organisation

Principles of Organisation

cells make up all living things
a tissue is a group of specialised cells working together to perform a specific function
organs are formed from a number of different tissues working together to perform a specific function
organs are organised into organ systems which work together to perform a specific function

The Human Digestive System

digestion = breaking down large insoluble food molecules into smaller soluble molecules

It is made up of the following organs

glands (salivary glands and pancreas) which produce digestive juices containing enzymes which break down food
stomach which produced hydrochloric acid to kill bacteria and provide the optimum pH for protease enzyme to work
small intestine where soluble molecules are absorbed into the blood
liver which produces bile which is stored in the gall bladder which helps with the digestion of lipids
large intestine absorbs water from undigested food to produce faeces which pass out of the body through rectum and anus

enzymes = biological catalysts

present in many reaction so they can be controlled
can break up large molecules and join small ones
they are protein molecules and their shape is vital to its function
this is because they each have a uniquely shaped active site where the substrate binds to form enzyme-substrate complex

Lock and Key Hypothesis

shape of substrate is complementary to active site of enzyme so they bind to form an enzyme-substrate complex
once bound, reaction takes place and products are released from the surface of the enzyme

enzymes require an optimum pH and temperature because they are proteins
optimum temperature ~ 37^oC
- rate of reaction increases as temp increases up to optimum
- eventually reaction stops because when temp is too hot, bonds in the structure break so active site is denatured
- this means substrate can no longer fit therefore enzyme can no longer work

Different enzymes

amylase	protease	lipase
breaks down starch into glucose	breaks down proteins into amino acids	breaks down fats into fatty acid and glycerol
produced in salivary glands, pancreas and small intestine	produced in stomach, pancreas and small intestine	produced in pancreas and small intestine

soluble glucose, amino acids, fatty acids and glycerol pass into the bloodstream to be carried to cells all over the body and are used to build new carbohydrates, lipids and proteins - some glucose used in respiration

Food Tests

sugar	starch	protein	lipid
benedict’s solution + heat	iodine solution	biuret solution	sudan III solution
high quantity = red medium quantity = yellow/green	+ve = blue/black	+ve = purple	+ve = red layer on top
-ve = blue	= brown/orange	-ve = blue	-ve = orange/red solution

Bile

produced in the liver and stored in the gallbladder
it has 2 main roles
1. alkaline to neutralise hydrochloric acid which comes from the stomach - the enzymes in the small intestine have a higher optimum pH than those in the stomach
2. breaks down large drops of fat into smaller ones - emulsification - the larger surface area allows lipase to chemically break down the lipid faster

The Heart and Blood Vessels

double circulatory system = there are two circuits
1. deoxygenated blood
2. oxygenated blood

Pathway of Blood

→ deox. enters right atrium

→ passes through to right ventricle

→ exits through pulmonary artery

→ goes to lungs

→ gaseous exchange occurs and blood is ox.

→ ox. blood travels through pulmonary vein

→ enters left atrium

→ passes through to left ventricle

→ exits through aorta

→ ox. blood is taken to cells which use oxygen for respiration

→ ox. blood is now deox. blood

→ deox. blood travels back to heart via vena cava

Structure of the Heart

muscular walls provide a strong heartbeat
thicker muscular wall in left ventricle because blood needs to be pumped all over body whereas from right it only needs to go to lungs
4 chambers which separate deox. and ox. blood
valves to ensure no backflow of blood
coronary arteries cover the heart to provide its own ox. blood supply

Heart Rate

natural resting HR (70 bpm) is controlled by pacemaker cells in right atrium
they provide stimulation through small electrical impulses which pass as a wave across the heart muscle
this causes contraction
without this the heart would not pump fast enough to deliver required amount of oxygen to the whole body
artificial pacemakers can be used for individual’s with an irregular heartbeat - it is an electrical device that produces a signal causing the heart to beat as normal

Blood Vessels

Arteries	Veins	Capillaries
carry blood away from the heart	carry blood towards the heart	allow blood to flow very close to cells to enable substances to to move between them
thick muscular walls make them strong	wide lumen to allow the low pressure blood to flow through	one cell thick walls to create a short diffusion pathway
elastic fibres allow them to stretch and constrict so they can withstand the high pressure creating by pumping of the heart	valves to prevent backflow of blood	permeable walls so substances can move across them

Gas Exchange System

the lungs are found in the thorax and are protected by your ribcage; they supply oxygen to your blood and remove carbon dioxide

Gas exchange system is made up of:

trachea - wind pipe which air moves through
intercostal muscles - which contract and relax to ventilate the lungs
bronchi - air from trachea move into these and they lead to each lung
bronchioles - bronchi split into these and air moves in
alveoli - bronchioles lead to alveoli; air sacs where gaseous exchange occurs
diaphragm - separates lungs from digestive organs; flatten during contraction (inhalation)

Gas Exchange

upon inhalation, alveoli fill with oxygen
blood in the capillaries surrounding alveoli is deox. and has high CO₂ concentration
oxygen diffuses into bloodstream down the concentration gradient as bloodstream in capillaries has low O₂ concentration
carbon dioxide diffuses into alveoli down the concentration gradient as air in alveoli has low CO₂ concentration

→ Alveoli Adaptations

small in size and large in number creating a large surface area for diffusion to take place over
capillaries provide a large blood supply maintaining the concentration gradient
the alveoli has very thin walls so there is a short diffusion distance

Ventilation

the ribcage moves up and out + diaphragm moves down so volume of chest cavity increases
increased volume = lower pressure
air is drawn into chest as air moves from high pressure (the environment) to low pressure (the lungs)
the opposite happens during exhalation

Components of Blood

plasma	red blood cells	white blood cells	platelets
liquid that carries components in the blood: rbc, wbc, platelets, glucose, amino acids, CO₂, urea, hormones, proteins, antibodies, antitoxins	carry oxygen molecules from lungs to all body cells biconcave disc shape provides large surface area no nucleus to allow more room for carrying O₂ contain haemoglobin which binds to O₂to form oxyhaemoglobin	part of the immune system have a nucleus some produce antibodies some engulf and digest pathogens some produce antitoxins	help blood clot at site of wound clot dries and hardens to form scab allowing new skin to grow no nucleus without them cuts would result in excessive blood loss

CHD - Coronary Heart Disease

this is when coronary arteries are blocked with built up fatty material resulting in less blood flow to the heart reducing its oxygen supply which can lead to heart attack

Solutions:

stents are metal mesh tubes inserted into arteries to keep them open
+ effective in lowering the risk of heart attack
+ quick recovery from surgery
- risk of heart attack during procedure or infection after
- there is a chance of blood clots forming near stent (thrombosis)
statins are drugs which reduce the levels of LDL (bad cholesterol)
+ they reduce risk of strokes, CHD and heart attacks
+ they increase levels of HDL (good cholesterol)
- need to be taken continuously which may be inconvenient
- can have side effects
- may not have immediate effect as it slow down at the rate it is deposited