Internal surfaces

Question 1

What are mucous membranes?

Answer 1

Line internal tubes which open to the exterior: the alimentary, respiratory and urinary tracts

Consists of:

• epithelium lining lumen
• lamina propria (adjacent layer of connective tissue). This contains blood and lymph vessels, immune cells and some smooth muscle cells
• ALIMENTARY ONLY muscularis mucosae (smooth muscle)

Question 2

What are serous membranes?

Answer 2

Thin, two-part membranes lining closed cavitities: peritoneum, pleural sacs and pericardial sac

Secrete a lubricating fluid to reduce friction

Consists of:

• simple squamous epithelium (mesothelium) which secretes the watery lubricating fluid
• thin layer of connective tissue which attaches epithelium to adjacent tissues. This also carries blood vessels and nerves

Question 3

How do the heart, lungs and gut develop embryonically in terms of membranes?

Answer 3

They develop next to a bag-like cavity into which they invaginate, so they each become surrounded by serous membrane (but do not lie within the serous cavity itself)

Question 4

What are parietal and visceral serosa?

Answer 4

Parietal serosa is the outer wall of the membrane, beneath this is the lubricating fluid, then the visceral serosa encapsulates the organ

Question 5

What is the gut mesentery?

Answer 5

Folds of membranous (serous) tissue that attaches itself to the intestinal tract

Question 6

How many layers does the gut wall have and what are their names?

Answer 6

1. Mucosa (innermost)
2. Submucosa
3. Muscularis externae (external muscle layers)
4. Serosa (outermost)

Question 7

Describe the mucosa of the gut wall

Answer 7

From the lumen outwards, consists of epithelium, lamina propria and muscularis mucosae
Lamina propria often contains Peyer’s patches (aggregations of lymphocytes)
The muscularis mucosae contains mucosal glands

Question 8

Describe the submucosa of the gut wall

Answer 8

A layer of connective tissue containing glands, arteries, veins and nerves

Question 9

Describe the muscularis externae of the gut wall

Answer 9

Two layers of smooth muscle: outer longitudinal layer (long thin nuclei in relaxed cells) and inner circular layer (nuclei in centre of cells)
Creates successive peristaltic waves to move luminal contents along the gut

Question 10

Describe the outermost layer (serosa) of the gut wall

Answer 10

A serous membrane, consisting of simple squamous epithelium (mesothelium) and connective tissue (cells not normally contiguous). Mesentery of arteries, veins and nerves

Question 11

What is the difference between adventitia and serosa?

Answer 11

In the abdomen:

• Peritoneal organs are covered in serosa
• Retroperitoneal organs are covered in adventitia (loose connective tissue)

Question 12

Describe the layers of the oesophagus from the lumen outwards

Answer 12

Stratified squamous non-keranitised epithelium [mucosa]
Lamina propria [mucosa]
Muscularis mucosa-thin layer of smooth muscle cells [mucosa]
Submucosa
Muscularis externa-to move food by peristalsis
Adventitia-thin layer of connective tissue

Question 13

Describe the layers of the stomach from the lumen outwards

Answer 13

Simple columnar epithelium for absorption
Gastic mucosa (secretes acid, digestive enzymes and gastrin)
Muscularis mucosa
Submucosa
Muscularis externa-3 layers (oblique, circular and longitudinal)
Rugae-folds of gastric mucosa forming longitudinal ridges in empty stomach)

Question 14

Describe the layers of the jejunum (second part of SI) from the lumen outwards

Answer 14

Villi
Pilicae circulares-circular folds of mucosa/submucosa that project into gut lumen
Simple columnar epithelium for absorption
Jejunal mucosa (with muscularis mucosa)
Submucosa
Muscularis externae (2 layers)

Question 15

Describe the layers of the large intestine (colon) from the lumen outwards

Answer 15

Crypts of Liberkuhn
Simple columnar epithelium (produce mucous, absorb water and electtrolytes)
Peyer’s patches
Mucosa (muscularis mucosa is indistinct at magnification)
Submucosa
Muscularis externae

Question 16

What is contained within the conducting and respiratory portions of the respiratory tract?

Answer 16

Conducting-nasal cavity to bronchioles

Respiratory-bronchioles to alveoli

Question 17

Describe the layers of the trachea from the lumen outwards

Answer 17

Pseudostratified ciliated columnar epithelium
Submucosa with seromucous glands (number decreases closer to bronchioles)
Fibroelastic membrane with trachealis muscle
C-shaped Hyaline cartilage to prevent oesophageal collapse
Adventitia

Question 18

Describe the layers of the bronchus from the lumen outwards

Answer 18

Pseudostratified ciliated epithelium
Smooth muscle
Submucosa, contains glands
Crescent-shaped cartilage (smaller than in trachea)

Question 19

Describe the layers of a bronchiole from the lumen outwards

Answer 19

Simple ciliated columnar epithelium (but in smaller sacs not ciliated and in terminal bronchioles ciliated cuboidal)
Smooth muscle
Alveoli-no cartilage needed

Question 20

Describe the structure of an alveolus

Answer 20

Simple epithelium-alveoli are purely epithelial
Type 1 cells-squamous, cover 90% of surface area and permit gas exchange with capillaries
Type 2 cells-cuboidal, cover 10% surface area and product surfactant
Macrophages line the surface for phagocytosis of microbes and dust
Gas exchange occurs across blood-air barrier. Erythrocytes spend less than 1 second in alveolar capillaries. Alveoli are surrounded by a network of capillaries and elastic fibres, held by smooth muscle

Question 21

Describe the tissue structure of the urter

Answer 21

Transitional epithelium
Fibroelastic lamina propria
Circular muscularis externa

Question 22

Describe the tissue structure of the bladder wall

Answer 22

Transitional epithelium-impermeable to urine due to thick plasma membrane and tight junctions between cells
Smooth muscle in the lamina propria
3 interwoven layers of muscularis externae

Question 23

Describe the tissue structure of the urethra

Answer 23

Transitional epithelium (in penile urethra the epithelium is stratified columnar)
Lamina propria
Muscularis externa (2 layers)
Adventitia

The stellate urethral lumen becomes ovoid as urine passes through