Human Reproductive System - Biology PDF

## Organisms and Environment ### 13.1 Human Reproductive System - We learnt that flowering plants can reproduce sexually and/or asexually - How about humans? Humans carry out sexual reproduction only - Their reproductive systems are specialized for this way of reproduction ### A Male Reproductive...

## Organisms and Environment ### 13.1 Human Reproductive System - We learnt that flowering plants can reproduce sexually and/or asexually - How about humans? Humans carry out sexual reproduction only - Their reproductive systems are specialized for this way of reproduction ### A Male Reproductive System - Fig 13.1 shows the front and side views of the male reproductive system: - **Front View:** - Ureter - Urinary bladder - Erectile tissue - Urethra - Testis - Penis - **Side View:** - Right ureter - Seminal vesicle - Prostate gland - Rectum - Cowper's gland - Epididymis - Scrotum - Urinary bladder - Vas deferens - Erectile tissue - Penis - Urethra - Testis - **Note:** structures in brackets do not belong to the reproductive system - **3D Model 13.1** ### The Male Reproductive System consists of 1. A Pair of gamete-producing organs: **testes** - They produce sperm (male gametes) and make sex hormones - They are located in a sac called the **scrotum**, which hangs outside the abdominal cavity. This keeps the testes at 2-3 degrees Celsius lower than the body temperature (32 degrees Celsius). The lower temperature is optimal for sperm development. 2. A system of ducts: **epididymis, vas deferens, and urethra** - **Duct:** **Function:** - **Epididymis:** It is a long coiled tube that lies on each testis. It stores sperms temporarily. - **Vas Deferens**:(or sperm duct): It carries sperms from the epididymis to the urethra - **Urethra:** It discharges semen out of the body during ejaculation. (It also serves to discharge urine.) *The prostate gland enlarges in many men over the age of 50. The enlarged gland may press part of the urethra and make it narrower. Thus urination becomes difficult.* 3. Glands: **Seminal Vesicles, Prostate gland**, and **Cowper’s gland** - They secrete **seminal fluid** into the ducts. Seminal fluid: - **Provides a medium for sperms to swim in.** - **Contains sugars that act as an energy source for sperms** - **Contains mucus for lubrication.** - **Is alkaline.** It helps neutralize any acidic urine in the male’s urethra and acidic secretions in the female’s vagina. - *The seminal fluid and the sperms make up the semen* 4. A **copulatory organ: penis** - It contains **erectile tissue** and many blood vessels - It transfers semen into the female’s vagina during sexual intercourse. ### B Female Reproductive System - Fig 13.3 shows the front and side views of the female reproductive system: - **Front View:** - Ovary - Funnel-shaped opening of oviduct - Cervix - Vagina - **Side View:** - Funnel-shaped opening of oviduct - Ovary - Cervix - Rectum - Vagina - Oviduct - Uterus - Oviduct - Uterus - Urinary bladder - Urethra - **Note:** Structures in brackets do not belong to the reproductive system. ### The Female Reproductive System consists of: 1. A pair of gamete-producing organs: **ovaries** - They produce ova (or egg cells) (female gametes) and female sex hormones (estrogen, progesterone) secreted by ovaries 2. A pair of **oviducts** - Each of them has a funnel-shaped opening near an ovary. - They are lined with ciliated epithelial cells. The cilia beat to sweep the ovum or the early embryo toward the uterus. - It is the site of fertilization. 3. A **uterus** - It is a pear-shaped organ. It has a thick muscular wall with a lining rich in blood supply. - It is the site of implantation of the embryo. - It protects the embryo or foetus and provides a stable environment for it to develop in. - Its muscular wall contracts to push out the foetus during childbirth. - At the lower end of the uterus is a ring of muscle called the cervix. The cervix dilates to allow the foetus to pass through during childbirth. 4. A **vagina** - Holds the penis and receives the semen during sexual intercourse. - Its environment is acidic. This can reduce bacterial growth. - It acts as the birth canal for the foetus. ### Practical 13.1 Examination of Mammalian Reproductive Systems - **Procedure:** 1. Your teacher will show you the reproductive systems o a dissected male rat and a dissected female rat. 2. With the help of the photographs below, identify different structures of the reproductive systems. - **Male:** - Seminal vesicle - Prostate gland - Cowper’s gland - Penis - Testis - Epididymis - Vas deferens - Urethra - **Female** - Ovary - Oviduct - Uterus - Vagina *"Compared with humans, male rats have proportionally larger seminal vesicles"* *"Unlike humans, the uterus of female rats is V-shaped and has two branches"* ### Key Learning: 1. **What are the main structures of the male reproductive system and their functions?