case 4 Flashcards
What happens in the absence of food
occasional burst of intense activity called a
Migrating Motor Complex (M.M.C.) from
stomach - S.I. (stimulated by motilin) - Empties stomach of large particulates
- removes “sloughed off” epithelial cells
- prevents bacteria in colon moving into S.I
small intestinal reflexes
Ileogastric (“ileal Break”):
Glucose & Fat in ileum gastric motility
Gastro-colic:
gastric distension colon motility (defecation)
Gastro-ileal:
gastric distension ileal motility +
ileocaecal valve relaxes
Ileocaecal valve (between small and large intestine)
- normally closed
Opens – peristaltic wave reaches it
- as part of gastroileal reflex
opioids and gut function
Constipation = side effect of opiates • Opioid receptors (μ, δ, κ) in gut: enteric nerves, muscle & epithelia • Receptor activation: – Activates K+ channels – Inhibits Ca2+ channels – Inhibits cAMP production motility secretion
why does holistic care matter
Aid understanding of clinical problems
Improve relationship between healthcare
professionals and patients
Increase compliance
Increase satisfaction from patients and from
healthcare providers
Increasingly patient experience is used to develop
services and measure outcomes
what is palliative care
an approach that improves the quality of life of patients and their families facing the problems associated with life-threatening illness, through the prevention and relief of suffering by means of early identification and impeccable assessment and treatment of pain and other problems, physical,
psychosocial and spiritual.
what level is the duodenojejunal junction
L2
which parts of the large instestine are intra or retroperitoneal
Ceacum: intraperitoneal.–Appendix: intraperitoneal.–Ascending colon: retroperitoneal.–Transverse colon: intraperitoneal.–Descending colon: retroperitoneal in 2/3rds of humans.–Sigmoid colon: intraperitoneal.–Rectum: intraperitoneal.
what are epiploic appendages
small punches of peritoneum filled with fat.Along colon and upper part of rectum.Can become inflamed.
tenia coli
= 3 separate longitudinal ribbons of smooth muscle: mesocolic, free and omental coli.They contract lengtgwise to form hustra.
McBurneys point
name given to the point over the right side of the abdomen that is one-third of the distance from theanterior superior iliac spineto the umbilicus(navel).This point roughly corresponds to the most common location of the base of the appendix where it is attached to thececum
ileocecal valve
Remains closed most of the time.–Opens briefly to let the contents of the small intestine exit.–Closes again quickly to prevent any materials in the large intestine from leaking back.
functions of the colon
- Absorption of water and electrolytes from the chyme to form solid faeces.
- Storage of faecal matter until it can be expelled.
• The proximal half of the colon is concerned primarily with absorption.
• The distal half of the colon is concerned primarily with storage.
• Intense colon wall movements aren’t required for the functions of the colon, and so the movements of the colon are normally very sluggish.
lymphatic drainage of the abdominal organs
Sup/inf pancreatoduodenal, mesocolic, right L gastric, hepatic, splenic, sup inf mesenteric —coeliac–intestinal trunk–cisterna chyli–thoracic duct.
large intestine histology
Mucosa–Columnar epithelium- large number of mucus secreting goblet cells.–No villi. –Appendix= MALT.•Submucosa–Meissner’s/Submucosal Plexus. •Muscularis Propria–Circular & longitudinal muscles. –Myenteric (Auerbach’s) plexus. –Teniae coli- bands of outer longitudinal muscles.•Serosa
mixing movements (haustrations) - segmestation
2.5cm of circular muscle contracts, occasionally constricting the lumen closed. also the longditudinal musc - teniae coli contracts. This causes the unstimulated part to bulge out into haustrations. provide minor propulsions of colonic contents. after a few mins new haustral contractions occur so faecal material is dug into and rolled over-exposed tk mucosal surface and fluid are absorbed.
how much faeces in expelled each day
80-200ml.
propulsive movements/mass
in cecum and ascending result from slow haustral contractions. 8-15 hours to move chyme from ileocecal valve through colon. from cecum to sigmoid mass movements can take over propulsion. Only occur 1-3 a day.
