B5 - The Living Body

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Types of Skeleton

Internal Skeleton has many advantages over an external skeleton:

  • It provides an internal framework for the body
  • Grows with the rest of the body
  • Flexible due to many joints
  • Allows easy attachments
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Cartilage and Bones

Cartilage and Bones are living tissues containing living cells.

Long bone has a long shaft containing bone marrow with blood vessels. Cartilage at ends.

Hollow so are stronger and lighter.

Ossification is stages of bone growth. At the start the bone is just cartilage. But this is slowly replace with bone. 

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Breaking of Bones

Even though bones are very strong they can be easily be broken with a sharp knock.

Bones of elderly people can lack calcium and phosphorus, which can result in osteoporosis.
This makes there bones prone to fractures.

In an accident it can be dangerous to move a person with a suspected bone fracture. Broken vertebrae in backbone can damage the spinal chord, resulting in paralysis or death. 

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Synovial Joints (ball and socket joints, hinge joints) contain synovial fluid, a synovial membrane, ligaments and cartilage.

 Ball and socket joints have a wider range of movements compared to hinge which is restricted to up and down movements.

Forearm is lowered and raised by antagonistic muscles (biceps and triceps)
Raising - bicep contracts, tricep relaxes
Lowering - tricep contracts, bicep relaxes

The elbow is acting as a fulcrum (pivot) in the lever of moving the arm

Each part of a synovial joint has a special function:

  • Synovial Fluid - acts as a cushion against shock and a lubricant for easy movement
  • Synovial Membrane - keeps synovial fluid in
  • Cartilage - protect bone heads from rubbing on each other and shock absorber
  • Ligaments - holds bones in place 
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Circulatory System

Many animals need a blood circulatory system to ensure all their cells receive enough food and oxygen and to remove waste products (Carbon Dioxide)

As blood flows through Arteries, Veins and Capillaries, the blood pressure decreases.

Veins have valves - this means there is no backward flow of blood

High blood pressure would damage the fragile walls of the capillaries

Single Circulatory System (Fish) - single blood circuit of the heart, gills and body

Double Circulatory System (Mammals) - two circuits, heart and lungs (form oxygen), heart and rest of body (oxygen to body cells)
Double Circulatory system requires a 4 chamber heart (two atria - receive blood (from lungs and body) and 2 ventricles - distribute blood (to lungs and body)) 

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Cardiac Cycle

Cardiac cycle is the sequence of events as blood enters and leaves the heart.

  • muscles of the 2 atria contract together  - receive blood through the the atrio-ventricular 
  • two ventricles relax                               -  valves which prevent back flow into atria


  • Two ventricles then contract to force blood to lungs and around body.

Semi-lunar valves prevent backward flow into the ventricles

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Heart Rate

More muscle activity = greater demand for oxygen and food
Heart rate increases when muscular activity increases

Heart rate increase when....
Adrenaline (hormone) is present. Adrenaline prepares the body for "fight or flight" 

Pace makers = group of muscles in heart which can control the heart rate, by producing an electric current to stimulate muscle contraction.

Artificial pacemakers can be placed near the heart to send an electrical signal to the heart muscle.

An electrocardiogram (shows electric pulses through heat) and a echocardiogram (video of heart in action) can both be used to chow any irregular heart actions.

Two pacemakers, (sino-atrial node (SAN) and atrio-ventricular node (AVN)) generate electrical impulses to coordinate heart. The SAN causes the atria to contract and to stimulate the AVN. The AVN send impulses to make the ventricle to contract.

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Hole in Heart

The heart cannot work properly with a hole in between the two walls of the heart. The only way to fix this is to have open surgery.

A 'hole in the heart' allows blood to cross sides in the heart. So this means the blood leaving the Atria is much less as some of it escapes and crosses. 
Less blood means there is less oxygen being transported to muscles meaning you have less energy.


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Hole in Heart - 2

When the oxygen crosses sides, it causes the mixing of oxygenated and de-oxygenated blood. Resulting in arterial blood carrying less oxygen.

In a unborn baby circulation is different because the lungs don't function until they are born. Therefore they don't need a double circulatory system, so they have a hole in their heart which closes up when they are born.

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Repairing Heart

Heart cannot work properly with damaged or weak valves.

They can be repaired or replaced with surgery.

Damaged or weak valves makes you have a lower blood pressure and poor circulation as blood can flow backwards.

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Blood Transfusions

Blood transfusion is where you put blood from a person into a patients blood stream, who is in need. Only however, if they have the same blood type.

Agglutination is a reaction when different blood types which aren't compatible mix. The red blood cells and plasma the react, endangering the patients life.

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Types of respiratory system

Amphibians are restricted to moist habitats.

