30.1 ANIMAL DEVELOPMENT BEGINS WITH REPRODUCTION
Reproduction, growth, and development are shared features of ALL multicellular life. A. REPRODUCTION IS ASEXUL OR SEXUAL
ASEXUAL REPRODUCTION – offspring contain genetic info from only one parent and are identical to the parent and each other. Advantageous in environments that don’t change much over time.
EX. Include aphids, some types of lizards
SEXUAL REPRODUCTION – requires genetic info from two parents. Advantageous in changing environments.
GAMETES – products of meiosis, haploid sex cells that carry genetic info from each parent (sperm/eggs)
ZYGOTE – diploid product of fertilization, new offspring.
EXTERNAL FERTILIZATION – males and females release gametes into the same environment and fertilization occurs outside the body. Especially common in aquatic animals. Unique “recognition” proteins on the surface of gametes keep sperm cells from fertilizing eggs of the wrong species.
EX. Salmon, sponges, corals, sea urchins, some amphibians
INTERNAL FERTILIZATION – a male deposits sperm inside a female’s body, where fertilization occurs. After copulation, animals may lay hard-shelled eggs or bear live young. B. DEVELOPMENT IS INDIRECT OR DIRECT
DEVELOPMENTAL BIOLOGISTS – study the stages of an animal’s growth as cells specialize and interact to form tissues, organs, and organ systems.
Differentiation and pattern formation involve complex interactions between the DNA inside cells and external signals such as hormones, interactions regulate formation of each structure. Homeotic Genes- develop control development in humans and all other animal species.
DIFFERENTIATION – the process by which cells in organs activate unique combinations of genes to acquire their specialized functions.
PATTERN FORMATION – process by which genes determine the overall shape and structure of the animal’s body. (EX. # of segments, placement of limbs)
INDIRECT DEVELOPMENT – offspring spends early life as larva.
LARVA – an immature stage that looks different from the adult EX. Caterpillar, tadpoles, maggots
METAMORPHOSIS – process by which the larva matures into an adult
DIRECT DEVELOPMENT – at birth, offspring resemble a smaller version of its parents.
30.2 MLES PRODUCE SPERM CELLS
REPRODUCTIVE SYSTEM – organ system that produces and transports gametes
GONADS – Testes or ovaries, paired primary sex organs in each male/female system. Secondary sex organs include network of tubes that transport the gametes.
GERM CELLS – contained in the gonads, cells that give rise to gametes.
In both sexes, hormones control reproduction and promote the development of
SECONDARY SEX CHARACTERISTICS – features that distinguish sexes but do participate directly in reproduction.
EX. Wider hips in females, facial hair and deep voices in adult males. A. MALE REPRODUCTIVE ORGNS ARE INSIDE AND OUTSIDE THE BODY
TESTES – paired set of male gonads
Location of testes and scrotum outside the abdominal cavity allows the testes to maintain a temp about 3 degrees Celsius cooler than the rest of the body, Necessary for sperm development.
EPIDIDYMIS – tightly coiled tube that receives and stores sperm from on testis.
VAS DEFERENS – from epididymis, sperm moves into this duct that travels upward out of the scrotum, bends behind the bladder, and connects with the left or right EJACULATORY DUCT. The two ducts empty into the URETHRA.
SEMINAL VESICLES – accessory glands, which opens into each vas deferens, secrete most of the fluid in semen.
Semen secretion includes fructose and prostaglandins.
PROSTGLANDINS – hormone-like lipids that may stimulate contractions in the female reproductive tract, helping to propel sperm.
PROSTATE GLAND – wraps around part of the urethra and contributes a thin, milky, alkaline fluid that activates the sperm to swim.
One typical human ejaculation delivers more than 100 million sperm cells
Two cancers of the male reproductive system originate in the prostate gland and testes. Prostate cancer is the second most common type of cancer in men. Testicular cancer – mutated germ cells in the testes divide out of control forming lumps. B. SPERMATOGENESIS YIELDS SPERM CELLS
SPERMATOGENESIS – the production of sperm, a continuous process that begins when a male reaches puberty and continues throughout life.
