Week 6 Flashcards
(40 cards)
1
Q
What germ layer is muscle derived from?
A
- Mesoderm: specifically the paraxial (myotome forms skeletal muscle) and lateral plate mesoderm (splanchic forms cardiac, blood vessel and gut muscle)
2
Q
How does skeletal muscle develop?
A
- Skeletal muscle of the neck and trunk develops from the myotome of the paraxial mesoderm
- The mytotome divides into the epimere (back muscles- innervated by dorsal rami) and hypomere (muscles of thorax and abdomen- innervated by ventral rami)
- Skeletal muscle of the limbs develops from myoblasts that migrate laterally from the somites
- This part of the somite develops into muscle as it is in contact with the neural tube
3
Q
Describe the formation of skeletal muscle from myoblasts:
A
- Myoblasts undergo frequent divisions:
- They coalesce to form multinucleated, snycytial muscle fibres
- The nuclei within these developing fibres are displaced to the periphery of the cell
- As the myoblasts mature and form these fibres they express more myosin and actin which produce contractile filaments (sarcomeres are the smallest contractile unit)
4
Q
How is skeletal muscle growth regulated?
A
- Upstream activators from the dorsal ectoderm, notochord and neural tube initiate activation of genes important in skeletal muscle development
- Myf-5 and MyoD are positive regulators of muscle growth; and if they are BOTH knocked out, skeletal muscle will not form
- Myostatin is a negative regulator of skeletal muscle growth; if it is knocked out it will cause myostain-related muscle hypertrophy
5
Q
What is muscular dystrophy?
A
- A family of genetic diseases characterised by repeated degeneratin and regnerations of various muscle group during postnatal life
e. g. Duchenne’s muscular dystrophy: a membrane associated protein called dystrophin is lacking which makes the muscle fibres more susceptible to damage when they are stressed
6
Q
Describe slow vs fast twitch muscle fibres:
A
- Slow (type I) Muscle Fibres:
- Small fibres
- Appear red
- Many mitochondria and large amounts of myoglobulin
- Greater resistance to fatigue
- Found in back muscles
- High % of these fibres make up muscles of endurance athletes - Fast (type II) Muscle Fibres:
- Larger fibres
- There are two types:
2a Fast oxidative:
- Many mitochondria and high myoglobin
- Large amounts of glycogen
- Anaerobic glycolysis
- High content in middle distance athlete muscle
2b. Fast glycolytic:
- Less mitochondria and myoglobin
- Stores lots of glycogen
- Generate a high peak of muscle tension
- Fatigue rapidly
- Rapidly contract
- Found in high content in short distance sprinters and weight lifters
7
Q
Can muscle fibres change in phenotype?
A
- There is some plasticity, muscle fibres can respond to exercise by undergoing hypertrophy or becoming more resistant to fatigue (more like type I)
- These changes are associated with changes in gene expression
8
Q
What are satellite cells?
A
- Smal cells closely apposed to muscle fibres within the basal lamina
- Involved in muscle fibre growth
- Thought to represent persistant myoblasts
- Proliferate and fuse to form regenerating muscle fibres
9
Q
Descibe the origin of cardiac muscle:
A
- Cardiac muscle is derived from the lateral plate mesoderm, specifically the splanchnic mesoderm
- The cardiac muscle cells develop not by fusion but by the joining together of cells at junctions called intercalated dics
10
Q
What are the histological features of cardiac muscle:
A
- Branched cells
- Striated
- Attached end to end with intercalated discs
- Centrally placed nuclei
11
Q
Describe the origin of smooth muscle:
A
- Smooth muscle is derived from the lateral place mesoderm, specifically the splanchnic mesoderm
- In addition to this it is derived from local mesoderm (mesenchyme)
12
Q
What are the histological features of smooth muscle?
A
- Centrally located nucleus, one per cell
- No striations
- Usually lining hollow tubes or hollow organs
- Retains the ability to regenerate and multiply e.g smooth muscle lining uterus must proliferate during pregnancy
13
Q
What are the 2 main types of smooth muscle?
