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The Digestive System Mouth---bite, chew, swallow

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1 The Digestive System Mouth---bite, chew, swallow
Pharynx and esophagus----transport Stomach----mechanical disruption; absorption of water & alcohol Small intestine--chemical & mechanical digestion & absorption Large intestine----absorb electrolytes & vitamins (B and K) Rectum and anus---defecation

2 Types of Digestion Mechanical – mouth, stomach,SI, LI
Chemical – mouth, stomach, SI

3 Layers of the GI Tract 1. Mucosal layer 2. Submucosal layer
3. Muscularis layer 4. Serosa layer

4 Mucosa Epithelium stratified squamous (in mouth, esophagus & anus) = tough simple columnar in the rest secretes enzymes and absorbs nutrients specialized cells (goblet) secrete mucous onto cell surfaces enteroendocrine cells---secrete hormones controlling organ function Lamina propria loose connective tissue contains BVs and lymphatic tissue Muscularis mucosae thin layer of smooth muscle causes folds to form in mucosal layer responsible for local food movements

5 Submucosa Loose connective tissue Meissner’s plexus
containing BV, glands and lymphatic tissue Meissner’s plexus part of the enteric nervous system - “brain of the gut” parasympathetic division only - sensory and motor neurons vasoconstriction of blood vessels to gut controls contraction of muscularis mucosa controls the secretory cells of the mucosal epithelium connected to the myenteric plexus (in the muscularis layer)

6 Muscularis Skeletal muscle = voluntary control
in mouth, pharynx , upper esophagus and anus control over swallowing and defecation Smooth muscle = involuntary control inner circular fibers & outer longitudinal fibers mixes, crushes & propels food along by peristalsis Auerbach’s plexus (myenteric plexus) both parasympathetic & sympathetic innervation of circular and longitudinal smooth muscle layers part of the Enteric nervous system controls overall GI tract motility

7 Serosa An example of a serous membrane
Covers all organs and walls of cavities not open to the outside of the body Covering the digestive organs in the peritoneal cavity = visceral peritoneum Secretes a serous fluid Consists of connective tissue covered with simple squamous epithelium

8 Peritoneum Peritoneum Peritoneal cavity visceral layer covers organs
parietal layer lines the walls of body cavity Peritoneal cavity potential space containing a bit of serous fluid

9 The Mesenteries of the GI tract
Mesentery – small intestines  parietal peritoneum Mesocolon – large intestine  parietal peritoneum Lesser omentum – liver  stomach Greater omentum

10 The path of food: oral cavity/teeth/salivary glands
oropharynx/epiglottis esophagus stomach small intestine: duodenum small intestine: jejunum small intestine: ileum large intestine: ascending colon large intestine: transverse colon large intestine: descending colon sigmoid colon rectum anus

11 Mouth Oral cavity proper---the roof = hard, soft palate and uvula
floor – geniohyoid, mylohyoid – contains the tongue lips and cheeks-----contains buccinator muscle that keeps food between upper & lower teeth Vestibule---area between cheeks and teeth Lined with an oral mucosa (stratified squamous epithelium & lamina propria) Lining of the cheeks = buccal mucosa Lining of the maxilla and mandible = alveolar mucosa (gingiva) Landmarks: lingual frenulum, labial frenulum, uvula Shortened lingual frenulum can impede movement of the tongue within the mouth

12 Tongue physiological functions
manipulation of food for chewing and swallowing production of digestive enzyme speech made of extrinsic and intrinsic muscles that control movement and the shape of the tongue extrinsic – control the movement of the tongue in and out of the mouth, manipulates food, hold the tongue in position and forms the floor of the mouth intrinsic – originate from and insert into the connective tissue of the tongue, alter the shape and size of the tongue for speech and swallowing lamina propria layer of the mucosa contains the lingual glands for the secretion of mucus and lingual lipase

