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structure and function of living organisms BI1002 > digestive system > Flashcards

digestive system Flashcards

1
Q

Oral cavity: teeth, tongue palate

A

tongue- intrinsic and extrinsic muscles in the tongue - allowing so much movement
frenulum=under tongue
palate- seperates oral cavity and nasal cavities
transverse mucosal ridges - for swallowing
hard and soft plate

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2
Q

salivary glands

A

salivary gland - 3 major pairs (secretion on demand)
parotid: serous(runny watery secretion) - very long duct, serous secretion enters mouth by 2nd upper molar
submandibular: seromucous secretion (watery/thick)-long thinduct
sublingual: mucous secretion(thick)-lots of short ducts under neath tongue
also have hundreds of salivary glands-secreting continuously to keep mouth moist

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3
Q

Pharynx

A

channels food down into oesophagus- area covers back of mouth down to bottom of pharynx
made of superior/middle/inferior constrictor muscles

larynx - seperates what u swallow from breathing

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4
Q

Oesophagus

A

muscular tube connecting pharynx to stomach, passes through the diaphragm.
no part in digestion
passes food on as quick as possible

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5
Q

Stomach: structure & functions

A

parts of stomach:
cardiac and pyloric sphincter- control entry/exit of the stomach
fundus-small top bit-air swallowed goes here
body-middle
pylorus-bottom connecting to duodenum
lesser and greater curvature

rugae: folds in the stomach- allows for expansion and contraction of the stomach
(folds dissapear as stomach gets full-reappear when stomach empties)

Functions:
* Some protein digestion(pepsin)
* Reduction of solid food to
loose, semisolid chyme
* Delivery of chyme to duodenum
Acts as a hopper
*Receives materials irregularly,
stores and delivers them regularly
to duodenum until empty
Makes Intrinsic Factor
*needed for absorption of vitamin
B12 in intestine

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6
Q

Small intestine – regions: duodenum, jejenum, ileum
DUODENUM

A

DUODENUM(25cm)-C-shaped, bent around head of pancreas, on back wall of abdomen
*Receives acid material from stomach; protected by mucus glands
*Receives products of pancreas and bile from liver - common duct
Digestive secretion to duodenum: Bile from liver + pancreatic juice from pancrease with digestive enzymes

JEJUNUM(1m)+ILEUM(2m)
*Tightly folded within abdomen
*Completes digestion, absorbs its products into blood and lymph streams
*All have similar structure, some subtle differences

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7
Q

(liver & pancreas)
peritoneum & mesenteries

A

Visceral peritoneum
Parietal peritoneum

Folds of peritoneum = mesentaries

Hold gut in position
Contain many big blood vessels

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8
Q

small intestine movements

A

Peristaltic movements propel food along
Intermittent churning movements for mixing: segmentation
Movements controlled by myenteric plexus of nerves within muscle layers of gut wall

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9
Q

bile + secretion of bile

A

Continuous secretion of bile,
intermittent secretion from pancreas
- both to common duct, sphincter to duodenum
- bile stored in gall bladder until
pancreatic secretions released
Both secretions released when chyme enters duodenum; sphincter relaxes, gall bladder contracts, bile and pancreatic juice mixes with chyme.

Bile: allows mixing of pancreatic
enzymes and fatty food material: lowers surface tension and emulsifies fat

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10
Q

Large intestine – ileo-caecal junction and parts of large intestine

A

ileo caecal junction- end of small intestine, guarded by ileo caecal valve
food arrives 3-4hrs after swallowing
((appendix-nearby, variable in
position and length (2-20 cm)
Blind ending tube
Prone to abscess formation))

caecum-first part
colon – ascending, transverse, descending, sigmoid(AKA pelvic colon)
- ascending and descending colon have no mesentaries-attached to rear abdominal wall

rectum - Rectum is normally empty: distension of its walls triggers
defecation:

Contraction of colon, relaxation of involuntary
sphincter. Voluntary sphincter gives conscious control
anal canal

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11
Q

(microscopic)
Oral cavity/mucosal lining:
*Masticatory mucosa
*Ordinary lining mucosa
*Specialised mucosa, tongue
Tongue and lingual papillae: taste buds
filiform, fungiform and circumvallate

