Fluid flow Flashcards
Circulatory System definition
- what organisms don’t need it - what they use instead
- Bulk flow defn.
- A system that transports nutrients, wastes and signalling molecules (i.e. hormones) between body tissues
- v. small organisms don’t need it -> rely on diffusion (only good if small, flat or porous)
- large animals move fluid through bodies by bulk flow
- Bulk Flow: Movement of fluid as a result of a pressure gradient
- How fluid is moved
- 3 components of circulatory system
-Moved by generating pressure in one part of circuit to create pressure gradient
- 3 parts;
- Pump (all involve muscle contraction)
- System of tubes
- Fluid
Types of Circulatory systems;
- open and closed
- what fluid within each one called
-2 other types of fluid
- Open Circulatory system: Circulatory fluid comes in direct contact w/ tissues in spaces (sinuses)
- Hemolymph is the fluid that circulates these systems
- Closed circulatory system: Circulatory fluid stays w/in blood vessels
- Blood is fluid that circulates this system (plasma + cells)
Other fluids: Interstitial (ECF that bathes tissues) and Lymph
Evolution of Circulatory Systems -> Overview
- what evolved to do first
- Driving force for evolution
- First evolved to transport nutrients
- very early on began to serve as a respiratory function (has been driving force for evolution of this system)
- O2 limits what an organism can do metabollically
- Other things that affect oxygen delivery requirements;
- metabolism, altitude, size, level of activity, endothermic
Common features of vertebrate circulatory system
- Closed (blood separate from tissue fluid)
- note: not all invertebrates have open - 2 or more contractile chambers of myocardial tissues, w/ valves to ensure unidirectional blood flow
- 2 or more heart chambers - progressive increase in separation of blood flow to gas exchange organs and rest of body
Advantages of closed circulatory system (3)
- Can generate higher pressures - blood flows more rapidly )means quicker nutrient and waste transport)
- Resistance in blood vessels can be changed (blood flow can be more tightly regulated and easily redirected to specific tissues)
- Cellular elements and transport molecules kept within vessels (means specific molecules have evolved w/ closed system - i.e. haeme)
*generally support higher lvls of metabolic activity
2 types of myocardium used to generate contractile force
-which one prominent over time
- Spongy: meshwork of loosely connected cells (not hugely efficient)
- Compact: Tightly packed cells arranged in a regular pattern (no space for blood -> lead to evolution of coronary circuit)
- downside: v. dependent on coronary circuit
*shift from mostly spongey to compact over time
Number of Heart chambers over time
-what current groups have
- Vertebrate hearts are first to have 2 chambers
- all have at least 1 atrium and one ventricle
- Heart evolved from 2 chambers in fish to three in amphibians and reptiles, and four in crocodilians, mammals and birds
Fish Heart
- requirements
- what two chambers allow
- what made of
- what emerged in this heart
- First group to develop multi-chambered heart
- gills require more efficient circulatory system working at higher pressure
- 2 chambers allow separate collection and pumping of blood (also continuous blood flow)
- gills require more efficient circulatory system working at higher pressure
- mostly spongy myocardium
- emergency of polarised contraction (posterior -> anterior)
Fish circulation
- Ventrical located ventral to atrium (gravity helps blood flow)
- Most of pressure from ventricular contraction dissipated passing through gills
- blood flowing to tissues is at relatively low pressure (still good enough for tuna and marlin)
- Most of pressure from ventricular contraction dissipated passing through gills
Amphibian Heart
- no. of chambers
- How blood flow occurs
-type of myocardium tissue
- 3 chambered (2 atria, 1 ventricle)
- Oxgenated blood from lungs -> left atrium, deoxygenated from tissues -> right atrium
- both types of blood enter 1 ventricle (v. little mixing - trabeculae may help)
- mostly spongy myocaridum
- evolved separately to lungfish heart (even tho similar)
Amphibian Circulation
- features
- extra way can get oxygen - how it helps
- Partially separated pulmonary and systemic circuits
- means can have higher systemic pressures
- Gas exchange also occurs at skin, buccopharyngeal mucosa
- oxygenated blood from skin mixes w/ deoxygenated - supplies heart with O2
- only pulmonary circuit has separate venous return to heart
Reptile hearts (turtles, snakes and lizards)
- chambers (no.)
