Urinary System

Function of kidney

* Filters blood
* Produces **filtrate**
* Next, kidneys process the filtrate
* Toxins/wastes can leave the body
* Needed substances get returned to the blood

Urine

Refined filtered blood

Function of ureter (+ how does it accomplish this function)

Carry urine from the kidneys (via peristalsis) to the bladder for temporary storage

Function of urinary bladder

Temporarily stores urine

Function of urethra

Drains the bladder

Nephron-glomerulus (function, environment)

* Functional unit of the kidney
* Blood is processed in a **porous, high pressure** capillary cluster
* **Filtration occurs in the glomerulus**
* Water and small molecules are forced out
* Much of their filtrate the body needs to keep
* The filtrate is **concentrated and refined in various tubules** and leaves the body as urine

Function of Bowman’s (glomerular) capsule

Where filtrate collects

Function of tubules

* Filtrate moves through tubules
* Most water is reabsorbed
* Ions and small molecules selectively reabsorbed

Urine formation: filtration (where does this occur, where does filtrate go)

* Glomerulus
* Blood passes through capillaries in glomerulus and is filtered into Bowman’s capsule

Urine formation: tubular reabsorption (+ where does most reabsorption happen)

* Filtrate moves through tubules and water, glucose, amino acids, and various ions are reabsorbed back into the blood
* Waste products are not absorbed
* Most (75-80%) happens in proximal convoluted tubule

Urine formation: tubular secretion

Substances in blood move to tubules to be excreted

What does filtrate contain?

Filtrate includes water and small molecules (i.e. ions, glucose, amino acids NOT large molecules like RBCs and large proteins) 

Glomerulus (characteristics/capillary types, supplied/drained by, function)

* Cluster of fenestrated capillaries
* Porous
* HIGH pressure
* Supplied by afferent arteriole
* Drained by efferent arteriole
* Filtration occurs here

What happens to large substance that do not become filtrate?

They are reabsorbed into the blood

Urinary system: electrolytes

The urinary system helps maintain homeostasis through the regulation of electrolyte levels

Kidneys: acid-base balance

* Kidney can remove acid to urine
* Helps keep blood at correct pH

Kidneys: blood pressure regulation (associated system, what supplies relevant substances)

* Renin-angiotensin-aldosterone system (RAAS)
* Renin from juxtaglomerular cells
* Aldosterone from adrenal cortex

Medulla and salt concentration

* Medulla has salt gradient
* Descending loop
* Permeable to water
* Water reabsorbed to body (water leaves filtrate)
* Ascending loop
* NOT permeable to water
* Solutes resorbed actively and passively (solutes leave filtrate)

What is specific gravity?

Measure of solids in a solution

What does the specific gravity of urine mean?

The specific gravity of urine is higher than that of water, meaning that urine has more solutes

Color of urine

* Pale yellow to amber in color
* Color represents solute concentration
* Darker = more solute

What should/should not be in urine

Normal contents:


1. Water (\~95% of volume)
2. Nitrogenous wastes


1. Urea
2. Creatinine
3. Uric acid

Abnormal contents:


1. Any large molecules
2. Significant amounts of glucose, ketones, proteins, RBC/WBCs
3. Any crystallized substances

Relation of blood and urine

Urine is refined filtered blood

Male vs. female urethra

Males have a longer internal and external urethra that passes through their prostate

Retroperitoneal

* Means behind the peritoneum
* The kidneys are behind the peritoneum