Digestive Flashcards
What are the two different ways of dividing the abdomen?
Quadrants: Right upper, left upper, left lower, right lower
9 Squares: Right hypochondrial, epigastric, left hypochondrial, right flank, umbilical region, left flank, right groin, pubic region, left groin
What are the layers of the abdominal wall (superficial to deep)?
Skin Camper's fascia (fatty) Scarpa's fascia (membranous) External obliques Internal Obliques Transversus abdominis Transversalis fascia Extraperitoneal fascia Parietal peritoneum
What are the muscles of the abdomen, their nerve supply and their actions?
- Rectus Abdominus: vertical fibre direction. Flex trunk, support abdomen. Supplied by ant. rami of thoracic spinal nerves
- External obliques: Inferomedial fibre direction. Flex trunk when both sides active, or bend trunk to same side when one side activated. Supplied by ant. rami of thoracic spinal nerves
- Internal obliques: Superomedial fibre direction. Flex trunk when both active, bend trunk when one active. Supplied by ant. rami of thoracic and some L1 spinal nerves
- Transversus abdominis: Transverse fibre direction. Support abdominal wall. Supplied by ant. rami of thoracic and some L1 spinal nerves.
What is the rectus sheath?
In the upper 3/4 of the abdomen, the rectus sheath surrounds rectus abdominis- it comes off the medial sides of the other abdominal muscles
In the lower 1/4 of the abdomen, the rectus sheath only covers the front of the rectus abdominis, with the transversalis fascia and parietal peritoneum beneath.
The rectus sheath’s posterior covering stops around halfway between the umbilicus and the pubic bones, in order to prevent clamping of the inferior epigastric artery.
What is the arterial, nervous and venous supply of the abdomen?
Arterial:
- Superior epigastric (from int. thoracic) and inf. epigastric (from ext. iliac). These run benath the rectus abdominis muscle on the transverse fascia and within the rectus sheath, to anastomose.
Venous:
Thoracoepigastric veins drain to axillary vein
Superficial epigastric veins drain to femoral vein
Nervous:
Lat. and ant. cutaneous branches of T7-12, as well as the hypogastric nerve from L1
What are the dermatomes of the torso?
T10 covers the navel
T9/8/7 extend upwards, and T11/12/L1 extend downwards in bands.
What is the lymphatic drainage of the abdomen?
The two upper quadrants drain superolaterally into the anterior axillary nodes
The two lower quadrands drain inferolaterally into the superior inguinal nodes
The posterior torsos drain into the posterior axillary nodes.
What is the peritoneum and mesentery, and how are they sensitive?
It resembles a fist in a balloon- visceral covers the fist, with the space between, and then the outer border if the parietal peritoneum. Parietal peritoneum senses pain, touch, temperature and pressure. It is supplied by the somatic nerves, the phrenic nerve and the obturator nerve.
The visceral peritoneum and mesentery are sensitive to to stretch by the ANS.
What is the difference between intra- and retro-peritoneal structures?
Intraperitoneal structures are completes wrapped in visceral peritoneum and are suspended by mesentery
Retroperitoneal structures are between the peritoneum and the body wall, without a mesentery. (pancreas, kidneys, distal duodenum, asc/desc colon and upper 2/3 of rectum.
What is the difference between the greater and lesser sacs?
The greater sac is the peritoneal cavity proper, while the lesser sac is located behind the lesser omentum and the stomach, formed due to rotation of the foregut
The omental foramen leads into the lesser sac, as the lesser omentum has a free edge by the liver. The lesser sac is bounded posteriorly by the Inferior vena cava.
What are the paracolic gutters?
They are sulci lateral to the ascending and descending colon, in front of the parietal peritoneum. They create a pathway for fluid to migrate around the abdomen. The right one is more important as it’s larger and continuous with the lesser sac.
These are clinically significant as they have a role in pain referral depending on where fluid migrates to.
What are the structures in the fore, mid and hindgut?
Foregut: Pharynx, lower resp. tract, oesophagus, stomach, liver, biliary apparatus, pancreas, proximal half duodenum
Midgut: Distal half duodenum, jejunum, ileum, caecum, appendix, ascending and prox. 2/3 transverse colon
Hindgut: Distal 1/3 transverse colon, descending and sigmoid colon, rectum, 2/3 anal canal.
