18 — reproduction in humans Flashcards

Question

How to prevent HIV infection [3]

Answer 1

Controlling spread of HIV: [3] • ensuring use of sterlised needles in medical equipment [1] • keeping to one sex partner or do not have sex [1] • not sharing instrument that will break the skin and be contaminated with blood, e.g. toothbrush and razors. [1]

Answer 2

Day 1-5 (Menstrual flow stage) ● Menstruation occurs. Both oestrogen and progesterone level are low and menstruation occurs as uterine lining could not be maintained. [1] ● During menstruation, the uterine lining breaks down and flows out through the vagina. Damage to blood vessels causes bleeding. [1] Day 6-13 (follicle stage) ● Follicle in one of the ovaries start to develop in response to follicle stimulating hormone from pituitary gland. [1] ● The developing follicle secrete hormone, oestrogen for the repair and growth of the uterine lining.[1] Level of estrogen is the highest. Day 14 (ovulation stage) ● Follicle matures to become Graafian follicle ● Surge /increase in oestrogen production caused the pituitary gland to release the luteinizing hormone. [1] ● Ovulation occurs whereby a mature ovum is released from the Graafian follicle.[1] Corpus Luteum stage (day 15 - 28) * Progesterone prepares the uterine lining for the fertilised egg by causing it to thicken further, and supplying it with blood capillaries. * Progesterone inhibits ovulation

Answer 3

Produces alkaline, milky fluid that contains nutrients and enzymes which nourish and activates the sperms and helps them to swim towards the egg.

Answer 4

When the sperms reach the ovum, sperms release acrosome enzymes to break down the ovum membrane. Only one sperm nucleus enters the ovum; [1] As soon as a sperm enters the egg, the membrane of the egg changes such that no other sperms can enter. The sperms that were unable to fertilise the egg eventually die. Fertilisation occurs when the nucleus of the sperm fuses with the nucleus of the ovum, forming a zygote; [1] The zygote divides by mitosis to form a ball of cells, embryo; [1] Embryo moves along the oviduct towards the uterus by peristalsis of the oviduct muscles and sweeping motion of the cilia lining the inner surface of the oviduct; [1] and is implanted in the uterine lining of the uterus during implantation for further development; [1] Corpus luteum in the ovary continues to produce progesterone to maintain the thickness of uterine lining until the formation of the placenta takes over; [1] [4]: Early development The fertilised egg, zygote continues to divide by mitosis to form a ball of cells called an embryo. [1] The embryo travel along the oviduct towards the uterus by the contraction of the oviduct muscles via peristalsis [1] and with the help of the sweeping motion of cilia lining the inner surface of the oviduct. [1] Embryo implants into the uterine lining of the uterus during implantation. [1] [5]: After fertilisation, Zygote divide by mitosis to become a ball of cells called embryo.[1] Embryo move towards uterus by peristalsis by the wall of the fallopian tube and sweeping motion of the cilia.[1] Embryo implanted in the uterine lining/wall of uterus. [1] In the ovary, Graafian follicle develops into corpus luteum, which secretes progesterone to maintain the thickness of the uterine lining. [1] Embryonic villi grow into the maternal uterus lining forming the placenta which becomes the site of exchange of substances between the fetus and the mother through the umbilical cord. [1] Amniotic sac is formed around the fetus with amniotic fluid to cushion the fetus against shock. (along with any 2 more points): Finger-like projections called villi, containing the blood vessels from the embryo, grow into the uterine lining, forming the placenta. The placenta secretes progesterone and oestrogen, maintaining the thickness of uterine lining. In the placenta, oxygen and nutrients diffuse from maternal to foetal capillaries, and are delivered to the foetus via the umbilical cord, while metabolic waste products such as urea and carbon dioxide are removed. The amniotic sac develops, containing amniotic fluid that protects foetus from physical injury/allows for movement for muscular development/trains the foetus' digestive system.

Answer 5

The process where the embryo embeds itself in the uterus lining

Answer 6

If fertilisation occurred, the ovary continues secreting oestrogen and progesterone, keeping their levels high. Hence, these hormones maintain the uterine lining even after day 28, in preparation for the implantation of the embryo. The lining does not break down, and there is no menstruation.

Answer 7

Ovulation occurs on day 14, where a mature ovum is released from an ovary into an oviduct. The egg can be fertilised up to 48 hours (2 days) after its release from the ovary. Sperms can live for three to four days in the female reproductive system. Therefore, if sexual intercourse takes place between days 11 to 16, there is a higher chance of fertilisation. This period is known as the fertile period. Thus the fertile period, the days where sexual intercourse would lead to the highest chance of pregnancy, is from day 10 to 15. The rest of the days make up the infertile period of the menstrual cycle.

Answer 8

The placenta secretes progesterone, to maintain the thickness of the uterine lining throughout pregnancy. [1] The placenta is the site of exchange of substances between mother and fetus by diffusion whereby nutrients such as glucose, amino acids and oxygen will diffuse from the mother’s blood to the fetus’s blood across the placenta/ Metabolic waste products such as urea and carbon dioxide will diffuse from the fetus’s blood to the mother’s blood, across the placenta; [1] Antibodies from the mother’s blood will diffuse into the fetus’s blood to protect the fetus from diseases; [1] Blood system of the mother and fetus are separated by blood spaces at the placenta to prevent mixing and possible agglutination of blood due to difference in blood pressure and blood type, which may potentially harm foetus; [1]

Answer 9

Maternal and foetal blood types may be incompatible, and direct mixing of blood would lead to agglutination of red blood cells which is dangerous both mother and foetus. The mother's blood pressure is higher than that of the foetus, which may burst foetal blood vessels if they were connected.

Answer 10

Unprotected sexual intercourse, where semen containing HIV comes into contact with the mucous membrane of an uninfected female's vagina. Or when vaginal fluids containing HIV come into contact with the mucous membrane of an uninfected male's urethra. By sharing contaminated needles, such as between drug addicts. By blood transfusion with blood from an infected person. During pregnancy, where the virus travels from an infected mother to the foetus.

Answer 11

Cilia lining the inner surface of the fallopian tube sweep the fertilised egg/ zygote/ embryo along the fallopian tube/ oviduct towards the uterus. [1]

Answer 12

Similarity: The progesterone level of the pregnant woman in the first 3 months is at about 25-30 arbitrary units [1] which is about the same level as the progesterone level of the non-pregnant woman at day 22/ highest level of the menstrual cycle. [1] Difference: The progesterone level of the pregnant woman changes along the 9 months with low levels at 30 arbitrary units for the first 3 months before increasing to 100-150 arbitrary units for the next 5 months and reaching the maximum of 250 arbitrary units at the 9th month. [1] while the progesterone level of the non-pregnant woman shows a regular repeated pattern per month for 9 months with the maximum level reaching 25 arbitrary units in each month. [1]

Answer 13

The release of a mature egg from the ovary around day 14 of the menstrual cycle