7. Human Reproduction Flashcards
1
Q
Sexual Reproduction
Definition
A
Sexual reproduction is the process involving the fusion of the haploid nuclei of the male and female gametes to form a zygote.
It produces a new organism that is gentically distinct from the parents.
Sexual reproduction involves meiosis.
2
Q
Testis (singular) / Testes (plural)
Function
A
Function:
- Produces sperm
- Produces testosterone, the male sex hormone, from puberty onwards
- Male sex hormones are responsible for the development and maintenance of the secondary sexual characteristics in males.
3
Q
Epididymis
Structure & Function
A
Structure:
- A narrow, tightly-coiled tube that is attached to each of the testes
Function:
- Stores inactive sperms from the testes temporarily (to allow them to mature) before they enter the sperm duct
4
Q
Scrotum
Structure & Function
A
Structure:
- Pouch-like sac that holds the testes
Function:
- Outside the main body cavity to keep the testes slightly below body temperature for sperm development
5
Q
Sperm duct
Structure & Function
A
Structure:
- Tube connecting testes to urethra
Function:
- Carries sperm from the testes to the urethra
6
Q
Urethra (Male)
Structure & Function
A
Structure:
- A tube which passes from the bladder through the center of the penis to the exterior
Function:
- Provides a common passage for the discharge of semen and urine
Urine and semen cannot pass through simultaneously (controlled by sphincter muscles at the base of the bladder).
7
Q
Prostate Gland
Structure & Function
A
Structure:
- Located below the bladder
Function:
Secretes fluid to:
- Activate and nourish sperms
- Neutralise the acidity in the female reproductive tract
- Provide a medium for sperm to swim
Semen = sperm + fluid from prostate gland.
8
Q
Penis
Function
A
Function:
- The male erectile organ which enters the vagina of a woman during sexual intercourse to deposit semen.
9
Q
Sperm
Structure & Function
A
Structure:
Head:
- ~ 2.5 µm wide
- Contains a large nucleus with small amount of cytoplasm
- Nucleus carries a haploid set of chromosomes (23 including X/Y chromosome)
- Acrosome at the front containing enzymes which break down part of the egg membrane to allow sperm to penetrate the egg during fertilisation
Middle piece:
- Contains many mitochondria to provide energy for sperms to swim towards the egg
Flagellum:
- Beating movement of the flagellum enables the sperms to swim towards the egg
Function:
- To fertilise the ovum
- To provide the haploid set of chromosomes
10
Q
Ovary
Structure & Function
A
Structure:
- Ovaries are small, oval-shaped glands located on either side of the uterus
Function:
- Produces ova which are released from ovaries when they are matured (during ovulation)
- Produces oestrogen and progesterone, female sex hormones
- Female sex hormones are responsible for the menstrual cycle and the development and maintenance of the secondary sexual characteristics in females.
