Chapter 15 The Urinary System

Functions of the Urinary System 1. Elimination of waste Nitrogenous wastes Toxins Drugs 2. Regulates homeostasis (kidney function) Water balance Electrolytes Acid-base balance in the blood Blood pressure RBC blood cell production Activation of vit. D

Organs of the Urinary system Kidneys Ureters Urinary bladder Urethra

Urinary System Organs Kidneys are major excretory organs Urinary bladder is the temporary storage reservoir for urine Ureters transport urine from the kidneys to the bladder Urethra transports urine out of the body

Location of the Kidneys Retroperitoneal - against dorsal wall T12 to L3 Right lower than left Attached to ureters, renal blood vessels, & nerves at renal hilus Atop kidney is adrenal gland

Anterior Inferior vena cava Aorta Peritoneal cavity (organs removed) Peritoneum Supportive tissue layers Renal vein • Renal fascia anterior posterior Renal artery • Perirenal fat capsule Body of vertebra L2 • Fibrous capsule Body wall (a) Posterior Figure 25.2a

Coverings of the Kidneys 1. Renal capsule Surrounds kidney 2. Adipose capsule protection keeps kidney in location

Regions of the Kidney Renal cortex – outer region Renal medulla – inside the cortex Renal pelvis – inner collecting tube

Kidney Structures Medullary pyramids – triangular regions of tissue in medulla Renal columns – extensions of cortex-like material inward Calyces – cup-shaped structures that funnel urine towards renal pelvis

(a) Photograph of right kidney, frontal section (b) Diagrammatic view Renal hilum Renal cortex Renal medulla Major calyx Papilla of pyramid Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule (a) Photograph of right kidney, frontal section (b) Diagrammatic view Figure 25.3

Blood Flow in the Kidneys

Blood and Nerve Supply Renal arteries deliver ~ 1/4 (1200 ml) of cardiac output to the kidneys each minute Arterial flow into and venous flow out of the kidneys follow similar paths Nerve supply is via sympathetic fibers from the renal plexus

Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein Cortical radiate vein Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein Interlobar artery Segmental arteries Renal vein Renal artery Renal pelvis Ureter Renal medulla Renal cortex (a) Frontal section illustrating major blood vessels Figure 25.4a

Nephrons Structural and functional units of the kidneys that forms urine About 1 million per kidney Main structures a. Glomerulus b. Renal tubule

Glomerulus Specialized tuft of capillaries Arterioles on both sides (maintains high pressure) Large afferent arteriole Narrow efferent arteriole Capillaries covered with podocytes from the renal tubule Glomerulus sits within a glomerular (Bowman’s) capsule (1st part of the renal tubule)

Figure 25.5

Nephrons Renal corpuscle Glomerulus + its Bowman’s capsule Allows filtrate to pass from plasma into the glomerular capsule

Renal Tubule Glomerular (Bowman’s) capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule

Figure 25.5

Renal Tubule Proximal convoluted tubule (PCT) Functions in reabsorption and secretion Loop of Henle with descending and ascending limbs Freely permeable to water Distal convoluted tubule (DCT) Function more in secretion than reabsorption

Types of Nephrons 1. Cortical 2. Juxtamedullary entirely in cortex most nephrons 2. Juxtamedullary at boundary of cortex & medulla

Nephrons Cortical nephrons—85% of nephrons; almost entirely in the cortex Juxtamedullary nephrons Long loops of Henle deeply invade the medulla Extensive thin segments Important in the production of concentrated urine

Peritubular Capillaries Arise from efferent arteriole Normal, low pressure capillaries Attached to venule Cling to renal tubule Reabsorb substances from collecting tubes Urine Formation Filtration Reabsorption Secretion

Kidney Physiology: Mechanisms of Urine Formation The kidneys filter the body’s entire plasma volume 60 times each day Filtrate Blood plasma minus proteins Urine <1% of total filtrate Contains metabolic wastes and unneeded substances

Mechanisms of Urine Formation Glomerular filtration Tubular reabsorption Returns all glucose and amino acids, 99% of water, salt, and other components to the blood Tubular secretion Reverse of reabsoprtion: selective addition to urine

Glomerular capillaries Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule Rest of renal tubule containing filtrate Peritubular capillary Three major renal processes: Glomerular filtration To cortical radiate vein Tubular reabsorption Tubular secretion Urine Figure 25.10

Filtration Nonselective passive process driven by hydrostatic presure Water and solutes smaller than proteins are forced through capillary walls (Filtrate same as blood plasma) Blood cells cannot pass out to the capillaries Filtrate - collected in glomerular capsule and leaves via the renal tubule

Afferent arteriole Glomerular capsule Glomerular (blood) hydrostatic pressure (HPg = 55 mm Hg) 10 mm Hg Blood colloid osmotic pressure (Opg = 30 mm Hg) Net filtration pressure Capsular hydrostatic pressure (HPc = 15 mm Hg) Figure 25.11

Glomerular Filtration Rate (GFR) Volume of filtrate formed per minute by the kidneys (120–125 ml/min)

Reabsorption Peritubular capillaries reabsorb - Some water, Glucose, Amino acids, Ions Some passive, most active Most reabsorption occurs in proximal tubule Not Reabsorbed Nitrogenous waste products - Urea - Uric acid - Creatinine Excess water

Secretion – Reabsorption in Reverse Materials move from peritubular capillaries into renal tubules H+ & K+ Creatinine Materials left in renal tubule move to ureter

Tubular Secretion Eliminates undesirable substances that have been passively reabsorbed (e.g., urea and uric acid) Rids the body of excess K+ Controls blood pH by altering amounts of H+ or HCO3– in urine