Sexual Reprodiction In Humans🍆 Flashcards
What is the scrotum?
- Contains the testes
* Hang outside - cooler
What are the testes?
Contain the seminiferous tubules where spermatogenesis occurs
What is the epididymis?
Where the spermatozoa mature
What is the vas deferens?
Connects the epididymis to the urethra
What is the seminal vesicle?
Produces a secretion that aids the mobility of the spermatozoa and nourishes the sperm
What is the prostate gland?
Produces a secretion that neutralises the alkali of the urine and helps protect sperm from acidic secretions in the female body
What is the urethra?
Tube that carries urine and spermatozoa out the body
What is the penis?
Intromittent organ used to insert spermatozoa into the reproductive system of the female
What does the fluid from the accessory glands do?
- Maintains sperm mobility
- Provides nutrients
- Alkaline to neutralise acidity of urine in urethra and vagina
What is the ovary?
Oogenesis occurs here
What is the oviduct/fallopian tube?
- Site of fertilisation, where a spermatozoon fuses with an oocyte
- At fertilisation, a zygote is formed, which then moves down the oviduct towards the uterus
What is the uterus?
Embryo implants in the endometrium and then continues to develop in the uterus
What is the endometrium?
- Mucous membrane that lines the uterus
* Thickens during menstrual cycle in preparation for possible implantation of an embryo
What is the cervix?
Narrow passage forming the lower end of the uterus
What is the vagina?
During sexual intercourse, spermatozoa are deposited at the top of the vagina
What are the gametes?
- Haploid cells
- Contain half the full, diploid number of chromosomes
- Contains one chromosome from each homologous pair
What is gametogenesis?
Production of gametes
Where does spermatogenesis occur?
In the seminiferous tubules of the testes
What are spermatozoa?
Plural of spermatozoon (sperm)
Spermatogenesis process
•Germinal epithelial (2n) cells undergo mitosis to form spermatogonia (2n)
•Spermatogonia undergo mitosis form primary spermatocytes (2n)
•Primary spermatocytes undergo meiosis 1 to form haploid secondary spermatocytes (n)
-these complete meiosis 2 to form spermatids (n)
•Spermatids mature to form sperm (differentiation)
What is differentiation?
Development of specialised structures within the cell
Describe the sperm head
Contains a haploid nucleus
What is the acrosome of the sperm?
Releases enzymes that digest the zona pellucida in the acrosome reaction
Describe the body of the sperm
Contains mitochondria which release energy as ATP, e.g. used for flagellum
What is the function of the flagellum/tail?
Propels sperm using energy (ATP)
What is the function of Sertoli cells?
Nourishes and protects the sperm
What is the function of interstitial cells (cells of Leydig)?
Found in testes and secrete testosterone
What is the function of testosterone?
- Hormone involves in stimulating the process of spermatogenesis
- Induces male secondary sexual characteristics
How do spermatozoa move into the epididymis?
By peristalsis and the action of the cilia
Where does oogenesis produce oocytes?
In the ovaries
Process of oogenesis
•Oogonia divide by mitosis to form primary oocytes (2n)
-primary oocytes begin meiosis but stop at prophase 1
•Germinal epithelial cells also divide to form follicle cells, which surround the primary oocyte
•Several follicles begin to develop but only one matures into a Graafian follicle
•Primary oocyte completes meiosis 1 to form a secondary oocyte (n) and polar body (n)
•Mature Graafian follicle moves to the surface of the ovary where it releases the secondary oocyte (ovulation)
•Secondary oocyte then begins meiosis 2 but stops at metaphase 2
•If a sperm cell enters the oocyte and fertilisation occurs, then the secondary oocyte completes meiosis 2 forming an ovum and a second polar body
•The nucleus of the sperm fuses with the nucleus of the secondary oocyte to form the zygote
Oogenesis simple
•Germinal epithelial cells (2n) -mitosis •Oogonia (2n) -mitosis •Follicle cells and primary oocytes (2n) -meiosis (stops at prophase 1) -complete meiosis 1 •Secondary follicle and secondary oocyte (n) and first polar body -meiosis 2 (stops at metaphase 1) •Graafian follicle and secondary oocyte (n) -ovulation •Corpus luteum and released secondary oocyte (n) -fertilisation -completes meiosis 2 •Zygote (2n) and second polar body
What occurs before birth?(oogenesis)
- Oogonia divide by mitosis to form primary oocytes
* Germinal epithelial cells also divide to form follicle cells
What occurs once a month when a girl reaches puberty? (Oogenesis)
- One follicle develops into a Graafian follicle
* Primary oocyte completes meiosis 1 to form a secondary oocyte and a polar body
Why is it important that the oocyte contains as much cytoplasm as possible?
