4.1 Sexual AReproduction In Humans Flashcards
What is the cell that begins oogenesis and where is its position? n?
Germinal Epithelium, and are the outer layer of cells of the ovary. They are diploid, 2n
(Oogenesis) What type of division does the germinal epithelium undergo and what are the products?
Undergoes mitosis many times to produce diploid oogonia and more germinal epithelium.
After growth and development of an oogonium, what is the product called?
A diploid primary oocyte.
At which stage does the primary oocyte stop meiosis I? And until when?
Meiosis I is stopped at prophase I, until puberty.
At puberty, what is the product after a diploid primary oocyte has gone through meiosis I fully?
The product is a haploid secondary oocyte, with a smaller first polar body.
At what stage of meiosis II does the secondary oocyte stop? Until when?
It stops at Metaphase II, until the egg is fertilised.
After the secondary oocyte is fertilised, what is the product?
A haploid ovum, with a second polar body.
Why are polar bodies formed?
Because the cell must divide its genetic material, but wants to keep as much cytoplasm as possible, so one cell has half genetic material and some cytoplasm, and one has half genetic material and most of the cytoplasm.
What surrounds a primary oocyte and how is it formed?
Diploid follicle cells, which are produced from germinal epithelium cells dividing. Diploid follicle cells surround the primary oocyte to form a primary follicle.
What is another name for a secondary follicle when it has matured?
A Graafian follicle.
Describe briefly the process of ovulation.
The Graafian follicle migrated to the surface of the ovary and bursts, releasing the secondary oocyte.
Where does fertilisation take place? What is the next product of oogenesis?
Fertilisation takes place in the oviduct, and an ovum with a second polar body is formed.
What happens to the Graafian follicle after ovulation? What happens if the egg is fertilised?
It becomes the corpus luteum/yellow body and degenerates. If fertilisation occurs, it produces hormones.
What is the structure that surrounds the cell membrane of the secondary oocyte?
A carbohydrate layer called the zona pellucida.
What are cortical granules? Where are they?
They are secretory organelles that prevent the entry of more than one sperm. They are found at the periphery of the cytoplasm of a secondary oocyte.
What are the cells that surround the secondary oocyte and provide nutrients?
Corona Radiata.
What is the sequence of layers of the secondary oocyte/ Graafian follicle, from inside to outside?
Secondary oocyte, zona pellucida, cells of corona radiata, antrum, theca.
What does the oocyte release that attract sperm to it?
Chemoattractants.
How long are spermicide viable for? What is their most fertile time period?
Viable for 2-5 days but most fertile between 12-24 hours after ejaculation.
When is a secondary oocyte most fertile?
Within 24 hours of ovulation, when it is in the oviduct.
Describe Capacitation.
Cholesterol and glycoproteins are removed from the cell membrane over the acrosome in the spermicide head. Hours later, the membrane is more fluid and permeable to calcium ions.
Describe the second stage of fertilisation, the acrosome reaction.
The acrosome of the sperm head releases proteases and digests the cells of the corona radiata. When the acrosome touches the zona pellucida, it ruptures and releases the protease acrosin, which digests the zona pellucida.
The cell membranes of secondary oocyte and sperm fuse and spermicide head enter cytoplasm, to form an ovum
What is the cortical reaction?
After sperm head entry, the SER of the oocyte releases calcium ions, which makes the membranes of cortical granules fuse with the cell membrane and release their enzymes by exocytosis. The zona pellucida becomes hard and expands, making a fertilisation membrane which prevents more sperm penetrating: polyspermy.
What happens about 24 hours after fertilisation and the Meiosis II?
Mitosis combines sperm nucleus and ovum nucleus, as the sperm and ovum chromosomes line up on the cell’s equator. This is now a zygote. The first mitotic division occurs and two cells are formed.
What is the ball of cells dividing by mitosis called up until it is 10 weeks and has organ formation?
And embryo
What is an embryo called after 10 weeks?
A foetus.
What is the sequence of mitotic division called between 2 cells and 16 cells?
Cleavage.
How long does it take for the embryo to form 16 cells, and what is this called?
3 days to form a morula.
What happens after 7 days of cleavage?
The morula becomes hollow and is called a blastocyst.
