Module 2 - Reproductive Anatomy Flashcards
What happens in sexual reproduction?
There is the fusion of haploid gametes to form the diploid cell, the zygote
What happens in asexual reproduction?
New individuals are generated through mitotic cell division
What is parthenogenesis?
Example of asexual reproduction
Egg develops without being fertilised
Doesn’t need a male to breed
E.g. honeybees, male are fertile haploid adults that arise by parthenogenesis
2 types of parthenogenesis:
- Haploid parthenogenesis: Meiosis ——–> Oocyte —-> Haploid zygote
- Diploid parthogenesis: Has 2 types, Automixis and Apomixis.
Automixis: Meiosis -> Oocyte -> Fuse with other oocyte -> diploid zygote
Apomixis: Mitosis -> Female egg cell -> diploid egg
Benefit of sexual reproduction over asexual
Animals that use sexual reproduction are more likely to be able to adapt to changes in the environment than asexual. Fertilisation in sexual reproduction shuffles and reshuffles genes, generating a lot of diversity.
How are reproductive cycles controlled?
By hormones like melatonin secreted by the pineal gland - regulated by environmental cues e.g. sunlight
Why are environmental cues in reproductive cycles important?
Because animals only reproduce when there is sufficient energy sources and environmental conditions that favour the survival of the offspring
At what stage of the reproductive cycle does ovulation occur?
The midpoint
2 reproductive cycles in a female
Ovarian and uterine
What 2 phases are in the ovarian cycle?
Follicular (follicle grows) and luteal phase (corpus luteum forms and then degenerates)
What 3 phases are in the uterine cycle?
Menstrual flow,
Proliferative phase - rising oestradiol levels cause endometrial lining to proliferate and thicken
Secretory phase - corpus luteum secretes progesterone which allows endometrium to become receptive to blastocysts
What 2 hormones secreted by the pituitary gland work together to control ovulation?
Follicle Stimulating Hormone (FSH) and LH (Luteinising Hormone)
What hormones are secreted by the ovaries in the menstrual cycle?
Estrogen and progesterone
Do animals that reproduce asexually also exhibit reproductive cycles?
Yes.
For example, the Daphnia, during winter, there’s a sexual phase. Diapausing egg is made from mating. Then it switches over to asexual phase and becomes parthenogenic cycle.
When is asexual reproduction advantageous?
In stable environments as it perpetuates successful genotypes precisely and there can be more offspring produced
What is courtship behaviour?
When an individual adopts certain behaviour that results in mating e.g. an animal who reproduces asexually adopting a female behaviour when the hormone oestradiol is high and witches to male like behaviour when the level of hormone progesterone is high. The progesterone is good as it inhibits muscular contractions once an egg has been fertilised.
2 types of fertilisation
- External fertilisation - female released eggs into environment where male then fertilises them. Zygote development occurs outside the body. Male and female release outside in a medium like water
- Internal fertilisation - sperm deposited near or in female reproductive tract and fertilise eggs within the tract. Zygote development occurs inside body
What kind of habitat is required in external fertilisation?
Moist habitat so gametes dont dry out and sperm needs to be able to swim to fertilise eggs.
Why is timing crucial in external fertilisation?
Eggs and sperm need to be released at the same time in order to fertilise
How do animals find their mates?
Pheromones - chemicals released by one animal that can influence the physiology and behaviour of others individuals of the same species
What does internal fertilisation allow?
The union of gametes to occur in moist environments even if the animal is on land
Protects the offspring from predation or dispersal
Means fewer eggs are required to ensure a successful number of offspring survive
2 Advantages of internal fertilisation
- More offspring survive due to protection and parental care
- Successful fertilisation more likely
3 disadvantages of internal fertilisation
- Requires more energy to find a mate
- Fewer offspring produced
- Large investment from female parent may leave her vulnerable
3 advantages of external fertilisation?
