3. Integrating Cell Into Tissues Flashcards
1
Q
Define tissue
A
Groups of cells that are similar in structure and function and adapted to perform a specific function
2
Q
Define an organ
A
Estate where two or more tissues are combined to create a structural unit that has a particular function that or some of its parts
3
Q
Which three types of cells in the body remain separated from each other?
A
The ova, The spermatozoa and the corpuscles of the blood (red and white blood cells)
4
Q
During very early embryo development which three layers of the embryo are formed from the surface inwards?
A
The ectoderm,mesoderm and the endoderm
5
Q
From which layers of the embryo are epithelium cells divide from?
A
All three layers
6
Q
Which layer of the embryo are nerve cells derived from?
A
The ectoderm
7
Q
Which layer of the embryo or muscle and connective tissue derived from?
A
Mainly the mesoderm
8
Q
Which layer of the embryo are the mucosa derived from?
A
The Endoderm
9
Q
How are surface proteins produced at the early developmental stage and what do they facilitate?
A
They are produced by cells of the same type congregating together to produce surface proteins that anchor cells together and facilitate cell-to-cell communication. The cells are basically woven together with extracellular and intracellular proteins to create discrete tissue
10
Q
What are the four main categories of body tissue?
A
1) epithelial tissue
2) connective tissue (includes blood, cartilage, bone, teeth and fat)
3) muscle tissue
4) nerve tissue`
11
Q
When do cells first coalesce?
A
During embryogenesis when they stick together after dividing, as opposed to separating out
12
Q
What does the human blastocyst consist of?
A
The blastocyst cavity, the trophoblast and the inner cell mass (embryoblast)
13
Q
What does the inner cell mass develop into?
A
The embryo
14
Q
What does the trophoblast become?
A
The placenta
15
Q
What cell does all cells of the body come from?
A
The epiblast
16
Q
What four things hold cells together?
A
1) Cell-cell adhesion molecules
2) Extracellular matrix proteins (fibres)
3) Internal-external scaffolding
4) Close proximity of cells- pressure effects
17
Q
What are the three main component of connective tissue?
A
1) cells - mainly mature fibroblasts/ fibrocytes, fixed adipocytes, reticular cells (found in lymphatic tissue)
2) fibres - collagen, elastin, reticular fibres
3) ground substance - glucosaminoglycans e.g. hyaluronic acid
18
Q
What part of the connective tissue bears the mechanical stress?
A
The extracellular matrix, made up of fibres and ground substance.
19
Q
What is the primary cell of connective tissue and what ability does it have?
A
Mesenchymal stem cells (immature fibroblast cell).
Have the ability to inter-convert between different connective tissue cell types.
20
Q
What are the six functions of connective tissue?
A
- Binding and supporting.
- Protecting.
- Insulation.
- Storing reserve fuel and cells.
- Transporting substances within the body.
- Separation of tissues.
21
Q
What type of tissue are nerves found in?
A
Connective tissue with branches that go to the edge of the epithelium (but epithelium itself has no nerves) and smooth muscle
22
Q
What does connective tissue consist of?
A
- Extracellular matrix is plentiful
- Cells are sparsely distributed within in
- Matrix is rich in fibrous polymers especially collagen, and it is the matrix rather than the cells that bear most of the mechanical stress
23
Q
How do connective tissue cells interact?
A
Direct attachments between one cell and another are rare
24
Q
What does epithelial tissue consist of?
A
- cells are tightly bound into single layered sheets called epithelia
- extracellular matrix is scant, consisting mainly of the basal lamina which underlies the epithelium
25
What is the function of the basal lamina?
Anchor down epithelium and connect the cells to underlying connective tissue thus stabilising the basal ends of the epithelial cells.
26
How are epithelial cells attached to each other?
- Cell to cell adhesion molecules.
- strong intracellular protein filaments (part of the cytoskeleton) cross the cytoplasm of each cell and attach to specialised junctions in the plasma membranes to prevent the cells from stretching too much
- these junctions in turn attach adjacent cells to each other or to the underlying basal lamina
27
What part of the epithelium bears the most mechanical stress?
The cell to cell adhesion molecules.
28
What can mesenchymal stem cells produce?
