The Urinary System

The Urinary System Consists of:

Kidneys 2Forms urine from plasma to excrete waste products.Regulates the volume, electrolytes and pH of blood and tissue fluid by excreting or conserving minerals, H ions, bicarbonate, and water.

Ureters 2BladderUrethra

Ureters, bladder and urethra are concerned with the elimination of urine.

The Kidney

Retroperitoneal (behind the peritoneum) on either side of the back bone in the upper abdominal cavityPartially protected by the lower rib cage.Adipose tissue and the renal fascia cushion the kidneys and help hold them in place.Hilus- an indentation on the medial side; renal artery enters, renal vein and ureters emerge.

Kidney-internal structure

Renal cortex - outer area, made of renal corpuscles and convoluted tubules.

Renal medulla (pyramids)- middle area, made of loops of Henle and collecting tubules.

Renal Pelvis- a cavity formed by the expanded end of the ureters within inner layer of the kidney

extensions around the papillae (tip) of the pyramids are called calyces, which collect urine.

Nephron - the structural and functional unit of the kidney.

1 million per kidney.

Two major parts Renal corpuscleRenal tubule

Renal Corpuscle - consists of Glomerulus surrounded by a Bowman’s capsule.

Glomerulus - a capillary network between an afferent arteriole and an efferent arteriole(smaller).Bowman’s Capsule - the expanded end of a renal tubule that encloses the glomerulus

• inner layer has pores and is very permeable.• contains renal filtrate (potential urine).

Nephron continued:

Renal Tubule consists of:proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting tubule.

Collecting tubules unite to form papillary ducts that empty urine into the calyces of the renal pelvis.

Peritubular Capillaries arise from the efferent arteriole and surround all parts of the renal tubule.

Blood Vessels of the kidney:Pathway:

abdominal aortarenal arterysmall arteries in the kidneyafferent arteriolesglomeruliefferent arteriolesperitubular capillaries small veins in the kidney renal vein inferior vena cava.

Two sets of capillaries provide for two sites of exchanges between the blood and tissues in the process of urine formation.

Formation of urine:

Glomerular filtration:takes place from the glomerulus to Bowman’s capsule.

high blood pressure (60mmHg) in the glomerulus forces plasma, dissolved materials, and small proteins out of the blood and into Bowman’s capsule.

the fluid is now called filtrate; which is similar to the plasma from which it is formed.

Filtration is selective only in terms of size; blood cells and large proteins remain in the blood.

Glomerular filtration rate

GFR is 100-125 ml/min

Increased blood flow to the kidney increases GFR.

Decreased blood flow to the kidney decreases GFR.

Tubular reabsorption

• Takes place from the filtrate in the renal tubule to the blood in the peritubular capillaries

• 99% of the filtrate is reabsorbed, only 1% becomes urine.

Active Transport Passive Transport Osmosis Pinocytosis

• Renal threshold – there is a limit as to how much of a substance can be reabsorbed.

• Hormones that affect reabsorption- aldosterone, atrial natriuetic hormone(ANH), antidiuretic hormone (ADH), and parathyroid hormone(PTH).

Tubular Secretion

Takes place from the blood in the peritubular capillaries to the filtrate in the renal tubule.

Creatinine and other waste products such as urea, ammonia, and metabolic products of medications may be secreted into the filtrate to be excreted in the urine.

Secretion of H+ ions helps maintain pH of blood.

Flow of Filtrate/UrineFiltrate is first formed at the glomerulus and is collected by Bowman’s capsule.

The filtrate composition is altered by reabsorption and secretion in the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and finally in the collecting tubules forming the urine.

Kidneys and Acid/Base Balance

The kidneys have the greatest capacity to compensate for normal and abnormal pH changes.

If the body fluids are becoming too acidic, the kidneys excrete H+ ions and return HCO3- ions to the blood.

If the body fluids are becoming too alkaline, the kidneys return H+ ions to the blood and excrete HCO3- ions.

Other Functions of the Kidneys

Secretion of renin by juxtaglomerular cells of the afferent arteriole; when blood pressure decreases.

Angiotensin II causes vasoconstriction and increases secretion of aldosterone. Both increase blood pressure!

Secretion of erythropoietin in response to hypoxia; stimulates RBM to increase rate of RBC production.

Activation of vitamin D - conversion of inactive forms to active form.

Elimination of Urine: the function of the ureters, urinary bladder, and urethra.

URETERSEach extends from the hilus of a kidney to the lower posterior side of the urinary bladder.

Peristalsis of smooth muscle layer propels urine toward bladder.

The Urinary Bladder

A muscular sac below the peritoneum and behind the pubic bones.Serves as a reservoir for urine; and contracts to eliminate urine.In women, below the uterus.In men, above the prostate gland.

