IV. CIRCULATORY SYSTEM
A. Overall components – Blood, blood vessels, heart
B. Overall function – Transport nutrients, gases, hormones, waste, immunity, temperature regulation
C. Ontogeny & Phylogeny – First system to be functional in development; Similar embryology in all vertebrates, Individual variation within species
D. BLOOD
1. Plasma [serum is plasma minus clotting factors]
2. Formed Elements
a. Erythrocytes
1. Hemoglobin – Red blood pigment for carrying oxygen
2. Iron – Needed for hemoglobin synthesis
b. Leukocytes – Immunity, Antibody production, Phagocytosis
c. Platelets – Clotting of blood
3. Hemopoiesis- Formation of blood cells; Sites in adult include liver, kidney, spleen, and red bone marrow, depending on the vertebrate class.
a. Blood islands – Located in the wall of the yolk sac is the earliest site of hemopoiesis in vertebrates
b. Hemocytoblasts – Stem cells
E. HEART
1. Development – Functional by 30 hours in chick (21 day incubation) and 4 weeks in humans (280 day gestation)
2. Heart wall
a. Endocardium – Inner, shiny lining of heart chambers
b. Myocardium
1. Striated
2. Intercalated disks
c. Epicardium – Outermost layer
3. Parietal & Visceral Pericardium; Pericardial cavity – Parietal pericardium is part of the pericardial sac surrounding the heart; Visceral pericardium is synonym for epicardium; Pericardial cavity is between parietal & visceral pericardium.
4. GILL BREATHING FISH
a. Single circuit pump with the following four chambers:
b. Sinus Venosus –Pacemaker of heart
c. Atrium
d. Ventricle
e. Conus arteriosus [trunk]
f. AV Valve – One way valve between atrium & ventricle to prevent back flow of blood
g. Semilunar valve – One way valve between ventricle & conus arteriosus to prevent back flow of blood
h. Bulbus arteriosus – Muscular expansion of ventral aorta to ensure steady blood flow in some fish
5. LUNGFISH & AMPHIBIANS
a. Two circuit heart
b. Interatrial septum – Partial or complete
c. Interventricular septum/Ventricular trabeculae – Partial division of ventricles
d. Spiral Valve – Found in dipnoans and anurans & attempts to divide conus arteriosus
6. AMNIOTES
a. Two circuit heart – More complete divisions of heart than in lungfish & amphibians.
b. Two atria & Two ventricles
c. Sinus venosus
1. Pacemaker (fish through reptiles)
2. Becomes the Sinoatrial node in birds and mammals which is their pacemaker located in the wall of the right atrium
3. Beating – Pacemaker sets the pace for the entire heart
d. Interatrial septum – Complete
1. Foramen ovale – Embryonic hole between right and left atria
2. Auricle – Expansions of atria in mammals only.
e. Interventricular septum [complete in birds, crocodiles & mammals]
f. Bicuspid valves in mammals; Tricuspid valves in mammals; Semilunar Valves
g. Fate of conus arteriosus – Divides into three trunks in reptiles; divides into two trunks in birds and mammals
h. Circulation through heart [Cava from systemic circulation – R.A. – R.V. – Pulmonary trunk/arteries – Lungs – Pulmonary veins – L.A. – L.V. – Aorta – Systemic circulation]
F. BLOOD VESSELS
1. ARTERIES carry blood away from the heart: Ventral aorta; Dorsal aorta; Aortic arches
2. Ventral aorta & Arches:
a. FISH
1. Afferent branchial artery
2. Gill capillaries
3. Efferent branchial artery
4. Shark – pseudobranchial artery is efferent branchial artery of arch 1
5. Teleosts – 1 & 2 gone
6. Lungfish –Pulmonary artery from 6th aortic arch – efferent
b. TETRAPOD
1. General pattern
a. Embryo – 6 arches, 1 and 2 rapidly regress
b. Internal carotid A – 3rd arch plus paired dorsal aortae
c. 5th aortic arch – Gone in most
d. Pulmonary artery – 6
e. Common carotid A. – From ventral aorta
f. External carotid A. – From common carotid artery
2. AMPHIBIANS
a. Urodeles –Ductus caroticus present, retains 5th aortic arch
b. Anurans – No ductus caroticus after metamorphosis
3. REPTILES
a. Two aortic trunks
b. One pulmonary trunk
4. BIRDS & MAMMALS
a. One aortic trunk (3&4)
b. One pulmonary trunk (6)
c. R 4th stays in- birds
d. Left 4th stays in mammals
e. Subclavian A in mammals from part of R. 4th arch
f. Ductus arteriosus – In fetus only, this is a bypass of blood flow to the non- functional lungs from the pulmonary trunk to the aorta.
g. Carotids same as general pattern
3. Dorsal Aorta
a. General pattern
1. Paired in head & pharynx
2. Single in trunk
3. Caudal A.
b. Ventral Visceral branches
1. Celiac A. – Supplies stomach, pancreas, liver
2. Mesenteric A. – May be more than one; supplies intestine
c. Lateral visceral branches
1. Urogenital
d. Somatic branches
1. Skin, spine, muscles
2. Subclavian A. —>Brachial A. – Supplies arm
3. Iliac A. —>Femoral A. – Supplies leg
4. VEINS (Veins start as capillaries & carry blood towards the heart)
a. Cardinal stream
1. SHARK
a. Common Cardinal Vein
1. Anterior Cardinal – Drains head
2. Posterior Cardinal – Drains kidney, body wall, gonads – most except digestive structures
2. AMPHIBIANS – Most of Postcardinal disappears in anurans, but persists in urodeles
3. AMNIOTES
a. Postcava (Inferior or caudal vena cava) takes the place of Posterior Cardinal Vein; Drains some of hindlimbs in crocodiles, all of hindlimbs in mammals and eventually drains most of trunk and tail in addition to hind limbs
b. Azygous/hemiazygous[from R. posterior cardinal in mammals; provides alternate route from structures caudal to diaphragm in mammals]
c. Precavae (Superior or cranial Vena cava)[from Common Cardinal V]
d. Internal Jugular [from Anterior cardinal V.]
b. Renal Portal Stream
1. Definition of Portal – Vein that begins and ends in a capillary bed
2. FISH – Drains tail to kidney
3. AMPHIBIANS– Drains hindlimbs to kidneys
4. REPTILES & BIRDS – Bypasses kidneys and goes to postcava
5. MAMMALS – Not present
c. Abdominal Stream
1. SHARKS
a. Iliac – From pelvic fins
b. Subclavian – From pectoral fins to common cardinal V.
2. AMPHIBIANS
a. Ventral – single
b. No forelimbs
3. REPTILES
a. Double
b. No forelimbs
4. MAMMALS
a. In fetus only
b. Umbilical V./Round ligament of liver is remnant in adult
c. Ductus venosus/ligament venosum remnant in adult
d. Hepatic Portal Stream/Hepatic Sinuses– All vertebrates have this stream & is similar in all vertebrates
– Vitelline V. – From yolk sac to heart
– Subintestinal V.
– Hepatic Portal System – Develops from one vitelline V. and Subintestinal Vein
– Hepatic Sinuses – Develops within liver from vitelline veins
e. Mammalian Fetal Circulation– Liver is bypassed by Ductus Venosus and Lungs are bypassed by Ductus Arteriosus & Foramen Ovale of interatrial septum