Anatomy and Physiology for Nurses

Anatomy (the study of body structures) and physiology (the study of body functions) are foundational sciences for nursing practice. A nurse in any clinical setting — from a medical-surgical ward in Tawam Hospital to a pediatric clinic in Dubai Health Authority — must understand normal anatomy and physiology to recognize abnormal findings, monitor patient status, anticipate complications, and communicate effectively with physicians and other healthcare professionals. This chapter covers the major body systems relevant to the HAAD nursing examination.

The Cell: Basic Unit of Life

The cell is the structural and functional unit of all living organisms. While cells vary enormously in size, shape, and specialized function, they share common features:

Cell membrane: A phospholipid bilayer with embedded proteins that controls what enters and exits the cell (selectively permeable). It contains receptor proteins for hormones and neurotransmitters.

Cytoplasm: The gel-like substance within the cell (cytosol + organelles) where metabolic reactions occur.

Key organelles:

• Nucleus: Contains DNA (genetic material); controls cell activities; site of RNA synthesis
• Mitochondria: “Powerhouse of the cell” — site of ATP production through oxidative phosphorylation; have their own DNA
• Ribosomes: Site of protein synthesis (translation of mRNA)
• Endoplasmic reticulum (ER): Rough ER (studded with ribosomes — protein modification and transport); Smooth ER (lipid synthesis, drug detoxification)
• Golgi apparatus: Modifies, packages, and ships proteins to their destinations
• Lysosomes: Contain digestive enzymes; break down worn-out organelles and foreign material (phagocytosis)
• Centrosome: Organizes microtubules; involved in cell division

Cell division:

• Mitosis: Somatic cells divide to produce two identical daughter cells (for growth and repair)
• Meiosis: Germ cells divide to produce gametes (sex cells — sperm and eggs) with half the chromosome number; produces genetic variation

The Integumentary System

The skin is the largest organ of the body (approximately 2 m² in adults; 15% of body weight). It consists of three layers:

Epidermis: Outermost layer; avascular; composed of keratinized stratified squamous epithelium. Layers from superficial to deep: stratum corneum, lucidum (only in palms/soles), granulosum, spinosum, basale (germinativum — stem cells divide here). Melanocytes in the basale produce melanin (skin pigment).

Dermis: Middle layer; vascular; connective tissue containing collagen and elastin fibers; contains nerve endings, hair follicles, sebaceous glands, sweat glands, blood vessels.

Subcutaneous tissue (hypodermis): Innermost layer; adipose tissue (fat); attaches skin to underlying structures; insulation and energy storage.

Functions of the skin: Protection (barrier against pathogens, UV radiation, dehydration); temperature regulation (sweating, vasodilation/vasoconstriction); sensory reception (touch, pressure, temperature, pain); vitamin D synthesis (UVB converts 7-dehydrocholesterol to cholecalciferol/vitamin D3); excretion (sweat — water, salts, urea).

The Musculoskeletal System

Bones

The adult skeleton has 206 bones divided into two main divisions:

Axial skeleton (80 bones): Skull (cranium + facial bones), vertebral column (7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, 4 fused coccygeal), thoracic cage (12 pairs of ribs + sternum).

Appendicular skeleton (126 bones): Upper limbs (shoulder girdle — clavicle and scapula; humerus, radius, ulna; 8 carpal bones; 5 metacarpals; 14 phalanges), Lower limbs (pelvic girdle — ilium, ischium, pubis; femur, tibia, fibula; 7 tarsal bones; 5 metatarsals; 14 phalanges), pectoral and pelvic girdles.

Bone types: Long bones (humerus, femur), short bones (carpals, tarsals), flat bones (skull, sternum, scapula), irregular bones (vertebrae), sesamoid bones (patella).

Bone tissue: Compact (outer layer — dense, provides strength) and spongy (inner layer — trabecular, red marrow for hematopoiesis). Bones are composed of osteoblasts (bone-forming cells), osteoclasts (bone-resorbing cells), and osteocytes (mature bone cells).

Joints

Types of joints:

• Synovial (diarthrotic): Free movement; joint cavity with synovial fluid; includes hinge (elbow), ball-and-socket (hip, shoulder), pivot (atlantoaxial), condyloid (wrist), saddle (thumb CMC), gliding (intercarpal)
• Cartilaginous (amphiarthrotic): Slight movement; bones separated by cartilage — symphysis (pubic symphysis) and synchondrosis (costal cartilage)
• Fibrous (synarthrotic): Immovable; bones united by fibrous tissue — sutures (skull), gomphoses (teeth in sockets), syndesmoses (distal tibiofibular joint)

Muscles

Types of muscle tissue:

• Skeletal (voluntary): Attached to bones; striated; under conscious control; responsible for movement, posture, and breathing
• Cardiac (involuntary): Found only in the heart; striated; autorhythmic (pacemaker cells); intrinsic contraction
• Smooth (involuntary): Walls of hollow organs and blood vessels; non-striated; controlled by autonomic nervous system, hormones, local factors

Muscle contraction mechanism (Sliding Filament Theory):

1. Nerve impulse arrives at neuromuscular junction
2. Acetylcholine released → binds to receptors on muscle cell membrane
3. Depolarization spreads through T-tubules → sarcoplasmic reticulum releases Ca²⁺
4. Ca²⁺ binds troponin → tropomyosin moves → myosin binding sites on actin exposed
5. Myosin heads bind to actin → power stroke (actin slides over myosin)
6. ATP binds to myosin → detachment from actin
7. ATP hydrolysis re-cocks myosin head

Key muscle groups: Quadriceps (knee extension), Hamstrings (knee flexion, hip extension), Biceps (elbow flexion), Triceps (elbow extension), Deltoid (shoulder abduction), Gluteus maximus (hip extension), Gastrocnemius/soleus (plantar flexion — walking, standing).