What are the cells around the outside of the blastocyst called? What do they divide to make? Where does the blastocyst move to?
Outer cells called trophoblast she and they form an inner cell mass on one side. The blastocyst moves from oviduct into uterus.
What is the process called where the blastocyst embeds on the endometrium wall?
Implantation
What does the trophoblast develop into?
Develops into the chorion, and its cells move into trophoblastic villi and form much larger chorionic villi.
What do chorionic villi do?
They acquire blood capillaries which connect to the umbilical artery and vein. These blood vessels connect the embryo to the uterus through the umbilical cord.
What are the maternal tissues of the placenta?
Projections from the endometrium wall that fit between the chorionic Villi.
Briefly list the roles of the placenta. 5 main points
- Endocrine organ
- Exchange between mother and foetus
- Physical barrier between foetal and maternal circulation
- Provides passive immunity from mother to foetus
- Prevent attack from mothers immune system
Explain how the placenta allows area of exchange between mother and baby.
Lacunae are inter-villous spaces that contain the mothers blood and surround chorionic villi.
Rate & efficiency increased because:
Chorionic microvilli
Small distance across the wall of chorionic villi
Conc gradient maintained by a countercurrent flow
What is exchanged between a mother and foetus’ blood?
Nutrients, waste products, and respiratory gases.
Why is the placenta important as a physical barrier?
Protects the fragile capillaries from higher blood pressure in mother,
Protects foetus from the mothers changes in blood pressure.
How does the placenta provide immunity?
Maternal antibodies cross the placenta and attack pathogens without attacking the foetal cells.
How does the placenta provide protection from the mother’s immune system?
Cells of the wall of the chorionic villi fuse together so there are no spaces between them, forming a syncitium, this prevents migratory immune cells from the mother from getting to the foetal blood.
How does the placenta sometimes fail at providing immunological protection?
- Spontaneous abortions caused by response similar to rejection of a transplanted organ.
- Rhesus disease, where rhesus -ve mother creates antibodies that attacks a rhesus +ve foetus. Causes it to destruct foetal blood cells
- an abnormal immune response can cause pre-eclampsia which is very high blood pressure of mother.
What drugs/ virus can pass through placenta to foetus?
Rubella,
Nicotine and heroin
What are the 4 significant hormones in the menstrual cycle?
Follicle Stimulating Hormone, Luteinising Hormone, Oestrogen, Progesterone
What is the feedback system that controls the menstrual cycle?
Negative feedback
Which Hormone is secreted by the Hypothalamus in the brain? What does this stimulate?
Gonadotrophic Releasing Hormone, which stimulates the anterior pituitary gland to secrete FSH and LH.
What does FSH do?
It stimulates the development of primary follicles in the ovary, and causes them to develop a fibrous outer layer called the Theca.
FSH stimulates Thecal cells to secrete oestrogen.
The Theca secretes fluid into the Antrum.
Only one develops into a Graafian follicle.
What 2 things does the oestrogen do, after it has been secreted by the Thecal cells?
It stimulates the build up of the endometrium, and inhibits the further secretion of FSH.
What does a high level of Oestrogen cause?
It continues to build up the endometrium wall, but also stimulates the Anterior Pituitary Gland to secrete Luteinising Hormone
What does LH do when the it is secreted by the APG?
It stimulates ovulation, and the Graafian follicle releases the secondary oocyte.
It also stimulates the conversion of the Graafian follicle into the corpus luteum / yellow body.
What does the Corpus Luteum secrete? What does it do?
Corpus Luteum secretes Progesterone, which maintains the lining of the endometrium, so it is ready for implantation.
The Progesterone and Oestrogen both inhibit FSH and LH, to prevent development and ovulation. When FSH and LH get really low, the corpus Luteum begins to degenerate, so the endometrium lining is not maintained and it’s shed and Oestrogen levels are low.
What happens when the oestrogen levels are low?
It is no longer inhibiting FSH, so the Hypothalamus begins the cycle again.
Typically how long is a pregnancy and when does the timeframe start?
Between 39-40 weeks
Starts from the first day of the last period until birth.
Where is the amnion derived from?
The inner cell mass of the blastocyst.
When does amniotic fluid accumulate? How long does it accumulate for?
