MODULE 2: cells and tissues

What is the nucleus?

Contains DNA

Directs protein synthesis & most cellular processes and functions

Cytoplasm

Consists two compartments

1. Cytosol

2.Organelles

Mitochondria

Cellular power house. Produce cellular energy ATP.

Ribosomes

Where proteins are made

Rough ER

Manufactures membrane and extracellular proteins proteins and phospholipids, covered in ribosomes.

Smooth ER

Site of lipid metabolism, production of steroids, breakdown of stored carbohydrates

Golgi apparatus

Modifies, concentrates and packages proteins and releases substances stored by the cell.

Peroxisomes

Breaks down toxic substances within the cell.

Cytoskeleton

Network of tubules providing structure to the cell.

Centrosomes

Anchor point for the cytoskeleton, cilla ,flagella

Cillia

Short finger like projections of the cell surface which enhance surface area and can move substances along surface of cell

Flagella

Sperm tail, long cellular extension to propel the cell.

Structure cell membrane

Flexible structure that define the extent of the cell by separating 2 fluid compartments

1. Intercellular fluid- fluid in cell

2. Extracellular fluid- fluid outside cell

3. Phospholipid bi-layer hydrophilic heads and hydrophobic tail

4. Proteins-transport substances, enzyme activity, receptors for signal transduction, membrane junctions (to bind to other cells), attachment of cytoskeleton, cell to cell recognition.

5. Carbohydrates-form pattern on cell surface to identify self to immune cells

6. Glycoproteins:combined lipid and carbohydrates

7. Cholesterol: stabilises membrane allowing mobility and flexibility

Passive transport

Occurs without use of cellular energy and occurs two ways.

1. Diffusion: substances move across the cell membrane down their concentration gradient. Lipid soluble pass through phospholipid bilayer, while waste soluble ones need protein channels (small molecules) or carriers (large membranes) this is called facilitated diffusion.

2. Filtration: occurs when pressure forces substances across membranes. This happens in capillaries due to blood pressure especially in kidney gromeruli where filtration is high

Osmolarity& Osmosis

Total solute concentration in a solution. Water moves from low to high concentration of osmolarity (osmosis)

Of ICF and ECF osmolarity are equal no water movement occurs (steady state)

Active transport

Requires energy and the use of ATP to move substances across the cell membrane up against their concentration gradient.

Solute (protein pumps)

Main method of active transport, dominated by the sodium potassium pump. There are 2 mechanisms of this form of transport:

1. Primary active transport: ATP is used to change protein shape allowing it to “pump the solutes across the membrane”

2. Secondary active transport: the energy from primary active transport is stored and able to be used to help other substances cross (glucose) cross membrane against its concentrations gradients via co-transport with NA+. When sodium diffused back across cell membrane through co transporter

Vascular transport

Transport using vesicles.

This is how the cell moves large particles of fluids across its membrane. It uses special proteins that need energy to work. The cell wraps substance in a small bubble like a sac called vesicle. This vesicle carries the substances to the other side of the membrane and then releases it.

Exocytosis: vesicles within the cell bind to and fuse with the cell membrane, then release their contents outside the cell.

Endocytosis: substances from exterior of the cell are wrapped in a small bit of plasma membrane and moved into the cell. This is how macrophages (cells from our immune system) engulf foreign objects and bacteria

Intracellular fluid

All the fluid found inside all body cells, making up 2/3 of total body weight (TBW) or about 40% of body mass

Extracellular fluid

Fluid in the body not contained within body cells. Makes up 1/3 of TBW- about 20% of body mass.

ECF can be divided in to

1. Interstitial fluid: makes up 4/5 of the ECF. This is all the fluid outside body cells, mostly bound within connective tissues, except blood.

2. Plasma: the ECF of blood, making up remaining 1/5 of the ECF.

Cell cycle and division

Life cycle involves 2 main phases essential for body growth and tissue repair.

1. Interphase: the cell grows, produces protein and prepares for cell division by replicating its organelles and DNA

2. Cell division: it’s the process by which the cell replicates itself.

3. Mitosis or meitosis is the process of replication and division of DNA

4. cytokinesis is when organelles replicate and the cells divide in to daughter cells.

Mitosis

Somatic body cells undergo chromosomal replication and division. Use to generate 2 identical daughter cells

Meiosis

Sex cells undergo chromosomal division process used to generate four new daughter cells that differs from the original sex cell. Half DNA in each daughter cell compared to the progenitor (parent) cell

Tissue

Groups of cells get were similar in structure work together to perform a relatively specific function.

Major types of tissues

1. Nervous tissue- internal communication (brain, spinal cord, nerves)

2. Muscle tissues - contracts to cause movement

3. Epithelial tissue- forms boundaries between different environments, protects, secretes, absorbs and filters.

4. Connective tissue- supports, protects, binds other tissues together.

Structural elements connective tissue

Cells: fibroblasts, adiposecytes, macrophages, lymphocytes, fat cells, mast cells, neutrophil

Fibres: provide strength and support : collagen, elastic, & reticular

Ground substance: fills space between fibres

Extracellular matrix: ECM combination of fibres and ground substance that give connective tissue its physical properties