REPRODUCTION IN HUMANS Flashcards
What are the parts of the male reproductive system?
- Testes
- Epididymis
- Scrotum
- Sperm ducts (vas deferens)
- Prostate gland
- Seminal vesicles
- Bulbourethral/Cowper’s glands
- Urethra
- Penis
Describe the testes and their function.
- Produce male sex hormones (e.g. testosterone)
- Produce male gametes (sperm)
Describe the epididymis and its function.
Narrow, tightly-coiled tube leading from the end of each testis. Stores active sperms.
Describe the scrotum and its function.
Pouch-like sac outside the body that holds and protects the testes.
It has a lower temperature than body temperature to allow sperms to develop properly.
Describe the sperm ducts and their function.
Long tubes that lead from the epididymis. They transport sperm from the epididymis to the urethra during ejaculation.
Describe the prostate gland and its function.
Large gland that secretes fluid directly into the urethra, nourishing and protecting the sperm.
Describe the seminal vesicles and their function.
- Store sperms
- Secrete fluid that contains nutrients to provide energy for sperms (in semen)
Ducts from the seminal vesicles connect to the sperm ducts.
Describe the bulbourethral glands and their function.
Pea-sized glands beneath the prostate that produce fluid which contributes to semen.
Describe the urethra and its function.
- Carries sperm in semen to the outside of the body
- Transports urine from the urinary bladder to the outside of the body
Why does urine not pass out of the bladder during ejaculation of semen?
Presence of sphincter muscle at the base of the bladder controls the release of urine.
Describe the penis and its function.
Consists of cylinders of spongy erectile tissue around the urethra, containing numerous blood vessels. When filled with blood, the penis becomes erect, allowing it to enter the vagina during sexual intercourse to deposit semen.
What are the parts of the female reproductive system?
- Ovaries
- Oviducts (fallopian tubes)
- Uterus
- Cervix
- Vagina
Describe the ovaries and their function.
- Produce female gametes (ovum)
- Produce female sex hormones (e.g. estrogen, progesterone)
Describe the oviducts and their function.
Narrow tube leading from the ovary to the uterus, allowing ovum to be released and fertilised here.
Oviducts have:
1. Funnel-like opening: easier for ovum to enter the oviduct
2. Cilia on the inner lining: help move ovum to the uterus
Describe the uterus and its function
- Thick muscular organ (can stretch during pregnancy)
- Lined by endometrium (uterine lining) that is richly supplied with blood vessels, allowing the implantation of the embryo after fertilisation
- Breaks down monthly in menstruation
Describe the cervix and its function.
Circular ring of muscle at the lower end of the uterus that opens into the vagina.
It enlarges during birth to allow the passage of the foetus.
Describe the vagina and its function.
- Thin-walled chamber that leads from the vulva to the uterus, allowing sperm to be deposited.
- Forms the birth canal
What are the parts of the male gamete (sperm)?
- Head
- Middle piece
- Tail
What is the function of the head?
Head contains:
ACROSOME
- contains digestive enzymes that break down the outer membrane of an ovum for fertilisation to occur
CYTOPLASM
HAPLOID NUCLEUS
What is the function of the middle piece?
Contains numerous mitochondria arranged spirally to provide energy for the sperm to move
What is the function of the tail?
Beats to propel the sperm forwards
How does the ovum move in the oviducts?
Beating cilia and waves of muscular contraction in the oviducts move it along into the uterus.
What are the main phases and durations of the menstrual cycle?
- Menstrual Phase (Day 1 to 5)
- Proliferative Phase (Day 6 to 13)
- Ovulation (Day 14)
- Secretory Phase (Day 15 to 28)
When is the fertile phase of the cycle?
Day 11 to 16
What happens during the menstrual phase?
- Endometrium breaks down and flows out of the body
- Progesterone production stops
What happens during the proliferative phase?
- Ovaries secrete estrogen, causing the repair and growth of the endometrium
- Endometrium becomes thicker
What happens during ovulation?
