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circulatory (cardiovascular) system
composed of a pump (heart), fluid (blood) and conduits (blood vessels)
functions of the CV system
- deliver O2 and nutrients to the tissues
- remove CO2, metabolites and metabolic waste from the tissues
- vehicle for delivery of hormones
- provide pressure for filtration of blood by kidney
- circulate specialized immune cells
- temperature control
- hydraulic force for limb extension (clams)
- wing expansion (insects)
- penile erection (mammals)
Animals with no circulatory systme
- simple, usaully small, aquatic
- nutrients, gases and wastes can diffuse between the cells and the environment and a circulatory system is not needed
- some aquatic animals have a flat body shape or a highly branched gastrovascular cavity to provide max SA for exchange
combination gut and circulatory system
"circulatory system" in sponges
- gas diffusion
- semi-random nutrient distribution
- no true body cavity
"circulatroy system" in Cnidaria
- diffusive gas exchange through epidermal gastrodermal cells
- large anenomes have internal folds of gastrodermic mesentaries
Open circulatory systems
- blood or circulating fluid is not kept separate form the tissue fluid
- the most simple systems squeeze tissue fluid (hemolymph) through and around intercellular spaces
- usually a pump or heart
- anthropods, some mollusks and some other invertebrates use this system
closed circulatory systems
- keeps the blood and tissue fluid separate
- one or more muscular hearts and a branching network of vessels (the vascular system) move the blood
- closed circulatory system
- the large dorsal and ventral vessels are connected by 5 vessels that serve as hearts
- the dorsal vessel is also pulsatile
- direction of blood flow is controlled by one-way valves
Advantages of closed CV systems
- blood pressure and flow are higher. Therefore, nutrient delivery and waste removal are more rapid
- closed systems can direct the blood to specific tissues and vary flow as needed
- cellular elements and large molecules that aid in transport can be kept within the vessels
Vertebrate circulatory systems
- closed systems and hearts with two or more chambers, valves prevent backflow then the heart contracts
- have arteries, veins, arterioles, capillaries, and venules
- a theme in vertebrate evolution is a progressive separation of the blood that goes to the respiratory organs from the blood that goes to the rest of the body
- this culminates in two circuits: a pulmonary circuit and a systemic circuit
vessels that carry blood away from the heart
vessels that carry blood to the heart
arteries give rise to smaller vessels (arterioles), which feed blood into the capillaries
thin walled vessels through which materials are exchanged between blood and the tissue fluid
small vessels which connect the capillary beds with the larger veins
- most fish have two chambered hearts: a thinly muscled atrium to recieve blood and a heavily muscled ventricle to pump blood
- blood is pumped to the gills (capillary beds) for gas exchange, then through the aorta to the rest of the body
- blood pressure is low in the aorta, and the rest of the systemic circulation bc the narrow gill spaces dissipate flow force. this does not seem to hamper fish
- have evolved a primitive lung from an out-pocketing of the gut this permits them to breathe air when the water becomes anoxic or dries up
- the posterior pair of modified gill arches directs some of the blood coming from the heart to the lung, and a new vessel carries oxygenated blood from the lung back to the heart. The anterior pair of arches have non-functional gills (exchange CO2 but not O2) blood is directed appropriatly depending on weather the fish is air or water breathing
- the heart has a partly divided atrium: the left side recieves deoxygenated blood from the lung, the right side recieves deoxygenated blood from the rest of the body
- 3-chambered hearts with one ventricle and two atria
- one atrium receives deoxygenated blood from the body; the other receives oxygenated blood from the lungs
- mixing of blood in the ventricle is minimized by a partial separation. Deoxygenated blood is directed to the pulmonary circuit; oxygenate blood is directed to the aorta
- the partial separation of pulmonary and systemic separation permits delivery of blood in the aorta and tissues at a higher pressure than in non-air breathing fish
- reptilian (except crocodilian) hearts have two atria and a ventricle that is partially divided, so mixing of oxygenated and deoxygenated blood is minimized. Crocodilians have an actual four chambered heart
- reptiles have a large range of metabolic needs, from very active states to resting states with very low metabolism
- they do not have to breate continuously
- the lung circuit can be bypassed when they are not breathing
- turtles, snakes, and lizards have two aortas and a ventricle that is imcompletely divided by a septum. Although actually 3-chambered, the heart is functionally four-chambered
- when the animal is not breathing, this setup allows constriction of blood vessels in the lung circuit and shunting of blood through both aortas to the systemic circuit
- during a breath, resistance to flow through the pulomonary circulation is low, blood flow is high. When diving, there is an increase in resistance in pulmonary circulation, and a redution in cardiac output associated with bradycardia
- have a true four-chambered heart and two aortas, one from each ventricle, with a channel connecting them
- when a crocodile is breathing, higher pressure in the left ventricle and aorta is communicated to the channel; this prevents right-ventricle blood from entering the aorta and right ventricle blood flows to the pulmonary circuit
- when the animal is not breathing (diving), pressure builds up in the right ventricle until it exceeds that of the right aorta. Blood from both ventricles flows through the two aortas and the systemic circuit, and little blood flows into the pulmonary circuit
The human heart
- the left and right sides of the human heart, may be thought of as separate pumps.
