Organisation of the Human Body

Organisation of the Human Body and Survival

• Living organisms share functional characteristics such as growth, movement, reproduction, respiration, circulation, digestion, excretion, responsiveness, and adaptability.
• Adaptability refers to the ability to adjust to changing conditions and maintain homeostasis.
• Many organisms use oxygen when expending energy to carry out essential processes like respiration, circulation, digestion, excretion, and homeostasis.

Levels of Organisation

• Human beings are complex organisms composed of biological systems that underpin normal physiology.
• There are six biological levels of organisation providing a framework of understanding the complexity of the human body.
• The Bachelor of Medical Studies courses use seven levels of organisation as opposed to the accepted six.

Homeostasis

• Homeostasis is a self-regulating process that maintains internal stability in a living organism despite external changes.
• Maintaining homeostasis involves regulating the body's internal environment and responding to external threats by body systems, organs, tissues, and cells.
• Parameters regulated through homeostasis include body temperature, blood glucose, cell osmolarity, blood acidity/pH, oxygen tension, and blood solute concentration.
• Homeostatic regulation involves sensory receptors that detect and report changes, control centres (mostly in the brain) that process stimuli, and effectors (muscles and glands) that solicit a response.
• The relationship between sensory receptors and responding effectors is called feedback.
• Negative feedback counteracts the initial stimulus, while positive feedback amplifies the initial stimulus.

Anatomy and Physiology

• Anatomy and physiology are key areas in medical learning.
• Anatomy is the science concerned with the bodily structure of humans, animals, and other living organisms, and is especially revealed by dissection and the separation of parts
• Physiology is the science detailing the chemistry and physics behind basic body functions.
• Anatomy is often divided by the level of organisation, while physiology is often divided by organ system.

Anatomical Terminology

• Directional terms are used to describe anatomy from a point-of-view, as the human body is three-dimensional.
• Anatomists base standard anatomical terminology on an 'anatomical position', the universal gold standard for anatomical description.
• Directional terminology describes the position of an individual in the anatomical position.
• There are hundreds of directional terms, including:
  • Anterior: Towards the front
  • Posterior: Towards the back
  • Superior: Towards the head
  • Inferior: Towards the feet
  • Medial: Towards the middle
  • Lateral: Towards the edges
  • Superficial: Towards the surface
  • Deep: Away from the surface
  • Rostral/Ventral: Towards the superior-anterior tip
  • Caudal/Dorsal: Towards the inferior-posterior tip
  • Proximal: The innermost part of a limb or structure
  • Distal: The outermost part of a limb or structure
  • Ipsilateral: On the same side of the body
  • Contralateral: On opposite sides of the body
• Directional anatomical places are imaginary flat surfaces used as reference points in describing the positions and relationships of body parts.
• The three primary directional places are:
  • Sagittal plane: Divides the body into left and right portions.
  • Coronal plane: Divides the body into front (anterior) and back (posterior) portions.
  • Transverse plane: Divides the body into upper (superior) and lower (inferior) portions.

Pathology

• Pathology studies diseases, their causes, development mechanisms, and impact on the body.
• Pathologists diagnose diseases by examining tissues, organs, and fluids using techniques like microscopy, molecular testing, and imaging.
• Pathology contributes to medical research, treatment development, and the advancement of medical knowledge.
• Four key pathology subspecialties are:
  • Anatomical, focusing on tissues and organs.
  • Clinical, involving lab analysis of bodily fluids.
  • Molecular, using molecular and genetic techniques.
  • Forensic, investigating causes of sudden or suspicious deaths.

Injury and Inflammation

• Several agents that could cause injury to the human body include trauma, extreme temperature, particulate matter, infection, radiation, hypoxia/ischemia, infarction, immunological reactions, genetic factors, nutritional imbalances etc.
• The human body uses a range of responses i.e. defence mechanisms to injury.
• Defence mechanisms: Neural reflex, Fight/flight response, Inflammation, Enzymzes, Acid in stomach, Bacteria in gut, Macrophages
• Surface barriers include Skin and Mucous membranes.
• Internal defenses include Fever, Inflammation, Phagocytes, Antimicrobial proteins and Natural killer cells.
• Adaptive defenses include Humoral immunity (B cells) and Cellular immunity (T cells).
• Inflammation is the body's natural and protective response to injury, infection, or irritation, with redness, swelling, heat, pain, and sometimes loss of function at the affected site.
• Stages of inflammation:
  • Injury, infection, or irritation triggers the inflammatory response.
  • Blood vessels widen, allowing increased blood flow.
  • Blood vessel permeability increases, allowing immune cells and proteins movement.
  • White blood cells move toward the injury site to engulf and destroy pathogens.
  • Immune cells engulf and digest foreign substances and microbes.
  • Cells release cytokines and prostaglandins, which regulate and amplify the inflammatory response.
  • Anti-inflammatory signals are released once threat neutralized, starting tissue repair.
  • Uncontrolled chronic inflammation may lead to tissue damage.

