3

Unit 1 - Biology and disease

AQA

AS Biology

Unit 1:

Biology & DiseaseMiss ClarkeSummary Notes

3.1.3 Cells and Transport

TopicSyllabus Statement What I need to know:NotesRevisedExam Q

Cells The structure of an epithelial cell from the small intestine as seen with an optical microscope.

The appearance, structure and function of plasma membrane, including cell-surface membrane, microvilli, nucleus, mitochondria, lysosomes, ribosomes, endoplasmic reticulum, Golgi apparatus

Transmission v scanning electron microscopes.

The difference between magnification and resolution.

Cell fractionation and ultracentrifugation

Plasma Membranes The structure of triglycerides (both saturated and unsaturated and phospholipids.

The emulsion test for lipids.

The arrangement of phospholipids, proteins and carbohydrates in the fluid-mosaic model of membrane structure.

The role of the microvilli in increasing the surface area of cell-surface membranes.

Diffusion Diffusion and effect of surface area, difference in concentration and the thickness of the exchange surface (Ficks Law).

The role of carrier proteins and protein channels in facilitated diffusion.

Osmosis Osmosis and water potential

Active Transport The role of carrier proteins and the transfer of energy in the transport of substances against a concentration gradient.

Absorption Absorption of the products of carbohydrate digestion. The roles of diffusion, active transport and co-transport involving sodium ions.

Cholera Cholera structure (prokaryotic cell)

Causes and symptoms of cholera.

Oral rehydration solutions (ORS) and ethical issues

3.1.4/5 Lungs and heart

TopicSyllabus Statement What I need to know:NotesRevisedExam Q

Lung Function The structure of the human gas exchange system - alveoli, bronchioles, bronchi, trachea and lungs.

The features of the alveolar epithelium as a gas exchange surface.

The exchange of gases in the lungs.

Calculation of pulmonary ventilation

The mechanism of breathing.

The biological

basis of lung

disease

The course of infection, symptoms and transmission of pulmonary tuberculosis.

The effects of fibrosis, asthma and emphysema on lung function.

Explain the symptoms of these diseases and conditions affecting the lungs in terms of gas exchange and respiration

Risk factors for lung disease.

3.1.5 Heart

TopicSyllabus Statement What I need to know:NotesRevisedExam Q

Heart structure and

function

The structure of the human heart and its blood vessels

Pressure and volume changes and associated valve movements during the cardiac cycle.

Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity.

Roles of the SAN, AVN and bundle of His.

Cardiac output as the product of heart rate and stroke volume.

Analyse and interpret graphs data relating to pressure and volume changes during the cardiac cycle.

The biological basis

of heart disease

Atheroma as the presence of fatty material within the walls of arteries.

The link between atheroma and the increased risk of aneurysm and thrombosis.

Myocardial infarction and its cause in terms of an interruption to the blood flow to heart muscle.

Risk factors associated with coronary heart disease: diet, blood cholesterol, cigarette smoking and high blood pressure.

Describe and explain data relating to the relationship between specific risk factors and the incidence of coronary heart disease.

Microscopes

Units of measure

1 meter = 1,000 mm = 1,000,000 m = 1,000,000,000 nm

1 millimeter (mm) = 1/1000 m1 micrometer (m) = 1/1,000,000 m = 1/1000 mm1 nanometer (nm) = 1/1,000,000,000 m = 1/1000,000 mm = 1/1000 m

Examples:

Frog egg = 1mm

Human egg = 100 m

Most animal cell = 10 to 30 m

Most plant cells = 10 to 100 m

Prokaryotic cells = 1 m

Mitochondria = 0.5 to 1 m

Chloroplast = 5 m

Nucleus = 7 m

Virus = 10 to 300 nm

Ribosome = 30 nm

Magnification:

The ratio of how much bigger a sample appears when viewed under the microscope than its actual size.

The resolution limits how much detail can be seen.

Calculating magnification from photographs:

Magnification = length in photograph

Real length

Calculating real length from photographs:

Real length = Length in photograph

Magnification

NB for both, convert the length in the photograph into the same units that are used for the specimen. This is usually in micrometers.

