Download unit 4: the circulatory and excretory systems

UNIT 4: THE CIRCULATORY AND EXCRETORY SYSTEMS.The circulatory system.It is the way the internal milieu is renewed, that is the medium all the cells live. This
medium gives the cells all the nutrients that they need and the cells also excrete the
waste products released during metabolism through it.
The internal milieu is made up of the interstitial plasma, a fluid found in the spaces
between cells. The interstitial plasma is renewed thanks to the circulatory system.
We can say that the circulatory system is a way of transporting substances and heat in
our bodies.
Components of the circulatory system.-
A liquid: the blood
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A group of tubes: the blood vessels, which bloods run through.
There are three types of blood vessels: arteries, veins and capillaries.
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A bomb that moves the blood through the blood vessels: the heart.
THE BLOOD.The blood is a tissue, the only tissue that is liquid. It is a viscous fluid with a salty taste.
The human body contains around 5,5 liters of blood.
Composition of blood:
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Blood plasma: is a yellowish substance made of water containing various
dissolved molecules: mineral salts, nutrients, waste products (urea, uric acids,
carbon dioxide…), etc.
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Blood cells: there are three types of blood cells: erythrocytes, leukocytes and
trombocytes.
. Erythrocytes or red blood cells: they are disk-shaped and have no nucleus.
They contain hemoglobin, a red pigment responsible for the blood’s red colour
which transports oxygen from the alveoli of the lungs to the rest of the body’s
cells. There are around 5 million per mm3 of blood.
. Leukocytes or white blood cells: There are different types (neutrophils,
eosinophils, basophils, lymphocytes and monocytes) and all of them help to
protect the body from infection. There are around 7000 per mm3 of blood.
. Trombocytes or platelets: They aren’t true cells, they are cell fragments. They
contain substances that allow the blood to clot, preventing hemorrhages. There
are around 300000 per mm3 of blood.
The functions of blood.-
It transports nutrients and oxygen to all cells.
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It transports hormones, which play an essential role in controlling bodily
functions.
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It collects waste products released during cell metabolism, like urea, uric acid
and carbon dioxide.
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It helps to regulate temperature. The blood works like a central heating system,
moving body heat from the warm areas to the cooler ones.
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It plays an essential role in protecting the body from infection.
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It takes part in the process of blood coagulation or blood clotting. It is a
mechanism to prevent blood loss when a blood vessel is broken.
The blood group systems:
People have different types of blood; it depends on different proteins located in the
membranes of red blood cells.
There are two main blood group systems:
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The ABO system: this is made of four blood types: A, B, AB and O.
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The rh system; it can be positive or negative.
In a transfusion we need take into account both systems.
THE BLOOD VESSELS.There are three types of blood vessel:
1) Arteries:
They carry the blood away from the heart. As they get further away from the
heart, they gradually branch out into narrower vessels leading to the different
organs. These vessels then divide into even smaller ones called arterioles.
2) Capillaries:
These are microscopic blood vessels which branch out from the arterioles and
are found in every body tissue.
Their walls are formed by a single layer of flat cells which allow substances to
be exchanged quickly between the blood and the cells.
3) Veins:
Capillaries come together to form thicker venules. The venules then form veins.
These veins take blood back to the heart.
There are valves inside the veins which allow blood to flow towards the heart
but not in the opposite direction.
Each organ has an artery that provides blood and a vein that takes blood away.
The two blood vessels are usually named with that organ.
THE HEART.It is the organ that pumps the blood inside of the blood vessels.
The heart is made of a powerful wall of muscular tissue called the myocardium. The
inside is covered by a thin layer of cells, the endocardium, and the outside is covered by
a double membrane, the pericardium.
Structure:
The heart is divided into two halves, right and left, by an internal wall. The two halves
are not connected in any way.
Each half is then divided again into the upper chamber, the atrium, and the lower
chamber, the ventricle. The heart therefore has two atria and two ventricles. Between
the atrium and the ventricle on each side there is a valve: the atrioventricular valve. The
valve between the right atrium and ventricle is called the tricuspid valve, and the one
between the let atrium and ventricle is called the bicuspid or mitral valve.
