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Copyright © 2011 Pearson Education, Inc.

Urinary System II Overview

Nephron filtration

Urine composition

Organs of the urinary system

Ureters, urinary bladder, urethra

Urination


Kidney Physiology:Mechanisms of Urine Formation

• The kidneys filter entire plasma volume

• ~60 times each day

• Filtrate

• Blood plasma minus large proteins

• Urine

• <1% of total filtrate

• Contains metabolic wastes and unneeded substances


Mechanisms of Urine Formation

1. Glomerular filtration

2. Tubular reabsorption

• Returns glucose and amino acids,

• 99% of water and electrolytes

3. Tubular secretion

• Reverse of reabsoprtion

• selective addition to urine

Copyright © 2011 Pearson Education, Inc. Figure 24.10

Corticalradiateartery

Afferent arteriole

Glomerular capillaries

Efferent arteriole

Glomerular capsule

Rest of renal tubulecontaining filtrate

Peritubularcapillary

To cortical radiate vein

Urine

Glomerular filtration

Tubular reabsorption

Tubular secretion

Three majorrenal processes:

Mechanisms of Urine Formation


Glomerular Filtration

• Filters large particles from plasma

• RBC, WBC and large proteins are too big

• Everything else comes through fenestrated capillaries

• Efficient filter

• Larger molecules are not filtered

• Hormones help regulate filtration rate


Osmosis


Tubular Reabsorption• Selectively returns molecules to blood

• Microvilli increase absorption

No fenestrated capillaries

• Material travels through endothelial cells

• Glucose and other needed components

• transcellular

lumen

blood


Tubular Reabsoption1. PCT (proximal convoluted tubule)

• Site of most reabsorption

• Glucose & amino acids

• 65% of Na+ and water

• Sodium (Na+) reabsorption via sodium/potassium pump

• Generates energy for other transports

Copyright © 2011 Pearson Education, Inc. Figure 25.18a

Cortex

Outermedulla

Innermedulla

(a)

(b)

(c)

(e)

(d)

Na+ (65%)GlucoseAmino acids

H2O (65%) and many ions (e.g.Cl– and K+)

300

Milliosmols

600

1200

Blood pH regulation

H+,NH4

+

HCO3–

Somedrugs

Active transport(primary or secondary)Passive transport

(a) Proximal convoluted tubule: • 65% of filtrate volume reabsorbed • Na+, glucose, amino acids, and other nutrients actively transported; H2O and many ions follow passively • H+ and NH4

+ secretion and HCO3– reabsorption to

maintain blood pH (see Chapter 26) • Some drugs are secreted


Tubular Reabsoption1. Loop of Henle

• Extends into kidney medulla

• Descending limb:

• Permeable to H2O

• Ascending limb:

• Permeable to Na+, K+, Cl

Copyright © 2011 Pearson Education, Inc. Figure 25.18b

H2O

(b) Descending limb of loop of Henle • Freely permeable to H2O • Not permeable to NaCl • Filtrate becomes increasingly concentrated as H2O leaves by osmosis

(a)

(b)

(c)

(e)

(d)

Cortex

Outermedulla

Innermedulla

300

Milliosmols

600

1200


Copyright © 2011 Pearson Education, Inc. Figure 25.18c

Na+

Urea

Cl–

Na+

Cl–

K+

(c) Ascending limb of loop of Henle • Impermeable to H2O • Permeable to NaCl • Filtrate becomes increasingly dilute as salt is reabsorbed

(a)

(b)

(c)

(e)

(d)

Cortex

Outermedulla

Innermedulla

300

Milliosmols

600

1200



Tubular Reabsoption

3. DCT (distal convoluted tubule) and collecting duct

• Reabsorption is hormonally regulated

• ADH (antidiuretic hormone)

• Can reclaim all water if needed

• ADH needed to reclaim water

Copyright © 2011 Pearson Education, Inc. Figure 25.18d

Na+; aldosterone-regulatedCa2+; PTH-regulatedCl–; follows Na+

(d) Distal convoluted tubule • Na+ and Ca2+ reabsortion regulated by hormones • Cl– cotransported with Na+

(a)

(b)

(c)

(e)

(d)

Cortex

Outermedulla

Innermedulla

300

Milliosmols

600

1200



Tubular Secretion

• Reabsorption in reverse

• Eliminates molecules from plasma that passively reabsorbed

• urea and uric acid

• Potassium (K+)

• Controls blood pH

• altering [H+ ] or [HCO3– ]


Loop of Henle

Osmolalityof interstitialfluid(mOsm)

Innermedulla

Outermedulla

Cortex Active transport

Passive transport

Water impermeable

The ascending limb:• Impermeable to H2O• Permeable to NaClFiltrate becomes increasingly dilute as NaCl leaves, eventually becoming hypotonic to blood.

