Download Circulatory System * General Aspects

Circulatory System – General Aspects
• In small invertebrate organisms, no circulatory
system is necessary, as diffusion distances are
short.
• With greater size, diffusion from the external
environment becomes insufficient and a
circulatory system is required to transport
materials within the body.
Circulatory System – General Aspects
• Two types of circulatory systems are present
among invertebrates:
– Open System = more primitive, heart pumps blood
out through vessels to various parts of the body.
Return vessels are absent so blood oozes back to
heart via interstitial spaces.
– Closed System = advanced condition, also present in
all vertebrates; blood never leaves vessels. Delivery of
nutrients occurs via diffusion across thin-walled
capillaries.
• Amphioxus shows intermediate condition = both
outgoing and return vessels present, but no
capillaries connecting them.
Fig 12.4 – Microcirculation in a closed vascular system
Functions of Circulatory System
•
•
•
•
•
Facilitate gas exchange
Delivery of nutrients
Removal of wastes
Transport of hormones
3 Subcomponents (all mesodermal in origin):
– Blood Vascular System = includes heart, arteries (carry
blood away from heart), capillaries (gas and nutrient
exchange), and veins (carry blood back to heart)
– Hemopoietic Organs = sites of blood cell production
– Lymphatic System = thin-walled vessels that carry fluid
from interstitial spaces back to blood stream
Fig 12.2 – Blood pressure and crosssectional areas of the different vessels
of the blood vascular system.
Fig 12.11 – Basic vertebrate blood vascular system circulation,
as illustrated in a shark
Single and Double Circulation
• Fishes = possess single circulation pattern
– Blood passes through heart only once during each
complete cycle
– Sequence: Heart  Gills  Body  Heart
• Amniotes = possess double circulation pattern
– Blood passes through heart twice during each
complete cycle
– Sequence: Heart  Lungs  Heart  Body  Heart
• Intermediate condition with characteristics of
both present in lungfish, amphibians and some
reptiles
Fig 12.6 – Single and double circulation circuits in vertebrates
Developmental Anatomy
• General Principles:
• Main vessels develop in association with
major centers for metabolic activity.
• Primitive adult conditions are demonstrated in
transitory embryonic stages in advanced
vertebrates.
– “Ontogeny recapitulates phylogeny” works well
for the circulatory system.
Developmental Anatomy
• Developmental Stages
1. Primitive Condition = heart pumps blood anteriorly
through ventral aorta  passes through paired aortic
arches  into paired dorsal aortae  to capillary
network of yolk sac  drain to vessels leading back to
heart.
— Yolk sac is site of formation of first blood vessels and first
blood cells in the embryo.
2. Systemic Arteries branch off dorsal aortae to supply
developing organs and gut.
— Each organ develops a capillary bed that merges into
systemic veins leading back to heart.
3. Yolk Sac is supplied and drained by systemic veins
(Portal System) in Osteichthyes and Amphibians. Yolk
sac supplied via Vitelline Arteries and drained by
vitelline veins in Chondrichthyes and Amniotes.
Developmental Anatomy
• Developmental Stages
4. As the Liver develops, it is supplied by veins leaving
the yolk sac (= Hepatic Portal System) which pass
through the liver capillary network then coalesce into
veins passing back to the heart.
5. In Amniotes the Allantois (=extraembryonic
membrane functioning in waste storage) develops
and is supplied by allantoic artery and drained by
allantoic vein.
– Allantoic vein initially passes directly to back of heart, but
later becomes incorporated into capillary bed of liver.
Some anatomical bypass of liver capillary network in birds
and reptiles, but not in mammals.
– Associated with nutritional role of chorioallantoic
membrane of the placenta in mammals. Functions solely in
respiration in birds and reptiles.
Developmental Anatomy
• Accessory Circuits
• Embryonic stages of all vertebrates except most
primitive (cyclostomes) possess a Renal Portal
System supplying capillary beds of kidney.
– Renal Portal System also present in all adult
vertebrates, except for cyclostomes and mammals,
although in birds and reptiles much of the portal
supply bypasses the kidney capillary network.
• Aortic Arches shift from gill circulation positioned
on main aortic trunk (gill-breathers) to side circuit
associated with other structures (lung-breathers).
Blood
• A specialized connective tissue in which the
intercellular material is entirely fluid (plasma)
• Plasma components include …
– Stable components = inorganic salts and blood
proteins (e.g., albumin = increases osmotic
pressure of blood, fibrinogen = clot formation,
globulins = immunological role).
