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Dt3 Animal Biology (Year 1, UU) Summary Campbell
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A summary of the required chapters from Campbell biology for subtest 3 of Animal Biology (year 1 Biology UU).
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16 CirculatieHoofdstuk 43 Transportsystemen
43.1 Circulatory systems link exchange surfaces with cells
Diffusion is the random thermal motion of particles. When there is a difference in
concentration, diffusion can lead to net movement.
For multicellular organisms direct exchange between every cell and the environment
is impossible. Two types of adaptations have been made: arranging cells in a way
that many or all cells are in contact with the environment (flatworms) or a circulatory
system.
Gastrovascular cavities put many cells in contact with the environment, enabling
hydras and jellies to not need a circulatory system. It functions in distribution of
substances and digestion and branches into the tentacles. Fluid bathes the inner and
outer tissue layers, allowing gas and waste exchange.
A circulatory system has 3 components: circulatory fluid, vessels, and a heart:
muscular pump that uses metabolic energy to elevate the fluid’s hydrostatic pressure:
pressure fluid exerts on vessels. It connects the aqueous environment of the body
cells to the organs that exchange gases, absorb nutrients, and dispose of waste.
In an open circulatory system the heart pumps hemolymph or interstitial fluid into
interconnected sinuses: spaces surrounding organs. Heart relaxation draws
hemolymph back through the pores which then close with valves when the heart
contracts. Body movement periodically squeezes the sinuses, helping circulation.
Benefits are: less energy costing because of lower hydrostatic pressure, and
additional functions like leg extending in spiders.
In a closed circulatory system blood is confined to vessels that branch into smaller
ones to infiltrate tissues. Chemical exchange occurs between the blood and
interstitial fluid and interstitial fluid and cells. Benefits are: higher blood pressure
enables more effective delivery of nutrients in larger animals, and blood distribution
can be regulated.
Cardiovascular system: heart and blood vessels in vertebrates. There are three
main types of blood vessels: arteries carry blood from the heart to organs. Within
organs arteries branch into arterioles which convey blood to capillaries:
microscopic vessels with thin porous walls, which form networks called capillary
beds. Capillaries converge again into venules which converge into veins that carry
blood back to the heart.
The heart of all vertebrates contains two or more chambers. Chambers receiving
blood are called atria and chambers pumping blood out are called ventricles.
Sharks, rays, and bony fish have a single circulation: single loop. Their heart
consists of two chambers: 1 atrium and 1 ventricle. Heart contraction pumps blood to
the gills where gas exchange occurs after which oxygen rich blood is carried to
tissues. In single circulation blood passes 2 capillary beds before returning to the
heart, the blood pressure drop in the gill capillary bed limits the blood flow rate in the
rest of the body.
Amphibians, reptiles, and mammals have two blood flow circuits: double circulation.
In the pulmonary (or pulmocutaneous) circuit the right heart side pumps oxygen
poor blood to the gas exchange tissues. In the systemic circuit the left side pumps
,oxygen rich blood to capillary beds in tissues. Blood pressure in this circuit is much
higher.
Adaptations in intermittent breathers enable the circulatory system to bypass the
lungs:
Amphibians have three chambers: 2 atria and 1 mixed ventricle. When
underwater, lung blood flow is shut off and blood flow continues to the skin.
In the 3 chambered heart of turtles, snakes, and lizards, an incomplete septum
divides the ventricle.
In crocodilians the ventricles are divided by a complete septum, but both
circuits connect where the arteries exit the heart, allowing valves to shunt
blood flow away from the lungs.
Birds and mammals have 2 atria and 2 completely divided ventricles and can’t vary
blood flow to the lungs without varying blood flow throughout the body. They need
this powerful four chambered heart because they are endotherms and need O2.
43.2 Cycles of heart contraction in double circulation
Overall organisation in mammals: the right ventricle pumps blood to the lungs via
pulmonary arteries (dextra and sinistra) where it flows to capillary beds and returns
via pulmonary veins to the left atrium. The left ventricle then pumps blood via the
aorta to the body. The aorta branches first into the coronary arteries (heart muscle),
then into the truncus brachiocephalicus with arotis carotis communis sinistra
and dextra (forelimbs and head). The aorta descends into the abdomen and legs.
Oxygen poor blood from the head and forelimbs joins in the superior vena cava and
from the abdomen and hindlegs in the inferior vena cava, both empty into the right
atrium.
The heart is located behind the sternum. The atria have thin walls and serve as
collection chambers. Blood flows to the ventricles in relaxation, the remainder by atria
contraction. The ventricles have thicker (especially the left) muscular walls. Cardiac
output is determined by the heart rate (/min.) and stroke volume (mL/ contraction),
the average in humans is 5L/min.
In the cardiac cycle the contraction phase is systole (0.1 atrial 0.3 ventricular) and
the relaxation phase diastole (0.4).
4 heart valves prevent backflow, these flaps of connective tissue open when pushed
from one side and closed when pushed from the other. The atrioventricular AV
valves lie between an atrium and ventricle and are anchored by strong fibres to
prevent them from turning inside out during systole. Semilunar valves are located at
the exits.
The lub-dub sound is produced by the recoil of blood against the closed AV valves
“lub” and the vibrations of closing semilunar valves “dub”.
Heart murmur is produced when blood squirts backward through a defective valve.
Heart contractions are coordinated by autorhythmic cells in the wall of the right atrium
called the sinoatrial SA node which produces electrical impulses which spread
throughout the heart via gap junctions. These impulses reach the skin and can be
seen in an electrocardiogram. During atrial contraction caused by the SA node, the
impulses reach other autorhythmic cells in the atrioventricular AV node, which
delays the impulse for 0.1s before they spread to the heart apex and the ventricles
, contract, allowing the atria to fully empty. Electrical impulses are conducted by
purkinje fibres.
The sympathetic and parasympathetic divisions are responsible for regulating the
pacemaker function of the SA node. Hormones like epinephrine or body temperature
also increase heart rate.
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