Blood Vessels and Circulatory Systems

Blood Vessels: The Human Transport System

• Blood vessels are crucial for transporting nutrients, waste, and chemical messengers throughout the body.
• They also maintain a healthy fluid balance and defend against invaders.
• Organisms with one or two germ layers rely on diffusion for cell needs, as they don't require a circulatory system.
• Animals with three germ layers need a circulatory system to support cells not directly exposed to the outer environment.

Primary Tissue Layers

• Endoderm: Innermost layer, forms digestive and respiratory tracts, and various organs.
• Mesoderm: Middle layer, develops into muscle, connective tissues, and blood vessels.
• Ectoderm: Outer layer, forms the skin and nervous system.

Simpler Circulatory Systems

• Open System: Lack closed blood vessels. Instead, interstitial fluid/blood mixture (hemolymph) bathes organs directly within a body cavity (sinus). This system is common in animals with low metabolisms.

Closed Circulatory Systems

• Closed system: Have true blood vessels. Blood is pumped through these vessels to all parts of the body.
• Variation across species influences the structure and function (number of atria and ventricles, etc.). For example, fish have a simpler one-circuit system, while mammals have a more complex two-circuit system.

Two-Circuit Circulatory System

• Systemic Circulation: Loops between the body and heart, transporting oxygenated blood to tissues and deoxygenated blood back to the heart.
• Pulmonary Circulation: Connects the lungs and heart, carrying deoxygenated blood to the lungs for oxygenation and returning oxygenated blood to the heart.

Arteries

• Carry blood away from the heart (Artery = Away).
• Transport blood rapidly under high pressure.
• Most carry oxygenated blood, except the pulmonary artery which carries deoxygenated blood to the lungs.
• The artery wall has three layers: inner lining (endothelium); Middle smooth muscle layer and an outer layer of connective tissue with elastin, allowing stretching and recoil.

Arterioles

• Arterioles branch off arteries.
• Their smooth muscle walls allow the nervous system to regulate blood flow to specific areas of the body.
• Vasoconstriction and vasodilation help in regulating blood flow and temperature.

Capillaries

• Capillaries are the smallest blood vessels and form a network for nutrient and waste exchange.
• They consist of a single layer of endothelial cells, allowing for diffusion between cells and blood.
• Pre-capillary sphincters control blood flow to specific capillary beds.

Veins

• Veins carry blood toward the heart, receiving deoxygenated blood from the body.
• Pulmonary veins carry oxygenated blood from the lungs to the heart.
• Veins have thinner walls and valves to prevent backflow.
• Skeletal muscles help pump blood back toward the heart.

Blood Pressure

• Blood is always under pressure, highest during heart contractions (systolic). Lowest between beats (diastolic).
• Pressure is measured with a sphygmomanometer.
• Normal blood pressure is typically 120/80 mm Hg.

High Blood Pressure

• Factors causing high blood pressure include high sodium intake, and blocked arteries.
• High blood pressure can damage organs like the brain, kidneys and eyes.
• Lifestyle choices like diet and exercise can help in preventing high blood pressure.

High Sodium Diet

• A high sodium intake contributes to increased blood pressure.
• Sodium intake leads to increased water in the vessels via osmosis.

Homework

• Complete practice sheets.
• Section 11.3 (Page 494, questions 1-7)

Explore the vital role of blood vessels in the human circulatory system. This quiz covers the characteristics of different tissue layers, the types of circulatory systems, and how organisms adapt based on their cellular structure. Test your knowledge on how these systems maintain health and fluid balance in the body.