During weeks 4 and 5 of development _____ germ cells located in the wall of the yolk sac migrate to the ____ ____.
2. gonadal ridge
Gametogenesis is the production of converting _____ germ cells into human gamets (oocytes and spermatozoa) and involves the process of _____ which reduces the number of chromosomes (n=23), resdistributes chromosomal material to ensure genetic variablity, and exchanges a small amount of maternal and paternal DNA through _____ _____.
1. primordial germ cells
3. homologous recombination (crossover)
Male gametes are produced through a process called _____.
Describe the process of spermatogenesis.
Primordial germ cells (diploid, 46 chromosomes) from the wall of the yolk sac arrive in the primitive testis during week 4 of embryonic development and remain dormant until pubertyl Type A spermatogonia undergo mitosis to make more Type A spermatogonia and also Type B spermatogonia. Type B spermatogonia enter meiosis I to form primary spermatocytes (diploid) which then complete meiosis I to form 2 secondary spermatocytes (haploid) which then go on to complete meiosis II to form 4 spermatids.
Through a process called _____ spermatids undergo changes resulting in sperm.
What is capacitation? (relates to sperm)
a process ejaculated sperm must go through to become capable of fertilization of an oocyte. occurs in the female reproductive tract
Female gametes are derived from ____ ____ in the ovaries. All ___ _____ (diploid) are formed by the 5th month of fetal ife and remain dormant in ____ (cell cycle stage) of meiosis I until puberty. During an ovarian cycle, the ____ ___ will complete meiosis I to form a ____ ___ (haploid) and remains arrested in ____ (cell cycle stage) of meisosis II until/if fertilization occurs. At fertilization, the ____ ____ completes meiosis II to form a ____ ____.
1. primary oocytes
2. primary oocytes
4. primary oocyte
5. secondary oocyte
7. secondary oocyte
8. mature oocyte
At ovulation, the oocyte is surrounded by what 2 layers?
1. zona pellucida
2. outer corona radiata
What 3 layers must a spermatozoa penetrate to fertilize an oocyte? (list in order)
1. corona radiata
2. zona pellucida
3. plasma membrane of oocyte
What 3 processes occur after a spermatocyte has entered an oocyte?
1. oocyte completes meiosis II and forms the female pronucleus
2. zona pellucida becomes impenetrable to other spermatozoa
3. head of the sperm separates for the tail, swells, and forms the male pronucleus
(pronuclei are nuclei of sperm and oocyte fusion of their genetic material-membranes dissolve)
What are 3 results of fertilization?
1. restoration of diploid number of chromosomes
2. determination of chromosomal sex
3. initiation of cleavage
Fertilization normall occurs in the ____ of the uterine tube.
True or false: Fertilization is followed by cell divisions occuring in the uterine tube in preparation for implantation in the uterine body.
What is the name for the series of mitotic divisions the fertilized ovum must undergo? What are the names of the cells produced as a result?
When the dividing mass of cells (blastomeres) reach the 16-cell stage it is called a ____. The ____ enters the uterus on the 3rd of 4th day after fertilizaiton and a cavity within the developing zygote begins to appear. At this point, the morula is referred to as a ____ which has a ____ cavity and inner and outer cell layers. The inner cell mass will develop into the ____ and the outer cell mass will develop into the _____.
1. morula (aka zygote)
4. blastocyst cavity
The outer cell layer of the zygote, called the ____, has what functions?
develops into the placenta and membranes that nourish and protect the developing organism
If all goes well beforehand, implantation is completed during week ____.
What 2 layers does the trophoblast develop into during implantation and what are their functions?
cytotrophoblast: has distinct cell boundaries and undergoes mitotic division to form the synctiotorphoblast
synctiotrophoblast: (cell boundaries are blurred so whole thing looks like a blob with nuclei) grows into the endometrium to make a connection with endometrial (maternal) blood vessels and glands producing the hormone human chorionic gonadotropin (hCG)
True or false: week 2 is focused on the development of a 2 layered embryo and is called the "Week of 2s".
What occurs during the week of 2s?
- trophoblast differentiates into cytotrophoblast and synctiotrophoblast
- embryoblast forms epiblast and hypoblast
- extraembryonic mesoderm splits into somatpleure and splanchnopleure
- 2 cavities form: amniotic sac and yolk sac
What is ectopic pregnancy? Where can the blastocyst potentially implant? H
1. implantation of the blastocyts outside of the uterine cavity
2. sites for ectopic pregnancy include the uterin tube, abdominal cavity, peritoneal covering of intestines
development of the 3 basic embyronic layers: ectoderm, endoderm, and mesoderm
Gastrulation begins with formation of the ___ ___ on the dorsal surface of the epiblast. It is visible as a narrow groove with slighlty bulging regions on either side.
Cells of the epiblast migrate toward the primitive streak and slip beneath it through a process known as _____ to form the inner-placed embryonic ____. Some cells lie btwn the epiblast and the ____ (same as previous blank) to form ____ (middle layer). The remaining cells form the _____ (outer layer).
