CH. 23 URINARY Exam 3 Rebecca Effler SUMMERTIME

Urinary System

Contains six principal organs: two kidneys, two ureters, urinary bladder, and urethra.

Functions of the Kidneys

-Filter blood and excrete toxic metabolic wastes

-Regulate blood volume, pressure, and osmolarity

-Secrete erythropoietin (production of RBCs) and renin (blood pressure)

-Regulate electrolytes and acid-base balance

-Synthesize calcitriol

-Clear hormones from blood

-Detoxify free radicals

-In starvation, synthesize glucose from amino acids

Nitrogenous Wastes

Waste substances produced by the body that contain nitrogen, including urea, uric acid, and creatinine.

Urea

A nitrogenous waste product from protein catabolism, constituting 50% of nitrogenous wastes.

Uric Acid

A product of nucleic acid catabolism.

Creatinine

A product of creatine phosphate catabolism.

Blood Urea Nitrogen (BUN)

The level of nitrogenous waste in blood, with a normal concentration of 10 to 20 mg/dL.

Azotemia

Elevated BUN that may indicate renal insufficiency

Uremia

A syndrome characterized by diarrhea, vomiting, dyspnea, and cardiac arrhythmia stemming from the toxicity of nitrogenous waste; treatment is hemodialysis or organ transplant

Excretion

The process of separating wastes from body fluids and eliminating them, carried out by four body systems:

-Urinary

-Respiratory

-Integumentary

-Digestive

Renal Fascia

Connective tissue covering that binds the kidney to the abdominal wall, located immediately deep to the parietal peritoneum.

Perirenal Fat Capsule

Cushions the kidney and holds it into place

Fibrous Capsule

Encloses the kidney, protecting it from trauma and infection; collagen fibers extend from the fibrous capsule to the renal fascia

Hilum

receives renal nerves, blood vessels, lymphatics, and ureter

Renal Parenchyma

glandular tissue that forms urine.

Two zones of parenchyma

-Outer renal cortex (renal columns): extensions of the cortex that project inward toward sinus

-Inner renal medulla (renal pyramids): 6 to 10 with a renal papilla (convergence)

Renal Circulation

Kidneys receive about 21% of cardiac output.

Nephron

The basic functional unit of the kidney

Renal Corpuscle

Part of the nephron that filters the blood plasma.

Renal Tubule

A long, coiled tube in the nephron that converts the filtrate into urine.

Blood Filtration

Blood is filtered at the Bowman's capsule; <70,000 mw passes through, including water

Vascular Pole

Side of renal corpuscle where the afferent arteriole enters and the efferent arteriole exits

Urinary Pole

Side of the renal corpuscle where the renal tubule begins

Proximal Convoluted Tubule

Important solutes reabsorbed

Loop of Henley

Consists of descending (thick) limb, thin limb - permeable to H2O, and ascending (thick) limb

Distal Convoluted Tubule

Part of the nephron following the loop of Henley

Collecting Tubule

Final segment of the nephron where urine is collected

Filtration Membrane

Contains three components: Fenestrated endothelium, basement membrane, and filtration slits

Fenestrated Endothelium

Contains large filtration pores but small enough to exclude blood cells

Hematuria

Blood in urine

Basement Membrane

Proteoglycan gel with negative charge; prevents many blood proteins from escaping blood

Proteinuria

Protein in urine

Filtration Slits

Podocyte foot processes (pedicels) wrap around the capillaries; have negatively charged filtration slits preventing negative anions from exiting blood

Glomerular Filtration Rate (GFR)

Amount of filtrate formed per minute by both kidneys; Average GFR - 105 mL/min, 150-180L/day

Filtrate Reabsorption

99% of filtrate is reabsorbed (only 1-2 L/day are excreted)

High GFR Consequence

If GFR is too high, too much water and electrolyte loss can lead to dehydration

Low GFR Consequence

If GFR is too low, wastes may be reabsorbed that should be eliminated

Blood Hydrostatic Pressure (BHP)