** - **Male Reproductive System (side view):** - **(Urinary bladder)** - **Seminal vesicle:** secrete seminal fluid which - provides a medium for sperms to swim in - contains sugars that act as an energy source of sperms - contains mucus for lubrication - neutralizes acidic urine in the male’s urethra and acidic secretions in the female’s vagina. - **Prostate gland** - **Cowper’s gland** - **Vas deferens:** carries sperms from the epididymis to the urethra - **Urethra:** discharges semen out of the body - **Penis:** transfers semen into the female’s vagina. - **Scrotum:** - holds the testes - allows an optimum temperature for sperm development 2. **What are the main structures of the female reproductive system and their functions?** - **Female Reproductive System (front view):** - **Oviduct:** transports the ovum or the embryo to the uterus; site of fertilization. - **Ovary:** produces ova and female sex hormones - **Cervix:** dilates to allow the foetus to pass through during childbirth - **Vagina:** holds the penis and receives semen during sexual intercourse; acts as the birth canal for the foetus - **Uterus:** site of implantation of the embryo; protects the embryo or foetus and provides a stable environment for it to develop in; its muscular wall contracts to push out the foetus during childbirth. ### 13.2 Human Gametes - Sexual reproduction in humans involves the fusion of a sperm (male gamete) and an ovum (female gamete.) What are the structures of these gametes and how are they formed? ### A Structure of Human Gametes 1. **Sperms:** - A sperm looks like a tadpole. It is very small, about 0.05 mm long. - It consists of three parts: - **Head:** contains a cap called the acrosome and a nucleus - **Midpiece:** contains many mitochondria - **Tail:** - **Acrosome:** contains enzymes for penetration into the ovum during fertilization - **Nucleus:** contains a haploid number of chromosomes (i.e., 23 chromosomes) - **Mitochondria:** packed with many mitochondria; release energy for swimming. - **Tail:** beats to drive the sperm forward 2. **Ova:** - An ovum is spherical in shape. Its diameter is about 0.1 mm. It is much larger than the sperm as it contains a lot of food reserves. - It cannot move by itself. - It consists of a nucleus, cytoplasm, and a cell membrane covered by a jelly coat. - **Cytoplasm:** contains food reserves for the early development of the embryo - **Nucleus:** contains a haploid number of chromosomes (i.e. 23 chromosomes) - **Cell Membrane:** - **Jelly Coat:** ### Key Learning: - Compare the structure of a sperm and ovum: - **Sperm:** - **Size:** Smaller (about 0.05mm long) - **Shape:** Like a tadpole - **Movement:** Can swim using its tail - **Food reserves:** Very little (uses sugars in seminal fluid) - **Number of chromosomes in the nucleus:** Haploid number (i.e. 23 chromosomes) - **Ovum:** - **Size:** Much Larger (about 0.1 mm in diameter) - **Shape:** Spherical - **Movement:** Cannot move by itself. - **Food reserves:** Much more food reserves - **Number of chromosomes in the nucleus:** Haploid number (i.e. 23 chromosomes) ### Right and Wrong - Sperms contain mitochondria while ova do not. - **Both sperms and ova contain mitochondria, but sperms have a higher density of mitochondria than ova.** ### Historical Note - Tiny person in sperm: In 1677, Antoni van Leeuwenhoek used his microscope to observe a sample of semen. He saw “small animals with tails” (which were actually sperms) in it. Leeuwenhoek shared his findings with other scientists. More people started to study how human life began. Some people proposed that each sperm contained a tiny person inside. This now disproved idea was accepted by many people at that time. ### B Production of Gametes 1. **Production of Sperms:** - Production of sperms begins at puberty and occurs throughout the life of a male. It takes place in coiled tubes called seminiferous tubules inside the testes. - **At puberty, cells between the seminiferous tubules begin to produce more male sex hormones.** The increased levels of male sex hormones stimulate the cells near the walls of the tubules to divide mitotically to produce more cells. These cells then undergo meiotic cell division to become sperms. The sperms finally pass into the epididymis, where they develop motility and are stored temporarily. In general, a man can produce millions of sperms every day. 2. **Development of Ova:** - Production of ova begins in the ovaries of the foetus before birth. - At birth, the ovaries contain tens of thousands of immature ova. - Each ovum is surrounded by layers of follicle cells, forming a follicle. These follicles do not develop further until puberty. - **At puberty, the body begins to produce more female sex hormones.** A regular cycle of events in the ovary starts to occur. The increased levels of female sex hormones stimulate several follicles in the ovaries to develop further. They grow in size and move towards the surface of the ovaries. Usually only one follicle will become fully mature at a time. - **This mature follicle finally bursts to release the ovum into the funnel of the oviduct.** This process is called ovulation. After ovulation, the ruptured follicle becomes the yellow body (or corpus luteum). It degenerates if fertilization does not occur. - **Ovulation occurs about every 28 days, starting from puberty to about the age of 50.