Chapter 24The Digestive System

Structures and functions, fig 24.1

Digestive System Organs Alimentary Canal Accessory Digestive Organs

Digestive Processes Ingestion Secretion Propulsion Digestion Absorption Defecation

Anatomy of the Digestive System

________________ Mouth, Pharynx, and Esophagus Stomach Small Intestine Large Intestine

___________ Digestive Organs Teeth, Tongue, Salivary Glands Liver and Gallbladder Pancreas

Functions

1. _______________ taking food into the mouth2. _______________ release of water, acid,

buffers, & enzymes into lumen of GI tract3. ___________ and __________ churning &

propulsion of food thru GI tract4. ______________ mechanical & chemical

breakdown of food5. _________________ passage of digested

products from the GI tract into blood & lymph6. ___________ elimination of feces from GI tract

Mouth, Pharynx, & Esophagus

Anatomy Mouth

Lips and Cheeks Palate Tongue Salivary Glands Teeth

Pharynx Esophagus

Digestive Processes Mastication Deglutition

Mouth (oral or buccal cavity) fig 24.5

Formed by cheeks, hard & soft palate, tongue

Where mechanical AND chemical digestion begin _____________ - chewing

Bolus- soft, flexible mass ______________ – enzyme, initiates

breakdown of starch ______________ – enzyme in saliva, works in

stomach to breakdown dietary triglycerides

Tongue

accessory organ skeletal muscles covered w/ mucous membrane

Attached to hyoid, styloid process, mandible Extrinsic muscles manuever food -chewing, form bolus, force

back for swallowing Intrinsic muscles alter shape and size during speech &

swallowing Dorsal & lateral surfaces covered w/_____________ -

which are projections of lamina propria Many contain taste buds - ______________ Lacking taste buds - touch, increase friction

____________ – secrete mucus, & serous fluid that contains lingual lipase

Teeth figure 24.7

Accessory digestive organs in _________ __________

Crown, neck, root – major external regions _______________ - calcifed CT, gives shape

and rigidity, harder than bone, majority of tooth ________________- covers dentin on crown,

hardest substance in body, protects tooth from wear & tear of chewing, and acids

________________ - CT containing bv, nerves, lymphatic vessels

Dentitions figure 24.8

______________ teeth = primary, milk, or baby teeth – begin to erupt @ 6 months 20 in full set All are lost between age 6 to 12

______________ or secondary teeth 32 teeth

8 incisors – chisel shaped for cutting 4 canine or cuspid – pointed to tear and shred 8 premolars or bicuspid – crush and grind 4 first molars (age 6) – crush and grind 4 second molars (age 12)- crush and grind 4 third molars or wisdom teeth (age 17)- crush and grind

Oral mucosa

Non-keratinized stratified squamous ______________ – membrane that lines a

body cavity that opens to the exterior Of mouth and tongue- contain small salivary

glands that open into oral cavity Labial, buccal, palatal, and lingual Make small contribution to saliva

Salivary glands figure 24.6

Keep mouth & pharynx mucous membranes moist

Cleanse mouth & teethWhen food enters mouth, secretion Lubricates, dissolves, begins chemical

digestion3 major glands (in pairs)- parotid,

submandibular, sublingual glands

Control of salivation

______________ stim= continuous secretion ______________ stim= dominates during stress

resulting in dryness of mouth If body dehydrated, saliva not secreted dry

mouth sensation of thirst Feel & taste of food stimulate receptors in taste

buds nuclei in brain stem parasymp impulse via facial & glossopharyngeal nerves to stimulate salivation Smell, sight, sound or thought of food may also stim.

4 basic layers of GI tract fig 24.2

Variations, but same basic organization in esophagus, stomach, small & large intestines

From inner to outermost (starting inside the __________) Mucosa Submucosa Muscularis Serosa

Layers of GI tract

1. ____________ - lines lumen, has 3 layers: ______________-

mouth, pharynx, esophagus, & anal canal= non-keratinized stratified squamous for protective function

stomach & intestines = simple columnar, w/ tight junctions for secretion & absorption

Cells renew every 5-7 days (rapid reproduction) Some epithelium = exocrine - mucus secreting cells Enteroendocrine cells secrete hormones into bloodstream

________________ –areolar CT, many bv & lymphatic vessels, nutrients tissues of body

Supports epithelium & binds to muscularis mucosa Contains most mucosa-associated lymphoid tissue

(MALT) – lymphatic nodules containing immune cells• Also found in tonsils, s.i., appendix and l.i.