Resolution

The smallest separation at which two separate objects can be distinguished (or resolved). The greater the resolving power, the more detail can be seen. The resolution of an image is limited by the wavelength of radiation used to view the sample. When objects in the specimen are smaller than the wavelength of the radiation being used, they do not interrupt the waves, and so are not detected. The resolving power of a light microscope is limited by the wavelength of light (400-600nm for visible light). Objects closer than 200nm will still only be seen as one point, no matter how great the magnification. Electrons have a much lower wavelength than light. A beam of electrons has an effective wavelength of less than 1 nm. Electron microscopes have higher resolution. Light Microscopy

Most widely used form of microscopy. Specimens are illuminated with light Focussed using glass lenses. Modern microscopes - Compound microscopes use several lenses to obtain high magnification. Light microscopy has a resolution of about 200nm: View cells, and large organelles but not the details of organelles Specimens can be living or dead. Specimens often need to be stained with a coloured dye to make them visible. Many different stains are available that stain specific parts of the cell such as DNA, lipids, cytoskeleton, etc.

Electron Microscopy.

Developed in 1930s.

Uses a beam of electrons to "illuminate" the specimen. Electrons behave like waves. Produced using a hot wire Focussed using electromagnets Detected using a phosphor screen or photographic film A beam of electrons has an effective wavelength of less than 1 nm. Resolving power is enough to view small sub-cellular ultrastructure. Mitochondria, ER and membranes can be seen in detail.Problems

Specimens must be fixed in plastic or covered in heavy metals. Viewed in a vacuum. Therefore, specimens must be dead. The electron beam can damage specimens. Must be stained with an electron-dense chemical, usually heavy metals like osmium, lead or gold. People argue that many observed structures could be artefacts - due to the preparation process and not real.Transmission electron microscope (TEM)

Works much like a light microscope. A beam of electrons is passed through a thin specimen. Electrons are focussed to form an image on a fluorescent screen or on film. Most common form of electron microscope. Best resolution 0.2 nm Creates a 2-dimensional flat image.The scanning electron microscope (SEM)

A fine beam of electron is scanned onto a specimen. Electrons are scattered by the surface, due to the heavy metal covering. A fluorescent screen or film is used to detect the reflected electrons. This has poorer resolution 10 nm Gives 3-dimentional images of surfaces.

The electrons do not have to pass through the sample in order to form the image.

Larger, thicker structures can be seen under the SEM.

Separating Cell Components

Cell Fractionation

The separation of different parts and organelles of a cell. Relative proportions of each organelle can be discovered. Biochemical contents of each organelle can be investigated.Process:1. Place tissue (e.g. liver, heart, leaf, etc) in ice-cold isotonic buffer.

Cold to stop enzyme reactions.

Isotonic to stop osmosis.

Buffer to stop pH changes.

2. Grind tissue in a blender to break open cells homogenation.

3. Filter to remove insoluble tissue e.g. fat, connective tissue, plant cell walls, etc. This filtrate is now called a cell-free extract.Differential Centrifugation

A centrifuge is a piece of equipment, driven by a motor, that puts an object in rotation around a fixed axis, applying a force that is perpendicular to the axis.

The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density.

Svedberg unit used to compare sizes of ribosomes a measure of their density.

Process:

1. Centrifuge filtrate at low speed and remove pellet.

2. Repeat at increasingly higher speeds.3. Each pellet removed contains structures of lower density.Density gradient centrifugation.

The cell-free extract is centrifuged in a dense solution Eg sucrose or caesium chloride The fractions separate out into layers with the densest fractions near the bottom of the tube.HeaviestNuclei

Mitochondria

Lysosomes

LightestRibosomes

Cells

Cell = the smallest unit of life.

All living organisms are made of cells.

There are unicellular organisms that consist of one cell:

Bacteria

Blue-green bacteria

Protozoa

Yeast

These individual cells must carry out all of the essential life proceses

Other organisms are made of many cells.

These are multicellular organisms:

Animals

Plants

Mushrooms

Seaweed

In these the life processes can be delegated to different organs and tissues.

Two main divisions of cells

Prokaryotic cells:

Bacteria

Blue-green bacteria

Eukaryotic cells

Animals

Plants

Fungi

Protoctista

Pro = before

Eu = true

Karyo = nucleus

Prokaryotic Cells Example:

Cholera Vibrio cholerae Prokaryote = before the nucleus

Simple cells containing no membrane bound organelles

Considered to be the earliest form of life on Earth.

