Session 1 ILOs - Intro to gut and internal structure Flashcards
Describe the main processes of the GI tract
- Break down food both physically and chemically
- Absorb nutrients
- Expel what we don’t want!
Outline the broad functions of the various regions of the GI tract (mouth, oesophagus, stomach, duodenum, jejunum, ileum, large intestine)
Mouth:
- Physical break down
- Initial digestive enzymes e.g. amylase
- Infection control
Oesophagus:
- Rapid transport via peristalsis
- Upper oesophageal sphincter = prevent air entering GI tract
- Lower oesophageal sphincter = prevent stomach acid reflux
Stomach:
- Storage
- Production of chyme
- Infection control e.g. against HCL
- Secrete intrinsic factor
Duodenum:
- Neutralisation and osmotic stabilisation of chyme (very hypertonic and acidic) with HCO3 rich secretions
- Continue digesting with pancreatic secretions and bile = both common bile duct and pancreas enter the duodenum
Jejunum:
- Nutrient absorption as highly folded (some ileum)
Ileum:
- Water and electrolyte absorption (some jejunum)
- Bile recycling
- B12 absorption
Large intestine: - Final water reabsorption - Temporary storage before exit - Final electrolyte absorption (some bile salt absorption and fatty acid production)
Describe the anatomy and function of the peritoneal cavity
The peritoneal cavity is a potential space found between the parietal and visceral layers of the peritoneum
Peritoneal cavity is formed by peritoneum which is layers of mesothelium (simple squamous epithelium) which is serous in nature to secrete serous fluid
The peritoneum can form mesenteries, omentum and peritoneal ligaments
Anatomy:
- Peritoneum lines the walls of the abdominal cavity (parietal layer) and lies on abdominal and pelvic organs (visceral layer)
- Between its two layers (parietal and visceral) is the peritoneal cavity
Function:
- Protection of the abdominopelvic organs
- Connect organs with each other
- Maintain the position of organs by suspending them with ligaments
- Prevent friction while organs move
Describe the organisation and function of mesenteries
Mesenteries - double folds of peritoneum:
- Comprised of both layers of the peritoneum (visceral and parietal)
Main function:
- Attaches the intraperitoneal organs to the abdominal wall e.g. small intestine mesentery suspends the jejunum and the ileum
- Provides neuro-vascular communication between organs and the abdominal wall
Describe the basic structure of the autonomic nervous system in relation to its influence on the gastrointestinal tract
Generally:
- The sympathetic NS turns OFF the gut
- The parasympathetic NS turns ON the gut
Sympathetic NS:
- Cell bodies reside in the CNS, short pre-ganglionic neurones and long post-ganglionic neurones
- Preganglionic fibres synapse in the sympathetic chain normally but NOT for the gut - instead nerves coalesce to form the splanchnic nerves (greater, lesser and least nerves)
- Works by reducing blood flow to abdominal organs which reduces their function (blood redirected to organs)
Parasympathetic NS:
- Cell bodies reside in the CNS, long pre-ganglionic neurones and short post-ganglionic neurones (synapse in the walls of effector organs)
- Important nerves: Vagus nerve and pelvic splanchnic nerves (S2-4)
Describe the properties of the enteric nervous system, and its relationship to the autonomic nervous system
Enteric NS (sensory mainly)
- One of the divisions of the nervous system
- Can operate independently of the ANS but has many connections with it
2 main nerve plexuses (where nerves and vessels recombine):
- Submucosal (Meissner’s)
- Within the submucosa
- Involved with controlling secretions and blood flow - Myenteric (Auerbach’s)
- In-between the muscle layers
- Involved with controlling gut motility
Describe the role of the major hormones of the gut (gastrin, cholecystokinin, secretin, GIP and somatostatin)
Gastrin (endocrine)
- Triggered by stretch or food
- Released by G cells (causes parietal cells to release acid)
Cholecystokinin (endocrine)
- Triggered by fat breakdown products, amino acids or acid
- Released by I cells in duodenum and jejunum
- Increases pancreatic/gallbladder secretions
- Therefore bile and digestive enzymes go through the sphincter of Oddi and into the duodenum
Secretin (endocrine)
- Triggered by fatty acids or H+
- Released by S cells in duodenum
- Causes more HCO3 to be released from pancreas/gall bladder (neutralise chyme acid)
GIP (stimulated by all food groups)
- Triggered by fatty acids, sugars or amino acids
- Released by cells in duodenum/jejunum
- Causes decreased insulin production = reduced gastric acid production
Somatostatin (paracrine)
- Stimulated by low pH
- Released by D cells and travels across to act on G cells to reduce gastrin production
- Therefore reduces gastric acid production
Describe the epithelial cell types of the major divisions of the alimentary tract
Start and end of tract:
- Stratified squamous (non-keratinised)
- This is where the physical stress is
- Secretes mucus
Everything in-between!
