Digestive System Part 2

• 1. Food ingested: by mouth
• 2. Mechanical digestion: chewing
• 3. Chemical digestion: Salivary amylase begins chemical breakdown of starch
• 4. Propulsion: initiated by swallowing
• 5. Pharynx and Esophagus: pass food from mouth to stomach

• passes food and fluids to esophagus and gives air to trachea
• -lined with stratified squamous epithelium and mucus glands
• -two skeletal muscle layers for swallowing
• 1. inner longitudinal
• 2. outer pharyngeal constricters

Swallowing: involving 22 seperate muscle groups and involves 3 phases

• (within deglutition)
• bolus is forced into oropharynx

• (within deglutition)
• -controlled by medulla and lower pons
• routes sealed off except into digestive tract (probably so we don't choke)

• (within deglutition)
• moves food through pharynx and esophagus

• muscular tube going from laryngopharynx to stomach
• travels through mediastinum and pierces diaphragm
• joins stomach at cardiac orifice

nonkeratinized stratified squamous epithelium

its folder longitudinally and flattened

skeletal (superiorly) to smooth muscle (inferiorly)

• when the cardiac (gastroesophageal) Sphyncter does not close when food is in stomach
• -causes pregnancy, obesity, weak sphyncter
• -superior stomach can move into thoracic cavity

• is a result with acid irritating the esophagus
• -if chronic then esophageal cancer can result

• Amylase: carbs-glucose
• Lingual Lipase: fats-fatty acids

• Pepsin: proteins-polypeptides
• HCl: pepsinogen-pepsin, destroys pathogens

Bile Salts: fats-fatty acids

• Amylase: carbs-glucose
• Trypsin: polypeptides-peptides
• Lipase: fats-fatty acids

• peptidase: peptides-amino acids
• sucrase: sucrose-glucose
• maltase: maltose-glucose
• lactase: lactose-glucose

chemical breakdown of proteins and food is converted into chyme

surrounds cardiac orifice and cardic sphincter

dome shaped region beneath diaphragm

• made of antrum and canal whih terminates at pylorus
• -pylorus extends to duodenum

holding the small intestines in place

sympathetic and parasympathetic fibers of autonomic nervous system

• celiac trunk (gastric artery
• corresponding veins (gastric veins)

part of hepatic portal system

• allows stomach to churn, mix, and pummel food physically
• breaks down food into smaller fragments

Goblet cells: produce double layer coat of alkaline insoluble mucus with bicarbonate in between

contain gastric glands that secrete gastric juice, mucus, and gastrin

secrete acid mucus

secrete HCl and intrinsic factor needed for Vitamin B12 (nucleic acid metabolism and RBC maturation) absorption in small intestines

produce pepsinogen

(pepsinogen activated to pepsin by HCl in stomach and pepsin breaks down proteins to polypeptides)

• Secretes:
• -Gastrin: stimulates gastric glands to increase there secretion, stimulates gastric emptying
• -Histamine: activates parietal cells to release HCl
• -Serotonin: stimulates gastric muscle contractions
• -Cholecystokinin (CCK): allows pancreatic and bile enzymes to be released
• -Ghrelin: release when stomach is empty stimulating hunger and appetite

• thick coat of bicarbonate-rich mucus on wall
• epithelial cells joined by tight junctions (damaged cells are replaced quickly)
• gastric glands that have cells impermeable to HCl

• bacteria Helicobacter pylori (H. pylori)
• burrs a hole through the mucusa and allows HCl to further irritate the lining

• 1. bacteria secretes ammonia, neutralized the HCl
• 2. secretes cytotoxin that damages mucosal cells
• 3. produces proteins that sepertate cells tight junctions

• 1. holds food
• 2. degrades food physcially and chemically
• 3. delivers chyme to small intestine
• 4. Enzymatically digests proteins to polypeptides to pepsin
• 5. secretes intrinsic factor required for absorption of vitamin B12 (needed for DNA synthesis and erythropoeisis)

Cephalic (reflex), Gastric, and Intestinal phase

• happens before food enters stomach
• -Excitatory: think, smell, taste, see
• enhanced secretory activity (reflex) only happens when we want or like food we see
• -Inhibitory: loss of appetite/depression, decrease in stimulation of parasympathetic division