- special feature
- type of tissue
- 3 chambered heart (2 atria, 1 ventricle)
- Have complex ventricular structure (3 sub chambers divided by muscular ridges)
- ridges separate flow of oxygenated and deoxygenated blood
- small in turtles, but large in lizards and snakes (less mixing)
- ridges separate flow of oxygenated and deoxygenated blood
- mostly compact myocardium
- 2 aortas rather than one
Reptile circulations
- extra features
- what it allows reptiles to do
- Left aorta takes oxygenated blood from left side; right aorta takes blood from both sides of ventricle to body
- if reptile stops breathing, contraction of blood vessels in lung = increased resistance
- blood diverted from lungs into systemic circuit when not breathing (extra aorta allows this)
- if reptile stops breathing, contraction of blood vessels in lung = increased resistance
Crocodile heart
- heart chambers
- no of aortas
- what they allow
- 4 chambered heart
- 2 aortas
- Blood bypasses lungs when animal is submerged (pulmonary pressure increases, opens valve - means less oxygen goes to lungs, more goes to body)
Avian and Mammalian Hearts
- chambers
- separation of blood?
- pressure
- type of myocardium
- 4 chambered w/ valves to prevent backflow of blood
- ventricles separated by intraventricular septum
- Is COMPLETE separation of oxygenated and de-oxygenated blood
- very different pressures in pulmonary and systemic circuits
*compact myocardium
Advantages of Separate pulmonary and Systemic Circulations (3)
- Oxygenated and deoxygenated blood cannot mix -> systemic circulation receives blood with highest O2 content (v. efficient)
- Maximises respiratory gas exchange (large gradient)
- Pulmonary and systemic circuits can operate under different pressures (allows nutrients to get to tissues faster)
Other evolutionary changes in cardiovascular system
- Specialised electrical conduction
- Myocardial cell replication
- Specialised electrical conduction
- pacemaker cells present v. early in evolution (allows rhythmic activity)
- Fish and amphibia first to demonstrate ordered contraction
- mammals have specialised conduction pathways (better co-ordinated contraction)
- Myocardial cell replication
- ability to efficiently replace lost myocardial cells disappears around appearance of endothermy (frogs can generate heart cells)
- Mammals can’t generate significant numbers of new ventricular myocytes after birth
Blood
- what it is
- 2 components
Blood: fluid in heart and blood vessels
-Divided into plasma portion (water component - has ions, organic solutes and proteins) and cellular portion (produced from stem cells in bone marrow)
Red Blood cells
- functions
- shapes
-Advantages of biconcave erythrocyte shape
-Are the most numerous cellular component
-Specialised for oxygen transport
-Shape varies - round, oval or biconcave
Advantages of biconcave;
-Large SA, sort distance b/w interior and exterior edge (favors diffusion
-can deform to squeeze through small capillaries
-can tolerate a degree of swelling w/out bursting
Blood flow around body
-5 types of blood vessels blood encounters
Blood flow through Heart;
- how moves
- How gradients generated (2 factors)
-Blood encounters 5 types of vessels; each w/ different structural features and functions
->veins, arteries, venules, arterioles, capillaries
Blood flow through heart;
-blood flows passively down pressure gradients
-gradients generated by venous return and contraction of heart
*unidirectional heart valves stop backwards blood flow
The Cardiac Cycle
- what it is
- Systole and diastole
-Cardiac Cycle: the electrical and contractile (mechanical) events associated with the movement of blood through the heart during a single heart beat
Systole: contraction; blood forced into next chamber or out into circulation
Diastole: Relaxation; blood enters the chamber
*atria contract together; ventricles contract together
Electrical activity of the heart
- how generated
- How electrical activity travels in heart
- Cardiac cycle involves rhythmic contraction of heart chambers in response to electrical activity (depolarisation)
- is initiated in sinoatrial node
