BIO EXAM 3B

Cardiovascular System Overview

General Structure and Function

The cardiovascular system is responsible for transporting blood, nutrients, gases, and waste products throughout the body. It consists of the heart, blood vessels, and blood, and is essential for maintaining homeostasis.

• Organs besides the heart: Blood vessels (arteries, arterioles, capillaries, venules, veins), lungs, kidneys, liver, and brain are key components.

• Types of blood vessels:

  • Elastic arteries: High flow, high pressure, low resistance, large diameter. Function: Propel blood during systole and diastole, maintain blood pressure and flow.

  • Muscular arteries: High flow, high pressure, low resistance, lower elasticity. Function: Distribute blood to organs and tissues, regulate flow through resistance.

  • Arterioles: Lower flow, lower pressure, high resistance. Function: Major control of systemic vascular resistance (SVR), regulate blood flow into capillaries.

  • Capillaries: Lowest flow, lowest pressure, highest resistance. Function: Site of exchange for gases, nutrients, and waste between blood and tissues.

  • Veins: Low pressure, high volume, low resistance. Function: Return blood to the heart, act as blood reservoir, contain valves to prevent backflow.

Capillary Types and Functions

Classification and Properties

Capillaries are specialized for exchange and vary in structure depending on their location and function.

• Continuous capillaries: Most common, found in muscle, skin, and brain. Characterized by uninterrupted endothelial lining.

• Fenestrated capillaries: Found in organs with high filtration or absorption (kidney, intestine, endocrine glands). Have pores for increased permeability.

• Sinusoidal capillaries: Found in bone marrow, liver, spleen. Large gaps allow passage of proteins and cells.

Blood Volume Distribution

Arteries vs. Veins

Blood volume is unevenly distributed between arteries and veins.

• Arteries: 15% of total blood volume

• Veins: 60% of total blood volume (high compliance, blood reservoir)

• Capillaries: 5% of total blood volume

Cardiac Output (CO)

Calculation and Comparison

Cardiac output is the volume of blood pumped by the heart per minute.

• Formula: $CO = ext{Heart Rate} imes ext{Stroke Volume}$

• Example: For a heart rate of 70 bpm and stroke volume of 75 mL: $CO = 75 ext{ mL/beat} imes 70 ext{ beats/min} = 5250 ext{ mL/min} = 5.25 ext{ L/min}$

• This is comparable to the entire blood volume of the body.

Cardiac Output: Systemic vs. Pulmonary Circulation

Comparison

Despite differences in blood volume, the cardiac output of the systemic and pulmonary circuits is the same, as the stroke volume of each ventricle is equal.

Preload, Afterload, and Frank-Starling Law

Definitions and Relationships

• Preload: The initial stretching of cardiac myocytes prior to contraction, related to end-diastolic volume (EDV).

• Frank-Starling Law: Increased preload leads to increased strength of contraction, similar to the length-tension relationship in skeletal muscle.

• Afterload: The pressure the heart must overcome to eject blood, primarily determined by arterial diastolic pressure.

Stroke Volume (SV) and Related Parameters

Calculation and Significance

• Formula: $SV = EDV - ESV$

• EDV (End-Diastolic Volume): Volume of blood in the ventricle at the end of filling.

• ESV (End-Systolic Volume): Volume of blood remaining after contraction.

Blood Flow Distribution at Rest

Organ-Specific Percentages

• 25% to muscle at rest

• 20% to kidneys

• 13% to brain

• 10% to skin

• 20% to other organs

Flow, Pressure, and Resistance

Conceptual Relationships

• Formula: $Flow = rac{ ext{Difference in Pressure}}{ ext{Resistance}} = rac{MAP}{TPR}$

• MAP (Mean Arterial Pressure): Average pressure in arteries during one cardiac cycle.

• TPR (Total Peripheral Resistance): Resistance to blood flow offered by all systemic vasculature.

Mean Arterial Pressure (MAP)

Calculation and Importance

• Formula: $MAP = ext{Diastolic Pressure} + rac{1}{3}( ext{Systolic Pressure} - ext{Diastolic Pressure})$

• MAP is crucial for ensuring adequate tissue perfusion.

Short-Term and Long-Term Regulation of Blood Pressure

Neural and Hormonal Mechanisms

• Short-term: Vasoconstriction via sympathetic nervous system (SNS), epinephrine, norepinephrine.

• Long-term: Renal regulation via hormones (aldosterone, vasopressin/ADH, atrial natriuretic peptide).

Baroreceptors and Chemoreceptors

Roles in Cardiovascular Regulation

• Baroreceptors: Located in carotid sinus and aortic arch, sense changes in blood pressure and mediate reflex adjustments.

• Chemoreceptors: Located in carotid and aortic bodies, respond to changes in blood O2, CO2, and pH, influencing cardiovascular and respiratory centers.

Key Hormones in Blood Pressure Regulation

Functions and Mechanisms

• Epinephrine (adrenaline): Increases heart rate, stroke volume, and vasoconstriction.

• Angiotensin II: Part of the RAAS, stimulates vasoconstriction and aldosterone release.

• Aldosterone: Promotes sodium and water retention, increasing blood volume and pressure.

• Atrial natriuretic peptide (ANP): Promotes sodium and water excretion, lowering blood pressure.

• Vasopressin/ADH: Increases water retention and vasoconstriction.

• Erythropoietin (EPO): Stimulates red blood cell production in response to low oxygen, not a primary driver of blood pressure.

Summary Table: Key Parameters and Formulas

Parameter	Definition	Formula
Cardiac Output (CO)	Blood pumped per minute	$CO = HR imes SV$
Stroke Volume (SV)	Blood pumped per beat	$SV = EDV - ESV$
Mean Arterial Pressure (MAP)	Average arterial pressure	$MAP = ext{Diastolic} + rac{1}{3}( ext{Systolic} - ext{Diastolic})$
Flow	Blood movement through vessels	$Flow = rac{MAP}{TPR}$

Additional info:

• Some context and definitions were expanded for clarity and completeness.

• Hormonal regulation and receptor functions were inferred from standard cardiovascular physiology.