Session 8: Internal Surfaces of the Body

Internal surfaces are covered by what two types of membrane?

- Mucous

- Serous

Mucous membranes

Line internal tubes that open to the exterior

Examples of locations of mucous membrane

- Alimentary tract (GI tract)

- Respiratory tract

- Urinary tract

- Reproductive tract

The layers of a mucous membrane

1. epithelial layer

2. connective tissue layer (lamina propria)

3. smooth muscle layer (muscularis mucosae)

Serous membranes

Thin, two-part membranes that line certain closed body cavities (spaces that do not open to the exterior)

Organs that do not move freely e.g., the oesophagus, are surrounded by a connective tissue layer (an ____) that adheres the organ to the surrounding structures

adventitia

During embryonic development, which three organs develop next to a bag-like cavity into which they invaginate?

- Heart

- Lungs

- Digestive tract

Which three organs are enveloped by serous membranes?

- Heart = pericardial sac

- Lungs = pleural sacs

- Digestive tract = peritoneum

Peritoneum

membrane that lines the abdominal cavity

pleural sacs

surround the lungs

pericardial sac

surrounds the heart and helps prevent overfilling.

Serous membranes surrounding the peritoneum, pleural sacs and pericardial sacs secrete a ____ fluid that promotes relatively friction-free movement of the structures that they surround

lubricating

The layers within the pericardial sac

1. Visceral pericardium = inner

2. Pericardial cavity = middle

3. Parietal pericardium = outer

Most digestive organs lie within the ____ cavity

abdominopelvic

Mesentery

Double layer of peritoneum extending from the posterior body wall, supplying blood vessels, lymphatics and nerves to the intestines. It is also a site of fat storage

The gastrointestinal tract sections

1. Oesophagus

2. Stomach

3. Colon

4. Rectum

5. Small intestine = duodenum, jejunum, ileum

The four layers of the gut tube

1) Mucosa

2) Submucosa

3) Muscularis externae

4) Serosa or adventitia

Mucosa

The innermost layer of the human digestive tract; in some parts of the digestive system, it contains mucus-secreting cells and glands that secrete digestive enzymes

Submucosa

The layer of connective tissue directly under the mucosa of an open body cavity.

Muscularis externae

Usually smooth muscle layers (Skeletal in part of the esophagus), commonly arranged in an inner circular and an outer longitudinal layer (GI Tract)

Serosa

outermost layer; serous fluid eliminates friction

Adventitia

A thin layer of loose connective tissue that binds an organ to surrounding tissues or organs

Aggregations of lymphocytes present in the lamina propria, particularly distal ileum where they form...

Peyer's patches

What glands can you find in the submucosa of the gut wall (duodenum)?

Brunner's glands

External muscle of gut wall (muscularis externa)

Two layers of smooth muscle

1) Outer longitudinal

2) Inner circular

What is the purpose of the muscularis externa lining the gut wall?

create successive peristaltic waves to move luminal contents of the gut along the gut via control by enteric nervous system

Muscularis externa of gut wall nerves

- Auerbach's (or myenteric) plexus of nerves

The mesentery is a double layer of ___

Peritoneum

containing arteries, veins and nerves

Histology of the serosa of the ileum

Serosa

- External simple squamous epithelium (mesothelium)

Oesophagus histology

Oesophageal mucosa

Epithelium = stratified squamous non-keratinized (withstands abrasion)

Lamina propria = loose connective bearing blood and lymph vessels, some smooth muscle cells and many cells of immune system

Muscularis mucosae = thin layer of smooth muscle

Outer layers of the oesophagus

Submucosa = subtending layer of connective tissue containing mucus-secreting glands

Muscularis externa = mix of smooth and skeletal muscle layers (inner - circular; outer - longitudinal) that move food by peristalsis

Adventitia = thin outermost of connective tissue to anchor organ

Four regions of the stomach

cardia, fundus, body and pylorus

The mucosa and submucosa are folded into ___ when empty

rugae

The contractions of the three layers of muscle in the stomach are useful for what function?

