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Larry M. Frolich, Ph.D. Yavapai College, Dept. of Biology. Anatomy and Physiology of the Kidney: A micro-engineering marvel that maintains osmotic homeostasis in our body. Baseline physiology understanding is often common sense: What do you already know about the kidney and what it does?.
Yavapai College, Dept. of BiologyAnatomy and Physiology of the Kidney:A micro-engineering marvel that maintains osmotic homeostasis in our body
Baseline physiology understanding is often common sense: What do you already know about the kidney and what it does?
The Challenge: Appreciate the kidney’s elegant fluid flow engineering solution to minimizing fluid loss while maintaining osmotic balance and secreting metabolic waste products
To get there, we need to know:
Cortex has concentration of glomeruli where filtration happens
Medulla or core of pyramid appears striated due to oriented collecting ducts that unite into minor calyx at apex of pyramid
Minor calices are open spaces where urine collects at apex of pyramid
Minor calices empty into larger major calices which merge to form renal pelvis
Urine passes from renal pelvis into ureterInside the kidney
LAYERS OF URETER
Pronephric kidney in fetus shows segmental body plan
Fish with dorsal renal tissue lateral to vertebral column for most of length
In human, metanephric kidney migrates from inferior to superior
Variation in kidney shape not uncommon (horseshoe kidney
Ureter also from intermediate mesodermAscent of the kidney in development
Always oriented with glomerulus towards cortex, collecting duct heading towards calyx at apex of pyramid in center of kidneyNephron: the functional unit of the kidney(understand how one nephron works and you understand how the kidney works)
Reabsorption and Secretion: Proximal Convoluted Tubules
Concentration of Urine: Collecting Duct—Loop of Henle establishes concentration gradientHow does the kidney remove waste products from the blood and maintain osmotic balance in the body? (THE STORY OF BOWMAN AND HENLE)
Friedrich Gustav Jakob Henle
Sir William Bowman
Kidneys are 0.5% of total body weight but receive over 20% of blood pumped by the heart
Special epithelial cells (podocytes) surround capillary
Fenestrated endothelial cells of capillaries, and slits between podocytes allow plasma with dissolved solutes to leave blood at rapid rate and filter into capsular space
Molecules smaller than 3nm filter through including water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes. Proteins and cells are too large.Step 1. Filtration—Bowman’s Capsule/Glomerulus
Water, ions, and glucose are reclaimed from glomerular filtrate back into capillaries that surround tubule by reabsorption
Sodium is actively pumped across epithelial cells of tubule (Na-K pump using ATP)
Wastes including uric acid are secreted from blood in surrounding capillaries into interior of tubuleStep 2. Reabsorption and Secretion—PCT
Concentration gradient into center of medulla allows concentration of urine in collecting duct
Hormonal control of permeability of collecting duct membrane determines ultimate concentration of urineStep 3. Concentration—Collecting Duct. (Loop of Henle creates concentration gradient)
DIABETES AND THE PCT
Constant thirst and bed-wetting are symptoms of diabetes. Why?
High sugar levels in blood leads to high sugar levels in filtrate at glomerulus
This sugar-rich filtrate cannot be fully reabsorbed across proximal convoluted tubule resulting in higher volume of fluid, with dissolved sugar left in tubule.
This leads a need for more frequent urination (or bed-wetting in children) and frequent thirst to replace lost fluid
Early 20th century physicians diagnosed diabetes by tasting the patient’s urine!
AND THE LOOP OF HENLE