Chapter 5 ( Fertilisation and organogenesis) Flashcards
Function of fertilization
- provides for the recombination of paternal and maternal genes, thus restoring the original diploid number of chromosomes
- activates the eggs to begin development.
What is fertilization
This is the union of male and female gametes to form a zygote.
spermatozoa come into contact with the eggs by
random movement.
What happens when the head of a spermatozoon hits the vitelline membrane
the acrosome at the tip of the head bursts open, releasing a substance (sperm lysin) which softens the vitelline membrane at the point of contact.
What’s capacitation
This is an activating process involving the removal of a layer of glycoprotein and plasma proteins from the outer surface of the sperm.
Capacitation takes how many hours?
7hrs
membrane becomes more permeable to Ca** which have the dual effects of?
increasing the beating activity of the sperm tail and promoting the acrosome reaction.
What’s acrosome reaction?
acrosome membrane fuses with the cell membrane, which starts the release of acrosomal enzymes which pierce the egg membranes.
What enables the spermatozoon to penetrate into the cytoplasm of the egg?
Acrosome reaction
Further sperms are prevented from entering the ovum by
cortical reaction
What is cortical reaction?
cortical granules migrating through the plasma membrane and applying themselves to the inner surface of the vitelline membrane fluid which cause the thickening of the vitelline membrane
What is fertilization membrane?
Thickened vitelline which appears to lift off from the egg surface
How is the nucleus of the sperm and ovum fuse ?
Commonly the nuclear membranes break down, a spindle is formed, and the now visible sperm and egg chromosomes arrange themselves on the spindles as in mitosis.
Development of zygotes starts with
cleavage,
What is cleavage ?
zygote dividing repeatedly by mitosis into progressively smaller cells or blastomere.
List and explain the different yolk distribution
- Homolecithal or isolecithal: Even distribution of yolk
- Telolecithal: yolk is concentrated towards one pole known as the vegetal pole
- centrolecithal: The amount of yolk is large, and it is collected compactly in the centre of the egg cell.
- Discoidal eggs: The amount of yolk is so enormous that the non-yolky part of the cell forms a mere microscopic spot, or blastodisk, on top of the yolk mass
What is equal and holoblastic cleavage ?
(furrow extend completely through the egg).
little or no yolk, the cleavage divisions
are symmetrical, resulting in blastomeres of equal size
What is a meroblastic cleavage
a moderate amount of yolk is concentrated towards the vegetal pole; this causes cleavage to be unequal, the cell at the animal pole being smaller than the ones beneath.
The The small and large cells of meroblastic cleavage are called ___respectively
micromeres and
macromeres
The mass of cells is known as the ____, and its cavity as the ______, and the cellular layer of the _____.
- blastula
- blastocoel
- blastoderm
What type of Cleavage is
superficial and meroblastic?
Centrolecithal
What is a radial Cleavage example
Successive tiers of equal sized blastomere come to lie one directly over another, and the whole embryo may posses several mirror-image planes and cleavage is indeterminate e.g. sea star,
What is Spiral Cleavage?
Example of organisms.
The newly formed blastomeres comes to lie over and between two earlier ones, and as a result, pack themselves tightly together rather than just lightly contacting each other as do many radially cleaving embryos e.g. molluscs, annelids, nemertean and some planarian, platyhelminthes.
What is a Bilateral Cleavage?
Nematodes): The different sizes of blastomeres (usually two) are confirmed to separate areas in the blastula,
The formation of organs occurs in the embryo after what process?
gastrulation
What is gastrulation process.
rearrange until they reach the places they will occupy in the adult, and the three germ layers of ectoderm, endoderm and mesoderm characteristics of triploblastic animals are formed.
The three basic layers
undergo ______ to give rise to the final organs.
morphogenetic movement
What are epithelial cells?
These are cells in close formation adhering to one another, forming a sheet or compact mass)
What are mesenchymal cells?
These are much more individually mobile cells
Epithelial cells form organs in the following ways:
(1) by local thickening of the layer; forming for instance a neural plate
(2) by the separation of layers to leave a space; as in coelom formation
(3) by folding a layer; as in early neural tube formation
(4) by fusion of once separate masses; as in later neural tube formation;
(5) by breaking up of layers to produce mesenchyme cells; as in formation of gut wall and neural crest
Mesenchyme forms organs in the following ways
(1)by aggregation into mass as in bone formation
(2) by attachment to another mass as in the formation of skeletal capsules.
(3)by secondary rearrangement into epithelia as in the formation of blood vessels.
The ectoderm gives rise to?
Neural tube,sensory organs and epidermis
The endodermis gives rise to
The epithelial lining of the intestine and the outgrowth (respiratory system, endocrine, digestive system and urinary tissues )
The mesoderm is divided into 3 regions namely
Dorsal epimere, central mesomere and ventral hypomere
The dorsal epimere forms the
Skeletal muscles and vertebrae
The central mesomeres forms the
Kidney and gonads
The ventral hypomere forms the
Heart: The muscular organ responsible for blood circulation.
Peritoneum: The lining of the abdominal cavity.
Mesenteries: Membranes that support and stabilize internal organs.
Smooth muscle: Found in various organs like the digestive tract and blood vessels.
Connective tissue: Supports and binds various tissues throughout the body.
The ventral hypomere is divided into
Outer somatic, inner splanchnic and the cavity between them; coelom
The epimere coelom segments to give
a series of somites, separated from the rest of the mesoderm
The epimere migrate and differentiate into three cell types:
Sclerotome: Forms the cartilage and bone of the vertebrae.
Dermatome: Develops into the dermis of the skin.
Myotome: Gives rise to skeletal muscles of the body.
