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Histology > Epithelium > Flashcards

Epithelium Flashcards

1
Q

What are the functions of tight junctions?

A

Prevent the passage of molecules between 2 adhesion cells.

Tight junctions prevent the displacement of proteins to maintain the polarization of cells.

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2
Q

Where are tight junctions located?

A

At the apical part of the cell.

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3
Q

What transmembrane proteins are present in a tight junction?

A

Described as claudins, occludins and JAMs (Junctional Adhesion Molecules).

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4
Q

How does the actin filament interact with the transmembrane proteins?

A

Actin filaments don’t interact directly with the proteins but instead through ZO-1, ZO-2 and ZO-3 which mediate this connection.

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5
Q

Can water cross tight junctions?

A

In some types of epithelia, tight junctions can be crossed by water solutes through different mechanisms. E.g. certain types of claudin can create channels.

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6
Q

What is the main way to pass a tight junction?

A

In a cell with a tight junction, the main way to pass would be through the transcellular membrane.

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7
Q

What components of the body are regarded as epithelial tissue?

A 
Boundary epithelia (epithelium)
Glands
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8
Q

What are the shared features of the epithelia?

A
  • Cell polarization - sides of cells not all the same.
  • Cell contiguity: adhesive structures - cells are attached to each other with almost no space in between.
  • Apical surface specializations.
  • Avascularity - no vascular system in the epithelia.
  • Structural organization to form membranes - can organise together to form membranes.
  • Relationships with underlying connective tissue
  • Presence of keratin intermediate filaments
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9
Q

Describe a pathology caused by tight junctions coming apart.

A

Leaky bowel syndrome is when gap junctions in the interstinal cells come apart, thus allowing a large amoung of indigestible gluten molecules to seep into the underlying tissue and incite the nervous system.

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10
Q

What are the different anchoring junction mechanisms?

A

Adherens junctions, desmosomes, focal adhesion and hemidesmosomes.

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11
Q

What are adheren junctions composed of?

A

Adherens junctions are mainly composed of transmembrane proteins that interact with the one in the adjacent cells.

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12
Q

Identify and describe different classifications of the CAM family (adhesion molecules).

A

Cadherins are calcium dependent proteins.

Integrins are transmembrane glycoproteins which have an extracellular part that interacts with extracellular components.

Slectins mainly mediates interactions between cells of the blood.

Ig-superfamily CAMs are involved in immunological functions.

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13
Q

Describe the how CAM molecules are involved in adheren junctions.

A

Cadherins create a space of around 30nm, which contains Ca2+. The transmembrane proteins make contact with the proteins inside the cytoplasm and these will interact with the actin filaments of the cytoskeleton.

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14
Q

Describe the structure of desmosomes (macula adherens).

A

The proteins in the cytoplasmic side are placophillin, plakoglobin and desmoplakin.

They are joined by transmembrane proteins called desmoglein and desmocollin, which interact depending on the presence of Ca2+.

The yellow proteins then interact with intermediate filaments.

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15
Q

Describe the main differences between desmosomes and adheren junctions.

A

Adheren junctions have microfilaments, while desmosomes have intermediate filaments.

AJs have catenin family proteins while desmosomes have plakins.

Both use different transmembrane proteins in the family of cadherins.

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16
Q

How do gap junctions mediate communication?

A

They mediate communication by creating channels on the membrane and allowing passage of small cells.

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17
Q

What is the function of gap proteins?

A

Gap proteins mediate communication between epithelial cells.

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18
Q

Describe the how proteins are arranged in gap junctions.

A

The proteins that compose the gap junctions are called connexin. One one cell there will be 6 connexins forming a connexon.

This is the same in an adjacent cell, where they will communicate with each other and form an open gap. This gap can be closed to stop the passage of molecules.

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19
Q

What molecules can pass through gap junctions?

A

Small molecules with size lower than 1000 daltons can pass through the gap junction.

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20
Q

How can gap junctions be controlled?

A

The opening and closure of the gap can be controlled by changes in pH and concentration of Ca2+ ions. A high Ca2+ and pH will close the gap.

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21
Q

What are the apical surface specializations characteristic of epithelial tissue?

A

Cillia
Microvilli
Keratin - particular type of layer on top of the epithelia that accumulates on the epidermis where there is a layer of dead cells filled with keratin.

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22
Q

What are the different types of cillia?

A

Common cilia
Primary cilia
Sensitive cilia (olfactory epithelium)
Nodal cilia

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23
Q

What are cillia?

A

Cilia are mobile protrusions.

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24
Q

What is the cilium supported by?

A

The structure supporting the cilium is the interaction between the microtubules and the motor protein along the microtubules.

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25
Q

What does a cilium consist of?

A

A cilia will have a basal body and a flagellum.

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26
Q

Describe the ultrastructure of cillia.

A

It can be seen that they have 9 couples of microtubules and 2 in the middle.

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27
Q

Describe features of the primary cilium.

A

Lacks the 2 central microtubules.
Lacks dynein (immotile)
Present in most cells.
Its function is for a sensory organelle.

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28
Q

Why are proteins that drag particles up and down the cilia important?

