Shela S.
Ambas February 16, 2019
BSBA – NATSCI 1 Mr. Jho Jurado
1. Flowering Plants
Non Flowering Plants
2. Cardiovascular system of Animals
Blood Circulation - The circulatory system is the continuous system of tubes through which the
blood is pumped around the body. It supplies the tissues with their requirements and removes
waste products. In mammals and birds the blood circulates through two separate systems - the
first from the heart to the lungs and back to the heart again (the pulmonary circulation) and the
second from the heart to the head and body and back again (the systemic circulation) (see
diagram 8.12). The tubes through which the blood flows are the arteries, capillaries and veins.
The heart pumps blood into arteries that carry it away from the heart. The arteries divide into
very thin vessels called capillaries that form a network between the cells of the body. The
capillaries then join up again to make veins that return the blood to the heart.
Arteries - carry blood away from the heart. They have thick elastic walls that stretch and can
withstand the surges of high pressure blood caused by the heartbeat (the pulse, see later). The
arteries divide into smaller vessels called arterioles. The hole down the center of the artery is
called the lumen. There are three layers of tissue in the walls of an artery. It is lined with
squamous epithelial cells. The middle layer is the thickest layer. It made of elastic fibers and
smooth muscle to make it stretchy. The outer fibrous layer protects the artery (see diagram 8.13).
The pulse is only felt in arteries.
The Pulse - The pulse is the spurt of high pressure blood that passes along the aorta and arteries
when the left ventricle contracts. As the pulse of blood passes along an artery the elastic walls
stretch. When the pulse has passed the walls contract and this helps push the blood along. The
pulse is easily felt at certain places where an artery passes near the surface of the body. It is
strongest near the heart and becomes weaker as it travels away from the heart. The pulse
disappears altogether in the capillaries.
Capillaries - Arterioles divide repeatedly to form a network penetrating between the cells of all
tissues of the body. These small vessels are called capillaries. The walls are only one cell thick
and some capillaries are so narrow that red blood cells have to fold up to pass through them.
Capillaries form networks in tissues called capillary beds. The capillary networks in capillary
beds are so dense that no living cell is far from its supply of oxygen and food (see diagram 8.14).
The Formation Of Tissue Fluid And Lymph- The thin walls of capillaries allow water, some
white blood cells and many dissolved substances to diffuse through them. These form a clear
fluid called tissue fluid (or extracellular fluid or interstitial fluid) that surrounds the cells of
the tissues. The tissue fluid allows oxygen and nutrients to pass from the blood to the cells and
carbon dioxide and other waste products to be removed from the tissues (see diagram 8.15).
Veins - Capillaries unite to form larger vessels called venules that join to form veins. Veins
return blood to the heart and since blood that flows in veins has already passed through the fine
capillaries, it flows slowly with no pulse and at low pressure. For this reason veins have thinner
walls than arteries although there have the same three layers in them as arteries (see diagram
8.16). As there is no pulse in veins, the blood is squeezed along them by the contraction of the
skeletal muscles that lay alongside them.
Veins also have valves in them that prevent blood flowing backwards (see diagram 8.17a and b).
Regulation Of Blood Flow - The flow of blood along arteries, arterioles and capillaries is not
constant but can be controlled depending upon the requirements of the body. For example more
blood is directed to the skeletal muscles, brain or digestive system when they are active.
Regulation of the blood flow to the arterioles of the skin is also important in controlling body
temperature. The size of the vessels is adjusted by the contraction or relaxation of smooth muscle
fibres in their walls.
Oedema And Fluid Loss - Oedema is the swelling of the tissues due to the accumulation of
tissue fluid. This may occur because the tissue fluid is prevented from returning to the
bloodstream and accumulates in the tissues. This may be caused by physical inactivity (e.g. long
car or plane trips in humans) or because of imbalances in the proteins in the blood. This is what
causes the “pot-belly” of the malnourished child or worm-infested puppy.
Loss of body fluid can be caused not only by drinking insufficient liquid but also through
diarrhea and vomiting or sudden loss of blood due to haemorrhage. The effect is to reduce the
volume of the blood which decreases the blood pressure. This could be dangerous because the
supply of adequate blood to the brain depends upon maintaining the blood pressure at a constant
level.
To compensate for the loss of fluid various mechanisms come into play. First of all the blood
vessels contract in order to try and maintain the pressure. Then, since the loss of fluid tends to
make the blood more concentrated and increases its osmotic pressure, fluid is drawn into the
blood from the tissues by osmosis
The Spleen - The spleen is situated near the stomach. It has a rich blood supply and acts as a
reservoir of red blood cells. When there is a sudden loss of blood, as happens when a
haemorrhage occurs, the spleen contracts to release large numbers of red blood cells into the
circulation. The spleen also destroys old red cells and makes new lymphocytes but it is not an
essential organ because its removal in adult life seems to cause few problems.
Important Blood Vessels Of The Systemic (Body) Circulation - Blood is pumped out into the
body via the main artery, the aorta. This takes the blood to the head, the limbs and all the body
organs. After passing through a network of fine capillaries, the blood is returned to the heart in
the largest vein, the vena cava (see diagrams 8.8, 8.12, 8.18 and 8.19).
Arteries and veins to and from many organs often run alongside each other and have the same
name e.g. the renal artery and vein serve the kidney, the femoral artery and vein serve the
hind limbs and the subclavian artery and vein serve the forelimbs. However, blood to the head
passes along the carotid artery and returns to the cranial vena cava via the jugular vein.
One variation on this arrangement is found in the blood vessels that serve the digestive tract. A
variety of arteries take blood from the aorta to the intestines but blood from the intestines is
carried by the hepatic portal vein to the liver where the digested food can be processed (see
diagram 8.12). This vessel is unlike others in that it transports blood from one organ to another
rather precious Betine Diagram 8.18 - The main arteries and veins of the horse
Blood Pressure - The blood pressure is the pressure of the blood against the walls of the main
arteries. The pressure is highest as the pulse produced by the contraction of the left ventricle
passes along the artery. This is known as the systolic pressure. Pressure is much lower between
pulses. This is known as the diastolic pressure. Blood pressure is measured in millimetres of
mercury. A blood pressure that is higher than expected is known as hypertension while a
pressure lower than expected is known as hypotension.
3. Adult heart Circulation
There are three main types of blood vessels:
1. Arteries. They begin with the aorta, the large artery leaving the heart. Arteries carry
oxygen-rich blood away from the heart to all of the body's tissues. They branch several
times, becoming smaller and smaller as they carry blood farther from the heart..
2. Capillaries - These are small, thin blood vessels that connect the arteries and the veins.
Their thin walls allow oxygen, nutrients, carbon dioxide, and other waste products to pass to
and from our organ's cells.
3. Veins - These are blood vessels that take blood back to the heart; this blood lacks oxygen
(oxygen-poor) and is rich in waste products that are to be excreted or removed from the
body. Veins become larger and larger as they get closer to the heart. The superior vena cava
is the large vein that brings blood from the head and arms to the heart, and the inferior vena
cava brings blood from the abdomen and legs into the heart
