Circulation Flashcards
Why is diffusion only efficient over small distances
- Diffusion is only efficient over small distances, because the time (t) it takes to diffuse is proportional to the square of the distance (x)t=x^2/2DWhere D is the diffusion coefficient (flux/gradient)~10 micron^2/s for proteins in cell cytoplasm
- For most cells in multicellular organisms, exchange is generally facilitated by specialized structures.
how do protostomes do internal transport
- Protosomes with simple body plans (cnidarians, such as jellies, sponges, flatworms, and nematodes are usually aquatic /parasitic with little or no specialized circulatory systems
- These animals live in fluid environments and have body walls that are only two cells thick, so diffusion of nutrients through the surface is adequate
- Jellies and flatworms have gastrovascular cavities that help minimize diffusion distances for digestion and circulation
how do larger animals do circulation
- A circulatory system has:
- A circulatory fluid
- A set of interconnecting vessels
- A muscular pump like the heart
- The circulatory systems connects the fluid that surrounds cells with organs that exchange gases, absorb nutrients, and dispose of wastes
- Circulatory systems can be open or closed
what is open circulation
- Found in Insects, other arthropods, and most molluscs
- Internal fluid is circulated through the body cavity
- There is no distinction between blood and the interstitial fluid (hemolymph)
- Pressure rapidly dissipates requiring faster heart rate and/or accessory hearts
what is closed circulation
- Found in some invertebrates (annelids, cephalopods) and all vertebrates
- blood is confined to vessels and distinct from interstitial fluid
- Substance moves from blood → IF; IF → cells
- More efficient at transporting circulatory fluids to tissues and cells (maintains the pressure gradients)
what types of blood vessels do we have, and how long in total
- By adulthood we have ~100,000 km of blood vessels in our body (2x circumfrence of earth)
- Arteries branch into arterioles and carry blood from heart to capillaries
- Network of capillaries called capillary beds are the site of chemical exchange b/w blood and interstitial fluid
- Venules converge into veins and return blood from capillaries to the heart
- Arteries and veins are distinguished by direction of blood flow (not O2 content)
describe single circulation
- Vertebrate hearts emerged ~500 mya with two or more chambers
- Blood enters through an atrium and is pumped out through a ventricle
- Bony fish, rays, and sharks have a single circulation with two-chambered hearts
- In single circulation, blood leaves the heart and passes through two capillary beds before returning
- One disadvantage no ‘fresh’ perfusion of the heart (blood around heart has less oxygen, results in low activity)
- low pressure
describe circulation in amphibians
- Vertebrate hearts emerged ~500 mya with two or more chambers
- Blood enters through an atrium and is pumped out through a ventricle
- Bony fish, rays, and sharks have a single circulation with two-chambered hearts
- In single circulation, blood leaves the heart and passes through two capillary beds before returning
- One disadvantage no ‘fresh’ perfusion of the heart (blood around heart has less oxygen, results in low activity)
- low pressure
describe circulation in Mammals and Birds
- Mammals and birds have a four chambered heart with two atria and two ventricles
- Oxygen-rich blood and oxygen poor blood do not mix
- Oxygen-rich blood is delivered from the heart to the rest of the body through the systemic circuit
- Blood travels separately between the heart and the lung surfaces through the pulmonary circuit
- Mammals and birds are endotherms and required more O2 than ectotherms (higher metabolic rates)
describe heart rates across some animals big to small
Shrew: 8-1,500 beats/min
Mouse: 55 bpm
Human: 70 bpm
Elephant: 28 bpm
what is cardiac output
Cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume (the amount of blood pumped in a single contraction)
- Humans: ~70 bpm * 70 ml = ~4.9L/min = 7056 L/day
what is pulmonary circuit
Pulmonary circuit:
- Pulmonary artery: de-oxygenated blood from right ventricle to the lungs
- Pulmonary veins: return oxygenated blood to the left atrium form the lungs
what is the systemic circuit
Systemic circuit:
- Aorta: Ascending/descending branches stemming from the left ventricle, distribute oxygenated blood through the body
- Superior/inferior vena cava: bring de-oxygenated blood back to right atrium
describe the valves of the heart
- The atrioventricular (AV) valves control blood flow within the heart, between the atria and ventricles
- The semilunar valves control cardiac output via the aortic and the pulmonary arteries
- Backflow of blood through defective valve causes a heart murmur
describe the basic anatomy of the human heart
- Two Atria have relatively thin walls and serve as collection chambers for blood returning to the heart
- The ventricles have thicker walls and contract much more forcefully, ejecting blood to distal sites
- Heart wall: muscle (myocardium), encapsulated between an inner lining (endocardium) and a fibrous, protective sheath (pericardium)
what are the two parts of the heart beat
The contraction, or pumping, phase is called systole; the relaxation, or filling, phase is called diastole
what are the three steps of the cardiac cycle
- The heart is fully relaxed, the atria fill with blood, and all valves are closed. AV valves are then pushed open and ventricles begin to fill.
- When ventricles are about 80% full, the atria contract and fully fill the ventricles
- Ventricles begin to contract, forcing the AV valves to close; as the contraction builds, it forces open the SL valves.
What are cardiac muscle cells and how do crabs and lobsters coordinate their cardiac cycle
- Cardiac muscle cells are autorhythmic, they contract without any signal from the nervous system
- Crabs and lobsters rely on signals from the brain
what do the SA and AV nodes do
- The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract (70 beats/min)
- Impulses from the SA node travel to the atrioventricular (AV) node
- At the AV node, impulses are delayed and then travel to the Purkinje fibres that make the ventricles contract.
how does a heart beat look like on a electrocardiogram
- Signals from SA node spread through the atria (P wave)
- Signals are delayed at AV node (P-Q segment)
- Bundle branches pass signals to heart apex (Q)
- Signals spread throughout ventricles (R)
- Ventricles contract (S-T segment)
- Repolarization (T wave)
what are pacemakers
replacers activity of SA and AV nodes.
Used when people have irregular heart rates, usually at old age.
how does the nervous system regulate heart beat
- The Pacemaker is regulated by two portions of the nervous system: sympathetic and parasympathetic divisions
- The sympathetic division speeds up the pacemaker (Norepinephrine, NE)
- The Parasympathetic division slows down the pacemaker (Acetylcholine, ACh)
what else regulated the heart beat besides the nervous system
The Pacemaker is also regulated by hormones (e.g. thyroid hormone) and temperature (~10 bpm higher / ºC)
what are Baroreceptors
Baroreceptors located in the heart muscle, aorta and carotid arteris (supply blood to the brain) provide blood pressure information to the medulla → SA node