Chapter 17The Urinary System

Structures we’ll talk about tonight…

•Kidneys•Ureters•Bladder•Urethra

KidneysLocation—under back muscles, behind

parietal peritoneum, just above waistline; right kidney usually a little lower than left

Internal structure Renal cortex—outer layer of kidney substanceRenal medulla—inner portion of kidneyRenal pyramids—triangular divisions of medullaRenal papilla—narrow, innermost end of

pyramid

KidneysRenal Microscopic structure—nephrons are

microscopic units of kidneysThey help with the formation of urine

Cortical nephrons—85% of totalJuxtamedullary nephrons—specialized role in

concentrating urineThey consist of:

Bowman’s capsule—the cup-shaped topGlomerulus—network of blood capillaries

surrounded by Bowman’s capsule

KidneysNephron parts continued:

Proximal convoluted tubule—first segmentLoop of Henle—extension of proximal tubule;

consists of descending limb, loop, and ascending limb

Distal convoluted tubule—extension of ascending limb of loop of Henle

Collecting tubule—straight extension of distal tubule

What are the functions of the kidneys?

What happens when you only have 1?

KidneysFunctions

Excretes toxins and nitrogenous wastesRegulates levels of many chemicals in bloodMaintains water balanceHelps regulate blood pressure

Not much changes when you only have 1 kidney!

Formation of Urine Occurs by a series of three processes that

take place in successive parts of nephronFiltration—goes on continually in renal

corpuscles; glomerular blood pressure causes water and dissolved substances to filter out of glomeruli into Bowman’s capsule; normal glomerular filtration rate 125 ml per minute

Formation of Urine Reabsorption—movement of substances out

of renal tubules into blood in peritubular capillaries; water, nutrients, and ions are reabsorbed; water is reabsorbed by osmosis from proximal tubules

Secretion—movement of substances into urine in the distal and collecting tubules from blood in peritubular capillaries; hydrogen ions, potassium ions, and certain drugs are secreted by active transport; ammonia is secreted by diffusion

Formation of UrineControl of urine volume –

Antidiuretic hormone (ADH) = “water-retaining hormone” or “urine-decreasing hormone”

Aldoesterone = “salt- and water-retaining hormone”

Atrial natriuretic hormone (ANH) = opposite effect of aldosterone

Influence of water on urine productionPredict the

changes that would occur in the urine of a runner who had just completed a marathon.

Predict the changes that would occur in the urine production of a person who just ate a jumbo bag of popcorn with extra salt.

Practical ApplicationMarathon runner Bag of salty popcornProteinuria will

probably occurProbably dehydratedUrine production less

than normalSalt loss via sweat –

impact on hormone production?

What if they drank a lot of water during the marathon? Sports drinks?

Decreased salt reabsorption with the greatly increased salt intake.

Larger amount of salt excreted through the urine.

What urine can tell usUrinalysis—examination of the physical,

chemical, and microscopic characteristics of urine; may help determine the presence and nature of a pathological condition

What sort of info can we obtain in doing a urinalysis?

Ureters Structure—narrow long tubes with expanded

upper end (renal pelvis) located inside kidney and lined with mucous membrane and muscular layer

Function—drain urine from renal pelvis to urinary bladder

Urinary BladderStructure

Elastic muscular organ, capable of great expansion

Lined with mucous membrane arranged in rugae, like stomach mucosa

FunctionsStorage of urine before voidingVoiding

UrethraStructure

Narrow tube from urinary bladder to exteriorLined with mucous membraneOpening of urethra to the exterior called urinary

meatusFunctions

Passage of urine from bladder to exterior of the body

Passage of male reproductive fluid (semen) from the body

MicturitionPassage of urine from body (also called

urination or voiding)Regulatory sphincters

Internal urethral sphincter (involuntary)External urethral sphincter (voluntary)

Bladder wall permits storage of urine with little increase in pressure

MicturitionEmptying reflex

Initiated by stretch reflex in bladder wallBladder wall contractsInternal sphincter relaxesExternal sphincter relaxes, and urinationEnuresis—involuntary urination in young child

MicturitionUrinary retention—urine produced but not

voidedUrinary suppression—no urine produced but

bladder is normalIncontinence—urine is voided involuntarily

May be caused by spinal injury or strokeNeurogenic bladder—paralysis or abnormal function of

the bladder, preventing normal flow of urine out of the body

Types include urge, stress, and reflex

Renal and Urinary DisordersObstructive disorders interfere with normal

urine flow, possibly causing urine to back up and cause hydronephrosis or other kidney damageRenal calculi (kidney stones) may block ureters,

causing intense pain called renal colicTumors—renal cell carcinoma (kidney cancer)

and bladder cancer are often characterized by hematuria (blood in the urine)

Renal and Urinary DisordersUrinary tract infections (UTIs) are often

caused by gram-negative bacteriaUrethritis—inflammation of the urethraCystitis—inflammation or infection of the urinary

bladderPyelonephritis—inflammation of the renal pelvis

and connective tissues of the kidney; may be acute (infectious) or chronic (autoimmune)

Hydronephrosis—enlargement of renal pelvis and calyces

Renal and Urinary DisordersGlomerular disorders result from damage to

the glomerular–capsular membrane of the renal corpuscles

Nephrotic syndrome accompanies many glomerular disorders

Proteinuria—protein in the urineHypoalbuminemia—low plasma protein

(albumin) level; caused by loss of proteins to urine

Edema—tissue swelling caused by loss of water from plasma as a result of hypoalbuminemia

Renal and Urinary Disorders

Acute glomerulonephritis is caused by delayed immune response to a streptococcal infection

Chronic glomerulonephritis is a slow inflammatory condition caused by immune mechanisms and often leading to renal failure

Renal and Urinary DisordersKidney failure or renal failure occurs when the

kidney fails to functionAcute renal failure—abrupt reduction in kidney

function that is usually reversibleChronic renal failure—slow, progressive loss of

nephrons caused by a variety of underlying diseasesEarly in this disorder, healthy nephrons often

compensate for the loss of damaged nephrons

Renal and Urinary Disorders

Loss of kidney function ultimately results in uremia (high BUN levels) and its life-threatening consequences

Complete kidney failure results in death unless a new kidney is transplanted or an artificial kidney substitute is used