A

masticatory mucosa:
Gingiva & hard palate-Stratified squamous keratinised epithelium
Firmly anchored to underlying bone by collagen fibres in submucosa

ordinary lining mucosa:
Anywhere other than top surface of tongue, gingiva & hard palate - Inside of lips, Underside of tongue, Soft palate, Gums away from gingiva
Stratified, squamous, non-keratinised epithelium
Lots of minor salivary glands in submucosa

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12
Q

common plan of hollow tube parts of gut:
Mucosa, submucosa, muscularis externa, adventitia

A

Layers:
1. Mucosa - the lining,
This has 3 layers: epithelium, lamina propria (connective tissue layer), and the muscularis mucosae (thin layer of muscle)

  1. Submucosa - connective tissue outside mucosa, contains many blood vessels, lymphatics TF gives position for things to get in/out
  2. Muscularis mucosa- muscle layer, 2 layers-most of gut it is smooth muscles, inner most layer runs circularly, outer most runs longitudinally
    ==>Contracting circular layer-makes gut narrow
    Contract longitudinal- scrunches gut up
    THESE MUSCLES Drive peristaltic movements in hollow tube parts of gut
  3. adventitia

nerves networks/plexus:
Muscle layers act semi independently from nervous system - (interic nervous system) in walls of gut.
Muscularis mucosae(in mucosae layer) has network of nerves sitting on outside-controls contraction of cells in that muscle layer. =meissners plexus
Muscularis externa- similar network sitting between inner + outer layer = auerbachs plexus

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13
Q

 Oesophagus: epithelium and muscle; folds

A

lining is: stratified squamous non-keratinised epithelium
(Because there is no absorption in oesophagus - just transporting into stomach)

mucus secreting glands - At top-lubricates what’s swallowed
At bottom-protects wall from stomach acids that may get to the oesophagus

muscle type in muscularis externa: voluntary skeletal at top, smooth at bottom and mixed in middle
Reason: swallowing is voluntary - then automatic systems take over to digest

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14
Q

Stomach: epithelial lining, gastric glands and muscle layers

A

epithelial: simple columnar(all mucous sells)
–> with gastric pits followed by gastric glands
surface mucous cells - keeps acid away from cells(protective mechanism)

gastric glands- makes hydrochloric acid + pepsinogen

2 types of cells:
parietal cells(oxyntic)-makes HCl
chief cells(zymogen)-makes pepsin

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15
Q

Small intestine;
plicae circulares, villi and microvilli; epithelium
crypts of leiberkuhn

A

Plicae circulares-submucosal layer(just folds in the duodenum wall) - this is to increase SA for the villi

Villi - mucosal layer (increases SA for microvilli)

Microvilli - Apical plasma membrane layer (form brush border) (most microscopic)

crypts of leiberkuhn (between villi)
Epithelium on villus: can only be simple epithelium to allow absorption-although very hostile environment TF cells only live a few days - cells must be continually replaced(by cells deep in the crypts)

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16
Q

Large intestine: epithelium, goblet cells, deep crypts, muscle

A

Purpose of lg. intestine: Prepare materials you can’t digest for expulsions

TF compress down/concentrating by removing water/ions/solutes(no villi)

Krypton of lieberkuhm - to produce replacement cells- ALSO produce goblet cells(mucous secreting glands)

muscle:
Longitudinal muscle layer - 3 ribbons of muscle(called taeniae coli)
Eg. Ascending colon, transverse colon, descending colon
* contraction causes bulge = haustrae

17
Q

Anal canal – epithelium, sphincters

A

muscle sphincters:
smooth muscle- relaxes when rectum needs to empty
skeltal muscle on outside-voluntary control when ready to empty

simple columnar epithelium->SSNK epithelium

18
Q

regulation of gastric secretion and motility - phases

A

Regulated by combination of nervous and hormonal factors
3 phases of secretion:
*cephalic
*gastric
*intestinal

19
Q

gastric phase
control of HCl secreting parietal cells

A

–Neural negative feedback
*stretch receptors and chemoreceptors routed via the submucosal plexus - peristalsis stimulated
–Hormonal negative feedback mechanisms → emptying
*distension, partly digested proteins, caffeine, stimulate the G (enteroendocrine) cells
*gastrin secretion is:
–inhibited at pH < 2
–stimulated when pH rises
*gastrin is transported in the blood to the gastric glands
–stimulates gastric secretions
–contraction of lower esophageal (cardiac) sphincter
–. motility
–relaxes pyloric sphincter

*stimulation by three signal chemicals
–gastrin
–acetylcholine
–histamine
All three needed for strong H+ secretion