11
Q
Oviduct (fallopian tube)
Structure & Function
A
Structure:
- Narrow, muscular tube leading from ovaries to uterus, with a funnel-like opening lying close to the ovaries
- Cilia lining the wall of the oviduct
Function:
- Transports the ovum to the uterus by the beating of cilia lining the walls of the oviduct and peristaltic movement
- Site of fertilisation
12
Q
Uterus
Structure & Function
A
Structure:
- The hollow, pear-shaped organ in a woman’s pelvis
Function:
- Site of implantation of the fertilised egg and fetal development
- Offers protection and a stable internal environment for the embryo to develop
- Its inner lining forms part of the placenta to supply nutrients and oxygen to the fetus and to remove carbon dioxide and nitrogenous waste from the fetus
- Its muscular wall contracts to expel the fetus at birth
13
Q
Cervix
Function
A
Function:
- Connects the uterus to the vagina
14
Q
Vagina
Function
A
Function:
- Holds the penis during copulation (i.e. sexual intercourse) to receive sperm
- The birth canal for the fetus
15
Q
Ovum
Structure & Function
A
Structure:
- Abundant cytoplasm containing small amount of yolk
- Spherical with a large nucleus containing a haploid set of chromosomes
- Surrounded by an additional outer membrane
Function:
- To provide nutrients for the development of the embryo before implantation
- To provide the haploid set of chromosomes
16
Q
Sperm vs Ovum
A
Similarities:
- Both nuclei contain a haploid set of chromosomes (i.e. 23 chromosomes)
Differences:
- Millions of sperms released at each ejaculation while only one ovum is released once every menstrual cycle
- Sperm is relatively small (length of ~0.06mm) while ovum is relatively large (length of ~ 0.12mm)
- Sperm is very active, using its flagellum to move towards the ovum while the ovum is inactive and cannot move by itself
- Sperm has minimal cytoplasm while ovum has abundant cytoplasm
- Differences in structure & function
17
Q
Menstruation
Process
A
Menstruation (Day 1 – 5 of a 28-day cycle):
- Low levels of oestrogen and progesterone
- Causes the uterine lining to break down and shed in the form of menstrual blood out of the body through the vagina
18
Q
After Menstruation
Process
A
After menstruation (Day 6 – 13 of a 28-day cycle):
- Ovaries produce oestrogen
- Oestrogen stimulates the repair and growth of the uterine lining. The utering lining becomes thick and spongy with blood vessels.
19
Q
Ovulation
Process
A
Ovulation (Day 14 of a 28-day cycle):
- Oestrogen production drops rapidly
- One of the two ovaries releases an ovum into the oviduct. This process is known as ovulation.
20
Q
After Ovulation
Process
A
After ovulation (Day 15 – 28 of a 28 day cycle):
- Ovaries produce progesterone
- Progesterone stimulates the uterus to maintain the uterine lining by causing it to thicken further and be supplied with blood capillaries, preparing it for implantation of the embryo
- Progesterone also inhibits ovulation and further development of ova
- Oestrogen production decreases
- If the ovum is not ferilised, progesterone levels decrease and the uterine lining breaks down. Another menstrual cycle begins.
21
Q
Natural Variation in the Menstrual Cycle
Explain
A
- The menstrual cycle for an adult female ranges from 21 days to 33 days, with an average of about 28 days.
- Stress, tiredness, unbalanced diet, or malnutrition may alter or stop the menstrual cycle and change the interval between periods.
22
Q
Fertile and Infertile Phases / Periods of the Menstrual Cycle
A
Fertile period:
- After ovulation, an ovum can survive for about one to two days (day 14 to day 16) in the oviduct.
- Sperms can live for about three to four days in the female reproduction system. This means that sperms released into the vagina at around day 11 have a chance to fertilise the ovum.
- Hence, the fertile period is approximately day 11 to day 16.
Infertile period:
- The rest of the days of the cycle make up the infertile period. Sperms released into the vagina are less likely to fertilise the egg.
23
Q
Fertilisation
Process
A
- The ovum released from the ovary is usually surrounded by a few layers of follicle cells.
- To penetrate the ovum, the acrosome of the sperm releases enzymes to disperse the follicle cells and break down part of the ovum membrane for the sperm to enter.
- Only one sperm nucleus enters the ovum. The haploid sperm nucleus fuses with the haploid ovum nucleus, and a fertilised egg or diploid zygote is formed.
- As soon as the sperm has entered the ovum, the membrane of the ovum changes so that no other sperms can enter. The remaining sperms, which do not fertilise the ovum, eventually die.
24
Q
Hormones secreted if fertilisation occurs
A
If the ovum is fertilised, the embryo secretes the human chorionic gonadotropin (a hormone), which maintains the secretion of progesterone and oestrogen by the ovary until the placenta is able to take over their production.
25
Implantation
| Process
1. Cilia lining the oviduct sweep the fertilised egg or zygote along the oviduct.
2. Peristaltic movement of the oviduct also helps the zygote move towards the uterus.
3. The zygote divides by mitosis to form a hollow ball of cells called the embryo.
4. It takes about five days for the embryo to reach the uterus.
5. The developing embryo moves down the uterus and eventually embeds itself in the uterine lining.
26
Development of Placenta and Amniotic Sac After Implantation
1. After implantation, finger-like projections called villi (contain blood capillaries of the emrbyo), grow from the embryo into the uterine lining.
