Structures and Functions of the Musculoskeletal, Respiratory and…

Table of Contents

Structures and Functions of the Musculoskeletal, Respiratory and Cardiovascular Systems

These three systems work as one functional unit during movement. The musculoskeletal system creates force and provides stability; the respiratory system supplies oxygen and removes carbon dioxide; the cardiovascular system transports gases, nutrients, hormones and heat. A physiotherapist must understand both the individual structures and the way they adapt together during rest, exercise, illness and recovery.

Why this integrated topic matters

Walking to a treatment area, transferring from bed to chair or completing a strengthening programme requires coordinated muscle contraction, joint control, ventilation and circulation. A problem in one system changes the demands on the others—for example, respiratory disease can cause muscle deconditioning, heart failure can limit exercise by reducing perfusion, and a painful joint can increase heart rate and breathing effort. Anatomy and physiology therefore guide safe assessment, dosage, monitoring and referral.

Learning outcomes

Describe the organisation and functions of bones, joints, skeletal muscles and connective tissues.
Explain how skeletal muscle produces movement and how joints provide stability and mobility.
Trace air from the upper airway to the alveoli and explain ventilation, gas exchange and respiratory control.
Describe the heart, blood vessels and circulation and relate cardiac output to exercise.
Explain how the three systems respond to physical activity and how pathology alters exercise tolerance.
Apply anatomy and physiology to physiotherapy assessment, positioning, exercise prescription and safety escalation.

1. Musculoskeletal system

The musculoskeletal system consists of bones, joints, skeletal muscles, tendons, ligaments, cartilage, fascia and associated connective tissues. It provides a framework for the body, protects organs, permits movement, maintains posture and stores minerals. Bone marrow also contributes to blood-cell formation.

1.1 Functions of the musculoskeletal system

Function	Structures involved	Physiotherapy significance
Support and posture	Skeleton, joints, ligaments, fascia and postural muscles	Alignment, balance, sitting tolerance and efficient gait depend on load sharing.
Movement	Skeletal muscles crossing joints, tendons, bones and neural control	Exercise restores strength, range, coordination and functional independence.
Protection	Skull, vertebral column, rib cage and pelvis	Protective anatomy explains precautions after fractures, spinal or thoracic injury.
Mineral storage	Bone matrix, especially calcium and phosphate	Bone density influences fracture risk, loading and fall-prevention advice.
Haematopoiesis	Red bone marrow	Anaemia or marrow disease may reduce exercise tolerance and recovery.
Heat production	Muscle contraction and shivering	Exercise produces heat; monitor hydration, environment and fatigue.

1.2 Bone structure and classification

A long bone has a shaft (diaphysis), expanded ends (epiphyses), a periosteum, compact bone, spongy bone, a medullary cavity and articular cartilage at joint surfaces. The periosteum contains vessels, nerves and cells involved in growth and repair. Compact bone provides dense outer strength; trabecular/spongy bone reduces weight and distributes loads.

Bone type	Examples	Functional value
Long	Femur, tibia, humerus, radius and ulna	Levers for movement and load transfer.
Short	Carpals and tarsals	Stability, shock distribution and small gliding movements.
Flat	Scapula, sternum, ribs and skull bones	Protection and broad muscle attachment.
Irregular	Vertebrae, facial bones and pelvis	Complex protection, weight transfer and attachment.
Sesamoid	Patella and small sesamoids in hands/feet	Protect tendons and improve the mechanical advantage of muscles.

1.3 Joints and connective tissues

A joint is a connection between bones. Joints are classified structurally as fibrous, cartilaginous or synovial and functionally according to the amount of movement allowed.

Fibrous joints: joined by dense connective tissue; most are stable with little movement, such as skull sutures.
Cartilaginous joints: joined by cartilage; permit limited movement, such as intervertebral discs and the pubic symphysis.
Synovial joints: have a joint cavity, articular cartilage, fibrous capsule, synovial membrane and fluid; examples include the shoulder, hip and knee.

Synovial type	Movement/example
Plane	Gliding; intercarpal and intertarsal joints.
Hinge	Flexion/extension; elbow and interphalangeal joints.
Pivot	Rotation; atlanto-axial and proximal radioulnar joints.
Condyloid	Flexion, extension, abduction, adduction; wrist and metacarpophalangeal joints.
Saddle	Thumb carpometacarpal joint; permits opposition.
Ball-and-socket	Multiaxial movement; shoulder and hip.

