Bio25.txt

• Processes food, extracts the nutrients from it, and eliminates the residue
• Ingestion: intake
• Digestion: mechanical, chemical breakdown
• Absorption
• Compaction
• Defecation

Food for: 1. Fuel- carbohydrates 2 . Raw materials- CHONS 3 . Essential nutrients- vitamins, minerals

• Motility: mixing, propulsion
• Secretions: exocrine (digestive juices) and endocrine(hormones)
• Digestion: mechanical and chemical
• Absorption:designed to maximize (not regulated)

• Mechanical: the physical breakdown of food into smaller particles, exposes more food surface to the action of digestive enzymes
• Chemical: a series of hydrolysis rxns that break down dietary macromolecules into their monomers,; carried out by digestive enzymes produced by the salivary glands, stomach, pancreas, and small intestine

• epithelium
• lamina propria
• submucosa
• circular smooth muscle
• longitudinal smooth muscle
• serosa

molars, canines

stretching

lower esophageal sphincter

gastric lipase, intrinsic factor

gallbladder

small intestine

epinephrine

liver

• pharynx
• stomach
• duodenum
• jejunem
• ileum
• ascending colon
• transverse colon
• decending colon
• rectum

carboxypeptidase

large intestine

• macromolecues
• a. carbohydrates
• b. proteins
• c. fats

• absorbable units (products)
• a. monosaccharides (glucose, fructose, galctose)
• b. amino acids
• c. monoglycerides, fatty acids

• mesenteries: connective tissue sheets + adipose tissue
• fxns: holds abdomial viserca in their proper relationship to each other, provide passageway for blood vessels and nerves, contain lymph nodes for immunity, isolates infection
• lesser omentum: extends from liver to the superior margin of the stomach
• greater omentum: lager, fatty "apron" from the inferior margin of the stomach, loosely covering the small intestines

• mucosa
• inner lining of digestive tract
• epithelium
• lamina propria - loose connective tissue
• musclaris mucosae - thin layer, smooth muscle
• increase surface area for absorption

• submucosa
• thick layer of loose conncetive tissue containing blood vessels and lymphatics
• transport nutrients
• submucosal nerve plexus - regulates secretions

• muscularis externa
• circular smooth muscle - narrowing motions
• longitudinal smooth muscle - shortening motions
• myenteric nerve plexus - regulates motility

• serosa
• visceral peritoneum (reduces friction)

*plexuses - regulate, coordinate enteric nervous system (ENS), a subdivison of the ANS

short (myenteric) reflexes: stretching or chemcial stimulation, myenteric nerve plexus stimulate contactions, such as peristalic contractions of swallowing, completely in the GI tract, separate of CNS

long (vagovagal) reflexes: autnonmic nerve fibers, sensory signals to brain, and motor commands back to GI tract, PSNS increased activity, and SNS decreased activity

paracrine secretions: histamine

hormonal reflex: endocrine gland > capilliaries > target cell, gastrin and secretin

fxns: ingestion, taste and sensory repsonses, mastication, chemical diegestion (starch), swallowing, speech, respiration

teeth: masticate food, increase surface area of food for absorption, decrease particle size, chewing, mix with saliva for taste

• incisors: used to bite off a piece of food
• canies: act to puncture and shred food
• premolars/molars: crushing and grinding food

• secrete 1.0 to 1.5L of saliva/day
• under ANS regulation
• PSNS: stimulates the glands to produce abundant, thin slaiva rich in enzymes
• SNS: brief, produces less abundant, thicker saliva with more mucus

fxns: moistens/lubricates (mucus), digest starch (salivary amylase), dissolves food (taste), and antibacterail (lysozyme + IgA)

parotid glands, submandibular, sublingual glands

mumps is a parotid inflammation and swelling caused by a virus

• upper esophageal sphincter: closes + allows food bolus to pass down, keeps air out, pharyngeal constirctors muscles - force food downward when swallowing
• lower esophageal sphincter: relaxes to admit food + protects the esophageal mucosa from teh erosive effects of stomach acid ("heartburn")