- spreads across the atria and then to ventricles via atrioventricular node
- is initiated in sinoatrial node
Electrical activity and blood flow of the heart
- orderly spread of electrical activity leads to co-ordinated contraction of heart chambers
- SA node deploarises spontaneously
- atria depolarise together, contract together -> blood to ventricles
- delay during atrio-ventricular spread of depolarisation -> blood flows to ventricles
- ventricles depolarise together, contract together -> blood flows to artieries
Monitoring cardiac efficiency (2 methods)
-their definitions and features
- Cardiac output: the amount of blood pumped by the heart every minute
- heart rate x stroke volume (volume of blood pumped per stroke)
- stroke volume is difference b/w amount of blood that collects in ventricle during diastole and what is left at end of systole
- heart rate x stroke volume (volume of blood pumped per stroke)
- Blood pressure: pressure exerted by blood on arterial walls
- depends on cardiac output and peripheral resistance
- is highest during ventricular contraction (systolic pressure)
- depends on cardiac output and peripheral resistance
How to measure blood pressure
- Done with a sphygmomanometer (pressure monitor) and stethoscope
- Relies on fact that smooth (laminar) blood flow is silent, while turbulent blood flow is audible
Control and regulation of circulation
- Heart rate controlled by autonomic nervous system
- Brain regulatory centers monitor incoming info about BP/Volume - act via ANS
- ANS has 2 branches; sympathetic (fight or flight) and parasympathetic (rest and digest)
- increase and decrease heart rate respectively
- ANS has 2 branches; sympathetic (fight or flight) and parasympathetic (rest and digest)
Dive Reflex
- what it is
- what declines specifically
-Tachycardia - what is it
- Diving mammals conserve blood oxygen stores by slowing HR during dives (aka Diving bradycardia - decreased HR)
- Decreased heart rate relative to anticipation of dive depth
- stroke volume remains constant - decline is in cardiac output
- is an ancient response to oxygen insufficiency
- Tachycardia = increased HR
Blood pressure in diving seals
- what happens to HR, stroke volume, cardiac output and blood pressure
- special feature
- Seals demonstrate integrated, body wide reorganisation of cardiovascular function
- if HR drops, stroke volume doesn’t change, cardiac output drops
- blood pressure maintained by increasing peripheral resistance
- if HR drops, stroke volume doesn’t change, cardiac output drops
- diving seal shows arterial constriction of all blood vessels except in lung, brain, heart and eyes
Other phyiological adaptations for diving
-2
- Enteer hypometabolic state (low metabolism)
- Very high oxygen storing capacity
- greater blood volume
- greater O2 carrying capacity of blood (mobilise more RBC from spleen)
- more myoglobin in muscles
Hydrodynamics;
- Flow
- Velocity
- relationship to flow rate and cross sectional area
Two most important terms to describe movement of fluids:
- Flow (Q): volume of fluid transferred per unit time (cm3/sec)
- Velocity (V): Distance travelled by fluid per unit time (Cm/sec)
Velocity is proportional to flow rate (as flow increases, so does velocity)
- BUT, inversely proportional to cross sectional area
- if cross-sectional area increases, velocity decreases (narrower vessel - the faster the velocity of flow)
Determinants of Fluid Flow
- flow and pressure - flow and resistance
- Flow is;
- proportional to pressure gradient (as pressure increases, so does flow)
- inversely proportional to resistance (as resistance increases, flow decreases)
Poiseuille’s Law
-what it describes relationship between
-Is the relationship between fluid flow, pressure differences and resistance
Pressure Gradient and fluid flow
- general concepts
- pressure generation in cardiovascular system
- Fluid flows from high pressure to low pressure
- is proportional to the pressure difference between two areas (larger the difference, higher the flow)
- mainly generated by contraction of heart in cardiovascular system
- gravity also contributes
Resistance and Fluid flow
- what is resistance?
