Studied by 1 person2 types of closed circulatory systems
double and single
single circulatory system (SCS)
blood flows once through the heart for a complete circuit around the body, only one cardiac cycle is completed
examples of single circulatory system
fish, annelid worms
SCS: blood pressure in arteries
high due to heart contraction
SCS: blood pressure in gills
first set of capillaries for gaseous exchange, pressure lowers due to small diameter of the blood vessels
SCS: blood pressure in body tissues
exchange of nutrients and waste so pressure drops even more than in gills
SCS: blood pressure in veins
blood returns to the heart quite slowly at a low pressure
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
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
double circulatory system (DCS)
blood flows through the heart twice in one complete circuit, made up of 2 separate circulations: pulmonary and systematic
pulmonary circulation
heart - lungs - heart
systematic circulation
heart - body - heart
examples of a DCS
mammals, birds
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
why do multicellular organisms need transport systems?
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
SA of cube
6s²
volume of cube
s³
SA of sphere
4(pi)r2
volume of sphere
4/3(pi)r3
an effective transport system must include:
a liquid transport medium, vessels that carry transport medium, pumping mechanism
SA determines...
supply
volume determines...
demand and diffusion rate
open circulatory system
very few vessels - blood pumped from heart into haemocoel, low pressure, transport medium is in direct contact with body tissue
haemocoel
open body cavity
open circulatory systems are found in...
small animals with low metabolic rate - invertibrates, most insects, some molluscs
haemolymph
insect blood - doesn't carry gases, only dissolved nutrients
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.
blood flow
movement of blood through the vessels from the arteries to capillaries and then into the veins
blood pressure
a measure of the force that blood exerts against the vessel walls
blood flows from a place of ______ to a place of _______
high pressure, low pressure
sequence of blood vessels
arteries - arterioles - capillaries - venules - veins
structures common to arteries and veins
lumen, endothelial layer, wall
lumen
a hollow passage way blood flows through
endothelial layer
squamous endothelial cells, smooth so blood can flow easily without resistance
components vessel wall
elastic fibres, smooth muscle, collagen
elastic fibres
composed of elastin, allow stretch and recoil which provides flexibility - stretch and recoil happens with every pump of the heart
smooth muscle
contracts or relaxes to alter the size of the lumen
collagen
provides structural support, maintains shape and volume of vessel
descriptive words for muscle
contracts, relaxes
descriptive words for lumen
constricts, dilates
tunica intima
inner layer of endothelial cells
tunica media
middle layer of smooth muscle and elastic fibres
tunica externa
outer layer of connective tissue contains collagen
artery wall
thick to withstand greater blood pressure
artery lumen
small to maintain flow rate
artery endothelium
folded allowing them to expand during blood surges
function of arteries
carry oxygenated blood away from the heart with the exception of the pulmonary artery
structure of arteries close to the heart
lots of elastic fibres and little smooth muscle, lots of collagen
structure of arteries further away from the heart
less elastic fibres and a higher proportion of smooth muscle, less collagen
role of elastic fibres
maintains elasticity, stretch at high pressure of blood which reduces pressure and accommodates for higher volume of blood
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
function of arterioles
link arteries and capillaries
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
rate of blood flow equation
1/total cross sectional area
flow rate equation
cross sectional area x velocity
if cross sectional area increases, what decreases?
velocity
function of veins
carry blood away from the tissue to the heart
function of venules
link capillaries to veins
vein wall
thinner as low blood pressure
vein lumen
low friction, less resistance to blood flow
vein endothelium
single layer of smooth squamous endothelial cells
how is blood flow maintained in veins?
one way valves and location of veins between large muscles
one way valves in veins
flaps/infolding of inner lining at regular intervals along length of veins, prevent backflow of blood due to gravity
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
blood flow in veins
low pressure, against gravity
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
capillaries
microscopic blood vessels that form extensive networks in all tissues, site of substance exchange between tissue fluid and blood
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
fenestrations
gaps
explain why there are large capillary networks
large surface area - faster rate of diffusion of substances into and out of blood
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
explain why walls are a single endothelial layer thick in capillaries
short diffusion distance - faster rate of diffusion
explain why there are fenestrations in capillaries
increases permeability for exchange - more exchange happens
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
explain why veins have no pulse
the surges of blood produced by heart contraction are lost when blood flows through capillaries
explain why blood flows at a much lower pressure in veins than in arteries
they receive blood that has moved through the capillary bed
explain why blood flows easily through veins
low resistance due to wide lumen and smooth thin endothelium
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
ultrafiltration
which molecules can fit through fenestration gaps in capillaries under high pressure
blood
solution that consists of plasma (which contains dissolved substances), erythrocytes, leucocytes and platelets
role of blood
transports substances, acts as a buffer to minimise pH changes, homeostasis of temperature
erythrocytes
red blood cells, transport O2 and CO2
leucocytes
white blood cells - immune function
tissue fluid
bathes cells - same composition of blood without plasma proteins and erythrocytes
tissue fluid formation
ultrafiltration - blood plasma that is forced through fenestrations out of the capillaries. depends on 2 opposing pressures that cause movement of fluid in opposite directions
role of tissue fluid
all exchange of materials between blood and cells is through it.
hydrostatic pressure (PH)
pressure exerted by water on the walls of a vessel due to the surges of blood during heart contractions, forces fluid out of the capillary
oncotic pressure (PO)
tendency of water to move back into the capillary by osmosis
what determines net flow of fluid in and out of a capillary?
balance between PH and PO
PH > PO
net flow out of the capillaries
PH < PO
net flow back into the capillaries
what creates oncotic pressure?
large plasma proteins in blood mean water potential in blood is lower than in tissue fluid
hydrostatic pressure at arterial end if capillary
4.6kPa
oncotic pressure at arterial end of capillary
-3.3kPa
net pressure difference at arterial end of capillary
1.3kPa
hydrostatic pressure at venous end of capillary
2.3kPa
oncotic pressure at venous end of capillary
-3.3kPa
net pressure difference at venous end of capillary
-1.0kPa
how much tissue fluid returns to the blood?
90%
what happens to the tissue fluid that doesn't return to the blood?
it enters the lymphatic system
Note
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