StructureFunction

Cell wallProvide shape

Protect against rupture by osmosis

Some protection against other organisms

Rigid

Made of peptidoglycans polymers of sugars and amino acids

Plasma membranePhospholipids and proteins

Proteins include enzymes for metabolic processes

Eg respiration, nucleic acid synthesis (in all) and photosynthesis (in some)

Fluid mosaic

Barrier for selective exchange of nutrients and waste products

Movement by diffusion (including osmosis) and active transport

DNASingular, circular chromosome

DNA helix

In cytoplasm, not nucleus

Attached to plasma membrane

Eg E.coli 4 x 106 base pairs (A, C, T and G), about 4000 genes

RibosomesSmaller than in eukaryotic cells

Site of protein synthesis

FlagellaHollow cylinder

Made of rigid protein strands (flagellin)

Arise from basal bodies in plasma membrane in some bacteria

Rotate from base like a rotor blade

Bring about movement

PlasmidsAdditional hereditary material

Small rings of DNA, 10 30 genes

In cytoplasm of some, not all, bacteria

Eg antibiotic resistance

Can be transferred through conjugation tubes

Exploited as vectors in genetic engineering

CapsuleTangled mat of polysaccharide fibres

Slimy physical barrier

Outer protective layer in some bacteria

Protects against chemicals and dessication

Protects against attack by phagocytic cells

Helps bacteria to form colonies

Eukaryotic Cells

Eukaryote = true nucleus

These cells contain organelles

Cell membrane

Thin layer found round the outside of all cells.

Made of phospholipids and proteins.

Controls the movement of materials in and out of cell.

Microvilli

Small finger-like extensions of the cell membrane found in certain cells

eg, epithelial cells of the intestine and kidney.

Increase surface area.

Cytoplasm Watery solution within cell membrane.

Contains:

Enzymes for metabolic reactions

Sugars, salts, amino acids in solution.

Organelles

Membranous sacs.

Compartmentalise portions of the cytoplasm.

Increase the surface area for reactions.

Allow metabolic reactions to be sequenced.

Isolate potentially harmful chemicals.

Nucleus

The largest organelle (10m diameter).

Controls cells activities.

Store genetic material chromosomes which are made of DNA.

Spherical

Surrounded by nuclear envelope:

2 membranes filled with fluid

Nuclear pores enable mRNA to enter the cytoplasm.

Interior is nucleoplasm which is full of chromatin (DNA/protein).

Nucleolus is a dark region of chromatin, site of RNA transcription.

Mitochondrion

Site of aerobic respiration in all eukaryotic cells.

2.5 to 5 micrometers long.

Spherical or rod shaped

Double membrane

Inner membrane folded into cristae - large surface area.

Internal space is the matrix, a solution of metabolites and enzymes.

Also contain loops of DNA.

ATP synthase (stalked particles) are on the inner membrane.

Site of latter stages of respiration.

Metabolically active cells contain numerous mitochondria.

Number of cristae also increases with increased activity.

Ribosomes

Smallest and most abundant organelles

Not membranous

Site of protein synthesis

Made in nucleolus

Made of protein and RNA

Found either in cytoplasm or attached to the rough endoplasmic reticulum (RER)

Larger type (80S)

Often found in groups called polysomes

Endoplasmic reticulum (ER)

An elaborate system of membranes.

Forms part of the cytoplasmic skeleton.

Extends from the nuclear membrane.

Series of flattened stacks called cisternae.

Enables substances to be synthesised and transported.

Rough ER (RER)

Studded with ribosomes, gives it rough appearance

Polypeptides synthesised by ribosomes are passed into it.

Pass proteins to Golgi body for further processing.

Smooth ER (SER)

No ribosomes.

Involved in synthesising and transporting steroids.

Vesicles

Small membrane bound organelles.

Deliver substance around cell.

Take substances:

From ER to Golgi

From Golgi to cytoplasm - lysosomes

From Golgi to cell membrane for exocytosis secretory vesicles

Eg release of digestive enzymes.

Golgi body (Golgi apparatus)

Series of flattened membrane sacs.

Similar structure to ER.

More compact and curved.

Transports proteins from the RER to the cell membrane

Vesicles of RER fuse with the Golgi on one side

Contents of the vesicles enter the Golgi

Steroids may be modified.

