tissue structure

Question 1

what is a tissue?

Answer 1

• The substance and structure of part of the body
• A collection of similar cells that are spatially grouped together in an organised/hierarchal manner to fulfil a particular function.

Question 2

how are structure and function intimately linked

Answer 2

e.g. tissues found in an arm: bone, muscle, fatty vessels etc

Question 3

what are tissues made from?

Answer 3

The general structure of all tissues is that cells are carefully arranged within an extracellular matrix (mainly made from protein mixtures), which holds them in place and in many cases forms the bulk material of the tissue.

Question 4

‘extracellular’ refers to the fact that?

Answer 4

this material is outside the cells, whilst ‘matrix’ indicates that this is a substance in which the cells are embedded.

Question 5

Proteins in the extracellular matrix tend to be shaped appropriately to fulfil the specific function of the tissue. For example… in bone vs skin?

Answer 5

they form strong fibres in bone but are more flexible in skin allowing it to stretch.

Question 6

in all cases, the extracellular matrix proteins are?

Answer 6

made by cells, can be modified by cells, and provide the structural properties of the tissue (i.e. its strength and flexibility)

Question 7

what are the types we need to know (4)

Answer 7

1. bone
   
   2. skeletal
   3. nerves
   4. skin

Question 8

Long bone structure contains two distinct types of bone tissue: which are?

Answer 8

• compact (cortical) bone which is dense and forms a hollow cylinder within which there is:
  
  • less dense cancellous bone which has a honeycomb appearance.

Question 9

Why might bones have this structure, rather than being entirely compact bone?

Answer 9

• would be too heavy
• would be too brittle and break easily on impact

Question 10

what is the structure of bone like?

Answer 10

Dense structure containing cells and numerous canals in which blood vessels, lymph vessels and nerves (so we can perceive sensation) are located.

Question 11

strength comes from (…) and hardness comes from (…)

Answer 11

collagen, mineral component

Question 12

bone cells:

• what do osteoblasts do

Answer 12

form bone, secrete collagen and organise the mineralisation.

Question 13

what do osteroclasts disassemble (resorb) bone ?

Answer 13

in order to remodel it into an optimal shape.

Question 14

how do we maintain normal bone structure and function?

Answer 14

Balance in activity between the two cell types maintains it allows it to respond to changes during growth, repair, loading etc. The balance shifts through life and in conditions such as osteoporosis, periods of reduced loading, hormonal changes, corticosteroid drugs etc.

Question 15

Other important aspects of bones

Answer 15

• Bone marrow contains stem cells (and adipose tissue)– Hematopoietic stem cells (make leukocytes, erythrocytes and thrombocytes)
  – Mesenchymal stem cells (multipotent)
  * Mineral component acts as reservoir for Ca2+
  * Ends coated with articular cartilage (smooth and resilient – lacks the mineral component).

Question 16

Describe the structure and location of the THREE (3) types of muscle tissues in the body.

Answer 16

1. Skeletal Muscle

• Structure:
  
  • Long, cylindrical fibers.
  • Striated(striped appearance due to the arrangement of sarcomeres).
  • Multi-nucleated(more than one nucleus per cell).
• Location:
  
  • Attached to bones(e.g., biceps, quadriceps, triceps).

2. Smooth Muscle

• Structure:
  
  • Spindle-shapedfibers (short).
  • Non-striated(no visible stripes).
  • Single nucleusper cell.
• Location:
  
  • Walls of hollow organs(e.g., stomach, intestines, blood vessels, bladder).

3. Cardiac Muscle

• Structure:
  
  • Short, branched fibers.
  • Striated(like skeletal muscle).
  • Single nucleusper cell (sometimes two).
  • Connected byintercalated discsfor coordinated contraction.
• Location:
  
  • Heart(myocardium).

Question 17

Give their functions and briefly outline how the nervous system controls these tissues.

Answer 17

https://www.notion.so/tissue-structure-19800bb3982d80798cafc0c274ff08d0?pvs=4#1cd00bb3982d805590f0f4d7080320f8

Question 18

skeletal muscle

• what are myofibres

Answer 18

long thin multi-nucleated cells that are specialised to suit their contractile function (contain myofibrils)

Question 19

how are myofibres packed together

Answer 19

in a highly aligned manner with supporting extracellular matrix.

Question 20

what do myofibres have a lot of?

Answer 20

Lots of mitochondria

Question 21

Network of collagen that runs through the muscle and surrounds the myofibres is gathered together to form

Answer 21

tendons that join muscle to bone.

Question 22

characteristics of tendons:

Answer 22

• High tensile strength
• Mainly collagen (plus some elastic fibres)
  
  • Variety of sizes and shapes

Question 23

What is the function of tendons running through pulleys?

Answer 23

Tendons pass throughfibrous pulleysto stay close to bones, preventingbowstringingand ensuring efficient movement, especially in the hands and feet.

Question 24

What are tenocytes, and what is their role in tendons?

