The thoracic cavity is the chamber of the body of vertebrates, protected by the thoracic wall. The central compartment of the thoracic cavity is the mediastinum. There are two openings of the thoracic cavity, a superior thoracic aperture known as the thoracic inlet and a lower inferior thoracic aperture known as the thoracic outlet; the thoracic cavity includes the tendons as well as the cardiovascular system which could be damaged from injury to the back, spine or the neck. Structures within the thoracic cavity include: structures of the cardiovascular system, including the heart and great vessels, which include the thoracic aorta, the pulmonary artery and all its branches, the superior and inferior vena cava, the pulmonary veins, the azygos vein structures of the respiratory system, including the Diaphragm, trachea and lungs structures of the digestive system, including the esophagus, endocrine glands, including the thymus gland, structures of the nervous system including the paired vagus nerves, the paired sympathetic chains, lymphatics including the thoracic duct.
It contains three potential spaces lined with mesothelium: the paired pleural cavities and the pericardial cavity. The mediastinum comprises those organs; the cavity contains two openings one at the top, the superior thoracic aperture called the thoracic inlet, a lower inferior thoracic aperture, much larger than the inlet. If the pleural cavity is breached from the outside, as by a bullet wound or knife wound, a pneumothorax, or air in the cavity, may result. If the volume of air is significant, one or both lungs may collapse, which requires immediate medical attention. Thoraxlesson3 at The Anatomy Lesson by Wesley Norman
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
Oligochaeta is a subclass of animals in the phylum Annelida, made up of many types of aquatic and terrestrial worms, including all of the various earthworms. The oligochaetes contain the terrestrial megadrile earthworms, freshwater or semiterrestrial microdrile forms, including the tubificids, pot worms and ice worms and several interstitial marine worms. With around 10,000 known species, the Oligochaeta make up about half of the phylum Annelida; these worms have few setae or "bristles" on their outer body surfaces, lack parapodia, unlike polychaeta. Oligochaetes are well-segmented worms and most have a spacious body cavity used as a hydroskeleton, they range in length from less than 0.5 mm up to 2 to 3 metres in the'giant' species such as the giant Gippsland earthworm and the Mekong worm. Terrestrial oligochaetes are known as earthworms and burrow into the soil; the four main families with large numbers of species are Glossoscolecidae, Lumbricidae and Moniligastridae. Earthworms are found in all parts of the world except for deserts.
They have a requirement for moist surroundings and the larger species create burrows that may go down several metres while young individuals and smaller species are restricted to the top few centimetres of soil. The largest numbers are found in acid soils. A few species are found in trees, among damp moss and in the debris that accumulates in leaf axils and crevices; the majority of aquatic oligochaetes are small, slender worms, whose organs can be seen through the transparent body wall. They burrow into the sediment or live among the vegetation in shallow, freshwater environments; some are transitional between terrestrial and aquatic habitats, inhabiting swamps, mud or the borders of water bodies. About two hundred species are marine in the families Enchytraeidae and Naididae; the first segment, or prostomium, of oligochaetes is a smooth lobe or cone without sensory organs, although it is sometimes extended to form a tentacle. The remaining segments have no appendages; these tend to be longer in aquatic forms than in the burrowing earthworms, can have a variety of shapes.
Each segment has four bundles of chaetae, with two on the underside, the others on the sides. The bundles can contain one to 25 chaetae, include muscles to pull them in and out of the body; this enables the worm to gain a grip on the mud as it burrows into the substrate. When burrowing, the body moves peristaltically, alternately contracting and stretching to push itself forward. A number of segments in the forward part of the body are modified by the presence of numerous secretory glands. Together, they form the clitellum, important in reproduction. Most oligochaetes are detritus feeders, although some genera are predaceous, such as Agriodrilus and Phagodrilus; the digestive tract is a tube running the length of the body, but has a powerful muscular pharynx behind the mouth cavity. In many species, the pharynx helps the worm suck in food, but in many aquatic species, it can be turned inside out and placed over food like a suction cup before being pulled back in; the remainder of the digestive tract may include a crop for storage of food, a gizzard for grinding it up, although these are not present in all species.