Bone, cartilage, muscle, marrow, tendon/ligament, adipose tissue and connective tissue: produces most of the extracellular fibres that anchor cells into place or make tissue
29
In culture what do mesenchymal stem cells convert into and what do these produce?
Quickly converts to a mature fibroblasts and produces fibronectin, laminin and collagen that allows cells to adhere to plastic or glass surfaces
30
Why is hyaluronic acid put into cosmetics?
To moisturise as it is full of sugars so water is drawn into the skin and gets into the dermal layer and makes the skin expand
31
Why is collagen put into cosmetics?
Draws water in which prevents wrinkles
32
What happens to bone marrow with age?
It stores fat and is gradually replaced by it
33
Where are epithelial tissues found?
Lining all the cavities and free surfaces of the bodyq
34
What do the specialised junctions between epithelial cells help to do?
Help to form tissue barriers and inhibit the movement of water, solutes and cells from one compartment to another
35
What do epithelia rest on?
A supporting bed of connective tissue which is via a basement membrane that contains many different proteins
36
What is formed when the supporting bed attaches the epithelial layer to other tissues such as muscle tissues?
Tissues join together in various combinations to form larger functional units called organs
37
Why are epithelial cells described as polar cells?
Have distinct apical, lateral and basal surfaces which each have different specialised structures for different functions.`
38
What are apical domain modifications on epithelial cells?
- Microvilli,
- Stereocilia,
- Cilia.
39
What are the lateral surface specialisations in epithelial cells?`
- Tight junctions,
- Adherens junctions,
- Desmosomes (Adhesion plaques),
- Gap junctions,
- Cell adhesion molecules.
40
What are the basal surface specialisations in epithelial cells?
- Hemi Desmosomes,
- Focal adhesions,
- Integrins,
- Proteoglycans,
- Cell adhesion molecules.
41
What are tight junctions?
- near apical end of cell on lateral borders
| - long cell to cell fusion point
42
function of tight junctions?
- Seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
- Prevent movement of larger molecules from the lumen into deeper tissue layers of the organ.
• Eg tight junctions near the apical surfaces of cells lining the digestive tract help to keep enzymes, acids and wastes in the lumen from reaching the base lateral surfaces and damaging the underlying tissues and organs.
- But in the gut, can transiently open to allow small molecules (sugars, AAs, water) to cross to underlying tissues - paracellular trans
43
What are adhesion junctions?
Almost always found 1/3rd distance from luminal surface
• Found in pairs
• Formed from intracellular actin filaments
• Linked to E-cadherin proteins
• E-Cadherins cross the intercellular space and bind with transcellular E-cadherins from adjacent cells.
• Found throughout this region as ‘a belt of adhesion’
Sometimes called ‘adhesion belt’
44
In what tissue are adhesion junctions found and what is their main function?
Only found in epithelial and endothelial cells.
Functions as tissue stabilising factor and additional transport barrier.- important in blood brain barrier
45
What are desmosomes?
* The strongest of all the cell-to-cell adhesions
* Found ~ ½ way between top and bottom of cells
* Random distribution pattern
* Cytokeratin fibres intracellularly, E-cadherins intercellularly (spring-like)
* joins the intermediate filaments in one cell to those in a neighbour
46
In what tissue are desmosomes found and what is their main function?
Found in tissues that experience intense mechanical stress (e.g. cardiac muscle, bladder tissue).
Provide mechanical strength and prevent tissue destruction.
*it is the only adhesion found in skin cells*
47
What are gap junctions?
* Found close to the base epithelial cells.
* Only spermatozoa, erythrocytes and other motile cells do not have gap junctions.
* Made up of cylinders of proteins (Connexins) arranged in a hexagonal pattern (Connexon) that open and close (requires ATP).
* A pair of connexons (1 on each adjacent cell) come together to form a channel.
48
In what tissue are gap junctions found and what is their main function?
Role to quickly communicate changes in intercellular molecular composition (e.g. electrolyte and energy changes).
Allows free movement of small molecules from one cell to another (e.g. ions Ca2+ mainly, most sugars, amino acids).
This is important in smooth and cardiac muscle contraction - allows wave of electrical impulse. Therefore, vastly distributed in cardiac and smooth muscle cells.
49
What change occurs to gap junctions in preparation for birth?