20
Q

cephalic phase

A

-Cause
-sensations & thoughts
-Effect
-Cerebral cortex hypothalamus
-Parasympathetic - vagus (x cranial nerve)

21
Q

intestinal phase

A

Excitatory
*stretch receptors respond
*chemoreceptors detect fatty acids, & glucose in the chyme in the duodenum
*enteroendocrine cells in the stomach release gastrin
*increases gastric peristalsis and gastric emptying

Inhibitory
*Enterogastric reflex
*Enterogastrone secretion
enteroendocrine cells in the small intestine release:
»Cholecystokinin (CCK)
»Gastric inhibitory peptide (GIP)
»Secretin
–they inhibit gastric secretion

22
Q

pancreas

A
  1. Parasympathetic impulses along vagus (X) nerves
  2. Stimulates secretion of pancreatic enzymes
  3. Acidic chyme containing partially digested fats (fatty acids) and proteins (amino acids) in the small intestine
  4. CCK and secretin are secreted from small intestine travel through blood to stimulate pancreas
  5. Stimulates secretion of pancreatic juice rich in bicarbonate ions
  6. Stimulates secretion of pancreatic juice rich in digestive enzymes
23
Q

liver

A
  1. Parasympathetic impulses along vagus (X) nerves stimulate bile production by liver
  2. Fatty acids and amino acids in chyme entering the duodenum stimulate secretion of cholecystokinin (CCK) into blood.
    Acidic chyme entering duodenum stimulates secretion of secretin into blood.
  3. CCK causes contraction of gallbladder
  4. Secretin enhances flow of bile rich in HCO^- 3, from liver
24
Q

hormones gastrin and CCK feedbacks/routes

A

each step causes/promotes next step -however 2 inhibitors of previous steps

1.Food in stomach
=>2. Release of gastrin from stomach mucosal cells
=>3. Gastrin circulates in blood and returns to stomach
=>4. Gastrin stimulates secretion of HCI and pepsin, and increases motility of stomach

=>lowers pH inhibiting 2. + => 5. Increases delivery of acid chyme to small intestine

(acid in chyme)
=>6i. Release of secretin by intestinal mucosa
Release of bile from gallbladder.
(Undigested fats and + proteins in chyme)
=>6ii. Release of cholecystokinin by intestinal mucosa

6ii. causes 3 different things:
->slows movement of stomach TF inhibiting 2.

=>7. release of bile from gallbladder. Bile salts emulsify fats
=>8. Release of digestive enzymes from pancreas

6i. => 9. Release of bicarbonate solution from pancreas neutralizes acid

7., 8. and 9. => Digestion of food

25
Q

control of appetite - satiety signals, peripheral hunger signals, long term satiety signals

A

satiety signals:
“Ileal Brake” – all slow gastric emptying
*Cholecystokinin(CCK)
Secreted in response to food
Reduces appetite & inhibits eating
In hypothalamus neurotransmitter to inhibit eating
*Glucagon-like peptide-1
From intestine, in response to food
*Peptide YY (PYY)
From intestine, in response to food

peripheral hunger signals:
-Mediated by ghrelin
-Only GIT hormone to increase food intake
-Secreted by endocrine cells of gastric mucosa
-Increases hunger, growth hormone secretion & fat stores
-Binds to GHSR in hypothalamus
(Growth Hormone Secretagogue Receptors)

LT satiety signals:
Leptin
Insulin
Oestrogen
–May act to lower body weight
–May target anorexigenic pro-opiomelanocortin (POMC) neuron

26
Q

leptin -control of apetite

A

*Arcuate Nucleus (ARC)
*POMC
*pro-opiomelanocortin
*CART
*cocaine-amphetamine regulated transcript
*Stimulated by leptin
*Increases activity of melanocortin pathway
*Both hormones and receptors
*Suppresses appetite

27
Q

melanocortin system

A

*Peptides adrenocorticotropin & melanocyte-stimulating (MSH) hormones
*Anorexigenic ->makes you not want to eat
*Occurs in arcuate nucleus of hypothalamus
*Integrates long term & short term signals
*Activated by POMC and CART
*Inhibited by NPY and AgRP

28
Q

NPY/AgRP neurones

A

*Neurons suppressed by insulin & leptin
*Stimulation releases NPY and AgRP
Removal of inhibition
*Neurotransmitters in hypothalamus
*NPY
Activates its receptor which are GPCR
Stimulates eating
*AgRP
Binds to & inhibits MC4R
Inhibits anorexigenic effects of a-MSH