A
- Multiunit:
- Functionally independent smooth muscle cells
- Often innervated by a single nerve terminal
- Never contract simultaneously
- Derived from local mesoderm (mesenchyme)
e. g. smooth muscle in walls of blood vessels - Visceral:
- Bundles of smooth muscle cells
- Connected by gap junctions
- Contract simultaneously
- Derived from lateral (splanchnic) mesoderm
- e,g, smooth muscle in walls of intestine
14
Q
List the muscle types from most to least in regenerative capacity:
A
- Smooth > skeletal > cardiac
15
Q
What is the difference between hyperplasia and hypertrophy?
A
- Hyperplasia: growth in number of cells
- Hypertrophy: growth in size of cells
16
Q
What are connective tissues?
A
- Connective tissues support, connect or separate different types of tissues and organs
- Exist throughout the whole body except in the CNS
- Mesenchymal type tissues
- Connective tissues have 3 major components:
1. Fluid or ground state component
2. Fibres
3. Cells
17
Q
What are the development origins of connective tissues?
A
- Most connective tissues are derived from the mesoderm (although some skeletal components of the head are derived from neural crest cells which are ectoderm)
- Mesenchyme directly gives rise to most of the body’s connective tissues
18
Q
What is mesenchyme?
A
- Mesenchyme is a type of animal tissue comprimsed of cells embedded in a mesh of proteins in fluid (ECM)
- Cells within the mesenchyme can migrate easily
- Mesenchyme directly gives rise to most of the body’s connective tissues
- Mesenchyme interacts with epithelial cells to help form nearly every organ in the body
- Cells can undergo a epithelial to mesenchymal transition (cells go from being structured and lacking mobility in epithelium to being embedded in protein/fluid and highly motile)
- The EMT can cause the metastasis of tumours
19
Q
What are the 5 types of mesenchymal cells?
A
- chondroblasts
- lipoblasts
- fibroblasts
- osteoblasts
- myoblasts
20
Q
What are the components of connective tissue?
A
- Cells
- Fibres .e.g collagen, elastin and reticular
- Extracellular matrix e.g. glycoproteins and proteoglycans
21
Q
Describe the kind of fibres present in connective tissue:
A
- Collagen:
- Tough and flexible
- Resists stretching
- Most abundant
e. g. 90% of tendons are made up on collagen - Reticular fibres:
- Fine delicate fibres
- Supports individual cells
e. g. reticular fibres surround individual sheets of hepatocytes in the liver - Elastin fibres:
- Individual microfibrils embedded in the matrix
- Made up of the protein elastin
- Found in connective tissue that can stretch
e. g. elastic cartilage of ear
22
Q
Describe the ECM of connective tissue?
A
- The fluid/ground state in which the connective tissue cells exist in
- The composition of the extracellular matrix depends on the type of tissue
- Can be gel like e.g. in adipose tissue
- Can be very strong (many fibres) e.g. in tendons
- Can be hard e.g. in bones as it is ossified
- Can be fluid-like e.g. in blood, as proteins are dissolved into it
23
Q
Give examples of the most commonly known connective tissues:
A
Examples of connective tissues are:
- Blood
- Bone
- Cartilage
- Fat
- Fibrous connective tissue e.g. tendons
- Loose connective tissue e.g. under skin
24
Q
What are the connective tissue classifications:
A
- Loose connective tissue:
- Loosely arranged collagen fibre and many cells
e. g. adipose tissue and blood - Dense connective tissue:
- Densely packed collagen fibres and sparse cells (fibroblasts
- Exists in 2 forms:
2a. Dense irregular:
- woven pattern of fibres
- can resist tension from any direction
e. g. dermis of skin and non-lactating breast tissue
2b. Dense regular:
- parallel fibre bundles
- resists force in one direction
e. g. tendons, ligaments and bone
- Cartilage:
- chondrocytes + collagen fibres + protein matrix + water
- contains hyaluronic acid
- There are 3 types: hyaline, fibrous and elastic
25
What are the 3 types of cartilage and where are they found?
1. Hyaline:
- Flexible and resists compression
e. g. in trachea, bronchi and the end of bones
2. Fibrocartilage:
- Tough and resists compression
e. g. intervertebral discs
3. Elastic cartilage:
- Elastic
e. g. external ear, larynx and epiglottis
26
How is cartilage formed?
