Understanding Homeostasis

• Homeostasis is an organism's ability to maintain a stable internal environment despite external changes.
• It's crucial for cells, tissues, and organs to function correctly and survive.
• Homeostatic mechanisms continuously adjust body temperature, pH, blood glucose, and fluid balance, keeping them within specific ranges.

Key Components of Homeostasis

• Receptors detect internal or external environmental changes, signaling a control center.
• Control centers receive and process receptor information, coordinating a response.
• Effectors, like muscles or glands, carry out the response to restore balance.
• Negative feedback mechanisms reverse changes to maintain stability, such as body temperature regulation.
• Positive feedback mechanisms amplify initial changes for a rapid response, like blood clotting.

Temperature Regulation

• Maintaining a stable core body temperature, around 37°C in humans, is essential.
• Mechanisms to increase body temperature: shivering, vasoconstriction, and increased metabolism.
• Mechanisms to decrease body temperature: sweating, vasodilation, and decreased metabolism.
• The hypothalamus in the brain is the control center for temperature regulation.

Fluid and Electrolyte Balance

• Regulating water and electrolyte balance (ions) is crucial.
• Antidiuretic hormone (ADH) regulates water reabsorption in the kidneys.
• Aldosterone regulates sodium and potassium balance.
• Thirst and kidney function are key factors in maintaining fluid balance.

Blood Glucose Regulation

• Insulin, from the pancreas, lowers blood glucose by promoting glucose uptake by cells.
• Glucagon, also from the pancreas, raises blood glucose by stimulating glucose release from the liver.
• The liver and pancreas work together to keep blood glucose levels in a narrow range.

pH Balance

• Stable pH (around 7.35-7.45 in blood) is maintained through buffer systems, respiration, and kidney function.
• Buffers neutralize excess acids or bases in the blood.
• The lungs regulate pH by controlling blood carbon dioxide levels.
• The kidneys excrete acids or bases to maintain pH balance.

Disruptions of Homeostasis

• Imbalances in homeostatic mechanisms can lead to health issues and diseases.
• Diabetes results from impaired blood glucose regulation, either from insufficient insulin or insulin resistance.
• Dehydration occurs when fluid loss exceeds fluid intake, disrupting fluid and electrolyte balance.
• Heatstroke occurs when temperature regulation fails, leading to dangerously high body temperatures.
• Infections can disrupt homeostasis.

Infection

• Infection is the invasion and multiplication of pathogenic microorganisms in the body.
• Pathogens include bacteria, viruses, fungi, protozoa, and parasites.

Types of Pathogens

• Bacteria are single-celled organisms causing disease by releasing toxins or invading tissues directly, like Streptococcus.
• Viruses are infectious agents replicating inside host cells, causing cellular damage, such as influenza virus.
• Fungi are eukaryotic organisms causing infections on the skin, in the lungs, or systemically, like Candida.
• Protozoa are single-celled eukaryotic organisms causing diseases like malaria and giardiasis, such as Plasmodium.
• Parasites live on or inside a host organism and obtain nutrients from it, like tapeworms.

Transmission of Infections

• Direct contact: physical contact between an infected and a susceptible person, e.g., touching, kissing, or sexual contact.
• Indirect contact: occurs through contaminated objects (fomites) like surfaces or utensils, e.g., touching a contaminated doorknob.
• Droplet transmission: spread of pathogens through respiratory droplets from coughing or sneezing, e.g., influenza.
• Airborne transmission: spread of pathogens through small particles suspended in the air, e.g., tuberculosis, measles.
• Vector-borne transmission: spread of pathogens by vectors like mosquitoes or ticks, e.g., malaria, Lyme disease.
• Foodborne and waterborne transmission: occurs through contaminated food or water sources, e.g., Salmonella, E. coli, cholera.

Body's Defense Mechanisms

• Physical barriers: skin, mucous membranes, and cilia prevent pathogens from entering the body.
• Chemical barriers: secretions like saliva, tears, and stomach acid contain antimicrobial substances.
• The innate immune system provides a rapid, non-specific response.
  • Includes cells like macrophages, neutrophils, and natural killer (NK) cells.
  • Inflammation is a key component, with redness, swelling, heat, and pain.
• The adaptive immune system provides a specific and long-lasting response.
  • Involves B cells and T cells.
  • B cells produce antibodies that neutralize pathogens.
  • T cells directly kill infected cells or help activate other immune cells.
  • The adaptive immune system develops immunological memory.

Immune Response

• Antigen presentation: immune cells display pathogen-derived antigens to T cells.
• Activation of T cells leads to the production of cytotoxic and helper T cells.
• Cytotoxic T cells kill infected cells.
• Helper T cells activate B cells and enhance the activity of other immune cells.
• B cells differentiate into plasma cells, which produce antibodies.
• Antibodies bind to pathogens, neutralizing them or marking them for destruction.
• Memory cells are long-lived B and T cells that provide immunological memory.

Types of Infections

• Localized infections are confined to a specific area, e.g., skin or urinary tract infection.
• Systemic infections spread throughout the body via the bloodstream, e.g., sepsis.

Diagnosis of Infections

• Physical examination involves assessing symptoms and signs of infection.
• Laboratory tests include blood tests, urine tests, cultures, and imaging.
• Cultures involve growing pathogens from samples to identify the specific organism.
• Molecular tests detect pathogen DNA or RNA to confirm the presence of an infection.

Treatment of Infections

• Antibiotics treat bacterial infections.
• Antivirals treat viral infections.
• Antifungals treat fungal infections.
• Antiparasitics treat parasitic infections.
• Supportive care includes rest, hydration, and pain relief.

Prevention of Infections

• Vaccination involves administering weakened pathogens to stimulate an immune response.
• Hygiene practices like handwashing and covering coughs prevent the spread of infections.
• Sanitation and clean water sources are essential for preventing waterborne infections.
• Safe sexual practices prevent the transmission of sexually transmitted infections.
• Vector control measures reduce the risk of vector-borne diseases, e.g., mosquito control.
• Isolation precautions are used in healthcare settings to prevent the spread of infections.