Transport in Animals

why do multicellular organisms require transport systems?

• high metabolic demands

• large SA:V ratio

• hormones made in one place but needed in another

• food digested in one place but needed in another

• waste products of metabolism need to be removed from everywhere into excretory organs

what do circulatory systems contain?

• transport medium

• vessels for transport medium

• pumping mechanism to move the transport medium

mass transport system

when substances are tranpsorted in a mass of fluid with a mechanism for moving the fluid around the body

open circulatory systems (insects)

• transport medium is haemolymph

• haemolymph is not enclosed in vessels

• haemolymph is always under low pressure

• haemolymph flowing to a tissue cannot be varied

• haemolymph returns to heart via an open ended vessel

closed circulatory systems

• transport medium is blood

• blood is enclosed in vessels

• blood supplied to organs can be varied

• blood returns to heart

single closed circulatory system (fish)

• blood travels once through the heart for each complete circulation of the body

• blood passes through two sets of capillaries: in the first, oxygen and carbon dioxide is exchanged, in the second, substances are exchanged between the blood and cells

• this causes the blood pressure to drop, limiting the efficiency of exchange processes

• however, in fish, their countercurrent exchange mechanism, their weight being supported by water, and no need for temperature regulation reduces the metabolic demands allowing them to be active even with a single closed circulatory system

double closed circulatory system

• two types of circulation: pulmonary and systemic

• pulmonary circulation: blood being pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide and then returning back to the heart

• systemic circulation: blood being pumped from the heart to the body to provide oxygen to cells and then returning back to the heart

what do elastic fibres do?

can stretch and recoil to provide vessel walls with flexibility

what does smooth muscle do?

contracts or relaxes, changing the size of lumen

what does collagen do?

provides structural support to the vessel

arteries

• elastic fibres

• smooth muscle

• collagen

• smooth endothelium for easy blood flow

arterioles

• more smooth muscle than arteries

• less elastin than arteries as less pulse surge

• same amount of collagen

capillaries

• microscopic

• lumen only 10µm wide

• made of endothelial cells

adaptations of capillaries

• large surface area for the diffusion of substances into and out of the blood

• slow movement of blood in capillaries gives more time for exchange by diffusion

• single endothelial cell thick therefore thin diffusion distance

veins

• valves to prevent backflow of blood

• lots of collagen

• less elastic fibre

• wide lumen

• smooth endothelium for easy blood flow

what are the adaptations for blood in veins to move against gravity under low pressure?

• valves to prevent backflow

• muscle contractions in arms and legs force blood back to the heart

• chest movements act as a pump to send blood back to the heart

positive cooperativity

• erythrocytes enter capillaries in lungs with relatively low oxygen level, making a steep concentration gradient between the inside of the erythrocytes and the air in the alveoli

• one oxygen molecule bind to a haem group of the Hb molecule, and the Hb molecule changes shape, making it easier for the next oxygen molecules to bind

• the oxygen is bound to the Hb, with free oxygen concentration staying low, therefore a steep diffusion gradient is maintained until all the Hb is saturated with oxygen

adaptations of erythrocytes

• biconcave shape for large surface area

• no nucleus for more space for oxygen

bohr effect

in active tissues with higher partial pressures of carbon dioxide, haemoglobin gives up oxygen more readily

what is the affect of the bohr effect in the lungs?

less carbon dioxide in the lungs, so Hb will not give up oxygen easily, instead it will bind easily

describe the relationship between fetal and adult haemoglobin (hint: fainting during pregnancy)

fetal Hb has a higher affinity for oxygen than adult Hb, so when the mother’s oxygenated blood flows past the deoxygenated fetal blood, the fetal Hb removes the oxygen from the maternal blood

where is carbon dioxide transported to?

• 5% in plasma

• 10-20% converted into carbaminohaemoglobin

• 75-80% converted into hydrogen carbonate ions

journey of deoxygenated blood into heart and lungs to oxygenated blood to body

inferior vena cava (from lower body) + superior vena cava (from upper body) → right atrium → tricuspid valve → right ventricle → semi lunar valves → pulmonary artery → lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → semi lunar valves → aorta → body

what valves open/close at A, B, C, and D? (A - bottom left, B - top left, C - top right, D - bottom right)

A - AV valves close, B - SL valves open, C - SL valves close, D - AV valves open

what is diastole?

relaxation

what is systole?

contraction

myogenic

initiates its own rhythmic contractions without the need of electrical signals from the brain

journey of a heartbeat

• wave of excitation from the SAN, causing atrial systole, initiating heartbeat - (non-conducting tissue prevents excitation passing directly to ventricles)

• AVN picks up this electrical activity and stimulates the Bundle of His (conducting tissue made of Purkyne fibres) after a short delay

• this tissue conducts a wave of excitation to the apex of the heart, spreading out to the ventricles, therefore initiating ventricle systole

why does the AVN impose a slight delay?

to ensure the atrial systole has finished before ventricular systole begins

tachycardia

rapid heartbeat

bradycardia

slow heartbeat

ectopic heartbeat

extra heartbeat

atrial fibrillation

arrhythmia - fast fibrillations

describe an ECG trace with reference to P, Q, R, S and T

• at P, SAN sends a wave of excitation causing atrial systole (atrial depolarisation)

• in the short PR interval, AVN stimulates the Bundle of His and Purkyne fibres

• in QRS, the Purkyne fibres send a wave of excitation to across the ventricles and down to the apex (ventricular depolarisation)

• at T, ventricular systole occurs (ventricular repolarisation)