a section of ocr as f221 notes

1

OCR BIOLOGY UNIT F221

Blood tests

1. Put a band (tourniquet) around the arm to make the vein stand out2. Clean the area around the vein with an alcohol based solution3. Push a sterile needle, attached to a sterile syringe into the vein4. Pull back the plunger of the syringe to suck the blood into the syringe5. When the necessary volume of blood has been extracted, remove the syringe and needle, loosen the

tourniquet and press a small ball of cotton wool over the wound, then apply a suitable dressing (plaster).

Making a blood film

1. Place a small drop of blood near the edge of a clean microscope slide2. Place the end of another slide (the spreader) on the sample slide3. Hold the spreader at an angle of approx 30oC and push it along the slide, spreading the drop of blood

into a smear.4. Label the slide with the patient’s details and allow it to air dry, so the cells stick to the slide5. Fix the slide using alcohol, this preserves the cells6. Stain the slide using a Romanowsky stain, e.g. Wright’s or Leishman’s. The stain is poured over the

slide, left for approx 2 minutes and the excess is washed off with water.

Differential stain

E.g. Leishman’s, makes some structures appear darker or a different colour. In a blood film the nucleus of leucocytes will be stained purple, this allows neutrophils, lymphocytes and monocytes to be identified from each other by the shape of their nuclei.

Haemocytometer

A special counting chamber designed for counting blood cells. It has a central platform with grooves either side of it. There is a tiny grid etched onto the platform, this looks a bit like graph paper. In the centre of the grid there are some triple lined squares, these measure exactly 0.2 x 0.2 mm. When you put the cover slip on top the platform is exactly 0.1mm below the cover slip. This means that when you look at one of the triple lined squares under the microscope you are looking at a volume of 0.1 x 0.2 x 0.2 = 0.004 mm3.

If we are counting erythrocytes, the sample is diluted with Dacie’s fluid; the blood is diluted 1 in 200.

Each triple lined square has a volume of 0.004 mm3, the blood was diluted 200 times and we count five triple lined squares (0.004 x 5 = 0.02 mm3).

Revision notes for JCB section of module

2

So if the number of cells counted in the five triple lined squares is E, the number of red cells in 1 mm3 of blood is:

1 /0.02 x E X 200

= E X 10 000

If cells lie on top of the triple lines around the edge of the square, we apply the NORTHWEST RULE. If a cell lies on the middle of the triple lines on the north or west of the grid, we count it; if it is lying on the south or east of the grid, we miss it out.

Counting leucocytes

A different dilution is used (1 in 20) and the four corner squares are used to count the cells.

Types of blood cell

Red blood cells (erythrocytes)

Biconcave discs, transport oxygen and some carbon dioxide. Their shape means they have a relatively large surface area to volume ratio to speed up gas exchange. Their cytoplasm is packed with a pigment called haemoglobin, this associates reversibly with oxygen. Mature red blood cells have no nucleus; this gives them more room for haemoglobin. Erythrocytes are also very small and flexible so they can be flattened against capillary walls; this reduces the distance that gases have to diffuse across and speeds up gas exchange.

Leucocytes (white blood cells)

Neutrophils

Have small granules in the cytoplasm. These cells engulf microorganisms by phagocytosis.

Lymphocytes

Have a large, darkly stained nucleus surrounded by a thin layer of clear cytoplasm. There are two kinds, B lymphocytes and T lymphocytes. B – produce antibodies; T- several functions including cell destruction.

Monocytes

Largest kind of leucocyte. They have a large, bean shaped nucleus and clear cytoplasm. They spend 2 to 3 days in the circulatory system, then move into the tissues. They then become macrophages, engulfing microorganisms and other foreign material.

Platelets

Fragments of giant cells called megakaryocytes. They are involved in blood clotting


3

Calculating magnification

Remember the units

10-3 mm millimetre

10-6 µm micrometre

10-9 nm nanometre

Magnification = Size of structure in the picture

Real size of the structure

Real size = Size of structure in the picture

Magnification

Always measure structures in pictures in millimetres. You can convert it into micrometers by multiplying it by 1000 (or add three zeros)

The plasma membrane

Cell membranes are made up of two kinds of molecules.