13 Salivary Glands Parotid Gland – development at 4 to 6 weeks
duct = Stensen’s duct blood supply – external carotid artery parasympathetic nerve supply from IX sympathetic innervation by superior cervical ganglion Submandibular gland – development at 6 weeks duct = Wharton’s duct opens lateral to the lingual frenulum blood supply from facial and lingual arteries parasympathetic supply – facial nerve Sublingual gland – development at 8 to 12 weeks small ducts = ducts of Rivinus larger duct = Bartholin’s duct empty with the SM duct at the sublingual caruncle blood supply – sublingual and submental arteries facial nerve innervation Salivary Glands

14 Salivary Glands minor salivary glands 600 to 1000 glands
small aggregates of secretory tissue present in the submucosa not found in the gingiva and anterior hard palate predominantly mucus glands except the lingual glands (von Ebner’s glands) found on the tongue – open into troughs surrounding the circumvallate papilla labial, lingual, palatal, buccal, glossopalatine and retromolar glands

15 Saliva 600-1000ml/day Wet food for easier swallowing
Dissolves food for tasting Bicarbonate ions buffer acidic foods bulemia---vomiting hurts the enamel on your teeth Chemical digestion of starch begins with enzyme (salivary amylase) Protects mouth from infection with its rinsing action---1 to 1 and 1/2qts/day oral fluid is mixed or whole saliva – includes secretions from all three major glands + minor glands plus desquamated epithelial cells, microorganisms, food, debris, inflammatory cells and serum components

16 Saliva Components: 1. water 2. enzymes: amylase, lipase, lyzozyme
3. mucins, mucus 4. multiple electrolytes: sodium, postassium, chloride, calcium, magnesium 5. glucose, amino acids, urea, uric acid and lipids 6. secretory Igs – IgG and IgM and IgA 7. growth factors & hormones: EGF, insulin,

17 Saliva functions: 1. buffering – bicarbonate, phosphate ions
protection against demineralization caused by bacterial acids resulting from the breakdown of sugars 2. Pellicle formation many salivary proteins bind to the surface of the teeth and oral mucosa – forms a thin film = salivary pellicle several of these proteins bind calcium to protect the tooth 3. maintenance of tooth integrity saliva is saturated with calcium and phosphate ions at the tooth surface the high concentration of calcium and phosphate results in maturation of the enamel – increases surface hardness

18 4. antimicrobial action 5. tissue repair 6. digestion 7. taste
barrier function provided by mucins saliva also contains a spectrum of proteins with antimicrobial activity – histatins, lysozyme, lactoferrin and peroxidase also the presence of antibodies – IgA is the major salivary Ig (results in agglutination of microbes and prevents their adherence to oral tissues) 5. tissue repair variety of growth factors are present in saliva many promote tissue growth and differentiation 6. digestion amylase and lipase 7. taste solubilizes food substances – allows binding to taste receptors located in taste buds

19 Salivation controlled by the ANS
parasympathetic system provides a constant supply of saliva to keep the mucus membranes moist and to lubricate the food Increased salivation – parasympathetic system stimulation of taste receptors are conveyed to the cerebral cortex to the salivatory nuclei in brainstem returning impulses via the parasymp system travel via CN 7 & 9 Decreased salivation – sympathetic system

20 Digestion in the Mouth Mechanical digestion = mastication or chewing
breaks food into pieces mixes food with saliva so it forms a bolus Chemical digestion salivary amylase breakdown of complex carbohydrates into smaller pieces activity dependent upon pH lingual lipase secreted by glands in tongue begins breakdown of triglycerides into fatty acids and glycerol

21 Teeth: -grinding, tearing and shearing of food
-two main divisions: crown and root -crown: above gum-line -innermost layer - pulp (nerves/blood vessels) -outer covering of specialized calcified connective tissue - dentin -covered with a layer of enamel -root: entry of nerves and blood vessels -secures the tooth into the jaw (cementum) -covered by a periodontal membrane - unites with gums

22 Primary and Secondary Dentition
-primary: 20 teeth starting at 6 months -secondary/adult: between 6 and 12 years = 32 teeth 8 incisors - biting 4 canines (cuspids) - tearing 8 premolars (bicuspids) - grinding 12 molars (tricupids) - grinding ** third pair of molars (wisdom teeth) may not erupt -impacted

