Week 7 Study Guide: Blood Flow and Regulation of Blood Pressure

Week 7 Study Guide: Blood Flow and Regulation of Blood Pressure

Blood Flow and Vessel Dynamics

1. Contraction and Relaxation of Vascular Smooth Muscle

   • Contraction of vascular smooth muscle causes vasoconstriction, or a narrowing of vessel diameter.

   • Relaxation of vascular smooth muscle causes an increase in vessel diameter, or vasodilation.

Characteristics of Blood Vessels

2. Physical Characteristics of Blood Vessels

   • Arteries: Thick, muscular walls; elastic layers allowing for expansion and recoil; carry high-pressure blood away from the heart.

   • Arterioles: Smaller than arteries; muscular walls; regulate blood flow into capillary beds; serve as resistance vessels.

   • Capillaries: Microscopic; one-cell thick walls; site of exchange of gases, nutrients, and waste; connect arterioles and venules.

   • Venules: Small vessels that gather blood from capillaries; walls are thinner than arterioles; collect deoxygenated blood.

   • Veins: Thinner walls than arteries; larger lumen; contain valves to prevent backflow; return blood to the heart under lower pressure.

3. Metarterioles vs. Arterioles

   • Metarterioles are short vessels that directly connect arterioles to capillaries.

   • Function of Metarterioles: They regulate blood flow into capillary beds, acting as precapillary sphincters to control perfusion of tissues.

Properties of Artery Walls

4. Key Property of Artery Walls

   • The ability to sustain the driving pressure created by the heart is due to their elasticity and smooth muscle control, which allows for expansion during systole and recoiling to maintain pressure during diastole.

   • Reference: see Figure 15.5.

Blood Pressure Definitions

6. Systolic and Diastolic Pressure

   • Systolic Pressure: The maximum pressure in the arteries during ventricular contraction.

   • Diastolic Pressure: The minimum pressure in the arteries during ventricular relaxation.

7. Pulse Pressure

   • Definition: The difference between systolic and diastolic pressures.

   • Calculation Formula: $ext{Pulse Pressure} = ext{Systolic Pressure} - ext{Diastolic Pressure}$.

8. Mean Arterial Pressure (MAP)

   • Explanation: MAP is the average pressure in a person's arteries during one cardiac cycle; it is crucial for perfusing tissues.

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

   • MAP relates to cardiac output (CO) and total peripheral resistance (TPR) via the equation: $ext{MAP} = ext{CO} imes ext{TPR}$.

Effects on Mean Arterial Pressure

10. Increase in Blood Flow into Arteries

    • If blood flow into the arteries increases while blood flow out remains unchanged, MAP will increase.

11. Peripheral Resistance and MAP

    • If peripheral resistance increases, MAP will increase due to reduced capacity for blood to flow out of the arteries.

12. Decrease in Blood Volume

    • If the volume of blood circulating through the system decreases, blood pressure will decrease due to reduced volume reaching arterial systems.

Homeostatic Regulation of Blood Pressure

13. Systems Responsible for Regulation

    • The two systems responsible for homeostatic regulation of blood pressure are the nervous system and the endocrine system.

    • Reference: see Figure 15.9.

14. Compensatory Mechanisms for Decreased Blood Volume

    • The cardiovascular system compensates for decreased blood volume through:

      • Increased heart rate and contractility (cardiac compensation).

      • Peripheral vasoconstriction (vascular compensation).

15. Baroreceptor Reflex and Blood Pressure

    • In response to increased blood pressure, baroreceptors detect the change and stimulate increased parasympathetic activity and decreased sympathetic activity to lower heart rate and promote vasodilation, returning blood pressure to normal.

16. Sympathetic and Parasympathetic Activity

    • A decrease in blood pressure results in increased sympathetic activity and decreased parasympathetic activity.

    • Increased sympathetic activity elevates heart rate, force of contraction, and induces vasoconstriction (narrowing of arterioles).

Autonomic Regulation of Heart Function

18. Parasympathetic Activity

    • An increase in parasympathetic activity will decrease heart rate, decrease force of contraction, and facilitate vasodilation (widening of arterioles).

Orthostatic Hypotension

19. Definition and Mechanisms

    • Orthostatic Hypotension: A form of low blood pressure that occurs when standing up from sitting or lying down.

    • Initially, blood pressure falls due to gravitational pooling of blood in the veins, leading to decreased venous return and cardiac output.

Fluid Dynamics in Blood Vessels

20. Total Cross-Sectional Area and Velocity of Flow

    • As total cross-sectional area increases (as blood transitions from arteries to capillaries), the velocity of flow decreases. This phenomenon allows for efficient exchange of substances in the capillaries.

21. Exchange at Capillaries

    • Types of exchange between plasma and interstitial fluid at capillaries include diffusion of gases (O2 and CO2), nutrient uptake (glucose), and waste removal (urea).

Capillary Dynamics

22. Filtration vs. Absorption

    • Filtration: Movement of fluid out of capillaries into interstitial space due to hydrostatic pressure.

    • Absorption: Movement of fluid back into capillaries from interstitial space due to osmotic pressure.

23. Hydrostatic Pressure Role

    • Hydrostatic pressure pushes water out of capillaries, decreasing along the length of the capillary as energy is lost to friction and resistance (reference Figure 15.18).

24. Osmotic Pressure Gradient

    • The osmotic pressure gradient between plasma and interstitial fluid is created by the presence of solutes in plasma, particularly proteins.

    • Colloid Osmotic Pressure (π): The pressure exerted by proteins in the plasma that draws water into the capillaries, counteracting hydrostatic pressure effects.

