WEEK ELEVEN - Stomach, liver, gall bladder, pancreas and small intestine Flashcards
Describe the gross and microscopic anatomy of the stomach
gross anatomy
- Muscular sac in upper left abdominal cavity - inferior to diaphragm **
- moves eg inspiration/expiration/distensions
- holding chmaber for food = Internal volume - 50mL [empty] → up to 4L when full** [dependent on M/F, size etc]
- **pH 2-3 **[due to HCl sec into stomach]
- STARTS chemical digestion of protein/small amt fat –> most digestion = s intest
- regions
cardia -inside cardiac orifice
fundus - superior bulge
body - main portion of body
pylorus -narrow inferior end - opens to duodenum - has sphincter
- has rugae in mucosa + submucosa
microscopic anatomy
FOUR LAYERS [from lumen –> out]
1. mucosa
- simp.col.glandular.epi
- lamina propia
- submucosa
- muscularis externa [smoo.musc layers]
- inner oblique layer
- mid circular layer
- outer longitudinal - serosa
Name four cell types found in the gastric mucosa and state their functions
gastric glands sec. gastric juices = total of 2 - 3 L /day
- mucous cells [goblet cells]
- sec mucus for stomach wall protection - parietal cells
- sec H+ / Cl- = HCl in stomach lumen
- sec IF = for vitamin E absorption in s.intest = RBC production - chief cells
- sec pepsinogen [converted to pepsin by HCl]
- protein digesting enzyme - enteroendocrine cells [G cells]
- sec gastrin and ghrelin [hormones] –> bloodstream = stims gastric activity
State three reasons as to why the stomach does not digest itself
- mucus coat
- thick alkaline coat protects against acidic HCl environment - rapid epithelial cell replacement
- sloughed off after **3 - 6 days **–> digested w/ food
3.** tight junctions **
- prevent gastric juice from seeping between cells and digesting lamina propria layer
Describe how the three phases of gastric function are regulated
**phase one - cephalic
**- sight, smell, taste, thought of food activates brainstem centres
- **vagus nerve stims gastric secretion and motility **
- vagus nerve stims gastric sec before food is even swallowed
**phase two - gastric
**- activated by presence of food/semi-digested protein - detected via stretch or ^ pH
- when food stretches stomach = short myenteric + long vagovagal reflex activated
- - reflexes stim gastric sec // histamine and gastrin also stim acid/enzyme sec
- sec stim by
> ACh from parasym fibres
> histamine [from gastric enteroendocrine cells]
> gastrin [from pyloric G cells]
**POSITIVE FEEDBACK CONTROL - GASTRIC SECRETION **
- Goal = release acid and enzymes → stomach
- Peptides cause acid and pepsinogen release → causes MORE peptides in stomach → causes acid + pepsinogen release
**phase three - intestinal **
- Duodenum regulates gastric activity through hormones + nervous reflexes
1. initially gastric activity briefly ^ [if duodenum is stretched or AAs in chyme cause gastrin release] THEN
2. secretin, CCk, GIP and enterogastric reflex inhibit gastric secretion and motility as duodenum processes what is already in it
- enterogastric reflex - duodenum inhibits stomach = caused by acid and semi-digested fats in duodenum
- chyme stims duodenal cells to release secretin, CCK, GIP [these all supply gastric sec and motility]
Describe the gross and microscopic anatomy of the liver, gall bladder, bile duct system and pancreas
liver, gallbladder, pancreas = accessory organs of the digestive systems –> all release important sec –> s intest to continue digestion
liver anatomy
- 1.4kg organ = inf to diapragm on R abdomen **
- FOUR lobes = R, L, caudate, quadrate
- falciform ligament** separates L/R
- round ligament = remnant of umbilical cord
- interior of liver compose of tiny cylinders = **hepatic lobules [2mm x 1mm]
- each cyclinder has central v. surrounded by hepatocyte cell sheets [hepatocyte cells filter blood –> central v]
- THREE structures found between caudate and quadrate lobe**
1.** hepatic portal vein [hpv]**
- nutrient rich, O2 poor blood –> liver
- provides 70% blood to liver
- **hepatic artery proper **
- O2 rich, nutrient poor to liver
- provides 30% blood to liver
3**. bile duct **
- collects bile from bile canaliculi between hepatocyte sheets
- secretes bile from liver via hepatic ducts
gallbladder
- adheres to inferior surface **between R and quadrate lobes **
- ~ 10cm long
- function = **store/conc. bile **
**bile ducts **
- bile flow - passes from:
bile canaliculi > bile ductules > R/L hepatic ducts
> hepatic ducts join = common hepatic duct
> common hepatic duct + cystic duct from gallbladder = bile duct
> bile duct + pancreatic duct = hepatopancreatic ampulla which empties –> duodenum via major duodenal papilla
pancreas
- Retroperitoneal endocrine + exocrine gland posterior to stomach **
- 12-15cm long x 2.5 cm thick
- sec insulin + glucagon –> blood **
- sec pancreatic juice –> duodenum for digestive func.