60 mm Hg; high in glomerular capillaries because afferent arteriole is larger than efferent arteriole

Hydrostatic Pressure in Capsular Space

18 mm Hg

Colloid Osmotic Pressure (COP)

32 mm Hg; Glomerular filtrate is almost protein-free; no significant COP

Net Filtration Pressure (NFP)

The balance of blood hydrostatic pressure, hydrostatic pressure in capsular space, and colloid osmotic pressure

Regulation of Glomerular Filtration

Only way to adjust GFR from moment to moment is to change glomerular blood pressure

Renal Autoregulation

The ability of the nephrons to adjust their own blood flow and GFR without external (nervous or hormonal) control

Myogenic Mechanism

-Changes in blood pressure and regulating diameter of afferent arteriole

-if blood pressure is high, the afferent arteriole is smaller

-If the blood pressure is low, the afferent arteriole is higher

Tubuloglomerular Feedback

-Tubular system sends message to glomerulus about flow rate

-if tubular flow is high, the afferent arteriole is smaller

-if tubular flow is low, the afferent arteriole is higher

Sympathetic Control

-During strenuous exercise or circulatory shock, the afferent arteriole constricts limiting flow to the glomerulus and reduces GFR and urine output

-Redirects blood from the kidneys to the heart, brain, and skeletal muscles

Hormonal Control

-Renin-Angiotensin-Aldosterone Mechanism

-System of hormones that controls blood pressure and GFR

Low MAP

Kidneys secrete renin.

Renin

Modifies angiotensinogen (liver) to angiotensin I.

Angiotensin I

Converted to angiotensin II by angiotensin converting enzyme ACE (lungs and kidneys).

Angiotensin II

-Initiates thirst and fluid intake

-Causes vasoconstriction of arteries

-Stimulates adrenal cortex to release aldosterone- promotes Na+ and H2O reabsorption in the distal convoluted tubule

-All elevate blood pressure

Tubular Reabsorption

Removes solutes from filtrate and returns them to blood.

Tubular Secretion

Removes additional waste from blood and adds to filtrate (secretes into the tube).

Tubular Fluid

Fluid in the PCT and DCT.

Proximal Convoluted Tubule (PCT)

Reabsorbs about 65% of glomerular filtrate into peritubular capillaries

Regulatory Pumps

Move materials to and from the tubes and tissue fluid in the tubule epithelial cells.

Sodium Reabsorption

Creates osmotic and electrical gradients that drive the reabsorption of water and other solutes.

Na+-H+ Antiport

Pumps Na+ into tubule epithelial cell and H+ (excess acid) into tubular fluid.

Na+-K+ Pumps

Pumps Na+ out of the cell and into the peritubular capillaries and pumps K+ into the epithelial cells (active transport requires ATP).

Sodium-Glucose Transporter

Transfers both sodium and glucose into epithelial cells.

Glycosuria

Before glucose can be reabsorbed, it is secreted into urine (indicates high plasma glucose levels).

Cl--Anion antiport

Pumps Cl- into the epithelial cell and other anions into tubular fluid.

K+-Cl- symport

Pumps both ions out of the cell and into the peritubular capillaries.

Tubular reabsorption of nitrogenous wastes:

-Urea passes through epithelium with water

-Nephron reabsorbs about half of urea in tubular fluid

-Remaining levels in blood are safe

Tubular reabsorption of water:

-Two-thirds of water in filtrate is reabsorbed in PCT

-Water follows solutes by osmosis through both paracellular and transcellular routes

Nephron loop

-Primary function is to generate osmotic gradient that enables collecting duct to concentrate urine and conserve water

-Thick segment reabsorbs 25% of Na+, K+, and Cl- in filtrate

Waste removal

Includes urea, uric acid, bile acids, ammonia, creatinine, morphine, penicillin, aspirin, and other drugs

