Chapter 49- Animal Reproduction

Vitelline coat/ zona pellucida (mammals)

A gel-like matrix of proteins, glycoproteins, or polysaccharides located immediately outside the plasma membrane of the egg cell

Inhibin

A hormone that has a negative feedback effect on the hypothalamus and pituitary, and directly inhibits FSH secretion from the pituitary

Prepuce/foreskin

A loose fold of skin that covers the glans, is removed in many cultures

Budding

A mechanism of asexual reproduction in which a new individual grows and develops while attached to the parent. The offspring may then break free from the parent or remain attached to form a colony

Fragmentation

A mechanism of asexual reproduction in which pieces separate from the body of a parent and regenerate into new individuals

Fission

A mechanism of asexual reproduction in which the parent separates into two or more offspring of approximately equal size. Depending on the species may be transverse or longitudinal

Vagina

A muscular canal which leads to the exterior

Labia majora

A pair of fleshy, fat-padded folds that run from front to rear on either side of the opening to the vagina

Uterus

A specialized saclike organ for embryo development

Acrosome

A specialized secretory vesicle at the head of the sperm that forms a cap over the nucleus and contains enzymes and other proteins that help the sperm attach to and penetrate the surface coatings of an egg

Placenta

A specialized temporary structure which connects the embryo to the uterus and facilitates the transfer of nutrients from the blood of the mother to the embryo and the movement of wastes in the opposite direction

Egg white

A thick solution of proteins that surrounds the vitelline coat in some animals. Added while the egg, whether or not it has been fertilized, is in transit through the oviduct

Vas deferens

A thick-walled, muscular tube, which leads from the epididymis into the abdominal cavity. They empty into the urethra just below the bladder

Hymen

A thin flap of tissue that partially covers the opening of the vagina when a human female is born

Testes

Male gonad

Ova

Mature, haploid female gametes. Are nonmotile cells, typically much larger than sperm of the same species. It retains almost all of the cytoplasm of the parent cell to concentrate nutrients and other molecules required for development. Has stored nutrients and cytoplasmic determinants required for at least the early stages of embryonic development, has coats of one or more kinds to protect from mechanical injury and infection, and in some species offer protection to the embryo after fertilization, and has mechanisms that prevent it from being fertilized by more than one sperm cell

Spermatozoa

Mature, haploid male gametes. Are usually motile cells, driven through a watery medium by the whiplike beating of the flagellum that extends from the posterior end of the cell. Contains mitochondria which produce ATP used as the energy source for flagellar beating

Clonal reproduction

Most asexual reproduction, in which the offspring are genetically identical to one another and to the parent

Slow block to polyspermy

Occurs within minutes of fertilization, is an alteration of the egg coat so that no further sperm can attach and penetrate the egg

Fast block to polyspermy

Occurs within seconds of fertilization, is a wave of membrane depolarization that prevents additional sperm from fusing with the egg

Prostaglandins

Are released by the degenerating endometrium and add to uterine contractions to expel debris

Menstruation

Begins at day zero of the uterine cycle, is when blood and tissue breakdown products are released from the uterus to the outside through the vagina

Hermaphroditism

Both mature egg-producing and mature sperm-producing tissue is present in the same individual

Follicle

Cells that surround the developing primary oocytes/ secondary oocytes which grows and develops and becomes filled with fluid. One usually develops to maturity with release of the egg by ovulation. If two or more develop, fraternal twins or multiples can result

Primary oocyte

Diploid, with replicated chromosomes in preparation for meiosis I in oogenesis. Do not complete meiosis until fertilization in most animals, usually halting development at the end of the first meiotic prophase within a few weeks after the female is born, remaining in the ovary until the female is sexually mature. They then advance to the metaphase of the second meiotic division and are released from the ovary at intervals that vary depending on the species

Primary spermatocyte

Diploid, with replicated chromosomes in preparation for meiosis I in spermatogenesis

Greater vestibular glands

Have openings near the entrance to the vagina and secrete a mucus-rich fluid that lubricates the vulva

Amplexus

How frogs typically mate, a reflex response in which the male clasps the female tightly around the body with his forelimbs, stimulating the female to shed a mass of eggs into the water through the cloaca. As the eggs are released, they are fertilized by sperm released by the male

Sequential hermaphroditism

Individuals change from one sex to the other

Simultaneous hermaphroditism

Individuals develop functional ovaries and testes at the same time

Gonadotropin-releasing hormone (GnRH)