Ligaments connect bone to bone and guide or limit movement. Tendons connect muscle to bone and transmit force. Cartilage reduces friction and distributes compression. Fascia encloses and links muscles, vessels and organs, allowing force transmission and movement between tissue layers.

1.4 Skeletal muscle structure and contraction

A skeletal muscle is organised from whole muscle to fascicles, muscle fibres, myofibrils and sarcomeres. The sarcomere contains actin and myosin filaments. A motor neuron releases acetylcholine at the neuromuscular junction; an action potential travels along the muscle membrane and triggers calcium release. Calcium permits actin–myosin cross-bridge cycling, using ATP to generate tension.

Concentric contraction: muscle shortens while producing force, such as rising from a chair.
Eccentric contraction: muscle lengthens under tension, such as lowering into a chair or controlling a step down.
Isometric contraction: tension develops without visible joint movement, such as holding a bridge position.
Agonist, antagonist and synergist: muscles may produce the main movement, oppose it or assist/stabilise it.
Motor-unit recruitment: the nervous system increases force by recruiting more motor units and raising firing frequency.

1.5 Muscle fibre characteristics and adaptation

Feature	General description	Training/clinical link
Type I (slow oxidative)	Fatigue-resistant, rich in mitochondria and capillaries.	Important for posture and endurance; promoted by sustained low-to-moderate activity.
Type II (fast)	Higher force and power, fatigue more rapidly.	Needed for stairs, transfers and protective reactions; can weaken quickly with immobilisation.
Hypertrophy	Increase in muscle fibre size after progressive loading.	Supports strength rehabilitation when tissue healing permits.
Atrophy	Loss of muscle size/force from inactivity, denervation, disease or undernutrition.	Early mobilisation, graded exercise and adequate nutrition help prevent functional decline.

1.6 Physiotherapy application

Assess posture, alignment, active and passive range, muscle length, strength, tone, coordination, balance, gait and functional tasks.
Match loading to tissue healing, pain response, bone quality, cardiopulmonary reserve and the patient’s goals.
Use progressive overload, specificity, recovery and safe variation rather than increasing all exercise variables at once.
Teach joint protection, body mechanics, energy conservation and safe use of mobility or assistive devices.
Protect healing tissues and monitor for disproportionate pain, swelling, neurovascular change, fever or unexplained loss of function.

2. Respiratory system

The respiratory system includes the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, lungs, alveoli, pleura and respiratory muscles. Its principal functions are ventilation, gas exchange, acid–base regulation, voice production, smell and airway defence.

2.1 Conducting and respiratory zones

Nose/mouth filter, warm and humidify incoming air.
Pharynx and larynx conduct air; the epiglottis helps protect the airway during swallowing.
Trachea divides into right and left main bronchi, then lobar and segmental bronchi.
Bronchioles regulate airflow through smooth muscle and lead to terminal bronchioles.
Respiratory bronchioles, alveolar ducts, sacs and alveoli form the gas-exchange zone.

The right lung has three lobes; the left has two and a cardiac notch. Visceral pleura covers the lungs and parietal pleura lines the thoracic wall. Pleural fluid reduces friction, while negative intrapleural pressure helps maintain lung expansion.

2.2 Respiratory muscles and mechanics

Muscle/group	Action	Clinical observation
Diaphragm	Descends during inspiration, increasing thoracic volume.	Paradoxical or reduced movement may indicate weakness or fatigue.
External intercostals	Elevate ribs during inspiration.	Chest expansion and symmetry can be observed or palpated.
Accessory inspiratory muscles	Sternocleidomastoid, scalenes and pectorals assist when demand is high.	Neck/shoulder recruitment and tripod posture may indicate increased work of breathing.
Abdominal and internal intercostal muscles	Assist forced expiration and coughing.	Weakness can reduce cough effectiveness and secretion clearance.

During quiet inspiration, diaphragm contraction lowers pressure in the thorax and draws air in. Quiet expiration is mainly elastic recoil. Airflow depends on pressure gradients and airway resistance; narrowing, secretions or loss of elastic recoil increase the work of breathing.

2.3 Gas exchange and transport

In the alveoli, oxygen diffuses across the alveolar–capillary membrane into blood and carbon dioxide diffuses in the opposite direction. Efficient exchange requires adequate ventilation, perfusion, surface area, diffusion distance and haemoglobin. Oxygen is mainly carried bound to haemoglobin; carbon dioxide is mainly transported as bicarbonate.

