CELL JUNCTIONS.pptx

DR NILESH KATE
MBBS,MD,ACME
PROFESSOR
DEPT. OF PHYSIOLOGY
CELL
JUNCTIONS.

OBJECTIVES.
At the end of the class, you must know
 Intercellular communication.
 Enumerate the different types of intercellular
communications.
 Describe the mode of action of different
chemical messengers / second messenger
system.
 Apoptosis PY1.3, 1.4
 Define “apoptosis”, Explain the mechanism by which
apoptosis takes place in the cell &. List few examples of
apoptosis

Intercellular communication.
 Unicellular organisms
 Multi-cellular organism
 Cells- tissue – organs- system – body.
 Need –
 Communication
 Shape – (Cytoskeleton)
 Support
 Special functions.
Tuesday, December 6, 2022

Intercellular junctions
 Cell adhesion molecules
 Prominent parts of intercellular connections by
which attached to basal lamina and to each other.

TYPES
 Cadherins
 Adhesion molecules of IgG subfamily
 Selectins
 Integrins

TYPES
 Cadherins – Ca dependent molecules mediate
cell to cell adhesion through homophilic
binding.
 Adhesion molecules of IgG subfamily – IgG
immunoglobulins binds to various antigens
 Selectins – lectin like domains binds to
carbohydrates.
 Integrins – heterodimers that binds to various
receptors.

Mechanism of adhesion
 Homophilic binding – to like moleccules
 Heterophilic binding – to different
molecules.
 Anchorage with cytoskeleton – inside the
cell
 Binding to laminins – family of large cross
shaped molecules to receptor domains.

Functions of cell adhesion
molecules
 Signal transmission in & out of cell.
 Nervous system – Embyonic development &
formation.
 Tissue holding
 Inflammation & wound healing
 Metastasis of tumour

Types of intercellular
junctions
 Tight junctions
 Adherens
junctions
 Gap junctions

TIGHT JUNCTIONS
 Called Zona occludens
or occluding zone
 Outer layer of PL fused
with each other
 Obliterate the space
between cell
 Does not allow
transport/movement of
ions or other solutes.

Example
 Blood brain barrier
 Blood retinal
barrier.
 Intestinal mucosa.
 Blood testes barrier

ADHERENS JUNCTIONS
 Zona adherens
 Cell adhere to each
other by dense
accumulation of
proteins at cell surface
 Types
 Desmosomes – both
cells
 Hemidesmosomes –half

GAP JUNCTIONS
 2 membranes of cell are
connected by channel proteins
 Allow exchange of
substances/ions between cells.
 Permit transport of
substances, propogation of
electrical potential & exchange
chemical messengers.
 Examples – Heart & intestinal
mucosa.

CHEMICAL MESSENGERS /
SECOND MESSENGER SYSTEM.
 Special associated proteins.
 Receptors
 First messengers
 Second messengers.

HORMONES RECEPTORS.
 Characteristics
 Specificity .
 Location .
 Internal
 External .
 Regulation of number.
 Down regulation
 Up regulation .

STRUCTURE OF RECEPTORS.
 Recognition domain.
 Coupling domain.

CLASSIFICATION OF RECEPTORS.
 Receptor kinase
 Receptor linked kinase.
 G-protein coupled receptors.
 Ligand gated ion channels.

MECHANISM OF ACTION OF
HORMONES.
 Through change in membrane
permeability.
 Through effect on gene expression.
 Through second messengers.
 Through tyrosine kinase activation.

THROUGH CHANGE IN MEMBRANE
PERMEABILITY.
 Hormones bind with external receptors.
Conformational change in protein of receptors.
Opening of Na, K, Ca channel.
Movement of ions.

THROUGH EFFECT ON GENE
EXPRESSION.
Figure 7-7: Steroid hormone action

THROUGH SECOND MESSENGERS
SYSTEM.
 Adenyl cyclase- cAMP system.
 Guanyl cyclase –cGMP system.
 Membrane phoshpolipase- phospholipid
system.
 Calcium- calmodulin system.

ADENYLATE CYCLASE-CAMP
(Sutherland 1961)

PHOSPHOLIPASE-C-CA2+ (CONTINUED)

CA2+- calmodulin system(CONTINUED)

THROUGH TYROSINE KINASE ACTIVATION.

Apoptosis PY1.3, 1.4
Define “apoptosis”, Explain the
mechanism by which apoptosis
takes place in the cell &. List few
examples of apoptosis

APOPTOSIS
PROGRAMMED CELL DEATH.
 Apo – away & Ptosis – Fall, greek word
meaning – loosening or falling.
 Def – “ It is a process of programmed cell
death in which body cell die and get
absorbed under genetic control”
 Also called “Cell Suicide”

Mechanism.
Environmental process –
Inflammation.
Internal stimuli – lack of
oxygen & nutrients.
Fas – Transmembrane
proteins produced by NK
cells & T-Lymphocytes.
Free radicals,
Growth factors
deprivation.
Apotosis.

TUMOUR NECROSIS FACTOR.
 Activation of group of
cysteine proteases
inactivates enzymes –
Caspases in mitochondrion.
 This causes cell to undergo
DNA fragmentation,
condensation of cytoplasm
and chromatin
 Cell breaks & remnants
removed by phagocytosis.

PHYSIOLOGICAL SIGNIFICANCE
 Plays an important role in embryonal
development and in adulthood
 To remove un-needed cells.

Examples.
 Regression of duct
system during sex
differentiation in the
foetus.

Examples.
 For degeneration and
regeneration of
neurons in CNS & for
formation of synapse.

Examples.
 For removal of
inappropriate clones
of immune cells.

Examples.
 Responsible for
cyclical shedding of
endometrium at the
time of menstruation.

Examples.
 For cell shed from the
tip of the villi in the
small intestine.

APPLIED.
 Autoimmune diseases, degenerative diseases and
cancers.
MAJOR CAUSES OF AUTOIMMUNE DISEASES.
Auto-immune diseases Auto –antibodies are formed against.
Type -1 DM Pancreatic islets B cells
Myasthenia gravis Nicotinic cholinergic receptors
Multiple sclerosis Myelin basic protein.
Hashimoto’s thyroiditis. Thyroid gland cells
Rhematoid arthritis Collagen tissue.

OBJECTIVES.
At the end of the class, we learned...
 Intercellular communication.
 Enumerate the different types of intercellular
communications.
 Describe the mode of action of different
chemical messengers / second messenger
system.
 Apoptosis PY1.3, 1.4
 Define “apoptosis”, Explain the mechanism by which
apoptosis takes place in the cell &. List few examples of
apoptosis

CELL JUNCTIONS.pptx

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie CELL JUNCTIONS.pptx

Ähnlich wie CELL JUNCTIONS.pptx (20)

Mehr von Dr Nilesh Kate

Mehr von Dr Nilesh Kate (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

CELL JUNCTIONS.pptx