Transport in animals

Why do multicellular organisms require transport systems (4)

High metabolic rates

Small surface area to volume ratio - increased diffusion distances and slower diffusion rates

high metabolic rates

to transport/remove gases/waste products

what is an open circulatory system

when the transport medium is pumped straight from the heart into the body cavity and not contained within vessels

what is haemocoel (2)

Open body cavity in animals with open circulatory system

Has direct access to all the cells

what is haemolymph (3)

Transport medium insects

Contains no oxygen and carbon dioxide

Transports food, nitrogenous waste products and cells involved in defence against disease

describe transport in insects (4)

Open circulatory system

Heamolymph exits heart and flows through haemocoel at low pressure

Exchange occurs between tissues/cells and the heamolymph

Heamolymth returns to heart through an open ended vessel

Disadvantage of transport in insects (3)

Haemolymph circulates at low pressure

Steep concentration gradients cannot be maintained

Amount of haemolymph flowing to a particular tissue cannot be changed

describe the features of a closed ciculatory system (4)

Transport medium is carried by closed vessels

Blood never comes in contact with the tissues/cells

Substances diffuse in and out through walls of the blood vessels

Amount of blood reaching different parts can be controlled

Blood circulation in fish (3)

Blood leaves the heart at high pressure

Passes through first set of capillaries in the gills where the blood becomes oxygenated

Passes through second set of capillaries when it reaches the body tissues

Disadvantage for single circulatory system (3)

Blood leaves the heart at high pressure but after passing through first set of capillaries to gain oxygen blood pressure decreases

Blood moves slowly to body tissue

Limits how rapid oxygen can be transferred to body cells

Advantage of double circulatory system (4)

Blood loses pressure after flowing through lungs

So passes through heart again

Pumped to body tissues at high pressure

Oxygen reaches body tissues rapidly - more efficient

3 different tissues in blood vessels

Elastic fibres

Smooth muscle

Collagen

role of arteries

transport high pressure blood away from the heart - oxygenated except for pulmonary artery

role of arterioles

Connect arteries to capillaries

role of capillaries

Form a network through all body tissues

For exchange of substances from blood to tissues

role of venules

Connect capillaries to veins

role of veins

carry low pressure blood back to heart - deoxygenated except for pulmonary vein

function of superior vena cava

Carries deoxygenated blood from head and upper body to heart

function of inferior vena cava

Carries deoxygenated blood from lower parts of the body to heart

Tissue composition in arteries (3)

Elastin - to withstand the high pressure blood and regulate pulse surges

Smooth muscle - to constrict the size of lumen

Collagen outer layer - provides structural stability - prevents bursting under high pressure

Tissue composition of arterioles (2)

Less elastin than arteries - blood flows at relatively low pressure - no pulse surges

More smooth muscle than arteries - to constrict size of lumen to control blood flow to individual organs

function of endothelium tissue in blood vessels

Provide smooth surface for blood to flow easily

what happens during vasoconstriction (2)

Smooth muscles in arteriole contract

Prevents blood flow to capillary bed

what happens during vasodilation (2)

Smooth muscles in arteriole relax

increase blood flows into capillary bed

Adaptations of capillaries (4)

Form an extensive network - capillary bed - to increase surface area for diffusion

Total cross sectional area of capillary bed is larger than the arteriole, so blood slows down - more time for diffusion to occur

Small lumen - so that RBC have to travel one by one

Thin wall made of single layer of endothelial cells- decreased diffusion distance

Tissue composition of venules

Few elastic fibres as the blood travels at low pressure

Tissue composition of Veins (4)

Lots of collagen

Few elastic fibres

Valves in medium sized veins to prevent backflow

Large lumen

Adaptations of body to ensure low pressure blood reaches the heart (3)

Veins have valves - ensures blood only flows 1 way to the heart

Many big veins run between active muscles - when the muscles contract the veins are squeezed and the blood is forced towards the heart

Breathing movements of the chest act as a pump - pressure changes move blood from veins in chest and abdomen to the heart

Components of blood

RBC

Glucose

Amino acids

Platelets

WBC

Fats

Plasma

Plasma proteins - albumin

Oxygen/CO₂

Hormones

functions of blood (3)

transport substances

transports heat so involved in thermoregulatory system

maintains diffusion gradients

Waste products that diffuse out of cells (3)

Carbon dioxide

Lactic acid

Urea

what is oncotic pressure

Tendency for water to move into blood

About -3.3kPa

What causes water to move into capillaries by osmosis

Plasma proteins (e.g. albumin) are soluble in water so decreases water potential of blood in the capillaries

Hydrostatic pressure

The pressure experienced by blood due to heart’s contraction

What is in tissue fluid

Mostly water

Oxygen

Glucose and mineral ions

how is tissue fluid formed (2)