Switch from connexin 34 to connexin 45 occurs in the myometrium (main function to induce uterine contractions) of the uterus.
50
What are Hemi-Desmosomes?
• Attach not to cells but a layer of extracellular matrix
e.g. fibronectin, collagen and laminin fibres
• Intracellular intermediate filaments of cytokeratin
attached to laminin through integrins
• Basal lamina attached to connective tissue layer
through elastin, fibrillin and other collagens
51
In what tissue are hemi-desmosomes found and what is their main function?
Only found in epithelial tissue on the basal surface of epithelial cells.
Main function is to anchor epithelial cells to the basal lamina and prevent loss to external surface (e.g. by pressure effect).
52
What are focal adhesions?
Intracellular actin filaments attached to fibronectin (in the basal lamina) through integrins. When bound to fibronectin, conformational change results in binding
to collagen fibres
The basal lamina layer is attached to connective tissue layer through elastin, fibrillin and other collagens.
53
What is the main function of focal adhesions?
Anchoring of epithelial cells to basal lamina.
54
contrast hemi-desmosomes and focal adhesions?
* Similar function to hemidesmosomes – attachment to basal lamina
* Uses Intracellular actin filaments (instead of cytokeratin)
* Uses integrins (just like hemidesmosomes)
* Binds to fibronectin (instead of laminin)
55
What ion do all adhesion properties require?
Calcium
56
What are integrins?
• Transmembrane heterodimers (alpha and beta).
* Important role in cohesive forces holding tissues together.
* Facilitate intracellular cytoskeleton - extracellular matrix adhesion.
* Always work as alpha-beta dimer
• Weak binders of extracellular matrix as dimer pair. Phosphorylation by Focal Adhesion Kinase produces heterotetramer which has greater binding capacity therefore stronger bond.
57
What organ contains all 4 tissues?
Mucosal membrane
58
How do cells that touch each other communicate?
Through gap junctions
| • Cells of different types need different communication systems (e.g. nerves and hormones)
59
How do Epithelial cells adhere to epithelial cells?
through cell surface proteins
60
How do Epithelial cells adhere tobasal lamina (extracellular matrix)?
through cellular adhesion molecules – this makes epithelial tissues
61
How do Tissues adhere to other types of tissue (e.g. nerves to blood vessels)?
through connective tissue fibres
| • leads to organ formation
62
Function of adherence proteins?
* To maintain the survival and structure of the cells and hence of tissues
* To prevent pathogens from gaining entry to the internal environment
63
What structures make up the mucosal membrane?
- Epithelium,
- Lamina propia,
- Muscularis mucosa.
64
What is epithelium?
Epithelium is an avascular tissue composed of cells that cover the exterior body surfaces and line internal closed cavities and body tubes that communicate with the exterior. Epithelium also forms the secretory portion (parenchyma) of glands and their ducts.
65
What are the three characteristics of epithelium?
- Closely adhere to each other by cell-cell adhesion molecules,
- Exhibit functional and morphological polarity,
- Attached to underlying basement membrane.
66
What is lamina propia?
The lamina propria is a thin layer of loose areolar connective tissue, which lies beneath the epithelium
67
What is muscularis mucosa?
A thin discontinuous smooth muscle layer inferior to the lamina propia.
68
Where is the mucosal membrane normally found? (Give examples)
- Lines all the moist hollow internal organs of the body.
E.g. GI tract, urinary tract, respiratory tract.
- continuous with the skin at various body openings
e.g. eyes, ears, inside nose, inside mouth, lips, vagina, urethral opening, anus
69
What does most mucosal membrane secrete and what does it contain?
They secrete mucus, a thick protective fluid which contains:
- Mucins (muc1),
- Immunoglobulins (IgA),
- Electrolytes (e.g. NaCl),
- Antiseptic enzymes (lysozymes).
70
What are the general functions of the mucosal membranes?
- Stop pathogens and dirt from entering the body,
- Prevent bodily tissue from becoming dehydrated,
- Lubricate the surface.
71
What are the layers of the GI tract?
- lumen
- mucosa lining lumen
- muscularis mucosae - thin discontinuous smooth muscle layer
- submucosa - connective tissue layer with blood vessels, lymph vessels and nerves.