23 Pharynx Funnel-shaped tube extending from internal nares to the esophagus (posteriorly) and larynx (anteriorly) Skeletal muscle lined by mucous membrane Deglutition or swallowing is facilitated by saliva and mucus starts when bolus is pushed into the oropharynx sensory nerves send signals to deglutition center in brainstem (medulla oblongata)

24 Esophagus Collapsed muscular tube In front of vertebrae
Posterior to trachea Posterior to the heart Pierces the diaphragm at hiatus Esophagus Mucosa = stratified squamous Submucosa = large mucous glands Muscularis = upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth upper & lower esophageal sphincters are prominent circular arrangements of smooth muscle

25 Physiology of the Esophagus - Swallowing
1. Voluntary phase---tongue pushes food to back of oral cavity stimulates receptors in the oropharynx message travels to the deglutition center in the MO and lower pons 2. Pharyngeal stage (involuntary) breathing stops & air passages are closed vocal cords close epiglottis becomes bent over airway (glottis) as larynx is lifted controlled by autonomic nervous system 3. Esophageal phase (involuntary) - Peristalsis pushes food down circular fibers behind bolus contract longitudinal fibers in front of bolus also contract to shorten the distance of travel and widens the espophagus lower esophageal sphincter relaxes as food approaches the stomach

26 Anatomy of Stomach Size when empty Parts of stomach
large sausage stretches due to rugae Parts of stomach cardic portion fundus body pyloric portion – narrows at the pyloric sphincter bolus mixes with gastric juice in the stomach to form chyme stomach empties as small squirts of chyme leave the stomach through the pyloric sphincter

27 Muscularis Three layers of smooth muscle--outer longitudinal, circular & inner oblique Permits greater churning & mixing of food with gastric juice Serosa Simple squamous epithelium over a bit of connective tissue Also known as visceral peritoneum

28 Histology of the Stomach - Mucosa
simple columnar epithelium with embedded surface mucus cells epithelial cells form columns of secretory cells = gastric glands that line narrow channels called gastric pits glands - for the secretion of gastric juice mix of water, HCl, enzymes and hormones

29 Hydrochloric acid (parietal cells) converts Pepsinogen (from chief cells) to the enzyme pepsin = protein digestion HCl from the parietal cells is secreted as H+ and Cl-ions the H+ comes from the absorption of water into the parietal cell combination of water and CO2 by carbonic anhydrase creates carbonic acid which dissociates into HCO3- and H+ ions proton pumps actively pump H+ into the lumen of the stomach the bicarbonate is pumped into the blood in exchange for Cl-ions Cl- channels then allow the diffusion of these Cl- into the lumen Intrinsic factor (parietal cells) absorption of vitamin B12 for RBC production Gastric Mucosa

30 Gastric Mucosa Secretions
Parietal cells: HCl and Intrinsic Factor Chief cells: enzymes: pepsin and gastric lipase pepsin is secreted as the inactive form pepsinogen converted by contact with HCl gastric lipase – splits short-chain triglycerides (e.g. in milk) into two fatty acids and a monoglyceride (glycerol + one FA)

31 Stomach--Chemical Digestion
Protein digestion begins HCl denatures (unfolds) protein molecules HCl transforms pepsinogen into pepsin that breaks peptides bonds between certain amino acids Fat digestion continues gastric lipase splits the triglycerides in milk fat HCl kills microbes in food Mucous cells protect stomach walls from being digested

32 Absorption of Nutrients by the Stomach
Water especially if it is cold Electrolytes Some drugs (especially aspirin) & alcohol Gastric mucosal cells contain alcohol dehydrogenase that converts some alcohol to acetaldehyde more of this enzyme found in males than females 5 different forms of ADH – some more efficient then others

33 Gastric phase of digestion
starts once food reaches the stomach neural and hormonal regulation to promote gastric secretion and motility neural regulation: distension of the stomach stimulates stretch mechanoreceptors – stimulates production of gastric juices impulses travel via the parasympathetic neurons – stimulates the flow of gastric juice, causes waves of peristalisis to mix the food with the juice and move food into the SI chemoreceptors monitor pH of the stomach chyme as juice is being made as the pH of the stomach chyme decreases (becomes more acidic) –creates a negative feedback loop as the food leaves the stomach and the stretching of the wall lessens – this inhibits this path hormonal regulation: digestive hormones gastrin, secretin, CCK, GIP

