Key points of the urinary system in the anatomy and physiology. Including hormones produced for the regulation of fluid. Including reflexes such as micturition and the storage reflex. Female vs. Male urethra.
Urinary System:
- Kidneys: Urine forming organ
- Ureter: Duct that channels urine from the kidney to the urinary bladder
- Urinary bladder: Smooth muscle-walled sac used for the temporary storage of urine
- Urethra: Tube through which urine is eliminated from the body
- In males, also serves as the duct for the passage of semen for the reproductive system
Primary Function
- Filter the blood, Remove waste products
- Convert the filtrate to urine and Eliminate the urine
Secondary functions
- Formation of calcitriol
- Production and release of erythropoietin
- Regulation of: Ion levels, Acid-base balance and Blood pressure (water levels)
- Potential to engage in gluconeogenesis
- General theme is that kidneys condition the blood
Location of the kidneys:
- Along the posterior abdominal wall
- Partially protected by the rib cage
- Between T12 & L3 vertebrae
- Left kidney sits slightly higher than right kidney
- Posterior to the parietal peritoneum
- Only anterior surface is covered called the retroperitoneal space
- Surrounded and supported by several tissue layers (inside to outside)
- Fibrous capsule
- Renal capsule
- Maintains kidney shape, protects it from trauma, serves as a barrier to pathogens
- Perinephric fat
- External to fibrous capsule
- Provides cushioning and support for kidney
- Renal fascia
- External to perinephric fat and Anchors kidney to surrounding structures
- Perinephric fat: Outermost layer surrounding kidney
Sectional Anatomy of the Kidney:
- Kidney is arranged into two distinct region
- Renal cortex = Outer region
- Renal medulla = Inner region
- Renal columns: Projections of the cortex that project into medulla and subdivide the medulla
into the renal pyramids
- Renal pyramids: Striated appearance
- Corticomedullary junction: Where base of pyramid lies against the cortex
- Renal papilla: Apex of pyramid
- Renal lobe: Another means of subdividing the kidney
- Consists of a pyramid, adjacent columnar material, and the renal cortex to the capsule
- Renal sinus : Urine drainage area, Medially located; organized into:
, - Minor calyces: Smallest; One for each pyramid
- Major calyces: 2-3 per kidney;Form from minor calyces
- Renal Pelvis: Forms from major calyces
- Hilum: Region through which the vessels, nerves, and ureter enter/exit into the kidney
- Renal arteries, Renal veins, Lymph vessels
- Nerves: Parasympathetic nerves from CN X (vagus) and Sympathetic nerves from T10 -
T12 of spinal cord
Nephron: Functional filtration unit of the kidney. Two major units:
- Renal corpuscle: Point of contact between the blood and the “filtering” tubule
- Renal tubule: Modifies the filtrate to create urine
- Both units reside primarily in the cortex
- Exception is the Nephron loop (Loop of Henle)
Renal Corpuscle:
- Glomerulus: Ball like tuft of capillaries
- H2O are solutes are filtered from the blood
- Composition of filtrate is similar to plasma but will eventually be converted to urine by
the tubular component
- Afferent Arterioles: Supply blood to the glomerulus
- Efferent Arterioles: Carry blood not filtered by the tubular component from the glomerulus
- Is an arteriole because no O2 or nutrients are delivered nor wastes picked up by
glomerulus
- Glomerular capsule: aka Bowman’s capsule
- Expanded double-walled invagination cupping the glomerulus
- Visceral layer directly overlays the glomerular capillaaries
- Parietal layer is the external impermeable layer of simple squamous epithelium
- Capsular space receives the filtrate
- Two opposing poles
- Vascular pole: Point where afferent and efferent arterioles connect with glomerulus
- Tubular pole: Point where renal tubule originates
Renal Tubule: Single tube, single layer of cells
- Proximal convoluted tubule (PCT): Located entirely within the cortex
- Contains filtered fluid
- Lined with simple cuboidal epithelium
- Tall, apical microvilli
- Nephron loop: aka Loop of Henle
- Hairpin loop that dips into the medulla
- Descending limb: Enters into medulla
- Ascending limb: Returns to cortex
- Both limbs have thick and thin segments
- Thick segments lined with simple cuboidal epithelium
- Thin segments lined with simple squamous epithelium
- Distal convoluted tubule (DCT): Extends beyond the thick segment of the ascending limb of the
Nephron loop
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