Chapter 29 - Development and Inheritance PART 1 Flashcards
What is Embryonic Period?
Embryonic Period:
Extends from fertilization through 8th week of development
What is Fertilization?
Fertilization:
Merging of genetic info from Haploid Sperm and Haploid Secondary Oocyte
Sperm swim from Vagina to Cervix
Sperm pass through Uterus and Uterine Tubes mainly due to contraction of walls of these 2 structures
For Fertilization to occur:
Sperm must penetrate the Corona Radiata and the Zona Pellucida
What is Path of Sperm?
1- Corona Radiata
2- Zona Pellucida
3- Plasma membrane of Secondary Oocyte
4- Cytoplasm of Secondary Oocyte
How can Sperm Penetrate into Oocyte?
Enzymes on sperm’s Acrosome, along with Tail movement, allow sperm to penetrate Corona Radiata
Glycoprotein ZP3 in Zona Pellucida is a receptor for the sperm
Membrane proteins in the sperm Head bind to ZP3, and Acrosomal enzymes are released to digest a path in the Zona Pellucida
What is Male Pronucleus?
The Haploid Nucleus in the Head of the sperm becomes the Male Pronucleus
What is Female Pronucleus?
The Haploid Nucleus of the fertilized Ovum becomes the Female Pronucleus
What is Syngamy?
Syngamy:
When Male and Female Pronuclei merge
Form a Diploid Zygote
What is Day 1 Cleavage?
Cleavage:
Day 1
Zygote begins Mitotic Division after fertilization (about 24 hours)
Fist division takes about 6 hours
Successive divisions take less time
What Happens on Day 2 after Fertilization?
A second Cleavage is completed
Yielding 4 cells
What Happens on Day 3 after Fertilization?
By end of Day 3:
There is 16 cells
Blastomeres:
Each division yields smaller and smaller cells called Blastomeres
What Happens on Day 4 after Fertilization?
Day 4:
Morula:
The cluster of cells resembles a mulberry and is called Morula
Morula:
Still surrounded by Zona Pellucida
Still the size of the Zygote
What Happens on Day 4 or 5 after Fertilization?
Morula:
Enters Uterine Cavity
Nourished by Uterine Milk, a Glycogen-rich secretion from Endometrial Glands, in addition to stored nutrients from the Cytoplasm
What is Blastocyst?
Blastocoel:
At the 32-Cell Stage, the fluid now inside the Morula rearranges the Blastomeres into a large, fluid-filled Blastocyst Cavity
Blastocyst:
The mass is now called a Blastocyst
Still same size as original Zygote
As Blastocyst is formed:
Two different cell populations arose:
1- Embryoblast:
Inner cell mass
Will develop into the Embryo
2- Trophoblast:
Outer cell mass
Will develop into Outer Chorionic Sac surrounding the Fetus, and Fetal portion of Placenta
What is Implantation?
Blastocyst remains free in Uterine Cavity for about 2 days and then implants by attaching to the Endometrium at around 6 days after Fertilization
Implantation:
Usually occurs in either the posterior portion of the Fundus or the Body of the Uterus
The Inner Cell Mass orients toward the Endometrium
What happens after Implantation?
After Implantation:
The Endometrium is called Decidua
Decidua:
Separates from the Endometrium after the Fetus is delivered
Has different regions named based on their positions relative to the site of the implanted Blastocyst
1- Decidua Basalis
2- Decidua Capsularis
3- Decidua Parietalis
What happens on Day 8 after Fertilization?
About 8 days after Implantation:
a- Trophoblast develops into the:
1- Syncytiotrophoblast
2- Cytotrophoblast
b- Embryoblast develops into 2 layers:
1- Hypoblast (Primitive Endoderm)
2- Epiblast (Primitive Ectoderm)
Cells of these structure form a flat disc called the Bilaminar Embryonic Disc
Amniotic Cavity forms the Epiblast
What is Yolk Sac?
Also on 8th day:
Exocoelomic Membrane forms
Hypoblast and Exocoelomic Membrane together form the Yolk Sac
What is Amnion and Amniotic Cavity?
Amnion forms the roof of the Amniotic Cavity
Eventually, it surrounds the entire embryo and fills with Amniotic Fluid
What happens on Day 9 after Fertilization?
Lacunae:
Small spaces called Lacunae form
What happens on Day 12 after Fertilization?