Fish gills only work in water


  • Simple Lungs
  • Use moist permeable skin to obtain oxygen
  • Permeable skin makes it possible for excessive water loss - could lead to death


  • Obtain oxygen from water
  • Water is forced over filaments
  • Do not survive in air 
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Gaseous Exchange

When humans breathe in...
 - Ribs are moved out and up
 - Diaphragm flattens
 - Chest volume increases and pressure decreases
 - Higher outside pressure forces air inside
When humans breathe out...
 - Ribs are moved in and downwards
 - Diaphragm curves upwards
 - Chest volume decreases and pressure increases
 - the increase of pressure forces air out of lungs and body

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Gaseous Exchange - 2

Total lung capacity consits of:

  • Tidal Air - air normally breathed in and out 
  • Vital Capacity - maximum amount of air which can be exchanged
  • Residual Air - amount of air which cannot be forced out of lungs

Exchange of gasses takes place by diffusion between the alveoli (bulges of air sacs) and the air in the air sacs

Diffusion occurs because the oxygen concentration in the air is higher than in the deoxygenated blood capillaries around the alveoli.

Exchange surfaces are adapted for gas exchange. They have a large surface area and a good blood supply. They are moist, permeable and only one cell thick.

Spirometer = Way to measure lung capacities and rate of air flow. Can be used to help detect lung disease.

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Respiratory Diseases

Asbestosis = industrial disease, resulting from breathing in asbestos fibres. The fibres cause inflammation and scaring of lung tissue reducing gaseous exchange.

Cystic Fibrosis - inherited disease, where too much mucus is produced in the bronchioles causing breathing difficulties

Lung Cancer - increased chance by smoking. Lung cells grew rapidly reducing the surface area available for gaseous exchange.

Asthma - symptoms include, wheezing, tight chest and difficulty in breathing. Inhalers used to relieve these symptoms
During an asthma attack, the lining of airways become inflamed, mucus and fluid build up in airways and the muscles around the bronchioles contract, narrowing the airways.

Breathing in Fish - the respiratory system in fish allows a through flow of water

Breathing in humans - air must go in and out of the same structures. So chemical particles (tar and asbestos fibres) can be trapped in air sacs.

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Physical Digestion

Physical Digestion = breaking food into smaller pieces.

Physical digestion is important because:

  • it allows the food to pass more easily through digestive system
  • it prepares the food for chemical digestion by giving it a larger surface area
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Chemical Digestion

Enzymes break down carbohydrates, fats and proteins in chemical digestion.

Mouth - carbohydrase breaks starch to sugar
Starch is broken down in two steps - first the starch is broken in to maltose. The maltose is the broken down into glucose 

Stomach - protease breaks down protein into amino acids 

Small Intestine - lipase breaks down fat into glycerol and fatty acids
The gall bladder stores bile. Bile is released into the small intestine to emulsify fats, increasing their surface area for efficient digestion.

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Chemical Digestion

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Food Absorption

Food molecules need to be small to be able to pass through the walls of the small intestine and dissolve in the blood or lymph. This means they have to be small and soluble.

Digested carbohydrates and proteins are soluble so these can easily diffuse through the walls of the small intestine and into the blood.

However the digested fat molecules are not soluble in water or plasma so cant run through the blood stream or it would clog up blood vessels. 
The fat molecules diffuse through the walls of the small intestine and into the lymph.

The small intestine is adapted for efficient absorption of food by having an extensive lymphatic system of lacteals which contain lymph.
The small intestines have a large surface area created by:

  • many villi in the walls of the small intestine
  • many micro-villi from the walls of the villi 
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Lymphatic System


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  • Excess and unwanted amino acids are broken down in the liver, to form urea.
  • The urea is then taken in the blood stream to the kidneys.
  • Blood containing waste (e.g. Urea) enters the kidney through the renal artery. Blood without waste exits through the renal vein.
  • Each kidney has  an outer cortex and an inner medulla. Waste removed from the kidney leaves through the ureters as urine.
  • The blood flows through the kidneys at high pressure so filtration can take place. Water, salt and glucose is reabsorbed by the blood to be used again.

Each kidney has millions of microscopic kidney tubules (nephrons) where filtration takes place to form urine.

Each nephron has:

  • a network of capillaries (glomerulus) surrounded by a capsule - this form the filtration unit 
  • a region where material such as glucose can be selectively reabsorbed
  • a region where reabsorption of some salt and water takes place
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Kidney - 2


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Dialysis Machine

A dialysis machine is used when someone has a kidney failure. The machine has many tubes containing blood, surrounded by a liquid. The machine acts as an artificial kidney and removes urea from the blood.

As urea molecules are small, they diffuse through the membrane. A dialysis machine also uses different sizes of tubes, so it slightly increases pressure during diffusion.

The dialysis fluid contains sodium salts, so it is the same or slightly lower than the desired blood concentration. This maintains the sodium levels in the blood.

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Regulating Urine Concentration

After drinking a large quantity of water, the quantity of urine produced increases and the urine concentration decreases.