What germ layer does the gut develop from and how does the gut fold to create the tubes?
Endoderm.
Lateral and longitudinal folding cause the formation of a gut tube, while the fore and hindgut close off and the midgut remains open to the yolk sac. Eventually the orophangeal and anal membranes rupture and the tube is complete
The lumen of the tube is initially open, but then plugs with epithelilum and is then recanalized
What is the arterial supply of the embryonic gut and how does this help in classifying it?
Foregut: celiac trunk
Midgut: Superior mesenteric artery
Hindgut: Inferior mesenteric artery
How does the oesophagus form?
Initially is is one tube with the trachea, but it partitions and rapidly elongates. However, there can be fistula (connection) and atresia (blockage) between them if part of the esophagus partitions and a lower part forms a fistula with the trachea.
There can also be hiatal hernia, where the esophagus fails to lengthen and pulls the stomach into the thorax
How does the stomach form? 3 stages. What are some possible malformations/
- Foregut tube starts to dilate
- Continues to dilate, rotation 90 degrees clockwise (long axis). Anterior mesogastrium moves right, post. to left. Note that the posterior mesogastrium begins to hang down under gravity, and the two borders fuse to form the greater omentum
- Continues to dilate. Rotates 90 degrees coronally, so that the right boundry makes the lesser curvature and the left boundary becomes the greater curvature.
Hypertrophic pyloric stenosis can occur when the pylorus is much thicker than usual, blocking chyme’s exit into the duodenum, resulting in bile-less vomit.
How does the liver, bile duct and pancreas form?
Hepatic diverticulum divides into 2: Larger sup. structure becomes liver, smaller inf. structure becomes biliary apparatus.
The bile duct is attached to the vent. duodenum,, although it moves posteriorly as the duodenum rotates.
The pancreas develops between both mesogastric layers- initially there is a bud on the dorsal and ventral mesogastrium. As the biliary tree rotates dorsally, the ventral fuses with the dorsal and they both anastomose with one pancreatic duct remaining (sometimes an accessory duct remains betwen the original dorsal pancreas and the duodenum)
The liver is then attached to the ventral parietal peritoneum by the falciform ligament. The lesser omentum connects liver and stomach, the gastrolienal ligament connects stomach and spleen, and the lienorenal ligament connects sleep with kidney.
How does the midgut form? What are some possible congenital malformations?
Initially it is U shaped, with crainial and caudal limbs either side of the SMA. It then herniates into the umbilical cord as it grows, before the midgut loop rotates counterclockwise through to 270 degrees. Eventually the herniation retracts and the cecum and appendix drop into lower abdomen.
It is possible for the gut to remain herniated into the the place the umbilical cord used to be if the cord doesn’t close properly
There can also be meckel’s diverticulum, where the navel is open to the gut tube.
How does the hindgut form? What are some possible malformations?
- Initially there is the cloaca, which connects the anal and urinary canals. Eventually a urorectal septum extens between the two, separating them
The upper 2/3 of the anal canal is hindgut, receiving blood supply from IMA, whereas the lower 1/3 comes from proctoderm. - Can have hirschprung’s disease, where some colon is dilated and cannot relax for peristalsis.
- Can have imperforated anus
- Can have rectal atresia- blockage between the anal canal and rectum, with possible fistulas to urethra, bladder or vagina
How does nutrition affect health?
- Affects health outcomes very strongly- impacts progression and treatment of chronic disease.
What factors influence our nutrition choices?
Components of our environment- food production, distribution, preparation, labels, our own perception of meals
The person themselves- our genetics, physiology, lifestyle and needs
We are also affected by our food due to the carbs, proteins, fats, vitamins and minerals we receive.
What is the difference between nutrition for a population and nutrition for a person?
Nutrition goals for a population are based on disease statistics, average current diets, as well as widely acceptable guidelines (one size fits all)
Nutritional goals for a person will differ as everybody’s lifestyle, metabolism and genes are different.
There are differences for everyone in age, stage and physiology.
What is a DALY?
Daly = Disability adjusted life year.
It is calculated as years of life lost + years of life with a disability.
What are the main 4 suggestions of the MoH food and nutrition guidelines?
