11. Animal Physiology : 11.4 Sexual Reproduction Flashcards
Define sexual reproduction.
A form of reproduction that involves the fusion of two haploid gametes, each containing a random selection of chromosomes, allows for an enormous number of different combinations resulting in unique individuals
List the names of production of gametes in males and females.
Spermatogenesis in males
Oogenesis in females
Define gametogenesis.
The process by which cells of the germinal epithelium undergo cell division and differentiation to form haploid gametes.
What is spermatogenesis?
The production of sperms which takes places in testes.
What is the testes composed of?
- Seminiferous tubules
- Interstitial cells (sometimes called leydig cells) : produce the hormone testosterone which allows spermatocytes to complete and mature
Explain the stages of spermatogenesis briefly.
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What is the process of forming a Graafian follicle?
Primary follicles form into granulosa - secondary follicle
Then the secondary follicles develop fluid filled cavities - tertiary follicles
Graafian follicles: the formation of all the smaller fluid-filled cavities fusing together to form one cavity
What happens when sperm is deposited in the female’s body?
They go towards the egg to fertilise it
Some form for chemotaxis is involved in guiding the sperm to the egg
Fertilisation starts once sperm reaches the egg
What is meant by fertilisation?
The fusing of two gametes: an egg cell and a sperm cell
What happens when more than one sperm fertilises an egg?
Results in a polyploid offspring (called polyspermy)
Explain the 5 steps of fertilisation briefly.
- Sperm penetrates the follicle cells and binds to the receptors of the zona pellucida
- Acrosomal reaction:
- hydrolytic enzymes make a hole in zona pellucida allowing the sperm to make its way to the plasma membrane of the egg - Egg and sperm touch and fuse
- Sperm nucleus enters egg cytoplasm and activates egg. this affects the complexion of second meiotic division and rise in intracellular concentration of calcium.
- Cortical reaction:
- hardens zona pellucida and prevents polyspermy
- release mixture of enzymes from cortical granules and diffuse into zona pellucida and hardens the layer and destroy sperm receptors to prevent more sperm binding
Explain the acrosomal reaction.
Hydrolytic enzymes released by exocytosis and these enzymes make a hole in zona pellucida allowing the sperm to make its way to the plasma membrane of the egg
Explain the cornical reaction.
Brief: hardens the zona pellucida and prevents polyspermy
- release of enzymes from cortical granules
- these enzymes diffuse into zona pellucida
- they alter the shape by hardening the layer and destroying the sperm receptors to prevent more sperm from binding
What is external fertilisation?
A method of fertilisation in which two haploid gametes, a sperm and an egg cell fuse together outside the parents body
What is internal fertilisation?
The transfer of sperm into the female’s body for fertilisation to occur.
Why are vast quantities of eggs and sperm produced in marine ecosystems?
- to increase chances of fertilisation
- environemental factors can impact the survival
- predators
- male and female sex cells are released within a short distance of each other so fertilisation rate is low
Why are chances of fertilisation high with internal fertilisation?
- the sex cells are closer together when released
- sperms need to swim to egg
- fewer sperms and eggs but proximity between the two increases success rate
What happens after fertilisation?
- ovum divides by mitosis and after 48 hours there is a four-cell embryo
- embryo still in oviduct
- embryo divides slowly and migrates down to uterus
- after 7 days, embryo reaches uterus
What happens in blastocyst?
- embryo reaches uterus
- embryo is about 125 cells
- the inner cell mass forms embryo
- the outer cell layer develops into placenta and other tissues needed for fetal developement
What is the blastocyst made up of?
It is made up of a thin-walled hollow structure that contains an outer layer of cells and a cluster of cells called the inner cell mass.
Why is implantation of blastocyst in the endometrium essential for the continuation of pregnancy?
As the uterine lining provides the developing embryo with necessary nutrients and oxygen.
How is endometrium maintained througout pregnancy?
Through the continued production of progesterone and estrogen
What occurs at early pregnancy?
- Embryo starts to produce human chorionic gonadotropin (hCG)
- hCG stimulates the corpus luteum to continue the production of progesterone and estrogen
- It ensures that the corpus luteum remains until the placenta is fully established
Loss of corpus luteum = miscarriages - The placenta takes over the role of the hormones secretion to maintain the uterine lining throughout pregnancy
What is the placenta?
Organ which facilitates the exchange of material between the fetus and its mother
What is villi and what does it do?
Villi: fingerlike projections that originate in the chorion
- Provides a maximum surface area for contact with the maternal blood
- Maternal blood collects in these spaces
The fetal blood circulates in capillaries which lie very close to the surface of the villi
What is the placenta’s two most important functions throughout pregnancy?
- Exchange of material to keep the fetus alive
2. Production of progesterone and estrogen
Substances from mother to fetus:
Oxygen Glucose, amino acids, vitamins and minerals Water Hormones Drugs Some viruses
Substances from fetus to mother:
Carbon dioxide
Urea
Water
Hormones
What does the fetal arteries do?
- Bring deoxygenated blood from the fetus to the placenta
- All fetal arterioles fuse to form the fetal arteries
What does the fetal veins do?
Brings oxygenated blood back from placenta to the fetus
All fetal venules form the fetal vein
Where can fetal veins and arteries be found?
In the umbilical cord which connects the fetus to the uterine wall.
Explain the functions of the umbilical artery and vein.
The umbilical artery transports waste material from the fetus to the mother via the placenta.
The umbilical vein transports nutrients from the mother to the fetus.
What is the difference between umbilical artery and vein?
The blood in the artery contains less glucose than vein.
What is gestation and what happens during this stage?
Gestation: the time that the embryo develops within the female’s body
- Starts with fertilisation and ends at birth
Explain the correlation between time and body mass of the gestation period.
The heavier the animal, the longer the gestation period.
Because:
Smaller mammals often have offpsring that are helpless and need a lot of protection
Larger mammals have live young that are well developed already at birth
What occurs when the baby is ready to be born?
- placenta stops producing progesterone
- secretes oxytocin
- progesterone levels drop
- estrogen levels rise and induces the development of oxytocin receptors on muscles on uterine wall
What does oxytocin do?
- stimulates the uterine muscles and causes to contract
- strongest stimulator of uterine contractions
- more oxytocin = stronger contractions
- contractions occur until fetus is released
Explain the process of releasing the baby.
- uterus contracts, cervix opens and amniotic sac breaks
- contractions may continue until baby is out the vagina
What stimulates milk production after birth?
Prolactin. A hormone produced by the anterior pituitary gland
How does estrogen affect the environment?
- hormones ingested is released without being broken down
- increasing levels of estrogen impacts sperm production and sex ratios of fish
- changes in fish development is accepted to be due to estrogen pollution
