Anatomy of Blood Capillaries
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Questions and Answers

What is the peak of the aortic pressure pulse termed as?

  • Mean aortic pressure
  • Pulse pressure
  • Systolic pressure (correct)
  • Diastolic pressure

    • What happens to systolic pressure as the pressure pulse travels down the blood vessels?

  • It remains the same
  • It fluctuates
  • It decreases
  • It increases (correct)

    • What is the average blood pressure in adults?

  • 100/60 mmHg
  • 140/90 mmHg
  • 110/70 mmHg
  • 120/80 mmHg (correct)

    • What is the method of measuring blood pressure using a catheter called?

    <p>Direct method</p> Signup and view all the answers

    What is the usual method of measuring blood pressure?

    <p>Sphygmomanometry</p> Signup and view all the answers

    What is the pulse rate usually equal to?

    <p>Heart rate</p> Signup and view all the answers

    What happens to systolic and diastolic pressures with aging?

    <p>They gradually increase</p> Signup and view all the answers

    What is the blood pressure in a newborn?

    <p>80/40 mmHg</p> Signup and view all the answers

    Which of the following factors does not affect blood pressure?

    <p>Body temperature</p> Signup and view all the answers

    In adults before 45 years, which of the following is true about blood pressure?

    <p>Males have higher blood pressure than females</p> Signup and view all the answers

    What happens to blood pressure during deep quiet sleep?

    <p>It decreases</p> Signup and view all the answers

    What is cardiac output?

    <p>The volume of blood ejected by each ventricle per minute</p> Signup and view all the answers

    What is the formula to calculate cardiac output?

    <p>Heart Rate X Stroke Volume</p> Signup and view all the answers

    What happens to blood pressure when cardiac output increases?

    <p>It increases</p> Signup and view all the answers

    What is stroke volume?

    <p>The difference in volume before and after ventricular contraction</p> Signup and view all the answers

    What is the formula to calculate ejection fraction?

    <p>EF = SV / EDV</p> Signup and view all the answers

    What is the normal heart rate in well-trained athletes at rest?

    <p>50 beats/min</p> Signup and view all the answers

    What is the effect of enhanced vagal activity on heart rate?

    <p>It decreases heart rate</p> Signup and view all the answers

    What is the intrinsic heart rate in adults?

    <p>100 beats/min</p> Signup and view all the answers

    What is the effect of blockade of both parasympathetic and sympathetic nerves on heart rate?

    <p>It increases the heart rate</p> Signup and view all the answers

    What is the effect of increased blood pressure on heart rate through the baroreceptor reflex?

    <p>It decreases heart rate</p> Signup and view all the answers

    What is the normal stroke volume?

    <p>70 ml</p> Signup and view all the answers

    What is the function of the precapillary sphincter in blood capillaries?

    <p>To regulate blood flow to the capillaries</p> Signup and view all the answers

    Which type of capillary is found in the kidneys?

    <p>Fenestrated capillaries</p> Signup and view all the answers

    What is the function of the skeletal muscle pump in veins?

    <p>To aid in the return of blood to the heart</p> Signup and view all the answers

    What is the equation for calculating blood flow?

    <p>Q = ΔP / R</p> Signup and view all the answers

    What is the purpose of the thoracic pump?

    <p>To aid in the return of blood to the heart</p> Signup and view all the answers

    What is the site of highest resistance to blood flow?

    <p>Arterioles</p> Signup and view all the answers

    What is the function of the endothelial cells lining the capillaries?

    <p>To aid in the exchange of substances</p> Signup and view all the answers

    What is the term for the volume of blood contained in the arteries?

    <p>Stressed volume</p> Signup and view all the answers

    What is the purpose of the venous valves?

    <p>To prevent backflow of blood</p> Signup and view all the answers

    What happens to velocity of blood flow as vessel diameter increases?

    <p>It decreases</p> Signup and view all the answers

    Which nerve is involved in the Bainbridge reflex?

    <p>X nerve</p> Signup and view all the answers

    What is the name of the phenomenon where the strength of cardiac contraction increases with increasing frequency of stimulation of the myocardium?

    <p>Treppe phenomenon</p> Signup and view all the answers

    What is the primary stimulus for the chemoreceptor reflex?

    <p>Increase in pCO2</p> Signup and view all the answers

    What is the term for the regulation of stroke volume by changes in the end-diastolic length of cardiac fibres?

    <p>Starling's law of the heart</p> Signup and view all the answers

    Which of the following is NOT a factor that affects peripheral resistance?

    <p>Blood pressure</p> Signup and view all the answers

    What is the term for the measurement of cardiac output?

    <p>Fick-method</p> Signup and view all the answers

    What is the main source of intrinsic regulation of cardiac output?

    <p>Changes in end-diastolic length of myocardial fibres</p> Signup and view all the answers

    Which of the following is an extrinsic factor that regulates cardiac output?