The blood enters the heart through the atrium by veins (two venaes cavae on the right
and four pulmonary veins on the left) and leaves the heart from the ventricles through
arteries ( the pulmonary artery on the right and the aorta on the left). At the beginning of
each of these arteries are the sigmoid valves, made of three membranes, which prevent
blood from flowing back to the heart after it has left.
Functioning of heart:
The heart is like a pump that collects blood from the veins and then pumps it out into
the arteries.
This movement is called the heartbeat. Each heartbeat has three phases: atrial systole,
ventricular systole and diastole that form the cardiac cycle.
Characteristic of the circulatory system.The human circulatory system is closed, double and complete.
It is closed because blood always flows inside the blood vessels.
It is complete because there isn’t a mix of blood rich in oxygen and blood poor in
oxygen.
It is double because blood passes two times through the heart in a complete run, there
are two circuits: the systemic circulation and the pulmonary circulation.
Systemic circulation:
It carries the blood to cells of the organs except the lungs. It provides cells with the
oxygen and nutrients they need, and takes away waste products.
Pulmonary circulation:
It carries the blood to the lungs. This is where gas exchange takes place.
THE LYMPHATIC SYSTEM.It is a complementary system of the circulatory system.
Some of the blood plasma filters out of the capillaries into the body tissues. This fluid is
the interstitial plasma. The lymphatic system collect excess interstitial plasma made by
the lymph and returns it to the blood.
This system is made of the lymph, lymph vessels and lymph nodes. There are two types
of lymph vessels: lymph capillaries and lymph veins.
Lymph capillaries are blind. This mean that they are closed at one end and interstitial
plasma filters into them. This plasma is then known as lymph plasma. This travels along
the lymph veins to the blood stream.
The lymph nodes are located in various parts of the route followed by some lymph
vessels. They release lymphocytes into the lymph plasma.
Lymphocytes and lymph plasma combine to form lymph.
Functions of the lymphatic system.-
It collects the excess of interstitial plasma and returns it to the blood.
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It helps to protect the body from infection.
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It collects the products of fat digestion from the small intestine.
THE EXCRETORY SYSTEM.The excretory system is made of the urinary system and a number of other organs and
systems that contribute to the excretion of waste products. They are:
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Respiratory system: It removes carbon dioxide from the blood and expels it from
the body.
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Sweat glands: they are found in the skin, and they produce sweat. The main
function is the elimination of excess heat by evaporation of water. But some
excretory substances are also expelled from the body in sweat.
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Liver: It eliminates products resulting from the breakdown of hemoglobin from
old red blood cells. These products are added to bili, which drains into the
intestine. From here, it is expelled from the body. It also eliminates a small
amount of cholesterol and some toxic substances.
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Urinary system: It is the most important part of the excretory system. It
eliminates excretory products like urea or uric acid in the form of urine.
It is made of a pair of kidneys, and the urinary tracts made of ureters, the urinary
bladder and the urethra.
A kidney is made up of the renal cortex, the renal medulla and the renal pelvis.
Urine is formed in the cortex and medulla, and it contains excretory substances
and drains into the renal pelvis.
Each kidney is formed of over a million nephrons, which filter the blood and
produce urine.
The urinary tract collects urine from the kidneys and lead to the outside of the
body. It includes:
. Ureters: two narrow tubes that connect the renal pelvis of the kidney to the
urinary bladder, an elastic sac where urine collects before it is expelled from the
body.
. Urethra: this duct leads the urine outside the body.
The urethra is different in men and women. In men is a duct common to the
urinary system and the reproductive system. This means that semen passes
through it as well as urine, but not at the same time. In women, the urethra is
separate from the reproductive system.
The function of the urinary system is the production of urine; a liquid obtained
from the filtration the blood and made up of water, and different excretory
products, mainly urea and uric acid.
Urine is produced in two phases: glomerular filtration and tubular reabsorption.