Digestive System

Functions

  1. Eating & Drinking

  2. Digestion - breaking down food

    1. Physical- chewing, & mixing

    2. Chemical - enzymes to break down large molecules (carbs → glucose; lipids → fatty acids

  3. Secretion - enzymes, mucus homones

  4. Absorption - Mostly in stomach intestine & Colon

  5. Waste elimination


ORGANS

  1. oral cavity - tongue: taste, swallowing, chewing | Teeth

  2. Esophagus

  3. Stomach - P and C digestion, lil of absoption

  4. Small intestine - Relaxed 22ft - digestion & absorption

  5. Large(Colon) - Absorb H2O, form & store feces (undigestible waste products)

    1. Rectum - store feces → anal canal →Anus (opening)

Appendix - vestigal organ


Oran cavity

  1. Many small unnamed glands in tongue and vestibule -KEEP MOUTH CLEAN

  2. Saliva - H2O, mucus, cells, enzymes like lysosomes, etc.

  3. three pair of salivary glands - secrete Amylase(enzyme for starch)and secrete upon stimulation

    1. Parotid - behind mandible

    2. Submandibular

    3. Sublingual

  4. Teeth

    1. Deciduous/baby (20)

    2. Permanent teeth (32)

      1. Enamel

      2. Dentin

      3. cementum part of tooth looks like dentin but structurally helps

      4. Periodontal Ligaments - Connective tissue

      5. Madible

      6. Root canal (blood vessels)

      7. Gingiva thin layer of muscle covered by vestibule tissue

  5. Tongue - skeletal muscle
    aid speech, chewing, swallowing, taste

Swalloeing 1. tongue pushes bolus backward 2, pushes downward, causes uvula to elevate & closes nasopharynx 3. tongue push fruther down, epiglottis covers larynx 4. skeletal muscle in upper esophagus contracts & pushes bolus into esophagus
then in the middle & lower esophagus smooth muscle pushes food into stomach


Taste papillae on superior surface of tongue

  • fungiform - several 100 taste buds (chemoreceptors)

  • filiform - create a rough surface → friction, grip

  • vallate/circumvallate -

all of papillae have nerve ending for touch & texture


Digestive tract histology: inside→outside

Muscosa

  1. Epithelium

  2. Lamina propria (Connective Tissue)

  3. Muscle - muscularis muscosa

Submucosa - thicker layer of connective tissue -

  1. BV’s & nerves

Muscularis externa: Circular Muscle fibers (contract→ narrower) → linear muscle fibers (contract→shorter)

depending where - Adominopelvic cavity → peritoneum (thin layer of epi and connective tissue)

esophagus and of colon and rectum - binds to adventitia ( b/t trachelis msucle and esophagus is adventitia esophagus and vertibral column

Types of movement through material in the track

  • Peristalsis muscle contracts and relaxes

  • Segmentation


Esophagus - only mucus glands

Voluntary - upper esophageal sphincter

middle - transition
involuntary - lower esophageal sphinter or cardiac sphincter


Stomach - j-shaped

  1. Physiological valve

  2. cardiac stomach

  3. fundus (dome)

  4. rugae

  5. corpus (body)

  6. pyloric stomach (sphincter)

  7. pyloric valve

Function of stomach

  1. store food

  2. mix and ch with acid and enzymes

  3. Protein breakdown

  4. absorption

Stomach Histology

  • mucosa and submucosa have longitudinal folds - rugae (expansion and surface area)

  • muscularis externa (only one with 2, rest have 2)

    • 1. inner oblique

    • 2. middle circular

    • 3. outer longitudinal

  • Gastric glands

    • stem cells

    • chief cells - secrete pepsinogen

    • Parietal cells - secrete HCL acid

      • Proton pump - H ion which cause a Cl ion to passively diffuse out with it

      • SO pepsiongen +HCl= pepsin(protase

    • ENT (pink cell) enteroendocrine cell → Gastrin & serotonin → into interstitial fluid → blood

Control & gastric activity

  • 10% Cephalic phase - brain (thoughts, smell, food)

  • 90%Gastric phase - food into stomach (80% of activity) → pepsinogen, HCL, gastrin() , seratonin(stimulates muscles)

  • Turns off- Intestinal phase - when chyme enters duodenum from stomach

    cholecystokinenin - inhibits stomach secretions

  • How we neutralize acidity in duodenum - gets lots of bicarbonate ions (HCO3^-) from duodenum, pancreas, bile H ion + bicarbonate ion →← H2CO3


Small intestine

Functions -

1. Produce and use enzymes from pancreas to breakdown chyme

  1. absorb tiny molecules

small particles - nucleic acids water soluable (can go straight into blood plasma)

Lipids/insoluble - lymph capillary

  1. screte stuff

  • Duodenum (1ft~) receives enzymes from pancreas and bile from liver

  • Jejunoilum

  1. mucosa → Microvilli increasing SA w/ base having intestinal glands

  2. Muscularis mucosae - 1. Circula 2. Longitudinal

  3. Folds in mucosa & submucosa called plicae circularis

  4. duodenum ONLY - Duodenal glands in submucosa secrete Bicabonate ion


Nonsoluable– hydrophobic → fear 

Lipoproteins- lipids(hydrophobic) + proteins(hydrophilic) = soluble in water

amphipathic two feelings

Spherical structure = MICELLE →w/ a protein & lipid that form in the gut is called Chylomicron (big compared to lipid, too big to into capillary)


Lacteals in small intestine - Lymphatic capillaries = extremely permeable


Other activity that occurs in SI

  • Chemical digestion by Pancreatic enzymes

  • Emulsification of fat by bile


Surface coat or Brush border enzymes - digestion enzymes made in the instestine that stay attached to the microvilli

Pancreas -Scecretes pancreatic juice - also endocrine organ (regulate blood glucose levels)

  1. H2O

  2. HCo3 - base to neutralize acid from stomach

  3. digestie ensymes lipases, amylases(carbs), proteases, nucleases(dna/rna)


Endocrine part of pancreas - Antagonistic HORMONES

  • insulin - lowers blood glucose levels by stimulating cells to take up glucose

  • Glucagon - increase blood glucose levels


Liver - treating plant fro all absorbed nutrients except for lipids

  • produces bile - byproduct of Hb breakdown(coming from spleen)

  • emulsifying agent - break large lipids into smaller

  • Produce hormones -

  • Regulates hormones

  • regulate blood chemistry

  • Lipases from liver turns fat into fatty acids and glycerol

Lobes of liver

  1. large right love

  2. smaller left lobe

  3. Quadrate lobe

  4. Caudal Lobe

only organ to have venous and arterial supply going in.

Hepatic portal vein - Carries all absorbed nutrients, minerals, etc, expect lipids

Hepatis artery

postal system when blood passes through two capillary bed in the systems circut


Hepatocytes - liver cells

Sinusoid

hepatic portal vein

Hepatic artery
Discontinuous sinusoids - allows ___ molecules to easily go in and out of the hepatocytes


Gall bladder

Large Intestine & Colon

  • Ileocecal valve

  • Ascending -transverse descending-sigmoid colon -rectum-anal canal

  • Haustra

  • Colon - longitudinal band of muscle is discontinuous


Diff type of peristalsis = MASS PERISTALSIS 20-30 mins after?

  • 3x a day everything in the LI → rectum

Reabsorption MEGA important or dehydration happens and create

IF colon moving too fast → colon not absorbing more water = diarrhea

Too slow too much absorption or resisting urge to defecate = constipation

losing water → losing bicarbonate → should drink water w/ electrolytes


Appendix - vestigal organ