4. Sexual reproduction in Humans Flashcards
What is the function of the vas deferens?
They carry sperm from the epididymus to the urethra and towards the penis.
What is the function of the prostate gland?
It secretes a Zn2+ mucus to neutralise the acidity of the urethra and vaginal tract.
What is the function of the seminal vesicle?
It secretes nutrients such as fructose for the sperm to maintain their motility.
What is the function of the urethra?
It carries semen and urine to the penis.
What is the function of the epididymus?
It is where sperm mature and become motile.
What is the function of the testes?
They are made from seminiferous tubules, which are the site of spermatogenesis.
What is the function of the scrotum?
Loose skin made to hold the testes outside of the body at their optimum temperature.
What is the function of the penis?
It is inserted into the vagina during sexual intercourse.
What is the function of the ovary?
It is the site of oogenesis, releasing a secondary oocyte at ovulation alternates each month.
What is the function of the oviduct?
It is the site of fertilisation, and contains ciliated epithelial cells to sweep the oocyte towards the uterus.
What is the function of the cervix?
It is a ring of muscle and connective tissue to prevent infection.
What is the function of the vagina?
It has muscular walls which open at the vulva for contractions during birth.
What is the function of the uterus?
It is where the foetus develops.
What is the function of the perimetrium?
It is the thin, outside layer of the uterus.
What is the function of the myometrium?
It is the muscular, second-innermost layer of the uterus.
What is the function of the endometrium?
It is the innermost mucus membrane of the uterus which builds and sheds monthly, and is the blastocyst site of implantation.
What are the three layers of the uterus?
Perimetrium
Myometrium
Endometrium
What is gametogenesis?
The production of gametes in the sex organs
What is spermatogenesis?
The formation of sperm in the testis.
What is oogenesis?
The formation of secondary oocytes in the ovary.
Describe spermatogenesis
Diploid cells of the germinal epithelium divide by mitosis to make diploid spermatogonia. The spermatogonia divide many times by mitosis, making more spermatogonia. Some enlarge, making primary spermocytes. The diploid primary spermocytes undergo meiosis I, making secondary spermatocytes, which are haploid. These then undergo meiosis II, making haploid spermatids which mature into spermatozoa.
State the stages of spermatogenesis
Germinal epithelium cell –> Spermatogonia –> Primary spermocytes –> Secondary spermatocytes –>Spermatids –> Spermatozoa
Apart from those involved in spermatogenesis what other cells are in the testes?
Leydig cells which secrete testosterone, helping sperm formation and maturation as well as the development of secondary sexual characteristics, and Sertoli cells which secrete a fluid which nourishes the developing sperm and protects them from the males immune system.
Describe sperm structure
The head contains a haploid nucleus, covered at the anterior end by the acrosome, which contains hydrolytic enzymes, used at facilitation. The middle piece is packed with mitochondria, which provide ATP for movement.
State the parts of a sperm
Acrosome
Cell membrane
Nucleus
Centriole
Mitochondria
Flagellum
Axial filament
Describe oogenesis
Before birth, cells in the germinal epithelium of the ovary divide by mitosis to make diploid oogonia. The oogonia divide many times by mitosis and enlarge, making primary oocytes and more oogonia. The primary oocytes begin meiosis I in the ovaries. Germinal epithelium cells also divide to make follicle cells which surround the primary oocyte, making primary follicles. From puberty, the primary follciles develop and just before ovulation, a primary oocyte completes meiosis I making a secondary oocyte, and the primary follicle develops into a Graafian follicle. The secondary oocyte is released out of the ovary and begins meiosis II but stops until fertilisation has taken place.
State the stages of oogenesis
Germinal epithelium cell –> Oogonium –> Primary oocyte (at birth) –> Secondary oocyte –> Ovum (at fertilisation)
What happens to the Graafian follicle after the secondary oocyte is released?
After ovulation, the Graafian follicle becomes the corpus luteum. If fertilisation occurs, it produces hormones, but otherwise it regresses.
At which part of meiosis II does the secondary oocyte stop unless fertilised?
Metaphase II.
Describe the structure of the Graafian follicle
A glycoprotein layer called the zona pellucida surrounds the cell membrane of the secondary oocyte. The periphery of the cytoplasm contains cortical granules, secretory organelles which prevent polyspermy. Corona radiata cells surround the secondary oocyte and provide nutrients. There is also an antrum and a theca,
Why is fertilisation described as a process?
As it may take hours between sperm being deposited in the vagina and the completion of the fusion of the genetic material of the gametes.
What is capacitation?
The removal of cholesterol and glycoproteins from the cell membrane over the acrosome in the sperm head. Over several hours the membrane becomes more fluid and more permeable to calcium ions. Meanwhile. the tail motion changes to a whipping movement, increasing sperm motility. The sperm respond to the oocytes chemo attractants and swim towards the oviduct
What is the acrosome reaction?
The acrosome releases hydrolytic enzyme which digest the cells of the corona radiata. On contact with the zona pellucida the acrosome membrane ruptures and releases more enzymes which hydrolyse the zona pellucida around the secondary oocyte. The cell membranes of the secondary oocyte and the sperm fuse, producing an ovum.
What is the cortical reaction?
When the sperm attatches to the secondary oocyte, the oocytes smooth endoplastic reticulum releases calcium ions into the cytoplasm. They make the cortical granules fuse with the cell membrane and release their contents of enzymes by exocytosis. The zona pellucida is chemically modified and expands and hardens, making a fertilisation membrane, preventing polyspermy.
