Diversity of cell types in multicellular organism

Question 1

Give examples of different cell types

Answer 1

(cells are organised into tissues)

• epithelial
• nervous tissue
• connective tissue
• muscle tissue

Question 2

What is differentiation?

Answer 2

The process of producing different cell types

Question 3

What is epithelia and the cells within?

Answer 3

• epithelial cells form sheets that cover the inner and outer body surfaces
- absorptive cells have microvilli to increase SA
- ciliated cells have cilia which beat to move substances over the sheet
- secretory cells secrete substances out onto the sheet

Question 4

What are the types of epithelial tissue and their example?

Answer 4

• simple squamous (lung)
• simple cuboidal (kidney)
• simple columnar (stomach)
• pseudo-stratified columnar (trachea)
• stratified squamous (oesophagus)
• stratified cuboidal (sweat gland)
• stratified columnar (salivary duct)
• transitional (bladder)

Question 5

What do secretory epithelial cells do?

Answer 5

• often collected together to form glands for secretion of substances eg gastric juice and mucus

• exocrine glands: secrete product into ducts
• endocrine glands: secrete hormones into the blood

Question 6

How are neurones specialised and how do they work?

Answer 6

• specialised for communucation

• The axon conducts electric signals away from the cell body

Question 7

What are rod cells and how do they work?

Answer 7

• Specialised sensory cells in retina

• layers of disks contain light sensitive pigment rhodopsin
• light evokes an electrical signal transmitted to the brain

Question 8

What are red blood cells specialised for?

Answer 8

• Specialised for transportation of oxygen so major protein component is haemoglobin

Question 9

How many red blood cells does 1cm^3 of blood contains?
and can they replicate?

Answer 9

• 5 billion erythrocytes

• can no longer replicate due to loss of nuclei and internal membranes. Their lifespan is ~120 days

Question 10

What is connective tissue and give examples of specialised forms?

Answer 10

• they fill spaces between epithelial sheets and tubes (fibroblasts and other cells secrete extracellular matrix)

• bone: calcium salts deposited in the cell matrix to form solid bone
• adipocytes: produce and store fat

Question 11

What does skeletal muscle do?

Answer 11

move joints, strong rapid contraction. striated

Question 12

where is smooth muscle found?

Answer 12

found in digestive tract, bladder, arteries and veins. not striated

Question 13

What does cardiac muscle do?

Answer 13

Only found in heart- produces heart beat. Adjacent cells linked by electrically conducting junctions

Question 14

What does totipotent mean?

Answer 14

able to differentiate into any type of cell- eg embryonic stem cells

Question 15

How does differentiation occur in adult organisms?

Answer 15

• pluripotent stem cells produce cells of a particular tissue
• monopotent stem cells produce only one type of cell
• differentiation is the end point- once a cell has fully differentiated it has limited or no capacity to divide

Question 16

How does differentiation happen from stem cells in the bone marrow? (hemopoiesis)

Answer 16

1) hematopoeitic stem cells collected from bone marrow
2) these become either lymphoid progenitor cells or myeloid progenitor cells
3) lymphoid progenitor cells become T-Cells or B-cells
4) Myeloid progenitor calls become other blood cells eg RBC, platelets, neutrophyls etc

Question 17

How is homeostasis maintained?

Answer 17

• Differentiated cells have a limited lifespan

• Apoptosis- programmed cell death

• Two main gene families involved- Bcl-2 family (regulation) and caspase (execution)

Question 18

What happens when apoptosis goes wrong?

Answer 18

• Too little
- cancer
- autoimmune diseases (immune cells)
- prolonged viral infection

• Too much
- neurodegenerative diseases
- autoimmune diseases
- additional tissue damage following trauma
- progression of AIDS

Question 19

How does apoptosis go wrong?

Answer 19

• apoptosis controlling genes damaged or aberrantly expressed
• inappropriate triggering
• interference by exogenous genes (viral, bacterial, parasitic)

Question 20

What are the mechanisms of differentiation?

Answer 20

• cells are genetically identical, differentiated cells express different subsets of genes (transcriptome and proteome)

• tissue specific gene expression is primarily regulated at the level of transcription

• development of organs and drug safety

Question 21

Give a summary of specialisation

Answer 21

• Cells within a multicellular organism are genetically identical although they perform different functions
• stem cells can give rise to multiple cell types
• differentiation is normally irreversible
• differentiation is achieved through expression of different subsets of genes in different cells