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2 types of closed circulatory systems

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2 types of closed circulatory systems

double and single

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single circulatory system (SCS)

blood flows once through the heart for a complete circuit around the body, only one cardiac cycle is completed

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examples of single circulatory system

fish, annelid worms

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SCS: blood pressure in arteries

high due to heart contraction

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SCS: blood pressure in gills

first set of capillaries for gaseous exchange, pressure lowers due to small diameter of the blood vessels

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SCS: blood pressure in body tissues

exchange of nutrients and waste so pressure drops even more than in gills

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SCS: blood pressure in veins

blood returns to the heart quite slowly at a low pressure

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limitations of single circulatory systems

blood flows very slowly, prevents formation of large concentration gradients which limits supply rate of oxygen and nutrients, only supports animals with low activity level/cold-blooded

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why can fish be very active despite having a SCS?

efficient GA due to adaptations in gills (countercurrent mechanism), body weight is supported by water, cold blooded, overall low metabolic demand

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double circulatory system (DCS)

blood flows through the heart twice in one complete circuit, made up of 2 separate circulations: pulmonary and systematic

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pulmonary circulation

heart - lungs - heart

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systematic circulation

heart - body - heart

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examples of a DCS

mammals, birds

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advantages of a DCS

blood must enter lungs at low pressure as to not damage lung capillaries, heart can increase pressure of blood once its completed pulmonary circuit, supports animals with a higher metabolic demand

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why do multicellular organisms need transport systems?

  1. SA/V decreases - distances between cells in the body and outer surface of the body get larger. 2. higher level of activity - higher demand for resources

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SA of cube

6s²

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volume of cube

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SA of sphere

4(pi)r2

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volume of sphere

4/3(pi)r3

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an effective transport system must include:

a liquid transport medium, vessels that carry transport medium, pumping mechanism

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SA determines...

supply

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volume determines...

demand and diffusion rate

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open circulatory system

very few vessels - blood pumped from heart into haemocoel, low pressure, transport medium is in direct contact with body tissue

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haemocoel

open body cavity

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open circulatory systems are found in...

small animals with low metabolic rate - invertibrates, most insects, some molluscs

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haemolymph

insect blood - doesn't carry gases, only dissolved nutrients

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insect circulatory system

open - heart is segmented and pumps blood along a single main artery which opens up into the haemocoel. haemolymph is returned to heart through a series of valves.

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blood flow

movement of blood through the vessels from the arteries to capillaries and then into the veins

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blood pressure

a measure of the force that blood exerts against the vessel walls

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blood flows from a place of ______ to a place of _______

high pressure, low pressure

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sequence of blood vessels

arteries - arterioles - capillaries - venules - veins

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structures common to arteries and veins

lumen, endothelial layer, wall

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lumen

a hollow passage way blood flows through

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endothelial layer

squamous endothelial cells, smooth so blood can flow easily without resistance

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components vessel wall

elastic fibres, smooth muscle, collagen

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elastic fibres

composed of elastin, allow stretch and recoil which provides flexibility - stretch and recoil happens with every pump of the heart

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smooth muscle

contracts or relaxes to alter the size of the lumen

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collagen

provides structural support, maintains shape and volume of vessel

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descriptive words for muscle

contracts, relaxes

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descriptive words for lumen

constricts, dilates

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tunica intima

inner layer of endothelial cells

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tunica media

middle layer of smooth muscle and elastic fibres

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tunica externa

outer layer of connective tissue contains collagen

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artery wall

thick to withstand greater blood pressure

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artery lumen

small to maintain flow rate

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artery endothelium

folded allowing them to expand during blood surges

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function of arteries

carry oxygenated blood away from the heart with the exception of the pulmonary artery

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structure of arteries close to the heart

lots of elastic fibres and little smooth muscle, lots of collagen

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structure of arteries further away from the heart

less elastic fibres and a higher proportion of smooth muscle, less collagen

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role of elastic fibres

maintains elasticity, stretch at high pressure of blood which reduces pressure and accommodates for higher volume of blood

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how do arteries maintain constant smooth blood flow?

between heart contractions, elastic fibres recoil which increases the blood pressure and pushes it further into the artery, this evens out surges of blood and helps to maintain a constant flow

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function of arterioles

link arteries and capillaries

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structure of arterioles

less elastin due to less blood surges, more smooth muscle to control blood flow into individual organs, less collagen due to reduced pressure

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rate of blood flow equation

1/total cross sectional area

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flow rate equation

cross sectional area x velocity

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if cross sectional area increases, what decreases?

velocity

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function of veins

carry blood away from the tissue to the heart

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function of venules

link capillaries to veins

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vein wall

thinner as low blood pressure

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vein lumen

low friction, less resistance to blood flow

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vein endothelium

single layer of smooth squamous endothelial cells

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how is blood flow maintained in veins?

one way valves and location of veins between large muscles

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one way valves in veins

flaps/infolding of inner lining at regular intervals along length of veins, prevent backflow of blood due to gravity

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how does location of veins between large muscles maintain blood flow in veins?

when muscles contract the veins are squeezed forcing blood towards the heart

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blood flow in veins

low pressure, against gravity

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how do breathing movements help blood flow in veins?

when the diagphragm contracts, it descends into abdomen this increases pressure in the abdomen, thus squeezing the abdominal veins, decreases pressure in the thoracic cavity creating a pressure gradient between abdomen and thorax this forces blood from the abdominal to the thoracic veins

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capillaries

microscopic blood vessels that form extensive networks in all tissues, site of substance exchange between tissue fluid and blood

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capillary structure

walls consist of a single layer of endothelial cells, narrow lumen so RBCs are pushed against endothelium, creating short diffusion distance for oxygen transfer and nutrient exchange. small fenestrations in the wall that enables substance exchange

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fenestrations

gaps

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explain why there are large capillary networks

large surface area - faster rate of diffusion of substances into and out of blood

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explain why the total cross-sectional area of capillaries is always larger than that of the arterioles that supply them

flow rate decreases and blood moves more slowly - provides more time for exchange of substances and doesn't cause thin walls to burst - more exchange happens

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explain why walls are a single endothelial layer thick in capillaries

short diffusion distance - faster rate of diffusion

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explain why there are fenestrations in capillaries

increases permeability for exchange - more exchange happens

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explain why capillaries have a narrow diameter

slows down movement of blood and reduces the diffusion distance of O2 - means more exchange happens and faster

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explain why veins have no pulse

the surges of blood produced by heart contraction are lost when blood flows through capillaries

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explain why blood flows at a much lower pressure in veins than in arteries

they receive blood that has moved through the capillary bed

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explain why blood flows easily through veins

low resistance due to wide lumen and smooth thin endothelium

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explain the large cross section of lumen compared to circumference in veins

provides low resistance which is needed as blood flows at a slow rate

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ultrafiltration

which molecules can fit through fenestration gaps in capillaries under high pressure

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blood

solution that consists of plasma (which contains dissolved substances), erythrocytes, leucocytes and platelets

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role of blood

transports substances, acts as a buffer to minimise pH changes, homeostasis of temperature

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erythrocytes

red blood cells, transport O2 and CO2

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leucocytes

white blood cells - immune function

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tissue fluid

bathes cells - same composition of blood without plasma proteins and erythrocytes

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