Lacunae fuse to form Lacunar Networks
Extraembryonic Mesoderm develops:
1- The cells form a connective tissue layer around the Amnion and Yolk Sac
2- Large cavities develop that fuse and form the Extraembryonic Coelom
What is Chorion?
Chorion:
Extraembryonic Mesoderm and Trophoblast together form the Chorion
Chorion surrounds the embryo, and later the Fetus
Chorion:
Blocks antibody production by the mother
Promotes production of T Lymphocytes to suppress the immune response in the Uterus
Produces Human Chorionic Gonadotropin (hCG)
What is Gastrulation?
Gastrulation:
First major event of the 3rd week of development
The 2-layered embryonic disc transforms into a Trilaminar Embryonic Disc:
1- Ectoderm
2- Mesoderm
3- Endoderm
Gastrulation is associated with the rearrangement and migration of cells from the Epiblast
What are the Steps of Gastrulation?
1- Formation of the Primitive Streak:
Primitive Streak establishes the Head and Tail ends of the embryo
2- Cells of the Epiblast move inward below the Primitive Streak and undergo invagination
3- Following that, the 3 Germ Layers form:
Endoderm
Mesoderm
Ectoderm
What are the Structures produced by Endoderm?
1- Epithelial lining of GIT (except Oral Cavity and Anal Canal)
And Epithelium of its glands
2- Epithelial lining of Urinary Bladder, Gallbladder, and Liver
3- Epithelial lining of Pharynx, Eustachian Tubes (auditory tubes), Tonsils, Tympanic Cavity (middle ear), Larynx, Trachea, Bronchi, and Lungs
4- Epithelium of Thyroid Gland, Parathyroid Gland, Pancreas, and Thymus
5- Epithelial lining of Prostate and Bulbourethral Glands (Cowper’s Glands), Vagina, Vestibule, Urethra, and associated glands such as Greater Vestibular Glands (Bartholin’s Glands), and Lesser Vestibular Glands
6- Gametes (Sperm and Oocytes
What are the Structures produced by Mesoderm?
1- All Skeletal and Cardiac muscle tissue, and most Smooth muscle tissue
2- Cartilage, Bone, and other connective tissues
3- Blood, Red Bone Marrow, and Lymphatic tissue
4- Blood vessels and Lymphatic vessels
5- Dermis of skin
6- Fibrous Tunic and Vascular Tunic of Eye
7- Mesothelium of Thoracic, Abdominal, and Pelvic Cavities
8- Kidneys and Ureters
9- Gonads and Genital Ducts (except Germ Cells)
10- Dura Mater
What are the Structures produced by Ectoderm?
1- All Nervous tissue
2- Epidermis of skin
3- Hair Follicles, Arrector Pili muscles, Nails, Epithelium of skin glands (Sebaceous and Sudoriferous), and Mammary Glands
4- Lens, Cornea, and Internal Eye Muscles
5- Internal and External Ear
6- Neuroepithelium of Sense Organs
7- Epithelium of Oral Cavity, Nasal Cavity, Paranasal Sinuses, Salivary Glands, and Anal Canal
8- Epithelium of Pineal Gland, Pituitary Gland, and Adrenal Medullae
9- Melanocytes (Pigment Cells)
10- Almost all Skeletal and connective tissue components of Head
11- Arachnoid Mater and Pia Mater
What is Notochord?
Notochordal Process:
About 16 days after fertilization, Notochordal Process forms
Notochord:
By day 22-24, the Notochordal Process becomes the solid cylinder called Notochord
Notochord:
Important for induction, the process whereby the inducing tissue stimulates development of a responding tissue to develop into a specific structure
Induces the development of Vertebral Bodies, and the Nucleus Pulposus of Vertebral Discs
What Structures Form during the 3rd Week of Development?
1- Oropharyngeal Membrane
2- Cloacal Membrane
3- Allantois
What is Neural Plate?
Notochord induces development of Neural Plate
Neural Plate develops Neural Folds as the Lateral Edges become more elevated
Neural Groove:
Depressed midregion of the Neural Fold
What is Neurulation?
Neurulation:
1- As Neural Folds approach each other and fuse, the Neural Tube is formed
2- Some of the Ectodermal Cells from the Neural Tube migrate to form several layers of cells called the Neural Crest
What happens 4 Weeks after Fertilization?
