Ch. 23- The Digestive System

Anatomy of the Small Intestine

1) 20 feet long---- 1 inch in diameter 2) Large surface area for majority of absorption 3) 3 parts: (Duodenum-- 10 inches, Jejunum- 8 feet, Ileum- 12 feet) 4) Runs from pyloric sphincter to the ileocecal valve (Food travels from the duodenum to the jejunum to the ileum)

Composition of Bile

1) A yellow-green, alkaline solution containing bile salts, bile pigments, choleterol, neutral fats, phospholipids, and electrolytes 2) Bile salts are cholesterol derivatives that: (Emulsify fat, Facilitate fat and cholesterol absorption, Help solubilize cholesterol) 3) Bile leaves the liver via: (Bile ducts, which fuse into the common hepatic duct, Bile is concentrated in the gall bladder) 4) Bile capillaries 5) Hepatic ducts connect to form common hepatic duct 6) Cystic duct from gallbladder & common hepatic duct join to form common bile duct 7) Common bile duct & pancreatic duct empty into duoden

Functions of Microvilli

1) Absorption and digestion 2) Digestive enzymes found at cell surface on microvilli 3) Recieves pancreatic juices from pancreas

Cells of Intestinal Glands

1) Absorptive cell 2) Goblet cell 3) Enteroendocrine (Secretin, Cholecystokinin, Gastric inhibitory peptide) 4) Paneth cells (secretes lysozyme)

Serosa

1) An example of a serous membrane 2) Covers all organs and walls of cavities not open to the outside of the body 3) Secretes slippery fluid 4) Consists of connective tissue covered with simple squamous epithelium 5) This is the visceral peritoneum

Submucosa

Loose connective tissue: Containing Blood vessels, glands, and lymphatic tissue

Liver Functions-Protein Metabolism

1) Deamination= removes NH2 (amino group) from amino acids so can use what is left as energy source 2) Converts resulting toxic ammonia (NH3) into urea for excretion by the kidney 3) Synthesizes plasma proteins utilized in the clotting mechanism and immune system 4) Convert one amino acid into another

Other Liver Funtions

1) Detoxifies the blood by removing or altering drugs & hormones (thyroid & estrogen) 2) Removes the waste producte- bilirubin 3) Releases bile saltes help digestion by emulsification 4) Stores fat soluble vitamins A, B12, D, E, K 5) Stores iron and copper 6) Phagocytizes worn out blood cells & bacteria Kupffer cells 7) Activates vitamin D (the skin can also do this with 1 hr of sunlite a week)

Defecation

1) Distension of rectal walls caused by feces: (Stimulates contraction of the rectal walls, Relaxes the internal anal sphincter) 2) Voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs

Digestive Processes in the Mouth

1) Food is ingested 2) Mechanical digestion begins (chewing) 3) Propulsion is initiated by swallowing 4) Salivary amylase begins chemical breakdown of starch (carbohydrates) in the mouth 5) The pharynx and esophagus serve as conduits to pass food from the mouth to the stomach

Pharynx

1) From the mouth, the oro- and laryngopharynx allow passage of: (Food and fluids to the esophagus, Air to the trachea) 2) Lined with stratified squamous epithelium and mucus glands 3) Has two skeletal muscle layers: (Inner longitudinal, Outer pharyngeal constrictors)

Regulation of Gastric Emptying

1) Gastric emptying is regulated by (The neural enterogastric reflex, Hormonal mechanisms) 2) These mechanisms inhibit gastric secretion and duodenal filling 3) Carbohydrate- rich chyme quickly moves through the duodenum 4) Fat- laden chyme is digested more slowly causing food to remain in the stomach longer

Greater Omentum, Mesentary, Mesocolon

1) Greater Omentum hangs down over intestines like an apron 2) Mesocolon secures the LI to parietal peritoneum 3) Mesentery connects body organs to the body wall and provides routes for blood vessels and nerves to reach digestive organs

Microscopic Anatomy of the Liver

1) Hepatacytes are the structural and functional units of the liver (Hepatocytes arranged in lobules) 2) Sinusoids in between hepatocytes are blood-filled spaces 3) Kupffer cells phagocytize microbes & foreign matter 4) Hepatocytes' functions include: (Production of bile, Processing bloodborne nutrients, Storage of fat-soluble vitamins, Detoxification) 5) Secreted bile flows between hepatocytes toward the bile ducts in the portal triads

Blood Supply to the Liver

1) Hepatic portal vein (Nutrient rich blood from stomach, spleen & intestines) 2) Hepatic Artery from branch off the aorta 3) Both send blood to the sinusoids

Gastrointestinal Tract Activities

1) Ingestion- taking food into the digestive tract 2) Propulsion- swallowing and peristalsis (Peristalsis is waves of contraction and relaxation of muscles in the organ walls that propel contents from one point to another) 3) Mechanical digestion- chewing, mixing, and churning food 4) Chemical digestion- catabolic breakdown of food 5) Absorption- movement of nutrients from the GI tract to the blood or lymph 6) Defection- elimination of indigestible solid wastes

