Tissues and Epithelia

Question 1

Define tissue

Answer 1

Tissue is a group of similar cells grouped together to perform a specific function.

Question 2

Define organ

Answer 2

Organs are two or more tissues combined to create a structural unit that has a particular function.

Question 3

How are tissues held together at a molecular level in the lateral surface

Answer 3

• Tight junctions
• Adherens junctions
• Desmosome (adhesion plaque)
• Gap junction
• Cell adhesion molecules

Question 4

How are tissues held at a molecular level in the basal surface

Answer 4

• Hemi-desmosome
• Focal adhesions
• Integrins
• Proteoglycans
• Cell adhesion molecules

Question 5

What is the structural relationship between the epithelia and the lamina propria

Answer 5

The lamina propria is loose connective tissue in the mucosa which supports the delicate mucosal epithelium. The allows the epithelium to move freely with respect to deeper structures which provides for immune defence.
The laminar propria is a connective tissue layer that is part of the mucosa that prevents ingress of pathogens

Question 6

What is the structural relationship between the epithelia and the muscularis mucosae.

Answer 6

The muscularis mucosae is the outermost layer of the mucosa which is composed of smooth muscle fibres oriented in different ways (circular and longitudinal), which keeps the mucosal surface and underlying glands in a constant stat of agitation, which enhances contact between epithelium and contents of the lumen.
The muscularis mucosae folds mucosa to increase surface area which helps absorb substances from the lumen and prevents ingress of pathogens

Question 7

How is the structure of the urinary tract related to the function of the mucosa

Answer 7

Structual unit in the kidney is the nephron. The corpuscle lining is squamous epithelium. The lining of the collecting ducts is cuboinal epithelium
The muscle layer first appears in the ureta and the bladder, (containing muscularis mucosa, lamina propria, etc).
The epithelium is known as urothelium, which can either be relaxed or stretched. The epithelial cells produce mucus and protects the bladder from damage by acidic urine. The tight junctions are very well packed and prevents leakage to inner cell layers.
The urethra has a structure similar to the bladder. The mucus glands produce a lot of mucus to prevent ingress of pathogens

Question 8

How is the structure of the respiratory tract related to the function of the mucosa

Answer 8

The respiratory tract is split into the conducting portion (nasal cavities to bronchioles), and the respiratory portion (bronchioles to alveoli).
Trachea and primary bronchi -
Mucosa: epithelial layer is several cells deep and the surface is covered in cilia. Lamina propria is very thin and there is no longitudinal muscularis mucosa layer.
Submucosa: Connective tissue layer contains mainly collagen and elastic fibres. Contains seromucous glands which produce a watery mucus that thickens during infection. There is no outer layer of smooth muscle
Secondary and tertiary bronchi - Has a similar histology to the primary bronchi but the cartilage is no longer present as full circle of rings.
Epithelium is pseudostratified and ciliated. It is bound by smooth muscle. It is supported by seromucous glands in the submucosa and the airways is kept open with crescent shaped cartilage.
Alveolus - Capillaries lined with flattened specialised epithelial cells.
-Folds in the basal lamina allow for expansion of the air sacs when air is drawn into the lungs
- At the junction small amounts of collagen provide to the mucosa
-Connective tissue muscle layers in the mucosa are created by the collagen and elastin fibres.

Question 9

What are epithelia

Answer 9

Epithelia are sheets of continous cells of varied embryonic origin, that cover the external surface of the body and line internal surfaces, including the body’s vessels

Question 10

What are the embryonic origins of epithelial cells.

Answer 10

Epithelial tissues are derived from all the embryological germ layers:
-From ectoderm (e.g., the epidermis)
-From endoderm (e.g., the inner and outer lining of the gastrointestinal tract)
-From mesoderm (e.g., the linings of body cavities)

Question 11

Describe the ways in which epithelial are classified are classified

Answer 11

Epithelial can either be simple or stratified/compound. Both simple and stratified can be squamous, cuboidal and columnar. Simple can also be pseudostratified, whilst compound can be transitional.

Question 12

How do you differentiate between simple and stratified epithelia from micrographs

Answer 12

Simple epithelia are one cell layer thick whilst stratified/compound epithelia are more than one cell layer thick, (many layers).

Question 13

Explain the position, structure and function of the basement membrane

Answer 13

Position: The basement membrane lines the basal side of epithelial and endothelial tissue.
Structure: The basement membrane is a special type of extracellular matrix. They are thin sheet-like extracellular structures.
Function: They provide a substrate for organs and cells and relay important signals for the development of organs and for differentiation and maintenance of the tissue.

