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small intestines Flashcards

1
Q

what is the location of brunners glands?

A

First few centimeters of duodenum

between the pylorus of the stomach and papilla of vater

papilla of vater —> opening where ducts opening brining bile and pancreatic juices to the duodenum

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2
Q

what is the function of brunners gland ?

A

secrete alkaline mucus :

Protect from stomach acid

neutralization of acid ( bicarbonate )

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3
Q

what is the stimulate for brunners glands ?

A

Tactile or irritating stimuli

Vagal stimulation

GI hormones —> secretin ( which is secreted when stomach acidity is high )

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4
Q

what is the inhibition stimuli for brunenrs glands?

A

Sympathetic stimulation

in excitable ppl it can be a cause of ulcer

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5
Q

what is the location of crypt of lieberkuhn ?

A

Entire surface of small intestine

between intestinal villi

Villi -> projections to increase absorptive area in the small intestine

Crypt –> pit between 2 villis

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6
Q

what are the type of epithelium found on the crypts and villi ?

A

Goblet cells —> moderate amount

Enterocytes —> large amount

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7
Q

what is the function of goblet cells ?

A

secrete mucous

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8
Q

what is the function of enterocytes ?

A

enterocytes on the crypts —> secrete large quantities of water and electrolytes

Enterocytes on the VILLI —> absorb water , electrolytes and end products of digestion

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9
Q

describe the secretions of intestinal secretion ?

A

succus entericus formed by enterocytes of crypts

Secretion are almost pure Extra cellular fluid with ph of 7.5 to 8

These secretions are absorbed at the villi

Flow of fluid from the crypts into villi acts as a watery vehicle for the absorption of substances from the chyme

Daily secretion 1800 ml/day

Secretion of watery fluid by crypts :

Active secretion of CL ions into crypts

Active secretion of bicarbonate ions

Electrical drag of positively charged sodium ions into secreted fluid

Osmotic movement of water

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10
Q

what are the sides of epithelial cells in small intestine crypts ?

A

basolateral —> towards the blood

Apical/brush border —> towards the lumen

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11
Q

what is present n the basolateral side ?

A

Na K 2 CL pump

CL in moves into the cell through this co transporter

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12
Q

what is present on the apical side ?

A

CL channels

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13
Q

what control CL secretion on the apical side ?

A

regulated by certain hormones or neurotransmitters which are present on the BASOLATERAL SIDE

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14
Q

describe the secretion of CL :

A

1- neurotransmitter/ hormones like VIP bind to the receptor on the basolateral side

2- CAMP is produced

3- Cl channels will open the apical side

4- CL ions are secreted

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15
Q

how does CL get into inside the cell?

A

The sodium, potassium , 2 CL pump on the basolateral side

2 negative ions ( 2CL ) are pumped in with 2 positive ions ( Na and K )

these pumps are also found in the kidney

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16
Q

describe the secretion of Na?

A

it follows Cl secretion passively

Paracellular : Things are flowing through TIGHT JUNCTIONS - direct route —> osmosis

Transcellular –> things pass through the membrane

Water also is secreted in the lumen following the NaCL

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17
Q

where are the digestive enzymes found in small intestines?

A

Enterocytes of mucosa especially covering villi

will contain digestive enzymes that will digest specific food substances while they are being absorbed through the epithelium

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18
Q

what are the digestive enzymes ?

A

peptidase : splitting small peptides into amino acids

Sucrase , maltase, isomaltase, lactase —> splitting disaccharides into monosaccharides

Intestinal lipase : Splitting neutral fats into glycerol and fatty acids

Epithelial cells deep in the crypts continually undergo mitosis forming new digestive enzymes new cells migrate tips of villi

allow rapid repair of excoriation that occur in the mucosa

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19
Q

what are the ways the surface area is increased?

A

Valvulae conniventes ( folds of kerckring )
–> especially in well developed in the duodenum and jejunum , increase the surface area there fold of absorptive mucosa

Villi :

Epithelial surface of small intestine , absorptive area is enhanced to another 10 folds

Microvilli : Brush border contains 1000 microvili, absorptive area is enhanced to another 20 folds

Arrangement of vascular system for absorption of fluid and absorbed material , arrangement of central lacteal for absorption

The vessels are very close to the enterocytes making the function is more effective

Lacteals in the middle of the vascular arrangement

Lacteals are for the absorption of fats which eventually go into thoracic duct then back into circulation

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20
Q

describe the daily water turnover in GIT?