Mixing of ingested food with enzymes and mucus to form chyme

Gastric glands in the mucosa of the stomach and what they secrete

Simple branched tubular glands

Secrete mucus, HCl, digestive enzymes and digestive hormones

Adaptation of the small intestine (jejunum) which amplifies surface area of the organ - promoting efficient nutrient absorption

- Plicae circulares

- Villi

Small intestine (jejunum) histology

Large aggregations of lymphoid follicles found in the ileum

Peyer's patches

What types of cells are found in the crypts of Lieberkühn of the colon - that secrete mucus?

Goblet cells

The organisation of the muscularis externa of the colon changes. The longitudinal muscle reorganises into three bands known as ___ ___

Taeniae coli

The mucosa of the colon contains ___ ___ epithelium

simple columnar epithelium

Crypts of Lieberkuhn

Colon epithelium

Simple columnar epithelium

Anus epithelium

Stratified squamous non-keratinised epithelium

A hotspot for malignant transformation in the colon where frequent metaplasia occurs (change of one differentiated cell type to another)

Recto-anal junction or the 'squamocolumnar junction' (SCJ)

Respiratory tract - conducting portion

Nasal cavity to terminal bronchioles

Respiratory tract - respiratory portion

Respiratory bronchioles, alveolar ducts, alveoli = site of gaseous exchange

What type of epithelium is found in the roof of the nasal cavity?

Ciliated olfactory receptor cells (olfactory epithelium)

What types of glands can be found in the olfactory epithelium in the roof of the nasal cavity?

Bowman's glands = produce fluid to dissolve odiferous substances

Structure of Bowman's glands in the nasal cavity?

Branched tubuloalveolar

The lamina propria in the nasal cavity is richly vascularised with ___ ___

Venous plexuses

What type of cartilage can be seen in the trachea?

C-shaped hyaline cartilage

The fibroelastic membrane in the trachea contains the ___ muscle which relaxes when you swallow and contracts when you cough

trachealis muscle

What type of epithelia can be found in the wall of the trachea?

Pseudostratified ciliated columnar epithelium

What types of glands can be found in submucosa of the trachea?

Seromucous (tubuloacinar) glands

Wall of the trachea

E = Epithelium (pseudostratified ciliated columnar)

LP = Lamina propria

C = C-shaped hyaline cartilage

SM = Submucosa with seromucous (tubuloacinar) glands

What is this image showing?

A bronchus

What type of epithelium can be found in the bronchus?

Pseudostratified ciliated columnar epithelium

Bronchus

E = Epithelium (pseudostratified ciliated columnar)

M = Smooth muscle

G = Glands in submucosa

C = Crescent-shaped hyaline cartilage

What types of epithelium lines smaller respiratory bronchioles?

Cuboidal epithelium

Difference between bronchus and bronchiole structure

Bronchiole = no cartilage to keep the lumen open

Bronchus = crescent-shaped hyaline cartilage to keep lumen open

Smaller, respiratory bronchioles have no smooth muscle and are lined with ___ epithelium

cuboidal

A respiratory bronchiole

E = Epithelium (simple columnar: varies from ciliated to cuboidal)

M = Smooth muscle

A = Alveoli

a) Type I pneumocytes function

b) Type of epithelium found in type I pneumocytes

a) Extremely thin alveolar cells that are adapted to carry out gas exchange

b) Simple squamous epithelial cells

a) Type II pneumocytes function

b) Type of epithelium found in type II pneumocytes

a) Production of alveolar surfactant

b) Cuboidal epithelial cells

Macrophages found lining the alveolar surface which phagocytose foreign particles

Dust cells

Type I pneumocytes account for ___% of alveolar cell population but cover ___% of surface area of the alveoli

Type I pneumocytes account for 40% of alveolar cell population but cover 95% of surface area of the alveoli

