Studied by 4 people
3 main forms of animal reproduction:
some organisms reproduce without any form of sex some organisms can change sex some species have both male and female organs
Sexual reproduction
the creation of an offspring by fusion of haploid gametes, male sperm and female eggs, to form a diploid zygote
Asexual reproduction
creation of offspring without the fusion of egg and sperm
Budding
a simple form of asexual reproduction found only among invertebrates
New individuals arise from outgrowths of existing ones
fission
How many invertebrates reproduce asexually, the separation of a parent into two or more individuals of about the same size
Fragmentation
breaking of the body into pieces, some or all of which develop into adults
Parthenogenesis
the development of a new individual from an unfertilized egg
hermaphroditism
each individual has both male and female reproductive systems
Most animals exhibit reproductive cycles related to changing seasons and are controlled by...
hormones and environmental cues.
Ovulation
the release of mature eggs at the midpoint of a female cycle
Seasonal temperature is often an important cue in reproduction, ______ can decrease reproductive success
climate change
Fertilization
the union of egg and sperm, can be external or internal
Why is a moist habitat is always required for external fertilization
to allow sperm to swim to the egg and to prevent the gametes from drying out
Internal fertilization
is an adaptation that enables sperm to reach an egg despite a dry external environment.
Internal fertilization requires behavioral interactions and compatible copulatory organs
pheromones
chemicals released by one organism that influence the physiology and behavior of individuals of the same species
Internal fertilization is typically associated with production of...
fewer gametes but the survival of a higher fraction of zygotes
Internally fertilized eggs of birds and other reptiles have...
shells and internal membranes that protect against water loss and physical damage as the embryos develop
in many animals, parental care helps...
ensure survival of offspring
gonads
In most species, they have organs that produce gametes
More elaborate systems include...
sets of accessory tubes and glands that carry, nourish, and protect gametes and developing embryos
Monogamy is relatively common among animals. (True or false)
FALSE Monogamy is relatively rare among animals
Males and/or females of some species have evolved mechanisms to...
decrease the chance of their mate mating with another individual
mammary glands
are not part of the reproductive system but are important to mammalian reproduction
Within the glands, small sacs of epithelial tissue secrete milk
During spermatogenesis
your testicles make several million sperm per day
______ sperm per second are made by the end of a full sperm production cycle.
1,500
You can regenerate up to _______ sperm. This may seem like overkill, but you release anywhere from_____ sperm cells in a single milliliter of semen
8 billion, 20 to 300 million
An average ejaculate is about _____.
5ml
Gametogenesis
the production of gametes
Spermatogenesis
the formation of sperm, is continuous and prolific
Oogenesis
the development of a mature egg, is a prolonged process
Immature eggs form in the female embryo but do not complete their development (meiosis)until years or decades later
Mammalian reproduction is coordinated by hormones from the...
hypothalamus, anterior pituitary, and gonads
Gonadotropin-releasing hormone (GnRH)
secreted by the hypothalamus and directs the release of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) from the anterior pituitary
FSH and LH
stimulate sex hormone production by the gonads
Testosterone is the main...
androgen
Estrogens consist of mainly...
estradiol and progesterone
Sex hormones function in...
gamete production, sexual behavior, and the development of primary and secondary sex characteristics
Sertoli cells
FSH stimulates to nourish developing sperm
Leydig cells
LH causes these to produce testosterone and other androgens, which in turn promote spermatogenesis
Testosterone regulates the...
production of GnRH, FSH, and LH through negative-feedback mechanisms
Sertoli cells secrete the hormone...
inhibin, which reduces FSH secretion from the anterior pituitary
Hormones closely link the _____ of female reproduction
two cycles
Changes in the ovaries define the...
ovarian cycle
Changes in the uterus define the...
menstrual cycle (also called the uterine cycle)
in each menstrual cycle, the...
endometrium thickens with blood vessels in preparation for embryo implantation If an embryo does not implant in the endometrium, the endometrium is shed in a process called menstruation
Cells of the uterine lining can sometimes...
migrate to an abnormal, or ectopic, location Swelling of these cells in response to hormone stimulation results in a disorder called endometriosis
After about 500 cycles, human females undergo...
menopause, the cessation of ovulation and menstruation
Menopause is very normal among animals. (true or false)
False, Menopause is very unusual among animals
Menopause might have evolved to...
allow a mother to provide better care for her children and grandchildren
Menstrual cycles are characteristic only of...
humans and some other primates
The endometrium is shed from the uterus in a bleeding called menstruation
Sexual receptivity is not limited to a time frame
Estrous cycles
characteristic of most mammals
The endometrium is reabsorbed by the uterus
Sexual receptivity is limited to a “heat” period called estrus
The length and frequency of estrous cycles vary from species to species
Conception
fertilization of an egg by a sperm, occurs in the oviduct
cleavage
The resulting zygote begins to divide by mitosis in a process
blastocyst
Division of cells gives rise to it, a ball of cells with a central cavity After blastocyst formation, the embryo implants into the endometrium
Pregnancy, or gestation
is the condition of carrying one or more embryos in the uterus
Duration of pregnancy in other species correlates with...
body size and maturity of the young at birth The roughly nine months of human gestation are divided into three trimesters of equal length
The first trimester is the main period of...
organogenesis, development of the body organs
What happens in the first trimester?
