Urinary System Functions Chapter 25

Functions of the Urinary System

• Regulates plasma ion concentrations, blood volume and pressure, and plasma pH.
• Conserves nutrients by limiting excretion.
• Eliminates organic wastes and synthesizes hormones.

Anatomy of the Urinary System

• The kidneys and pancreas are classified as retroperitoneal organs.
• The renal cortex is the outer portion of the kidney, typically lighter in color.
• The renal medulla is the inner portion of the kidney, consisting of renal pyramids.

Renal Structures

• Renal pyramids are triangular areas of tissue within the medulla.
• Renal columns are extensions of the cortex that separate the renal pyramids.
• Renal papillae are funnel-like structures at the ends of renal pyramids, leading to urine drainage.

Urine Drainage System

• Minor calyx collects urine from renal papillae and directs it to major calyces.
• Major calyx is formed by the convergence of several minor calyces and drains urine into the renal pelvis.
• Renal pelvis is where major calyces converge and leads to the ureter.

Nephron Structure and Function

• Each kidney contains approximately 1 million nephrons, the functional units of the kidneys.
• Nephrons consist of several segments including Bowman's capsule, proximal tubule, loops of Henle, distal tubule, and collecting duct.
• The flow of urine follows the pathway: collecting duct → papillary duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder.

Types of Nephrons

• Cortical nephrons primarily located in the renal cortex, making up 85% of nephrons with shorter loops of Henle.
• Juxtamedullary nephrons are situated near the medulla, contain vasa recta, and account for 15% of nephrons.

Epithelial Tissue in Nephrons

• Most renal tubular regions are lined with simple cuboidal epithelium, except for the nephron loop and certain limbs which have simple squamous epithelium.

Nephron Processes

• The three fundamental functions of nephrons include filtration, reabsorption, and secretion.
• Filtration occurs at the glomerulus, allowing blood plasma and substances to enter Bowman's capsule.
• Tubular reabsorption retrieves water, ions, and substances from the nephron back into the bloodstream.
• Tubular secretion moves wastes, drugs, and excess ions from peritubular capillaries into the nephron.

Renal Corpuscle and Associated Cells

• The renal corpuscle consists of Bowman's capsule and the glomerulus, where filtration occurs.
• Mesangial cells regulate glomerular filtration rate by contracting and adjusting blood flow through capillaries.
• Podocytes form filtration slits to filter smaller molecules during glomerular filtration.
• Macula densa cells monitor electrolyte concentration and regulate glomerular filtration by influencing arteriole constriction.

Hormonal Regulation

• Juxtaglomerular cells in the afferent arteriole secrete renin to help regulate blood pressure.
• Aldosterone from the adrenal cortex increases sodium reabsorption and potassium secretion in the distal tubule.
• Anti-diuretic hormone (ADH) increases water reabsorption in the distal tubule, helping maintain fluid balance.

Urinary Sphincters

• Internal urethral sphincter controls involuntary opening and closing of the urethra.
• External urethral sphincter consists of skeletal muscle allowing voluntary control over urination.

This quiz covers the essential functions of the urinary system, as outlined in Chapter 25. Participants will learn about the regulatory roles of the kidneys, as well as their anatomical significance. Get ready to test your knowledge on the key concepts associated with urinary function.