34 Anatomy of the Small Intestine
20 feet long----1 inch in diameter Large surface area for majority of absorption 3 parts duodenum---10 inches jejunum---8 feet ileum---12 feet ends at ileocecal valve

35 Functions of Microvilli
Small Intestine SI has specific structures that increase surface area plica circularis permanent ½ inch tall folds that contain part of submucosal layer not found in lower ileum cannot stretch out like rugae in stomach villi Contains vascular capillaries and lacteals (lymphatic capillaries) microvilli produces a cell surface feature known as brush border Functions of Microvilli Absorption and digestion Digestive enzymes found at cell surface on microvilli - digestion occurs at cell surfaces

36 Intestinal Glands Small Intestine - Mucosal layer: Epithelial layer
Absorptive cells –absorb nutrients in the chyme cells at the bottom of the mucosa form Intestinal Glands Goblet cells - Unicellular glands that are part of simple columnar epithelium Enteroendocrine cells found within the Intestinal glands secretin cholecystokinin gastric inhibitory peptide Paneth cells secretes lysozyme kills bacteria Intestinal Glands

37 Absorptive cells: – production of brush-border enzymes (“intestinal juice”) -1 to 2 liters per day -enzymes are made and inserted into the microvilli of the absorptive cells -BB enzymes: enzymes for the digestion of carbohydrates, proteins (peptidases) and nucleic acids -

38 SI mucosal layer cont.... lamina propria of the SI contains areolar connective tissue plus an abundance of mucosa-associated lymphatic tissue – MALT solitary lymphatic nodules in the distal part of the ileum groups of nodes in the ileum – Peyer’s patches

39 Mechanical Digestion in the Small Intestine
1. Weak peristalsis in comparison to the stomach---chyme remains for 3 to 5 hours starts at the lower portion of the stomach and pushes the chyme forward reaches the end of the ileum after 90 – 120 minutes then another wave starts in the stomach 2. Segmentation---local mixing of chyme with “digestive juices” in the SI does NOT push the food through the tract move chyme back and forth over the lining of the SI done in specific segments of the SI most rapid in the duodenum and slows at it reaches the ileum

40 Small Intestine-Chemical Digestion
-protein and carbohydrate digestion via synthesis of the brush border enzymes by the intestinal glands -enterokinase -maltase, sucrase, lactase, a-dextrinase -aminopeptidase, dipeptidase -phosphatases and nucleosidases -enzymes are expressed on the surface of absorptive cells – external digestion -resulting monosaccharides, amino acids and nucleotides are internalized by the absorptive cell -SO carbohydrate and protein digestion stops in the interior of the absorptive cell

41 Small Intestine-Chemical Digestion
BUT - duodenum is also the site for secretion of the pancreatic juice: pancreatic amylase, pancreatic lipase + 4 proteases: trypsin, chymotrypsin, elastase, carboxypeptidase 1-2 qt./day at pH 7.6 proteases are made in the pancreas as inactive forms eg. Trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase Trypsinogen converted to trypsin by the brush border enzyme enterokinase Activated trypsin then converts other three proteases into their active forms

42 SI: Absorption of digested nutrients
occurs via diffusion, facilitated transport, osmosis and active transport water: 90% absorption occurs in the SI – 10% in the stomach and LI carbohydrates – absorbed as monosaccharides by either facilitated or secondary active transport fructose passes through the apical membrane of the absorptive cells via facilitated transport glucose and galactose are transported via secondary active transport created by the active transport of Na+ (eg. Na/glucose symporter) glucose and galactose compete for the saccharide site on this transporter all three monosacarrides leave through the basal surface of the absorptive cell and enter the blood via facilitated transport