Primary Brain Vesicles:
Head end of the Neural Tube develops into 3 enlarged areas called Primary Brain Vesicles
1- Prosencephalon (Forebrain)
2- Mesencephalon (Midbrain)
3- Rhombencephalon (Hindbrain)
What is Somites?
Somites:
By about 17th day after fertilization
Paired cube-shaped structures called Somites form
By end of 5th week:
42-44 pairs of Somites are present
Each Somite differentiates into:
1- Myotome
2- Dermatome
3- Scleotome
What is Angiogenesis?
Angiogenesis (formation of blood vessels):
At beginning of 3rd week
Begins with the development of Blood Islands
When does Heart start to develop?
Heart:
On day 18 and 19
Begins to develop in the Head end of the embryo in a region of Mesodermal Cells called the Cardiogenic Area
1- A pair of Endocardial Tubes forms
2- The tubes fuse to form a Primitive Heart Tube
What is Chorionic Villi?
Embryonic Tissue invade the Uterine wall and erodes Uterine Blood vessels
Blood fills spaces called Lacunae
By end of 2nd week, Chorionic Villi develop
By end of 3rd week, blood vessels develop in the Chorionic Villi and connect to the embryonic heart
What is Umbilical Cord?
Vessels connecting the heart do so by way of the Umbilical Arteries and Umbilical Veins through the Connecting Stalk, which eventually becomes the Umbilical Cord
What is Placenta?
Placentation:
Process of forming the Placenta
Placenta:
Site of exchange of nutrients and wastes between mother and fetus
Produces hormones used to sustain pregnancy
Beginning of 12th week, Placenta has 2 parts:
1- Fetal Portion (Chorionic Villi)
2- Maternal Portion (Decidua Basalis of the Endometrium)
When fully developed, Placenta is shaped like a pancake and has many function
What is Organogenesis?
Organogenesis:
All major organs develop between the 4th through 8th weeks
Embryonic Folding:
Flat embryo folds into a 3D cylinder
Occurs during 4th week
What is Primitive Gut?
Lateral Folds form and, as they move towards the midline, they incorporate the Yolk Sac into the embryo as the Primitive Gut
What is Proctoderm?
Proctoderm:
On the outside of embryo is a cavity in the Tail region called Proctoderm
What is Cloacal Membrane?
Separates Cloaca from the Proctoderm
What is Pharyngeal Arches?
5 Pairs of Pharyngeal Arches (Branchial Arches) also develop on each side of the future Head and Neck regions during the 4th week
Pharyngeal Clefts:
Between each Pharyngeal Arches
Pharyngeal Pouches:
Meet the Pharyngeal Clefts
When do Limbs begin to develop?
By middle of 4th week, Upper Limbs Buds begin to develop
By end of 4th week, Lower Limbs Buds and the Heart Prominence form
At end of 4th week, Embryo has a Tail
During 5th week:
Brain and Head develop rapidly and the Limbs develop further
By 7th week:
Regions of the Limbs become distinct and Digits appear
By end of 8th week:
Eyelids come together
Tail disappears
External Genitalia begin to differentiate
Digits are distinct and no longer webbed
What is Fetal Period?
Fetal Period:
Begins at 9th week after fertilization
Tissues and organs that developed during the Embryonic Period grow and differentiate
Very few new structures appear during this period
What is Teratogen?
Teratogen:
Any agent or influence that is able to cause developmental defects in an embryo or fetus
Any number of chemicals and drugs may be considered Teratogens:
1- Alcohol:
Most common
Fetal Alcohol Syndrome
2- Other:
Viruses, industrial chemicals, some hormones, antibiotics, cocaine, etc…
3- Cigarette Smoking:
During pregnancy has been implicated as a cause of low infant birth weight, Cardiac abnormalities, Anencephaly, higher infant and fetal mortality rates
4- Ionizing Radiation:
Mother’s exposure to X-rays or radioactive isotopes during pregnancy
May cause Microencephaly
Mental Retardation
Skeletal deformities
What is Prenatal Diagnostic Tests?
Fetal Ultrasonography:
Used to determine more accurate fetal age
Confirm pregnancy
Determine fetal position
Identify multiple pregnancies
What is Amniocentesis?
Amniocentesis:
Remove some Amniotic Fluid surrounding developing fetus
Analyzing it and fetal cells for genetic abnormalities
Between 14-18 weeks
Guided by Ultrasound
What is Chorionic Villi Sampling?