- Little energy needed to find a mate
- Many offspring produced
- Offspring not in competition with parents
3 disadvantages of external fertilisation
- Many gametes do not survive or are not fertilised
- Zygotes and embryos are unprotected
- No parental care means many offspring don’t survive into adulthood
What is the source of food for marsupial zygotes?
Yolk inside egg
When is the embryo of a marsupial born?
Relatively premature stage compared to placental mammals: completes development externally in a pouch which contains mammary gland (produces milk for small baby)
Differences between placental mammals and marsupials
Placental animals:
1. Nourish fetus via placenta
2. Most diversified mammals
3. Have ossified patellae and corpus collosum
4. Dominant and large population
Marsupial:
1. Give birth to undeveloped young and nourish them in pouch
2. Less diverse
3. Smaller population
3 main types of mammals
- Monotreme - young hatches from egg and then mother nurtures it into adulthood: produces milk (lactates)
- Marsupial - birth developed young, lactate
- Placental - small gestation period. Lactates
Where is sperm produced
The testes produce sperm in seminiferous tubules
What temperature are the testes maintained at?
About 2 degrees below core body temperature
Path of the sperm
From the seminiferous tubules of a testis, the sperm pass into the coiled duct of an epididymis. During ejaculation, the sperm are propelled from each epididymis through a muscular duct (the vas deferens)
The ejaculatory ducts open into the urethra
3 sets of accessory glands in males
- Semina vesicles
- Prostate gland
- Bulbourethral glands
These produce secretions that combine with sperm to form semen (because gametes need a moist environment and these are the 3 glands that provide the moist environment)
Acronym: VG
Vesicular Gland
Acronym: A
Ampulla
Acronym: BP
Prostate
Acronym: DD
Ductus deferens / Vas deferens
Acronym: GP
Glans Penis
Acronym: PS
Penile Shaft
Acronym: T
Testis
What is spermatogenesis?
Formation and development of sperm. All 4 products of meiosis develop into mature gametes
Acronym: TE
Testicle (Testis + Epididymis)
Acronym: EB
Epididymis
What is the outer layer of each ovary packed with?
Follicles each consisting of an oocyte, a partially developed egg, surrounded by support cells
Name for premature sperm on the outside of a testis tube?
Spermatocyte
Where does the oviduct extend from?
The uterus towards funnel-like opening at each ovary
Sperm on the inside of testis tube
Spermatozoa
Upon ovulation, what happens in the female anatomy
Cilia on the epithelial lining of each oviduct helps collect the egg by drawing fluid from the body cavity into the oviduct.
Together, with wavelike contractions of the oviduct, the cilia conveys the eggs down the duct to the uterus.
The inner lining of the uterus, the endometrium, is richly supplied with blood vessels
The neck of the uterus, the cervix, opens into the vagina
What occurs inside the ovaries:
Oogenesis: development of mature oocytes is a prolonged process in the human female
- immature eggs form in the ovary of female embryo but do not complete their development until teenage years
- cytokinesis during meiosis is unequal with almost all the cytoplasm segregated to a single daughter cell (the large cell from this is destined to become the egg, the other products are known as polar bodies and degenerate)
The endocrine control of reproduction begins with what…
The hypothalamus which secretes Gonadotropin-Releasing Hormone (GnRH)
This hormone then directs the anterior pituitary gland to secrete FSH and LH
In females, FSH and LH act on ovaries to produce estrogens
In males, FSH and LH act on testes to produce androgens
Negative feedback loop in hormone control
If you’re producing too much estrogen/androgen, the pathway between hypothalamus and ovaries/testes stops to get it back into a homeostatic level. This pathway below age of 8 is kept low.
Gonads produce and secrete 3 major types of sex hormones
- Androgens - principally testosterone
- Oestrogen - principally oestradiol
- Progesterone
How much more testosterone do men have than females in the blood?
10x higher
How much more oestradiol do women have than males?
10x
Peak progesterone levels are much higher in what gender?
Female
When females hit menopause, what happens to the sex hormones?
The sex hormones plummet
Do hormones control sex phenotype or is it just genetic determined?