• 1. tongue compresses food against palate to form a bolus
• 2. bolus passes into pharynx. misdirection of bolus is prevented by tongue blocking oral cavity, soft palate blocking nasal cavity, and epiglottis blocking larynx
• 3. upper esophageal sphincter constricts and blous passes downward
• 4. peristalisis drives bolus down esophagus. esophagus constricts above bolus and dilates and shortens belown it
• 5. lower esophageal sphincter relaxes to admit bolus to stomach

• 2400x/day
• gravity: how most goes to stomach, 1-2 seconds
• peristalisis: how large food goes to stomach, 4-8 seconds

*acid reflux: weak LES, aka "heartburn"

a wave of muscular contraction that pushes the bolus ahead of it, triggered by stretch receptors of the short reflex

• food storage organ
• digestion- mechanically breaks up food, liquifies it, begins chemical diegestion

• *smooth muscles: lontiguidonal, circular, oblique
• pyloric sphincter: "gate watcher"; regulates the passage of chyme into the duodenum

• rugae: mucosa and submucosa are flat, smooth when stomach is full, but as it empites, these layers form longitudinal folds called rugae, allows for digestion and absorption
• mucous cells: secrete mucus
• parietal cells: secrete hydrochloric acid and intrinsic factor
• chief cells: secrete the enzymes gastic lipase and pepsinogen
• G cells: hormones - gastrin + paracrine messangers (histamine)

• secretions: 2-3L/day
• food + gastric secretions = chyme

• HCl has a pH ~ 1
• stimulated by: PSNS (ACh), histamine, gastrin
• fnxs: dissolves food/denatrues proteins, kills bacteria - non specific resistanc, activates pepsin and gastric lipase

indicators: heartburn, ulcers; prilosec - proton pump inhibitor

• inactive proteins called zymogens are converted into active enzymes by the removal of some amino acids
• pepsinogen (zymogen), HCl removes some amino acids and coverts it to pepsin
• fxn: digest proteins to shorter peptide chains, which then pass to small intestine

• secreted by parietal cells
• fxn: essential to the absorption of vitamin B12 by the small intestine (ileum)
• without B12 hemoglobin cannot be synthesized and pernicious anemia develops

• arriving food stretches the stomach, activates receptive-relaxation response in which the stomach relaxes to accomodate more food
• peristalic waves: set by pacemaker cells in stomach of longitudinal layer, deploarization, action potential, then waves
• 3 waves/min
• strong wave: increased smooth muscle
• small wave: about 3 or 4 mL of chyme squirt thru to the dudenum each time
• neural imput: increased number of action potentials, increased contraction force

• mechanical digestion: big peices into small peices
• chemcial digestion: 15% of protein diegstion by pepsin, 10-15 % of fat digestion by gastric lipase
• not much absorption, except for some drugs (asprin)

• the stomach responds to the sight, smell, taste, or thought of food
• vagus nerve stimulates gastric secretions before food is swallowed
• thought, sight, smell > PSNS activity (to stomach via vagus) > increased secretions, increased motility

• food in the stomach activates gastric activity
• increased pH, increased enzymes, increased PSNS (vagus) + ENS
• ACh (secreted by PSNS), histamine, and gastrin stimulate (increase) gastric secertions and increase motility
• food stretches the stomach and activates myentertic nerve plexus and vagovagal reflex

• doudenum responds to arriving chyme, moderates gastric activity
• stimulators: stretch, amino acids, fats, acid
• enterogastric reflex: duodenem sends inhibitory signals to teh stomach by way of enteric nervous system
• intestinal gastrin stimulate the stomach - secretin, cck, enterogastric relex inhibit gastric secretions and motility, while duodenum process chyme. sympathetic nerve fibers suppress gastric activity while vagus (PSNS) stimulation of stomach is inhibited

• decreased PSNS, increased SNS
• increase secretin and increase CCK
• decreace gastric secretion, decrease motiltiy