Week 4-5 for 6-7 months
What does the amniotic sac have after 4 months?
Urine from the foetus
What is is amniotic fluid?
98% water, urea, salts, a little protein and trace of sugar.
What can the volume of amniotic fluid tell you and why?
If the foetus’ swallowing reflex is normal because they tend to swallow around 500ml per day.
What does the amniotic fluid do?
Maintain temperature Provides lubricant Contributes to lung development Allows movement to exercise muscles Shock absorber
What happens during the first trimester of pregnancy?
Brain hemispheres,
electrical activity in brain
Eyes, mouth and ears visible and heart beats
Foetus makes involuntary movements
What happens in the second trimester of pregnancy?
Some open their eyes
Movements can be felt
What is hCG and where is it secreted from? What does it do?
Human Chorionic Gonadotrophin. 6 days after fertilisation the blastocyst secretes it
After implantation, Chorion secretes it.
It maintains the corpus luteum in its secretion of Progesterone, which maintains the endometrium lining.
How long is hCG secreted for?
First 16 weeks
The corpus luteum and placenta secretes oestrogen and progesterone, which inhibits….
-FSH so no more follicles mature Inhibits -LH to ovulation does not occur -prolactin so milk isn't made Progesterone inhibits oxytocin, so myometrium and milk ducts don't contract
What else does oestrogen do when secreted during pregnancy?
- Stimulates growth of the uterus to accommodate for foetus
- stimulates growth of mammary glands, and increases their blood supply (mainly during 3rd trimester)
What happens at the very end of pregnancy?
The foetus secretes hormones to the mother, and her progesterone levels in the blood decline, so oxytocin and prolactin is no longer inhibited.
Oxytocin is secreted which has a positive feedback on itself, secreting more and making the myometrium of the uterus contract.
Prolactin stimulates mammary glands to synthesis milk. Milk is released when oxytocin stimulates muscles around milk ducts to contract.
Which feedback does FSH have on Oestrogen at the beginning of the cycle?
Positive
What effect does LH have on FSH
Positive feedback
What feedback does Oestrogen have on, FSH LH, Prolactin, Oxytocin
Negative
Positive
Inhibit
Inhibit
In males, what does LH or ICSH do?
Stimulate Leydig cells to secrete testosterone, which effects sleek development and secondary sexual characteristics
What do germinal epithelium ceos form when they go through mitosis in males?
They form diploid spermatogonia and more germinal epithelium cells.
What forms after spermatocytes grow and enlarge?
Forms diploid primary spermatocytes and more soermatogonia
When primary spermatocytes undergo Meiosis I, what’s formed?
Secondary spermatocytes which are haploid
What happens when secondary spermatocytes undergo Meiosis II?
They make haploid spermatocytes
What do spermatids mature into?
Spermatozoa/ sperm
When is sperm produced?
At puberty
What modifications do spermatocytes cells have?
An acrid one filed with enzymes that help with fertilisation
Lots of mitochondria in the middle piece to give energy
Flagellum to propel it when it is mixed into semen
What are Sertoli cells and where are they found?
They secrete a fluid that nourishes the spermatid and protects it from the male’s immune system.
They are found in the testes between the stands of developing spermatids
Where is sleek produced?
In seminiferous tubules in the testes
What are seminiferous tubules?
Coiled tubes. The outer layer are germinal epithelium and they undergo mitosis and meiosis so that sperm are formed.
Cells get closer and closer to the lumen of the tubules.
What happens when spermatozoa reach the lumen?
They move through tubule and collect in the vasa efferentia which are coiled tubes that carry spermatocytes to the head of the epididymis. They remain here until they become motile.
What happens during ejaculation?
Motile spermatozoa pass into the vas deferens and move towards the penis. On the way, seminal vesicles secrete mucus into the vas deferens, which contains fructose for energy. The sperm and mucus pass through the ejaculatory duct, which passes through the prostate gland, where zinc contains by fluid is secreted.
What is the purpose of the fluid secreted by the seminal vesicles and prostrate gland?
- maintain sperm mobility
- provide nutrients
- neutralise acidity of urine in urethra
- neutralise acidity if vaginal tract
What is the mixture of sperm, seminal mucus and prostate fluid known as?
Semen
