D115 Unit 6 Cohort Notes: RAAS, Kidney Disorders, and GI Pathophysiology

D115 Unit 6 Cohort Notes: RAAS, Kidney Disorders, and GI Pathophysiology

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Western Governors University

D115 Advanced Pathophysiology for the Advanced Practice Nurse

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Unit 6: Renin–Angiotensin–Aldosterone System (RAAS)

Purpose and Physiological Role

The Renin–Angiotensin–Aldosterone System (RAAS) is a critical hormonal cascade responsible for maintaining systemic blood pressure, extracellular fluid volume, and electrolyte balance. It functions primarily as a compensatory mechanism during states of reduced renal perfusion, hypotension, or decreased sodium concentration.

What Triggers RAAS Activation?

RAAS is activated when the kidneys detect:

• Reduced arterial blood pressure

• Decreased sodium delivery to the distal tubules

• Reduced circulating blood volume

These conditions signal the body to conserve sodium and water in order to restore perfusion and pressure.

Step-by-Step Mechanism of RAAS

The RAAS pathway unfolds through a coordinated, multi-organ process:

1. The liver continuously produces and releases angiotensinogen into the bloodstream.

2. In response to low renal perfusion, the juxtaglomerular cells of the kidneys secrete renin.

3. Renin enzymatically converts angiotensinogen into angiotensin I.

4. Angiotensin-converting enzyme (ACE), primarily produced in the pulmonary endothelium, converts angiotensin I into angiotensin II.

5. Angiotensin II acts as the primary effector hormone of the system.

Physiological Effects of Angiotensin II

Angiotensin II exerts several potent effects that collectively increase blood pressure and volume:

• Stimulates aldosterone secretion from the adrenal cortex

• Enhances sodium and water reabsorption in the distal nephron

• Promotes potassium excretion

• Causes arteriolar vasoconstriction, increasing systemic vascular resistance

Acute Pyelonephritis

Definition

Acute pyelonephritis is an infection involving one or both kidneys, specifically affecting the renal pelvis, calyces, interstitium, and tubules. It represents a severe form of upper urinary tract infection.

Who Is at Risk?

Risk factors include:

• Urinary tract obstruction

• Vesicoureteral reflux

• Female sex due to anatomical predisposition

Causative Pathogens

The condition is most commonly caused by ascending bacterial infections, particularly:

• Escherichia coli

• Proteus species

• Pseudomonas aeruginosa

Pathological Changes

The infection primarily damages renal tubules. Healing often results in:

• Fibrosis

• Tubular atrophy

• Permanent scarring, especially after recurrent infections

Clinical Manifestations

Patients typically present with:

• Fever and chills

• Flank or groin pain

• Dysuria and urinary frequency

• Costovertebral angle tenderness
  Older adults may exhibit nonspecific symptoms such as malaise or low-grade fever.

Diagnosis and Management

Diagnosis is confirmed through urinalysis and urine culture. White blood cell casts, if present, strongly suggest renal involvement. Blood cultures and imaging are reserved for complicated cases.

Treatment consists of targeted antibiotic therapy for 2–3 weeks, with follow-up cultures recommended if symptoms recur.

Acute Glomerulonephritis

Definition

Acute glomerulonephritis refers to inflammatory injury of the glomeruli, which may arise as a primary renal disorder or secondary to systemic disease.

Etiology

Common causes include:

• Immune-mediated responses

• Infections

• Ischemic injury

• Exposure to toxins or drugs

• Vascular disorders

Pathophysiology

Inflammation disrupts the glomerular filtration barrier, including the endothelium, basement membrane, and podocytes. This leads to impaired filtration and progressive nephron damage.

Disease Progression

Symptoms may develop gradually, allowing significant renal injury to occur before clinical recognition. Severe cases may present with oliguria and rapid loss of renal function.

Diabetes Insipidus: Diagnostic Differentiation and Management

How Is Diabetes Insipidus Diagnosed?

The desmopressin (ADH analog) test is used to differentiate between central (neurogenic) and nephrogenic diabetes insipidus.