At arterial end of capillary hydrostatic pressure is higher than oncotic pressure (4.7kPa)

Blood plasma forced out through gaps in endothelium of capillary

What causes tissue fluid to move back into capillaries (2)

At venous end of capillary hydrostatic pressure is lower than oncotic pressure

Tissue fluid moves back in by osmosis

How much tissue fluid re-enters the capillary

about 90%

What happens to 10% of tissue fluid that does not go back into the capillary (2)

Drains into system of blind ended tubes called lymph capillaries

The fluid is now called Lymph

composition of lymph

Water

Fatty acids

Lymphocytes

High amounts carbon dioxide

Fewer oxygen and nutrient molecules than plasma and tissue fluid

How does lymph return to the blood (3)

Lymph capillaries join to form larger vessels

Squeezing of body muscles transports lymph through it

Vessels have one way valves

Where does lymph return to the blood

By flowing into left and right subclavian veins (under the collar bone - clavicle)

Adaptaions of erythrocytes (2)

Biconcave shape - increased surface area

No nucleus - more space for haemoglobin

Name of compound when oxygen is bound to haemoglobin

Oxyhaemoglobin

Equation for oxygen binding to haemoglobin

Hb + 4O₂ ⇌ Hb(O₂)₄

what is positive cooperativity

When quaternary structure of haemoglobin changes after first oxygen molecule has bound to allow rapid binding of more oxygen molecules - haemoglobin gains affinity for oxygen

How does oxygen enter erythrocytes (3)

In lung capillaries erythrocytes have low levels of oxygen

Air in alveoli has high levels of oxygen

Oxygen diffuses into erythrocyte by diffusion down concentration gradient

How does oxygen leave erythrocytes

In body cells there is low levels of oxygen

In erythrocytes high levels of oxygen

Oxygen diffuses into body cells by diffusion down concentration gradient

Explanation of oxygen dissociation curve in humans

Initially as partial pressure of oxygen increases, %saturation of haemoglobin increases slowly.

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As soon as first oxygen molecule is bound, quaternary structure changes (positive cooperativity). Haemoglobin’s affinity for oxygen increases. Second and third oxygen molecules are added rapidly, and haemoglobin saturation increases rapidly. Fourth oxygen molecule is harder to load

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At high partial pressure of oxygen, all haem groups are bound to oxygen and the haemoglobin is fully saturated

Why do erythrocytes have high oxygen saturation in the lungs

there is a high partial pressure of oxygen

What happens to oxygen when erythrocytes reach body tissues (5)

• Cells in body tissue respire aerobically so they use up oxygen

• The partial pressure of oxygen is low. Haemoglobin saturation decreases

• As soon as first oxygen molecule is released, quaternary structure changes. Affinity decreases.

• If partial pressure drops even more, more oxygen molecules will dissociate rapidly

• Last oxygen molecule only unloads when partial pressure is very low in very active tissue

Why does 4th oxygen molecule only bind at high partial pressures

3 haem groups are already binded, so chance of oxygen molecule colliding with 4th haem group is relatively low

describe the Bohr effect

As partial pressure of carbon dioxide increases, oxygen affinity of haemoglobin decreases

benifits of the Bohr effect (2)

• In lungs partial pressure of CO₂ is low so oxygen affinity of haemoglobin is high, so it becomes more saturated

• In active tissues with high partial pressure of CO₂ oxygen affinity of haemoglobin decreases, so oxygen more readily dissociates

How does CO2 decrease oxygen affinity of haemoglobin (4)

CO₂ is transported in blood as carbonic acid (H₂CO₂)

This dissociates to produce H⁺ ions

H⁺ ions bind to haemoglobin and changes quaternary structure

Oxygen affinity reduced

Name of compound when CO₂ binds to haemoglobin

Carbaminohaemoglobin

How does fetal blood gain oxygen

Deoxygenated fetal blood and oxygenated maternal blood pass closely in the placenta (but do not mix)

Oxygen moves into fetal blood down concentration gradient

How is transfer of oxygen from maternal to fetal blood made more efficient (2)

Fetal haemoglobin has slightly higher oxygen affinity than maternal haemoglobin

Carbon dioxide diffuses from fetal blood to maternal blood - lowering maternal haemoglobin oxygen affinity

why is it important that fetal haemoglobin has higher oxygen affinity than adult haemoglobin

Why does fetal haemoglobin not have too high oxygen affinity

Because then the oxygen would not dissociate into fetal tissues

How is steep concentration gradient for oxygen maintained in erythrocytes

Oxygen is bound to haemoglobin so concentration of free oxygen remains low

In what ways is CO2 transported in the blood

5% dissolved directly in the plasma

20% bound to haemoglobin to form carbaminohaemoglobin

75% as hydrogen carbonate ions (HCO3-)

