Topic 11.4: Reproduction Flashcards
What is label A?
Spermatozoa
What is label B?
Germline epithelium
What is label C?
Sertoli cells
What is label D?
Leydig cells
What is the function of the testes and what are they composed of?
The testes are composed of seminiferous tubules which produce sperm
What does the germline epithelium cells line and what will they divide to make?
Each tubule is surrounded by a basement membrane which is lined by germline epithelium cells
The germline epithelium will divide by mitosis to make spermatogonia
What will spermatogonia divide by to make?
spermatogonia (which divide by meiosis to make spermatozoa)
What are spermatozoa nourished by?
The developing spermatozoa are nourished by Sertoli cells
What is the function of leydig cells?
Outside of the tubules are blood capillaries and interstitial cells (Leydig cells), which produce the male sex hormone, testosterone
Outline the processes involved in spermatogenesis within the testes, including mitosis, cell growth, the two divisions of meiosis and cell differentiation (6)
Spermatogenesis describes the production of spermatozoa (sperm) in the seminiferous tubules of the testes
The first stage of sperm production requires the division of germline epithelium by mitosis
These cells (spermatogonia) then undergo a period of growth
This is followed by two meiotic divisions that result in four haploid daughter cells
These haploid cells then differentiate to form sperm cells
The developing sperm cells are nourished throughout by the Sertoli cells
What is the role of LH in spermatogenesis?
LH: Stimulates the interstitial cells (Leydig cells) to produce testosterone
What is the role of testosterone in spermatogenesis?
Testosterone: Stimulates the (second) meiotic division of spermatogonia and the maturation of spermatozoa through differentiation
What is the role of FSH in spermatogenesis?
FSH: Stimulates the (first) meiotic division of spermatogonia
What is label A?
corpus albicans
What is label B?
corpus luteum
WHat is label C?
secondary oocyte
What is label D?
Mature (Graafian) follicle
What is label E?
Germline epithelium
What is label F?
Primordial follicles
function of germline epithelium, primordial follicles, mature follicles and secondary oocyte (5)
The ovary contains follicles in various stages of development
Egg cells within primordial follicles have been arrested in prophase I and have yet to undergo meiotic division
Egg cells within mature follicles have begun meiotic division and are released from the ovary as secondary oocytes (arrested in prophase II)
The ruptured follicle develops into a corpus luteum that will, in time, degenerate into a corpus albicans
The germline epithelium functions as an epithelial layer separating ovarian tissue from the rest of the body - it is not involved in oocyte development
Outline the processes involved in oogenesis within the ovary, including mitosis, cell growth, the two divisions of meiosis, the unequal division of cytoplasm and the degeneration of polar body (9)
Oogenesis describes the production of female gametes (ova) within the ovary
The process begins during foetal development, when a large number of cells (oogonia) are formed by mitosis before undergoing a period of growth
These cells begin meiosis but are arrested in prophase I until puberty
At puberty, some follicles continue to develop each month is response to FSH secretion
These follicles complete the first meiotic division to form two cells of unequal size
The cell with less cytoplasm is a polar body (which degenerates), while the larger cell forms a secondary oocyte
The secondary oocyte begins the second meiotic division but is arrested in prophase II (until fertilisation)
It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilisation occurs, will complete meiosis
The second meiotic division will produce an ovum and a second polar body
WHat is label A?
acrosome
what is label B?
nucleus
WHat is label C?
centriole
What is label D?
mitochondria
WHat is label E?
microtubules
What is label F?
cortical granules
What is label G?
zona pellucida (jelly coat)
WHat is label H?
plasma membrane
What is label I?
cytoplasm
What is label J?
nucleus
What is label K?
corona radiata (layer of cells which nourish egg)
Outline the role of the epididymis in the production of semen (2)
Epididymis
Testicular fluids are removed, concentrating the sperm
Sperm mature and develop the ability to swim
Outline the role of the seminal vesicle in the production of semen (2)
Seminal Vesicle
Adds nutrients (including fructose) for respiration
Secretes prostaglandins, causing contractions to the female system and helping sperm move towards the egg
Outline the role of the prostate gland in the production of semen
Prostate Gland
Secretes alkaline fluid which neutralises vaginal acids (changes pH from 4 to 6 which aids sperm motility)
What are two similarities between spermatogenesis and oogenesis?
Both processes result in the formation of haploid gametes
Both processes involve mitosis, growth and meiosis
What is the difference in location between spermatogenesis and oogenesis?
spermatogenesis is in the testis; oogenesis is in the ovary
What is the difference in number of gametes produced between spermatogenesis and oogenesis?
s- life long production (millions); o- fixed amount (only about 400 mature)
What is the difference in gametes per germ cell between spermatogenesis and oogenesis?
s- 4; o- 1
What is the difference in beginning of process between spermatogenesis and oogenesis?
s- begins at puberty; o- begins during fetal development
What is the difference in timing of gamete formation between spermatogenesis and oogenesis?
s- continuous (any time); o- once a month (menstrual cycle)
What is the difference in end of process between spermatogenesis and oogenesis?
s- fertility is life long but reduces; o- fertility stops at menopause
What is the difference in timing of gamete release between spermatogenesis and oogenesis?
