Download (2026): BIO 208 Chapter 29: Development & Inheritance and more Quizzes Advanced Education in PDF only on Docsity!
Development Gradual modification of anatomical structures & physiological characteristics from fertilization to maturity
Inheritance Transfer of genetic material from generation to generation
Differentiation - Creation of different types of cells required in development
- Occurs through selective changes in genetic activity --> As development proceeds, some genes are turned off, others are turned on
- Involves changes in genetic activity of some cells but not others
Fertilization (Conception) When development begins
Embryonic Development - Occurs during first two months after fertilization
- Embryology: the study of these events
Fetal Development - Begins at start of 9th week
Prenatal Development Embryonic & fetal development stages
Postnatal Development - Commences at birth
- Continues to maturity (the state of full development or completed growth
Genetics The study of mechanisms responsible for inheritance
Fertilization - Fusion of two haploid gametes each containing 23 chromosomes
- Produces zygote containing 46 chromosomes
- Occurs in uterine tube within a day after ovulation --> Secondary oocyte travels a few centimeters --> Spermatozoa must cover distance between vagina & ampulla
Spermatozoon - Delivers paternal chromosomes to fertilization site
- Travels relatively large distance
- Small, efficient, & highly streamlined
Oocyte Activation - Contact and fusion of cell membranes of sperm and oocyte
- Follows fertilization
- Oocyte completes meiosis II, becomes mature ovum
Polyspermy - Feriliztion by more than one sperm
- Prevented by cortical reaction
Cortical Reaction Releases enzymes that:
- Inactivate sperm receptors
- Harden zone pellucida (thick, transparent, glycoprotein membrane around unfertilized ovum)
Femal Pronucleus Nuclear material remaining in ovum after oocyte activation
Male Pronucleus - Swollen nucleus of spermatozoon
- Migrates to center of cell
Fertilization 1. Acrosomal enzymes from multiple sperm create gaps in the corona radiate. A single sperm then makes contact with oocyte membrane, and membrane fusion occurs, triggering oocyte activation & completion of meiosis
- Pronucleus Formation Beings: the sperm is absorbed into the cytoplasm, & the female pronucleus develops
- Spindle Formation & cleavage Preparation: the male pronucleus develops & single fibers appear in preparation for the first cleavage division
- Amphyimixis: fusion of female pronucleus & male pronucleus (moment of conception) cells becomes zygote with 46 chromosomes
- Cleavage Begins: the first cleavage division nears completion about 30 hours after fertilization
Induction - Cells release chemical substances that affect differentiation of other embryonic cells
- Can control highly complex development
4 Stages of First Trimester 1. Cleavage
- Sequence of cell divisions begin immediately after ferilization
- Zygote becomes a per-embryo, which develops into multicellular blastocyst
- Ends when blastocyst contacts uterine wall
- Implantation
- Begins with attachment of blastocyst to endometrium of uterus
- Sets stage of formation of vital embryonic structures
- Placentation
- Occurs as blood vessels form around periphery of bastocyst & placenta develops
- Embryogenesis
- Formation of viable embryo
- Establishes foundations for all major organ systems
Cleavage & Blastocyst Formation Blastomeres: identical cells produced by cleavage divisions
Morula:
- Stage after three days of clevage
- Pre-embryo is solid ball of cells resembling mulberry
- Reaches uterus on day 4
Blastocyst:
- Formed by blastomeres
- Hollow ball with an inner cavity known as blastocoele
Trophoblast:
- Outer layer of cells separate outside world from blastocoele
- Cells responsible for providing nutrients to developing embryo
Inner cell mass:
- Clustered at end of blastocyst
- Exposed to blastocoele
- Insulated from contact with outside environment by trophoblast
- Will later form embryo
Gatrulation & Germ Layer formation - Formation of third layer of cells
- Cells in specific areas of surface move toward central line known as primitive streak
Primitive Streak
- Migrating cells leave surface & move between two layers
- Creates three distinct embryonic layers, or germ layers:
- Ectoderm: consists of the superficial cells that did not migrate into interior of inner cell mass
- Endoderm: consists of cells that face blastocoele
- Mesoderm: consists of poorly organized layers of migrating between ectoderm & endoderm
Ectodermal Contributions Integumentary system:
- Epidermis, hair follicles, hairs, nails, & glands communicating with the skin
Skeletal system:
- Pharyngeal cartilages & their derivatives in adults (portion of sphenoid, the auditory ossicles, the styloid processes of the temporal bones, the cornu & superior rim of the hyoid bone)
Nervous system:
- All neural tissue, including brain & spinal cord
Endocrine system:
- Pituitary gland & adrenal medullae
Respiratory system:
- Mucous epithelium of nasal passageway