- the left pump delivers blood to the systemic circuit
- the right pump delivers blood to the pumonary circuit
between the atria and ventricles prevent backflow into the atria when the ventricles contract
pulmonary valve and aortic valve
prevent backflow into the ventricles
flow of blood through the human CV system
- the right atrium recieves blood from the superior and inferior vena cavas
- from the right atrium, blood goes to the right ventricle
- the right ventricle sends blood through the pulmonary artery to the lung
- pulmonary veins return oxygenated blood to the left atrium
- from the left atrium, blod goes to the left ventricle
- the left ventricle sends blood through the aorta to the body and the capillary beds
- blood returns to the right atrium via veins
more muscular than right because the resistance of the systemic circuit is much greater than that of the pulmonary circuit
ventricle contraction and relaxation then atria contract
What makes the sounds of the cardiac cycle (the "lub-dup")?
the closure of heart valves
What makes heart murmers?
what does it sound like?
- defective valves
- whooshing sounds following lub
mammals - fetal heart
blood oxygenated in placenta, not lungs
opening from right atrium to the left atrium in fetal development
connects the pulmonary artery to the aorta
What do you use to measure blood pressure
sphygmomanometer and stethoscope
Normal blood pressure
initiate action potentials without revous stimulation
maintain electricial contact between cardiac cells
primary pace maker of mammalian heart located at the juncture of the superior vena cava and right atrium
What is the role of the autonomic nervous system in controlling heart rate
Acetylcholine and norepinephrine from teh parasympathetic and sympathetic nerve endings slow and increase the rate respectively
How does a normal heart beat begin and end?
- Starts with an action potential in the sinoatrial node.
- Action potential spreads through the atrial cells, causing them to contract unison.
- The ventricles do not contract in unison with the atria because there are no gap junctions between the cells of the atria and ventricle.
Bundle of His
bundle of fibers that carry the action potentials from the atrioventricular node to the ventricles after the atria has fired.
evenly distribute the action potential from the bundle of His throughout the ventricular muscle. The delary insures that the atria contract before the ventricles
Depolarization of the ventricular muscles
- Starts with Na creating an action potential.
- Sustained opening of Ca channels maintains depolarization
Resistance to flow caries inversly with...
What controls the smooth muscles
neuronal and hormonal control
arteries and arterioles
- lie between arterioles and venules and exchange materials between blood and tissue through their thin walls.
- Blood flows slowly through them, dissipates high pressure of the arteries because of large volume
windows in capillary walls of endothelial cells
- the sum of the two opposing forces in capillary beds.
- colloidal osmotic pressure - large proteins molecules in the capillary push water back into the blood
- blood pressure - push water into surrounding tissue from blood
CO2 and HCO3-
A driving force to pull water back into the capillaries.
What happens to CO2 after it diffuses into the plasma?
It is converted into HCO3-
What does the increasing bicarbonate concentration do?
increases the osmotic presuure at the venous end of the capillary bed possible a major factor in pulling water back into the capillaries
capillaries of the brain do not have fenestrations, so very few substances besides lipid-soluble molecules can pass through the capillaries of the brain, a highly selective barrier
veins: because of their high capacity to store blood (they are distensible)
Pressure in veins is very low, how does the body get blood back to the heart?
- vessel squeezing by skeletal muscles
- limited smooth muscle contraction
what is the purpose of one-way valves in veins?
the prevent backflow
How do varicose veins develop?