    <p>Nervous control</p> Signup and view all the answers

    Study Notes

    Blood Vessels

    • Arteries:
      • Thick-walled, with extensive elastic tissue, smooth muscle, and connective tissue
      • Under highest pressure
      • Stressed volume: volume of blood contained in arteries
    • Arterioles:
      • Smallest branches of arteries
      • Extensive smooth muscle in walls
      • Site of highest resistance to blood flow
      • Innervated by sympathetic adrenergic nerve fibers (α-Adrenergic receptors cause constriction, β2-Adrenergic receptors cause relaxation)
    • Capillaries:
      • Lined by a single layer of endothelial cells
      • Site of exchange of nutrients, gases, water, and solutes between blood and tissues
      • Lipid-soluble substances diffuse across capillary wall
      • Water-soluble substances use pores to cross capillary wall
      • Not all capillaries are perfused with blood at all times (selective perfusion)
    • Venules and Veins:
      • Venules: thin-walled
      • Veins: modest amount of elastic tissue, smooth muscle, and connective tissue
      • Large capacitance (capacity to hold blood)
      • Contain largest percentage of blood in the cardiovascular system
      • Unstressed volume: volume of blood contained in veins

    Velocity of Blood Flow

    • V = Q/A (velocity = flow / cross-sectional area)
    • Changes in diameter alter velocity of flow:
      • Increase in diameter: decrease in velocity
      • Decrease in diameter: increase in velocity
    • Blood flow at each level is the same
    • Velocity of blood flow is highest in the aorta and lowest in capillaries (advantageous for exchange across capillary wall)

    Blood Flow, Pressure, and Resistance

    • Blood flow is determined by:
      • Pressure difference (driving force) between two ends of a vessel
      • Resistance of the vessel to blood flow
    • Q = ΔP/R (blood flow = pressure difference / resistance)
    • Major mechanism for changing blood flow is changing resistance in the arterioles

    Pressure

    • Blood flows from high pressure to low pressure areas
    • Ejection of blood into the aorta by the left ventricle results in a characteristic aortic pressure pulse
    • Peak of the aortic pressure pulse: systolic pressure (SP)
    • Lowest pressure in the aorta: diastolic pressure (DP)
    • PP = SP - DP (pulse pressure)
    • Mean aortic pressure (MAP) is the average pressure during the aortic pulse cycle

    Arterial Blood Pressure

    • Characteristic changes occur in SP, DP, and MAP as the pressure pulse travels down the blood vessels
    • Away from the heart, SP rises, and DP falls
    • MAP slightly declines due to resistance in the arteries
    • Arterial BP measured using a sphygmomanometer (blood pressure cuff) on the upper arm is slightly different from the pressure measured in the aorta or other distributing arteries

    Measurement of Blood Pressure

    • Direct method (invasive): most accurate means of measuring blood pressure directly within an artery using a catheter
    • Indirect method (noninvasive): uses a sphygmomanometer (e.g., mercury-filled sphygmomanometer) to measure blood pressure in the brachial artery
    • Measurement of blood pressure can be done by palpitation or auscultation

    Physiological Factors Affecting Arterial Blood Pressure

    • Age: BP increases with age
    • Sex: differences in BP between males and females
    • Race: differences in BP between different racial groups
    • Gravity: BP in upper parts of the body is higher than in lower parts, especially during standing
    • Meals: digestion increases BP
    • Emotions and exercise: increase BP
    • Sleep: deep quiet sleep decreases BP, while sleep with dreams increases BP

    Factors that Affect Blood Pressure

    • Cardiac output
    • Peripheral resistance
    • Vessel elasticity
    • Blood volume

    Cardiac Output

    • Definition: volume of blood ejected by each ventricle per minute
    • Normal cardiac output: 5L/min in adults
    • Cardiac output is affected by:
      • Heart rate
      • Stroke volume
      • Peripheral resistance
      • Vessel elasticity
      • Blood volume

    Regulation of Heart Rate

    • Autonomic influence: tonic influence of the autonomic nervous system (ANS) on the SA node
    • Influence by higher centers: effects of reflexes on heart rate
    • Baroreceptor reflex: ↑ BP → ↑ BR → ↑ vagal tone → ↓ HR
    • Bainbridge reflex: venous engorgement of atria and great veins → ↑ HR
    • Chemoreceptor reflex: ↓pO2, ↑pCO2, and ↓pH → ↑ CR → ↑ respiratory center → ↑ ventilatory drive

    Regulation of Stroke Volume

    • Nervous stimuli
    • End-diastolic length of cardiac fibers (Starling's law of the heart)

    Regulation of Cardiac Output

    • Intrinsic regulation: changes in the end-diastolic length of myocardial fibers (Starling's law of the heart) and frequency-induced regulation (staircase or Treppe phenomenon)
    • Extrinsic regulation: nervous control, humoral control, and blood gases

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    Description

    This quiz covers the structure and function of blood capillaries, including their composition, types, and blood pressure. It also compares capillaries to arteries and veins.

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