• slow stomach emptying of chyme, gives duodenum time to work
• digest speed: fast - 2-4 hrs toast, carbs//slow 4-6 hrs bacon eggs

• largest gland: 3 lbs
• fxns: secretes bile, detoxifies blood before leaving GI tract
• *blood flows to liver via hepatic portal vein

stores/concentrates bile

• bile: contains minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids
• bilirubin: decomposition of hemoglobin, color stool brown
• bile acids (bile salts): steroids synthesized from cholesterol
• lecithin: a phospholipid that aid in fat digestion and absorption

* bile flow: recycled several times, only way to eliminate cholesterol

about 5% of bile salts are lost in feces

• pancreatic duct: runs lengthwise, joins bile duct at hapatopancreatic sphincter
• hepatopancreatic sphincter: controls the release of both bile and pancreatic juice into the duodenum (sphincter of Oddi)

• pancreatic zymogens (enzyme precursor) trypsinogen, converted to trypsin by enterokinase (secreted by mucosa of small intestine)
• CCK (cholecystokinin): stimulatory effect on the gallbladder, increases bile flow, stimulation of pancreatic enzyme secretions, positive feedback mechanism on pacrease, gallbladder, negative feedback mechanism on stomach
• secretin: stimulates an abundate bicarbonate solution
• HCO3-: flueshes enzymes from pancreas

• 9-12 ft. long, almost all digestion occurs here
• duodenum: first 10 inches, receives stomach contents, pancreatic juice, and bile, and enzymes take over chemcial digestion
• jejunum: next 40% of small intestine, thick, muscular, most digestion and absorption occurs here
• ileum: last 60%, thin, less muscular, less vascular, B12/bile salt absorption
• ileocecal sphincter: regulates passage of food residue into the large intestine; prevents feces from backing up

• in addition to CCK + secretin, secrete intestinal juice
• intestinal juice: water, mucus, NaCl, HCO3-
• 1-2 L secreted/day
• goblet cells: secrete mucus
• intesintal cypts (pores): epithelial cells are sloughed off and digested

• both endocrine and exocrine secretions
• endocrine: insulin and glucagon secreted into the blood
• exocrine: carry thur a duct - digestive enzymes into duodenum (lipase, amylase), zymogens (becoming proteases), duct cells secrete sodium bicarbonate, the bicarbonate buffers HCl arriving from the stomach

• circular folds: promotes more thorough mixing and nutrient absorption
• villi: finger-like projections, increase surface area 600x(200-300m2), increase absorption efficency
• microvilli: brush border, increase absorptive surface area, carry out final stages of chemcial digestion, contact digestion - chyme must contact brush border, enzymes are not secreted into lumen
• lymphatic vessels: absorbe fats/soluble vitamins, absorbed into lymph, "milky" consistancy

• most diegstiable carbohydrate is starch
• first digested into oligosaccharides ( 8 glcuose residues long), then 2nd into disaccharide maltose, finally into glucose, which is absorbed by small intsetine
• process begins in the mouth: salivary amylase hydrolizes starch inot oligosaccharides
• pancreatic amylase: chyme mixes with pancreatic amylase, converted to oligosaccharides an maltose
• complete digestion: chyme contacts brush border, maltase hycroslyzes maltose to glucose, immediately absorbed

• Mouth: no digestion
• stomach: pepsein hydrolyzes certain peptide bonds, breaking them into shorter polypeptides and small amount of free amino acids, about 10-15% of dietary protein digestion
• pancrease: trypsin and chymotrypsin take over protein digestion by hydrolyzing polypeptied chains into short oligopeptides
• brush border enzymes: dipeptidase, aminopeptidase take apart one amino acid at a time

absorption: action by the brush border enzymes, contact digestion, absorbed as amino acids


*absorptive cells of infacts can take up intact proteins, and release them into the blood, this allows IgA from breastmilk to pass into infants bloodstream and confer passive immunity from mother to infant

