Aging of the Urinary Tract:Kidney

Lower Urinary Tract

Nephron & Renal Circulation

Table 19-1Major Functions of the Kidney

Water and electrolyte regulationMetabolic products excretionHydrogen ion excretion and maintenance of blood pH

Endocrine functions:Renin-angiotensin secretion (blood

pressure)Vitamin D activation (Ca++ metabolism)Erythropoietin secretion

(hematopoiesis)

Renal GlomerulusGlomerulus: Tufts of capillaries between afferent and efferent renal arterioles. Filtration is through a fenestrated endothelium separated from the basal membrane by podocytes. Filtrate is the same as plasma but without proteins.

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Renal Tubules divided into:• Proximal Tubule, mostly reabsorption of water & solutes• Loop of Henle, mostly reabsorption of water & salt • Distal Tubule, mostly water & salt (under influence of aldosterone) reabsorption and acidification of urine• Collecting Duct, water reabsorption under the influence of ADH (antidiuretic hormone from posterior pituitary)

Distal and Collecting Tubules function is regulated by ADH (antidiuretic hormone)

• secreted by neuroendocrine hypothalamus• stored and released from the posterior pituitary

Juxtaglomerular Apparatus: • located between affarent artery and distal tubule• secretes the enzyme renin• renin acts on the liver protein angiotensinogen to form angiotensin I, and angiotensin is transformed into angiotensin II in the lungs• angiotensin II is a very potent hypertensive substance; it also stimulates the release of aldosterone from the adrenal cortex

PosteriorHypophysis

OxytocinVasopressinAntidiuretic Hormone (ADH)

Fig. 1.11 Diagramme des principales hormones hypophysiotropes de l'hypothamalus et des hormones du lobe posterieur de l'hypophyse.

smooth musclesof uterus

mammaryglandrenal

collectingducts

Hypothalamus, Posterior Hypophysis, and their Hormones Hypothalamus

Figure 19-2

Table 19-2 Common Renal Problems in the Elderly

Renal FailureImpaired drug excretionUrinary tract infectionsHypertensionMiscellaneous disorders:

TuberculosisNephritisDiabetes, etc.

Table 19-3 Some Signs of Renal Failure

Generalized edema

Acidosis

Increased circulating non-protein nitrogen (urea)

Increased circulating urinary retention products (e.g. creatinine, uric acid)

Table 19-4 Selected Causes of Acute Renal Failure

PRE-RENAL:Loss of body fluidsInadequate fluid intakeSurgical shock or myocardial infarction

RENAL:Drug toxicityImmune reactionsInfectious diseasesThrombosis

POST-RENAL:Urinary tract obstruction

Table 19-6 Drugs and the Aging Kidneys

Questions: Is the drug excreted primarily by the kidney?How competent are the kidneys?What are the side-effects?What are the consequences of drug toxicity when the kidney is impaired?

Etiopathology of Renal Drug Toxicity:High renal blood flowIncreased drug concentration and accumulation in kidneyIncreased hepatic enzyme inhibition in the elderlyIncreased autoimmune disorders in the elderly

Functions of the bladder• Filling with urine from the kidneys• Micturition: emptying of bladder by muscle contraction and opening of sphincters.

• Principle muscle: Detrusor muscle• Sphincters: Internal (involuntary; smooth muscle) and external (voluntary to some degree; skeletal muscle)

Table 19-10 Neural Control of Micturition

Muscle (Ty pe) Parasympathetic

Nerves (Cholinergic)

Sympathetic Nerves

(Adrenergic) Somatic Nerves

Detrusor (smooth muscle)

Contraction +++

Relaxation +

No effect

Internal sphincter (smooth muscle)

No effect Contraction

++ No effect

External sphincter (striated muscle)

No effect No effect Relaxation

++

Figure 19-5

Figure 19-6

Motivation to be continent

Table 19-7Physiologic Requirements for Continence

Adequate cognitive function

Adequate mobility and dexterity

Normal lower urinary tract function

Storage:

Table 19-7Physiologic Requirements for Continence

No involuntary bladder contractions

Appropriate bladder sensation

Closed bladder outlet

Low pressure accommodation of urine

Emptying:

Table 19-7Physiologic Requirements for Continence

Normal bladder contraction

Lack of anatomic obstruction

Coordinated sphincter relaxation & bladder contraction

Absence of environmental/iatrogenic barriers

Table 19-8 Age-Related Changes Contributing to

Incontinence

In FemalesEstrogen deficiency

Weak pelvic floor and bladder outletDecreased urethral muscle tone

Atrophic vaginitis

In MalesIncreased prostatic sizeImpaired urinary flowUrinary retention

Detrusor muscle instability

Table 19-9 Management of Urinary Incontinence Type Management Stress Exercises

Alpha-adrenergic agonistsEstrogenSurgery

Urge Bladder relaxantsSurgery

Overflow alpha-adrenergic antagonistsCatheterization

Functional Habit trainingScheduled toiletingHygienic devices

•Weakness of pelvic muscles

•Inability to avoid voiding when bladder full

• overdistended, non-contractile blood

• cognitive, emotional problems