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

This quiz covers the three main functions of the urinary system, including excretion, regulation, and synthesis. It reviews the roles of the system in maintaining blood pressure, blood volume, and pH balance.