Proteins may acquire tertiary/quaternary structure.

Other groups may be added.

Vesicles bud off the other side and move into the cytoplasm.Lysosomes

A type of vesicle.

Contain enzymes.

Used to breakdown unwanted toxins or organelles to recycle materials.

Eg used in phagocytosis.

Summary of differences between prokaryotic and eukaryotic cells

Prokaryotic cellsEukaryotic cells

Extremely small ( atmospheric pressure = Expiration

If atmospheric pressure > intrapulmonary pressure = Inspiration

Pressure differences are achieved in the thoracic cavity

Through the action of the intercostals muscles and positioning of the diaphragm.

A pleural sac surrounds each lung.

The outer membrane is attached to the rib cage, the inner to the lungs.

The inner cavity is at a pressure below atmospheric pressure.

This prevents the lungs deflating.

When the thorax moves, the lungs do too.

Alveoli are elastic and collapse if not held stretched by the thorax.

The secrete surfactant which prevents them sticking together.

Mechanism of inspiration

Contraction of diaphragm

Contraction of external

intercostal muscles

Flattens and descends

Pulls ribs upwards and

Outwards

Thorax cavity lengthens

Diameter of thorax increases

Increase in thorax volume

Lungs expand

Alveolar pressure drops

Pressure gradient established

From atmosphere to alveoli

INSPIRATION

Mechanism of expiration

Relaxation of diaphragm

Contraction of internal

Intercostal muscles

Returns to domed position

Ribs move downwards

And inwards

Thorax cavity shortens

Diameter of thorax

Decreases

Decrease in thorax volume

Elastic recoil of lungs

Lungs decrease in size

Increase in intrapulmonary pressure

Pressure gradient established from

Alveoli to atmosphere

EXPIRATION

Forced inspiration/expiration

Abdominal muscles used

This greatly increases intrapulmonary pressure

Eg. coughing or blowing up balloon.

Measurements of pulmonary ventilation

Spirometer

Measures volumes of air expired and inspired

Used to diagnose ventilation deficiencies

Creates a spirogram

Tidal volume (TV):

Volume of air breathed in or out during quiet breathing

About 500cm3 in adults

Breathing rate = the number of inspiration/expiration cycles per minute

Pulmonary ventilation = tidal volume X breathing rate

ie the volume of air breathed in or out per minute during quiet breathing.

The biological basis of lung disease

Pulmonary tuberculosis

Tuberculosis (TB) is an infectious disease

It is caused by the bacterium Mycobacterium tuberculosis.

TB most commonly affects the lungs but also can involve almost any organ of the body.

Today TB usually can be treated successfully with antibiotics.

Transmission

Someone who has a TB lung infection coughs, sneezes, shouts, or spits.

People who are nearby can then possibly breathe the bacteria into their lungs.

A person can become infected with TB when minute particles of infected sputum are inhaled from the air.

You don't get TB by just touching the clothes or shaking the hands of someone who is infected.

Tuberculosis is transmitted primarily from person to person by breathing infected air during close contact.

There is a form of atypical tuberculosis, however, that is transmitted by drinking unpasteurized milk. Course of infection

When the inhaled tuberculosis bacteria enter the lungs, they multiply.

This causes a local lung infection (pneumonia).

The local lymph nodes associated with the lungs may also become involved with the infection and usually become enlarged.

In addition, TB can spread to other parts of the body.

The body's immune (defense) system, however, can fight off the infection and stop the bacteria from spreading.

The immune system does so ultimately by forming scar tissue around the TB bacteria and isolating it from the rest of the body.

If the body is able to form scar tissue around the TB bacteria, then the infection is contained in an inactive state.

Such an individual typically has no symptoms and cannot spread TB to other people.

The scar tissue and lymph nodes may eventually harden, like stone, due to the process of calcification of the scars (deposition of calcium from the bloodstream in the scar tissue).

These scars often appear on x-rays and imaging studies like round marbles and are referred to as a granuloma.

Sometimes, however, the body's immune system becomes weakened, and the TB bacteria break through the scar tissue and can cause active disease, referred to as secondary TB.

TB can spread to other locations in the body:

The kidneys, bone, and lining of the brain and spinal cord (meninges).

Symptoms

TB infection usually occurs initially in the upper part of the lungs.