When veins become stretched the valves no longer do their job
How does walking or running affect veinus flow?
the skeletal muscles in the legs act as auxiliary vascular pumps and return blood to the heart from the veins of the lower body
How does breathing affect venus blood flow?
creates negative pressure (suction), which pulls blood and lymph toward the chest area
how do smooth muscles affect venus blood flow?
in large veins nerar the heart smooth muscles also contract with exercise, increasing venous return and cardiac output
if a greater volume of blood is returned to the heart, which streches the cardiac muscle cells the heart contracts more forcefully. (the strength of the muscle contraction is proportional to the initial length of the muscle fibers)
moves tissue fluid that accumulates outside of capillaries
what is the path that lymph travels through the body and where does it end up?
lymph moves from small to larger vessels and finally empties into the toracic ducts that empty into large veins at the base of the neck.
What moves lymph through the body?
lymph is moved through vessels by skeletal muscle contractions (however lower vertebrates, except fish, have lymph hearts) and the vessels have smooth muscle and one-way valves to prevent backflow
- major sites of lymphocyte production
- the nodes are also filters that have phagocytic cells to remove microbes and foreign matter
- hardening of arteries
- often leads to heart attack or stroke
deposits formed at the damaged sites on the lining of arteries and narrows the lumen of the artery. Platelets stick to plaque and form clots (thrombusses) further blocking arteries
invites fivrous connective tissue and calcium deposits, making arteries less elastic
blocks an artery causing a heart attack (mycardial infarction, MI)
embolism lodges in a vessel in the brain
fluid matrix of blood
plasma minus clotting proteins
cellular components of blood
- RBC (erythrocyes)
- White blood cells (leukocyes)
- Platelets (cell fragements)
a measure of the cellular portions as a percentage of total blood volume
- Make up most of the cells in blood
- Mature ones are biconcave, flexable and packed with hemoglobin
- Responsible for transporation of O2
- Generated in/by the stem cells of bone marrow of lone bones
A hormone responsible for regulation of RBCs from the kidney in response to hypoxia-inducible factor
a transcription factor inducing EP (erythropoietin) produced by tissues experiencing hypoxia
- Generates 2 million RBC/second
- Location where cells divide multiple imes and produce hemoglobin
- When the hemoglobin level reaches 30% of the cell volume, cell organelles and nucleus break down (mammals only) and the cell enteres circulation
- Each cells lives ~120 days
Spleen's Function with RBCs
- Serves as a reseroir for old blood cells that have been squeezed and ruptured
- Cell remants are broken down by macrophages
White blood cells responsible for breaking off cell fragments (platelets)
contrain enzymes and chemicls necessary for blood clotting
- exposed when blood vessels are damaged
- activates platelets
Released by sticky activated platelets that activate other platelets and initiate clotting
Chemical cascade for blood clotting
- Cell damage activates platelets
- Activation platelets convert inactive prothrombin to active thrombin
- Thrombin causes the plasma protein fibrinogen to polymerize forming firbrin threads
- Fibrin threads form a meshwork to seal the damages vessel and provide a base for scar tissue
Contents of plasma
- Gases, ions, nutrients, proteins, hormones, and other chemicals
- Ions - mainly Na+ and Cl-
- Nutrients - glucose, amino acids, lipids, lactic acid, and cholesterol
- Proteins - albumin, antibodies, hormones, and carrier molecules
Plasma vs tissue fluid
Plasma has a higher concentration of proteins
Neural and hormonal mechanisms
Control the circulatory system at a local and systemic levels.
- Tissues regulating its own blood flow via contriction or dilation of aterioles
- Total autoregulatory actions influence the pressure and composition of blood
- Nervous and endocrine systems respond to any changes by influencing breathing, heart rate, and blood distribution
- Constrcition or relaxation of sphincters regulates blood enters a capillary bed
- Low O2 and high CO2 levels cause smooth muscle to relax and increase flow in the capillary beds
- excess blood
- Activities that incrase metabolism of the tissue also increase blood flow or hyperemia in the tissue.
sympathetic response that causes most vascular smooth muscles to contract, reducing blood flow. Chronic firing
- Released by sympathetic neurons and causes smooth muscle of aterioles to relax and dialte, increasing blood flow
Hormones responsible for arteriole constriction
Control center for heart rate and blood vessel constriction
- Inputs from many sympathetic and parasympathetic aresas
Stretch receptors in the aorta and carotid artery that provide information on blood pressure to the medula
Atrial natriuretic factor
- Hormone released when the atria are receiving too much venous return
- Stimulates the kidney to excrete sodium and water
- Results in reduced blood volume and pressure
- Stimulate the medulla regulatory system when O2 content falls too low or CO2 becomes too high
- Emotions and anticipation may cause the medulla to signal an increase in heart rate and blood pressure