________________- thin layer of smooth muscle Puts mucous membrane of stomach & s. i. into many

small folds ↑ SA for digestion & absorption movements insure absorptive cells fully exposed

2. _________________- areolar CT binds mucosa to muscularis Highly vascular __________________- portion of ENS- regulates

movements of mucosa & bv vasoconstriction Sensory – act as chemoreceptors & stretch receptors Interneurons – connect myentric & submucosal Motor - innervates secretory cells of epithelium

May contain glands and lymphatic tissue

3. _____________- mouth, pharynx, & superior-mid esophagus = skeletal muscle- swallow Skeletal muscle forms external anal sphincter Thru rest of tract: smooth muscle- generally found

in 2 sheets (exception- stomach has 3): Inner = circular layer outer = longitudinal layer Involuntary contractions breakdown food Mix food w/ secretions & propel it along tract Between 2 sheets: ________________ (ENS)- mostly

controls GI tract motility- freq & strength of contraction

4. __________- found in portions of GI tract suspended in abdominopelvic cavity serous membrane: areolar CT & simple

squamous epithelium AKA- visceral peritoneum Esophagus lacks this layer, has adventitia

instead- single layer of areolar CT & no simple squamous

Peritoneum figure 24.4

largest serous membrane of bodyconsists of a layer of simple squamous

(mesothelium) w/ supporting areolar CT __________________- lines abdominopelvic

cavity wall __________________- covers some organs in

cavity, is serosa peritoneal cavity- slim space between these layers

• contains serous fluid

Peritoneum (2)

___________________- organs lie on posterior abdominal wall covered by peritoneum on their anterior surface kidneys and pancreas

Bind organs to each other & walls of abdominal cavity Contain bv, lv, & nerves -supply organs Contains large folds between viscera:

1. ___________________ outward fold of serous coat of small intestine; binds to posterior ab wall

2. ___________________ binds large intestine to posterior ab wall; carries bv & lv to intestines

*both hold intestines loosely in place

Peritoneum (3)

3. ________________- attaches liver to anterior ab wall & diaphragm, (liver = only digestive organ attached to anterior wall)

4. ________________- 2 folds in serosa, suspends stomach & duodenum from liver, contains some lymph nodes

5. _______________- largest part of peritoneumHangs loosely like a “fatty apron” over transverse colon &

coils of small intestineContains considerable adipose & many lymph nodes,

contributes macrophages & plasma cells to combat infection & prevent spread of infection

Esophagus figure 24.10

Extends from laryngopharynx esophageal hiatus (surrounded by diaphragm) stomach

Stratified squamous epithelium Muscularis: superior 1/3 = skeletal

Intermediate 1/3 = skeletal & smooth Inferior 1/3 = smooth

At each end is sphincter ____________ – skeletal, regulate pharynx esophagus ____________ – smooth, regulate esophagus stomach

Adventitia- not serosa (no simple squamous cells) Secretes mucus, transport food No production of enzymes, no absorption

Deglutition (swallowing) - 3 phases

Movement of food from mouth to stomach ________________ stage- bolus forced back into

oropharynx by movement of tongue _______________ stage- bolus stimulates receptors in

oropharynx deglutition center in medulla & pons Soft palate & uvula close off nasal cavity Epiglottis closes off opening to larynx Bolus moves thru oro & laryngopharynx

________________ stage- bolus enters esophagus Peristalsis- progression of coordinated contractions &

relaxations of circular & longitudinal layers of muscularis Mucus to lubricate & reduce friction

Stomach

FunctionsAnatomy

Surface Epithelium Gastric Glands Secretory Cells

Digestive Processes Regulation of Gastric Secretion Gastric Motility and Emptying

Stomach functions figure 24.11

Mixes saliva, food & gastric juices to form __________ – semifluid mixture of partially digested food

reservoir for holding before release into s.i. secretes ___________ (2-3L/day), contains:

HCl - kills bacteria & denatures proteins Pepsin begins the digestion of proteins Intrinsic factor- aids absorption of vitamin B12 Gastric lipase - aids digestion of triglycerides

Secretes ___________ into blood when stomach is distended or pH is too high

Stomach anatomy figure 24.11

4 main regions: Cardia Fundus Body Pylorus

Pyloric sphincter Lesser curvature Greater curvature ____________ – large folds of mucosa when

stomach is empty

Histology of stomach fig 24.12, 13

Mucosa – simple columnar = surface mucous cells that extend into lamina propria forming columns of ____________ secretory cells – gastric glands which line gastric pits

Mucous neck cells- secrete mucus Parietal cells- secrete intrinsic factor & HCl Chief cells- secrete pepsinogen & gastric lipase

