BIO 140 Chapter 26: Urinary System Functions

Urinary System Functions

• The urinary system has three main functions: excretion, regulation, and synthesis
• Excretion functions: rid the body of organic wastes, excess nutrients, and aid the liver in detoxification
• Regulation functions: maintain blood plasma levels, blood volume, blood pressure, and blood pH, and regulate electrolyte balance and H+ levels in the blood

Regulation of Blood Pressure and Blood Volume

• The urinary system regulates blood pressure and blood volume by adjusting water retention and loss
• Erythropoietin production helps regulate blood pressure
• Renin hormone triggers the RAAS system to regulate blood pressure

Synthesis Functions

• The urinary system synthesizes erythropoietin, a factor for RBC production
• The system synthesizes calcitriol, the active form of vitamin D, which increases calcium absorption from the GI tract

Mechanisms of Urinary System Functions

• Filtration: filters waste out of the blood
• Reabsorption: reabsorbs necessary substances from the filtrate back into the bloodstream
• Secretion: secretes unnecessary substances from the bloodstream into the nephron
• Excretion: removes waste from the body

Major Structures of the Urinary System

• Kidneys: surrounded by perirenal fat and renal fascia, with a renal capsule and hilum
• Ureter: transports urine to the bladder
• Urinary bladder: has a trigone, urinary rugae, and detrusor muscles
• Urethra: has different regions in males and females, with internal and external sphincters

Kidney Sectional Anatomy

• Renal capsule: outermost fibrous covering
• Cortex: outermost functional layer
• Renal column: between renal pyramids, leads to calyxes
• Medulla: innermost functional layer, consists of renal pyramids and renal columns
• Renal pyramid: has a vertical osmotic gradient and vascularization

Renal Vasculature

• Renal artery: divided into interlobar, arcuate, and interlobular arteries
• Afferent arteriole: leads to the glomerulus
• Efferent arteriole: leads to the peritubular capillary
• Interlobular vein: leads to the renal vein

Nephron Structure and Function

• Nephron: the structural and functional unit of the kidney
• Consists of renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct
• Types of nephrons: cortical and juxtamedullary
• Renal corpuscle: holds the glomerulus and attaches to the PCT
• Glomerulus: has a capillary network, fenestrated capillaries, and a lamina densa
• Podocytes: have pedicels that form filtration slits

Proximal Convoluted Tubule and Loop of Henle

• PCT: has simple cuboidal epithelium with microvilli to increase absorption surface area
• Loop of Henle: has simple squamous epithelium and an ascending limb
• Distal convoluted tubule: has simple cuboidal epithelium without microvilli, and is influenced by adrenal cortex's corticosteroids

JG Apparatus and Collecting Duct

• JG apparatus: consists of juxtaglomerular cells and macula densa cells
• Important substances: renin and erythropoietin
• Collecting duct: has simple cuboidal epithelium and connects to the renal pelvis