Anatomy Ch 24

Digestion & Absorption - to break down food into molecules and then absorb them.

• The GI tract - it runs from mouth to anus
• 30 feet long

• Primary:
• 1. Oral cavity
• 2. pharynx - naso, oro, hypo
• 3. Esophagus
• 4. Stomach
• 5. Intestines - small & large bowel
• - - small = duodenum, jejunum, ileum
• - - large = cecum, ascending, transverse, descending colon, sigmoid colon, rectum
• 6. anus

• Accessory Organs:
• 1. teeth, tongue, salivary glands
• 2. liver
• 3. gallbladder
• 4. pancreas

• Motility - mixing and moving of substances
• Peristalsis - alternating contracting & relaxing of smooth muscle
• The GI tract mixes and propels through churning and peristalsis.

• 1. Mechanical digestion - physical chewing & chruning
• 2. Chemical digestion - enzymes, HCl

Absorption - absorb products of digestion (nutrients, drugs) at the molecular level (a.a. not proteins)

M-S-M-S

• M = Mucosa
• S = Submucosa
• M = Muscularis
• S = Serosa

• Mucosa is the innermost layer - surrounds the lumen
• Has 3 regions (layers)
• 1. Epithelium - stratified squamous (upper) - simple columnar (lower) (absorption)
• 2. Lamina Propria - loose areolar CT - some absorption occurs here
• 3. Muscularis mucosa -smooth muscle layer - ridges (folds) for more SA so above absorbs better.

Absorption occurs in the epithelium & lamina propria regions

• Submucosa = CT layer (blood vessels, lymph, & nerves)
• - some absorption occurs here
• Submucosal nerve plexus called the Plexus of Meissner that controls movement of the muscularis mucosa & gastrointestional secretions.

• Muscularis has two types of tissue layers:
• 1. Voluntary - single layer of skeletal muscle - occurs from oral cavity to upper esophagus & also at the external anal sphincter.

• 2. Involumtary - double layer of smooth muscle - from lower espohagus to internal anal sphincter. Arranged in two sheets:
• a. longitudinal (outer)
• b. circular (inner)

• - The myenteric pleus called the Plexus of Auerbach (ANS) is between the two muscle layers and controls muscularis contraction/ relaxation
• b

• Serosa is also known as the visceral peritoneum
• - it attaches areas of the lower GI to the surrounding structures
• - it is simple squamous epithelium (outer) + CT (inner)
• - it is found in the abdominopelvic cavity

- in the esophagus it is called the adventitia and is only CT (no epithelium)

The ENS is the brain of the gut - it is part of the ANS (sym & para) but the ENS can function independantly

1. Plexus of Auerbach - Myerteric plexus = motor (GI motility) - located in the muscularis between the muscle layers

2. Plexus of Meissner - in the Submucosal layer - controls movement of secretions

• Parasympathetic tells the GI to rest & digest
• Vagel nerve innervates the top half → ACh
• Sacral never innervates botton half → ACh

• Sympathetic nerves that innervate the GI tract arise from the thoracic and upper lumbar area of the spinal cord.
• Sympathetic = GI inhibition (fight or flight) → NOR

Chemoreceptors = activated by the presence of chemicals found in food

stretch receptors = activated by food pushing against the walls of the GI organ

The hypothalamus

• Peritoneum - 2 layers
• 1. Perietal layer - lines abdominal wall
• 2. Visceral layer - on organs
• Paritoneal cavity is between them
• - Made of simple squamous epithelial with loose CT underneath (mesothelial tissue)

The peritoneum has large folds that weave between the visera and hold the organs together.

• 1. Greater omentum - fat apron - colon ↔ stomach
• 2. Falciform ligament - liver ↔ anterior abdominal wall 3. Lesser omentum - liver ↔ stomach
• 4. Mesentray - small intestine ↔ abdominal wall
• 5. Mesocolon - large intestine ↔ abdominal wall

Yes. A perforated viscus can reslt in an acute life-threatening form of peritonitis because bacteria gain access to the peritoneal cavity.

Pancreas & Kidneys - they are covered anteriorly with parietal peritoneum

Also the ascending & decending colons (large intestine) and the duodenum of the small intestine are retroperitoneal.

