Topic 16: Cells, tissues and communication

Question 1

Identify 4 main cell types

Answer 1

Epithelium, muscle, nervous and connective

Question 2

identify and describe features of epithelial cells (classification, location, junctions, role of basal lamina/0

Answer 2

• Present where tissues come in contact with air or water - the only tissues that are air- and water-tight
• Classified based on:
  • Apex - apical aspect and Base - basal aspect
  • number of layers:
    
    • 1 layer: simple
    • 2 or more layers: stratified
    • 1 layer, but the position of nuclei are not the same → look stratified: pseudostratified
  • shapes of cells:
    
    • Flat and spindle-like: squamous
    • Cube-like: cuboidal
    • Column-like: columnar
  • Layer of epithelial cells sits on top of basil lamina - a layer of extracellular matrix then comes the connective tissues then muscle tissues.
  • The epithelial cells are held together by different junctions, aka anchoring junction, and the cytoskeleton.
    
    • Desmosome:
      
      • Each cell has many desmosome plaques which is attached to the plasma membrane inside and have connecting proteins pointing outwards to connect with other connecting proteins of neighboring cells.
      • There are intermediate filaments connecting many plaques within a cell together.
    • Hemidesmosome: similar mechanism to desmosome, but
      
      • This plaque has connecting proteins pointing to the basal lamina → anchor the epithelial cells to the matrix
  • Neighboring cells want to exchange substances or molecules → gap junction: area with tube-like structures to allow substances to move across the tissue layer
  • There are also tight junctions to prevent water moving through the cell layer. → water-tight
  • Substances going pass epithelial cells will do active transport via apical membrane, then passive transport via basal membrane
  • Cancer cells usually originate from epithelial cells → basal lamina helps contain cancerous cells in one place. → benign tumour
  • If the cancerous cells are able to break the basal lamina layer, they will spread out to other tissues and structure. → harder to trace and becomes malignant tumour

Question 3

Classify and describe features of different types of muscle tissues

Answer 3

• Skeletal muscles: only voluntary one
  
  • attached to skeletons and responsible for voluntary movement
  • straight, striated and unbranched
  • multiple peripheral nuclei
• Cardiac muscles: make up the heart
  
  • straight, striated and branched
  • have intercalated discs which are the area where gap junctions and desmosomes allow cell-to-cell communication → hold cells strongly together
  • single peripheral nucleus
• Smooth muscles: line every hollow organs except for the heart
  
  • spindle-shaped, non-striated
  • single central nucleus

Question 4

Identify and describe components of connective tissue

Answer 4

• cells - living part
• fibers - extracellular matrix
• ground substances (water, salts, proteins, etc.) - extracellular matrix

Question 5

Which tissues animals depend on to coordinate their movement and behaviors?

Answer 5

Nervous tissues with action potential and neurotransmission between neurons to deliver electric signals

Question 6

Describe the pathways in which steroid hormones, protein hormones and neurotransmitters cause cellular responses

Answer 6

• Protein hormones:
  
  • move into cells via receptors integrated in plasma membrane
  • usually associated with increased production of cAMP from ATP
  • cAMP then relay signals via many proteins to alter physiology of the cells and cellular responses - really fast, seconds to minutes
• Steroid hormones
  
  • diffuse through the plasma membrane then bind to intracellular receptors to move into the nucleus
  • hormone-receptor complex then interacts with specific DNA sequence to alter protein synthesis - may take up to hours
• Neurotransmitters
  
  • released when there is action potential
  • neurotransmitter receptors on post-synaptic nerves are coupled with channels to allow depolarisation and transmission of signal to the next neuron.

Question 7

Describe the pathway in which stress response happens in hypothalamus-pituitary-adrenal axis

Answer 7

• When there is stress present threating the balance of homeostasis, hypothalamus released CRH which travels down to the pituitary gland, triggering the release of ACTH.
• ACTH then enters bloodstream, but there is only one cell that have receptors for ACTH which is adrenal cortex.
• Adrenal cortex then produced cortisol which helps:
  
  • increase sugar and protein breakdown → energy for mitochondria to make more ATP → the body now produces more energy to prepare and cope with stress.
  • increase blood glucose levels
  • anti-inflammatory effects
• Cortisol has negative feedback on hypothalamus and pituitary gland to prevent accumulation which can result in excessive and prolonged stress and affect immune system.