Inner Surfaces Of The Body Flashcards
Describe the histological lining of the oral cavity
The Oral cavity is made up of several areas which differ in its histological conformation. Generally all have a mucosa and submucosa, however the epithelial type and thickness of the submucosa.
The epithelium of the oral cavity is universally stratified squamous. In mobile areas such as the underside of the tongue, the cheeks, the lips and the soft palate and floor of the mouth is non-keratinised. However in less mobile areas, such as the upper surface of the tongue, hard palate and gingiva it is keratinised. The mucosa is completed with the lamina propria.
The submucosa contains collagen fibres and accessory salivary glands where the lining does not overlay bone. In areas associated with bone, such as the gingiva and hard palate, the submucosa is thin. In other areas, such as the soft palate and tongue, the submucosa is thicker.
Describe the mucosa, submucosa and muscularis externa of the oesophagus
Mucosa - the epithelium is stratified squamous non-keratinised throughout, however where GORD exists the lower part of the tube may have undergone metaplasia to glandular epithelium typical of the stomach. The lamina propria contains loose connective tissue with various cells including fibroblasts, macrophages and mast cells. It also has blood and lymphatic vessels. The muscularis mucosa exists deep to this which consists of smooth muscle.
Submucosa - this layer contains mucus glands whose ducts empty into the oesophagus. It is also made up of loose connective tissue and blood vessels.
Muscularis externa - the upper third of the oesophagus consists of skeletal muscle under voluntary control to initiate the perastalic wave of contraction. The middle third consists of a mixture of both skeletal and smooth muscle cells, where as the lower third contains only smooth muscle cells.
The outer most layer is the connective of the adventita.
Describe the mucosa, submucosa and muscularis externa of the stomach
Macroscopically the lining of the stomach is organised into rugae, which aid in the stretching of the stomach during filling.
Mucosa - the epithelium of the stomach is that of simple columnar ‘glandular’ cells. These are organised into gastric pits, which become gastric glands into which mucus cells, parietal cells and chief cells secrete their products into the stomach lumen. The lamina propria lays deep to this, while the muscularis mucosa consists of smooth muscle which functions to contract and aids in the release of secretions of the gastric glands.
Submucosa - this is a connective tissue layer which contains blood vessels, lymphatic vessels and nerves, which form the ganglia of the PNS neurones of the vagus nerve supplying the secretory cells and muscularis mucosa.
Muscularis externa - three layers of smooth which are innervated by the vagus nerve and which function in receptive relaxation and coordinated contraction from fundus to pyloris.
The stomach is surrounded by peritoneum since it is an intraperitoneal organ.
Describe the mucosa, submucosa and muscularis externa of the small intestines
As with mucosa elsewhere, it consists of epithelium, lamina propria and muscularis mucosa. The epithelium is one of simple columnar epithelium which have an absorptive role and which possess tight junctions between then to polarise the cells and regulate movement of substances between the lumen and blood. The cells have microvilli which form a brush border within which number out digestive enzymes, including isomaltase, lactase and sucrase. The lamina propria is a loose connective tissue layer which bares a rich vascular and lymphatic network in order to absorb nutrients and lips respectively. The muscularis mucosa underlies this layer. The mucosa is organised into villi. The crypts the mucosa forms are involved in stem cell replicaiton and differentiation, mucous secretion and Paneth cell formation. In some areas aggregates of lymphatic tissue (GALT) are present, called Peyer’s Patches. These are utilised by the bacterium salmonella typhi in enteric fever
The submucosa contains glands with larger blood vessels.
The muscular externa consists of two layers of smooth muscle which functions in segmentation of the luminal contents and the slow caudal movement which occurs between meals. There is overall caudal movement due to the higher rate of firing of the proximal-most pacemaker cells.
The proximal 1/4 of the duodenum, the jejunum and the ilium are all intraperitoneal and so are surrounded externally by the visceral layer of peritoneum. The distal 3/4 of the duodenum is secondary retro peritoneal and so fused to the posterior abdominal wall.
The small intestine is organised into plicae circularis, macroscopic folds which increase surface area and formed due to the tone of the muscularis externa.
How is absorption promoted along the small intestine?
- microvillous adaptations on the epithelial cells increase surface area.
- mucosal folding into villi also increase the surface area.
- submucosal folding create plicae circulares which further increase the surface area for absorption. The are abundant and large in the duodenum, however become progressively smaller and fewer in number as the small intestine progress, and are almost absent in the ilium.
- there is a short diffusion distance for substances to pass into the circulation since the blood and lymph vessels are locates beneath the epithelial cells in the lamina propria.
How is the small and large intestine differentiated between on an abdominal X-ray?
Intestine is viable on X-ray where gas is present within it as it for as a natural contrast against surrounding tissue.
Small intestine - centrally located, plicae circulares form lines which run the entire width of the lumen, should be about 3cm in width.
Large intestine - peripherally located, form haustra which do not transverse the entire lumen, should be no larger than 6cm, while the sigmoid colon should be no larger than 9cm.
