Chapter 26: The Urinary System BIO 211 Lab Instructor: Dr. Gollwitzer

Today in class we will: Identify the major function of the urinary system Identify the major components of the urinary system and their functions Trace the path of filtrate/urine through the urinary system Begin our discussion on the organs and anatomical structures of the urinary system: Kidneys Gross anatomy Position Sectional anatomy Renal flow Blood supply and blood flow

Introduction Major function: 2 major components: To excrete waste products 2 major components: Kidneys: Produce urine = Fluid containing water, ions, small soluble compounds and toxic substances Urinary tract: Transports and stores urine prior to elimination Consists of: Ureters – paired tubes from the kidney to the bladder Urinary bladder – muscular sac for temporary storage of urine Urethra – from bladder to exterior Kidneys  urine  ureters  urinary bladder  urethra  exterior

Figure 26-1

Figure 26-3

Kidneys: Gross Anatomy Paired organs on either side of vertebral column; left slightly superior to right Reddish-brown, kidney-bean shaped Adrenal glands on superior surface Approximate size of hand Hilum = depression where blood vessels (renal artery and vein) and lymphatic vessels, nerves, and ureter pass into/out of kidney

Figure 26-2a

Kidneys: Position Retroperitoneal (“behind”): Between muscles of dorsal body wall and parietal peritoneum Behind parietal peritoneum of abdominal cavity in retroperitoneal space; separated by parietal peritoneum Position in abdominal cavity maintained by: Overlying peritoneum Contact with adjacent visceral organs 3 concentric layers of supportive CT

Figure 26-2b

Kidney: CT layers Renal capsule – tough layer of collagen fibers, covers outer surface of kidney Adipose capsule – thick middle layer, surrounds renal capsule; cushions kidney Renal fascia – dense, fibrous outer layer (also surrounds adrenal gland) Anchors kidney to surrounding structures Fuses with deep fascia (surrounding muscles of body wall) and peritoneum When renal fascia torn  floating kidney Dangerous because of potential twisting/kinking of ureters and blood vessels

Kidney: Sectional Anatomy Renal cortex – outer layer in contact with renal capsule; appears grainy Renal columns – bands of cortical tissue that extend into renal medulla and separate renal pyramids Renal medulla: Inner layer adjacent to renal cortex; looks like strands of combed hair Consists of 6 – 18 renal pyramids (triangular structures) Base of each pyramid in contact with cortex Tip forms renal papilla Striations = loops of Henle and collecting ducts of nephrons (functional units of kidney) Ducts discharge urine in to cup-shaped minor calyx

Kidney Figure 26-4, a,b

Kidney: Sectional Anatomy Renal lobe: Functional component where urine production occurs Consists of: Renal pyramid + Overlying renal cortex + Adjacent renal columns Note: Think 3D – visualize handful of waffle cones = Kidney Ice cream = cortex Cone = medulla Paper around each cone = renal columns

Kidney: Renal Flow Renal papillae from several renal pyramids discharge into a minor calyx 4-5 minor calyces discharge into a major calyx 2-3 major calyces form the renal pelvis = Large funnel-shaped chamber that fills most of renal sinus and connects to ureter

Kidney Renal sinus = internal cavity lined by inner surface of renal capsule

Nephrons Microscopic, tubular structures in cortex of renal lobe Functional/filtration unit of kidney = where urine production begins Approx. 1.25 million/kidney Consists of: Renal corpuscle = filtering body Renal tubule (equivalent to 85 miles) = urine collecting and concentrating tube

Figure 26-6, 7th edition

Kidney: Renal Corpuscle Round structure consisting of: Glomerulus Bowman’s capsule

Kidney: Renal Corpuscle Glomerulus Ball of intertwined fenestrated capillaries (approx. 50) Parietal and visceral epithelia separated by capsular space Visceral epithelium Covers glomerular capillaries Consists of podocytes (= large simple squamous cells) with “feet” = pedicels Narrow gaps between adjacent pedicels = filtration slits – allow filtrates to enter Bowman’s capsule

Kidney: Renal Corpuscle Bowman’s capsule Cup-shaped body Encircles glomerular capillaries Collects filtrate forced out of capillaries in capsular space Connected to initial segment of renal tubule

Kidney: Renal Corpuscle Blood arrives at renal corpuscle via afferent arteriole and leaves via efferent arteriole In renal corpuscle, BP forces fluid and dissolved solutes out of glomerular capillaries (fenestrated) into capsular space (between glomerulus and capsule) = filtration  protein-free solution (filtrate)

Figure 26-8

Kidney: Renal Tubule Filtrate (tubular fluid) leaves renal corpuscle and enters renal tubule Has 3 sections: 2 coiled/twisted segments (located in the cortex) Separated by a U-shaped tubule (located partially or completely in the medulla)

