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11. Animal physiology > Sexual reproduction > Flashcards

Sexual reproduction Flashcards

1
Q

What is gametogenesis?

A
  • Production of female and male haploid gametes cells
  • The germinal epithelium undergoes cells division to differentiate into gamete cells
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2
Q

What happens in oogenesis during pregnancy?

A
  • The production of ova (female gametes) in the ovaries before birth
  • The outer layer of ovaries called germinal epithelium undergoes mitosis forming diploid cells called oogonia in the first 7 months of pregnancy
  • The oogonia in the fetus’ ovaries grow in size and enter meiosis 1, forming a layer of follicle cells. Together known as primary follicles
  • Next the oogenesis process pauses until puberty starts
  • Most primary follicles never reach maturity
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3
Q

What happens in oogenesis during puberty?

A
  • Hormone FSH stimulates the continued development of several primary follicles
  • Only one of them will reach maturity
  • Meiosis 1 occurs, dividing the primary follicle into two cells
  • One of them is a secondary oocyte and a small cell called polar body (unequal division)
  • Now the secondary oocyte enters meiosis 2 and leaves the ovary with is layer of follicle cells: ovulation
  • Remains of the follicle in the ovary develop into corpus luteum
  • If the secondary oocyte is fertilised by a sperm, chemical changes trigger the completion of meiosis 2.
  • When meiosis 2 is complete, the s.o. becomes an ovum between the end of meiosis 2 and fusion of the two nuclei
  • The second polar body is produced at completion of meiosis 2
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4
Q

What is spermogenesis?

A
  • Production of sperm (male gamete) within the testes from puberty onward
  • Testes contain tubules, called seminiferous tubules (where sperm cells develop)
  • Leydig cells in the interstitial space of the testis produce the hormone testosterone, allows spermatocyte to complete meiotic division form spermatozoa
  • The outer layer of seminiferous tubules is made of germinal epithelium. The cells in it divide by mitosis producing 2 diploid spermatogonia
  • One spermatogonia will become a sperm, the other remains germinal epithelium
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5
Q

What happens to the spermatogonia that becomes a sperm?

A
  • The spermatogonia grows into a primary spermatocyte (2n), carries out meiosis 1 to produce 2 secondary spermatocyte (n)
  • Each secondary spermatocyte carry out meiosis 2 to form two spermatids (4 in total)
  • Spermatids become associated with sertoli cells (compose lining of seminiferous tubules)
  • This helps spermatids to differentiate into spermatozoa (immature sperm)
  • Sertoli cells provide support and nutrition to develop the sperm cells
  • Speratozoa matures fully and move along seminiferous tubule lumen to sperm duct and pass through epididymis
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6
Q

What are the similarities between oogenesis and spermatogenesis?

A

Similarities
- Both gametes are specialised haploid cells
- Both processes involve mitosis and two rounds of meiosis, cell growth and differentiation
- Mitosis results on many new cells, which have the potential to grow into gametes
- Meiosis results in haploid gametes

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7
Q

What are the differences between oogenesis and spermatogenesis?

A
  • Structure of gametes: ova is large, immobile, large cytoplasm, surrounding layer of follicle cells. Sperm is small, mobile, little cytoplasm, acrosome contains enzymes
  • Daughter cell per meiotic division: 1 ovum produced after meiosis 2, polar bodies do not from ova, 4 sperm cells at end of meiosis 2
  • Frequency production: 1 per menstrual cycle, men continuously puberty onwards
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8
Q

How does the timing of the process in spermatogenesis and oogenesis differ?

A
  • Spermatogenesis, production is continuous, from puberty onward
  • Oogenesis, finite process, starts before brith, forms 40,000 primary oocytes, happens with puberty in menstrual cycle, ends with menopause, hormonal changes
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9
Q

What is the role of testosterone in spermatogenesis?

A
  • Stimulates meiotic divisions of spermatognia into spermatozoa
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10
Q

Be able to draw seminiferous tubules and an ovary

A
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11
Q

Be able to draw a mature sperm and egg

A
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12
Q

Explain the structure and function of a sperm.

