Clinical Pathology: Diseases, Causes and Pathogenesis

Posted on Feb 16, 2026 in Medicine & Health

Feedback System

FEEDBACK SYSTEM. When there are changes in the internal environment of the body, the body’s feedback system acts to return it to the normal equilibrium condition. A feedback system includes three basic components:

  • Receptor
  • Control Centre
  • Effector

Receptor

A receptor is a body structure that monitors or detects changes in the internal environment of the body.

Control Centre

A control centre receives input from receptors and generates output in the form of nerve impulses, hormones or other chemical signals.

Effector

An effector is a body structure that receives output from the control centre and responds to its commands.

Types of Feedback Systems

There are basically two types of feedback systems:

  1. Positive feedback system
  2. Negative feedback system

Negative Feedback System

A negative feedback system responds to reverse or decrease changes in the internal environment. Example: regulation of blood pressure.

(Stimulus Increase in heart rate) – (Blood pressure increases) – (Receptor Baroreceptor activates and sends input to the control centre in the form of nerve impulses) – (Control Centre Brain collects input and sends output) – (Effector Blood vessels receive output and dilate) – (Blood pressure decreases) – (Blood pressure back to normal; body returns to homeostasis).

Positive Feedback System

A positive feedback system responds to increase the change in the internal environment. Example: normal childbirth.

(Stimulus Contraction of uterine wall forces the baby’s head/body to the cervix) – (Stretching of the cervix) – (Receptor Stretch-sensitive nerve cells send input to the control centre in the form of nerve impulses) – (Control Centre Brain collects input and sends output by releasing oxytocin) – (Effector Uterine muscles contract more forcefully) – (Baby’s body stretches the cervix more). Increased stretching of the cervix causes release of more oxytocin, which results in further stretching of the cervix.

Cell Injury

CELL INJURY Cells are the basic unit of tissues, which form organs and systems in the human body. Cell injury is defined as the effect of a variety of stresses that cause changes in a cell’s internal as well as external environment. The cellular responses to stress depend on many factors and cell injury can be either reversible or irreversible.

Cellular Adaptation

Cellular adaptation is a process by which a cell survives in an adverse situation. These are temporary or permanent changes in the shape, size or type of cell. Examples: atrophy, hypertrophy, hyperplasia, etc.

Reversible Cell Injury

If the stress applied to the cell is mild to moderate and the stress is removed, cells recover back to their normal state; this phenomenon is known as reversible cell injury.

Irreversible Cell Injury

If the stress applied to the cell is severe, it may lead to cell death and the cells never recover; this phenomenon is known as irreversible cell injury.

Etiology / Causes of Cell Injury

There are a variety of causes or stresses which can cause cell injury. They can be mainly classified into two classes:

  1. Genetic causes
  2. Acquired causes

Genetic Causes

When cell injury occurs due to defects in genes or chromosomes, these are genetic causes. They include the following types:

  1. Developmental defect
  2. Cyto-genetic defect
  3. Single gene defect
  4. Multifunctional inheritance disorder
Developmental Defect

Defects that occur during the early development of fetal life.

Cyto-genetic Defect

Defects related to abnormalities of chromosomes; these can be structural or numerical.

Single Gene Defects

Also known as Mendelian disorders and occur due to a defect in a single specific gene.

Multifunctional Inheritance Disorder

Disorders that occur due to defects in multiple genes.

Acquired Causes

Other than genetic causes, there are many acquired causes responsible for cell injury. These include:

  1. Hypoxia / ischemia
  2. Physical agents
  3. Chemical agents
  4. Microbial agents
  5. Immunological agents
  6. Nutritional derangements
  7. Psychogenic factors

Mediators of Inflammation

MEDIATORS OF INFLAMMATION Factors or chemicals that mediate the process of inflammation by vascular and cellular events are known as mediators of inflammation. These mediators can be either cell-derived or plasma-derived.

Properties of Mediators

Mediators are released from cells or from plasma proteins in response to certain stimuli. Mediators act on different targets. They may have similar actions on different target cells or different actions on different target cells. They may act on the cells that produced them or on other body cells. Common actions of mediators are increased vascular permeability, vasodilation, fever and pain. Mediators have a short lifespan.