Digestive system:
- Mucous epithelium & anus, salivary glands
Endodermal Contributions Endocrine system:
- Thymus, third gland, & pancreas
Respiratory system:
- Respiratory epithelium & associated mucous glands
Digestive system:
- Mucous epithelium (except mouth & anus), exocrine glands (except salivary glands), liver, & pancreas
Urinary system:
- Urinary bladder & distal portions of the duct system
Reproductive system:
- Distal portions of the duct system, stem cells that produce gametes
Embryonic Disc - Oval, three-layered sheet
- Produced by gastrulation
- Will form body of embryo --> Rest of blastocyst will be involved in forming extra embryonic membranes
Formation of the Extraembryonic Membranes
- Support embryonic & fetal development
Yolk sac
- Begins as layer of cells spread out around outer edges of blastocoele to form complete pouch
- An important site of blood cell formation
Amnion
- Combination of mesoderm & ectoderm
- Ectodermal layer enlarges & cells spread over the inner surface of the amniotic cavity
- Mesodermal cells create an outer layer
- Continues to enlarge through development
- Amniotic fluid: surrounds & cushions developing embryo or fetus
Allantois
- Sac of endoderm & mesoderm
- The base later gives rise to the urinary bladder
Chorion
- Combination of mesoderm & trophoblast
- Blood vessels develop within mesoderm
- Rapid-transit system for nutrients that links embryo with trophoblast
- First step in creation of functional placenta
Chorionic Villi - In contact with lateral tissues
- Create intricate network within endometrium carrying lateral blood
Endocrine Placenta - Synthesized by syncytial trophoblast, released into the maternal bloodstream
Human chorionic gonadotropin (hCG)
- Appears in material bloodstream soon after implantation
- Provides a reliable indication of pregnancy (makes a pregnancy test positive)
- Pregnancy ends if absent
Human placental lactose (hPL)
- Prepares mammary glands for milk production
- Synergistic with growth hormone at other tissues --> Ensures adequate & protein is available for the fetus
Placental prolactin
- Helps convert mammary glands to active status
Relaxin
- A peptide hormone secreted by placental & corpus luteum during pregnancy
- Increases flexibility of pubic symphysis, permitting pelvis to expand during delivery
- Causes dilation of cervix
- Suppresses release of oxytocin by hypothalamus & delays labor contractions
Progesterone
Estrogens
Embryogenesis - Body of embryo begins to separate from embryonic disc
- Body of embryo & internal organs start to form
- Folding & differential growth of embryonic disc produce bulge that projects into amniotic cavity --> Projections are head fold & tail fold
Organogenesis Process of organ formation
Second Trimester Fetus grows faster than surround placenta
Third trimester - Most of the organ systems become ready
- Growth rate starts to slow
- Largest weight gain
- Fetus & enlarged uterus displace many of mother's abdominal organs
Pregnancy & Maternal Systems - Developing fetus is totally dependent on maternal organ systems for nourishment, respiration, & wast removal
- Maternal adaptations include increases in: --> Respiratory rate & tidal volume --> Blood volume --> Nutrient & vitamin intake --> Glomerular filtration rate --> Size of uterus & mammary glands
Stages of Labor 1. Dilation stage
- Begins with onset of true labor
- Cervix dilates
- Fetus begins to shift toward cervical canal
- Highly variable in length, but typically lasts over eight hours
- Frequency of contractions steadily increases
- Amniochorionic membrane ruptures (water breaks)
- Expulsion stage
- Begins as cervix completes dilation
- Contractions reach maximum intensity
- Continues until fetus has emerged from vagina --> Typically less than two hours
- Placental stage
- Muscle tension builds in walls of partially empty uterus
- Tears connections between endometrium & placenta
- Ends within an hour of delivery with ejection of placenta, or afterbirth
- Accompanied by a loss of blood
Episiotomy - Incision through perineal musculature
- Needed if vaginal canal is too small to pass fetus
- Repaired with sutures after delivery
Cesarean Section (C-section) - Removal of infant by incision made through abdominal wall
- Opens uterus just enough to pass infant's head
- Needed if complication arise during dilation or expulsion stages
Premature Labor - Occurs when true labor begins before fetus has completed normal development
- Newborns' chances of survival are directly related to body weight at delivery
- Refers to birth at 28-36 weeks
- Newborns have a good chance of surviving & developing normally
Immautre Delivery - Refers to fetuses born at 25-27 weeks of gestation
- Most die despite intensive neonatal care
- Survivors have high risk of developmental abnormalities
Difficult Deliveries: Forceps Delivery - Needed when fetus faces mother's pubis instead of sacrum
- Risks to infant & mother are reduced if forceps are used --> Forceps resemble large, curved salad tongs --> Used to grasp head to fetus