s- any time; o- monthly cycle
What is the difference in meiotic divisions between spermatogenesis and oogenesis?
s- uninterrupted; o= arrested
What is the difference in germ line epithelium between spermatogenesis and oogenesis?
s- involved in gamete production; o- not involved in gamete production
Describe the process of fertilisation, including the acrosome reaction, penetration of the egg membrane by a sperm and the cortical reaction (10)
When the sperm enters the female reproductive tract, biochemical changes to the sperm occur in the final part of its maturation (capacitation)
The sperm is attracted to the egg due to the release of chemical signals from the secondary oocyte (chemotaxis)
Fertilisation generally occurs in the oviduct (fallopian tube)
To enter the egg membrane, the sperm must penetrate the protective jelly coat (zona pellucida) surrounding the egg via the acrosome reaction
The acrosome vesicle fuses with the jelly coat and releases digestive enzymes which soften the glycoprotein matrix
The membrane of the egg and sperm then fuse and the sperm nucleus (and centriole) enters the egg
To prevent other sperm from penetrating the fertilised egg (polyspermy), the jelly coat undergoes biochemical changes via the cortical reaction
The cortical granules release enzymes that destroy the sperm-binding proteins on the jelly coat
Now fertilised, the nucleus of the secondary oocyte completes meiosis II and then the egg and sperm nuclei fuse to form a diploid zygote
Outline the role of hCG in early pregnancy (5)
The endometrium is a blood-rich environment in which an implanted zygote can grow and it is sustained by the hormone progesterone
If progesterone levels aren’t maintained (i.e. the corpus luteum degenerates), then the endometrium will be sloughed away (menstruation)
A fertilised zygote develops into a blastocyst that secretes human chorionic gonadotrophin (hCG)
hCG maintains the corpus luteum post-ovulation so that the blastocyst can remain embedded in the endometrium and continue to develop
Gradually the placenta develops and produces progesterone (at around 8 - 10 weeks), at which point the corpus luteum is no longer needed
Outline early embryo development up to the implantation of the blastocyst
After fertilisation, the zygote undergoes several mitotic divisions to create a solid ball of cells called a morula (at around 4 days)
Unequal divisions beyond this stage cause a fluid-filled cavity to form in the middle - this makes a blastocyst (at around 5 days)
The blastocyst consists of:
An inner mass of cells (this will develop into the embryo)
An outer layer called the trophoblast (this will develop into the placenta)
A fluid filled cavity (called the blastocoele)
These developments all occur as the developing embryo is moving from the oviduct to the uterus
When the blastocyst reaches the uterus, it will embed in the endometrium (implantation)
Explain how the structure and function of the placenta maintain pregnancy (6)
The placenta is a disc-shaped structure that nourishes the developing embryo
It is formed from the development of the trophoblast upon implantation and eventually invades the uterine wall
The umbilical cord connects the fetus to the placenta and maternal blood pools via open ended arterioles into intervillous spaces (lacunae)
Chorionic villi extend into these spaces and facilitate the exchange of materials between the maternal blood and fetal capillaries
Nutrients, oxygen and antibodies will be taken up by the fetus, while carbon dioxide and waste products will be removed
The placenta is expelled from the uterus after childbirth
Explain how the hormonal role in secretion of estrogen and progesterone, maintain pregnancy (4)
The placenta also takes over the hormonal role of the ovary (at around 12 weeks)
Estrogen stimulates growth of the muscles of the uterus (myometrium) and the development of the mammary glands
Progesterone maintains the endometrium, as well as reduces uterine contractions and maternal immune response (no antibodies against fetus)
Both estrogen and progesterone levels drop near time of birth
State that the fetus is supported and protected by the amniotic sac and amniotic fluid (4)
The fetus develops in a fluid-filled space called the amniotic sac
Amniotic fluid is largely incompressible and good at absorbing pressure, and so protects the child from impacts to the uterine wall
The fluid also creates buoyancy so that the fetus does not have to support its own body weight while the skeletal system develops
Finally, amniotic fluid prevents dehydration of the tissues, while the amniotic sac provides an effective barrier against infection
WHat materials are exchanged from the maternal blood to the fetal supply? (9)
oxygen, glucose, lipids, water, minerals, vitamins, antibodies, hormones, amino acids
What materials are exchanged from the fetal blood to the maternal blood? (4)
carbon dioxide, urea, hormones, water
utline the process of birth and its hormonal control, including the changes in progesterone and oxytocin levels and positive feedback (9)
The process of childbirth is called parturition and is controlled by the hormone oxytocin
After nine months, the fetus is fully grown and takes up all available space in the uterus, stretching the walls of the uterus
This causes a signal to be sent to the brain, releasing oxytocin from the posterior pituitary
Oxytocin inhibits progesterone, which was inhibiting uterine contractions
Oxytocin also directly stimulates the smooth muscle of the uterine wall to contract, initiating the birthing process
The contraction of the uterine wall causes further stretching, which triggers more oxytocin to be released (causing even more contraction)
Additionally, the fetus responds to the cramped conditions by releasing prostaglandins which cause further myometrial contractions
As the stimulus causing oxytocin release is increased by the effects of oxytocin, this creates a positive feedback pathway
Contractions will stop when labour is complete and the baby is birthed (no more stretching of the uterine wall)