The ____ extends from the primitive node to the oropharyngeal membrane and plays and inductive role in organ formation. Formation of the ____ (same as previous) occurs during ____ (embryonic cell layer) formation.
In the adult, the notocord perists in the intervertebral discs as ___ ___. What is its fxn?
1. nucleus pulposus
2. gel like substance of intervertebral discs that is composed primarily of water and loose network of collagen. allows vertebral discs to withstand compression and torsion
True or false: Gastrulation results in defining 3 important orientations: cranial-sacral axis, right-left orientation, dorsal-ventral orientation.
True or false: The embryonic disc begins as a flat rounded structure. It will continue to grow and elongate in a cephalocaudal direction. This results in a folding of the cranial and caudal ends creating head and tail folds. The heart which originates in the most cranial position will swing down to the position of the future thorax. Thus gastrulation, or formation of the germ layers, continues in caudal segments while cranial structures are differentiating, causing the embryo to develop cephalocaudally.
True or false: Lateral folding of the embryo completes the formation of the adult form by extending laterally first and then ventrally closing off body cavities.
During lateral folding, the yolk sac persists for a while and is later pinched off. A body cavity is formed around the tube of endoderm which forms the ____. The cavity is lined with cells from the ____ mesoderm and persists as the parietal layer of serous membranes. Cells from the ___ mesoderm develop into smooth and cardiac muscle cells.
True or false: during lateral folding, two important precursor structures are formed: the neural plate (from ectoderm) and somites (from mesoderm).
Neuralation: The notocord induces the overlying ectoderm around the center of the embryo to thicken and form the ___ ____. The central ends (of previous blank) make up the _____. The (previous blank) forms a groove which deepens. The lateral edges of the group migrate toward each other to form the primitive spinal cord. During this time, ___ ____ __ form at the edges of the neuroectoderm. These cells migrate through the embryo to form adult structures.
1. neural plate
3. neural crest cells
True or false: An important concept in nervous system development is the mitosis of cells and migration to their adult location. Any interruption in this 2 step process can produce a developmental effect.
Where are neural crest cells originally located? What do they go on to form in the body?
1. neural tube. undero mitosis and exit neuroepithelium to migrate to their adult locations in the body
2. In the nervous system neural crest cells make important contributions to:
- Schwann cells, PNS myelinated cells, dorsal root ganglia, some cranial nerve ganglia and numerous autonomic ganglia, gut intrinsic innervation-myenteric plexus and submucosal plexus, the adrenal medulla, part of the meninges surrounding CNS.
2. In the head and neck neural crest cells contribute to:
- part of head mesenchyme, forming parts of facial bones, muscles, and ligaments, odontoblasts and the dentin producing cells of teeth.
3. In skin neural crest cells contribute to making the pigment-producing cells, melanocytes.
What is DiGeorge syndrome? What are sx? What is it caused by?
1. deletion in chromosome 22
2. subtle craniofacial anomalies, cardiovascular anomalies, sometimes thymic and parathyroid aplasia
3. results from abnormal migration and differentiation of head and neck neural crest cells
What are neural tube defects? Etiologies of neural tube defects? Severity?
1. congenital birth defects typically caused by failure of neural tube closure and/or induction of bony neural arches of spinal cord
2. mutlifactorial etiology: some genetic and some environmental
3. range in severity from spina bifida occulta (mildest form of spina bifida) to fatal anencephaly (missing large part of brain and spinal cord)
What are the 3 layers of mesoderm?
1. paraxial mesoderm
2. intermediate mesoderm
3. lateral plate mesoderm
What is the paraxial mesoderm composed of and what do its components develop into?
paraxial mesoderm cells are close to the midline and are organized into segments called somites. there are occipital, cervical, thoracic, lumbar, sacral, and coccygeal pairs of somites.
sclerotome somites surround the spinal cord to form the vertebral column and form tendons/cartilage/bone
dermomytome is composed of mytome and dermatome. mytome provides the segmental muscle component and the dermatome forms the dermis of the back.
What does the intermediate mesoderm differentiate into?
What does the lateral plate mesoderm differentiate into?
parietal and visceral laters line the intraembryonic cavity and surround organs
List examples of adult structures formed from the 3 primary germ layers.
- Ectoderm (outer layer)- organs and structures that maintain contact with the outside world: nervous system, sensory epithelium of ear, nose, and eye, skin, hair, nails, pituitary, mammary, sweat glands and enamel of the teeth.
- Mesoderm (middle layer) - connective tissues, tendons, cartilage, bone, muscle, some urogenital structures, blood cells, adrenal cortex
- Endoderm Layer (inner layer) - gastrointestinal tract; epithelial lining of the respiratory tract; parenchyma of the thyroid, parathyroids, liver, and pancreas, stroma of the tonsils and thymus, the epithelial lining of the urinary bladder, urethra and lining of the tympanic cavity and auditory tube
see image on pg 20 of notes