Untitled Quiz

Study Notes

Animal “pumps”

Three types of animal pumps are:
- Contractile chamber: Heart chambers act as pumps
- Skeletal muscle: Contracts to propel flow
- Pulsating blood vessels: Tube-like hearts found in invertebrates and early vertebrates

Heart Structure Across Taxa

Fish hearts are in series.
- Chambers contract in sequence,
- Valves are passive and open and close due to changes in pressure
- Blood flows directly into spongy myocardium
- Teleosts have a bulbus arteriosus
- Cartilaginous fishes have a conus arteriosis
- Teleosts (bony fishes) have a bulbus arteriosus, which is a volume and pressure reservoir
Amphibian hearts have three chambers.
- Two atria and one ventricle
- Left atrium receives oxygenated blood from the lungs
- Right atrium receives deoxygenated blood from the body and oxygenated blood from the skin
- Ventricle keeps oxygenated and deoxygenated blood separated
- Trabeculae (ridges in the ventricle) create a spiral fold within the conus arteriosus that keeps blood separate
Turtles, lizards, and snakes have a “five-chambered” hearts.
- Two atria, one ventricle, and the conus is absent
- Ventricle divided into three chambers:
  - Cavum venosum: Connects to systemic aortas
  - Cavum pulmonale: Connects to pulmonary artery
  - Cavum arteriosum:
Shunting in reptile hearts:
- Right to Left (RL) shunting occurs when the blood from the right ventricle flows directly to the left ventricle. This is often associated with diving.
- Left to Right (LR) shunting allows blood to flow from the left ventricle to the right ventricle to oxygenate the heart. The functions of both are still being debated by scientists.
- RL and LR shunting allow reptiles to better regulate their blood flow in different environments.

Oxygen Supply to the Heart:

Mammalian and avian hearts: Supplied with oxygen from the coronary vessels
Spongy myocardium of most teleosts: No coronary vessels. Oxygen from blood flowing into the heart chamber
Ancestral hearts: Not well oxygenated
Some fishes: Compact outer layer and spongy inner layer. Some species also utilize a network of blood vessels that run from the inner chamber of the heart to the outer layer, creating a type of “coronary” system.
Some octopuses: Blood supply originates from the chamber cavity and travels through “coronary veins.”
Percentage of compact myocardium increases with migration effort

Blood Supply to Mammalian Hearts:

Mammalian heart requires a lot of oxygen and nutrients due to constant activity
Myocardial cells are compact, so blood from the ventricles cannot directly perfuse them
Coronary arteries provide oxygen and nutrients to the cardiac muscle

Mammalian Cardiac Cycle:

Pressure gradients cause blood to move from atria to the ventricles
Ventricular contraction drives blood to the aorta or pulmonary artery
Two phases of the cardiac cycle:
- Diastole: Relaxation phase, blood enters the heart
- Systole: Contraction phase, blood forcefully expelled into circulation

Cardiac Output (CO)

Cardiac output is the volume of blood pumped per unit time.
CO (mL/min) = HR (beats/min) x SV (mL/beat)
Heart Rate (HR) can be modified by the nervous and endocrine systems
- Bradycardia: Slow heart rate
- Tachycardia: Fast heart rate
Stoke Volume (SV) is modulated by nervous, hormonal, and physical factors

Frank-Starling Mechanism:

Stretching of the cardiac muscle increases the force of contraction.
The more the heart fills, the stronger the force of contraction
Increased heart rate leads to faster ventricular filling, resulting in a stronger contraction and increased cardiac output.
A larger heart can hold more blood than a smaller heart, leading to a higher stroke volume and greater cardiac output if other factors are equal (e.g. heart rate).