What is cleavage?
When the embryo is moving down the oviduct, dividing many times by mitosis.
What is the ball of 16 cells formed in three days called?
A morula.
What is the hollow ball of cells formed in seven days called?
A blastocyst.
Describe the structure of a blastocyst
The cells around the outside of the blastocyst are trophoblasts, which divide to make an inner cell mass inside the blastocoele. After nine days, trophoblastic villi protrude from the blastocysts ane pentrate the endometrium to implant.
What parts of the blastocyst forms the placenta?
The trophoblast becomes the chorion, an outer membrane surrounding the embryo and placenta, while the inner cell mass forms the embryo and the amnion.
What are the major roles of the placenta?
As an endocrine organ, producing hormones to support the pregnancy
Exchange between the mother and foetus’s blood
A physical barrier between the foetal and maternal circulation
Providing passive immunity to the foetus
Protection from the mothers immune system
How is the placenta adapted for efficiency?
Chorionic villi have microvilli, increasing surface area and having a short diffusion distance for diffusion, active transport, pinocytosis and osmosis. It has a concentration gradient which is maintained by counter-current flow.
What does the umbilical cord consist of?
Two umbilical arteries and one umbilical vein.
What does the umbilical artery have?
High blood pressure
Low O2
High CO2
Low glucose
High urea
What does the umbilical vein have?
Low blood pressure
High O2
Low CO2
High glucose
Low urea
What is pregnancy?
The time from the first day of the last period until birth, lasting around 39 weeks.
How does the amnion grow throughout pregnancy?
Initially the amnion is in contact with the embryo but in weeks 4-5, amniotic fluid accumulates and increases volume for 6-7 months, with the foetus adding urine from 4 months. The fluid pushes the amnion out, eventually as far as the chorion, the inner layer of the placenta.
What is amniotic fluid comprised of?
It is 98% water, a solution of urea, salts, proteins and sugar with some foetal cells.
What is the function of amniotic fluid?
Maintains the foetus’s temperature
Provides lubrication and allows movement
Contributes to lung development
Acts as a shock absorber
By the end of pregnancy, what is the volume of amniotic fluid in the amnion?
1dm3.
How many trimesters is pregnancy divided into?
Three.
What does the first trimester include?
Conception, implantation and embryogenesis, and is where all major organs are laid down.
What does the second trimester include?
Mostly development of the foetus.
What does the third trimester include?
Where all major structures are complete and the foetus’s mass triples.
What does the menstrual cycle consist of?
A system of positive and negative feedback, operating between the events involving the brain, the ovaries and the uterus.
What are the significant hormones of the menstrual cycle?
Follicle stimulating hormone (FSH)
Luteinising hormone (LH)
Oestrogen
Progesterone
What stimulates the anterior pituitary gland on day 0?
GnRH secreted by the hypothalamus.
Describe the changes in concentration of FSH in the plasma during the menstrual cycle
FSH is secreted on day zero which stimulates the development of primary follicles in the ovary. Concentration increases as the mature Graafian follicle is stimulated to produce oestrogen. Concentration then decreases as progesterone is also secreted, having negative feedback on FSH
Describe the changes in concentration of LH in the plasma during the menstrual cycle
LH is secreted on day zero and reaches its maximum concentration on day 14, to induce ovulation. Its high concentration causes the Graafian follicle to release the secondary oocyte. It has a positive feedback on FSH. As the Graafian follicle converts to the corpus luteum and secretes progesterone, LH is inhibited and concentrations decrease.
What hormones does the placenta produce?
hCG
Oestrogen
Progesterone
FSH
LH
Prolactin
What is the function of FSH and where is it secreted in females?
Secreted by the anterior pituitary gland, it stimulates the Graafian follicle and has positive feedback on oestrogen early on in the menstrual cycle.
What is the function of LH and where is it secreted in females?
Secreted by the anterior pituitary gland, it stimulates ovulation and has a positive feedback on FSH. It also stimulates the conversion of the Graafian follicle to the corpus luteum.
What is the function of oestrogen and where is it secreted?
Secreted by the theca, corpus luteum and the placenta, it inhibits prolactin synthesis. It also rebuilds the endometrium and has a negative feedback on FSH and a positive feedback on LH.
What is the function of progesterone and where is it secreted?
Secreted by the corpus luteum and the placenta, it maintains the endometrium and inhibits oxytocin during pregnancy. It also has negative feedback on FSH and LH.
What is the function of oxytocin and where is it secreted?
Secreted by the hypothalamus, it stimulates the contraction of muscle in the myometrium and the contraction of muscle in milk ducts.
What is the function of prolactin and where is it secreted?
Secreted by the anterior pituitary gland, it stimulates milk synthesis in pregnancy.
What is the function of hCG and where is it secreted?
Secreted by the anterior pituitary gland, blastocyst and placenta, it maintains the corpus luteum.
What is the function of FSH and where is it secreted in males?
Secreted by the anterior pituitary, stimulates sperm development.
What is the function of LH and where is it secreted in males?
Secreted by the anterior pituitary gland, stimulates the Leydig cells.
What is the function of testosterone and where is it secreted?
Secreted by leydig cells, stimulates sperm development and secondary sexual characteristics.
