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Foundations of Biomedical Sciences 1 > FAE: Tissue Organisation > Flashcards

FAE: Tissue Organisation Flashcards

1
Q

What are tissues?

A

Collections of similar cells and any material that surrounds the cells - they may contain several different cell types to achieve its function

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2
Q

What 3 things is tissue classification based on

A

1) the type /structure of cells
2) the composition of ECM
3) functions of cells in tissues

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3
Q

What are the 4 major types of adult tissue?

A

1) epithelial
2) connective
3) muscle
4) nervous

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4
Q

Describe the features of epithelia

A
  • They exist as sheets
  • They line almost all internal cavities (respiratory and digestive tracts) and cover body surfaces (epidermis)
  • They rest on a basement membrane (BM, ECM)
  • They never function on their own
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5
Q

Describe blood vessels in relation to the epithelium

A
  • Epithelial cells depend on diffusion from blood vessels to obtain nutrient (O2 and glucose)
  • Blood vessels are never found within an epithelium, they never pass through the BM
  • They are found in tissue beneath the epithelium, normally in connective tissue
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6
Q

What do all epithelia sit on?

A

A basement membrane

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7
Q

What is the basement membrane?

A

The extracellular matrix consisting of proteins outside of the epithelial cell

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8
Q

Describe the basement membrane

A
  • Very dense as it contains some of the largest proteins in the body which cross link to one another to form a dense meshwork
  • They can have a function e.g. a filter in the kidney
  • Relevant in cancer as different tumours have different abilities to penetrate it and migrate (metastasis)
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9
Q

What 4 parameters is the classification of epithelial cells based upon?

A

1) cell shape
2) layer structure
3) surface specialisation
4) location and function

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10
Q

When can the classification of epithelial cells change?

A

When a cell is becoming pre-carcinogenic and changing its function

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11
Q

What are the three types of epithelial cell shape?

A

1) squamous (flattened) e.g. cells lining blood vessels/some on the skin
2) cuboidal (like a cube)
3) columnar

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12
Q

What are the three types of epithelial layer structure?

A

1) simple - single layer of cells
2) pseudostratified - a single layer with all cells attached to the basement membrane but looks like many layers
3) stratified - multi-layered, cells adhere to each other by junctions

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13
Q

What are the three types of epithelial surface specialisation?

A

1) ciliated - cilia on the surface beat
2) brush border (microvilli) - has projections and actin holds its rigid, increases surface area
3) keratinised e.g. epithelium of skin - outer layer of dead cells + keratin proteins with new cells growing below and pushing older cells upwards, stratified

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14
Q

What are two ways that epithelial cells can vary based on location and function?

A

1) respiratory - ciliated columnar pseudostratified with goblet cells interspersed
2) transitional - the shape of cells varies, found only in the urinary tract in the bladder, stratified
- the cells are cuboidal when the bladder is empty but squamous when full

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15
Q

What do all glands arise from?

A

Epithelia - division then ingrowth from a solid block of epithelium

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16
Q

What are the two types of gland?

A

1) exocrine

2) endocrine

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17
Q

What is an exocrine gland and how does it form?

A
  • A gland that secretes to a surface via a duct and remains attached to the epithelium from which they originate e.g. sweat glands
  • Some cells in the gland become specialised to form a duct, others to form the secretory product
  • The final form of exocrine glands can differ depending on whether the duct that they deliver their product through branches, coils and how many times it does this (can classify glands in this way)
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18
Q

What is an endocrine gland and how does it form?

A
  • A gland that produces a hormone and secretes it into the blood stream e.g. Islets of Langherhans
    1) the initial mass of epithelium detaches from the epithelia from which it originated
    2) the immature gland sends out signals and recruits blood vessels (small capillaries) into it so that these capillaries can receive the hormones that are produced by the gland
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19
Q

What are the 3 mechanisms for exocrine secretion?

