Cells in health and disease

LO: Describe homeostasis and the processes which are involved in cell protection, movement, nutrition, communication, energy production and renewal

Homeostasis is the process by which internal variables are kept within a normal range of values

Cells

Protection
Nutrition
Communication
Energy
Movement
Recycling and renewal

Phospholipid bilayer - prevent charged/large molecules moving in or out, impermeable

Transcytosis - apical to basal (top to bottom)

Cytoskeleton

Actin in high abundance
Microtubules - cilia and for mitosis
Intermediate filaments
Lamins - DNA structure
Desmosome - 'rungs' between cells, cell adhesion to connect cells
Hemi-desmosome - connect cell to basement membrane

Waste disposal

Autophagy - disposal of self cells
Heterophagy - disposal of non-self cells

Communication

Type	How it communicates
Synaptic	Between muscle and nerve releases chemicals that bind to receptors on muscle
Autocrine	Releases chemicals that bind to receptors on self
Paracrine	External chemical release near receptors on different cell
Endocrine	External chemical release into blood and travel blood to the receptor on different cell

Signals

Pathogens
Damage to neighbouring cells
Contact with neighbouring cells
Contact with extracellular matrix
Growth factors
Hormones
Cytokines
Cell surface receptors/intracellular receptors

Action of receptors

Open ion channel
Activate a G-protein
Activate a receptor tyrosine kinase
Activate a non-receptor tyrosine kinase
Activate a transcription factor
MAP-kinase: Activated by binding of a signalling molecule to a receptor tyrosine kinase causing cell to divide

Growth Factors

Promote entry of cells into cell cycle
Remove block on cell cycle progression
Prevent programmed cell death
Enhance synthesis of cell components

Cell renewal

Checkpoints check DNA is normal
CDKIs (Cyclin dependent kinase inhibitor) - enforce checkpoints
Cyclins and cyclin-dependent kinases drive the cell cycle

Extracellular matrix

Anchors cells and keep them upright
Controls cell proliferation and migration
Scaffold for renewal
Forms tissue microenvironment

Stem cells

Self-renewal
Asymmetric division: 1 mature and 1 stem cell after each division

flowchart LR
	A[Totipotent/Embryonic] --> B[Adult/Tissue]
	B --> Multipotent

Regenerative medicine

Reprogramming cells to achieve properties of embryonic stem cells

flowchart LR
	SRC1[Somatic cells]
	SRC2[Gene for 'stemness']
	DST[Induced pluripotent stem cells/iPS]
	
	E[ ]:::empty
	classDef empty height: 0, width: 0
	
	SRC1 --- E
	SRC2 --- E
	E --> DST