The usual symptoms that occur with an active TB infection are;

General tiredness or weakness

Weight loss,

Fever, and night sweats.

If the infection in the lung worsens, then further symptoms can include:

Coughing

Chest pain

Coughing up of sputum (material from the lungs) and/or blood

Shortness of breath.

If the infection spreads beyond the lungs, the symptoms will depend upon the organs involved.

Pulmonary Fibrosis

Pulmonary Fibrosis involves scarring of the lung. Gradually, the air sacs of the lungs become replaced by fibrotic tissue. When the scar forms, the tissue becomes thicker. Diffusion distances are increased. This causes an irreversible loss of the tissues for efficient gaseous exchange.Symptoms

Shortness of breath, particularly with exertion Chronic dry, hacking cough Fatigue and weakness Discomfort in the chest Loss of appetite Rapid weight lossCauses

It could be an autoimmune disorder, and there may genetic predisposition.

The fibrotic processis a reaction to microscopic injury to the lung.

Macrophages accumulate in connective tissue.

They stimulate the creation of fibrous tissue.

Associations have been made with the following: Inhaled environmental and occupational pollutants Cigarette smoking Diseases such as Scleroderma, Rheumatoid Arthritis, Lupus and Sarcoidosis

The after effects of a viral infection Certain medications Therapeutic radiationAsthma

Asthma causes the bronchi to become inflamed and swollen.

Bronchi are more sensitive than normal.

It could be inherited.

It could also be caused due to a lack of exposure to certain substances in early childhood.

Triggers:

Certain substances, or triggers, can irritate them:

House dust mites

Animal fur

Pollen

Tobacco smoke

Cold air

Chest infections.

Symptoms:

When the bronchi are irritated, they become narrow and the muscles around them tighten.

This can increase the production of sticky mucus.

This causes wheezing and coughing and shortness of breath.

Pulmonary ventilation is reduced.

This effects the maintenance of efficient concentration gradients in the alveoli.

This results in inefficient gas exchange.

The severity of the symptoms of asthma differs from person to person, from mild to severe.

The narrowing of the airways is usually reversible - occurring naturally, or through the use of medicines.

A severe asthma attack can be life threatening and may require hospital treatment.

Emphysema

Emphysema causes the walls of the alveoli to break down.

Larger air spaces are formed.

Total surface area available for gas exchange is greatly reduced.

Causes:

The single most common cause of emphysema is smoking.

Heavy cigarette smokers are most at risk from emphysema and chronic bronchitis.

The damage to your airway begins when tobacco smoke temporarily paralyses the cilia that line the bronchial tubes.

These hairs usually sweep irritants and pathogens out of the airways,

The temporary paralysis prevents them from doing this.

The irritants remain in your bronchial tubes and pass into your alveoli

This inflames the tissue and damaging the walls.

Breathing in industrial pollutants can also contribute to the development of emphysema.

In a few, rare cases (about 2%) emphysema is the result of defective genes. This type is called alpha antitrypsin (AAT) deficiency emphysema. AAT is a protein that blocks the action of an enzyme that breaks down the walls of the alveoli. If you are deficient in the protein, it can lead to progressive damage that will eventually result in emphysema.Symptoms

Shortness of breath when exerting yourself.

Eventually, this shortness of breath may occur even when you are at rest.

Difficulty breathing

Coughing

Wheezing

Excess mucus production

A bluish tint to the skin (cyanosis)The HeartPosition

Middle of thorax

Above diaphragm

Behind sternum

Between 2 lungs

Partially overlapped by left lung

Apex points towards left of thorax.

Cardiac muscle

Major tissue in the heart wall is cardiac muscle

Cardiac muscle tissue = myocardium

Branching cells which can share nuclei

Cells are cross striated like skeletal muscle.

Transmit electrical excitation

Capable of contracting and relaxing repeatedly for life.

Blood supply

Provided by coronary artery

Delivers oxygenated blood to the heart muscle

Branches from aorta

Receives 5% of total cardiac output

Dense capillary network

Coronary veins return blood to heart directly into right atrium through coronary sinus.

Associated Blood Vessels

Vena Cava

Carries deoxygenated blood from body tissues into right atrium.Pulmonary artery

Carries deoxygenated blood from right ventricle to lungs Pulmonary vein

Carries oxygenated blood from lungs back to left atrium. Aorta

Carries oxygenated blood from left ventricle to respiring body tissues.Internal structure

Atria (sing. Atrium):

Relax to receive blood from veins:

Venae cavae into right atrium

Pulmonary veins into left atrium.