The Cardiovascular System

The cardiovascular system consists of the heart, blood vessels, and blood — it transports nutrients, oxygen, hormones, and waste products throughout the body.

The Heart

Location: In the mediastinum, between the lungs, two-thirds to the left of midline, posterior to the sternum.

Four chambers:

• Right atrium: Receives deoxygenated blood from the body via superior and inferior vena cavae
• Right ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery (only artery carrying deoxygenated blood)
• Left atrium: Receives oxygenated blood from the lungs via pulmonary veins (only veins carrying oxygenated blood)
• Left ventricle: Pumps oxygenated blood to the body via the aorta (thickest wall — 3x thicker than right ventricle)

Cardiac conduction system: SA node (sinoatrial node — the natural pacemaker, 60–100 bpm) → AV node (atrial-ventricular node — slight delay to allow atrial contraction to complete) → Bundle of His → Right and left bundle branches → Purkinje fibers → Ventricular muscle contraction.

Cardiac cycle: Diastole (relaxation — ventricles fill) → Atrial systole (atrial contraction — “atrial kick,” completes ventricular filling) → Ventricular systole (contraction — ejection) → Isovolumetric relaxation.

Cardiac output (CO) = HR × SV:

• Normal CO = 70 bpm × 70 mL/beat = ~5 L/min
• Stroke volume determined by preload (venous return), afterload (arterial resistance), and contractility

Blood Vessels

Arteries: Carry blood away from the heart (usually oxygenated except pulmonary artery); thick muscular walls to withstand high pressure; smallest arteries are arterioles (site of major resistance). Capillaries: One cell thick; site of exchange (nutrients, gases, waste); only place where exchange occurs. Veins: Carry blood toward the heart (usually deoxygenated except pulmonary veins); thin walls; contain valves (especially in legs) to prevent backflow; large diameter → low resistance → blood pools here (capacitance vessels).

Major arteries: Aorta → common carotid → subclavian → brachial → radial/ulnar; Aorta → iliac → femoral → popliteal → anterior/posterior tibial. Major veins: Internal jugular → subclavian → brachiocephalic → SVC; Great saphenous vein (longest vein in body — surface); Small saphenous vein.

The Respiratory System

Anatomy:

• Upper respiratory tract: Nose, nasopharynx, oropharynx, laryngopharynx, larynx (contains vocal cords)
• Lower respiratory tract: Trachea (cartilaginous rings — C-shaped to allow food passage through esophagus behind it) → Carina (bifurcation at T4/T5) → Right main bronchus (wider, shorter, more vertical than left — so aspirated objects more commonly go right) → Bronchi → Bronchioles → Terminal bronchioles → Respiratory bronchioles → Alveolar ducts → Alveoli.

Alveoli: ~300 million alveoli in adult lungs; provide ~75 m² of surface area for gas exchange; extremely thin walls (0.1–0.5 µm); surrounded by pulmonary capillaries; Type I pneumocytes (gas exchange) and Type II pneumocytes (produce surfactant).

Surfactant: A phospholipid-protein mixture produced by Type II pneumocytes that reduces surface tension in alveoli, preventing their collapse during expiration. Deficiency in premature infants → Respiratory Distress Syndrome (RDS) of the newborn.

Pulmonary ventilation: Inspiration (active — diaphragm contracts, external intercostals contract → thoracic cavity expands → intrapulmonary pressure drops below atmospheric → air rushes in) and expiration (passive — muscles relax → elastic recoil → intrapulmonary pressure rises → air expelled).

Gas exchange: Occurs by diffusion across the alveolar-capillary membrane. Partial pressure gradients drive oxygen into blood and CO₂ out.

Lung volumes: Tidal volume (TV) ~500 mL; Inspiratory reserve volume (IRV) ~3000 mL; Expiratory reserve volume (ERV) ~1200 mL; Residual volume (RV) ~1200 mL. Vital capacity (VC) = TV + IRV + ERV ≈ 4700 mL.

The Nervous System

Central nervous system (CNS): Brain (cerebrum — conscious thought, voluntary movement; cerebellum — coordination and balance; brainstem — cardiorespiratory centers) and spinal cord (31 pairs of spinal nerves; reflex arcs).

Peripheral nervous system (PNS): Somatic nervous system (voluntary — skeletal muscle) and autonomic nervous system (involuntary):

• Sympathetic (fight or flight): Dilates pupils, accelerates HR, increases BP, bronchodilation, inhibits digestion, increases blood glucose
• Parasympathetic (rest and digest): Constricts pupils, slows HR, decreases BP, bronchoconstriction, stimulates digestion

Neurons: Cell body (soma), dendrites (receive signals), axon (conducts signals away). Most neurons are amitotic (cannot divide) — neurons lost are not replaced.

Neurotransmitters: Acetylcholine (neuromuscular junction, parasympathetic), norepinephrine (sympathetic), dopamine (reward, movement), serotonin (mood, sleep), GABA (inhibitory), glutamate (excitatory).

⚡ Exam tip: The left ventricle has the thickest wall of all heart chambers — it pumps blood to the entire body (systemic circulation). The right ventricle pumps only to the lungs (pulmonary circulation). Blood flows: RA → RV → lungs → LA → LV → body → RA. Surfactant is produced by Type II pneumocytes — deficiency causes RDS in premature infants.

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