The circulation of blood and structure of mammalian heart Flashcards
What circulatory system do mammals have?
Closed double circulatory system
Closed- blood remains within the blood vessels
Double circulatory system- blood passes through the heart twice in one circuit. One circuit delivers blood to the lungs and another delivers blood to the rest of the body
Why do mammals require a double circulatory system?
To manage the pressure of blood flow.
-Blood flows through lungs at lower pressure, preventing damage to capillaries in alveoli + reduces speed at which blood flows so more time for gas exchange
-Oxygenated blood from lungs then goes back through heart to be pumped out at higher pressure to rest of body. This ensures the blood reaches all the respiring cells in the body
What is cardiac muscle?
Thick muscular layer that is:
- myogenic- can contract + relax without nervous or hormonal stimulation
- never fatigues- as long as it has a constant supply of O2
What are the coronary arteries?
Supply the cardiac muscle with oxygenated blood + branch off from the aorta
If become blocked, cardiac muscle wont receive O2 so wont be able to respire so cells will die. This results in myocardial infarction (heart attack)
Relate the structure of the chambers to their function
Atria- Thinner muscular walls as don’t need to contract as hard as not pumping blood far + elastic walls to stretch when blood enters
Ventricles- Thicker muscular walls to contract with more force + pump blood under high pressure. Left ventricle has thicker muscular wall than right as it has to contract with more force + pump blood at a high pressure around the body
Types of valves
Semi-lunar valves- in aorta + pulmonary artery
Atrioventricular valves- between atria + ventricles
Bicuspid (left)
Tricuspid (right)
Open when pressure is higher behind the valve + close when pressure is higher in front of the valve
They prevent backflow of blood
What is the function of the septum?
Separates oxygenated blood + deoxygenated blood. Maintains a high conc of O2 in oxygenated blood to maintain conc gradient to enable diffusion at respiring cells
Compare the structure +function of each blood vessel
Arteries- Thicker muscular layer than veins so constriction + dilation can occur to control vol of blood. Elastic layer thicker than veins to help maintain blood pressure + walls can stretch. Wall thickness is thicker than veins to prevent vessels bursting due to high pressure. No valves
Arterioles- Thicker muscular layer than in arteries to help restrict blood flow into capillaries. Thinner elastic layer than arteries as pressure is lower. Wall thickness is thinner as pressure is lower. No valves
Veins- Thinner muscular layer so cant control blood flow. Elastic layer is thinner as pressure is lower. Wall thickness is thinner as low pressure so low risk of bursting. Contain valves
Capillaries- No muscular or elastic layer. Wall is one cell thick which provides short diffusion distance for exchanging materials and slows the blood so there is more time for gas exchange
Describe what happens during diastole?
-Atria +ventricular muscles relax
-Blood enters atria via pulmonary vein + vena cava
-Blood flowing into atria increases pressure in the atria as theres a larger volume of liquid
Describe what happens during atrial systole
-Atria muscular walls contract which decreases the volume but increases the pressure causing the AV valves to open so blood can flow into the ventricles.
-Ventricular muscular walls are relaxed
Describe what happens during ventricular systole
-After short delay, ventricle muscular walls contract which decreases volume but increases pressure causing AV valves to close ( to prevent backflow) + semi lunar valves to open
-Blood is pushed out of ventricles into arteries
What is cardiac output + how do you calculate it?
Volume of blood which leaves one ventricle in one minute
cardiac output = heart rate x stroke volume
Heart rate- Beats of heart per min (min-1)
Stroke volume- Volume of blood that leaves heart each beat (dm³)
What is tissue fluid?
A watery substance containing water, glucose, amino acids, fatty acids, ions and O2. It bathes tissues + supplies these nutrients to cells
How is tissue fluid formed?
Capillaries have small gaps in the walls so liquid + small molecules can be forced out
As blood enters the capillaries from the arterioles, the smaller diameter results in a high hydrostatic pressure, so water + small molecules are forced out
This is known as ultrafiltration
How is tissue fluid reabsorbed?
-Large molecules (RBC’s, large proteins + platelets) remaining in capillaries create lower water potential
-Towards venule end of capillary, hydrostatic pressure is lowered due to loss of liquid but the water potential is low
-Water re-enters by osmosis + carries waste which is dissolved in tissue fluid
-Not all liquid is reabsorbed by osmosis as equilibrium will be reached, so rest of tissue fluid is absorbed into lymphatic system + eventually drains back into bloodstream near heart
