Biology Unit 4.1 - Sexual Reproduction in Humans Flashcards
How are gametes produced?
Produced in paired glands called gonads:
- Male gametes called spermatazoa are produced in the testes
- Female gametes called egss or ova are produced in the ovaries
Describe the male reproductive system…
Conists of a pair of testes contained in an external sac called the scrotum, which is connected to the penis by genital ducts, that have various accessory glands that provide the constituents of semen
What are the functions of the testes?
Produce haploid male gametes for fertilisation, and production of male hormones e.g., testosterone
Describe the structure of the testes…
- Consist of seminiferous tubules that contai spermatazoa and interstitial cells which produce testosterone
- Sperm produced is collect in the vasa efferentia and then pass to the head of the epididymis
- Pass through the vas deferens during ejaculation
What is the function of the scrotum?
External sac containing the testes
What is the function of the testes?
Produce perm and male testosterone
What is the function of the epididymis?
Location where sperm are stored and matured
What is the function of the vas deferens?
Sperm pass through here during ejaculation to the urethra before leaving the penis
What is the function of the seminal vescile?
Produces a mucus secretion which helps the mobility of the sperm
What is the function of the prostate gland?
Produces an alkaline solution to neutralise the acidity of the urine, and aids with sperm mobility
What is the function of the urethra?
Carries semen through the penis
What is the function of the penis?
Inserted into the vagina during sexual intercourse, where sperm is ejaculated
What is gametogenesis?
Production of gametes in the gonads, where spermatogenesis is the formation of sperm and oogenesis is the fomration of eggs or ova
Germinal epithelium cells of the testes and ovary undergo mitotic and meiotic cell divisions forming haploid gametes
Why is it important gametes are haploid?
Ensures that at fertilisation the diploid number is resotred
What occurs during spermatogenesis?
- Multiplication stage produces spermatagonia that then grow to full size
- Spermatagonia divide to produce primary spermatocytes
- Undergo meiosis, and after the first meiotic division haploid secondary spermatocytes are formed
- Form spermatids after the second meiotic division
- Differentiate to form spermatazoa
What are sertoli cells?
Cells found in the walls of the seminiferous tubules, which secrete a fluid which supplies oxygen and removes waste products, which also protects the spermatazoa from the immune system
What is the midpiece of the spermatazoa ?
Contains mitochodnria in a spiral which provide ATP for movement
What is the nucleus of the spermatazoa?
Contains the haploid number of chromosomes from the male, which fuses with the nucleus of the ova
What is the acrosome of the spermatazoa?
Contain protease enzyme, which digests corona radata cells
What is the function of the ovaries?
Lie inside the abdomen and produce ova
What is the function of the fallopian tubes?
Location of fertilisation
What is the function of the uterus?
Location where the fetus develops
What is the function of the endometrium?
Mucus membrane that internally lines the uterus and is well supplied with blood
Ova fuse here during fertilisation
What is the function of the cervix?
Ring of muscle, which is the opening of the uterus
What is the function of the vagina?
Where sperm are released during sexual intercourse
What is oogenesis?
Process which produces ova, that occurs is three stages, most of which occurs in the ovaries
What occurs before birth?
- Germinal epithelium undergoes mitosis form oogonia and primary oocytes
- Primary oocytes divide by meiosis, which stops at prophase I
- Germinal epithelium divides to form follicle cells, which surround primary oocytes to form primary follicles
- Primary oocytes do not mature until just before ovulation
- Two million are formed, but only 45- develop into secondary oocytes
What occurs during puberty?
- Hormones stimulate further development of follicles
- Only one matures into a Graafian follicle
- Primary oocyte form haploid secondary oocyte and a small polar body
- During ovulation Graafian follicle releases the secondary oocyte into the fallopian tube
- Secondary oocyte begins the second meiotic division, which is stooped at metaphose II
What occurs after fertilisation?
- Second meiotic division is completed to form a large ovum and second polar body
- Nucleus of the ovum fuses with that of the sperm to form a zygote
- This develops into an embryo
What occurs in males during sexual intercourse?
- Penis is inserted itno the vagina to introduce sperm into the reproductive tract
- Sexual excitement results in an erection, caused by dilation of arteries entering the penis, flow of arterial blood into spongy tissue, and constriction of veins leading out
- Raises blood pressure and increases blood volume
- If this continues orgasm will be reached
- Muscles of the prostate gland, seminal vesicles, vasa deferentia and urethra contract
- Semen is ejaculated, containing up to 400 million spermatozoa
What occurs in females during sexual intercourse?
- Blood supply to the sexual organs is increased
- Labia swell and clitoris may become erect
- Vagina explands and extra mucus fluid is secreted; lubricates the action of the penis
- Orgasm occurs, resulting in muscular contraction of the vagina and uterus
How is sperm transported in the female?