Oral cavity - beginning of digestion -enzymes + mastication (chewing and tearing to produce a "bolus")

• 1. Lips - speech, hold food as you eat
• 2. Cheeks - hold food as you eat
• 3. Vestibule - space between the lips & gums
• 4. Hard/ Soft palate - keeps food out of nasal cavity
• 5. Uvula - Flips up when swallowing to keep food out of nasopharynx.

• 1. parotid
• 2. sublingual
• 3. submandibular
• - produce 1 - 1.5 L of saliva/ day - provides lubrication and starts chemical breakdown.

• Saliva:
• a. Salivary amylase - carbs
• b. lysosyme - anti- bac ; dissolves cell wall
• c. buffers - HCO^3- & PO^4-
• d. mucus - lubricant
• e. H₂O - dissolve food into molecules
• f. IgA - immune to eliminate invaders
• - small amt of waste- urea, uric acid

Secretes lingual lipase - breaks down triglycerides - must be activated by HCl in the stomach.

• 1. Mucous membrane lining
• 2. Skeletal muscle
• - extrinsic - manuaver food in mouth
• - intrinsic - changes the tongue shape
• 3. Papillae - cevered with taste buds
• 4. Septum - midline - lingual glands
• 5. Lingula frenulum - connects tongue to floor

• Regions:
• 1. Crown - above the gum line
• 2. Neck - below gum - hard to see
• 3. Root - below gum line

• Layers:
• 1. Enamel - hardest substance in man - made of calcium salts.
• 2. Dentin - majory of tooth - calcium salts - harder than bone
• 3. Pulp cavity - CT w/ vessels & nerves
• 4. Root Canal - extension of pulp cavity
• 5. Cementum - connects root to periodontal ligament

• 20 deciduous "baby" teeth - 6 mos → 6 years
• desiduous means "falling out at maturuty"

• 32 adult teeth
• - Incisors - bite
• - cuspids (canines) - tearing
• - molars - chew & grind

• 1. alveolar processes (gomphosis) - sockets in bone
• 2. gingiva - gums
• 3. periodontal ligament - dense CT - connects tooth to socket

Gingivitis - inflamation of the gingiva - caused by plaque (biofilm)

Periodontal disease - bacteria gets past gum line and is able to affect underlying structures - cementum

• Thrid molars are called wisdom teeth - erupt after age 17 or not at all.
• If there is not room for them to erupt they may become impacted and have to be surgically.

• Dental caries are cavities - tooth decay caused by various bacteria (strep mutans & viridans, lactobacilli)
• that disolve enamel

• 1. Nasopharynx
• 2. Oropharynx
• 3. Larygopharynx (hypopharynx)

Skeletal muscle - passage from oral cavity to esophagus - also used by respiratory system

Aids in mechanical (mastication) & chemical digestion (amylase & lipase)

Esophagus - connects pharynx to stomach - secrets mucus for lubrication - mediastinal, posterior to trachea (10" muscular tube) does not absorb or digest.

• 4 muscle layers: M-S-M-A
• Mucosa, Submucosa, Muscularis, Adventitia (only CT - no epithelium)

• Muscularis:
• - upper 1/3 = skeletal
• - middle 1/3 = both
• - lower 1/3 = smooth

• Sphincters - involved in swallowing process
• UES - Upper Esophageal Sphincter - Skeletal
• LES - Lower Esophageal Sphincter - Smooth

Hiatal hernia - stomach herniated (moves upward) through LES = pain & reflux

• GERD = GastroEsophageal Reflux Disease
• Incompetent LES - ↑ abdominal P = gastric acid enters esophagus
• Rx = diet - elevate bed - antacids,
• H₂ blockers (zantac - blocks histamine which is an H₂ receptor)
• Proton pump inhibitors - (nexium, prilosec, pepcid) protons = H⁺

1. Buccal phase- Voluntary -extrinsic muscles - tongue movement - forces food back to pharynx

• 2. Pharyngeal stage - involuntary - medulla & pons control it (Deglutition center = swallowing) - food moves from oropharynx → espohagus
• - swallowing reflex - touch receptors on uvula & soft palate stimulate it
• a. uvual moves up - stop food → nasopharynx
• b. Epiglittis shuts - stop food → trachea
• c. UES - Relaxes
• d. Breathing stops
• e. Food bolus enters esophagus

• 3. Esophageal stage - through esophagus → stomach
• - Bolus is moved by peristalsis (coordinated muscle contraction & relaxation that pushed food forward)
• - LES relaxes
• - food enters stomach