____________________ cells also part of gastric gland G cells- secretes gastrin, which stimulates gastric acitivity,

located mainly at pyloric antrum Muscularis – 3 layers: outer-longitudinal, mid-

circular, inner-oblique

Chemical digestion in stomach

food may remain in fundus for hr, salivary amylase works chyme mixes w/gastric juices & lingual lipase activated HCl denatures proteins & stimulates secretion of

hormones that promote flow of bile and pancreatic juice Also, acidity kills microbes

Enzymatic digestion of proteins begins w/pepsin Gastric lipase breaks down short chain triglycerides

(BUT, optimum pH is 5-6) Pancreatic lipase is more important

Small amt of nutrients absorbed in stomach Mucous cells absorb some water, ions, some f.a., drugs

(such as aspirin) & alcohol

What prevents auto-digestion?

_____________ secreted in inactive form: pepsinogen cannot digest proteins inside chief cells Pepsinogen pepsin in presence of HCl or

other active pepsin

Stomach epithelium protected by 1-3 mm of _______________ secreted by surface mucous cells & mucous neck cells

3 Phases of digeston, p 937

_________________ sight, smell, thought or initial taste activates neural centers in cerebral cortex, hypothalamus, & brain stem Facial and glossopharygeal nerves stimulate saliva

secretion Vagus nerve stimulates gastric juice secretion (all to prep mouth & stomach for food to be eaten)

Phases (2) figure 24.24

_________________ food in stomach, digestion begins Neural regulation- when either of following occur, sets off

negative feedback loop submucosal plexus activates parasym & enteric neurons peristalsis & gastric secretion

Stretch receptors monitor distention Chemoreceptors monitor pH

Hormonal regulation- gastrin regulates gastric secretions, released in response to distension, partially digested proteins, pH (food present), caffeine, or Ach (parasymp)

Glands to secrete large amt. gastric juice Strengthens contraction of LES stomach motility Relaxes pyloric sphincter

Phases (3)

_________________ – food enters small intestine, inhibitory effects to slow exit of chyme from stomach (contrary to cephalic & gastric) Neural regulation: Enterogastric reflex- duodenum distention signals

stretch receptors medulla oblongata inhibit parasym & activate symp. contraction of pyloric sphincter gastric emptying

Hormonal regulation: (see also table 24.8) Secretin – acidic chyme stimulates release

• stimulates secretion of pancreatic juice & bile, rich in HCO3 -

• Inhibits release of gastric juice• Enhances effects of CCK

Cholescystokinin (CCK)- secreted in response to a.a. & f.a.• stimulates secretion of pancreatic juice rich in digestive enzymes• causes ejection of bile from gallbladder• Causes opening of hepatopancreatic ampulla• induces satiety

Gastric motility and emptying

Several minutes after food enters, peristaltic waves body pylorus every 15-25 sec, create chyme, & forces @ 3mL into duodenum = ________________

During gastric phase, emptying is proportional to volume ingested due to distension & stretching of smooth mus. Extremely large amts of food motility

2-4 hr after meal stomach usually empties carbs take least amt of time, followed by protein-rich meal Lipid rich meals cause slowest emptying

f.a. & a.a. in duodenal chyme slows stomach motility Gastrin motility, secretin and CCK emptying

Small Intestine & Accessory Organs

Small Intestine Duodenum, jejunum, ileum, ileocecal sphincter Villi, Microvilli, plicae circulares

Liver Hepatic portal vein & hepatic artery Hepatic vein Bile duct

GallbladderPancreas

Functions of small intestine

_________________ mixes chyme w/ digestive juices & brings food into contact w/mucosa for absorption

_______________ propels chyme thru s.i. Completes digestion of carbs, proteins & lipids Begins & completes digestion of nucleic acids ____________ about 90% of nutrients and water

Other 10% in stomach & large intestine

Peristalsis and Segmentation

Anatomy of small intestine fig 24.17

3 regions: Duodenum- shortest (10 in), retroperitoneal,

pyloric sphincter jejunum Jejunum- 3 ft, extends to the: Ileum- 6 ft, joins w/ l.i. at ileocecal sphincter

Differences seen in microanatomy: _______________ in duodenum _______________ in ileum

Histology of small intestine fig 24.18, 19

Epithelium– simple columnar, many types: ________________ cells- digest & absorb nutrients in chyme ________________cells- secretes mucus

Additional glandular epithelial cells found in intestinal glands- crypts of Lieberkuhn – in mucosa of all s.i. Paneth cells- secrete lysozyme (bacteriocide), are also

phagocytic Enteroendocrine cells:

S cells- secretes secretin (stim secretion p.j & bile) CCK cells- secretes CCK (stim secretion p.e., release of bile) K cells- secretes (GIP) glucose-dependent insulinotropic peptide

Histology (2)

In the lamina propria: MALT Solitary lymphatic nodules in ileum Aggregated lymphatic follicles= Peyer’s patches in ileum

Submucosa: _____________ or _____________- secrete alkaline

mucus to neutralize gastric acid in chyme Lymphatic tissue may extend into

Serosa absent in duodenum

3 specializations that absorption in s. i.