- Enjoy a variety of nutritious foods every day: Plenty of fruit & vege. Plenty of breads and cereals (wholegrain). Some milk and milk products, low and reduced fat. Some legumes, nuts, seeds, eggs, poultry, red meat with fat removed.
- Choose and prepare foods and drinks with minimal added (sat) fat, low in salt (iodised salt preferable) and with little added sugar
- Make plain water your first choice
- If you drink alcohol, keep intake low.
Why is the recommendation to eat a variety of nutritious foods in place?
- Veges and fruit provide vit. C, A, K, phytochemicals, minerals, fibre
- Wholegrains contain fibre, vit. B, E, minerals, carbs, protein, phytochemicals, protect against cancers, obesity, CVD
- Dairy protects against osteoporosis
- Legumes contain protein, minerals, vit. A, E, fatty acids- protect against cancer, diabetes, CVD
Why is the recommendation to prepare your own food/drink or to choose carefully in place?
- Difference in energy density of preprepared foods- more easy to overeat
- NaCl is bad for hearts, kidneys, blood vessels
What are the branches of the celiac artery?
Left Gastric (runs superiorly) Common Hepatic (runs right) Splenic (runs left)
Where do the main abdominal arteries branch from the aorta?
Celiac- upper border of L1
SMA- L1
IMA- L3
What is the arterial, nervous, venous, and lymphatic supply of the foregut?
Artery- coeliac axis
Veins- Portal vein
Lymph- Pre-aortic nodes at T12 (pre-aortic)
Nervous- Coeliac plexus (T12)
What is the overall anatomy of the stomach? What is its blood supply?
The fundus of the stomach is located at aprox. rib 5/6, with the oesophagus coming in at the edges of costal cartilage 7 & 8. The distal end lies at the L1 vertebral level.
The stomach has multiple layers of muscle- outer longitudinal, middle circular, and inner oblique layers.
The lesser curvature is supplied by left and right gastric arteries, with the greater curvature supplied by left and right gastro-omental arteries, from the splenic and ch arteries respectively
The fundus is supplied by the short gastric artery, a banch of the splenic artery.
What is the anatomy of the duodenum, and what is its blood, lymph, venous and nerve supply?
It is divided into 4 parts:
1: superior (trans-pyloric)
2: Descending
3: Inferior
4: Ascending to duodenojejunal flexure.
part 1 is intraperitoneal, part 2-4 are retroperitoneal.
Arterial supply: Part coeliac, part SMA- sup half- superior pancreaticoduodenal artery. inferior half: Inferior pancreaticoduodenal artery.
Nervous: Sup: Coeliac plexus (T12) Inf: SMPlexus, L1
Venous: Sup: Portal vein. Inf: SMVein (then portal)
Lymph: Sup: Pre-aortic coeliac nodes (T12) Inf: Pre-aortic SMNodes (L1)
What is the neurovascular and lymph supply of the midgut? How is it divided, identified and how does it sit?
Supplied by SMA, SMV, SMP (L1) and SMN (L1)
Divided into Jejunum (identifiable by 1-2 arcades with long branches) and ileum (identifiable by multiple arcades with short branches)
Suspended by mesentery to allow ingress/egress of neurovascular structures.
What is the NV/lymph supply of the midgut small intestine?
- Jejunal and ileal arteries
- SMPlexus
- SMVein
- SMNodes
What is the meaning of the flexures in the large intestine? Where is the transition from midgut to hindgut?
- Hepatic flexure is related to the liver (RHS)
- Splenic flexure is related to the spleen (LHS)
- Transition occurs 2/3 along the transverse colon
What is the structure and function of the large intestine?
Has haustrae (sacculations of wall), appendices epiploicae (fatty tags), teniae coli (long. muscles continuous with small intestine muscles) and an appendix. Function is to absorb water and electrolytes, and store undigested material before its expulsion. The large intestine is found in almost all 9 parts of the abdomen (except the umbilical)
What are the different arterial supplies of the large intestine?
- Caecum and appendix- caecal and appendicular arteries
- Ascending colon- right colic artery
- Proximal 2/3 trans. colon- middle colic & marginal artery
- Distal 1/3 trans colon- marginal and left colic arteries
- Descending colon- left colic artery
- Sigmoid colon- sigmoid artery
NB marginal artery is anastomotic point between mid and hindgut- arteries after this come from L3 and so do veins, lymph etc.