A

1) merocrine - standard exocytosis
2) apocrine - in sweat, mammary and prostate glands
3) holocrine - only in sebaceous glands of skin

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20
Q

Describe merocrine secretion

A

1) the protein products to be secreted are translated and fed through to the RER
2) the proteins are assembled into vesicles which move to one surface of the cell
3) the vesicles fuse with the membrane and release the product
- ∴ exocrine cells have a lot more vesicles than normal cells

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21
Q

Describe apocrine secretion

A

1) the whole top half of the cell breaks up and is released
2) the secretory contents are transported to one side of the cell
3) the cell membrane ruptures and breaks down into large vesicles which are released (cell then regrows this part)

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22
Q

Describe holocrine secretion

A

The whole cell breaks up and becomes its secretory product

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23
Q

What are the two possible functions of cell junctions?

A

1) to keep epithelial sheets tightly bound through attachment (anchoring junctions)
2) to allow functional integrity of cells by selective barriers/communication (tight/gap junctions)

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24
Q

What are the 3 types of anchoring junctions?

A

1) adherens junction - joins actin bundles in neighbouring cells
2) desmosome - joins intermediate filaments in neighbouring cells (strongest)
3) hemidesmosome - anchors IM filaments in a cell to the BM

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25
Q

Describe the structure of (hemi)desmosomes

A
  • Inside the cell are filaments bound to linker proteins
  • The linker proteins are bound to adhesion molecules (integrin) which either bind to identical adhesion molecules on adjacent cell (des) or to matrix (hemi-des)
  • The junction is rigid to hold cells together
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26
Q

Describe the IM filaments in (hemi)desmosomes

A
  • (hemi)desmosomes are linked by rope-like bundles of IM filaments which cannot stretch but can coil to facilitate bending in epithelial sheets
  • The type of IM filament varies depending on the cell type e.g. keratin filaments in skin
  • IM filaments bind des-des, hemides-hemides or hemides-des
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27
Q

Describe the plaques at (hemi)desmosomes

A
  • The plaque between the junctions contains linker proteins and in between two plaques is a cleft with adhesion molecules
  • Adhesion molecules (e.g. desmoglein and desmocolin) only bind homophilically
  • Strength is achieved as linker proteins cluster ∴ adhesion molecules are very dense
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28
Q

Describe adherens junctions (adhesion belts)

A
  • Primarily concerned with cell shape
  • Structure: homophilic binding between adhesion molecules (e.g. cadherin dimers) between cells and linker proteins
  • rigid actin filaments stretch across a cell between junctions, pulling two sides together, often giving the cell a columnar shape
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29
Q

What is the function of a tight junction?

A
  • It performs a barrier function by preventing material passing between two adjacent cells
  • This is important when pumping material along concentration gradients actively e.g. nutrient in the digestive tract across epithelial cells into the tissue fluid below it
  • ∴ it prevents osmosis/diffusion as the junctions act as a seal
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30
Q

How does a tight junction work?

A
  • It brings two membranes of adjacent cells so close together that nothing can pass/move between the cells
  • The tight junction proteins (e.g. claudin and occludin) bind homophilically on adjacent cells
31
Q

What is the function of a gap junction?

A
  • It promotes movement of material between the cytoplasms of two adjacent cells through a very small cytoplasmic bridge between proteins
  • It only allows exchange of very small molecules as the pore is narrow
  • It compensates for the position of a cell in an epithelial sheet in relation to a blood vessel ∴ it has a homeostatic function in the equilibration of materials between cells
32
Q

Describe the structure of a gap junction

A
  • One gap junction contains many smaller channels
  • A channel is made up of 6 proteins (different types of connexins) which come together in a circular arrangement to form a connexon with a central channel
  • When two identical connexons in different CSMs overlay each other, this forms a continuous channel, allowing cytoplasms to connect through the hole
  • If the channels move apart and are not aligned, they close ∴ channels can be inserted into CSM and find a partner before opening
33
Q

What is connective tissue?

A

The ECM and the supporting cell population (proteins and sugars) e.g. CT in skin = dermis, in gut = mucosa

34
Q

What are the 3 forms of connective tissue?

