Urinary System

Regulation of blood ionic composition

Na⁺, K⁺, Ca²⁺, Cl⁻, and phosphate.

Regulation of blood pH

Excreting H+ and conserving HCO₃⁻

Regulation of blood volume

Conserving or eliminating water.

Regulation of blood pressure

Secreting renin and adjusting renal resistance.

Production of hormones

Calcitriol (Vitamin D) and Erythropoietin (RBC production).

Excretion of wastes

Ammonia, urea, bilirubin, creatinine, and uric acid.

Location

Retroperitoneal (behind the peritoneal lining) in the posterior abdominal wall.

Renal Capsule

Deepest; fibrous sheet maintaining kidney shape.

Adipose (Fat) Layer

Middle; cushions against trauma and anchors the kidney.

Renal Fascia

Superficial; thin connective tissue anchoring the kidney to surrounding structures.

Urinary System

Kidneys → Ureters → Urinary Bladder → Urethra.

Cortex

Outer light-colored region of the kidney.

Medulla

Inner darker region containing pyramids.

Lobe

One pyramid plus its overlying cortex.

Flow of Urine

Papilla (apex of pyramid) → Minor Calyx → Major Calyx → Renal Pelvis → Ureter.

Filtration

The process occurring in the renal corpuscle where fluid is forced out of the blood.

Glomerulus

A capillary network involved in filtration.

Bowman's Capsule

The structure that encases the glomerulus.

Afferent arteriole

The arteriole that is larger in diameter, creating high pressure for filtration.

Efferent arteriole

The arteriole that is smaller in diameter compared to the afferent arteriole.

Glomerular Blood Hydrostatic Pressure (GBHP)

The pressure that promotes filtration by forcing fluid out of the glomerulus.

Blood Colloid Osmotic Pressure (BCOP)

The pressure that opposes filtration by pulling fluid back into the capillaries.

Capsular Hydrostatic Pressure (CHP)

The pressure that opposes filtration within the Bowman's capsule.

Fenestrated Capillary

A type of capillary that prevents formed elements like RBCs, WBCs, and platelets from leaving.

Basal Lamina

A layer that prevents large proteins from leaving the glomerulus.

Podocytes

Cells that prevent medium and small proteins from leaving during filtration.

Alterations in Filtration

High blood pressure increases GBHP; liver disease decreases BCOP.

Autoregulation

Mechanism by which blood flow is maintained despite changes in blood pressure.

Myogenic Autoregulation

Smooth muscle in afferent arteriole contracts when stretched (high BP) to slow flow.

Tubuloglomerular Autoregulation

Macula densa cells sense high $Na^+$/$Cl^-$ and inhibit Nitric Oxide (NO) to constrict the afferent arteriole.

Sympathetic Nervous System

Constricts renal vessels to divert blood to heart/muscles during stress.

Parasympathetic Nervous System

Controls bladder contraction (micturition).

RAA (Renin-Angiotensin-Aldosterone)

Hormonal mechanism that increases blood pressure/volume.

ADH

Hormone that increases water reabsorption (retains water).

ANP

Hormone that increases excretion of $Na^+$ and water (lowers BP).

Blood Flow Pathway

Glomerulus -> Efferent Arteriole -> Peritubular Capillaries (cortical nephrons) or Vasa Recta (juxtamedullary nephrons).

Filtered Ions

Na⁺, K⁺, Ca²⁺

Nitrogenous Wastes

urea, uric acid, creatinine, uroblin

Reabsorption

Moving substances from the tubule back into the blood.

Secretion

Moving substances from the blood into the tubule (to be peed out).

PCT

Reabsorbs 100% of glucose and amino acids; 65% of water and $Na^+$.

Loop of Henle (LOH)

Concentrates urine. Juxtamedullary nephrons have long loops for high concentration.

DCT/Collecting Duct - Principal Cells

Reabsorb Na+ (Aldosterone) and Water (ADH).

DCT/Collecting Duct - Intercalated Cells

Secretes H+ to adjust blood pH.

Parathyroid Hormone (PTH)

Stimulates reabsorption of Ca2+ in the DCT.

Excretion Formula

excretion = (filtration + secretion) - reabsorption

Urea

From amino acid breakdown.

Uric Acid

From nucleic acid breakdown.

Creatinine

From creatine phosphate in muscle.

Urobilin

From hemoglobin breakdown.

Normal Urine

Clear/yellow, mild odor, pH 4.6-8.0, Specific Gravity 1.001-1.035.

Anuria

No urine output (<50ml/day).

Hematuria

Blood in urine.

Dysuria

Painful urination.

Calculi

Kidney stones.

Pyelonephritis

Kidney infection (starts as Cystitis/Bladder infection).

What are the normal ranges for pH, PaCO2, and HCO3?

pH (7.35-7.45), PaCO2 (35-45), HCO3 (22-26)

What determines the cause of acid-base imbalance?

The factor (CO2 or HCO3) that matches the pH direction (Acid or Base) is the cause.

What condition is indicated by a pH of 7.20 and a PaCO2 of 50?

Respiratory Acidosis.