- Columnar (highly specialised)
e. g. surface mucous cells in the stomach that secrete mucus and HCO3 to protect the stomach lining from acid
Describe the specialised cell types of the alimentary tract and their function (stomach, small intestines plus duodenum specifically, colon)
Stomach:
- Surface mucous cells in the stomach secrete mucus and HCO3 to protect the stomach lining from acid
Small intestines:
- Enterocytes have microvilli (brush border)
- Goblet cells produce mucus to protect from friction, chemical damage and bacterial invasion
- Crypts constrain enteroendocrine cells (control gut), stem cells (ensure continuous barrier) and Paneth cells (antibacterial proteins)
Duodenum specifically:
- Brunner’s glands
- Produce alkaline mucous material into crypts to help protect against acid environment
Colon:
- Goblet cells produce mucus to protect and support the microbiome
- Higher density of Na/K+ transporters to help reabsorb water
Describe the layers of the gut and the most prominent features of each
- Mucosa (3 layers)
a. Epithelium - selective barrier (transport)
b. Lamina propria - immune heavy layer
c. Muscularis mucosa - keeps epithelium in contact with the gut content - Submucosa
- Dense connective layer of blood vessels, glands etc.
- Contains submucosal (Meissner’s) plexus - Muscularis
- Controls peristalsis
- Inner circular layer (reduces diameter)
- Outer longitudinal layer (reduces length)
- Between two muscles is the myenteric (Auerbach’s) plexus - Serosa
- Blood vessels, lymph vessels and adipose tissue
- Continous with mesenteries
Describe the muscles of the anterolateral abdominal wall and their innervation
4 main muscles:
- External obliques
- Fibres run infero-medial direction
Origin: 5th-12th ribs
Insertion: Iliac crest and pubic tubercle (creates inguinal ligament)
Action: Contralateral contraction of trunk and compresses abdominal viscera - Internal obliques
- Fibres run perpendicular direction to external obliques
Origin: Lateral part of inguinal ligament, iliac crest and thoracolumbar fascia
Insertion: 10th-12th ribs, pubic crest, into line alba via aponeurosis
Action: Ipsilateral contraction of trunk - Transverse abdominus
Origin: Inguinal ligament, medial iliac crest, thoracolumbar fascia and costal cartilages 7-12
Insertion: Pubic crest, into line alba via aponeurosis
Action: Core stability and compresses abdominal contents - Rectus abdominus
Origin: Pubic crest, pubic tubercle, public symphysis
Insertion: Costal cartilages 5-7 and diploid process
Action: As well as assisting the flat muscles in compressing the abdominal viscera, also stabilises the pelvis during walking and depresses the ribs
Nerve supply:
- All 4 by thoracoabdominal nerves (T7-T11)
- 1-3 by subcostal nerve (T12)
Describe the anatomy of the rectus sheath above and below the arcuate line
- Approximately midway between the umbilicus and the pubic symphysis, all the aponeuroses move to the anterior wall of the rectus sheath
- The point where the posterior layer of the rectus sheath ends is the arcuate line!
Above the arcuate line:
- Rectus abdominus is enclosed by the aponeuroses both anterior and posterior
Below the arcuate line:
- Rectus abdominus is only covered anteriorly by the aponeuroses
- Rectus abdominis is in direct contact with the transversalis fascia (connected to the parietal peritoneum)
List four quadrants and nine descriptive regions of the abdomen
Four quadrants:
- Right upper quadrant
- Left upper quadrant
- Right lower quadrant
- Left lower quadrant
Nine regions:
- Right hypochondriac region
- Epigastric
- Left hypochondriac region
- Right lumbar region
- Umbilical region
- Left lumbar region
- Right iliac region
- Pubic/hypogastric region
- Left iliac region
Describe the basic organisation of the peritoneal ‘ligaments’ (Falciform ligament, lesser omentum, gastro-colic ligament, gastro-splenic ligament)
Falciform ligament:
- Sickle-shaped ligament attaches the anterior surface of the liver to the anterior abdominal wall
- Its free edge contains the ligamentum teres, a remnant of the umbilical vein
Lesser omentum:
- Double layer of visceral peritoneum and attaches from the lesser curvature of the stomach and the proximal part of the duodenum to the liver
- Two parts: the hepatogastric ligament (the flat, broad sheet) and the hepatoduodenal ligament (the free edge, containing the portal triad)
Gastro-colic ligament:
- Portion of the greater omentum between the greater curvature of the stomach and the transverse colon
Gastro-splenic ligament:
- Portion of the greater omentum that connects the top third of the greater curvature of the stomach to the splenic hilum
