Lecture 1
Introduction to human
physiology;
Cell physiology; cell membrane;
protein synthesis.
Dr: Lina Naji Adam
What is Physiology?
• Definition: Physiology is the scientific study of the functions and
mechanisms in a living organism.
• It explores how cells, tissues, and organs work together to maintain
life.
• Branches of Physiology:
• Cell Physiology
• Organ/System Physiology (e.g., cardiovascular, respiratory)
• Pathophysiology – abnormal functions during diseases
CELL PHYSIOLOGY
• The Cell – The Basic Unit of Life
• All living organisms are composed of
cells.
• Human cells are eukaryotic, meaning
they contain a nucleus and
membrane-bound organelles.
Main Parts of the Cell:
• Cell Membrane (Plasma
Membrane)
• Cytoplasm
• Nucleus
• Organelles (e.g., mitochondria,
ribosomes)
CELL MEMBRANE
• Structure of the Cell Membrane:
• Phospholipid Bilayer: Two layers of phospholipids (hydrophilic heads +
hydrophobic tails)
• Proteins: Integral (span across the membrane)Peripheral (attached to
the surface)
• Cholesterol: Stabilizes membrane fluidity
• Carbohydrates: Attached to lipids/proteins for cell recognition
Functions of the Cell Membrane:
• Acts as a barrier separating internal from external environments
• Controls entry and exit of substances
• Receives signals (via receptor proteins)
• Involved in cell communication and adhesion
Transport Across the Cell Membrane
• Cells need to get nutrients in and waste out. There are two main
ways:
• 1. Passive Transport (no energy needed):
• 2. Active Transport (needs energy):
Passive transport Active transport
ATP
Diffusion Facilitated diffusion
1. Passive Transport (no energy needed):
Type What Happens Example
Movement of particles
Diffusion from high to low Oxygen entering a cell
concentration
Water entering a dry
Osmosis Movement of water
raisin
Uses protein channels Glucose entering
Facilitated Diffusion
to move particles muscle cells
EXTRACELLULAR
FLUID
Channel protein Solute
CYTOPLASM
Carrier protein Solute
2. Active Transport (needs energy):
Type What Happens Example
Moves particles
Sodium-potassium
Active transport from low to high
pump
concentration
Cell eats large White blood cells
Endocytosis
particles or fluids taking in bacteria
Releasing
Cell releases
Exocytosis hormones like
substances
insulin
EXTRACELLULAR [Na+] high Na+
FLUID [K+] low Na+
Na+ Na+ Na+
Na+ Na+
Na+
[Na+] low P ATP
Na+ [K+] high P
CYTOPLASM ADP
Cytoplasmic Na+ bonds to Na+ binding stimulates Phosphorylation causes
the sodium-potassium pump phosphorylation by ATP. the protein to change its
conformation, expelling Na+
to the outside.
P
P
Extracellular K+ binds Loss of the phosphate K+ is released and Na+
to the protein, triggering restores the protein’s sites are receptive again;
release of the phosphate original conformation. the cycle repeats.
group.
Transport Across the Cell Membrane:
Transport Type Description Energy Required?
Movement from high to low
Simple Diffusion No
concentration
Facilitated Diffusion Uses carrier or channel proteins No
Movement of water across a semi-
Osmosis No
permeable membrane
Movement against concentration
Active Transport Yes
gradient (e.g., Na⁺/K⁺ pump)
Endocytosis Cell engulfs material into vesicles Yes
Exocytosis Release of material from vesicles Yes
ORGANELLES AND THEIR FUNCTIONS
Organelle Function
Contains DNA; controls gene expression and cell
Nucleus
activity
Produces ATP; known as the "powerhouse" of the
Mitochondria
cell
Ribosomes Sites of protein synthesis
Rough Endoplasmic Reticulum (RER) Synthesizes proteins (ribosomes attached)
Smooth ER Synthesizes lipids and detoxifies chemicals
Modifies, sorts, and packages proteins and lipids for
Golgi Apparatus
transport
Lysosomes Contains digestive enzymes; breaks down waste
Peroxisomes Breaks down fatty acids and toxins
Centrioles Important in cell division
Cytoskeleton Maintains cell shape and allows movement
PROTEIN SYNTHESIS
• Importance of Protein Synthesis
• Proteins are essential for:
• Structure (muscles, skin)
• Enzymes (speed up chemical reactions)
• Hormones (insulin, growth hormone)
• Immune system (antibodies)
• Transport (hemoglobin, membrane channels)
• Six major functions of membrane proteins:
– Transport
– Enzymatic activity
– Signal transduction
– Cell-cell recognition
– Intercellular joining
– Attachment to the cytoskeleton and
extracellular matrix (ECM)
Signal
Enzymes
Receptor
ATP
Transport Enzymatic activity Signal transduction
Glyco-
protein
Cell-cell recognition Intercellular joining Attachment to the
cytoskeleton and extra-
cellular matrix (ECM)
Two Main Stages:
• 1. Transcription (in the nucleus)
• DNA → mRNA
• Process:
• RNA polymerase binds to DNA.
• DNA unwinds and complementary mRNA is
synthesized.
• mRNA leaves the nucleus and enters the
cytoplasm.
• 2. Translation (in the cytoplasm at
ribosomes)
• mRNA → Protein
• Process:
• Ribosome reads mRNA codons (three-letter
codes).
• tRNA brings the correct amino acid to each
codon.
• Amino acids are linked to form a polypeptide
chain (protein).
Post-Translational Modifications
• Proteins are often modified in the
Golgi Apparatus (e.g., folding,
tagging, transportation).
ER
Transmembrane
glycoproteins
Secretory
protein
Glycolipid
Golgi
apparatus
Vesicle
Plasma membrane:
Cytoplasmic face
Extracellular face
Transmembrane
Secreted glycoprotein
protein
Plasma membrane:
CLINICAL CONNECTIONS FOR NURSING
• Cystic Fibrosis: A mutation affects a membrane protein that controls
chloride transport.
• Diabetes: Insulin is a protein hormone – its synthesis and secretion
are crucial.
• Antibiotics: Some antibiotics target bacterial ribosomes, blocking
their protein synthesis.
• Cancer: Often involves mutations in cell cycle proteins, leading to
uncontrolled division.
Reference:
• Hall, J. E., & Hall, M. E. (2020). Guyton and Hall textbook of medical
physiology e-Book. Elsevier Health Sciences.
