Learning Objectives
Master the Physiology of Normal Aging across all major organ systems. Understand the transition from peak function to a state of increased susceptibility to disease, driven by genetic, epigenetic, and metabolic alterations such as telomere shortening and mitochondrial dysfunction.
1. Cardiovascular & Respiratory Systems
Aging in the thoracic cavity is characterized by structural stiffness and a loss of elastic recoil, leading to reduced physiological reserves and altered lung volumes.
| System | Key Physiological Shifts | Structural Hallmarks |
|---|---|---|
| Cardiovascular | ↓ Arterial compliance (↑ stiffness), ↑ Aortic diameter, ↓ Max heart rate. | Sigmoid-shaped interventricular septum; Aortic/mitral valve calcification. |
| Respiratory | ↑ Lung compliance (↓ elastic recoil), ↓ Chest wall compliance (↑ stiffness), ↓ FEV1/FVC. | ↑ Residual Volume (RV), Unchanged TLC, ↑ A-a gradient, ↑ V/Q mismatch. |
2. Renal, Gastrointestinal & Immune Systems
The “internal milieu” shifts toward decreased filtration and a weakened adaptive immune response, often referred to as immunosenescence.
| System | Key Changes | Clinical Impact |
|---|---|---|
| Renal | ↓ GFR (↓ nephrons), ↓ Renal Blood Flow (RBF). | Voiding dysfunction (incontinence); ↓ hormonal function. |
| Immune | ↓ Naïve B and T cells; preserved memory cells. | Impaired response to new antigens (pathogens, vaccines). |
| Gastrointestinal | ↓ LES tone, ↓ gastric mucosal protection. | ↓ Colonic motility (constipation risk). |
Activity:
3. Musculoskeletal, Senses & Skin
Aging involves the progressive loss of structural integrity in the skin, bones, and muscles, alongside a decline in sensory acuity.
| System | Manifestation | Key Terms |
|---|---|---|
| Musculoskeletal | ↓ Muscle mass, ↓ Bone mass, and joint cartilage thinning. | Sarcopenia (muscle loss) and Osteopenia (bone loss). |
| Skin | Atrophy; ↓ Dermal collagen and elastin. | Solar elastosis (UVA photoaging); Senile purpura. |
| Special Senses | Impaired accommodation, ↓ hearing, ↓ smell/taste. | Presbyopia (vision) and Presbycusis (hearing). |
4. Nervous & Reproductive Systems
While brain volume and hormonal production decrease, functional capacity is often preserved until late in the aging process.
| System | Key Findings | Mechanism / Details |
|---|---|---|
| Nervous | ↓ Brain volume, ↓ Cerebral blood flow. | Mild cognitive decline; function generally preserved. |
| Reproductive (F) | Vulvovaginal atrophy, ↑ pH. | Exhaustion of ovarian follicles (↓ Estrogen). |
| Reproductive (M) | Prostate enlargement, Testicular atrophy. | ↓ Spermatogenesis: longer refractory period. |
Activity
High-Yield Mnemonics & Tips:
- Respiratory “Up/Down” Rule: ↑ RV, ↑ V/Q mismatch, ↑ A-a gradient, but Total Lung Capacity (TLC) stays the SAME.
- Immune “Memory” Rule: You keep your Memory cells (B & T), but you lose your Naïve cells. This is why seniors are at high risk for new infections.
- Sigmoid Septum: A classic USMLE imaging finding in elderly patients; a “bulge” in the septum due to myocardial hypertrophy that isn’t necessarily a disease.