Semester notes on FLG 211.
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Unit 1 - Introduction to physiology and cell biology
UNIT 1.1 – INTRODUCTION TO PHYSIOLOGY
WHAT IS LIFE
If an organism has most of these characteristics then it is alive:
• Response to stimuli
Characteristics of living organism
• Adapt to their environment
• Growth
• Reproduction
• Composed of cells
• Maintain homeostasis
• Undergo metabolism (Use of energy)
• Open systems (Intakes and outlets-> Air, food signals, etc.)
• Have a life cycle
• Evolve
HOMEOSTASIS
Maintenance of a stable internal environment in the body
Dynamic state of equilibrium → to bring new balance
Internal conditions change, but always within relatively narrow limits
Body compensates through feedback mechanism
− Lack of compensation leads to many pathophysiological conditions
Homeostasis scenario:
The person eats something, the plasma takes up lots of carbohydrates, blood sugar increases. A number of signals are
released which will increase production and release of insulin. When the blood with increased levels of carbohydrates
reaches the pancreas and the beta cells of the pancreas with receptors for glucose get activated they start a pathway for
the release of insulin. Insulin release causes storage of glucose as glycogen in the liver, this happens until we return to
normal blood sugar level.
MICAELA DE JAGER 1
, FLG 211 Copyright Micaela de Jager
HOMEOSTASIS
Homeostatic control system:
Make sense of signals and illicit
Receptors = gather data and detect changes a response through effectors
Afferent pathway
Control Centre = receives data & sends messages (usually to the brain)
Efferent pathway
Effectors = What responds to change (organ, tissue, cells)
Most homeostatic control mechanism Rare in the body
Oppose initial change Reinforces/increase initial stimulus
Shut down original stimulus or reduce its intensity
Examples: Examples:
- Regulation of body temperature - Birth of baby
- Regulation of blood glucose - Blood clotting
MICAELA DE JAGER 2
,FLG 211 Copyright Micaela de Jager
GENETIC INFORMATION All living things carry
genetic information
Genetic information stored as DNA sequence is duplicated and passed on to daughter cells
DNA New 2 DNA molecules are identical to parent DNA
Located in nucleus
Direct synthesis of all proteins in the body
Non-dividing cell
Chromatin = DNA + histone protein
During cell division
Chromatin threads coil and condense into chromosomes
Consist of 2 sister chromatids + centromere
Via transcription & translation
Protein synthesis
o Genetic material from DNA to RNA
o mRNA is transported out of nucleus into cytoplasm
o Synthesis of protein in the cytoplasm
MACROMOLECULES
• Built by combining subunits
- All living things contain macromolecules (DNA → Made of nucleotides, 4 different kinds)
- Organisms use simple building blocks and combine them in different layers to form complex molecules.
- It’s easier to assemble small molecules to form big molecules than to assemble large molecules.
If damage occurs, it will be easy to replace.
• Allows for diversity from identical building blocks
• Self-assemble
MICAELA DE JAGER 3
, FLG 211 Copyright Micaela de Jager
PLASMA MEMBRANE
Living cells are surrounded by a (plasma) membrane
Following fluid mosaic model
➢ Made up of a lipid bilayer
• hydrophilic heads → polar
• hydrophobic tails → nonpolar
➢ Physical barrier
Separates the intracellular fluid from the extracellular fluid
➢ Semi-permeable
Only certain materials are allowed to pass through
Ions are charged and cannot pass through the membrane so they
are assisted by proteins embedded in the membrane (Carrier,
Channel, etc. proteins).
Once it's inside the cytoplasm they are moved around by
diffusion and passive & active transport (needs energy)
CELL SIGNALLING
Cells communicate by
Mechanism to receive, adapt, and respond to intracellular and extracellular signals using signalling molecules
Signals can be:
• nutrients
3 stages:
• growth factors
• hormones 1. Reception
• neurotransmitters 2. Transduction
• toxins 3. Response
MICAELA DE JAGER 4
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