A

Ingested - 2000 ml

Endogenous secretion - 7000 ml

Total input - 9000 ml

98% of this fluid reabsorbed - 8800 ml

100 ml is lost in the stool daily

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21
Q

describe water absorption ?

A

Water is transported through the intestinal entirely by diffusion / osmosis

driven by electrochemical gradients established by active transport of ions and other solutes

When chyme is dilute enough water is absorbed through intestinal mucosa into blood by osmosis

Water can be transported from the blood into intestine if the chyme is hyperosmotic

IF chyme is hypoosmolar/tonic —> water will get absorbed and go to the blood ( cuz less solutes and water leave )

IF chyme is hyper osmolar /tonic —>water will go the gut —> cuz more solutes and water will stay

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22
Q

describe absorption of sodium?

A

Sodium is secreted 20 to 30 gms

ingested -5 to 8 gm from food

intestines must absorb 25-35 gm/day

less than 0.5% is lost in the feces

Active transport of sodium : NA/K atpase ) from epithelial cells into paracellular spaces at basolateral membrane

Sodium moves down the electrochemical gradient from chyme through the brush border –> diffusion

Secondary active transport : Sodium also co transported by specific carrier proteins, Na- Glucose co- transporter, Na amino acids co transporter and Na-H exchanger –> SODIUM IS WELL KEPT INSIDE

Na/H counter transporter found in the lumenal side

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23
Q

what enhances sodium absorption ?

A

Aldosterone

Osmotic movement of water by paracellular and transcellular pathways

24
Q

describe primary active transport of NA?

A

Na/K pump on the basolateral side facing blood

this pumps Na back into blood and K into the cell

this will cause the level of Na inside the cell to decrease making electrochemical gradient