How is hydrogen carbonate formed in the blood

Carbon dioxide in erythrocytes reacts with water to form carbonic acid

CO2 + H2O ⇌ H2CO3

Carbonic acid dissociates into hydrogen ions and hydrogen carbonate

H2CO3 ⇌ H+ + HCO3-

HCO3- moves into plasma

Benefits of converting carbon dioxide to carbonic acid (2)

Allows CO2 concentrations in erythrocyte to be kept low

So steep concentration gradient is maintained for CO2

What is chloride shift

hydrogen carbonate ions move out of erythrocyte into plasma

But since they have negative charge if they move out the RBC becomes positively charged

To maintain the electrical charge of the cell, chloride ions (Cl-) move into the RBC

Function of carbonic anhydrase enzyme

Speeds up reaction CO2 + H2O ⇌ H2CO3

How does carbon dioxide leave the blood

HCO3- ions move from plasma into RBC

Chloride ions move out down an electrochemical gradient

HCO3- reacts with H+ to form H2CO3

H2CO3 is broken down into CO2 + H2O by carbonic anhydrase

CO2 moves into plasma and diffuses into the alveoli

What happens to free H+ ions in RBC after H₂CO₃ dissociates

H+ ions bind to haemoglobin to form haemoglobinic acid in a reversible reaction which acts as a pH buffer

How does breathing help with filling of heart (2)

Inhaling increases thoracic volume so thoracic pressure decreases

Causes increased blood flow to heart due to negative pressure

Which heart valves have chordae tendinae

Only the atriventricular valves

Function of the chordnae tendinae

Prevent the atrioventricular valves from turning inside out due to pressure exerted by ventricular contraction

Function of septum

Prevents oxygenated and deoxygenated blood from mixing

Valve between right atrium and right ventricle

Tricuspid Valve/ Right atrioventricular valve

Valve between right ventricle and pulmorary artery

Pulmonary valve or

Right semilunar valve

Valve between left atrium and left ventricle

Bicuspid valve/ Mitral valve/ Left atrioventricular valve

Valve between left ventricle and aorta

Aortic valve or

Left semilunar valve

Stages of cardiac cycle

Atrial systole

Ventricular systole

Diastole

What happens during atrial systole (3)

Atria contract

Blood is forced into ventricles

Atrioventricular valves are open

What happens during ventricular systole (4)

Ventricles contract

Atrioventricular valves close

Semilunar valves open

Blood flows into pulmonary artery and aorta

What happens during diastole (3)

Atria and ventricles are relaxed

Atrioventricular valves are open

Semilunar valves are closed

How long is an average cardiac cycle

0.7 seconds

In what pressure condition do the atrioventricular valves open

When pressure in atria is greater than pressure in ventricle

In what pressure condition do the atrioventricular valves close

When pressure in ventricles is greater than pressure in atria

In what pressure condition do the semilunar valves open

When pressure in ventricles is greater than pressure in pulmonary artery and aorta

In what pressure condition do the semilunar valves close

When pressure in pulmonary artery and aorta is greater than ventricles

Why is cardiac muslce described as being myogenic

Because it contracts on its own without external stimulus

How are heart contractions coordinated (5)

• sinoatrial node (SAN) sends a wave of electrical excitation

• this travels to the atrioventricular node (AVN) causing the atria to contract

• After short delay AVN stimulates the Bundle of His

• Bundle of His splits into 2 and conducts excitation to apex of heart

• At apex Purkyne tissue spread out through walls of both ventricles causing it to contract

What is the advantage of non-conductive tissue seperating the right atrium and right ventricle

Ensures that ventricles only contract after the atria contract and all the blood has been transferred to the ventricles

From where do the ventricles contract

Ventricles contract from the bottom

What is the SAN made of

SAN is made of specialised cells

Function of pericardium

Prevent heart from expanding too much

Equation for cardiac output

Cardiac output = heart rate x stroke volume

What is the heart rate

number of heart beats in one minute

ranges from 60 to 100bpm in resting adult

What is the stroke volume

volume of blood pumped out of a ventricle during each contraction

What is an ectopic heartbeat

An extraheart beat which is not part of the usual rhythm

What is atrial fibrillation

When random and rapid contractions of the atria occur

What is bradychardia

Slow heartbeat

What is tachychardia

Fast heartbeat

Caused by stress, fear, excercise

Why can electrical excitation not travel straight from SAN to ventricles

There is a layer of non-conducting tissue seperating the right atrium from right ventricle

how do fish keep active with only a single circulatory system (4)

countercurrent system for efficient gas exchange

water supports body weight

ectotherms so do not need to regulate body temperature

all these reduce metabolic demands

difference between adult and fetal haemoglobin

adult - 2 beta 2 alpha subunits

fetal - 2 gamma 2 alpha subunits