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Human Reproduction

Male Reproductive System

Testes

Gonad: organ that produces sex cells in animals.

Testes are male gonads.

Develop inside the body first but descend into the scrotum few weeks before birth.

Epididymis

  • Seminiferous tubules joint to form epididymis.

  • Sperm are matured and stored here.

Testes, Sperm Duct and Urethra

  • Epididymis leads to sperm duct (vas deferens).

  • Sperm duct takes sperm to urethra.

  • Urethra is dual functioning.

Male Reproductive Glands

  • Seminal vesicle

  • Prostate gland

  • Cowper’s gland

    • These glands produce seminal fluid which nourishes the sperm and provides a medium in which to swim.

Sperm Structure

  • Sperm and egg producing cells are diploid.

  • Divide by meiosis to form sperm and egg cells.

  • Sperm and egg are therefore haploid.

Male Hormone

Testosterone

  • Responsible for the development of the primary and secondary male sexual characteristics.

  • Primary sexual characteristics are presence of reproductive parts.

  • Secondary sexual characteristics refer to features other than sex organs that distinguish males from females.

Male Secondary Sexual Characteristics

  • Growth of pubic, facial and body hair.

  • Enlargement of larynx and ‘breaking’ of voice.

  • Increased muscular development and bone development.

  • Growth spurt at puberty.

  • Increased secretion of sebum in skin.

Female Reproductive System

The Ovary

  • These produce eggs and female hormones.

  • All eggs in the ovary are present at birth.

  • After puberty 20 eggs mature each month, only one will be released while the rest die.

The Fallopian Tube (oviduct)

  • Fallopian tubes are muscular.

  • Funnels at the tip of each tube catch the egg after it is released from the ovary.

  • The egg is moved along the tube by cilia and musuclar peristalsis.

  • The egg is either fertilised or dies in the fallopian tube.

The Uterus (womb)

  • Muscular structure

  • Outer wall made of involuntary muscle.

  • Inner lining is called the endometrium.

  • This lining thickens each month with cells and blood vessels to nourish the embryo.

Vagina

  • Elastic muscular tube 10cm long.

  • Holds penis during sexual intercourse.

  • Forms the birth canal.

  • Lined with cells that produce mucous. This serves to protect against entry of pathogens.

Female Hormones

Oestrogen and Progesterone

  • Cause maturing and enlargement of breasts.

  • Widening of pelvis to allow for birth.

  • Growth of pubic and underarm hair.

  • Growth spurt.

Ovary

  • Produce hormones and egg.

  • When meiosis of eggs is complete, egg is surrounded within a structure called the Graafian follicle.

  • Produces oestrogen.

  • After ovulation the follicle fills with yellow cells and becomes the corpus luteum.

  • Secretes progesterone.

Menstrual Cycle

  • 28 day sequence of events that produces an egg and prepares the body for pregnancy.

  • Begins at puberty and ends at menopause.

Days 1-5

  • Old endometrium breaks down and sheds, referred to as menstruation.

  • New egg produced in ovary by meiosis.

Days 6-14

  • Oestrogen produced by Graafian follicle.

    • Builds up endometrium

    • Prevents development of more eggs

Day 14

  • Ovulation occurs when Graafian follicle bursts to release egg into fallopian tube.

Day 14-28

  • Graafian follicle develops into corpus luteum.

    • Thickens endometrium.

    • Also prevents new eggs forming.

  • Egg that is released by day 16 is dead if it is not fertilised. Days 12-16 are known as fertile window.

  • If fertilisation does not take place corpeus luteum degenerates around day 22, results in a reduction of progesterone levels. Lining of uterus breaks down again on day 28 and menstrual cycle beings on day 1.

Menstrual Disorder

Fibroids

  • Tumours of the uterus.

  • Result of overproduction of cells.

  • Benign

  • Slow growing, often asymptomatic if small.

  • Common between age 35-45.

  • As they enlarge, they produce heavy and prolonged menstrual bleeding.

    • Leads to anaemia, pain, miscarriage, infertility.

Cause

  • Unknown

  • Possibly in response to oestrogen

Treatment

  • Small fibroids - monitor frequently

  • Large fibroids - surgery

  • Hysterectomoy

Copulation

Sexual Arousal

  • Penis erect

  • Vagina lubricated

Act of Copulating

  • Penis is inserted into and moved inside vagina

Orgasm

  • Sperm is released fro the penis (ejaculation).

  • Contraction of vagina and uterus.

Insemination

  • Release of sperm into the female.

