Smooth Muscle Histology and Blood Pressure Regulation

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Questions and Answers

What effect does an increase in End Diastolic Volume have on stroke volume and cardiac output?

It decreases both stroke volume and cardiac output.

It increases both stroke volume and cardiac output. (correct)

It increases stroke volume and decreases cardiac output.

It has no effect on stroke volume or cardiac output.

During physical activity, which blood vessels experience constriction according to sympathetic nervous system responses?

Brain and skin

Coronary vessels and muscle tissues

Gut and kidneys (correct)

All blood vessels receive equal dilation

Which component is primarily responsible for increasing contractility of the heart during physical activity?

Sympathetic nervous system activation (correct)

Increased levels of calcium in the blood

Decreased ductility in the heart muscle

Lowered levels of noradrenaline

What is the typical cardiac output of the heart at rest?

5L/min Signup and view all the answers

How does high intensity interval training specifically affect blood pressure in hypertensive individuals?

It reduces blood pressure effectively. Signup and view all the answers

What happens to systemic vascular resistance when blood flow is increased?

It decreases. Signup and view all the answers

Following exercise, what typically occurs in the sympathetic nervous system?

There is a reflexive drop in activity. Signup and view all the answers

Which of the following statements about muscle tissue blood flow at rest is accurate?

Muscles receive about 3mL/min/100g. Signup and view all the answers

Which characteristics define smooth muscle?

Uni-nucleated and spindle shaped Signup and view all the answers

What is the formula for Mean Arterial Pressure (MAP)?

MAP = CO x TPR Signup and view all the answers

What happens during vasoconstriction?

Activated sympathetic system causes smooth muscles to contract, increasing resistance Signup and view all the answers

What primarily regulates heart rate under resting conditions?

Parasympathetic vagus nerve via the cardioinhibitory center Signup and view all the answers

Which statement is false regarding the regulation of heart rate?

The parasympathetic system actively regulates blood vessel diameter Signup and view all the answers

What does cardiac reserve represent?

The difference between resting and maximal cardiac output Signup and view all the answers

How is the heart rate affected by sympathetic activity?

Heart rate increases due to stimulation of β1 adrenergic receptors Signup and view all the answers

Which condition describes tachycardia?

Abnormally fast heart rate exceeding 100 beats per minute Signup and view all the answers

Study Notes

Smooth Muscle Histology

Smooth muscle cells are uni-nucleated, spindle-shaped, and non-striated
They are autorhythmic, meaning they can contract on their own without external stimulation
Smooth muscle cells are capable of dividing and regenerating

Regulation of Blood Flow and Pressure

Blood flow moves from high pressure to low pressure
The pressure gradient is created through the contraction of the heart muscle
Contraction of the ventricles generates high blood pressure (BP) in the aorta, which pushes blood through the systemic circulation
Mean arterial pressure (MAP) is determined by cardiac output (CO) and total peripheral resistance (TPR)
- MAP = CO x TPR
- CO = Cardiac output = SV x HR
Blood pressure varies directly with changes in CO and TPR
Changes in one variable are quickly compensated for by changes in the other variables

Regulation of Total Peripheral Resistance

For blood to move through blood vessels (BVs), BP must overcome the opposing pressure in the peripheral circulation (TPR)
TPR is regulated by the sympathetic nervous system (neural)
- Vasoconstriction (activation of the sympathetic nervous system) leads to increased resistance (TPR) due to contraction of smooth muscle in blood vessel walls
- Vasodilation (reduced activation of the sympathetic nervous system) leads to decreased resistance (TPR) due to relaxation of smooth muscle in blood vessel walls
The parasympathetic system has NO effect on blood vessel diameter regulation

Regulation of Cardiac Output (CO)

At rest, CO is approximately 5.25 L/min:
- CO ( mL/min) = HR (75 beats/min) x SV (70 ml/beat)
Maximal CO is 4-5 times resting CO in non-athletic individuals
Maximal CO can reach 35 L/min in trained athletes
Cardiac reserve is the difference between resting and maximal CO
Resting heart rate (HR) is regulated by the cardioinhibitory center (in the medulla oblongata) via the parasympathetic vagus nerve
During stress, the cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation

Regulation of Heart Rate (HR)

The sinoatrial (SA) node is the heart's rhythm generating center
The SA node has intrinsic activity of about 100 action potentials/min
Resting heart rate is considerably lower than the SA node's intrinsic activity
The SA node is regulated by the autonomic nervous system (ANS)
- Sympathetic activity:
  - Noradrenaline and adrenaline acting on β1 adrenergic receptors
  - Effect: heart rate increases
- Parasympathetic activity:
  - Vagus nerve (cranial nerve X) via acetylcholine acting on muscarinic receptors
  - Effect : heart rate decreases
  - Other factors influencing HR
    - Positive chronotropic factors (increase heart rate):
      - Adrenaline, caffeine
    - Negative chronotropic factors (decrease heart rate):
      - Beta-blockers, such as Propranolol
Tachycardia: abnormally fast heart rate (>100bpm), can lead to fibrillation if persistent
Bradycardia: heart rate slower than 60 bpm

Regulation of Stroke Volume (SV)

Intrinsic control:
- If ventricular wall is stretched before contraction, contractile force increases
- Increased End Diastolic Volume (EDV) (meaning the ventricle chamber is stretching and putting pressure on the ventricular wall) → SV ↑ → CO ↑
Extrinsic control:
- Sympathetic stimulation:
  - Noradrenaline ( & adrenaline injection) acting on β1 adrenergic receptors
  - Effect: increased contractile force

Cardiovascular Changes Associated with Physical Activity

High intensity interval training (HIIT) has the most significant effects in reducing BP in hypertensive individuals.
Average blood pressure is 93 mL/g of mercury
The heart pumps 5L/min → cardiac output
Blood vessel (BV) branching
- Coronary vessels → 5%
- Brain → 15%
- Gut → 25%
- Kidneys → 20%
- Muscles → 20% = 1 L/min is going to the muscles at REST = 3 mL/min/100g of muscle tissue at REST
- Skin → 5%
Less resistance = more blood flow = lower BP due to decreased SVR (systemic vascular resistance)
The sympathetic nervous system (SNS) innervates certain BVs to constrict
- During exercise:
  - SNS tells coronary arteries to dilate → relaxes the brain and heart
  - SNS constricts the gut → stops 25% of CO to the gut
  - SNS constricts the kidney by a small percent
  - SNS dilates muscles significantly
  - SNS constricts the skin significantly
  - Blood redistribution: 30% of blood is being redirected from the gut to skin, mainly to muscle tissues → increases 1L/min to 20L/min in intense exercise → 200 mL/min/100g of muscle tissues of blood in athletes
SNS tells those BVs to dilate by increasing:
- Adrenaline
- Noradrenaline
- Nitric-oxide in BVs → tells them to relax
- Prostaglandins → another chemical that tells BVs to relax
SNS goes to the heart:
- Increased contraction
- Increased HR
During exercise:
- Significant increase in BP
- Increase in CO
- Increase in HR
- Increase in contractility → more blood gets pumped out
- Increase in SVR
- Increase in mean arterial pressure of mercury (93 mL/g), will continue to increase and can go up to 170 mL/g of mercury
After exercise, a reflexive drop in SNS
- Decrease in adrenaline at REST
- Decrease in noradrenaline at REST
- Maintained increased nitric-oxide
- Maintained increased prostaglandins
- Nitric-oxide and prostaglandins → tells BVs to relax and dilate = drops SVR, heart output back to normal rate, contractility back to normal rate, BV resistance will be reduced (easier for blood to move), BP is lower
Individuals with hypertension can benefit from increased BP during exercise

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Description

This quiz covers key concepts of smooth muscle histology, including the structure and functions of smooth muscle cells. Additionally, it explores the regulation of blood flow and pressure, highlighting the relationship between cardiac output and total peripheral resistance. Test your understanding of these critical physiological mechanisms.