_________________ (circular folds) – folds in mucosa & submucosa, permanent ridges In duodenum to mid- ileum Enhance absorption by SA & cause chyme to spiral thru

____________- fingerlike projection of mucosa, SA Lacteal- lymph capillary inside villus nutrients absorbed thru epithelial cells pass thru wall of lacteal

lymph or blood capillaries blood ___________ - projections of apical surface of

absorptive epithelium greatly surface area of plasma membrane form fuzzy line = brush border- contains several digest. enzymes

Digestion of carbohydrates

______________- destroyed by pH ________________- in pancreatic juice, acts in

small intestine Acts on glycogen and starch but not cellulose

-dextrinase- brush border enzyme works on -dextrins after amylases work on starch

3 brush border enzymes- ________ _________ ________ work on their respective disaccharides monosaccharides absorbed

Digestion of proteins

Starts in stomach __________ fragments proteins peptides Pancreatic juice enzymes continue protein

peptide, each breaking peptide bonds between different a.a. Trypsin Chymotrypsin Carboxypeptidase Elastase

__________ of brush border complete digestion Aminopeptidase- cleaves a.a. at amino end Dipeptidase- splits dipeptides

Digestion of lipids

Lipase- splits triglycerides & phospholipids Lingual- works in stomach Gastric- works in stomach Pancreatic- works in s.i., where most lipid digestion

occurs Triglycerides f.a. and monoglyceride

In order to be digested, lipid globules must be ___________ - globule is broken down to several globules, done by _____________ Bile salts- amphipathic molecules that interact with lipid

globule and watery intestinal chyme surface area of small globule allows for area on which

pancreatic lipase works

Absorption figure 24.20

Passage of digested nutrients from ___________ to_______ or _________ Diffusion Facilitated diffusion Osmosis Active transport

___% in _________, 10% in stomach & l.i.Undigested & unabsorbed passes thru l.i.

Monosaccharides

Form in which all carbs are absorbedLumen apical surface via facilitated

diffusion (fructose) or active transport (glucose & galactose)

All 3 monos thru basolateral membrane to capillaries liver via hepatic portal system general circulation (if not removed by hepatocytes)

Amino acids, dipeptides, tripeptides

Most proteins absorbed via active transport in duodenum & jejunum ½ proteins come from food ½ digestive juices and dead cells

________% of protein in s.i. is absorbedDifferent transporters for different a.a.a.a. basolateral membrane to

capillaries via diffusion liver (like monos)

Absorption of lipids

Via simple diffusion Bile salts surround f.a. & monoglycerides in chyme

making more soluble, form tiny spheres= __________ Micelles can also solubilize vitamins A, E, D, K & cholesterol

Micelles ferry f.a. & monoglycerides to brushed border diffuse micelle absorptive cells Inside cell recombine form triglycerides Aggregate w/ phospholipids & cholesterol coated w/protein =

_____________ exocytosed lacteals liver & adipose tissue Lipoprotein lipase breaks down triglycerides in chylomicron & f.a.

& glycerol diffuse hepatocytes or adipocytes Bile salts reabsorbed in ileum liver for recycling

Lipoprotein figure 25.13

Nutrients to blood and lymph

Liver functions

produces___- lipid emulsifier *main digestive fnc filters blood- destroying worn out RBC, WBC,

bacteria & other foreign material in venous blood draining GI tract

metabolizes carbs, lipids, protein processes drugs & hormones Excrete _______- byproduct hemoglobin break storage of glycogen, some vitamins & minerals Phagocytosis – ____________ Activation of vitamin D

Liver anatomy & histology fig 24.15

Right and left lobe, falciform ligamentLobule = functional unit of liver

6 sided, consists of hepatocytes arranged around a central vein. Blood flows from:

_________ at each corner _________ c.v. Bile duct- collect bile flowing thru canaliculi from

hepatocytes Hepatic portal vein- blood from GI tract Hepatic artery- oxygenated blood

Kupffer cells in sinusoids (large capillaries)

Hepatic blood flow figure 24.16

Gallbladder

Bile secreted by hepatocytes stored hereMucosa– simple columnar, rugaeSmooth muscle causes bile _________Along w/storage, functions to concentrate

bile water & ions absorbed in mucosa

Flow of bile figure 24.14

Bile production & release from g.b.