A

They serve as a type of antenna to sense chemical signals and relay them into the cell.

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29
Q

Give an example of pathology related to dysfunctioning cillia.

A

There are pathologies related dysfunctioning cillia. E.g. PCD, which is a group of several hereditary disorders which may cause sterility.

Another syndrome that causes sterility is Kartagener’s syndrome where there is an absence of dynein arms.

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30
Q

What are microvilli?

A

They are protrusions of the apical plasma membrane with a length of around 1-2 microns and so are not visible through the light microscope.

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31
Q

What is the function of microvilli?

A

A cell will process thousands of microvilli, they are used to increase the apical surface, especially in cells that need to absorb substances.

32
Q

Describe the structure of microvilli.

A

The structure consists of actin filaments running in parallel and bound to the basal surface where more actin filaments (terminal web) are present.

Proteins are bound to the actin filaments.

33
Q

Describe the structure of stereocillia.

A

Composed of actin filaments with erzin and fimbrin that will cross link the actin bridges.

There are cytoplasmic bridges that interconnect stereocilia to each other.

They are bound to a network of 𝝰-actinin which are present in the basal part of stereocilia.

34
Q

Where are stereocillia located?

A

Located in the epithelium, mainly in the lining epithelium of the epididymis and in the sensory cell of the inner ear epithelia.

35
Q

Describe the location and function of stereocillia in the inner ear?

A

Sensory stereocilia are found in the inner hair cells and outer hair cells of the organ of corti.

The first is involved in reception of sound waves, the second in the reception of the displacements of the body in space.

36
Q

What specialisations are there in the basal domain?

A

Hemidesmosomes
Infoldings
Basal lamina

37
Q

Describe infolding basal membrane and its function.

A

Infoldings of the basal membrane can only be seen with an electron microscope.

They are found in cells of the body where material needs to be transported, e.g. Epithelial cells of the distal tubules of the kidney.

38
Q

What are epithelial cells nourished by?

A

One of the characteristics of epithelial cells is to not have blood vessels.

Therefore they are nourished by connective tissues that are always present in epithelial cells. The structure is called extracellular matrix/basal lamina.

Substances diffuse from vessels found in connective tissues.

39
Q

How can the basal lamina be visualized? What size is it?

A

The basal lamina has a thickness of 40-100nm and is produced by the same epithelial cell.

Their structure is only visible under TEM.

40
Q

How can the basal lamina be observed under a light microscope?

A

The basal lamina together with the reticular lamina can be observed under a light microscope via a PAS and AZAN staining.

41
Q

Describe the structure of the basal lamina.

A

They are composed of 2 layers - lamina lucida on top of lamina densa.

42
Q

What is underneath the basal layer? What is it made up of?

A

Underneath the basal layer is a layer of reticular lamina, which is made up of connective tissues.

43
Q

How can a metastasis of epithelial tumours form?

A

When the basal membrane breaks and the epithelial cells can pass through the basal lamina, this can form metastasis of epithelial tumours.

44
Q

What are functions of epithelial tissues?

A

Protection
Absorption/secretion
Special functions

45
Q

State the lining epithelia of the body.

A

External body surfaces: epidermis

Interior body cavities: endothelium, mucosa, mesothelium (pericardium, peritoneum, pleura)

46
Q

How are the different epithelial cells classified?

A

Shape of cell: squamous, cuboidal or columnar

No. of cell layers: simple (one) or stratified (multiple)

Presence of specialization, e.g. cillia, microvilli…etc.

47
Q

Give examples of simple squamous epithelium.

A

Mesothelium - serous epithelium
Endothelium - blood vessels
Alveolar epithelium

48
Q

Describe the structure of the mesothelium in general.

A

The mesothelium is mainly made by simple squamous cells attached to the basal membrane.

Serous membrane (serosa) is made up by the 2 layers of mesothelium. They secrete a serous liquid that covers particularly the pericardium and the pleura.

49
Q

Describe the structure of the mesothelium in the lungs.

A

One of the mesothelium layers is called pleura visceralis, the other is pleura parietalis.

In between these 2 layers is the pleura fluid (serous) which comes from the blood plasma and is quickly exchanged.

50
Q

What are pneumocytes?

A

There are 2 types: the big green ones shown in the diagram (ignore) and the flat ones that make the borders of the alveoli.

Type 2 pneumocytes release surfactants which prevent the collapse of alveoli.

51
Q

Describe the endothelium.

A

Endothelium is a simple squamous epithelium that makes up the inner lining of blood and lymphatic vessels.

The cells are joined by cell junctions. Around the capillary, there are basal lamina.

Endothelium can be easily studied at the level of capillaries as they are usually made up of a single cell layer.

52
Q

What are the different types of capillaries?

A

Continuous capillaries
Fenestrated capillaries
Sinusoidal capillaries

53
Q

When are continuous capillaries needed?

A

When communication not needed between the blood vessels and connective tissues or other surrounding tissues.

54
Q

When are fenestrated capillaries needed?

A

When communication is needed between blood vessels and surrounding tissues.

