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Arteries and Veins

Arterial Distribution and Venous Collection Systems Hemodynamics is the study of the physical laws of blood circulation. It therefore addresses the properties of both the “content” (i.e., blood) and the “container” (i.e., blood vessels). In Chapter 18 , we discussed the properties of the blood. This chapter is primarily concerned with the properties of the blood vessels. The circulation is not a system of rigid tubes.…

Blood

Blood is a complex fluid consisting of plasma—extracellular fluid rich in proteins—and of formed elements—red blood cells (RBCs), white blood cells (WBCs), and platelets. Total blood volume is ~70 mL/kg body weight in the adult woman and ~80 mL/kg body weight in the adult man (see Table 5-1 ). Blood Composition Whole blood is a suspension of cellular elements in plasma If you spin down a sample of…

Organization of the Cardiovascular System

Elements of the Cardiovascular System The circulation is an evolutionary consequence of body size Isolated single cells and small organisms do not have a circulatory system. They can meet their metabolic needs by the simple processes of diffusion and convection of solutes from the external to the internal milieu ( Fig. 17-1 A ). The requirement for a circulatory system is an evolutionary consequence of the…

Circuits of the Central Nervous System

Elements of Neural Circuits Neural circuits process sensory information, generate motor output, and create spontaneous activity A neuron never works alone. Even in the most primitive nervous systems, all neurons participate in synaptically interconnected networks called circuits. In some hydrozoans (small jellyfish), the major neurons lack specialization and are multifunctional. They serve simultaneously as photodetectors, pattern generators for swimming rhythms, and motor neurons. Groups of these…

Sensory Transduction

Sensory receptors convert environmental energy into neural signals Sensation is a cognitive process that requires the full powers of the central nervous system (CNS). Sensation begins with the sensory receptors that actually interface with the world, and these receptors use energy from the environment to trigger electrochemical signals that can be transmitted to the brain—a process called sensory transduction. An understanding of transduction processes is crucial…

The Autonomic Nervous System

When we are awake, we are constantly aware of sensory input from our external environment, and we consciously plan how to react to it. When we are asleep, the nervous system has a variety of mechanisms to dissociate cortical function from sensory input and somatic motor output. Among these mechanisms are closing the eyes, blocking the transmission of sensory impulses to the cortex as they pass…

Synaptic Transmission in the Nervous System

After meticulous study of spinal reflexes, Charles Sher­rington N10-2 deduced that neurons somehow communicate information, one to the next, by a mechanism that is fundamentally different from the way that they conduct signals along their axons. Sherrington had merged his physiological conclusions with the anatomical observations ( Fig. 13-1 ) of his contemporary, the preeminent neuroanatomist Santiago Ramón y Cajal. N10-1 Ramón y Cajal had proposed…

Physiology of Neurons

Neurons receive, combine, transform, store, and send information Neurons have arguably the most complex job of any cell in the body. Consequently, they have an elaborate morphology and physiology. Each neuron is an intricate computing device. A single neuron may receive chemical input from tens of thousands of other neurons. It then combines these myriad signals into a much simpler set of electrical changes across its…

The Neuronal Microenvironment

Extracellular fluid in the brain provides a highly regulated environment for central nervous system neurons Everything that surrounds individual neurons can be considered part of the neuronal microenvironment. Technically, therefore, the neuronal microenvironment includes the extracellular fluid (ECF), capillaries, glial cells, and adjacent neurons. Although the term often is restricted to just the immediate ECF, the ECF cannot be meaningfully discussed in isolation because of its…

Organization of the Nervous System

The human brain is the most complex tissue in the body. It mediates behavior ranging from simple movements and sensory perception to learning, memory, and consciousness. It is the organ of the mind and accounts for the human capacity for invention, discovery, and language. Many of the brain's functions are poorly understood. In fact, the most prominent function of the human brain, its capacity to think,…

Cellular Physiology of Skeletal, Cardiac, and Smooth Muscle

The primary function of muscle is to generate force or movement in response to a physiological stimulus. The human body contains three fundamentally different types of muscle adapted to specialized functions. Skeletal muscle is responsible for the voluntary movement of bones that underlies locomotion and work production. Skeletal muscle also controls the breathing cycle of the lungs via contraction of the diaphragm and functions as a…

Synaptic Transmission and the Neuromuscular Junction

The ionic gradients that cells maintain across their membranes provide a form of stored electrochemical energy that cells can use for electrical signaling. The combination of a resting membrane potential of −60 to −90 mV and a diverse array of voltage-gated ion channels allows excitable cells to generate action potentials that propagate over long distances along the surface membrane of a single nerve axon or muscle fiber.…

Electrical Excitability and Action Potentials

Cellular communication in the nervous system is based on electrical and chemical signaling events that are mediated by ion channels. Certain types of cells, including neurons and myocytes, have a remarkable property called electrical excitability. In cells with this property, depolarization of the membrane above a certain threshold voltage triggers a spontaneous all-or-none response called an action potential. This action potential is a transient, regenerative electrical…

Electrophysiology of the Cell Membrane

Physics is concerned with the fundamental nature of matter and energy, whereas the goal of medical physiology is to understand the workings of living tissue. Despite their different perspectives, physics and physiology share common historical roots in the early investigations of charge and electricity. In the late 1700s, Luigi Galvani, a professor of anatomy in Bologna, Italy, used the leg muscles of a dissected frog to…

Transport of Solutes and Water

The cells of the human body live in a carefully regulated fluid environment. The fluid inside the cells, the intracellular fluid (ICF), occupies what is called the intracellular compartment, and the fluid outside the cells, the extracellular fluid (ECF), occupies the extracellular compartment. The barriers that separate these two compartments are the cell membranes. For life to be sustained, the body must rigorously maintain the volume…

Regulation of Gene Expression

In this chapter, we discuss general principles of gene structure and expression as well as mechanisms underlying the regulation of tissue-specific and inducible gene expression. We will see that proteins (transcription factors) control gene transcription by interacting with regulatory elements in DNA (e.g., promoters and enhancers). Because many transcription factors are effector molecules in signal-transduction pathways, these transcription factors can coordinately regulate gene expression in response…

Signal Transduction

Even single-cell organisms must respond to environmental challenges, which necessitated the development of signal-transduction mechanisms. The evolution of multicellular organisms required the evolution of cell-to-cell communication within the organism to coordinate between cells activities ranging from the induction of embryonic development to the integration of physiological responses. All cells receive and process information. External signals such as odorants, metabolites, ions, hormones, growth factors, and neurotransmitters can…

Functional Organization of the Cell

In the minds of many students, the discipline of physiology is linked inextricably to images from its past. This prejudice is not surprising because many experiments from physiology's proud history, such as those of Pavlov on his dogs, have transcended mere scientific renown and entered the realm of popular culture. Some might believe that the science of physiology devotes itself exclusively to the study of whole…

Foundations of Physiology

What is physiology? Physiology is the dynamic study of life. Physiology describes the “vital” functions of living organisms and their organs, cells, and molecules. For centuries, the discipline of physiology has been closely intertwined with medicine. Although physiology is not primarily concerned with structure—as is the case for anatomy, histology, and structural biology—structure and function are inextricably linked because the living structures perform the functions. For…

Appendix 5

Endothelium The endothelium is the single-cell-thick lining of all blood vessels that is in direct contact with the blood stream. In arteries and veins, the endothelium is the inner most surface of the vessel, overlying the deeper wall components, such as layers of smooth muscle (see eFig. A5.1 ). In the capillaries, endothelial cells and the basal lamina layer upon which they rest constitute the entire…