1. THE HUMAN BODY
NUTRITION
Nutrition is the taking of nutrients, organic substances and mineral ions, the
absorption and the assimilation of them.
There’re 4 apparatus involved in nutrition:
Digestive: It transforms food into nutrients that can be used by the body
and absorbs the nutrients through blood. Also it is in charge of producing
faeces. We find that this occurs in the alimentary canal or gut that begins
on the mouth and end on the anus.
Respiratory: It is involved in gas exchange.
Excretory: It expels substances toxic materials, waste products from
metabolism and substances in excess of requirements.
Circulatory: Transport all these substances around the body.
DIGESTIVE.
Food passes to cells by mechanical and chemical process. This process begins in
the mouth.
Mouth. In the mouth ingestion begins when food enters the alimentary canal
and it is converted into a bolus by a process called mastication in which food
is cut and mixed with saliva. 3 things are involved in mastication:
o Teeth, they carry out physical digestion cutting the food. Adults have
32 teeth; meanwhile children have 20 because they don’t have
molars.
These teeth are formed by:
 Enamel: the hardest tissue in the body. It is made up of
calcium salts and it can’t be renew. That is way tooth care
is so important.
 Dentine: forms the major part of the tooth. It is harder
than bone and it is also made of calcium salts deposited in
a framework of collagen fibers that contain canals that are
extended to the pulp cavity.
 Cement: similar to membrane but without canals.

2. 

Periodontal membrane: bundles of collagen fibers, joining
the cement covering to the jawbone so that the tooth is
hold firmly.
Pulp cavity: it is in the inside of the tooth and it contains
tooth-producing cells, blood vessels and nerve endings so
that it detects pain.
As teeth are very important for mastication they should be treated
correctly. We find that when we eat food with lots of sugar, bacteria
change this sugar into acids that remove calcium and phosphate from
the enamel. Like this bacteria can enter the tooth infecting the pulp
cavity.
This can be avoided by:



Eating food with little sugar.
A regular and effective brushing of teeth
Finishing a meal with fruit followed by rinsing with
water.
o The tongue, it is a muscle that helps to swallow, taste buds and that
mixes the pieces of food with saliva.
o Saliva, saliva starts chemical nutrition. It is composed by a
biocatalyzercalled amylase which breaks starch into glucose using
hydrolysis reactions (Reactions that work with water) and
hydrogencarbonate that creates an Alkaline condition so that amylase
can work. Also this saliva lubricates the food with mucus. This saliva
is produced in the salivary glands and in the mouth we have 3 pairs.
Pharynx, a simple tool lubricated so that food goes down. In this pharynx
there is a muscle called epiglottis that is forced across the top of the trachea
whenever food is swallowed. This is done so that food doesn’t go through
the trachea and we find that it is an involuntary reflex, so we can say that
swallowing is partially voluntary and partially involuntary.

3. Oesophagus, here food continues travelling to the stomach through the
contraction of the oesophagus in a movement called peristalsis. So we can
say that the pharynx and the oesophagus carry out mechanical nutrition.
Stomach, in the stomach digestion begins when the bolus enters through the
cardiac splinter. This bolus is processed mechanically and chemically.
o Mechanic digestion occurs because the bolus mixes with enzymes
through the movement of the stomach.
o Chemical digestion occurs because proteins in the bolus are broken
into more simple elements called Peptides. This occurs thanks to an
enzyme called pepsin.
We find that pepsin needs an acidic ph to work. These acidic ph is
created by the hidrocolic acid giving the stomach a ph of 2.
As the ph is very low the walls of the stomach have to be covered
by mucus so that the acid doesn’t damage the stomach. As
amylase needs an alkaline ph to work, here the digestion of starch
is stopped.
All these produces a creamy liquid called chime that goes out of the
stomach through the pyloric splinter.
The small intestine. In the small intestine digestion finish and absorption begins.
This organ consists of the following parts:
Duodenum, this part is in charge of chemical digestion. The
duodenum has a ph of 8 for permitting different enzymes to work.
 Amylase, as food is not enough time in the mouth not all the
starch is transformed into maltose. So this process finis in the
small intestine. In the small intestine amylase is produced by
the pancreas and is inside the pancreatic juice.
 Protease breaks the peptides obtained in the stomach into
amino acids.
 Lipase breaks lipids into fatty acids and glycerol. However we
find that here we have a problem because all these reactions
take place with water but lipids DO NOT react with water.
For this we use the bile that emulsifies lipids dividing lipids
into small droplets to help Lipase in transforming them into
fatty acids and glycerol. This bile is produced by the liver but
it is stored on the Gall Bladder.

4. All these enzymes are in the pancreatic juice that also has
hydrogencarbonate to neutralize the ph of the chime that comes from the
stomach. This pancreatic juice is done by the pancreas.
Also there is an enzyme produced by the cells in the intestine wall
called maltase. This maltase breaks maltose into glucose.
The jejunum and the ileum. However the main function of the small
intestine is not digestion but absorption and this function is carried on
these parts. Absorption consists in the passing of digested food
molecules across the lining of the gut into the blood.
We find that in this part amino acids and glycerol + fatty acids
pass to the blood and monosaccharides pass to the lymphase. That is
the reason why the small intestine is surrounded of blood and why
after a meal we feel a bit dizzy because blood concentrate near the
small intestine.
For this purpose we find that the small intestine is very long (7m)
for having enough time to absorb all substances. Also we find that the
small intestine is covered by lining. This lining is folded and each of
the folds is called vilus (singular) or villi (plural). The lining is folded
for increasing the surface of absorption and for making it easier the
epithelium of the villi has tiny hairs for absorption called microvillus.
Pancreas, gland that produces pancreatic juice and hormones such as
insulin.
Liver, the liver apart of creating bile and of creating and alkaline ph,
it is very because:
 When food molecules pass to the blood the liver controls that
these molecules go to the place where they need to be used,
when they are needed and in the right amounts.
 Also it stores glycogen and can interconverse glycogen and
glucose so that the glucose concentration remains constant.
 Also it is responsible of the interconversion of amino acids.
This means that aminos in the structure of amino acids can be
transferred and moved to other places. This is done because
an excess of aminos is toxic. So the liver takes some aminos
and expels them through urine or sweat.
 Of the removal of red blood cells.

