Circulation and Gas Exchange - Chapter 42 Flashcards
how do exchanges occur with the environment in unicellular organisms?
diffusion - which is proportional to the square of the distance and is thus only efficient over small distances: t = x^2/2D
how is exchange facilitated in cells in multicellular organisms?
specialized structures
explain internal transport in gastrovascular cavities
animals that live in fluid environments and have body walls only 2 cells thick have diffusion of nutrients through the surface
- like jellies and flatworms
list the 3 components of the circulatory system
circulatory fluid, a set of interconnecting vessels, and a muscular pump (heart)
the circulatory system connects the fluid that surrounds cells with organs that exchange gases, absorb nutrients, and dispose of wastes
- can be open or closed
describe an open circulatory system
internal fluid is circulated through the body cavity, and is the same as the fluid that bathes the cell (no distinction between blood and interstitial fluid), they need faster heart rates
describe a closed circulatory system
all vertebrates have one, blood is confined to the vessels, is distinct from (not the same as) interstitial fluid, more efficient that open circulatory systems, substances move blood -> IF -> IF -> cells
arteries branch into arterioles and carry blood away from the heart to capillaries
capillary beds are the sites of chemical exchange between blood and interstitial fluid
venules converge into veins and return blood from capillaries to the heart
how are arteries and veins distinguished?
the direction of blood flow - arteries carry blood away from the heart
single circulation - occurs in bony fish, rays, and sharks
- blood enters through the atrium and is pumped out through a ventricle
- single circulation with a two chambered heart
- uses less energy
- one disadvantage is no “fresh blood” goes to the heart
other vertebrates have evolved double circulation
- oxygen rich and oxygen poor blood are pumped separately
- oxygen-rich blood delivered from the heart to the rest of the body through the systemic circuit
- blood travels separately between the heart and the respiratory surface (pulmonary circuit)
heart rates vary greatly across vertebrates, according to mass
cardiac output definition
the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume (amount of blood pumped in a single contraction)
heart wall structure
muscle (myocardium) encapsulated between an inner lining (endocardium) and a fibrous, protective sheath (pericardium)
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
four valves prevent backflow of blood in the heart
- the atrioventricular valves (AV) also known as tricuspid and bicuspid valves separate the right/left atria and ventricles
- the semilunar valves (also known as the aortic and pulmonary valves) control blood flow to the aorta
- backflow of blood through a defective valve causes a heart murmur
the cardiac cycle
two phases:
systole (the contracting phase)
diastole (the filling phase)
describe the cardiac cycle in 3 steps
- the heart is fully relaxed, the atria fill with blood, and the valves are closed. AV valves are then pushed open and ventricles start to fill
- when ventricles are about 80% full, the atria contract and fully fill the (still relaxed) ventricles
- ventricles begin to contract, forcing AV valves to close, as the contraction builds, forcing SL valves open
cardiac muscle cells are auto rhythmic (they contract without any signal from the nervous system)
two nodes in the heart coordinate the beating of the heart
- sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract (70 beats per minute)
- impulses from the SA node travel to the atrioventricular node (AV)
- at the AV node, impulses are delayed and then travel to the Purkinje fibres that make the ventricles contract
the electrocardiogram is a graph that shows heart beats
the pacemaker is regulated by two portions of the nervous system: sympathetic and parasympathetic divisions
- sympathetic speeds up the pacemaker
- parasympathetic slows down the pacemaker
temperature can affect our pacemaker
about 10 bpm higher per degree Celsius
what is the vessels cavity called?
the central lumen
what is the epithelial layer that lines blood vessels called?
the endothelium
arteries have thicker walls than veins, as they are subject to high pressure from the ventricles, and are thus much more elastic
veins don’t have muscles, but they have lots of valves to restrict the backflow
capillaries are only slightly wider than a red blood cell
blood pressure and velocity depend on vessel diameter
slowest at the capillaries, as a result of high resistance and large total cross-sectional area
- necessarily slow for nutrient exchange
blood flow in capillary beds
exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries (difference between blood pressure and osmotic pressure drives fluid out of capillaries)
- blood proteins and blood cells are too large to pass through the endothelium
blood flows through only 5-10% of the body’s capillaries at any given time
for example, out gut capillaries don’t need to be filled at all times (but vital organs do)
what two mechanisms regulate the distribution of blood in capillary beds?