Its release by the hypothalamus is the beginning of the ovarian cycle, and it stimulates the pituitary to release FSH and LH

Oviparous animals

Lay eggs that contain the nutrients needed for development of the embryo outside of the mother's body

Leydig cells

Located in the tissue surrounding the developing spermatocytes, produce the male sex hormones known as androgens. Stimulated by LH to release testosterone

Reproduction

Part of a life cycle in which individuals grow, develop, and reproduce according to instructions encoded in DNA

Independent assortment

Random combinations of maternal and paternal chromosomes in gamete nuclei

Luteinizing hormone (LH)

Released by the pituitary, interacts with FSH to stimulate the follicular cells to secrete estrogens. A burst in secretion stimulates the follicle cells to release enzymes that digest away the wall of the follicle, causing it to burst and release the egg, which is ovulation. This also initiates the last phase of the menstrual cycle, the luteal phase, where the remaining follicle cells at the surface of the ovary grows into the corpus luteum

Follicle-stimulating hormone (FSH)

Released by the pituitary, stimulates 6 to 20 primary oocytes in the ovaries to be released from prophase of meiosis I and continue through the meiotic divisions

Mating

The pairing of a male and a female for the purpose of sexual reproduction

Copulation

The physical act involving the introduction of the male's accessory sex organ into a female's accessory sex organ to accomplish internal fertilization

Estradiol

The primary estrogen

Oogenesis

The production of mature, haploid egg cells through meiotic division. Only one of the cell products of meiosis develops into a functional egg

Spermatogenesis

The production of mature, haploid sperm cells through meiotic division. All four products of meiosis develop into functional sperm

Oogonia

The production of mitotic divisions of the germ cells in females, give rise to gametes

Spermatogonia

The production of mitotic divisions of the germ cells in males, give rise to gametes

Parthenogenesis

The production of offspring by the growth and development of an egg without fertilization. The offspring may be haploid or diploid depending on the species. The egg derives from meiosis in the female parent so the offspring are not genetically identical to the parent or to each other

Circumcision

The removal of the foreskin

Spermatid

Haploid, the four products of meiosis II in spermatogenesis

Ootid

Haploid, the one main product of meiosis II in oogenesis. A second polar body is produced as well

Scrotum

A bag-like structure that keeps the testes cooler than the body core, at an optimal temperature for sperm development

Baculum

A bone in the penis (found in many mammalian species but not humans) that helps maintain the penis in an erect state

Germ cells

A cell line that is set aside early in embryonic development and remains distinct from the other, somatic cells of the body, formed by gametes. During development, these collect in specialized gamete-producing organs called gonads

Epididymis

A coiled storage tubule attached to the surface of each testis. Rhythmic muscular contractions of this move the sperm into the vas deferens

Progesterone

A female sex hormone that stimulates growth of the uterine lining and inhibits contractions of the uterus. It has a negative feedback effect on the hypothalamus and pituitary, inhibiting the secretion of GnRH so FSH and LH are not released, diminishing the signal for follicular growth. In its absence, menstruation begins

Marsupium

An abdominal pouch within which the embryo attaches to nipples and continues its development

Corpus luteum

An enlarged, yellowish structure that came from remaining follicle cells at the ovary's surface. It acts as an endocrine gland and secretes estrogens, large quantities of progesterone, and inhibin. Gradually degenerates if fertilization does not occur as cells are destroyed by phagocytosis and blood supply is cut off

Clitoris

Contains erectile tissue and has the same embryonic origins as the penis. Is partly covered by the labia minora, and the rest is within the body

Oogonium

Diploid, produced by mitosis of female germ cell in ovary

Spermatogonium

Diploid, produced by mitosis of male germ cell in testis

Secondary spermatocyte

Half the diploid number of chromosomes, the product of meiosis I in spermatogenesis

Gametes

Egg and sperm

Ovulated

Eggs that are released into the oviducts as immature eggs

Acrosomal reaction

Enzymes in the acrosome are released from the sperm and digest a path through the egg coats. The sperm then follows the path until its plasma membrane touches and fuses with the plasma membrane of the egg. This activates the egg to complete meiosis and begin development

Uterine/Menstrual cycle

Events in the uterus that prepare it to receive the egg if fertilization occurs

Egg shell

Extra layer of protection outside the egg white in some animals. Added while the egg, whether or not it has been fertilized, is in transit through the oviduct