5. 
Of the breakdown of alcohol and toxins in a process called
detoxification. The liver does this to protect other tissues but
in this process the liver harms itself. Alcohol in high
concentration can seriously harm the liver.
Large intestine. The large intestine is formed by the:
Colon -Ascendent.
-Transversal
-Descendent.
o Rectum
o Anus.
The substances that reach the large intestine are those that couldn’t be
absorbed.
However water, vitamins and mineral salts are useful in the body so they
have a second change to pass to the bloodstream in a process called
reabsorption.
What is left creates the faeces. These faeces contain fiber that is
undigested cellulose that help the movement of faeces through the large intestine
and that also helps cleaning the intestine.
All these substances that are not needed by the body are expelled through
the anal splinter which is in charge of defecation.
RESPIRATION:
Respiration is done because we need to take O2 for cell respiration and expel
Co2 that results from cell respiration.
Glucose + oxygen = energy + carbon dioxide + water
This gas exchange occurs on the gas exchange surface. This surface has to be:
o Thin, because gases have a shorter distance over which to diffuse.
o Large surface area, so that many molecules of gas can diffuse at the same
time.
o Moist, because cell die if not kept moist.
o Well ventilated, so that the concentration gradients for oxygen and
carbon dioxide are kept up by a regular fresh supply of air
o Close to a blood supply: So that gases can be carried from and to the
cells.

6. In humans air can enter through the nose or through the mouth. We find that
is better that the air enters through the nose because in the nose the air is warm
up and also it is filtered so that particles of dust don’t reach the lungs.
Air continues its travel to the lungs through the pharynx that is a tube
common to digestion and to respiration.
Then the air continues through the larynx, that is where the vocal cords are.
These vocal cords are a set of membranes that can vibrate when air passes
through them creating different sounds.
Also we find with the trachea another tube with C-shape and that is covered
with cartilage so that it doesn’t collapse during inhalation. These trachea is
covered with ciliated cells that move and push mucus with trapped microbes and
dust away from the lungs.
This trachea divides in 2 bronchus that divide into several bronchioles and
we find that these bronchioles end in some sacs called alveolus. These alveolus
are the gas exchange surface where gas exchange takes place. They are
surrounded by blood vessels forming a thin and humid surface for allowing gas
exchange and for taking the oxygen to the cells.
The action of breathing.
In the action of breathing the diaphragm, the intercostals muscles and pleural
membrane.
When we breathe in air the external intercostals muscles contract and pull the rib
cage upwards. Also the diaphragm muscles contract and move downwards and the
pleural membrane reduce the friction during breathing. All these increase the volume of
the thoracic cavity to reduce the pressure of the lungs. This is done because air moves
from places where there is a higher pressure to places with a lower pressure so air goes
inside the lungs.
For breathing out the muscles return to their normal shape. This makes the lungs
to have the same pressure as the atmosphere forcing the air to go out.
Breathing and exercise.
During exercise muscles work hard so they need to release more energy through
cellular respiration. This is the reason why:
The breathing rate is increased.
The tidal volume is also increased. This means that more air is breath in per
breath.

7. Asthma.
Asthma is a disease that occurs when breathing is difficult. This occurs because:
The muscles in the wall of the bronchi contract.
The lining of the bronchi leaks sticky mucus.
An asthma attack can be mended if:
The factor causing asthma is removed
Using a bronchodilator, a spray that contains a drug that relaxes bronchial
muscles.
Smoking:
Smoking is the inhaling the smoke from burning tobacco and paper. This smoke
is harmful because:
It is hot
It has a drying effect.
It contains harmful chemical.
The smoke irritates the lungs. However the worst part is the chemical that tobacco
contains. These chemicals can cause:
Addiction in the case of nicotine. We also find that nicotine is a stimulant that
makes the heart beat faster raising the blood pressure.
Reduction of the oxygen supply in the case of carbon monoxide. This CO
attaches to the hemoglobin in red blood cells. This means that red blood cells
carry CO instead of oxygen.
Cancer in lung, mouth and larynx.
Destruction of cilia. This means that mucus with particles of dust accumulate on
the lungs.
Emphysema, when the walls of the air sacs are destroyed. So the surface for gas
exchange is reduced a lot.

8. THE CIRCULATORY SYSTEM.
The circulatory system is in charge of transporting all kind of substances around
the body. This system is formed by:
Blood Vessels
The heart
Blood.
BLOOD VESSELS: is a system of tubes arranged in such a way that they all
eventually lead back to the heart. These blood vessels contain blood and can be:
Arteries carry blood from the heart to other tissues and have a high pressure.
In these arteries blood moves freely so that when bleeding comes from an
artery blood goes out at the heart beating rate and very fast. Also we find
that arteries carry blood with lot of oxygen (this is the reason why blood is
red) and that arteries have the form of a circle surrounded with a thick layer
of muscles.
Veins move blood from the tissues to the heart. Here blood doesn’t move
freely because veins have some flaps. This is done because blood normally
in veins has to go against pressure. So when bleeding, blood goes slower and
with a purplish color because in veins blood carries more Co2 than O2.
Finally we find that veins have the form of an ovoid and a thin layer of
muscles.
Capillaries are a network or bed extended through all the tissues through
which nutrients and O2 passes from the arteries to the tissues by diffusion..
For helping diffusion capillaries are 1 cell thick, so substances have a
thinners surface over which to diffuse and also are highly branched for
increasing the surface of diffusion. We find that these capillaries are
constantly supplied with fresh blood and thatcapillaries have the diameter of
red blood cells so that they have to move in a line squeezing and loading the
O2. Near capillaries the lymphatic system is found that carries lymphs in
lymphatic vessels that carry fats and defenses.