Major Mediator Categories

Cell-derived mediators

  • Vasoactive amines
  • Arachidonic acid metabolites (eicosanoids)
  • Lysosomal components
  • Platelet activating factor
  • Cytokines
  • Free radicals / oxygen metabolites and nitric oxide

Plasma-derived mediators

  • The kinin system
  • The clotting system
  • The fibrinolytic system
  • The complement system

Cell-Derived Mediators

  1. Vasoactive Amines — They give the earliest inflammatory response. Main types: histamine, serotonin (5-hydroxytryptamine) and neuropeptides.
  2. Arachidonic Acid Metabolites (Eicosanoids) — Arachidonic acid is a fatty acid constituent of the phospholipid cell membrane. It is released from the cell membrane by phospholipases. Prostaglandins are major arachidonic acid metabolites.
  3. Lysosomal Components — Inflammatory cells (neutrophils and monocytes) contain lysosomal granules which act as inflammatory mediators. They are responsible for chemotaxis, degradation of bacteria and release of enzymes such as collagenase.
  4. Platelet Activating Factor — Released from basophils, mast cells, endothelium and platelets. Actions: increased vascular permeability, vasodilation, adhesion and chemotaxis.
  5. Cytokines — Polypeptide substances produced by activated lymphocytes and monocytes. Major functions include promoting adhesion and vasodilation.
  6. Oxygen Metabolites and Nitric Oxide — Oxygen-derived metabolites are released from activated leukocytes and contribute to microbial killing and tissue injury.

Hypertension

HYPERTENSION The term hypertension refers to high blood pressure. It is a chronic medical condition in which blood pressure is abnormally high. It occurs when blood vessels become narrowed, causing blood to exert more pressure on the heart and vessel walls.

Types of Hypertension

  1. Primary (essential) hypertension
  2. Secondary hypertension

Primary Hypertension

Also known as essential hypertension. About 95% of patients with high blood pressure have primary hypertension. The exact causes are generally unidentified.

Secondary Hypertension

Secondary hypertension arises from other medical conditions such as kidney disease, arterial disease, heart disease or endocrine disorders. It is less common, affecting 5–10% of hypertensive patients, and is more common in younger people.

Pathogenesis of Hypertension

The pathogenesis is multifactorial and complex. Mechanisms include:

  1. Increased arteriolar resistance
  2. Chronic renal failure
  3. Sympathetic activation
  4. Activation of the RAAS (renin–angiotensin–aldosterone system)

Increased Arteriolar Resistance

An increase in arteriolar resistance can raise arterial blood pressure. Causes include thinning and fracturing of elastin, increased collagen deposition and increased wall thickness. This increases the risk of stroke, coronary artery disease and congestive heart failure.

Chronic Renal Failure

When the kidneys do not function properly they fail to excrete normal amounts of sodium, leading to sodium and water retention, increased blood volume and hypertension.

Sympathetic Activation

Stress and other factors lead to activation of the sympathetic nervous system, causing increased release of nor-epinephrine, increased cardiac output and increased systemic vascular resistance.

Activation of RAAS

RAAS stands for renin–angiotensin–aldosterone system. Renin is released by the kidney and angiotensinogen by the liver; together they lead to activation of aldosterone and sodium retention, contributing to hypertension.

Asthma

ASTHMA Asthma can be categorized into four major types:

  1. Extrinsic (atopic) asthma
  2. Intrinsic (non-atopic) asthma
  3. Drug-induced asthma
  4. Occupational asthma

Extrinsic Asthma

Also known as atopic or allergic asthma. It is the most common type and occurs due to allergens. It usually begins in childhood or early adult life.

Intrinsic Asthma

Also known as non-atopic or non-allergic asthma. It generally occurs due to lung infections or other non-allergic triggers and typically develops later in adult life.

Drug-Induced Asthma

Triggered by the use of certain medications such as aspirin, NSAIDs and some beta blockers.

Occupational Asthma

Caused by exposure to specific substances in the workplace such as chemicals, dust and gases.

Stages of Respiration

There are three stages of respiration:

  1. Breathing (ventilation)
  2. Internal respiration (gas exchange between blood and tissues)
  3. Cellular respiration (cellular use of oxygen to produce energy)

Mechanism of Breathing

Two phases: inspiration and expiration.

Respiratory Diseases

The diseases or disorders related to the respiratory system include many conditions such as:

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)

Asthma (Clinical)

Asthma is a chronic, inflammatory, reversible airway disease in which a person’s airways become inflamed, narrow and swell and produce extra mucus, making it difficult to breathe. Asthma requires ongoing management and affects the airways of the lungs.

Etiology
  1. Smoking
  2. Cold or dry air
  3. Air pollutants
  4. Food chemicals
  5. Certain medications
  6. Family history
  7. Obesity
  8. Lung infections
Pathogenesis

The pathogenesis of an asthmatic attack can be described as: activation of T-helper cells → release of cytokines → stimulation/activation of plasma B cells → generation of IgE antibodies → binding of IgE to mast cells → entry of foreign particles/antigens/allergens → antigen–antibody complex → degranulation of mast cells → release of inflammatory mediators (histamine, leukotrienes, prostaglandins).