- Cartilage is derived from the paraxial mesoderm which gives rise to the somites; specifically cartilage is derived from the sclerotome
- Forms the basis of the formation of many bones, as the axial skeleton is deposited as cartilage which is then later ossified
27
How does endochondral ossification occur?
- The bone collar forms around the hyaline cartilage model
- Osteoprogenitor cells differentiate into osteoblasts
- Osteoblsts secrete osteoid against the shaft of the cartilage model
- The primary ossification centre is formed
- Cartilage matrix begins to deteriorate
- Vascularisation of the centre of the model occurs
- Secondary ossification centres form in the epiphyses (end of bone)
- Ossification of the epiphyses
- Hyaline cartilage remains only in the epiphyseal growth plates
28
What are some disorders of cartilage:
1. Osteoarthritis: hyaline cartilage in synovial joints thins (not a developmental disorder)
2. Achondroplasia: reduced proliferation of chondrocytes in the epiphyseal plates of long bones causes dwarfism
3. Cancers:
e. g. echondroma- tumour occurs inside bone and expands it
29
Does cartilage have good repair mechanisms?
- Cartilage has limited repair mechanisms
- Chondrocytes have limited migratory capacity
- There is no blood supply to hyaline cartilage
- Damaged hyaline cartilage is often replaced as fibrocartilage (a loss of function)
30
What are the 5 types of cell junction?
1. Zonula occludens (tight junctions)
2. Zonula adherens
3. Macula adherens (desmosome- spot junction)
4. Gap junctions
5. Hemidesmosomes
31
Describe zonula occludens (tight junctions):
- The most apically located junction
- Completely encircles the cell
- They seal gaps between epithelial cells (stop material from moving from the apical and basolateral surfaces of the cell)
- This means in order to move from the apical compartment to the basolateral compartment the material must diffuse through the cell
- Major protein type are the claudins
32
Describe zonula adherins:
- Also encircles the cell and provides adhesion
- Connects the actin filament bundle of one cell with that of the next cell forming an adhesion belt
- The zonula adherins junctions of two neighbouring cells are connected by cadherin proteins
33
Describe macula adherens (desmosomes):
- These are plaque-like thickenings on the membranes of adjacent cells
- Connects the intermediate filaments (keratin/desmin) in one cell to those in the next cell
- The intermediate filaments are joined from cell to cell by cadherins
34
Describe gap junctions:
- Allows for the passage of small water soluble molecules (e.g. ions) between cells
- Allows for electrical coupling between cells
- Form intracellular channels called connexins between cell pores
35
Describe hemidesmosomes:
- Connect the basal surface of an epithelial cell to the underlying basal lamina
- The extracellular domains of the integrins bind to a laminin protein in the basal lamina
- An intracellular protein binds via an anchor protein (plectin) to keratin intermediate filaments
36
What are CAMs?
- Cell adhesion molecules
- Organise cells into complex tissues and maintain boundaries
- The type of CAMs expressed by a cell determines what kind of cell it can bind to
37
What are the important molecules involved in cell adhesion?
1. Ig superfamily,
- Proteins with selectins with heterophilic or homophilic attachments to either integrin ligands or Ig superfamily proteins of a different or the same type
2. Cadherins:
- With homophilic attachments to cadherins of the same type, or by the way of catanins to the cytoskeleton
3. Selectins:
- With heterophilic attachments to carbohydrate ligands
4. Integrins:
- With heterophilic attachments to different ligands in the ECM
- They can link the actin cytoskeleton of a cel to various external structures
38
What is the role of e-cadherin in development?
- The first cadherin to be expressed in development
- Keeps the cells of the early embryo in contact to allow compaction of the blastocyst inner cell mass to occur
- During gastrulation, EMT occurs and e-cadherin expression is lost
39
How are cells sorted within tissue?
- Cells essentially test bonds with eacother and trade weaker bonds for stronger bonds
e. g. finding the cells with the same adhesion molecules that they do
- Cells with the strongest adhesion segregate to the middle
40
How can changes in cadherin expression mediate morphogenesis?
- At neurulation, N-cadherin begins to be expressed which allows the cells to re-adhere and form the neural tube as well as the somites
- If N-cadherin is overexpressed in the neural crest cells they will fail to emerge from the neural tube
