Skeletal and Cardiovascular Systems

Quick Answer: Bones adapt to mechanical loading through remodeling (Wolff's Law), with osteoblasts building and osteoclasts resorbing bone tissue. The cardiovascular system increases cardiac output (Q = HR x SV) during exercise, with typical maximal values around 20-25 L/min in trained athletes. Systolic blood pressure rises with exercise intensity while diastolic remains stable.

Bone Anatomy and Physiology

Bone Types

Bone Composition

Bone Cells

Wolff's Law and Bone Remodeling

Wolff's Law states that bone adapts to the loads placed upon it:

• Increased loading (weight training) → bone deposition → increased bone density
• Decreased loading (immobilization, bed rest) → bone resorption → decreased bone density

Bone Remodeling Process

1. Osteoclasts resorb old or damaged bone tissue
2. Osteoblasts deposit new bone matrix
3. Mineralization occurs over several weeks
4. Osteocytes maintain the mature bone tissue

Exam Tip: Weight-bearing and resistance exercises are particularly effective for increasing bone mineral density, making them important for osteoporosis prevention.

Factors Affecting Bone Health

Connective Tissue

Tendons

Ligaments

Cartilage

Key Point: Cartilage is avascular (no blood supply) and has very limited healing capacity when damaged.

Cardiovascular Anatomy

Heart Structure

The heart has four chambers and functions as two pumps:

Heart Valves

Blood Flow Pathway

1. Deoxygenated blood → Superior/Inferior vena cava → Right atrium
2. Right atrium → Tricuspid valve → Right ventricle
3. Right ventricle → Pulmonary valve → Pulmonary arteries → Lungs
4. Oxygenated blood → Pulmonary veins → Left atrium
5. Left atrium → Mitral valve → Left ventricle
6. Left ventricle → Aortic valve → Aorta → Body

Cardiac Output

Cardiac Output (Q) is the volume of blood pumped by the heart per minute:

Formula

Q = HR x SV

Where:

• Q = Cardiac output (L/min or mL/min)
• HR = Heart rate (beats/min)
• SV = Stroke volume (mL/beat)

Typical Values

Exam Tip: Resting cardiac output is similar in trained and untrained individuals (~5 L/min). The difference is that trained individuals achieve this with lower HR and higher SV (cardiac efficiency).

Factors Affecting Stroke Volume

Blood Pressure Responses to Exercise

Blood pressure is expressed as systolic/diastolic (mmHg):

Normal Values

Exercise Blood Pressure Responses

Expected systolic values during maximal aerobic exercise:

• Untrained: ~180-200 mmHg
• Trained: ~200-220 mmHg

Warning Sign: Failure of systolic BP to rise with increasing intensity or a drop during exercise may indicate cardiac dysfunction—contraindication for continued exercise.

Heart Rate

Maximum Heart Rate Estimation

Age-predicted HRmax = 220 - age

Important: This formula has a standard deviation of approximately 10-12 bpm. Individual variation is significant, and actual HRmax should be determined through maximal testing when precision is needed.

Training Heart Rate Zones

Oxygen Delivery: The Fick Equation

VO2 = Q x (a-vO2 difference)

Where:

• VO2 = Oxygen consumption (mL/min or L/min)
• Q = Cardiac output (L/min)
• a-vO2 difference = Arterial minus venous oxygen content (mL O2/L blood)

Typical Values

Exam Tip: Improvements in VO2max come from increases in both cardiac output (central adaptation) and a-vO2 difference (peripheral adaptation—improved oxygen extraction by muscles).