Study Guide: The Cardiovascular System II – Blood Vessels (Chapter 18)

The Cardiovascular System II: Blood Vessels

Overview of Blood Vessels

The vasculature is a network of billions of blood vessels that transport blood throughout the body, facilitating the exchange of gases, nutrients, and wastes. Collectively, these vessels measure over 60,000 miles in length.

• Arteries: Distribution system, carrying blood away from the heart under high pressure.

• Capillaries: Exchange system, allowing for transfer of substances between blood and tissues.

• Veins: Collection system, returning blood to the heart.

Structure and Function of Arteries and Veins

Blood vessels are composed of three main layers:

• Tunica intima: Innermost layer, lined by endothelium.

• Tunica media: Middle layer, primarily smooth muscle and elastic fibers.

• Tunica externa: Outermost layer, connective tissue.

Types of Blood Vessels

Type	Structure	Function
Elastic arteries	Extensive elastic laminae in tunica intima and media	Conduct blood under high pressure
Muscular arteries	Thick tunica media (smooth muscle)	Control blood flow to organs
Arterioles	Thin walls, dispersed smooth muscle	Regulate blood pressure, feed capillary beds
Venules	Thin walls, little smooth muscle	Drain capillary beds
Veins	Thin smooth muscle, large lumen, valves	Return blood to the heart

Blood Vessel Functions

• Conduct blood under high pressure

• Control blood flow and regulate blood pressure

• Feed and drain capillary beds

• Return blood to the heart

Atherosclerosis

Atherosclerosis is the leading cause of death in the developed world, affecting large and medium-sized arteries. It is characterized by the formation of plaques composed of lipids, cholesterol, calcium salts, and cellular debris within the tunica intima, often at vessel branching points or curves.

Development and Treatment

• Injury to endothelium (from high blood pressure, cholesterol, toxins, etc.) leads to inflammation and plaque formation.

• Clots may form, causing myocardial infarction or stroke.

• Treatment includes lifestyle changes, medications, and possible surgical interventions such as stents or bypass grafts.

Hemodynamics: Physiology of Blood Flow

Hemodynamics refers to the study of blood flow, which is influenced by pressure and resistance. Blood pressure is the outward force exerted by blood on vessel walls, while resistance is any opposition to blood flow.

• High blood pressure can rupture vessel walls; low pressure can cause cell death due to insufficient perfusion.

• Key equation: $P = CO \times R$ (Pressure = Cardiac Output × Resistance)

Factors Affecting Blood Pressure

• Peripheral resistance: Vessel radius, blood viscosity, vessel length

• Cardiac output: Heart rate × stroke volume

• Blood volume: Influenced by water intake and loss

Blood Pressure in Circulation

• Systolic Pressure: Pressure during ventricular contraction (~110–120 mm Hg)

• Diastolic Pressure: Pressure during ventricular relaxation (~70–80 mm Hg)

• Pulse Pressure: Difference between systolic and diastolic (~40 mm Hg)

• Mean Arterial Pressure (MAP): Average pressure in systemic arteries during a cardiac cycle. $MAP = DBP + \frac{SBP - DBP}{3}$

Pressure in Pulmonary and Systemic Circuits

Circuit	Pressure
Pulmonary arteries	15 mm Hg
Pulmonary veins	5 mm Hg
Systemic arteries	120 mm Hg (systolic), 80 mm Hg (diastolic)
Arterioles	80–35 mm Hg
Capillaries	35–15 mm Hg
Venules	15–5 mm Hg
Veins	5–0 mm Hg

Mechanisms of Venous Return

• Valves prevent backflow

• Smooth muscle contraction

• Skeletal muscle pump

• Respiratory pump

Disorders of Blood Pressure

Hypertension

• Chronic high blood pressure; "silent killer" due to lack of symptoms

• Associated with coronary artery disease, stroke, heart failure, dementia, kidney disease

• Treatment: Lifestyle modifications and medications

Hypotension

• Low blood pressure; can cause shock, loss of consciousness, organ failure

• Causes: Reduced blood volume (hypovolemic shock), decreased cardiac output (cardiogenic shock), excessive vasodilation (anaphylactic or septic shock)

Capillary Structure and Function

• Capillaries are the site of exchange between blood and tissues.

• Three types: Continuous (least leaky), Fenestrated (moderately leaky), Sinusoidal (leakiest).

Type	Location	Function
Continuous	Skin, nervous tissue, muscle	Permit narrow range of substances
Fenestrated	Kidneys, endocrine glands, small intestine	Allow large volumes of fluid and larger substances
Sinusoidal	Liver, bone marrow, spleen	Allow large substances such as cells

Capillary Exchange Mechanisms

• Filtration: Movement of fluid by pressure or gravity

• Hydrostatic Pressure (HP): Drives water out of capillary

• Osmotic Pressure (OP): Draws fluid into capillary

• Net Filtration Pressure (NFP): $NFP = Filtration - Reabsorption$

Edema

• Excessive water in interstitial fluid

• Peripheral edema: legs and feet

• Ascites: abdomen

• Causes: Increased HP, decreased OP, lymphatic obstruction

Disorders: Cerebrovascular Accident (CVA)

• Ischemic: Blockage of brain artery (treated with clot-dissolving meds)

• Hemorrhagic: Ruptured cerebral artery (treated with surgery)

• Risk factors: Hypertension, atherosclerosis, diabetes, smoking, hypercholesterolemia, atrial fibrillation

• Symptoms: Sudden paralysis, vision loss, speech difficulty

Summary: The Big Picture of Blood Vessel Anatomy

Blood vessels are essential for distributing blood, maintaining pressure, and facilitating exchange. Disorders such as atherosclerosis, hypertension, and hypotension can significantly impact health, and understanding the structure and function of vessels is crucial for diagnosis and treatment.

Additional info: Some images and tables were inferred for completeness and clarity based on textbook conventions.