Urinary System

Functions of Urinary System

• Filter Blood• Regulation of Blood Volume/Pressure• Regulation of the solute concentration of the Blood• pH regulation of extracellular fluid• Regulation of RBC synthesis [erythropoietin]• Vitamin D activation

Anatomy of the Urinary System

Kidneys• Primary organs of the

urinary system• Located between the

12th thoracic and 3rd lumbar vertebrae.• Right is usually lower

due to liver.

• Held in place by connective tissue [renal fascia] and surrounded by thick layer of adipose [perirenal fat]

Kidneys

• Renal Arteries carry 15-30% of total cardiac output to the kidneys.

UretersEach ureter is about 25 cm (10 in.) long and carries urine from the renal pelvis to the urinary bladder via peristaltic waves.

Valve-like flap of internal mucous membrane covers bladder opening one way flow of urine into the bladder

Review

• Draw a rough diagram of a kidney. Label the:• Cortex• Medulla• Pelvis

• How is the composition of the ureter similar to the composition of the alimentary canal? How is it different?

Bladder• The Urinary Bladder is a

‘temporary storage’ reservoir for urine.• Empty = in pelvis• Full = above the symphysis

pubis

• Urethral sphincter: band of muscles encircling the opening to the urethra.

Bladder Layers

1. Mucous Coat• Folds called rugae• Thickness of this tissue

changes as the bladder expands and contracts

2. Submucous coat• Elastic connective

fibers

3. Muscular coat• Detrusor muscle

4. Serious coat• Connective tissue

Bladder

Is it really an emergency to leave class in order to micturate (pee)? • 150mL – urge to urinate• 300mL – intense sensation to urinate• 600mL – sensation of pain

• So next time you need to leave class, you are to take a 500mL water bottle. If its full when you come back then you don’t have to stay after class. (lol jk jk)

Urethrathin walled tube – conveys urine from bladder to external environment. Similar structure to ureterSphincters: internal urethral [involuntary] & external urethral [voluntary]

• Male Urethra• 20 cm long [7-8 in]• Transports both urine &

semenEternal urethral orifice

opens at tip of penis

• Female Urethra• 3-4 cm long [1.5 in]• External urethral orifice

opens just anterior to the vaginal opening

Micturition (Urination)

• External urethral sphincter controls urination• Voluntary skeletal muscle• Under constant contraction• Urination occurs when muscle relaxes

• At least 500 mL (17 oz) of urine must be eliminated every day • removes potential toxic materials from the body.

• A normal adult eliminates from 1.5 L (1.6 qt) to 2.3 L (2.4 qt) of Urine a DAY (depending).

• http://www.youtube.com/watch?v=qMR-rAVlbV0&feature=related

Review

1. Write two “quiz” questions about information we’ve discussed so far

2. See if your neighbor can answer the questions.

3. If they can’t, explain the answer to them.

Nephrons

• Each kidney contains over a million nephrons [functional structure]

• Blood enters the nephron from a network that begins with the renal artery.

• This artery branches into smaller and smaller vessels –and enters each nephron as an afferent arteriole.

Nephrons• The afferent arteriole

enters the Glomerular Capsule (Gomerulus).

Nephrons

• Blood leaves through the smaller efferent ateriole

• Passes through the peritubular capillaries (remember for later)

• Leaves the kidneys through the renal veins

Nephron

1) Glomerular Filtration

• Fluid diffuses from the high pressure afferent arteriole to the low pressure Bowman’s Capsule

• Glomerular filtrate in proximal convoluted tubule (PCT) similar to plasma

• H2O, Na+, Cl-, glucose, amino acids, Ca+, Mg+, K+, micronutrients [zn, cu, fe]

• Urea & Creatinine

1) Glomerular Filtration

Affect Filtration Rate

• Change in pressure• vasoconstriction /

vasodialation of arterioles• Increase / decrease in

blood pressure

• Solute concentration• More proteins = less

osmosis

Regulating Filtration Rate

• Sympathetic nervous system• Alters blood pressure

• Renin• Enzyme secreted by the

juxtaglomerular cells to constrict efferent arteriole.

2) Tubular Reabsorption

Where’s it Reabsorbed?

• From the [high concentration] Proximal Convoluted Tubule & Loop of Henle

• To [low concentration] peritubular capillaries

What’s Reabsorbed?

Active Transport • Glucose• Amino Acids• Acids

• Ascorbic, lactic, citric, etc.

• Ions• P, S, Ca, K, Na

Osmosis/Diffusion • Water

3) Tubular Secretion• Active transport of substance in blood to renal tubules

• Penicillin, histamine, phenobarbital, H+, K+, ammonia.

• In Distal Convoluted Tubule and Collecting Duct• http://www.youtube.com/watch?v=aQZaNXNroVY

Excretion• Highly inefficient Urine• H2O• Urea • Creatinine • Ammonia• Uric Acid• Oxalate• Na+, Cl-, K+, H+, HCO3

- (small amounts)

Review

• Label where the three steps of urine formation occur in the nephron• Glomerular filtration• Tubular Reabsorption• Tubular Secretion

• Draw a rough diagram of a nephron. (see on right)

Kidney Stones

Statistics:• Kidney stones affect more than a million

Americans each year• Twelve to 24 million Americans will develop

stones in their lifetime• There are approximately 350,000 new stone

cases reported each year.• In the United States, 7 to 10 of every 1,000

hospital admissions are due to kidney stones.

Kidney Stones (Calculi)• Mineral salt crystals that

precipitate from urine.• Small as a grain of sand • Large as a golf ball. • The size, shape, and

location of the stone can cause many different symptoms.

• http://www.youtube.com/watch?v=16ewFJ-iQtw

• Most are extremely small and pass through without any symptoms

• Large calculi can obstruct renal ducts or the ureters.

• Causes severe pain.