A
  • Haploid nucleus
  • Acrosome contains digestive enzymes to aid entry into the ovum
  • Many mitochondria, release energy to aid movement
  • Tail made of protein microtubules to aid movement
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13
Q

Explain the structure of an egg.

A
  • Haploid nucleus
  • Jelly layer called zona pellucida prevents polysperm (more than one sperm to enter)
  • Vesicles and cortical granules contain digestive enzymes, release into the zona pellucida to prevent polysperm
  • Cytoplasm rich in nutrients for the developing embryo after fertilisation
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14
Q

Explain the structure of an egg.

A
  • Haploid nucleus
  • Jelly layer called zona pellucida prevents polysperm (more than one sperm to enter)
  • Vesicles and cortical granules contain digestive enzymes, release into the zona pellucida to prevent polysperm
  • Cytoplasm rich in nutrients for the developing embryo after fertilisation
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15
Q

What is fertilisation?

A
  • The fusion of a sperm cell and an ovum to form a diploid zygote
  • At the point when sperm cells are attracted towards the secondary oocyte, meiosis 2 is not complete (is not yet an ovum)
  • As soon as the sperm reaches the secondary oocyte, mechanism started that prevents more than one sperm from passing through
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16
Q

How does fertilisation prevent polyspermy?

A
  • Polyspermy: entry of more than one sperm into a single oocyte
  • When the sperm cell digests through the zona pellucida it reaches the oocyte membrane
  • Complementary receptors on the head of the sperm bind with proteins on the oocyte membrane, enabling membranes of the two gametes to fuse together
  • Once the sperm nucleus enters the oocyte, meiosis 2 continues, which releases the second polar body and formation of mature ovum
  • When the membranes fuse, the movement of cortical granules is triggered
  • Granules move from cytoplasm to membrane, releasing enzymes that digest receptor proteins, causes zona pellucida to harden
  • Enzymes released by exocytosis. When zona pellucida hardened, no more sperm can enter
17
Q

What are the features of external fertilisation?

A
  • In aquatic animals, sperm are surrounded by fluid medium, sperm released into the environment, fertilisation can occur externally
  • External fertilisation: fish and amphibians
  • Very large quantities of ova and sperm produced, due to risk of predators eating then or being washed away, increase chances
18
Q

What are the features of internal fertilisation?

A
  • Sperm need to be released into a fluid medium (semen) into internal reproductive tract of the female animal
  • Animals: birds and mammals
  • Gametes are close in proximity to each other, protected from predators, gamete numbers smaller
19
Q

How is the blastocyst implanted in the uterus?

A
  • The fertilised ovum divides by mitosis to form 2 diploid nuclei (two-cell embryo)
  • Another round of mitosis forms a four-cell embryo, this repeats until the embryo forms a hollow ball called blastocyst
  • The blastocyst contains group of cells: blastomeres, will eventually develop into fetus
  • The embryo called blastocyst found in oviduct and is surrounded by protective extracellular coat (zona pellucida)
  • After 7 days: blastocyst consists of 125 cells, reaches the uterus and z.p. breaks down
  • The blastocyst now requires external nutrition supply which it obtains by implanting into endometrium (uterus lining)
  • Outer layer of blastocyst forms finger-like projections, allows to penetrate endometrium
  • Exchange of nutrients and O2 with mothers blood can occur
20
Q

What is the implantation of blastocyst in the endometrium essential for continuation of pregnancy?

A
  • The uterine lining provides the developing embryo with necessary nutrients and oxygen
  • The blastocyst used up the nutrient supplied by the egg cell
21
Q

What are the two categories of gestational duration in mammals?

A
  • Gestation period 38 weeks
  • Altricial species: infants that are immobile, unable to obtain food after birth, have shorter gestation periods e.g. humans
  • Precocial species: species born in advanced state, able to move around, good vision, feed independently, longer gestation period e.g. ducks, horses
22
Q

How do you compare the animal size and development of young at birth?