Thin walled

Elastic

Contract to push blood into ventricles:

Rings of muscles surround veins at their point of entry

Contract to close off veins.

Prevents reflux of blood into veins.

Ventricles:

Myocardium thicker than atria.

Distance to ventricles is very small.

Myocardium of left ventricle 3 times thicker than right.

Creates higher blood pressure in systemic circulation:

Essential for efficient function of organs.

Allow for tissue fluid formation.

Lower blood pressure in pulmonary circulation:

Prevents rupture of delicate pulmonary arteries.

Separated by septum.

Relax to receive blood from atria.

Contract to push blood through arteries:

Left ventricle into aorta.

Right ventricle into pulmonary artery.

Valves

Responsible for heart sounds.

Ensure unidirectional flow of blood though heart.

Atrioventricular valves:

Between atria and ventricles.

Prevent blood flowing back into atria when ventricles contract.

Higher pressure in ventricles causes them to close back towards atria.

Causes lub sound.

Chordae tendinae:

Fibrous cords

Attach loose edge of valves to wall of ventricle.

Attached by papillary muscle:

Contract when ventricle contracts.

Tighten the chordae tendinae.

Tricuspid valve:

3 flaps.

Right side of heart.

Bicuspid valve (mitral valve):

2 flaps.

Left side of heart.

Semilunar valves:

At entrance of aorta and pulmonary artery.

Hence aortic and pulmonary valves.

Prevent back flow of blood into ventricles.

When ventricles relax

Pressure in ventricle drops below pressure in arteries.

Causes valves to fill with blood.

Creates dub sound

The Cardiac Cycle

A rhythmic series of events.

Resulting in each beat of the heart.

At rest, average 72 beats per minute.

One cardiac cycle = approx 0.83 secs.

Diastole:

Relaxation of atria and ventricles.

Atria fill with blood from veins.

Pocket valves close dub.

Blood starts to move into ventricles.

Atrial systole:

Atria contract.

Increases pressure.

Pushes blood into ventricles.

Passes though atrioventricular valves.

Ventricles remain relaxed.

Ventricular systole:

Ventricles contract.

Atria relax.

Higher pressure in ventricles than atria.

Atriventricular valves close lub.

Pocket valves open.

Blood flows into arteries.

Pressure Changes During the Cardiac Cycle.

Blood always flows from a high pressure to a lower pressure, unless prevented by valves.

Graph starts at atrial systole

Point at which atrial pressure rises above 0 kPa

Ventricular systole occurs when pressure in ventricles exceeds pressure in atria.

A.V. valves close.

Causes increase in pressure in atria.

Blood flows into arteries when pressure in ventricles exceeds pressure in arteries.

Pocket valves open.

Diastole occurs when pressure in ventricles drops below pressure in arteries.

Pocket valves close.

Pressure in arteries maintained relatively high.

Due to elastic recoil of artery walls.

Atrioventricular valves open when pressure in ventricles drops below pressure in atria.

Pressure in atria rises back towards 0 kPa as they fill with blood.

Extra detail:

Electrocardiogram (ECG)

Electrodes placed on skin.

Changes in voltage displayed on oscilloscope:

P wave = electrical excitation of atria

QRS complex = excitation of ventricles.

T wave = recovery (repolarisation) of ventricles.

Phonocardiogram (PCG):

Records heart sounds.

Caused by valves closing.

Lub dub.

Conducting tissues of the Heart

The heart beat is initiated from within the heart muscle.

Heart muscle is myogenic:

It is self exciting.

It can contract on its own without needing nerve impulses.

It maintains a continuous, inherent rhythm through electrical excitation of localised areas.

This leads to contraction of cardiac muscle.

This is called myogenic stimulation.

Modified cardiac muscle cells coordinate this sequence of events.

They conduct the excitation through the walls of the heart.

Sino Atrial Node (SAN): Small group of specialised cells. In wall of right atrium. Near opening of superior vena cava. Referred to as the pacemaker. Initiates the heart beat. Electrical excitation passes across both atria causing them to contract.