9. THE HEART: the heart is a muscle specialized on the pumping of blood.
However we find that not all animals have the same heart. The heart has been changing
through evolution. Fishes only have 2 chambers in their heart, amphibians 3, reptiles all
have 3 chambers except crocodiles and birds and mammals have 4 chambers. This
means that our heart is composed of 4 chambers 2 atrium that receive blood with a low
pressure from veins coming from the lungs or tissues and 2 ventricles that expel blood
from the heart with a high pressure through arteries.
We find that having 4 chambers is good because like this deoxygenate blood is
not going to mix with oxygenated blood so the heart’s efficiency is going to improve.
The heart has 2 movements:
Syshole (contraction)
Diashole (relaxation)
We find that the heart is an especial organ because it doesn’t need to rest and it
is constantly beating. There are 3 types of muscles:
Striated muscles: For physical exercise. It is a strong and a voluntary
muscle.
Smooth muscle: It a muscle located on the viscera. It is weak and
involuntary.
Cardiac muscle: A types of muscle only found on the heart. It is
involuntary and strong.
How does the heart function?

10. Blood carrying oxygen in the pulmonary vein enters the heart through the left
atrium. From there it passes to the left ventricle. We find that this chamber has above
the bicuspid valve so that the blood doesn’t return to the atrium and also that it has very
thick walls so that the blood is pumped with enough pressure for reaching all the tissues
of the body. When the blood has finally been pumped it goes to the aorta the main
artery of our body that transports this oxygenated blood to the tissues; this aorta divides
into the renal artery (that goes to the kidneys), the hepatic (that goes to the liver) and the
femoral (that goes to the legs). Then tissues take the oxygen and expel carbon dioxide.
Then the deoxygenated blood returns to the heart through the Vena Cava, the main vein
of our body and reaches the right atrium where the pacemaker that controls the beating
of the heart is located. Then deoxygenated blood passes to the right ventricle that has
above the tricuspid valve that avoids blood going back to the right atrium; this chamber
has a thin wall because blood doesn’t need much pressure for going to the lungs. Finally
deoxygenated blood goes out of the heart through the pulmonary arteries that carry
blood to the lungs where deoxygenated blood turns into oxygenated blood.
The pacemaker.
We find that the muscles of the heart never become fatigued even when the heart
is beating at its fastest when doing exercise. This occurs because every contraction is
immediately followed by a relaxation. This pattern of contraction and relaxation is keep
by electrical signals sent by the pacemaker located on the wall of the right atrium. The
pacemaker is responsible of:
That the atria contract just before the ventricles so that blood doesn’t flows back
to the ventricles.
That the heartbeat is fast enough to meet the demands of the tissues of nutrients.
If the pacemaker works badly the heart pumps at a rhythm of 30 beats per minute
that is less than half the normal rate. In these cases an artificial pacemaker is installed
that send smalls electrical charges that put the basic rate on 72 beats per minute. The
battery of this artificial pacemaker has to be replaced every year.
THE BLOOD: The blood is a viscous substance that transports nutrients and
oxygen all around the body and we find that it is viscous for helping the heart pumping.
Blood is composed by:
Red blood cells. These cells carry O2 and we find that they are red because
of hemoglobin, the pigment that carries the O2, and because of iron
contained by the red blood cell. These cells don’t have a nucleus for having
more space for carrying O2. This types of cells are small and flexible for
going through capillaries.

11. White blood cells. These cells are in charge of defenses. We find that there
are 5 types of White blood cells, the most important ones are:
o Phagocytes eat bacteria and viruses that might cause infection. This
is called phagocytosis. They have an irregular shaped nucleus that
allows the cell to go through gaps in the walls of capillaries. Also
they have enzymes in their cytoplasm for digesting microorganism
and a sensitive cell surface for detecting them.
o Lymphocytes produce antibodies that are proteins that help in the
defense against disease. They have a very big nucleus that contains
many copies of genes that control the antibody production.
Platelets: A type of cell in charge of clotting wounds. These cells are sticky
and join together forming a barrier when there is a wound for avoiding that
blood goes out. Platelets also don’t have a nucleus and we find that they
can release blood-clotting enzymes.
Plasma: it is a watery liquid in which all the previous cell are found
floating. This liquid constitutes the 55% of the volume of blood.
So we could say that the blood functions are:
To transport O2 from the lungs to the rest of the tissues and Co2 from the
tissues to the lungs. RBC
To transport nutrients (amino acids and glucose) fro the digestive system
to the body. RBC
To transport waste (lactic acid and urea) to the kidney and the bladder.
RBC
To maintain the core body temperature (37ºC) thanks to a good
circulation. Plasma
Keep and optimum ph in the tissues. Plasma.
To kill invaders (bacterias and viruses) WBC