Treatment Strategies

Neurogenic Diabetes Insipidus

Management includes ADH replacement therapy using desmopressin administered orally, intranasally, or intravenously. Treating the underlying cause, such as trauma or tumors, is essential.

Nephrogenic Diabetes Insipidus

Treatment focuses on removing causative agents (e.g., lithium), ensuring adequate hydration, correcting electrolyte imbalances, and administering thiazide diuretics to reduce urine output. Dietary sodium and protein restriction may be beneficial.

Gastroesophageal Reflux Disease (GERD)

Definition

GERD is a chronic motility disorder characterized by the backward flow of acidic gastric contents into the esophagus, resulting in mucosal injury and inflammation.

Pathophysiology

GERD occurs when the lower esophageal sphincter (LES) fails to maintain adequate resting tone, allowing reflux of acid and pepsin. This dysfunction may result from transient LES relaxation or structural weakness.

Contributing Factors

Conditions that increase intra-abdominal pressure exacerbate GERD, including obesity, pregnancy, coughing, vomiting, and heavy lifting.

Clinical Manifestations

Common symptoms include heartburn, epigastric pain after meals, chronic cough, laryngitis, asthma exacerbations, and sinusitis.

Diagnostic Evaluation

Upper endoscopy is the primary diagnostic tool, often accompanied by biopsy to exclude Barrett’s esophagus, a premalignant condition.

Treatment Approaches

Glomerulonephritis

Overview

Glomerulonephritis encompasses a group of inflammatory renal disorders affecting the glomeruli, impairing waste removal and fluid regulation.

Types of Glomerulonephritis

Causes

Etiologies include infections, autoimmune diseases, drug toxicity, hypertension, diabetes, genetic disorders, and malignancies.

Clinical Features

Acute disease presents with hematuria, edema, and hypertension, whereas chronic disease manifests with proteinuria, nocturia, fatigue, and generalized edema.

Diagnosis and Treatment

Diagnosis relies on laboratory testing, imaging, and renal biopsy. Management includes antibiotics (if infectious), immunomodulatory therapies, blood pressure control, dietary modification, dialysis, or transplantation in advanced cases.

Nephrotic Syndrome

Definition and Key Features

Nephrotic syndrome is a clinical condition characterized by:

• Heavy proteinuria (>3.5 g/day)

• Hypoalbuminemia

• Generalized edema

• Hyperlipidemia

Pathophysiology

Damage to the glomerular filtration barrier increases permeability, allowing albumin loss. This results in decreased plasma oncotic pressure, fluid shifts into interstitial spaces, RAAS activation, and worsening edema.

Types and Causes

Primary forms include minimal change disease and focal segmental glomerulosclerosis. Secondary causes include diabetes, amyloidosis, infections, and systemic diseases.

Complications

Patients are at increased risk for infections, thromboembolism, nutritional deficiencies, and cardiovascular disease.

Management Strategies

Dietary Management

Nutritional therapy plays a foundational role in the management of nephrotic syndrome. A normal protein diet, adjusted according to the patient’s nutritional status, is recommended to prevent muscle wasting while avoiding excess protein intake. High-protein diets are discouraged because they can exacerbate proteinuria and accelerate renal damage. Sodium restriction is essential to reduce edema and fluid retention. In patients receiving long-term corticosteroid therapy, particularly those who are overweight or obese, caloric intake should be carefully regulated to prevent steroid-induced weight gain and metabolic complications.

Pharmacologic Therapy

Pharmacologic treatment is directed toward inducing remission, reducing proteinuria, and controlling associated symptoms. Corticosteroids, particularly prednisone, remain the cornerstone of therapy for inducing remission in many forms of nephrotic syndrome. When steroid resistance or frequent relapses occur, immunosuppressive agents such as cyclophosphamide and cyclosporine are employed to suppress immune-mediated glomerular injury.

