|
Anatomy is the science of the structure of living organisms. To
fully understand a structure, one must also understand its function
in the animal (physiology). Therefore, anatomy is almost inseparable
from physiology, which can be described as functional anatomy.
A vertebrate animal’s structures include:
Integument
The integument is the skin and associated glands and structures.
The integument separates the animal from its environment and protects
it from trauma and pathogens. In most cases, it is relatively impervious
to harmful substances. Amphibians, however, ‘breathe’
through their skin in part, and it is permeable to a large array
of harmful chemicals; thus great care must be taken in their housing.
Musculoskeletal System
Locomotion (movement) is possible because of the musculoskeletal
system, which is comprised of skeleton (bones) and muscles. Locomotion
occurs when muscles contract against the articulated (jointed) skeleton.
Nervous System
The animal coordinates its activities by means of its nervous system.
The brain and the spinal cord are continuous through an opening
at the base of the skull, comprising the central nervous system
(CNS). The CNS is in contact with other parts of the body through
the nerves (peripheral nervous system).
The nervous system is divided into the somatic system (voluntary
control over skeletal muscle), and the autonomic system (involuntary
control over cardiac muscle, smooth muscle and glands). The autonomic
system is divided into the sympathetic and the parasympathetic nervous
systems, both of which innervate many organs. In general, the sympathetic
nervous system is activated in the ‘fight or flight’ response,
whereas the parasympathetic system operates when the animal is relaxed.
The sensory organs (those of vision, hearing, taste/smell, etc,)
are typically complex and fascinating in both structure and function.
Endocrine System
In addition to the action of the nervous system, many fundamental
body functions are controlled by hormones secreted by the endocrine
glands. At the base of the brain lies the master gland, the pituitary.
It secretes a number of hormones, including those that govern the
sex organs, and thyroid and adrenal glands. These, in turn, control
basic physiological functions such as water/salt balance, metabolic
rate, reproduction, growth, and development.
Circulatory System
The circulatory system consists of the heart, and venous and arterial
systems. It is the means by which blood is moved through the body.
Vertebrate animals have closed blood circulatory systems wherein
blood vessels connect the heart to all areas of the body. The heart
pumps blood to the respiratory system, where it picks up oxygen
and releases carbon dioxide. Blood also carries nutrients from the
digestive tract and liver, and delivers toxins and nutrients to
the liver for processing, to the kidneys for filtration, and so
on.
Oxygenated blood is ultimately pumped to tiny, thin-walled capillaries,
wherein the blood gives up its oxygen and nutrients to the tissues
and in turn takes from them carbon dioxide and other waste products.
However, vertebrate classes have a range of circulatory structures.
Fish have a primitive circulatory system. Blood is pumped (by a
relatively inefficient two-chambered heart) to the gills (where
it picks up oxygen and releases carbon dioxide) and directly on
to the body tissues. The flow of blood through the system is somewhat
sluggish.
Amphibians have a more developed circulatory system wherein the
blood is pumped to the lungs and skin separately from the systemic
system; the heart is divided into two atria and one partially divided
ventricle, producing a double route. This system creates a higher
blood pressure and consequently, there is a more efficient flow
of blood than is seen in fish.
Reptiles have three-chambered hearts. Oxygenated blood stays on
the left side of the ventricle, and deoxygenated blood stays on
the right side.
Birds and mammals have a fully divided circulatory system; the mammal’s
heart is divided into two halves. The right half pumps blood to
the lungs, where it picks up oxygen (pulmonary circulation) and
returns it to the heart. The left half then pumps the oxygenated
blood to the body tissues (systemic circulation). Like mammals,
birds have four-chambered hearts, but they are proportionately larger
than the hearts of other animals. The bird’s circulatory system
functions at high speed - while the human heart may beat 160 times
per minute when the human is running, the heart of a small bird
beats many times more per minute, depending on species and level
of activity.
Respiratory System
Gas exchange in vertebrates takes place in the respiratory system.
In lungs or gills, needed oxygen is collected from the environment,
and waste carbon dioxide is released. The gases are exchanged between
the respiratory organs and the rest of the body by blood, via the
cardiovascular system. The respiratory system is also involved in
the regulation of the acid-base balance.
Respiration in air-breathing animals is a two-phase process. In
the first phase, air is brought into the lungs through inhalation.
The oxygen moves from the lungs to the heart via blood. The heart
pumps the oxygen-rich blood to all parts of the body.
Cells use the oxygen to produce energy (cellular respiration). The
waste product of cellular respiration, carbon dioxide, diffuses
from the cells to the bloodstream. This blood flows to the heart
through veins, and thence to the lungs; carbon dioxide is then expelled
from the body by exhalation, and the cycle is complete.
The respiratory structures of organisms vary, but reptiles, mature
amphibians and all birds and mammals breathe air with lungs (although
most amphibians also respire through their skin).
Digestive and Excretory Systems
Digestive systems of various animals differ - for example, while
all animals have mouths, some have teeth and others do not. Regardless,
food is ingested and digested. In the stomach, gastric and intestinal
juices break down (digest) the food; the mixture of food and secretions
is called chyme. Chyme is pushed down the alimentary canal by rhythmic
contractions of the muscles (peristalsis). Nutrients in chyme are
absorbed mainly in the small intestine.
Unabsorbed nutrients (and waste products and secretions from the
liver) move to the large intestine, and are then expelled as feces.
The bloodstream moves water (and water soluble substances) from
the intestines to the kidneys, where wastes are removed. Most of
the water and salts are returned to the body, but waste products,
other salts and excess water are excreted.
Reproductive System
In vertebrate animals, reproduction involves the union of the female
ovum (made in the ovary) and male sperm (made in the testis).
Mammals
Fertilization is internal; the male deposits sperm into the female’s
vaginal opening. The fertilized egg develops in the womb of the
female, and she gives birth to living young.
Birds
Fertilization is internal; the male deposits sperm into the female’s
cloaca. The fertilized egg is expelled from the body and is incubated
by the parent(s) in the nest.
Reptiles
Fertilization is internal. Some reptiles are oviparous; they
lay eggs that are deposited in a ‘nest’ and left to
develop and hatch without parental attention. Some snake and lizard
species are viviparous; they give birth to live young.
Amphibians
Depending on the species, amphibians may employ internal or external
fertilization.
Most amphibians lay their eggs in water; the young develop and
mature without parental assistance. A few amphibians, however,
guard their eggs until they hatch. The Australian Rheobatrachus
silus swallows its eggs; the eggs incubate in the frog’s
stomach, and the young crawl out through the parent’s mouth.
The Surinam toad (Pipa pipa) carries its eggs in pockets of skin
on its back; the young hatch three months later.
Fish
Depending on species, fertilization may be external or internal,
and parental care ranges from nil to elaborate.
To learn more about general anatomy or the anatomies of amphibians,
birds, mammals and reptiles, choose an item from the right-hand
menu.
|