All the major structures are present by 8 weeks, and the embryo is called a fetus Changes occur in the mother: Mucus plug in the cervix to protect against infection Growth of the placenta and uterus Cessation of ovulation and the menstrual cycle Breast enlargement Nausea is also very common
What happens in the second trimester?
The fetus grows and is very active The mother may feel fetal movements Hormone levels stabilize The placenta takes over the production of progesterone, the hormone that maintains the pregnancy
What happens in the third trimester?
The fetus grows and fills the space within the embryonic membranes Childbirth begins with labor, a series of strong, rhythmic uterine contractions that push the fetus and placenta out of the body Labor is regulated by prostaglandins and hormones such as estradiol and oxytocin
Estradiol
Activates oxytocin receptors on uterus
Oxytocin
from fetus and mother’s posterior pituitary, Stimulates uterus to contract, Stimulates placenta to make Prostaglandins that stimulate more contractions of uterus
Three stages of Labor:
Thinning and opening of the cervix, or dilation Expulsion, or delivery, of the baby Delivery of the placenta
Postnatal care in mammals includes...
lactation, the production of mother’s milk
Contraception
the deliberate prevention of pregnancy, can be achieved in several ways Contraceptive methods fall into three categories: Preventing release of eggs and sperm (pill) Keeping sperm and egg apart (condom) Preventing implantation of an embryo (IUD)
Ultrasound imaging is used to...
detect fetal condition
Amniocentesis and chorionic villus sampling
use a needle to obtain fetal cells for genetic analysis
Causes of infertility are quite varied, with men and women equally affected (True or false)
True
In vitro fertilization (IVF)
mixes eggs with sperm in culture dishes and returns the embryo to the uterus at the eight-cell stage
(ICSI)
Sperm or sperm nuclei can also be injected directly into an oocyte
In general, what is the ploidy (n) state of human cells?
Diploid except for gametes
A hermaphrodite is an animal that __________.
contains both male and female reproductive systems in its body
What is not a form of asexual reproduction?
Hermaphroditism
What reproductive method is universal among mammals?
Internal fertilization
In which of the following pairs are the terms mismatched?
External fertilization: terrestrial environments
Some insect females are able to store sperm in __________ until environmental conditions are favorable for the development of their offspring.
spermathecae
Immediately after ovulation into the coelom, an egg is collected into the __________.
oviduct
How do egg cells enter the oviduct after ovulation?
Currents created by cilia bring fluid inside, carrying the egg cell along.
Vestibular glands
secrete lubricating fluid
Where do developing sperm cells undergo meiosis?
In the seminiferous tubules
The __________ is/are the site of testosterone production in the testis.
Leydig cells
In many mammals, the testes are located outside the abdominal cavity within the scrotum because __________.
sperm are unable to mature properly at the higher temperatures found within the abdominal cavity
Which part of the male reproductive tract stores sperm as they mature?
Epididymis
Which structure is part of the excretory and reproductive systems in males?
Urethra
Which part of the human sperm carries a haploid set of chromosomes?
Head
In mammals, meiosis to produce the female egg cell is initiated in the __________.
ovary
In spermatogenesis, each primary spermatocyte gives rise to __________sperm.
four
At what point does the secondary oocyte complete meiosis?
After contact between sperm and egg membranes
Compared to polar bodies, the amount of cytoplasm found in an animal egg cell is __________.
greater
In males, FSH __________.
stimulates development of sperm cells in the testes
After ovulation occurs, the empty follicle __________.
changes into the corpus luteum and makes hormones
Concentrations of which hormone stimulate the hypothalamus to increase or decrease hormones that stimulate sperm production in the testes?
Testosterone
What is the source of the hormones that, when suddenly absent, are directly responsible for the onset of menstruation?
Corpus luteum
Through which of the following does a human sperm cell not have to pass in order to fertilize an egg?
Ovary
A vasectomy is an effective technique for birth control in males because it __________.
severs the route used by the sperm to exit the male's body
Animals that have external fertilization are most likely to reproduce in which of the following areas:
shallow lake
Human sperm cells first arise in the…
Seminiferous tubules
In excreted urine, a reliable "marker" that a pregnancy has initiated is…
human chorionic gonadotropin (hCG)
A vasectomy
prevents sperm from entering the male urethra
In a lactating mammal, the two hormones that promote milk synthesis and milk release, respectively, are…
Prolactin and oxytocin
Asexual reproduction results in offspring that are genetically identical to their parent. What type of cell process occurs to generate this type of offspring?
mitosis
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