Mass movement is modified peristalsis
sequence of events for mass movement
constrictive ring occurs in responce to distended part of colon, usually in transverse, rapidly, the 20 or more centimetres of colon distal to the constrictive ring lose their haustrations and instead contract as a unit, propelling the faecal material in this segment en masse further down the colon. When they have forced a mass of faeces into the rectum, the desire for defecation is felt.
small intestinal reflexes
- Ileogastric reflexes: distention of ileum leased to decreased gastric motility.
- Gastro-ileal reflexes: increased gastric distention leads to increased ileal motility and ileocaecal valve relaxes.
- The ileocaecal valve is normally closed. It opens (gastroileal reflex) when a peristaltic wave reaches it.
regulation of peristaltic contractions
slow waves determine frequency, basic electrical rhythm. Resting potential of -40 to -60mV. size of slow wave modulated nerves and hormones. contraction of smooth and striated muscle in intestinal wall will only occur if potential of slow wave exceeds threshold. then voltage gated Ca channels open inc Ca inc contraction.
interstitial cells of Cajal
pacemaker cells in GI. create slow waves that lead to contraction of smooth muscle.
modulation of slow waves
Food stimulates nerve and hormonal activity:
Increase or decrease size of the maximum depolarisation.
Nerves (intrinsic & extrinsic)
ACh, Substance P depolarisation (= contraction)
NO, VIP, opioids hyperpolarisation (= ↓ contraction)
Noradrenaline hyperpolarisation (= ↓ contraction)
Hormones
Motilin depolarisation (= contraction)
Secretin, G.I.P. hyperpolarisation (= ↓ contraction)
Adrenaline hyperpolarisation (= ↓ contraction)
enterochromaffin cells
main mechano and chemo sensory cells. Stimulation causes release of seratonin intracellularly, stimulates sensory nerves via 5-HT3 receptors. diff stimuli cause stim or inhibitory responses to parasymp NS. SERT removes seratonin to terminate signal.
defacation
most of the time rectum is empty because of A weak functional sphincter which exists between the sigmoid colon and the rectum, therefore preventing the entry of food into the rectum.
The sharp angulation at the junction between the sigmoid colon and the rectum that contributes additional resistance to filling of the rectum.
When a mass movement forces faeces into the rectum the desire to defecate occurs including reflex contraction of the rectum and relacation of anal sphincters.
how is continual dribble of feacal matter through anus prevented
by tonic constriction of:
1. An internal anal sphincter, a several-centimetres-long thickening of the circular smooth muscle that lies immediately inside the anus
2. An external anal sphincter, composed of striated voluntary muscle that both surrounds the internal sphincter and extends distal to it.
o The external sphincter is controlled by nerve fibres in the pudendal nerve, which is part of the somatic nervous system and therefore is under voluntary, conscious or at least subconscious control; subconsciously, the external sphincter is usually kept continuously constricted unless conscious signals inhibit the constriction.
defacation reflex-intrinsic
intrinsic reflex mediated by local enteric NS in rectal wall. When faeces enter the rectum, distention of the rectal wall initiates afferent signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing faeces toward the anus.
As the peristaltic wave approaches the anus, the internal anal sphincter is relaxed by inhibitory signals from the myenteric plexus; if the external anal sphincter is also consciously, voluntarily relaxed at the same time, defecation occurs.
The intrinsic myenteric defecation reflex functioning by itself normally is relatively weak.
parasympathetic defacation reflex
needed for effective defacation. involves sacral segments of the spinal cord. When the nerve endings in the rectum are stimulated, signals are transmitted first into the spinal cord and then reflexly back to the descending colon, sigmoid, rectum, and anus by way of parasympathetic nerve fibres in the pelvic nerves.
