4
Chapter 1
extracellular matrix is analogous to reinforced concrete. The
fi bers of the matrix, particularly collagen, which constitutes
one-third of all bodily proteins, are like the reinforcing iron
mesh or rods in the concrete. The carbohydrate-containing
protein molecules are analogous to the surrounding cement.
However, these latter molecules are not merely inert pack-
ing material, as in concrete, but function as adhesion/recog-
nition molecules between cells. Thus, they are links in the
communication between extracellular messenger molecules
and cells.
Organs and Organ Systems
Organs are composed of the four kinds of tissues arranged in
various proportions and patterns, such as sheets, tubes, lay-
ers, bundles, and strips. For example, the kidneys consist of
(1) a series of small tubes, each composed of a single layer of
epithelial cells; (2) blood vessels, whose walls contain varying
quantities of smooth muscle and connective tissue; (3) exten-
sions from nerve cells that end near the muscle and epithelial
cells; (4) a loose network of connective-tissue elements that
are interspersed throughout the kidneys and include the pro-
tective capsule that surrounds the organ.
Many organs are organized into small, similar subunits
often referred to as
functional units,
each performing the
function of the organ. For example, the kidneys’ functional
units, called nephrons, contain the small tubes mentioned in
the previous paragraph. The total production of urine by the
kidneys is the sum of the amounts produced by the two mil-
lion individual nephrons.
Finally we have the organ system, a collection of
organs that together perform an overall function. For exam-
ple, the kidneys, the urinary bladder, the tubes leading from
the kidneys to the bladder, and the tube leading from the
bladder to the exterior constitute the urinary system.
Table
1–1
lists the components and functions of the organ systems
in the body.
Table 1–1
Organ Systems of the Body
System
Major Organs or Tissues
Primary Functions
Circulatory
Heart, blood vessels, blood
Transport of blood throughout the body’s tissues
Digestive
Mouth, salivary glands, pharynx, esophagus, stomach,
large and small intestines, pancreas, liver, gallbladder
Digestion and absorption of nutrients and water;
elimination of wastes
Endocrine
All glands or organs secreting hormones: Pancreas,
testes, ovaries, hypothalamus, kidneys, pituitary,
thyroid, parathyroid, adrenal, intestinal, thymus, heart,
and pineal, and endocrine cells in other locations
Regulation and coordination of many activities in the
body, including growth, metabolism, reproduction, blood
pressure, electrolyte balance, and others
Immune
White blood cells, spleen, thymus
(also see: Lymphatic system)
Defense against pathogens
Integumentary
Skin
Protection against injury and dehydration; defense against
pathogens; regulation of body temperature
Lymphatic
Lymph vessels, lymph nodes
Collect extracellular fl uid for return to circulation;
participate in immune defenses
Musculoskeletal
Cartilage, bone, ligaments, tendons, joints, skeletal
muscle
Support, protection, and movement of the body;
production of blood cells
Nervous
Brain, spinal cord, peripheral nerves and ganglia,
sense organs
Regulation and coordination of many activities in the
body; detection of changes in the internal and external
environments; states of consciousness; learning; cognition
Reproductive
Male: Testes, penis, and associated ducts and glands
Female: Ovaries, fallopian tubes, uterus, vagina,
mammary glands
Production of sperm; transfer of sperm to female
Production of eggs; provision of a nutritive environment
for the developing embryo and fetus; nutrition of the infant
Respiratory
Nose, pharynx, larynx, trachea, bronchi, lungs
Exchange of carbon dioxide and oxygen; regulation of
hydrogen ion concentration
Urinary
Kidneys, ureters, bladder, urethra
Regulation of plasma composition through controlled
excretion of salts, water, and organic wastes
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