• 1. Cardia - surrounds superior opening
• 2. Fundus - rounded superior portion
• 3. Body - large central poriton
• 4. Pylorus - where stomach connect to duodenum
• - pyloric atrium - connect to body of stomach
• - pyloric canal - leads into duodenum
• - pyloric sphincter - separates pyloric canal from duodenum

Pyloric stenosis - in infatns pyloric sphincter is too tight - food cant drain properly & backs up in system - Projectile vomit - with force

• 1. Storage
• 2. Mechanical breakdown - mixing
• 3. Chemical breakdown
• 4. Produce IF (intrinsic factor) - for absorption of B₁₂
• 5. Turn Bolus in to Chyme - soupy mixture of bolus + gastric juices (vomit) by mixing
• 6. Absorption of alcohol & aspirin ( no nutrients - food particles still to big to be absorbed.

• 1. amylase - from saliva - carbs
• 2. lipase - lingual (tongue) + gastric (cheif cells) - triglycerides
• 3. pepsin - cheif cells makes pepsingoen that turn into pepsin (in presence of HCl) - it is proteolytic - it breaks down proteins into a.a. - proteins

1. simple columnar

• Excrine: (secrete products into ducts → external)
• 2. Parietal cells - make HCl & IF
• - - HCl (made by proton pump within the cell) - pH 2
• ACh, gastrin, histamine stimulate parietal cell to make HCl - denatures proteins & kills bacteria
• - - IF - Intrinsic factor - need for B₁₂ absorption
• 2. Chief cells - pepsinogen → pepsin (in presence of HCl - breaks down proteins
• 3. Mucous cells - mucus

• Endocrine (Secrete into blood stream)
• G Cells - Gastrin (Hormone) that stimulates chief & parietal cells

• The vagus nerve supplies the stomach. Vagus nerve originates in the medulla (CN 10 - cranial nerve 10)
• Neurotransmitter is ACh which stimulates cells to secrete their products.

• 1. Cephalic Phase
• 2. Gastric Phase
• 3. Intestinal Phase

• Cephalic - before food enters the mouth - prepares stomach for food - can be triggered by smell, sight, or thoughs of food.
• - lasts only minutes

• Stimulation is parasympathetic - vagus nerve makes ACh which triggers secretions.
• - histamine - stimulates parietal cells to make HCl
• - Mucous
• - pepsinogen → pepsin (HCl) - (made by chief cells)
• - gastrin - hormone that stimulates chief & parietal cells (Made by G cells)
• - HCl - denatures proteins & kills bacteria (made by parietal cells (proton pumps)
• - Lipase + amylase in saliva

Gastric phase = when the food reaches the stomach - mixing + gastric juices - neural & hormonal control

• parasympathetic response
• 1. Stretch receptors - expansion of stomach
• 2. Chemoreceptors - low pH (stomach acid)
• 3. Chemo + stretch receptors = mixing waves
• Negative feetback system

• Secretions
• - mucous, pepsinogen, && HCl continue
• - Gastrin - made by G cells in presence of peptides in chyme - travels in blood stream to stomach to stimulate parietla & chief cells

Intestinal Phase - when food reaches small intestine (duodenum) - sympathetic (inhibits gastric motility) - stimulated by duodenal stretch (chyme in)

• Neural - inhibitory reflex -
• Duodenal stretch → medulla →sympathetic output → pyloric sphincter constricts and gastric mixing stops

• Secretions:
• CCK - cholecystokinin - made in duodenum (CCK cel)

• Secretin - made by S cells in duodenum in response to low pH.
• - Inhibits chief cells & parietal cells (No HCl)
• - stim pancreas to make buffer HCO_3- (neutralize HCl)
• - Stim liver to make bile

3-4 hours min

Parietal cell and Chief cells

Stretch & Chemo receptots stimulate mixing waves for digestion.

