Corona radiata (embryology)
Encyclopedia
- For the structure in neuroanatomyNeuroanatomyNeuroanatomy is the study of the anatomy and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems, and thus we can begin to speak of...
, see Corona radiataCorona radiataIn neuroanatomy, the corona radiata is a white matter sheet that continues caudally as the internal capsule and rostrally as the centrum semiovale. This sheet of axons contains both descending and ascending axons that carry nearly all of the neural traffic from and to the cerebral cortex...
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The corona radiata surround an ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
or unfertilized egg cell, and consist of two or three strata (layers) of follicular cells. They are attached to the outer protective layer of the ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
, the zona pellucida
Zona pellucida
The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...
, and their main purpose in many animals is to supply vital proteins to the cell. They are formed by follicle cells adhering to the oocyte before it leaves the ovarian follicle, and originate from the squamous granulosa cells present at the primordial stage of follicular development. The corona radiata is formed when the granulosa cells enlarge and become cuboidal, which occurs during the transition from the primordial to primary stage. These cuboidal granulosa cells, also known as the granulosa radiata, form more layers throughout the maturation process, and remain attached to the zona pellucida after the ovulation of the Graafian follicle. For fertilization to occur, sperm cells rely on hyaluronidase (an enzyme found in the acrosome of spermatozoa) to disperse the corona radiata from the zona pellucida of the secondary (ovulated) follicle, thus permitting entry into the perivitelline space and allowing contact between the sperm cell and the nucleus of the oocyte.
The corona radiata are layers of follicle cells, that protect the secondary oocyte as it passes through the ruptured follicular wall, on its way to the infundibulum of the uterine (AKA fallopian) tubes. In order for fertilization to occur, the sperm must break through this layer of follicular cells by secreting the enzyme hyaluronidase
Hyaluronidase
The hyaluronidases are a family of enzymes that degrade hyaluronic acid.In humans, there are six associated genes, including HYAL1, HYAL2, HYAL3, and PH-20/SPAM1.-Use as a drug:...
. It takes the secretions of dozens of sperm to weaken the layer enough for one sperm to penetrate.