A

1) soft
2) hard (bone)
3) semi-hard (cartilage) - can be deformed but readopts its original position to an extent

35
Q

What does soft connective tissue (SCT) consist of?

A

1) cells embedded in the ECM e.g. fibroblasts which synthesise and secrete the contents of the ECM (proteins and sugars) and have lots of RER and immune cells
2) the majority of the SCT is the ECM (cells are sparse) which is of variable composition, depending on its function
3) capillaries to provide nutrients/oxygen
4) nerves
- SCT has large blood vessels/nerves, especially near muscle where big blood vessels would affect the muscle function (∴ only small capillaries in muscle)
5) proteoglycan (+ water) - gel like substance

36
Q

What are the functions of SCT?

A

1) space filler and mechanical support
2) attachment and protection
3) highway for nutrients
4) site of immunological defence
5) storage for fat and calcium (calcium is stored and then mobilised by hormones when needed in other parts of the body)

37
Q

What are the types of SCT?

A

1) mesenchyme - the cells look like fibroblasts but go on to specialise, found in embryonic tissue
2) loose (areolar) - found in the mesentery (intestine, abdominal wall) and the hypodermis
3) dense - found in tendons, dermis, capsules (around organs and synovial joints)
4) reticular - cells which look like stars, found in bone marrow and lymph nodes
5) adipose - fat cells

38
Q

Describe the ECM

A
  • The ECM consists of proteins (glycoproteins) and glycosaminoglycans (GAGs, large sugar residues), forming a large, hydrated gel
  • The major proteins of the ECM are synthesised and secreted by fibroblasts and are some of the largest in the body
39
Q

What are the 3 major proteins of the ECM?

A

1) collagen - involved in the tensile strength of ECM, found in tendons, dense CT and ligaments
2) elastin (elastic fibres) - involved in elasticity of ECM
3) adhesive - adhesion proteins for fibroblasts and other cells

40
Q

Describe the structure of collagen

A
  • Rod-shaped triple helix of polypeptides (up to 480nm long) which is not extensible (can deform but not stretch)
  • In some ECM, they come together to form thick, rigid, resistant fibrils which decrease in thickness further from the epidermis
  • Humans have >20 specialised collagen proteins whose size and shape vary according to functions
41
Q

What are the 4 types of collagen?

A

1) Type I - in skin, bone, tendons and teeth (dentine)
2) Type II - in cartilage
3) Type III - in blood vessels and skin (dermis)
- I-III are fibrillar collagens (normal)
4) Type IV - sheet collagens (no triple helix) only found in the BM

42
Q

Describe elastic fibres

A
  • Extensible and prominent in skin, blood vessels and lungs
  • Complementary to collagen
  • They are joined by covalent bonds ∴ when they stretch they remain linked
  • They store energy when they stretch, which is released as they passively recoil, pushing blood through circulation in blood vessels ∴ found in major arteries which need to expand and relax due to high BP
  • Associated with proteins e.g. fibrillin (microfibril) coating which is not involved in contraction
43
Q

What happens with the synthesis and break down of elastic fibres?

A
  • Embryonic and juvenile fibroblasts synthesise elastic fibres profusely
  • Adults make very little but the fibres are very resilient and long-lived - they can withstand > 2 billion cycles of stretch-recoil before losing elasticity
  • UV breaks it down and it is not replaced
44
Q

What do adhesive proteins do in the ECM?

A
  • They bind to transmembrane receptors called integrins on cells, attaching cells to the matrix
  • The integrins are associated with actin and depending on what the actin does, they can be involved in holding a cell in place or movement of the cell
45
Q

Describe the integrins in the ECM

A
  • They are different from those associated with hemidesmosomes as these are individual molecules sparsely dotted around the membrane
  • They bind to the same molecules as in a hemidesmosome but are associated with actin instead of IM filaments
  • All integrins are dimers, consisting of 2 protein subunits (alpha and beta) which determine which adhesive protein it binds to
  • A change to the integrins may allow cells to detach and move e.g. in metastasis as the integrin can no longer bind
46
Q

What are the 3 types of adhesive protein?

