3.2 - Animal Reproduction And Development

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Sexual reproduction

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Reproduction involving the union of gametes (haploid cells) to form diploid individual

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Asexual reproduction

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Reproduction without sex

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Budding

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• Manner in which some simple multicellular offspring
  
• New individuals form as outgrowths or buds from bodies of older animals
  
• Bud grow by mitotic cell division and cells differentiate before bud breaks away from parent
  
• Bud is genetically identical to the parent and may grow as large as the parent before it becomes independent
  

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Regeneration

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• Pieces of an organism can regenerate complete individuals
  
• Occurs when an animal is broken by an outside force
  

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Parthenogenesis

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• Production of an organism from an unfertilized egg
  
• Some species of fish, amphibians, and reptiles
  

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Gametes

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Haploid cells produced by gametogenesis, a process that involves meiotic cell divisions

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Gametogenesis

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The specialized series of cellular divisions that leads to the production of gametes

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Mating (or spawning)

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Bringing gametes together

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Fertilization

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Fusing gametes

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Zygote

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• Single diploid cell created by the union of the haploid sperm and haploid egg in fertilization
  
• Will develop into an embryo
  

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Vitelline envelope

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Inner, proteinaceous layer of a sea urchin egg

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Acrosome

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Membrane-enclosed structure at the front of the sperm head first to fuse with the egg membrane and enter the egg cell

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Blocks to polyspermy

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• First responses to sperm entry
  
• Mechanisms that prevent more than one sperm from entering egg
  

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Cumulus

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Thick layer made up of a loose assemblage of maternal cells in a gelatinous matrix that surround and protects a mammalian ovum

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Zona pellucida

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• Glycoprotein envelope beneath the cumulus which functions similarly to the vitelline envelope in sea urchins
  
• Jelly-like substance that surround the mammalian ovum when it is released from the ovary
  

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External fertilization

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• Occurs in aquatic environments
  
• Gametes are brought together by releasing them into the water
  
• Also called spawning
  

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Internal fertilization

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• Release of sperm into the female reproductive tract
  
• Occurs in all terrestrial animals and some aquatic animals
  

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Primary sex organs

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Gonads - site where gametogenesis occurs

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Accessory sex organs

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All additional components of an animal's reproductive system

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Copulation

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Physical joining of male and female accessory sex organs

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Genitalia

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External sex organs

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Dioecious

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Species that have separate male and female members

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Monecious (Hermaphroditic)

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Species where single individual may produce both sperm and eggs

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Oviparous

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• Animals lay eggs in the environment and their embryos develop outside the mother's body
• Ex//: Terrestrial animals - insects, reptiles and birds protect eggs from desiccation with waterproof membranes or shells

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Viviparous

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• Animals retain the embryo within the mother's body during its early developmental stages
  
• Ex//: Exists in all vertebrate groups except crocodiles, turtles, and birds
  

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Semen

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• Product of the male reproductive system
  
• Contains sperm and a complex mixture of fluids and molecules that support sperm and facilitate fertilization
  

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Testes (Testis)

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The male gonads - the organs that produces the male gametes

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Scrotum

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Pouch of skin outside of the body cavity that contains testes

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Epididymis

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Coiled tubules in the testes that store sperm and conduct sperm from the seminiferous tubules to the vas deferens

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Urethra

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In most mammals, the canal through which urine is discharged from bladder and which serves as the genital duct in males

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Vas deferens

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Duct that transfers sperm from the epididymis to the urethra

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Ejaculatory duct

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• A canal formed by the union of the vas deferens and the duct from the seminal vesicle
  
• Passes through the prostate
  
• Semen passes through them at time of ejaculation
  

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Seminal vesicles

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• Pair of glands that are positioned below the urinary bladder and lateral to the vas deferens - empty into vas deferens just before it joins urethra
  
• Secrete 60% of the volume of semen
  

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Prostate gland

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• Contributes about 30% of the volume of semen
  
• Surrounds the urethra at its junction with the vas defens
  
• Supplies an acid-neutralizing fluid to the semen
  
• Secretes clotting enzyme that causes fibrinogen from seminal vesicles to convert semen into clotted, gelatinous mass
  
• Secretes fibrinolysin which dissolves clotted semen and liberates sperm
  
• Produces protaglandins which stimulate contractions of the female reproductive tract
  

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Bulbourethral glands

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• Secretory structures
  
• Produce a small volume of an alkaline, mucoid secretion that helps neutralize the acidity in the urethra and lubricate it to facilitate passage of semen immediately preceding climx
  

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Penis

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An accessory sex organ of male animals that enables the male to deposit sperm in the female's reproductive tract

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Erection

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• Nervous system's response to sexual stimulation
  
