Circulatory Systems
- Circulatory systems have evolved ways
to increase gas transport efficiency
- Consider features of blood, blood vessels, and heart(s).
Gas transport efficiency of blood
- Only limited amounts of gases can dissolve in blood (a warm, open Coke is "flat")
- Respiratory pigments (e.g., hemoglobin) increase carrying capacity of blood for O2
- Red blood cells each contain 250,000 hemoglobin molecules.
Open Circulatory Systems
- Blood bathes the body tissues directly.
- Blood does not remain inside blood vessels for its entire circuit.
- There is no distinction between "blood"
and "interstitial fluid."
Open circulation in insects
Open circulation in insects
- Dorsal heart(s) pump body fluids
- Sluggish flow through body cavities
- Efficient enough for transport of food and wastes, but not O2 and CO2
- How are gases transported?
Closed Circulatory Systems
- In which the blood is confined to blood vessels through the entire circuit.
- There is a distinction between blood and interstitial fluid.
Closed circulation in earthworms
Closed circulation in earthworms
- Dorsal and ventral vessels connected
by 5 pairs of pulsating tubes ("hearts")
- Gas exchange is across capillaries of body wall -- under moist, mucous-covered skin.
- If earthworm is too wet…
- If earthworm is too dry...
Evolution of 4-Chambered Heart
- 2 chambers in fish
- 3 chambers in amphibians
- 4 chambers in reptiles, birds, mammals.
Fish
Fish
- Two chambers = 1 atrium, 1 ventricle
- Blood goes to gills, then to body.
- Blood loses pressure in the gills, so...
- Blood flow through the body is slow.
Amphibians
Amphibians
- 3 chambers = 2 atria, 1 ventricle
- Blood goes to the lungs, then...
- Returns to the heart
for second push
before going to the body.
- Blood flow in body is faster than in fish.
Problems with having 1 ventricle
- In the ventricle, oxygenated blood returning from the lungs mixes with deoxygenated blood returning from the body.
- How can amphibians live with this?
Ways around the "problem"
- An amphibian’s skin is smooth and moist.
- Amphibian metabolism is relatively low.
- Interior of ventricle directs flow.
Reptiles, Birds, Mammals
- Much higher metabolism
- Body covered with scales, feathers, fur
- Cannot tolerate mixing in ventricle.
Four-chambered heart
Coordination of contraction
- The 2 atria contract before the 2 ventricles.
- Cardiac muscle contracts spontaneously at different rates (70 to 30 bpm).
- "Pacemaker" (SA node) sets the rate.
Wave of contraction
- Spreads from SA node across the two atria.
- Wave delayed briefly at AV node.
- Stimulus carried rapidly to all parts of the two ventricles by the bundle of His.
Medical applications
- Artificial pacemaker
- Heart attack
-- coronary artery blocked
-- cardiac muscles dies
-- wave of contraction interrupted
Electrocardiogram (ECG)
Electrocardiogram (ECG)
- P wave = atria contract
- QRS wave = ventricles contract
- T wave = ventricles relax
Heart sounds
- Lub-dup… lub-dup… lub-dup.
- Sounds = snapping shut of the one-way valves that prevent backflow.
- Lub = atrioventricular (AV) valves.
- Dup = semilunar valves (where blood exits ventricles)
Blood pressure
- Systolic pressure = peak pressure after contraction (120 mm Hg in upper left arm)
- Diastolic pressure = low point between beats (typically 80 mm Hg)
- Measure with sphygmomanometer and
a stethoscope.
How to take blood pressure
Sounds in stethoscope 1
- If cuff presssure is greater than systolic
- Blood flow is stopped
- No sound
Sounds in stethoscope 2
- If cuff pressure is less than systolic
and greater than diastolic
- Blood flow is bursts of turbulence
- Sound of turbulence.
Sounds in stethoscope 3
- If cuff pressure is less than diastolic
- Blood flow is smooth
- No sound
Hypertension
- 20% have high blood pressure
(= diastolic pressure > 90 mm)
- Asymptomatic => long "silent" period
- 150/100 shortens life of 35 yr old male
by 12 years!
Life & Health Insurance
- Check blood pressure
- Urine test
- Blood test
- Smoking or non-smoking
Hypertension: Causes of Death
- Atheroscelerosis <=> HBP
- Heart attack
- Stroke
- Kidney failure
Kidney failure
- High blood pressure in the glomerulus increases the amount of filtrate
- Overworked nephrons "harden"
- Toxins (urea) builds up in blood
Artificial kidney
- Kidney dialysis machine:
-- Blood in semipermeable tube
-- Toxins diffuse into balanced salt "bath".
-- Requires a few hours, twice a week
- Peritoneal dialysis: Balanced salt solution put into abdominal cavity, suctioned out half an hour later.
Key Points
- Increased efficiency of circulatory system
- Evolution of closed circulatory system
and 4-chambered heart
- Pumping efficiency of heart (ECG, valves)
- Medical applications