  • Contractions of uterus and fallopian tubes move sperm to fallopian tubes within 5 minutes.

  • If an egg is present it uses chemotaxis to attract sperm.

Fertilisation

Fusion of egg and sperm nuclei to form diploid zygote.

  • Acrosome releases enzymes to digest the egg membrane.

  • A number of sperm may reach the egg at the same time.

  • Sperm loses its tail and the head enters the egg.

  • Sperm and egg nuclei fuse to form zygote.

  • Chemical reaction of membrane prevents other sperm entering.

Implantation

Embedding of the fertilised egg into the lining of the uterus.

  • Occurs 6-9 days after fertilisation.

  • Zygote has grown into embryo.

  • Amnion develops around embryo, secretes amniotic fluid which surrounds embryo and acts as a shock absorber.

  • Placenta forms after

Placenta Formation

  • After implantation embryo forms chorion.

  • This develops projections (chorionic villi) which forms placenta with the blood vessels of the mother in the endometrium.

  • Placenta allows nutrients, wastes, gases, antibodies and hormones to be exchanged between the blood of the mother and the embryo.

  • Blood of mother and embryo don’t mix as:

    • Blood groups might not be compatible

    • Blood pressure of mother’s system may cause damage to embryo.

    • Placenta makes progesterone.

    • Umbilical cord connects placenta with embryo. Contains blood vessels which circulate blood between embryo and placenta.

Zygote Development

  • Zygote contains 46 chromosomes, 23 from egg, 23 from sperm.

  • Divides rapidly by mitosis to grow.

  • Referred to as morula.

  • Morula forms hollow ball of cells called blastocyst.

  • Outer layer of blastocyst forms trophoblast, later develops into placenta and amnion.

  • Blastocyst contains stem cells.

  • Blastocyst moves along fallopian tube and attaches to endometrium.

  • Conception is successful fertilisation and implantation of fertilised egg.

  • Marks beginning of pregnancy.

Embryo Development

10 days after fertilisation inner cell mass forms embryonic disc.

Consists of 3 germ layers:

  • Ectoderm

  • Mesoderm

  • Endotherm

One to five weeks after fertilisation

  • Heart forms, starts to beat.

  • Brain develops

  • Limbs begin to form

Six weeks after fertilisation

  • Eyes are visible

  • Mouth, nose, ears are forming.

  • Skeleton is at early stages of development.

Eight weeks after fertilisation

  • Major body organs formed

  • Sex glands developed into ovaries or testes.

  • Bone begins to replace cartilage.

  • Embryo is now called foetus.

Twelve weeks after fertilisation

  • Nerves and muscle become co-ordinated allowing arms and legs to move.

  • Gestation period is 266 days or 9 months.

Birth

  • Hormones oestrogen and progesterone are produced throughout pregnancy firstly by the corpus luteum (3 months) and then by placenta. Placenta acts as endocrine gland.

  • Immediately before birth placenta stops making progesterone. Walls of uterus begin to contract.

  • Pituitary gland releases oxytocin, causes further contractions.

  • Labour begins.

Stage 1: 12 hours

  • Contraction of the uterus pushes the foetus towards the cervix. Causes cervix to dilate.

  • Amnion breaks and releases amniotic fluid through vagina.

Stage 2: 20 minutes - 1 hour

  • Foetus passes through cervix and birth canal head first.

  • Umbilical cord is tied and cut. Leaves a scar which becomes navel.

Stage 3: 10 - 15 minutes

  • Baby is born

  • Uterus contracts and expels afterbirth (umbilical cord and placenta)

Breast Feeding

Lactation

  • Sceretion of milk from mammary glands.

  • Colostrum produced first days after birth.

  • Milk production triggered by release of prolactin by pituitary.

  • Colostrum and breast milk provides baby with essential antibodies to protect from infection.

  • Ideal balance of nutrients for baby.

  • Has little fat making it easier to digest than milk.

Birth Control

  • Removing possibility of conception is contraception.

  • Achieved by preventing egg and sperm meeting.

Mechanical Contraception

  • Male - use of condoms

  • Female - use of diaphragms

Chemical Contraception

  • Use of the pill - contains oestrogen and progesterone which prevents ovulation.

  • Use of spermicide.

Surgical Contraception

  • Sperm ducts cut and tied (vasectomy)

  • Fallopian tubes cut and tied (tubal litigation)

Natural Contraception

  • No intercourse during fertile period

  • Identify time of ovulation by:

    • Monitoring body temperature (rises slightly after ovulation)

    • Mucous secreted in cervix (changes texture after ovulation)