Bio Chapter 46 - Animal Reproduction

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