12. Blood types:
We can distinguish different types of blood due to the type of proteins that red
blood cells have in their surface. We find that when we are babies red blood cells
create anti-bodies against other types of red blood cells. So if they give you blood
from another type of blood that it is not yours you will die. This occurs because
your antibodies attack the other red blood cells creating a huge reaction. Blood
can be:
A: if red blood cells have A proteins in their surface. This blood creates
antibodies against B.
B: red blood cells contain B proteins. This blood creates antibodies
against A.
AB: contains proteins AB. It doesn’t create antibodies so it is considered
the Universal acceptor.
O: It doesn’t contain proteins but it crates antibodies against AB so it is
considered the Universal Donor.
We find that this blood can be positive or negative depending on the Rhesus
Facto. If you contain the RH protein you are positive if not, negative.
This can create problems if the pregnant woman is negative and the baby is
positive because during the first pregnancy the mother’s blood creates antibodies
against the positive factor of the baby. However the problem occurs during the second
pregnancy because the mother’s antibodies created before attack the baby. For avoiding
this nowadays doctors give neutralizers to the mother during the first pregnancy so that
she doesn’t create antibodies.
We find that blood has to have an adequate pressure. This pressure needs to
carry blood to the working tissues, but it must not be so high that it damages the blood
vessels. This blood pressure can be increased by:
Making the ventricles contract more powerfully
Narrowing the diameter of the arteries.
This contraction of arteries creates the pulse that can be felt whenever an artery
is pressed to a flat surface. When the pressure is high it is called systolic pressure
when it is low: diastolic pressure. This pressure it is also determinate by the exercise
because when doing exercise muscles work hard and so they need more oxygen and
glucose to produce energy through respiration, so they need an increase of blood
circulation. This is achieved by:
The heart pumps more blood per minute
Sphincters open to increase blood flow and close to decrease blood flow
to lees important areas.

13. Also we find that blood has to have the correct amount of glucose because if
concentrations are too high it can be harmful. These glucose concentrations are
controlled by some hormones released by the pancreas:
Insulin it stimulates the removal of glucose from the blood by turning
it into glycogen so that it is stored.
Glucagon it stimulates the release of glucose into the blood by
turning glycogen into glucose so that it is used.
THE EXCRETORY APPARATUS.
It is in charge of expelling waste products from metabolism that contain nitrogen
and that if are stored are toxic. Also we find that the excretory apparatus is in charge of
expelling the excess of water. We find that this apparatus does this by:
Homeostasis: Keeps internal conditions of the medium of cells constant.
This medium is a solution similar to RINGER’s solution that surrounds cells
and that has always to be constant with the same ph, etc…
Osmo regulations: Keeps balance of water.
For carrying out these functions urea must be expelled. Urea is the form in
which nitrogen is transformed into in the liver for then being filter in the kidneys. When
it is filtered it transforms into urine that is expelled out of the body. However also we
find that CO2 from respiration and salts in excess from diet need to be expelled.
How I said before the kidneys are the responsible of filtering the blood and
removing these harmful substances. Kidneys have 1 million nephrons which are the
basic unit that composes kidneys and that filters blood. This is done like this:
Blood enters with a high pressure from the renal artery the Bowman´s capsule which
is the first part of the nephrons. However we find that a lot of substances enter the
Bowman´s capsule, including useful substances. These substances continue going
through the coiled tube on which useful substances return to blood. Then they reach the
loop of Henlé on which salt concentrations are altered so that water that is needed in the

14. organism returns to blood and finally urine goes to the collecting tube that uses an antidiuretic hormone that controls urine production such as for example when we are
sleeping; also we find that this hormone controls osmoregulation in the collecting duct
so that we do not expel water that we need. Well we find that all bowman´s capsules
form the cortex and that all collecting ducts are orientated to the medulla so that they are
near the Ureter because when blood has finally been filtered and urine has finally been
produced it continues its travel through the ureters. These ureters carry urine to the
bladder where it is stored and from there urine is carried through the urethra to the
outside of the body. We find that the urethra is longer in men than in women. This is the
reason why women have more infections.
How you can see kidneys are very important; we find that apart of detoxifying blood
they are responsible of increasing calcium absorption and of stimulating red blood cells
production which is done through a hormone called erythropoietin.
The problem is that sometimes kidneys work badly because of:
Drugs and alcohol that causes diabetes and high blood pressure.
Kidney stones that can be caused by a genetic disorder or by an excessive
absorption of calcium. These stones block the ureter and are very painful.
How you can see we can’t work without kidneys because they are very
important so for solving these problem we can choose to do 2 things:
Dialysis that replaces the work kidneys do. There are 2 types of dialysis:
o Hemodialysis: In this process blood is taken with a needle,
filtered and then put back. This process has to be done 3 times a
week during 3-4h.
o Peritoneal dialysis: Instead in this process toxins in the blood
are taken through the stomach membrane. It is done every day
during 60 minutes.
Hemodialysis
Done by professionals
Good
Peritoneal Dialysis.
More freedom because it can be
done at home.

15. Can be done with
problems.
abdominal Does not require many food
restrictions.
Allows contact with other people Better choice if you have bleeding
that have the same problem as you. problems.
It doesn’t use blood thinners.
Done in the hospital.
Has to be done every day.
You are tired the day of the As you don’t have the help of
treatment.
professionals perhaps you have
problems for doing it.
Bad.
Problems if you have a low blood It can cause infection of the lining
pressure.
of the belly.
Risk of infection.
The other option is a kidney transplant although you have the risk that
your immune system rejects the tissue and attacks it. For stopping this
you would have to take drugs.
THE NERVOUS SYSTEM.
We find that on mammals there are 3 systems in charge of coordination:
The nervous system that deals with rapid but short-lasting responses
The endocrine system that carries out slower but longer lasting responses.
Locomotor system formed by muscles and bones.
So we can say that the differences between the nervous system and the endocrine
system are:
Nervous System.
Very rapid.
Endocrine System.
Can be slow.
Electrical impulses, travelling along Chemical messengers, travelling in the
nerves.
bloodstream.
Usually completed within seconds
May take years before completed.
Often confined to one are of the body. Usually noticed in many organs so that
So that we can say that the response is we can say that the response is

