Sexual Reproduction in Humans

Question 1

MALE REPRODUCTIVE SYSTEM

Question 2

Penis

Answer 2

Organ adapted to transfer the sperm into the vagina during sexual intercourse

Question 3

Testes

Answer 3

Produce gametes (spermatozoa) and the hormone testosterone

Surrounded in a skin sac called the scrotum

Question 4

Vas Deferens

Answer 4

Carries sperm towards the penis during ejaculation

Question 5

Seminal Vesicle

Answer 5

Secretes an alkaline, nutrient rich fluid onto the sperm in the vas deferens forming semen

The alkaline nature serves to neutralise any remaining acidic urine in the urethra and acidic conditions in the vagina

Question 6

Prostate Gland

Answer 6

Secretes an alkaline fluid containing zinc ions onto sperm in the vas deferens

Question 7

Urethra

Answer 7

Carries semen and urine out of the body

Question 8

Epididymis & Seminiferous Tubules

Answer 8

Spermatozoa are made in the seminiferous tubules and stored in the epididymis to mature and become mobile

Question 9

Spermatogenesis

Answer 9

Occurs in the seminiferous tubules of the testes

1. The diploid germinal epithelium divides by mitosis to form
2. spermatogonia, that also divide by mitosis resulting in cells that increase in size forming
3. primary spermatocytes which divide by meiosis to form haploid
4. secondary spermatocytes after the first division, and eventually
5. spermatids after the second meiotic division
6. Spermatozoa mature and differentiate into a sperm

Question 10

Sertoli & Interstitial Cells

Answer 10

Sertoli cells:
-provide nutrients to the developing spermatozoa

Interstitial cells:
-in between seminiferous tubules and secrete testosterone to stimulate spermatogenesis

Question 11

FEMALE REPRODUCTIVE SYSTEM

Question 12

Vagina

Answer 12

A muscular walled structure

Sperm is deposited here during sexual reproduction and the foetus passes through here during birth

Question 13

Cervix

Answer 13

Ring of muscle at the neck of the uterus

Question 14

Ovary

Answer 14

Produces gametes up to secondary oocyte stage

Also produces hormones progesterone and oestrogen

Question 15

Fallopian Tube / Oviduct

Answer 15

Tube lined with ciliated epithelium which waft the secondary oocyte from the ovary to the uterus

Question 16

Uterus

Answer 16

A specialist organ where the embryo implants into the blood rich endometrial layer and grows to term

If there is no fertilisation, this layer is shed during menstruation

Question 17

Oogenesis

Answer 17

Takes place in an ovary up to secondary oocyte stage prior to birth. Diploid germinal epithelium cells divide by mitosis to make oogonia that will increase in size forming primary oocytes

1. Germinal epithelium cells divide to form diploid follicle cells making primary follicles
2. Primary oocytes present at birth are stopped in prophase of meiosis I
3. Secondary oocytes and a small polar body are formed when the primary oocyte completes meiosis I, this happens from puberty onwards
4. The secondary follicle containing the haploid secondary oocyte matures into a graafian follicle
5. One graafian follicle migrates to the surface of the ovary and bursts releasing the secondary oocyte, this is ovulation
6. Meiosis II begins but stops at metaphase II until fertilisation
7. The Graafian follicle becomes the corpus lute after ovulation - if fertilisation occurs it will produce hormones, otherwise it degenerates

Question 18

FERTILISATION

Question 19

Capacitation & the Acrosome Reaction

Answer 19

1. Sperm swim to the fallopian tube
2. Capacitation increases the permeability of the membrane in front of the acrosome
3. The acrosome releases proteases that digest the corona radiata
4. The acrosome membrane ruptures releasing hydrolase enzymes which digest the zona pellucida on contact
5. The membranes of the sperm and secondary oocyte fuse and the genetic material of the sperm enters the secondary oocyte

Question 20

The Cortical Reaction

Answer 20

6. Cortical granules fuse with the cell membrane and alter the zona pellucida to form the fertilisation membrane, which prevents polyspermy
7. Meiosis II completes, forming the ovum and the second polar body
8. Sperm and ovum nuclei fuse, and a diploid zygotic nucleus is formed

Question 21

IMPLANTATION

Question 22

Implantation

Answer 22

• Immediately following fertilisation, mitotic divisions of the newly formed zygote occur-this is called cleavage. A hollow ball of cells called the blastocyst is produced and this implants into the endometrial lining of the uterus

-The placenta forms from the outer blastocyst cells that extend into the endometrium linking the foetus to the mothers tissues to collect nutrients

-The blastocyst secretes Human Gonadotrophic Hormone (HCG) which maintains the corpus luteum, the corpus lute produces progesterone which:
1. maintains the endometrium
2. inhibits the production of FSH and LH
3. supresses contraction of the uterine wall
This has the effect of preventing menstruation and the formation of a new follicle

-When formed, the placenta takes over producing HCG and after 16 weeks it takes over the production of progesterone, it also produced oestrogen that stimulates the growth of the uterus and mammary glands

Question 23

PREGNANCY

Question 24

Chorionic Villi

Answer 24

Extend into the maternal blood and have microvilli to increase surface area, thin walls for easy diffusion and blood flows in a counter current direction to the maternal blood to maintain diffusion gradients along the whole blood vessel

Cells also fuse together preventing the mothers white blood cells from entering the foetal blood

Antibodies can pass through though conveying some immunity

Question 25

Intervillous Spaces

Answer 25

Contain maternal blood and bathe chorionic villi This means mothers blood and foetal blood do not mix, and changes in maternal blood pressure do not damage delicate foetal capillaries

Question 26

Umbilical Arteries

Answer 26

Carries deoxygenated blood and waste materials away from the foetus to the chorionic villi where gas exchange and excretion occurs

Question 27

Umbilical Veins

Answer 27

Carries oxygenated blood and nutrients to the foetus

Question 28

Amniotic Fluid

Answer 28

Acts as a shock absorber protecting the foetus from bumps

Question 29

MENSTRUAL CYCLE

Question 30

The Menstrual Cycle

Answer 30

A series of hormonal and physiological changes involving the brain, ovaries and uterus - controlled by the hormones: -LH (luteinising hormone) -FSH (follicle stimulating hormone) -Oestrogen -Progesterone

Question 31

Negative Feedback

Answer 31

FSH is released from the anterior pituitary gland at the start of the cycle. It stimulates the maturation of a follicle and the production of oestrogen. Oestrogen builds up and inhibits FSH secretion, this is negative feedback and results in a decrease in FSH levels The level of oestrogen, secreted by the developing follicle, increases in the blood which triggers the repair of the endometrium ; this inhibits FSH production and stimulates LH production The corpus lute produces progesterone that further develops the endometrium. With no implantation falling FSH and LH levels cause the corpus luteum to degenerate. This means progesterone levels fall, the endometrium breaks down and is lost during menstruation. FSH is no longer inhibited and the cycle is initiated again A high level of LH from the anterior pituitary gland initiates ovulation and the graafian follicle becomes the corpus luteum

Question 32

Birth

Answer 32

After 39 weeks of development, hormonal changes stimulate birth of the foetus 1. Just before birth oestrogen levels increase and progesterone levels decrease - the uterine wall can now contract. As progesterone was inhibiting oxytocin and prolactin, these hormones can be released again 2. The posterior pituitary gland secretes oxytocin that stimulates uterine contractions. Positive feedback occurs when the uterine contractions in turn stimulate more oxytocin to be produced 3. The anterior pituitary gland secretes prolactin stimulating the production of milk by the mammary glands