A
  • Compare gestation periods with adult body masses according to development of the young at birth (altricial or precocial)
  • For both categories, the length of gestation period is positively correlation with adult body mass
  • Not always true, some gestation periods similar, but different body masses
23
Q

What role does hCG play in early pregnancy?

A
  • After the blastocyst is implanted into the endometrium, the hormone hCG is secreted
  • Secreted in first 8-10 weeks
  • Stimulates corpus luteum in the ovary to maintain secretion of oestrogen and progesterone (develop uterus more)
  • Stimulate growth of placenta and uterine enlargement
  • Inhibits menstruation
  • After 12 weeks hCG declines, placenta takes over role of stimulating secretion of the hormones
  • Pregnancy kits detect presence of hCG in urine
24
Q

What role does progesterone play during pregnancy?

A
  • Secreted by the placenta, inhibits the production of oxytocin by the pituitary gland, in brain (negative feedback)
  • Inhibits contractions of muscles of uterus wall (avoid giving birth)
  • End of pregnancy, fetus produces oestrogen, signals to stop progesterone production (negative feedback)
  • This in turn initiates oxytocin production at start of labour (positive feedback)
25
Q

What role does oestrogen play during pregnancy?

A
  • At the end of pregnancy, it is produced by fetus and the placenta
  • Makes the uterine wall more sensitive to oxytocin
  • It inhibits progesterone production, in turn stimulates oxytocin production (positive feedback)
26
Q

What hormones are involved during labour?

A
  • Labour: oxytocin stimulates contractions of muscles in myometrium
  • Stretch receptors in cervix detect contractions, sends signal to increase oxytocin secretion (positive feedback loop)
  • Slowly increases contractions rhythmically
27
Q

What happens during birth?

A
  • Cervix muscles cause it to dialte and widen, the contractions cause amniotic sac to burst
  • Amniotic fluid passes through cervix, baby pushed out
  • Baby pushed out, umbilical cord cut
28
Q

What happens after birth?

A
  • Uterine contractions continue, causing placenta to separate from uterine wall
  • Mother births placenta and remains of umbilical cord
29
Q

What is the placenta and what does it do?

A
  • Contains blood vessels that maximise exchange of substances between mother and fetus without direct contact between them
  • Produces hormones
  • Fetus connected with an umbilical cord and found inside the amniotic sac, filled with amniotic fluid
30
Q

Explain the structure of the placenta.

A
  • Complex arrangement of blood vessels arranged inside placental villi, maternal blood flow is found around villi (number of villi increases)
  • Maternal and fetal blood never directly mix, yet very short distance between them, exchange nutrients and gases
  • Maternal blood flows out of the blood vessels and pools in spaces surrounding the placental villi, the spaces are called inter-villous spaces
  • Placental membrane is selectively permeable, restricts exchange of substances
31
Q

What are substances that can move across the barrier from mother to fetus?

A
  • O2 (diffusion), antibodies and hormones (endocytosis), water (osmosis), glucose (facilitated diffusion), harmful substances (alcohol, pathogens)
32
Q

What substances can move across the barrier from fetus to mother?

A
  • CO2, water, urea, hormones (exocytosis)
33
Q

How does the placenta regulate hormones?

A
  • The degenerating corpus luteum releases hormones that support the initial stages of pregnancy up to 9 weeks
  • The placenta then releases oestrogen to stimulate growth of uterus and mammary glands
  • The placenta releases progesterone to support lining of the uterus to maintain pregnancy
  • If placenta fails to initiate hormones production, miscarriage occurs
34
Q

What is oestrogen pollution? What are its consequences?

A
  • Synthetic oestrogen introduced as contraceptive, increased usage, found in environment
  • Accumulation of hormones from human sewage
  • Can lower average sperm count in males, reduced fertility
  • Cause certain fish to have female characteristics
  • Correlation, casual link, not enough evidence
  • Possible procedure to reduce levels in waterways are expensive, require more research

11. Animal physiology (4 decks)

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