The oesophagus includes "calciferous glands" that maintain calcium balance by excreting indigestible calcium carbonate into the gut. A number of yellowish chloragogen cells surround the intestine and the dorsal blood vessel, forming a tissue that functions in a similar fashion to the vertebrate liver; some of these cells float in the body cavity, where they are referred to as "eleocytes". Most oligochaetes have no gills or similar structures, breathe through their moist skin; the few exceptions have simple, filamentous gills. Excretion is through small ducts known as metanephridia. Terrestrial oligochaetes secrete urea, but the aquatic forms secrete ammonia, which dissolves into the water; the vascular system consists of two main vessels connected by lateral vessels in each segment. Blood is carried forward in the dorsal vessel and back through the ventral vessel, before passing into a sinus surrounding the intestine; some of the smaller vessels are muscular forming hearts. The blood of oligochaetes contains haemoglobin in all but the smallest of species, which have no need of respiratory pigments.
The nervous system consists of two ventral nerve cords, which are fused into a single structure, three or four pairs of smaller nerves per body segment. Only a few aquatic oligochaetes have eyes, then they are only ocelli. Nonetheless, their skin has several individual photoreceptors, allowing the worm to sense the presence of light, burrow away from it. Oligochaetes can taste their surroundings using chemoreceptors located in tubercles across their body, their skin is supplied with numerous free nerve endings that contribute to their sense of touch. Oligochaetes occur in every continent in the world occupying terrestrial and marine habitats. Of the 1700 known aquatic species, about 600 are 100 inhabit groundwater. Aquatic oligochaetes occur in most groups, with the Naididae b
The pelvic cavity is a body cavity, bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet, its lower boundary is the pelvic floor. The pelvic cavity contains reproductive organs, the urinary bladder, the pelvic colon, the rectum. In the female, the uterus and vagina occupy the interval between these viscera; the rectum is placed in the curve of the sacrum and coccyx. The pelvic cavity contains major arteries, veins and nerves; these structures coexist in a crowded space, disorders of one pelvic component may impact upon another. The pelvis has an anteroinferior, a posterior, two lateral pelvic walls; the parietal peritoneum is attached here and to the abdominal wall. The lesser pelvis is the space enclosed by the pelvic girdle and below the pelvic brim: between the pelvic inlet and the pelvic floor; this cavity is a curved canal, deeper on its posterior than on its anterior wall. Some consider this region to be the entirety of the pelvic cavity. Others define the pelvic cavity as the larger space including the greater pelvis, just above the pelvic inlet.
The lesser pelvis is bounded in front and below by the pubic symphysis and the superior rami of the pubis. The lesser pelvis contains the pelvic colon, rectum and some of the sex organs; the rectum is in the curve of the sacrum and coccyx. In the female, the uterus and vagina occupy the interval between these viscera; the pelvic splanchnic nerves arising at S2-S4 are in the lesser pelvis. The greater pelvis is the space enclosed by the pelvic girdle in front of the pelvic brim, it is bounded on either side by the ilium. It is considered part of the abdominal cavity; some consider this region part of the pelvic cavity, while others reframe the classification question by calling the combination the abdominopelvic cavity. The greater pelvis supports the intestines, transmits part of their weight to the anterior wall of the abdomen; the femoral nerve from L2-L4 is in the greater pelvis, but not in the lesser pelvis. Internal iliac artery median sacral artery ovarian artery sacral plexus splanchnic nerves femoral nerve The pelvis can be classified into four main types by measuring the pelvic diameters and conjugates at the pelvic inlet and outlet and as oblique diameters.