25
describe the absorption of chloride ions?
in duodenum and jejunum Cl ions diffuse along the electrical gradient --> absorption of sodium ions causes electeronegativity (cuz its leaving the chyme) in the chyme and electropositivity in the paracellular spaces ----> this causes Cl ions to move from the cyhm into the cell in ileum, chloride absorption at the brush border occur through : Cl-HCO3 exchanger --> pump Cl inside and HCO3 out Cl exits through the CL channels present on the basolateral membrane
26
describe the absorption of bicarbonate ions?
Large quantities of bicarbonate have been secreted in the duodenum in both bile and pancreatic juices ---> large quantities are absorbed in the upper parts of small intestine in the duodenum and jejunum HCO3 is reabsorbed indirectly Source of H ions is intracellular CO2 and water , converted to H and HCO3 HCO3 is reabsorbed in blood H ions are secreted in lumen in exchange for Na and bind with HCO3 to form H2CO3 forming CO2 and water ---> NEEDS CARBONIC ANHYDRASE Water becomes part of chyme and CO2 expired after absorption in blood Jejunum has net absorption of NaHCO3
27
describe secretion of bicarbonate and absorption of chloride ions in the ileum and large intestine ?
In ileum and large intestine : Cl-HCO3 exchange mechanism in apical membrane ( CL in and HCO3 out ) Cl transporter instead of HCO3 transporter in the basolateral membrane will get rid of the Cl coming in the apical side ileum has net absorption of NaCL Bicarbonate ions secreted in the lumen neutralize the acid products formed by bacteria we need HCO3 in the lumen in large intestine and ileum to neutralize the acidity formed by bacteria
28
describe the absorption of nutrients in small intestine ?
all carbohydrates are absorbed as monosaccharide - most abundant is glucose 80% 20% of absorbed monosaccharides is composed of entirely of galactose and fructose Na-glucose co transporter-secondary active transport of glucose from the lumen through the brush border into the epithelial cells and FACILITATED DIFFUSION though basolateral membrane Galactose is similar to glucose enter via SGLT1 n leave via GLU2 Fructose is transported by facilitated diffusion only enter via GLUT 5 then leave by GLUT 2 Proteins are absorbed as dipeptides , tripeptides, amino acids ( Na-Co transport mechanism ) Monoglycerides and fatty acids are absorbed after being dissolved in bile micelles , converted to new triglycerides and releases as CHYLOMICRONS
29
Describe mixing contraction ( segmentation )?
Segmentation contraction '' chop '' the chyme two to three times per minute Mix the chyme and expose it to pancreatic enzymes and secretion Basic electrical rhythm determines the frequency of segmentation Maximum is 12 per minutes in duodenum and jejunum Ileum frequency 8 per minute Also help propel the food down the intestine Although slow waves causes segmentation , background excitation by MYENTERIC NERVE PLEXUS IS REQUIRED TO MAKE THEM EFFECTIVE
30
describe propulsive contraction / peristalsis ?
Behind the bolus ( Excitation ) In front of the bolus ( inhibition ) Propel the cyhme Hormonal and nervous signals and control peristalsis Faster in proximal and slower in terminal intestines , so forward movement of chyme is slow
31
what is released behind the bolus?
Excitatory transmitters : ACH, substance P, neuropeptide Y ) are released in circular muscle
32
what is released in front of the bolus ?
Inhibitory pathways : VIP, nitric oxide are activated in circular muscle
33
what hormones that enhance intestinal motility ?
Gastrin CCK insulin motilin Serotonin
34
what are hormones that inhibit intestinal motility ?
Secretin Glucagon
35
what are the movements caused by muscularis mucosa and muscle fibers of the villi?
Contract intermittenlty Mucosal folds increase surface area exposed to chyme - increase absorption
36
describe the significance of ileocecal valve ?
ileocecal valve : protrudes into the lumen of cecum Is forcefully closed when excessive pressure build up in the cecum , prevent backflow of fecal content from the colon into small intestine Wall of ileum upstream from the ileocecal valves has thickened circular muscle called ILEOCECAL SPHINCTER , remains mildly constricted and slows emptying of ileum Gastro-ileal reflux --> occur after meal and intensifies peristalsis in the ileum to empty contents in the cecum Feedback control of ileocecal sphincter : Reflex from cecum through MYENTERIC PLEXUS and the extrinsic autonomic nerves especially by way of prevertebral sympathetic ganglion
37
what secretes Secretin ?
S cells of mucosa of upper small intestine
38
what stimuli secretin secretion ?
H ions ( low PH ) Fatty acids
39
what does secretin do ?
pepsin secretion pancreatic bicarbonate secretion Biliary bicarbonate secretion Growth of exocrine pancreas Contraction of pyloric sphincter
40
what secretin inhibits ?
Gastric acid secretion Mild effect on motility of GIT
41
what releases CCK?
I cells of mucosa of upper small intestine
42
what stimulates CCK?
Amino acids Fats , fatty acids , monoglycerides
43
what does CCK do?
Augments the action of secretin ( alkaline pancreatic juices ) Gall bladder contraction
44
what does CCK inhibit ?
Gastric secretion , motility and emptying appetite
45
what releases GIP?
Mucosa of upper small intestine
46
what stimulates GIP?
Fatty acids amino acids carbohydrates but to less extent
47
what does GIP inhibits?
Mildly motor activity
48
what secretes motilin?
Stomach and upper duodenum
49
what stimulates motilin ?
Fasting
50
what does Motilin stimulate?
Gi motility by stimulating migrating myeolectricial complex
51
what is intestinointestinal reflex?
Mediated by enteric neurons and vagus nerve overdistention of one segment of intestine relaxes smooth muscles in the rest of the intestines
52
what is gastroileal reflex?
mediated by VAGUS NERVE Elevated secretory and motor functions of stomach increase motility of terminal part of ileum and accelerates movement of material through ILEO CECAL SPHINCTER
53
describe diarrhea caused by cholera?
Subunit of cholera toxin enters the epithelial cell Excess CAMP formation Cl channels open up and CL flows into intestinal crypts Na ions are also pumped into crypts to go along the chloride Extreme osmosis of water from blood follows the NaCL result in increase electrolytes and water content of intestinal content causing diarrhea
54
describe celiac disease ?
Genetically predisposed autoimmune response Toxic effect of gluten present in rye , wheat, rice ,corn inappropriate immune response from T cells intestinal epithelial cells damage LOSS OF VILLI and flattening of mucosa managed with gluten free diet m bowel function is generally restored , the mucosa returns to normal if foods containing gluten are strictly excluded from the diet , although this may be difficult to achieve
55
describe paralytic ileus ?
Abdominal surgeries Trauma to intestines inhibition of smooth muscle --> Activation of opioids receptors --> decrease intestinal motility Irritation in peritoneum reflux inhibition due to increased discharge of noradrenergic fibers in the splanchnic nerves diffuse decrease in peristaltic activity in small intestine ---> contents not propelled ---> distention of gas and fluids in pockets intestinal peristalsis returns in 6 to 8 hours followed by gastric peristalsis and colonic activity takes 2 to 3 days to return Relieved by passing tube through nose down to the small intestine and aspirating the fluid and gas ( out )
56

PHYSIOLOGY-Y2S2 (12 decks)

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