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

Grace J.
January 2, 2026January 2, 2026
D115, MSN, Western Governors University

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Western Governors University

D115 Advanced Pathophysiology for the Advanced Practice Nurse

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Date

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

Purpose and Physiological Importance

The Renin–Angiotensin–Aldosterone System (RAAS) is a vital hormonal mechanism that plays a key role in regulating systemic blood pressure, maintaining extracellular fluid volume, and balancing electrolytes. This system acts primarily as a compensatory response to conditions such as decreased renal blood flow, low blood pressure, or reduced sodium levels. By doing so, it helps restore and maintain hemodynamic stability and homeostasis.

What Stimulates RAAS Activation?

RAAS is triggered when the kidneys sense specific physiological changes, including:

A decline in arterial blood pressure
A decrease in sodium delivery to the distal tubules
A reduction in circulating blood volume

These signals prompt the body to conserve sodium and water, aiding in the restoration of adequate blood pressure and tissue perfusion.

Stepwise Mechanism of RAAS Activation

The RAAS involves a multi-organ cascade described as follows:

Step	Organ/Site	Action
1	Liver	Produces and releases angiotensinogen into the bloodstream.
2	Kidney (juxtaglomerular cells)	Secretes renin in response to low perfusion.
3	Blood	Renin converts angiotensinogen into angiotensin I.
4	Lungs (pulmonary endothelium)	ACE converts angiotensin I to angiotensin II.
5	Adrenal cortex	Releases aldosterone under stimulation by angiotensin II.
6	Kidneys and blood vessels	Aldosterone promotes sodium retention; angiotensin II causes vasoconstriction.

Physiological Effects of Angiotensin II

Angiotensin II, the main effector hormone, produces multiple effects:

Stimulates aldosterone secretion, enhancing sodium and water reabsorption in the kidneys.
Promotes potassium excretion to maintain electrolyte balance.
Induces arteriolar vasoconstriction, increasing systemic vascular resistance and raising blood pressure.

Acute Pyelonephritis

What Is Acute Pyelonephritis?

Acute pyelonephritis is an infection that affects one or both kidneys, specifically targeting the renal pelvis, calyces, interstitial tissue, and renal tubules. It is a severe type of upper urinary tract infection that can lead to significant renal damage if untreated.

Who Is Susceptible?

Risk factors that predispose individuals include:

Urinary tract obstructions, such as stones or strictures
Vesicoureteral reflux, especially in children
Female anatomical factors that facilitate ascending infections

Which Microorganisms Cause It?

The infection usually arises from bacteria traveling upward from the lower urinary tract, most commonly:

Escherichia coli (the predominant pathogen)
Proteus species
Pseudomonas aeruginosa

What Are the Pathological Changes?

The infection mainly harms renal tubules, leading to:

Fibrosis and scarring due to inflammation
Tubular atrophy from repeated injury
Permanent loss of functional renal tissue after recurrent episodes

What Are the Symptoms?

Typical clinical features include:

High fever and chills
Flank or groin pain
Dysuria and increased urinary frequency
Tenderness at the costovertebral angle
Older adults may present atypically with fatigue or mild fever rather than classic symptoms.

How Is It Diagnosed and Treated?

Diagnosis relies on urinalysis and urine culture; the presence of white blood cell casts strongly suggests renal involvement. Blood cultures and imaging may be required for complicated cases. Treatment involves targeted antibiotics for 2 to 3 weeks, with follow-up cultures if symptoms persist or recur.

Acute Glomerulonephritis

What Is Acute Glomerulonephritis?

Acute glomerulonephritis is characterized by inflammation and injury to the glomeruli. It may occur as a primary kidney disorder or secondary to systemic conditions.

What Causes It?

The condition can result from:

Immune-mediated mechanisms (e.g., post-infectious)
Infectious agents
Ischemic damage
Exposure to toxins or drugs
Vascular diseases

How Does It Affect the Kidney?

Inflammation compromises the glomerular filtration barrier (including endothelial cells, basement membrane, and podocytes), causing reduced filtration efficiency and progressive nephron damage.

What Is the Clinical Course?

Symptoms often develop slowly, allowing significant renal injury before detection. Severe cases may present with decreased urine output (oliguria) and rapid kidney function decline.

Diabetes Insipidus: Diagnosis and Management

How Is Diabetes Insipidus Diagnosed?