Phospholipids – form the bulk of the membrane

Proteins- scattered around in the membrane

Also, some molecules of carbohydrate and cholesterol may also be present.

Phospholipids

Made of a glycerol molecule with a phosphate group and two fatty acid chains attached. The phosphate group is hydrophilic (water loving) because it has a charge. It is soluble in water. The fatty acid chains are made of hydrocarbons. They are hydrophobic (water hating). They have no charge and are insoluble in water.

The phospholipids pack together in a membrane. They form a bilayer. There is water both inside and outside the cell. The fatty acid tails (hydrophobic) pack together away from the water. The hydrophilic heads arrange themselves on the outside of the membrane, facing the water.


4

Membrane system Function

Plasma membrane Partially permeable. Retains cell contents

Rough endoplasmic reticulum Ribosomes synthesise proteins. Membranes package them for distribution around the cell

Smooth endoplasmic reticulum Synthesis of lipids including steroids

Golgi apparatus Synthesis of glycoproteins, polysaccharides and hormones, production of lysosomes

Nuclear envelope Regulates exchange between cytoplasm and nucleus

Organelles

Lysosomes Contain enzymes for intracellular digestion

Nucleus Contains DNA and regulates cell activity

mitochondrion Aerobic respiration and production of ATP

Chloroplast Absorbance of light energy and production of carbohydrates in photosynthesis

Comparison of plant and animal cells

organelles Animal cell Plant cell

Nucleus Yes Yes

Nucleolus Yes Yes

Ribosomes Yes Yes

Cell wall No Yes

Plasma membrane Yes Yes

Golgi apparatus Yes Yes

Rough endoplasmic reticulum Yes Yes

Smooth endoplasmic reticulum Yes Yes

Mitochondrion Yes Yes


5

Chloroplasts No Yes (only in leaf / green parts)

Permanent vacuole No Yes

Cytoskeleton Yes Yes

Water potential and diffusion

Diffusion

The net movement of a substance from a region where it is in higher concentration to a region where it is in lower concentration. This continues until the molecules are evenly distributed. This is a passive process as it does not require additional energy.

Facilitated diffusion

Molecules that are soluble in water or charged particles (ions), cannot diffuse through the phospholipid bilayer. They use proteins to help. This is called facilitated diffusion. Some of the protein channels are permanently open. The protein channel is lined with hydrophilic amino acids and water.

Molecules can also diffuse through the membrane by binding to carrier proteins. The molecule binds to the carrier protein, this causes the protein to change shape and release the molecule on the other side of the membrane. No additional energy is used so the process is passive. An example of this is glucose diffusing into red blood cells through carrier proteins.

Osmosis

This is a special kind of diffusion. Water potential can be used to explain it. Water potential is the tendency of a solution to gain or lose water. Pure water has the highest possible water potential of zero. Adding solutes to water decreases its water potential – it makes it more negative. Water molecules will move by osmosis from a region of higher water potential to lower water potential across a selectively permeable membrane. This occurs until the water potential is the same on both sides – an equilibrium has been reached.

Isotonic – a solution with the same water potential as a cell

Hypertonic – a solution with a lower water potential than the cell

Hypotonic – a solution with a higher water potential than the cell

Keeping the osmotic balance

Glucose and other solutes will dissolve in blood plasma and lower the water potential, it is mainly the concentration of electrolytes in plasma and cells that is responsible for maintaining a water potential balance. Electrolytes are ions with a positive or negative charge. Positively charged ions are cations, negatively charged ions are anions. An electrolyte test measures sodium, potassium, chloride and bicarbonate ions; other plasma ions such as calcium, magnesium and phosphate can also be tested for. The electrolyte level range is narrow,


6

monitoring levels in hospital are essential and can indicate conditions such as tachycardia and cardiac arrest (low); raised levels, above 6.0 mmol dm-3 are associated with bradycardia and heart failure.

Active transport

The movement of a substance across a cell membrane against its concentration gradient using energy from ATP. The substance passes from an area where it is in low concentration to an area where it is higher. The substance is transported using a specific carrier protein.

Most cells contain a sodium-potassium pump. This is a carrier protein that uses ATP energy to transport sodium ions out of the cell and potassium ions into the cell.

