mammalian lecture 4-23

Organic Anions and Renal Excretion

• Organic anions include bile salts, benzoylates, and subsalicylate.
• They are transported out of cells using the organic anion transporter, which relies on $ ext{alpha-ketoglutarate}$ to create a gradient of $ ext{dicarboxylates}$ for effective transport.
• Examples of substances excreted via this mechanism:
  • Bile salts
  • Aspirin
  • Artificial sweeteners (like saffron)
  • Preservatives from sodas

Urea and Penicillin Transport

• Urea is removed from the body via passive diffusion; it moves from high to low concentration.
• Early use of probenecid to prolong penicillin's effect:
  • Probenecid blocks penicillin's transport out through the organic anion transporter, thereby retaining penicillin in the system longer.

Kidney Filtration and Excretion

• The kidneys filter approximately 20% of the incoming blood; about 70% of that is effectively filtered, while the rest is reabsorbed or secreted.
• Excretion calculation:
  • Excreted amount = Filtered amount - Reabsorbed amount + Secreted amount.

Glomerular Filtration Rate (GFR)

• GFR is an important measure to evaluate kidney function.
• Can be calculated by measuring clearance rates of substances (e.g., creatinine):
  • Clearance rate formula:
    ext{Clearance} = rac{ ext{Excretion rate (mg/min)}}{ ext{Plasma concentration (mg/mL)}}
• Important to consider demographic differences: different clearance tables may be required for different populations (e.g. Caucasians vs. African Americans due to muscle mass differences).

Clearance Measurement

• Creatinine is a standard substance used to measure GFR; its levels are fairly consistent across individuals.
• Urine tests involve measuring creatinine clearance to estimate kidney function.
• 100% reabsorption is noted with inulin (used for GFR measurements) while glucose clearance is often zero in healthy individuals due to complete reabsorption.

Nephron Function

• Major nephron processes:
  1. Filtration - Occurs in the glomerulus; only here is blood filtered.
  2. Reabsorption - Can occur throughout the nephron.
  • Key substances reabsorbed: ions (sodium, chloride, potassium, calcium) and glucose in the proximal tubule.
  1. Secretion - Among substances secreted: urea and potassium.
  2. Excretion - Final step where urine is produced.
• Importance of potassium balance in kidney function:
  • Necessary for heart and neuronal functions.
  • Hypokalemia (low potassium) and hyperkalemia (high potassium) can affect heart rhythm and muscle function.

Micturition Process (Urination)

• Urine is stored in the bladder until micturition occurs.
• Internal and external sphincters control urination:
  • The internal sphincter is involuntary (smooth muscle).
  • The external sphincter is voluntary (skeletal muscle).
• Stretch receptors in the bladder signal fullness, triggering urination via parasympathetic stimulation and reflex responses.

Kidney Stones and Gout

• Kidney stones can form from crystallization of uric acid (related to gout) due to dehydration or high uric acid levels.
• Uric acid builds up when there is either excess production or insufficient excretion.
• Treatment for gout: anti-inflammatory agents and uricosuric agents (like Probenecid) increase urate excretion, but require adequate hydration to prevent kidney stones.

Immune System Overview

• Components of immunity involve distinguishing self vs. non-self entities (pathogens like bacteria, viruses).
• Innate Immunity:
  • Immediate and non-specific response.
  • Includes physical barriers (skin, mucous membranes) and immune cells (neutrophils, macrophages).
• Adaptive Immunity:
  • Specific response, longer to activate (weeks).
  • Involves T cells, B cells, and memory responses.

Main Cell Types in Immunity

• Neutrophils: Frontline responders against pathogens, responsible for pus formation.
• Monocytes/Macrophages: Engulf and digest pathogens; involved in tissue repair.
• Dendritic Cells: Antigen-presenting cells; process foreign material and activate lymphocytes.
• Natural Killer Cells: Attack virus-infected cells and cancerous cells.

Hematopoiesis and Lymphoid Tissues

• Hematopoiesis occurs in the bone marrow; produces various blood cells including leukocytes involved in immunity.
• Primary Sites: Bone marrow and thymus (for T cells).
• Secondary Sites: Spleen, lymph nodes, and mucosa-associated lymphoid tissues that facilitate immune responses.