Download Lecture 4- Introduction to Circulatory System by Dr. Istiak Mahfuz

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The circulatory system, also called the cardiovascular system, is an organ system that
permits blood to circulate and transport nutrients (such as amino acids and electrolytes),
oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to
provide nourishment and help in fighting diseases, stabilize temperature and pH, and
maintain homeostasis. The study of the blood flow is called hemodynamics. The study of
the properties of the blood flow is called hemorheology.
Hemodynamics (AmE) or hæmodynamics (BrE), meaning literally "blood flow, motion
and equilibrium under the action of external forces", is the study of blood flow or the
circulation. It explains the physical laws that govern the flow of blood in the blood
vessels.
Hemorheology, also spelled haemorheology (from the Greek ‘αἷμα, haima "blood"
and rheology), or blood rheology, is the study of flow properties of blood and its
elements ofplasma and cells. Proper tissue perfusion can occur only when blood's
rheological properties are within certain levels. Alterations of these properties play
significant roles in disease processes.[1] Blood viscosity is determined by plasma
viscosity, hematocrit (volume fraction of red blood cell, which constitute 99.9% of the
cellular elements) and mechanical properties of red blood cells.
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As a living organism our body requires energy to work and stay alive. They must take in
nutrients and expel waste products. In the case of animal cells, this means that they
must take in carbohydrates and oxygen, and release carbon dioxide.
To do such vital functions for our survival animals need a circulatory system. if we didn’t
then we would not be able to survive since our organs would not receive the oxygen and
nutrients.
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Diffusion is the movement of particles (ions or molecules) from an area of higher
concentration to an area of lower concentration.
Osmosis is the diffusion of water from a hypotonic solution into a hypertonic solution
across and selectively permeable membrane.
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Cnidarians are only two cell layers thick and have a sac-like body plan consisting of a
body wall surrounding a central gastrovascular cavity, which is a structure found in some
animals that serves as the main site of both digestion and distribution of substances
throughout the body.
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For example, let's take a look at a very simple cnidarian, the hydra. Hydras are very small
aquatic animals which capture prey with their tentacles and then deposit it into their
gastrovascular cavity.
Food is digested right there in the cavity and the nutrients are distributed throughout
the animal. Notice that the gastrovascular cavity extends throughout the entire body,
including the tentacles so that every cell of the hydra has direct contact with either the
cavity or the water surrounding the animal.
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Gastrovascular cavities work well for aquatic animals with two cell layers, but cannot
support animals that have many layers of cells, especially those that don't live in the
water. For these more complex animals, the digestive and circulatory systems became
separated and specialized to perform the more complicated processes needed to
support many cell layers and life out of water.
There are two main types of circulatory systems: open circulatory systems and closed
circulatory systems.
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A closed system forces blood through vessels that extend throughout the body of the
organism.
Since the system is “closed” the blood never leaves the vessels.
This system is beneficial to larger organisms because the blood is kept at a higher
pressure which allows for more efficient circulation within the organism.
Blood is pumped through a system of vessels BUT is only partially contained in these
vessels.
Most of the time the blood is pumped through open cavities back to the heart.
This system is beneficial to arthropods and mollusks because the blood comes
into direct contact organs and tissues.
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A closed system forces blood through vessels that extend throughout the body of the
organism.
Since the system is “closed” the blood never leaves the vessels.
This system is beneficial to larger organisms because the blood is kept at a higher
pressure which allows for more efficient circulation within the organism.
Blood is pumped through a system of vessels BUT is only partially contained in these
vessels.
Most of the time the blood is pumped through open cavities back to the heart.
This system is beneficial to arthropods and mollusks because the blood comes
into direct contact organs and tissues.
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