1. Transport systems in multicellular animals

Created by

Nethra

Cards (11)

Need for specialised transport systems:
Multicellular animals have high metabolic demands = so diffusion over long distances, not enough to supply quantities needed
SA:V ratio = gets smaller as organism gets bigger --> so diffusion distances bigger + amount of SA available to absorb/remove substances becomes smaller
Molecules [ex: hormones/enzymes] may be made in one place but needed in another
Food will be digested in 1 organ system = but need to be transported to every cell for respiration + other aspects of cell metabolism
Waste products = need to be removed from cells + excreted
3 summarised reasons for need of specialised transport systems:
Increasing transport distances
SA:V ratios
Increasing levels of activity
Common features of circulatory systems:
Have a liquid transport medium that circulates around system
Have vessels that carry transport medium
Have a pumping mechanism to move blood around system
Mass transport systems: when substances are transported in a mass of fluid with a mechanism for moving fluid around body
Help to = Maintain diffusion gradients, ensure effective cell activity [ex: circulatory system]
Open circulatory system
Very few vessels to contain transport medium = pumped straight from heart to body cavity of animal
Open body cavity called = haemocoel
In haemocoel transport medium under low pressure
It comes into contact with tissues & cells = where exchange happens between transport medium and cells
Transport medium returns to heart through an open-ended vessel
Closed circulatory system:
Blood enclosed in blood vessels + doesn’t come into contact with cells of body
Heart pumps blood around body under pressure, blood returns to heart
Substances leave + enter blood by diffusion through blood vessel walls
Amount of blood flow can be adjusted by widening/narrowing blood vessels
Most closed circulatory systems contain blood pigment that carries respiratory gases
Single closed circulatory system:
Found in fish + annelid worms
Blood travels only once through heart for each complete circulation of blood
Blood passes through 2 sets of capillaries before returning to heart:
--> in 1st = it exchanges o2 + co2
--> in 2nd = different organ systems, substances exchanged between blood & cells
Due to passing through 2 sets of narrow vessels = blood pressure drops --> blood returns to heart slowly
Limits efficiency of exchange = animals with this system have low activity
Fish = exception as they have an efficient single circulatory system = can be very active
Have a countercurrent gas exchange system = allows them to take in lots of o2 + body weight supported by water + don’t need to maintain body temp
--> reduces metabolic demands combined with efficient exchange system = allows them to be active with a SCS.
Oxygenated blood flows from gills --> rest of the body --> returns to heart
Heart only has 1 atrium + 1 ventricle
Double closed circulatory system:
Birds & mammals = active + maintain own body temp
Most efficient system for transporting substances around body
Involves 2 separate circulations:
Blood pumped from heart --> lungs [to pick up o2 + unload co2] --> returns to heart
Blood flows through heart --> travels around body --> returns to heart
So in DCCS:
Blood travels through heart for each circuit of body
Each circuit to lungs + body = only passes through one capillary network --> so high pressure + fast blood flow can be maintained
Advantages of double circulation:
When blood enters capillary network pressure + speed drops
Blood only has to pass through one capillary network unlike single circulation which has to pass through 2 capillary networks before returning to heart
As a result = double circulation maintains higher blood pressure + average speed of flow --> increased pressure & speed helps maintain steeper conc gradient allowing efficient exchange of nutrients and waste with surrounding tissue