5-2: Connective Tissue And Muscle

Question 1

Q: What is connective tissue?

Answer 1

A: The general name given to a family of tissues including cartilage, bone, tendons and ligaments as well as those commonly referred to as loose or dense connective tissue

Question 2

Q: 4 common features of connective tissue.

Answer 2

A: The support cells which maintain the tissue are not attached to one another (i.e. unlike epithelial cells)

The majority of the volume in most connective tissues is taken up by extracellular matrix

Other cells may be present, for example those with immunological functions

The tissues are derived from mesenchyme, an embryonic tissue principally associated with the mesoderm layer of the early three layer embryo

Question 3

Q: What are the 3 types of ECM?

Answer 3

A: Fibrillar structures

Viscous liquid component which provides

Other molecules whose main function is in binding to cells via specific cell surface receptors and mediating their attachment to the ECM

Question 4

Q: What do fibrillar structures provide? ECM type.

Answer 4

A: strength against tensile forces applied to the tissue; main protein components are collagen, elastin and fibrillin. 

Question 5

Q: What does the viscous liquid component provide? ECM type.

What are its main molecular components?

Answer 5

A: resistance to compressive forces.
also provides a solvent in which oxygen, nutrients, waste products and small signalling molecules can diffuse

The main molecular components are complex negatively charged polysaccharides which bind water and Na+ ions and are mainly glycosaminoglycans or proteoglycans. .

Question 6

Q: How is the outside surface of the skin recognised?

Answer 6

A: (called the epidermis) cells stain a pale blue colour

Question 7

Q: What is the layer below the epidermis? How are individual cells separated?

Answer 7

A: layer of dense connective tissue called the dermis.

Individual cells are separated by pink staining ECM

Question 8

Q: Are fibrous components seen more clearly in loose or dense connective tissue?

Answer 8

A: more clearly seen in the loose connective tissue found deeper down in the skin

The fibres are less closely packed and you will see that both thick and thin fibres are present

Question 9

Q: What are the cellular components of loose connective tissue ECM?

Answer 9

A: The support cells are fibroblasts = have a spindly shape with correspondingly pointed looking nuclei

Other cells are mainly migratory white blood cells such as lymphocytes and neutrophils

Two types of cell which are normally resident in loose connective tissue but are related to white blood cells are the macrophages and mast cells

Question 10

Q: What are the cellular components of dense connective tissue ECM?

How does it vary in tendons and ligaments? Why?

Answer 10

A: The support cells are fibroblasts = have a spindly shape with correspondingly pointed looking nuclei

The dense connective tissue of skin is known as dense irregular connective tissue because the fibres are randomly oriented to give the tissue equal strength in all directions

In some locations – such as tendons and ligaments – strength is required in a single direction, and in this case the collagen and other fibres are aligned in parallel and the tissue is known as dense regular connective tissue

Question 11

Q: What is responsible for synthesising the ECM?

Answer 11

A: fibroblasts

Question 12

Q: Describe the fat cells/adipocytes that form part of loose connective tissue.

Answer 12

A: Part of the loose connective tissue in the skin contains a large number of fat cells or adipocytes. These appear white and large.

majority of cell is taken up by a single large vacuole containing lipid with all the rest of the cell (nucleus, cytoplasm, organelles) squeezed in a thin rim around the outside. The ECM components of the tissue lie between the fat cells

Question 13

Q: How does cartilage appear under a microscope?

Answer 13

A: Appear as large purple staining regions easily identified at low magnification

Question 14

Q: What are the support cells of cartilage? How are they recognised? Where do they lie?

Answer 14

A: chondrocytes - well separated from each other

recognise by blue staining nucleus

They each lie in their individual pale staining regions, called lacunae. The remaining space, staining purple, is the ECM of the cartilage

Question 15

Q: What is hyaline cartilage?

Answer 15

A: dense fine network of collagen fibres and the glycosaminoglycans rich in sulphated sugars produce a fairly homogenous appearance in hyaline cartilage

Question 16

Q: Describe fibrocartilage.

Answer 16

A: Fibrocartilage contains thicker collagen fibres oriented to provide tensile strength in a particular direction, for example the intervertebral discs

Question 17

Q: What is elastic cartilage?

Answer 17

A: Elastic cartilage contains additional elastic fibres to provide pliability and resilience (for example in the external ear)

Question 18

Q: How do substances reach chondrocytes (cartilage)?

Answer 18

A: Cartilage is unusual in that it has no blood vessels and substances reach the chondrocytes by simple diffusion through the ECM

Question 19

Q: Describe bone as connective tissue.

Answer 19

A: specialised connective tissue where the ECM (termed osteoid) has become mineralised with calcium phosphate crystals to provide great compressive strength

Question 20

Q: What is compact/dense bone?