The plasma membrane of cells lining the kidney tubules give an example of transport mechanisms working together. E.g. active transport pumps sodium ions out of the cell and potassium ions in; low sodium ions within the cell allows them to diffuse in bringing other ions and molecules in at the same time using the same carrier proteins; water moves in by osmosis; substances move from the cell to the capillary by diffusion.

Endocytosis and Exocytosis

• Endocytosis is the transport of large particles into the cell in vesicles formed by invagination of the cell surface membrane.

• Exocytosis is the reverse process and is used to secrete proteins, e.g. digestive enzymes, out of the cells

• Energy is required (ATP)

• Cholesterol is taken into cells by endocytosis in the form of low-density lipoproteins which binds to specific proteins in the cell membrane. It is released for use by the cell and the receptor protein returns to the cell surface membrane for use again. Some people have an inherited condition “ familial hypercholesterolemia”, they have high levels of cholesterol in their blood and suffer from heart attacks early in life. People suffering from this have been found not to have specific LDL receptors so their cells cannot take up LDL’s from the blood.

Preventing blood loss

• If possible put on some disposable gloves

• Reassure the person – get them to sit / lie down

• Look carefully at the wound – it might be necessary to cut the clotting away to see it clearly, e.g. make sure there is no glass there.

• If there is nothing in the wound, place a large pad of clean cloth onto the wound and press it down firmly using your hand.

• Use a bandage to hold the pad in place


7

If an object is stuck in the wound.................

• Don’t remove it!

• Make a pad in the shape of a ring and place it on the wound so that it surrounds the object

• Use a bandage to apply pressure on the ring around the sides of the wound. The pressure should push the edges of the wound together.

• If the wound is in an arm or leg, raise it higher.

• If the blood soaks through the first pad, don’t remove it but put another on top.

How blood clots:

• When tissues are damaged they are exposed to the air. Collagen fibres (in the connective tissue) are exposed and platelets stick to them.

• The platelets release a substance that makes them sticky, the platelets clump together to form a plug – this forms an initial barrier. Calcium is needed for this process.

• Leucocytes collect at the site and the exposed tissues just below the endothelium release an enzyme called thromboplastin

• Platelets also break down and release thromboplastin.

• Thromboplastin catalyses the conversion of an inactive plasma protein, prothtrombin into thrombin. This reaction also requires calcium ions.

• Thrombin is an active enzyme. It hydrolyses a large soluble plasma protein called fibrinogen into smaller units. It does this by reducing the activation energy needed for the reaction to occur.

• The smaller units join together (polymerise) to form long, insoluble fibres of fibrin (a protein). This process also requires calcium ions.

• The fibrin fibres pile up and form a mesh over the wound. Blood cells become trapped in the mesh and form a blood clot. The clot dries to form a scab, this prevents further blood loss. It also stops pathogens getting into the wound.


8

Enzymes – key facts and terms

• Optimum – the best temperature and pH that enzymes work at.

• Denatured – when the shape of the enzyme’s active site is changed irreversibly

• Substrate – the chemical that is reacting

• Active site – the area on the enzyme that the substrate fits into.

• They are globular proteins with a highly specific tertiary structure.

• Enzymes have an active site. This is exactly the right shape for one specific substrate to fit in. It works like a key fits into a lock.

• An enzyme-substrate complex is formed. Due to the very close fit the enzyme exerts forces on the substrate and the activation energy required is lowered.

• After the reaction has taken place, the enzyme is unchanged and can be used over and over again.

Giving blood

Key terms:

• Buffer solution - maintains constant pH

• Isotonic - same water potential (as cytoplasm)

• Blood is collected from the donor, a small sample is collected for testing, the donation is stored in a plastic bag, blood needs to be stored in the correct conditions so it does not clot.

Blood storage

Why is blood stored at 4OC

• Blood must be stored at temperatures low enough to prevent enzyme activity.

• Blood proteins (e.g. Haemoglobin) must not be allowed to denature

• If we freeze blood ice crystals would form inside the red blood cells, these would damage the cell membranes so the cells would be destroyed when the blood thawed out.

Why do we use a buffer solution?

• pH affects enzyme activity. pH measures how acid or alkaline a solution is.

