By U. Abbas. Montana State University-Bozeman.
The low arterial pressure results zone 1 condition can be created when a patient is placed on in reduced blood flow in the capillaries at the lung’s apex cheap diabecon 60caps mastercard, a mechanical ventilator purchase diabecon 60caps line, which results in an increase in alve- while capillaries at the base are distended and blood flow olar pressure with positive ventilation pressures. A zone 1 condi- tion can also be created in the lungs of astronauts during a Gravity Alters Capillary Perfusion spacecraft launching. The rocket acceleration makes the In an upright person, pulmonary blood flow increases almost gravitational pull even greater, causing arterial pressure in linearly from apex to base (Fig. To prevent or minimize a is affected by gravity, and it can be altered by changes in zone 1 from occurring, astronauts are placed in a supine po- body positions. The measurement of blood flow in a subject sus- where pulmonary arterial pressure, caused by the increased pended upside-down would reveal an apical blood flow ex- hydrostatic effect, is greater than alveolar pressure (see Fig ceeding basal flow in the lungs. As cardiac out- result, blood flow in a zone 2 condition is determined not put increases with exercise, the increased pulmonary arterial by the arterial-venous pressure difference, but by the dif- pressure leads to capillary recruitment and distension in the ference between arterial pressure and alveolar pressure. The functional importance of this is that venous Since gravity causes capillary beds to be underperfused pressure in zone 2 has no effect on flow. In zone 3, venous in the apex and overperfused in the base, the lungs are of- pressure exceeds alveolar pressure and blood flow is deter- ten divided into zones to describe the effect of gravity on mined by the usual arterial-venous pressure difference. CHAPTER 20 Pulmonary Circulation and the Ventilation-Perfusion Ratio 345 Alveolar Venous Arterial pressure pressure pressure (mm Hg) (mm Hg) (mm Hg) Zone 1 0 PA > Pa > PV 2 0 2 2 4 0 6 2 Zone 2 Pa > PA > PV 8 0 2 10 Pulmonary 0 artery 2 14 2 16 2 Zone 3 18 6 Pa > PV > PA 20 8 2 22 10 24 12 2 Blood flow FIGURE 20. In zone 2, arterial pressure exceeds alveolar pressure, tion of pulmonary blood flow. The three and blood flow depends on the difference between arterial and zones depend on the relationship between pulmonary arterial alveolar pressures. Blood flow is greater at the bottom than at the pressure (Pa), pulmonary venous pressure (Pv), and alveolar pres- top of this zone. In zone 1, alveolar pressure exceeds arterial pressure ceed alveolar pressure, and blood flow depends on the normal ar- and there is no blood flow. Note that arterial pressure in- ditions in which alveolar pressure is increased (e.
Nervous Tissue and the © The McGraw−Hill Anatomy generic diabecon 60caps with mastercard, Sixth Edition Coordination Central Nervous System Companies buy diabecon 60 caps on line, 2001 358 Unit 5 Integration and Coordination Direction of action potential Vesicle releasing neurotransmitter Synaptic vesicles chemical Axon Axon membrane Mitochondrium Neurotransmitter chemical Membrane of postsynaptic cell Axon terminal Synaptic cleft FIGURE 11. When an action potential reaches the axon terminal, neurotransmitter chemicals are released into the synaptic cleft. Synaptic transmission occurs if sufficient amounts of the neurotransmitter chemicals are released. Define the terms depolarization and repolarization and illus- axon terminal of a presynaptic neuron and a dendrite of a post- trate these processes graphically. The axon terminal (synaptic knob), is the distal portion of the presynaptic neuron at the end 9. Describe the mechanism by which a neurotransmitter af- of the axon; it is characterized by the presence of numerous mito- fects impulse conduction across a synapse. When an action potential reaches the axon terminal, some of the vesicles respond by releasing their GENERAL FEATURES neurotransmitter into the synaptic cleft, a tiny gap separating OF THE BRAIN the presynaptic and postsynaptic membranes. If a sufficient num- The brain is enclosed by the cranium and meninges and is bathed ber of nerve impulses occur in a short time interval, enough neu- in cerebrospinal fluid. The tremendous metabolic rate of the brain rotransmitter will accumulate within the synaptic cleft to makes it highly susceptible to oxygen deprivation. Neurotransmitters are decomposed by enzymes present in Objective 10 Describe the general features of the brain. Synaptic transmission may be affected by various drugs or Objective 12 List the metabolic needs of the brain. Caffeine is a stimulant that increases the rate of The entire delicate CNS is protected by a fixed bony encase- transmission across the synapse. The drug strychnine profoundly re- duces synaptic transmission; it affects breathing and paralyzes brain and a flexible vertebral column surrounding the spinal respiratory structures, causing death. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 359 Over 200 neuropeptides have been identified within the brain, yet most of their functions are not well understood.
Simultaneously phos- The described pathogenetic mechanisms are congruent phate excretion is reduced with hyperphosphatemia with histopathologic findings in PHPT order diabecon 60 caps visa. This stimulates the parathyroid glands generic 60caps diabecon fast delivery, which the iliac crest is intact. The number of osteoclasts indeed in turn increases the level of circulating parathyroid is increased but their depth of resorption is less than nor- hormone. The number of BMU (bone mineral units) is also in- – Tertiary hyperparathyroidism is the result of long- creased, meaning that the number of osteoblasts is elevat- standing secondary hyperparathyroidism due to chron- ed, producing more osteoid matrix, but without a distur- ic renal failure. In about 50% of all cases of PH- parathyroid glands function autonomously. These results demonstrate that bone mass in those pa- tients is increased. Only in 4% of all cases, advanced bone resorption, formation of primitive woven bone and brown * This chapter originally appeared in: von Schulthess GK, tumors can be observed. Zollikofer Ch L (2001) Musculoskeletal Diseases - Diagnostic Imaging and Interventional Techniques. Springer-Verlag Italia, While the trabecular bone mass of the iliac crest and Milan spine in early stages of PHPT (and also in SHPT) may be 84 J. Freyschmidt increased, cortical bone resorption may take place simul- ready be taking place when the trabecular structures of taneously. This is best visualized with X-rays of the hands the iliac crest are still normal. I believe that the preference of re- be distinguished: sorption of cortical bone is a problem of vascular perfu- 1. Slight or moderate diffuse or patchy osteosclerosis Classic signs of advanced PHPT (Fig. An early increase of bone mass is best demonstrated by – Wispy and woolly coarsening of trabeculae, if the prim- quantitative computed tomography (QCT).