What is the structure, function and supply of the rectum?
- Rectum pierces pelvic diaphragm to become anal canal. It is best sectioned into 3 parts:
- Sup. 1/3 is intraperitoneal, supplied by sup. rectal artery (IMA), drained by sup. rectal vein, supplied by IMPlexus and IMNodes.
- Mid 1/3 is retroperitoneal & supplied by middle rectal branch of internal iliac artery & drained by mid. rectal vein (goes to common iliac and IVC)
- Inf. 1/3 is infraperitoneal & supplied by inferior rectal branch of internal pudendal artery, drained by inf. rectal vein (goes to common iliac and IVC)
Both are supplied by inf/sup hypogastric nerve plexus and have lymph to internal iliac nodes
What is the portal system?
The Splenic and SM veins drain into the portal vein, going to the liver. The IMV joins the splenic vein beforehand, to prevent it being squished. The portal vein is formed at level L1 in the trans-pyloric plane.
What is the nervous supply of the gut?
- Parasymp- vagus nerve, pelvic splanchnic nerves (S2-4)
- Sympathetic- ganglion chain using thoracic, lumbar and sacral splanchnic nerves- but only exiting the chain from levels T5-L2.
What is the autonomic supply of the gut regions?
F: Greater splanchnic nerve (T5-9), Vagus nerve
M: Lesser Splanchnic nerve (T10-11), Vagus nerve
H: Lumbar/Sacral splanchnic nerve (L1-2), Pelvic splanchnic nerve (S2-4)
Why is abdominal pain referred and where do the different regions refer pain to?
Pain is referred, as the visceral afferents return to the plexus and chain before being sent up the spinal cord. The brain doesn’t know where it’s coming from as it thinks it’s a somatic nerve- just uses the dermatomes of the spinal nerves to refer it and diffuse the pain between the contributers.
Foregut- pain to epigastric region
Midgut- pain to umbilical region
Hindgut- pain to suprapubic region
What is the pathology of appendicitis pain referral?
Initially, broad diffused pain from midgut (referred to to umbilical region).
Eventually, appendix gets so large that it touches the parietal peritoneum and the nociceptors for that specific dermatome ar initiated as parietal peritoneum has somatic sensory supply- pain is low acute in the right inguinal region.
What are the general layers of the gut tube and what are their structures and functions?
Luminal: Mucosa. Consists of:
- Epithelium- offers protection (physical or chemical), secretion and absorption. It receives its nutrients via diffusion from the lamina propria
- Lamina Propria- supports the epithelium, and is the functional layer- has blood vessels, lymphs and nerves. It consists of connective tissue fibres (collagen etc)
- Muscularis mucosae: Inner circular/outer longitudinal layers of muscle that produce micro-movement of the mucosa separate to the muscularis externa.
Submucosa: Like lamina propria, but larger scale
Muscularis externa: Responsible for coordinated contraction and relaxation of inner circular and outer longitudinal layers- peristalsis. Rezuires narrowing and shortening of tube. Stomach has 3 layers. Mostly all smooth muscle (apart from oesophagus- some skeletal)
Adventitia/serosa: Adventitia is outermost connective tissue when the structure touches other structures. Serosa is the visceral peritoneum, which covers the structure when it is only in contact with ‘empty’ space.
What is ascites and peritonitis?
Ascites- accumulation of fluid (peritoneal) causing abdominal swelling, pressure and distortion of organs
Peritonitis- physical, chemical, bacterial trauma to peritoneum causes inflammation
What are the different types of salivary secretory cells and what are their structures and functions?
Serous acinus- contains myoepithelial cells, which have contractile properties for squeezing out secretions. They contain zymogens, or pre-enzymes, which form the enzyme amylase. They produce watery secretions
Mucous acunus- cells resemble goblet cells, with nuclei squished along the bottom to make room for mucus granules. Produces mucus to lubricate.
What is special about the ducts of the salivary glands?
They appear striated, as they are packed with mitochondria. This is to help them with active transport, of Na+ and Cl- in, and HCO3- and K+ out, forming an effective buffer.
What are the salivary glands, and what cell types do they have?
