Located in the nucleus of the cell, it is a complex of genetic material consisting of DNA and proteins that condense to form chromosomes in eukaryotic cell division. Sperm chromatin is different. During spermatogenesis, the chromatin of the male germ cells (spermatogonia) are remodelled into a more tightly packaged and compact structure, a process associated …
Author Archives: Brian Hopkins
Chromophores
Molecules responsible for the color of the blood due to their absorption of light atdifferent wavelengths. One example is hemoglobin whose absorption of near-infrared light is oxygen status dependent in tissue. See Functional near-infrared spectroscopy (NIRS), Hemoglobin
Chromatid
One of two thread-like daughter strands of DNA that form when a chromosome divides longitudinally through the action of a spindle during metaphase of mitosis or during anaphase of meiosis to become separate chromosomes, which were held together by one or more centromeres before mitosis began. See Anaphase, Centromere, Chromatin, Chromosome, DNA (deoxyribonucleic acid), Meiosis …
Chorion
The outermost of two membranous sacs that completely surround the developing embryo and fetus. In mammals, it forms the fetal contribution to the placenta. See Amnion (or amniotic sac), Ascending genital tract infection, Blastula, Chorionic villus sampling, Monozygotic twins, Placenta
Chorionic villus sampling
The removal and genetic analysis of tissue from villi (hair-like projections of the chorion membrane surrounding the fetes) in the uterus via the cervix during early pregnancy, and used to test for chromosomal abnormalities such as Down’s syndrome (see figure below). Transcervical chorionic villus sampling See Amniocentesis, Amnion, Chorion, Down’s syndrome
Choreiform movements
Those resembling the jerky involuntary movements characteristic of chorea, mainly affecting the face and extremities, and that are prominent under stress. Choreiform movement disorders in children have recently been subjected to treatment trials involving thalamic stimulation. Evident in Tardive dyskinesia, their presence has also been found as a behavioral sign in some juvenile delinquents. See …
Chordin
A factor or binding protein secreted from the dorsal mesoderm that is involved in the induction of the early nervous system. Moreover, along with noggin, it regulates (or inhibits) Bone Morphogenetic Proteins (BMPs), which is a protein family consisting of nine structurally related proteins belonging to the transforming growth factor beta superfamily,and furthermore plays a …
Cholinergic neurotransmitter system
A system in the brain using the neurotransmitter acetylcholine that is based in the mesencephalic reticular activating system, and which distributes acetylcholine throughout the brain. This system has a widespread energising influence on brain activity, through both sympathetic and parasympathetic nervous systems, and is closely tied to sustained attention and alerting. Cholinergic receptors binding to …
Chondrification
The second phase of skeletogenesis (the growth or formation of the skeleton) during embryogenesis, it is the process by which dense mesenchyme tissue is converted into cartilage and bone. Chondrification of the vertebrae and limb bones begins in the sixth embryonic week in the human. As growth continues, bone is continuously remodelled through the action …
Cholesterol
A fatty-like, white crystalline substance that is a steroid lipid found in large concentrations in the blood, brain, liver, muscle, spinal cord, and other organs and tissues, with liver being the most important site for its synthesis. Both the liver and dietary intake (e.g., dairy products, fish, meat, poultry) are the main sources of cholesterol. …