43 SI: Absorption of digested nutrients
proteins – absorbed as amino acids by active transport in the duodenum and jejunum amino acids absorbed come from the food and from the digestive enzymes and the degrading absorptive cells different transporters carry different amino acids some enter through Na+/amino acid symporters others through H+ amino acid symporters enter into the blood via diffusion % of the proteins present in chyme in the SI are digested and absorbed

44 SI: Absorption of digested nutrients
Fat droplets coated with bile salts Fat globule Bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Epithelium of small intestine of lacteal Lacteal fats – absorbed via simple diffusion 95% absorbed in the small intestine bile induced emulsification results in breakdown of a fat into 2 fatty acids + a monoglyceride (one fatty acid + glycerol) the fatty acids are either short-chain or long chain short chain fatty acids and cholesterol move into absorptive cell via diffusion long chain fatty acids and monoglycerides require combination with bile in the form of a micelle micelle “ferries” the fatty acids and MGs into the absorptive cells bile returns to the SI lumen to “pick up” more FAs and MGs once inside the cell – FAs and MGs are reassembled into triglycerides these fats aggregate with phospholipids, apolipoproteins and cholesterol in the absorptive cell to form chylomicrons which enter the lacteal large pores of the lacteal allow for the passage of chylomicrons

45 Fat Processing chylomicrons enter the blood at the subclavian veins
removed from the blood as they pass through the liver liver expresses lipoprotein lipase (LPL) – breaks down the chylomicron into fatty acids, monoglycerides and cholesterol cholesterol is used to make bile cholesterol, TGs and apoplipoproteins are assembled into HDL or VLDL VLDL breaks down into LDL (by LPL enzyme) adipose cells are also capable of taking up chylomicrons and breaking them down via the LPL enzyme

46 Absorption in the SI Blood that enters the SI villi is rich in oxygen, poor in nutrients Blood that exits the villi is poor in oxygen and rich in nutrients BUT: venous blood may also be contaminated with toxins SO: blood from SI flows into the liver via the hepatic portal vein – to be filtered prior to emptying via the hepatic vein into the inferior vena cava

47 Absorption of Water 9 liters of fluid dumped into GI tract each day
Small intestine reabsorbs 8 liters Large intestine reabsorbs 90% of that last liter Absorption is by osmosis through cell walls into vascular capillaries inside villi

48 Anatomy of Large Intestine
5 feet long by 2½ inches in diameter Ascending & descending colon are retroperitoneal Cecum & appendix Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx Anal canal = last 1 inch of GI tract internal sphincter----smooth muscle & involuntary external sphincter----skeletal muscle & voluntary control

49 Histology of Large Intestine
Muscular layer internal circular layer is normal outer longitudinal muscle taeniae coli = shorter bands tonic contractions of these bands puckers the LI into pouches = haustra (pouches) formed (also called diverticulum) epiploic appendages Serosa = visceral peritoneum Appendix contains large amounts of lymphatic tissue

50 Histology of Large Intestine
Mucosa smooth tube -----no villi or plica folds mostly contains absorptive cells with microvilli in its epithelial component + goblet cells both absorptive and goblet cells are located in long tubular structures called Intestinal glands absorptive cells are for the absorption of water and salt ONLY! goblet cells secrete mucus Submucosa & mucosa contain lymphatic nodules – contribute to immunity

51 Mechanical Digestion in Large Intestine
Smooth muscle of muscularis = mechanical digestion Peristaltic waves (3 to 12 contractions/minute) haustral churning----relaxed pouches are filled by muscular contractions in the haustra below it gastroilial reflex = when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room for new chyme Also intensifies the peristaltic waves in the ileum and the older chyme then enters the caecum gastrocolic reflex = when stomach fills, a strong peristaltic wave moves contents of transverse colon into rectum

52 Chemical Digestion in Large Intestine
No enzymes are secreted only mucous – by the goblet cells in the intestinal glands BUT - chyme is aacted upon by the action of bacteria bacterial based chemical digestion NOT human-based Bacteria ferment: undigested carbohydrates - carbon dioxide & methane gas undigested proteins - simpler substances (indoles, skatoles, hydrogen sulfide)----odor turn bilirubin into simpler substances that produce color of feces Bacteria also produce vitamin K and B in colon

