Work 3: Cardiovascular system: Blood Vessels and Circulation

• Artery: blood vessel that carries blood away from the heart and branches into smaller vessels
• Arterioles: smallest arteries that branch into capillaries for nutrient and waste exchange
• Capillaries: tiny vessels where nutrients and wastes are exchanged, connecting arterioles and venules
• Venules: small blood vessels that carry blood to veins
• Vein: larger blood vessel that returns blood to the heart
• Pulmonary circuit: moves blood from the right side of the heart to the lungs and back
• Systemic circuit: moves blood from the left side of the heart to the head and body and back to the heart
• Arteries have thicker walls than veins due to higher blood pressure
• Arterioles: small arteries leading to capillaries with diminished wall thickness
• Capillaries: microscopic channels for perfusion and exchange of gases and substances
• Types of capillaries:

  • Continuous: most common type
  • Fenestrated: has pores for larger molecules
  • Sinusoid: flattened with large openings for passage of large molecules
• Metarterioles and Capillary Beds:

  • Arterioles give rise to metarterioles in capillary beds
  • Precapillary sphincters regulate blood flow
  • Thoroughfare channel connects metarteriole to venule
  • Arteriovenous anastomosis connects arteriole directly to venule
• Venules: extremely small veins that join multiple capillaries to form veins
• Veins have valves to prevent backflow, while venules do not
• Blood flow: movement of blood through vessels, tissues, and organs
• Blood pressure: force exerted by blood on vessel walls or heart chambers
• Components of Arterial Blood Pressure:

  • Systolic and diastolic pressures
  • Pulse pressure
  • Mean arterial pressure
• Cardiac output: measurement of blood flow from the heart through the ventricles
• Compliance: ability of a compartment to expand to accommodate increased content
• Blood volume affects pressure and flow:

  • Hypovolemia decreases pressure and flow
  • Hypervolemia increases pressure and flow
• Viscosity of blood: thickness affecting flow and resistance
• Blood vessel length and diameter affect resistance and flow
• Disorder: Arteriosclerosis results in the hardening and narrowing of arteries
• Atherosclerosis can result from plaques formed by the buildup of fatty, calcified deposits in an artery
• Plaques can take other forms, such as a buildup of connective tissue within the artery wall
• The primary purpose of the cardiovascular system is to circulate gases, nutrients, wastes, and other substances to and from the cells of the body
• Small molecules like gases, lipids, and lipid-soluble molecules can diffuse directly through the membranes of the endothelial cells of the capillary wall
• Glucose, amino acids, and ions use transporters to move through specific channels in the membrane by facilitated diffusion
• Glucose, ions, and larger molecules may also leave the blood through intercellular clefts
• Larger molecules can pass through the pores of fenestrated capillaries, and even large plasma proteins can pass through the great gaps in the sinusoids
• Water moves by osmosis
• The mass movement of fluids into and out of capillary beds requires a transport mechanism far more efficient than mere diffusion, known as bulk flow
• Filtration: volumes of fluid move from an area of higher pressure in a capillary bed to an area of lower pressure in the tissues
• Reabsorption: movement of fluid from an area of higher pressure in the tissues into an area of lower pressure in the capillaries
• Two types of pressure interact to drive these movements: hydrostatic pressure and osmotic pressure
• Approximately 24 liters per day are filtered, whereas 20.4 liters are reabsorbed, with the rest of the fluid picked up by capillaries of the lymphatic system
• Lymphatic vessels have valves to ensure unidirectional flow, eventually draining into the subclavian veins in the neck
• The lymphatic system's important function is to return the fluid (lymph) to the blood, acting as recycled blood plasma
• In order to maintain homeostasis in the cardiovascular system, blood flow must be redirected continually to the tissues as they become more active
• The cardiovascular system engages in resource allocation, directing more blood to active tissues like skeletal muscles, the heart, and the lungs during exercise