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Lecture notes Biomedical Sciences (BSc) BB2712 Principles of Human Disease
Lecture Notes BB2712 Principles of Human Disease at Brunel University
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BB2712 Principles of Human DiseaseI. Introduction of the module
Principles of human disease
- The principles of human disease can be split into two main subjects:
o Pathology: To study the mechanisms and processes of human diseases
o Clinical medicine: To learn about treatment and prevention of diseases
Medical terminology
- Disease: Malfunctioning of body or mind
- Aetiology: What is the cause of the disease?
- Pathology: Structural and functional abnormalities that are expressed as diseases of
organs or systems
- Pathogenesis: How the etiologic agents cause a disease, i.e. morphological and functional
changes in the body
- Lesion: Unit of abnormality, usually anatomical
- Symptoms: What is the patient complaining about?: pain, anxiety, restlessness
- Signs: What a doctor detects on exam: e.. lump, irregular heart beat
- Inflammation: Redness, swelling, heat, pain, loss of function
- Prognosis: The prospect of recovery or survival from a disease
- Epidemiology: The study of causes, distribution and control of a disease in a population
Diagnosis
- The diagnosis of a disease is based on the symptoms & signs and the results of laboratory
tests
- Medical conditions and their relevant pathological tests:
o Anaemia:
Haemoglobin of less than 12g/100ml for women and 13.5g/100ml for men
o Diabetes:
Fasting glucose level more than 7mmol/L
o Nephritis:
RBC or protein in urine sample
o Acute inflammation:
Increase number of neutrophil count
- Some medical conditions can be diagnosed early by their symptoms and signs, e.g. tetanus
and chickenpox
Health & Disease
- WHO definition:
o Health: complete physical, mental and social well-being not merely absence of
disease
o Disease: Expression of discomfort due to structural or functional abnormality
o Normal: The most frequent state in a population as defined by age distribution,
gender etc. This can be determined by a reference range, this is the range that is
most frequent in a population.
- Illness or ill health:
o Well defined abnormality, e.g. tumour
o Poorly defined abnormality, e.g. depression
, o A failure of homeostasis or adaptation, e.g. mountain sickness
- Each disease is characterised by a set of features:
o Aetiology (cause)
o Pathogenesis (mechanism)
o Manifestations (morphological, functional and clinical changes (signs and
symptoms))
o Complications (secondary effects) → infection of one area affects another area
o Prognosis (outcome)
- Syndrome:
o A disease characterised my multiple abnormalities, e.g. Down syndrome
- Lesion:
o The structural abnormality responsible/results due to ill health, e.g. rash, growth on
skin, patch of dead heart muscle in case of myocardial infarction
- Classification of diseases:
o Causative agent, e.g. infectious, genetic or nutritional (kwashiorkor)
o Inflammatory / Degenerative / Neoplastic
o Acute (days to weeks) / Chronic (months to years)
o System involved, e.g. cardiovascular, respiratory, neural, endocrine
o Primary cause (unknown or unclear) / Secondary cause (known)
o Congenital (abnormality present at birth) / Acquired
o Mild / Moderate / Severe
o Benign / Malignant
- What is the cause?
o Environmental agents:
Physical
Chemical
Nutritional
Infections
Physiological
o Genetic factors:
Genes
Sex
Immunological
Diseases like diabetes, hypertension and cancer are known to be multifactorial, meaning
that there could be more than one cause
- Agents can cause disease differently:
o One agent → one disease – e.g. Malaria
o Several agents → one disease – e.g. Diabetes
o One agents → several diseases – e.g. Smoking
Pathogenesis
- Sequence of events in cells & tissues in response to a stimulus/pathogen starting from the
initial stimulus to the ultimate expression of disease (mechanism of disease).
- The disease process:
External and internal factors affect cell, tissue or organ → structural and functional changes
→ symptoms and signs
- Examples:
o Inflammation:
Body response to many microorganisms and other harmful agents causing
tissue injury
, o Carcinogenesis:
The mechanism by which cancer-causing agents result in the development
of tumours
o Disordered immunity:
Undesirable effects of immune system
o Space occupying lesions (e.g. tumour)
Destroying, displacing or compressing adjacent heathy tissues
o Deposition of excessive or abnormal material in an organ
E.g. amyloid in brain with Alzheimer’s disease
o Abnormally sited tissues
As a result of invasion → metastasis (tumour)
o Loss of healthy tissue
From a surface (e.g. ulceration) or within a solid organ (infarction)
o Obstruction
Obstruction to formal flow within a tube (asthma, cancer of larynx)
- Functional abnormalities:
o Insufficient secretion of a cell product
E.g. lack of insulin secretion in diabetes mellitus
o Impaired nerve conduction
o Impaired contractility of a muscular structure
Defect in muscles, e.g. Duchenne muscular dystrophy
Defect in neuromuscular transmission, e.g. Myasthenia gravis
Prognosis and treatment
- Prognosis (how a patient is expected to do after disease is diagnosed)
o Lung cancer (squamous cell): survival – 5 years, 15-20%
o Lung cancer (small cell): survival – 5 years, 5%
o Myocardial infarction: survival – 10 years, 50%
- What treatment is suitable for a particular patient?
Symptoms and mediators
- Pain: Nerve ending stimulation by mechanical, thermal or chemical agents
- Swelling: Increase number or size of cells, or accumulation of fluid
- Fever: Interleukin-1 release by leukocytes and PGE2 acts on hypothalamus
- Bleeding: Rupture of vessel, coagulation (clotting) defect
- Cough: Irritation of respiratory mucosa results in stimulating of vagal nerve
- Vomiting: Stimulation of vomiting centre in medulla due to vagal impulses
- Itching: Mast cell degranulation and release of histamine
- Diarrhoea: - Malabsorption of food results in osmotic retention of water in
stool
- Decrease transit time: increased motility of intestine due to
infection
- Shortness of breath: Increased blood CO2 or decrease blood O2 concentration
Reporting a disease and disease prevention
- Prevalence rate is the total number of patients (old and new) in the population, divided by
the number of individual in the population at a given time. It is used to describe chronic
infection such as tuberculosis
, - Incidence rate is the total number of new cases reported in a specific time period (usually a
year) divided by the size of the population at risk. It is used for notifiable diseases such as
meningitis
- Mortality rate is the number of total deaths divided by the total number of people in the
population per unit time, usually expressed as number of deaths per 1000 individuals per
year
- Disease prevention:
o Primary:
Prevent the development of a disease. This could be in primary health care
(sanitisation/clean water) or behavioural modification (limiting alcohol
intake/stop smoking)
o Secondary:
Detection and intervention of a disease at an early stage, e.g. cervical or
breast screening for early detection of cancer
o Tertiary:
Intervention that prevent worsening of an established disease and to
improve quality of life through rehabilitation, e.g. managing diabetes and
preventing its complications, physiotherapy after accident
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