Sublingual- mostly mucus
Submandibular- mixed
Parotid- mostly serous
What is the composition and function of saliva?
- 99% water
Also has some carb-rich glycoprotins called mucins: lubrication, protection from bacterial adhesion
Bicarbonate ions- counteract bacterial secretions, protect against acidity of vomit
Lysozyme- breaks bacterial cell walls
Lactoferrin- counteracts iron-dependent bacteria
Immunoglobulin A- counteracts general bacteria and viruses
Also some digestion through amylase (sugars), lipase (fatty acids), Haptocorrin (binds and protecte B12) and Kallikrein (a cascade to increase salivary blood flow)
What is the function of the oesophagus? What is unique about it?
Rapid transport of food to the stomach
Contains skeletal muscle in upper third for voluntary control of swallowing
Epithelium is thick and stratified squamous for sacrificial epthelium
Submucosa is loose to permit compression and expansion of main tube during swallowing
What are some problems that can occur with the oesophagus?
Oesophageal varices- liver cirrhosis can lead to portal backflow, so blood accumulates in the oesophageal arteries- can cause haemorrhage
Reflux oesophagitis- acid reflux causes damage to the oesophagus- loss of epithelia continuity and increased lymph tissue size. Can flow into barrett’s oesophagus, where there is a semipermanent transition from squamous to glandular epithelium- this can also cause cancer
How can nutritional status be assessed?
- diagnosis, screening, intervention, monitoring, policy setting, programme evaluation and nutritional surveillance
Why is nutritional status important? How does it affect medicine?
1/3 patients admitted to hospital are malnourished, assoc. with higher morbidity, infections, complications, mortality, treatment requirements, longer hospital stays and greater cost, as well as lower healing, convalescence and quality of life.
We ask about it for past medical and family history, in terms of medications to prevent drug interation, a diet or social history, a systems review, during a physical exam, for laboratory evaluation, and as part of assessing and planning treatment.
What is the ABCDE of nutrition assessment?
A- Anthropometric (weight, height/arm span, circumferences, percentage weight loss, body composition, distribution of body fat)
B- Biochemistry- detects subclinical or marginal deficiencies, gives support to other data, gives response to supplementation, checks nutrients in blood or urine
C- Clinical- signs and symptoms, measurement of functional status and oral health, cognitive, drug use
D- Dietary evaluation- measure food and beverage intake compared to dietary requirements, food consumption patterns, supplement usage, feeding practices and food security. Compare to recommended dietary intakes, guidelines and plate/pyramid models
What are the methods of assessing diet?
Food history
Food frequency questionnaire
24 hour recall
Food records
What are the different methods of evaluating anthropometry?
BMI
Percentage age weight loss (Usual weight-current weight)/usual weight (x100)
Body composition- fat + lean tissue, cell mass + excell mass + fat, bone + protein + H2O + fat
Distribution of body fat- waist: hip ratio, waist circumference
What are the three phases of swallowing, and their descriptions?
Oral phase- voluntary, requiring soft palate elevation, and movement of the tongue posteriorly to prevent regurgitation. Has a prep phase (chewing, positioning bolus) and a transfer phase
Pharyngeal phase- Controlled reflexively, to protect the airway and any further propulsion. Involves elevation of larynx and closure of vocal cords to close mouth and airways (upper & lower)
Oesophageal phase- transfer of food bolus from UES to the LOS. Combines primary (initiated by swallowing) and secondary (reflexive- peristalsis from stretch)
How is swallowing controlled?
By both cortex and brainstem
Swallowing centre receives input from psot. mouth and upper pharynx. Swallowing muscles innervated via cranial nerves
What are the oesophageal sphincters?
Upper- prevents entry of air into stomach and reflux into pharynx during peristalsis. Consists of cricopharyngeus, inf. pharyngeal constrictor and cervical oesophagus
Lower: near squamocolumnar junction, specialized smooth muscle, can relax transiently (regular intervals in upright position to release air from stomach)
How does peristalsis get innervated?
ANS innervation, from submucosal and myenteric plexuses
What is GORD, why does it occur and what happens?
Gastro-Oesophageal reflux disorder is the movement of gastric contents into the oesophagus, which erodes it. It occurs due to transient LOS relaxation. This can be due to a hypotensive muscle sphincter (drugs, food), a hiatus hernia (loss of sphincter support due to stomach herniation through the diaphragm) and impaired oesophageal peristalsis, reducing clearance.