- muscularis externa - smooth muscle with muscle fibres going in two directions (inner circular muscle and outer longitudinal muscle)
- serosa - connective tissue containing collagen and elastin fibres with some smaller arteries and veins and nerve fibres
72
What does the gastric mucosa secrete?
Secretes acids, digestive enzymes and the hormone ghrelin (stimulates appetite) gastrin (stimulates secretion of HCl).
73
What are rugae?
Folds of the gastric mucosa forming longitudinal ridges in empty stomach.
Allow the stomach to stretch to accommodate large volume of material.
74
What are the functions of the mucosa in the GI Tract?
1. To absorb substances from the lumen- mucosa folds, microvilli and peristaltic actions aid this
2. Prevent ingress of pathogens- lamina propia contains lympathic tissue which helps with this and so does the Muscularis mucosae
3. Move contents and expel waste- Muscularis externa carries out peristalsis to aid this
75
What is peristalsis?
the involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wavelike movements that push the contents of the canal forward.
76
Describe the structure and function of the layers of the oesophagus?
1. Mucosa - 3 layers of epithelium, lamina propria and muscularis mucosae
Epithelium – stratified squamous non-keratinised (withstands abrasion)
2. Submucosa - subtending layer of connective tissue containing mucus-secreting glands
3. Muscularis externa – smooth muscle layers
(inner – circular; outer – longitudinal) which move a bolus of food by peristalsis
77
What part of the urinary tract does not have mucosal membranes?
Membranes in the kidney are not considered mucosal membranes because they do not have muscularis mucosa.
78
What is the purpose of the muscularis externa in the ureters?
Stop ureter expanding and bursting. Not for peristalsis - contents will move into the bladder due to gravity.
79
What type of epithelium is present in the urinary tract?
Simple squamous and cuboidal in the kidney.
• Corpuscle lining is ‘flattened’ (squamous) epithelium - to allow quick movement of water across surfaces
• Lining of collecting ducts is ‘square shaped’ (cuboidal) epithelium
• Proximal tubes contain ciliated surface - to help movement of fluid through and increases surface area
Transitional epithelium (urothelium) in the ureters, bladder and urethra.
In the urethra it changes to stratified squamous and then keratinised squamous epithelium towards the end.
80
Where does the smooth muscle layer(muscularis externa) first appear in the urinary tract?
Muscle layer first appears in the ureter and the bladder
| - Inner longitudinal muscle and Outer circular muscle - opposite of GI tract
81
How many layers are there in the muscularis externa of the stomach? What are they?
3 layers of smooth muscle in stomach -
| oblique, circular and longitudinal
82
What are the functions of epithelial tissue?
* Provide physical protection - protect exposed and internal surfaces from abrasion, dehydration and destruction by chemical or biological agents.
* Control permeability - any substance that enters or leaves your body must cross an epithelium
* Provide sensation - neuroepithelia contain sensory cells
* Produce specialised secretions - epithelial cells that produce secretions are called gland cells
* Lubrication
83
What are the layers of the basement membrane?
* the basal lamina - the layer closer to the epithelium restricts the movement of proteins and other large molecules from the underlying connective tissue into the epithelium.
* Reticular lamina - the deeper portion of the basement membrane consists mostly of the reticular fibres and ground substance which gives strength.
* Collagen matrix
* Proteoglycan(intercellular cement)
84
What is the structural unit in the kidney?
Nephron
85
What is the function of transitional epithelium?
Transitional epithelium cells stretch (distend) readily in order to accommodate fluctuation of volume of the liquid in an organ.
86
What does fat act as in an expanding bladder ?
Shock absorber
87
What are the surface cells of the transitional epithelium called and what is their function?
Umbrella cells which secrete mucus to protect the lining of the bladder from the acidic urine.
88
What do the transitional epithelium in the bladder (urothelium) do?
When bladder fills with urine the cells flatten out.
| Shapes of the surface cells differ: rebounded in the relaxed state and patterned in the distended state
89
How is the bladder protected against acidic urine?
Epithelial cells produce mucus, which also allows things to slide and stops ingress of pathogens
90
What do tight junctions in the bladder achieve?
Prevents leakage to inner cell layers
91
What does mucus in the urethra prevent?
Ingress of pathogens
92
What is the function of the Urinary tract?
