Parenchyma is the bulk of a substance. In animals, a parenchyma comprises the functional parts of an organ and in plants parenchyma is the ground tissue of nonwoody structures; the term "parenchyma" is New Latin from word Greek παρέγχυμα parenchyma, "visceral flesh" from παρεγχεῖν parenkhein, "to pour in" from παρα- para-, "beside", ἐν en-, "in" and χεῖν khein, "to pour". Erasistratus and other anatomists used it to refer to certain human tissues, it was applied to some plant tissues by Nehemiah Grew. The parenchyma is the functional parts of an organ in the body; this is in contrast to the stroma, which refers to the structural tissue of organs, the connective tissues. In the brain, the parenchyma refers to the functional tissue in the brain, made up of the two types of brain cell and glial cells. Damage or trauma to the brain parenchyma results in a loss of cognitive ability or death. Lung parenchyma is the substance of the lung outside of the circulation system, involved with gas exchange and includes the alveoli and respiratory bronchioles.
In cancer, the parenchyma refers to "The portion of a tissue that lies outside the circulatory system and is responsible for carrying out the specialized functions of the tissue". In plants, "parenchyma" is one of the three main types of ground tissue, the most common, it can be distinguished through their thin cell wall as compared to other cells. Parenchyma cells make up the bulk of the soft parts of plants, including the insides of leaves and fruits; the dictionary definition of parenchyma at Wiktionary
The skull is a bony structure that forms the head in vertebrates. It provides a protective cavity for the brain; the skull is composed of two parts: the mandible. In the human, these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone; the skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, several sensory structures such as the eyes, ears and mouth. In humans these sensory structures are part of the facial skeleton. Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, fixing the position of the ears to enable sound localisation of the direction and distance of sounds. In some animals such as horned ungulates, the skull has a defensive function by providing the mount for the horns; the English word "skull" is derived from Old Norse "skulle", while the Latin word cranium comes from the Greek root κρανίον.
The skull is made up of a number of fused flat bones, contains many foramina, fossae and several cavities or sinuses. In zoology there are openings in the skull called fenestrae. For details and the constituent bones, see Neurocranium and Facial skeleton The human skull is the bony structure that forms the head in the human skeleton, it forms a cavity for the brain. Like the skulls of other vertebrates, it protects the brain from injury; the skull consists of two parts, of different embryological origin—the neurocranium and the facial skeleton. The neurocranium forms the protective cranial cavity that surrounds and houses the brain and brainstem; the upper areas of the cranial bones form the calvaria. The membranous viscerocranium includes the mandible; the facial skeleton is formed by the bones supporting the face Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial joints formed by bony ossification, with Sharpey's fibres permitting some flexibility.
Sometimes there can be extra bone pieces within the suture known as sutural bones. Most these are found in the course of the lambdoid suture; the human skull is considered to consist of twenty-two bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone, two temporal bones, two parietal bones, the sphenoid and frontal bones; the bones of the facial skeleton are the vomer, two inferior nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, two lacrimal bones. Some sources count the maxilla as having two bones; some of these bones—the occipital, frontal, in the neurocranium, the nasal and vomer, in the facial skeleton are flat bones. The skull contains sinuses, air-filled cavities known as paranasal sinuses, numerous foramina; the sinuses are lined with respiratory epithelium. Their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn into the nasal cavity.
The foramina are openings in the skull. The largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels; the many processes of the skull include the zygomatic processes. The skull is a complex structure; the skull roof bones, comprising the bones of the facial skeleton and the sides and roof of the neurocranium, are dermal bones formed by intramembranous ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain are formed by endochondral ossification, thus frontal and parietal bones are purely membranous. The geometry of the skull base and its fossae, the anterior and posterior cranial fossae changes rapidly; the anterior cranial fossa changes during the first trimester of pregnancy and skull defects can develop during this time. At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements fuse together into solid bone.
The bones of the roof of the skull are separated by regions of dense connective tissue called fontanelles. There are six fontanelles: one anterior, one posterior, two sphenoid, two mastoid. At birth these regions are fibrous and moveable, necessary for birth and growth; this growth can put a large amount of tension on the "obstetrical hinge", where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein; as growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous sutures, one coronal, one lambdoid, one sagittal suture; the posterior fontanelle closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanelle is located at the junction of the parietal bones. Careful observation will show that you can count a baby's heart
Twin reversed arterial perfusion
Twin reversed arterial perfusion sequence—also called TRAP sequence, TRAPS, or acardiac twinning—is a rare complication of monochorionic twin pregnancies. It is a severe variant of twin-to-twin transfusion syndrome; the twins' blood systems are connected instead of independent. One twin, called the acardiac twin or TRAP fetus, is malformed; the heart is missing or deformed, hence the name acardiac, as are the upper structures of the body. The legs may be present or missing, internal structures of the torso are poorly formed; the other twin is normal in appearance. The normal twin, called the pump twin, drives blood through both fetuses, it is called reversed arterial perfusion because in the acardiac twin the blood flows in a reversed direction. TRAP sequence occurs in 1 in 35,000 pregnancies overall; the acardiac twin is a parasitic twin that fails to properly develop a heart, therefore does not develop the upper structures of the body. The parasitic twin, little more than a torso with or without legs, receives its blood supply from the host twin by means of an umbilical cord-like structure, much like a fetus in fetu, except the acardiac twin is outside the host twin's body.
