unit 5 biology

Arteries

• carry blood away from the heart to the body

• High pressure in them as it’s being pumped by the heart

• The blood is oxygenated. The red blood cells have haemoglobin which bond with oxygen making oxyhemoglobin which cause the blood to have a bright red colour

• Deep inside the body

Veins

• carry blood from the body to the heart

• Low pressure

• Due the low pressure valves are needed to prevent back flow and help compensate for the lack of pumping force to help with directional flow

• Due to less oxygenated blood has a dark red appearance and it’s closer to the surface

Capillaries

• between the artistries and veins and Carry blood to and from the cells of the body

Capillaries structure

Capillaries

(Site of nutrient and gas exchange)

Inner Layer

:

• Lumen – Very narrow (about 5-10 µm in diameter)
  Why: The narrow lumen forces red blood cells to pass through one by one, which slows down the blood flow and enhances exchange with tissues.

• Endothelium – Single layer of endothelial cells
  Why: This thin layer allows quick and efficient exchange of oxygen, carbon dioxide, nutrients, and waste between blood and tissues.

Outer Layer

:

• Basement membrane – Very thin support layer
  Why: Provides structural support without obstructing the exchange of gases and nutrients.

Size of Capillaries:

• Capillaries are the smallest blood vessels, with a diameter of about 5-10 µm (micrometers). Their size allows for the efficient exchange of gases, nutrients, and waste.

veins structure

Inner Layer

:

• Lumen – Large (about 8-15 mm in diameter)
  Why: The wide lumen allows blood to flow more easily at lower pressure.

• Endothelium – Smooth layer, contains valves
  Why: Prevents blood from flowing backward due to low pressure.

Middle Layer

:

• Elastic tissue – Small amount
  Why: Veins don’t need to stretch and recoil as much as arteries because they deal with low-pressure blood flow.

• Smooth muscle – Thin layer (about 0.1–0.5 mm thick)
  Why: Veins are less involved in controlling blood flow, so the muscle layer is much thinner than in arteries.

Outer Layer

:

• Connective tissue – Thicker than in arteries
  Why: Supports the vein and maintains its shape under low pressure.

Size of Veins:

• Typically have a larger lumen than arteries (ranging from 8-15 mm). Veins carry blood back to the heart, usually at low pressure, and therefore need more space for slower-moving blood.

Arteries structure

Arteries

(Carry blood away from the heart under high pressure)

Inner Layer

:

• Lumen – Small (about 4-10 mm in diameter)
  Why: Keeps blood under high pressure to move quickly away from the heart.

• Endothelium – Smooth layer of endothelial cells
  Why: Reduces friction and helps prevent clotting, allowing smooth blood flow.

Middle Layer

:

• Elastic tissue – Thick, allows stretch and recoil
  Why: Helps the artery expand with each heartbeat and recoil to maintain blood pressure.

• Smooth muscle – Thick layer (about 0.5-2 mm in thickness)
  Why: Regulates blood flow by constricting or dilating the vessel.

Outer Layer

:

• Connective tissue – Thick
  Why: Provides strength and durability to withstand the high pressure of blood being pumped through.

Size of Arteries:

• Typically have a larger diameter compared to veins and capillaries (ranging from 4–10 mm depending on the artery). Arteries need to carry blood under higher pressure and over greater distances.