Human Circulatory System: Components and Function
Human Circulatory System
In humans, the circulatory system comprises two main systems: the blood circulatory system and the lymphatic circulatory system.
Blood Circulatory System
The circulatory system distributes nutrients and oxygen throughout the body, while collecting waste products of cellular metabolism for elimination. The human circulatory system, like other vertebrates, consists of blood vessels, blood, and the heart.
Blood Vessels
- Arteries: Carry blood from the heart to the organs. Their walls are thick, tough, and elastic to handle high pressure.
- Veins: Carry blood from the organs towards the heart. Their walls are thinner and less elastic, circulating blood under lower pressure.
- Capillaries: Connect arteries and veins. Their thin walls allow for the exchange of nutrients, oxygen, CO2, and waste with cells.
Blood
Blood is a liquid that circulates inside blood vessels and performs several functions:
- Nutrition: Transports nutrients from the digestive system to cells.
- Respiration: Carries oxygen from the lungs to cells and CO2 in reverse.
- Excretion: Collects waste for the excretory system.
- Defense: Carries immune cells.
- Thermoregulation: Helps regulate body temperature.
Blood Components
- Plasma: A yellowish liquid, mostly water, with dissolved substances like proteins, carbohydrates, fats, minerals, and gases.
- Blood Cells: Three types: red cells, white cells, and platelets.
- Red Blood Cells: Lack a nucleus and contain hemoglobin, transporting oxygen and CO2.
- White Blood Cells: Participate in immune functions.
- Platelets: Involved in blood clotting.
The Heart
The heart is a muscular organ that pumps blood through the vessels. It’s located in the chest, between the lungs. Its walls are made of cardiac muscle (myocardium), responsible for involuntary contractions. The heart is divided into two halves: right and left, separated by a muscular septum (interventricular septum). Each half has an atrium (top) and a ventricle (bottom). Ventricle walls are thicker, pumping blood to the body.
Heart Valves
- Mitral Valve: Connects the left atrium and ventricle.
- Tricuspid Valve: Connects the right atrium and ventricle. These valves ensure one-way blood flow.
Blood Flow
Veins enter the atria: four pulmonary veins (oxygenated blood) enter the left atrium, and two venae cavae (deoxygenated blood) enter the right atrium. Arteries exit the ventricles: the pulmonary artery exits the right ventricle (to the lungs), and the aorta exits the left ventricle (to the body). The heart has its own coronary arteries and veins for oxygen and nutrient supply.
Heart Function
The heart’s function involves two coordinated movements: contraction (systole) and relaxation (diastole). Valve malfunctions can cause blood backflow, producing heart murmurs.
Circulation Types
Humans have a dual and complete circulatory system. It’s dual because blood passes twice through the heart, and complete because oxygen-rich and CO2-rich blood don’t mix, thanks to the interventricular septum.
- Pulmonary Circuit: Between the heart and lungs. Deoxygenated blood from the body enters the right atrium, then the right ventricle, and goes to the lungs via the pulmonary artery. Oxygenated blood returns to the left atrium via the pulmonary veins.
- Systemic Circuit: Oxygenated blood from the left atrium enters the left ventricle and is distributed by the aorta to the body. Deoxygenated blood returns to the right atrium via the venae cavae.
Lymphatic Circulatory System
The lymphatic system handles excess fluid between cells, returning it to the blood, and absorbs fats in the intestine.
Excretion and Excretory System
Excretion is the process of removing waste from cellular metabolism. Organs involved include the kidneys, lungs, sweat glands, and liver.