Medical Imaging

• Medical imaging uses technologies to visualise internal body structures.
• Key imaging modalities include: - X-ray: Uses ionising radiation and is commonly used for bone examinations. - Computed Tomography (CT): Uses X-rays from multiple angles to create detailed cross-sectional images. - Ultrasound: Uses sound waves to create real-time images of internal organs. - Magnetic Resonance Imaging (MRI): Employs magnetic fields and radio waves to generate detailed images of soft tissues. - Nuclear Medicine: Uses radioactive substances for imaging and functional studies. - Interventional Radiology: Uses imaging guidance to perform minimally invasive procedures.

Biopsychosocial Model and Behavioural Science

• The biopsychosocial model determines health and illness as the result of interactions between biological, psychological, and social factors.
• This model recognises interconnected elements that influence health outcomes.
• The healthcare process is patient-centered by addressing physical, psychological, and social aspects.
• Behavioural sciences systematically study animal behaviour through disciplines like psychology, sociology, anthropology, and neuroscience.
• Factors relating to behavioural science that are considered important in medical practice include:
  • Social determinants of health: External factors that significantly influence an individual's health outcomes.
  • Patient behaviours: Actions and choices individuals make in relation to their health.
  • Doctor-patient relationship: Communication and relationship between doctors and patients.

Chemical Level of Organisation

• Humans are made of smaller units at different levels of complexity.
• Units include:
  • Atoms: The smallest units of stable matter.
  • Elements: Pure substances consisting only of atoms of the same type.
  • Compounds: Substances consisting of atoms of one or more elements, joined by a chemical bond.
• Atoms consist of many subunits known as subatomic particles.
• Key subatomic particles include:
  • Protons: Positively charged, found in the nucleus.
  • Neutrons: Neutral charge, located in the nucleus.
  • Electrons: Negatively charged, orbit the nucleus.

Organic Compounds

• Organic compounds consist of carbon and hydrogen atoms.
• Organic compounds contain functional groups that confer unique chemical properties.
• Carbon creates complex molecular structures through tetravalent bonding.
• There are three main kinds of organic macromolecules: carbohydrates, proteins, and lipids.
• Carbohydrates, composed of carbon, hydrogen, and oxygen (1:2:1 ratio), serve as a primary energy source.
• Proteins are composed of amino acid chains, performing functions such as structural support and enzymatic catalysis.
• Lipids are hydrophobic organic molecules, with roles in energy storage, insulation, and structural components of cell membranes.
• Glucose is a monosaccharide key for cellular respiration.
• Polysaccharides, such as starch and cellulose, are complex carbohydrates made up of multiple sugar units.
• Carbohydrates also contribute to the formation of cell walls and cell signalling.
• Living organisms store carbohydrates, like glycogen in animals and starch in plants.
• Proteins are structural components in living organisms; collagen provides strength and elasticity to connective tissues.
• Proteins act as enzymes, transporting molecules across cell membranes as well as transducing cell signals.
• Lipids are hydrophobic and serve as a component of cell membranes and provide insulation, composed of triglycerides, phospholipids and steroids.

Principles of Molecular Interactions

• Chemical bonds are attractive forces that hold atoms together.
• There are primary (intramolecular) as well as secondary (intermolecular) chemical bonds.
• The three types of primary bond are covalent, ionic, and metallic.
• Covalent bonds are formed by the sharing of electrons between nonmetal atoms.
• Ionic bonds are formed when a metal atom transfers electrons to a nonmetal atom.
• Metallic bonds involve a sea of delocalized electrons shared between metal atoms.

Secondary Bonds

• These are weaker than primary bonds.
• They occur with uneven charge distribution creating a dipole
• Four kinds of secondary bonds:
  • Ion-dipole: Between ions and polar molecules in a solution.
  • Hydrogen: Involving hydrogen attached to an electronegative atom.
  • Dipole-dipole: Between the positive end of a polar molecule and the negative end of another polar molecule
  • Dispersion: Temporary fluctuations in electron distribution.
• Anabolic reactions involve the synthesis of complex molecules from simpler ones.
• Catabolic reactions involve the breakdown of complex molecules into simpler ones.
• Both processes are crucial in maintaining the balance of energy and biomolecules within living organisms.

Regulation of Homeostasis

• For life systems to optimally function, tissues and cells require appropriate conditions.
• Homeostasis is defined as the regulation of the internal environment to maintain appropriate, life-sustaining conditions.
• Homeostasis is a dynamic steady state achieved through mechanisms for proper functioning of cells, tissues, organs and systems.
• Broadly speaking, homeostasis involves detection, integration, and response.
• Homeostatic control parameters include concentration of nutrients, gases, pH levels, electrolytes, temperature, extracellular fluid volume, and waste products.