Renal Failure

RENAL FAILURE Renal failure, also known as kidney failure, occurs when kidneys lose their ability to effectively filter waste products and excess fluids from the blood. This condition can lead to buildup of toxins and fluids in the body, causing various complications and can become life-threatening if not managed appropriately.

Based on severity it can be divided into:

  1. Acute renal failure (acute kidney injury)
  2. Chronic renal failure (chronic kidney disease)

Acute Renal Failure (Acute Kidney Injury)

Acute renal failure (acute kidney injury, AKI) occurs when there is a sudden loss of kidney function and the kidneys become unable to filter waste products from the blood. It develops rapidly over hours or days. It can be reversible but if not treated can progress to chronic renal failure.

Types
  1. Pre-renal failure
  2. Intra-renal (intrinsic) failure
  3. Post-renal failure
Pre-renal Failure

Occurs when there is a sudden decrease in blood flow to the kidneys (e.g., hypovolemia, low blood pressure, cardiac failure).

Intra-renal Failure

Occurs when there is direct damage to the kidney itself due to injury, inflammation or infection (e.g., acute tubular necrosis, glomerulonephritis, interstitial nephritis).

Post-renal Failure

Occurs when there is obstruction of urine flow from the kidneys to the bladder and out of the body (e.g., stones, tumour, strictures).

Etiology / Causes
  1. Prerenal: low blood pressure, hypovolemia, cardiac failure
  2. Intrarenal: acute tubular necrosis, glomerulonephritis, interstitial nephritis
  3. Postrenal: kidney stones, bladder tumour, blood clots

Chronic Renal Failure (Chronic Kidney Disease)

Chronic renal failure (chronic kidney disease, CKD) is defined as gradual loss of kidney function over time. It is generally progressive and irreversible. It eventually leads to end-stage renal disease (ESRD) when sufficient nephrons have been damaged and the kidney fails completely.

Stages of CKD
  1. Stage 1: GFR ≥ 90
  2. Stage 2: GFR 60–89
  3. Stage 3: GFR 30–59
  4. Stage 4: GFR 15–29
  5. Stage 5: GFR < 15
Causes / Etiology
  1. Diabetes
  2. Hypertension
  3. Pyelonephritis
  4. Urinary tract infections
  5. Glomerulonephritis
  6. Interstitial nephritis
  7. Polycystic kidney disease
Pathogenesis

Pathogenesis of chronic renal failure involves progressive nephron loss, compensatory hyperfiltration of remaining nephrons, glomerulosclerosis and further decline in glomerular filtration rate leading to end-stage renal disease.

Anaemia

ANAEMIA Anaemia is a medical condition defined as a deficiency in the number or quality of red blood cells (RBCs) or reduced haemoglobin concentration or hematocrit (PCV) below the normal range. In anaemia, the oxygen-carrying capacity of blood is reduced. Normal haemoglobin ranges are: male 13 g/dl, female 11–12 g/dl.

Types of Anaemia

There are many types of anaemia, but the syllabus focuses on these:

  1. Iron deficiency anaemia
  2. Megaloblastic anaemia
  3. Sickle cell anaemia
  4. Thalassemia

1. Iron Deficiency Anaemia

Iron deficiency anaemia is a type of anaemia in which there is lack of iron in the body. Bone marrow needs iron to synthesize haemoglobin. Without it, the body cannot make enough haemoglobin leading to decreased oxygen-carrying capacity. It is the most common type of anaemia and is also known as microcytic hypochromic anaemia.

Causes
  1. Blood loss: menstrual periods, gastrointestinal bleeding, trauma or injury
  2. Low iron diet: less consumption of foods such as green leafy vegetables, beans, pumpkin seeds, tofu, meat
  3. Increased requirement: pregnancy, lactation, childhood (growth)
  4. Poor absorption: inflammatory bowel disease, celiac disease, gastric surgery
Pathogenesis

The pathogenesis involves several stages affecting body iron stores and subsequent impact on RBC production:

  1. Iron depletion — body uses iron stores (liver, spleen, bone marrow); serum ferritin decreases.
  2. Iron-deficient erythropoiesis — insufficient iron for haemoglobin synthesis; changes in transferrin and ferritin levels.
  3. Iron deficiency anaemia — RBCs become smaller (microcytic) and paler (hypochromic); haemoglobin levels fall and oxygen-carrying capacity is reduced.