Although the reason is not understood, it is apparent that deoxygenated blood from the pump twin is perfused to the acardiac twin. The acardiac twin grows along with the pump twin, but due to inadequate oxygenation it is unable to develop the structures necessary for life, presents with dramatic deformities. Although no two acardiac twins are alike, twins with this disorder are grouped into 4 classes: Acephalus, anceps and amorphus. Acephalus – The most common type, lacking a head, though it may have arms. Thoracic organs are absent, disorganized & unidentifiable tissues take their place. Anceps – The acardius has most body parts, including a head with face and incomplete brain. Organs, though present, are crudely formed. Acormus – This type has no apparent body and the umbilical cord is attached to the neck, but x-rays or dissection reveal thoracic structures in the apparent head. One had a leg attached to the head; this may be due to embryopathy degenerating a once normal embryo. Amorphus – This extreme form not only lacks a head and limbs, but any internal organs, consists of tissues with blood vessels branching from the umbilical cord.
Some may only be stem cell tumors. The acardiac twin may be described as a hemiacardius, which has an incompletely formed heart, or a holoacardius, in which the heart is not present at all; the pump twin is structurally normal, although it is smaller than normal, but due to some of the related problems including the rapid growth of the acardiac twin and heart failure due to high output, there is a high mortality rate for the pump twin if left untreated. The rate of fatality depends on the relative size of the acardiac twin. If the abnormal twin is greater than 50% of the size of the pump twin, the survival rate for the pump twin is only 10%. TRAP sequence can be diagnosed using obstetric ultrasound. Doppler interrogation will confirm that blood flow in the acardiac twin is in the reverse direction, entering via the umbilical cord artery and exiting through the vein. If left untreated, the pump twin will die in 50–75% of cases. After diagnosis and amniocentesis are used to rule out genetic abnormalities in the pump twin.
A procedure may be performed which will stop the abnormal blood flow. The acardiac twin may be selectively removed; the umbilical cord of the acardiac twin may be surgically cut, separating it from the pump twin, a procedure called fetoscopic cord occlusion. Or a radio-frequency ablation needle may be used to coagulate the blood in the acardiac twin's umbilical cord; this last procedure is the least invasive. These procedures increase the survival chances of the pump twin, to about 80%; the pump twin will be monitored for signs of heart failure with echocardiograms. If the pump twin's condition deteriorates, the obstetrician may recommend early delivery. Otherwise, the pregnancy continues normally. Vaginal birth is possible unless the fetus is in distress, although it is recommended that the delivery take place at a hospital with NICU capabilities. Thefetus.net gfmer.ch
In human anatomy, the neurocranium known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the skullcap; the remainder of the skull is the facial skeleton. In comparative anatomy, neurocranium is sometimes used synonymously with endocranium or chondrocranium; the neurocranium is divided into two portions: the membranous part, consisting of flat bones, which surround the brain. In humans, the neurocranium is considered to include the following eight bones: 1 ethmoid bone 1 frontal bone 1 occipital bone 2 parietal bones 1 sphenoid bone 2 temporal bonesThe ossicles are not included as bones of the neurocranium. There may variably be extra sutural bones present. Below the neurocranium is a complex of openings and bones, including the foramen magnum which houses the neural spine; the auditory bullae, located in the same region, aid in hearing. The size of the neurocranium is variable among mammals.