2. The villi and the uterine lining in which the villi are embedded in make up the placenta.
3. A tube called the umbilical cord attaches the embryo to the placenta.
4. A membrane known as the amniotic sac or amnion develops at the same time as the placenta.
5. The membrane encloses the embryo in a fluid-filled space known as the amniotic cavity.
6. The fluid is known as the amniotic fluid.
27
Amniotic Fluid
| Function
Function:
- **Absorbs shock, supports and cushions** the fetus before birth
- As it cannot be compressed, it **protects the fetus against mechanical injury**
- Allows the fetus a certain degree of movement, which **promote muscular development**
- **Lubricates and reduces friction** in the vagina or birth canal during birth
28
Placenta
| Function
Function:
- Performs the function of nutrition, gaseous exchange, and excretion
- It allows oxygen and nutrients to diffuse through the placenta from the mother's blood to the fetal blood
- It allows carbon dioxide and urea to diffuse through the placenta from the fetal blood to the mother's blood
- It allows protective antibodies to diffuse from the mother's blood to the fetal blood to protect against certain diseases
- It produces progesterone which maintains the uterine lining in a healthy state during pregnancy
29
Adaptations of Placenta
1. The fetal part of the placenta consists of the chorion which produces numerous finger-like projections called chorionic villi (embryonic villi). These projections increase the total surface area to volume ratio to increase the rate of diffusion of substances.
2. Chorionic villi are surrounded by maternal blood spaces supplied with blood from the arterioles at low pressure. Low pressure ensures that there is sufficient time for efficient transfer of nutrients and waste materials between maternal and fetal blood.
3. Blood capillaries of the fetus are separated from the mother's blood by only a thin layer of tissue. Thin barrier ensures that the exchange of substances by diffusion occurs efficiently.
4. Maternal and fetal bloods are only a short distance away but they do not mix. The two blood systems do not mix to prevent damage to the fetus' blood vessels due to the mother's higher blood pressure. It is also to prevent agglutination if mother and child do not have compatible blood types.
30
Umbilical Cord
| Function
Function:
- Attaches fetus to the placenta
- Contains two umbilical arteries that transport deoxygenated blood and metabolic waste products from fetus to placenta
- Contains one umbilical vein that transports oxygenated blood and food substances from placenta to fetus
31
Sexually Transmitted Infections (STIs)
| What is it? How can it be transmitted?
A sexually transmitted infection (STI) is a disease that is spread through sexual intercourse. STIs are caused by bacteria or viruses.
STIs can be transmitted from an infected person to an uninfected person via:
- semen,
- fluid in the vagina, and
- blood.
*Human Immunodeficiency Virus (HIV) is a type of STI.*
32
Acquired Immune Deficiency Syndrome (AIDS)
| Description
- Acquired immune deficiency syndrome (AIDS) is caused by human immunuodeficiency virus (HIV).
- HIV destroys the body's immune system by destroying the lymphocytes.
- A person infected with HIV is unable to produce sufficient antibodies to protect themselves from other infections.
- It may take months to years before HIV infection develops into AIDS. Infections that are normally mild may become fatal for a person with AIDS.
- Currently, there is no cure for HIV.
33
Modes of Transmission of HIV
1. Unprotected sexual intercourse with an infected person
2. Passed from mother to fetus during pregnancy
3. Blood transfusion with blood from an infected person
4. Sharing of hypodermic needles with an infected person
34
How to Prevent HIV Infection
1. Educating the public about how it spreads, and what precautions can be taken
2. Using a condom when having sexual intercourse
3. Not abusing drugs as drug addicts tend to share needles
4. Not sharing instruments that can break skin and get contaminated with blood (e.g. razors, toothbrushes)
5. Making sure that the needles used in acupuncture, ear-piercing, or tattooing are sterilised
6. Keeping to one sex partner and avoiding casual sex
