Share in your Facebook group Copy Please sign in or register to post comments. A cell is the basic, living, structural and functional unit of the body. Cell biology is the scientiic study of cellular structure and function.
Since the back Anatomy chapter 3 homeostatic imbalances use the spine as a lever in maintaining balance, the forces upon the IVD's and vertebrae are much greater than the forces of the body weight above.
During spinal movement, the peripheral anulus bulges slightly posterior during extension, anteriorly during flexion, and towards the side of lateral bending. This is opposite to what some might think.
Concurrent with bulging is disc contraction on the contralateral side Poisson effect. The healthy nucleus remains near its normal position with only slight movement towards the anular bulge. Because the nucleus is strongly hydrophilic and encased, its pressure is never zero, even if completely unloaded.
This "preloaded" factor offers an inherent tension which offers greater resistance to compression and lateral flexion forces. The "swollen" state of the nucleus also creates a constant pressure directed peripherally to the fibers of the anulus Fig.
The hydrophilic characteristic of the nucleus decreases during constant load and advanced age, and this fact contributes to the reduction of spinal flexibility. The preload pressure of the nucleus is enhanced by about lb of inherent pressure exerted by the anulus and intervertebral ligaments.
In the static position, the load on a disc is much greater than the superimposed body weight. This is the result of the center of gravity being anterior to the disc causing a bending moment that must be resisted by posterior muscle action that increases the compression force.
During forward flexion, the L3 disc is subjected to about double the body weight above. If only a lb external load is added eg, a child being liftedthe disc carries a force three times the superimposed body weight.
These pressures are substantially increased in the sitting position. During erect dynamic activities, disc forces rise to double static forces without the addition of external load. Reaction to Axial Tension. When a vertebral motion unit is subjected to elon- gation eg, during vertical stretching, A-P and lateral bending, rotation while flexed, mechanical traction, or hanging from a horizontal barthe vertebral bodies tend to separate, the disc thickens, nuclear pressure reduces, and vertical anular fiber tension towards the periphery of the disc increases.
Tensile loads produce perpendicular normal stresses that are readily absorbed by the criss-crossed anular layers and relatively larger parallel shear stress in the anulus that has little resistance.
This is an early factor in most disc failures Fig. Reaction to Axial Compression.
When a vertebral motion unit is under axial compression eg, body weight, with or without external loadthe vertebral bodies tend to approximate, the disc flattens, nuclear pressure increases, the end plates are subjected to greater pressure, and anular fiber tension increases from forces projected laterally from the nucleus.
Forces are normally transmitted evenly throughout the nucleus. The closed, pressurized container of the nucleus conforms to the law of Pascal which states that "any external force exerted on a unit area of a confined liquid is transmitted undiminished to every unit area of the interior of the containing vessel.
A disc is stiffer under compression than tension because nuclear pressure is increased under compression. This centralized loading tends to deflect the end-plates away from the disc at the periphery so that the dimension of the disc increases centrally and the center of the end-plate becomes deformed.
Such loading cannot produce disc rupture unless the disc is burst by an unusually heavy and fast axial force even if the disc is torn, but the disc does bulge especially laterally and anteriorly as it flattens.
If excessive loading fractures an end-plate centrally, the nucleus tends to be driven into the vertebral body traumatic Schmorl's node. When compression load to a motion unit becomes excessive, the unit fails with fracture of the end-plate or vertebral body with little damage to the disc.
Bending and torsional stresses appear to be more dangerous to disc integrity than axial loads. However, once a disc becomes degenerated, the stress of compression load substantially increases. Central end-plate fractures are more often associated with a healthy disc with a firm nucleus that generates maximum bending moments at the plate.
In contrast, peripheral end-plate fractures are commonly associated with a degenerated nucleus where most forces are carried via the outer anulus. Reaction to Asymmetrical Forces. When a disc is loaded unilaterally, the disc initially becomes wedge-shaped and the normally parallel vertebral plateaus form an angle Fig.
This vertically stretches the anular fibers opposite to the weight-bearing side, but this action is quickly counteracted by opposite forces transmitted laterally from the nucleus to help the disc return to its normal shape.
This self-stabilization factor is the product of a healthy nucleus and anulus working as a mechanical couple. Reaction to Oblique Forces.Chapter 6 - Skeletal System Skeletal Cartilages. Basic Structure, Types, and Locations Skeletal cartilages are made from cartilage, surrounded by a layer of dense irregular connective tissue called the perichondrium.; Hyaline cartilage is the most abundant skeletal cartilage, and includes the articular, costal, respiratory, and nasal cartilages.; Elastic cartilages are more flexible than.
Visual icons highlight clinical applications, homeostatic disorders, key concepts, questions with figures, study outline, and questions. Bullets point to chapter objectives and checkpoint questions.
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6 INTRODUCTION TO PHYSIOLOGY AND HOMEOSTASIS Diaphragm (a) Right lateral view (b) Anterior view Cranial cavity Spinal cavity Surface anatomy is the study of external structures and their relation to deeper structures.
For example, the breastbone (sternum) and parts of ing cell structure and function is discussed in Chapter 5 under the.
Ross and Wilson Human Anatomy and Physiology PDF 12th Edition - Free ebook download as PDF File .pdf), Text File .txt) or read book online for free. 2. What is the difference between anatomy and physiology? 3. Identify and describe the three invisible planes that divide the human body and how they divide homeostasis homeostatic imbalance homeostatic mechanisms metabolic rate metabolism molecules negative feedback organ organ system Lesson Learning the Key Terms A. a force that. Below are links to the free, downloadable Word Doc and PDF versions of the latest edition () of the Guidelines for the Use of Fishes in Research.. Both the Word and PDF versions contain useful internal and external hyperlinks.
The Principles of Anatomy and Physiology, 14th Edition continues to set the standard for the discipline. The authors have maintained a superb balance between structure and function and continue to emphasize the correlations between normal physiology and pathophysiology, normal anatomy and pathology, and homeostasis and homeostatic imbalances.
Homeostatic imbalances. Decompression sickness Decompression sickness (DCS) is a condition in which gases dissolved in the blood or in other body tissues are no longer dissolved following a reduction in pressure on the body.