3.2.2 Circulatory Systems Flashcards
The Needs for a Circulatory System
The cells of all living organisms need a constant supply of reactants for metabolism
- e.g. oxygen and glucose
- these materials are gained from the environment g via exchange surfaces
Single called organisms can gain oxygen and glucose directly across their surface membranes and the molecules can diffuse to all parts of the cell quickly due to short diffusion dist5ances
Larger organisms gain these reactants via specialised exchange surfaces, but because they are made up of many layers of cells, the time taken for substances such as glucose and oxygen to diffuse to every cell in the body would be far too long
- the diffusion distances involved are too great
To solve this problem, their exchange surfaces are connected to a mass transport system
For example:
- the digestive system is connected to the circulatory system
- the lungs are connected to the circulatory system
Circulatory systems are systems that transport fluids containing oxygen, nutrients and waste
Single and Double Circulatory Systems
There are two different models of circulatory systems, single circulatory systems and double circulatory systems
- in a single circulatory system, the blood passes through the heart once during one complete circuit of the body
- in a double circulatory system, the blood passes through the heart twice during one complete circuit in the body
Fish have a single circulatory system while mammals have a double circulatory system
Single Circulatory System in Fish
Deoxygenated blood is pumped to the gills from the heart
The gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood
The oxygenated blood flows from the gills to the rest of the body
- it travels through the capillaries in organs, delivering oxygen and nutrients
The blood returns to the heart
The heart only has one atrium and one ventricle
Double Circulatory System in Mammals
In mammals, the blood passes through the heart twice during a single circuit of the body
As a result, the mammal heart has a left side and a right side, with a wall (septum) diving the two
- the left side contains oxygenated blood and the right side contains deoxygenated blood
Blood in the right side of the heart leaves and travels to the lungs
The blood returns too the left side of the heart before being pumped around the rest of the body
Once the blood passed through all the other organs and tissues, it returns to the right side of the heart
- in general, any blood that has just passed through an organ goes straight back to the heart, not any other organ
- the hepatic portal veins is the exception to this rule, it allows blood from the gut to flow to flow to the liver
The Heart
A hollow, muscular organs located in the chest cavity which pumps the blood
Cardiac muscle tissue is specialised for repeated, involuntary cardiac contraction without rest
Arteries
Blood vessels which carry blood away from the heart
The walls of the arteries contain lots of muscle and elastic tissue and a narrow lumen, to maintain high blood pressure
Arteries range from 0.4-2.5 cm in diameter
Arterioles
Small arteries which branch from larger arteries and connect to capillaries
These are around 30 micrometers in diameter
Capillaries
Tiny blood vessels (around 5-10 micrometers in diameter) which connect Arterioles and venues
Their size means they pass directly past cells and tissue and perform gas exchange and exchange of substances such as glucose
Venules
Small veins which join capillaries to large veins
They have a diameter of 7 micrometers-1 mm
Veins
Blood vessels which carry blood back towards the heart
The walls of veins are thin in comparison to arteries, having less muscle and elastic tissue but a wider lumen
Valves help maintain blood flow back towards the heart
Advantages of Double Circulation
It is believed that a double circulatory system has evolved from the single circulatory system as there are several benefits to a double circulatory system
When blood enters a capillary network, the pressure and speed drops significantly
In a single circulatory system, the blood has to pass through 2 capillary networks before returning to the heart
In a double circulatory system, the blood only passes through 1 capillary network before returning to the heart
As a result, the double circulation maintain higher blood pressure and average speed of flow
- this increased pressure helps to maintain a steeper concentration grenadines which allows for the efficient exchange of nutrients and waste with the surrounding tissues
Open and Closed Circulatory Systems
Circulatory systems are either open or closed
In a closed circulatory system, blood is pumped around the body and is always contained within a network of blood vessels
- all vertebrates and many invertebrates have closed circulatory systems
In an open circulatory system, blood is bot constrained within blood vessels, but it is pumped directly into body cavities
- organisms such as arthropods and molluscs have opened circulatory systems
The Human Circulatory System
Humans have a close double circulatory system
- in one complete circuit of the body, blood passes through the heart (the pump) twice
The right side of the heart pumps deoxygenated blood to the lungs for gas exchange
- this is the pulmonary circulatory system
Blood then returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (as high pressure) around the body
- this is the systemic circulatory system
Circulatory Systems in Insects
Insects have one main blood vessel
- this is the dorsal vessel
The tubular heart in the abdomen pumps haemolymph (this is what blood in insects is called) into the dorsal vessel
The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
Haemolymph surround the organs and eventually renters the heart via one-way valves called Ostia
Unlike the blood in a mammals circulatory system, the haemolymph is not specifically directed towards any organs in an insect
Insects are able to survive with this less efficient system because oxygen is delivered directly to their tissues via tracheae (a system of tubes) that connect directly to the outside
