Anatomie en Fysiologie
43.1- Circulatory systems link exchange surfaces with cells throughout
the body
• Diffusion; Random thermal motion
- Result in net movement
- Only rapid over very small distances
• Simple body plan; Adaptation for efficient exchange
- Places many or all cells in direct contact with the environment.
- Each cell can exchange materials directly with the surrounding medium.
• Animals that lack a simple body plan display an alternative adaptation for efficient
exchange→ circulatory system
- Move fluid between each cell’s immediate surroundings over body tissue.
- Result: exchange with environment and exchange with body tissues both occur
over very short distances.
Gastrovascular cavities
• Gastrovascular cavity; A central cavity with a single opening in the body of certain
animals, including cnidarians and flatworms, that functions in both the digestion and
distribution of nutrients.
- An opening at one end connects the cavity to the surrounding water
- Fluid bathes both the inner and outer tissue layers, facilitating exchange of gases
and cellular waste.
- Cells lining the cavity have direct access to nutrients released by digestion.
- Nutrients need to diffuse a short distance to reach the cells of the outer tissue
layer.
• Planarians and most flatworms survive without a circulatory system.
- Their combination of a gastrovascular cavity and a flat body is well suited for
exchange with the environment.
- Flat body optimizes exchange by increasing surface area and minimizing diffusion
distances.
Open and closed circulatory systems
Circulatory system:
- A circulatory fluid
- A set of interconnecting vessels
- Muscular pump (heart)
• Heart; powers circulation by using metabolic energy to elevate the circulatory fluid’s
hydrostatic pressure, the pressure the fluid exerts on surrounding vessels.
- The fluid then flows through the vessels and back to the heart.
, • Circulatory system functionally connects the aqueous environment of the body cells
to the organs that exchanges gases, absorb nutrients and dispose of wastes.
Open circulatory system; a circulatory fluid (hemolymph) is also the interstitial fluid that
bathes body cells.
- Heart pumps the hemolymph through the circulatory vessels into interconnected
sinuses; spaces surrounding the organs.
- Within the sinuses the hemolymph and body cells exchange gases and other
chemicals.
- Relaxation of the heart; Hemolymph go back through pores which have valves
(kleppen) that close when the heart contracts (samentrekt).
- Body movements periodically squeeze the sinuses → circulating the hemolymph.
- Spiders use the hydrostatic pressure of their open circulatory system to extend
their legs.
Closed Circulatory system; a circulatory fluid (blood) is confined to vessels and is distinct
from the interstitial fluid.
• One or more hearts pump blood into large vessels that branch into smaller ones that
infiltrate the tissues and organs.
• Chemical exchange occurs between the blood and the interstitial fluid, as well as
between the interstitial fluid and body cells.
• Vertebrates (gewervelde dieren), Cephalopods and annelids.
• Blood pressure is high enough to enable the effective delivery of O2 and nutrients in
larger and more active animals.
,The lower hydrostatic pressures typically associated with open circulatory systems allows
them to use less energy than closed systems.
Organization of vertebrate circulatory systems
• Cardiovascular system: Blood circulates to and from the heart through an amazingly
extensive network of vessels.
• Three main types of blood vessels:
- Arteries; carry blood from heart to organs throughout the body.
*branch into arterioles in organs
- Capillaries; arterioles convey blood to capillaries; microscopic vessels with very
thin porous walls.
*Capillary beds; network of capillaries infiltrate tissues passing within a few cell
diameters of every cell in the body
*dissolved gases and other chemicals are exchanged by diffusion between the
blood and the interstitial fluid around the tissue cells.
- Veins; Capillaries converge into venules and venules converge into veins; vessels
that carry blood back to the heart.
• Arteries carry blood away from the heart toward capillaries and veins return blood
toward the heart from capillaries.
• Portal veins; carry blood between pairs of capillary beds
• The hepatic portal vein; carries blood from capillary beds in the digestive system to
capillary beds in the liver.
• The hearts of all vertebrates contain two or more chambers
- Atria; chambers that receive blood entering the heart.
- Ventricles; Chambers responsible for pumping blood out of the heart.
Single circulation
= a circulatory system consisting of a single pump and circuit, in which blood passes from the
sites of gas exchange to the rest of the body before returning to the heart.
• Heart have two chambers; atria and ventricle.
• Blood entering the heart collects in the atrium before transfer to the ventricle.
• Ventricle pumps blood to a capillary bed in the gills (kieuwen).
- Net diffusion of O2 into the blood and of CO2 out of the blood.
• Blood leaves the gills, the capillaries converge into a vessel that carries oxygen rich
blood to capillary beds throughout the body.
• Gas exchange in the capillary beds happen and blood enters veins that returns to the
heart.
• In a single circulation, blood leaves the heart passes through two capillary beds
before returning to the heart.
• Blood flows through a capillary bed → blood pressure drops substantially.
- The drop in blood pressure in the gills limits the rate of blood flow in the rest of
the body.
• If the animal swims → The contraction and relaxation of its muscles help accelerate
the relatively sluggish (traag) pace of circulation.
, Double Circulation
= Circulatory system consisting of separate pulmonary and systemic circuits, in which blood
passes through the heart after completing each circuit.
• The pumps for the two circuits are combined into a single organ → heart
1. Pulmonary circuit; the right side of the heart pumps oxygen-poor blood to the
capillary beds of the gas exchange tissues, where there is a net movement of O 2
into the blood and of CO2 out of the blood
2. Systemic circuit; Begins with the left side of the heart pumping oxygen-enriched
blood from the gas exchange tissues to capillary beds in organs and tissues
throughout the body.
- Exchange of O2 , CO2, nutrients and waste products.
- The now oxygen-poor blood returns to the heart, completing the circuit.
• Blood pressure is higher in systemic circuit than in pulmonary circuit.
Evolutionary variation in double circulation
• Some vertebrates with double circulation are intermittent breathers (periodiek)
•
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