Question 14

How do you distinguish between serous and mucous membranes

Answer 14

Mucous membranes line certain internal tubes which open to the exterior for example: the gastrointestinal tract, the respiratory tract, the urinary tract.

Serous membranes are thin two-part membranes which line certain closed body cavities, (spaces which do not open to the exterior), and the viscera and line: the peritoneum (which envelops many abdominal organs), the pleural sacs (which envelops the lungs), the pericarial sac (which envelops the heart).

Question 15

What does a mucous membrane consist of

Answer 15

-An epithelium lining the lumen of a tube
-An adjacent layer of connective tissue often referred to as the lamina propria
-A third layer consisting of smooth muscle cells, referred to as the muscularis mucosae
-Carries blood and lymphatic vessels and nerves

Question 16

What do serous membranes consist of

Answer 16

• A simple squamous epithelium (mesothelium), that exudes the watery lubricating fluid
• A thin layer of connective tissue that attaches the epithelium to adjacent tissues
• Carries blood and lymphatic vessels and nerves

Question 17

What do simple squamous epithelia look like and what are their anatomical locations and histological features in relation to their function

Answer 17

Simple squamous are wider than they are tall. They are flat plates. Their functions include fast material exchange and barrier to fluids. It is a barrier in the brain and central nervous system. They line the blood vessels and the pleural and peritoneal cavities. They are used for lubrication (mesothelium), gas exchange, water, nutrient and waste product exchange. They are used for barrier (Bowman’s capsule, skin, oesophagus, conjunctivae of eye, the brain).

Question 18

What do simple cuboinal epithelia look like and what are their anatomical locations and function

Answer 18

Simple cuboinal epithelia are a single layer of polygonal cells whose height and width are approximately equal. They line the pancreatic duct, and thyroid gland follicles. Their functions include:
-absorption and conduit (in exocrine glands).
-Absorption and Secretion (in kidney tubules).
-Barrier/covering in ovaries
-Hormone synthesis, storage and mobilisation (in thyroid).

Question 19

What do simple columnar epithelia look like and what are their anatomical location and function

Answer 19

Simple columnar are a single layer of cells whose heights are greater than their width. They line the intestinal glands (crypts of Leiberkuhn), in the mucosa of the colon, and the jejunum. Their functions include:
-Absorption (small intestine and colon, gallbladder)
-Secretion (stomach lining and gastric glands, small intestine and colon).
-Lubrication (small intestine and colon)

Question 20

What do pseudostratified epithelia look like and what are their anatomical location and function

Answer 20

Pseudostratified epithelia are tissues where all cells make contact with the basement membrane but not all of the cells reach the cell surface. Therefore, the nuclei lie in different levels giving the impression of multiple cell layers. Pseudostratified epithelia are in the upper respiratory tract, such as lining of nasal cavity, trachea and bronchi. Their functions include:
-Secretion and conduit (respiratory tract, ductus deferens).
-Mucus secretion (respiratory tract).
-Particle trapping and removal (respiratory tract).

Question 21

What is the anatomical location and function of stratified squamous non-keratinised epithelium

Answer 21

Stratified squamous epithelia contain multiple layers of cells, the outermost of which are thin squamous epithelial cells. They line the vagina, (where the cells are rich in glycogen which helps destroy non-native bacteria and viruses), and the oesophagus, protecting it from abrasion. Locations include:
- Oral cavity, oesophagus, vagina, part of the anal canal, surface of cornea, inner surface of eyelid
Functions include:
- Protection against abrasion in all sites
- Reduces water loss but remains moist in all sites

Question 22

What is the anatomical location and function of stratified keratinised epithelium

Answer 22

Stratified squamous keratinised epithelium contain multiple layers of cells, the outermost which are squamous cells that have lost their nuclei and cornified (become squames of keratin). This outermost layer is called the stratum corneum and:
- greatly reduces water loss and ingress
- prevents ingress of toxins
- protects against abrasions
- reduces microbial colonisation
- Sheilds against UV light damage
Locations include:
- Surface of the skin (epidermis)
- Limited distribution in oral cavity

Question 23

What are the anatomical location and function of transitional epithelia and its structure

Answer 23

Surface cells vary in shape (columnar/cuboinal/squamous). They can either be relaxed or stretched. Locations include:
- Urinary tract: from renal calyces to ureters to bladder to proximal urethra
Their functions include:
- Distensibility
- Protection of underlying tissue from toxic chemicals

Question 24

What is the anatomical location and function of stratified cuboinal epithelium and its structure

Answer 24

Stratified cuboinal epithelium contain multiple layers of cuboinal epithelia. They line the ducts of the sweat glands/ glandular ducts, and their main function is absorption of materials and secretion of products (water and salts).

