Chapter 25: The Urinary System

Question 1

Urinary System Organs:

Answer 1

o 2 Kidneys
o 2 Ureters
o 1 Urinary Bladder
o 1 Urethra

Question 2

Nephrology:

Answer 2

Study of the Kidneys

Question 3

Urology:

Answer 3

Study of entire Urinary System.

Question 4

Urine Flow:

Answer 4

o 1) Kidneys make urine.
o 2) Ureters transport urine to the bladder.
o 3) Urinary bladder stores urine (regulated by urinary sphincters).
o 4) Urethra transports urine from bladder to the external urethral orifice & out of body.

Question 5

Macroscopic Anatomy of Kidney:

Answer 5

o	4-5” long, 2-3” wide, 1” thick (bar of soap).
o	Found just above the waist between the peritoneum & posterior wall of abdomen (retroperitoneal).
o	Protected by 11th & 12th ribs with the right kidney lower.
o	Renal (fibrous) capsule = transparent membrane that maintains organ shape.
o	Perirenal fat capsule = Adipose capsule that protects and anchors.  
o	Renal fascia = dense, irregular connective tissue that anchors kidneys to posterior body wall.

Question 6

Anatomy of Ureters:

Answer 6

o 10-12” long.
o 1 to 10 mm in diameter (think about renal stones!!).
o 3 tunics:
o Mucosa (transitional epithelium with goblet cells).
o Muscularis (inner longitudinal and outer circular layers smooth muscle—3rd layer distally.
o Adventitia.
o Extends from renal pelvis to bladder.
o Retroperitoneal.
o Enter posterior wall of bladder.
o Flow results from peristalsis, gravity & hydrostatic pressure.

Question 7

Anatomy of Urinary Bladder:

Answer 7

o Hollow, distensible muscular organ with capacity for 700-800 mL.
o Rugae of urinary bladder allow stretching.
o Trigone is smooth flat area bordered by 2 ureteric openings and internal urethral orifice.
o Detrusor muscle & internal/external urethral sphincter.

Question 8

Location of Female Urinary Bladder:

Answer 8

o Posterior to pubic symphysis.
o Females: Urinary bladder is anterior to vagina & inferior to uterus.
o Females: pubic symphysis goes to bladder goes to vagina lastly to the rectum.
o Males: Pubic symphysis to bladder lastly to rectum.

Question 9

Histology of Urinary Bladder:

Answer 9

o	3 Tunics:
o	Mucosa = transitional epithelium with rugae.
o	Muscularis: detrusor muscle (3 layers) = inner, outer longtitudinal & inner circular.
o	Adventitia (urinary bladder is retroperitoneal).

Question 10

Urination (Micturition):

Answer 10

o MICTURITION = urination = a reflex involving the sacral spinal cord, the parasympathetic & sympathetic nervous systems, and voluntary conscious control.
o Internal urethral sphincter: circular smooth muscle fibers at OPENING to urethra (involuntary control).
o External urethral sphincter: skeletal muscle (modification of urogenital diaphragm muscle), inferior to internal urethral sphincter, voluntary control.

Question 11

Urinary Incontinence:

Answer 11

o Urinary incontinence = inability to hold urine.
o Normal in 2 or 3 year olds because neurons to sphincter muscles are not developed.
o Stress Incontinence = anything that increases abdominal pressure (coughing, sneezing, laughing, exercising, pregnancy).
o Other causes of incontinence:
o Spinal cord injuries.
o Injury to nerves controlling micturition.
o Damage to external urethral sphincter.
o Irritation of bladder or urethra.
o Obstructed urinary outlet.
o Certain drugs.

Question 12

Macroscopic Anatomy of Urethra:

Answer 12

o Females:
o 1.5 inches long
o External urethral orifice is between the clitoris and the vaginal opening
o Males:
o 6 to 8 inches long
o Internal urethral orifice to prostate to urogenital diaphragm to penis
o Male urethra has dual role of discharging both semen AND urine, but not at the same time.

