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Organization of
the human body
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Organization of the body in animals
Animals present some characteristics that distinguish them
from unicellular organisms and provide specific advantages:
• cells are specialized;
• there is hierarchical organization; cells are organized into
tissues which compose organs that work together in systems;
• cells communicate and cooperate.
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The human body
The human body has four types of tissues:
• epithelial tissue;
• connective tissue;
• muscle tissue;
• nervous tissue.
These tissues form organs which are organized into eleven
systems.
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Epithelial tissues
Epithelial tissues are formed by
one or more layers of cells of
regular shape that don’t contain
blood vessels.
They cover the surfaces of organs
and blood vessels.
epithelium
The epithelium rests on a
basement membrane and its cells
are continuously replaced.
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Functions of epithelial tissues
Epithelial tissues have different functions:
• protection and covering;
• controlled exchange of substances;
• secretion (endocrine and exocrine glands);
• sensory reception (receptors).
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Connective tissues
Connective tissues fill and connect different parts of the body.
They are formed by cells dispersed in a solid, semi-solid or fluid
matrix.
They are divided into connective tissues – proper and special
connective tissues.
Proper connective tissues include:
• loose connective tissue;
• dense connective tissue;
• fat tissue.
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Special connective tissues
Type of tissue
Functions
Matrix
bone tissue
protection, support, storage of
calcium and phosphorus
solid matrix
cartilage
protection of joints in response to
friction and tension
resistant, strong and
flexible matrix
blood
supply oxygen and nutrients to
tissues, waste removal,
immunological function, regulation
of body temperature
fluid matrix (plasma)
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Muscle tissues
Muscle tissues are formed by elongated cells, called fibers,
that can contract and relax, facilitating movement.
There are different types of muscle tissues:
• skeletal or striated muscle which contracts voluntarily;
• smooth muscle which contracts involuntarily;
• cardiac muscle (in the heart) which contracts involuntarily.
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Nervous tissue
Nervous tissue is formed by
neurons and glial cells.
dendrites
Neurons are cells that present:
cell body
• a cell body, containing the
nucleus;
• dendrites, specialized in the
reception of stimuli ;
• an axon, that transports nervous
signals from the cell to other
neurons or organs.
axon
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Integumentary system
The integumentary system covers and protects the body.
It consists of skin and accessory organs (glands, nails, hair,
sensory receptors and free nerve endings).
epidermis
The skin is formed by two main
layers:
• epidermis;
• dermis.
Below the dermis is the
hypodermis – a layer of fat
tissue.
hypodermis
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dermis
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Skeletal system
The skeletal system supports and protects the internal
organs, supports muscles, produces (in the red bone
marrow) blood cells, and is involved in calcium equilibrium.
axial
skeleton
The skeleton is divided into the:
• axial skeleton (skull, rib cage,
vertebral column);
• appendicular skeleton (upper and
lower limbs, shoulder girdle, pelvic
girdle).
appendicular
skeleton
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Skeleton and muscles
The skeleton provides rigid support for mucles, with which it
forms an integrated system.
Bones act as levers, producing ordered movements with help
from coordinated action of different muscles.
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Homeostasis
Homeostasis is the body’s ability to maintain a stable inner
environment even when external conditions change.
To maintain homeostasis, cells communicate via signal
molecules.
There are two mechanisms used to maintain homeostasis:
• positive feedback;
• negative feedback.
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Thermoregulation
Body temperature control (thermoregulation) is an
important part of homeostasis.
Humans are endothermic, with a body temperature around
37 °C. Thermoregulation occurs by controlling the
production of internal heat and the exchange of heat
between the body and the environment (perspiration,
vasoconstriction, vasodilation, muscle activities).
The control center of body temperature is the
hypothalamus.
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Stem cells and cell differentiation
totipotent
pluripotent
Stem cells are
undifferentiated cells that can
proliferate, generating copies
of themselves or specialized
cells.
multipotent
Stem cells can be divided into:
•
•
•
•
unipotent
© Zanichelli editore 2016
totipotent cells;
pluripotent cells;
multipotent cells;
unipotent cells.
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Regulation of cell growth and death
The growth and regeneration of cells is regulated by several
signal molecules. When cells proliferate without control, it is
possible to develop hyperplasia or tumors.
Cell death can occur through two mechanisms:
• apoptosis - a controlled death;
• necrosis - caused by trauma.
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