Chromosomes are not enough to determine sex - needs signa from gonads
What gene determines the production of testosterone from the testes?
The SRY gene - this gene will determine whether its a male or not since females dont have this gene.
What occurs in spermatogenesis (what does FSH and LH do on the body)?
FSH stimulates Sertolli cells within the seminiferous tubules to nourish developing sperm
LH causes Leydig cells to produce testosterone and other androgens to promote spermatogenesis in the testes.
The main cause of spermatogenesis:
FSH
What regulates blood levels of GnRH, FSH and LH
Testosterone regulates blood levels of GnRH, FSH and LH through inhibitory effects on the hypothalamus and anterior pituitary
What is inhibin, what is it produced by and what does it act on?
A hormone that in males, is produced by Sertolli cells, acts on the anterior pituitary gland to reduce FSH secretion
What happens in the ovarian cycle?
Follicle grows with egg inside it. During ovulation, the follicle is released into oviduct. Corpus luteum that used to surround follicle remains in ovaries and degenerates.
Why do menstrual flows occur?
As the follicle grows inside ovary, so does the uterus grow its uterine wall. As the follicle is released, the thick uterine wall is ready to house the embryo should be fertilised. If not fertilised, corpus luteum degenerates. Uterine lining (endometrium) is sloughed off and repeats every month.
What hormones indicate pregnancy?
If a female gets pregnant, progesterone levels will remain high to protect the embryo (due to its role in maintain uterine wall). If not pregnant, progesterone levels will drop and uterine lining will slough off.
During ovulation, there is a surge of
FSH (which is what causes ovulation)
Small rise of LH
Also surges of oestradiol and progesterone
When do progesterone levels surge?
After the middle of the cycle (14 days)
Difference between estrogen and oestradiol
Estrogen is a group of hormones which oestradiol is one of them
Is there a clear menstrual cycle in most animals
No, hence no bleeding. It is instead called the estrus cycle
Stages of the Estrus cycle
Anestrus: start of the cycle where everything (hormones) is relatively low
Proestrus - surge of hormones e.g. FSH just like humans. Then, the surge of progesterone a few days later. This is when the implantation of the embryo happens
Estrus phase - female is sexually receptive. ovarian follicles mature and estrogen secretion hits its peak
Luteal phase (Diestrus) - Corpus luteum produces progesterone to maintain uterine wall or sloughs off if not pregnant
When does implantation of embryo usually happen
Luteal phase (Diestrus)
What phase of the ovarian cycle is coordinated with the uterine cycle and why?
Follicular phase of ovarian cycle is linked with proliferative phase of uterine cycle.
Oestradiol secreted in increasing amounts by growing follicles signals the endometrium to thicken.
What hormone stops animals and humans from getting pregnant again while nursing a baby?
Prolactin
There are different types of estrus cycles:
Polyestrous: going into estrus multiple times in a year (cats, cows)
Seasonal polyestrous: long day and short day depending on pineal gland’s detection of sunlight ensures that animals only go to estrus in specific season
Monoestrus: only comes into estrus once a year
True or false. Some animals have semen induced ovulation
True. The act of mating causes females to come into ovulation.
What is the process when a zygote begins series of cell divisions
Cleavage
After the egg is released from the ovary into the oviduct to form an oocyte, what happens?
Day 0 - Fertilisation
Day 1 - Zygote
Day 2: 2-cell stage (first cleavage)
Day 3-4: 4 cell stage and 8 cell stage (cleavages)
Day 5 - Blastocyte forms
Day 8-9: Implantation
Where does cleavage begin
Begins in the oviduct as the embryo is moved towards the uterus by peristalsis and the movement of cilia
How is the placenta formed?
- Implantation of human embryo is initiated by the trophoblast (the outer epithelium of the blastocyst)
- Enzymes secreted by the trophoblast during implantation break down lining of endometrium and invades itself into the lining of the uterus cells. These trophoblast cells then form the placenta
- Following invasion/implantation, the trophoblast continues to expand into the endometrium and four new membranes
- Although these extraembryonic membranes arise from the embryo, they enclose specialised structures outside the embryo
How is pregnancy detected in early-pregnancy tests?
hCG from embryo passes from the maternal blood to urine
5 days after fertilisation, what is produced?