A

1) fibronectin - abundant is lots/all CT
2) tenascin - produced at wounds
3) laminin - predominant (but not exclusive) in BM, allows epithelia to bind to the BM via hemidesmosomes and more diffuse integrins

47
Q

What is the function of the basement membrane?

A
  • Separates CT from the epithelial layer
  • Acts as a physical barrier to cells, maintaining the integrity of tissues
  • It is much more dense than the ECM below ∴ it makes a good molecular filter e.g. in the kidney
48
Q

How are GAGs normally present and what is the exception?

A
  • GAGs are synthesised as proteoglycans (GAGs attached to protein chain)
  • Exception: hyaluron, few common features but common properties
49
Q

Describe the structure of glycosaminoglycans (GAGs)

A
  • A GAG is a repeating polymer of a disaccharide made from hexose sugars (70-200 sugars long)
  • Basic structure of all GAGs is the same: amino group, hexose sugar and COO-/SO3- ∴ they are very highly negatively charged
  • The side chains can vary
50
Q

Describe the GAGs complex in the ECM

A
  • Due to their v negative charge, they are very hydrophilic so absorb water and dissolve in it, forming a jelly-like structure which has some resistance - water is sucked into the matrix by an osmotically active ion cloud until fully hydrated
  • They adopt a random conformation and highly extended shapes that occupy huge volumes as the sugar chains are too stiff to fold into compact structures
  • The water in the complex creates swelling pressure (turgor) that enables the ECM to withstand compressive forces, allowing the SCT to have some resistance to deformation
  • GAGs in CT constitute <10% of mass of ECM, but fill >95% of the volume as a porous hydrated gel
51
Q

What are the two classes of CT cells?

A

1) indigenous - involved in synthesis of ECM and storage e.g. adipose for lipid
2) immigrant - immune system cells

52
Q

Where do all indigenous cells of the SCT arise from and what is the exception?

A

Mesenchymal stem cells, except for mast cells

53
Q

What are the 3 types of indigenous SCT cells?

A

1) fibroblasts (most common) - produces ECM (different ratios of elements depending on the location)
2) adipocytes - fat storage, leptin secretion
3) mast cells - histamine secretion, formed in the embryo in the immune system (bone marrow) and then migrate to the CT where they divide and are involved in the immune response

54
Q

Describe immigrant cells in SCT

A
  • Largely leukocytes (WBCs)
  • e.g. neutrophils, monocytes/macrophages (phagocytic), dendritic cells (immune surveillance), eosinophils (parasitic infection), basophils and lymphocytes
  • These cells are normally not in the CT - normally circulating in the blood and then when infection occurs, they migrate from the blood vessels to the tissue
55
Q

What does the term somatic refer to?

A

The body as a whole and is usually used to describe the elements which make up the walls of the trunk and limbs
- includes bone, cartilage and skeletal muscle which are supplied by the somatic nervous system

56
Q

What does the term visceral refer to?

A

Viscera literally means bowels but includes all the organs in the trunk, head and neck - these are supplied by the visceral (autonomic) nervous system

57
Q

Describe the skin

A
  • Covers the outer surface of the body
  • The internal structures are separated by connective tissue into compartments
  • Only thin skin has hair in it, not thick skin (palms, soles) and it is thin as it is not exposed to as much abrasion
  • ∴ the epidermis (especially the cornified layer) is thicker in thick skin than in thin skin
58
Q

What are the functions of the skin?

A

1) protection - waterproofing
2) thermoregulation
3) provides sensory information about the surrounding environment
4) vitamin D synthesis by exposure to sunlight

59
Q

What are the three layers of the skin?

A

1) epidermis
2) dermis
3) hypodermis

60
Q

Describe the epidermis

A
  • Epithelium with no blood/nerve supply

- Made up of cells incl. keratinocytes (90%), melanocytes, Langherhans cells and Merkel cells

61
Q

What is the dermis composed of?

