IMED1001 - Cellular Physiology II

Types of Tissue

epithelial, connective, muscle, nervous

Nervous Tissue

- specialised for communication by electrical and chemical signals

- Neurons (nerve cells) detect stimuli and transmit messages

- Neuroglia protect and assist neurons.

- CNS: oligodendrocytes (myelin)

- PNS: Schwann cells (myelin)

Types of Muscular Tissue

Skeletal, Cardiac, Smooth

Function of Simple/Pseudostratified Epithelial Tissue

- Diffusion/filtration/secretion (e.g alveoli, blood and lymph vessels)

- Secretion/absorption (e.g ducts/glands/renal tubules)

- Mucus secretion (trachea, upper respiratory tract)

Function of Stratified Epithelial tissue

- Mechanical Protection (oesophagus, mouth, vagina)

- Secretion/protection (ducts of glands)

- Stretchyness (bladder, urethra)

Connective Tissue

Three basic components:

- cells

- protein fibres (collagen = strong, elastin = stretchy)

- ground substance (GS) (attracts water-modulates viscosity)

Types of Connective Tissue

- Connective Tissue Proper (Loose and Dense): Loose ones are more ground substances, less fibres. Dense ones have more fibres, less ground substance, e.g ligaments and tendons

- Supporting Connective Tissue (Cartilage and Bone): Cartilage are firm semisolid and contain variable amount of fibres. Bone is solid and calcified (collagen with calcium and salt added)

- Fluid Connective Tissue (Blood): ground substance, 45% cells, 55% plasma

How cells hold together with eachother (3 of them)

- Tight Junctions: very very close

- Desmosomes: very very strong

- Gap Junctions: Pass through

Tight Junctions

- plasma membranes of two adjacent cells are linked by cell adhesion proteins (claudins)

- seals gap between cells (nothing can pass between cells) (forces substances to go through cells, not around them)

- tight but not strong

- e.g stomach - tight junctions prevent digestive juices from seeping between epithelial cells

- TAKE IMAGE FROM SLIDE 20 OF CELLULAR PHYSIOLOGY 2

Desmosomes

- Super strong - holds cells together, resist mechanical stress

- cadherins proteins attach to the cytoskeleton (anchor cytoskeleton (intermediate filaments) to membrane plaque

- cannot prevent substances going between cells

- We also have Hemidesmosomes (half desmosomes anchor cells to the underlying basement membrane and prevents epithelia from being peeled away from underlying tissues)

- TAKE IMG FROM SLIDE 21 OF CELLULAR PHYSIOLOGY 2

Gap Junctions

- allows things to pass from one cell to the next

- formed by connexons (ring of proteins that spans the membranes of 2 adjacent cells. Each connexon = 6 transmembrane proteins (called connexins))

- Creates a pore connecting cytoplasms (allows direct communication between cells (shared cytoplasm). Ions, nutrients and other small solutes pass between cells. Located in cardiac and smooth muscle

- no ligand or receptor

- physical contact between cells involved

- connected 2 cytoplasms

- allows free passage for molecules/ions

IMG PRESENT

Cellular Communication

- most commonly involves a signal (ligand) produced by one cell that is receieved by a receptor on another cell

- Cellular Communication can be direct or via extracellular fluid

- Direct: juxtacrine (1) and gap junctions (3)

- via Extracellular fluid (ECF): Autocrine (2), Paracrine (4), Endocrine (5) and Neuronal (6)

Juxtacrine Cell Communication

- Physical contact between cells involved

- Transmembrane proteins and phospholipids

- receptor bound to one cell; ligand bound to the other - signal cannot diffuse away (notch signalling - neurons)

Autocrine Cell Communication

- cell signalling to itself

- signal molecule release into ECF

- short distances (usually less then 20 micrometres)

Paracrine Cell Communication

- other cells, not in physical contact

- signalling molecule release into ECF

- acts on nearby cells - short distances

Endocrine Communication

- long distances

- transport via bloodstream

- hormones bind to receptor (e.g insulin)

Neural Communication

- long distance

- target = nerve, muscle and gland

- noradrenaline, acetylcholine, many others