Biology Of Human Aging

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Biology Of Human Aging

Chapter 12

Urinary System


Outline

Review of the Structure and Function

•Kidneys / Ureters / Urinary Bladder / Urethra

Age-Related Changes

•Kidneys / Bladder and Urethra

Age-Related Dysfunctions

•Urinary iIncontinence

•Nocturia

•Dysfunctions Caused by the prostate gland

•Pyelonephritis

•Renal Calculi


Kidney Functions

Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine

Regulate volume and chemical makeup of the blood

Maintain the proper balance between water and salts, and acids and bases

Production of rennin to help regulate blood pressure and erythropoietin to stimulate RBC production

Activation of vitamin D


Other Urinary System Organs

Urinary bladder – provides a temporary storage reservoir for urine

Paired ureters – transport urine from the kidneys to the bladder

Urethra – transports urine from the bladder out of the body


Urinary System Organs

Figure 25.1a


Layers of Tissue Supporting the Kidney

Renal capsule – fibrous capsule that prevents kidney infection


Internal Anatomy

A frontal section shows three distinct regions

Cortex – the light colored, granular superficial region

Medulla – exhibits cone-shaped medullary (renal) pyramids

Pyramids are made up of parallel bundles of urine-collecting tubules

Renal pelvis – flat, funnel-shaped tube lateral to the hilus within the renal sinus


Internal Anatomy

Major calyces – large branches of the renal pelvis

Collect urine draining from papillae

Empty urine into the pelvis

Urine flows through the pelvis and ureters to the bladder


Internal Anatomy

Figure 25.3b


The Nephron

Nephrons are the structural and functional units that form urine, consisting of:

Glomerulus – a tuft of capillaries associated with a renal tubule

Glomerular (Bowman’s) capsule – blind, cup-shaped end of a renal tubule that completely surrounds the glomerulus


The Nephron

Renal corpuscle – the glomerulus and its Bowman’s capsule

Podocytes (cleft cells)


Renal Tubule

Proximal convoluted tubule (PCT) –with numerous microvilli and mitochondria

Reabsorbs water and solutes from filtrate and secretes substances into it

Loop of Henle – a hairpin-shaped loop of the renal tubule

Distal convoluted tubule (DCT) – cuboidal cells without microvilli that function more in secretion than reabsorption


Renal Tubule

Figure 25.4b


Capillary Beds

Figure 25.5a


Capillary Beds of the Nephron

Every nephron has two capillary beds

Glomerulus

Peritubular capillaries

Each glomerulus is:

Fed by an afferent arteriole

Drained by an efferent arteriole


Capillary Beds of the Nephron

Blood pressure in the glomerulus is high because:

Arterioles are high-resistance vessels

Afferent arterioles have larger diameters than efferent arterioles


Filtration Membrane

Figure 25.7a


Filtration Membrane

Figure 25.7c


Mechanisms of Urine Formation

Urine formation and adjustment of blood composition involves three major processes

Glomerular filtration

Tubular reabsorption

SecretionFigure 25.8


Ureters

Slender tubes that convey urine from the kidneys to the bladder

Ureters enter the base of the bladder through the posterior wall

This closes their distal ends as bladder pressure increases and prevents backflow of urine into the ureters

Ureters actively propel urine to the bladder via response to smooth muscle stretch


Urinary Bladder

Smooth, collapsible, muscular sac that temporarily stores urine

Outlined by the openings for the ureters and the urethra

Clinically important because infections tend to persist in this region


Urinary Bladder

Figure 25.18a, b


Urethra

Muscular tube that:

Drains urine from the bladder

Conveys it out of the body


Urethra

Sphincters keep the urethra closed when urine is not being passed

Internal urethral sphincter – involuntary sphincter at the bladder-urethra junction

External urethral sphincter – voluntary sphincter surrounding the urethra as it passes through the urogenital diaphragm


Age-Related Changes1. Kidney

Thickening of connective tissue capsule

Decrease in thickness of cortical region

General atrophy of cells and gradual decrease in kidney weight

Decrease in kidney functioning

Increase in the incidents of abnormal glomeruli and replacement of degenerated glomeruli by connective tissue (non-permeable)

Proteinuria (presence of protein in urine)

Increased abnormalities and degeneration of renal tubules

Blood vessels: thickening of walls, loss of muscular tissue, and atherosclerotic deposits

Decline in the ability to handle large changes in acid base levels


2. Bladder and UrethraWeakening and loss of elasticity of the muscles in the wallsInability to expand or contract lower bladder capacity in elderlyRetention of residual urine (100 ml) after urination in elderlyDelay in awareness of the need to urinateUrination in elderly may be urgent, & due to weakness of external

urethral sphincter elderly may be unable to reach the lavatory in timeUrination during night more common in elderly Weakness of the muscles of the pelvic cavity floor

ineffectiveness of external urethral sphincter urine leakage

(usually seen in sudden rise in pressure of bladder) cough or sneeze

This is called Stress Incontinence (more common in older women)

Age-Related Changes


Age-Related Dysfunctions

1. Urinary Incontinence Involuntary passing of urine through the urethra Incidents twice as high in women as in men Due to weakness of internal & external urethral sphincters &

uninhibited contractions of smooth muscles hyperactive bladder Significant problem in older persons marketing of adult diaper-

like undergarments is a profitable enterprise Also reduction of bladder volume & delayed sensation to urinate

due to muscle atrophy Post-menopausal women: estrogen deficiency weak muscles Involuntary urine passage is due to:

Mechanical conditions that elevate bladder pressure (cough or sneeze) Incomplete emptying of the bladder


2. Nocturia

Excessive urination at nightNot a serious condition by itself, yet disturbs sleepTaking drugs: bodily reactions to drugs (relaxation of sphincters

or stimulation of muscles)Not taking drugs: due to age related losses in bladder

distensibility & inability of kidney to concentrate here


3. Dysfunctions caused by the Prostate Gland

Reproductive organ, yet interferes with function of urinary system

Overall atrophy of prostate with aging, yet a lot of men experience

growth of prostate

Benign hyperplasia of prostate: compresses the urethra, difficulty

in urination, bladder never completely emptied

Increases pressure in glomerular capsules kidney malfunction

Symptoms: Reduced force behind urine stream, frequent

urination, inability to empty bladder

Treatment: surgery, transurethral resection


3. Dysfunctions caused by the Prostate Gland

Carcinoma: most frequent tumor of old men

Early stages: little or no urethral obstruction, unaware of tumor

Later stage: restrict urine flow, tumor too far advanced to be

treated

Regular examination, Digital Rectal Exam (DRE), PSA test

Drugs: lengthy remissions, surgery


4. Pyelonephritis

Inflammation of the kidney

Not restricted to older persons

Acute pyelonephritis is a bacterial infection that travels to the

kidney in the blood or lymphs

Causes swelling of kidney due to fluid build up

In severe cases, abscesses develop inflammation & pus

Chronic problem and causes extensive scar tissue in kidney

kidney failure

Responds well to antibiotic treatment

Serious condition (uremia)


5. Renal Calculi

Kidney stones, not restricted to elderly

Most stones do not cause significant symptoms

Passage of stones from kidney, ureter, & bladder strong muscle contractions episodes of severe pain

If stone lodged in ureter obstructs urine flow kidney damage, ulceration, vulnerable to infection

Cause: Ca2+, uric acid, cystine, magnesium, ammonium phosphate

Kidney stone formation related to:

Various kidney infections, high salt concentration in urine, Vit. A deficiency, tumor of parathyroid gland

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Biology Of Human Aging