Human Physio Renal function and fluid balance

# Structure & Function of the Urinary System

### Functions

* Regulation of extracellular fluid volume & blood pressure
* works with CVS to ensure tissues get enough O2 and BP within normal values
* Regulation of plasma osmolarity
* Maintenance of ion balance
* in response to diet intake, urinary loss helps to maintain proper levels of Na+, K+, Ca2+ ions
* Homeostatic regulation of pH
* remove or conserve either H+ or HCO3- (bicarbonate ions) as needed
* Excretion of waste
* removes metabolic wastes dissolved in plasma e.g. uric acid and creatine
* Secretion of hormones and enzymes
* erythropoietin (RBC production), renin (sodium balance and BP homeostasis) & vit D conversion to control Ca2+ balance

### Structure of nephron

the nephron is the functional unit of the kidney

Renal corpuscle filters blood plasma:

* Glomerulus capillary network
* Glomerular (Bowman’s) capsule double walled up surrounding glomerulus

Renal tubule filtered fluid passes into:

* proximal convoluted tubule
* descending, loop of henle (nephron loop) and ascending
* Distal convoluted tubule

Distal convoluted tubule of several nephrons empty into single collecting duct

## Renal exchange processes


* Urinary excretion of substance depends on its filtration, reabsorption and secretion.


### Glomerular filtration

Filtration barriers:

* Glomerular capillary endothelium
* Basal lamina
* Epithelium of Bowman’s capsule- podocytes



Forces that influence glomerular filtration:

* **Hydrostatic/blood pressure (55 mmHg)**
* pressure of flowing blood in glomerular capillaries
* favors movement of filtrate into Bowman’s capsule
* **Colloid osmotic pressure (30 mmHg)**
* plasma proteins entering capsule create a gradient that favors movement back into capillaries
* **Hydrostatic fluid pressure (15 mmHg)**
* in fluid up in enclosed Bowman’s capsule
* creates a gradient that favors movement back into capillaries

### Glomerular filtration rate (GFR)

* volume of fluid that filters into Bowman’s capsule per unit time
* average GFP 125mL/min or 180L/day
* Factors influencing GFP
* Net filtration pressure
* Filtration coefficient
* surface area of glomerular capillaries
* permeability between capillary & Bowman’s capsule
* 20% of plasma volume that pass through glomerulus is filtered
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