Chorionic Villi Sampling:
May be performed as early as 8 weeks
Done under ultrasound guidance
Insert catheter through Vagina and Cervix to collect tissue sample from Chorionic Villi
Goal to identify same genetic defects as seen with Amniocentesis
May be done through abdominal wall as with Amniocentesis
What is Maternal Alpha-Fetoprotein (AFP) Test?
AFP Test:
Not as informative as Amniocentesis or Chorionic Villi Sampling
Requires blood sample from mother
Used to detect AFP (protein produced by fetus at its highest levels between weeks 12-15) after week 16 of pregnancy, when levels go to 0
At this point, high levels indicate Neural Tube defect
What are Maternal Changes during Pregnancy?
First 3-4 months:
Corpus Luteum secretes Progesterone and Estrogens in low levels
From 3rd month to end of pregnancy:
Placenta produces high levels of these hormones
Chorion:
Secretes hCG to stimulate Corpus Luteum to produce Estrogens and Progesterone to inhibit menstruation until Placenta takes over
Secrete Estrogen after the first 3 or 4 weeks and Progesterone by 6th week
Week 9:
hCG levels peak
What is Relaxin?
Relaxin:
Secreted by Corpus Luteum and later by Placenta
Increases flexibility of Pubic Symphysis and ligaments of Sacroiliac and Sacrococcygeal Joints
Helps dilate Cervix during labor
What is Human Chorionic Somatomammotropin (hCS)?
Human Chorionic Somatomammotropin (hCS):
Also called Human Placental Lactogen (hPL)
Help prepare Mammary Glands for lactation
Help maternal growth
Regulate Metabolism in mother and fetus
What is Corticotropin-Releasing Hormone (CRH)?
Corticotropin-Releasing Hormone (CRH):
Secreted by Placenta
In non-pregnant people it is secreted by Hypothalamus
CRH is needed to increase secretion of Cortisol, which is needed for maturation of fetal lungs and production of surfactant
What happens to Uterus Late in Pregnancy?
Uterus continues to expand throughout pregnancy
Moving upward into the Abdominal Cavity until it almost fills it
Organs are pushed out of the way and pressure on Stomach may cause food to be displaced
This can cause Heartburn
How does Exercise affect Pregnancy?
In early pregnancy:
Mother tires easily and may suffer from morning sickness
Weight increases and posture changes as the pregnancy continues
Increased Relaxin levels cause a change in gait
What is Labor?
Labor:
Process that expels fetus from Uterus through Vagina
Initiated by interaction of several hormones
Control of contractions occurs via a positive feedback loop
What is True Labor?
True Labor:
Begins when Uterine contractions occur at regular intervals
Divided into 3 stages:
1- Stage of Dilation
2- Stage of Expulsion
3- Placental Stage
What is False Labor?
False Labor:
Associated with irregular contractions and no “show”
Discharge of blood with mucus
What is Puerperium?
Puerperium:
Following delivery, it takes about 6 weeks for the maternal reproductive organs and physiology to return to the pre-pregnancy state
Involution:
Reduction in size of Uterus
What are Adjustments of the Infant at Birth?
At birth, newborn begins to function independently:
1- Lungs able to exchange oxygen and CO2 thanks to surfactant that began to develop by end of 6th month
2- Respiratory Rate at birth is 45 bpm
Drops to normal 12 bpm within 2 weeks
After baby’s first breath, many changes to CV system:
1- Foramen Ovale close to become Fossa Ovalis
2- Ductus Arteriosus close to become Ligamentum Arteriosum
3- Umbilical Arteries fill with connective tissue
4- Umbilical Vein becomes Ligamentum Teres of Liver
What is Lactation?
Lactation:
Production and ejection of milk form Mammary Glands
PRL:
Secreted by Anterior Pituitary Gland
Major hormone stimulating milk production
Oxytocin:
Secreted by Hypothalamus and store in Posterior Pituitary Gland
Causes release of milk into Mammary Ducts via the Milk Ejection Reflex
What are the Benefits Associated with Breast Feeding an Infant?
1- Chemical composition of mother’s milk is ideal for baby’s brain development, growth, and digestion
2- Several types of WBC are in milk
3- Antibodies are present
4- Breast feeding supports optimal infant growth
5- Breast Feeding leads to reduction in several diseases