Question 13

Disorders of Urinary System:

Answer 13

o Urethritis: inflammation/infection of urethra (more common in females).
o Cystitis: inflammation/infection of urinary bladder.
o Pyelitis: inflammation/infection of renal pelvis and calyces (where urine collects).
o Pyelonephritis: inflammation or infection of kidneys (very serious, may require IV antibiotics).

Question 14

General Kidney Overview:

Answer 14

o Kidneys filter the blood & return most of the water and solutes to the blood.
o Blood comes into a glomerulus (big ball of capillaries)… filtration pushes large amounts of plasma and MOST solutes into a capsular space… the rest of the kidney (nephron tubules) is concerned with RECLAIMING the solutes that our bodies want to KEEP the wastes stay in the tubules and eventually become urine.

Question 15

Overview of Kidney Functions:

Answer 15

o	Excrete wastes.
o	Regulate volume of blood.
o	Regulate blood pressure.
o	Renin (from juxtaglomerular cells of kidney)& RAA system (renin-angiotensin-aldosterone).
o	Regulate composition of blood.
o	Electrolytes and osmolarity.
o	Secrete hormones.
o	Help regulate acid-base balance.
o	Detoxify free radicals and medications.
o	Gluconeogenesis during starvation.

Question 16

Examples of Wastes:

Answer 16

o Nitrogenous wastes:
o NH3 from protein breakdown to Urea (liver).
o Creatinine (from creatine PO4 from muscle).
o Uric acid (purines = building blocks for RNA, DNA, acetyl-CoA).
o Bilirubin and byproducts.
o Foreign substances (meds, environmental toxins).
o Excess vitamins and mineral salts (ions).
o Excess water.

Question 17

The Nephron:

Answer 17

o Functional Unit of the Kidney.
o Over one million in each kidney.
o Each contains a renal corpuscle and renal tubule.
o Renal corpuscle = site of plasma filtration
o Glomerulus is capillaries where filtration occurs.
o Glomerular (Bowman’s) capsule is double-walled epithelial cup that collects filtrate.
o Renal tubule (resorption).
o 1) proximal convoluted tubule.
o 2) loop of Henle dips down into medulla.
o 3) distal convoluted tubule.
o Collecting ducts (excretion).

Question 18

Basic Functions of Nephrons:

Answer 18

o Filtration of blood (renal corpuscle).
o Reabsorption of important solutes (back into blood) within the formed filtrate (renal tubule).
o Secretion of wastes/solutes INTO the filtrate (collecting ducts).

Question 19

Internal Anatomy of Kidney:

Answer 19

o RENAL CORTEX
o Outer, superficial layer… smooth…light in color.
o 90% of blood entering kidney perfuses the cortex.
o 80 to 85% of kidney nephrons are located in the cortex = cortical nephrons.
o RENAL MEDULLA
o Inner layer, darker red-brown color.
o Contains 6 to 10 Renal pyramids per kidney.
o Renal Papilla = tip of each renal pyramid.
o Renal Column = extensions of cortex between pyramids.
o Renal Lobe = renal pyramid + renal cortex above it + ½ of each adjacent renal column.
o Renal pyramids have a striped appearance because they contain (roughly parallel) renal tubules & ducts
o Renal papillae contain papillary ducts
o Minor and Major Calices drain urine from papillary ducts into the renal pelvis ureter.

Question 20

Blood Vessels Around the Nephron:

Answer 20

o Glomerular capillaries are formed between the afferent & efferent arterioles.
o Efferent arterioles give rise to the peritubular capillaries and vasa recta.

Question 21

Blood Supply of Kidney:

Answer 21

o Kidneys receive 25% of resting cardiac output via renal arteries.
o CO (5.25 L/min)=SV (70 mL/beat) X HR (75 beats/min).
o Thus, kidneys receive more >1 L of blood/minute.
o Renal circulation is unique:
o Afferent arteriole to glomerular capillaries to efferent arteriole.
o Afferent arteriole has larger diameter than Efferent arteriole.
o Each nephron has 2 different capillary beds:
o Glomerular capillaries where filtration of blood occurs
o High pressure and specialized for filtration.
o Vasoconstriction & vasodilation of afferent & efferent arterioles produce large changes in renal filtration.
o Peritubular capillaries carry away reabsorbed substances from filtrate.
o Low pressure, thus adapted for reabsorption.

