Analytic epidemiological studies aim to investigate and identify factors associated with the presence of disease within populations, through the investigation of factors which may vary between individual members of these populations. Details on study designs appropriate for these investigations are given elsewhere. Conceptually, this involves investigating the disease experience amongst different 'groups' of animals within an overall population, distinguished according to the factor(s) of interest. These factors can be classified as one of the components of the 'epidemiological triad' of Host, Agent and Environment, many of which are closely interrelated with each other.
The Blood Brain Barrier refers to the mechanisms in place around the microvasculature of the brain to ensure optimal neural functioning. Endothelial cells are the structural basis of the blood brain barrier and are joined by tight cellular junctions formed by the transmembrane proteins the occludins and the claudins.
Blood cells develop in the bone marrow from a common stem cell in the process known as haematopoiesis. Once mature, cells are divided into groups that reflect their morphological and functional characteristics including the erythrocytes, or red blood cells, the granulocytes, the agranulocytes and the megakaryocytes.
Development of the Central Nervous System (CNS) includes development of the brain, spinal cord, optic and auditory systems, as well as surrounding supporting cells including ependymal cells, astrocytes, oligodendrocytes and microglia. Information within this page will exclude development of the Peripheral Nervous System (PNS) which includes nerve and ganglia formation.
Camelids are becoming more common in general practice and so an understanding of anaesthesia techniques is becoming more important. The same techniques used in other species can be adapted and used in camelids including both local and general anaesthesia.
It is important that all aspects of haemostasis can be independently evaluated. This will help to identify the phase affected and to pinpoint what the abnormality is. There are tests available to assess primary haemostasis, secondary haemostasis and fibrinolysis.
As in any animal, anaesthesia in a horse carries a risk, although it is much higher than that of other domestic species. It is therefore important to try and minimise these risks as much as possible when performing any procedure. Problems can be encountered at any stage of the anaesthetic and so each stage shall be considered separately here.
The air in the alveoli is renewed regularly, thanks to the ventilation process. Gas exchange in the lungs takes place between the blood in the capillary network surrounding the alveoli, and the air in the alveoli itself.
The heart is located in the thoracic cavity in between the lungs, 60% of it lying to the left of the median plane. The hearts lateral projection extends from rib 3 to 6. Most of the hearts surface is covered by the lungs and in juveniles it is bordered cranially by the thymus. Caudally the heart extends as far as the diaphragm. Variations in position and size exist among individuals depending on species, breed, age, fitness and pathology. Roughly speaking, the heart is responsible for about 0.75% of the bodyweight.
The keratin in the epidermis, when cornified and thickened, is referred to as horn. Horn is particulary resistant to mechanical and chemical damage. The dermis of horn gives the structures their 3-D structure and shape. Cattle, some sheep, goats and antelope posess horns and these are permanent organs. Breeds without horns are termed polled breeds. Deer posess antlers, which are temporary organs that develop during the rutting season and are then shed.
IgG is the major antibody in blood plasma, and constitutes at least 80% of all antibodies in the body. It is the smallest immunoglobulin, so can readily leave the blood plasma and enter tissues. They can also cross the placenta, providing adaptive immunity to the foetus when the mother is under attack. IgG is also present in breast milk.
Because viruses invade host cells to take over a host's cellular machinery, the innate system has a more difficult time detecting viruses as foreign agents. However, there is a give-away element of the viral attack that the innate system can recognize: the double-stranded RNA (dsRNA) produced by a virus in its replication phase. Because mammalian cells only ever produce single-stranded RNA, the presence of dsRNA signals a foreign intruder. dsRNA can be detected by TLR-3R on the cell surface or intracellularly by the presence of dsRNA-dependent protein kinase.
Sexual differentiaton by default follows a pathways for development of female internal and external genitalia, requiring no active intervention. Endocrine activity of the testes, production of Androgens by Leydig cells and Mullerian Inhibiting hormone (MIH) by Sertoli cells, is required for sexual differentiation to be diverted down the male genitalia development pathway.
Measures of effect and impact can be calculated using the same contingency table used to calculated measures of strength of association.
The mediastinum divides the thoracic cage into two halves. It extends from the Spine to the Sternum and contains many structures including blood vessels, nerves, oesophagus, trachea and heart.
The surface of the inner wall of all of the body cavities is lined by a serous membrane which consists of a single layer of flat epithelium with a thin underlying propria (connective tissue). Within the thoracic cavity, this is known as the pleura. The visceral pleura which coats the outer surface of the lung is derived from the splanchnic mesoderm. The parietal pleura lining the thoracic cavity is derived from somatic mesoderm. The pleural cavity is a potential space between the two areas of pleural membrane, which normally are adhesed to each other.
The spinal cord is constructed of the marginal layer which has axons and white matter, the mantle which contains cell bodies and grey matter and the spinal canal. This canal conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain, conducts motor information from the brain to various effectors and acts as a minor reflex center.
The thymus has a key role in the maturation of prothymocytes into mature T cells. In juvenile animals the thymus produces significant numbers of new T lymphocytes but as the animal matures this production decreases and T cell population is maintained by division of mature T cells.
The thyroid gland lies in the neck, in front of the upper part of the trachea. Two types of hormones are produced, which are the iodine containing hormones; tri-iodothyronine(T3) and thyroxine (T4). Thyroid hormones regulate the basal metabolic rate and are important in the regulation of growth of tissues, particularly nervous tissue. Release stimulated by TSH from the pituitary. The second type of hormone produced from the thyroid gland is calcitonin, which regulates blood calcium levels along with parathyroid hormone and acts to reduce blood calcium by inhibiting its removal from bone.
Blood vessel formation is a combination of the following three processes: Vasculogenesis: the formation of blood vessels from endothelial progenitor cells; Angiogenesis: the sprouting of new capillaries from pre-existing vessels; and Arteriogenesis: the remodelling of newly formed or pre-existing vascular channels into larger and more muscular arterioles.