Sexual Reproduction is the biological process of forming a new individual through the fusion of two very specialized cells known as gametes. The fusion process is also known as fertilization. The larger gamete is known as the egg or ovum, while the smaller one is known as the sperm.
Asexual reproduction is the biological process of forming a new individual from a single parent without the fusion of gametes (ex. Without fertilization)
Puberty
Puberty is the development process where as child’s body matures into an adult body where he or she is now capable of reproduction.
This process is triggered by:
-release of hormones from the brain to the gonads, which are the organs responsible for the production of sperms and eggs. In males, the gonads are the testes and in females, the gonads are the ovaries.
-in response to the hormonal signals from the brain, the gonads begin secreting sex hormones (such as testosterone and oestrogen)
-the gonads also initiate gametes production. In the testes, sperm are produced, while in the ovaries, eggs begin maturing
-the secondary sexual characteristics also begin to develop
Secondary characteristics:
Male:
-onset at age 11 to 15 years old
-predominant growth of facial, underarm, chest, abdominal and pubic hair
-broadening of chest and shoulders
-enlargement of penis and testes
-Sebaceous (oil) and sweat glands become more active, leading to acne in severe cases
-Deepening of voice as larynx enlarges
-Increased muscle mass and strength; increase in height
Female:
-onset at age 9 to 13 years old
-predominant growth of underarm and pubic hair
-broadening of hips and enlargement of breasts
-sebaceous (oil) and sweat glands become more active, leading to acne in severe cases
Male Reproductive System
Functions of organs in male reproductive system:
Testis:
-production of male gametes (sperm)
-production of male sex hormones
Epididymis:
-temporary storage of sperm
-muscles in epididymis contract to ejaculate sperms
Sperm duct:
-transport sperm from epididymis to the urethra
Glands (seminal vesicles, prostate gland, bulbourethral/ cowper’s glands):
-production of seminal fluid:
-alkaline to neutralize acidity in female reproductive tract
-activates sperms by causing them to swim freely
-nourish sperms with nutrients
Penis:
-insertion into vagina when erected
Physiology of erection and ejaculation:
1) Arterioles bringing blood to the penis and its erectile tissue dilate
2) Blood begin entering the erectile tissues and fills up the blood spaces in the erectile tissue
3) Penis becomes turgid
4) Epididymis contracts
5) Semen is released
Female Reproductive system:
Ovary:
-Production of female gametes (ova) and release of mature ovum
-Production of female sex gametes
Oviduct:
-Deliver mature ovum from ovary to uterus
-Beating of cilia to move ovum along oviduct
-Muscular and had strong contractions
Uterus (or womb):
-muscular and elastic, to push foetus out during birth
-soft and smooth endometrium prepares for implantation of fertilized egg
Endometrium (uttering lining):
-muscular and elastic, to push foetus out during birth
-soft and smooth endometrium prepares for implantation of fertilized egg
Structure of sperm:
Acrosome:
-contains acrosin, a protease enzyme, released by the sperm upon contact with the membrane surrounding the ovum
-acrosin aids in digesting away the membrane, also known as zona pellucida, which surrounds the cell membrane of the ovum. This allows the sperm’s cell membrane to eventually fuse with that of the ovum
Nucleus:
-contains the male genes that will eventually be combined with the female genes in the ovum during fertilization
Minimal cytoplasm:
-the thinner cytoplasm reduces resistance to the motion of the sperm towards the ovum
Middle piece:
-consists of spiral mitochondrion
-the mitochondrion supplies energy for the beating of the tail
Tail (or flagellum):
-beats to propel the sperm towards the ovum
Differences between sperm and the ovum:
Shape:
-The sperm had 3 distinct regions, namely the head, the middle piece, and the tail
-The ovum is spherical
Size:
-The sperm’s size is small
-The ovum’s size is large
Numbers:
-200 to 500 million sperm cells per seminal discharge
-one ova is released on an average of about 28 days
Motility:
-The sperm is motile and move by beating of flagella
-The ovum is non-motile and is swept along oviduct by cilia lining the walls of the oviduct or by contractions of the muscles in the oviduct walls
Lifespan:
-The sperm die rapidly in open air. It dies within a few hours in the vagina and has a lifespan of 2 to 5 days in the oviduct
The ovum can only survives 24 hours if unfertilized
Menstrual Cycle:
Menstrual Cycle refers to a cycle of physiological changes that occur in a fertile woman’s reproductive system. This cycle of events is essential for reproduction to occur. The average period of each cycle is about 28 days. However, it may also range between 14 to 35 days, depending on stress levels and lifestyle. The cycle is under the control of hormones. This cycle can be divided into 3 events that occur sequentially:
Menstruation – Follicular Phase – Day 1 to 14:
-The beginning of each cycle (Day 1) is marked by menstrual bleeding, or menstruation
-This involves the discharge of blood and the breakdown product of the thick uterine lining from the vagina.
-Such discharge could happen up to 7 days.