The roof may contain ridges such as the temporal crests. The neurocranium arises from paraxial mesoderm. There is some contribution of ectomesenchyme. In Chondrichthyes and other cartilaginous vertebrates this portion of the cranium does not ossify; the neurocranium is formed by the endocranium, the lower portions of the cranial vault, the skull roof. These are not fused in fishes, a proper neurocranium is only found in land vertebrates. Evolutionarily, the human neurocranium has expanded from comprising the back part of the mammalian skull to being the upper part: during the evolutionary expansion of the brain, the neurocranium has overgrown the splanchnocranium; the upper-frontmost part of the cranium houses the evolutionarily newest part of the human brain, the frontal lobes. Cranial cavity
Medical genetics is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics differs from human genetics in that human genetics is a field of scientific research that may or may not apply to medicine, while medical genetics refers to the application of genetics to medical care. For example, research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics, while the diagnosis and counselling people with genetic disorders would be considered part of medical genetics. In contrast, the study of non-medical phenotypes such as the genetics of eye color would be considered part of human genetics, but not relevant to medical genetics. Genetic medicine is a newer term for medical genetics and incorporates areas such as gene therapy, personalized medicine, the emerging new medical specialty, predictive medicine. Medical genetics encompasses many different areas, including clinical practice of physicians, genetic counselors, nutritionists, clinical diagnostic laboratory activities, research into the causes and inheritance of genetic disorders.
Examples of conditions that fall within the scope of medical genetics include birth defects and dysmorphology, mental retardation, mitochondrial disorders, skeletal dysplasia, connective tissue disorders, cancer genetics and prenatal diagnosis. Medical genetics is becoming relevant to many common diseases. Overlaps with other medical specialties are beginning to emerge, as recent advances in genetics are revealing etiologies for neurologic, cardiovascular, ophthalmologic, renal and dermatologic conditions; the medical genetics community is involved with individuals who have undertaken elective genetic and genomic testing. In some ways, many of the individual fields within medical genetics are hybrids between clinical care and research; this is due in part to recent advances in science and technology that have enabled an unprecedented understanding of genetic disorders. Clinical genetics is the practice of clinical medicine with particular attention to hereditary disorders. Referrals are made to genetics clinics for a variety of reasons, including birth defects, developmental delay, epilepsy, short stature, many others.
Examples of genetic syndromes that are seen in the genetics clinic include chromosomal rearrangements, Down syndrome, DiGeorge syndrome, Fragile X syndrome, Marfan syndrome, Neurofibromatosis, Turner syndrome, Williams syndrome. In the United States, Doctors who practice clinical genetics are accredited by the American Board of Medical Genetics and Genomics. In order to become a board-certified practitioner of Clinical Genetics, a physician must complete a minimum of 24 months of training in a program accredited by the ABMGG. Individuals seeking acceptance into clinical genetics training programs must hold an M. D. or D. O. degree and have completed a minimum of 24 months of training in an ACGME-accredited residency program in internal medicine, pediatrics and gynecology, or other medical specialty. Metabolic genetics involves the diagnosis and management of inborn errors of metabolism in which patients have enzymatic deficiencies that perturb biochemical pathways involved in metabolism of carbohydrates, amino acids, lipids.
Examples of metabolic disorders include galactosemia, glycogen storage disease, lysosomal storage disorders, metabolic acidosis, peroxisomal disorders and urea cycle disorders. Cytogenetics is the study of chromosomes and chromosome abnormalities. While cytogenetics relied on microscopy to analyze chromosomes, new molecular technologies such as array comparative genomic hybridization are now becoming used. Examples of chromosome abnormalities include aneuploidy, chromosomal rearrangements, genomic deletion/duplication disorders. Molecular genetics involves the discovery of and laboratory testing for DNA mutations that underlie many single gene disorders. Examples of single gene disorders include achondroplasia, cystic fibrosis, Duchenne muscular dystrophy, hereditary breast cancer, Huntington disease, Marfan syndrome, Noonan syndrome, Rett syndrome. Molecular tests are used in the diagnosis of syndromes involving epigenetic abnormalities, such as Angelman syndrome, Beckwith-Wiedemann syndrome, Prader-willi syndrome, uniparental disomy.
Mitochondrial genetics concerns the diagnosis and management of mitochondrial disorders, which have a molecular basis but result in biochemical abnormalities due to deficient energy production. There exists some overlap between molecular pathology. Genetic counseling is the process of providing information about genetic conditions, diagnostic testing, risks in other family members, within the framework of nondirective counseling. Genetic counselors are non-physician members of the medical genetics team who specialize in family risk assessment and counseling of patients regarding genetic disorders; the precise role of the genetic counselor varies somewhat depending on the disorder. Although genetics has its roots back in the 19th century with the work of the Bohemian monk Gregor Mendel and other pioneering scientists, human genetics emerged later, it started to develop, albeit during the first half of the 20th century. Mendelian inheritance was studied in a number of important disorders such as albinism and hemophilia.
