Circulatory System Blood 4e NOTES Fall 2022 (1)

The Circulatory System: Blood Summary

Overview of the Circulatory System

The circulatory system, also known as the cardiovascular system, is crucial for sustaining life, and it consists of a network of blood vessels, the heart, and blood. The heart functions as a muscular pump, facilitating the flow of blood throughout the body while generating pressure during its contractions.

Components of the Circulatory System

• Blood: The vital fluid that transports oxygen, nutrients, and waste products.

• Heart: Composed of four chambers (two atria and two ventricles) which work together to pump blood and maintain circulation.

• Blood Vessels: Include arteries, veins, and capillaries, which are responsible for transporting blood to and from the heart.

  • Arteries: Thick-walled vessels that carry blood away from the heart, typically oxygenated (except for pulmonary arteries).

  • Veins: Thinner-walled vessels that return deoxygenated blood to the heart (except for pulmonary veins).

  • Capillaries: Tiny vessels where the exchange of gases, nutrients, and wastes occurs between blood and tissues.

Functions of the Circulatory System

Transportation

The circulatory system is essential for transporting:

• Oxygen (O2) from the lungs to the cells of the body.

• Carbon Dioxide (CO2) from the cells to the lungs for exhalation.

• Nutrients from the digestive tract to every cell in the body for energy and growth.

• Metabolic Wastes (like urea) to the kidneys for filtration and excretion.

• Hormones from endocrine glands to target organs, enabling regulatory processes.

Protection

The circulatory system also plays a critical role in:

• Providing immunity and defense against pathogens through white blood cells and antibodies.

• Preventing excessive blood loss through clotting mechanisms, protecting the body from hemorrhage.

Regulation

It helps regulate:

• Fluid balance and distribution throughout the body, ensuring homeostasis.

• The pH of extracellular fluids to maintain a stable environment for cellular functions.

• Body temperature through the regulation of blood flow to the skin.

Blood Components

Composition

Blood is composed of:

• Liquid part (Plasma): Makes up approximately 55% of blood volume, consisting of water, electrolytes, and proteins.

• Formed elements: Account for about 45% of blood volume and include:

  • Erythrocytes (Red Blood Cells): Comprising 44% of blood, they contain hemoglobin, which binds oxygen. They have a unique biconcave shape that increases their surface area for gas exchange.

  • Leukocytes (White Blood Cells): Less than 1% of blood; crucial for the immune response. They are divided into two categories: granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes and monocytes).

  • Platelets: Cell fragments involved in hemostasis (less than 1%), play a key role in blood clotting.

Blood Plasma

• Composition: Comprises about 92% water and 7% plasma proteins, which include:

  • Albumin (58%): Essential for regulating osmotic pressure and maintaining blood volume.

  • Globulins (37%): Function as transport proteins (e.g., transporting hormones) and antibodies that combat pathogens.

  • Fibrinogen (4%): A crucial protein for blood clotting, forming fibrin threads to stabilize clots.

  • Other Solutes (<1%): Include electrolytes (sodium, potassium), nutrients (glucose, amino acids), and gases (oxygen, carbon dioxide).

Hemostasis (Blood Clotting)

Phases

1. Vascular spasm: Immediate constriction of blood vessels following injury to reduce blood flow and loss.

2. Platelet plug formation: Platelets adhere to the exposed collagen and each other at the injury site, forming a temporary plug.

3. Coagulation: The coagulation cascade leads to the conversion of fibrinogen to fibrin, creating a mesh that solidifies the clot and traps blood cells.

Key Factors

• Various clotting factors produced in the liver are essential.

• The process involves both intrinsic and extrinsic pathways, which activate a common pathway leading to Factor X activation, ultimately forming a stable blood clot.

Blood Types

ABO System

• Type A: Has antigen A on the surface of red blood cells.

• Type B: Has antigen B.

• Type AB: Has both antigens, making it the universal recipient.

• Type O: Has neither antigen, making it the universal donor.

Rh Factor

• Rh-positive: Presence of D antigen on red blood cells.

• Rh-negative: Absence of D antigen.

• Antibodies in plasma respond to foreign antigens to prevent incompatible blood transfusions, which can lead to severe reactions