Entero/ gastric reflex - sympathetic response that inhibits gastric mixing

• CCK - Cholecystokinin - HORMONE - that is produced in the duodenum.
• - production is stimulated by a.a.'s, FAs, TGs

• CCK =
• - ↑ pancreatic juice
• - sphincter of Oddi opens (controls bile flow)
• - gall bladder contraction - releases bile
• - pyloric sphincter closes - feel full

• Secretin =
• - made by S cells in duodenum in response to low pH.
• - Inhibits chief cells & parietal cells (No HCl)
• - stim pancreas to make buffer HCO3- (neutralize HCl) - Stim liver to make bile

• In clusters called acini that make pancreatic juice.
• Cells:
• 1. islets of langerhans (endocrine)- Alpha cells = glucagon, Beta cells = insulin - 1% of pacreatic cells
• 2. acini - make pancreatic juices:
• - - HCO₃^- to neutralize HCl
• - - trypsin - protein breakdown
• - - lipase - lipid breakdown
• - - Ribo/ deloxyribo nucleases - break down nucleotides

Pancreatic juice is H₂O, enzymes, and HCO_3- (buffer)

• All enzymes are produces in an inactive form to prevent autodigestion
• Digestive Enzymes:
• 1. Pancreatic amylase - carbs
• 2. Trypsin - proteins - proteolytic
• 3. Pancreatic lipase - TGs
• 4. Ribonuclease & Deoxyribonuclease

Pancreas is stimulated by CCK and Secretin from the duodenum.

Liver - largest gland - 2 lobes divided by falciform ligament

• Hepatocyte - primary liver cell - makes bile
• Kuppffer cells - fixed macrophages (from monocytes) that eat debris

• Lobule = functional unit of the liver (hexagon)
• Portal Triad:
• 1. portal vein
• 2. hepatic artery
• 3. bile duct

• Bile is made in the liver and stored in the gallbladder.
• Bile is made of :
• - H₂O
• - Bilirubin - necessary for heme
• - Bile salts -emulsification of fat

• Functions:
• - realsed from GB by CCK
• - emulsifies fats (break down into tiny pieces so lipase can break it down)
• - pH about 8
• - no food = sphincter of Odi closes and GB fills with bile

Hyperbilirubinemia is a byporduct of brakdown of the heme group of HGb - it presents as jaundice - yellow skin, eyes (sclera), musous membranes.

• 1. prehabitic jaundince - caused by increased production of bilirubin (hemolysis)
• 2. hepatic - liver is diseased and unable to process biliriubin (hepatitis, cirrhosis)
• 3. post hepatic - obstruction (stones, cancer)

• 1. Carbohydrate metabolism - insulin (anabolic )& glucagon (cat)
• 2. Lipid metabolism - TG storage - blood fa, TG, & cholesterol levers
• 3. Protine metabolism - break down into a.a = NH₃ + urea as byproducts
• 4. Metabolism & detoxification of drugs & hormones
• 5. Excrete bilirubin in bile
• 6. make bile salts - from bile acid
• 7. Make clotting factors - complement, albumin, cholesterol
• 8. Store KADE, B₁₂, iron, copper
• 9. Immune - Kupffer cells
• 10. Vitamin D activation - skin & kidneys

• 1. Duodenum (10")
• 2. Jejunum (3 ft)
• 3. Ilium (6 ft)

• 1. Cecum
• 2. Colon
• 3. Rectum
• 4. Anus

• 1. Ascending colon (R) - curve = hepatic flexure
• - retroperitoneal
• 2. Transverse colon (across) - curve = splenic flexure
• 3. Descending colon (Anatomic L) - retro
• 4. Sigmoid colon - s shaped - leads to rectum → anal canal → anus

• Appendix = located in the cecum
• Ileocecal valve = located between the ilium of the small intestine & cecum of Large Intestine - it regulates entry of chyme into LI

• Small intestine - majority of digestion/ absorption occurs here - 90 % off all absorption (food & water)
• - recieves chyme from stomach & secretions from liver & pancreas
• - chemically & mechanically breaks down chyme

10 feet long - 1" in diameter

• 1. Plica - circular mucosal/submucosal folds - ↑ surface area & causes chyme to spiral
• 2. Villi - fingerlike projections - ↑ surface area - contains lacteals to absorb lipids (in lamina propria of mucosa)
• 3. Microvilli - on villi - brush border - digestive enzymes insterted in cell membrane

• Cells: Has same 4 layers M-S-M-S
• Cells types in muccosa:
• 1. simple columnar for absortion/ digestion
• 2. goblet cells - mucous
• 3. crypts of Lieverkuhn - exocrine = intestinal juice
• 4. endocrine - S cells → secretin → HCO₃^-
• - CCK cells - pancreatic enzymes
• 5. Paneth cells - immune - regulates flora - lysozyme - phagocytosis
• 6. MALT - Mucosa Associated Lymphoid Tissue
• - Peyers patches & lymphatic follicles - found in lamina propria