** In other words, about 400 to 500 ova are released over the 30-40 years of a woman’s reproductive life. ### Key Learning: - **What are the differences between the production and development of sperms and ova?** | | Sperms | Ova | |----------------|-----------------------------|---------------------------------------------| | **Location** | Testes | Ovaries | | **Time of Occurrence** | Begins at puberty; Occurs throughout life | Early stages occur before birth; Further development occurs cyclically from puberty to about the age of 50 | | **Quantity** | Millions of sperms are produced every day | Usually only one follicle becomes fully mature and releases an ovum about every 28 days | ### 13.3 Secondary Sexual Characteristics in Humans - Increased production of sex hormones during puberty does not only stimulate sperm production in males and development of ova in females, but also leads to the development of **secondary sexual characteristics**. - **Male:** - Larynx enlarges and voice deepens - Shoulders broaden. The body becomes more muscular. - Beard grows - Hair grows in armpits and pubic area - Penis and testes grow larger - **Female:** - Breasts develop. - More fat is deposited under the skin. - Hair grows in armpits and pubic area. - Hips become wider (broaden). *"Primary sexual characteristics" refer to the reproductive organs that we are born with.* ### Key Learning: - Compare the secondary sexual characteristics in males and females: - **Similarity:** Hair grows in armpits and pubic area - **Difference:** - **Males:** - Larynx enlarges and voice deepens - Shoulders broaden. The body becomes more muscular. - Beard grows - **Females:** - Breasts develop. - Hip broadens. - More fat is deposited under the skin. ### 13.4 Menstrual Cycle - We learnt that an ovum is released into the oviduct about every 28 days. If the ovum meets a sperm in the oviduct, fertilization may occur. The fertilized ovum will develop into an embryo. - To prepare for the implantation of the embryo, the **uterine lining thickens** and its blood supply increases before ovulation. If fertilization does not occur, the thickened uterine lining will break down. The cycle of building up and breaking down of the uterine lining is called the **menstrual cycle**. Key events in the cycle are shown below: - The first day of menstruation is considered Day 1 of the cycle. - **Days 1 to 5:** - If fertilization does not occur, the yellow body degenerates. - The thickened uterine lining breaks down. - The uterine lining (including some blood) and the unfertilized ovum are discharged through the vagina. This process is called menstruation. It lasts about 5 days. - Some follicles in the ovary start to develop. - **Days 6 to 13:** - Follicles continue to develop. - The uterine lining thickens and the blood supply increases to prepare for the implantation of an embryo. - **Day 14:** - Ovulation occurs. - **Days 15 to 28:** - The ruptured follicle becomes the yellow body, which releases a hormone to increase and maintain the thickness of the uterine lining. - The uterine lining becomes very thick. It is ready to receive an embryo. - **If fertilization occurs and the woman gets pregnant, the degeneration of the yellow body is delayed.** The uterine lining does not break down. Instead, it continues to thicken. Menstruation does not occur until the baby is born. - **Figure 13.16 shows the changes in the thickness of the uterine lining in relation to the events occurring in the ovary**. - **The first menstruation occurs at puberty.** The menstrual cycle repeats until about the age of 50, when a woman reaches menopause. At menopause, ovulation and menstruation become less regular and gradually stop. Then the woman can no longer become pregnant. - **Fertile period:** - After ovulation, an ovum is capable of being fertilized for 1 to 2 days only. As sperms can live in the female body for up to 5 days, the highest chance for a woman to get pregnant is to have sexual intercourse a few days before and after ovulation. This period is called the fertile period. ### Key Learning: - **What are the key events in the menstrual cycle?** - The menstrual cycle lasts about 28 days. - **Time** | **Key Events** - **Days 1 to 5** | The thickened uterine lining breaks down. Menstruation occurs. - **Days 6 to 13** | The uterine lining thickens to prepare for the implantation of an embryo. - **Day 14** | Ovulation occurs. - **Days 15 to 28** | The uterine lining becomes very thick. It is ready to receive an embryo. ### Learning Through Examples: - The graph below shows the changes in the thickness of the uterine lining of a woman from 29th May to 2nd July. - **Questions:** 1. How long did menstruation last in this woman in June? Explain your answer with a piece of evidence from the graph. 2. In which period (P, Q, R or S) would there be a high chance of pregnancy if sexual intercourse took place? Explain your answer. 