• lingual lipase: digests small amount of fat in the mouth
• gastric lipase: 10-15% of dietary fat digested
• pancreatic lipase: 85-90% fat digestion, emulsification droplets - contain lecithin and bile acids - attracted to the surface of fat globule, agitation by intestinal segmentation breaks up fat into droplets and coating of lecithin and bile acids keeps it broken up, exposing more surface area for enzymatic action

products of lipase action: two free fatty acids, and one monoglyceride

• micells: hydrophobic side faces inward, bile phospholipids and cholesterol diffuse into the enter of the micelle, micelle passes down bile duct into duodenum, they absorb fat soluble vitamins, more choesterol, and the FFA and monoglycerides of fat digestion, then absorbed in small intestin
• within brush border, FFA and monoglycerides are resynthesized into triglycerides, golgi complex forms chylomicrons, they are taken into the lymph, thur lymphatics to blood

• fat soluble vitamins: A, D, E - absorbed with other lipids as described in lipid absorption
• water soluble vitamins: C, B - absorbed by simple diffusion
• vitamin B12: absorbed only if bound to intrinsic factor
• minerals: electrolytes, absorbed by simple diffusion, and active transport
• water: absorbed by osmosis, follwing the absorption of salts and nutrients that create an osmotic gradient

• fluids: 8 - 9L/day - 85%
• secretions 7L/day
• food and drink: 99% absorbed, 1200 mL water, 800g solids per day ingested
• salivary secretions: 1500 mL
• gastric secretions: 200 mL
• bile: 500 mL
• pancreatic secretion: 6700 mL

excretion of cells: 17 billion/day, whole epithelium replaced in 5 days (susceptical to cancer drugs)

• segmentation: a movement in which stationary ringlike constricitons appear at several places along the intestine and then relax as new constrictions form elsewhere
• used to churn chyme and bring it into contact with the mucosa for contact digestion and nutrient absorption
• 12x/min in the duodenum, 8-9x/min in the ileum
• less frequent distally, slow progression of chyme toward colon, intensity is modified by nervous and hormonal influences
• migrating motor complex: peristalic wave, become successive and overlapping, milk chyme toward colon over 2 hr period, removes remaining food, limits bacterial infection
• enhanced segmentation in the ileum relaxs the sphincter, cecum fills with residue, sphincter shuts prevents reflux of cecal contents

• about 4 ft. long, less surface area, no villi, trillions of bacteria (800 species)
• cecum: ileocecal sphincter
• appendix: populated with lymphocytes, source of immune cells
• ascending, transverse, decending colon
• sigmoid colon: s-shaped
• rectum: straight
• internal anal sphincter: smooth muscle
• external anal sphinctre: skeletal muscle

• temporary storage
• removes water
• concentrates undigested material (500ml - 150 ml)
• secretions: mucus (goblet cells)
• digestion: bacteria digestes cellulocse, absorbable sugars > absorption > sugars from bacterial metabolism > nacl, water vitamins K and B

• haustral contractions: occur every 30 mins, churns, mixes the residude promotes water and salt absorption, passes residue distally to another haustral
• mass movement: occur 1-3 times/day, triggered by the filling of the stomach and duodenum, occur in the transverse and sigmoid colon

• stimulated by the stretching of the rectum
• intreinsic defecation: myentereic nerve plexus, stretch singals of plexus in descending and sigmoid colon and rectum, activates peristalic wave that drives feces downward, relaxes internal anal sphincter
• parasympathetic defecation reflex: stretch singal to spinal cord, motor signal returns by way of pelvic nerve to intensify perilstalsis in decending and sigmoid and rectum, and to relax internal anal sphincter
• **these are involuntary control, infants and spinal cord injuries

• voluntary control
• external anal sphincter: must be voulunarily relaxed, prolonged distortion > reversed peristalis > contents moved backwards until next mass movement

B. carbohydrate

D. spleen

C. longtiudinal

B. digest protein

intrinsic factor; pepsin

A. lower esophageal sphincter

D. cephalic

A. CCK and secretin are hormones secreted by the pancrease

B. stimulates the pancrease to release HCO3-

B. liver; gall bladder; fats