PBL 4 week 4 pbl xx gi block

Question Answer
How long is the large intestine? 1.3m
Give the functions of the large intestine storage of food residues prior to their elimination, secretion of mucous, which lubricates the faeces to ease their passage, absorption of most of the water and electrolytes remaining in the residue
what is different about the longitudinal smooth muscle of the large intestine? it's thickened to form longitudinal bands called taeniae coli. The tone of the smooth muscle in the taeniae causes the wall of the large intestine to pucker into pocket-like sacs called haustra
What are the ascending and descending colon closely attached to? the posterior abdominal wall (retroperitoneal)
What is the transverse colon attached to? the posterior abdominal wall by a short mesentery
What is suspended from the lower border of the transverse colon? the greater omentum, a large apron-like sheet of mesentery that contains fat
what does the superior mesenteric artery supply? ascending colon and first part of transverse colon
what does the inferior mesenteric artery supply? remaining part of transverse colon, descending colon and rectum
What's the caecum? the caecum is a blind ended tube about 7cm long leading from the ileocecal valve to the colon
what's the role of the caecum in humans? no significant digestive role
what attaches to the posteromedial surface of the caecum? the vermiform appendix, a small blind pouch about the size of a finger, containing lymphoid tissue
where does the vermiform appendix attach to? posteromedial surface of the caecum
what is inflammation of the appendix known as? appendicitis
what does the rectum form? The last 15cm of the digestive tract
what is the rectum? an expandable organ for the temporary storage of faeces
what triggers the urge to defecate The movement of faecal material into the rectum triggers the urge to defecate
what's the last portion of the rectum called? the anal canal
what does the anal canal contain? small longitudinal folds called anal columns
what's on the distal end of the anal columns? the columnar epithelium becomes stratified squamous epithelium
what's the exit of the anal canal? the anus
what happens to the epidermis at the anus? there the epidermis becomes keratinised and identical to the surface of the skin
what sort of muscle and control does the internal anal sphincter have? smooth muscle, involuntary control
what sort of muscle and control does the external anal sphincter have? skeletal muscle, voluntary control
what is the diameter of the colon like in comparison to the small intestine? about 3x that of the small intestine, but its wall is much thinner. NO VILLI
what sort of cells does the colon have a lot of? many mucous cells (goblet cells) – the mucous provides lubrication as the faecal material becomes drier and more compact
does the mucosa of the large intestine produce enzymes? No, any digestion from enzymes will have been from the small intestine
are the motility movements of the large and small intestine similar? movements of the colon are similar to the small intestine but at a slower pace
what are the propulsive movements of the colon like? since the colon functions to store food residues and absorb water, the propulsive movements are relatively sluggish
what sort of movements are seen in the distal parts of the colon? short range peristaltic waves are seen in the distal parts of the colon
what are mixing movements called? haustrations
what are the mixing movements like in the colon? segmentation movements that mix the contents of the adjacent haustra.
what's the purpose of haustration? to squeeze and roll the faecal material around so that every portion of it is exposed to the absorptive surfaces of the colonic mucosa, thus aiding the absorption of water and electrolytes
mass movements in the large intestine? several times a day, a vigorous propulsive movement of the colon occurs in which a portion of the colon remains contracted for rather longer than during a peristaltic wave. It results in the emptying of a large portion of the proximal colon
what are mass movements initiated by? intrinsic reflex pathways resulting from distension of the stomach and duodenum (gastrocolic reflex)
does the colon have a typical pacemaker activity? the colon has no typical pacemaker activity. it's mainly a mixture of short duration and long duration contractions controlled by parasympathetic nerve fibres
list the roles of the colon mix material without propulsion (for max water absorption), act as a storage site, cause aboral movement of content, expel faeces
what's the transmit time for the caecum to the rectum? 1-2 days, with the transit being the slowest at the caecum
do men or women have a shorter transit time? men have a shorter transit time than women, therefore increased faecal weight in men (higher water content)
what drugs reduce colonic motility? opiates (u receptors), anticholinergics, loperamide
what drugs increase colonic motility? laxatives, prucalopride (treats chronic constipation), linaclotide
what's a mesentery? a fold of tissue that attaches organs to the body wall. The word mesentery usually refers to the small bowel mesentery, which anchors the small intestines to the back of the abdominal wall.
what branches through the mesentery and why? Blood vessels, nerves, and lymphatics branch through the mesentery to supply the intestine.
what's the caecum? a pouch connected to the junction of the small and large intestines
name the different parts of the large intestine the ascending colon including the caecum and the appendix, the transverse colon including the colic flexures and transverse mesocolon,The descending colon, The sigmoid colon – the s-shaped region of the large intestine.