3. Megaloblastic Anaemia

Megaloblastic anaemia is characterised by unusually large abnormal RBCs called megaloblasts. It generally occurs due to deficiency of vitamin B12 (cobalamin) or folic acid (folate, vitamin B9). There is a nuclear maturation defect due to impaired DNA synthesis. It is also known as macrocytic normochromic anaemia.

Causes
  1. Decreased intake: inadequate intake of vitamin B12 (animal products) or folic acid (green leafy vegetables, nuts, seeds)
  2. Increased demand: pregnancy, lactation, growth
  3. Malabsorption: inflammatory bowel disease, celiac disease, Crohn’s disease, certain medications
Pathogenesis

(Lack of vitamin B12 and/or folic acid) → impaired DNA synthesis → defective nuclear maturation (nuclear maturation lags behind cytoplasmic maturation) → ineffective erythropoiesis → formation of macrocytes / megaloblasts → megaloblastic anaemia.

Symptoms
  1. Weakness
  2. Shortness of breath
  3. Pale skin
  4. Rapid heartbeat
  5. Headache
  6. Glossitis
Complications
  1. Congestive heart failure
  2. Vision problems
  3. Memory loss
  4. Infertility
  5. Pernicious anaemia
  6. Neurological disorders
Treatment / Management
  1. Vitamin B12 and folic acid rich diet
  2. Supplementation
  3. Medications
  4. Intravenous injections when necessary

4. Sickle Cell Anaemia

Sickle cell anaemia is an inherited genetic disorder characterised by sickle-shaped RBCs. It occurs due to production of abnormal haemoglobin (HbS). It is an autosomal recessive disorder and is a qualitative haemoglobinopathy. RBCs become rigid, sticky and less flexible. HbS is very sensitive to low O2 and there is premature death of RBCs (10–20 days lifespan).

Etiology

Caused by mutation in the beta chain of haemoglobin. Affected individuals inherit two copies of the mutated gene, one from each parent. Parents may be carriers (sickle cell trait).

Pathogenesis

Hemoglobin mutation: beta-globin chain mutation (single point mutation at 6th position; glutamic acid substituted with valine) → HbA changes to HbS (sickle haemoglobin) → sickling of RBCs → vaso-occlusion and haemolysis → sickle cell anaemia.

Symptoms
  1. Fatigue
  2. Jaundice
  3. Swelling
  4. Pain
  5. Frequent infections
  6. Delayed growth
  7. Stroke
  8. Organ damage
Complications
  1. Brain stroke
  2. Hypertension
  3. Erectile dysfunction
  4. Vision loss
  5. Organ failure
Management
  1. Medications: antibiotics, pain relievers
  2. Vaccinations
  3. Blood transfusion
  4. Bone marrow transplant

Thalassemia

Thalassemia is an inherited blood disorder characterised by abnormal production of haemoglobin due to mutations in genes that control haemoglobin production. It results in decreased production of one or more globin chains and is a quantitative disorder.

Types of Thalassemia

Two major types:

  1. Alpha (α)-thalassemia
  2. Beta (β)-thalassemia
α-Thalassemia

Characterized by decreased synthesis of alpha globin chains. There are four alpha chain genes on chromosome 16; deletions of one or more genes cause varying severity (from silent carrier to haemoglobin H disease and hydrops fetalis).

β-Thalassemia

Characterized by decreased synthesis of beta globin chains. There are two β genes on chromosome 11. Clinical classification includes minor (β+ or β0 carriers), intermedia and major (Cooley’s anaemia).

Causes

Primarily caused by genetic mutations passed from parents to children. Inheritance is autosomal recessive.

Pathogenesis

Reduced synthesis of globin chains → imbalance of globin chains → ineffective erythropoiesis, haemolysis and anaemia → clinical symptoms.

Symptoms
  1. Fatigue
  2. Weakness
  3. Pale skin
  4. Delayed growth
  5. Shortness of breath
  6. Iron overload
  7. Heart problems
Complications
  1. Iron overload
  2. Enlarged spleen
  3. Heart problems
  4. Bone abnormalities
  5. Stroke
Management
  1. Regular blood transfusions
  2. Bone marrow transplantation
  3. Medications and chelation therapy for iron overload
  4. Folic acid supplementation

Diabetes Mellitus

DIABETES MELLITUS Diabetes mellitus is a chronic metabolic disorder characterised by high blood glucose levels. It occurs either due to inadequate production of insulin by the pancreas or the body’s inability to effectively use insulin. Insulin is a hormone produced by the pancreas that helps regulate blood glucose by facilitating uptake of glucose into cells for energy.