Atrio Ventricular Node (AVN): Small group of specialised cells.

Between the 2 atria.

Electrical activity reaches the AVN

Delays passage of excitation down the septum

This enables the atria to empty before ventricles contract

Passes electrical excitation down septum.

Bundle of His:

Specialised non-contractile cardiac muscle fibres (Purkinje fibres)

Lead down the interventricular septum to apex.

Electrical excitation passes down this.

They radiate upwards from the apex around the ventricle walls.

Excitation passes up through these.

Ventricle contracts from apex upwards.

Cardiac output

Normal heart rate = approx 72 beats per minute.

Varies from 50 to 200 beats per minute.

Approximately 75 cm3 of blood pumped from each ventricle.

Cardiac output is the volume of blood pumped by one ventricle of the heart in one minute

Cardiac output = heart rate X stroke volume.

Measured in dm3min-1Heart Disease

Atheroma

An accumulation and swelling in artery walls that is made up of cells that contain lipids and fibrous connective tissue.

Also referred to as plaques.

The swelling occurs between the endothelium lining and the smooth muscle wall of the artery

They occur due to macrophages that have taken up low-density lipoprotein (LDL).

This is associated with high cholesterol levels.

This is associated with high levels of saturated fats in the diet.

The plaque calcifies and hardens over time.

Aneurysm

Atheroma can cause weakening of the arterial wall.

Can be due to atheroma.

This can lead to a localized, blood-filled dilation (balloon-like bulge) of a blood vessel.

Aneurysms most commonly occur in:

Arteries at the base of the brain causing a stroke

Aorta.

The bulge in a blood vessel can burst.

This results in haemorrhage.

The larger an aneurysm becomes, the more likely it is to burst.

Thrombosis

Thrombosis occurs if a plaque breaks through the endothelium.

It develop a rough surface.

This causes the formation of a clot or thrombus inside a blood vessel.

This obstructs the flow of blood through the circulatory system.

It can be dislodged, being carried down into smaller arteries, blocking blood flow.

The tissue affected is starved of essential nutrients and oxygen.

When thrombosis affects important arteries it can be fatal or cause serious illness:

In the coronary arteries it may cause a heart attack myocardial infarction

In the brain with blood it may cause a stroke.

Coronary Heart Disease

Coronary heart disease (CHD) occurs due to the accumulation of plaques within the walls of the coronary arteries.

These supply the myocardium (the muscle of the heart) with oxygen and nutrients.

Most individuals with CHD show no evidence of disease for decades as the disease progresses.

Gradually, blood flow to the heart muscle reduces.

This puts extra strain on the heart.

Myocardial infarction

Myocardial infarction is commonly known as a heart attack. Occurs when a dislodged thrombosis enters a coronary artery, or one of its branches.

The blood supply to a part of the heart is interrupted.

The resulting ischemia or oxygen shortage, if left untreated for a sufficient period, can cause damage and/or death of heart tissue.

It is the leading cause of death for both men and women all over the world.

Infarction = tissue death due to oxygen starvation.

It can be the cause of cardiac arrest, which is the stopping of the heartbeat.

Severe myocardial infarction may lead to heart failure, in which the pumping action of the heart is impaired.

Symptoms of acute myocardial infarction include;

chest pain (typically radiating to the left arm or left side of the neck)

shortness of breath nausea, vomiting palpitations, sweating, and anxiety (often described as a sense of impending doom).

Risk factors Hereditary factors can increase the risk of high cholesterol and high blood pressure.

High cholesterol:

Essential for cell membranes.

However, high levels can cause plaques.

Due to a high concentration of low-density lipoproteins in the blood.

This is linked to high levels of saturated fats in the diet.

High blood pressure.

Puts more stress on blood vessels.

Increases risk of aneurysms or thromboses.

Can also cause blood vessels to harden and thicken, reducing blood flow

Various risk factors:

Salt can increase blood pressure

Smoking:

Nicotine causes a narrowing of arteries, leading to high blood pressure.

Carbon monoxide reduces how much oxygen is carried of haemoglobin.

The heart works harder to supply the tissues with oxygen.

This also increases blood pressure.

Stress

To reduce the risk of heart disease:

Increase intake of antioxidants eg vitamin C

Increase fibre intake - cellulose

Age Incidence increases in men over 60 and women over 65.

HC/2014