• Nerve endings release neurotransmitter that causes endothelial cells to release NO
  
• Diffuses into muscle cells and stimulates to produce cGMP
  
• cGMP causes muscle cells to relax resulting in dilation of arteries and increase of blood flow to penis causing swelling of erectile tissue
  

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Ovaries (Ovary)

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• Any female organ in plants or animals that produces an egg
  
• Located on either side of the lower abdominal cavity

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Follicle

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• Functional unit of the ovary
  
• Primary oocyte surrounded by a layer of nutritive cells
  

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Ovulation

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Release of an egg from an ovary

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Oviducts

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In mammals, the tube serving to transport eggs to the uterus or to the outside of the body

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Uterus

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• Specialized portion of the female reproductive tract that holds the embryo and nurtures it in its early development
  
• Also called a womb
  

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Cervix

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The opening of the uterus into the vagina

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Endometrium

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The epithelial lining of the uterus

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Vagina

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In female animals, the entry to the reproductive tract

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Germ cells

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A reproductive cell or gamete of a multicellular organism

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Spermatogenesis

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Gametogenesis leading to the production of sperm

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Seminiferous tubules

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The tubules within the testes within which sperm production occurs

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Spermatogonia

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• In animals, the diploid progeny of a germ cell in males
  
• Multiply by mitosis
  
• Stem cells
  
• Self-regenerating and also produce progeny, spermatocytes
  

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Primary spermatocyte

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Progeny of spermatogonia that enter meiosis

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Secondary spermatocyte

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• Produced when primary spermatocytes undergo the first meiotic division (reduction division) to form
  
• 2 haploid cells
  

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Spermatids

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• One of the products of the second meiotic division of a primary spermatocyte
  
• Four haploid spermatids which remain connected by cytoplasmic bridges, are produced for each primary spermatocyte that enters meiosis
  

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Sperm

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Tiny gametes of males that move by beating their flagella

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Oogenesis

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Gametogenesis leading to the production of an ovum

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Oogonium

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In animals, the diploid progeny of a germ cell in females

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Primary oocyte

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In many species, a primary oocyte enters prophase of the first meiotic division then remains in developmental arrest for a long time before resuming meiosis to form a secondary oocyte and a polar body

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Secondary oocyte

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In oogenesis, the daughter cell of the first meiotic division that receives almost all the cytoplasms

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Ootid

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In oogenesis, the daughter cell of the second meiotic division that differentiates into the mature ovum

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Ova

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Female gamete

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Polar body

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A nonfunctional nucleus produced by meiosis during oogenesis

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First polar body

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Receives almost none of cytoplasm in first meiotic division

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Second polar body

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Produced by asymmetrical division of the cytoplasm in second meiotic division (division of large, secondary oocyte)

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Leydig cells

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• Adjacent to seminiferous tubules in the testicle
  
• Produce testosterone in presence of luteinizing hormone (LH)
  

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Sertoli cells

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Cells in the seminiferous tubules of the testes that nurture the developing sperm

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Ovarian cycle

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In human females, the monthly cycle of events by which eggs and hormones are produced

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Uterine (menstrual) cycle

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In human females, the monthly cycle of events by which the endometrium is prepared for the arrival of a blastocyst

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Menopause

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In human females, the end of fertility and menstrual cycling

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Corpus luteum

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• A structure formed from a follicle after ovulation
  
• Produces hormones important for the maintenance of a pregnancy
  

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Menstruation

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The process by which the endometrium breaks down and the sloughed-off tissue, including blood, flows from the body

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Blastocyst

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• An early embryo formed by the first division of the fertilized egg (zygote)
  
• In mammals, a hollow ball of cells
  

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Pregnancy (gestation)

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The period during which the embryo of a mammal develops within the uterus

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Trimesters

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• The three stages of human pregnancy
  
• Approximately 3 months in each length
  

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Fetus

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Medical and legal term for the stages of a developing human embryo from about the 8th week of pregnancy (point at which all major organ systems have formed) to the moment of birth

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Placenta

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The organ in female mammals that provides for the nourishment of the fetus and the elimination of the fetal waste products

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Organogenesis

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The formation of organs and organ systems during development

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Contraception

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Birth control methods that prevent fertilization or implantation (conception)

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Abortion

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Any termination of pregnancy whether induced or natural (in which case called spontaneous abortion) that occurs after a fertilized egg is successfully implanted in the uterus

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Artificial insemination

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An infertility treatment that involves the artificial introduction of sperm into the woman's reproductive tract

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Assisted reproduction technologies (ART)

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Any of several procedures that remove unfertilized eggs from the ovary, combine them with sperm outside the body, and then place fertilized eggs or egg-sperm mixtures in the appropriate location in the female's reproductive tract for development