BISC 101 Lecture Notes - Lecture 16: Superior Vena Cava, Pulmonary Circulation, Pulmonary Vein
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13 Jul 2015
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BISC 101 – Lecture 16 – Circulation and Gas Exchange: Part I
Circulatory Systems
•Circulatory systems link exchange surfaces with cells throughout the body
•Every organism must exchange materials with its environment
oExchanges ultimately occur at the cellular level
•Diffusion time is proportional to the square of the distance
oDiffusion is only efficient over small distances
•In small and thin animals, cells can exchange materials directly with the surrounding
medium
•In most animals, cells exchange materials with the environment ia a fluid – filled
circulatory system
Gastro vascular Cavities
•Some animals lack a circulatory systems
oEx: Cnidarians like jellyfish and hydra, and flatworms have elaborate gastro
vascular cavities
•A gastro vascular cavity functions in both digestion and distribution of substances
throughout the body
•Body wall enclosing the gastro vascular cavity is only two cell layers thick
Open and Closed Circulatory Systems
•More complex animals have either open or closed circulatory systems
•Both systems have three basic components
oCirculatory Fluid: Blood or hemolymph
oSet of tubes: Blood vessels
oMuscular pump: The heart
•The circulatory system connects the fluid that surrounds cells with the organs that
exchange gases, absorb nutrients, and dispose of wastes
•,Open Circulatory System: Blood flows freely within the body cavity/sinuses and bathes
the organs directly
oEx: Insects, arthropods and most molluscs
oAll the blood is not enclosed in blood vessels
oBlood is pumped into a cavity called a hemocoel, where the blood mixes with the
interstitial fluid
oHemolymph: Blood mixed with interstitial fluid
oAs the heart beats and the animal moves, the hemolymph circulates around the
organs within the body cavity and then re – enters the heart
•Closed Circulatory System: All of the blood is confined to blood vessels and is separate
from the interstitial fluid
oBlood travels uni – directionally in vessels
oClosed systems are more efficient at transporting circulatory fluids to tissues and
cells
oThe heart sustains a high pressure necessary for the blood to reach all of the
extremities of the body
Organization of Vertebrae Closed Circulatory Systems
•Humans and other vertebrates have a closed circulatory system, often called the
cardiovascular system
•The three main types of blood vessels are
oArteries: Blood flow away from the heart, most arteries carry oxygenated blood
except the pulmonary artery
oVeins: Blood flow towards the heart, most veins carry deoxygenated blood ,
except the pulmonary vein
oCapillaries: Exchange of O2, CO2, nutrients, and waste between blood and body
tissues
•Arteries branch into arterioles and carry blood to capillaries
•Capillary Beds: Network of capillaries that is the site of chemical exchange between the
blood and interstitial fluid
•Venules converge into veins and return blood from capillaries
•Vertebrate hearts contain two or more chambers
•Blood enters through an atrium and is pumped through a ventricle
Single Circulation
•Bony fishes, rays, and sharks have single circulation with a 2 – chambered heart
•In single circulation, blood leaving the heart passes through 2 capillary beds
•During one complete cycle of flow through the body, blood passes through the heart only
once
Double Circulation
•Amphibians, reptiles and mammals have double circulation
•Deoxygenated and oxygenated blood are pumped separately from the right and left
sides of the heart
•During one complete cycle of flow through the body, blood passes through the heart
twice
•Double circulation maintains higher blood pressure in the organs than does single
circulation
•Sufficient blood pressure is needed to send blood from the heart then eventually back to
the heart
•Blood pressure is higher in larger animals in which since blood must move large
distances around the body before it arrives back at the heart
•Animals that have double circulation systems need blood to be supplied to their tissues
quickly due to their high metabolic rates
•This need ensures sufficient blood flow because the transport functions of blood include
supplying the tissues with O2 and nutrients needed to continue activities including
chemical reactions
Amphibians
•Oxygen – poor blood flows through a pulmocutaneous circuit to pick up oxygen through
the lungs and skin
•Frogs and amphibians have a three chambered heart
o2 atria and 1 ventricle
•The two atria receive blood from the two different circuits
oPulmocutaneous and systemic
•Some mixing of the blood in the hearts ventricle is present which reduced the efficiency
of oxygenation
•The ventricle pumps blood into a forked artery that splits the output into both circuits
•This circulation has the ability to re – direct blood to the skin instead of the lungs when
underwater
Reptiles