3.1.2 Transport in animals Flashcards
Types of circulatory systems
- Open circulatory system
- Closed circulatory system
- Single circulatory system
- Double circulatory system
Open circulatory system
- Invertebrate, insects.
- Transport medium (haemolymph) pumped directly to the open body cavity (haemocoel), very few transport vessels
- Transport medium pumped at low pressure and will transport food and nitrogenous waste, not gases - transported via tracheal system
- Once exchange has taken place at the cells + tissues, transport medium returns to the heart through an open-ended vessel.
Closed circulatory systems
- All vertebrates (fish + mammals) + some invertebrates (annelid worms)
- Transport medium (blood) remains inside of the vessels (blood vessels)
- Gases + small molecules can leave the blood by diffusion of due to high hydrostatic pressure
- Closed circulatory systems transport oxygen and CO2, O2 is usually transported by a pigmented protein (haemoglobin)
Single closed circulatory system
- Blood only passes through the heart once per cycle (Fish)
- Blood passes through two sets of capillaries
Immediately after being pumped out of the heart, the blood flows through capillaries in the gills to become oxygenated - Blood then flows through capillaries delivering blood to the body, before returning back to the heart
- System wouldn’t enable efficient gas exchange for mammals, but works for fish due to counter-current flow mechanism
Double closed circulatory system
- Blood passes through the heart twice per cycle (Birds + most mammals)
- One circuit of blood vessels carries blood from the heart to the lungs for gas exchange
- Second circuit of blood vessels carries blood from the heart to the rest of the body to deliver oxygen and nutrients + collect waste
Types of blood vessels
Arteries
Arterioles
Veins
Venules
Capillaries
Arteries
Smooth muscle layer:
Thicker than veins so that constriction and dilation can occur to control the volume of blood
Elastic layer:
Thicker than veins to help maintain blood pressure. The walls can stretch and recoil in response to the heartbeat.
Collagen layer:
Collagen outer layer to provide structural support
Wall thickness:
Thicker than veins to help maintain blood pressure
Arterioles
Smooth muscle layer:
Thicker than in arteries to help restrict blood flow to capillaries
Elastic layer:
Thinner than in arteries as the pressure is lower
Collagen layer:
Thinner
Wall thickness:
Thinner as pressure is slightly lower
Capillaries
No smooth muscle layer
No elastic layer
No collagen layer
- One cell thick consisting of only a lining layer.
-Provides a short diffusion distance for exchanging materials between the blood and cells
-Form capillary beds at exchange surfaces
- Narrow diameter to slow blood flow
- RBC can only just fit through + squashed against the walls - maximises diffusion
Venules
Thin layer of smooth muscle
No elastic layer
No collagen layer
- Very thin wall.
- Several venules join to form a vein
- Has valves
Veins
Smooth muscle layer:
Relatively thin so it cannot control the blood flow
Elastic layer:
Relatively thinner as the pressure is much lower
Collagen layer:
Contains lots of collagen
Wall thickness:
Thin as the pressure is much lower so there is low risk of the vessel bursting.
The thinness means the vessels are easily flattened, helps the flow of blood up to the heart
- Contains valves
Tissue fluid
Capillaries have small gaps in their walls so that liquid and small molecules can be forced out - forms tissue fluid
Hydrostatic pressure - pressure exerted by liquid
Oncotic pressure - tendency of water to move into the blood via osmosis
Interaction of hydrostatic + oncotic pressure is responsible for the formation and reabsorption of tissue fluid.
Tissue fluid formation
-As blood enters the capillaries from the arterioles, the smaller dimeter results in high hydrostatic pressure
- Pressure forces water, glucose, amino acids, fatty acid, ions + oxygen out of the capillaries at the arterial end
- Solution forced out is tissue fluid - bathes the cells in substances they need.
