Lecture 8.1: Internal Surfaces of the Body Flashcards
Membrane Types
• Mucous membranes (mucosae singular, mucosa)
• Serous membranes (serosae singular, serosa)
Mucous Membranes: Where?
Mucous membranes line internal tubes that open to the exterior:
• Alimentary tract
• Respiratory tract
• Urinary tract
• Reproductive tract
The layers of a mucous membrane (3)
1) An epithelium lining the lumen of a tube, the type depends on the site
2) An adjacent layer of connective tissue often referred to as the lamina propria
3) In the alimentary tract, a 3rd layer of smooth muscle cells is present: the muscularis mucosae
What are Serous Membranes?
Serous membranes are thin, two-part membranes that line certain closed body cavities (spaces that do not open to the exterior)
Development of Serous Membranes
During embryonic development, the heart, lungs, and digestive tract develop next to a bag-like cavity, into which they invaginate (turned inside out or folded back on itself to form a cavity or pouch)
This way, they become enveloped by serous membranes
What do Serous Membranes Envelop?
• The Peritoneum, which envelops many abdominal organs
• The Pleural Sacs, which envelop the lungs
• The Pericardial sac, which envelops the heart
What do serous membranes secrete?
These serous membranes (or serosae) secrete a lubricating fluid that promotes relatively friction-free movement of the structures that they surround
The Pericardial Sac: Outwards to Inwards
Parietal Pericardium
Pericardial Cavity
Visceral Pericardium
Pleurae of Lungs: Outwards to Inwards
Parietal Pleura
Pleural Cavity
Visceral Pleura
Where do most digestive organs lie?
Abdominopelvic Cavity
The Peritoneum
Most digestive organs lie within the abdominopelvic cavity, which is covered by the visceral layer of the peritoneum
The cavity wall is lined by the parietal peritoneum
Serous fluid allows movement of the organs during digestion
What is the Mesentery?
A 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
Retroperitoneal Organs
Include (most of) the pancreas and oesophagus, the kidneys, ureters, and ascending and descending colon
The Gastrointestinal Tract
Oesophagus
Stomach
Small Intestine (Duodenum, Jejunum, Ileum)
Colon
Rectum
The 4 Layers of the Gut Tube
1) A mucosa surrounding the lumen (epithelium, lamina propria, muscularis mucosae), the epithelium is simple columnar throughout, bookended by stratified squamous non-keratinised epithelium
2) A submucosa (loose irregular CT)
3) External layers of circular and longitudinal smooth muscle (muscularis externae)
4) An outer serosa (or adventitia at either end)
Layers of the Mucosa of the Gut Wall: Outwards to Inwards
Muscularis mucosae
Lamina propria
Epithelium
Peyer’s Patches (Mucosa of Gut Wall)
Aggregations of lymphocytes are often present in the lamina propria, particularly distal ileum where they form Peyer’s patches
The Submucosa of the Gut Wall
A layer of loose irregular connective tissue bearing glands, arteries, veins, lymphatics and nerves
Glands within the submucosa
External Muscle of the Gut Wall
Two layers of smooth muscle comprise the muscularis externa:
• Outer longitudinal smooth muscle layer
• Inner circular smooth muscle layer
The muscularis externa creates successive peristaltic waves to move luminal contents along the gut under the control of the enteric nervous system
The Serosa of the Gut Wall
Simple Squamous Epithelium (Mesothelium)
Connective Tissue
Mesentery (double layer of visceral peritoneum) containing arteries, veins and nerves
Layers of the the Oesophagus: Outwards to Inwards
Muscularis externa (comprised of skeletal muscle only in the upper 1/3 of the oesophagus)
Submucosa
Mucosa (Muscularis mucosae, Lamina propria, Epithelium)
Oesophageal Mucosa (3 Layers)
Muscularis mucosae: thin layer of smooth muscle
Lamina propria: loose connective tissue bearing blood and lymph vessels, some smooth muscle cells and many cells of immune system
Epithelium: stratified squamous non-keratinized (withstands abrasion)
Outer Layers of the Oesophagus
Submucosa: subtending layer of connective tissue containing mucus secreting glands
Muscularis externa: a mix of smooth and skeletal muscle layers (inner– circular; outer– longitudinal) that move food by peristalsis
Adventitia: thin outermost layer of connective tissue to anchor organ
Regions of the Stomach (4)
The stomach has four distinct regions:
• Cardia
• Fundus
• Body
• Pylorus
Gastric Glands of the Stomach
They are located on the fundus and body regions of the stomach
They produce acidic gastric juice
The Main Function of the Pylorus and Cardia
Mucus Production
Rugae
The mucosa and submucosa is folded into rugae when empty
Muscularis of the Stomach: Layers and Function
Longitudinal Layer
Circular Layer
Oblique Layer
Contractions of the three layers of muscle allows thorough mixing of ingested food with enzymes and mucus to form chyme
Gastric Glands in the Mucosa of the Stomach
These are simple branched tubular glands lined with simple columnar epithelium
The various types of gastric glands feature different specialised cells that produce mucus, hydrochloric acid, digestive enzymes and digestive hormones
Isthmus
Stem cells are located in the isthmus (neck) linking gastric pits and glands, and these turn over every 4-7 days
Layers of the Small Intestine (Jejunum): Outwards to Inwards (3)
Muscularis Externa
Submucosa
Jejunal mucosa (simple columnar epithelium, lamina propria and muscularis mucosae