Question 22

Histology of Blood Vessels:

Answer 22

o Afferent arteriole
o Lined by endothelium
o Wall includes smooth muscle fibers with alpha-1 adrenergic receptors NE (sympathetic)
o Some modified smooth muscle fibers called juxtaglomerular cells (JG cells) secrete renin stimulates formation Angiotensen II (Systemic BP inc.).
o Glomerular capillaries
o Fenestrated capillaries, very porous.
o Basement membrane restricts passage only of large plasma proteins.
o Efferent arteriole
o Lined by endothelium.
o Wall includes smooth muscle fibers with alpha-1 adrenergic receptors (sympathetic).
o Smaller in diameter than afferent arteriole.

Question 23

Nerve Supply to Kidney:

Answer 23

o Renal nerves come off of the superior mesenteric ganglion… contain mostly sympathetic postganglionic neurons.
o Enter hilum of kidney and follow branches of renal artery to the afferent and efferent arterioles.
o Regulates blood flow in/out of nephron.

Question 24

Overview of Renal Physiology:

Answer 24

o Nephrons and collecting ducts perform 3 basic processes:
o Glomerular filtration: A portion of the blood plasma is filtered into the kidney.
o Tubular reabsorption: Water & useful substances are reabsorbed back into the blood.
o Tubular secretion: Wastes are removed from the blood & secreted into the filtrate (which eventually becomes urine).

Question 25

Histology of Renal Corpuscle:

Answer 25

o Bowman’s capsule surrounds capsular space=double-walled cup with a parietal layer (outer wall), capsular space & visceral layer (inner).
o Podocytes cover capillaries to form visceral layer.
o Simple squamous cells form parietal layer of capsule.
o Glomerular capillaries: arise from afferent arteriole & form a ball (fenestrated capillaries!) before emptying into efferent arteriole.

Question 26

Filtration Membrane:

Answer 26

o Stops all cells (RBCs) and platelets.
o Stops large plasma proteins.
o Stops medium-sized proteins, not small proteins.
o Any molecule

Question 27

Juxtaglomerular Apparatus:

Answer 27

o Structure where afferent arteriole “kisses” the DCT.
o Juxtaglomerular cells are modified sm. muscle cells in afferent arteriole (granular looking cells that secrete RENIN into blood) leads to respond to stretch so they are mechanoreceptors.
o Macula densa = monitors and relays Na+ info to juxtaglomerular cells.
o Mesangial cells =decrease GFR (contraction = less surface areas) vice-versa.
o If systemic blood arteriole pressure is too high, too much blood will be going through glomerulis = Glomerular filtration pressure becomes too high
o Remedy: smooth muscle in afferent arteriole contracts, causing less flow into arteriole, less glomerular filtration pressure, and less filtrate will be going into the collecting ducts (allows more time to reabsorb filtrate (small proteins, Na+, H2O).
o Mesangial cells contracts around glomerulis = less surface area for filtration.
o If Systemic blood pressure is too low it increases glomerular filtration pressure.
o If filtration rate is too high, too much filtrate moves too quickly through the tubules. So, less Na+ and H20 is able to be resorbed into the peritubular capillaries.
o The macula densa cells detects too much filtrate in the DCT (Na+/ H2O) and the JG cells releases chemicals that cause the afferent arteriole to constrict) which allows more time for Na+/H20 to be reabsorbed into the capillaries (renin angiotensin II = reduces flow).
o If filtration rate is too low, The JG apparatus releases chemicals to dilate the afferent arteriole. (less renin = increased flow)

Question 28

Glomerular Filtrate:

Answer 28

o Water, Electrolytes, Glucose, Fatty acids, Amino acids.
o Nitrogenous wastes:
o Urea (main way body gets ride of excess Nitrogen from amino acid deamination) produced in the liver.
o Creatinine: manufactured in liver and used for ATP production in muscle
o Vitamins.
o Few small proteins/polypeptides.