These parasympathetic signals greatly intensify the peristaltic waves as well as relax the internal anal sphincter, thus converting the intrinsic myenteric defecation reflex from a weak effort into a powerful process of defecation that is sometimes effective in emptying the large bowel all the way from the splenic flexure of the colon to the anus.
what other effects does defecation signals entering the spinal cord initiate
Taking a deep breath
Closure of the glottis
Contraction of the abdominal wall muscles to force the faecal contents of the colon downward and at the same time the pelvic floor is relaxed downward and pull outward on the anal ring to evaginate the faeces
how can defacation reflexes be purposfully activated
taking a deep breath to move the diaphragm downward and then contracting the abdominal muscles to increase the pressure in the abdomen, thus forcing faecal contents into the rectum to cause new reflexes.
• Reflexes initiated in this way are almost never as effective as those that arise naturally, for which reason people who too often inhibit their natural reflexes are likely to become severely constipated.
what influences rate of secretion of mucus
direct, tactile stimulation of the epithelial cells lining the large intestine and by local nervous reflexes to the mucous cells in the crypts of Lieberkühn.
• Stimulation of the pelvic nerves from the spinal cord, which carry parasympathetic innervation to the distal one half to two thirds of the large intestine, also can cause marked increase in mucus secretion.
This occurs along with increase in peristaltic motility of the colon.
what can emotional disturbances do to mucis
• During extreme parasympathetic stimulation, often caused by emotional disturbances, so much mucus can occasionally be secreted into the large intestine that the person has a bowel movement of ropy mucus as often as every 30 minutes; this mucus often contains little or no fecal material.
functions of mucus in the large intestine
Protects the intestinal wall against excoriation.
Provides an adherent medium for holding faecal matter together.
Protects the intestinal wall from the great amount of bacterial activity that takes place inside the faeces.
Plus the alkalinity of the secretion (pH of 8.0 caused by large amounts of sodium bicarbonate) provides a barrier to keep acids formed in the faeces from attacking the intestinal wall.
Diarrhea Caused by Excess Secretion of Water and Electrolytes in Response to Irritation
- Whenever a segment of the large intestine becomes intensely irritated, as occurs when bacterial infection becomes rampant during enteritis, the mucosa secretes extra large quantities of water and electrolytes in addition to the normal viscid alkaline mucus.
- This acts to dilute the irritating factors and to cause rapid movement of the faeces toward the anus.
- The result is diarrhoea, with loss of large quantities of water and electrolytes.
- But the diarrhoea also washes away irritant factors, which promotes earlier recovery from the disease than might otherwise occur.
where is Cl- secreted
- Electrogenic Cl- secretion occurs in crypts of both the small and the large intestine. • Cl- secretion is markedly stimulated by secretagogues such as ACh and other neurotransmitters.
- Cl- secretion is the major component of the ion transport events that occur during most diarrhoeal disorders.
three transport pathways on the basolateral membrane for Cl-
- Na-K pump
- Na/K/Cl cotransporter
- Two types of K+ channels (IK1 and BK1)
• In addition, a Cl- channel (cystic fibrosis transmembrane regulator (CFTR)) is present on the apical membrane.
how is the Cl- secretory system energized
by the Na-K pump, which generates a low [Na+]i and provides the driving force for Cl− entry across the basolateral membrane through Na/K/Cl cotransport.
• As a result, [Cl−]i is raised sufficiently that the Cl− electrochemical gradient favors the passive efflux of Cl− across the apical membrane.
consequence of the many transport processes
the transepithelial voltage becomes more lumen negative, thereby promoting voltage-dependent Na+ secretion.
• This Na+ secretion that accompanies active Cl− secretion presumably occurs through the tight junctions (paracellular pathway).
• Thus, the net result is stimulation of NaCl and fluid secretion.
what does Cl- secretion require
• Normally (i.e., in the unstimulated state), the crypts secrete little Cl− because the apical membrane Cl− channels are either closed or not present.
• Cl− secretion requires activation by cyclic nucleotides or [Ca2+], which are increased by any of several secretagogues:
1. Bacterial exotoxins (i.e. enterotoxins)
2. Hormones and neurotransmitters
3. Products of cells of the immune system (e.g. histamine)
4. Laxatives
K ion secretion
• Passive K+ secretion is the primary mechanism for net colonic secretion.