Control of Salivation

1) Intrinsic glands keep the mouth moist 2) Extrinsic salivary glands secrete serous, enzyme-rich saliva in response to: (Ingested food which stimulates chemoreceptors and pressoreceptors) 3) Strong sympathetic stimulation inhibits salivation and results in dry mouth

Deglutition (Swallowing)

1) Involves the coordinated activity of the tongue, soft palate, pharynx, esophagus and 22 separate muscle groups 2) Buccal phase- Bolus is forced into the oropharynx 3) Pharyngeal- esophageal phase- controlled by the medulla and lower pons (All routes except into the digestive tract are sealed off by the medulla and lower pons) 4) Peristalsis moves food (Bolus) through the pharynx to the esophagus

Muscularis

1) Made up of circular and longitudinal sheets of tissue 2) Skeletal muscle= voluntary control (In mouth, pharynx, upper esophagus and anus, Control over swallowing and defecation) 3) Smooth muscle= involuntary control (Inner circular fibers & outer longitudinal fibers, Mixes, crushes, & propels food along by peristalsis) 4) Auerbach's plexus (Both parasymphathetic & sympathetic innervation of circular and longitudinal smooth muscle layers)

Parts of the Peritoneum

1) Mesentery 2) Mesocolon 3) Lesser omentum 4) Greater omentum 5) Peritonitis= inflammation (Traima, Rupture of GI tract, Appendicitis, Perforated ulcer)

Digestion of Carbohydrates

1) Mouth- Salivary amylase 2) Esophagus & stomach--- nothing happens 3) Duodenum---- pancreatic amylase 4) Brush Border enzymes act on disaccharides (Produces monosaccharides-- fructose, glucose & galactose, Lactose intolerance)

Overview of GI tract Functions

1) Mouth- bite, chew, swallow (Starch digestion) 2) Pharynx and esophagus- transport 3) Stomach- mechanical disruption; chemical digestion, absorption of water and alcohol 4) Small intestine- chemical and mechanichal digestion and absorption 5) Large intestine- absorb electrolytes and vitamins (B and K) 6) Rectum and anus- defecation

Digestion of Lipids

1) Mouth- lingual lipase 2) Small intestine (Emulsification by bile from the liver, Pancreatic lipase- splits into fatty acids & monoglyceride, Nearly all lipid digestion occurs in duodenum, No enzymes in brush border)

Layers of the GI tract

1) Mucosal layer 2) Submucosal layer 3) Muscularis layer 4) Serosa layer

Esophogus

1) Muscular tube going from the laryngopharynx to the stomach 2) Travels through the mediastinum and pierces the diaghragm 3) Joins the stomach at the cardiac orifice

Mouth

1) Oral or Buccal Cavity: (Is bounded by lips, cheeks, palate, and tounge, Has the oral orifice as its anterior opening, Is continuous with the oropharynx posteriorly) 2) To withstand abrasions: (The mouth is lined with stratified squamous epithelium, The gums, hard palate, and dorsum of the tongue are slightly keratinized)

Mouth

1) Oral or buccal cavity (Is bounded by lips, cheeks, palate, and tongue, Has the oral orifice as its anterior opening, Is continuous with the oropharynx) 2) To withstand abrasions: (The mouth is lined with stratified squamous epithelium, The gums, hard palate, and dorsum of the tongue are slightly keratinized)

Teeth

1) Primary and permanent dentitions have formed by age 21 2) Primary- 20 deciduous teeth that erupt at intervals between 6 and 24 months 3) Permanent- enlarge and develop causing the root of deciduous teeth to be resorbed and fall out between the ages of 6 and 12 years (There are usually 32 permanent teeth, All but the third molars have erupted by the end of adolescence)

Salivary Glands

1) Produce and secrete saliva that: (Cleanses the mouth, washes away food and bacteria, Moistens and dissolves food chemicals, Aids in bolus formation, Contains enzymes that break down starch, Lubricates the mouth) 2) Three pair of extrinsic glands- parotid, submandibular, and sublingual 3) Intrinsic salivary glands (buccal glands)- scattered throughout the oral mucosa

Saliva: Source and Composition

1) Secreted from serous and mucous cells of salivary glands 2) A 97-99.5 water, hypo-osmotic, slightly acidic solution containing (Electrolytes- Na+, K+, Cl-, PO42-, HCO3-, Digestive enzyme- salivary amylase, Proteins- mucin, lysozyme, defensins, and IgA, Metabolic wastes- urea and uric acid)

Absorption and Feces Formation

1) Some electrolytes are absorbed- Na+ and Cl- 2) After 3-10 hours, 90% of H2O has been removed from chyme 3) Feces are semisolid by time reaches transverse colon 4) Feces= dead epithelial cells, salts, bile pigments, undigested food such as cellulose, bacteria (live & dead)

Digestion of Proteins

1) Stomach (HCL denatures or unfolds proteins, Pepsin turns proteins into peptides) 2) Pancreas (Digestive enzymes-- split peptide bonds between different amino acids, Brush border enzymes- aminopeptidase or dipeptidase- split off amino acid at amino end of molecule or split dipeptide)

