Basic Physiology for Anaesthetists

Описание

Section 1
Chapter
The basics
General organization of the body
Physiology is the study of the functions of the body,
its organs and the cells of which they are composed. It
is often said that physiology concerns itself with
maintaining the status quo or ‘homeostasis’ of bodily
processes. However, even normal physiology is not
constant, changing with development (childhood,
pregnancy and ageing) and environmental stresses
(altitude, diving and exercise). Many diseases and
their systemic effects are caused by a breakdown of
homeostasis.
Anaesthetists are required to adeptly manipulate
this complex physiology to facilitate surgical and critical care management. Therefore, before getting
started on the areas of physiology which are perhaps
of greater interest, it is worth revising some of the
basics – the next five chapters have been whittled
down to the absolute essentials.
How do the body’s organs develop?
The body is composed of some 100 trillion cells. All
life begins from a single totipotent embryonic cell,
which is capable of differentiating into any cell type.
This embryonic cell divides many times and, by the
end of the second week, gives rise to the three germ
cell layers:

Ectoderm, from which the nervous system and
epidermis develop.

Mesoderm, which gives rise to connective tissue,
blood cells, bone and marrow, cartilage, fat and
muscle.

Endoderm, which gives rise to the liver, pancreas
and bladder, as well as the epithelial lining of the
lungs and gastrointestinal (GI) tract.
Each organ is composed of many different tissues, all
working together to perform a particular function.
For example, the heart is composed of cardiac muscle,
Purkinje fibres and blood vessels, working together to
propel blood through the vasculature.
How do organs differ from body
systems?
The organs of the body are functionally organized
into 11 physiological ‘systems’:

Respiratory system, comprising the lungs and
airways.

Cardiovascular system, comprising the heart and
the blood vessels. The blood vessels are
subclassified into arteries, arterioles, capillaries,
venules and veins. The circulatory system is
partitioned into systemic and pulmonary circuits.

Nervous system, which comprises both neurons
(cells which electrically signal) and glial cells
(supporting cells). It can be further subclassified
in several ways:
– Anatomically, the nervous system is divided
into the central nervous system (CNS) consisting
of the brain and spinal cord, and the peripheral
nervous system (PNS) consisting of peripheral
nerves, ganglia and sensory receptors which
connect the limbs and organs to the brain.
– The PNS is functionally classified into an
afferent limb conveying sensory impulses to
the brain and an efferent limb conveying motor
impulses from the brain.
– The somatic nervous system refers to the
parts of the nervous system under conscious
control.
– The autonomic nervous system (ANS) regulates
the functions of the viscera. It is divided into
sympathetic and parasympathetic nervous
systems.
– The enteric nervous system is a semiautonomous system of nerves which controls
the digestive system.

Muscular system, comprising the three different
types of muscle: skeletal muscle, cardiac muscle
and smooth muscle.
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