Somatic cells in the human are haploid or diploid? and contain _____
diploid 46 chromosomes. 44 are autosomes. 2 are sex chromosomes: In the male one X chromosome and one Y chromosome. In the female paired XX chromosomes.
The Production of Germ cells is a result of _______, and these are haploid/diploid? with how many chromosomes (#autosomes/sex chromosomes)
As a result of meiosis the germ cells are haploid cells i.e. with half the number of chromosomes. 22 autosomes and 1 X chromosome in ovum. 1 X or one Y chromosomes in sperm.
Briefly describe sperm development/motility
During development the sperms become relatively small motile cells with a head containing the chromosomal material and a tail containing numerous mitochondria for energy. Once released the sperm has little metabolic reserves and so once released it cannot survive for long.
Sertoli cells are found where? what hormones act on them?
Found in seminiferous epithelium. Testosterone causes them to secrete androgen binding protein that concentrates more testosterone in the tissue.
Describe the ovum
It is a very large non motile cell with a large amount of cytoplasm and a considerable reserve of nutritional material.
Development of Ovum. what is a Graafian (mature) follicle.
A mature ovarian follicle in which the oocyte attains its full size and the surrounding follicular cells are permeated by one or more fluid filled cavities.
Once the ovum is released it is surrounded by a very thick basement membrane like structure called:
the zona pellucida.
What is the corona radiata?
The cells that surround the zona pellucida are a layer known as the corona radiata.
Both zona pellucida and corona radiata have a similar function or effect: __________
they both may be involved in prevention of more than one sperm fertilizing an ovum.
When does the ovum completes the first meiotic division?
just before ovulation.
What is the first polar body?
While chromosomes are equally divided, most of the cytoplasm is retained with one of the secondary oocytes. The other becomes the first polar body (chiefly nucleus and small amount of cytoplasm).
So what occurs after the first meiotic division?
The first polar body is expelled and the nucleus of the ovum starts the second meiotic division but only proceeds as far as metaphase.
How long does the ovum remain in metaphase of the second meitotic division?
It will remain in metaphase until fertilization occurs.
What is the location where Fertilization most often occurs?
Generally occurs in the fallopian tubule (oviduct) within 24 hours.
Fertilization occurs when:
a single ovum and a single sperm unite. The chromosomal material unites and Second meiotic division is completed to restore the diploid number of chromosomes The second polar body degenerates.
fertilization is the union of :
A haploid male gamete (sperm) and A haploid female gamete (ovum).
Only one sperm will penetrate the
zona pellucida.
After fertilization what happens to the sperm tail?
it is lost and the head develops into the male pronucleus.
At fertilization, what happens to the fale and female pronuclei
meet and nucleoplasm of the pronuclei become arranged as chromosomes that attach to the mitotic spindle.
So, Pronuclei become arranged as chromosomes and attach to the mitotic spindle, what occurs next?
Separation of the chromosomes and cleavage of the cytoplasm gives rise to two cells.
Fertilization restores______, Determines ________, marks the beginnin of ____________,
Restores diploid number of chromosomes � 46 in humans.; Determines the sex of the individual; Starts the process of cell division � known as cleavage.
What is a Zygot?
The fertilized ovum is known as a zygote.
As the process of cleavage of cells continues with the cell numbers doubling every division, what happens to the size of the zygote?
The zygote does not increase in size so that the cells become progressively smaller.
What is Cell cleavage?
it is a continuous process in which rapid mitotic divisions result in a large number of small cells known as blastomeres.
What is the list of zygote cleavage and the days they occur?
Day 1-2Cells; Day 2-4 cells; Day 2.5-8 cells; Day 3-16 Cells (THE MORULA); Day 4-64 cells! (BLASTOCYST); Day5-108 Cells (BLASTOCYST)
what is the morula stage?
The spherical embryonic mass of blastomeres formed before the blastula and resulting from cleavage of the fertilized ovum. IT IS Day 3-16 cells! The rapid division of cells in the zygote results in the outside of the zygote developing bulges (looks like a mulberry hence the rationale for naming this the morula stage).
During this process of cell cleavage, what is happening to the zygote? where is it at the morula stage?
the zygote is moving along the uterine tube towards the body of the uterus. The morula stage is usually when the zygote enters the uterine cavity.
When does the zygote begin to differentiate and become different types of cells?
During the morula stage cells start to differentiate and to become different types of cells.
What is a blastocyst?