SEMINIFEROUS TUBULES – about 200 coiled, 50 cm long tube contained in each testis, produce sperm
Germ cells are diploid and contain 46 chromosomes, divides mitotically. One daughter cell remains in the tubule wall, the other cell becomes a
PRIMARY SPERMATOCYTE – diploid that accumulates cytoplasm and moves closer to the tubule’s lumen (central cavity)
SECONDARY SPERMATOCYTE – 2 daughter cells yielded by meiosis division of primary spermatocytes
SPERMATIDS – after secondary under meiosis II, forms four round, haploid cells, contain 23 chromo.
ACROSOME – cap-like structure that covers the head of the sperm and releases enzymes to help it penetrate the egg cell.
The entire process from germ cell to mature sperm cell takes 74 days in human males C. HORMONES INFLUENCE MALE REPRODUCTIVE FUNCTION
GONADOTROPIN-RELEASING HORMONE (GnRH) – secreted by the hypothalamus, this water soluble hormone travels in the bloodstream to the anterior pituitary and stimulates release of FOLLICLE-STIMULATING HORMONE (FSH) and LUTEINIZING HORMONE (LH) – induces endocrine cells in testes to produce TESTOSTERONE, sperm cannot form without testosterone, effects include
EX. Development of secondary sex characteristics, puberty, hair growth, growth spurt, deepens voice
30.3 FEMALES PRODUCE EGG CELLS
More complicated for 2 reasons 1) In females, meiosis begins before birth, pauses, and resumes at sexual maturity. Does not complete until sperm cell fertilizes egg cell. 2) Egg cell production is cyclical, under the control of several interacting hormones whose levels fluctuate monthly A. FEMALE REPRODUCTIVE ORGANS ARE INSIDE THE BODY
OVARIES – paired female sex cells in the abdomen which produces both egg cells and sex hormones.
OOCYTES – the cells that give rise to mature egg cells, nestled in a fluid-filled FOLLICLE.
UTERINE TUBES – also called fallopian tubes or oviducts, two tubes where the single most mature oocyte are kept for fertilization.
CANDIDA ALBICANS – causes vaginal yeast infections when overgrown
VULVA – external female genitalia made up of the labia, clitoris, and vaginal opening
Secondary sex characteristics include the wider and shallower shape of the pelvis, accumulation of fat around hips, a higher pitched voice, and BREAST – contains fatty tissue, collagen, milk ducts. B. OOGENESIS YIELDS EGG CELLS
OOGENESIS – making of an egg cell, begins with a diploid germ cell containing 46 chromosomes. Each germ cell grows, accumulates cytoplasm, replicates DNA, and divides mitotically, becoming 2 PRIMARY OOCYTES. Cytoplasm partitioned unequally, oogenesis produces cells of different sizes. End of meiosis I, primary oocyte has divided into small haploid polar body, and larger haploid SECONDARY OOCYTE, ea 23
OVULATION – release of the secondary oocyte from its follicle. Following ovulation, ruptured follicle transforms into a gland called a CORPUS LUTEUM. Meiosis halts at metaphase II and does not resume unless fertilization occurs. OVUM –mature haploid egg cell, contains 23 chromosomes.
Females, one germ cell yields one functional egg cell and three smaller polar bodies. C. HORMONES INFLUENCE FEMALE REPRODUCTIVE FUNCTION
OVARIAN CYCLE – controls the timing of oocyte maturation in the ovaries
MENSTRUAL CYCLE – prepares the uterus for pregnancy
ESTROGEN & PROGESTERONE signal the hypothalamus to secrete GnRH. Estrogen has two roles in the ovarian cycle. At low concentrations, it inhibits the release of both LH and FSH. But around day 14 of the cycle, a spike in estrogen accumulation triggers the release of additional LH and FSH from anterior pit. D. HORMONAL FLUCTUATIONS CAN CAUSE DISCOMFORT
Ex. PMS, menstrual cramps (with or without PMS) – arises from smooth muscle contractions of uterus E. CONTRACEPTIVES PREVENT PREGNANCY
Birth control pills, patches, vaginal rings, injections, and implants ALL contain a synthetic form of progesterone, which mimics the hormonal effects of pregnancy. Each prevents ovulation.