During strenuous exercise or in hot conditions the body produces more sweat to cool down. The quantity of urine produced decreases and the urine concentration increases

The pituitary gland produces the Anti-diuretic hormone (ADH) which controls the concentration of urea by:

  • increasing the permeability of kidney tubes so that more water is reabsorbed
  • using a negative feedback system to control ADH production
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Carbon Dioxide Concentration

Carbon Dioxide at high concentration is toxic and must be removed from the body.

The body is more sensitive to the level of carbon dioxide that to that of oxygen.

An increase in carbon dioxide in the blood is dectected by receptors in the carotid artery.

Nerve impulses infrorm the brain, which causes the rate of breathing to increase to remove more carbon dioxide via the lungs.

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Hormone in the Menstrual Cycle

  • FSH (Follicle stimulating hormone) - stimulates an egg to develop in an ovary.
  • LH (Luteinising hormone) - controls ovulation
  • Progesterone - maintains uterus wall
  • Oestrogen - repairs the uterus wall

FSH & LH are released from the pituitary gland in the brain.

Negative feedback mechanisms (which restore the situation after change) control the levels of the sex hormones in the menstrual cycle. The cycle is triggered by the receptors in the hypothalamus.

If fertilisation does not occur the levels of oestrogen and progesterone decrease. When oestrogen and progesterone levels are low, menstruation occurs.

A message is sent to the hypothalamus that hormone levels are low again. This starts the cycle again.

If an egg is fertilised, the levels of progesterone remain high and no FSH is produced, so no more eggs develop and the uterus lining does not break.

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Fertility in Humans

Fertility in humans can be controlled by the use of artificial sex hormones by controlling egg release and implantation.

The contraceptive pill prevents ovulation
Fertility drugs help to ensure ovulation

Artificial sex hormonse prevent ovulation by making the body think its pregnant and this inhibits FSH release. Eggs therefore are not stimulated to develop.

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Infertility treatments

There are many method of treating infertility (inability to proudce babies):

  • artificial insemination - sperm is placed into the vagina via a syringe
  • using FSH - stimulates egg development
  • IVF (in vitro fertilisation) - eggs is fertilised by sperm outside of the body
  • egg donation - an egg is donated from another female, then fertilised and placed inside the uterus
  • surrogacy - fertilised egg is paced inside a surrogate mother (different female)
  • ovary transplant from another female

Fertility treatments increases the chance of a successful fertilisation and pregnancy. This is very important for couples who feel incomplete without a family. However, not all agree with such treatments which are expensive fro the individuals and for the NHS.

All fertility treatments raise moral issues, and they also have risks and benefits

Ovary donations, egg donation and surrogacy raise medical issues (such as rejection) and moral issues (paternity)

Some treatments are very expensive and have a low average success rate.

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Foetal Screenings

A developing foetus can be checked to see if there is any abnormalities (e.g. in its growth or genetic makeup)

Checking can be done by:

  • amniocentesis (extracting and testing cells in amniotic fluid)
  • chromosomal analysis (using a blood test to test cells for any chromosome abnormalities)

These can raise some ethical issues - which is it right to interfere with a natural process and whether an unborn foetus has the right to life

These techniques also carry a small risk of causing the expulsion of the foetus.

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Growth rate

A balanced diet and regular exercise can increase growth.

Extreme heights are caused by hormone imbalance or genes

Different parts of the foetus and a grow at different rates - e.g the head grows and develops earlier than the rest of the body

Babies length, mass and head size is regularly checked to give an early warning of any growth problems - possibly due to malnourishment or hormone imbalance

Human growth hormone is produced by the pituitary gland and it stimulates general growth.

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Life Expectancy

Human life expectancy has increased recently due to:

  • fewer deaths from industrial diseases
  • better housing - fewer cases of disease such as tuberculosis
  • healthier diet and lifestyle
  • advances in modern medicine - anitbiotics and transplants

Many people living longer has many personal and national concequences such as longer retirement to enjoy but a bigger burden on pension funds and health services

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Organ Donations

The supply of donations organs is limited due to little amount of donors and also by restrictions of use due to no tissue matching and size and age

These problems can be managed by using mechanical organs.
The disadvantages of using mechanical replacents is:

  • dependance on a power supply
  • materials used
  • size
  • bodily reactions to them

You can donate blood, bone marrow (as we make more) and kidneys (as we can live with only one)

Organ donation from a dead donor is allowed after conferring with the relatives and are certain the person is brain dead.

Dead donors bring up many ethical issues - human rights, the acceptance of surgery on a dead body and someone has died to get the organ

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Organ Donations - 2

Transplants are at risk of being rejected by the recipients body and so need life-long immuno-suppressive drug treatment, which can lead to the body not being able to protect itself from microorganisms.

People over 18 can be put on the donors register so their organs can be used after death.

There are long lists for people who need donors.

Some countries have an opt out system which assumes that organs can be donated without asking permission. Some people object to this system as they say it is against human rights.

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