Chapter 43: Animal Reproduction Flashcards
What are the four sex steroids?
- Cholesterol
- Oestrogen
- Progesterone
- Testosterone
What happens to sex hormones before puberty?
held at low level due to negative feedback
What happens to sex hormones during puberty?
feedback loop is down regulated (Hypothalamic receptors for sex-hormones will become less sensitive.)
Gametes
eggs, sperm produced by meiosis
zygote
formed from the fusion of male and female gametes during fertilization (diploid)
What processes in sexual reproduction lead to diversity?
gametogenesis and fertilization, through independent assortment and the recombination of alleles of chromosomes
Haploid
one set of chromosomes
Diploid
two sets of chromosomes
Gametogenesis
produces gametes in meiosis from the germ cell one
What are the two types of gametogenesis?
- Spermatogenesis
2. Oogenesis
What do the primary sex organs produce?
haploid cells via gametogenesis
What is the path of male sex organs to produce gametes?
testis–>spermatogonia–>sperm
What is the path of female organs to produce gametes?
ovary–>oogonia–>egg
What are the functions of the accessory sex organs?
facilitate fertilization (penis and vagina)
What is spermatogenesis and where does it occur?
it is the process of sperm production; occurs in the seminiferous tubules of the testes.
How does spermatagonia proliferate, what type of division?
mitosis; throughout a male’s lifespan
How many sperm does a primary spermatocyte produce?
four haploid sperm: 2 with X and 2 with Y
Oogenesis: describe the pathway
female germ cell–>mitosis–>oogonium–>mitosis–>primary oocyte–>first meiotic division–>secondary oocyte(n) & first polar body–>second mitotic division–>ootid(n) & second polar body–>ovum(n) & polar bodies degrade
How many eggs does each oogonium produce?
one
In what form are the female sex cells stored and for how long?
primary oocyte stored in prophase for up to 50 years
When does the second mitotic division occur in oogenesis?
after fertilization.
Where does oogenesis occur
in fetal ovaries during gestation
how many primary oocytes exist at puberty?
~200,000
How many primary oocytes will mature during a woman’s fertile years?
~450
What is the optimal temperature for testes?
slightly lower than body temp
Where are the sperm produced?
seminiferous tubules
Where do the sperm mature?
epididymis
where do the sperm go after maturation?
to the urethra through vas deferens
Where does the production of semen occur?
in seminal vesicles, prostate gland, bulbourethral glands
How does semen exit body?
join in urethra and are ejaculated through the penis by muscle contractions
What is the composition breakdown of the semen?
5% sperm
70% seminal fluid (from seminal vesicles- thick mucus, protein, fructose, prostaglandins which cause contractions in females)
25% prostate fluid (thin, milky fluid that makes uterine environment more hospitable to sperm; enzymes that convert semen to gelatinous mass)
What are Leydig cells?
produce male sex hormones: testosterone
Name components of the sperm cell
acrosome tip, head containing nucleus, mid piece containing centriole and mitochondria
Describe the pathway of Spermatogenesis
primordial germ cell–>spermatogonia–>mitosis–>primary spermatocytes–>first meiotic division–>secondary spermatocytes–>second meiotic division–>spermatids & differentiating spermatids
Lumen
the most developed cells are on the inside and the least developed cells are on the outer part of this tubule
Sertoli cells
nurture developing spermatids
Sperm
mature version of spermatids. sperm travels down lumen, and has compact nucleus, little cytoplasm, and flagella-like tail and many mitochondria
acrosome
head of the sperm which contains enzymes for entering the egg (breakdown)
Epididymis
location where sperm mature and become fully motile
Vas deferens
carries sperm to urethra
Seminal vesicles and prostate gland
provide secretions to nurture and aid sperm during fertilization
Penis
carries sperm to the outside
Emission
sperm and secretions move to the base of the penis to form semen
Ejaculation
occurs when the muscles at the base of the penis contract to force semen out of the urethra
Positive feedback in male reproductive system?
hypothalamus produces GnRH to stimulate the anterior pituitary to release LH and FSH
GnRH
Gonadotropin-releasing hormone
What does the release of LH cause?