To provide nourishment for the developing embryo until it reaches the endometrium
How does the oocyte ensure it contains as much cytoplasm as possible?
- Achieved by polar bodies (n) being formed in both meiosis 1 and meiosis 2
- These are very small and cannot be fertilised
What is a follicle?
- The development of oocytes takes place in follicles
- Situated in outer region of the ovary
- Small sac-like structure consisting of a ball of cells surrounding a single germ cell
Where does fertilisation occur?
Deep inside female’s body - oviduct
Process of sexual intercourse
•Spermatozoa are ejaculated out of the epididymis
•They travel up the vas deferens and out through the urethra
•Spermatozoa are deposited at the top of the vagina and swim out of the vagina, through the cervix, along the endometrium and into the oviduct
-sperm meets secondary oocyte which has been released from the ovary
What is the function of the secretions from the seminal vesicle?
Aid spermatozoa mobility
What is the function of the secretions from the prostate gland?
Neutralises the alkali of any urine in the urethra
Process of capacitation
- Before a sperm cell can fertilise the oocyte, capacitation must occur
- Biochemical process that occurs several hours after the sperm enter the female reproductive tract
- The membrane surrounding the acrosome in the head of the sperm becomes more permeable and prepares for the acrosome reaction that will occur when the sperm attempt to enter the oocyte
Process of the acrosome reaction
•Once capacitation has occurred, the sperm cell is ready to enter the oocyte
•When a sperm comes into contact with the outer jelly layer of the oocyte, the acrosome reaction is triggered
•Acrosome membrane ruptures and hydrolase enzymes are released
-these enzymes digest their way through the zona pellucida
•The membranes of the sperm and the oocyte fuse and the genetic material from the sperm then enters the oocyte
Process of the cortical reaction
- The contents of the cortical granules fuse with the cell membrane of the oocyte and cause a modification of the zona pellucida
- A fertilisation membrane then forms, which prevents polyspermy
What happens after the entry of the sperm’s genetic material?
- The stimulates the secondary oocyte to complete meiosis 2
- The haploid nucleus of the sperm fuses with the haploid nucleus of the oocyte to form the diploid nucleus of the zygote
What is cleavage?
- After fertilisation has occurred, the zygote moves down the oviduct
- The zygote rapidly divides by mitosis to form a hollow ball of cells called the blastocyst
Process of implantation by the blastocyst
When the blastocyst reaches the uterus, it implants in the endometrium
What is the chorion?
The outer layer of the blastocyst
What is the trophoblast?
- The outer layer of the chorion
* Forms the chorion and the ammiom
What are chorionic villi?
- The chorion develops chorionic villi
- Absorb nutrients through the endometrium
- Long thin shape means that they have a large surface area
Where does the placenta develop?
Between the chorion tissues of the mother and the foetus
What is the function of FSH? (menstrual cycle)
- Secreted by anterior pituitary gland
- Stimulates maturation of follicle in the ovary
- Stimulates production of Oestrogen
What is the function of oestrogen?(menstrual cycle)
- Released by ovarian follicle
- Inhibits FSH (low levels)
- Stimulates release of FSH and LH (critical levels)
- Triggers repair and growth of endometrium
What is the function of LH? (Menstrual cycle)
- Released from the anterior pituitary gland
- Promotes ovulation
- Promotes development of corpus luteum from Graafian follicle
What is the function of progesterone? (Menstrual cycle)
- Released by corpus luteum
- High levels inhibit FSH
- Sharp decrease (along with oestrogen) triggers menstruation
What happens if implantation doesn’t occur?
