Oxygen exchange in fish and mammals occurs differently because of the differences in their circulatory systems:

Fish

Fish have a single circulatory system, where blood is pumped from the heart to the gills to be re-oxygenated. The oxygenated blood then flows to the rest of the body and back to the heart. This process is called gill circulation.

Mammals

Mammals have two separate circulatory systems: the pulmonary system and the systemic system. The pulmonary system pumps blood from the heart to the lungs and back, while the systemic system pumps blood to the body and back. The left atrium receives oxygen-rich blood from the lungs and passes it to the left ventricle.

The circulatory systems of mammals are more efficient than those of fish because the pulmonary and systemic circuits are separated. This separation allows for more efficient oxygenation and delivery.

A double circulatory system is a circulatory system where blood passes through the heart twice and has two different circuits. It is important because it allows oxygenated blood to be separated from deoxygenated blood, which increases the efficiency of oxygen transport and energy production in the body.

he circulatory systems of fish and mammals have adapted to their environments in different ways:

Circulation

Fish have a single circulatory system, while mammals have a double circulatory system:

Fish: Fish have a single loop that carries blood from the heart to the gills, then to the rest of the body, and back to the heart. This system is energy efficient and well-suited to aquatic environments, where water resistance helps blood flow. However, it mixes oxygenated and deoxygenated blood, which reduces the efficiency of oxygen delivery to tissues.

Mammals: Mammals have a double circulatory system with a pulmonary circuit and a systemic circuit. The pulmonary circuit pumps blood from the heart to the lungs and back, while the systemic circuit pumps blood to the body and back. This system separates oxygenated and deoxygenated blood, which allows for more efficient oxygen and nutrient delivery to body tissues.

Heart

The heart of a mammal has four chambers, two atria and two ventricles. This structure helps to separate oxygenated and deoxygenated blood.

Blood volume

The proportion of blood in the major vessels of fish is probably less than in mammals.

Here are some common diseases that affect the circulatory systems of fish and mammals:

Heart failure

Also known as congestive heart failure, this occurs when the heart muscle is damaged or weakened, making it unable to pump enough blood through the body. It often occurs after other heart problems, such as a heart attack or coronary artery disease.

Heart attack

Also known as myocardial infarction, this occurs when the heart muscle is damaged due to a lack of blood reaching the heart.

Arrhythmia

Also known as an irregular heartbeat, this prevents the heart from pumping blood normally. Some arrhythmias are harmless, but others can be life-threatening.

Peripheral artery disease

Also known as peripheral vascular disease (PVD), this affects the arteries connected to the head, stomach, arms, and legs.

Angina

A type of chest pain caused by decreased blood flow into the heart.

Aortic aneurysm

A common aortic disease that occurs when the aorta, the body's largest blood vessel, becomes weakened and bulges outwards.

Atherosclerosis

A buildup of plaque in the arteries that causes them to narrow over time, restricting blood flow.

Hypertension

Also known as high blood pressure, this is the most common circulatory system health problem.

Stroke

A heart disease that occurs due to problems with blood flow to the brain.

Scientists study and compare the circulatory systems of different species by examining the structure and function of the heart, blood vessels, and other components of the circulatory system:

Heart structure

The structure of the heart varies between species, including the number of atria and ventricles. For example, humans and dogs have two atria and two ventricles, while fish have one atrium and one ventricle.

Blood vessel structure

Blood vessels can vary in size and thickness, and some blood vessels can constrict or dilate to change the rate of blood flow.

Circulatory system type

There are two main types of circulatory systems: open and closed. In an open system, circulatory fluid passes freely among tissues, while in a closed system, blood is contained within vessels.

Embryo development

Scientists can study the development of embryos to theorize about the evolution of circulatory systems.

Genetic manipulation

Scientists can use genetic manipulation to turn off genes and observe the effects on the development of the circulatory system.

The circulatory systems of vertebrates are generally more similar to each other than those of invertebrates. However, there are many variations in the circulatory systems of vertebrates, which are related to the different requirements of living in water and on land.

The Function of Gills

The carbon dioxide diffuses in the water and the oxygen diffuses into the oxygen-poor blood through the capillaries.