Overview at buffalo.edu Diagram at southwest.tn.edu Photo of model Anatomy photo:44:os-0502 at the SUNY Downstate Medical Center - "The Male Pelvis: Articulated bones of male pelvis" Anatomy photo:44:os-0503 at the SUNY Downstate Medical Center
The vertebral column known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs; the vertebral column houses a cavity that encloses and protects the spinal cord. There are about 50,000 species of animals; the human vertebral column is one of the most-studied examples. In a human's vertebral column there are thirty-three vertebrae; the articulating vertebrae are named according to their region of the spine. There are twelve thoracic vertebrae and five lumbar vertebrae; the number of vertebrae in a region overall the number remains the same. The number of those in the cervical region however is only changed. There are ligaments extending the length of the column at the front and the back, in between the vertebrae joining the spinous processes, the transverse processes and the vertebral laminae.
The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are alike, with minor variation; these regions are called the cervical spine, thoracic spine, lumbar spine and coccyx. There are twelve thoracic vertebrae and five lumbar vertebrae; the number of vertebrae in a region overall the number remains the same. The number of those in the cervical region however is only changed; the vertebrae of the cervical and lumbar spines are independent bones, quite similar. The vertebrae of the sacrum and coccyx are fused and unable to move independently. Two special vertebrae are the axis, on which the head rests. A typical vertebra consists of two parts: the vertebral arch; the vertebral arch is posterior. Together, these enclose the vertebral foramen; because the spinal cord ends in the lumbar spine, the sacrum and coccyx are fused, they do not contain a central foramen.
The vertebral arch is formed by a pair of pedicles and a pair of laminae, supports seven processes, four articular, two transverse, one spinous, the latter being known as the neural spine. Two transverse processes and one spinous process are posterior to the vertebral body; the spinous process comes out the back, one transverse process comes out the left, one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin. Above and below each vertebra are joints called facet joints; these restrict the range of movement possible, are joined by a thin portion of the neural arch called the pars interarticularis. In between each pair of vertebrae are two small holes called intervertebral foramina; the spinal nerves leave the spinal cord through these holes. Individual vertebrae are named according to their position. From top to bottom, the vertebrae are: Cervical spine: 7 vertebrae Thoracic spine: 12 vertebrae Lumbar spine: 5 vertebrae Sacrum: 5 vertebrae Coccyx: 4 vertebrae The upper cervical spine has a curve, convex forward, that begins at the axis at the apex of the odontoid process or dens, ends at the middle of the second thoracic vertebra.
This inward curve is known as a lordotic curve. The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra, its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a kyphotic curve; the lumbar curve is more marked in the female than in the male. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two; this curve is described as a lordotic curve. The sacral curve begins at the sacrovertebral articulation, ends at the point of the coccyx; the thoracic and sacral kyphotic curves are termed primary curves, because they are present in the fetus. The cervical and lumbar curves are compensatory or secondary, are developed after birth; the cervical curve forms when the infant is able to sit upright. The lumbar curve forms from twelve to eighteen months, when the child begins to walk. Anterior surfaceWhen viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic.
From this point there is a rapid diminution, to the apex of the coccyx. Posterior surfaceFrom behind, the vertebral column presents in the median line the spinous processes. In the cervical region these are short and bifid. In the upper part of the thoracic region they are directed obliquely downward.
Cerebrospinal fluid is a clear, colorless body fluid found in the brain and spinal cord. It is produced by the specialised ependymal cells in the choroid plexuses of the ventricles of the brain, absorbed in the arachnoid granulations. There is about 125mL of CSF at any one time, about 500 mL is generated every day. CSF acts as a cushion or buffer for the brain, providing basic mechanical and immunological protection to the brain inside the skull. CSF serves a vital function in cerebral autoregulation of cerebral blood flow. CSF occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord, it fills the ventricles of the brain and sulci, as well as the central canal of the spinal cord. There is a connection from the subarachnoid space to the bony labyrinth of the inner ear via the perilymphatic duct where the perilymph is continuous with the cerebrospinal fluid. A sample of CSF can be taken via lumbar puncture; this can reveal the intracranial pressure, as well as indicate diseases including infections of the brain or its surrounding meninges.
