Human reproduction

asexual reproduction

• doesn’t involve sex cells or fertilisation.

• Only one parent is required.

• no fusion of gametes and no mixing of genetic information.

• cells divide by mitosis

• therefore, offspring are genetically identical to the parent and to each other. They are clones.

sexual reproduction

• new organisms are produced from the fusion of a male sex cell with a female sex cell.

• This fusion of gametes is called fertilisation.

How is the structure of sperm adapted to move towards to egg?

• Head contains the genetic material for fertilisation in a haploid nucleus.

• The acrosome in the head contains enzymes so sperm can penetrate the egg.

• The middle of sperm packed with mitochondria to release energy needed to swim and fertilize the egg.

• The tail (flagellum) enables the sperm to swim.

Describe how fertilisation takes place

1. semen is ejaculated into the vagina, near the cervix.

2. sperm swim from the uterus into the oviducts.

3. if sperm meets an egg in the fallopian tubes, fertilization may occur.

what happens to the egg and sperm during fertilization?

• head of sperm cell releases enzymes.

• these digest a protective layer surrounding the egg.

• sperm passes through egg cell membrane.

zygote (fertilized egg)

23 chromosomes carried by sperm cell fuse with the 23 chromosomes in egg nucleus.

haploid

half the number of chromosomes needed for fertilization (23)

embryo

develop from a zygote (fertilized egg) and can differentiate into any cell type.

Ovary

• produces eggs (ova) which are released into the oviduct/fallopian tube (during ovulation.)

• produces sex hormones

Oviduct

• egg passes through the oviduct to the uterus.

• fertilization can occur if sperm are present.

Uterus

the place where the fetus develops during pregnancy

Cervix

ring of muscle at the opening of the uterus

vagina

where sperm are deposited during sexual intercourse.

endometrium (lining of uterus)

has a good blood supply for implantation of an embryo

muscular wall of uterus

• stretches to allow growth of embryo

• pushes fetus out during labour

Testis

produces sperm, the male gamete

vas deferens (sperm duct)

tube which sperm pass through to the seminal vesicle and urethra.

seminal vesicle

produces semen (sperm + fluid)

urethra

carries urine and sperm from the body (tube at the end of the penis)

penis

contains erectile tissue, used to introduce sperm into the vagina during ejaculation (sexual intercourse.)

erectile tissue

• swells when filled with blood.

• makes penis erect

scrotum

sac of skin that hold testes outside the abdominal cavity.

prostate glands

• sperm duct joins to urethra.

• produces semen (the fluid sperm swim in)

how does the placenta provide for the fetus?

• fetus receives all oxygen and nutrients from the diffusion of the mothers blood into the placenta.

• fetus gets rid of waste products (urea and carbon dioxide) via diffusion of blood in the placenta.

• happens via diffusion and active transport

requirements for the embryo/fetus

• oxygen

• glucose

• amino acids

• mineral ions

• vitamins

amniotic fluid

• provides a stable environment

• acts as a shock absorber to the developing fetus.

describe the first stage of birth (early and active labour)

1. regular contractions that end when cervix is fully dilated.

2. early labour - lasts until cervix is 3cm dilated. Mild/moderate cramp.

3. active labour - contractions become closer together, longer and more intense. Cervix dilates 3cm-7cm.

4. transition phase - contractions very intense. cervix becomes 10cm dilated.

describe the second stage of birth

baby descends through birth canal

describe the third stage of birth

mother delivers the placenta from the uterus after the baby is born.

secondary sexual characteristics

influence of sex hormones during puberty leads to changes in physical appearance, and the development of sex organs.

testosterone

• male sex hormone

• produced by cells between the tubules of the testes

changes testosterone causes to boys

• pelvis remains narrow

• greater proportion of body mass becomes muscle (instead of fat.)

• hair develops on pubic region, body, face and underarms.

• deepening of voice.

• sperm production

• penis and testicles enlarge.

oestrogen

• female sex hormone

• produced by follicle cells in ovaries

changes oestrogen causes to girls

• pelvis enlarges and hips widen.

• breasts grown with fat deposits.

• greater proportion of body mass maintained as fat.

• hair develops on underarms and pubic region.

menstrual cycle

• lasts approximately 28 days.

• lining of uterus is prepared for pregnancy.

summarise the menstrual cycle

1. Day 1 - women sheds uterus lining (menstruation)

2. FSH released from pituitary gland.

3. first 14 days - oestrogen levels in bloodstream rise.

4. LH released from pituitary gland.

5. next 14 days - egg travels down the oviduct. ovulation occurs. egg moved by tiny hairs in oviduct.

6. uterus lining sheds. process repeats.

explain the role of oestrogen in the menstrual cycle

• produced in ovaries.

• causes uterus lining to grow.

• stimulates the release of LH

explain the role of progesterone in the menstrual cycle

further promotes growth of uterus lining

explain the role of FSH in the menstrual cycle

• follicle stimulating hormone

• stimulates the growth of a new egg in the ovary.

• growing egg cell is helped by cluster of cells around it, called a follicle.

explain the role of LH in the menstrual cycle

• luteinising hormone.

• causes the release of the egg from its follicle (ovulation)

• causes follicle cells in the ovary to switch from oestrogen to progesterone.