Ventilation: movement of air into and out of the lungs.
Perfusion: blood flow through pulmonary capillaries.
Diffusion: movement across the respiratory membrane down a partial-pressure gradient.
Ventilation–perfusion matching: blood flow should reach adequately ventilated alveoli; mismatch reduces gas exchange.

2.4 Volumes, capacities and control

Term	Meaning	Why it matters in rehabilitation
Tidal volume	Air moved during a normal breath.	Changes with posture, exercise, pain and respiratory disease.
Inspiratory reserve volume	Extra air inhaled after a normal inspiration.	Reduced chest expansion can affect activity and secretion clearance.
Expiratory reserve volume	Extra air exhaled after a normal expiration.	May be reduced by obesity, abdominal pressure or restriction.
Residual volume	Air remaining after maximal expiration.	Increases with air trapping in obstructive disease.
Vital capacity	Maximum exhaled after maximum inhalation.	Useful when considering restrictive weakness or thoracic limitation.
Minute ventilation	Respiratory rate × tidal volume.	Rises during exercise; excessive effort or poor recovery is a warning.

The medulla and pons coordinate breathing. Chemoreceptors respond mainly to carbon dioxide, hydrogen ions and oxygen. Voluntary control can modify breathing briefly, but automatic control maintains ventilation during sleep and activity.

2.5 Respiratory physiotherapy

Assess respiratory rate, rhythm, depth, oxygen saturation, breath sounds when within scope, cough, sputum, chest expansion, posture and exercise response.
Use positioning, breathing control, thoracic expansion, active cycle of breathing, supported cough and airway-clearance techniques according to assessment and local protocol.
Progress mobilisation to prevent deconditioning, atelectasis, venous stasis and loss of functional independence when medically appropriate.
Teach inhaler technique or breathing strategies only within competence and in coordination with the prescribing team.
Stop activity and escalate for severe breathlessness, cyanosis, new confusion, chest pain, syncope, rapidly falling oxygen saturation or exhaustion.

Clinical scenario: secretion retention

A postoperative patient has shallow breathing, a weak cough and audible secretions. Check alertness, pain control, oxygenation and medical restrictions. Position safely, encourage supported breathing and coughing if appropriate, mobilise gradually and reassess. Escalate if the patient cannot clear secretions, develops worsening work of breathing or becomes hypoxaemic. Document objective findings and response rather than writing only “patient tolerated treatment.”

3. Cardiovascular system

The cardiovascular system consists of the heart, blood and blood vessels. It maintains tissue perfusion, transports oxygen and carbon dioxide, distributes nutrients and hormones, removes waste and contributes to temperature and acid–base regulation.

3.1 Heart structure

The heart lies in the middle mediastinum within the pericardial sac. The right atrium receives systemic venous blood; the right ventricle pumps to the lungs; the left atrium receives pulmonary venous blood; and the left ventricle pumps to the aorta. The tricuspid, pulmonary, mitral and aortic valves maintain one-way flow.

Venae cavae → right atrium.
Right atrium → tricuspid valve → right ventricle.
Right ventricle → pulmonary valve → pulmonary arteries → lungs.
Pulmonary veins → left atrium.
Left atrium → mitral valve → left ventricle.
Left ventricle → aortic valve → aorta → body.

3.2 Electrical conduction and cardiac cycle

SA node: initiates the normal rhythm and atrial depolarisation.
AV node: delays conduction so the ventricles can fill.
AV bundle and bundle branches: carry the impulse through the septum.
Purkinje fibres: distribute the impulse through ventricular myocardium.

Diastole allows filling; systole ejects blood. Cardiac output = heart rate × stroke volume. Preload, contractility and afterload influence stroke volume. During graded exercise, sympathetic stimulation generally increases heart rate and contractility, while venous return and cardiac output rise to support active muscles.

3.3 Blood vessels and circulation

Vessel	Structure/function	Physiotherapy relevance
Arteries	Thick, elastic or muscular walls carry blood away from the heart under higher pressure.	Palpable pulses and arterial disease influence exercise and wound healing.
Arterioles	Small resistance vessels that regulate tissue blood flow and pressure.	Vasoconstriction/vasodilation changes skin colour, temperature and exercise response.
Capillaries	Thin exchange vessels for gases, nutrients and waste.	Microcirculation affects tissue healing and oedema.
Venules and veins	Low-pressure return vessels with valves in many regions.	Calf-muscle pump, movement and compression may support venous return when appropriate.