The desmopressin (ADH analog) test differentiates between two forms of diabetes insipidus (DI):

Type of DI	Response to Desmopressin
Neurogenic (central)	Increase in urine osmolality
Nephrogenic	No significant change in urine osmolality

What Are the Treatment Approaches?

Neurogenic DI:

Administer desmopressin via oral, nasal, or intravenous routes to replace ADH.
Address underlying causes such as trauma or tumors.

Nephrogenic DI:

Remove offending agents like lithium.
Maintain adequate hydration and correct electrolyte imbalances.
Use thiazide diuretics to decrease urine output.
Dietary modifications, including sodium and protein restriction, may help.

Gastroesophageal Reflux Disease (GERD)

What Is GERD?

GERD is a chronic condition where acidic stomach contents reflux into the esophagus, causing mucosal injury and inflammation.

How Does GERD Develop?

The primary mechanism involves the failure of the lower esophageal sphincter (LES) to maintain sufficient tone. This allows acid and pepsin reflux, either due to transient LES relaxations or structural weakness.

What Factors Worsen GERD?

Increased intra-abdominal pressure from obesity, pregnancy, coughing, vomiting, or heavy lifting can exacerbate reflux.

What Symptoms Are Common?

Heartburn and epigastric discomfort after meals
Chronic cough and hoarseness
Asthma exacerbations and sinus infections

How Is GERD Diagnosed?

Upper endoscopy with biopsy is the main diagnostic tool to assess mucosal damage and exclude premalignant conditions like Barrett’s esophagus.

What Treatments Are Available?

Treatment Category	Description
First-line	Proton pump inhibitors (e.g., omeprazole)
Second-line	H2 receptor antagonists (e.g., famotidine)
Adjunctive	Antacids, prokinetics
Lifestyle	Weight loss, dietary changes, bed elevation
Surgical	Laparoscopic fundoplication for refractory cases

Glomerulonephritis Overview

What Is Glomerulonephritis?

Glomerulonephritis refers to a group of inflammatory disorders targeting the kidney’s glomeruli, leading to impaired filtration and fluid regulation.

What Are the Types and Causes?

Type	Features
Acute	Sudden onset, often following infection
Chronic	Progressive deterioration leading to CKD

Common causes include infections, autoimmune diseases, drug toxicity, hypertension, diabetes, genetic factors, and malignancies.

What Are the Clinical Features?

Acute cases manifest hematuria, edema, and hypertension.
Chronic cases show proteinuria, nocturia, fatigue, and generalized edema.

How Is It Diagnosed and Managed?

Diagnosis involves laboratory tests, imaging, and renal biopsy. Treatment varies from antibiotics to immunosuppressants, with blood pressure control and dietary management. Advanced cases may require dialysis or transplantation.

Nephrotic Syndrome

Definition and Characteristics

Nephrotic syndrome is marked by heavy proteinuria (>3.5 g/day), hypoalbuminemia, generalized edema, and hyperlipidemia.

Pathophysiology

Damage to the glomerular filtration barrier increases permeability, allowing albumin loss and resulting in decreased plasma oncotic pressure. This leads to fluid shifting into tissues and activation of RAAS, worsening edema.

Types and Causes

Primary causes include minimal change disease and focal segmental glomerulosclerosis, while secondary causes involve diabetes, amyloidosis, infections, and systemic illnesses.

What Complications Arise?

Patients face heightened risks of infections, thromboembolism, nutritional deficits, and cardiovascular problems.

Management Strategies

Dietary Management

Maintain a balanced protein intake to prevent muscle loss but avoid excess protein to reduce renal strain.
Restrict sodium to control edema.
Caloric intake should be moderated, especially in patients on corticosteroids to prevent metabolic side effects.

Pharmacologic Therapy

Corticosteroids like prednisone induce remission.
Immunosuppressants (cyclophosphamide, cyclosporine) are used for steroid-resistant or relapsing cases.
Diuretics manage edema (loop diuretics and potassium-sparing agents).
ACE inhibitors and ARBs reduce proteinuria and preserve renal function.

Complication Management

Strict blood pressure control using nifedipine, hydralazine, and beta-blockers.
Prevent thromboembolism through early mobilization and monitoring.
Infection prevention with prophylactic antibiotics if necessary.
Address hypovolemia with intravenous albumin as needed.

Peptic Ulcer Disease (PUD) Overview

What Is PUD?