53 Absorption & Feces Formation in the Large Intestine
food has now been in the GI tract for 3 to 10 hours solid or semisolid form in the LI due to water reaborption = feces feces – water, salts, sloughed-off epithelial cells, bacteria, products of bacterial decomposition, unabsorbed and undigested materials 90% of all water absorption takes place in the SI – 10% in the LI but the LI is very important in maintaining water balance Excess water in feces = diarrhea Insufficient water in feces = constipation also absorbs some electrolytes---Na+ and Cl- can also absorb some vitamins

54 Fiber feces also contains materials undigestible by human enzymes = Fiber Three types of fiber: dietary fiber - indigestible plant carbohydrates (cellulose, lignin and pectin) soluble fiber – dissolves in water (beans, barley, broccoli, prunes, apples and citrus) forms a gel that slows the passage of materials through the colon also helps to lower blood cholesterol – binds to bile salts to prevent their reabsorption liver must make more bile – so it gets the cholesterol component of bile from LDL in the blood – lowers LDL levels also acted upon by bacteria – carbon dioxide and methane gas insoluble fiber – woody or structural parts of the plant (skins of fruits and vegetables, coatings around bran and corn) passes though the colon relatively unchanged

55 Defecation Gastrocolic reflex moves feces into rectum
Stretch receptors signal sacral spinal cord Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter External sphincter is voluntarily controlled

56 Digestive Hormones production of digestive hormones
gastrin – by the G cells of the stomach lining stimulates production of gastric juice and encourages emptying of the stomach also relaxes the sphincter between the ileum and cecum (ileocecal) gastric inhibitory peptide – antagonist to gastrin CCK – by the enteroendocrine cells of the SI (presence of fatty acids) CCK stimulates the release of pancreatic juice and bile (synthesis and increased gallbladder contraction) also slows the emptying of the stomach decreases gastric juice production secretin – by the enteroendocrine cells of the SI secretin stimulates the release of bicarbonate from the pancreas – neutralizes chime decreases gastrin production and release increases pepsinogen role in water regulation – activates the release of ADH from posterior pituitary

57 Digestive Feedback systems
emptying of the stomach: production of gastrin – stimulates emptying production of GIP/enterogastrone and CCK – inhibits emptying pancreatic juice production: secretin and CCK – stimulation of production bile production: CCK – stimulation of secretion Pancreas Stomach Entero- gastrone Gall- bladder Liver Duodenum Secretin CCK Stimulation Inhibition Gastrin Key

58 Anatomy of the Pancreas
5" long by 1" thick Head close to curve in C-shaped duodenum pancreatic duct joins common bile duct from liver Opens 4" below pyloric sphincter

59 Histology of the Pancreas
Acini- dark clusters 99% of gland produce pancreatic juice Islets of Langerhans 1% of gland pale staining cells produce hormones alpha cells, beta cells, delta cells, F cells

60 Endocrine cells secrete near a capillary
1 to 2 million pancreatic islets Contains 4 types of endocrine cells Alpha cells (20%) produce glucagon Beta cells (70%) produce insulin Delta cells (5%) produce somatostatin F cells produce pancreatic polypeptide

61 Composition and Functions of Pancreatic Juice
1 + 1/2 Quarts/day at pH of 7.1 to 8.2 Contains water, enzymes & sodium bicarbonate Digestive enzymes pancreatic amylase, pancreatic lipase, proteases trypsinogen---activated by enterokinase (a brush border enzyme) chymotrypsinogen----activated by trypsin procarboxypeptidase---activated by trypsin proelastase---activated by trypsin trypsin inhibitor---combines with any trypsin produced inside pancreas ribonuclease----to digest nucleic acids deoxyribonuclease

62 Anatomy of the Liver and Gallbladder
weighs 3 lbs. below diaphragm right lobe larger gallbladder on right lobe size causes right kidney to be lower than left Gallbladder fundus, body & neck

