Tissues

Question 1

Define the term ‘epithelium’ and describe the basic functions of epithelial surfaces, those covering the body and lining internal structures.

Answer 1

Epithelial tissue covers surfaces and separates compartments.
It has no contact inhibition, and forms cell-cell and cell-ECM junctions to fill any gaps.
Also has secondary functions, determined by its thickness (thin = diffusion, thick = protection) and presence of cilia (movement) and microvilli (absorption).

Question 2

Describe the types of surface epithelia and explain how the structural properties of each correlates with its functions.

Answer 2

Simple

o Squamous e.g. Alveoli and Capillaries. Thin to allow for easy diffusion.
o Cuboidal e.g. Lining of nephrons. Perform secretion and absorption/pumping.
o Columnar e.g. Lining digestive tract. When ciliated, move mucus

Stratified

o Squamous e.g. Epidermis. Thick, and layers can be sloughed off to allow new growth.
o Cuboidal e.g. ducts of sweat glands. Protection.
o Columnar e.g. Pharynx. Protection and secretion.

Question 3

Describe the epithelial components of the liver and kidney.

Answer 3

Liver
o Hepatocytes
o Arranged in rows (or cords) between blood vessels
o Multiple functions including secretion.
o Support epithelial cells line blood vessels and bile ducts.

Kidneys
o Epithelial cells
o Arranged into nephrons
o Multiple functions including filtration of blood, partial absorption of filtrate
o Support cells line blood vessels and renal pelvis which receives toxic urine.

Question 4

Consider the consequences of abnormal function of covering and lining epithelia.

Answer 4

o Over/Under proliferation - cancer
o Over/Under Secretion
o Loss of ciliary beat

Question 5

Define the term ‘gland’ and describe the basic functions of glandular epithelium.

Answer 5

Glands are collections of multi or single cellular secretory epithelial cells.

• Endocrine: Secretes into blood e.g. Adrenal Cortex
• Exocrine: Secretes to surface e.g. Sweat glands

Can also be simple or compound glands, which can have linear or acinar structures.

Acinar ducts usually used for secretion, as it would be difficult to expel the substances in the long tubular ducts

Question 6

Consider the consequences of abnormal glandular function.

Answer 6

Over production – Pituitary giantism
Under production – Pituitary dwarfism

GSH abnormal production

Question 7

Define the term ‘connective tissue’ and describe its basic functions.

Answer 7

Connective tissue - tissue that connects, supports, binds, or separates other tissues or organs, typically having relatively few cells embedded in an amorphous matrix, often with collagen or other fibres, and including cartilaginous, fatty, and elastic tissues.

Includes fibres (collagen and elastic), ground substance, tissue fluid and loose connective tissue (e.g. fixed and transient cells)

Question 8

Describe the matrix, fibre and cellular components of connective tissue and explain the function of each.

Answer 8

Fibres
• Collagen - Makes up 30% body weight. Flexible, but inelastic with great tensile strength. 19+ types?
• Elastic Fibres - Protein Elastin. Stretch 1.5x length and return to original shape. Microfibrils and amorphous component. Found in sheets. Yellow colour.

Ground Substance
• Proteoglycans (Protein core and GAGS)
• Hyaluronic Acid
• Glycoproteins

Tissue Fluid

Loose Connective Tissue
• Fixed cells – Fibroblasts, Macrophages, Adipocytes, Mast cells
• Transient cells – White Blood Cells

Question 9

Consider the consequences of abnormal function of connective tissues.

Answer 9

• Blood / bone marrow - leukaemia
• Loose / dense - loss/abnormal fibres
• Cartilage - tear
• Bone – osteoporosis
• Epidermolysis bullosa (EB) is a group of inherited connective tissue diseases that cause blisters in the skin and mucosal membranes. It is a result of a defect in anchoring between the epidermis and dermis, resulting in friction and skin fragility.

Question 10

Describe muscle tissue types and function

Answer 10

• Has the ability to contract and produce force and movement, often connected to bone, excitable
• Three types of muscle tissue: cardiac, smooth muscle (internal organs) and skeletal muscle
• Long thin cells
• Cytoplasm of cells packed with contractile apparatus

Question 11

Describe neural tissues and its function

Answer 11

• For communication – can carry information in the form of chemical and electrical signals from one part of the body to another
• Made up of two types of cells: Neurons + support cells (glial cells)
• Receives, generates and transmits electrical signals
• Integrates information
• Concentrated in the brain and spinal cord but also include a network of cells that extend to virtually every part of the body

Question 12

Compare and contrast collagen and elastic fibres

Answer 12

Collagen
•	30% body weight
•	Inelastic but flexible
•	Great tensile strength
•	19 types (+), made by fibroblasts
•	Type I in tendons
•	Type III is reticulin
•	Type IV in basal lamina (non-fibrous)

Elastic fibres

• Protein elastin
• Stretch 1.5 times
• Microfibrils and amorphous component
• Generally in sheets rather than fibres
• Yellow colour (aorta)

Question 13

Describe different types of dense connective tissue

Answer 13

• Dense regular –made up of parallel collagen to form tense structures e.g. tendons and ligaments
• Dense irregular – made up of randomly aligned collagen e.g. muscle, nerve sheaths, sebaceous glands

Question 14

Describe the development of exocrine and endocrine glands

Answer 14

• During development, epithelial cells grow downward into their supporting connective tissue.
• In the development of exocrine glands, they remain connected to the parent epithelium, and a hollow center, or lumen, forms to create a duct that provides a passageway for secretions to move to the surface of the epithelium and into the external environment.
• In endocrine glands, they lose the connecting bridge of the cells that links them to the parent epithelium. Their secretions then go directly into the bloodstream.

Question 15

How does epithelial tissue maintain coverage of surfaces?

Answer 15

No contact inhibition
Cell-cell junctions
Cell-ECM junctions

Question 16

Where is the basement membrane found?

Answer 16

Between epithelium, the mesothelium and the endothelium.

Matrix layer made up of basal lamina cells and reticular lamina, composed of a network of collagen and laminin filaments embedded in proteoglycans

Question 17

Describe desmosomes

Answer 17

adhering junctions which attach the intermediate filaments of the cytoskeletons of neighbouring cells. Dense glycoprotein plaques seen with EM

Question 18

Describe hemidesmosomes

Answer 18

strong junctions that anchor intermediate filaments of the cells cytoskeleton to the fibrous matrix proteins such as laminin in the ECM. Connects skin to basal lamina

Question 19

What % body weight is collagen?

Answer 19

30%