It causes heartburn, regurgitation and a sour taste in the mouth- worse after lying down/eating
It can cause peptic stricture due to fibrosis, barrett’s oesophagus and cancer
What is Barrett’s oesophagus?
Formation of columnar epithelium in lieu of squamous epithelium within the oesophagus due to repeated acid exposure- secretes alkaline substances. This also increases the patient’s risk of adenocarcinoma.
What are the two types of oesophageal cancer?
Adenocarcinoma- promoted by barretts, in LOS region
Squamous cell carcinoma- caused by smoking, alcohol, diet- more likely proximal
What are some common structural disorders of the oesophagus?
Ring/Web- mucosal membrane found distally
Zenker’s diverticulum- Excessive pressure on pharynx causes balooning, and trapping of food there
Stricture- narrowing of oesophagus due to fibrous scar formation
Oesophageal candidiasis- white plaques form on oesophagus
Ulcers
Eosinophilic oesophagitis- allergy mediated as eosinophils infiltrate it
What are some common motility disorders of the oesophagus?
- Dysphagia (difficult swallowing)
- Achalasia- degeneration of oesophageal nerves- loss of distal peristalsis, failure of LOS to relaw
- Diffuse oesophageal spasm: simultaneous onset of oesophateal contractions, can cause chest pain
- Nutcracker oesophagus- v. high amplitude contractions
- Scleroderma: Damage to submucosa, causing no movement of oesophagus- no peristalsis, no LOS tone, severe reflux
What are the main functions of the stomach?
Acts as a reservoir for food, and is able to release it in closely controlled bursts as chyme
Adjusts osmolarity of its contents before their release into the SI
Antrum is a sort of ‘grinding mill’ regulating particle size into the duodenum
Acid, IF, pepsinogen, mucus, prostaglandin, HCO3- secretion
How is gastric emptying usually controlled, and what can go wrong with it?
Controlled by feedback from the duodenum regarding its acidity, fats, amino acids and osmolarity.
It requires an intact antrum, pylorus and duodenum, as well as normal vagal and hormonal function
Rapid gastric emptying occurs typically after gastric surgery or when taking prokinetics.
This is largely due to a dilated duodenum & jejunum causing the presence of large, hyperosmolar food particles in the small bowel causing more chyme to be drawn into the duodenum, and more water, causing diarrhoea, vomiting, cramping with eating.
Delayed gastric emptying id due to deficiency in the vagal nerve. It causes a variable rate of glucose absorption and abdominal discomfort, as well as bloading and early satiety
What does gastric acid do? How is it regulated?
Gastric acid sterilizes the stomach (except H. pylori)
Denatures proteins
Helps with B12/Fe absorption
Regulaged by a negative feedback loop:
Acid is produced by parietal cells. Parietal cells are stimulated by ECL cells, which secrete histamine to activate parietal cells. These are stimulated by G cells which secrete gastrin. D cells secrete somatostatin to inhibit G cells, and they are stimulated by low pH.
Achlorhydria (low/absent gastric acid) can allow bacterial overgrowth, a decreased absorption of Fe, and increased infection risk.
ACh from the vagus nerve also stimulates parietal, ECL and G cells, which in turn is caused by stomach distension, as well as the sight, thought or smell of food.
What do the parietal cells do and how are they protected?
They produce acid by taking in Cl- from the blood in exchange for HCO3-, and sending out H+ in exchange for K+.
They are protected by HCO3- rich mucus on the surface of the stomach. These protect the gastric epithelium. If the mucus is not present, the stomach is exposed to its acid and ulcers can form. If it isn’t replenished, healing said ulcers is also much harder
What can cause abnormal secretion of gastric acid?
Increased- Either H pylori in gastritis or gastrin producing tumors
Decreased- loss of parietal cells, as in pernicious anaemia, vagotomy or some drugs.
What is the role of CCK and secretin in digestion?
