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
describe the shared structure of veins and arteries
- A vessel’s cavity is called the central lumen
- The epithelial layer that lines blood vessels is called the endothelium
- The endothelium is smooth and minimized resistance
- Arteries and veins have an endothelium, smooth muscle, and connective tissue
how are veins and arteries different
- Arteries have thicker walls than veins to accommodate high pressure of blood pumped from heart
- In the thinner-walled veins, blood flows back to the heart mainly as a result of gravity and muscle action
- Veins have valves, arteries do not
how is blood moves in veins
- One-way valves in veins prevent backflow of blood
- Blood is moved through veins by smooth muscle contraction, skeletal muscle contraction, and expansion of the vena cava with inhalation
describe capillaries
- Capillaries are only slightly wider than a red blood cell
- Capillaries have thin walls, the endothelium plus its basal lamina, to facilitate the exchange of materials
What is Systolic and Diastolic pressure
- Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries
- Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure
what is a pulse
A pulse is the rhythmic bulging of artery walls with each heartbeat
what are some things that contribute to blood pressure
- The recoil of elastic arterial walls plays a role in maintaining blood pressure
- The resistance to blood flow in the narrow diameters of tiny capillaries and arterioles dissipates much of the pressure
how do you measure blood pressure
- measures arm above elbow as it is level with the heart
- Cuff is inflated with air to stop blood flow
- Stethoscope is used to listen below cuff for heartbeat
- At a certain pressure the heart beat is audible (systolic pressure ~120mm Hg)
- At a lower pressure the sound changes and goes away (diastolic pressure ~70 mm Hg)
What happens to blood pressure and velocity in capillaries
- Physical laws governing movement of fluids through pipes affect blood flow and blood pressure
- Velocity of blood flow slowest in capillary beds, as a result of high resistance and large total cross-sectional area.
- Blood flow in capillaries necessarily slow for the exchange of materials
how does exchange happen in capillaries
- The exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries
- The difference between blood pressure and osmotic pressure drives fluid out of capillaries, more strongly at the arteriole end
- Most blood proteins and all blood cells are too large to pass through the endothelium
what does the lymphatic system do
- The lymphatic system returns fluid that leaks out from the capillary beds
- Lymphatic system drains into veins in neck
- Valves in lymph vessels prevent backflow of fluid
What do lymph nodes do
- Lymph nodes are organs that filter lymph and play an important role in the body’s defense
- When body is fighting an infection, lymph nodes become swollen and tender
what is Endema
Endema is swelling caused by disruptions in the flow of lymph
does blood flow everywhere all at once
- Blood flows through only 5-10% of the body’s capillaries at any given time
- Capillaries in major organs are usually filled to capacity
- Blood supply varies in many other sites
what two mechanisms regulated the distribution of blood in capillary beds
- Two mechanisms regulated the distribution of blood in capillary beds
- Constriction or dilation of arterioles that supply capillary beds
- Precapillary sphincters control flow of blood between arterioles and venules
how does gravity affect blood pressure
- Blood pressure is generally measured for an artery in the arm at the same height as the heart (at rest 120mm Hg/70 mm Hg systole/diastole)
- Gravity has a significant effect on blood pressure
- Fainting caused by inadequate blood flow to the head
- Animals with long necks require a very high systolic pressure to pump blood a great distance against gravity (Giraffe: 280/180 mm Hg)
what chemicals influence blood pressure
- Nitric oxide a major inducer of vasodilation
- The peptide endothelin preduced by endothelial cells lining vessels, is a strong inducer of vasoconstriction
- Vasocontriction and vasodilation are often couple to changes in cardiac output that affect blood pressure
How does the body regulate blood pressure
- Homeostatic mechanisms regulate arterial blood pressure by altering the diameter of arterioles
- Vasoconstriction is a contraction of smooth muscles in arteriole walls; it increases blood pressure
- Vasodilation is the relaxation of smooth muscle in the arterioles; it causes blood pressure to fall
what is plasma
Plasma, ~55% of blood volume, is mostly water containing inorganic salts (electrolytes) and specialized proteins)
what do proteins do in blood
Proteins influence blood pH, and help maintain osmotic balance between blood and interstitial fluid and function in lipid transport, immunity, and blood clooting
besides plasma and proteins what else is in blood
Suspended in blood plasm are erythrocytes (majority), leukocytes and platelets, which occupy ~45% blood volume
where do blood cells come from
erythrocytes, leukocytes (5 types) and platelets all develop from a common source of stem cells in the red marrow of bones, to replenish the body’s blood cells
what is EPO
- The hormone erythropoietin (EPO) stimulates erythrocyte production when O2 delivery is low
- Physicians can use recombinant EPO to treat people with conditions such as anemia
What are Erythrocytes
- 5-10 um concave, disk shaped cells (oval in camels)
- Packed with hemoglobin, an iron containing protein that transports O2
- mature erythrocytes lack nuclei and mitochondria
- lifetime ~120 days
- made in red marrow of certain bones
- RBCs destroyed in liver/spleen
- Kidneys detect low O2 and secrete erythropoietin → stimulates RBC production
what are Leukocytes
- 5 major types: Monocytes, neutrophils, basophils, eosinophils, and lymphocytes
- function in defence either by phagocytizing bacteria and debris (N/Es and macrophages) or by mounting immune response against foreign substances (T/B cells)
- They are found both in and outside the circulatory system
- Can attach to or roll along edge of blood vessel, stick to proteins on walls. Can cross through certain parts to enter tissue.
what are platelets
- Fragments of specialized bone marrow cells
- serve both sturctural and molecular functions in blood clotting
- Platelets are activated by exposed collagen fibres in damaged tissue of vessel wall, ‘foreign’ substances or by thrombin
- Upon activation they change shape and form platelet plug and release clotting factors
how does blood clotting work
- Coagulation is the formation of a solid clot from liquid blood
- A cascade of complex reactions converts inactive fibrinogen to fibrin, forming a clot
- A blood clot formed within a blood vessel is called a thrombus and can block blood flow
- Blood vessel: constricts to reduce blood flow
- Platelet plug: Platelets adhere, activate, and aggregate to form a temporary plug
- Coagulation: fibrin mesh forms to stabilize the clot