Answer 20

A: The relatively solid region around the edge of the bone shaft is known as compact bone or dense bone

Question 21

Q: What is found within compact/dense bone?

Answer 21

A: Within it there are the support cells of bone, called osteocytes, within lacunae. There are also other cavities containing blood vessels.

Question 22

Q: What do minerals in bone prevent?

Answer 22

A: The mineral prevents free diffusion

Question 23

Q: What are canaliculi in bone? What do they provide?

Answer 23

A: small channels called canaliculi provide a pathway for diffusion of O2 and nutrients from the blood vessels to the osteocytes.

Question 24

Q: How is bone structure arranged? Structural units? ECM? Collagen fibres?

Answer 24

A: In transverse section on that slide it can be seen that bone is arranged in structural units called osteons or Haversian systems which have a central canal containing blood vessels, with the ECM of the bone arranged in concentric layers around this central canal. The collagen fibres are oriented differently in each layer to provide additional strength

Question 25

Q: What is spongy/cancellous bone? What are the bony structures here called and arranged?

Answer 25

A: The central part of a bone has spaces between the bone tissue, and is known as spongy bone or cancellous bone

The bony structures here are called trabeculae, and they are usually arranged in the way that best resists the mechanical stresses on the bone

Question 26

Q: What is the space between the trabeculae filled with?

Answer 26

A: filled with bone marrow, the site of developing blood cells. There may also be fat cells. 

Question 27

Q: What cells lay down new bone? What cells reabsorb bone?

Answer 27

A: New bone is laid down by cells called osteoblasts and bone is reabsorbed by cells called osteoclasts

Question 28

Q: How do the processes of bone laying and reabsorption relate?

Answer 28

A: Normally the two processes are in balance but they allow deposition of new bone to be adjusted to strengthen bone in regions of mechanical stress or to heal a wound. There can be net bone production during growth, or net resorption resulting from disuse in immobile patients or from osteoporosis

Question 29

Q: How do most bones start off? By which process do they become bone?

Answer 29

A: Most (though not all) bones start as cartilage precursors in the foetus, which then get converted to bone – a process known as endochondrial ossification.

Elsewhere the bone is lined with a.

Question 30

Q: How long do cartilaginous region persist in long bones?

Answer 30

A: at the growth plates between the shaft and heads until the bone has reached its adult length.

Question 31

Q: What lines the bone surface where it forms part of a joint? What lines it elsewhere?

Answer 31

A: cartilage

layer of dense connective tissue – the periosteum

Question 32

Q: What is the periosteum?

Answer 32

A: layer of dense connective tissue

Question 33

Q: What type is the majority of muscle? What is it an example of? Explain its appearance.

Answer 33

A: The majority of muscle in the body is skeletal muscle, connected to part of the skeleton and acting across a joint to move one bone in relation to another

This is an example of a striated muscle, named for the striped appearance due to the repeating sarcomeres that make up the contractile apparatus

Question 34

Q: What can you work out by comparing the transverse and longitudinal sections of muscle?

Answer 34

A: how the muscle is made up of a bundle of myofibrils, each containing multiple nuclei arranged around their perimeter

Question 35

Q: What are myofibrils made from?

Answer 35

A: These are made up of a large number of precursor cells which have fused together to make a syncytium in which the contractile apparatus in the cytoplasm becomes continuous

Question 36

A: What is attached to the round edge of each myofibril?

Answer 36

A: an ECM containing collagen fibres that are ultimately continuous with those of the tendons or bones on which the muscle acts

Question 37

Q: What is cardiac muscle an example of? How does it differ from skeletal muscle?

Answer 37

A: Cardiac muscle (which you will study in more detail next term) is also a form of striated muscle, but in this case the muscle cells remain separate and are connected end to end at structures called intercalated discs.
Some cardiac muscle cells have become specialised to form the

Question 38

Q: What can some cardiac muscle cells specialise to form?

Answer 38

A: conducting system of the heart

Question 39

Q: What controls skeletal muscle?

Answer 39

A: innervation from motor neurons

Question 40

Q: What is smooth muscle associated with?

Answer 40

A: the form associated with organs and vessels

Question 41

Q: What controls smooth muscle?

Answer 41

A: autonomic nervous system

Question 42

Q: How is the contractile apparatus organised differently from striated muscle?

Answer 42

A: The contractile apparatus is differently organised from striated muscle, with no repeating units being visible

Question 43

Q: Describe the smooth muscle contraction type.

Answer 43

A: can contract to a smaller fraction of its relaxed length and can maintain contraction for very much longer times

Question 44

Q: What is the speed and strength of skeletal muscle contractions?

Answer 44

A: rapid powerful