Both inhibit gastric acid secretion and gastric emptying
CCK releases pancreatic enzymes and bile
Secretin stimulates HCO3- from the pancreas and bile ducts
What is the pathology of a peptic ulcer? IE causes, transmission, effects, treatment, side effects
Caused by H pylori infection, which is acquired in childhood and leads to lifelong infection and chronic gastritis. It’s associated with childhood living conditions
It is infected orally-orally, usually by sharing food
It typically infects the antrum, and is often asymptomatic. However, if the ulcer develops it forms a cavity due to the erosion of the mucosa- it can cause bleeding if it perfs a vessel. It presents as burning epigastric pain, worse during and after eating, as well as possible bleeding and upper digestive tract obstruction
Treated by eradicating with triple therapy antibiotics for 1 week, and has a low recurrence rate once successfully treated.
Can cause atrophic gastritis and achlorhydria, which can allow infection of bacteria and tumors to form.
What are the two types of gastric cancer?
Intestinal type is well differentiated cells with tubular pattern, more likely found in the antrum and associated with H.Pylori.
Diffuse type lack gland and have poor differentiation of cells, more likely associated with genetic factors
Patients present with discomfort, early satiety, pain after meals, anorexia and weight loss.
How is B12 absorbed in the body?
- CBl protein in food comes from the mouth, bound to Hepatocorrin to protect it from the stomach acid.
- CBl and HC are split in the duodenum
- IF secreted by parietal cells binds with CBl and all travel to ileum
- Taken up by receptors on the brush border of the ileum, and IF is released once they are in the cell
Then either: Transported via HC to the liver, where B12 is recycled in the bile via enterohepatic circulation
OR
CB takes it to cells where it is required for DNA synthesis
What is the pathology of Folate/B12 deficiency, and how can you tell these apart?
Both present as anaemia, with macrocytosis of RBCs, presenting as high mean cell volume. However, folate deficiency does not show degeneration of the spinal cord as B12 does.
Decreased B12 causes decreased methylation ability, resulting in decreased DNA reproduction- so cells with a high turnover will be negatively affected
What is required to absorb B12 and what test can you do to figure out where the issue is?
Requires- Acid to release CBl from food
- IF secretion from parietal cells
- Normal pancreatic secretion
- Normal ilial function
Can perform schilling test- give radioactive B12, and fill receptors by injecting normal B12 intramuscularly. Measure B12 in urine- not a stomach issue if B12 is bound to IF
If IF isn’t normal, test for ileal dysfunction by repeating with oral IF and seeing if it’s fixed by this
How do you determine whether B12 deficiency is due to an autoimmune disorder or not?
Most likely pernicious anaemia/autoimmune gastritis:
- Check for antibodies to parietal cells and intrinsic factor, for a low acid output (visible if gastrin is high) and evidence of other autoimmune diseases
How do you treat B12 deficiency?
Needs replacement in high doses- 1000ug every week for 4-6 weeks.
If not a dietary depletion, then needs maintenance of 1000ug every three months
Why does terminal ileal resection cause B12 deficiency?
Loss of ileal receptors- Failure to absorb B12, bile salts
Bile salts can also irritate the colon and impair the absorption of fats
Why does partial gastrectomy cause B12 deficiency?
Loss of gastric acid secretion so B12 in food can’t be released
Atrophic gastritis (bile reflux)- causes loss of parietal cells and IF secretion
Failure of normal stimulation of pancreas
What are the key functions of fats?
Energy/fuel source
Required for fat-soluble vitamin transfer
Provide essential fatty acids
Important for insulation/protection
What are the different types of fats and their structures?
Triglycerides (fatty acids) - Polyunsaturated (many double bonds) - Monounsaturated (one double bond) - Saturated (no double bonds - Trans (previous double bonds filled) Unsaturated fats are liquid at room temperature, with mono less susceptible to spoilage. Saturated fats are always at room temperature
Sterols
- only found in animal foods. Multiple ring structure
Create bile acids, sex and adrenal hormones, vit D and cell membranes
The liver produces 80% of our cholesterol per day, and a buildup in our arteries causes atherosclerosis.
What is the process of fat digestion?
Lingual lipase from mouth begins digesting fats
Gastric lipase hydrolyzes a small amount of fat in the stomach
Bile emulsifies the fat, which is then further split into monoglycerides, glycerol and fatty acids by pangreatic and intestinal lipase
In the large intestine, some fat and cholesterol exit via feces.
How is fat transported?