Roles of Intestinal Juices and Brush Border Enzymes

1) Submucosal layer has duodenal glands (Secretes alkaline mucus) 2) Mucosal layer contains intestinal glands = Crypts of Lieberkuhn (Secretes intestinal juice, Secretes brush border enzymes)

Liver Functions-Lipid Metabolism

1) Synthesize cholesterol 2) Synthesize lipoproteins---- HDL and LDL (used to transport fatty acids in bloodstream) 3) Stores some fat 4) Breaks down some fatty acids

Classification of Teeth

1) Teeth are classified according to their shape and function (Incisors- chisel shaped teeth adapted for cutting or nipping, Canines- conical or fanglike teeth that tear of pierce, Premolars and molars- have broad crowns with rounded tips and are best suited for grinding or crushing) 2) During chewing, upper and lower molars lock together generating crushing force

Digestive Process

1) The GI tact is a "disassembly" line (Nutrients become more available to the body in each step) 2) There are six essential activities: (Ingestion, Propulsion, and Mechanical Digestion, Chemical Digestion, Absorbtion, and defection)

Liver

1) The largest gland in the body 2) Superficially has four lobes- right, left, caudate, and quadrate

Associated Structures to the Liver

1) The lesser omentum anchors the liver to the stomach 2) The hepatic blood vessels enter the liver at the porta hepatis 3) The gallbladder rests in a recess on the inferior surface of the right lobe

Stomach Lining

1) The stomach is exposed to the harshest conditions in the digestive tract 2) To keep from digesting itself, the stomach has a mucosal barrier with: (A thick coat of bicarbonate-rich mucus on the stomach wall, Epithelial cells that are joined by tight junctions, Gastric glands that have cells impermeable to HCL) 3) Damaged epithelial cells are quickly replaced

Digestion in the Stomach

1) The stomach: (Holds ingested food, Degrades this food both physically and chemically, Delivers chyme to the small intestine, Enzymatically digests proteins with pepsin, Secretes intrinsic factor required for absorption of vitamin B12) 2) Chemical breakdown of proteins begins in the stomach 3) The pylorus of the stomach is continuous with the duodenum through the pyloric sphincter

Gall Bladder

1) Thin-walled, green muscular sac on the ventral surface of the liver 2) Stores and concentrates bile by absorbing its water and ions 3) Releases bile via the cystic duct, which flows into the bile duct

Liver Functions-Carbohydrate Metablolism

1) Turn proteins into glucose 2) Turn triglycerides into glucose 3) Turn excess glucose into glycogen and store in the liver 4) Turn glycogen back into glucose as needed

Tooth Structure

1) Two main regions- crown and the root 2) Crown- eposed part of the tooth above the gingiva (gum) 3) Enamel- acellular, brittle material composed of calcium salts and hydroxyapatite crystals is the hardest substance in the body (Encapsules the crown of the tooth) 4) Root- portion of the tooth embedded in the jawbone 5) Neck- constriction where the crown and root come together 6) Cementum- calcified connective tissue (Covers the root, Attaches it to the periodontal ligament) 7) Periodontal ligament (Anchors the tooth in the alveolus of the jaw, Forms the fibrous joint called a gomaphosis) 8) Gingival sulcus- depression where the gingiva borders the tooth 9) Pentin- bonelike material deep to the enamel cap that forms the bulk of the tooth 10) Pulp cavity- cavity surrounded by dentin that contains pulp 11) Pulp- connective tissue, blood vessels, and nerves 12) Root canal- Portion of the pulp cavity that extends into the root 13) Apical foramen- proximal opening to the root canal 14) Odontoblasts- secrete and maintain dentin throughout life

Peritoneum

A slippery serous membrane: 1) Peritoneum (visceral layer covers organs, Parietal peritoneum are sheets of connective tissue that lines the walls of body cavitys) 2) Peritoneal cavity (Potential space containing a bit of serous fluid)

Glands of the Stomach Fundus and Body

Gastric glands of the fundus and body have a variety of secretory cells: 1) Mucous neck cells- secrete acid mucus 2) Parietal cells- secrete HCL and intrinsic factor 3) Chief cells- produce pepsinogin

Lesser Omentum

Membrane that suspends the stomach and duodenum from the liver

Mucosa

Mucosa- epithelium laying on connective tissue and a thin layer of muscle: 1) Epithelium (Secretes enzymes and absorbs nutrients, Specialized cells secrete mucous, Enteroendocrine cells secrete hormones controlling organ function) 2) Submucosa or Lamina propria (Made up of thin layer of loose connective tissue, Contains BV and lymphatic tissue) 3) Muscularis mucosae- thin layer of smooth muscle (Causes folds to form in mucosal layer, Increases local movements increasing absorption with exposure to "new" nutrients) 4) Serosa layer of mucosa

Histology of Small Intestine

Structures that increase surface area: 1) Plica circularis (Permanent 1/2 inch tall folds that contain part of submucosal layer, Not found in lower ileum, Can not stretch out like rugae in stomach) 2) Villi (1 Millimeter tall, Core is lamina propria of mucosal layer, Contains vascular capillaries and lacteals) 3) Microvilli (Cell surface feature known as brush border)