Heart Lec1: Anatomy & Evolution

Why is the heart the first organ to develop in mammals?

Birds have yolk to provide food in embryo, but humans don’t. Nutrients and waste transfer occurs in circulatory system.

Name the body cavity that the heart is located in.

Thoracic cavity, mediastinum.

What is the heart encased in? (2)

• Pericardial fluid

• Pericardium (sac)

Name the three layers of the myocardium.

• Endocardium (inner)

• Midcardium

• Epicardium (outer)

What are the two main functions of the heart?

Maintain blood circulation and blood pressure

Why do smaller animals have a faster HR than larger animals?

Because it takes longer for blood to circulate through a larger animal’s body.

Explain the dual-pump system of the mammalian heart.

1. Pulmonary circuit (pumps to lungs)

2. Systemic circuit (pumps to body)

Which class of animals has more than one heart?

Annelids (earthworms), arthropods (flies), eel-like creatures.

Describe the fish heart.

Two chambered (one atrium, one ventricle), gills oxygenate blood through countercurrent exchange.

Describe the frog heart. Why is it sufficient?

Three chambers (divided atria, undivided ventricle) causes blood mixing in the ventricle. This is okay because frogs are small and don’t require large supply of oxygenated blood.

Describe the reptilian heart in snakes.

Three-chambered (undivided ventricle).

Describe the reptilian heart in turtles.

Three chambered, ventricle is partially separated into multiple chambers.

Describe the reptilian heart in lizards.

Four chambers, ventricle partially divided but closes fully during contraction.De

Describe the reptilian heart in crocodiles.

Four chambered, but blood mixing in aortic arch (Foramen of Panizza).

Describe the avian (bird) heart.

Same as humans/mammals.

What are the two extra openings in the fetal heart? Why are they present?

1. Ductus arteriosus (mixing in aorta)

2. Foramen ovale (mixing between atria)

They are present to reduce BP in undeveloped heart/lungs. They close after birth.