- acinar cell ducts –> converge onto pancreatic duct = accessory duct opens to duodenum @ minor duodenal papilla + bypasses the Sphincter of Oddi= allows pancreatic juice to be released –> duodenum even when bile is not
Describe the digestive secretions and functions of the liver
liver sec. **500-1000 mL/day bile **
bile = green fluid [minerals, bile acids, cholesterol, bile pigments, fats and phospholipids]
- pigment from bilirubin [product of Hb breakdown]
- L intestine bacteria metabolise bilirubin –> urobilinogen [brown poo colour]
bile acids = steroids synthesised from cholesterol
- **bile acids + lecithin **[phospholipid] = aid in **digestion/absorption of fat **
Describe the function of the gall bladder
func = store/conc. bile
- bile backs up into gallbladder from filled bile duct
- between meals = bile conc. by factor of 20
Describe the digestive secretions of pancreas
Pancreatic juice = alkaline mixture of water, enzymes, zymogens and **sodium bicarbonate **
Acini [acinar cells] secrete zymogens and enzymes
- Zymogens [trypsinogen, chymotrypsinogen, procarboxypeptidase] = break proteins down –> peptides and AAs
- Other enzymes
- pancreatic amylase = digests starch
- pancreatic lipase = digests fat
- ribonuclease = digests RNA
- deoxyribonuclease = digests DNA
pancreatic ducts sec. sodium bicarbonate = ^ pH
- important for enzyme function/tissue protection
Explain how hormones regulate secretions of gallbladder & pancreas
**1. Cholecystokinin [CKK]
**- released from duodenum on arrival of acid/fat
- causes gallbladder contraction
- sec. of pancreatic enzymes
- relaxation of hepatopancreatic sphincter
- Secretin
- released from duodenum in response to **acidic chyme **
- stims all ducts to sec more HCO3- to **neutralise chyme in s. intest ** - Glucose-dependent insulinotropic peptide ([GIP]
- from s.intest
- stims pancreas to sec insulin in response to chyme in duodenum
Describe the gross & microscopic anatomy of the small intestine
- most chemical digestion occurs in s.intestines
- total s.intestine length = **6.35m **
-
duodenum [25cm] = retroperitoneal w/ pancreas
duodenum receives pancreatic juice + bile from hepatopancreatic spincter and accessory duct - jejunum [next 2.5m] in UPPER abdomen
most digestion/nutrient absorption occurs here - ileum [last 3.6m] in LOWER abdomen
microscopic anatomy
- lumen = simp.col.epi
- muscularis externa [inner circ, outer long]
- ^ SA provided by great length, villi, microvilli and plicae circulares
- circular folds [plicae circulares] up to 10mm tall [only in mucosa/submucosa] ^ SA = slows flow of chyme = promotes more mixing/nutrient absoprtion
Describe the types of movements that occur in the small intestine
segmentation
- mixing/churning = segments of chyme
- occurs ~ 12 times/ min in duodenum
- Patterned localised firing of enteric neurons = random ringlike constrictions in the** inner circular layer of muscularis externa **
peristalsis
- Migrating motor complex –> controls waves of contracts in **BOTH muscular externa layers **
- peristalsis begins in duodenum, but each wave moves further down [after absorption occurs –> waves gradually move chyme to colon]
- takes two hrs to pass full length of s.intest
- **refilling of stomach
