Urinary System

I. Introduction A. Organs/Structure 1.Kidneys 2.Ureter 3.Urinary Bladder 4.Urethra

Introduction B.Function 1.Removes waste material from blood 2.Primary organ responsible for monitoring blood composition

II. Kidneys A.Function 1.Maintain homeostasis by regulating blood composition (water, electrolytes), pH, & blood volume 2.Secrete hormone erythropoietin to control rate of RBC production 3.Vitamin D activation 4.Renin – secreted to maintain blood volume and pressure

Kidneys B.Anatomy 1.Shape & size: bean-shaped; 4-5 oz, 4”x3”x1” enclosed in tough fibrous capsule 2.Location a)Retroperitoneal – between T12 & L3 b)Left is slightly higher, surrounded by fat for protection 3.Cortex a)Outer margin b)Dips into medulla between pyramids, creating renal columns

Kidneys 4. Medulla a) inner portion b) Divided into triangular structures  Pyramids c) Pyramids have striated appearance 5. Hilus a) medial, concave depression b) site where renal blood vessels enter/leave the kidney and where ureter exits

Kidney 6. Renal Pelvis a) funnel-shaped expansion of upper ureter that collects urine b) major/minor calyces – divisions of renal pelvis

Kidney 7. Nephron - Cortex a) functional unit: ≈ 1 million/ kidney b) Renal corpuscle 1.Glomerulus – cluster/ball of capillaries 2.Bowman’s capsule – thin-walled expansion of proximal tubule that forms a cup over the glomerulus

Kidney C) Renal tubules 1.Proximal convoluted tubule: in cortex, highly coiled 2.Descending and ascending: Loop on Henle; found in medulla 3.Distal convoluted tubule: cortex; highly coiled 4.Collecting tubule: collects and delivers urine to calyx

Kidneys d) Renal Arteries: arteriole  capillaries  arteriole 1.Afferent arteriole brings blood to glomerulus a)Blood is filtered  no loss of O 2 2.Efferent Arteriole: blood (minus filtered fluid) exiting glomerulus a)Smaller diameter than efferent b)Causes blood to back-up in the glomerulus which ↑ filtration rate 3.Peritubular Capillary a)Efferent arteriole branches into capillaries which surround renal tubule 4.Juxtaglomerular apparatus a)Associated with afferent and efferent arterioles b)Controls renin secretion in order to control blood volume and blood pressure

III. Urine Formation A.Glomerular Filtration  180 L/ 24 hours 1.Passive, non-selective process 2.Movement of water + dissolved substances from capillaries to Bowman’s capsule 3.Similar to tissue fluid 4.Glomerular Filtration Rate a)Volume of filtrate formed each minute b)Factors 1.Total surface area available for filtration 2.Filtration membrane permeability 3.Net Filtration Pressure (NFP) a) Hydrostatic pressure created by afferent and efferent arteriole sizes

Urine Formation 5. Regulation of GFR: need to maintain fairly constant GFR a) Intrinsic controls 1.Renal autoregulation 2.Adjustment of resistance to blood flow (vasoconstrict or vasodilate afferent arteriole) b) Extrinsic controls 1. sympathetic nervous system controls a)During stress, when it is necessary to shunt blood to important organs, neural controls overcome autoregulation b)Afferent arterioles (i) Norepinephrine constricts afferent arteriole = ↓ filtrate formation

Urine Formation 2. Renin – released by juxtaglomerular cells a) Renin    angiotensis II b) Angiotensin II  potent vasoconstrictor of smooth muscle in arteriole wall = ↑BP c) stabilizes systemic BP d) partially restores glomerular filtration rate to normal levels

Urine Formation 3. Atrial Natriuretic Peptides (ANP) a) secreted by heart b) ↑Na + excretion, ↑glomerular filtration rate, ↓water reabsorption = ↑urine output

Urine Formation A.Tubular Reabsorption  Back to Blood 1.Filtered substances 2.Proximal convoluted tubule a)Most reabsorption b)Glucose reabsorbed via active transport 3.Sodium a)Sodium pump (active transport) moves Na + b)Various negatively charged ions follow 4.Water a)Follows b)Osmosis (passive)  water movement c)Water can leave descending loop of Henle

Urine Formation C. Tubular Secretion  Blood to Nephron 1.Substances move from peritubular capillaries 2.H+, NH3, K+

Urine Formation 1.Aldosterone a)Adrenal gland b)Released due to changes in blood concentrations of Na+ & K+ c)Distal convoluted tubule stimulated to reabsorb (by blood) Na+ & secrete K+ (into urine) d)↑ water reabsorption by blood leads to ↓ urine output

Urine Formation 2. Antidiuretic Hormone (ADH) a) hypothalamus produces - posterior pituitary releases b) released in response to ↓ blood water levels c) distal convoluted tubule wall permeability changes and water is reabsorbed by peritubular capillaries d) urine volume ↓

