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Chapter 29 - Human Development
Terms in this set (100)
How many sperm are found within one ejaculation?
How many sperm actually reach the egg?
2,000 - 3,000
How are the sperm destroyed?
By vaginal acid, drain out of the vagina, some fail to penetrate the mucus of the cervical canal, and about half of the sperm that get past the uterus go up the wrong uterine tube
How do sperm migrate?
Migration occurs by the snakelike lashing of their tails as they crawl along the female mucosa
How are sperm aided on their journey to the egg cell?
Aided by female physiology, strands of cervical mucus guide them through the cervical canal. uterine contractions may assist, chemical attraction (egg may release a chemical that attracts sperm from a short distance)
What is the fertilization of two or more sperm?
What two methods prevent polyspermy?
Fast block (which prevents binding of second sperm) and slow block (which creates an impenetrable fertilization membrane between the egg and sperm)
What are the first 16 days of development called?
What happens in the preembryonic stage?
Culminates the existence of an embryo: the zygote (fertilized egg cell) divides into hundreds of cells that then organize into the primary germ layers and the conceptus becomes firmly attached to the uterine wall
What steps does the preembryonic stage consist of?
Cleavage, implantation, and embryogenesis
What step of the preembryonic stage occurs 30 - 72 hours after fertilization?
What occurs first in the cleavage step?
Mitotic divisions of the zygote into smaller, identical blastomeres that occur in the first 3 days
Within 72 hours, what occurs next in the cleavage step?
The morula (solid balls of small cells) forms and the morula is free in the uterine cavity for 4 - 5 days and divides into 100 cells or so
What disintegrates to release blastocyst?
What is a hollow sphere with an outer layer of cells and an inner cell mass?
What part of the blastocyst helps form part of the placenta and play an important role in the nourishment of the embryo?
Outer layer of cells called the trophoblast
What part of the blastocyst will become the embryo?
Inner cell mass called the embryoblast
What part of the preembryonic stage is the attachment of a conceptus to the endometrium of the uterus?
When does implantation occur?
About 6 days after ovulation
What is the multinucleate mass of trophoblasts that grows into the uterus like little roots digesting endometrial cells along the way?
What also secretes human chorionic gonadotropin (HCG) that stimulates corpus luteum to secrete estrogen and progesterone?
What does progesterone do?
What does the syncytiotrophoblast become?
What part of the preembryonic stage is the arrangement of the blastomeres into the three primary germ layers?
What are the three primary germ layers?
Ectoderm, mesoderm, and endoderm
During embryogenesis, what forms between embryoblast and cytotrophoblast?
Formation of amniotic cavity
During embryogenesis, what flattens into an embryonic disc composed of ectodermal and endodermal cells?
During embryogenesis, what is a thickened cell layer that forms and is spread laterally as the mesoderm layer?
What is the innermost of the three primary germ layers of an embryo?
What does the endoderm give rise to?
The mucosae of the digestive and respiratory tracts and to their associated glands
What is the middle layer of the three primary germ layers of an embryo?
What does the mesoderm give rise to?
Muscle and connective tissue called mesenchyme (a loose network of cells)
What does the mesenchyme from the mesoderm become?
It's embedded in a gelatinous ground substance which differentiates into tissues such as smooth and cardiac muscle, cartilage, bone, and blood
What is the outermost layer of an embryo?
What does the ectoderm give rise to?
Epidermis, nervous system, lens, cornea, and internal ear
Once the three primary germ layers are formed, what is complete?
Embryogenesis is complete and an individual is considered an embryo
What are the nutritional roles of the placenta?
Permits nutrients such as glucose, amino acids, and fatty acids to diffuse from the maternal blood to the fetal blood
Stores nutrients such as carbs, protein , and iron in early pregnancy and releases them to the fetus later
What are the excretory roles of the placenta?
Permits nitrogenous wastes such as ammonia, urea, and uric acid to diffuse from fetal blood to the maternal blood so the mother can excrete them`
What are the respiratory roles of the placenta?
Permits oxygen to diffuse from mother to fetus and carbon dioxide from fetus to mother
What are the endocrine roles of the placenta?
Secretes estrogen, progesterone, and relaxin; allows other hormones synthesized by the conceptus to pass into the mother's blood and maternal hormones to pass into the fetal blood
What are the immune roles of the placenta?
Transfers maternal antibodies into the fetal blood to confer passive immunity on the fetus
What embryonic membrane is a transparent sac that encloses the fetus and amniotic fluid and is penetrated only by the umbilical cord?
What embryonic membrane is filled with amniotic fluid that protects the embryo from trauma, infection, and temperature fluctuations?
What embryonic membrane provides freedom of movement important for muscle development and prevents body parts from adhering to each other?
What embryonic membrane forms from maternal plasma filtrate and fetal urine and at term contains 700 - 1000mL of fluid?
What embryonic membrane encloses the yolk in vertebrates that lays eggs and serves in humans as the origin of the first blood and germ cells?
What is suspended from the ventral side of the embryo and contributes to the GI tract, blood cells, and future egg or sperm cells?
What is an elongated extraembryonic sac that is attached to the caudal gut of the embryo that gives rise to part of the urinary bladder and the foundation of the umbilical cord?
What is the outermost embryonic membrane that forms the fetal portion of the placenta?
What embryonic membrane functions includes fetal nutrition, waste removal, and hormone secretion?
What is a glycogen-rich secretion of the uterine tubes and endometrial glands?