Types of Diabetes Mellitus

  1. Type 1 diabetes mellitus
  2. Type 2 diabetes mellitus
  3. Gestational diabetes

Type 1 Diabetes Mellitus

Earlier known as insulin-dependent diabetes mellitus. It accounts for about 5–10% of cases. It occurs because of autoimmune destruction of beta cells of the pancreas, leading to insulin deficiency. Type 1 diabetes often develops during childhood or early adulthood.

Causes

Primarily an autoimmune disorder where the immune system attacks insulin-producing beta cells. The exact cause is not fully understood; genetic and environmental factors are believed to contribute.

Type 2 Diabetes Mellitus

Earlier known as non–insulin-dependent diabetes mellitus. It constitutes about 90% of diabetes cases. It occurs when cells become insulin resistant and over time may lead to relative insulin deficiency. It generally occurs later in life and is associated with physical inactivity, obesity and poor dietary habits.

Causes

Type 2 diabetes is mainly a lifestyle-related disorder with contributions from genetic factors. Risk factors include obesity, physical inactivity, unhealthy diet, age, gestational diabetes and polycystic ovary syndrome (PCOS).

Thyroid Diseases

The thyroid gland is a small butterfly-shaped endocrine gland present in the anterior neck below the larynx. It produces mainly three hormones: triiodothyronine (T3), thyroxine (T4) and calcitonin. T3 and T4 regulate body metabolism.

Stroke

STROKE A stroke can be defined as a ‘brain attack’. A stroke occurs when blood supply to a part of the brain is reduced or obstructed. Without oxygen and nutrients from the blood, brain cells cannot function and eventually die. Stroke is also known as cerebrovascular accident (CVA) and is a medical emergency.

Types of Stroke

  1. Ischemic stroke
  2. Haemorrhagic stroke

Ischemic Stroke

The most common type of stroke, accounting for about 85% of cases. It occurs when blood flow to the brain is reduced or blocked due to thrombus or embolus or atherosclerotic plaque.

Haemorrhagic Stroke

Occurs when a blood vessel in the brain ruptures, leading to bleeding into or around the brain tissues. It accounts for about 13–15% of strokes and can be intracerebral or subarachnoid bleeding.

Causes

  • Thrombus
  • Embolus
  • Vasculitis (inflammation of blood vessels)
  • Hypertension
  • Brain trauma
  • Arteriovenous malformation
  • Brain tumour
  • Diabetes
  • High cholesterol
  • Smoking / alcohol
  • Obesity
  • Age and family history

Symptoms

  • Sudden numbness or weakness of the face
  • Sudden confusion
  • Slurred speech
  • Sudden weakness in an arm
  • Difficulty walking
  • Sudden severe headache

Complications

  • Paralysis
  • Physical disabilities
  • Cognitive impairment
  • Memory loss

Treatment

Emergency treatment is required and may include anticoagulants, antiplatelets, antihypertensive drugs, surgery and thrombolytics (clot busters) where appropriate.

Peptic Ulcer

PEPTIC ULCER A peptic ulcer is a sore that forms in the lining of the stomach or the first part of the small intestine (duodenum) when stomach acid damages the lining. Peptic ulcers often result from an imbalance between protective and damaging factors.

Types of Peptic Ulcer

  1. Gastric ulcer
  2. Duodenal ulcer

Gastric Ulcer

Occurs in the stomach and often results from reduced defensive factors. Less common (15–25%). Epigastric pain typically occurs 1–2 hours after eating. Weight loss and haemorrhage may occur. Equal in both sexes.

Duodenal Ulcer

Occurs in the duodenum and often results from increased acid secretion. More common (70–80%). Epigastric pain typically occurs 2–5 hours after eating. Weight gain may occur. Haemorrhage is less common. More common in males.

Causes / Etiology

  1. Helicobacter pylori infection
  2. Nonsteroidal anti-inflammatory drugs (NSAIDs)
  3. Genetic factors
  4. Age
  5. Stress
  6. Smoking
  7. Alcohol
  8. Spicy foods

Pathogenesis

Due to etiological factors (H. pylori, NSAIDs, other factors) → imbalance between protective factors and damaging factors (bicarbonate, gastric acid, mucus, pepsin, prostaglandin, H. pylori) → decreased mucus production / increased HCl secretion → destruction of the mucus lining → peptic ulcer.

