Capillaries . The smallest of the blood vessels: capillaries.
Inside the air sacs, oxygen moves across paper-thin walls to tiny blood vessels called capillaries and into your blood. A protein called haemoglobin in the red blood cells then carries the oxygen around your body.
lungs
The tiny sacs insure that the maximum area of tissue can be in close contact with the blood vessels to facilitate gas transfer
There are three types of blood vessels; arteries, veins, and capillaries. Capillaries are tiny blood vessels.
Why are nephrons surrounded by many tiny blood vessels
alveoli
The tiny sacs in the synaptic knob are known as synaptic vessels. The synaptic vessels release chemicals into the bloodstream with each synapse.
These tiny air sacs are called alveoli. These alveoli are surrounded by capilaries tiny blood vessells. These capilaries have holes that are to small for blood cells to escape but are big enogh for oxygen molecules to pass in to the blood stream and attach to the haemoglobin in your blood.
Capillaries
capillary
I believe the tiny blood vessels are called capillaries, located in the lungs.
The thin walls of the blood vessels are capillaries around the alveolar sacs that permit diffusion of gases in every single red blood cell with oxygen inhaled ... they are thinner to improve the pressure gradient to allow more O2 in the capillaries, because the pulmonary capillaries have the lowest blood pressure in the body (normally)