Causes the Leydig cells to release testosterone
What does the release of FSH cause?
promotes spermatogenesis by Sertoli cells
Negative feedback in the Male reproductive system?
inhibin inhibits the production of GnRH and FSH, testosterone inhibits the production of GnRH and LH,, exogenous testosterone reduces output of GnRH, LH, FSH, reducing male effects
Where do the eggs mature?
female ovaries
What happens after the eggs mature?
swept into oviducts (fallopian tubes) by cilia
Where does fertilization occur?
upper regions of oviducts
What is the pathway of sperm deposited in the vagina?
move through the cervix into the uterus (womb), some continuing up through oviducts
What happens as the zygote passes down the oviduct?
it becomes a blastocyst through cell divisons
What happens when the blastocyst arrives in the uterus?
it implants in the endometrium, where a placenta forms and the embryo develops.
what do ovaries produce?
hormones (estrogen and progesterone) and eggs
What do estrogen and progesterone do?
regulate female development and the menstrual cycle. progesterone helps to maintain pregnancy
what is the reproductive cycle of a female?
menstrual cycle (28 days)
What is the pathway of the released egg?
ovum–>one end of the oviduct–>sweeps ovum to uterus–>fertilization occurs inside oviduct (fallopian tubes)
What is the pathway of the primary oocyte?
primary oocyte is surrounded by layer of follicle cells. 2 wks: ovulation (rupture of follicle and release of egg) occurs. Follicle remains and forms corpus luteum, which produces estrogen and progesterone for about 2 weeks.
Zona pellucida
glycoprotein envelope that interacts with sperm, initiates acrosomal reaction, and species-species recognition
Cumulus (Corona Radiata) Slide 33
derived from follicle cells, assists in fertilization
What does sperm penetration of egg trigger?
completion of second meiotic division, causes cortical granules to release contents, which render ZP impenetrable to further sperm
What happens when acrosomal enzymes are released?
allows sperm to penetrate zona pellucid
Follicles
eggs and surrounding cells; 6-12 grow and develop every month
Secondary oocyte
when one follicle outgrowth the others to fully mature and contains this
ovulation
process whereby a mature follicle erupts from the overt and the ovum is released towards one oviduct
Corpus Luteum
consists of the remaining follicle cells that will produce estrogen and progesterone for up to 2 weeks after ovulation. Will degenerate if the egg is not fertilized
Uterine cycle
if no blastocyst implanted, and corpus luteum stops producing progesterone, uterine lining deteriorates and sloughs off, which is called menstruation.
What do the cells covering the blastocyst secrete with implantation?
hCG, progesterone, and estrogen
Menstruation
sloughing off of the uterine lining (endometrium) if the egg is not fertilized. the endometrium supports the developing embryo.
Timeline of Menstruation: Day 0, 0-12, 12-14
0: endometrium sloughs off during menstruation
0-12: GnRH, FSH, LH, ovarian E levels rise and some follicles start to mature
12-14: E exerts positive feedback on anterior pituitary so there is a LH and FSH surge. LH stimulates ovulation and development of the corpus luteum
What does the corpus luteum produce?
E and P, which promotes endometrial growth and exerts negative feedback on pituitary to prevent continued LH and FSH, suppressing ovulation.
What happens when egg isn’t fertilized?
corpus luteum degenerates, endometrium sloughs off, E and P drops, GnRH, LH and FSH increase to trigger next cycle.
What do the ovaries produce?
E, P, eggs
Pregnancy
see slide 47
Hormone levels before puberty?
low GnRH, LH, FSH
Hormone levels at puberty?
increased GnRH, LH, FSH, mostly negative feedback between E, GnRH, LH, FSH between puberty and menopause
Menopause
usually late 40’s, ovaries shrink and # of primary oocytes and follicle cells decrease, menstrual cycles become irregular between ages 45-50 and eventually stop, E&P levels drop, LH and FSH remain high for a while
Theca Cells
produce testosterone
Granulosa cells
convert testosterone to estrogen, secrete inhibin, nourish gamete
What are some methods of contraception?
Vasectomy, Tubal Ligation,
Birth control pill
E & P: decrease GnRH, Decrease LH and FSH
What happens when there’s low E?
prevent new follicles from maturing
interfere with ovarian cycle
Low P?
thicken uterine lining and neck of cervix–> blocks sperm cells ; low level of hormone to prevent surge
The pill after:
Progesterone-inhibitor. binds to P receptors, interferes with normal signaling of progesterone and prevents stabilization of uterine lining.