Days 4 and 5 - 64 cells and 108 cells respectively. Further differentiation of morula cells occurs and there is an accumulation of fluid in the center of the mass of cell. This stage of development is now known as a blastocyst.
At what stage does the zygote will become implanted in the uterine wall.
Blastocyst Stage.
Describe Blastocyst Formation:
Fluid accumulation between cells results in a blastocyst cavity surrounded by a layer of flattened cells.
What is an embryoblast?
Some of the cells in the Blastocyst become aligned on one side as the "inner cell mass" or "embryoblast" which will develop into the embryo, the amnion and the yolk sac.
What is the trophoblast?
When the embryoblast forms, the remainder cells lining the cavity will become cells of the trophoblast which involved in implantation and later in the formation of the placenta.
True/False: When the blastocyst reaches the uterine cavity it can remain free for a few days before it becomes embedded in the endometrial wall of the uterus a process known as implantation.
True
Implantation of the blastocyst results in the formation of what?
Implantation of the blastocyst causes the outer layer of cells of the zygote to become a trophoblast layer that invades the endometrium of the uterus.
What are decidual cells?
Those endometrial cells that come in contact with the trophoblast enlarge and accumulate glycogen and lipids and then become known as decidual cells.
The Trophoblast cell layer matures in to the ____________.
Cytotrophoblast. Specifically, the trophoblast cell layer thickens and the cell membranes between individual cells are no longer visible� this tissue is now known as the cytotrophoblast.
The Cytotrophoblast cell layer matures into the ____________.
Syncytio-trophoblast. In Cytrotrophoblast, spaces (lacunae) develop between the cells and maternal blood flows into these spaces. The structure is then known as the syncytio-trophoblast.
What is the decidua and list its three parts:
When cells at the implantation site have changed to decidual cells, the lining of the uterus is then known as the decidua and is composed of 3 parts: Decidua basalis; decidua capsularis; decidua paretalis.
What is Decidua basalis?
the layer of the decidua that becomes the maternal part of the placenta.
What is Decidua capsularis?
the layer of the decidua that is the portion of the endometrium that pushes out as the embryo grows
What is the Decidua parietalis?
the layer of the decidua that becomes the remainder of the uterus.
What is the Chorion?
in human embryology, the cellular, outermost extraembryonic membrane, composed of trophoblast lined with mesoderm; it develops villi, becomes vascularized by allantoic vessels, and forms the fetal part of the placenta.
The Chorion arises when, the trophoblast becomes bathed in: ______________ and the trophoblast becomes arranged as _________________.
maternal blood.The trophoblast becomes arranged as villous -like projections known as chorionic villi. These will become part of the embryonic contribution to the placenta.
T/F: On luminal side the chorion become thicker and loses its villi.
False. On luminal side the chorion become thinner and loses its villi.
The chorion will develop blood vessels that:
carry embryonic blood between the embryo and the placenta via the umbilical vessels.
The amniotic sac grows faster than the chorionic sac so that:
eventually the chorionic space is obliterated by the amnion.
The Chorion and amnion fuse to form the:
�membranes� of the developing embryo.
The full term placenta consists of (1) and (2)
(1) chorionic villi from the embryo and (2) decidua basalis from the mother.
The placenta is usually attached to the _________________ wall of the uterus:
posterior wall of uterus so that it does not interfere with parturition (birth).
The placenta is a complex selective barrier allowing the diffusion of
Diffusion of oxygen, water, electrolytes.
How do glucose, amino acids, lipids and vitamins permeate the selective barrier?
Carrier systems exist for the transport of glucose, amino acids, lipids, vitamins.
Pinocytosis and leakage w/r/t the placenta can cause what kind of problems for fetus and mother?
Macromolecules and fetal blood cells can sometimes reach the maternal blood and this can result in Rh incompatibility.
List the Functions of the Placenta.
Endocrine, Respiratory, Digestive, Excretory, Protection of the fetus
describe the placenta function: Endocrine.
Produces hormones such as chorionic gonadotrophins, estrogens, progesterone.
describe the placenta function: Respiratory.
Provides gaseous exchange between fetal and maternal blood.
describe the placenta function: Digestive.
Allows nutrition to cross the placental barrier.
describe the placenta function: Excretory:
Metabolic products removed from the fetus are removed via maternal blood.
describe the placenta function: Protection of the fetus:
Placental membrane provides a barrier that protects the fetus from most but not all antigens.
Embryonic Development is traditionally divided into 3 successive stages starting at fertilization: list (and what weeks are associated?)Embryonic stage I �first 4 weeks.
