The Urinary System

1. Why do we need a urinary system?

A. Introduction

a. Regulate body composition and volume

b. Rid the body of nitrogenous wastes

c. Maintain body pH

2. Components and locations

a. 2 kidneys

b. 2 ureters

c. 1 urinary bladder

3. Other functions

cortexrenal columns

renal pyramids

ureter

calyces

The Urinary System

1. Kidneys

B. Review of structure and function

a. Cortex vs. medulla

b. Renal pyramids

c. Calyces

d. Renal pelvis

e. Renal tubule

i. Nephron

ii. Collecting duct

glomerulus

Bowman’s capsule proximal convoluted

tubule

distal convoluted

tubule

proximal straight tubule

distal straight tubule

loop of Henlecollecting duct

The Urinary System

1. Kidneys

B. Review of structure and function

f. The nephron

i. Bowman’s capsule

ii. Proximal convoluted tubule

iii. Proximal straight tubule

iv. Loop of Henle

v. Distal straight tubule

vi. Distal convoluted tubule

The Urinary System

1. Kidneys

B. Review of structure and function

g. Glomerular capsule

i. Afferent arteriole glomerulus efferent arteriole

ii. Blood-kidney barrier

The Urinary System

1. Kidneys

B. Review of structure and function

h. Filtrate formation

i. What is filtrate?

ii. How is it formed?

iii. How much is formed each day?

iv. What is tubular reabsorption?

v. What is anti-diuretic hormone (ADH) and what does it do?

The Urinary System

2. Ureters

3. Urinary bladder

4. Urethra

B. Review of structure and function

a. Internal urethral sphincter

b. External urethral sphincter

c. Micturition reflex

The Urinary System

1. Kidneys

C. Age-related changes

a. Loss of renal mass due to loss of glomeruli

i. Normal at age 40; 30% weight loss at age 80

ii. Another 30% of glomeruli abnormal at 80

b. Decreased glomerular filtration rate

i. Pre-40 normal = 125 ml/min

ii. By age 75, 50% function = ~60 ml/min)

c. Altered permeability = proteinuria

The Urinary System

C. Age-related changes

f. Decreased ability to handle body pH changes

1. Kidneys

d. Degeneration and loss of nephrons

i. Decreased ability to concentrate urine

ii. Decreased ability to clear some drugs

e. Diminished blood flow through kidneys

i. Normal at age 20 = 1,250 ml/min

ii. By age 80, 50% = ~600 ml/min

The Urinary System

2. Bladder and urethra

C. Age-related changes

a. Loss of muscle tone and elasticity

i. Bladder less able to expand and contract

ii. Normal capacity = ~600 ml; elderly = ~250 ml

iii. 100 ml urine may be retained after micturition

b. Loss of awareness of need to urinate

c. Increased frequency, especially at night

d. Loss of muscle tone in pelvic floor (stress incontinence)

The Urinary System

D. Age-related dysfunctions

1. Urinary incontinence

a. Results from:

i. Weakened sphincters

ii. Reduction in bladder volume

iii. Delayed sensation of need to go

iv. Muscle atrophy in pelvic floor (bedridden)

b. No evidence that normal aging causes incontinence, but 30% of elderly experience some level of incontinence

c. Decreased estrogen

The Urinary System

D. Age-related dysfunctions

2. Nocturia (excessive night urination)

a. 60% over 65 complain about it

b. Not a real problem except for loss of sleep

c. May be caused by drugs, loss of bladder elasticity, and inability to concentrate urine (increased urine volume)

The Urinary System

D. Age-related dysfunctions

3. Prostate gland dysfunctions

a. How is the prostate gland involved in urination?

b. Benign prostatic hyperplasia

i. Cause

ii. Symptoms

iii. Treatments

c. Prostatic carcinoma

i. Who gets it?

ii. Symptoms

iii. Treatments

The Urinary System

D. Age-related dysfunctions

4. Pyelonephritis

a. Bacterial infection

b. Most chronic cases occur in people >65

c. Kidneys swell with fluids, abscesses form, pus fills renal pelvis

d. Scar formation leads to renal insufficiency/failure

The Urinary System

D. Age-related dysfunctions

5. Renal calculi (kidneys stones)

a. Not a problem of aging, but becomes progressively more common with age

b. Causes poorly understood

c. Stones are usually passed, but in elderly they are more likely to form an obstruction

end

The Urinary System

E. Take home messages

1. Although there are a number of age-related changes, the kidneys are more than capable of maintaining homeostasis throughout lifespan

2. Some glomeruli and nephrons degenerate while others become abnormal; therefore, glomerular filtration rate decreases and ability to concentrate urine decreases

3. Ability to clear drugs can become a major issue