Health Science II SAQ PP

Regulation of Blood Pressure, Salt, and Water Balance

RAAS (Renin-Angiotensin-Aldosterone System)

• Function: Regulates blood pressure, salt, and water balance.
• Steps:
  • Renin release is triggered by low blood pressure or decreased sodium.
  • Angiotensinogen is converted to Angiotensin I by renin.
  • Angiotensin I is converted to Angiotensin II by ACE (Angiotensin-Converting Enzyme).
  • Angiotensin II functions:
    • Vasoconstriction to increase blood pressure.
    • Stimulates aldosterone release, leading to sodium and water retention.

Gastrointestinal Hormones

Gastrin and Cholecystokinin (CCK)

• Structural-Activity Relationship:
  • Share amino acid identity at the carboxyl terminal.
  • Functions influenced by structural similarities.

Gastrin

• Physiological Functions:
  • Stimulates gastric acid secretion by parietal cells.
  • Promotes gastric mucosa growth.

Cholecystokinin (CCK)

• Physiological Functions:
  • Stimulates gallbladder contraction to release bile.
  • Stimulates pancreatic enzyme secretion.
  • Reduces gastric motility and inhibits gastric emptying.

Gastric Emptying

Major Factors Slowing Gastric Emptying

• Presence of fats and proteins in the duodenum.
• Low pH (acidic chyme) entering duodenum.

Protein Regulators

• CCK:
  • Released by intestinal I-cells.
  • Inhibits gastric motility and gastric emptying.
• GIP (Gastric Inhibitory Polypeptide):
  • Released by intestinal K-cells.
  • Stimulates insulin release, inhibits gastric acid secretion, and reduces gastric motility.
• Secretin:
  • Released by intestinal S-cells.
  • Stimulates bicarbonate secretion from the pancreas to neutralize acid.
  • Inhibits gastric acid secretion.

Glomerular Filtration Rate (GFR)

Major Forces Determining GFR

• Hydrostatic and Oncotic Pressure:
  • Glomerular capillary hydrostatic pressure promotes filtration.
  • Oncotic pressure and Bowman's space hydrostatic pressure oppose filtration.
• Normal GFR Value: Approximately 125 mL/min.

Pulmonary Gaseous Exchange

Factors Affecting Efficiency

• Surface area of alveoli.
• Thickness of respiratory membrane.
• Partial pressure gradients.
• Ventilation-perfusion coupling.

Resting Membrane Potential (RMP)

Contributing Factors

• Differences in ion concentration across the membrane.
• Permeability of the membrane to ions.
• Significance:
  • Essential for action potential generation and cellular communication.

Neuron Specialization

Communication and Integration

• Dendrites: Receive signals.
• Cell Body: Integrates signals.
• Axon Hillock: Action potential initiation.
• Axon: Transmits signals.
  • Myelin sheath aids rapid signal transmission.

Acid-Base Disturbances

Types and Compensation

• Acidosis: Blood pH < 7.35.
• Alkalosis: Blood pH > 7.45.
• Compensation: Respiratory or renal adjustments to restore pH balance.

Hormonal Regulation

Three Classes of Hormones

1. Peptide Hormones
2. Steroid Hormones
3. Amino Acid-Derived Hormones

Differences Affecting Function

• Receptor Location: Cell surface or intracellular.
• Administration Routes: Oral, injection, etc.
• Heat and Enzymatic Sensitivity

Endocrine Pathways in GI Regulation

Neurocrine, Endocrine, Paracrine

• Neurocrine: Nervous system triggers hormone release.
• Endocrine: Hormones released into the bloodstream.
• Paracrine: Local hormone action.

Example - CCK

• Released in response to fatty acids/amino acids.
• Triggers pancreatic enzyme release and gallbladder contraction.

Homeostatic Control in Body Systems

Baroreceptor Reflex

• Components:
  • Sensors: Detect blood pressure changes.
  • Control Center: CNS processes signals.
  • Effectors: Adjust heart rate, vascular resistance.
• Feedback: Negative, to maintain stable internal environment.

Importance of Unidirectional Signal Flow

• Structural specialization in synapses ensures directionality.
• Refractory periods prevent backward signal propagation.