• Active K+ secretion is present throughout the large intestine and is induced both by aldosterone and by cAMP.
• K+ ions can be both passively and actively secreted.
• Active transport of K+ ions is subject to considerable segmental variation in the colon.
Whereas active K+ secretion occurs throughout the colon, active K+ absorption is present only in the distal segments of the large intestine.
Thus, in the recto-sigmoid colon, active K+ absorption and active K+ secretion are both operative and appear to contribute to total body homeostasis
active K+ secretion
Uptake of K+ across the basolateral membrane is a result of both the Na-K pump and the Na/K/Cl cotransporter (NKCC1), which is energized by the low [Na+]i that is created by the Na-K pump.
Once K+ enters the cell across the basolateral membrane, it may exit either across the apical membrane (K+ secretion) or across the basolateral membrane (K+ recycling).
The cell controls the extent to which secretion occurs, in part by K+ channels present in both the apical and the basolateral membranes.
When apical K+ channel activity is less than basolateral channel activity, K+ recycling dominates.
Indeed, in the basal state, the rate of active K+ secretion is low because the apical K+ channel activity is minimal in comparison with the K+ channel activity in the basolateral membrane. • Aldosterone stimulates active K+ secretion in surface epithelial cells of the large intestine, whereas cAMP enhances active K+ secretion in crypt cells.
In both cases, the rate-limiting step is the apical BK K+ channel, and both secretagogues act by increasing K+ channel activity.
how does aldosterone increase K+ secretion
increases passive K+ secretion by increasing Na-K pump activity and thus increasing electrogenic Na+ absorption.
The net effects are to increase the lumen-negative VTE and to enhance passive K+ secretion.
2. Second, aldosterone stimulates active K+ secretion by increasing the activity of both apical K+ channels and basolateral Na-K pumps
cAMP, Ca+ effect on K+
VIP and cholera enterotocin inc cAMP so stim K, Ca also stim active K secretion in both apical and basolateral channels.
• Because the stimulation of K+ channels is greater at the apical than at the basolateral membrane, the result is an increase in K+ secretion from the epithelial cell across the apical membrane.
• Stimulation of K+ secretion by cAMP and Ca2+, both of which also induce active Cl− secretion, contributes to the significant faecal K+ losses that occur in many diarrheal diseases.
absorption in large intestine: formation of feaces
- Most of the water and electrolytes in the chyme are absorbed in the colon, usually leaving less than 100ml of fluid to be excreted in the faeces.
- Nearly all the ions are absorbed, leaving only 1-5mEq each of sodium and chloride ions to be lost in the faeces.
- Most of the absorption in the large intestine occurs in the proximal half of the colon, giving this portion the name absorbing colon, whereas the distal colon functions principally for faeces storage until a propitious time for faeces excretion and is therefore called the storage colon.
absorptions of Na
activley transported, Na/k, Na/k/Cl, in ileum and LI. causes electrical potential gradiant which causes Cl absorbtion too. Tight junctions very tight so small back diffusion. • The overall electroneutral NaCl absorptive process is regulated by both cAMP and cGMP, as well as by intracellular Ca2+.
• Increases in each of these three intracellular messengers reduce NaCl absorption.
• Decreases in [Ca2+]I increase NaCl absorption.
• Decreased NaCl absorption is important in the pathogenesis of most diarrheal disorders.
Epithelial Na+ Channels and Distal Colon
- Epithelial Na+ channels are the primary mechanism of electrogenic Na+ absorption in the distal part of the colon.
- In electrogenic Na+ absorption, Na+ entry across the apical membrane occurs through epithelial Na+ channels (ENaCs) that are highly specific for Na+.
- These ENaCs are blocked by the diuretic amiloride (a potassium sparing diuretic).
- Na+ absorption in the distal part of the colon is highly efficient.
- Because this segment of the colon is capable of absorbing Na+ against large concentration gradients, it plays an important role in Na+ conservation.
- Na+ movement through electrogenic Na+ absorption is markedly enhanced by mineralocorticoids (e.g aldosterone).