-During this period, the hormone oestrogen is secreted in increasing concentration
-By Day 7, breakdown of the uterine lining stops and menstrual bleeding ceases as a result of relatively higher oestrogen concentration.
-Thus the uterine lining reaches a minimum thickness by Day 7
-A new ovum begins maturing and continues to mature beyond Day 7 under the influence of a complex interplay of hormones
-Beyond Day 7, the uterine lining begins to thicken again
Ovulation – Day 14:
-By Day 14, oestrogen level reaches a maximum
-A sudden surge in luteinizing hormone level then triggers the release of the mature ovum from one of the ovaries. The ovum then begins its passage through the oviduct towards the uterus.
-Upon release from the ovary, the mature ovum may only survive for 24 hours or less if it is not fertilized
-As the average lifespan of the sperm cell in the oviduct is about 72 hours or about 3 days, any deposition of semen into the female reproductive tract 3 days prior to ovulation may suggest that the woman can still conceive if she ovulates on Day 14.
-A conservative estimate of the fertile period of a woman is hence between Day 11 and Day 16
Luteal Phase – Day 14 to 18:
-After ovulation, the ovaries begin to produce high concentration of progesterone
-This encourages the proliferation (ex. Growth) of the uterine lining (or endometrium), resulting in the growth of more blood capillaries in the endometrial tissues. The uterine lining also becomes thicker, eventually reaching maximum thickness
-The thickness of the uterine lining is maintained mainly by the relatively high concentrations of progesterone
-The proliferation of the uterine is to prepare for the implantation of the fertilized egg
-If implantation does not happen (usually so when the egg is unfertilized) within Day 14 to Day 28, production of progesterone and oestrogen will fall sharply, resulting in the breakdown of the uterine wall.
-The unfertilized egg, together with the fragments of endometrial tissues, blood capillaries and blood, will be removed through menstrual bleeding
-Thus, this marks the beginning of a new cycle
Copulation and fertilization:
Copulation or sexual intercourse refers to the process of placing in the male genitalia into the female reproductive tract. However, fertilization refers to the fusion of the male and female gametes, restoring the diploid number of chromosomes in the zygote. Take note that copulation does not necessarily lead to fertilization.
Post-fertilization:
After the formation of the zygote, several cycles of cell division of the zygote occurs. Eventually, the zygote forms a ball of undifferentiated cells. This ball of cells then begins to form simple tissue layers and is now known as an embryo. In later stages of development, the embryo starts to from distinguishable organs and we term this as foetus. The foetus is nourished and protected by several structures found in womb.
Amniotic Sac and Amniotic Fluid:
The amniotic sac encloses the foetus in the amniotic cavity, which contains the amniotic fluid.
Function of amniotic fluid:
-supports and cushions the foetus while in the uterus
-absorbs shock, for example, if the mother has a fall
-protects the foetus against physical injury as it cannot be compressed
-acts as a lubricant and reduces friction in the birth canal during birth
-allows foetus to move freely during gestation
Placenta:
-the fetal blood system must be separated from the maternal’s system as the 2 systems are functioning at different blood pressure
-the foetus’ blood type may also be different from that of the mother. Mixing of different blood types may result in agglutination and this can be fatal.
Functions of Placenta:
-allows oxygen and nutrients (glucose, amino acids and mineral salts) to diffuse from the mother’s blood into the foetus’ blood
-allows excretory products (urea and carbon dioxide) to diffuse from the foetus’ blood into the mother’s blood
-allows antibodies (protection against diseases) to diffuse from the mother’s blood into the foetus’ blood
-produces progesterone which maintains the uterine lining during pregnancy
Umbilical Cord:
The umbilical cord attaches the foetus to the placenta and contains 2 umbilical arteries and 1 umbilical vein
Function of umbilical cord:
-umbilical arteries transport deoxygenated blood and metabolic waster products (urea) from foetus to the placenta
-umbilical veins transport oxygenated blood, nutrients (glucose, amino acids) and other useful substances (antibodies, hormones) form the placenta to the foetus
Sexually Transmitted Diseases:
Sexually transmitted diseases (STOs) or sexually transmitted infections (STIs) refer to :
-diseases transmitted mainly through sexual intercourse
-caused by bacteria and viruses
-affect the reproductive system (may also affect other body parts)
-may not show visible signs or symptoms, may pass on the disease unknowingly to their partners
-infections can be fatal
Examples:
-Syphilis
-Gonorrhea
-Acquired Immunodeficiency Syndrome (AIDS)
Symptoms , effect, and treatment for diseases:
Gonorrhea:
Cause:
-spherical bacteria
Transmission:
-sexual intercourse
-from infected mother to baby during birth
-sharing of injection needles with infected person
-transfusion of infected blood
Symptoms:
-painful sensation during urination
-discharge of pus from vagina or penis
Effects:
-infection of urethra
-infection of oviducts which may lead to infertility
-ectopic pregnancy
-infection of newborn’s eyes which may lead to blindness
Treatment:
-antibiotics, but some strains of the bacteria have developed drug-resistance
Syphilis:
Cause:
Spiral bacteria
Transmission:
-sexual intercourse
-from infected mother to baby during birth
-sharing of injection needles with infected person
-transfusion of infected blood
Symptoms:
-painless sores on penis, vagina, cervix or mouth
-non-itchy skin rashes
Effects:
-deformed joints
-paralysis
-insanity
-death
-newborn may be deaf or with abnormal teeth and bone
Treatment:
-antibiotics, only effective at early stage
Acquired Immune Deficiency Syndrome:
Cause:
Human Immunodeficiency Virus (HIV)
Transmission:
-sexual intercourse
-from infected mother to baby during birth
-sharing of injection needles with infected person
-transfusion of infected blood
Symptoms:
-weaken immune system
-loss of appetite and weight
-diarrhoea
-night sweat
-flu-like symptoms
Effects:
-immune system fails
-pneumonia
-tubercolosis
-brain infection
-kaposi sarcoma
Treatment:
-currently, there are no cures. However, cocktail of antiretroviral drugs is used to prolong lifespan and improve quality of lives of patients
Prevention of STDs:
To reduce the risk of contracting AIDs and control its spread:
-practise monogamy or abstinence
-wear a condom during intercourse
-do not abuse drugs
-do no share instruments that break the skin (toothbrush, razors, piercing, needles, tattoo needles) as it may be contaminated
-go to reliable practitioners who use sterilized/ disposable instruments
Birth Control:
Couples practise birth control for various reasons:
-prevent unwanted pregnancy
-family may not be financially ready
-couple may want to pursue career development and do not have time for a child
-family may already have enough children
-couple may want to space out the age-gap of their children
-the woman may be ill and physically unsuitable to go through a pregnancy (eg diabetic/ high blood pressure)
-population control legislation (eg. China’s One child policy)
-reduce risk of being infected with STIs
Options for Birth Control:
There are many options for birth control. Some forms of birth control only prevent pregnancy temporarily. Once the couple stops practising these methods, they are able to get pregnant again. However, it is irreversible once permanent birth control is executed. Below are some examples of birth control:
Natural:
Rhythm Method:
It is temporary. The woman tracks her menstrual cycle and avoids having intercourse during the fertile period. However, it is unreliable, as the menstrual cycle is easily disrupted by hormonal fluctuation in the woman’s body.
Withdrawal Method:
It is temporary. The man withdraws his penis just before ejaculation and sperms are not released into the vagina. However, it is unreliable as sperms may be present in pre-seminal fluids and the man may not be able to withdraw in time.
Chemical:
Spermicide:
It is temporary. A chemical is sprayed in the vagina to kill the sperms upon entry and render them unable to swim up to the oviducts. However, it is only 80% reliable. Some sperms may be resistant to the spermicide and can survive the journey towards the oviduct.
Mechanical:
Condom:
It is temporary. A rubber sheath is worn over the penis during intercourse and sperms are collected in the condom so that they cannot enter the vagina. The success rate is 99.9%, as microscopic tears may be present and sperms may leak through.
Diaphragm:
It is temporary. A rubber cap is fitted over the cervix and act as a barrier between the sperms and the ovum. The success rate is also 99.9%, because if the cap is not fitted properly, sperms can still enter the uterus and swim up to the oviducts.
Hormonal:
Pill:
It is temporary. The pill contains synthetic female hormones that prevent ovulation. The success rate is 99.9%, as women were reported to be impregnated even though they were put on pill.
Injection/Implant:
It is temporary. Synthetic female hormones are regularly injected directly or slowly released from an implanted tube into the blood stream to prevent ovulation. The success rate is 99.9%, as women were reported to be impregnated even they were put on hormonal treatment.
Surgical:
Ligation:
It is permanent. The oviducts are cut and tied up to prevent sperms from meeting the ovum. It is 100% reliable.
Vasectomy:
It is permanent. The sperm ducts are cut and tied to prevent sperms from being released into the urethra and out of the penis. It is 100% reliable.
Facilitated Reproduction:
There are couples who are not able to have children due to various physical conditions:
-the ovaries may be defective
-the oviducts may be blocked
-the uterus/ cervix may be too weak to sustain a pregnancy
-the sperms may be weak
-the man is unable to sustain an erection for penetration
-the woman may be suffering from other medical conditions ( eg. Diabetes / high blood pressure) which makes it difficult for her to conceive
As a result, these couples may turn to facilitated reproduction:
In- vitro Fertilization:
1) The woman is given hormonal treatment to stimulate multiple ovulation and the ova are harvested and screened for vitality
2) The sperms are also collected from the man and screened for vitality
3) A healthy sperm is then used to fertilize one ovum in a petri dish with the help of the microscope
4) The resulting zygote is allowed to divide before it is introduced into the uterus. Usually, up to 3 zygotes are introduced to increase the chances of successful implantations
5) If the zygote is successfully implanted, it can develop into an embryo and after 40 weeks, the foetus is ready for birth.
No comments:
Post a Comment