Signs and Symptoms

  1. Abdominal pain
  2. Heartburn
  3. Nausea and vomiting
  4. Unintended weight loss
  5. Bloating
  6. Dark blood in stools
  7. Appetite changes
  8. Indigestion

Complications

  1. Internal bleeding
  2. Gastric outlet obstruction
  3. Gastric cancer (long-term risk)
  4. Perforation

Treatment

  1. Antibiotics (for H. pylori)
  2. Proton pump inhibitors
  3. Antacids
  4. Avoidance of NSAIDs
  5. Lifestyle modifications
  6. Avoid spicy food, stop smoking and alcohol
  7. Regular exercise and dietary changes

Cancer

CANCER Cancer is a serious disease characterised by uncontrolled growth and spread of abnormal cells in the body. These abnormal cells can form tumours and spread via blood and lymphatic systems. Cancer is often named after the organ or cell type where it starts, such as breast cancer or lung cancer. Terms like neoplasm and tumour are also used.

Tumour

A tumour is an abnormal growth of cells that forms a mass or lump. It can be:

  1. Benign tumour
  2. Malignant tumour

Benign Tumour

Non-cancerous; does not usually invade other tissues and can often be surgically removed.

Malignant Tumour

Cancerous; can invade adjacent tissues and metastasize to distant sites via bloodstream or lymphatics.

Classification of Cancer

On the basis of tissue involved:

  1. Carcinomas
  2. Sarcomas
  3. Leukaemias
  4. Lymphomas

Carcinomas

Cancers that originate in epithelial cells (e.g., breast, lung).

Sarcomas

Cancers that arise from connective tissues (e.g., bone, muscle).

Leukaemias

Blood cancers starting in the bone marrow or blood-forming tissues.

Lymphomas

Cancers that originate in the lymphatic system (e.g., Hodgkin lymphoma).

Causes / Etiology

Cancer often arises from a combination of genetic, environmental and lifestyle factors. Primary causes include genetic mutations, environmental exposures, smoking, alcohol, age, viruses, bacteria, parasites, hormonal imbalances and chronic inflammation.

Signs & Symptoms

  1. Fatigue
  2. Weight changes
  3. Skin changes
  4. Bowel changes
  5. Persistent cough
  6. Breathing trouble
  7. Unexplained joint pain
  8. Fever / night sweats

Pathogenesis

Due to various genetic and environmental factors → mutations in genes → activation of growth-promoting oncogenes, alterations of genes regulating apoptosis, inactivation of tumor-suppressor genes → abnormal cell division and proliferation → tumour formation → metastasis → malignant tumour (cancer).

Rheumatoid Arthritis

RHEUMATOID ARTHRITIS Rheumatoid arthritis is a chronic autoimmune disorder characterised by inflammation of joints. The immune system mistakenly attacks the synovium (lining of joints), leading to pain, swelling, stiffness and progressive deformity if not treated early.

Causes

The exact cause is not fully understood but is believed to result from a combination of genetic, environmental and hormonal factors. Genetic predisposition (e.g., HLA-DR alleles) and environmental factors such as smoking increase the risk.

Pathogenesis

Various etiological factors → activation of immune cells (T cells, B cells) → formation of autoantibodies (e.g., rheumatoid factor) → release of inflammatory cytokines (IL-1, IL-6, TNF-α) → inflammatory damage to synovial membrane → erosion of cartilage and bone → joint swelling, pain and loss of function → rheumatoid arthritis.

Signs & Symptoms

  1. Fatigue
  2. Weakness
  3. Joint pain
  4. Swelling
  5. Stiffness (especially morning stiffness)
  6. Loss of joint function

Complications

  1. Osteoporosis
  2. Infections
  3. Cardiovascular issues
  4. Premature mortality

Treatment

  1. Medications (disease-modifying antirheumatic drugs, DMARDs)
  2. NSAIDs
  3. Corticosteroids
  4. Surgical approaches where necessary
  5. Physical exercise and rehabilitation
  6. Balanced diet

Osteoporosis

OSTEOPOROSIS Osteoporosis is a medical condition characterised by weakened bones that are more susceptible to fracture. Bones become so weak and brittle that a fall or even mild stresses such as bending over can cause a fracture. Osteoporosis-related fractures most commonly occur in the hip, wrist or spine.

Causes

  1. Aging
  2. Hormonal changes
  3. Nutritional deficiencies
  4. Genetics
  5. Menopause
  6. Medications (long-term corticosteroids)
  7. Lifestyle factors

Symptoms

Osteoporosis often develops without noticeable symptoms until a fracture occurs. However, signs may include back pain, loss of height, immobility and stiffness.

