Download Title: The Heart, Introduction and Evolution

Title: The Heart, Introduction and Evolution
1- We just looked at the composition and function of blood. However, for blood to
reach each of the body cells and exchange material with them it must be
constantly pumped by the heart through the body’s many miles of blood vessels
2- Interesting facts:
a- Your heart beats about 100,000 times each day or about 35 million beats
per year
b- Live to be 85 (slightly more than average) and this equals about 2.98
billion beats
c- Bill Gates could give you $40 each time your heart beats, for your whole
life, and still have a few billion left over
d- You have about 60 – 80 thousand miles (100,000 – 120,000 Km) of blood
vessels
e- Your heart pumps about 30X your own weight each minute (even while
sleeping)
f- The heart pumps 3,600 gallons of blood a day or 2.6 million gallons a year
Animal
Short Tailed Shrew
Hummingbird
Chicken
Cat
Human
African Elephant
Blue Whale
Galapagos Tortoise
Beats per Minute
1400
1360
275
150
60
30
18
6
Weight
3.6 grams
4.5 grams
Life Expectancy
2 years
3 years
4-5 Tons
100 Tons
78 years
85 years
125 years *
180 years
g- The heart of a blue whale weighs 1000 lbs, its aorta is 4.5 feet in diameter
and its total blood weight is 1400 lbs
* In 2003 a male Bowhead whale washed up in San Diego with a harpoon
imbedded in its side manufactured between 1780-1790. It’s not believed that
these types of harpoons were used after 1800. That would make the whale
over 200 years old! He was born when Thomas Jefferson was president and
died when Bill Clinton was president.
3- Evolution of the Heart – The heart is a marvel of evolution that ranges in function
from the very simple heart of invertebrates such as worms, to the more complex
structure of the squid to extremely complex animal hearts.
a- Invertebrates
1- Worms – The heart of the worm is no more than a muscular tube that
moves a blood-like material called hemocoele through the body via
peristaltic action
2- Sea squirts pump blood in one direction for several minutes and then
change its direction for several minutes
3- Mollusks have a 5 chambered heart (4 atria and 1 ventricle)
4- Annelids have 7 or more chambers
5- Squids have three separate hearts – 2 gill hearts that force blood under
pressure to the gills and one heart that forces oxygen rich blood to the
rest of the body
6- This diversity in structure is often explained by these organisms
relative small size, low metabolic activity and that the role of the
circulatory system is often less about respiratory exchange and more
about nutrient exchange which can be designed with more flexibility
4- In vertebrates the primary role of the circulatory system is transporting oxygen to
the cells. Therefore, a certain generalization of structure is necessary. Complexity
increase from fish to amphibians to reptiles and mammals
a- Vertebrates
1- Fish –
a- The fish heart is the simplest of vertebrate hearts.
b- It consists of two chambers, a thin walled atrium and a thicker
muscular ventricle. In fish blood is moved from the atrium to
the ventricles to the conus (tissue that does not pump but can
be stretched and squeezed)
c- From the conus the blood goes to the gills for oxygenation and
then to the body and then back to the atrium
d- Fish have a single circuit circulation
2- Amphibians –
a- The amphibian heart is a more complex double loop
circulation. Amphibians have three chambers: 2 atria and a
common ventricle
b- Amphibians have definitive aorta and pulmonary arteries
projecting from the conus
c- Both oxygen rich and poor blood are generally kept separate by
well-timed contractions of the right and left atrium. However,
there is sufficient mixing of the blood to produce “coldbloodedness” and a relatively slow metabolic rate
3- Reptiles
a- Like amphibians, reptiles also have a three chambered, two
loop circulation
b- Reptiles have 2 atria and 1 partially divided ventricle – some
people make the defensible argument that reptiles actually have
a 4 chambered heart but that the ventricular wall separation is
incomplete (ventricular septum (wall) defects as well as atrioventricular septum defects are common in people) Both
arguments are reasonable
c- As in amphibians there is mixing of the oxygen rich and
oxygen poor blood. However, this mixing is minimized by
timing of contractions and the partial wall.
d- Crocodiles are the lone exception among reptiles (as well as all
animals). The crocodile has a four chambered heart with full
ventricular separation (like birds and mammals). However the
right ventricle can pumps blood through two different vessels:
the pulmonary artery and the right systemic artery
i. By opening or closing a flap of tissue called the
“Foramen of Panizza” a crocodile can effectively
switch between normal and low oxygen conditions. He
does this by shutting off oxygen to the pulmonary
circulation.
ii. When underwater oxygenated blood is shunted away
from the lungs and mixes with oxygen rich blood
exiting the right aorta to other vital organs in the body
iii. Franklin and Axelsson two of the leading experts on
crocodile anatomy say that it is the most advanced heart
of any animal alive today
4- Birds and Mammals (including humans)
a- Birds and mammals are endothermic (warm blooded) with a
high metabolic rate and an efficient two-looped closed
circulation (pulmonary and systemic). Both birds and mammals
have 4 separate chambers: 2 atrium and 2 ventricles. There is
no mixing of oxygenated and deoxygenated blood in the
normal heart (No AVM malformations or interatrial, or
interventricuar malformations)
b- In birds and mammals:
1- Deoxygenated blood enters the right atrium through the
common vena cava (formed from the union of the superior
and inferior vena cava)
2- The deoxygenated blood then passes through the tricuspid
valve into the right ventricle
3- Deoxygenated blood is then pumped out of the right
ventricle through the pulmonary valve into a large artery
called the pulmonary trunk, which then branches into the
right and left pulmonary arteries to the lungs for
oxygenation
4- The left atrium receives the newly oxygenated blood
returning from the lungs through the four pulmonary veins
5- The oxygenated blood then passes through the biscuspid
(mitral) valve into the left ventricle
6- The left ventricle (the thickest part of the heart) contracts
and pushes blood through the aortic valve into the
ascending aorta (some of the blood flows from the
ascending aorta to the coronary arteries to nourish the
heart) the blood then passes into the aortic arch, where it
branches into the brachiocephalic trunk, the left common
carotid artery, the left subclavian artery and the descending
aorta.