16. localized.
widespread.
In charge of reflexes such as blinking In charge of growth and development
or the movement of the limbs.
of the reproductive system.
To continue I´m going to talk about the nervous system. Well the
Nervous System works with stimuli that is the information with which we
elaborate responses and we find that these stimuli can come from the exterior
(heath, light, waves…) or from the interior (pain, ph, concentration of substances
such as glucose, high temperature…)
All this information is collected by receptors (eyes, ears, nose, mouth,
skin or the wall of blood vessels) and is transmitted to the Central Nervous
System through sensorial nerves. This CNS synthesizes the information and
elaborates a response that is transmitted through motor nerves to the effectors
that do the response.
So we can say that the Nervous System is formed by the CNS and by the
PNS.
The Central Nervous System (CNS) elaborates responses and it is formed
by:
o The Encephalon is formed by:
 The Brain that is the most complex organ in the body. It
weighs 1.5 Kg and has 2 hemispheres. The Brain is
formed by neurons, grey matter outside and with matter
inside and we find that it is responsible of intelligence,
memory, language, the integration of sensorial
information, emotions…
 The cerebellum, it coordinates the movement of muscles
and balance so that it integrates information from the
inner ear, eyes and from the skin.
 Spinal bulb coordinates vital reflex such as respiration,
heartbeat, contraction of blood vessels… but also no vital
reflects such as swallowing, coughing…
 Hypothalamus, controls body temperature, thirst and
hunger.
 Limbic system, controls aggressiveness.
 Thalamus, in charge of the integration of functions.

17. For protection the encephalon has a cranium, 3 membranes called
meninges (the pia mater, Dura mater and the arachnoid) and a
liquid called cerebrospinal liquid located in chambers of the brain;
we find that this liquid has to have the proper levels of nutrients.
o The spinal cord has for protection a backbone formed by 33
vertebrae, 3 meninges and cerebrospinal liquid.
If we cut a slide of the spinal cord we would obtain this:
We find that the spinal cord is responsible of all reflects acts. I
mean of acts we don’t think about and that happen immediately because
they don’t have to go to the brain; sensory neurons transmit the
information to the sensorial part of the spinal cord, then through a
connector or relay neuron the information passes to the motor area that
elaborates a response transmitted by the motor neuron to the muscle.
These reflex acts are essential for survival and some examples are:
Stimulus
Response
Survival value.
Coughing
Particles
making Violent contraction of Prevents lungs being
contact with the lining the diaphragm and damaged or infected.
of the respiratory tree. internal
intercostals
muscles.
Pupil reflex
Bright light falling on Contraction of the Prevents bleaching of
the retina.
muscles of the iris.
the retina so that
vision remains clear.

18. Knee jerk.
Stretching of the Contraction of muscles The leg can support
tendon just under the in the upper thigh so the body´s weight
knee.
that the leg straightens. while walking.
Swallowing. Food particles making Contraction of the Prevents
food
contact with the back muscle of the epiglottis. entering
the
of the throat.
respiratory pathway.
However we find that the spinal cord also has other functions.
The Peripheral Nervous System (PNS) it is formed by nerves all around
our body. They are both sensorial and motor nerves so that this system is
responsible of transmitting the information It is formed by:
o 12 pair of cranial nerves that g out the encephalon.
o 31 pairs of spinal nerves that go out the spinal cord.
We find that the Nervous system works with specialized cells called neurons.
However we find that there are other cells called Glic cells that feed and protect
neurons.
These neurons don’t reproduce easily. Before we thought that they couldn’t
reproduce, however now we believe that neurons can reproduce in some places of the
nervous system through stem cells.
Also we find that neurons are not touching together. This was discovered by
Ramon y Cajal on 1906 and for that they received a Nobel Prize. So, how neurons
transmit nervous impulses?
The key are neurotransmitters. The current generates and goes through the axon,
when this current reaches the end plate the vesicles release neurotransmitters, these
neurotransmitters go into the Synaptical gap and enter the dendrites of the other neuron.
This is called Synapsis and it is a chemical process.

19. RECEPTORS.
How you have seen the Nervous system needs information to work. This
information is in the form of stimulus (changes in the environment that affect the
organism) and these stimuli are detected by receptors. So we can say that receptors
are the parts of the nervous system adapted to receive stimuli. There are different
kinds of receptors due to the different kind of stimuli:
Photoreceptors respond to light. Ex: rod cells in the retina of the eye.
Chemoreceptors respond to chemicals. Ex: taste buds.
Thermoreceptors respond to changes in temperature. Ex: Thermoreceptors in
the skin.
Mechanoreceptors respond to mechanical change. Ex: hair cells in ear
responsible of hearing and balance.
Receptors are also traducers as they convert stimulus into electrical impulses
that our brain can understand. Sometimes receptor cells are grouped together forming
tissues to form sense organs
The best example of a sense organ is the eye although there are also internal
receptors inside our body that for example detect blood temperature, ph…
The eyes are located on the sockets of the skull and they are fixed to it through
muscles.

20. We see images when rays of light from an object are focused onto the retina
and for this the lenses refract the rays. The problem is that in this process the image is
inverted and diminished so that the brain has to correct this in a process called
integration.
How much we have to refract the rays depends on the distance of the object. If
it is far rays almost go parallel; so Ciliary muscles holding the lens make it grow longer
and thinner. If instead the object is close the rays need to be refracted a lot so the lens
becomes short and fat.
The Endocrine System.
How you know animals have 2 systems in charge of coordination: the nervous
system and the endocrine system. To continue I´m going to talk about the endocrine
system that is in charge of carrying out responses that go on over a long period of
time.
The endocrine system functions with organs called glands that release
hormones into the bloodstream. These hormones are chemical messengers that are
released on small quantities and that can be either lipids or proteins.
Hormones can carry out their functions far away from where they are produced
(actually they can act on everything that is connected to the bloodstream) However