29
Q

the rumen(cows/bovine) -the fermentation vessel

A

The Rumen – 10-20% liveweight
*Cows produce ~150L of saliva/day
*Contents are 85-93% water
*Ruminal Papillae
*Stratified Squamous Epithelium – Keratinised
*Absorption still occurs here
*Cows spend ~8hrs/day grazing and ~8hrs ruminating
–material drawn back into the oesophagus and muscle contractions return it to the mouth
–Liquid rapidly re-swallowed, coarse material chewed again before swallowing
–Each bolus chewed 40-50 times

30
Q

reticulo-rumen microorganisms

A

*The rumen and reticulum provide a culture system for microorganisms
–>200 species - Mostly anaerobic bacteria and fungi
–Synbiotic relationship
(=Synbiotic-one organism relies on chemical processes of the other organism)
–Heterotrophic and Autotrophic (inc. methanogens)
–Chemostat
–Complex interrelationships – methanogens reduce efficiency but impact on growth of other species:

*Fermentation produces volatile fatty acids (VFAs) which are absorbed, gas & more microorganisms

*Structural changes during development:
–At birth the abomasum is the largest chamber
–at 18 months the reticulorumen occupies >90% of the stomach

31
Q

reticulum-first organ food enters in a cow

A

*Keratinised stratified squamous epithelium
*Particle sorting
*Muscularis mucosa
–Around top of each compartment
–Aid separation, mixing, breakdown
*Keratinised

32
Q

omasum

A

*Regulates entry of food into the abomasum
*May return food to the reticulo-rumen
*Water and VFA absorption

33
Q

abomasum

A

*True stomach – like the fundus
*Broadly the same digestive functions as humans
*Oesophageal Groove(neonatal-when head is up, provides direct path to abomasum)
*Simple Columnar
*Glandular
*Gastric pits
*Parietal & Chief

34
Q

DIGESTION/DIETS- cellulose, hemicellulose, lignin

A

cellulose:
*A chain of glucose units bound by beta-1,4-linkages
*Intramolecular H bonds
–↓ flexibility
–↑tensile strength
–↓solubility in water or dilute acid
*Intermolecular H bonds
*Allows the development of a crystalline lattice

hemicellulose:
–Mixture of: pentose, hexose, uronic acids bound to a beta-1,4-linked core composed primarily of xylose
–Closely bound to lignin than cellulose

lignin:
*A ‘poorly defined’ polymer of phenylpropane
*Binds to hemicellulose only
*Forms a matrix around cellulose
*↑strength under compression
*Lignification
–Significant factor in reducing digestibility

35
Q

cellulose digestion

A

90% of cellulose digestion is in the reticulorumen
*Transport of bacteria to fiber
Slow
Dependent on number of bacteria
*Nonspecific adhesion of bacteria to sites on substrate
Binds with Glycocalyx
Most commonly at cut or macerated areas
*Specific adhesions of bacteria with digestible cellulose
Cellulosome: Large, multienzyme complexes for adhesion and hydrolysis of cellulose
Fimbriae (Attachment Pili): Small (5-7 x 100-200 nm) structures in gram + & – bacteria

36
Q

starch + starch digestion

A

starch:
*Chief storage polysaccharide in plants
*Two components
–Amylose (Glucose units bound by α-1,4-linkages)
–Amylopectin (Glucose units by α-1,4-linkages with α-1,6-branch points)

digestion:
Rumen:
–47-95% digested in rumen
*Digested by alpha-amylase to oligosaccharides
–Found in cell-free rumen fluid, but 70% associated with particulate-bound microorganisms
–Activity increases in high grain diets
*Oligosaccharides degraded to glucose
–Protozoa uptake
–Stabilises fermentation
–Less readily passed from rumen
–Bacterial uptake
–Storage polysaccharide
–May accounts for as much as 50% of carbohydrate leaving rumen

37
Q

VFA production (volatile fatty acids- propionate, acetate and butyrate)

A

*Some factors that increase propionate, decrease methane
*Decreased forage and increased concentrate
*↑ propionate

*Decreased physical form of diet (Grinding, pelleting etc)
*↑ propionate

*Unsaturated fatty acids
*↑ propionate

structure and function of living organisms BI1002 (9 decks)

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