Mathematical approaches were devised
The calvaria or skullcap is the upper part of the neurocranium and covers the cranial cavity containing the brain. It forms the main component of the skull roof; the calvaria is made up of the superior portions of the frontal bone, occipital bone, parietal bones. In the human skull, the sutures between the bones remain flexible during the first few years of postnatal development, fontanelles are palpable. Premature complete ossification of these sutures is called craniosynostosis; the outer surface of the skull possesses a number of landmarks. The point at which the frontal bone and the two parietal bones meet is known as "Bregma"; the point at which the two parietal and occipital bones meet is known as "Lambda". Not only do these landmarks indicate the fontanelle in newborns, they act as reference points in medicine and surgery; the inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, together with numerous furrows for the lodgement of branches of the meningeal vessels.
Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind. On either side of it are several depressions for the arachnoid granulations, at its back part, the openings of the parietal foramina when these are present, it is crossed in front by the coronal suture and behind by the lambdoid suture, while the sagittal suture lies in the medial plane between the parietal bones. Most bones of the calvaria consist of internal and external tables or layers of compact bone, separated by diploë; the diploë is cancellous bone containing red bone marrow during life, through which run canals formed by diploic veins. The diploë in a dried calvaria is not red because the protein was removed during preparation of the cranium; the internal table of bone is thinner than the external table, in some areas there is only a thin plate of compact bone with no diploë. In the fetus, the formation of the calvaria involves a process known as intramembranous ossification.
Cross section image: skull/calv-inf—Plastination Laboratory at the Medical University of Vienna Cross section image: skull/calv-sup—Plastination Laboratory at the Medical University of Vienna
The spinal cord is a long, tubular structure made up of nervous tissue, that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord; the brain and spinal cord together make up the central nervous system. In humans, the spinal cord begins at the occipital bone where it passes through the foramen magnum, meets and enters the spinal canal at the beginning of the cervical vertebrae; the spinal cord extends down to between the second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the shorter spinal cord, it is around 45 cm in men and around 43 cm long in women. The spinal cord has a varying width, ranging from 13 mm thick in the cervical and lumbar regions to 6.4 mm thick in the thoracic area. The spinal cord functions in the transmission of nerve signals from the motor cortex to the body, from the afferent fibers of the sensory neurons to the sensory cortex, it is a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes.
It is the location of groups of spinal interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking; the spinal cord is the main pathway for information connecting the brain and peripheral nervous system. Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the foramen magnum, continues through to the conus medullaris near the second lumbar vertebra before terminating in a fibrous extension known as the filum terminale, it is about 45 cm long in men and around 43 cm in women, ovoid-shaped, is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk; the lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs. The spinal cord is continuous with the caudal portion of the medulla, running from the base of the skull to the body of the first lumbar vertebra.
It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots; the nerve roots merge into bilaterally symmetrical pairs of spinal nerves. The peripheral nervous system is made up of these spinal roots and ganglia; the dorsal roots are afferent fascicles, receiving sensory information from the skin and visceral organs to be relayed to the brain. The roots terminate in dorsal root ganglia, which are composed of the cell bodies of the corresponding neurons. Ventral roots consist of efferent fibers that arise from motor neurons whose cell bodies are found in the ventral gray horns of the spinal cord; the spinal cord are protected by three layers of tissue or membranes called meninges, that surround the canal. The dura mater is the outermost layer, it forms a tough protective coating. Between the dura mater and the surrounding bone of the vertebrae is a space called the epidural space; the epidural space is filled with adipose tissue, it contains a network of blood vessels.
The arachnoid mater, the middle protective layer, is named for its spiderweb-like appearance. The space between the arachnoid and the underlying pia mater is called the subarachnoid space; the subarachnoid space contains cerebrospinal fluid, which can be sampled with a lumbar puncture, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is associated with the surface of the spinal cord; the cord is stabilized within the dura mater by the connecting denticulate ligaments, which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The dural sac ends at the vertebral level of the second sacral vertebra. In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor axons. Internal to this peripheral region is the grey matter, which contains the nerve cell bodies arranged in the three grey columns that give the region its butterfly-shape; this central region surrounds the central canal, an extension of the fourth ventricle and contains cerebrospinal fluid.
The spinal cord is elliptical in cross section, being compressed dorsolaterally. Two prominent grooves, or sulci, run along its length; the posterior median sulcus is the groove in the dorsal side, the anterior median fissure is the groove in the ventral side. The human spinal cord is divided into segments. Six to eight motor nerve rootlets branch out of right and left ventro lateral sulci in a orderly manner. Nerve rootlets combine to form nerve roots. Sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots; the ventral and dorsal roots combine to form one on each side of the spinal cord. Spinal nerves, with the exception of C1 and C2, form inside the intervertebral foramen; these rootlets form the demarcation between the peripheral nervous systems. The grey column, in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons, motor neurons, neuroglia cells and unmyelinated axons; the anterior and posterior grey column present as projections of the grey matter and are known as the horns of the spinal cord.
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