Lecture 2 - anatomy Flashcards
4 layers of the GI tract
Mucosa (innermost)
Submucosa
External muscles
Serosa (outermost)
What does the mucosa consist of?
Epithelial cells
Lamina propria
Muscularis mucosa
What does the submucosa contain?
Connective tissue with:
- glands
- arteries
- veins
- nerves
Meissner’s plexus
External muscle of the GI tract
Outer longitudinal - divided into 3 bands (taeniae coli). Acts as a shuttle and shortens gut
Inner circular - for peristalsis and contains the Auerbach’s plexus
What does the serosa contain?
Blood vessels
Adipose tissue
Lymph vessels
Continuous with the mesenteries
Role of the mucosa epithelial layer
Selectively permeable barrier - facilitates the transport and digestion of food
- Promotes absorption via microvilli
- Produces hormones
- Produces mucus via goblet cells
Why does the GI tract contain mucus?
Decreases friction
Prevents chemical damage
Reduces bacterial invasion
Role of the lamina propria of the GI mucosa
Contains lymphoid nodules and macrophages - immune defense
Produces antibodies (IgA) - resistant to proteases which protects against bacterial and immune invasion
Role of the muscularis mucosae of GI mucosa
Layers of the smooth muscle orientated in different directions
Motility - prevents stasis which can cause infection
Keeps the epithelium in contact with the gut contents
Dynamic crypt contents
(peptic ulcers breach the muscularis mucosa)
What type of epithelium lines the oesophagus and distal anus
Stratified squamous
What type of epithelium lines the stomach and intestines
Simple columnar
Adaptations of the enterocyte
Enterocytes line the villi
Microvilli - brush border (increases SA)
Crypts
One cell thick
Goblet cells
Scattered between the enterocytes
Increasing number form the duodenum to the colon
Secretes mucus
Nucleus at base due to compression by mucus
Foveolar cells
Line the gastric mucosa and gastric pits (in stomach)
Secretes:
- mucus
- HCO3-
Secretions form a barrier to stomach acid
Folds of the GI tract
Stomach - rugae (temporary)
Small intestines - plicae circulares
Large intestines - haustra
Villi and microvilli
Villi
Found in absorptive areas - small intestines
Crypts
In small and large intestines
Crypts of Lieberkuhn
Contain specialised cells:
- Stem cells
- Paneth cells
- Enteroendocrine cells
Stem cells
Divide and replicate for epithelium regeneration every 2- 4 days
Paneth cells
Guard against infection
Protects stem cells (package and export antimicrobial proteins)
[at base of crypt and bright red]
Enteroendocrine cells
Secrete gut hormones:
- G cells - gastrin - stimulates gastric acid secretion from parietal cells
I cells - cholecystokinin - Stimates the gall bladder to contract and release bile
- S cells - secretin - Stimulates the release of HCO3- and water to dilute acid
[deeper in crypts and gastric glands]
Describe the glandular tissue of the gut
Acini - produce digestive enzymes
Intercalated ducts - transports secretions Interlobular ducts- secrete sodium bicarbonate into the main duct
Tubules
Examples of exocrine glandular structures
Salivary glands
Pancreas
Brunners glands
Secretion volumes per day
Saliva - 1.5 L Bile - 0.5 L Gastric secretions - 2L Pancreatic secretions - 1.5 L Small intestines - 1.5 L
Layers of the abdominal wall from superficial to deep
Skin
Fascia
Fat
External oblique
Internal oblique
Transverse abdominis
Rectus abdominis
Transversalis fascia
Peritoneum
Rectus sheath
The aponeurosis of the external oblique, internal oblique and transversus abdominis that surrounds the rectus abdominis
The superior 3/4 of the rectus abdominis is completely enclosed by the rectus sheath
The inferior 1/4 is only covered anteriorly. Posteriorly it is covered by the transversalis fascia and parietal pertitoneum
Peritoneal cavity
Seperate from the abdominal cavity
Serous membrane containing peritoneal fluid forming a potential space
Simple squamous
Envelops intraperitoneal viscera (Visceral peritoneum)
Lines the cavity wall - (parietal)
Retroperitoneal structures
Suprarenal glands Aorta and IVC Duodenum Pancreas Ureters and bladder Colon (ascending and descending) Kidneys Esophagus Rectum
Visceral peritoneum
Sympathetic and parasympathetic afferents
- Pain is poorly localised
- referred
- dependent on nerve
Parietal peritoneum
Somatic afferents
- localised pain
What does a mesentery contain?
Double fold of peritoneum that contains:
- blood vessels
- lymph vessels
- fat
- nerves
Arcuate line
Site of transition of the rectal sheath
Lower limit of the posterior layer of the rectal sheath
Half way between the umbilicus and pubic crest
What are the two major divisions of the peritoneal cavity?
Greater and lesser sacs
What is the connection between the greater and lesser sac?
The epiploic foramen (Foramen of Winslow)
Boundaries of the lesser sac
Anterior:
- quadrate lobe of the liver
- gastrocolic ligament and stomach
- lesser omentum
Posterior:
- pancreas
- left kidney
Cavities within the peritoneum that can collect fluid
Rectovisical - between the rectum and bladder
Rectouterine (pouch of Douglas) - between the rectum and uterus
Visicouterine - between the bladder and uterus
Symptoms of peritonitis
- feeling of fullness and bloating
- fever
- nausea and vomiting
- loss of appetite
- diarrhoea
- thirst
- low urine output
- inability to pass stool or gas
- fatigue
How do the splanchnic nerves enter the abdomen
Through the diaphragm at the 4th and 5th intercostal space