- Aldosterone increases electrogenic Na+ absorption by increasing Na+ entry through the apical Na+ channel and by stimulating activity of the Na-K pump.
voltage dependant Cl absorption
o Cl− may passively diffuse from lumen to blood across the tight junctions, driven by the lumen-negative transepithelial voltage (paracellular route).
o Alternatively, Cl− may diffuse through apical and basolateral Cl− channels.
o This usually occurs in the jejunum, ileum and the distal colon.
electroneutral Cl HCO3 exchange
o In the absence of a parallel Na-H exchanger, electroneutral Cl-HCO3 exchange at the apical membrane results in Cl− absorption and HCO3 secretion.
o This occurs in the ileum, proximal colon and the distal colon.
parallel Na H and Cl HCO3 exchange
o Electroneutral NaCl absorption can mediate Cl− absorption in the interdigestive period.• Absorption of sodium and chloride ions creates an osmotic gradient across the large intestinal mucosa, which in turn causes absorption of water.
what is the maximum absorption capacity of the large intestine
• The large intestine can absorb a maximum of 5-8 litres of fluid and electrolytes each day
bacterial action in the colon
colon bacilli.capable of digesting small amounts of cellulose, in this way providing a few calories of extra nutrition for the body.
This source of energy is of little importance in human beings.
• Other substances formed as a result of bacterial activity are vitamin K, vitamin B12, thiamine, riboflavin, and various gases that contribute to flatus in the colon, especially carbon dioxide, hydrogen gas, and methane.
• The bacteria-formed vitamin K is especially important because the amount of this vitamin in the daily ingested foods is normally insufficient to maintain adequate blood coagulation.
composition of faeces
¾ water ¼ solid matter 30% dead bacteria 10-20% fat 10-20% inorganic matter 2-3% protein 30% undigested roughage from the food and dried constituents of digestive juices, such as bile pigment and sloughed epithelial cells
properties of faeces
• The brown colour of faeces is caused by stercobilin, a derivative of bilirubin.
• The odour is caused by products of bacterial action; these products vary from one person to another, depending on each person’s colonic bacterial flora and on the type of food eaten.
The actual odoriferous products include indole, skatole, mercaptans, and hydrogen sulfide
change in size of cells
Atrophy - cell shrinking
This may be achieved by apoptosis, reduced functional activity, loss of innervation, reduced blood supply, diminished nutrition, loss of hormonal or growth factor stimulation.
Hypertrophy - increase in size of existing cells
It is accompanied by an increase in functional capacity.
The number of cells doesn’t change, the cells just get bigger
change in number of cells
Hyperplasia - increased number of cells caused by an increase in cell division.
Aplasia - decreased number of cells.
change in differentiation
Metaplasia - this is an adaptive response to environmental stimuli
Specialised cell types change their pattern of differentiation to a new mature stable cell type.
This allows them to withstand stress better
growth in cancer
- Metaplasia - this is an adaptive response to environmental stimuli
- Dysplasia - the enlargement of tissue by the proliferation of abnormal (metaplasia) cells, as a developmental disorder or an early stage in the development of cancer.
- Anaplasia - loss of intracellular structural differentiation within a cell often with increased capacity for multiplication, as in a malignant tumour.
- Cancer>metaplasia followed by dysplasia followed by anaplasia.
cell cycle - interphase
G1-normal cell functions + cell growth, duplication of organelles.
This is the phase where the cell is sensitive to growth factors (thus entering cell cycle) and anti-proliferative factors (thus not entering cell cycle). Once the cell has entered the cell cycle, there is no reversal – the point at which the cell enters the cell cycle and can no longer be affected by growth/anti-proliferative factors, is called the ‘restriction point’.
G0 – Cells that stay in G1 for a long time, and possibly never divide again are said to be in G0
S phase (synthesis phase) – DNA replication
G2 – Chromosomes begin to condense in preparation for the next mitotic division
Mitosis - prophase
– chromosome becomes visible, 2 pairs of centriole separate, and nucleus disintegrates.
Metaphase
chromatids move to a midline (equator)