Question 25

What is the anatomical location and function of stratified columnar epithelium and its structure

Answer 25

Stratified columnar epithelium contain multiple layers of columnar epithelia. Their locations include:
- conjunctiva of the eye
- some larger secretory ducts
- Some portions of the male urethra
Their functions include:
- Secretion of tears and other fluids
- Absorption of some excess materials produced elsewhere (spermatozoa cytoplasm during spermiation).
- Protection (prevention of tissues from the deleterious effects of urine).

Question 26

What are the different types of cell surface specialisation and their function

Answer 26

• Keratin - Prevents water loss and protects against abrasion
• Cilia - Controls micro-movement of luminal contents
• Goblet cells - Mucus secretions, moistens and lubricates
• Microvilli - Increases surface area for absorption and secretion
• Club cells - Protects bronchioles and acts as stem cells for respiratory epithelium
• Microfold cells - Allows rapid sampling of gut microflora
• Stereocilia - In the auditory system converts pressure waves into electrical signals

Question 27

What is the function of goblet cells

Answer 27

Goblet cells lack cilia on the apical surface and instead have microvilli.
There is a release of mucins through exocytosis
Water release is increased by the release of ions.

The main role of goblet cells is to secrete mucus in order to protect the mucous membranes where they are found. Goblet cells accomplish this by secreting mucins, large glycoproteins formed mostly by carbohydrates. The gel-like properties of mucins are given by its glycans (bound carbohydrates) attracting relatively large quantities of water

Question 28

What is the function of club cells

Answer 28

They are on the airway side of the terminal bronchioles and have a club like apical surface, with no cilia and no basal bodies
Their functions include:
- Protecting the bronchiolar epithelium - Secretion of a small variety of products, including club cell secretory protein uteroglobin and a solution similar in composition to pulmonary surfacatant

Question 29

What is the function of microfold cells

Answer 29

Microfold cells are found only in the small intestine and very close to the lymphatic nodules. Microfold cells have a folded extension that looks like a mushroom cap that samples the lumen by endocytosis. Their functions include:
* Trap pathogens and other molecules
* Prevent to underlying dendritic cells that process material
* Present to lymphocytes and macrophages that reside in a basal ‘pocket’ that is not linked to the basement membrane to raise an immune response or digestion
Although the microfold cells are important for the generation of a strong immune response, they also represent a weak point in the intestinal epithelium as many pathogens exploit them as a portal of entry.

Question 30

Explain the genetic cause of cystic fibrosis

Answer 30

The CFTR gene is mutated which means the protein isn’t functional. This means that chloride ions cannot be transported into and out of the cell. Deficiency of chloride ions release results in very sticky and immovable mucous., which is a key part of cystic fibrosis

Question 31

How are the epithelial cells affected by smoking and what are different examples of common respiratory diseases (Bronchitis)

Answer 31

• Acute bronchitis - Cough and mucus production, breathlessness for less than 3 months. Due to reduced lung function due to inflammation and swelling and narrowing of the lung airways and excess mucus in the lungs
• Chronic bronchitis - Chronic inflammation of the bronchi that produces a cough lasting more than 3 months in a 2-year period. Start of irreparable damage to the bronchioles and alveoli

Question 32

How are the epithelial cells affected by smoking and what are different examples of common respiratory diseases (Emphysema, COPD, asthma)

Answer 32

• Emphysema - Shortness of breath due to permanent widening of airspaces distal to the terminal bronchiole without fibrosis. Damage to air sac, loss of elastic recoil and permanent changes to the alveoli (fuse and enlarge).
• COPD - Chronic obstructive pulmonary disease - Umbrella condition that includes emphysema and chronic bronchitis
• Asthma - Wheeze, shortness of breath, chest tightness. Often has a trigger such as cold, exercise, allergens, etc. Caused by bronchospasm (tightening of the smooth muscle layer in the bronchi and bronchioles), obstruction from mucus and narrowing of the conducting airways