Anatomy and Physiology II Unit 2 Review: Vessels & Circulation

Key Concepts and Terminology

• Cardiovascular system consists of the heart, blood vessels, and blood that work together to transport oxygen, nutrients, and waste products throughout the body
• Blood vessels are hollow tubes that carry blood away from and towards the heart
  • Arteries carry oxygenated blood away from the heart to the tissues
  • Veins carry deoxygenated blood from the tissues back to the heart
  • Capillaries are the smallest blood vessels that connect arteries and veins, allowing for exchange of substances between blood and tissues
• Blood pressure is the force exerted by circulating blood against the walls of blood vessels
  • Systolic pressure is the maximum pressure during heart contraction (ventricular systole)
  • Diastolic pressure is the minimum pressure during heart relaxation (ventricular diastole)
• Cardiac output is the volume of blood pumped by the heart per minute, calculated as stroke volume multiplied by heart rate
• Resistance is the opposition to blood flow due to friction between blood and vessel walls, influenced by vessel diameter and blood viscosity

Structure of Blood Vessels

• Blood vessels have three main layers (tunics) that vary in thickness and composition depending on the vessel type
  • Tunica intima is the innermost layer consisting of endothelial cells, a basement membrane, and an internal elastic lamina
  • Tunica media is the middle layer composed of smooth muscle cells and elastic fibers, responsible for vasoconstriction and vasodilation
  • Tunica externa (adventitia) is the outermost layer made of connective tissue that anchors the vessel to surrounding structures
• Endothelial cells line the inner surface of blood vessels, providing a smooth, non-thrombogenic surface and regulating vascular tone, inflammation, and blood clotting
• Vascular smooth muscle cells in the tunica media contract or relax to change vessel diameter and regulate blood flow
• Elastic fibers (elastin) in the vessel walls allow for stretching and recoil during the cardiac cycle, contributing to the compliance of arteries
• Collagen fibers in the tunica externa provide tensile strength and prevent excessive stretching of the vessel wall
• Vasa vasorum are small blood vessels that supply oxygen and nutrients to the walls of larger vessels

Types of Blood Vessels

• Arteries are thick-walled, elastic vessels that carry oxygenated blood away from the heart under high pressure
  • Elastic arteries (aorta, pulmonary artery) have a large amount of elastic fibers in the tunica media, allowing for stretching and recoil during the cardiac cycle
  • Muscular arteries (coronary, renal) have more smooth muscle cells in the tunica media, allowing for greater vasoconstriction and vasodilation to regulate blood flow
  • Arterioles are small arteries that lead into capillaries, with a well-developed tunica media for precise control of blood flow
• Capillaries are thin-walled, narrow vessels that allow for exchange of substances between blood and tissues
  • Continuous capillaries (muscle, skin) have tight junctions between endothelial cells, limiting permeability
  • Fenestrated capillaries (intestines, endocrine glands) have small pores (fenestrae) in the endothelium, allowing for rapid exchange of substances
  • Sinusoidal capillaries (liver, spleen, bone marrow) have large, irregular openings and discontinuous basement membrane, facilitating cellular migration and exchange
• Veins are thin-walled, less elastic vessels that carry deoxygenated blood back to the heart under low pressure
  • Veins have a larger lumen and thinner walls compared to arteries, accommodating a larger blood volume at lower pressure
  • Venules are small veins that collect blood from capillaries and merge into larger veins
  • Most veins contain valves, which are folds of the tunica intima that prevent backflow of blood and facilitate unidirectional flow towards the heart

Blood Flow and Circulation Patterns

• Systemic circulation carries oxygenated blood from the left ventricle to the tissues and returns deoxygenated blood to the right atrium
  • Aorta is the largest artery that receives oxygenated blood from the left ventricle and branches into smaller arteries supplying the body
  • Superior and inferior vena cavae are the largest veins that return deoxygenated blood from the upper and lower body, respectively, to the right atrium
• Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs for oxygenation and returns oxygenated blood to the left atrium
  • Pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs
  • Pulmonary veins carry oxygenated blood from the lungs to the left atrium
• Coronary circulation supplies oxygenated blood to the heart muscle (myocardium) through the coronary arteries and returns deoxygenated blood via the coronary veins and coronary sinus
• Portal systems are specialized circulations where blood passes through two capillary beds before returning to the heart
  • Hepatic portal system carries nutrient-rich blood from the intestines to the liver for processing before entering the systemic circulation
  • Hypothalamic-hypophyseal portal system carries releasing hormones from the hypothalamus to the anterior pituitary gland for stimulating hormone secretion

Regulation of Blood Flow

• Autoregulation is the intrinsic ability of tissues to maintain relatively constant blood flow despite changes in blood pressure
  • Myogenic mechanism involves the contraction or relaxation of vascular smooth muscle in response to changes in intravascular pressure
  • Metabolic mechanism involves the release of local metabolites (adenosine, CO2, H+) that cause vasodilation when tissue metabolism increases
• Neural regulation of blood flow involves the autonomic nervous system, which can alter vascular tone and cardiac output
  • Sympathetic nervous system causes vasoconstriction (α1-adrenergic receptors) and increases heart rate and contractility (β1-adrenergic receptors)
  • Parasympathetic nervous system causes vasodilation (muscarinic receptors) and decreases heart rate (vagus nerve)
• Hormonal regulation of blood flow involves circulating hormones that can affect vascular tone and fluid balance
  • Antidiuretic hormone (ADH) increases water reabsorption in the kidneys and causes vasoconstriction, increasing blood volume and pressure
  • Atrial natriuretic peptide (ANP) increases sodium excretion and causes vasodilation, decreasing blood volume and pressure
  • Angiotensin II, a product of the renin-angiotensin-aldosterone system (RAAS), causes vasoconstriction and increases sodium and water retention, increasing blood pressure
• Endothelial factors, such as nitric oxide (NO) and endothelin, can cause local vasodilation or vasoconstriction, respectively, in response to shear stress and other stimuli

