Download An introduction to cells and tissues

An introduction to cells and tissues
Cells are living building blocks of all multicellular organisms
Aoife Gowran, TCD 2011
Chapter 2-Cellular Physiology
‘Human Physiology’, Sherwood
Principles of the Cell Theory
•  All new cells and new life arise only from
preexisting cells
•  Cells of all organisms are fundamentally similar
in structure and function
•  An Organism’s structure and function ultimately
depend on individual and collective structural
characteristics and functional capabilities of its
cells
THE CELL IS THE BASIC UNIT OF LIFE
Basic functions of cell
•  chemical production of energy (ATP)
•  obtains O2/nutrients from surrounding environment
•  eliminates waste materials from cell
•  manufacture of new proteins
•  functional activities of each cell depend on specific
structural properties of the cell
Basic Cell Functions
•  Control exchange of materials between cell & its
surrounding environment
•  Sensing and responding to changes in surrounding
environment
•  Reproduction
–  Exception, Nerve cells and muscle cells lose their ability to
reproduce during their early development
Specialist functions of cell
DIFFERENTIATION
•  Muscle cells contract
•  Bone cells deposit calcified matrix
•  Cells in retina of eye detect light
Mammalian cells
Sperm
Ovum
Neurones
5µm
100µm
400µm
Ultrastructure of mammalian cell
‘Typical’ Cell
10µm
Nucleus
•  largest single organized cell
component
•  Enclosed by a double-layered
nuclear envelope
•  Stores genetic material (genes) in the form of DNA
• Acts as a central control-point of cell function
•  Dictates which proteins should be made by cell
DNA - deoxyribonucleic acid
C= cytosine G= guanine
A= adenine T= thymine
T is a U (uracil) in mRNA
DNA packaging
1
2 Chromosomes
•  46 in human (23 pairs)
•  Genes located within chromosomes
•  Each gene codes for a protein
•  20,000-25, 000 genes
The genetic code
Gene (DNA)
Nucleic acid bases
A -adenosine
T -tyrosine (uracil in mRNA)
G -guanine
C -cytosine
Amino acids (20)
M
P
K
M -methione (ATG/AUG)
Mature protein
• All cells contain same genes
• Different cell types “switch on” different genes
• Express (make) different proteins
• Allows different cell types to have specific functions
- muscle cells contract
- bone cell deposit extracellular matrix
- cells lining GI tract secrete digestive enzymes
Making new proteins
Flow of genetic material
DNA
transcription
mRNA
(messenger ribonucleic acid)
translation
New Protein
FUNCTION
Cytoplasm
Includes all material inside
the cell except the nucleus
3 Components
1.  Cytosol - intracellular fluid; semi gelatinous, contains
nutrients and proteins, ions and waste products.
2. Inclusions - particles of insoluble material; direct contact with
cytosol e.g.,protein fibers, ribosomes and proteasomes.
3. Organelles - membrane bound compartments; play specific
roles in the function of the cell e.g., production of energy
Several ORGANELLES are contained
within the cytoplasm
Membranous: Mitochondria
Endoplasmic reticulum
Golgi complex
Lysosomes
Peroxisomes
Non-membranous: ribosomes, vaults,
cytoskeleton
Mitochondria
Small spherical; double membrane
Outer & inner membrane
Folded into leaflets - cristae
Central lumen – mt Matrix
Inter membrane space
•  Energy organelle
–  Major site of ATP (adenosine triphosphate) production
–  Contains enzymes for citric acid cycle and electron transport chain
ATP is used by the cell for cellular processes:
- Movement/Mechanical work
- Transport of molecules against a concentration gradient
-  Biochemical reactions
-  Synthesis of new chemical compounds
Cellular Energy Production
Cytosol
Glycolysis
anaerobic
aerobic
mt Matrix
mt Inner Membrane
Citric Acid Cycle
Electron Transport
Chain
Endoplasmic reticulum
Endoplasmic Reticulum (ER)
•  Elaborate fluid-filled membranous system
distributed throughout the cytosol
•  Primary function
–  Protein and lipid manufacture
•  Two types
–  Smooth ER (lipid synthesis)
•  Mesh of tiny interconnected tubules
–  Rough ER (protein synthesis)
•  Projects outward from smooth ER as stacks of
relatively flattened sacs
•  Surface has attached ribosomes
Golgi complex
Golgi Complex
•  Closely associated with ER
•  Consists of a stack of flattened, slightly curved,
membrane-enclosed sacs called cisternae
•  Number of Golgi complexes per cell varies with
the cell type
•  Functions “Protein post production”
–  Processes raw materials (RER) into finished products
–  Sorts and directs finished products to their final
destinations
–  Packages secretory vesicles to release by exocytosis
Lysosomes & Peroxisomes
Lysosomes
Cytoplasmic vesicle, high pH
Contain digestive enzymes
Function
Digestive system of the cell
They breakdown old worn out organelles,
bacteria, abnormal proteins
Products of digestion can be reused
Cytoskeleton
Microtubules
Micro filaments
Intermediate filaments
Functions
Cell shape
Internal organization
Intracellular transport
Assembly of cells into tissues
Movement
CYTOSKELETON
Outside cell
membrane
Inside cell
cytoskeleton
Gives cell mechanical support and structure
Supports organelles within cell
Allows cell to move
Cytoskeleton
Element
Function
Microtubules
• Transport secretory vesicles
• Movement of specialized cell
projections
• Form mitotic spindle during cell division
• Contain Tubulin protein
Microfilaments • Contractile systems
• Mechanical stiffeners
• Contain 2 chains of Actin protein
Intermediate
filaments
• Help resist mechanical stress
• Contain Keratin
Plasma Membrane
Plasma Membrane Structure
•  Fluid lipid bilayer embedded with proteins
–  Most abundant lipids are phospholipids
•  Polar end of phospholipid is hydrophilic
•  Nonpolar end of phospholipid is hydrophobic
•  Also has small amount of carbohydrates
–  On outer surface only
•  Cholesterol
–  Tucked between phospholipid molecules
–  Contributes to fluidity and stability of cell
membrane
Plasma Membrane
•  Extremely thin layer of lipids and protein that forms
outer boundary of every cell
•  Controls movement of molecules between the cell
and its environment
•  Participates in joining cells to form tissues and
organs
•  Plays important role in the ability of a cell to
respond to changes in the cell’s environment
How do cells respond to stimulus???
