BIOL130 Lecture 11
Page 1: Introduction
Course: BIOL130 Human Physiology
Topic: The Urinary/Renal System focusing on the basic renal process.
Instructor: Giulia Gurun M.S. Ph.D. MCD Biology, UC Santa Cruz
Page 2: Understanding the Basic Renal Process
Multiple choice question regarding the renal process. Correct choice is:
E) Fluid is filtered from glomerular capillaries into Bowman's space.
Other options represent misconceptions about renal processes.
Page 3: Filtration in Nephrons
Nephrons filter small amounts of plasma:
Plasma moves from glomerular capillaries into Bowman’s space (filtrate).
Tubular Reabsorption: Substances removed from the filtrate back to the bloodstream.
Tubular Secretion: Substances added from blood to the filtrate.
Water reabsorption occurs, and excess is excreted in urine.
Page 4: Importance of Water Reabsorption
Discussion prompt on why most filtered water is reabsorbed.
Key reason: To maintain fluid balance and prevent dehydration.
Page 5: Plasma Filtration in Nephrons
Only ~20% of plasma entering glomerular capillaries is filtered into Bowman’s space.
Page 6: Importance of Limited Plasma Filtration
Discussion prompt on the significance of filtering only a fraction of plasma volume.
Key reason: To control composition and volume of plasma effectively.
Page 7: Types of Nephrons
Two main types of nephrons:
Cortical Nephrons:
Short loops of Henle and mainly peritubular capillaries.
Most common type.
Juxtamedullary Nephrons:
Long loops of Henle and vasa recta.
Involved in urine concentration, found between cortex and medulla (about 15% of nephrons).
Page 8: Capillaries Associated with Nephrons
Nephrons relate to:
Glomerular Capillaries: Specialized for filtration (high blood pressure).
Peritubular Capillaries: Allow exchanges for reabsorption and secretion.
Page 9: The Glomerulus
Glomerulus contains fenestrated capillaries:
Allows large amounts of solute-rich fluid to pass through.
Fluid is usually low in protein content due to size constraints.
Page 10: Filtration Membrane
Composed of podocytes with foot processes:
Generates filtration slits, working with fenestrae to filter blood.
Model for how fluid passes into Bowman’s space.
Page 11: Glomerular Filtration
Passive process driven by hydrostatic pressure:
High efficiency due to large surface area and high glomerular hydrostatic pressure.
Glomerular Filtration Rate (GFR): Volume filtered per unit time (~180L/day).
Page 12: Impact of High Blood Protein on GFR
Discussion on how conditions like hepatitis C leading to hyperproteinemia affect GFR.
Increased protein levels in blood could reduce filtration efficiency due to increased oncotic pressure.
Page 13: GFR Regulation
GFR is influenced by vascular changes in the afferent and efferent arterioles.
Physiological regulation adjusts net glomerular filtration pressure to maintain average GFR (180L/day).
Page 14: Calculating Filtered Load
Filtered load = GFR x plasma concentration of substance:
Example: Glucose at 1g/L results in 180g/day.
Comparison shows absorption vs secretion of substances.
Page 15: Break
Page 16: Regulation of Substance Transport
Transport of substances is regulated by:
Membrane channels/transporters in tubular epithelial cells.
Regulation occurs via hormones and local factors.
Page 17: Tubular Reabsorption
Movement from tubular lumen to blood:
Begins with the filtration entering the tubule.
Na+ reabsorption primarily occurs actively, influencing the reabsorption of other substances.
Page 18: Limits on Substrate Reabsorption
Transport maximum (Tm) limits the reabsorption rate of substances:
Hyperglycemia can lead to glucosuria when plasma glucose exceeds Tm.
Page 19: Tubular Secretion
Movement from blood (peritubular capillary) to tubular lumen:
Includes disposal of drugs, waste elimination, and pH control.
Page 20: Division of Labor in the Tubule
Main site of reabsorption is the proximal convoluted tubule:
Features microvilli and specific transport proteins for Na+ and other ions.
Distal convoluted tubule fine-tunes substance excretion.
Page 21: Understanding Water Reabsorption
Question regarding the nephron segment with the most water reabsorption:
Correct answer: A) The proximal tubule.
Page 22: Sodium and Water Renal Processes
Na+ and water are freely filtered:
Active transport of Na+ in all segments except descending limb.
Water follows Na+ reabsorption according to permeability.
Page 23: Coupling of Water and Sodium Reabsorption
Water follows as Na+, Cl-, and other ions are absorbed, occurring passively by osmosis.
Page 24: Water Movement Across Epithelium
Water reabsorption is determined by:
Presence of aquaporin water channels, highly expressed in proximal nephron.
Absence in collecting ducts without ADH activity.
Page 25: Muddiest Point
Students prompted to note unclear topics for further clarification during study or office hours.