Lecture Twenty Two - Internal transport Flashcards
Why does diffusion not work if you are big?
Diffusion rate decreases with the square of distance between surfaces.
Cells must be functionally connected with the aqueous environment of the body.
If the animal is larger the distance over which something must be diffused is large then diffusion cannot occur.
How does invertebrate diffusion work?
Direct uptake from environment.
Requires direct contact with medium.
E.g. Hydra:
Do not need to use a circulatory system as there are only two body layers (central body cavity filled with water).
Direct diffusion of gasses through skin.
Gastrovascular cavity:
Diffusion of nutrients etc over short distance.
Simple circ system.
Serves as a gut and as a circ system.
What are open and closed circulatory systems?
Open:
Low pressure.
Distribution of blood not well regulated.
Return to heart slowly.
All organs in contact with blood - sloshing around internal cavity.
No vessels - cannot regulate where flow goes.
Closed:
High pressure.
Distribution of good well regulated.
return to the heart rapidly.
More efficient - blood contained in vessels throughout body.
When diffusion distance increases (either larger organisms or not living in water) organism must have a more complex circ system.
Describe vertebrate circulatory systems.
Closed circ system.
hert -> gas exchange -> arteries -> arterioles -> -> capillaries -> venules -> veins -> heart.
Blood supply correlated with metabolic requirement of animal and organ.
That is, the higher the metabolic activity, the higher the blood supply, as more O2 is required here.
Closed circ system allows of dynamic responses to O2 demand.
The larger the body, the slower the heart rate.
What is single circuit blood flow?
Found in fish.
Two chambered heart.
Pressure in gills must equal pressure in rest of body.
Volume change with heart contraction.
Blood makes one trip around the body every one time is passes through the heart.
What is double circuit blood flow?
Amphibian/reptilian:
Ventricle undivided.
Some mixing of blood.
Equal pressure.
Skin and lungs both receive blood (not reptiles).
Collection vessels = atrium.
Pumping vessels = ventricles.
Blood flows twice to the heart for every circuit of the body.
Mixing of oxygenated and deoxygenated blood occurs in the heart.
Mammalian/avian:
Complete division of ventricles.
Different pressure in pulmonary and systemic circuits.
Most effective oxygen delivery system.
Heart has four chambers and ventricles are divided so that oxygenated and deoxygenated blood do not mix.
Lung capillaries = blood flows slower (so that O2 can actually have time to diffuse into blood).
System ic capillaries - blood flows more quickly.
Pulmonary and systemic circuits operate simultaneously.
Distribution of blood to organs not equal or constant.
What is the structure of the mammalian heart?
Should be able to label a mammalian heart (have a look int he notes or on google).
Ventricles are muscular and do the pumping action.
Atrium are less muscular and collect blood and gently squeeze it into the ventricles.
Contraction = systole.
Relaxation = diastole.
Cardiac output = heart rate x stroke volume.
Each heart beat can be separated into stages (in an ECG).
1) Atrial systol:
The atria contract, forcing any remaining blood in the atria into the ventricles. The AV valves close behind the blood at the end of atrial systole. (P)
2) Ventricular systol:
The semilunar valves open a the ventricles contract, and the blood is forced into the arteries. (QRS)
3) Atrial and ventricular diastole:
The semilunar valves close, and blood returning to the heart flows ingot he atria. This blood flows through the open AV valves into the ventricles. (T)
How does the electrical coordination of the heart work?
Sinoatrial node is pacemaker.
Contraction is coordinated and rhythmic.
Delay between DA and AV nodes.
1) Signals from the SA node trigger systole int he atria.
2) Structure of the conducting tissues at the AV node slows down the signal (the ‘AV delay’).
3) When signals finally leave the AV node, they reach the ventricles by way of the bundle branches - ventricular systole begins.
4) Purkinje fibres allow the signal to quickly spread throughout the ventricles, triggering full ventricular systole.
Explain the features of the blood vessels.
Differ in properties and volume.
More blood in venous than arterial, velocity variable.
Elastic walls with smooth muscle.
Nearly all exchange in capillaries.
Flow in veins from muscular contraction.
At any given time there is more blood in the veins than in the arteries.
Explain blood pressure.
Pressure from cardiac output and peripheral resistance.
resistance always present.
Depleted when blood reaches veins.
Arterial pressure affected by posture.
Heart rate falls when lying.
Cause of postural dizziness.
Valves and sinuses prevent too much pressure.
Capillaries have a high area and low velocity - good because gas exchange needs time to occur.
What are sphincters in the blood vessels?
Sphincters help regulate where blood flows.
When sphincters are relaxed, capillaries can fill with blood.
When sphincter is contracted, blood flow is blocked from capillaries.
What are the components of blood?
Plasma - mostly water. Red blood cells - transport oxygen. White blood cells - immunological. Platelets - clotting factos. Cell numbers regulated to meet requirements.