Common Cardiovascular Disorders

• Atherosclerosis is the buildup of plaque (fatty deposits, cholesterol, and inflammatory cells) in the arterial walls, leading to narrowing and hardening of the arteries
  • Risk factors include high blood pressure, high cholesterol, smoking, diabetes, obesity, and sedentary lifestyle
  • Complications of atherosclerosis include coronary artery disease, peripheral artery disease, and stroke
• Hypertension (high blood pressure) is a chronic condition characterized by persistently elevated blood pressure ($\geq$ 130/80 mmHg)
  • Primary (essential) hypertension has no identifiable cause and accounts for 90-95% of cases
  • Secondary hypertension results from an underlying condition, such as kidney disease, endocrine disorders, or sleep apnea
• Aneurysms are abnormal bulges or weakening in the blood vessel walls, most commonly occurring in the aorta or cerebral arteries
  • Abdominal aortic aneurysms (AAA) are often associated with atherosclerosis and can rupture, leading to life-threatening internal bleeding
  • Cerebral aneurysms can rupture, causing subarachnoid hemorrhage and stroke
• Venous thrombosis is the formation of blood clots in the veins, often occurring in the deep veins of the legs (deep vein thrombosis, DVT)
  • Risk factors include prolonged immobility, surgery, pregnancy, obesity, and inherited thrombophilia
  • Complications of DVT include pulmonary embolism (PE), where the clot dislodges and travels to the lungs, causing respiratory distress and potentially death
• Varicose veins are enlarged, twisted veins, most commonly occurring in the legs due to incompetent valves and increased venous pressure
  • Risk factors include age, family history, pregnancy, obesity, and prolonged standing
  • Symptoms include visible bulging veins, pain, swelling, and skin changes (hyperpigmentation, ulceration)

Clinical Applications and Diagnostics

• Blood pressure measurement is a routine clinical assessment using a sphygmomanometer and stethoscope
  • Korotkoff sounds are the audible sounds used to determine systolic and diastolic blood pressure
  • Ambulatory blood pressure monitoring (ABPM) involves wearing a portable device that measures blood pressure at regular intervals over 24 hours
• Ankle-brachial index (ABI) is a non-invasive test used to assess peripheral artery disease (PAD) by comparing blood pressure in the ankles and arms
  • ABI $<$ 0.9 indicates PAD, while ABI $>$ 1.4 suggests calcified, non-compressible arteries
• Doppler ultrasound is a non-invasive imaging technique that uses sound waves to visualize blood flow in the vessels
  • Color Doppler shows the direction and velocity of blood flow, while spectral Doppler provides a graphical representation of blood flow over time
  • Doppler ultrasound is used to diagnose deep vein thrombosis, assess carotid artery stenosis, and evaluate blood flow in the umbilical cord during pregnancy
• Angiography is an invasive imaging technique that uses contrast media (dye) to visualize the blood vessels under X-ray
  • Coronary angiography is used to diagnose coronary artery disease and guide interventional procedures (angioplasty, stenting)
  • Cerebral angiography is used to diagnose and treat cerebrovascular disorders, such as aneurysms and arteriovenous malformations (AVMs)
• Vascular surgery involves surgical interventions to treat disorders of the blood vessels
  • Carotid endarterectomy is the removal of plaque from the carotid arteries to prevent stroke
  • Aneurysm repair involves placing a stent-graft (endovascular) or surgically replacing the weakened portion of the vessel (open repair)
  • Vein stripping is the surgical removal of varicose veins to alleviate symptoms and prevent complications (ulceration, thrombosis)

Key Takeaways and Study Tips

• Understand the structure and function of the different types of blood vessels (arteries, capillaries, veins) and their roles in the circulation
• Learn the key differences between systemic, pulmonary, and portal circulations, and how they work together to supply organs and tissues with oxygenated blood
• Familiarize yourself with the mechanisms of blood flow regulation, including autoregulation, neural, hormonal, and endothelial factors
  • Practice applying these concepts to different physiological scenarios (exercise, hemorrhage, etc.)
• Review the pathophysiology, risk factors, and complications of common cardiovascular disorders, such as atherosclerosis, hypertension, aneurysms, and venous thrombosis
  • Use mnemonics or acronyms to remember key information (e.g., ABCDE for signs of melanoma)
• Understand the principles and applications of various diagnostic tests and imaging techniques used to assess cardiovascular health
  • Practice interpreting sample test results or images to develop your clinical reasoning skills
• Integrate your knowledge of cardiovascular anatomy and physiology with other related systems (respiratory, renal, endocrine) to gain a comprehensive understanding of homeostasis
  • Create concept maps or flowcharts to visualize the relationships between different concepts and systems
• Utilize active learning strategies, such as summarizing key points, teaching others, or solving practice problems, to reinforce your understanding and retention of the material
  • Form study groups with classmates to discuss challenging topics and share different perspectives or learning strategies