Human Physiology: From Cells to Systems
Format: PDF / Kindle (mobi) / ePub
Organized around the central theme of homeostasis--how the body meets changing demands while maintaining the internal constancy necessary for all cells and organs to function--HUMAN PHYSIOLOGY helps you understand how each component of the course depends on the others and appreciate the integrated functioning of the human body. Author Lauralee Sherwood uses clear straightforward language, analogies, and frequent references to everyday experiences to help you learn and relate to the physiology concepts. The updated art program and new digital resources--including robust 3D animations--enable you to visualize important concepts and processes. By focusing on the core principles and sharing enthusiasm for the subject matter, Sherwood provides a solid foundation for future courses and careers in the health profession.
intercellular communication. The four types of chemical messengers differ in their source and the distance and means by which they get to their site of action. Paracrines are local chemical messengers whose effect is exerted only on neighboring cells in the immediate environment of their site of secretion. Because paracrines are distributed by simple diffusion within the interstitial fluid, their action is restricted to short distances. They do not gain entry to the blood in any significant
all times, it is not sur- sible for Laron dwarfism. In this condition, the person is abnormally short, despite having normal levels of growth hormone, because the tissues cannot respond normally to growth hormone. This is in contrast to the more usual type of dwarfism in which the person is abnormally short because of growth hormone deficiency. As another example, the toxins released by some infecting bacteria, such as those that cause cholera and whooping cough, keep second-messenger pathways
6. State three important roles of the Naϩ–Kϩ pump. 7. Describe the contribution of each of the following to establishing and maintaining membrane potential: (a) the Naϩ–Kϩ pump; (b) passive movement of Kϩ across the membrane; (c) passive movement of Naϩ across the membrane; and (d) the large intracellular anions. The Plasma Membrane and Membrane Potential 83 tance, a measure of the permeability of x, in Siemens (S), which is ⌬I/⌬V ; Vm is the membrane voltage; and Ex is the equilibrium
ICF K+ Depolarizing triggering event Time (msec) Na+ voltage-gated channel closed (activation gate closed; inactivation gate open) 1 Resting potential: all voltage-gated channels closed. 2 At threshold, Na+ activation gate opens and PNa+ rises. 3 Na+ enters cell, causing explosive depolarization to +30 mV, which generates rising phase of action potential. 4 At peak of action potential, Na+ inactivation gate closes and PNa+ falls, ending net movement of Na+ into cell. At the same time, K+
cell body and eventually terminates at other cells. The first portion of the axon plus the region of the cell body from which the axon leaves is known as the axon hillock. The axon hillock is the neuron’s trigger zone, because it is the site where action potentials are triggered, or initiated, by the graded potential if it is of sufficient magnitude. The action potentials are then conducted along the axon from the axon hillock to the typically highly branched ending at the axon terminals. These