3.4 Blood and its functions

Plasma: water, proteins, electrolytes, nutrients, hormones and waste.
Red blood cells: haemoglobin carries oxygen and contributes to carbon dioxide transport.
White blood cells: immune defence and inflammation.
Platelets and clotting proteins: haemostasis and repair.

3.5 Cardiovascular response to exercise

Response	Normal purpose	What to monitor
Heart rate rises	Raises cardiac output.	Excessive rate, irregular rhythm or slow recovery.
Stroke volume rises	More blood ejected per beat through increased venous return and contractility.	Fatigue, dizziness or signs of poor filling/perfusion.
Systolic blood pressure rises	Supports increased output.	Abnormal fall, excessive rise or symptomatic hypotension.
Blood flow redistributes	More flow to active muscle and skin; less to some inactive beds.	Skin colour, temperature, claudication and swelling.
Venous return increases	Muscle pump, respiratory pump and venoconstriction return blood to the heart.	Orthostatic symptoms and peripheral oedema.

3.6 Cardiovascular physiotherapy applications

Measure baseline pulse, blood pressure, oxygen saturation, respiratory rate, symptoms and perceived exertion when indicated.
Use graded aerobic conditioning, strengthening, breathing exercises, mobility and education according to diagnosis and prescribed limits.
Promote early mobilisation after illness or surgery while respecting lines, wounds, sternal precautions and haemodynamic stability.
Teach pacing, warm-up, cool-down, medication adherence support and warning symptoms without changing medication orders.
Assess falls risk, orthostatic response and peripheral circulation in patients with vascular disease or prolonged bed rest.

Red flags during activity

Stop and seek clinical review for new or worsening chest pressure, unexplained severe breathlessness, fainting, new neurological symptoms, pallor/cyanosis, sustained palpitations, severe blood-pressure abnormality or a patient who appears acutely unwell. Follow the facility’s emergency pathway and document the observed response.

4. Integration during movement

Step in a sit-to-stand	Musculoskeletal demand	Respiratory demand	Cardiovascular demand
Preparation	Foot placement, trunk flexion, anticipatory postural control.	Breath control and readiness.	Baseline perfusion and blood pressure.
Lift-off	Hip/knee extensors and ankle stabilisers generate force.	Increased ventilation begins.	Heart rate and venous return rise.
Extension	Hip and knee extension; balance reactions.	Oxygen demand increases.	Output redistributes to active muscle.
Recovery	Postural endurance and controlled breathing.	Ventilation returns toward baseline.	Monitor recovery time and symptoms.

5. Practical assessment checklist

Review diagnosis, precautions, medication effects, oxygen prescription, recent observations and functional goals.
Inspect posture, colour, swelling, breathing effort, movement quality and assistive equipment.
Record appropriate baseline vital signs and patient-reported symptoms.
Start with a low-risk task, explain the stop signal and keep the environment safe.
Monitor response during and after activity; compare with baseline rather than using a single number in isolation.
Stop, stabilise and escalate if symptoms or signs indicate deterioration.
Document dose, assistance, vital response, symptoms, education and plan.

6. Examination points and revision questions

High-yield points

Muscles create force, bones act as levers, joints guide movement and connective tissues stabilise or transmit load.
Gas exchange occurs across the alveolar–capillary membrane; ventilation and perfusion must be matched.
Cardiac output equals heart rate multiplied by stroke volume.
Arteries carry blood away from the heart; veins return blood; capillaries exchange substances.
Exercise responses must be interpreted alongside symptoms, diagnosis, medications and recovery.

Describe the structure and functions of a long bone and a synovial joint.
Explain the sliding-filament mechanism and distinguish concentric, eccentric and isometric contractions.
Trace air from the nose to the alveoli and explain how oxygen reaches skeletal muscle.
Compare the conducting and respiratory zones of the lungs.
Describe the chambers, valves and electrical pathway of the heart.
Explain how cardiac output and blood pressure change during graded exercise.
Discuss how respiratory, cardiovascular and musculoskeletal limitations combine to reduce walking tolerance.
List the observations that would make you stop a treatment session and escalate.

References for further study

Educational note: Apply local clinical protocols and prescribed precautions. This learning page does not replace medical review, supervised practical training or emergency procedures.