– Fluctuating components = glucose, fats, amino
acids, waste products (e.g., urea, uric acid),
hormones
Blood Cells
• No blood cells present in Amphioxus
– Restricted to low energy lifestyle
• Two general categories in all vertebrates:
1. Erythrocytes (RBCs) = involved in oxygen and
carbon dioxide transport
— Hemoglobin serves as respiratory pigment to
dramatically increase O2 carrying capacity of blood
2. Leukocytes (WBCs) = many actions –
immunological, phagocytic, etc.
— Most of these roles accomplished outside of
circulatory system
— Use circulatory system for transport to sites of action
Leukocytes (WBCs)
• Unlike RBCs, leukocytes contain nucleus and
all other subcellular organelles
• Have capacity for ameboid movement, many
of WBC functions are carried out after
movement across vessel wall = diapedesis
Other Blood Cell Types
• Platelets = disc-shaped cell fragments derived
from megakaryocytes in bone marrow
– Function in clotting
– Found only in mammals
• Thrombocytes = spindle-shaped cells
developmentally related to WBCs
– Function in clotting
– Found only in non-mammalian vertebrates
Human Blood Smear
Anucleate erythrocyte
Neutrophil (a WBC)
Platelet
Frog Blood Smear
Nucleated erythrocyte
Thrombocyte
WBC
Hemopoietic (blood-forming) Tissues
• Formation of blood cells continues throughout
lifetime (from stem cell precursors) to replace
dying blood cells.
• Embryonic Blood-forming Sites:
– Blood Islands in yolk sac in large-yolked eggs
– Chorion of placenta in mammals
• Becomes more localized later in embryonic
development:
–
–
–
–
–
kidney (sharks to reptiles and birds)
liver
spleen
thymus (not in hagfish ?)
diffuse sites in intestinal walls
Hemopoietic (blood-forming) Tissues
• Adult Blood-forming Sites
–
–
–
–
–
–
Spleen (except for mammals and birds)
Thymus (T-lymphocytes)
Kidney (lampreys, elasmobranchs, teleosts)
Gonads (elasmobranchs  leukocytes)
Liver (teleosts, amphibians, turtles)
Intestinal Walls  lymphoid elements (or walls in
other regions of digestive tract – esophagus, pharynx,
appendix)
– Bone Marrow (amphibians [frogs] – mammals)
– Bursa of Fabricius  lymphoid elements (birds) =
dorsal pouch off of cloaca (combined urinaryreproductive-anal opening)
Hemopoietic Tissues – Myeloid Tissue
Arrows = adipose cells
Bone Marrow
Arrows = developing blood cells
Embryonic Liver
Lymphatic System
• Functions to return interstitial fluid to blood stream
• Lymphatics not connected with arteries; have blind
capillaries and vessels.
• In Cyclostomes and Sharks there is no typical lymphatic
system.
– Instead possess an open system of sinusoids (low b.p., so
low interstitial fluid production in these groups).
• Teleosts possess paired lymph hearts (muscular
structures along lymphatics and at junctions with veins
that help propel lymph along vessels) and 2 major sets
of ducts:
– Paired subvertebral ducts (deeper)
– Paired lateral ducts
– A similar condition occurs in Tetrapod embryos.
Lymphatic System
• Amphibians with well-developed lymphatic
system, many with numerous lymph hearts
• Reptiles show complex system; reduction in
the number of lymph hearts and development
of valves in vessels to prevent backflow
• Birds & Mammals generally have no lymph
hearts in adults (although present in bird
embryos and in a few adult birds).
– Series of valves present to prevent backflow.
– Movement of lymph in conjunction with skeletal
muscle contraction.
Lymphatic System
• Intestinal region lymphatics particularly well developed
in advanced vertebrates.
• Most of the fats entering circulation from the gut do so
by way of the lymphatics (due to the large size of the
fat molecules and the incomplete endothelial lining of
lymphatic vessels, fatty lymph = chyle).
• Lacteals = lymphatic vessels leaving intestine carrying
chyle.
• Thoracic Ducts = lymphatics running along back of
body cavity, serve as collectors for lacteals.
– Major duct in mammals (single, paired in many primitive
vertebrates).
• Cisternae chyli = area where many tributaries feed into
thoracic duct (occurs in lumbar region)
Fig 12.46 –
Formation of
lymph
Fig 12.49 – Lymphatic system in a salamander. Note the prominence of the
lymph hearts for moving lymph within the lymphatic system.
Fig 12.48 – Lymphatic system in turtles
Figure 12.47
Fig 12.47 – Lymphatic circulation
and lymph nodes
Valve in
Lymph
Vessel in
mammal
Adipose tissue
Valve
Flow
Lymph vessel