Embryonic stage II � next 4 weeks; and Fetal stage - End of embryonic stages till birth.
Describe Embryonic stage I
�first 4 weeks- the Stage during which there is chiefly cell proliferation and migration. Period during which embryo if defective is usually lost.
describe Embryonic stage II
� next 4 weeks following stage I � it is the Stage during which most systems are developing- this stage is sensitive to teratogens etc.
describe Fetal stage
- from the end of the embryonic stage to birth � it is the stage of growth and differentiation � this stage is relatively insensitive.
at which stage is the embryo very sensitive to teratogens?
Embryonic stage II
Patterning: A fertilized ovum can be regarded as a _______________ with the potential for cells during cleavage to become any other cells type.
stem cell: During stages of cellular development various cell types arise that may during this particular phase of development act as temporary types. These cell types may later become more limited and finally become adult cell types.
Within one month of development most of the cell types in the body have a series of _________________ in them that identifies them as their specific cell type.
transcription factors
All cells start from cells in the zygote but during development, the role played by different cells is determined by a number of factors including:
Genetic control; Local environment; Migration of cells within specific time periods; Variable responses of cells in different time periods.
Cell differentiation.
In the blastocyst there are initially two populations of cells:
Those lining the cavity � the primary yolk sac � the trophoblast cells - involved in implantation and later formation of the placenta; AND A cluster of cells on one side known as the embryoblast � later to form the embryo.
Cells then differentiate to form a (2-layered) bilaminar disc composed of ___________ (on dorsal side) and ________ (ventral side).
ectoderm; endoderm
Ectoderm forms and lines the
amniotic cavity.
Endoderm forms and lines the
secondary yolk sac.
Development of The Germ Layers- the 3 - layered embryo. Viewed from above the ectoderm has a depression in the center known as the __________________ with elevations on ether side (and a small depression known as the ________).
primitive streak; primitive node
The ectodermal cells migrate _____________ and _______________ from this primitive streak to infiltrate between and separate ectoderm and endoderm layers to form the ______________.
anteriorly and laterally; mesoderm
During the third week of development cells at the anterior region form the (1) ________ and migrate forward to the (2) ______________.
notochord (The notochord will provide structural support to the developing embryo); (2) prochordal plate
A region anterior to the plate however has only two layers of cells the: ______ and _______ which later become the _________________
- ectoderm and endoderm to later become the bucco-pharyngeal membrane (also known as the oro-pharyngeal membrane).
A similar arrangement to the prochordal plate located at the caudal end as the:
caudal or caecal plate.
What is the neural tube? describe its formation and future function.
An anterior thickening of the ectoderm forms the neural plate. This develops folds resulting in a central groove. The neural groove deepens and the crests fold over to form a neural tube.
The neural tube will form the nervous system.
what are Neural Crest Cells? why are they significant?
Cells of neuroectodermal origin on either side of the neural tube are known as the neural crest cells. These are important in contributing to the formation of the peripheral nervous system and many of the structures of the face.
The remainder of the ectoderm (apart from the above described neural tube, etc) gives rise to the:
oral epithelium, epidermis and its adnexal structures.
describe the Folding of the Embryo that results in a 3-d embryo.
it folds both laterally and caudally results in a 3 dimensional embryo.
What are somites? How many are there?
Formation of block like regions of mesoderm alongside either side of the neural tube of the embryo are known as somites (there are 42 somites).
Each somite produces: (1, 2, and 3)
Sclerotome to give rise to 2 adjacent vertebrae and their intervertebral discs; Myotome � segmented mass of muscle; and Dermatome � connective tissue of the skin associated with each somite
The nervous system arises from what type of tissue?
ectoderm
What happens to the ectoderm that originally lined the amniotic cavity?
it forms the exterior surface of the embryo � the epidermis and its adnexal structures -, hair, nails , sweat glands; It also lines the stomodeum, the future oral cavity AND Tooth structures.
What is the developmental fate of Endoderm?
Endoderm on the ventral surface of the developing embryo is continuous with the lining of the yolk sac. As the embryo grows there is dorsal folding and pinching off so that embryo assumes a cylindrical shape; Endoderm then lines a central tube.
The endodermal tube has three portions:
Foregut - Forms the lining of the respiratory and digestive system; Midgut and Hindgut - Lining of most of the intestinal tract; and Glands associated with these regions.
Mesoderm Gives rise to:
Most of muscles. Bones. Connective tissues.Blood vessels. Heart. Blood.