- Force of ejaculation forces sperm through the cervix
- Most is deposited at the top of the vagina near the cervix
- Can survive for 48 hours
- Alkaline semen protects the sperm from the acid fluid of the vagina
- Sperm swim through the uterus into the fallopian tubes
- Only a small proportion reach the site of fertilisation
What occurs during fertilisation?
- Secondary occyte present in the fallopian tube, surrounded by corona radiata and the zona pellucida
- Only one sperm will of the several hundered that surround it will penetrate
What is capacitation?
Removal of cholesterol and glycoproteins from the cell membrane over the acrosome in the sperm head, causing the membrane to become more fluid and more permeable to calcium ions
What occurs during the acrosome reaction?
- Acrosome releases proteases
- Acrosome membrane ruptures, releasing more protease and acrosin, which hydrolyse the zona pellucida
- Sperm will attach to specific receptors in the zona pellucida
- Acrosome becomes inverted, forming a fine needle-like filament, which helps penetrate the zona pellucida
- Enzymes digest a path through into space between zona pellucida and secondary oocyte, where vigorous tail lashing helps the process
- The membrane surrounding the sperm head fuses with the secondary oocyte membrane, and movement stops
- Sperm nucleus enters the oocyte’s cytoplasm
What occurs during the cortical reaction?
- Entry of sperm forms fertilisation membranes
- Prevents polyspermy
- Sperm attaches to the secondary oocyte, its smooth endoplasmic reticulum releases calcium ions
- Causes cortical granules to fuse to the cell membrane and release enzymes by exocytosis
- Zona pellucida is chemically modified and expands, forming a fertilisation membrane
- Entry of sperm stimulates completeion of the second meiotic division
- Nuclei of th ovum and sperm are drawn together and fuse to form a diploid membrane
What occurs during mitosis?
- First mitosis combines the genetic material of the parents
- Sperm and ovum chromosomes join at the equator, forming a zygote
- Second polar body is expelled
What occurs during implantation?
- Zygote forms a hollow ball of cells called a blastocyst
- Development continues, where zygote reaches the uterus and embeds in the endometrium
- Outer layer, called a trophoblast, develops into the amnion and chorion
- Chorion will grow chorionic villi, which increases surface area for nutrient absorption and forms the placenta
- Chorion releases human chorionic gonadtrophic (hCG) to prevent degeneration of the corpus luteum
- Corpus luteum plays a key role in hormone production
How does the placenta function as an endocrine organ?
Produces hormones to support pregnancy
How does the placenta function as an exchange organ?
Exchanges nutrients, waste products and respiratory gases between the mother’s and foetus’ blodd
How does the placenta function as a physical barrier?
Protects feotal capillaries from damage by higher blood pressure and changes in blood pressure of the mother
How does the placenta prove passive immunity?
Maternal antibodies cross the placenta and attack pathogens but the foetal cells
How does the placenta protect against the mother?
Mother doesn’t make an immune response against the foetus or placenta:
* Cells of the wall of the chorionic villi fuse so there are no spaces between them
* Migratory immune cells can’t et through the foetal blood
Why is complete immunological protection provided by the placenta?
- Spontaneuos abortions are equivalent to the rejection of a transplanted organ
- Rhesus disease destroys foetal blood cells in a rhesus positive foetus of a rhesus negative mother
- Pre-eclampsia, leading to very high blood pressure
- Rubella virus can cross the placenta, as can nicotine and heroin
What is the umbilical chord?
Develops from the placenta and transfers blood between the mother and foetus:
* Blood entering the foetus is low in nutrients and deoxygenated
* Blood returning from the foetus is high in nutrients and oxygenated
What occurs during the menstrual cycle?
- Endometrium sheds through menstruation, which occurs from the first period until menopause
- Is a system of positive and negative feedback mechanisms involving the brain, ovaries and the uterus and many hormones
What is the function of FSH?
Stimulate the development of primary follicles in the overy, where one matures and forms the theca, which secretes fluid into the antrum and produces oestrogen
What is the function of LH?
Induce ovulation and cause the Graafian follicle to release a secondary oocyte
What is the function of the corpus luteum?
Secretes oestrogen and progesterone
What is the function of oestrogen?
- Triggers the rebuilding of the endometrium
- Inhibits FSH secretion by negative feedback
- Stimulates LH production
What is the function of progesterone?
Maintains the newly built endometrium
What is the amnion?
Membrane surrounding the foetus formed from the inner cell mass of the blastocyst
What are the functions of amniotic fluid?
- Push the amnion out as far as the chorion
- Maintains foetus temperature
- Provide lubrication
- Contribute to lung development
- Allow movement so muscles and bones function
- Acts as a shock absorber
What occurs during the first trimester?
Conception, implantation and embryogenesis, while all major organs are laid down
What occurs during the third trimester?
Major structures are complete, and is a major period of growth as fat is laid down
What is the function of oxytocin?
Causes contractions of the myometrium, which become stronger and more frequent as concentration increases
What is the function of prolactin?
Stimulate glandular tissue to synthesise milk, which is released when oxytocin causes muscle around the milk ducts to contract