A blastocyst
Few days after blastocyst forms, what happens?
Embryo is implanted into the endometrium of the uterus
What is a blastocyst
A sphere of cells surrounding a central cavity
6 stages of fertilisation
- Sperm makes contact with egg
- Acrosome (tip of the sperm) reacts with zona pellucida (the outside of the egg cell)
- Acrosome reacts with perivitelline space
- Plasma membranes of sperm and egg fuse
- Sperm nucleus enters egg
- Cortical granules fuse with egg plasma membrane which renders the vitelline layer impenetrable to other sperm (to stop other sperm fertilising the egg so only one can get in)
During the first trimester, the embryo secretes what?
Human Chorionic Gonadotropin (hCG)
What is the role of hCG
Acts like pituitary LH by maintaining the secretion of progesterone and oestrogens by the corpus luteum through the first few months of pregnancy.
During the first 2-4 weeks of development, the embryo obtains what
Nutrients directly from the endometrium
What is the development of the placenta paired with?
Paired with the embryo’s need for more oxygen as it gets bigger.
Placenta develops by the use of…
Villi (these increase the surface area for diffusion so oxygen can get in an CO2 can get out)
Role of the placenta
Transports nutrients, respiratory gases and wastes between embryo and the mother
How/what nutrients are travelled inside to the embryo and outside
Maternal blood enters the placenta in arteries, flows through blood pools in the endometrium and leaves via maternal veins.
Embryonic blood which remain in vessels enters the placenta through arteries and passes through where oxygen is acquired
How are materials exchanged between mother and embryo
By diffusion, active transport, selective absorption between the foetal capillary bed and the maternal blood pools
Maternal circulation has what materials?
Oxygen and nutrients. This is exchanged with foetal circulation
Foetal circulation has what materials?
CO2 and waste products. This is exchanged with maternal circulation
Just before birth, the foetus will contain what to determine its sex
Spermatogonia if its male
Oogonia if its female
During 2nd trimester, what happens
hCG secretion declines, corpus luteum deteriorates and the placenta takes over production of progesterone.
Labour requires 2 hormones:
Oestradiol
Oxytocin
Role of oestradiol and oxytocin in labour
Oestradiol is secreted from ovaries which activates oxytocin receptors on the uterus. Then, oxytocin is secreted from the foetus to the mothers posterior pituitary. Then, oxytocin stimulates uterus to contract. As it contracts, oxytocin stimulates placentas to make prostaglandins which stimulates more contractions of the uterus.
Contractions get more and more large which then leads to the baby getting out.
Positive feedback loop in labour
As the baby pushes against the cervix, the cervix stretches. Stretching of the cervix causes nerve impulses to be sent to the brain which stimulates posterior pituitary to release oxytocin. Oxytocin causes smooth muscle lining of the uterus to contract, hence causing a positive feedback loop.
How do birth control pills work?
By producing progesterone which tricks the body into thinking its pregnant, causing the vitelline layer to become impenetrable
Problem with steroid based and immunocontraceptives
Require physical control and repeated dosing/booster in order to be effective
What is the placenta equivalent in birds
The yolk. Inside the yolk is the albumen (egg white) and then develops a shell. As it develops the egg gets more and more shells.
In monotremes, there is no egg white. Whats the substitution for albumen
Mucoid coat deposition around the egg. Then,, a shell forms and then an epithelium
What substance nurtures the egg in marsupials
Deutoplasm
For marsupials, when does the shell rupture?
2/3 through gestation and then theres a placental attachment to the uterus and the embryo then develops from there.
How is genetic analysis done in pregnancies
Amniocentesis and chorionic villus sampling: a needle which obtains foetal cells from fluid or tissue surrounding the embryo.