Inflammatory Bowel Disease

INFLAMMATORY BOWEL DISEASE Inflammatory bowel disease (IBD) is a term used for chronic inflammatory conditions affecting the gastrointestinal tract, mainly the intestine. IBD is subdivided into:

  1. Crohn’s disease
  2. Ulcerative colitis

Crohn’s Disease

Characterised by chronic inflammation of the digestive tract. It can affect any part of the GI tract but most commonly impacts the terminal ileum (last part of the small intestine) and the colon.

Ulcerative Colitis

Causes chronic inflammation and ulcers in the lining of the large intestine (colon) and rectum.

Causes

The exact cause is not fully understood, but several factors play a role:

  1. Immune dysfunction
  2. Genetics
  3. Microbiome imbalance
  4. Autoimmune reactions
  5. Exposure to environmental triggers

Pathogenesis

Etiological factors → abnormal immune responses in the gut → activation of inflammatory mediators → inflammation in the GI tract (especially the colon) → inflammatory bowel disease.

Hepatitis

HEPATITIS Hepatitis means inflammation of the liver. It is most commonly caused by viruses but can also be caused by drugs, chemicals, autoimmune disease or metabolic abnormalities.

Types of Viral Hepatitis

  1. Hepatitis A (HAV)
  2. Hepatitis B (HBV)
  3. Hepatitis C (HCV)
  4. Hepatitis D (HDV)
  5. Hepatitis E (HEV)

Hepatitis A

Caused by HAV, usually transmitted by contaminated food or water or close contact with an infected person.

Hepatitis B

Caused by HBV and transmitted through blood, sexual contact or from mother to baby.

Hepatitis C

Caused by HCV and generally transmitted through blood-to-blood contact such as shared needles or contaminated medical equipment.

Hepatitis D

Caused by HDV and transmitted through blood and body fluids. HDV infection requires co-infection with HBV and can worsen liver damage caused by HBV.

Hepatitis E

Caused by HEV and transmitted via the fecal–oral route. It is usually acute and self-limiting.

Tuberculosis

TUBERCULOSIS Tuberculosis (TB) is a serious infectious disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs, though it can impact other parts of the body such as the kidneys, spine and brain. According to WHO, TB is one of the most prevalent infectious diseases worldwide.

Types of Tuberculosis

  1. Pulmonary tuberculosis
  2. Extrapulmonary tuberculosis
  3. Latent tuberculosis
  4. Active tuberculosis
  5. MDR (multidrug-resistant) tuberculosis

Pulmonary Tuberculosis

The most common form affecting the lungs; symptoms include persistent cough, chest pain and haemoptysis. Pulmonary TB is highly infectious.

Extrapulmonary Tuberculosis

Occurs outside the lungs and can affect organs such as kidneys, spine or brain. Symptoms depend on the organ involved.

Latent Tuberculosis

Non-active form where bacteria are present but not causing symptoms. People with latent TB are not infectious but can develop active TB if immunity weakens.

Active Tuberculosis

Stage when TB bacteria are actively multiplying and causing symptoms; this form is infectious and requires immediate treatment.

MDR Tuberculosis

Resistant to the two most effective first-line TB drugs (isoniazid and rifampin). It is more challenging to treat and requires second-line drugs.

Causes and Risk Factors

  • Infection with Mycobacterium tuberculosis
  • Weakened immune system
  • Undernutrition
  • Close contact with affected individuals
  • Smoking and alcohol
  • Travel and migration

Symptoms

  1. Persistent cough
  2. Chest pain
  3. Weight loss
  4. Fever
  5. Night sweats
  6. Fatigue
  7. Shortness of breath

Complications

  1. Tubercular meningitis
  2. Bone and joint TB
  3. Lymph node TB
  4. Renal TB
  5. Generalized lymphadenopathy

Treatment

Treatment typically involves a combination of antibiotics over an extended period (usually 6–9 months) according to national and international TB guidelines.

AIDS / HIV Infection

AIDS AIDS stands for acquired immunodeficiency syndrome. It is caused by the human immunodeficiency virus (HIV) which progressively damages the immune system, making the body unable to fight infections and certain cancers. AIDS is the advanced stage of HIV infection and is associated with opportunistic infections and malignancies.

HIV is a sexually transmitted infection (STI) and can be transmitted by unprotected sexual contact, sharing needles, mother-to-child transmission, and transfusion of infected blood products.

Stages of HIV Infection

  1. Acute HIV infection (primary stage)
  2. Clinical latency stage
  3. AIDS (advanced stage)

Acute HIV Infection

Occurs 2–4 weeks after exposure. Symptoms may resemble flu (fever, swollen lymph nodes, rash).