1) absorption of essential nutrients in the kidney
2) prevention of pathogen entry (especially in lower urinary tract)
3) removal of waste products
93
Why does bladder have a thick muscularis externa?
The detrusor muscle contracts during urination and also acts as a shock absorber when bladder expands and hits against tissues in the pelvis.
94
What is the function of the respiratory tract?
Gaseous transport and exchange.
95
What are the two parts of the respiratory tract?
Conduction part: nasal cavity to bronchioles. - bring gases in
Respiratory part: respiratory bronchioles to alveoli.
96
What is the pharynx?
throat
97
Why is the pharynx not considered to have a mucosal membrane?
No smooth muscle layer (muscularis mucosa).
It has skeletal muscle layer.
The trachea also does not have smooth muscle layer.
98
What type of cells make up the epithelium of the pharynx?
Stratified, squamous, non-keratinised
99
Structure of trachea and primary bronchi?
Mucosa, submucosa, c-shaped cartilage wall
100
What is the mucosa of the trachea and primary bronchi like?
The epithelial layer is several cells deep and the surface is covered in cilia. The lamina propria is very thin, no longitudinal muscularis mucosa layer
101
What is the submucosa in the trachea and primary bronchi like?
The connective tissue layer contains mainly collagen and elastin fibres and many fibroblasts. Also contains Seromucus mucous glands which produce a watery mucus that thickens during infection
102
What does the c-shaped hyaline cartilage of the trachea/ bronchi consist of?
Two layers:
- perichondrium that has fibroblasts that lay down collagen fibres
- chrodrogenic layer from which cartilage is formed
- the cells present can interconvert from chrondroblats to chondrocytes to make both hyaline and elastic cartilage
103
What are chondrocytes?
A cell which has secreted the matrix of cartilage and become embedded in it.
104
Why does the trachea not need smooth muscle to keep it open?
Has cartilage
105
What does the trachea branch into?
Two primary bronchi
106
Why are foreign objects more likely to lodge in the right bronchus?
Path of the right bronchus is more vertical than the left
107
What do secretions from the epithelium and submucosa glands of the trachea and bronchi contain?
- mucins and water to make mucus
- serum proteins to lubricate
- lysozyme to destroy bacteria
- anti-protease to inactivate bacterial enzymes
108
What is the mucociliary escalator?
Thick mucus in the airways trap inhaled particles including dust, food particles, and invading pathogens. A cillia wave (move 12 times/s, 250 cilli/cell) moves the mucus material to the oral cavity where the material can be swallowed.
109
What is the mucociliary escalator in the trachea like?
- Tracheal mucosa have approx 250 cilia
- Cilia beat at 12Hx beneath a moveable, viscoelastic mucus blanket
- thick basement membrane
- lamina propria rich in immune cells
- lots of goblet cells in epithelial layer
- layer of elastic fibres
110
What change occurs to the cartilage in secondary and tertiary bronchi?
No longer present as rings of cartilage. Appears as crescent shaped cartilage.
There is less cartilage present because not as much strength needed to hold tissue open.
111
Structure of secondary and tertiary bronchi
- epithelium is pseudostratified and ciliated
- bounded by smooth muscle - as some cartilage is lost
- supported by seromucuous glands in the submucosa
- airway kept open with crescent shaped cartilage
- no outer layer of smooth muscle
112
What structure do alveolar epithelium and the endothelium share and how is it specialised for function in the alveolar?
A fused basal lamina.
Folds in the basal lamina allow for expansion of the air sacs when air is drawn into the lungs.
113
What is the role of connective tissue muscle layers in the alveolar mucosa?
Connective tissue muscle layers are created by collagen and elastin fibres.
Collagen adds rigidity and elastin provides elastic recoil to return the sac to the empty state on exhalation.
114
structure of alveoli
- capillaries lines with flattened specialised epithelial cells attached to a fused basal lamina with even thinner epithelial cells of the air sac on the opposite side
- folds in basal lamina allow for expansion of sacs
- at the junction collagen adds rigidity to the mucosa surrounded by many layers of elastin fibres for elastic recoil
- connective tissue muscle layers in mucosa created by collagen and elastin fibres
115
What are the two layers of the basement membrane?
the basal lamina and the underlying layer of reticular connective tissue