30.4 SEXUAL ACTIVITY MAY TRANSMIT DISEASE TABLE 30.3 PG 619
Other animals and plants can also transmit their own forms of STD. EX. Viroids in plants. In the U.S. the most common STD is genital warts caused by over 40 strains of HPV, some cause cervical cancer. Most STDs are associated with an elevated risk for acquiring and transmitting HIV. Due to open sores that may pass viral particles, and any infection can cause inflammation and other defensive reactions, which attract the white blood cells that HIV infects.
30.5 THE HUMAN INFANT BEGINS LIFE AS A ZYGOTE A. FERTILIZATION INITIATES PREGNANCY
Of the 100 million sperm, only 200 arrive at the egg cell’s location in the uterine tube. Sperm must penetrate two layers to contact the ovum. Fertilization begins when the outer membrane of one sperm cell touches that of the secondary oocyte. Changes across the oocyte surface prevent other sperm from fertilizing the same egg. Sperm DNA released, meiosis complete. Zygote formation. B. THE PREEMBRYONIC STAGE ENDS WITH IMPLANTATION
PREEMBRYONIC STAGE – the first 2 weeks of prenatal development
CLEAVAGE – 36 hrs after fertilization, the zygote divides for the first time beginning period of mitotic cell division. Results in a solid ball of 16 or more cells. The mass of cells reaches the uterus 3-6 days later, the ball hallows out filling with fluid from the uterus in its center, called BLASTOCYST. INNER CELL MASS – few cells inside blastocyst, that will develop into the embryo itself. (also source of stem cells)
IMPLANTATION – process of blastocyst embedding in the lining of the uterus. Occurs within a week
HUMAN CHORIONIC GONADOTROPIN (Hcg) – secreted by blastocyst, basis of pregnancy test.
GASTRULA – resulting three layered structure of endoderm, ectoderm, and mesoderm. Marks the end of the preembryonic stage about two weeks after fertilization. C. ORGANS TAKE SHAPE DURING THE EMBRYONIC STAGE end of week 2 – end of week 8
FOUR MEMBRANES, THE PLACENTA, AND THE UMBILICAL CORD SUPPORT THE EMBRYO
Four thin layers of tissue that support, protect, and nourish the embryo occur in humans, mammals, birds, and nonavian reptiles.
YOLK SAC – manufactures blood cells for embryo, parts develop into intestines and germ cells. Outpouching forms by the 3rd week to form another membrane, ALLANTOIS – makes blood cells and gives rise to blood vessels in the umbilical cord.
AMNION – transparent sac that contains the amniotic fluid that cushions embryo, allows it to shift it position, and maintains a constant temp and pressure.
CHORION – outermost membrane of embryo. CHORIONIC VILLI – fingerlike projections that extend to the uterine lining and establish the beginning of the PLACENTA – structure that connects embryo with mother’s uterus. Placenta not completely developed until after 10 wks.
Carbon dioxide, urea, and other wastes pass from embryo to mother’s blood. Glucose, amino acids, oxygen, ions, and some antibodies pass from mother to embryo.
ORGAN FORMATION BEGINS IN HE THIRD WEEK OF DEVELOPMENT
Ectoderm cells develop into nervous system, sense organs, outer skin layer, hair, nails, and skin glands. Splits in the mesoderm cells develop into bone, muscle, blood, inner skin layer, and reproductive organs. Endoderm cells form organs of digestive and respiratory systems.
Between third and fifth week, heart appears, begins beating around day 22. By end of week 8, all organ systems are in place and embryonic stage of development is complete. Offspring is FETUS. D. ORGAN SYSTEMS BECOME FUNCTIONAL IN THE FETAL STAGE week 9 – 38 weeks
Organs begin to function and coordinate. Bone replaces cartilage. E. MUSCLE CONTRACTIONS IN THE UTERUS DRIVE CHILDBIRTH