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Biology 20: Circulatory System Cheat Sheet (DRAFT) by

Alberta Curriculum Biology 20 Body Systems: Circulation

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Functions of the Circul­atory System

Carries nutrients (O2) to cells
Takes waste away from cells
Distri­butes heat throughout the body
Regulates levels of body fluids
Sends chemicals messengers to different parts of the body (hormones)
Defends against foreign organisms

Types of Blood Vessels

Arteries
The muscul­ar-­walled tubes by which blood (mainly oxygen­ated) is delivered from the heart to all parts of the body, high pressure vessels
Arterioles
Small arteries that lead into capill­aries, still have high pressure but not as much as arteries
Capillaries
Composed of a single layer of cells, ideal for fluid and gas exchange
Venules
Small veins that lead from capill­aries, low pressure
Veins
Vessels that carry mainly deoxyg­enated blood to the heart that have a larger diameter than arteries, low pressure vessels

Arteries

Arteries carry blood away from the heart
Most arteries carry oxygenated blood (except the pulmonary artery that goes from heart to lungs)
They have thick walls with 3 layers:
Inner and outer walls: connective tissue
Middle layers: made of muscle fibres and elastic connective tissue
The walls stretch with every heart contra­ction and recoil after the blood has passed through

Arterioles & Venules

Arteri­oles:
- Middle layer is smooth muscle and elastic fibre
- Pressure is still high but less than arteries
- The diameter is controlled by the autonomic nervous system, messages from the ANS can cause vasoco­nst­riction or vasodi­lation
- Pre-ca­pillary sphincters regulate blood flow, so not all arterioles are open at any given time

Venules:
- Lined with smooth muscle, but not 3 layers (like seen in arteries)
- Not enough blood pressure to return blood to heart
  

Veins

- Mainly carry deoxyg­enated blood (exception of the pulmonary vein which brings blood from the lungs to the heart)
- Blood pressure in the veins is much lower than in the arteries therefore, veins are lined with valves to prevent backflow
- If blood pools, the vein will swell in front of the valve
- Blood moves through veins as the vein is squeezed by skeletal muscles
- Act as blood reservoirs (65% of total blood volume can be found in the veins)

Capill­aries

- Composed of a single layer of cells
- Small diameter, slows the flow of red blood cells
- Thin wall ideal for gas and fluid exchange
- Due to high surface area, the pressure drops signif­icantly
- 85% of fluid returns to capill­aries (remaining 15% returns via lymph)

Arteri­osc­lerosis

Arteri­osc­ler­osis: a group of disorders that cause the blood vessels to thicken, harden, and lose elasticity
Athero­scl­erosis: a degene­ration of blood vessels caused by the accumu­lation of fat deposits in the inner wall
Caused by a lipid build-up along with calcium and other minerals to form a plaque
Leads to high blood pressure, if this forms a blood clot and it breaks off, it can cause a heart attack

Aneurysm

Aneurysm: a bulge in the weakened wall of a blood vessel, usually an artery
Often due to athero­scl­erosis
If an aneurysm bursts, less oxygen and nutrients are delivered to the tissues, resulting in cell death
Stroke: aneurysm in the brain

Pulse & The Control of Blood Flow

Pulse
When the ventricle contracts, blood surges forward into arteries, when a pulse if felt, it is the artery expanding and contra­cting
Decreasing Blood Flow
Smooth muscles on arterial walls contract to decrease blood volume and pressure
Capillary Blood Flow
Precap­illary sphincters close off to limit blood volume and pressure in capill­aries
Throug­h-fare channels are always open to allow blood flow