- Flow and resistance relationship
- 4 factors that affect resistance
- Resistance: friction that opposes blood flow
- Flow INVERSELY proportional to resistance
- fluid loses some kinetic energy as heat when faced with resistance
- Factors that affect resistance;
- Tube length, tube radius, fluid viscosity and flow pattern
Tube length and fluid flow
Tube radius and fluid flow
-degree of flow change in response to radius change
-As tube length increases, resistance increases
- As tube radius decreases, resistance increases
- resistance is a function of fourth power of radius (therefore a small change in radius leads to a very big change in resistance)
Flow pattern and relation to resistance
-2 types of flow and their features
-More turbulent blood flow leads to increased resistance
- Laminar Flow:
- Fluid moves in concentric layers, w/ highest velocity in middle of tube
- Some friction between adjacent layers moving at different velocities - Turbulent Flow:
- Breakdown of laminar flow, radial fluid movement -> mixing
- Much higher resistance than laminar flow
Causes of turbulence
-cause in biological system too
- Likely with high density, low viscosity fluids travelling at high velocity through large diameter tubes
- also by irregularities in tube walls or abrupt change in dimensions
Haemodynamics - definition
-Refers to the forces generated by the heart and movement of blood through the cardiovascular system
Resistance to flow in the cardiovascular system
-what contributes most to change in resistance
- Viscosity and length not normally considered when assessing blood flow in vasculature
- Constant or slow to change unless disease
- Most important contributor to resistance in blood vessels is changes in vessel radius (smooth muscle)
Blood flow by regulating radius
-how constriction in one part affects other part
Definitions:
-Vasoconstriction and vasodilation
- Blood diverted between organs regulating blood vessel radius (smooth muscle contraction)
- constriction of blood vessel leads to increased pressure in another region
- leads to increase in peripheral resistance (increased blood pressure)
- constriction of blood vessel leads to increased pressure in another region
Vasoconstriction: Decrease in vessel radius
Vasodilation: increase in vessel radius
Special properties of flow in cardiovascular system (4)
- Blood viscosity is variable
- Blood pressure is pulsatile
- Blood vessel walls are distensible (not rigid)
- Blood flow is not always laminar
Variability of Blood viscosity
-3 factors and how changes in them affect fluid flow
-Blood is a suspension
Varies depending on;
-Haematocrit (proportion of RBCs)
-more = higher viscosity
-RBC shape
-Healthy RBCs flexible; decreased flexibility = increased viscosity
-flexibility lost with sickle cell anemia
-Blood flow
-blood tends to clot at low flow rates (low rate = increased viscosity)
-can occur during shock, hypotension, prolonged immobility
Blood pressure is pulsatile - why
- Variable pressure gradient = flow decreases between heart beats
- peaks in systole, troughs in diastole
Blood vessels are not rigid
- How -> veins and arteries compared
- How arteries dampen pressure changes
- Blood vessels are compliant (expand in response to pressure) and can be elastic (recoil when stretched)
- veins particularly compliant (Store blood)
- Arteries are particularly elastic (store pressure)
- dampen pressure changes - as pressure drops, artery recoils to constrict artery = higher minimum pressure
- blood enters, artery stretches and dilate to lessen pressure
Blood flow is not always laminar
- Normal changes in cardiovascular chamber dimension causes turbulence
- irregularities in blood vessel wall during disease can cause turbulence
Gravity and the cardiovascular system
- hydrostatic pressure -> definition
- features
- Hydrostatic pressure = pressure on a vertical column of fluid due to gravity
- is proportional to the height of the column
- gravity flows from high potential energy to low potential energy
- Blood pressure is influenced by both the pressure generated by the heart and the pressure exerted by gravity
Gravity and blood flow
-lying down and standing up
Lying down: all parts of body at same height -> hydrostatic pressure constant across circulation
-no gradient therefore gravity doesn’t affect flow (pressure will naturally decline as it moves from heart (due to resistance))
Standing Up: Gravity promotes movement of blood to feet; gravity opposes return of blood from feet to heart (decreased venous return)
- Blood moving into feet due to gravity exerts pressure on blood vessel walls -> higher blood pressure in feet * lowest BP at head, highest at feet; heart = somewhere in between
Venous Return -> 3 mechanisms that help veins defy gravity
- Gravity opposes return of blood from feet to heart via veins
- body has several mechanisms to promote venous return;
- Valves: facilitates unidirectional flow (stops backflow) -> located in peripheral veins
- Skeletal muscle pump: contraction of muscle squeezes veins - valves stop blood going back
- Respiratory pump: diaphragm drops during inhalation -> decreases pressure around heart, increases venous return.
- valves stop blood flowing backwards during exhalation
- body has several mechanisms to promote venous return;
*valves extremely important