Chemical
Physical
- Insulin
-drug
-stretch
-fluid flow
Sensor membrane protein
Biochemical pathways
GENES
Response (movement)
New protein
- Long-term adaptation
- Differentiation (become specialized)
- Programmed cell death
EXTRACELLULAR MATRIX (ECM)
• Biological “glue”
• Secreted by cells
• Meshwork of fibrous proteins in
a watery gel-like substance composed
of carbohydrate
1.
COLLAGEN
tensile strength
2.
ELASTIN
allows stretch and recoil
3.
FIBRONECTIN
cell adhesion
holds cell in position
Bone
- hard extracellular matrix
Skin
-flexible
Lung
- elastic
TISSUES OF THE BODY
A group of cells functioning together is a TISSUE
Exception Fusion of gametes 
fertilized egg
ONE CELL ALONE
IS NOT ENOUGH
Blastocyst
Tissue types
function dependent on structure
structure dependent on protein composition
1. NEURAL - neurones
3. MUSCLE - myocytes
Blood
Ciliated
Simple
Stratified
Basement
membrane
Bone
squamous
cuboidal
columnar
2. EPITHELIUM - epithelial
Cartilage
4. Connective tissues
Nervous tissue
–  Consists of cells specialized for initiating and
transmitting electrical impulses
–  Found in brain, spinal cord, and nerves
Epithelial tissue
–  Consists of cells specialized for exchanging
materials between the cell and its environment
–  Organized into two general types of structures
•  Epithelial sheets
•  Secretory glands
Muscle tissue
–  Specialized for contracting which generate
tension and produce movement
–  Three types of muscle tissue
•  Skeletal muscle
–  Moves the skeleton
•  Cardiac muscle
–  Pumps blood out of the heart
•  Smooth muscle
–  Encloses and controls movement of contents through
hollow tubes and organs
Connective tissue
–  Connects, supports, and anchors various body
parts
–  Distinguished by having relatively few cells
dispersed within an abundance of extracellular
material
–  Examples
•  Tendons
•  Bone
•  Blood
•  Cartilage
Cell-To-Cell Adhesions
•  Adhesions bind groups of cells into tissues and package
them into organs
•  Once arranged, cells are held together by three different
means
–  Extracellular matrix
•  Serves as biological “glue”
•  Major types of protein fibers interwoven in matrix
–  Collagen, elastin, fibronectin
–  Cell adhesion molecules in cells’ plasma membranes
(CAMs) temporary adhesion
–  Specialised cell junctions more permanent adhesion
Specialized Cell Junctions
•  Three types of specialized cell junctions
– Desmosomes
– Tight junctions (impermeable junctions)
– Gap junctions (communicating junctions)
Desmosomes
•  Act like “spot rivets” that
anchor two closely adjacent
nontouching cells
•  Most abundant in tissues
that are subject to
considerable stretching
Tight junctions
•  Firmly bond adjacent cells
together
•  Seal off the passageway
between the two cells
•  Found primarily in sheets
of epithelial tissue
•  Prevent undesirable leaks
within epithelial sheets
Gap junctions
•  Small connecting tunnels
formed by connexons
•  Especially abundant in
cardiac and smooth muscle
•  In nonmuscle tissues permit
unrestricted passage of
small nutrient molecules
between cells
•  Also serve as method for
direct transfer of small
signaling molecules from
one cell to the next
Blisters
Stress shears the proteins connecting the different
layers in the skin separate
Necrosis
Apoptosis
Cell
Renewal
Cell death
Tissue homeostasis
(remodelling)
Blastocyst
(totipotent)
Stem cells
Neural stem cells
(multipotent)