what's haustra? the small pouches caused by sacculation (sac formation), which give the colon its segmented appearance. The teniae coli run the length of the large intestine.
what does the gastrocolic reflex involve? It involves an increase in motility of the colon in response to stretch in the stomach and byproducts of digestion in the small intestine.
approximately how many litres of fluid are ingested each day? 2 litres
how many litres of fluid is in the gut and what does this consist of? salivary secretions, gastric secretions, bile, pancreatic secretions and intestinal secretions all add up to about 9000mL of total fluid in the gut
how much fluid is reabsorbed in the small intestine? 8000mL
how much fluid does the colon absorb? 1250mL
how much water is lost in faeces? 100-150mL
what happens to most electrolytes? most electrolytes are actively absorbed along the length of the small intestine, though the absorption of calcium/iron is restricted mainly to the duodenum
what can sodium flow through? sodium can passively flow through an iron channel, and, since water follows sodium, it helps the absorption of the majority of water throughout the intestines
what is there on the basolateral side? a Na+/K+ pump actively pumping sodium out of the enterocytes and into the blood, thus keeping a constant gradient for sodium to passively flow through at the apical end
How can sodium act as a co-transporter? helps to transport other things like amino acids, peptides, bile salts and vitamins into enterocytes via active transport. The sodium gradient provides energy for active transport of minerals, vitamins and metabolites
what type of porter is sodium? sodium is also an antiporter with H+ ions
what is sodium required for? Sodium is required for the transport of glucose into cells via the SGLT1 transporter. Glucose can then enter the blood via GLUT2 receptors on the basolateral surface
how is potassium absorbed? Potassium K+ moves passively along a concentration gradient set up by the absorption of water
what does the CFTR transporter do? pumps chloride into the lumen and this is due to the presence of bacteria (e.coli) which release heat stable enterotoxin that activate on an intracellular cascade (mainly cAMP/PKA) to signal the CFTR on the apical plasma membrane
how else is chloride absorbed into the cell? via a chloride-bicarbonate antiporter
what's an antiporter? a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions.
how do the bacteria live in the large intestine? live symbiotically within their human host. symbiotic refers to any diverse organisms that live together, but in this case, the relationship is not necessarily beneficial to both.
Give two examples of anaerobic species that live in the large intestine Clostridium perfringens and Bacteroides fragilis
Give a function of the intestinal flora Fermentation of indigestible carbohydrates (notably cellulose) and lipids that enter the colon. As a result of these fermentation reactions, short-chain fatty acids are produced, along with a number of gases which form about 500mL of gas each day
Give some gases that are produced as a result of flora fermentation reactions hydrogen, nitrogen, carbon dioxide, methane, hydrogen sulphide
what are short chain fatty acids absorbed by? Give some examples SCFA, including acetate (2C), propionate (3C), and butyrate (4C), are absorbed readily by the colon, stimulating water and sodium uptake at the same time
what are the intestinal bacteria able to synthesise? vitamin K
what do the colonocytes utilise the short chain fatty acids for? energy
does the upper gut have a high or low population of bacteria? very low populations
why does the upper gut have a very low population of bacteria? due to a range of factors including gastric acidity, propulsive motility, and pancreatic enzymes
how does the large intestine keep the contents in the proximal colon for long periods? has very stagnant motility with retropulsive contractions
what is the pH of the colon buffered by? bicarbonate secretion – this allows a large and complex bacterial ecosystem to develop
what is most of the contents of the colon? bacteria
how many different species of bacteria are in the colon? Up to 400 different species in the colon and the vats majority (99.9%) are strict anaerobes
what happens in the proximal colon? Fermentation chamber, absorption
what happens in the distal colon? storage and absorption
what are the absorptive mechanisms in the proximal colon? greater capacity, 95% chloride dependent Na transport
what are the absorptive mechanisms in the distal colon? Chloride dependent Na transport, amiloride sensitive
give luminal characteristics of the proximal colon liquid, pH 5-7, higher SCFA, active bacterial metabolism, carbohydrate fermentation, H2 production
give luminal characteristics of the distal colon semisolid, pH more than 7, less bacterial activity, amino acid fermentation, methane production
what's diarrhoea? Diarrhoea is an increase in the volume of stool (200mL or above) or frequency of defecation (3 or more watery or loose stools per day)
what's osmotic diarrhoea characterised by? Increase in amounts of poorly absorbed osmotically active solutes such as carbohydrates/magnesium sulphate. This causes decreased intestinal absorption, increasing the amount of water and Na+ in the lumen
when does osmotic diarrhoea basically occur? when too much water is drawn into the bowels. If a person has excessive salt in the diet which isn't fully absorbed, these can draw water from the body into the bowels, causing osmotic diarrhoea