Ovaries

Female gonad

Estrogens

Female sex hormones, are initially secreted at low amounts and have a negative feedback effect on the pituitary, inhibiting the secretion of FSH, but its secretion increases steadily and the high level now has a positive feedback effect on the hypothalamus and pituitary, increasing the release of GnRH and stimulating the pituitary to release a burst of FSH and LH. This increased level also converts the mucus secreted by the uterus to a thin and watery consistency making it easier for sperm to swim through

Internal fertilization

Fertilization that takes place in a watery fluid inside the body of the female. Occurs in annelids, some arthropods, and some mollusks, and in reptiles, birds, mammals, some fishes, and some salamanders. The sperm are released by the male close to or inside the entrance of the reproductive tract of the female and they swim through fluids until they reach and fertilize the egg. Some species have eggs that release molecules to attract sperm to its outer coats

External fertilization

Fertilization that takes place in a watery medium outside the body of both parents. Occurs in most aquatic vertebrates, bony fishes, and amphibians. Sperm and eggs are shed into the water, and the sperm swim until they collide with an egg of the same species. The gamete release is synchronized and the quantity of gametes released is relatively large. Some species have eggs that release diffusible attractant molecules

Seminiferous tubules

Found in the testes, where sperm proceed through all the stages of spermatogenesis

Secondary oocyte

Half the diploid number of chromosomes, the product of meiosis I in oogenesis. The other product is the first polar body

Ovoviviparous animals

Retain fertilized eggs within the body and the embryo develops using nutrients provided by the egg. When development is complete the eggs hatch inside the mother and the offspring are released to the exterior

Viviparous animals

Retain the embryo within the mother's body and nourish it during at least early embryo development. Development of the embryo takes place in the uterus

Cortical granules

Secretory vesicles just under the plasma membrane of the egg

Sertoli cells

Supportive cells that completely surround the developing spermatocytes in the seminiferous tubules and supply nutrients to the spermatocytes and seals them off from the body's blood supply. Stimulated by FSH to secrete a protein and other molecules required for spermatogenesis

Gonads

Testes and ovaries, specialized gamete-producing organs

Cloaca

The cavity in reptiles, birds, amphibians, and many fishes into which both the intestinal and genital tracts empty

Ovarian cycle

The cyclic events in the ovary leading to ovulation

Urethra

The duct that carries urine from the bladder to an opening at the tip of the penis, sperm joins in here as well

Zygote

The first cell of a new individual, produced by the fusion of a haploid sperm and egg during fertilization, which restores the diploid number of chromosomes

Gametogenesis

The formation of the male and female gametes

Cervix

The lower end of the uterus, which opens into a muscular canal

Testosterone

The main male sex hormone. Stimulates sperm production and controls the growth and function of male reproductive structures

Androgens

The male sex hormones

Vulva

The name for the collective external female sex organs

Monotremes

The only oviparous mammals, includes the echidnas and the duck-billed platypus

Polar bodies

The other products from oogenesis that form nonfunctional cells rather than an egg. They eventually disintegrate and do not contribute to fertilization or embryonic development in most species

Glans

The soft, cap-like structure at the end of the penis. Houses most of the nerve endings that produce erotic sensations

Oviduct

The tube through which the egg moves from the ovary to the outside of the body

Fertilization

The union of gametes that initiates development of a new individual

Endometrium

The uterine lining, which is formed by many layers of connective tissue with embedded glands and is richly supplied with blood vessels

Follicle cells

These surround the egg during its development in mammals. They grow from ovarian tissue and nourish the developing egg. They also make up part of the zona pellucida while the egg is in the ovary and remain as a protective layer after it is released

Cortical reaction

Triggered by Ca2+ ions, secretory vesicles in the egg fuse with the membrane and release their contents to the outside by exocytosis, which are enzymes that alter the egg coat so no further sperm can attach and penetrate the egg

Labia minora

Two folds of tissue that run from front to rear on either side of the opening to the vagina. At the anterior end of the vulva, they join to partly cover the head of the clitoris

Asexual reproduction

When a single individual gives rise to offspring without fusion of gametes

Sexual reproduction

When male and female parents produce offspring through the union of egg and sperm generated by meiosis

Polyspermy

When more than one sperm fertilizes an egg

Genetic recombination

When the alleles of parents are mixed into new combinations within chromosomes

Proliferative phase

When the endometrium begins to grow after menstrual flow ceases

Secretory phase

When the uterine lining continues to grow for fourteen days after ovulation if fertilization does not take place

Estrous cycle

When the uterine lining is completely reabsorbed if a fertilized egg does not implant during the period of reproductive activity