What percentage of DNA circulating the blood around the foetus is from the foetus itself?
10-15%
How do surrogates happen
In vitro fertilisation
Process of in vitro fertilisation (surrogate)
Involves combining oocytes and sperm in the laboratory
Fertilised eggs are incubated until they have formed at least eight cells and then transferred into the surrogate’s uterus for implantation
If mature sperm are defective or low in number, a whole sperm or spermatid nucleus is injected directly into oocyte
All vertebrate undergo a similar pattern of development. What are these 4 stages
- Fertilisation
- Cleavage
- Blastulation
- Gastrulation
What is gastrulation
Where ectoderm covers embryo, endoderm and mesoderm are inside
In what stage of a frog’s development does it nervous system develop
Neurula
The primitive streak in gastrulation ends up being what
The nervous system
In terms of depolarisation, what happens after the acrosome attaches onto the egg?
Normally, the membrane is negative; has negative potential.
As Na2+ flows into the membrane, the membrane becomes positive (as the resting membrane potential rises from 70mV to +20mV through ion channels.
How does depolarisation stop sperm from going into the egg?
Because depolarisation makes the membrane of egg positive, sperm are repelled by positive membranes.
What is the acrosomal reaction?
After contacting the egg, the release of acrosomal enzymes (proteases) needed to penetrate
2 different methods of the acrosomal reaction
- Fast block to polyspermy
- Slow block to polyspermy
Process of fast block to polyspermy
Sperm binding to egg membrane -> Na+ influx -> Membrane potential change -> Sperm cannot fuse with an egg that is +20mV
Process of slow block to polyspermy
Calcium is used which causes depolrisation and helps trigger cortical reaction to create hard casings and clip off other attached sperm
Calcium is also required for cortical granules to fuse with the membrane
The cortical granules contain enzymes
and macromolecules which lifts away the vitelline layer and hardens it into a protective envelope.
What is the cortical reaction
Release of granules (lysosomal enzymes) from oocyte caused by penetration
Do mammals use fast block polyspermy
No
During cleavage there is altering of what stages?
DNA synthesis and Mitosis
Purpose of cortical rotation
To make sure cells are where they’re supposed to be relative to the dorsal/ventral axis
Forms 2 poles: Animal pole (top), Vegetal pole (bottom)
Why are cleavages unequal in frogs
Because the egg rotates and so cleavage will produce smaller poles at animal pole and larger ones at vegetal (because vegetal cells incorporate yolk and are thus larger)
Changes in cell behaviour and cell cleavage patterns during early embryogenesis results in what
A 32-cell blastocyst consisting of inner cell mass, which will from the embryo, and the trophoblast which will form extraembryonic tissues.
7 Characteristics of gastrulation
Is at the end of cleavage
Dramatic reorganisation of the hollow blastula into a 2-layered or 3-layered embryo called a gastrula
A set of cells moves to the interior and establish cell layers
A primitive digestive tube is then formed
A lot of cell movement occurs in this stage to establish these layers
Has to be a hole in the middle (archenteron) - running from mouth to anus eventually
Is where 3 germ layers form
3 germ layers
Ectoderm (outside layer)
Mesoderm (middle layer)
Endoderm (lines digestive tract, inside layer)
What is the archenteron
The hole down the middle of a gastrula that forms into the digestive tract
Process of gastrulation in frogs
- Starts off as large, yolk-laden cells in the vegetal hemisphere with blastocoel walls
- Group of cells on dorsal side invaginate
- Crease begins - grey crescent
- Above crease becomes dorsal lip (the grey spot during cortical rotation that tells the animal which is the head end)
- Cells move into the interior towards animal pole to organise into layers
- Archenteron forms in interior
- Neural plate forms (becomes nervous system eventually)
What is invagination?
Where a surface folds in on itself to form a cavity, pouch or tube
What does the ectoderm form?
The nervous system and outer body layer
What does the mesoderm form?
Muscles and skeleton
What does the endoderm form?