To manage edema, diuretics are prescribed. Loop diuretics such as furosemide are effective in promoting fluid excretion, while potassium-sparing agents like spironolactone help prevent hypokalemia. Angiotensin-converting enzyme (ACE) inhibitors—including captopril, enalapril, and lisinopril—and angiotensin receptor blockers (ARBs) such as losartan and valsartan are used to lower intraglomerular pressure and significantly reduce proteinuria, thereby slowing disease progression.

Management of Complications

Hypertension is a frequent complication and requires strict control using agents such as nifedipine and hydralazine, with beta-blockers like atenolol added when necessary. Patients with nephrotic syndrome are at increased risk for thromboembolic events due to hypercoagulability; therefore, early mobilization and close monitoring for signs of thrombosis are essential.

Infection prevention is critical because urinary protein loss leads to immunoglobulin deficiency. Prophylactic penicillin V may be indicated in patients with gross ascites or sepsis risk, while active infections are treated with appropriate antibiotics such as cephalosporins or flucloxacillin. Hypovolemia resulting from excessive diuresis or fluid shifts may require intravenous albumin infusions to restore effective circulating volume.

Key Takeaways

Nephrotic syndrome is characterized by significant protein loss, fluid imbalance, and increased risk of thrombosis and infection. Effective management requires a combination of dietary regulation, pharmacologic therapy, and proactive complication prevention. Early diagnosis and timely treatment are essential to preserve renal function and improve long-term outcomes.

Peptic Ulcer Disease (PUD) Overview

Definition and Classification

Peptic ulcer disease refers to a disruption in the mucosal lining of the lower esophagus, stomach, or duodenum caused by acid and pepsin activity. Ulcers may present as acute or chronic lesions and range in severity from superficial erosions to deep, penetrating ulcers that increase the risk of bleeding or perforation.

Risk Factors

The most significant infectious cause of PUD is Helicobacter pylori infection. Medication-related factors include chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs) and aspirin. Lifestyle factors such as smoking and excessive alcohol consumption contribute to mucosal injury. Additional risk factors include chronic illnesses (e.g., COPD, cirrhosis), obesity, advanced age, low socioeconomic status, and genetic susceptibility.

Types of Ulcers and Clinical Presentation

Gastric ulcers commonly produce burning epigastric pain accompanied by nausea, bloating, and reduced appetite. Duodenal ulcers often cause pain on an empty stomach or during the night and are typically relieved by food intake. Esophageal ulcers are primarily associated with gastroesophageal reflux disease and present with heartburn and difficulty swallowing.

Diagnostic Evaluation

Upper gastrointestinal endoscopy remains the diagnostic gold standard, allowing direct visualization and biopsy of ulcers. Testing for H. pylori is performed via tissue biopsy or stool antigen testing. Laboratory investigations, including complete blood count and iron studies, help identify anemia secondary to chronic bleeding.

Treatment Approaches

H. pylori–Positive Ulcers

Standard therapy includes either clarithromycin-based triple therapy for 14 days or bismuth-based quadruple therapy for 10–14 days, both incorporating proton pump inhibitors (PPIs) to suppress acid secretion.

H. pylori–Negative Ulcers

Management consists of PPI monotherapy for 6–8 weeks, avoidance of ulcerogenic medications, and follow-up endoscopy to confirm healing.

Lifestyle and Surgical Considerations

Patients are advised to avoid NSAIDs, alcohol, and smoking. Dietary irritants should be minimized. Surgical intervention is reserved for refractory ulcers or life-threatening complications such as perforation or hemorrhage.

Overview of Pyelonephritis

Definition and Types

Pyelonephritis is an infection involving the renal pelvis, calyces, and interstitium. Acute pyelonephritis presents suddenly with systemic symptoms, whereas chronic pyelonephritis results from recurrent infections or persistent obstruction, leading to irreversible renal scarring.

Etiology and Pathophysiology

The most common causative organism is Escherichia coli, followed by Proteus and Pseudomonas species. Acute infection causes neutrophilic infiltration, renal edema, and purulent urine, while chronic disease leads to progressive fibrosis, tubular atrophy, and impaired concentrating ability.