55
Q

Where did pericyte cells originate? What is their function?

A

Pericyte cells are known to have come from stromal stem cells and will contribute to the functioning of blood vessels.

56
Q

Describe the structure of sinusoid capillaries.

A

The sinusoid has the largest communication between blood and the extracellular environment.

As they have pores, a large intracellular clift and the basal membrane will also be incomplete. It does have endothelial cells and pericytes.

57
Q

Describe the structure of fenestrated capillaries.

A

In the fenestrated capillary, there are some holes. The basal membrane is continuous and there are some intracellular clifts present. Also there is communication between the blood and the intracellular matrix.

Fenestrated capillaries are more ‘leaky’ and their membrane present pores.

58
Q

How can some molecules and water pass through the membrane?

A

Small molecules and water can easily pass through the membrane by simple diffusion.

Molecules can also pass between the cells in a paracellular way.

Additionally by active and passive transport.

Another way they can pass through the epithelia is through transcytosis. This is where vesicles are formed on both sides of the epithelia to transport molecules, in which they will fuse with the epithelia and release their contents either inside or out.

59
Q

Where are sinusoid capillaries mostly present?

A

Sinusoids are mainly present in liver, spleen and bone marrow.

In some areas there are no basal membranes where there are big gaps present, which allows easy passage of molecules. E.g. Formation of blood cells in the bone marrow, therefore need to allow for passage of cells.

60
Q

What are the 3 layers of the epithelium of veins and arteries?

A

Tunica externa, tunica media and the tunica intima.

61
Q

What is the tunica intima made by?

A

The tunica intima is mainly made by the endothelium.

62
Q

What is the tunica media made of?

A

The tunica media is mainly made of smooth muscle cells, which is thicker in the artery than in the vein. Also elastic fibres will permit elasticity.

63
Q

What is the tunica externa made of?

A

Tunica externa is mainly connective tissue. Also smaller vessels like the vasa vasorum are present within the bigger vessels.

64
Q

Why does the artery have an internal elastic membrane?

A

The artery has an internal elastic membrane which allows for elasticity.

65
Q

Describe the simple cuboidal epithelium and where its mostly like found.

A

One layer of cuboid cells.

Can be seen in kidney collecting tubes; striated salivary duct; ovarian surface; thyroid gland.

66
Q

Describe the simple columnar epithelium and where its mostly like found.

A

One cell layer with a nucleus in the centre of cells.

Cells are attached by zonula occludens.

There are brush borders present.

Typical example of intestine.

67
Q

What are ways for intestined to increase their absorptive surface?

A

Brush border (microvilli)

Villi - a protrusion of the way made by a connective tissue in the middle surrounded by epithelia.

Circular folds (plicae circulares)

68
Q

Describe the compositions of the tissues of the wall of intestine.

A

A mucosa is a layer that covers the internal surface that communicates with the external part. It’s composed of epithelial tissue, connective tissue and a small layer of muscle tissue called muscularis mucosae.

Below this is another layer of connective tissue called submucosa. Then below this is the muscularis externa, which is a double layer of muscle tissue that permits peristaltic movement.

69
Q

Describe the structure of the lining epithelium of the mucosa (intestinal wall).

A

Composed by enterocytes (columnar cells) attached to each other with junction complexes.

White circular structures called goblet cells, they form a particular type of gland.

There are microvilli on top of the enterocyte observable as a brushed border.

70
Q

State the features of a pseudostratified epithelium.

A

Ciliated
When stained, the cells seem closed one on top of each other.
Present in the respiratory tract

71
Q

What are the different types of cilliated cells in the trachea?

A

Mucous goblet cells - unicellular gland that produces mucus.
Serous cells - extended through the whole thickness of the epithelium, thus are all attached to the basal membrane.
Brush cells
Basal cells
Small granule cells - can be observed via silver staining, it seems to produce different types of proteins.

72
Q

What effect does smoking have on cillia?

A

Smoking decreases ciliary beat frequency.

Study shows how cilia are destroyed by nicotine, which causes accumulation of smoke and other materials in the respiratory tract, thus resulting in coughing.

73
Q

Why is the urothelium a transitional epithelium?

A

It becomes a certain thickness when the tract is empty, and is flat with a full bladder.

Transitional as several layers of cells with different shapes. The top is dome shaped, the middle is intermediate and the bottom is basal.

74
Q

Where is the urothelium located?

A

The renal pelvis, ureter, bladder and part of urethra.

75
Q

How does the urothelium help regulate the ureter?

A

When the bladder is empty, the epithelium is relaxed. It contains dome shaped cells tightly joined to avoid leaking.

When the bladder is full, cells squash one on top each other and cause different epithelium thicknesses.

76
Q

What is the function of transmembrane proteins on top of the urothelium?

A

Transmembrane proteins on top aggregate to form hexagons, these are called uroplakins.

They bind at the apical part of the cytoskeleton and form a barrier against the acidic nature of urine.

77
Q

Where is stratified squamous epithelium found?

A

Oral and esophageal mucosa
Corneal epithelium
Vaginal mucosa
Anal canal mucosa

Histology (21 decks)

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