• Proteins are held in their globular, tertiary structure by weak bonds. These also rely on weak positive and negative charges.


9

• The more acid, the more H+ ions present. These can affect the charges on the molecule. This causes the weak bonds to break. The enzymes tertiary structure is altered. The active site is no longer the right shape for the substrate to fit into. = DENATURED

How do we stop blood from clotting?

• Co factors are substances that are needed for an enzyme controlled reaction to occur.

• Calcium ions are needed for blood clotting enzymes to work.

• Calcium ions are normally in blood plasma and are released from damaged platelets.

• To stop blood from clotting calcium ions need to be removed.

• An anticoagulant is used to remove the calcium ions, e.g. Sodium citrate

Types of blood products

Type of stored blood product uses

Whole blood

Contains everything. Rarely used, except for severe blood loss

Leuco-depleted blood

Blood with as many leucocytes removed as possible. Important for patients who have lots of transfusions – less likely to provoke the immune system into making anti bodies

Packed red blood cells

The red cells are separated from the rest of the blood and stored. When needed the cells are diluted with a salt and sugar solution. Used to treat anaemia, replace red cells lost following surgery or childbirth

Platelets

Useful for patients with bone marrow failure; used following transplant and chemotherapy treatments and for patients with leukaemia

Clotting factors

Plasma from donations can be processed to provide clotting factors. There are many soluble proteins in plasma that help blood to clot. Haemophiliacs can be treated with transfusions of factor VIII

Plasma Plasma is from blood which all the blood cells have been removed. Fresh frozen plasma is used


10

during cardiac surgery to reverse any anti coagulant treatment and when a woman has lost a lot of blood during childbirth. It is also used to replace clotting factors after major transfusions or when clotting factors aren’t being produced, e.g. in liver disease.

Prior to donation the donor is asked a number of health questions about their health. Blood is screened for a number of infections including HIV and hepatitis C. The blood is also tested to find out what group it is. The distribution of different blood groups varies around the world. E.g. blood group A is present in approx 21% of the world’s population but in some groups of people such as the Lapps in Northern Scandinavia over 50% of the people have blood group A. Blood group B is quite rare, only 16% of the population have this group, but in Central Asia over 25% of the population may have it.

The lungs

• Tissue – a group of similar cells specialised to carry out the same function

• Organ – a structure made up of different kinds of tissue. E.g. Lung – squamous epithelium; elastic tissue

The specific cells of the lungs

Squamous epithelium, make up the alveoli:

• Thin, flattened cells

• Epithelium – a lining tissue

• Advantages – short distance between air in the alveoli and the blood in the capillary. This means gas exchange is very efficient

Goblet cells

• Shaped like a goblet (hence their name)

• Produce large amounts of mucus (a glycoprotein)

Dirt and bacteria in the air that is breathed in gets trapped in the mucus. When mucus reaches the throat it is swallowed. The dirt and bacteria is then destroyed by the acid and enzymes in the stomach

Ciliated epithelium cells

• Have tiny hairs called cilia.


11

• Beat together in a rhythm moving mucus back up the trachea into the throat.

• Cigarette smoke damages cilia

What does diffusion depend upon?

• Surface area – the number of cells in contact with the environment

• Volume – the space occupied by all the cells that need to be supplied with molecules.

• As the number of cells increases the volume increase. The surface area also increases but not as much

How does this relate to the lungs?

• Alveolus walls contain some elastic fibres, they allow the alveolus to expand and recoil when breathing in and out.

• Alveolus lined with a watery liquid. This contains a surfactant (detergent like). It lowers the surface tension of the alveoli. This reduces effort needed to breath in and inflate the lungs. Also has an antibacterial effect

What makes the lungs so good at diffusion?

• A large surface area:

– Bronchioles are highly branched –gives a large number of pathways for air to enter and leave the lungs

– Millions of alveoli in each lung

– Alveoli are highly folded, this gives an even greater surface area

• A thin surface

– The squamous epithelium cells in the alveoli are only 0.1 – 0.5 µm thick. This allows for rapid diffusion across them.