Clinical Manifestations

Acute pyelonephritis typically presents with fever, chills, flank pain, and urinary symptoms. Chronic disease may manifest as hypertension, progressive renal failure, electrolyte imbalance, and metabolic acidosis.

Diagnosis and Treatment

Diagnosis relies on urinalysis and urine culture. Imaging studies such as ultrasound and intravenous pyelography are useful in chronic cases. Treatment involves prolonged, culture-directed antibiotic therapy and correction of underlying structural abnormalities.

Renin–Angiotensin–Aldosterone System (RAAS)

Physiologic Overview

The RAAS is a hormonal cascade activated in response to decreased blood pressure, sodium depletion, or reduced circulating volume. Its primary function is to restore hemodynamic stability.

RAAS Cascade Summary

Angiotensin II causes vasoconstriction and stimulates aldosterone release, leading to sodium and water retention while promoting potassium excretion. ACE inhibitors and ARBs interrupt this cascade and are widely used in hypertension and renal disease.

Renal Calculi (Kidney Stones)

Overview and Pathogenesis

Renal calculi are crystalline aggregates formed from supersaturated urine. Stone formation involves supersaturation, precipitation, crystal growth, and inadequate inhibition by substances such as citrate.

Urine pH and Stone Type

Management and Prevention

Treatment focuses on pain control, hydration, and facilitating stone passage. Large or obstructive stones may require lithotripsy or surgical removal. Preventive strategies include increased fluid intake, sodium restriction, moderation of animal protein, and maintaining balanced calcium intake.

Renal Failure Overview

Acute and Chronic Renal Failure

Renal failure involves impaired filtration, fluid regulation, and electrolyte balance. Acute renal failure may be prerenal, intrarenal, or postrenal, whereas chronic kidney disease represents progressive, irreversible nephron loss.

Dialysis Modalities

Hemodialysis and continuous renal replacement therapy are used to manage advanced renal failure. While dialysis removes waste and excess fluid, it does not reverse kidney damage.

Urinary Tract Infections

Definition and Risk Factors

Urinary tract infections result from bacterial invasion of the urinary epithelium, most commonly by E. coli. Risk factors include sexual activity, pregnancy, menopause, urinary obstruction, and poor hygiene.

Clinical Features and Management

Cystitis presents with dysuria, urgency, and suprapubic pain, whereas pyelonephritis involves systemic symptoms such as fever and flank pain. Diagnosis is confirmed through urinalysis and culture. Treatment includes targeted antibiotics, hydration, and preventive education to reduce recurrence.

References

Centers for Disease Control and Prevention. (2023). Urinary tract infection (UTI).
https://www.cdc.gov

Kasper, D. L., Fauci, A. S., Hauser, S. L., Longo, D. L., Jameson, J. L., & Loscalzo, J. (2022). Harrison’s principles of internal medicine (21st ed.). McGraw-Hill.

National Institute of Diabetes and Digestive and Kidney Diseases. (2023). Kidney disease and renal failure.
https://www.niddk.nih.gov

Sung, J. J. Y., Kuipers, E. J., & El-Serag, H. B. (2020). Systematic review: The global incidence and prevalence of peptic ulcer disease. Alimentary Pharmacology & Therapeutics, 29(9), 938–946.

UpToDate. (2024). Management of nephrotic syndrome, pyelonephritis, and renal calculi. Wolters Kluwer.

Guyton, A. C., & Hall, J. E. (2021). Textbook of medical physiology (14th ed.). Elsevier.

Kumar, V., Abbas, A. K., & Aster, J. C. (2020). Robbins and Cotran pathologic basis of disease (10th ed.). Elsevier.

McCance, K. L., & Huether, S. E. (2019). Pathophysiology: The biologic basis for disease in adults and children (8th ed.). Elsevier.

National Institute of Diabetes and Digestive and Kidney Diseases. (2023). Kidney disease overview.

Feldman, M., Friedman, L. S., & Brandt, L. J. (2021). Sleisenger and Fordtran’s gastrointestinal and liver disease (11th ed.). Elsevier.