B3. The Circulatory System Flashcards
Function of the circulatory system
Multicellular organisms, like mammals, have a ___surface area to volume ratio, so they need a specialised _____ __________ _______to carry raw materials from specialised exchange organs to their _____ ____- this is the circulatory system
Multicellular organisms, like mammals, have a low surface area to volume ratio, so they need a specialised mass transport system to carry raw materials from specialised exchange organs to their body cells - this is the circulatory system
Structure of the circulatory system
The circulatory system is made up of _______ and _______ ________. The heart pumps blood through blood vessels (_________, ____________, _____and ____________) to reach different parts of the body.
The circulatory system is made up of the heart and blood vessels. The heart pumps blood through blood vessels (arteries, arterioles, veins and capillaries) to reach different parts of the body.
Figure 1: The circulatory system.
Figure 2: Some of the blood vessels in a mammalian circulatory system.
Tip: The gut is another name for the …
Tip: The gut is another name for the digestive tract or a part of it, e.g. the intestines.
Structure of the circulatory system
What does the blood transport? (4 things)
There are two circuits. One circuit takes blood from the _______ to the ______, then back to the ______ . The other loop takes blood around the rest of the _____ , so the blood has to go through the heart _______ to complete one full circuit of the body.
The heart has its own…?
- respiratory gases
- products of digestion
- metabolic wastes
- hormones
There are two circuits. One circuit takes blood from the heart to the lungs, then back to the heart. The other loop takes blood around the rest of the body, so the blood has to go through the heart twice to complete one full circuit of the body.
The heart has its own blood supply - the coronary arteries
Figure 3: Blood vessels of the heart.
Arteries
What do they do
(2 Features)
Arteries carry blood oxygenated blood (except pulmonary arteries) from the heart to the rest of the body.
- Their walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, which helps maintain the high pressure.
- The inner lining (called the endothelium) is folded, allowing the artery to stretch - this also helps it to maintain high pressure.
Arterioles
What are they?
Feature?
Arteries divide into smaller vessels called arterioles. These form a network throughout the body.
- Blood is directed to different areas of demand in the body by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow full blood flow.
Veins
What do they do?
Features (3)
Veins take oxygenated blood (except for at the lungs) back to the heart under large low pressure.
- They have a wider lumen than lumen equivalent arteries, with very little elastic or muscle tissue.
- Veins contain valves to prevent backflow of blood
- Blood flow through the veins is helped by contraction of the body muscles surrounding them
Exam Tip
An artery ….
you won’t get marks for writing that it contracts and relaxes, or expands.
Exam Tip
An artery stretches to cope with high pressure and then recoils under low pressure
- you won’t get marks for writing that it contracts and relaxes, or expands.
Capillaries
What are they?
What do they do?
Features (3)
Arterioles branch into capillaries, which are the smallest of the blood vessels.
Substances (e.g. glucose and oxygen) are exchanged between cells and capillaries, so they’re adapted for efficient diffusion.
- Capillaries are always found very near cells in exchange tissues (e.g. alveoli in the lungs), so there’s a short diffusion pathway.
- Their walls are only one cell thick, which also shortens the diffusion pathway.
- There are a large number of capillaries, to increase surface area for exchange. Networks of capillaries in tissue are called capillary beds.
Tip: Capillaries connect …at…
Venules are …. that connect to _____.
Tip: Capillaries connect arterioles and venules together at capillary beds. Venules are small blood vessels that connect to veins.
Tissue fluid
What is it?
What is it made from and how does it differ to blood and why?
Exchange of substances?
- Tissue fluid is the fluid that surrounds cells in tissues.
- It’s made from small molecules that leave the blood plasma, e.g. oxygen, water and nutrients. (Unlike blood, tissue fluid doesn’t contain red blood cells or big proteins, because they’re too large to be pushed out through the capillary walls.)
- Cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it. In a capillary bed, substances move out of the capillaries, into the tissue fluid, by pressure filtration.
Tissue fluid - Whole process starting from arterial end (5 steps)
1) At the arterial end, the hydrostatic pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid and overall outward pressure forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid.
2) As fluid leaves, the hydrostatic pressure reduces in the capillaries—so the hydrostatic pressure is much lower at the venule end of the capillary bed
3) Due to the fluid loss, and an increasing concentration of plasma proteins (which can’t leave the capillaries), the water potential at the venule end of the capillary bed is lower than in the tissue fluid.
4) This means that some water re-enters the capillaries from the tissue fluid at the venule end by osmosis
5) Any excess tissue fluid is drained into the lymphatic system which transports this excess fluid from the tissues and passes it back into the circulatory system.
Figure 4: The movement of fluid between capillaries, tissue fluid and lymph.