Type II pneumocytes account for ___% of the alveolar cell population, but cover only ___% of the alveolar surface

Type iI pneumocytes account for 60% of the alveolar cell population, but cover only 5% of the alveolar surface

Cells of the alveolus

- Simple squamous (type I) alveolar cells

- Cuboidal (type II) alveolar cells

- Alveolar macrophages (dust cells)

Urinary tract

Renal calyces

Cup-like cavities that collect urine and empty into the renal pelvis

The renal calyces are lined with ___ epithelium

Transitional

The ureter

TE = Transitional epithelium

LP = Fibroelastic lamina propria

ME = Muscularis externa

Importance of transitional epithelium in the urinary tract?

- Distensible = tissues can expand when bladder fills with urine

- Protection = (multiple layers thick) from cytotoxic effects of urine

The muscularis (smooth muscle) in the bladder wall is comprised of three poorly-delineated layers forming the ___ muscle

detrusor

Transitional epithelium (urothelium) of the bladder

The proximal region of the urethra is lined by ___ epithelium

Transitional

The female urethra is entirely ___

The male urethra has both ___ and ___ roles

The female urethra is entirely urinary

The male urethra has both urinary and reproductive roles

Distal regions of the urethra (which open to the outside) are lined with what type of epithelium?

Stratified squamous, non-keratinised epithelium

The penile urethra is enclosed by the __________.

Corpus spongiosum

What type of epithelium can be found in the penile urethra?

Stratified columnar epithelium

Does the peritoneal cavity connect to exterior?

Body cavities tubes and ducts that are enclosed and make no connection with the exterior of the body

Does the respiratory tract connect to exterior?

Body cavities tubes and ducts that ultimately connect with the exterior of the body

Does the pleural cavity connect to exterior?

Body cavities tubes and ducts that are enclosed and make no connection with the exterior

Does the pericardial cavity connect to exterior?

Body cavities tubes and ducts that are enclosed and make no connection with the exterior

Does the alimentary canal connect to exterior?

Body cavities tubes and ducts that ultimately connect with the exterior of the body

Does the cardiovascular system connect to exterior?

Body cavities tubes and ducts that are enclosed and make no connection with the exterior

Micrograph of oesophagus.

Identify B

Stratified squamous non-keratinised epithelium

Micrograph of oesophagus.

Identify D

Submucosa

Micrograph of oesophagus.

Identify A

Oesophageal lumen

Micrograph of oesophagus.

Identify G

Adventitia

Micrograph of oesophagus.

Identify H

Lamina propria

Micrograph of oesophagus.

Identify C

Muscularis mucosae

Micrograph of oesophagus.

Identify E

Mix of skeletal and smooth muscle of circular layer

Micrograph of oesophagus.

Identify longitudinal muscle layer

F

Histological section of small intestine

Identify structures

A =

B =

C =

D =

E =

F =

A = MALT

B = Submucosa

C = Circular muscle

D = Longitudinal muscle

E = Mesothelium (simple squamous epithelium of the serosa)

F = Mucosa

Histological section of villus

Identify structure

A =

B =

C =

D =

E =

F =

A = Goblet cell

B = Enterocytes (simple columnar epithelium)

C = Lamina propria

D = Isolated smooth muscle fibres

E = Muscularis mucosa

F = Blood vessels in submucosa

Histological section of region of colon

Identify structure

A =

B =

C =

D =

E =

F =

G =

A = Mesothelium comprised of connective tissue and simple squamous epithelium

B = Outer longitudinal smooth muscle

C = Inner circular smooth muscle

D = Region of loose or dense irregular connective tissue containing glands, adipose, nerve, immune cells and blood vessels

E = Structure that allows local movement of the mucosa

F = Mucous membrane comprised of simple columnar epithelium with supporting lamina propria and smooth muscle

G = Region of lymphoid tissue

Pathophysiology of Crohn's disease

Chronic inflammatory disorder affecting any region of the digestive tract, leading to fissuring (deep) ulceration of the gut wall