Sexual reproduction in humans Flashcards
What is the function of the ovary
Female sex organs that produce the female gametes (secondary oocytes) and secrete hormones oestrogen and progesterone.
What is the function of the uterus
Compact muscular organs made of three layers to nourish and protect a growing foetus:
1. perimetrium- thin layer around the outside
2. myometrium- muscle layer
3. endometrium- innermost layer supplied by blood. The embryo becomes implanted in the endometrium, and is shed each month if no embryo.
What is the function of the cervix
Neck of the uterus ( a muscular ring that closes the entrance to the uterus and dilates during birth).
What is the function of the fallopian tube (oviduct)
Connects the ovary to the uterus. Each tube ends in finger-like projections which collect the oocyte following ovulation. Ciliated epithelial cells line the oviduct and convey the secondary oocyte to the uterus.
What is the function of the urethra (female)
Connects to the bladder and allows a passage of urine
What is the function of the vagina
Muscular tube that leads outside of the body
What is the function of the seminal vesicle
Glands that secrete mucus into the vas deferens containing nutrients (e.g. fructose respired by sperm for energy)
What is the function of the Vas Deferens
Tube that takes sperm from testis to the urethra during ejactulation
What is the function of the prostate gland
Found at the base of the bladder that produces an alkaline secretion, neutralising any urine left in urethra, and aids sperm mobility.
What is the function of the urethra (male)
Tube that connects bladder to the outside, passes through the penis and transfers urine and semen outside
Sperm collect and mature here the seminiferous tubule
tubes found in the testis and is the site of sperm production (spermatogenesis)
What is the function of the epididymis
Sperm collect and mature here
What is the function of the testes
produce male gametes (spermatozoa)
What is the function of the scrotum
An external sac that holds the testes outside of the body for optimum sperm production (35 degrees celcius)
What is the function of the penis
An organ used to pass semen into the reproductive system
Where does spermatogenesis occur
seminiferous tubules
Aim of spermatogenesis
Produce many haploid gametes
Steps of spermatogenesis (cell types)
- germinal epithelium cells (dip)
- spermatogonia (dip)
- primary spermatocytes (dip)
- secondary spermatocytes (hap)
- spermatid (hap)
- spermatozoa (hap)
Steps of spermatogenesis (cell divisions)
- mitosis
- mitosis
- meiosis 1
- meiosis 2
- maturity and differentiation
Where in spermatogenesis are sperm cells most mature
At the lumen in a seminiferous tubule
Which cells assist with spermatogenesis and what are their functions
Sertoli cell- provides nourishment to spermatozoa and protect them from the male immune response as they are haploid cells (blood-testis barrier)
Leydig cell- stimulates spermatogenesis and maintains male secondary sexual characteristics
How are there many spermatozoa formed
Many seminiferous tubules makes for a large surface area
Describe the structure of a sperm head
-Haploid nucleus
-Nucleus covered by a lysosome called acrosome at the front (containing enzymes for fertilisation)
Describe the midpiece of a sperm
-Lots of mitochondria
-ATP for movement
-Spiral around the microtubules
What is the function of a tail for a sperm?
-lashing movements to be fast and motile (not until modified in the epididymis)
Where does oogenesis occur?
The ovaries
Steps of oogenesis (cell types)
- Germinal epithelial cell (dip)
- Oogonia/ Oogonium (dip)
- Primary oocyte (dip)
- Secondary oocyte (hap) + first polar body
- Ovum (hap) + polar bodies
What happens before birth in oogenesis?
-Germinal epithelium cells divide by mitosis into oogonia and more germinal epithelial cells.
-The oogonia continue to divide by mitosis and enlarge making primary oocytes and more oogonia.
-primary oocytes begin meiosis 1 but stop at prophase 1
-Germinal epithelial cells divide to form diploid follicle around the primary oocyte (primary follicles)
What happens from puberty onwards in oogenesis?
-FSH stimulates primary follicles to develop
-Before ovulation, meiosis 1 completes forming a haploid secondary oocyte (most of cytoplasm) and the first polar body (less cytoplasm).
-Secondary follicle develops into a Graafian follicle when mature
-Begins meiosis 2 but stops at metaphase 2.
What happens if secondary oocyte is fertilised?
-Meiosis 2 completes making an ovum and a second polar body.
-After ovulation the Graafian follicle becomes the corpus luteum and produces progesterone and some oestrogen.
How many secondary oocytes in the end?
Each month several follicles are formed but normally only one matures into a fully developed Graafian follicle.
What do follicles do for the oocyte?
provides nutrition and protection
What is the zona pellucida?
glycoprotein layer surrounding the cell membrane of the secondary oocyte
What is the corona radiata?
layer of follicular cells around the oocyte
What is FSH and its function
-Follicle stimulating hormone
-produced by anterior pituitary
-stimulates development of follicles of the ovary
What is LH and its function
-Luteinising hormone
-produced by anterior pituitary
-stimulates ovulation
What is oestrogen and its function
-secreted by ovaries
-thickens endometrium
What is progesterone and its function
-produced by corpus luteum (and then placenta if fertilised)
-maintains thick vascularised endometrium
Corpus luteum function
-remains of Graafian follicle
-secretes oestrogen and progesterone
-Inhibit FSH and LH
FSH feedbacks
gonadotrophic releasing hormone (GnRH) (Day 0) –> FSH stimulates follicles to produce… –> … oestrogen –> reduces FSH conc.
LH feedbacks
High concentration of LH (day 14) –> graafian follicle releases secondary oocyte –> increases concentration of FSH
Oestrogen feedbacks
FSH stimulates oestrogen to increase conc. –> triggers rebuilding of endometrium –> inhibits FSH by -ve feedback (reducing oestrogen conc. too) –> stimulates LH production by +ve feedback
Simple process of fertilisation (flowchart)
spermatozoa –> epididymis –> vas deferens –> urethra –> vagina –> cervix –> uterus –> oviduct
How long is fertilisation viable for?
24 hours (how long the secondary oocyte is viable for)
—> however sperm remain viable for 2-5 days, but most fertile for 12-24 hrs
Capacitation in fertilisation
-Removal (through hydrolysing) of cholesterol and glycoproteins from the cell membrane over the acrosome of the sperm head.
-More permeable to Ca+ ions, as the plasma membrane becomes more fluid
-Sperm motility increases
Acrosome reaction in fertilisation
sperm cell –> hydrolytic enzymes digest corona radiata –> acrosome membrane ruptures when reaching zona pellucida secreting more enzymes –> cell membranes fuse –> meiosis 2 completes –> ovum
Cortical reaction in fertilisation
-Sperm entry= Ca+ ions from SER of ovum
-Cortical granules release enzymes (exocytosis)
-Zona pellucida hardens and expands
-Fertilisation membrane (prevents polyspermy)
After fertilisation (implantation)
zygote -(clevage)-> blastocyst -(6 days)-> implantation –>blastocyst sectres HCG –>trophoblasts to chorionic villi
What is a blastocyst
A cluster of dividing cells made by a fertilized secondary oocyte (containing embryo)
What are trophoblasts
Cells that form on the outside of the blastocyst, that later form protusions called chorionic villi, that penetrate the endometrium and become the placenta when the foetus develops
