis

Spermatogenesis

• The start germ cells are produced • Contain the full 46 chromosomes (diploid)• Divide using mitosis • Begin to grow to create primary spermatocytes. • Primary Spermatocytes undergo Meiosis I and Meiosis

II • Form secondary spermatocytes or spermatids. • Spermatids have the correct amount of genetic

material (haploid). • Spermatids differentiate into spermatozoa, or sperm.

Mature Sperm

• Sperm are divided into three main parts – Head, Midpiece and Tail.

Hormonal Control of Spermatogenesis

• There are three hormones that control spermatogenesis:– Follicle Stimulating Hormone – FSH– Leuteinizing Hormone – LH– Testosterone

• The three hormones are all activated by

gonadotropin releasing hormone (GnRH), which is secreted by the hypothalamus.

Spermatogenesis and Hormonal Control in Males

Oogenesis and Hormonal Control in Females

• Ovaries contain follicles in varying stages of development– Follicles - where the developing oocytes are found.

• Before birth, the follicles develop into oogonia– Diploid cells (2x the normal amount of human

chromosomes undergo meiosis

• Oogonia grow into primary oocytes, which are

surrounded by a primary follicle (called zona pellucida).

Oogenesis and Hormonal Control in Females

• The primary oocyte undergoes meiosis, followed by unequal cell division

• First division creates a secondary oocyte and a polar body

• The follicle, that contains the secondary oocyte, releases it once a month to be fertilized

• This is called ovulation.

Oogenesis and Hormonal Control in Females

• Secondary oocyte is suspended until it is fertilized.

• If the secondary oocyte is fertilized as it travels down the fallopian tube, it will go through the second stage of meiosis. – ovum and a second polar body

• The ruptured follicle in the ovary forms a corpus luteum

Secondary Oocyte

Spermatogenesis and Oogenesis

Hormonal Control in Females

• In the female there are four hormones at work, during a process called the Menstrual Cycle:– Follicle Stimulating Hormone (FSH)

– Luteinizing Hormone (LH)

– Progesterone

– Estrogen

Menstrual Cycle

Compare Spermatogensis to Oogenesis, looking at the overall

process, hormones used, gametes produced and timing of

the process

Fertilization• Copulation – the act of coupling of male and

female in sexual intercourse

• Fertilization – the fusion of male and female gametes (also called conception)

• Sperm enters during copulation and fuses with the secondary oocyte, called fertilization, which will go through the last process of oogenesis.

Process of fertilization• Sperm swim up the uterus and into the oviducts. • One or more of the sperms reach the secondary oocyte.

• Sperm comes in contact with the zona pellucida.

• Head of the sperm contains the acrosome.

• Enzymes are released and the head, containing the genetic material can enter into the egg.

• This process is called capacitaiton.

Process of fertilization• The head of the sperm, which contains the

nucleus, fuses with the oocyte

• The cortical granules in the outer cytoplasm of the oocyte will release their contents through exocytosis. This is called a cortical reaction.

– Thickens the zona pellucida so that it becomes a fertilization membrane. (cannot be penetrated by other sperm cells)

Process of fertilization

• Sperm nucleus enters the oocyte, the completion of Meiosis II is triggered

• The male and female haploid nuclei come together to form the diploid nucleus of the zygote. (23 + 23 = 46)

• Fertilization is completed.

Fertilization

Early Development and Implantation• Cell goes through several cleavage divisions and forms the morula

• Morula reaches the uterus about four days after fertilization.

• Morula divides unequally, forming a blastocyst. – implants in the endometrium of the uterus about 7 days after

fertilization

• Cells on the outside of the blastocyst are called the trophoblast which grows villi into the endometrium and absorb nutrients from it.

• In about two weeks the placenta develops from the trophoblast cells.

Early Development and Implantation

• Trophoblastic cells will secrete human chorionic gonadotrophin (HCG).

• This hormone sustains the corous luteum which continue to produce progesterone, maintaining the endometrium.

Early Development and Implantation

Gestation

• The period of development in the mother’s body, lasting from conception to birth is called gestation. In humans, it is about 40 weeks.

• Embryo – The developing offspring in the first 2 months of gestation

• Fetus – development after 2 months

Gestation

• The embryo is contained, supported and protected by the amniotic sac and amniotic fluid.

The Placenta

• Develops from the trophoblast cells of the blastocyst

• Bring maternal and fetal blood supplies together

• Exchange is done by active transport and diffusio

• Connected by the umbilical cord

The Placenta

• Movement across the placenta involves: – Respiratory Gases

– Water

– Excretory products

– Antibodies

The Placenta• Placenta is an endocrine gland

• Produces HCG along with the blastocyst • HCG is to maintain the corpus luteum– secrete estrogen and progesterone for the first 16

weeks of pregnancy– corpus luteum breaks down

• Placenta secretes estrogen and progesterone.

The Placenta

Birth• About 38 weeks, the fetus is ready for birth

• Progesterone declines

• Fetus will send a signal to the extra-amniotic membranes, and prostagladins will be secreted

• The hormones will cause the wall of the uterus to contract.

Birth• Posterior pituitary releases oxytocin

• More stretching, the more oxytocin will be secreted

• Oxytocin stimulates the walls of the uterus to contract in a wave, to push the fetus down

• This process is known as labour

• Last stage of birth is the expelling of the placenta or afterbirth.

Hormonal Control of Birth and Gestation

Methods of Detection and IVF

• Pregnancy Test

• Amniocentesis

• In vitro fertilization– Ethical Issues?