21. hormones don’t act in all organs they only act on organs that recognize them on the
bloodstream. These organs are called target organs.
There are 3 different types of glands:
Exocrine glands. Those that produce hormones that do not go into the
blood stream. Ex: salivary, sweat and sebaceous glands that produces fats.
Mixed glands. Those that are both exocrine and endocrine glands. For
example the pancreas produces insulin and glucagon that go into the
bloodstream and pancreatic juice that goes to the small intestine.
Endocrine glands: are those that release hormones into the bloodstream.
Some examples of endocrine glands:
o Thyroid gland: produces thyroxin that controls the rate of
metabolism.
o Adrenal glands: produce adrenaline that improves immediate
performance although it increases blood pressure. It causes:
 Skin becomes pale as blood goes to the muscles.
 Deeper, more rapid breathing for creating energy through
cellular respiration.
 Heart beats more rapidly.
 Blood is diverted away from the digestive system by using
sphincters.
 Glycogen converts into glucose that is released into the
blood.
o Ovaries: produce oestrogen and progesterone that control puberty
in females.
o Testes: produce testosterone that controls puberty in men.
o Pancreas: as an endocrine gland it produces insulin and glucagon.
Insulin decreases glucose in the blood turning glucose into
glycogen; instead glucagon increases glucose. So we can say that
the pancreas has an antagonistic effect. This is done so that
glucose concentrations in the blood remain constant as glucose is
used as fuel by the brain. However if glucose concentrations are
very high we can have an illness called diabetes that is very
harmful because:
 It damages the retina of the eye
 It also damages the kidneys
 You feel tired, hungry and thirsty
 You produce a lot of urine.
How you can see the control of the levels of glucose is very
important. This is done like this:

22. The pancreas receives blood; if this blood has a lot of glucose you
have hyperglycemia. So the pancreas starts producing insulin.
Glucose is then used by the muscles or turned into glycogen by
the liver and then stored here or in the muscles. Instead if the
levels of glucose are to low you have hypoglycemia. The
pancreas detects this and starts producing glucagon that breaks
down glycogen into glucose in the liver.
o The pituitary gland is formed by:
 The adenohypophisis. It produces lot hormones such as the
human growth hormone. If we don’t have this hormone we
suffer dwarfism but if instead we have a lot we suffer
gigantism. However how tall you are depends on the gens
not in the amount of human growth hormones.
 The Neurohypophisis. A storing part that contains oxytocia
responsible of the contraction in pregnancy and ADH
(antideuretic hormone).
We find that the pituitary gland creates throphic hormones that
are those that go to other glands to stimulate hormone
production. Some examples of these hormones are:




Thyroid stimulating Hormone that goes to the thyroid so
that it makes thyroxin (T3, T4)
ACTH that goes to the adrenal glands on the kidneys so
that they produce adrenaline.
Follicle stimulating hormone that goes to the ovaries.
Luteizing hormone that goes to the testes.

23. Other hormones are the anabolic steroids and the EPO. They are known
as sports hormones as sometimes they are used for doping although they can
have secondary effects.
Anabolic steroids increase the volume of the muscles. They are like sexual
hormones so when you increase the number of these hormones in your
blood the body thinks that it doesn’t need more sexual hormones so people
that use this hormone might have sexual problems.
EPO increases the production of red blood cells so your muscles receive
more O2. This makes the blood viscous making harder the work of the
heart. Increasing blood pressure and heart and vascular problems.
All this hormone production is controlled by the feedback mechanism. The
hypothalamus is in charge of this process called hypophisis.
When the level of a hormone in the blood rises the system inhibits its
production so that the level is never too high. Instead if the levels are too low it
stimulates the production of the hormone.
Ex thyroxin levels in the blood are too low. Information reaches the
hypothalamus that through hypophisis makes the pituitary gland create TSH that goes
to the thyroid making it create thyroxin.
A very good example of how hormones function is in the development of sexual
maturity. The hypothalamus instructs the pituitary gland to stimulate the primary sex
organs so that they produce oestrogen/ testosterone. These hormones are released
into the bloodstream affecting target organs and developing secondary sexual
characteristics during years.
Testes begin producing sperm/ovaries begin the cycle of the egg
production.
Breasts develop / chest broadens, muscles become larger, voice deepens.
Hair grows under armpits and in the pubic region.
Vagina becomes larger /penis and scrotum becomes larger.
Muscles and bones.
Muscles are collections of very long muscles fibers that serve to move the
skeleton. Muscles function thanks to aerobic respiration carried out by the lungs
Glucose + oxygen = energy + carbon dioxide + water

24. However when doing hard exercise the lungs cannot take enough oxygen and
the heart can’t pump enough blood. So anaerobic respiration is carried out that
replaces the use of oxygen to obtain energy.
Glucose= energy + lactic acid.
The problem is that with this respiration we obtain 1/20 of the energy we
would obtain with the other respiration and that lactic acid is toxic. This harmful lactic
acid is oxidized to pyruvate by the heart, the liver and the kidneys. The problem is that
we need oxygen for doing this, what we call the oxygen debt. The reason why we
continue breathing fast after exercise.
Rest
Hard exercise
Recovery
Respiration
aerobic
Anaerobic- aerobic
Aerobic
Heart rate
70 beats/min
140 beats/min
140 beats/min
Breathing
15 breaths /min
50 breaths/min
50 breaths/min
Drugs-Medicines.
A drug is a chemical substance that alters the way in which our body works.
Medicines are also drugs but they are used for treating illnesses or disorders. So all
medicines are drugs but not all drugs are medicines.
We can classify drugs depending in how they affect our body:
Stimulants: speed up the action of the nervous system so they make you
feel confident and alert. Ex: caffeine, nicotine that affects the control of
the heart and the blood pressure and amphetamines.
Depressants: slow down the action of the nervous system so they make
you sleepy and less anxious. Ex: alcohol, cannabis, barbiturates.
Narcotics: depressants that attack the brain so they act as pain killers and
can cause euphoria. Ex: heroin.
Analgesics: not very strong pain killers. Ex: Aspirin, paracetamol, reflex.
Hallucinogens: Ex: LSD.
These drugs that are not use for medical reasons are called social drugs and
they can cause dependency. There are 2 types of dependency:

25. Psychological dependence if the person can’t leave the pleasure
sensations of the drug.
Physical dependence if the person needs the drug for the normal
working of the body.
When you have a physical addiction withdrawing the drug is very
difficult. You may have vomits, tremble, sweat and severe abdominal
pain.
This dependence can cause:
Malnourishments as drugs depress appetite.
Financial problems.
Infections from shared needles.
Danger if substances are mixed with the drug.
The most commonly used drug is the alcohol. However it is also a dangerous
drug that can cause severe effects:
At high concentrations it depresses the life-support centers so breathing
may stop.
Also it slows down impulses in peripheral nerves causing slower
reactions.
Also it causes flushing of the skin so blood goes to the skin causing
hypothermia in other parts of the body if temperatures are low.
Also it can upset normal sleep and cause cardiovascular problems.
Sex organs are stimulated but do not work well.
Liver is damaged as it works harder to detoxify the blood.
Cancer on the tongue and the esophagus.
Body cannot reabsorb water so the body becomes dehydrated.
Damage to the nervous system such as Alzheimer, sclerosis…
Reproduction.
Reproduction is the generation of new individuals so we can say that its aim is
to produce new individuals of the same specie and 2 individuals belong to the same
specie if they can reproduce and have fertile offspring. We find there are 2 types of
reproduction:

26. Asexual reproduction: The reproduction that does not involve the joining of
gametes from 2 parents. So we can say that there’s only 1 progenitor and
that descendants are identical among them and to the progenitor. So the
only variations occur due to mutation (a change in DNA). This is very bad for
evolution although it is good because reproduction is very easy.
Sexual reproduction: This type of reproduction needs 2 individuals
(Masculine and feminine) so that the genetic information is combined for
producing a new individual by mixing the 2 gametes in what we call
fertilization. This means that there is more variability between individuals.
The problem is that sometimes it is difficult that the 2 individuals meet at
the right season and that they have enough resources for growing the
offspring.
To continue I’m going to talk about the reproduction in humans. In humans as
in the rest of mammals we need 2 gametes:
Sperm produced by men in the testicles that at the same time that produce
sperm produce the hormone testosterone. Male gametes are small, are
motile and are produced in huge quantities 300 000 000 per day.
Ovules produced by women in the ovaries that at the same time produce
progesterone and oestrogen. Female gametes are quite big, do not move,
are produced in small quantities 1 per month and have lots of food.
Gametes are haploid cells which mean that they have only 23 chromosomes
when the rest of the cells have 46 so that they are diploid cells. This is like this so that
when the gametes join in fertilization they form a diploid cell called zygote which then
turns into a Fetus and finally into a newborn baby.
We find that all these production of sex cells is regulated by hormones and that
this production starts during puberty (when a person becomes physically able to
reproduce). This process is also regulated through hormones:The hypothalamus
instructs the pituitary gland to stimulate the primary sex organs so that they produce
oestrogen/ testosterone. These hormones are released into the bloodstream affecting
target organs and developing secondary sexual characteristics during years.
Breasts develop / chest broadens, muscles become larger, voice deepens.
Hair grows under armpits and in the pubic region.
Vagina becomes larger /penis and scrotum becomes larger.
The male apparatus.
It is called the urinogenital system because it also serves to carry urine.

27. Sperm cells are produced in the testes, carried to the Epydidimus that is the
beginning of the testes and that is a twisted tube and then they are carried through
the sperm duct. In their way they pass through several glands and finally they reach
the urethra that carries urine-sperm out of the body.
The female apparatus.
We find that ovules are released and produced in what we know as the
menstrual cycle that is controlled by a large number of hormones that prepare the
uterus for any fertilized ova and that control its development. This cycle lasts between
28-40 days and has 5 steps:
1. Menstruation. In this phase the uterus lining is shed and blood fragments of
tissue leave the body through the vagina and this is caused by a decrease of the
hormone progesterone and this process last more or less 5 days. As a lot of
blood is lost women need to have a diet rich in iron in the next days for the
repair phase.

28. 2. Repair phase. Blood vessels grow again in the lining of the uterus and the lining
thickens becoming stable. This is caused by an increase of the hormone
oestrogen. This phase lasts 6 days.
3. Ovulation. The Follicle stimulating Hormone coming from the pituitary gland
causes a special cell in the ovary to produce a sac around itself. This is what we
call the Graafian follicle the sac and the ovum. Once it is mature and coinciding
with the highest peak of oestrogen the ovum is released to the funnel of
oviduct meanwhile the sac (now called Corpus Luteum) remains covering the
wound that the ovum has left when it has gone; all this is produced by the
luteinizing hormone. This is what we call ovulation and lasts 3 days.
4. Receptive phase. The lining of the uterus is now completely developed. If
fertilization occurs the embryo is implanted in the lining; if not it is released in
the next menstruation. The lining is maintained by high levels of progesterone
and this lasts 6 days.
5. Premenstrual phase. The levels of progesterone slowly fall and the lining of the
uterus degenerates. However if the ovum was fertilized the concentrations of
progesterone remain high and the lining is conserved. This lasts 7 days.
So we can say that oestrogen repairs the lining and stimulates female sexual
characteristics meanwhile progesterone keeps the lining of the uterus. If women have
low levels of progesterone they are with a bad mood.
There are 3 ways of fertilizing the ovule:
COPULATION: Start when the ovule is released. This ovule moves through the
oviduct thanks to the cilia of the oviduct and to peristalsis (contractions in the
walls of the oviduct that move the ovule). If sexual relations occur the sperm
cells reach the ovule here and fertilization occurs. So fertilization is the joining
of an ovum and the head of a sperm so that the new cell contains genetic
material of both cells. However only one sperm cell can enter the ovule and
when this happens a barrier is formed so that other sperms do not enter. This
forms a zygote that turns into an embryo through mitosis that is attached to
the wall of the uterus and grows into a fetus during 9 months; however
sometimes the embryo doesn’t attach and goes away in what we call a
miscarriage. Also when it attaches a placenta starts to grow.
IN VITRO FERTILIZATION: The ovule is fertilized by sperm cell in a glass in a
laboratory and then the fertilized ovule is introduced in to the woman’s
uterus. However this is a difficult process and it is done when there is a
problem with the women’s ovules.
ARTIFICIAL INSEMINATION: This is done when there is a problem with the
man´s sperm. The sperm from a donor is introduced in the woman’s uterus
and it fertilizes the ovule. This is quite easy.