3. What is the significance of the change in the thickness of the uterine lining during period R? 4. If the woman gets pregnant, how will the curve in the above graph change? - **Suggested Answers** 1. **5 days** The thickness of the uterine lining decreased from 1/6 to 5/6. 2. **Period R** Ovulation should have occurred in period R. If sexual intercourse took place in this period, fertilization might occur. 3. **The thickening of the uterine lining serves to prepare for the implantation of an embryo.** 4. **The curve from 28/6 onward will not drop. Instead, it will remain at a high level.** - **Interpreting a graph of the thickness of the uterine lining against time:** - When reading a graph of the thickness of the uterine lining against time, note the following: - *A big drop indicates menstruation occurs* - *As sperms can survive for 5 days and the ovum can be fertilized for 1 to 2 days after ovulation, the fertile period spans about 7 days around the time of ovulation.* - *The uterine lining is the thickest. It is ready for the implantation of an embryo (Ovulation does NOT occur in this period).* - *Menstruation starts. This is the first day of the menstrual cycle.* - *Ovulation occurs about 14 days before the start of the next menstruation.* - *The curve drops again. This indicates the start of the next cycle*. - **The graph on the right shows the changes in the thickness of the uterine lining of a woman in a month. State the period (P, Q, R, or S) in which each of the following events is likely to have occurred. - *a. Menstruation - *b. Ovulation - *c. Implantation of an embryo if fertilization took place. ### Key Learning: - **What are the key events in the menstrual cycle?** - The menstrual cycle lasts about 28 days. - **Time** | **Key Events** - **Days 1 to 5** | The thickened uterine lining breaks down. Menstruation occurs. - **Days 6 to 13** | The uterine lining thickens to prepare for the implantation of an embryo. - **Day 14** | Ovulation occurs. - **Days 15 to 28** | The uterine lining becomes very thick. It is ready to receive an embryo. ### Learning Through Examples - The graph below shows the changes in the thickness of the uterine lining of a woman from 29th May to 2nd July. - **Questions:** 1. How long did menstruation last in this woman in June? Explain your answer with a piece of evidence from the graph. 2. In which period (P, Q, R or S) would there be a high chance of pregnancy if sexual intercourse took place? Explain your answer. 3. What is the significance of the change in the thickness of the uterine lining during period R? 4. If the woman gets pregnant, how will the curve in the above graph change? - **Suggested Answers:** 1. **5 days** The thickness of the uterine lining decreased from 1/6 to 5/6. 2. **Period R** Ovulation should have occurred in period R. If sexual intercourse took place in this period, fertilization might occur. 3. **The thickening of the uterine lining serves to prepare for the implantation of an embryo.** 4. **The curve from 28/6 onward will not drop. Instead, it will remain at a high level.** - **Interpreting a graph of the thickness of the uterine lining against time:** - When reading a graph of the thickness of the uterine lining against time, note the following: - *A big drop indicates menstruation occurs* - *As sperms can survive for 5 days and the ovum can be fertilized for 1 to 2 days after ovulation, the fertile period spans about 7 days around the time of ovulation.* - *The uterine lining is the thickest. It is ready for the implantation of an embryo (Ovulation does NOT occur in this period).* - *Menstruation starts. This is the first day of the menstrual cycle*. - *Ovulation occurs about 14 days before the start of the next menstruation*. - *The curve drops again. This indicates the start of the next cycle*. - **The graph on the right shows the changes in the thickness of the uterine lining of a woman in a month. State the period (P, Q, R, or S) in which each of the following events is likely to have occurred. - *a. Menstruation - *b. Ovulation - *c. Implantation of an embryo if fertilization took place. ### Key Learning: - **What are the key events in the menstrual cycle?** - The menstrual cycle lasts about 28 days. - **Time** | **Key Events** - **Days 1 to 5** | The thickened uterine lining breaks down. Menstruation occurs. - **Days 6 to 13** | The uterine lining thickens to prepare for the implantation of an embryo. - **Day 14** | Ovulation occurs. - **Days 15 to 28** | The uterine lining becomes very thick. It is ready to receive an embryo. ### Checkpoint - **Questions 1 to 3: State whether the statements are true or false.** 1. Menstruation lasts about 28 days. **False** 2. Ovulation occurs when the uterine lining becomes the thickest. **False** 3. Menstruation does not occur during pregnancy. **True** - **The photograph below shows a human ovary with a large yellow body inside. The graph shows the changes in the thickness of the uterine lining of a woman in July.** - **In which of the following periods is the condition of the yellow body shown in the photograph most likely to occur?** - a. 5th to 9th July - b. 13th to 17th July - c. 19th to 23rd July - d. 23rd to 27th July - **Answer: d. 23rd to 27th July**