Kidney: Renal Tubule Proximal convoluted tubule (PCT): Loop of Henle: First segment that exits Bowman’s capsule in Entrance opposite afferent/efferent arterioles Loop of Henle: Descending limb (turns toward renal medulla) Ascending limb (turns toward cortex) Distal convoluted tubule (DCT): Passes between afferent and efferent arterioles Empties into collecting duct in cortex

Figure 26-6, 7th edition

Kidney: Renal Tubule Tubular fluid changes in composition as it travels through each segment of the nephron Reabsorption of: Useful organic compounds (glucose, fatty acids, amino acids, vitamins etc) Ions (Na, K) Water (>90%) from tubular fluid and release them into the peritubular fluid – Secretion of waste products missed by filtration

Kidney: Juxtaglomerular Apparatus (JGA) Located where DCT and afferent arteriole are in close contact with each other and the renal corpuscle Formed by: JG cells Macula densa An endocrine structure that secretes: Hormone erythropoietin In response to low O2 Primary function Enzyme renin: Elevates BP and Na retention

Figure 26-8

Kidney: Types of Nephrons Nephrons from different locations differ in structure Cortical nephrons (85%) – in superficial cortex: Short loop of Henle; descends only slightly into renal medulla Efferent arteriole delivers blood to peritubular capillaries which surround entire renal tubule and drain into small venules  interlobular veins Juxtamedullary nephrons (15%) – near medulla: Long loop of Henle extends deep into medulla Peritubular capillaries connected to vasa recta = long, straight capillaries that parallel the loop of Henle

Figure 26-7 Figure 26–7

Kidney: Collecting System Collecting duct: Receives tubular fluid from DCT of several nephrons Begins in cortex and ends in medulla (at papillary duct) Papillary duct: Receives fluid from several collecting ducts Drains into minor calyx

Blood Supply to Kidneys Major function of kidneys is to filter blood Therefore, large volumes of blood delivered to kidneys (almost 20 gallons/hr!) Blood flow: Abdominal aorta  renal artery  segmental artery  interlobar artery  arcuate artery  interlobular artery  afferent arteriole  renal corpuscle glomerulus  efferent arteriole  For cortical nephrons:  peritubular capillary  venule  interlobular vein For juxtamedullary nephrons:  peritubular capillary  vasa recta  venule  interlobular vein Interlobular vein  arcuate vein  interlobar vein  segmental vein  renal vein

Figure 26-5

Today in class we will: Continue our discussion on the organs and anatomical structures of the urinary system: Urinary tract Ureters Urinary bladder Urethra Female Male Renal flow Blood supply

Urinary Tract Consists of: paired ureters, urinary bladder, urethra Responsible for urine transport, storage, and elimination Ureters: Pair of muscular tubes from kidney renal pelvis to urinary bladder Penetrate posterior, inferior wall of bladder Ureteral openings are slits to prevent backflow of urine when bladder contracts Every 30 seconds peristaltic contraction begins at renal pelvis and moves along ureter, forcing urine toward urinary bladder Different pathways in males and females: Due to variations in nature, size, position of reproductive organs Males – base lies between rectum and pubic symphysis Females – base sits inferior to uterus and anterior to vagina

Urinary Tract Urinary bladder: Hollow muscular organ/sac for temporary storage of urine; urine flows in until bladder distended and pressure closes urethral openings Can contain approximately 1 L (stretch receptors triggered at approx 200 mL) Held in place by umbilical ligaments Internal surface: Covered by transitional epithelium (“modified” columnar epithelium) Has has rugae (folds) that disappear as bladder fills Trigone Triangular base (area bounded by ureteral openings and entrance of urethra) Funnels urine into urethra as bladder contracts Neck (surrounds urethral opening) Contains internal urethral sphincter = smooth muscle  involuntary control over discharge of urine from bladder Smooth muscle layers of bladder wall form detrusor muscle – contraction compresses urinary bladder and expels contents into urethra

Urinary Tract Urethra: Female urethra: Extends from neck of urinary bladder to exterior of body Drains urine from bladder to exterior opening of body (external urethral meatus/orifice) Females and males differ in length and function Female urethra: Very short (1-2 in. long) From bladder to vestibule External urethral orifice/meatus = opening to outside between vagina and clitoris

Urinary Tract Male urethra: Extends from neck of bladder to tip of penis (6-8 in. long) 3 sections: Prostatic urethra - passes through prostate gland Membranous urethra Penetrates urogenital diaphragm (floor of pelvic cavity) Surrounded by external urethral sphincter (in males and females) = band of skeletal muscle Acts as a valve - at rest, contracted; must be voluntarily relaxed to urinate Penile (spongy) urethra – passes through penis: From urogenital diaphragm To external urethral orifice/meatus (opening to outside)

Figure 26-18