Clinical Latency Stage

Can last for several years; virus is still active but reproduces at low levels. Many people may have no or mild symptoms. Without treatment, this stage progresses to AIDS.

AIDS

The final stage characterised by severe immune deficiency, opportunistic infections and certain cancers. Symptoms include significant weight loss, persistent fever and severe infections.

Causes / Transmission

  • HIV-1 and HIV-2 types
  • Transmission via unprotected sexual contact
  • Sharing needles
  • Mother-to-child transmission
  • Infected blood transfusions or blood products

Pathophysiology

HIV particles bind to receptors on CD4+ lymphocyte cell surface → viral RNA undergoes reverse transcription → viral DNA integrates into host T-helper cell DNA → replication of HIV within T-helper cells produces new viral particles → infected helper T cells are destroyed → progressive immune deficiency.

Urinary Tract Infection

URINARY TRACT INFECTION A urinary tract infection (UTI) is an infection that occurs in any part of the urinary system, including the kidneys, ureters, bladder and urethra. Most infections involve the lower urinary tract (bladder and urethra) and are typically caused by bacteria.

Types

  1. Cystitis (bladder infection)
  2. Urethritis (urethra infection)
  3. Pyelonephritis (kidney infection)

Cystitis

Infection of the bladder. Symptoms include frequent painful urination, lower abdominal discomfort and cloudy or foul-smelling urine.

Urethritis

Infection of the urethra. It often causes burning during urination and urethral discharge.

Pyelonephritis

Infection of the kidneys. It is a more severe form of UTI and can cause high fever, flank pain, nausea and vomiting. It requires immediate treatment.

Causes

More than 90% of UTI cases are caused by Escherichia coli (E. coli). Other bacteria such as Klebsiella, Proteus and Enterococcus can also be involved.

  • Urinary retention
  • Sexual activity
  • Immune system disorders
  • Hormonal changes
  • Poor hygiene practices

Pathogenesis

Entry of bacteria into the urinary tract → adherence of bacteria to the epithelial lining → colonization and multiplication → immune response and inflammation → tissue damage → urinary tract infection. Some bacteria may resist immune responses and antibiotics leading to persistent infection.

Symptoms

  1. Frequent urge to urinate
  2. Burning sensation on urination
  3. Cloudy or discolored urine
  4. Blood in urine
  5. Fever
  6. Fatigue

Complications

  1. Chronic renal failure
  2. Bladder damage
  3. Prostatic infection in males
  4. Pregnancy complications
  5. Urethral strictures

Treatment

  1. Antibiotics
  2. Pain relievers
  3. Hydration
  4. Rest
  5. Maintain proper hygiene

Leprosy

LEPROSY Leprosy, or Hansen’s disease, is a chronic infectious disease caused by the bacterium Mycobacterium leprae. It primarily affects the skin, peripheral nerves, mucous membranes and eyes, leading to skin lesions, numbness, muscle weakness and deformities.

Types

  1. Tuberculoid leprosy
  2. Lepromatous leprosy
  3. Borderline leprosy
  4. Indeterminate leprosy

Tuberculoid Leprosy

Characterised by few well-defined skin lesions and nerve damage. The immune response is strong, limiting bacterial spread.

Lepromatous Leprosy

Features widespread skin lesions and nodules with multiple nerve involvement. The immune response is weaker, leading to extensive bacterial spread.

Borderline Leprosy

Intermediate form presenting features of both tuberculoid and lepromatous types; may progress or improve depending on the immune response and treatment.

Indeterminate Leprosy

Early stage with few symptoms and unclear diagnostic features; may progress to another type if not treated.

Causes

Caused by Mycobacterium leprae, a slow-growing pathogen affecting skin, peripheral nerves, mucous membranes and eyes. The exact mode of transmission is not fully understood but is believed to involve respiratory droplets and close contact. Other possible but less certain modes include fecal–oral route and contact with contaminated materials.

Symptoms

  1. Skin lesions
  2. Numbness
  3. Muscle weakness
  4. Deformities
  5. Loss of eyebrows or eyelashes

Pathogenesis

Entry of M. leprae (likely via the respiratory tract) → binding with Schwann cells and macrophages → immune response. A strong immune response may limit disease to mild lesions, while a weak immune response allows bacterial multiplication → damage to peripheral nerves → numbness, weakness and potential deformity → leprosy.

Treatment

Leprosy is treated with a combination of antibiotics over 6–12 months. Common drugs include rifampicin and dapsone, often given as part of multidrug therapy (MDT).