– The capillary walls are made up of a single layer of thin, flattened cells

• A steep diffusion gradient

– The blood circulation carries oxygenated blood away from the alveoli and brings deoxygenated blood to the alveoli

– Ventilation brings air rich in oxygen into the alveoli, air with increased carbon dioxide is removed from the alveoli

– The capillaries surrounding the alveoli are narrow, this slows down the blood flow and allows lots of time for efficient gas exchange


12

How are the alveoli adapted for efficient gas exchange?

– Dense capillary network is in close contact with the alveoli

– Movement of blood through the capillaries maintains the steep gradient

– Narrow width of capillaries means that erythrocytes are pressed close to the capillary wall and close to alveolar wall, thus reducing distance for gas exchange

How are the lungs adapted for efficient gas exchange?

All of the above and.....

– Remember to also include info on cartilage in trachea and bronchi keeping airways open

Measuring lung volumes

Definitions:

• Tidal volume – the volume of air breathed in and out with a normal breath. Usually about 0.5dm3

• If you breath out as much air as possible and then breath in as much air as possible (about 3.5dm3), this is known as the vital capacity.

• When you have breathed out as much air as possible, there is still about 1.5dm3 of air left in the lungs, this is the residual volume. It is important that some air is left in the lungs otherwise the walls of the alveoli would stick together and the lungs would not re-inflate easily.

A spirometer

• Measures lung volumes

• Helps diagnose and monitor conditions such as asthma.

Using one:

• Breath in air through a tube connected to a container of oxygen that floats in a tank of water.

• The floating container rises and falls as the person breaths in and out.

• The container has an arm attached to it, with a pen on the end, this draws a trace on some graph paper on a rotating drum

• Air breathed out passes through a chamber containing soda lime, this absorbs the carbon dioxide in the breathed out air before it returns to the oxygen chamber, (if the person re-breathed in the carbon dioxide it would cause an increase in their breathing rate)

• As the oxygen is used up the volume of oxygen in the chamber reduces and the trace shows a downward trend.


13

Peak flow meter

• Forced expiratory volume per second (FEV1) – the volume of air that can be breathed out in the first second of forced breathing out

• Peak expiratory flow rate (PEFR), the maximum rate at which air can be forcibly breathed out through the mouth

Using one:

• Stand up straight, make sure that the indicator is at the bottom of the meter

• Take a deep breath and fill your lungs completely with air

• Place the mouthpiece in your mouth, close your lips tightly around it

• Blow air out of your mouth into the meter as hard as you can in one blow.

• Record the reading.

• Reset meter and take two more readings, record the highest one

Respiratory arrest

What is respiratory arrest?

– It is when a person stops breathing. DO NOT get it confused with cardiac arrest, respiratory arrest does not necessarily mean the heart has stopped beating.

What causes respiratory arrest?

– Severe asthma, pneumonia

– An obstruction, e.g. Choking on food or object blocking trachea

– OD of drugs (heroin, barbiturates) that suppress the respiratory system

Whenever breathing has stopped or the pulse is weak, cyanosis occurs. This describes the bluish appearance of the skin especially around the lips, it is due to the build up of deoxygenated blood.

Respired air resuscitation

This is the first aid procedure that should be carried out on a person who is not breathing but still has a pulse (sometimes called rescue breathing)

1. Dial 999; if possible wear latex gloves and a breathing mask.

2. Roll the person onto his back; be careful not to twist the neck or spine. Pull the head back and lift the chin to open the airway.


14

3. Ensure nothing is blocking the airway

4. Gently pinch the person’s nose shut using the thumb and index finger. Place your mouth over the person’s mouth making a seal.

5. Breath slowly into the person’s mouth and watch their chest to see if it rises. Pause between each breath to let the air flow out.

6. If the person’s chest doesn’t rise, tilt the head back and try again.

7. After giving two breaths, check for a pulse, if the person has a pulse, continue rescue breathing. You should give one breath every five seconds.

8. If the person’s pulse stops, you should perform CPR (cardiopulmonary resuscitation)

In children.....

– Very similar, but the head doesn’t need to be tilted so far back

– Children or infants need one slow breath every three seconds

– On a baby, use your mouth to make a seal over the baby’s mouth and nose at the same time.

– Check for a pulse after a minute of rescue breathing (approx 20 breaths)


a section of ocr as f221 notes

Education