Negative Feedback

• Defined as a regulatory process where a homeostatic output serves to counteract and minimise deviations from a set point, ensuring system stability.
• Negative feedback involves sensors detecting deviations, a control centre determining responses, effectors carrying out responses.

Positive feedback

• Defined as a regulatory mechanism where the response to a stimulus amplifies the original change, often leading to a self-perpetuating cycle.
• It is seen in processes like blood clotting, uterine contractions, and certain immune responses.

Diseases due to Failure of Homeostatic Control

• These include:
  • Diabetes Mellitus: Arises in autoimmune destruction of pancreatic beta cells, leading to insufficient insulin production and impaired glucose regulation AND the failure of homeostasis in insulin resistance and beta cell dysfunction, resulting in inadequate insulin response and elevated blood levels.
  • Rickets: Arises from the failure of homeostasis in calcium and phosphate balance, leading to impaired mineralisation of bone matrix and skeletal deformities.

Mechanisms for Homeostasis of Elements Inside the Cell

• Body fluid is separated into distinct compartments.
• Two predominate compartments:
  • Intracellular (ICF)
  • Extra-cellular fluid (ECF)
• Extracellular fluid can be further classified as intravascular (IVF) and interstitial (ISF) fluid.
• A description of the terms are as follows:
• Fluid inside cells (ICF): Containing essential ions and molecules.
• Fluid outside cells (ECF): Comprising intravascular and interstitial fluids.
• Fluid within blood vessels (IVF): Including plasma, transporting nutrients, oxygen, and waste.
• Fluid in the spaces between cells (ISF): Providing a medium for exchange.
• Fluid intake must match fluid loss, or else dehydration will occur (regulated by antidiuretic hormone (ADH)).

Acid-Base Balance and pH

• Acids, bases, or salts dissolved in water separate to create component ions.
• Acids, bases, and salts are responsible for facilitating a number of essential biological processes.
• The partial pressure of free H+ and OH is commonly referred to as pH and is represented on a discrete scale from 0 to 14.
• The partial pressure of free H+ and OH is commonly referred to as pH and is represented on a discrete scale from 0 to 14.
• Maintenance of acid-base balance is significant.
• Conditions associated with the incorrect levels of pH include:
  • Acidosis: Excess acidity and is characterised by symptoms such as excitability and confusion.
  • Alkalosis: Excess basicity/alkalinity and is characterised by symptoms such as high neural activity.
• Variation in pH is seen across different body systems (stomach, saliva etc) and is determined by their underlying physiology.
• Acid-base balance is maintained by 'pH buffering systems', which aims to minimise variation in available H+ ion concentration through adding or removing protons.
• Three main buffering systems in the body include:
  • Bicarbonate: Present in bodily fluids; converts carbon dioxide into carbonic acid and subsequently into the bicarbonate ion.
  • Protein / Hb: Present in bodily fluids; proteins bind to H+ ions, thus removing them from circulation.
  • Phosphate: Present in bodily fluids; involves the conversion of dihydrogen phosphate into hydrogen phosphate.

Cellular Level of Organisation

• Cells are the structural and functional unit of all living organisms and may be prokaryotic or eukaryotic.
• Three main parts of a (eukaryotic) cell:
  • Nucleus, a membrane-bound organelle that houses genetic material.
  • Cytoplasm, the gel-like substance filling the cell's interior.
  • Plasma membrane, the selectively permeable outer boundary.
• The nucleus consists of a nucleolus, nuclear envelope, chromosomes, chromatin, and nuclear pores.
• The cytoskeleton provides cell and flexibility of the cell, and is composed of filamentous proteins, such as microtubules.
• This includes roles played by:
  • Microfilaments which provide structural support.
  • Microtubules which maintains cell shape.
  • Intermediate filaments which helps resist tension.
• Organelles are compartments within the cell that are compartmentalised from the surrounding cell environment.
• Key organelles and their functions include:
  • Nucleus where genetic material serves as the control center.
  • Rough Endoplasmic Reticulum (R.ER) is involved in protein synthesis, folding and transport.
  • Smooth Endoplasmic Reticulum (S.ER) is responsible for lipid synthesis and the storage of calcium ions.
  • Golgi body modifies and packages proteins for secretion.
  • Lysosomes contain enzymes for intracellular digestion.
  • Mitochondria produce ATP for energy.
  • Ribosomes synthesise proteins for energy.
• The plasma membrane controls the passage of substances in and out of the cell to maintain homeostasis, consisting of a double layer of phospholipids with hydrophilic heads and hydrophobic tails.
• The extracellular matrix (ECM) provides structural support to surrounding cells and tissues.
• Abnormalities in cell may lead to disease development.
• Dysregulation of golgi functioning may disrupt protein synthesis.
• Mitochondrial dysfunction can cause metabolic disorders.