Question 29

Histology of the Renal Tubule:

Answer 29

o Single layer of epithelial cells forms walls of entire nephron.
o Distinctive features due to function of each region:
o Microvilli.
o Cuboidal versus simple.
o Hormone receptors.
o Transporters.

Question 30

Histology of Proximal Convoluted Tubule:

Answer 30

o	Proximal convoluted tubule.
o	Simple cuboidal epithelium with brush border of microvilli that increase surface area.
o	Longest and most coiled.
o	>65% of reabsorption occurs:
o	100% of most organic solutes (glucose, amino acids).
o	65% of H20, Na+.
o	55-60% of K+ and Cl-.
o	Secretion also occurs:
o	Urea, uric acid, creatinine, NH3.
o	H+, HCO3-, prostaglandins, etc.

Question 31

Reabsorption Routes:

Answer 31

o Paracellular reabsorption (between cells).
o Transcellular reabsorption:
o Material moves through both the luminal (apical) and basolateral
membranes of the tubule cell by many transport mechanisms.

Question 32

Reabsorption of Bicarbonate, Na+ and H+ Ions:

Answer 32

o Na+ antiporters reabsorb Na+ and secrete H+
o PCT (proximal convoluted tuble)cells produce the H+ & release bicarbonate ion to the peritubular capillaries.
o Important buffering system.
o For every H+ secreted into the tubular fluid, one filtered bicarbonate eventually returns to the blood.

Question 33

Transport Mechanisms:

Answer 33

o Apical (or luminal) and basolateral membranes of tubule cells have different types of transport proteins.
o Reabsorption of Na+ is important:
o Several transport systems exist to reabsorb Na+ (symporters, antiporters).
o Na+/K+ ATPase pumps sodium from tubule cell cytosol through the basolateral membrane only.
o Water is only reabsorbed by osmosis:
o Obligatory water reabsorption occurs when water is “obliged” to follow the solutes being reabsorbed.
o Facultative water reabsorption occurs in collecting duct under the control of antidiuretic hormone.

Question 34

Glucosuria:

Answer 34

o Glucose transporters (SGLTs) can only move “so much” glucose =TRANSPORT MAXIMUM:
o SGLTs can not reabsorb glucose fast enough if blood glucose level is above 200 to 300 mg/dL (highly individual).
o If the TM is exceeded, some glucose remains in the urine (glucosuria).
o Common cause is diabetes mellitus.
o Rare genetic disorder produces defect in transporter that reduces its effectiveness.

Question 35

Histology of Loop of Henle:

Answer 35

o Primary functions:
o Reabsorb another 25% of filtrate.
o Create a salinity gradient to concentrate urine.
o Thin segments = simple squamous epithelium.
o Very low metabolic activity.
o Very permeable to water.
o Thick segments = simple cuboidal epithelium:
o Active transport of salts (Na+, K+, Cl-, Ca++).

Question 36

Transporters in the Loop of Henle:

Answer 36

o Thick segment of ascending Loop of Henle has Na+ K+ Cl- transporters that reabsorb these ions.
o K+ leaks through K+ channels back into the tubular fluid leaving the interstitial fluid and blood with a negative charge.
o Thick segment is impermeable to water.

Question 37

Histology of Distal Convoluted Tubule:

Answer 37

o Fluid arriving here still contains 25% of water and 10% of the salts of original filtrate.
o Simple cuboidal epithelium.
o Principal cells:
o Aldosterone receptors.
o Reabsorb sodium/H2O.
o Aldosterone from adrenal cortex and stimulated by angiotensin II = more H2O absorbed.
o Secrete potassium.
o ADH receptors: H20 channels aquiporins.
o Intercalated cells
o Secrete H+ (acid-base balance).
o Reabsorb K+ and HCO3- into blood.

