AP2 - Day 10 - Ch 19 pt 1_student.pdf

Chapter 19: The Kidneys

19.1 Functions of the Kidneys

• Kidneys maintain normal blood concentrations of ions and water.

• Key Roles:

  • Regulation of blood volume and composition.

  • Maintenance of electrolyte balance.

  • Homeostatic regulation of pH (H+ and HCO3-).

  • Excretion of metabolic wastes and xenobiotics.

  • Production of hormones such as EPO and conversion of Vitamin D to its active form.

19.2 Anatomy of the Kidneys

• The kidneys are located retroperitoneally at the level of the lower ribs.

• Urinary system components:

  • Renal arteries/veins

  • Ureters

  • Urinary bladder

  • Urethra

• Kidney structure:

  • Divided into an outer cortex and an inner medulla.

  • Contains nephrons (the functional unit of the kidney) which are critical for filtering blood.

19.3 Overview of Kidney Function/Physiology

• Nephrons play a vital role in urine formation through:

  • Filtration: Movement of fluid from blood to nephron.

  • Reabsorption: Moving substances from nephron back to blood.

  • Secretion: Adding substances from blood to nephron.

  • Excretion: Removing waste from the body as urine.

19.4 Filtration Process

• Filtration is a passive process similar to fluid filtration in systemic capillaries.

• Composition of filtrate: resembles plasma but lacks proteins.

• Key components of filtration barrier include:

  • Podocytes: Modified epithelial cells that surround glomerular capillaries, creating filtration slits.

  • Mesangial cells: Control blood flow by contracting.

  • Endothelium: Pores that allow passage of water and solutes.

Urine Analysis

• Urine appearance can indicate physiological states (e.g. darker urine suggests dehydration).

• Color chart-based indicators:

  • Beer-like color (dehydration)

  • Light yellow (well-hydrated)

Regulation of Filtration

• Glomerular Filtration Rate (GFR): Average filtration rate is 125 mL/min or 180 L/day.

• Factors influencing GFR:

  • Capillary hydrostatic pressure (blood pressure)

  • Colloid osmotic pressure (due to plasma proteins)

  • Capsule fluid pressure (pressure from fluid in Bowman's capsule)

• Myogenic response and tubuloglomerular feedback are mechanisms for autoregulation of GFR, maintaining stable kidney function despite fluctuations in systemic blood pressure.

Nephron Structure and Function

• The nephron consists of:

  • Bowman's capsule: Where filtration begins.

  • Proximal tubule: Site for reabsorption of nutrients.

  • Loop of Henle: Concentrates urine and maintains electrolyte balance.

  • Distal tubule: Further modifications of filtrate occur.

  • Collecting duct: Final adjustment of urine composition before excretion.

• Two types of nephrons:

  • Cortical nephrons (short loops)

  • Juxtamedullary nephrons (long loops for concentration).

Review Questions

1. What are the two capillary beds that make up the renal portal system?

   • glomerulus

   • Peritubular capillaries

2. What should filtrate consist of?

   • water and dissolved solutes

3. Describe the three filtration barriers in the order fluid passes through to become filtrate.

4. Which barrier contains podocytes?

5. What pressure is responsible for driving fluid out of glomerular capillaries?

6. Which pressures counteract filtration?