• How can this anatomy influence the urine output?

The Urinary Bladder continued:

Mucosa - Transitional epithelial tissue folded into rugae: permit expansion without tearing.

Trigone - triangular area on bladder floor; no rugae, does not expand; bounded by openings of ureters and urethra.

Detrusor Muscle - the smooth muscle layer, a spherical muscle; contracts to expel urine (reflex).

Internal urethral sphincter - involuntary, formed by detrusor muscle fibers around the opening of the urethra.

Urethra- Takes urine from the urinary bladder to the exterior

In women: 1-1.5 inches long; anterior to vagina.In men: 7 to 8 inches long; passes through the prostate gland and penis.

Also carries semen.

Contains the external urethra sphincter: skeletal muscle (voluntary).Exterior opening - urinary meatus.

The Urination Reflex- also called

micturition or voiding

Stimulus: stretching of the detrusor muscle by accumulating urine (200 - 400ml)

Sensory impulses to spinal cord, motor impulses return to derusor muscle, which contracts; internal urethral sphincter relaxes.

Voluntary control is provided by the external urtheral sphincter.

Characteristics of UrineNormal volume in 24 hours - 1-2 litersColor - straw, yellow, or amber

straw is dilute; amber is more concentrated

Turbidity or clarity – clear, hazy, cloudySpecific gravity - measures dissolved solids

normal range - 1.010 - 1.025water - 1.000; blood, sea water 1.010

pH - 4.0-8.0 average 6.0affected mainly by diet

Characteristics of Urine (cont’d)

95% water

5% dissolved salts, and nitrogenous wastesSalts include:

• Sodium (Na), Chloride (Cl), Calcium (Ca), Phosphate (PO4), and Hydrogen (H) ions, etc...

Nitrogenous wastes• urea - amino acid metabolism

• creatinine - creatine phosphate (muscle)

• uric acid - Nucleic acid (DNA, RNA) metabolism

Metabolites of medications (drugs)

Substances which are ABNORMAL to find in urine:

Glycosuria - glucose in the urineindicates hyperglycemia beyond renal threshold (Diabetes mellitus)

Ketonuria - ketones in the urineindicates malfunction in carbohydrate metabolism (seveve Diabetes mellitus), starvation, or high protein diet (protein/fat breakdown for energy)

Proteinuria - protein in the urineindicates kidney damage/disease

Substances which are ABNORMAL to find in urine: (continued)

Hematuria - blood in the urineindicates infection or kidney damage/disease

contamination from menstruation (normal)

Bacteriuria - bacteria in the urineindicates urinary tract infection (Cystitis/Nephritis)

urine will be cloudy - bacteria and wbcs

Microscopic examination of the urine:common findings

CellsSquamous epithelial

RBC, WBC

Spermatozoa

MicroorganismsBacteria

Yeast

Trichomonas

CrystalsUric acid

Triple phosphate

Calcium oxalate

Casts Hyaline

Granular

Cellular

Waxy

Other kidney function testsIntake/Output – measure fluids in/out, also used to prevent dehydration

In - drink & food (jello, soup, ice pop, etc)Out – urine, emesis, perspiration, bleeding, drainage, diarrhea, excessive respiratory activity

24 hour urine – all urine is collected for 24 hoursRandom vs first morning urine, clean catchUltrasoundIVP – intravenous pyelography: dye injected into vein, films taken Cystourethrosocpy – view interior of bladder, catheter may be used to destroy kidney stone

Kidney disease

Cystitis – bladder infection: bacteriuria, pyuria, frequency, urgency, dysuriaAcute/Chronic Glomerulonephritis – ag/ab from streptococcal infections damage the glomerulus: proteinuria, hematuriaIncontinence – involuntary loss of urine

85% female –Kegel exercise

Polycystic kidney – inherited, cysts replace normal kidney tissuePyelonephritis – kidney infection: symptoms similar to cystitis and fever, back pain, hematuria

Kidney disease continued

Renal calculi – kidney stones form from crystals: painful to pass (90% are passed), may become lodged, nausea, vomiting, back, abdominal,and/or groin pain.

Tx – shock wave therapy, increase fluid intake

Renal failure – uremia, deathOliguria, anuriaTx – dialysis, kidney transplant

Dialysis (Hemodialysis)

Patient’s blood is purified by exposing it to dialysate.

wastes diffuse into dialysate;cleaned blood is returned to patient.2-3 times/week; for 3-5 hours

Fistula/Graft artificial veinsurgically constructedcan withstand numerous needle puncturesmust be protected from injury

Kidney transplant

Risk of rejection

Cyclosporin/Neoral – supresses immune system

Demand exceeds supply