- FSH and LH levels fall
- This causes the corpus luteum to degenerate
- Progesterone levels also fall
- Endometrium breaks down and leaves the uterus during menstruation
Compare spermatogenesis and oogenesis
- Both produce haploid gametes
- Oogenesis begins before birth and ends at menopause, whereas spermatogenesis begins at puberty and continues for the rest of a males life
- Spermatogenesis is continuous, whereas oogenesis stops at prophase 1 and metaphase 2
- Spermatogenesis produces 4 functioning gametes, whilst oogenesis produces one with polar bodies forming as well
What happens to the uterus?
- Lining breaks down, menstruation occurs
- Lining thickens again
- Ovulation occurs (day 14)
- Uterus lining continues to thicken
What happens during pregnancy?
- Developing embryo releases hormone hCG
- The placenta secretes progesterone and oestrogen
- FSH and LH secretion are inhibited
What is the function of hCG during pregnancy?
Maintains corpus luteum for the 1st 16 weeks of pregnancy
What is the function of progesterone during pregnancy?
- Suppresses the uterine wall’s ability to contract
- Inhibits prolactin
- Promotes growth of mammary glands
What is the function of oestrogen during pregnancy?
- Stimulates growth of the uterus
- Promotes growth of the mammary glands
- Inhibits prolactin
What is prolactin?
- Released from the anterior pituitary gland
- Acts In prolactin receptors on mammary gland cells
- Milk production begins
- Inhibited by high levels of oestrogen and progesterone during pregnancy
What happens during birth?
•Oestrogen levels increase and progesterone levels decrease just before birth
-decrease in progesterone allows the uterine wall to contract
•Oxytocin is released by the posterior pituitary gland
•Prolactin is released by the anterior pituitary gland before and after birth
What is the function of oxytocin during birth?
- Stimulates the contraction of the uterine wall
* Acts on mammary glands to allow milk to be released from the nipple
Examples of positive feedback during birth
•Oxytocin stimulates contraction of the uterine wall
-contractions lead to more oxytocin being released
•Prolactin stimulates mammary glands to produce milk
-feeding causes more prolactin to be released and more oxytocin to be released
What is HPL?
- Protein hormone
- As hCG levels decline,HPL is secreted from the placenta
- It makes breast tissue receptive to oestrogen and progesterone
What is the placenta?
An organ that connects the developing foetus to the wall of the uterus via the umbilical cord
What are the functions of the placenta?
- Exchange of gases and nutrients
- Providing a barrier between the maternal and foetal blood and protection from the differences in maternal and foetal blood pressures
- Protection from the mother’s immune system
- Secretion of hormones
Explain the exchange of gases and nutrients in the placenta (functions of the placenta)
•Foetal and maternal blood flow in opposite directions in capillaries in the placenta
•Countercurrent flow
-maintains a conc gradient
-allows O2 and nutrients to diffuse into the foetus’ blood
-allows CO2 to diffuse out
•The foetal blood flows into and out of the placenta through the blood vessels in the umbilical cord
Explain the protection from the mother’s immune system (functions of the placenta)
As the foetus has different antigens from the mother, the mother’s immune system would attack the foetus if it came into contact with it
Explain the secretion of hormones (functions of the placenta)
The placenta secretes oestrogen and progesterone
What is the function of amniotic fluid?
•Surrounds the foetus
•Protects foetus from impacts
-acts as a shock absorber
What happens during ovulation?
- Secondary oocyte is passed into the oviduct
* Graafian follicle develops into the corpus luteum
Describe how FSH and oestrogen illustrate the principle of negative feedback in controlling ovulation
- FSH is secreted by the anterior pituitary gland
- High levels of FSH stimulate the release of oestrogen from the ovarian follicles
- Oestrogen Inhibits FSH
- Reduces production of oestrogen
- Allows ovulation
