Circulation + Blood Flashcards
Why is a circulatory system needed?
The circulatory system is needed because cells require a constant supply of oxygen and metabolites to release ATP in respiration. Since organisms are several layers of cells thick, they cannot rely on simple diffusion because the diffusion distances would be too long, leading to low surface area to volume ratio (SA:V) and increased metabolic demand.
What are the advantages of a circulatory system?
The advantages of a circulatory system include maintaining blood pressure and controlling the average speed of blood flow through capillaries, which helps maintain a steeper concentration gradient for efficient exchange of gases and nutrients.
What is a closed double circulatory system?
A closed double circulatory system is one in which blood is contained in vessels and flows to the lungs to be oxygenated. Oxygenated blood then flows from the lungs to the body tissues. Passes through heart twice.
What is the pulmonary circulatory system?
The pulmonary circulatory system involves the right side of the heart pumping deoxygenated blood to the lungs to be oxygenated.
What is the systemic circulatory system?
The systemic circulatory system involves the left side of the heart delivering oxygenated blood to the body tissues.
What is the pericardium?
The pericardium is a protective, tough fibrous tissue that encloses the heart.
What is the cardiac cycle?
The cardiac cycle is a series of contractions (systole) and relaxations (diastole) of the cardiac muscle, and it is a continuous process.
What happens during muscle contraction in the cardiac cycle?
During muscle contraction, the volume of the heart chamber decreases, causing the pressure to increase.
What happens during atrial systole?
During atrial systole:
- The atrial walls contract, decreasing the volume and increasing the pressure in the atrium.
- The pressure in the atrium becomes greater than the pressure in the ventricles, so the atrioventricular (AV) valves open.
- Blood is forced into the ventricles, which experience a slight increase in pressure and their volume increases as they are in ventricular diastole.
What happens during ventricular systole?
During ventricular systole:
- The ventricles contract, decreasing their volume and increasing the pressure.
- The pressure in the ventricles becomes greater than in the atria, causing the AV valves to close to prevent backflow.
- The pressure in the ventricles becomes greater than in the aorta and pulmonary artery (PA), forcing the semilunar valves to open.
- Atrial diastole occurs at the same time, causing the atria to begin filling with blood again.
What happens during diastole?
During diastole:
- Both the ventricles and atria relax.
- The pressure in the ventricles drops below that in the aorta and PA, causing the semilunar valves to close.
- The pressure in the atria becomes greater than in the ventricles, so the AV valves open and blood flows into the ventricles.
What is cardiac output?
Cardiac output is the volume of blood pumped by the heart per minute, calculated as:
Cardiac output = Heart rate × Stroke volume
What is heart rate?
Heart rate is the number of cardiac cycles or beats per minute.
What is stroke volume?
Stroke volume is the volume of blood pumped out of the left ventricle in one cardiac cycle.
What do ECGs measure? Describe the waves.
ECGs measure the electrical activity of the heart. The key waves include:
- P wave: Depolarisation of the atria, causing atrial systole.
- QRS complex: Depolarisation of the ventricles, causing ventricular systole; it is the largest due to the largest muscle mass.
- T wave: Repolarisation of the ventricles, resulting in ventricular diastole.
- U wave: Potentially caused by the repolarisation of Purkinje fibers.
What are the properties of arteries?
Arteries:
- Carry blood away from the heart (except the pulmonary artery).
- Have thick walls with collagen (tunica adventitia) to prevent overstretching, smooth muscle (tunica media) to withstand blood pressure, and elastic fibres to allow expansion when heart contracts and recoil when heart relaxes to maintain blood pressure.
- Have a narrow lumen and a pulse.
What are the properties of veins?
Veins:
- Carry blood back to the heart (except the pulmonary vein).
- Have thinner walls with collagen, smooth muscle, and elastic fibres.
- Have a wider lumen to prevent friction with endothelial walls and allow blood to return to the heart at an adequate speed.
- Contain valves to prevent backflow of blood.
What are the properties of arterioles?
Arterioles:
- Have a lower proportion of elastic fibres and more muscle cells than arteries.
- Can constrict to limit blood flow to specific organs, such as reducing blood flow to the intestines during exercise.
What are the properties of capillaries?
Capillaries:
- Have one-cell-thick endothelial walls with pores that form tissue fluid.
- Are part of capillary beds, which are important exchange surfaces.
- Have a narrow lumen and branch between cells to shorten the diffusion distance.
- White blood cells can squeeze through intercellular junctions.
What is tissue fluid?
Tissue fluid has almost the same composition as plasma but with fewer proteins, allowing for the exchange of substances between blood and tissues.
What happens at the arteriole end of the capillary?
At the arteriole end of the capillary:
- Oncotic pressure remains constant due to large proteins like albumin (lowers water potential in plasma) in the blood, creating a water potential gradient between capillaries and tissues.
- Hydrostatic pressure from the heartbeat is high.
- The hydrostatic pressure is greater than the osmotic pressure, so fluid is forced out of the capillary into the tissues.
- Hypertension may cause oedema due to fluid buildup.
What happens at the venule end of the capillary?
At the venule end of the capillary:
- The oncotic pressure remains the same, but the osmotic pressure is higher as nutrients have been taken up by cells.
- Hydrostatic pressure is lower, causing less fluid to move out of the capillaries.
- Some fluid may move back into the capillaries with waste products like carbon dioxide and urea.
What are the risk factors for coronary heart disease (CHD)?
Risk factors for CHD include:
- Genetic factors
- Age (risk increases with age)
- Sex (males are more likely to develop CHD)
- Hypertension (causes atheromas to develop)
- Smoking
- High concentrations of LDL (low-density lipoprotein), which promote the development of atheromas.
What is the role of haemoglobin in gas transport?
Haemoglobin improves the solubility of oxygen for efficient exchange and has a prosthetic group that allows reversible binding of oxygen to form oxyhaemoglobin.