Describe the histological make up of the olfactory area of the nasal cavity
There are two areas of the nasal cavity - the olfactory area and the larger respiratory area. The olfactory area is located at the superior boarder of the cavity in close proximity to the olfactory bulbs.. There are four cell types in this area:
- olfactory cells are bipolar neurones which transmit action potentials in response to olfactory stimuli back to the olfactory nerve, piercing the cribriform plate.
- supporting cells are analogous to glial cells since they support the olfactory cells. They are the pseudostratified (non-motile) ciliated epithelial cells.
- basal cells act to divide and differentiate into supporting or olfactory cells in order to replace them every 2-4 weeks.
- brush cells which are columner cells which express microvilli and are involving in transduction get odours to generate a nerve signal.
In the lamina propria are Bowman’s Glands/olfactory glands which produce mucous which helps trap odours and wash away older ones.
Describe the passage of air from through the nasopharynx, including the histology of the area.
From the nasal cavity air, which has been humidified and mixed with the aid of the conchae and paranasal sinuses, passes through the posterior choanae enter the nasopharynx. The nasopharynx extends from the sphenoid bone down to the soft palate and is at the level of the C1 vertebrae. It consists of respiratory epithelium which is pseudostratified ciliated columner epithelium. The major structure here is the nasotympanic tube/Eusacchian tube.
Describe the histology of the respiratory portion of the nasal cavity
This part of the cavity is lined by respiratory epithelium which exists with goblet cells, unlike at the olfactory area. At the vestibule of the nose larger hairs, called vibrissae, are present to act as a filter. The surface area for humidification of air, and the establishment of turbulent/mixing air flow, is allowed through the presence of conchae.
Describe the histology of the trachea and how structure relates to function
The trachea consists of the mucosa, submucosa and C-shaped hyaline cartilage which can exist in conjunction with a trachealis muscle contained within the fibroelastic membrane. This membrane forms the partition between the trachea and oesophagus. The epithelium is one of pseudostratified ciliated columnar epithelium with goblet cells. The goblet cells and cilia create the mucocilary escalator. The submucosa contains seromucous glands. There is no muscularis mucosa.
Describe the histological differences between the bronchi and bronchioles.
Bronchi are larger airways which consist of the respiratory epithelium with goblet cells. It also has a submucosa with seromucus glands, like the trachea, and cartilage which is more fragmented. The bronchi are basically continuations of the trachea but with more fragmented cartilage.
Bronchioles are thinner walled and have no cartilage supporting them. As a result they are held open by the alveoli surrounding them. Smooth muscle is present which functions to vary the diameter of the lumen And becomes abnormal in respiratory diseases such as COPD and asthma. They also have no goblet cells or seromucus glands, however they have non-ciliated Clara cells which secrete components of surfactant to stop the walls fusing together.
Describe the cellular make up and function of alveoli.
There are three types of cell in alveoli, the type I pneumocytes, type II pneumocytes and alveolar macrophages.
Type I cells are simple squamous epithelium which form part of the diffusion barrier for gas exchange between the alveolus and blood. The have a high surface area to volume ratio.
Type II cells are involved in the production of surfactant, which functions to reduce the impact of surface tension and prevent collapse of smaller alveoli into larger ones.
Alveolar macrophages are involved in the innate immune protection of the lungs.
Describe the interstitium of the lungs.
The interstitium is located between the endothelium of the blood vessels and epithelium of the alveoli. It is thin in order to promote gas exchange. It consists of the fused basement membranes together with collagen fibres and elastin, the latter of which provides the elastic recoil of the lungs. Intersititial lung disease thickens this tissue through formation of excess collagen which is thicker and less distensible, limiting chest expansion.
Describe the histological layers of the bladder.
The bladder is a highly muscular structure which consists of several layers of smooth muscle and lacks a submucosa. Instead, the mucosa is made up of transitional epithelium (urothelium) and an underlying lamina propria which is rich in smooth muscle. The muscularis externa consists of three layers of smooth muscle, forming the destructor muscle, which is under autonomic control from the hypogastric (SNS) and pelvic (PNS) nerves. The layers are arranged into differing alignments which are hard to make out. The mucosa is highly folded into rugae which, along with the transitional epithelium and receptive relaxation of the detours or muscle, aids in distension of the organ during filling. The bladder is a retro peritoneal organ.
Describe the histological structure and function of the ureter
The ureter is a retro peritoneal structure which receives urine from the kidney, via the renal pelvis, and delivers it to the bladder for storage. Like the bladder, it consists of urothelium and lacks any glands and also lacks a submucosa. The upper portion has two layers of smooth muscle making up the muscularis externa, however as it approaches the bladder it gains three layers. This muscle is involved in peristalsis or urine. Where the ureter meets the bladder, at an oblique angle, a vesicoureteral valve is formed to stop retrograde passage of urine. Where it is incompetent it can lead to a UTI and pyelonephritis.