Organs and ducts
Process of chick gastrulation
- Starts off as embryo with upper (epiblast) and lower (hypoblast) i.e. layers of cells on top of a yolk mass
- All cells to form embryo come from epiblast
- Starts off with the ectoderm and endoderm
- Cells move inwards to form primitive streak as they divide to form mesoderm cells
- The nervous system forms as the neural groove along the primitive streak. Directly under this, a neural tube forms which is where the spine forms. At the same time, the heart tube and the foregut form
- Primitive streak shortens to allow room for brain formation. IN neural groove, neural plates fold to create spine. Notochord then forms under that.
In placental animals, what needs to happen before gastrulation?
The blastocyst has to implant and the placenta has to form - this is the big difference between frogs, chicks and placental animals.
What happens in late stage neurulation
Neural folds are fused together to form a hollow cylinder that then detaches to become the neural tube which will become the spinal cord.
When does the notochord form?
As soon as gastrulation is complete (the 3 layers form)
What do signals from the notochord cause?
Inward folding of ectoderm to form neural plate that fuses to form neural tube and become the spine.
This all happens from signalling molecules secreted by mesodermal cells and other tissues that cause the ectoderm above the notochord to become the neural plate
Neuroectoderm has specialised signalling molecules that…
cause the neural plates to fold and then form the dorsal neural tube
When does organogenesis (formation of organs) start?
End of gastrulation
Cell determination
Cell or group of cells is committed to a fate: all layers start off the same but then differentiate
Cell differentiation
Specialisation in structure and function (different layers become different things)
Fate maps
When cells go through these fates, cells have to know whats left and right, anterior and posterior.
How do cells know their position?
Due to the prescence of proteins that tell them this:
Melanin which fills the animal hemisphere
Yolk fills vegetal hemisphere
Yolk and melanin therefore dictate the axes.
When does cortical rotation happen
On sperm entry. Animal pole becomes the point of sperm entry; forms dorsal-ventral axis.
How are the 3 layers formed in gastrulation?
- Cells of inner cell mass begin to differentiate as the amnion forms
- Gastrula develop when cells begin to migrate inward, forming an indentation
- Cells continue to push inward, forming the endoderm. Cells that remain on the outer surface of the gastrula are called the ectoderm
- The mesoderm is then formed as additional cells migrate inward between the endoderm and ectoderm
What is the last part of embryonic development
Limb formation
What signals play a big role in pattern formation (generation of complex organisations of cell fates in space and time)?
Inductive signals play a big role in pattern formation: development of spatial organisation (where certain parts need to be relative to other parts of the body), arrangement of organs and tissues
Limb formation is used to study pattern formation
Process of limb formation in chicks
- Chemical signal (signal A) starts the growth of a simple primordial limb bud
- That signal also turns on a secondary single, B, which causes the bud to grow more and activate localised signal, C
- Localised signal, C, will help bud have front and a back and that signal also turns on self reinforcing loop between C and another signal, D to make the limb longer
Cells of limb buds secrete what for what purpose
Their specific proteins to provide positional information
What does the tip of a limb bud secrete
Growth protein
What dictates the anterior-posterior axis and gives rise to posterior (digits) and anterior (thumb-like) structures?
The Zone of Polarising Activity (ZPA, mesoderm - more specifically the notochord). The notochord then secretes the Sonic the Hedgehog Protein (SHH) to help this process along.
What within the cells causes cells of fore and hind limbs to act differently to positional cues?
Early gene expression creates a different fore (e.g. wing) and hind (e.g. leg) limb.
Early gene expression is …. to that of other species but late gene expression is ….
Early gene expression is similar to other species e.g. dolphins with fins and humans start off the same but later gene expression in the distal limb bud causes digit.
How do we have fingers?
Later on in evolution, there was an extension of cartilage.
What is the reason why there’s evolved differences between related organisms
Late gene expression e.g. in humans, bats and horses, we start off the same. All of them have humerus, radius, ulna. Except, late gene expression causes the bat to form claws, we form fingers and horses form hooves.