Question 38

Reabsorption in the DCT:

Answer 38

o Removal of Na+ and Cl- continues in the DCT by means of Na+ and Cl- transporters.
o Na+ and Cl- then reabsorbed into peritubular capillaries.
o DCT is major site where parathyroid hormone (PTH) and calcitriol stimulate reabsorption of Ca+.
o Atrial Natriuretic Peptide = release from right atrium of heart due to activation of heart stretch receptors.
o Suppresses the release of aldosterone and ADH.
o Net effect is less Na is resorbed, so more Na is excreted into urine which decreases blood volume and BP.

Question 39

Secretion of H+ and Absorption of Bicarbonate by Intercalated Cells:

Answer 39

o Proton pumps (H+ATPases) secrete H+ into tubular fluid.
o Can secrete against a concentration gradient so urine can be 1000 times more acidic than blood.
o Cl-/HCO3- antiporters move bicarbonate ions into the blood.
o Intercalated cells help regulate pH of body fluids.
o Urine is buffered by HPO4 2- and ammonia, both of which combine irreversibly with H+ and are excreted.

Question 40

Reabsorption and Secretion in the Collecting Duct:

Answer 40

o By end of DCT, 95% of solutes & water have been reabsorbed and returned to the bloodstream.
o Cells in the collecting duct make the final adjustments.
o Strong concentration of urine is possible through the countercurrent exchange system.

Question 41

Histology of Collecting Ducts:

Answer 41

o	Primary functions: 
o	Conserve body water 
o	Fine-tuning of lytes 
o	Simple cuboidal epithelium
o	Principal cells:
o	Aldosterone receptors.
o	Reabsorption of sodium.
o	Secrete potassium.
o	ADH receptors:  H20 channels open due to aquaporins.
o	Intercalated cells:
o	Secrete H+ (acid-base balance).
o	Reabsorb K+ and HCO3-.

Question 42

Several Types of Diuretic Meds:

Answer 42

o	Osmotic diuretics (e.g., mannitol).
o	Diuretics that inhibit sodium reaborption and hence water resorption. 
o	Caffeine.
o	Inhibit sodium symporters at the DCT.
o	HCTZ  = hydrochorothiazide.
o	Loop diuretics act on ascending limb of Loop of Henle (interfere with medullary gradient—very powerful meds).
o	Lasix (furosemide).
o	Most diuretics have side effects.

Question 43

Urine:

Answer 43

o Average adult produces 1 – 2 L/day.
o Polyuria = more than 2 L/day.
o Diabetes mellitus (excess sugar that body needs to dump.
o Diabetes insipidus (excessive thirst insensitivity orno response to ADH = body needs to dump since increase in blood volume).
o Meds (e.g., diuretics).
o Oliguria = urine output

Question 44

Urine Composition:

Answer 44

o 95% water, 5% solutes.
o Urea, Na+, K+, PO4, SO4, creatinine, urate.
o Variable amounts of Ca++, Mg++, HCO3-, toxins, drug metabolites, etc.
o Osmolarity 50 – 1200 mOsm/L.
o Specific gravity = 1.001 to 1.028.
o pH is typically ~6.0 (acidic).
o Clear—color depends on hydration.

Question 45

Abnormal Findings in Urine:

Answer 45

Glucose (glycosuria), Blood (hematuria), Hb (hemoglobinuria), WBCs (pyuria), Protein (proteinuria), Albumin (albuminuria), Ketones (ketonuria), Bile pigments (bilirubinuria).

Question 46

Renal Function Tests:

Answer 46

o Urinalysis
o Blood analysis:
o BUN = blood urea nitrogen = measures blood nitrogen resulting from catabolism and anabolism of amino acids…BUN rises steeply in renal disease. (Normal: 10 = 20 mg/dL)
o Serum creatinine = results from catabolism pf creatine phosphate in skeletal muscle too much = renal disease. (Normal: 0.7 – 1.2 mg/dL)
o Functional tests:
o Renal clearance tests = how effectively kidneys remove a certain substance / minute (like creatinine).
o Glomerular filtration rate (GFR).