- A mature ovum is released from the ovaries
- Secretion of progesterone is stimulated
Ovum dies after 1-2 days if not fertilised
What happens during the secretory phase?
- Progesterone thickens the endometrium to prepare it for pregnancy
FERTILISATION OCCURS
1. Embryo implants in the endometrium
2. Levels of progesterone and estrogen continue to increase
FERTILISATION DOES NOT OCCUR
1. Levels of progesterone and estrogen drop
2. Endometrium disintegrates and leaves the body through the vagina
Which hormone prevents the development of more ova?
Progesterone
Describe the process of fertilisation in humans.
- During sexual intercourse, semen is deposited into the vagina
- Sperms swim up the oviducts and encounter the ovum, which is moved into the oviducts from the ovary by the muscular contraction of the oviducts
- Acrosome of the sperms releases enzymes to disperse the layer of cells surrounding the ovum and break down the outer membrane of the ovum
- 1 sperm will enter the ovum. Cell membranes of the sperm and ovum fuse, and the sperm nucleus enters the ovum. The cell membrane of the ovum changes as soon as a single sperm has entered, preventing other sperm from entering.
- Sperm nucleus fuses with the ovum nucleus, forming a zygote
Describe the development of the zygote.
- Cilia on the oviduct lining move the zygote towards the uterus.
- The zygote divides many times to form the embryo
- The embryo implants itself in the endometrium of the uterus after 5 to 7 days
- Some of the cells of the embryo develop to form the placenta, which attaches to the wall of the uterus and is connected to the embryo by the umbilical cord
- The amniotic sac develops at the same time as the placenta, and encloses the embryo in a fluid-filled space
- After 9 weeks, embryo has developed into a foetus
What is the function of the placenta?
- Provides nutrients (e.g. glucose, amino acids) and oxygen for the foetus
- Removes waste materials (e.g. urea, carbon dioxide) from the foetus
- Allows protective antibodies to diffuse from maternal blood into embryonic blood
- Provides a barrier that prevents maternal blood and embryonic blood from mixing
- Produces progesterone which maintains the endometrium during pregnancy
Why is it important that maternal blood and embryonic blood do not mix?
- Maternal blood pressure is much higher than embryonic blood pressure and damages vital tissues
- Mother and foetus might have different blood types, which can result in agglutination when blood is mixed
Describe the umbilical cord and its function.
Consists of an umbilical vein and two umbilical arteries
- Carries oxygenated, nutrient-rich blood to the foetus (umbilical VEIN)
- Carryes deoxygenated, nutrient-poor blood away from the foetus (umbilical ARTERY)
What is the function of the amniotic fluid?
- Cushion, support and protect the embryo from physical injury
- Maintain a regular temperature to keep the foetus warm
- Allow the foetus to move freely during development
What is the danger of HIV?
Human Immunodeficiency Virus progressively reduces the effectiveness of the infected person’s immune system. It progresses to AIDS in about 9 to 10 years after infection.
How is HIV transmitted?
- Sexual intercourse with an infected person
- Sharing and reusing contaminated needles during intravenous drug use, tattoo-making or body piercing
- Receiving a blood transfusion from an infected donor
- During pregnancy and childbirth
How can the spread of HIV be prevented?
- Having protected sex
- Abstinence from sex, or having sex with only one partner
- Not sharing objects that could be contaminated with blood/bodily fluids
- Screening of blood for HIV before blood transfusions
- Having infected mothers undergo antiretroviral therapies / give birth by cesarean section to minimise risk of transmission to foetus
- Having infected mothers avoid breastfeeding
What are the symptoms of AIDS?
- Persistent fever
- Skin rashes
- Weight loss
- Chronic diarrhoea
- Weakness
What are the symptoms of HIV?
- Kaposi’s sarcoma (cancer)
- Severe diarrhoea
- Weight Loss
- Pneumonia
- Tuberculosis