Enteric ganglionic neurons stimulate the stomach glands

• food enters stomach
• last 3-4 hours
• Excitatory: stomach distension,
• activation of stretch receptors,
• activation of chemoreceptors by peptides caffeine, and lowering pH,
• release of gastrin in blood (stimulates gastric glands to increase secretion=gastric emptying
• Inhibitory: pH lower than 2
• emotional upselt overrides parasympathetic division
• *ACh release, stimulates more gastric juice
• rise in pH stimulates gastrin secretion and HCl release (more acid for protein digestion)

Excitatory: low pH; partially digested food enters duodenum and encourages gastric gland activity

• Inhibitory: distension of duodenum, presence of fatty, acidic, hypertonic chyme, and/or irritants in duodenum
• -initiates inhibition of local reflexes
• -closes pyloric sphincter
• -small intestines release enterogastrones (CCK and Secretin), inhibit gastric secretion

• ACh
• histamine
• gastrin

• H2
• HCl

1.5 L

4L

• 6-10 inches
• to the top of the pelvis when filled

• 3
• minute

• Basic Electrical Rhythm
• pacemaker cells
• Cells of Cajal

• pacemaker cells
• longitudinal muscles of stomach
• * these cells are stimulated by the stretch

pylorus

• -small amounts to duodenum
• -backward into stomach for further mixing

• -neural enterogastric reflex
• -hormonal (enterogastrone) mechanisms

-they inhibit gastric secretion and duodenal filling

Carbohydrate-rich

fat-laden chyme, because its digested slower

• Duodenum: 10-12 inches
• Jejunum: 8 feet long
• Ileum: 11 feet long

• deep circular folds of the mucosa and submucosa
• forces chyme through and increase time of absorption

fingerlike extensions of mucosa

• brush border cells
• tiny projections of absorptive mucosal cells' plasma membranes
• also secrete digestive enzymes

• Crypts of Lieberkuhn
• secrete intestinal juice

• submucosa
• Ileum

Brunner's glands which neutralizes acidic chyme from stomach

• seperates right and left lobes of liver
• suspends liver from diaphragm and anterior abdominal wall

• remnant of fetal umbilical vein
• circular
• runs along free edge of falciform ligament

closed

• bile duct
• hepatic artery
• hepatic portal vein

each of the 6 corners of each liver lobule

hepatocyte (liver cell) plates radiating outward from central vein

• enlarged, leaky capillaries located between hepatic plates
• blood from hepatic portal vein and artery come through here and empties into central vein

• hepatic macrophages found in liver sinusoids
• they remove debris such as bacteria and worn out blood cells from blood

• 1. Production of Bile
• 2. Processing bloodborne nutrients
• 3. Storage of fat-soluble vitamins
• 4. Detoxification

• hepatocytes
• bile ducts
• portal triads

• yellow-green
• alkaline
• bile salts
• bile pigments
• cholesterol
• neutral fats
• phospholipids
• electrolytes

• cholesterol derivatives:
• -emulsify fat
• -facilitate fat and cholesterol absorption
• -solubilize cholesterol

bilirubin, waste product of heme

recycles them

• thin walled, green muscular sac on ventral surface of liver
• stores and concentrates bile by absorbing water and ions
• releases bile by cystic duct

• duodenum to release CCK and secretin into bloodstream
• this stimulates liver to produce bile

causes weak contractions of gallbladder

• gallbladder to contract
• hepatopancreatic sphincter to relax
• *Result: bile enters duodenum

• produces most digestive enzymes of any organs
• 1200-1500mL per day
• exocrine and endocrine gland

• 1. Typsin: polypeptides-peptides
• 2. Lipase: fat-fatty acids
• 3. Amylase: Carbs-glucose
• 4. Nucleases: Nucleic acid-nucleotides
• 5. Carboxypeptidase: polypeptides-peptides

*part of Exocrine function

• cluster of secretory cells
• contain zymogen granules with digestive enzymes

• (Beta cells of Islets of Langerhans)
• decreases blood sugar by removing it from blood into cells

• Alpha cells
• increases blood sugar by breaking down glycogen into glucose and fat.

water solution of enzymes and electrolytes

• Neutralizes acid chyme
• provides optimal environment for pancreatic enzymes
• enzymes are activated in duodenum

• -carbs and proteins are partially digested
• -no fat digestion takes place
• -chyme release slowly because low pH, mixing required for proper digestion
• -substances needed provided by liver
• -all nutrient absorption take place in small intestine

• -segmentation
• -initiated by pacemaker cell (Cajal cells)
• -Migrating Motility Complex (MMC) peristaltic activity

meal remnants, bacteria, mucosal cells, debris are moved into large intestine

~2 hours