constriction or dilation of arterioles that supply capillary beds and pre capillary sphincters control flow of blood between arterioles and venules
fainting is a reflex caused by inadequate blood flow to the head
that way blood doesn’t have to fight gravity to get to the brain (your head will be down)
vasoconstriction and vasodilation regulated blood pressure
vasoconstriction is the contraction of smooth muscle in arteriole walls (increases blood pressure)
vasodilation is the relaxation of smooth muscles in the arterioles (causes blood pressure to fall)
blood is a connective tissue made up of cells suspended in a liquid matrix called plasma
plasma is mostly water (about 55% of blood volume)
proteins influence blood pH
suspended in blood plasma are erythrocytes (majority), leukocytes, and platelets
erythrocytes
packed with hemoglobin, an iron-containing protein that transports oxygen
- lack nuclei and mitochondria when mature
- lifetime of about 120 days
what do erythrocytes, leukocytes, and platelets all develop from?
stem cells in the red marrow of bones, to replenish the body’s blood cells
which hormone stimulates erythrocyte production when O2 delivery is low?
erythropoietin (EPO)
what are platelets, and what are their functions?
platelets are fragments of specialized bone marrow cells, they serve both structural and molecular functions in blood clotting
how are platelets activated?
by exposed collagen fibres in damaged tissue of vessel wall, ‘foreign’ surfaces, or thrombin
- upon activation they change shape and form platelet plug and release clotting factors
define coagulation
the formation of a solid clot from liquid blood - a cascade of complex reactions converts inactive fibrinogen to fibrin, forming a clot
define thrombus
a blood clot formed within a blood vessel - can block blood flow
what are cardiovascular diseases?
disorders of the heart and the blood vessels
- cholesterol plays a central role in cardiovascular disease, as does inflammation
LDL and HLD
low-density lipoprotein (LDL) delivers cholesterol to cells for membrane production, high-density lipoprotein (HDL) scavenges excess cholesterol for return to the liver
risk for heart disease increases with a high LDL to HDL ratio
myocardial infarction definition (heart attack)
the damage or death of cardiac muscle tissue resulting from blockage of one or more coronary arteries, which supply oxygen-rich blood to heart muscle
stroke definition
death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head
hypertension (high blood pressure)
increases risk of heart attack or strokes
atherosclerosis
caused by the buildup of fatty deposits (plaque) within arteries
animals require large, moist respiratory surfaces of exchange of gases
how does gas exchange take place?
diffusion - gases diffuse down pressure (not concentration) gradients in lungs and other organs as results of differences in partial pressures
animals can use air or water as a source of O2 or respiratory medium
- in a given volume (and pressure) there is less O2 in water compared to air
aquatic animals and gas exchange
they use gills (which can be internal or external) - they create a large surface area for gas exchange
worms and gas exchange
their whole body is practically their respiratory system - they use diffusion across their skin - they live in moist environments
fish gills structure and function
fish gills use a countercurrent exchange system - blood flows in the opposite direction to water passing over the gills - water is always more saturated with O2 than the blood it meets, so it can diffuse according to its partial pressure
gas exchange in insects - tracheal system
every cell has its own “plumbing system”
- supply O2 directly to every cell
- respiratory and circulatory systems are separate
- network of branching tubes throughout the body
gas exchange in amphibians
ventilates its lungs by positive pressure breathing (forces air down the trachea by “gulping air” - it gets stored in the buccal cavity, then pushed into the lungs)
the avian (birds) respiratory system
they have 8 or 9 air sacs that function as bellows to keep air flowing through the lungs - air passes through the lungs in only one direction
the mammalian respiratory system
- branching ducts conveys air to the lungs
- air inhaled through the nostrils is filtered, humidified, warmed, and sampled for odours
- pharynx directs air to the lungs and food to the stomach
- swallowing moves larynx upward and tips the epiglottis over the glottis to prevent food from entering the trachea
keeping respiratory system clean
cilia and mucus line the epithelium and keep the respiratory system clean
where does gas exchange take place?
alveoli - air sacs at the tips of bronchioles, which have a moist film of the epithelium
- lack cilia and are susceptible to contamination
- surfactants coat the alveoli
mammals ventilate their lungs by negative pressure breathing (pulls air into the lungs)
lung volume increases and the diaphragm contracts
tidal volume definition
volume of air inhaled with each breath
vital capacity definiton
maximum tidal volume
sensors monitoring O2 and CO2 concentrations in the blood signal breathing control centres, which respond as needed
- additional modulation occurs in the pons, which is located next to the medulla in the brain
function of respiratory pigments
proteins that transport oxygen, greatly increase the amount of oxygen that blood can carry
- single hemoglobin molecules have 4 subunits, which harbour one iron-containing heme group
- each Hb can carry up to 4 O2 molecules
the hemoglobin dissociation curve