Small molecules cause micelles bind to large lipids to transport them across the apical membranes of the cells. They are then repackaged into chylomicrons, which are small and dense. They run in the bloodstream, giving off fatty acids to cells that need them, before remnant chylomicrons are endocytosed by the liver.
From here it can be stored or send out via:
Reverse transport pathway: HDL produced in liver, deliver cholesterol to tissues needing it
Endogenous Pathway: LDL produced in liver, drop off fatty acid and are taken back up by LDL receptors
What are the recommendations regarding fat in the diet?
Limit sat/trans fats to less than 10% of daily energy intake
Fats as a whole should make up approx. 20-35% of energy intake
Select low fat options and lean option, and minimize processed fats.
What is the structure of a chylomicron compared to other lipoproteins?
Chylomicrons contain a large amount of triglycerides, with barely anything else
VLDL contain mainly triglycerides
LDL contain mainly cholesterol
HDL contain mainly protein
What are the adaptations of the small intestine to maximise surface area?
Have plicae circularie- macroscopic folds in the wall of the intestine
Plicae are covered with villi, which in turn are covered in microvilli
What are the features of a villus and how are they adapted for absorption?
Villi have intestinal glands (crypts of lieberkuhn) beneath them, and project into the lumen of the intestine
The contain within them a lacteal, with smooth muscle fibres from the muscularis mucosae surrounding it in order to milk the lacteal.
There is also a small capillary with arteriole and venule (to the portal vein) within each villus.
In the elderly, decreased blood circulation can lead to malabsorption and potentially malnutrition as a consequence of this.
What are the main epithelial cells found within the small intestine? What are their functions?
Columnar absorptive cells (enterocytes)- their cell membranes contain enzymes that can be digestive (eg. glycosidases) or that activate other enzymes- eg. enterokinases or enteropepsins.
They have microvilli, and are covered with glycocalyx- this is enriched with glycoproteins, and acidic mucopolysaccharides. It forms a selective barrier which attracts desirable things (ie what its enzymes work on) and repels unwanted things
The actin within the cel is connected to its cytoskeleton, which helps to move the microvilli in a wave formation along with the villi themselves.
Goblet cells: Secrete mucus
Enteroendogrine cells- secrete CCK, sterotonin and somatostatin
Undifferentiated cells- generates new epithelium
Paneth cells- Mainly defence, through TNF and lysozymes
What are the roles of CCK, Serotonin and somatostatin in the small intestine?
CCK: Give negative feedback to stomach, reducing gastrin
Promotes enzyme release from the pancreas
Causes gall bladder to contract and release bile
Secretin- give negative feedback to stomach to decrease gastrin. Causes ductal cells in biliary tree to make and secrete HCO3-
Somatostain- causes decreased gastrin, increases absorption and increases smooth muscle contraction in the small intestine.
What are the special features of each section of small intestine?
Duodenum: C shaped, 25cm. Contains submucosal glands, which secrete HCO3- rich mucus, called brunner’s glands. They decrease in number throughout the small intestine.
Jejunum: 2.5m, suspended by mesentery. Have increased numbers of plicae for absorbing and digesting
Ileum: 3.5m, with very large lymphatic aggregates which appear red under the naked eye (called peyer’s patches). Main function is defense, as there are many bacteria next door in the Large intestine.
What is the structure and function of the lining of the large intestine?
Mucosa is smooth, with no villi, but has mucosal glands. These contain mainly columnar absorptive cells with a brush border (for vitamins, water and electrolytes) and goblet cells, secreting mucus for lubrication.
The lamina propria contains many lymphatic nodules
Muscularis externa contains outer longitudinal layer in three distinct bands (teniae coli), which segment the colon into haustra (for different rates of absorption and segmentation)
What is the transition in muscle and epithelium in the rectum/anus?
Epithelium moves from columnar epithelium to stratified squamous at the transverse folds
The internal anal sphincter is smooth muscle, while the external is skeletal muscle.
How do the rates of and movements of differentiating cells change in the different gastric regions?
Oesophagus: cells from basal parts move upwards, changing over days
Stomach: cells move upwards over days, and downwards over weeks/months
Small intestine: cells move upwards over days, and downwards over weeks/months
Large intestine: cells move upwards to replace others over days