63 Histology of the Liver Hepatocytes arranged in lobules comprised of hepatocytes Lobules are surrounded by branches off the hepatic portal vein Running between the hepatocytes of the lobules are blood filled spaces = sinusoids Also running between hepatocytes of a lobule are bile canals = bile canaliculi – join to form the bile ducts of the liver Kupffer cells phagocytize microbes & foreign matter

64 Gallbladder Bile Production Simple columnar epithelium No submucosa
Three layers of smooth muscle Serosa or visceral peritoneum Bile Production One quart of bile/day is secreted by the liver yellow-green in color & pH 7.6 to 8.6 Components water & cholesterol bile salts = Na & K salts of bile acids bile pigments (bilirubin) from hemoglobin molecule Flow of Bile Bile capillaries Hepatic ducts connect to form common hepatic duct Cystic duct from gallbladder & common hepatic duct join to form common bile duct Common bile duct & pancreatic duct empty into duodenum

65 Bile functions emulsification – breakdown of fats into fatty acids (long or short chain) + monoglycerides make the long-chain fatty acids and monoglycerides (which are large) more soluble in the watery environment of the chyme bile salts surround the long-chain fatty acids and form tiny spheres called micelles amphipathetic nature of bile salts – hydrophobic portion interacts with the fatty acids micelles are absorbed into the absorptive cell the long-chain fatty acids and monoglycerides then separate from the bile and move into the absorptive cells cytoplasm – leaving the micelles behind (move back into the chyme) micelles act as a lipid “ferry” also solubilize other large hydrophobic molecules like the fat-soluble vitamins (A, D, E, K) and cholesterol

66 Liver Functions--Carbohydrate Metabolism
Turn amino acids into glucose (gluconeogenesis) Alanine and glutamine Turn triglycerides into glucose Turns glycerol into glucose (gluconeogenesis) Turns odd number FAs into glucose (gluconeogenesis) Turn excess glucose into glycogen & store in the liver Turn glycogen back into glucose as needed Liver Functions--Protein Metabolism Deamination = removes NH2 (amine group) from amino acids Converts resulting toxic ammonia (NH3) into urea for excretion by the kidney Synthesizes plasma proteins utilized in the clotting mechanism and immune system Convert one amino acid into another Liver Functions --Lipid Metabolism Synthesize cholesterol - Synthesize lipoproteins----HDL and LDL (used to transport fatty acids in bloodstream) Stores some fat Breaks down some fatty acids for energy production (ATP)

67 Other Liver Functions Detoxifies the blood by removing or altering drugs & hormones (thyroid & estrogen) Releases bile salts help digestion by emulsification Stores fat soluble vitamins-----A, B12, D, E, K Stores iron and copper Phagocytizes worn out blood cells & bacteria Activates vitamin D (the skin can also do this with 1 hr of sunlight a week)

68 Digestion of Carbohydrates
Chemical Digestion Digestion of Proteins Digestion of Carbohydrates Stomach HCl denatures or unfolds proteins secretion of pepsinogen and activation by HCl - pepsin turns proteins into peptides Pancreas secretion of pancreatic juice which contains trypsin, chymotrypsin etc… Intestines synthesis of brush border enzymes-----aminopeptidase or dipeptidase------split off amino acid at amino end of molecule Mouth---salivary amylase inactivated in the stomach by the low pH Esophagus & stomach---nothing happens Duodenum secretion of pancreatic juice (amylase) synthesis of the brush border enzymes (maltase, sucrase & lactase) act on disaccharides produces monosaccharides--fructose, glucose & galactose lactose intolerance (no enzyme; bacteria ferment sugar)--gas & diarrhea

69 Digestion of Nucleic Acids
Digestion of Lipids Digestion of Nucleic Acids Mouth----lingual lipase Small intestine emulsification by bile pancreatic lipase within the pancreatic juice---splits into 2 fatty acids + a monoglyceride no lipid-digesting enzymes made by the brush border Pancreatic juice contains 2 nucleases ribonuclease which digests RNA deoxyribonuclease which digests DNA Nucleotides produced are further digested by brush border enzymes (nucleosideases and phosphatases) break the nucleotide into pentose, phosphate & nitrogenous bases Absorbed by active transport

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