Human Circulatory and Excretory Systems: Functions and Components
The Human Circulatory System
The interstitial fluid is the liquid found in the spaces between cells.
Blood is a viscous, salty liquid that runs inside the ducts of the circulatory system.
Blood Plasma
Blood plasma is a yellow liquid composed of water and various dissolved molecules.
Blood Cells and Platelets
- Red Blood Cells (Erythrocytes): These are the most numerous blood cells, with about 5 million present. They are disc-shaped, lack a nucleus, and contain hemoglobin, a red pigment responsible for the color of blood. Hemoglobin contains iron and carries oxygen from the lung alveoli to all body cells.
- White Blood Cells (Leukocytes): Found in the blood in smaller numbers than red blood cells, they defend the body against microbes. Types include:
- Granulocytes: Characterized by granular cytoplasm and a polilobulated nucleus.
- Agranulocytes: Includes lymphocytes and monocytes.
Granulocytes and monocytes destroy pathogens, while lymphocytes produce antibodies.
- Platelets: These are cell fragments containing substances that allow blood clotting, preventing hemorrhages.
Blood Vessels
- Arteries: Carry blood away from the heart. These vessels branch into smaller vessels called arterioles.
- Capillaries: Microscopic blood vessels that branch from arterioles and are found in all body tissues.
- Veins: Formed as capillaries gather into venules, which then become thicker vessels called veins.
The Heart
The heart is a hollow muscular organ that pumps blood constantly through contractions and relaxations. It consists of a thick inner wall called the myocardium, coated by the endocardium, and protected on the outside by the pericardium. It is divided into right and left halves by a septum, with each half subdivided into an upper chamber (atrium) and a lower chamber (ventricle).
Excretory and Metabolic Systems
Liver
The liver removes products resulting from the destruction of old red blood cells. These products become bile, which is dumped into the intestine and expelled. It also manages cholesterol and toxic substances.
Urinary System
Often called the excretory system, it is vital for eliminating waste products through urine.
Respiratory System
Provides oxygen to the blood and expels carbon dioxide from the body.
Sweat Glands
Found in the skin, these produce sweat to cool the body and expel certain waste substances.
Main Waste Molecules
- Carbon Dioxide: Originates from metabolic reactions that produce energy.
- Urea: Derived from the destruction of proteins and nucleic acids.
- Toxic Substances: Various ingested compounds processed by the body.