Hepatocytes secrete 800-1000mL/day Continuously release bile

_____ – neutral pH, water, bile salts, cholesterol, lecithin, bile pigments (biliruben), & ions

production & secretion if portal blood contains more bile acids

as digestion & absorption continue in s.i. bile release increases

When absorption , bile gallbladder _____________________ closed

Glucose, glycogen & gluconeogenesis

Liver helps maintain normal blood glucose Blood glucose

breakdown glycogen & release glucose Convert a.a. & lactic acidglucose=gluconeogenesis Convert galactose & fructose to glucose

Blood glucose Convert glucose to glycogen & triglycerides

_______________ – glucose formation from non-carbohydrate source When glycogen is depleted, lipids & proteins

catabolized

Glycogenesis & glycogenolysis 25.11

Gluconeogenesis figure 25.12

Lipid metabolism figure 25.14

Catabolism: __________ - triglyercides glycerol & f.a

Done by lipases Necessary for liver, muscle, adipose: f.a. ATP

Anabolism: _________ - liver & adipose: glu & a.a.lipids

Occurs when consume too many calories Triglyercides can be:

• Stored in adipose tissue• More rxns lipoprotein, phospholipids, & cholesterol

Plasma proteins & urea production

____________ (removal of NH2 or amine group from a.a.) occurs in hepatocytes a.a. used for:

ATP production Converted to carbohydrates and fats

Ammonia (NH3) is toxic & converted to ureaHepatocytes synthesize most ________

_________: Globulins & albumin (transport) Prothrombin & fibrinogen (clotting)

Pancreas figure 24.15

99% acini- ___________ function Secrete fluid & enzyme mixture = pancreatic juice

Pancreatic amylase- carbohydrate-digesting enzyme Trypsin, chymotrypsin, carboxypeptidase, & elastase- protein digesting

enz Pancreatic lipase- triglyceride digesting enzymes Ribonuclease & deoxyribonuclease- digest n.a.

1% Islets of Langerhans – __________ function Glucagon Insulin Somatostatin Pancreatic polypeptide

Pancreas (2)

2 passageways secretions small intestine: pancreatic duct- joins common bile duct

duodenum thru h.p. amp accessory duct = duct of Santorini

Pancreatic juice secretion stimulated by: _______________ _________ & ________ (in s.i) CCK also

opens hepatopancreatic ampulla

Large Intestine

AnatomyDigestive Processes

Water Electrolytes Vitamins

Defecation

Functions of the large intestine

Haustral churning, peristalsis, & _____________ drive contents of colonrectum

Bacteria in large intestine convert proteins to a.a., break down a.a., produce some B vitamins & ____________

Absorbs some water, ions & vitaminsForming feces______________ emptying the rectum

Anatomy of large intestine fig 24.22

cecum ascending transverse descending sigmoid colon rectum anal canal

Epithelium mostly simple columnar – absorptive & goblet cells, and are found lining intestinal glands– highly mucus prod.

___________ – 3 longitudinal bands of muscle extending along most l.i., Tonic contractions create pouches - ____________

Digestion in large intestine

_______________ – after meal, ileal peristalsis to force all chyme from ileum cecum Gastrin also relaxes ileocecal sphincter

Haustral churning- remain relaxed but after distended will contract

Peristalsis- slower than other areas of tract Mass peristalsis- strong wave from mid-transverse colon

quickly sending contents to rectum Is called a gastrocolic reflex- initiated by food in stomach Usually takes place 3-4 times/ day (immediately after meal)

____________ secreted, just mucus ____________ prepares chyme for elimination

Absorption, feces, & defecation

Chyme in l.i. 3-10 hr solid or semi-solid due to water absorption = feces Water, inorganic salts, GI mucosal cells, bacteria, products of

bacterial decomp, unabsorbed digested & undigested material

Water absorption here is crucial 0.5 -1.0 L enters, 100 - 200mL leaves Absorbs ions (Na+, Cl-) & some vitamins

Mass peristalsis _____________ – distention impulse parasym motor neuron causes contraction, also external anal sphincter- voluntary Bowel movements depend on diet, health, stress

Amt varies: 2-3/day to 3-4/week

Daily fluids