A

Mostly of CT with collagen, elastic fibres, fibroblasts, macrophages, adipocytes, blood vessels, nerves, glands and hair follicles

62
Q

Describe the hypodermis

A
  • Superficial facia - contains fat cells, fat (except in ear and eyelid), collagen, elastic fibres and loose CT
63
Q

What are the functions of superficial facia?

A

1) storage of water and fat - fat is a very important store of energy (liquid at room temp)
2) protection against mechanical shock as the fat (liquid) and water act as a cushion
3) thermal insulation as the fat and water provide an effective barrier against rapid loss of body heat
4) conduction, to transport nerves and blood vessels to the skin from other tissues

64
Q

Describe deep fascia

A
  • A highly organised CT layer beneath the superficial fascia which invests deep structures dividing the body into compartments
  • Denser CT which contains very little fat and the collagen fibres are more organised running in parallel fashion
  • Surrounds organ and muscles, forms capsules around organs, tendons and ligaments
65
Q

What are the functions of deep fascia?

A

1) conduction - blood vessels and nerves are transported, wrapped in deep fascia, forming neurovascular bundles that travel throughout the body
2) movement of muscle - skeletal muscles wrapped in deep fascia (which is inserted into the bone) are able to slide over each other
3) muscle attachment - some muscles e.g. temporalis and some limb muscles gain partial attachment from deep fascia
4) form capsules around organs and glands e.g. kidney and lymphnodes

66
Q

Describe how deep fascia allows movement of muscle

A
  • As the fascia inserts into bone, it creates sleeves around individual muscles and groups of muscle
  • This allows muscles to work independently, to slide on each other and to not interfere with function as in fascia there are also vessels and fluids
67
Q

What is the con of compartmentalisation of muscles?

A

If infection occurs in smaller compartments, leading to inflammation or swelling, it will have an effect on structures inside the compartments e.g. vessels or nerves, possibly cutting off blood supply to the foot region or damaging more delicate tissue
- this is bc collagen in fascia is inelastic ∴ cannot stretch

68
Q

What are thicknesses of fascia called and where are they found?

A

Condensation facia e.g. around the ankle joint to ensure long tendons from muscles in the leg can be held in position en route to the toes

69
Q

What are serous membranes?

A
  • Membranes that line the internal cavities consisting of mesothelium and supported by loose CT
  • Thin double layered structures with the inner layer being intimate with the viscera and the outer layer anchored to the body wall
  • There is a small space between the two layers filled with a v small quantity of fluid to minimise friction during movement e.g. in the pleura, this allows them to move against each other as the lungs expand and contract without casing any friction
70
Q

What are the 3 types of serous membranes?

A

1) the pleura - around the lungs
2) the pericardium - around the heart (fibrous)
3) the peritoneum - around the contents of the abdomen

71
Q

What is special about the pericardium?

A
  • The fibrous area of the pericardium is attached inferiorly to the diaphragm, superiorly to the vessels coming out of the heart and to the anterior wall of the thorax
  • This means that whatever position you’re in, your heart stays in the same place
  • This also minimises friction for the beating heart
72
Q

Describe the naming of arteries

A
  • Name vessels you can see with the naked eye
  • Arteries change their name when they enter a new region
  • Arteries can also be divided into sections by the position of a muscle
  • Collateral arteries ensure a continuous blood flow irrespective of the position of the body
73
Q

Summarise veins

A
  • Superficial veins are in the superficial facia
  • Pressure is low but need blood to flow in one direction
  • ∴ have valves which are one-way - close/open one way
  • Deeper veins are surrounded by skeletal muscle, which when contracted, squeeze blood upwards (through the correct open valve) - important in lower limbs
74
Q

What are the two cons about the lymphatic system?

A
  • Used as a way of transferring cancerous cells in metastasis
  • Can’t see it with the naked eye

Foundations of Biomedical Sciences 1 (9 decks)

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