11.9 Pressures in the Body

Pressure in the human body is a vital force that keeps us alive and functioning. From blood circulation to breathing, pressure gradients drive essential processes. Understanding how pressure works in different body systems helps us grasp the complexities of human physiology.

Blood pressure, measured as systolic and diastolic, is a key indicator of cardiovascular health. Other important pressure systems include intraocular pressure in the eyes, intrapulmonary pressure in the lungs, and cerebrospinal fluid pressure in the spinal column. These pressures work together to maintain our body's delicate balance.

Pressures in the Human Body

Functions of pressure in human body

• Pressure plays a crucial role in maintaining homeostasis and facilitating various physiological processes
  • Pressure gradients enable the flow of fluids and gases throughout the body
    • Blood pressure drives blood circulation (systemic and pulmonary)
    • Pressure differences allow for gas exchange in the lungs (oxygen and carbon dioxide)
  • Hydrostatic pressure maintains the shape and structure of cells and tissues
    • Intracellular and extracellular fluid pressures maintain cell volume and prevent collapse (osmotic balance)
  • Pressure changes are essential for sensory functions
    • Changes in pressure are detected by sensory receptors, such as baroreceptors and mechanoreceptors (touch and proprioception)
    • These receptors help regulate blood pressure, respiration, and other physiological processes (homeostatic feedback loops)

Systolic vs diastolic blood pressure

• Blood pressure is the force exerted by blood against the walls of blood vessels
  • Systolic blood pressure (SBP) is the maximum pressure during heart contraction (systole)
    • Normal SBP range: 90-120 mmHg
  • Diastolic blood pressure (DBP) is the minimum pressure during heart relaxation (diastole)
    • Normal DBP range: 60-80 mmHg
• Measurement of blood pressure
  • Typically measured using a sphygmomanometer and stethoscope (Korotkoff sounds)
  • Automatic blood pressure monitors use oscillometric methods (pressure oscillations)
• Importance of blood pressure in cardiovascular health
  • Maintaining blood pressure within a normal range is essential for proper organ perfusion and function
  • Hypertension (high blood pressure) can lead to cardiovascular disease, stroke, and kidney damage (atherosclerosis, aneurysms)
  • Hypotension (low blood pressure) can cause dizziness, fainting, and inadequate organ perfusion (shock, syncope)

Pressure variations across body systems

• Eyes
  • Intraocular pressure (IOP) is the fluid pressure inside the eye
    • Normal IOP range: 10-21 mmHg
  • Elevated IOP (ocular hypertension) can lead to glaucoma and damage to the optic nerve (vision loss)
• Lungs
  • Intrapulmonary pressure changes during breathing
    • Inspiration: Pressure decreases, allowing air to flow into the lungs (negative pressure breathing)
    • Expiration: Pressure increases, forcing air out of the lungs (positive pressure breathing)
  • Maintaining appropriate pressure gradients is essential for efficient gas exchange (ventilation and perfusion)
• Spinal column
  • Cerebrospinal fluid (CSF) pressure protects the brain and spinal cord
    • Normal CSF pressure range: 5-15 mmHg (lumbar puncture)
  • Elevated CSF pressure (intracranial hypertension) can cause headaches, vision problems, and neurological deficits (hydrocephalus, pseudotumor cerebri)
• Bladder
  • Intravesical pressure increases as the bladder fills with urine
    • Normal bladder pressure: 10-20 cmH2O (at capacity)
  • Increased bladder pressure triggers the micturition reflex, signaling the need to urinate (stretch receptors)
• Skeletal structure
  • Weight-bearing bones and joints experience compressive forces due to gravity and muscle action
  • Proper distribution of pressure is essential for maintaining bone health and preventing fractures (Wolff's law)
    • Uneven pressure distribution can lead to conditions such as osteoarthritis and stress fractures (biomechanical stress)

Fluid dynamics in the body

• Blood flow in vessels is governed by principles of fluid dynamics
  • Bernoulli's principle explains the relationship between fluid velocity and pressure in blood vessels
  • Laminar flow occurs in straight, uniform vessels, while turbulent flow may develop in areas of vessel branching or narrowing
  • Viscosity of blood affects its flow characteristics and resistance to movement
  • Poiseuille's law describes the factors influencing flow rate in blood vessels, including vessel radius and length