29. Other times you don’t want to have the ovule’s fertilization. In these cases you use
contraceptive devices for preventing pregnancy. They can be:
Understanding of the body cycles such as the rhythm method that consists in
avoiding having sexual relations during the fertile period or such as for example
withdrawal that consists in withdrawing the penis out of the vagina before
ejaculation. The problem is that this is not very reliable.
Physical barriers such as the condom, the IUD (a coil that irritates the lining of
the uterus or the diaphragm that avoid sperm entering the uterus. These
methods are quite reliable.
Chemicals such as spermicidal or the contraceptive pill which makes it difficult
to the ovule to attach to the walls of the uterus. Very reliable.
A surgical procedure such as female sterilization (oviducts are cut) or
vasectomy (the sperm duct is cut) they are 100% reliable but they are
permanent.
Other times fertilization occurs but the women doesn’t want to have the baby. So
an abortion could be carried that consists in an interruption of the pregnancy. The law
about abortion in Spain is:
Now: Free abortion up to 14 weeks.
1985: Abortion when there was a malformation, a risk for the mother or rape.
Before 1985: Illegal
On the future: Probably illegal.
Some times during copulation sexual diseases occur such as:
Gonorrhea: Caused by bacterium while doing penetrative sex. It can be treated
with antibiotics and causes pain when the urine passes, inflammation of the
testicles…
AIDS: Caused by a virus when having unprotected sex with an infected person.
It doesn’t have a cure and it consist in an immunodeficiency.
Syphilis: Caused by bacterium when doing unprotected sex with an infected
person. It can be treated with antibiotics and causes damage to the CNS.
Pregnancy.
During pregnancy the fertilized ovule turns into a baby in a process that last 9
months. In these months the fetus grows through mitosis and is developed as the cells
are organized into tissues and organs.
We find that during gestation the zygote needs controlled conditions to grow
and these conditions are remained stable by the placenta. A disc shaped organ that
grows in the wall of the uterus and that is in charge of:

30. The exchange of soluble materials such as foods, wastes and oxygen between
the mother and the fetus.
The physical attachment of the fetus to the wall f the uterus
Protection of the fetus from the mother’s immune system and against
dangerous fluctuation on the mother’s blood pressure
Secretion of hormones such as progesterone that maintain the lining of the
uterus, prevent contractions and the release of ovules.
So the placenta has a villi that extend deep into the wall of the uterus and that
have a thin surface that allow the exchange of substances so that the baby’s blood
never touches the mother’s blood. The problem is that this placenta grows old as the
pregnancy continues and so it doesn’t supply correctly the baby. This placenta has a
countercurrent flow that allows the diffusion of substances in one way or in another so
that all the parts of the baby are correctly supplied and we find that if we take out the
placenta before labor we could produce a big hemorrhage.
During pregnancy we have to check how the baby is doing in what we call
antenatal care that includes:
Checks on size and position of the baby by putting gentle pressure on the
woman’s uterus. The ideal position is that the head faces the cervix
Checks on Heart beat it has to be more or less twice than the mother’s.
Ultrasound scanning. Produces a picture of the fetus.
Weigh checks.
Blood tests for checking hemoglobin (the oxygen that arrives the baby), blood
group (if emergency transfusions are needed) and German measles antibodies.
Urine tests to check glucose levels and protein.

31. Vaginal examination to look for infections and to identify cancer cells and that
it is going to be big enough for the baby’s head.
Hormones: levels of oestrogen indicate how well the placenta is working.
Blood pressure
Amniocentesis. Consist on taking a sample of the amniotic fluid and cultivating
the cells that are floating there. This indicates us any abnormalities such as for
example of chromosome mutations. However it is very controversial as if you
see this maybe you are induced to abort.
When the fetus has completely developed the levels of progesterone falls and
the levels of oxytocia and oestrogen rise creating contractions of the uterus muscle.
These contractions become violent and break the amnion and the cervix dilates and
the baby goes out. This is what we call labor and when the baby is out it is needed to
cut the umbilical cord. However you cannot cut the umbilical cord freely because if not
you would cause a hemorrhage as important veins and arteries go through there.
You can feed the baby either with human milk or with bottle feeding.
Human milk.
Bottle feeding.
The milk contains food in the ideal An excess of proteins and of amino acids
proportions of nutrients.
may cause brain damage.
Saturated fatty acids that are difficult to
absorb.
Minerals are also quite high so kidneys
cannot cope with eat.
Contains antibodies (especially at the No antibodies
beginning when it is called colostrums).
Very low risk of infection
High risk of infection if the bottle is not
cleaned properly
No preparation, low cost and delivered at Quite expensive.
the right temperature.
Sometimes you can be pregnant of 2 babies. This can happen naturally or due
to fertility drugs. However this can occur in different ways:
Identical twins: When a single ovum is released from the ovary and is fertilized
but later divides into 2embryos. These babies are identical because they carry
the same genes.

32. Non-identical twins: When 2 ovules are released and fertilized. So they grow
separately and the babies borned are not identical twins as they don’t have
the same genes.