Although noted by Hippocrates, it was only in the 18th century that Emanuel Swedenborg is credited with its rediscovery, as late as 1914 that Harvey W. Cushing demonstrated CSF was secreted by the choroid plexus. There is about 125–150 mL of CSF at any one time; this CSF circulates within the ventricular system of the brain. The ventricles are a series of cavities filled with CSF; the majority of CSF is produced from within the two lateral ventricles. From here, CSF passes through the interventricular foramina to the third ventricle the cerebral aqueduct to the fourth ventricle. From the fourth ventricle, the fluid passes into the subarachnoid space through four openings – the central canal of the spinal cord, the median aperture, the two lateral apertures. CSF is present within the subarachnoid space, which covers the brain, spinal cord, stretches below the end of the spinal cord to the sacrum. There is a connection from the subarachnoid space to the bony labyrinth of the inner ear making the cerebrospinal fluid continuous with the perilymph in 93% of people.
CSF moves in a single outward direction from the ventricles, but multidirectionally in the subarachnoid space. Fluid movement is pulsatile, matching the pressure waves generated in blood vessels by the beating of the heart; some authors dispute this, posing that there is no unidirectional CSF circulation, but cardiac cycle-dependent bi-directional systolic-diastolic to-and-fro cranio-spinal CSF movements. CSF is derived from blood plasma and is similar to it, except that CSF is nearly protein-free compared with plasma and has some different electrolyte levels. Due to the way it is produced, CSF has a higher chloride level than plasma, an equivalent sodium level. CSF contains 0.3% plasma proteins, or 15 to 40 mg/dL, depending on sampling site. In general, globular proteins and albumin are in lower concentration in ventricular CSF compared to lumbar or cisternal fluid; this continuous flow into the venous system dilutes the concentration of larger, lipid-insoluble molecules penetrating the brain and CSF.
CSF is free of red blood cells, at most contains only a few white blood cells. Any white blood cell count higher. At around the third week of development, the embryo is a three-layered disc, covered with ectoderm and endoderm. A tube-like formation develops in the midline, called the notochord; the notochord releases extracellular molecules that affect the transformation of the overlying ectoderm into nervous tissue. The neural tube, forming from the ectoderm, contains CSF prior to the development of the choroid plexuses; the open neuropores of the neural tube close after the first month of development, CSF pressure increases. As the brain develops, by the fourth week of embryological development three swellings have formed within the embryo around the canal, near where the head will develop; these swellings represent different components of the central nervous system: the prosencephalon and rhombencephalon. Subarachnoid spaces are first evident around the 32nd day of development near the rhombencephalon.
At this time, the first choroid plexus can be seen, found in the fourth ventricle, although the time at which they first secrete CSF is not yet known. The developing forebrain surrounds the neural cord; as the forebrain develops, the neural cord within it becomes a ventricle forming the lateral ventricles. Along the inner surface of both ventricles, the ventricular wall remains thin, a choroid plexus develops and releasing CSF. CSF fills the neural canal. Arachnoid villi are formed around the 35th week of development, with aracnhoid granulations noted around the 39th, continuing developing until 18 months of age; the subcommissural organ secretes SCO-spondin, which forms Reissner's fiber within CSF assisting movement through the cerebral aqueduct. It disappears during early development. CSF serves several purposes: Buoyancy: The actual mass of the human brain is about 1400–1500 grams; the brain therefore exists in neutral buoyancy, which allows the brain to maintain its density without being impaired by its own weight, which would cut off blood supply and kill neurons in the lower sections without CSF.
Protection: CSF protects the brain tissue from injury when jolted or hit, by providing a fluid buffer that acts as a shock absorber from some forms of mechanical injury. Prevention of brain ischemia: The prevention of brai