Filtrate entering the loop of Henle is isotonic

The descending limb:• Permeable to H2O• Impermeable to NaClAs filtrate flows, it becomes increasingly concentrated as H2Oleaves the tubule by osmosis.

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCI

NaCI

NaCI

NaCI

NaCI


Hormones

• Antidiuretics hormone (ADH) creates concentrated urine

• Allows water to leave DCT

• Transports urea into collecting ducts

• Aldosterone

• Made in adrenal glands

• Reabsorption of Na+

• Secretion of K+


Diuretics

• Chemicals that enhance urination

• Osmotic diuretics

• Substances not reabsorbed

• Causes large water output

• ex. high glucose diabetic

• ADH inhibitors: alcohol

• Substances inhibit Na+ reabsorption

• ex. caffeine and many drugs


Characteristics of Urine

• Color and transparency

• Pale to deep yellow

• Urochrome – hemoglobin breakdown

• diet can alter color

• Cloudy urine may indicate infection


Physical Characteristics of Urine

• pH

• Slightly acidic, ~pH 6,

• Odor

• Slightly aromatic

• Ammonia odor may develop

• Altered by drugs


Chemical Composition of Urine

• 95% water and 5% solutes

• Nitrogenous wastes:

• urea, uric acid, and creatinine

• Other molecules (electrolytes)


Diabetes Mellitus

• “pass through sweet” – lots of sugary urine produced

• Cells can not take up excess glucose

• Glucose accumulates in the blood stream

• Kidneys filter out glucose, ends up in urine

• Attempts to dilute it yields large output volume.


ORGANS OF THE URINARY SYSTEM

Ureters, urinary bladder, urethra


Ureters

• Connect kidneys to bladder

• Carry urine

• Enter the base of the bladder

• As bladder fills ureters close, prevents backflow


UretersThree layers of wall of ureter

1. Lining of transitional epithelium

2. Smooth muscle muscularis

• Contracts when stretched

3. Outer adventitia of fibrous connective tissue


Renal Calculi “Kidney Stones”

• Kidney stones:

• Crystallized calcium, magnesium, or uric acid salts

• Form in renal pelvis

• Large stones block uretes

• cause backup and pain in kidneys


Urinary Bladder

• Muscular sac for urine


Urinary Bladder

• Layers of the bladder wall

1. Transitional epithelial mucosa

2. Thick detrusor muscle

• three layers of smooth muscle

3. Fibrous adventitia

• peritoneum on superior surface only


Urinary Bladder

• Trigone – formed by ureters and urethra

• Common infection site

• Rugae – ridges or folds

• Allows bladder expantion

Copyright © 2011 Pearson Education, Inc. Figure 25.21b

Ureter

Trigone

Peritoneum

Rugae

Detrusor muscle

Bladder neck

Internal urethralsphincterExternal urethralsphincterUrogenital diaphragm

Urethra

External urethralorifice

Ureteric orifices

(b) Female.

Urinary Bladder


Urinary Bladder

• Males—prostate gland surrounds the neck inferiorly

• Females—anterior to the vagina and uterus


Urethra

• Muscular tube drains urine from the bladder

• Mostly pseudostratified columnar epithelium,

• Varies between males and females


Urethra

• Sphincters

• Internal urethral sphincter

• Involuntary (smooth muscle)

• at bladder-urethra junction

• Contracts to open

• External urethral sphincter

• Voluntary (skeletal) muscle

• surrounds urethra at pelvic floor


Urethra (Female)

• Female urethra (3–4 cm):

• Bound to anterior vaginal wall

• External urethral orifice –

• anterior to the vaginal opening, posterior to the clitoris


Urethra (Male)

• Male urethra

• Carries semen and urine

• Three named regions

1. Prostatic urethra (2.5 cm) — within prostate gland

2. Membranous urethra (2 cm) — passes through urogenital diaphragm

3. Spongy urethra (15 cm) — passes through penis


Ureter

Trigone of bladder

Prostate

Membranous urethra

Prostatic urethra

Peritoneum

RugaeDetrusor muscle

Bladder neckInternal urethral sphincter

External urethral sphincterUrogenital diaphragm

Spongy urethraErectile tissue of penis

Ureteric orificesAdventitia

(a) Male. The long male urethra has three regions: prostatic, membranous and spongy.

External urethral orifice


Urination

• a.k.a.: urination, mitroturition or voiding”

• Three simultaneous events

1. Contraction of detrusor muscle (involuntary)

2. Opening of internal urethral sphincter (involuntary)

3. Opening of external urethral sphincter (voluntary)


Urination

• Urinary retention – in men a sign of BPH or prostate cancer.

• BPH – benign prostate hyperplasia

• Prostate growth

• Catheters are inserted to allow drainage of the urinary bladder

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