What is the only mode of nutrition for the first week after implantation and remains the dominant source of nutrients through the end of week 8?
What does the conceptus consume as it implants?
Decidual cells of the endometrium
What is the diffusion of nutrients from the mother's blood through the placenta into the fetal blood?
What kind of nutrition begins at 2 weeks and becomes increasingly important until birth which is 37 weeks after implantation?
At what week of prenatal development are all organs present?
What circulatory system is dependent on the placenta?
What is the placental circuit dependent on?
In what state does the circulatory become independent?
Neonatal (newborn) state
What classification is given to infant born before the start of week 37?
What weight are premature infants under?
What premature challenge is seen with insufficient surfactant causing alveolar collapse with exhaustion?
Infant respiratory distress syndrome (IRDS)
What premature challenge is due to an incompletely developed hypothalamus and low body temperature is countered with an incubator?
What premature challenge causes a difficulty in ingesting milk so the babies must be fed by nasogastric or nasoduodenal tubes?
Digestive system not well-developed
What premature challenge is seen by the failure to synthesize plasma proteins and can lead to edema, deficiency of clotting and jaundice from bile?
What is the abnormal structure or position of an organ at birth resulting from a defect in prenatal development?
Congenital anomaly (birth defect)
What are agents that cause anatomical deformities in the fetus?
What does the effect of teratogens depend upon?
Genetic suscpetibility of the embryo, the dosage, and the time of exposure
What are the three categories of teratogens?
Drugs and other chemicals, infectious diseases, and radiation such as X-rays
What was taken to relive morning sickness and as a sleeping aid but causes unformed arms or legs?
What is caused by alcohol abuse during pregnancy and is characterized by a small head, malformed facial features, cardiac and central nervous system defects, stunted growth, and behavioral signs such as hyperactivity, nervousness, and a poor attention span?
Fetal alcohol syndrome (FAS)
What is it called when a pair of chromosomes fail to separate?
What is the presence of an extra chromosome or lack of one and can be detected prior to borth by amniocentesis or by chorionic villus sampling (CVS)?
What is the examination of cells in a sample of amniotic fluid?
What is the examining of placental cells?
Chorionic villus sampling
What is the presence of one extra chromosome, producing a triplet set?
What is an XXX zygote that results from an egg receiving 2 X chromosomes fertilixed by X carrying sperm making a female child infertile and causing mild intellectual impairments?
What is an XX egg fetilized by a Y-bearing sperm, resulting in XXY combination making sterile males usually of average intelligence but with undeveloped testes?
Klinefelter syndrome (XXY)
What is an egg receiving no X chromosomes but fertilized by X carrying sperm and survivors are sterile, have no ovaries, and have a webbed neck and short stature?
Turner syndrome (XO)
What is the most survivable trisomy that includes impaired physical and intellectual development, short stature a relatively flat face with a flat nasal bridge, and enlarged tongue, stubby fingers, an mental retardation?
Down syndrome (Trisomy-21)
What is the degenerative changes that occur with age?
Which organ system ages the least?
Name two changes that occur with aging of the integumentary system.
Paper-thin loose skin that sags and skin that bruises easily and heals slowly
Name two changes that occur with aging of the skeletal system.
Osteopenia (loss of bone mass) and joint diseases (Synovial fluid is less abundant)
Name two changes that occur with aging of the muscular system.
Muscular atrophy (replaces lean body mass with fat) and loss of strength (fewer myofibrils and motor neurons)
Name two changes that occur with aging of the nervous system
Cerebral and neuronal atrophy and autonomic nervous system is less efficient at regulating body temperature and blood pressure
Name two changes that occur with aging of the sense organ vision
Vision has loss of flexibility and cataracts or cloudiness of lenses
Name two changes that occur with aging of the sense organ hearing
Hearing has the tympanic membrane and ossicle joints stiffen and hair cells and auditory nerve fibers die
Name changes that occur with aging of the sense organs taste and smell
They are blunted as receptors decline in number
Name two changes that occur with aging of the endocrine system
Pituitary gland is less sensitive to negative feedback inhibition by adrenal glucocorticoids and Type 2 diabetes is more common since more body fat decreases insulin sensitivity of other cells
Name two changes that occur with aging of the circulatory system
Atherosclerosis of other vessels increase BP and varicose veins increase due to weaker valves
Name two changes that occur with aging of the immune system
Amount of lymphatic tissue and red bone marrow decline and lymphocytes fail to mature
Name two changes that occur with aging of the respiratory system
Declining pulmonary ventilation and elderly are less able to clear lungs of irritants and pathogens
Name two changes that occur with aging of the urinary system
Renal atrophy because of loss of nephrons and atherosclerotic glomeruli and fluid balance is less responsive to antidiuretic hormone and sense of thirst is sharply reduced
Name two changes that occur with aging of the digestive system
Dental health affected by reduced saliva and gastric mucosa atrophies and secretes less acid and intrinsic factor
Name two changes that occur with aging of the male reproductive system
Gradual decline in testosterone secretion, sperm count, and libido and males are fertile into old age but impotence may occur due to atherosclerosis, hypertension, or medication
Name two changes that occur with aging of the female reproductive system
More abrupt, rapid changes due to menopause and ovarian follicels are used up, gametogenesis ceases, and ovaries cease production of sex steroids
What are the best ways to slow aging?
Good nutrition and exercise
What kind of exercise reduces bone fractures?
What kind of exercise reduces body fat and increases cardiac output and oxygen uptake?
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