- Hydrostatic pressure is higher than the oncotic pressure at the arterial end, so the net movement of liquid is out of the blood in the capillaries
Tissue fluid reabsorption
- Large molecules (plasma proteins) remain in the capillaries and lower the water potential of the blood remaining in the capillary
- Lowered WP results in higher oncotic pressure
- Venule end of the capillaries, hydrostatic pressure is low due to the loss of liquid, the WP is very low > the net movement of liquid is back into the capillary by osmosis
- Once equilibrium of the WP of the blood is reached, no more water from the tissue fluid can be reabsorbed back into the blood in the capillaries
- Remaining liquid absorbed into the lymphatic system + eventually drains back into the bloodstream near the heart > lymph
- Has a similar composition to plasma, does not contain the large plasma proteins and it has less oxygen + nutrients.
Mammalian heart
- Cardiac muscle is myogenic (automatically contracts + relaxes) + never fatigues
- Coronary arteries supply the cardiac muscle with oxygenated blood for aerobic respiration - provides ATP so cardiac muscle can pump automatically.
- Heart surrounded by pericardial membranes - inelastic membranes which prevent the heart from filling + swelling with blood.
Mammalian heart part 2
- Left ventricle has the thicker muscular wall so it can contract with more force + pump the blood at a higher pressure - all around the body
- Right ventricle pumps blood to the lungs, much closer + requires blood to flow slowly to allow time for gas exchange - muscular wall is much thinner, BP does not need to be pumped at as high a pressure
- Atria both have very thin muscular walls - blood only needs to be pumped from the atria into the ventricles, minimal pressure + force is required
Diastole
- Atria + ventricular muscles are relaxed
- Blood enters the atria via vena cava + pulmonary vein
- Blood flowing into atria increases the pressure within the atria and the atrioventricular valves open so blood can begin to flow into the ventricles
Atrial systole
- Atria muscular walls contract, increasing the pressure further - causes blood to flow into the ventricles, through the open atrioventricular valves
- Ventricular muscular walls are relaxed
Ventricular systole
-After short delay, ventricle muscular walls contract, increasing the pressure beyond that of the atria - causes atrioventricular valves to close and the semi-lunar valves to open
- Blood is pushed out of the ventricles into the arteries (pulmonary + aorta)
Cardiac output
Cardiac output = heart rate X stroke volume
Heart rate = beats of the heart per minute min-1
Stroke volume = volume of blood that leaves the heart each beat dm3
Components in control of the cardiac cycle
- Rate of contraction is controlled by wave of electrical activity
- Sinoatrial node (SAN) - located in the right atrium - pacemaker
- Atrioventricular node (AVN) - located near the border of the right and left ventricle within the atria
- Bundle of his runs through the septum - containing purkyne fibres.
Process of control of the cardiac cycle
- SAN releases a wave of depolarisation/excitation across the atria, causing it to contract
- AVN releases another wave of depolarisation when the first reaches it. A non-conductive layer between the atria and ventricles prevents the wave of depolarisation travelling down to the ventricles
- The bundle of His conducts the wave of depolarisation down the septum and the Purkyne fibres
- The apex + walls of the ventricles contract. A short delay before this happens - whilst AVN transmits the second waves of depolarisation
- Allows enough time for the atria to pump all the blood into the ventricles - the cells repolarise + cardiac muscle relaxes
Electrocardiogram (ECG)
- Waves of depolarisation can be measured using an ECG + interpreted to diagnose irregularities in heart rhythms
- Doesn’t directly measure the electrical activity of the heart, the differences in electrical activity in the skin which is caused by the electrical activity of the heart.
- Electrodes are stuck onto the skin to detect electrical activity
Types of abnormal heart rhythms
-Tachycardia: When the heart is beating at over 100bpm - normal during exercise but abnormally fast while at rest.
-Bradycardia: when the heart is beating less than 60bpm - many athletes have bradycardia as they are so fit that their cardiac muscle can contract harder + fewer contractions are required. If heart rate drops too low, an artificial pacemaker is required to regulate the HR.
- Fibrillation: when there is an irregular rhythm of the heart
- Ectopic heartbeat: when there are additional heartbeats that are not in rhythm, common to occur once a day but if happening more regularly, could indicate a serious health condition.