Peptic ulcer disease consists of mucosal erosions or ulcers in the lower esophagus, stomach, or duodenum due to acid and pepsin injury.

What Are the Risk Factors?

Helicobacter pylori infection is the main infectious cause.
Chronic NSAID or aspirin use contributes significantly.
Lifestyle factors like smoking and alcohol worsen mucosal damage.
Other factors include chronic illnesses, obesity, older age, low socioeconomic status, and genetics.

What Are the Types and Symptoms?

Ulcer Type	Location	Characteristic Features
Gastric	Stomach	Pain worsens after eating, weight loss, early satiety
Duodenal	Duodenum	Pain relieved by food, often nocturnal
Esophageal	Esophagus	Associated with GERD symptoms, dysphagia

How Is It Diagnosed?

Upper gastrointestinal endoscopy allows direct visualization and biopsy. Testing for H. pylori includes tissue biopsy or stool antigen assays. Blood tests help identify anemia from chronic bleeding.

What Treatments Are Recommended?

Condition	Treatment Approach
H. pylori-positive ulcers	Clarithromycin-based triple therapy or bismuth-based quadruple therapy with PPIs
H. pylori-negative ulcers	Proton pump inhibitors for 6–8 weeks, avoidance of ulcerogenic drugs

Lifestyle modifications include avoiding NSAIDs, alcohol, and smoking, with surgery reserved for complicated or refractory cases.

Overview of Pyelonephritis

What Is Pyelonephritis?

Pyelonephritis is an infection of the kidney’s pelvis, calyces, and interstitial tissue. It presents acutely with systemic symptoms or chronically due to recurrent infections causing scarring.

What Causes It and How Does It Progress?

The commonest pathogen is E. coli, followed by Proteus and Pseudomonas. Acute infections lead to inflammation and purulent urine, while chronic disease results in fibrosis and loss of concentrating ability.

What Are the Clinical Features?

Acute pyelonephritis causes fever, chills, flank pain, and urinary symptoms. Chronic cases may show hypertension, renal failure, and metabolic disturbances.

Diagnosis and Treatment

Urinalysis and culture confirm infection; imaging is useful in chronic disease. Treatment requires prolonged antibiotics and correction of any structural abnormalities.

Renin–Angiotensin–Aldosterone System (RAAS) Summary

Step	Organ/Site	Action
1	Liver	Releases angiotensinogen.
2	Kidney	Renin converts angiotensinogen to angiotensin I.
3	Lungs	ACE converts angiotensin I to angiotensin II.
4	Adrenal cortex	Aldosterone is secreted.
5	Kidneys & vessels	Sodium retention and vasoconstriction occur.

ACE inhibitors and ARBs block this cascade and are important in managing hypertension and kidney diseases.

Renal Calculi (Kidney Stones)

Overview and Formation

Renal calculi are crystalline masses formed in supersaturated urine. Their formation depends on supersaturation, crystal nucleation, growth, and insufficient inhibition by substances like citrate.

Relationship Between Urine pH and Stone Type

Urine pH	Stone Type
>7.0	Calcium phosphate
<5.0	Uric acid

Management and Prevention

Treatment includes pain control, hydration, and facilitating stone passage. Larger stones may require lithotripsy or surgery. Prevention involves increased fluids, sodium restriction, moderated animal protein intake, and balanced calcium consumption.

Renal Failure Overview

Acute vs. Chronic

Renal failure results from impaired filtration and fluid/electrolyte regulation. Acute renal failure can be prerenal, intrarenal, or postrenal. Chronic kidney disease (CKD) is progressive and irreversible.

Dialysis Modalities

Hemodialysis and continuous renal replacement therapies remove wastes and fluids but do not restore kidney function.

Urinary Tract Infections (UTIs)

What Are UTIs?

UTIs are bacterial infections of the urinary tract, predominantly caused by E. coli.

Risk Factors

Sexual activity, pregnancy, menopause, urinary obstruction, and hygiene affect risk.

Clinical Presentation and Management

Cystitis presents with dysuria, urgency, and suprapubic pain.
Pyelonephritis includes systemic symptoms like fever and flank pain.

Diagnosis is by urinalysis and culture. Treatment includes appropriate antibiotics, hydration, and preventive measures.

References

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

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

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

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.

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 and renal failure. https://www.niddk.nih.gov