Amphibians, reptiles ,mammals

Frogs and other amphibians have a three-chambered heart with two atria and one ventricle. The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous and systemic circulations. Separation aided by spiral valve in arteriosus Fig. 42.3b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The pulmocutaneous circulation leads to capillaries in the gas-exchange organs (the lungs and skin of a frog), where the blood picks up O2 and releases CO2 before returning to the heart’s left atrium. Most of the returning blood is pumped into the systemic circulation, which supplies all body organs and then returns oxygen-poor blood to the right atrium via the veins. This scheme, called double circulation, provides a vigorous flow of blood to the brain, muscles, and other organs because the blood is pumped a second time after it loses pressure in the capillary beds of the lung or skin.

In the ventricle of the frog, some oxygen-rich blood from the lungs mixes with oxygen-poor blood that has returned from the rest of the body. However, a ridge within the ventricle diverts most of the oxygen-rich blood from the left atrium into the systemic circuit and most of the oxygen-poor blood from the right atrium into the pulmocutaneous circuit. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Breathing lung , or skin According to air breathing if pulmonary are breath its resistance will decrease … more blood directed to lung If lung is collapse ….its resistance will be higher so blood flow to coetaneous increased

Amphibians in water, however, can obtain additional oxygen by diffusion through their skin. This process, called cutaneous respiration, helps to supplement the oxygenation of the blood in these vertebrates.

Reptiles A- Non-crocodilian reptiles B- Crocodilian reptiles A- Non-crocodilian Reptiles also have double circulation with pulmonary (lung) and systemic circuits. However, there is even less mixing of oxygen-rich and oxygen-poor blood than in amphibians. Although the reptilian heart is three-chambered, the ventricle is partially divided.

A- Turtle , lizard, …( non croco) Its ventricle is partially divided by muscular ridge ( septum muskelleist) Make separation between cavum pulmonar, cavum venosum, and cavum arteriosum Aided by free horizontal limb

Left atrium receive oxygenated blood Right atrium receive deoxygenated Right atrium contract before left (slightly) and its blood ejected to cavum pulmonar over the free edge of horizontal septum. Left atrium eject to cavum arteriosum Cavum venosum mix

Ventricle contract ; cavum venosum and cavum arteriosum eject to systemic arteries Cavum pulmonar eject to pulmonary artery Pulmonary artery has low BP so it receive before systemic

Diving or air breating Blood pressure in pulmonary artery play a role in ventilation or diving. No ventilation high resistance and higher blood pressure. In ventilation low Blood pressure.

Blood flow pattern through the squamate reptile heart

B- In crocodilians, birds, and mammals, the ventricle is completely divided into separate right and left chambers. In this arrangement, the left side of the heart receives and pumps only oxygen-rich blood, while the right side handles only oxygen-poor blood. Double circulation restores pressure to the systemic circuit and prevents mixing of oxygen-rich and oxygen-poor blood. Fig. 42.3c Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Ventricle divided completely Two systemic arch - left ---from right ventricle - right from left ventricle Both are connected by foramen panizzae

Crocodilian Heart Mechanism for breathing and diving Lungs not utilized Blood not pumped to lungs Foramen of Panizza Valve between aortic trunks to divert blood Allows left ventricle to pump to both arches when right ventricle closed Underwater right ventricle helps pump systemic blood

The crocodile heart Airbreathing

The crocodile heart Diving

Diving Semilunar valve closed when above water Semilunar valve forced open when submerged in water to divert pulmonary circulation (b) (a) Figure 13.16: Crocodilian blood circulation when (a) diving and when (b) on the surface.

Lungfish and Amphibian vs Dogfish Modifications of partial or complete partition in atrium Left and right atria Advent of lungs Double circulation Modification in conus arteriosus Semi-lunar valve modified to shunt deoxygenated blood to lungs (spiral valve)

The evolution of a powerful four-chambered heart was an essential adaptation in support of the endothermic way of life characteristic of birds and mammals. Endotherms use about ten times as much energy as ectotherms of the same size. Therefore, the endotherm circulatory system needs to deliver about ten times as much fuel and O2 to their tissues and remove ten times as much wastes and CO2.

Adult Heart Figure 13.19: Adult heart blood flow.

Fetal Circulation

Figure 13.35: Pre birth fetal circulation: liver (I), inferior vena cava (II), rt. atrium (III), lt. atrium (IV), ductus arteriosus into descending aorta.

Fetal Circulation (cont.) Oxygenation at placenta Umbilical veins supply fetus with oxy. blood Vein passes through liver and unites with post cava From right atrium, oxy. blood goes 2 directions To right ventricle To left atrium through foramen ovale Figure 13.36: Foramen ovale in fetal circulation system.

Fetal Circulation (cont.) In right ventricle, oxy. blood sent to pulmonary artery Lungs nonfunctional Ductus arteriosus diverts blood from lungs

Circulation At Birth Placenta shuts down Umbilical vein collapses- near falciform ligament Interatrial aperture closes (fossa ovalis) Ductus arteriosus closes (ligamentum arteriosum) Deoxygenated blood now enters right ventricle, pulmonary arteries, and continues to lungs Ductus venosus collapses (ligamentum venosum)