Plicae Circulares
Plicae circulares are circular folds of mucosa and submucosa projecting into the gut lumen
Peyer’s Patches in the Ileum
Peyer’s patches are large aggregations of lymphoid follicles found in the ileum providing immune surveillance
Nodules project into the mucosa, where they are covered with a layer of epithelium with relatively few goblet cells
Specialised ‘M cells’ in the epithelium transcytose antigens from the lumen to a reservoir of immune cells
Immunoglobulins are released back into the lumen
The Colon
There are no plicae circulares and no villi
Mucosa contains simple columnar epithelium
Goblet cells of the crypts of Lieberkühn are highly productive
The surface epithelial cells absorb water and electrolytes
The colon is supported by adventitia in retroperitoneal regions
Muscularis Externa in the Colon
The organisation of the muscularisexterna changes
The longitudinal muscle reorganises into three bands known as taeniae coli
Respiratory Tract: Conducting Portion
Stretches from the nasal cavity to the conducting bronchioles
Respiratory Tract: Respiratory Portion
Alveolar ducts and alveoli constitute the respiratory portion
This is where gas exchange takes place
Olfactory epithelium in the roof of the nasal cavity
Absence of goblet cells
Bowman’s glands (branched tubuloalveolar) produce fluid to dissolve odiferous substances
Ciliated olfactory receptor cellsare located in the thick olfactory epithelium
The lamina propria in the nasal cavity is richly vascularised with venous plexuses
Trachea and Oesophagus: Fibroelastic Membrane
The fibroelastic membrane contains the trachealis muscle, which relaxes when you swallow and contracts when you cough
Wall of the Trachea: Outwards to Inwards
Submucosa with seromucous (tubuloacinar) glands
Lamina propria
C-shaped cartilage(hyaline)
Epithelium (pseudostratified ciliated columnar)
Layers of a Bronchus: Outwards to Inwards
Hyaline cartilage (crescent-shaped)
Glands in submucosa
Smooth muscle
Epithelium (pseudostratified ciliated columnar)
Structure of Bronchiole: Outwards to Inwards + General
Alveoli
Smooth muscle
Epithelium (simple columnar: varies from ciliated through cuboidal)
Note that there is no cartilage to keep the lumen open
Smaller, respiratory bronchioles have no smooth muscle and are lined with cuboidal epithelium
Alveoli: Cells Present
Type I Pneumocytes
Type II Pneumocytes
Macrophages
Endothelial Cells
Alveoli: Type I Pneumocytes
Simple Squamous Epithelial Cells
Account for 40% of the alveolar cell population, but cover 95% of the surface area of the alveoli
Facilitate gas exchange with capillaries
Alveoli: Type II Pneumocytes
Cuboidal
Account for 60% of the alveolar cell population, but cover only 5% of the alveolar surface
They secrete surfactant (compounds that lower the surface tension/ interfacial tension between two liquids, between a gas and a liquid, or between a liquid and a solid)
Alveoli: Macrophages
Dust Cells line alveolar surface to phagocytose foreign particles
What forms the blood-air barrier in alveoli?
The membranes of Type I Pneumocytes and endothelial cells (as well as their fused basement membrane) form a blood-air barrier
What are alveoli surrounded by?
Alveoli are surrounded by a ‘basketwork’ of capillaries and elastic fibres
The Urinary Tract: Organs/Structures Involved
Kidney
Ureter
Bladder
Urethra
Renal Calyces
Collecting ducts gather filtrate produced by nephrons
Filtrate is delivered to the calyces (lined with transitional epithelium)
Urine then passes to the ureters
Layers of the Ureter: Outwards to Inwards (3)
Muscularis Externa
Fibroelastic Lamina Propria
Transitional Epithelium
Layers of Bladder Wall: Outwards to Inwards (6)
Serous Peritoneum (upper bladder- rest has an adventitia)
Muscularis is comprised of three poorly-delineated layers forming the detrusor muscle (smooth muscle)
Dense Irregular Connective Tissue
Transitional Epithelium
Ruga
Lumen
Transitional Epithelium of the Bladder
Impermeability to urine conferred by cells with a modified plasma membrane and intercellular tight junctions
Epithelium is distensible
The Female Urethra
The female urethra is entirely urinary
The Urethra: General Structure + Cells Present
The proximal region of the urethra (e.g. the prostatic urethra in males) is lined by transitional epithelium
The epithelium of rest of the urethra varies, stratified columnar epithelium is found and regions of pseudostratified epithelium
As with other systems that open to the outside, distal regions are lined with stratified squamous, non-keratinised epithelium
Layers of Penile Urethra: Outwards to Inwards
Cavernous Space in Corpus Spongiosum
Stratified Columnar Epithelium
Lumen
Mucosa
The moist, inner lining of some organs and body cavities
Glands in the mucosa make mucus
Submucosa
The submucosa is a thick layer of loose connective tissue that surrounds the mucosa
This layer also contains blood vessels, lymphatic vessels, and nerves
Glands may be embedded in this layer
Serosa
A smooth tissue membrane of mesothelium lining the contents and inner walls of body cavities, which secrete serous fluid to allow lubricated sliding movements between opposing surfaces
Adventitia
The adventitia is the outermost layer of the vessel and contains connective tissue, nerves, and the smaller vessels that supply the vessel wall with oxygen and nutrients (the vasa vasorum)