why might a person have excessive salt in the diet which isn't fully absorbed? this could be due to malabsorption or some sort of malabsorptive disease, e.g. coeliac disease. It can also be caused by pancreatic insufficiency, short bowel syndrome and inflammatory disease
what characterises secretory diarrhoea? an increase in active secretions and a decrease in absorption which is mainly due to the presence of bacterial enterotoxins
what do bacterial enterotoxins do? stimulate the release of anions, especially chloride ions. Therefore, to maintain a charge balance in the lumen, sodium is carried with it, along with water
What does E.coli do? Produces a heat labile toxin, which acts on the crypt cells (secretory) and hence causes increased secretion of chloride, sodium and water. This toxin also loosens the tight junctions between enterocytes (leakage of water) and cause intestinal vasodilati
what characterises inflammatory diarrhoea? exudation of mucus, blood and protein from sites of active inflammation into the bowel lumen. This is due to the damage of the intestinal mucosal cells, resulting in the loss of blood and fluid
what is inflammatory diarrhoea caused by? Inflammatory bowel disease – Crohn's disease, ulcerative colitis
Give some other causes of diarrhoea Virus (norovirus and rotavirus), and protozoa/parasites – giardia (giardiasis is the most common parasitic infection in humans)
describe the norovirus affects people of all ages, transmitted by faecally contaminated food or water (faecal and by person to person contact). It causes 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world
describe the rotavirus major cause of death and illness in infants in developing countries. Virus replicates in intestinal epithelial cells, infected cells damaged, leaves immature cells with dec absorptive capacity for sugar, water, and salts, so fluid accum in lumen so diarr
what does raised urea and creatinine suggest? a lowered GFR (kidney impairment). The GFR is reduced because of blood volume depletion
if urea increase is much higher than the creatinine then what does this suggest? suggests the kidneys are not receiving a proper blood supply, rather than intrinsic damage. Serum urea is higher, especially at low flow rates, because the kidneys reabsorb urea whereas creatinine is not reabsorbed
why would potassium be low? due to excessive loss from diarrhoea
7 things to reduce spread of infection aseptic technique, hand washing, cleaning and disinfection of wards, regular cleaning of toilets, waste disposal, educate patients, patient isolation
give three viruses that cause acute watery diarrhoea (dehydration) v.cholerae, e.coli, rotavirus
what causes bloody diarrhoea (dysentery) – intestinal damage, nutrient loss shigella
give five measures to prevent diarrhoea infection rotavirus and measles vaccinations, early breastfeeding and vitamin A supplementation, hand washing with soap, improved water quality, community wide sanitation promotion
what's osmolality the conc of a solution expressed as the total number of solute particles per kg (osmolarity is the same thing, except solute particles per litre)
what does high osmolality of a body compartment do? draws water into that compartment i.e. water will move towards more concentrated solutes
what does high osmolality in the blood result in? cellular dehydration, since water is drawn from the cells and into the blood.
what does low osmolality in the blood do? due to water being drawn into cells results in cellular over hydration and oedema. target is to have iso-osmotic compartments (where both compartments have equal osmotic pressure)
what are colloids? give an example molecules with a relatively large mollecular weight (nanograms) e.g. albumin
what are crystalloids? these are water and electrolytes (much smaller) e.g. saline and dextrose
what is normal saline 9g of NaCl in 1000mL.
what is saline 0.9% used to do? replace fluid and electrolytes. it is iso-osmotic with the normal blood concentrations. Therefore it is given to increase the amount of fluid in the blood vessels without changing the balance of electrolytes in the body.
what does dextrose contain? half amounts of NaCl as saline 0.9% + the dextrose sugar. The sugar can be absorbed and utilised by the body. Once its absorbed, there is just fluid remaining, so it is hypo-osmotic (initially iso-osmotic)
when is sodium bicarbonate 8.4% used and why? only used in emergencies because it is hyper-osmotic. it is used to manage cardiac arrest, metabolic acidosis, hyperkalaemia
fraction of colloids that remain intravascular after infusion? initially nearly 100%
fraction of saline that remains intravascular after infusion? 25%
fraction of dextrose that remains intracellular after infusion? 10%
what antiporter is there on cell surfaces? a K+/H+ antiporter. Therefore when patients have some acidic condition like metabolic acidosis) we should always think about the potassium levels
what does alkalosis lead to to do with potassium? hypokalaemia
what does acidosis lead to to do with potassium? hyperkalaemia
whats the max potassium conc for peripheral administration 40mmol/L
whats the max rate of potassium infusion? 10mmol/hr: faster only if cardiac monitoring/central lines are available (up to 20mmol/hr)
what must happen to potassium before it's administered? must be diluted as it is lethal otherwise

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