Blood vessels, blood pressure, Fick’s law in respiration
blood vessels in closed circulatory systems
- inner cell layer of all vessels is endothelium, a specialized epithelial cell
o arteries carry blood away from heart
§ usually oxygenated, but not in pulmonary artery
§ wide
§ thick walls
§ walls include flexible part to expand when blood is pumped in, also lots of smooth muscle to regulate diameter
· regulating diameter regulates blood pressure, like thumb over garden hose (Fig. 47.19)
o arterioles
o capillaries
§ these vessels are where exchange between blood and tissues/interstitial fluid happens, rest is just tubing to get to and from heart
§ thin walls, one cell layer thick (endothelium)
§ very short
§ every cell in an animal is near one
· blood comes in at high pressure
· endothelium has openings in it, so water and small solutes are squeezed out of the blood (Fig. 47.16)
§ Fluid flow through capillaries
· Blood comes in at high pressure and velocity
· Fluid part of blood leaks out into surrounding tissues (becomes interstitial fluid)
· As blood leaves capillaries it is
o Lower velocity and pressure
o More concentrated because fluid has leaked but bigger things like proteins cannot leak thru endothelium
· So, at end of capillaries insterstitial fluid reenters capillaries by osmotic pressure
· What does not reenter is drained by an open ended system of tubes, the lymphatic system
o Blockage of lymphatic system leads to buildup of interstitial fluid
o Often parasitic worms cause this blockage
§ Filariasis causing elephantiasis
§ Capillaries are arranged in capillary beds supplied by one arteriole
· sphincters control blood to capillary beds
o veinules and veins
§ carry blood back to heart
§ thin walls
§ one-way valves to keep blood from backing up
§ also skeletal muscle movement helps move blood through these vessels
Public health
- atherosclerosis
o damage to endothelium in arteries
o blood flowing at very high pressure and speed probably contributes to this
o endothelium gets fatty deposits which contain a lot of cholesterol
§ causes scar tissue to develop
§ Ca2+ is deposited (hardening of arteries) Plaque. Damage to endothelium can cause clot to form. (thrombus). If dislodged it is an embolus. Cause strokes and pulmonary emboli. Also buildup can cause heart attacks (myocardial infarction) if coronary arteries are blocked.
§ Treatment
· Open heart bypass surgery
· Balloon angioplasty
· Stent
Fick’s Law and Partial Pressure
Concept of partial pressure (the contribution of a particular gas to total air pressure).
- Sea level total air pressure is 760mm Hg
- O2 is 20.9% of total air, so PO2 is 760 X .209
- Mt Everest air pressure is 250mmHg
- So PO2 is 250 X .209
- So lots less O2 available at altitude (important for birds and alpine organisms)
Gas exchange – Fick’s Law
Q = kAP2-P1
D
Q is rate at which a substance diffuses between two locations
k is diffusion coefficient which depends on diffusing substance, medium it is diffusing through, and temp
A is area over which substance is diffusing
P2-P1is concentration difference
D is distance between locations
Animals can maximize Q by
- Maximizing k by using air as a medium when possible
o Things diffuse much faster in air than water
- Maximizing P2-P1
o One way by using air rather than water, water holds much less gas than air
§ One liter of air has 209 ml O2, one liter of water holds 7ml O2
§ So without hemoglobin we are dead – can’t dissolve enough oxygen in blood to supply our cells
o Also other ways (countercurrent exchange)
- Maximizing A by having a large a respirator surface area as possible
- Decreasing D by making the epithelial cells at respiratory surfaces very thin
Air is a better medium than water
- O2 content of air much higher than water (increasing P2-P1)
- O2 diffuses much more rapidly in air than water (increasing L)
- Animal must move water or air over respiratory surfaces, it takes a lot more energy to move water than air
o What affects solubility of gases in water?
§ Temp – higher is worse
§ Presence of solutes – seawater worse than freshwater
§ Partial pressure of gas in contact with water (opening pop)