Acid-base balance

Tubular secretion of H+ and bicarbonate ions regulates pH

Distal Convoluted Tubule (DCT) and Collecting Duct

-Reabsorbs variable amounts of water and salt, regulated by hormones

-Aldosterone, ADH, atrial natriuretic peptide, and parathyroid hormone

Aldosterone

-Steroid hormone that stimulates reabsorption of sodium to blood and secretion of potassium to urine

-"Salt-retaining hormone" - Cl- and water follow Na+

-Secreted by the adrenal cortex acts on DCT

Triggers for aldosterone secretion

-Blood Na+ concentration falls or K+ concentration rises

-Blood concentration rises or drop in blood pressure stimulates renin release, leading to aldosterone secretion.

Antidiuretic hormone (ADH)

-Stimulates water reabsorption by the kidney, secreted by posterior pituitary

-Makes collecting duct more permeable to water

-Water in the tubular fluid reenters the tissue fluid and bloodstream rather than being lost in urine

ADH triggers

Triggered by dehydration, loss of blood volume, and rising blood osmolarity.

Atrial natriuretic peptides

-Secreted by heart in response to high blood pressure, increases excretion of salt and water in urine

-THUS reducing blood volume and pressure!!!!

-Inhibits secretion of renin, ADH, and aldosterone

Parathyroid hormone (PTH)

-Secreted from parathyroid glands in response to calcium deficiency, increases phosphate excretion

-Because phosphate is not retained, calcium ions stay in circulation rather than precipitating into bone tissue as calcium phosphate

Water conservation

-Removes water from urine and returns it to blood

Water Reabsorptionby the Collecting Duct

-Begins in the cortex receiving fluid from several nephrons

-As urine passes through the increasingly salty medulla, waterleaves by osmosis, concentrating urine

The Collecting Duct

-Can produce a hypertonic urine

-Begins in the cortex where it receives tubular fluid from several nephrons

-CD runs through medulla, and reabsorbs water, making urine up to four times more concentrated

-Medullary portion of CD is more permeable to water than to NaCl

-As urine passes through the increasingly salty medulla,water leaves by osmosis, concentrating urine

Osmotic gradient maintenance

Kidney maintains an osmotic gradient in the renal medulla enabling the collecting duct to function.

Countercurrent multiplier

Mechanism by which the nephron loop continually recaptures salt and returns it to medulla

Descending limb of nephron loop

Permeable to water but not NaCl.

Osmolarity of tubular fluid

Increases as water moves into the ECF.

Ascending limb of nephron loop

Impermeable to water but has active transport mechanisms to move sodium, potassium, and chloride into the ECF.

Osmolarity reduction

Keeps reducing the osmolarity of the urine.

Recycling of urea

Adds to high osmolarity of deep medulla.

Urea permeability

Lower end of collecting duct is permeable to urea but neither thick segment of loop nor DCT is permeable to urea.

Urea cycling

Urea is continually cycled from collecting duct to the nephron loop and back.

Concentration of urea

Urea remains concentrated in the collecting duct and some of it always diffuses out into the medulla adding to osmolarity.

Composition of urine

Describes the composition and properties of urine.

Renal function calculations

Carry out some calculations to evaluate renal function.

Urinalysis

Examination of physical and chemical properties of urine.

Appearance of Urine

Varies from clear to deep amber depending on state of hydration.

Yellow color of Urine

Due to urochrome pigment from breakdown of hemoglobin.

Cloudiness or blood in Urine

Could suggest urinary tract infection, trauma, or stones; or might just be contamination with other fluids.

Pyuria

Pus in the urine.

Odor of Urine

Bacteria degrade urea to ammonia; some foods and diseases impart particular aromas.

Osmolarity of Urine

Ranges from 50 mOsm/L in a hydrated person to 1,200 mOsm/L in dehydrated person.

pH of Urine

Ranges from 4.5 to 8.2, usually 6.0 (mildly acidic).

Chemical composition of Urine

95% water, 5% solutes; normal components include urea and NaCl.

Normal Urine Volume

For average adult—1 to 2 L/day.