Urine Formation E. Composition 1.Urea a)by-product of amino acid catabolism b)50% reabsorbed; rest in urine 2.Uric Acid a)by-product of metabolism of organic bases in nucleic acids b)Little is excreted c)↑ uric acid in gout

Urine Formation 3. Composition varies with diet 4. Volume a) between 0.6 – 2.5 L/day b) due to intake, environmental temp., body temp., humidity, respiratory rate

V. Ureters ≈ 25 cm long A.Carry urine from pelvis to bladder B.Anatomy 1.Mucosa 2.Muscularis – 2 smooth muscle sheets  longitudinal & circular 3.Adventitia – connective tissue outer layer

Ureters C. Function: Plays active role in transporting urine through muscle contractions D. Homeostatic Imbalance 1.Renal caculi = kidney stones a)Size – most <5mm & pass without problems b)Pain – larger caculi may obstruct ureter, causing ↑ pressure in kidney  excruciating pain

Ureters C. Predisposing conditions 1.Frequent bacterial infections 2.Urinary retention 3.High levels of blood calcium 4.Alkaline urine D. Treatment 1.Shock wave lithotripsy 2.Acidification of urine  drink cranberry juice

V. Bladder A.Muscle sac that receives and stores urine 1.Collapsible 2.Male – prostate surrounds bladder neck B.Anatomy 1.Trigone a)Smooth triangular region in base of bladder (not muscular) b)Outlined formed by openings for both ureters and the urethra c)Infections tend to persist in this region

Bladder 2. Bladder wall a)Mucosa – contains transitional epithelium b)Muscular layer 1.Inner and outer longitudinal muscles 2.Middle circular layer c)Fibrous adventitia – outer connective tissue covering 3. Rugae – folds that occur when empty bladder collapses

Bladder C. Function 1.Stores urine temporarily 2.Holds ≈ 500 mL; Max: 800 – 1000 mL

VI. Urethra A.Canal for excretion of urine from body B.Anatomy – thin-walled muscular tube 1.Female: 1.5 in. long 2.Male: 8 in long; double function – carries both urine & semen

Urethra C. Internal urethral sphincter – Involuntary 1.At bladder/urethral junction (smooth muscle) 2.Contraction opens sphincter; relaxation closes it 3.Prevents leaking between voiding D. External urethral sphincter 1.Voluntary 2.Formed by skeletal muscle

Urethra E. Homeostatic Imbalance – Urinary Tract Infection 1.Improper toilet habits: female opening is close to anus 2.Sexual activity a)Intercourse drives bacteria into vagina and external genital region toward bladder b)Spermacide magnifies problem because it kills helpful bacteria, allowing infectious fecal bacteria to colonize vagina c)40% of all women get UTI’s 3.Urethral mucusa is continuous with bladder, uretal, kidney mucosa a) Inflammation of urethra (urethritis) can ascend the tract  cystitis  pyelonephritis

Urethra 4. Symptoms a)Dysuria – painful urination b)Urgency & frequency c)Fever d)Cloudy or blood-tinged urine e)Sever headache, backache, lower abdominal ache

VII. Congenital Abnormalities A.Horseshoe Kidney – 1 out of 600 births 1.Kidneys fuse across the midline, forming single, u-shaped kidney 2.Usually asymptomatic; may be assoc, with other abnormalities of kidney

Congenital Abnormalities B. Hypospadias – males only 1.Most common congenital abnormality of urethra 2.Urethral orifice located on ventral side of penis (corrected surgically ≈ 1 yr)

Congenital Abnormalities C. Polycystic Kidney Disease (PKD) – Group disorders 1.Fluid-filled cysts – interfere with renal function, leading to renal failure 2.Less severe form – 1 in 500 a) inherited in autosomal dominant fashion b) cysts develop gradually, no symptoms until 40 c) by 60’s, kidneys become knobby and enlarged, up to 30 lbs each

Congenital Abnormalities 3.More severe form – less common a)Autosomal recessive inheritance b)≈ ½ of newborns with recessive PKD die just after birth, survivors develop renal failure in early childhood c)Results from mutation in single gene 4.Treatment a)Renal dialysis b)Kidney transplant

VIII. Aging A.Kidneys 1.Only 3% of elderly have histologically normal kidneys 2.Kidney function↓ with age 3.Kidneys shrink as nephrons decrease in size and # 4.By age 80, GFR is ½ that of middle-aged adults 5.Diabetics are particularly at risk

Aging B.Bladder 1.Shrunken, with < ½ capacity of a young adult 2.Loss of bladder tone causes an increase in urination frequency 3.Nocturia (excessive urination at night) plagues 2/3’s of this group 4.Many eventually experience incontinence