What is meant by double circulation. Briefly describe how the heart is adapted to keep blood flowing in a double circulation?
What is meant by double circulation?
Double circulation refers to the circulation of blood through the heart twice
during one complete cycle of blood flow through the body. In organisms with
double circulation, blood is pumped through the heart twice: once to the lungs
for oxygenation and then back to the heart before being pumped to the rest of
the body to supply oxygen and nutrients to various tissues and organs.
The concept of double
circulation is essential for maintaining an efficient oxygen and nutrient
supply in organisms with high-energy demands, such as mammals and birds. It
ensures that oxygenated blood, rich in oxygen from the lungs or respiratory
organs, is effectively separated from deoxygenated blood, low in oxygen and
high in carbon dioxide, returning from the body's tissues.
The human circulatory system
provides an excellent example of double circulation:
1. Pulmonary
Circulation: The right side of the heart is responsible for
pulmonary circulation. Deoxygenated blood from the body returns to the right
atrium of the heart and is then pumped into the right ventricle. From the right
ventricle, the blood is sent to the lungs through the pulmonary artery. In the
lungs, the blood picks up oxygen and releases carbon dioxide through gas
exchange. Oxygenated blood then returns to the left atrium of the heart through
the pulmonary veins.
2. Systemic
Circulation: The left side of the heart is responsible for
systemic circulation. Oxygenated blood from the left atrium is pumped into the
left ventricle. From the left ventricle, the blood is pumped out into the
aorta, which distributes the oxygen-rich blood to all body tissues and organs.
In the tissues, oxygen is used for cellular respiration, and deoxygenated
blood, now rich in carbon dioxide, returns to the right atrium of the heart
through the superior and inferior vena cava.
The double circulation in
humans and many other animals ensures that oxygenated and deoxygenated blood do
not mix within the heart, maximizing the efficiency of oxygen delivery to
tissues and organs. This separation of oxygenated and deoxygenated blood allows
for a higher rate of oxygen uptake in the lungs and better oxygen delivery to
active tissues, supporting the high metabolic demands of warm-blooded and
active organisms.
Briefly describe how the heart is adapted to keep blood flowing in a double circulation?
The heart is adapted to
maintain a continuous flow of blood in a double circulation system through
various structural and functional adaptations. These adaptations ensure
efficient oxygenation of blood in the lungs and the delivery of oxygenated
blood to the body's tissues. Here's how the heart achieves this:
1. Four-Chambered
Heart: The heart of mammals, including humans, is four-chambered,
consisting of two atria and two ventricles. The atria receive blood from
different parts of the body, while the ventricles pump blood out of the heart.
This separation of chambers allows for efficient coordination of blood flow and
prevents the mixing of oxygenated and deoxygenated blood.
2. Valves: The
heart is equipped with valves that ensure one-way blood flow. The
atrioventricular (AV) valves separate the atria from the ventricles, while the
semilunar valves guard the exits of the ventricles. These valves open and close
in response to pressure changes in the heart, ensuring that blood moves in the
correct direction and does not flow backward.
3. Strong
and Efficient Contractions: The heart muscles, especially the
ventricular muscles, are strong and capable of powerful contractions. The left
ventricle, in particular, has thick and muscular walls, as it needs to pump
oxygenated blood to the entire body against higher resistance. This muscular
strength allows the heart to efficiently pump blood to the lungs and body.
4. Cardiac
Conduction System: The heart has a specialized electrical
conduction system that coordinates the rhythmic contraction of its chambers.
This system ensures that the atria contract together first to fill the
ventricles with blood before the ventricles contract to pump blood to the lungs
and the rest of the body. This coordination is crucial in maintaining an
organized and synchronized flow of blood.
5. Coronary
Circulation: The heart itself requires a constant supply of
oxygen and nutrients to function effectively. The coronary arteries branch off
from the aorta and supply oxygenated blood to the heart muscle. This ensures
that the heart receives the required nutrients to maintain its pumping efficiency.
6. Regulation
by Autonomic Nervous System: The heart's rate and force of
contraction are regulated by the autonomic nervous system, specifically the
sympathetic and parasympathetic divisions. The sympathetic division increases
heart rate and contractility during periods of increased demand or stress,
while the parasympathetic division slows down the heart rate during rest or
relaxation.
These adaptations of the heart
ensure that blood is efficiently pumped to the lungs for oxygenation and then
distributed to all body tissues for the delivery of oxygen and nutrients. By
maintaining a double circulation system, the heart effectively meets the
metabolic demands of the body and ensures proper oxygen supply for the
continuous functioning of vital organs and tissues.