Answer 24

Tenocytesare specialised tendon cells responsible for maintaining the tendon’s extracellular matrix. They aresparsely populatedwithin tendons.

Question 25

Why do tendons heal slowly?

Answer 25

Tendons have few blood vessels, leading to poor vascularization and slow healing after injury.

Question 26

What is the difference between tendons and ligaments?

Answer 26

- **Tendons** connect **muscle to bone**, allowing force transmission for movement. - **Ligaments** connect **bone to bone**, providing joint stability.

Question 27

How are tendons and ligaments similar in structure?

Answer 27

Both are composed of dense connective tissue, primarily made of Type I collagen, providing strength and durability.

Question 28

musculoskeletal system: - how does it work?

Answer 28

flexors and extensors work in antagonistic pairs - different classes of levers

Question 29

what are the diff layers of skin:

Answer 29

epithelial cells in the epidermis connective tissue muscle epithelial cells lining a sweat duct subcutaneous fat

Question 30

what is the epidermis

Answer 30

flat thin dead keratinocytes (full of keratin)

Question 31

what is the dermis

Answer 31

collagen and elastic fibres populated with fibroblasts, capillaries, nerve endings, sweat glands, hair etc

Question 32

blood vessels (capillaries) - what can diffuse out of the blood into the tissues

Answer 32

dissolved nutrients and oxygen

Question 33

there is a continuous exchange of fluid between where?

Answer 33

the inside of the capillaries and the surrounding tissue cell

Question 34

about how much of tissue fluid drains into lymphatic system

Answer 34

10%

Question 35

Larger vessels have more features e.g.

Answer 35

smooth muscle

Question 36

what is the difference between repair and regeneration?

Answer 36

repair is forming a scab on a site, leaving the scar, with the tissue never being the same as the surroundings regeneration is recreating the tissue to the point to what it was like during the original development

Question 37

what happens when injury happens

Answer 37

1. a: Fibrin becomes infiltrated with blood vessels and fibroblasts and is gradually replaced with new ECM proteins 2. b: Other cells from epidermis and dermis invade the area 3. c: Granulation tissue disappears and newly healed skin has characteristic layered appearance

Question 38

what happens after blood from damaged vessels fills the area and forms a clot

Answer 38

- Mesh of fibrin fibres formed from circulating fibrinogen - Inflammation (swelling, redness, heat, pain) - Fibrin clot provides temporary protection and supports migration of fibroblasts - Healed skin can take on a scarred appearance (fibrosis)

Question 39

what happens in bone repair:

Answer 39

a) Blood from damaged vessels clots and forms fibrin scaffold that supports migration of stem cells and new osteoblasts into the repair site (b) New blood vessels develop and the temporary fibrin scaffold is replaced with collagen (c) Gradually the fibrin scaffold is completely replaced with bone ECM and becomes mineralized (d) New bone ECM eventually remodels to become strong supporting bone

Question 40

Constant natural remodelling behaviour means that bone is?

Answer 40

well adapted to heal very well → healed bone can resemble undamaged bone.

Question 41

what happens in muscle repair:

Answer 41

(a) Fibrin scaffold forms and becomes populated with capillaries and fibroblasts (b) Stem cells in the muscle tissue multiply and produce new myoblasts that can fuse with damaged myofibres to repair them, or can merge to form new myofibres (c) New and repaired myofibres become fully integrated and the temporary fibrin scaffold is replaced by collagen and other ECM molecules

Question 42

what happens in tendon repair:

Answer 42

Tendons do not heal as well as the other tissues discussed before. (a)Fibrin scaffold supports ingrowth of tiny capillaries and fibroblasts (b)Fibrin gradually replaced with collagen (takes a long time due to poor blood supply) (c) Eventually collagen is remodelled to become strong and aligned (d)In some cases fibrosis can cause adhesions to form

Question 43

what happens in nerve repair:

Answer 43

(a) If an injury cuts an axon then the distal part disintegrates (b) Debris is cleared away by macrophages and Schwann cells (c) Schwann cells form a pathway: by aligning that can guide axon re-growth (d) Eventually this process can result in growth to the target and restoration of function Problems with gaps, rate of regeneration, and adhesions.

Question 44

blood vessels: angiogenesis - why is this key?

Answer 44

Important in embryonic development, wound healing, female reproductive cycle.

Question 45

what is excessive angiogenesis

Answer 45

associated with cancer, age-related macular degeneration, psoriasis, endometriosis etc. Insufficiency associated with chronic wounds and ischaemic heart disease

Question 46

what is the predominant ECM protein in most tissues

Answer 46

collagen

Question 47

what other components do we find in the ECM

Answer 47

Many different types of collagen * Glycosaminoglycans, proteoglycans, polysaccharides * Elastin * Fibronectin * Laminin

Question 48

Overall the body is a hydrogel meaning?

Answer 48

an interlocking mesh of fibrous proteins and other components, swollen with water. Embedded within this, and responsible for producing and maintaining it, are the cells.