1

Fig. 19.1. Spleen.

Spleen • White pulp – macrophages, monocyte storage

• Red pulp - (RBC) storage, and prod’n (in non-mammals)

Vertebrate hearts • Pericardial cavity – division in coelum

• Endocardium = endothelium of blood vessels

smooth

muscle endothelium

elastic tissue elastic tissue

smooth muscle endothelium

endothelium

smooth muscle,

elastic fibers

endothelium

valve

Artery

Arteriole

Capillary

Vein

Arteries contain

connective tissue

with elastin and

collagen

Veins include

valves

Vessel walls

Artery Vein

Vein Artery

2

Large arteries

• Elastic recoil from

arteries drives flow of

blood during diastole

• Arteries temporarily

expand and hold

pumped blood

Systole

Diastole

Veins

• Most of the blood volume is in venous system (60-70%) - resevoir

• Blood volume is variable

Vertebrate circulation Vertebrate circulatory systems are either a single circuit (fish) or double circuit (tetrapods) Early circulation - amphibian

26 day old human embryo p. 607

Heart and vessel development

Ventral aorta, aortic arches, dorsal aorta

3

Ancestral vertebrate pattern

VI V IV III II I

Heart

Ventral Aorta

Dorsal Aorta

Internal Carotid

1 2 4 3 5 6

Paired dorsal Aortae

Venous development

• Sinous venosus, hepatic portal system

Fish circulation • Heart is below pharynx, near gills

• 4 chambers in sequence

• Stiff tissue around heart allow sinus venosus suction during diastole (no collapse)

Fish circulation – Conus arteriosus – muscular, maintains

pressure during diastole

• Teleosts – bulbus arteriosus – enlarged elastic ventral aorta

4

Fish circulation

In fish, the aortic arches (AA) are the afferent and efferent branchial arteries

Aortic arches

Aortic arches in tetrapods • 3rd AA – Carotid

• 4th AA – Systemic arch (dorsal aorta - many branches!)

• 6th AA – Pulmonary arch

Tetrapod hearts

• Sinus venosus and conus arteriosis are lost/reduced

– sinus venosus reduced to junction of vena cava and rt. atrium

• Blood returns from two sources

5

Many tetrapods have incomplete separations

• Amphibians

• Dipnoi

• Ancestral crossopterygii

• Reptiles

Often not using lungs!

Most blood in systemic

Shunting a must

A fish with

pulmonary

circulation

In other fish,

swim bladders

supplied from

dorsal aorta

facing

2 3 4 5 6

Lungfish aortic arches

Aquatic

On land

Has incomplete separation of both rt. & lt. atria; and rt. & lt. ventricles

Yet two ‘streams’ are separate

O2 poor to 5th and 6th (back gills and lung).

O2 rich to 3rd and 4th.

Spiral valve in conus spiral

valve

AA 3 and 4

AA 5 and 6

Ventricle septum

Lungfish heart Amphibian circulation

• Metamorphosis – heart moves towards lungs

• AA’s are ‘traditional’ tetrapod: 3,4,6 (frog)

6

Amphibian heart • Atria are completely divided, ventricle

division is incomplete

– Yet very little mixing occurs

Amphibian heart

• Ventricle has spongy pockets (trabeculae)

• Trabeculae separate deoxy. and oxygenated blood in ventricle

trabeculae

trabeculae

Frog heart Frog heart

7

Frog heart

Ventricle

contraction

Frog heart

Frog spiral valve • Spiral valve in conus arteriosus

Ventral aorta

shortened

to truncus

arteriosus

Reptile circulation • Truncus arteriosus

has three trunks

P

LS RS

8

• When not ventilating lungs, pulmonary resistance increases, blood is shunted from rt ventricle to lt systemic

Reptile heart • High CO2, acidity causes Bohr effect and

hemoglobin loses affinity for O2

Reptile heart

Saturation curve shifts to the right

sea snake

Crocodilia heart

• Ventricles divided

• Crocodiles have foramen of Panizza connecting rt. and lf. systemic

• Lf systemic can receive rt. ventricle blood

Crocodilia heart

• Using lungs

– Foramen of Panizza allows Ox. blood into left systemic

Left to right shunt

higher pressure valve

9

• Diving-

– F. of P. allows mixed blood to flow into right systemic

Right to left shunt

Cog

lower pressure

Crocodilia heart Bird Mammal

p.618

• Systemic arch is one-sided in endotherms

Human heart development

One-way flow

in early

development

Adult mammal circulation

10

Amniote fetus circulation

• Oxygenated blood to fetus coming from outside, not lungs

–developing reptiles, birds, mammals

Fetal circulation • Blood flows through umbilical vein,

through ductus venosus to vena cava

Fetal circulation

• Most blood from lt atrium goes through foramen ovale to rt atrium

11

Fetal circulation • Meanwhile....some blood in right atrium

goes instead to right ventricle

Most right ventricle

blood goes through

ductus arteriosus

to aorta

At birth pulmonary pressure reduces below systemic

Foramen ovale Fossa ovalis

After a day or more:

Ductus arteriosus Ligamentum arteriosum

Neonatal circulation

Neonatal problems

Patent foramen ovale (20% of people) chest pressure causes flap to open, strokes

Patent ductus arteriosus Heart can become enlarged

12

Portal systems

• With portal system:

Veins branch again into capillaries

portal vein

Hepatic portal system

• Newly absorbed compounds are brought to liver

• Conservative: found in all vertebrates

Renal portal system • From hind limbs to kidney, resorbing

portion of kidney circulation

• All vertebrates except mammals