25. Bulk Flow into Lymph Capillaries

    • Bulk flow moves fluid, proteins, and bacteria into lymph capillaries, facilitating immune responses and fluid balance.

Chapter 19: Renal System

Functions of the Kidneys

1. Six Functions of the Kidneys

   • Regulation of blood volume and blood pressure.

   • Regulation of plasma ionic composition.

   • Regulation of plasma osmolarity.

   • Regulation of blood pH.

   • Excretion of wastes and foreign substances.

   • Production of hormones (e.g., erythropoietin, calcitriol).

Nephrons

2. Nephrons and Types

   • Nephrons are the functional units of the kidneys.

   • Cortical Nephrons: Located mostly in the cortex; short loops of Henle.

   • Juxtamedullary Nephrons: Long loops of Henle that extend deep into the medulla; critical for urine concentration.

3. Flow Pathway in a Nephron

   • Trace: Fluid enters from Bowman’s capsule → proximal convoluted tubule → descending loop of Henle → ascending loop of Henle → distal convoluted tubule → collecting duct → renal pelvis.

4. Renal Corpuscle

   • The renal corpuscle consists of Bowman’s capsule and the glomerulus.

   • Function: It is the site of filtration, where blood plasma is filtered into Bowman’s capsule.

5. Juxtaglomerular Apparatus

   • A structure formed by the distal convoluted tubule and the afferent arterioles; it regulates blood pressure and glomerular filtration rate via renin secretion and tubular feedback mechanisms.

6. Definition of Urine

   • Fluid is considered urine once it enters the collecting duct.

Kidney Processes

7. Three Processes of the Kidney

   • Filtration: Movement of fluid and solutes from blood into Bowman’s capsule.

   • Reabsorption: Transport of substances from renal tubules back into the blood.

   • Secretion: Movement of substances from blood into the renal tubules.

8. Osmolarity of Fluid in Bowman’s Capsule

   • Fluid entering Bowman’s capsule is nearly isotonic (300 mOsm) with plasma.

Kidney Function Measurements

9. Excretion Equation

   • The equation that relates excretion (E) to filtration (F), reabsorption (R), and secretion (S) is:
     $E = F - R + S$.

10. Filtration Barrier

    • The filtration barrier includes podocytes, foot processes, and filtration slits that prevent the passage of large molecules while allowing water and small solutes to pass.

Pressure and Filtration Gradient

11. Filtration Pressures

    • Glomerular Capillary Hydrostatic Pressure (PH): Average pressure measurement crucial for filtration.

    • Colloid Osmotic Pressure (π): Average osmotic pressure opposing filtration; depends on plasma proteins.

    • Bowman’s Capsule Hydrostatic Pressure (Pfluid): Pressure exerted by fluid in Bowman’s capsule, opposing filtration.

    • Net Filtration Pressure: The overall pressure that drives fluid from the glomerulus into Bowman’s capsule and is calculated by:
      ext{Net Filtration Pressure} = PH - ( ext{π} + Pf}.

12. Glomerular Filtration Rate (GFR)

    • Definition: The volume of fluid filtered from the renal glomerular capillaries into Bowman’s capsule per unit time.

    • Average Value for GFR: Approximately 125 mL/min.

Regulation of GFR

13. How GFR is Controlled

    • GFR is controlled by changing the resistance of the renal arterioles.

    • Increasing Resistance in Afferent Arterioles: Leads to a decrease in GFR due to reduced blood flow.

    • Increasing Resistance in Efferent Arterioles: Leads to an increase in GFR due to increased pressure in the glomerulus.

Responses to Filtration Changes

14. Myogenic Response vs. Tubuloglomerular Feedback

    • Myogenic Response: The ability of smooth muscle in arterioles to constrict or dilate in response to changes in blood pressure.

    • Tubuloglomerular Feedback: A mechanism in which the flow of fluid through the renal tubules influences glomerular filtration based on fluid composition and pressure detected by the macula densa cells.

15. RAAS Mechanism

    • Renin-Angiotensin-Aldosterone System (RAAS) activates in response to decreased blood pressure; renin is secreted by the juxtaglomerular apparatus, leading to the production of angiotensin II, which stimulates aldosterone release, promoting sodium and water reabsorption to increase blood pressure.

Mediated Transport in Kidneys

16. Characteristics of Mediated Transport

    • Specificity: Transport proteins allow the passage of specific substances.

    • Saturation: There is a limit to how much of a substance can be transported at one time.

    • Competition: Different substances may compete for the same transporter.

Plasma Concentration and Urine

17. Threshold for Substance Appearance

    • The plasma concentration at which a substance first appears in the urine is known as the renal threshold.

18. Filtration Saturation

    • Filtration doesn't exhibit saturation as the glomerular filtration is a passive process dictated by pressure, but reabsorption can exhibit saturation limits.

19. Plasma Glucose Concentration

    • Normal plasma glucose concentrations are < the renal threshold for glucose. Therefore, normally all glucose filtered is reabsorbed.

Reabsorption Mechanisms

20. Forces for Fluid Movement

    • The forces that cause fluid reabsorbed from the kidney tubule to move into the peritubular capillaries include osmotic pressure and hydrostatic pressure gradients.

21. Renal Secretion Process

    • In renal secretion, molecules move from the blood to the renal tubules.

22. Definition of Clearance

    • Clearance: The volume of plasma from which a substance is completely removed by the kidneys in a given time.

23. Determining GFR via Inulin

    • GFR can be determined by measuring the plasma concentration of inulin and the excretion rate of inulin using the formula:
      $ext{GFR} = rac{ ext{Excretion Rate of Inulin}}{ ext{Plasma Concentration of Inulin}}$.