= suppresses peristalsis **
= BUT stims **gastroileal reflex **
- relaxes ileocaecal valve [promotes forward movement of chyme from s.intest –> l.intest]
- preps s.intest to receive additional chyme from stomach
Describe how carbohydrates are digested and absorbed
digestion
starts in outh –> salivary amylase breaks down complex carbs [**polysaccharides/starch] **
- amylase digests 50% of starch by the time food reaches stomach
- remaining 50% digested by pancreatic enzyme [reduces starch –> ogliosacc/maltose] - takes 10 mins
- brush border enzymes - further break down ogliosaccharides [sucrose, lactose, maltose]
amylase, pancreatic enz, brush border enz
absorption
~ 80% of absorbed sugar = glucose –> sodium-glucose transporters** [SGLT]** transport glucose + galactose –> ECF
- sugar –> ECF = ^ osmo = draws **water osmotically from lumen into ECF via leaky tight junctions = solvent drag [transporting more glucose/other nutrients]
- solvent drag carries more glucose than SGLT [2-3x as much after high carb meal]
fructose = abs by facilitated diffusion** through brush border [**converted –> glucose **inside cell]
- glucose, galactose and small remainder of fructose transp –> out of cell then abs by blood caps in villus
*SGLT, osmosis/solvent drag, facilitated diffusion
Describe how proteins are digested and absorbed
Pepsin breaks proteins down → partially digested proteins, peptides and AAs [starts in stomach]
- pepsin has optimal pH of 1.5-3.5 [becomes inactivated in duodenum where it mixes w/ pancreatic juice -pH 8]
in s.intest –> panc.enz: trypsin/chymotrysin digest protein by **hydrolysing polypeptides –> ogliopeptides **
digestion completed by b.b.enz - peptidases which break down dipeptides / tripeptides –> individual AAs
AAs abs = AA contransporters move AAs –> epithalial cell
- then **facilitated diffsuion **moves AAs –> brush border –> blood
Describe how fats are digested and absorbed
large fat globules/lipids = broken up by segmentation in s.intest and emulsified by lecithin [phospholipid] and bile acids
panc.lipase breaks triglycerides –> FFAs + monoglycerides
- these digested fats = micelles surrounded by bile acids
- micelles pass through s.intest and abs/transport dietary and semi digested lipids –> lipids diffuse through brush border
Describe the gross anatomy of the large intestine
l.intest = 1.5m long x 6.5cm diameter in cadaver
mucosa in whole l.intest except anal canal
- simp.col.epi
- no circ folds/villi
- intestinal crypts [in lamina propia] produce mucus
regions
**1. caecum **
- inf. to ileocaecal valve
2. colon
- Ascending R, transverse, descending L colon, Sigmoid colon = S-shaped portion ending at anal canal
- asc + desc colon = retroperitoneal w/ serosa only on ant. surface
-
rectum
- 15cm
**4. anal canal
**- 3cm total length
- has columns separated by sinus [sec mucus]
- internal anal sphincter [smoo.musc]
- external anal sphincter [skel.musc of pelvic diaphragm]
- strat-squa.epi
muscularis externa = 3 longitudinal ribbon-like strips - each one called Tenia coli -
- contracts lengthwise = produces haustra
- Haustrum - each segmented bulge of intestine = slows down chyme movement, moves to next haustram as opposed to mass movements quickly through rectum