• Submucosa:
• 1. Brunners glands - secrete alkaline mucous to neutralize chyme

• Muscularis
• 1. Concentric muscle
• 2. Longitudinal muscle

Serosa - visceral peritoneum

1. Segmentation - local mixing -moves chyme back & forth slowly - chyme touches wall for absorption of nutrients - does not propel

2. Peristalsis - propels chyme forward slowly - over a period of 3 - 5 hours

• 1. Intestinal Juice
• - H₂O
• - HCO_3- (pH 7.6)
• - Enzymes

• Brush Border Enzymes:
• - Lactase - monosacarides
• - Sucrase - disacarides
• - Maltase -
• - Peptidase - proteins
• - mucleosidase - nucleotides

• Pancreatic juice + bile + intestinal juice = very liquidy for better absorption
• + brush border enzymes

• 1. Starts in mouth - salivary amalaise
• 2. Completed in duodenum - pancreatic amalaise
• 3. Brush border enzymes convert di- to mono-
• a. Maltase - glucose & glucose
• b. Sucrase - fructise & glucose
• c. Lactase - glucose & galactose

• Starts in stomach - pepsin - breaks into peptides
• Completed in duodenum - pancreatic juice trypsin
• Brush border enzymes - aminopeptidase & dipeptidase - break dipeptides into a.a.

• Stomach - Lingual lipase & gastric lipase - split TGs
• Duodenum - pancreatic lipase - breaks down TGs - after emulsification

• Small Intestine - Pancreatic juices:
• - Ribonuclease - digests RNA
• - Deoxyribonuclease - digests DNA
• Brush border enzymes - nucleosidase & phosphatase

• Nucleic Acids broken down into:
• 1. Nitroginous bases
• 2. Pentose sugar (mono)
• 3. Phosphate
• All are absorbed via active transport

• 90% absorption in Small Intestine
• 10% in colon

• Absorption - to pass nutrients from GI lumen to blood or lymph
• GI lumen to Cell & Cell to blood stream

• 1. simple dissusion - a.a. to BS
• 2. facilitated diffusion - carbs to cell & BS
• 3. active transport -
• primary - carbs to cell & a.a. to cell
• secondary - carbs to cell & a.a. to cell
• 4. osmosis - all water

Electrlytes absorbed via simple diffusion and Active transport (for both GI to cell & cell to BS)

• Vitamins
• - KADE are absorbed from micelles (bile salts) via simple diffusion
• - Water sol = simple diffusion
• - B₁₂ - must be bound to intrinsic factor (from stomach) them moved by active transport

• In GI tract - water moves by osmotic gradient → higher solute concentrations in cell
• 90% in Small Intestine
• 10% in colon

• 1. Ascending colon - retroperitoneal
• 2. Transverse colon
• 3. Descending colon - retroparitoneal
• 4. Sigmoid colon - sigmoid shaped

Mesocolon - viseral peritoneum that connects LI to posterior abdominal wall

Large Intestine = 5' long & 2.5" wide

• Completion of absorption - last 10% -
• Completion of digestion - via bacteria
• Absorption/ produciton of some Vitamins - by bacteria
• Formation of Feces - last 10% H₂O absorbed
• Defication

• M-S-M-S
• 1. lymphatic nodules in lamina propria (mucosa)
• 2. microvilli - no villi
• 3. Teniae coli - longitudinal smooth muscle - midline
• 4. Houstra - pouches
• 5. Epiploic appendages - fat on visceral peritoneum at the teniae coli

• Internal sphincter - smooth - involuntary
• External sphincter - skeletal - voluntary

Alternating contraction & relaxation that moves chyme into adjascent haustra.

Mass peristalsis = strong wave that move chyme int the rectum (gastrocolic reflex) - peristalsis is usually weaker in LI than SI

• Bacteria in Large Intestine - break down any remaining large particles into smaller substances
• - produce Vit K & B
• - gas is a product of bacterial fermemtaion (anerobes) - CH₄ (methane) & CO₂

Chyme in Large Intestine get last 10% of water absorbed from it - becomes solid mass

Diarrhea - ↑ motility - moving too fast for complete absorption of H₂O

Constipation - ↓ motility - more time for water to be absorbed

Feces in rectum triggers stretch receptors → parasympathetic motor signal initiates dification

Can also be triggered by mass peristalsis