Integration and Coordination

For the body to act as a unit, its parts must be integrated and coordinated. The nervous and endocrine systems control and adjust various organ functions from time to time, maintaining homeostasis.

The nervous (nercvus) system (fig. 1.13) consists of the brain, spinal cord, nerves, and sense organs. Nerve cells within these organs use electrochemical signals called nerve impulses (action potentials) to communicate with one another and with muscles and glands. Each impulse produces a relatively short-term effect on its target. Some nerve cells act as specialized sensory receptors that can detect changes occurring inside and outside the body. Other nerve cells receive the impulses transmitted from these sensory units and interpret and act on the information. Still other nerve cells carry impulses from the brain or spinal cord to muscles or glands, stimulating them to contract or to secrete products. Chapters 10 and 11 discuss the nervous system, and chapter 12 discusses sense organs.

Vertebra Azygos v

Aorta

Esophagus Right lung

Spinal cord

Spinal cord

Vertebra Azygos v

Aorta

Esophagus Right lung

Right atrium of heart

Right ventricle of heart

Visceral pleura

Pleural cavity -

Parietal pleura Sternum

Parietal Pleura

Left lung

Left ventricle of heart

Visceral pericardium Pericardial cavity Parietal pericardium Fibrous pericardium

Figure 1.9

A transverse section through the thorax reveals the serous membranes associated with the heart and lungs (superior view).

Right atrium of heart

Right ventricle of heart

Visceral pleura

Pleural cavity -

Parietal pleura Sternum

Plane of section

Mediastinum

Left lung

Left ventricle of heart

Visceral pericardium Pericardial cavity Parietal pericardium Fibrous pericardium

Plane of section

Mediastinum

Figure 1.9

A transverse section through the thorax reveals the serous membranes associated with the heart and lungs (superior view).

The endocrine (encdo-krin) system (fig. 1.13) includes all the glands that secrete chemical messengers, called hormones. Hormones, in turn, travel away from the glands in body fluids such as blood or tissue fluid. Usually a particular hormone affects only a particular group of cells, called its target tissue. The effect of a hormone is to alter the metabolism of the target tissue. Compared to nerve impulses, hormonal effects occur over a relatively long time period.

Organs of the endocrine system include the pituitary, thyroid, parathyroid, and adrenal glands, as well as the pancreas, ovaries, testes, pineal gland, and thymus gland. These are discussed further in chapter 13.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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