accessory digestive organs
- liver → produces bile
- gall bladder → concentrates and stores bile
- pancreas → secretes bicarbonate into duodenum to neutralize acidic chyme coming from stomach, also secretes six pancreatic digestive enzymes
saliva
chemical digestion of carbohydrates by alpha-amylase via hydrolysis
pepsin
digest proteins in stomach via hydrolysis starts as pepsinogen (a zymogen)
glucose metabolism
- low blood glucose: alpha cells in pancreas secrete glucagon
- glucagon stimulates glycogenolysis in liver → breakdown of glycogen storage in liver to form glucose to release into blood
- high blood glucose: beta cells in pancreas secrete insulin
- insulin: stimulates glycogenesis in liver → synthesis of glycogen for glucose storage in the liver and stimulates uptake of glucose from the blood into the cells
pancreatic enzymes
- lipase: hydrolysis of fats
- pancreatic amylase: hydrolyisis of carbohydrates
- ribonuclease: hydrolysis of RNA
- deoxyribonuclease: hydrolysis of DNA
- trypsin: cleaves peptide bonds at lysine and arginine
- chymotrypsin: cleaves peptide bonds at phenylalanine, tyrosine, tryptophan
small intestine
- digestion occurs primarily in the duodenum
- absorption occurs primarily in the jejunum and ileum
- villi: finger like projections on wall of small intestine, are hollow and blood vessels and one lymphatic vessel called a lacteal
- lacteal: absorb fats into lymph system
- proteins and carbs are absorbed into the blood vessels
large intestine
water and vitamin absorption
white blood cells
muscle group
- bundle of many fasciculi
- fasicle = bundle of many long tubular cells called muscle fibers
- myofibrils = fill most of the volume of muscle fibers (muscle cells), round tubes, long bundles of actin and myosin fibers, interwoven in repeating units called sarcomeres
sarcolemma
specialized membrane surrounding each muscle cell
sarcoplasmic reticulum
bundles of myofibrils are interwoven among muscle cell’s endoplasmic reticulum, called sarcoplasmic reticulum (SR) → stores and releases Ca 2+ to initiate the contraction sequence
sarcomere
- thick filament = myosin = motor protein → two myosin fibers = myosin filament
- thin filaments = microfibers (actin), troponin and tropomyosin
sliding filament mechanism
- in between contractions: ATP hydrolysis (ATP → ADP + Pi), provides energy required to straighten/cock myosin heads into high energy position
- myosin heads bind readily with actin, the only reason they aren’t bound continuously is due to tropomyosin protein, which covers binding portion of actin, when Ca 2+ enters → binds to tropomyosin and frees it from binding site (releases “clamp”) → myosin heads bind in straight position → after binding they release ADP and Pi → myosin heads relax back to their default bent position → myosin heads drag actin with them = power stroke → ATP binds to myosin again to release from actin filament → tropomyosin immediately rebinds to actin binding site → ATP molecule hydrolyzed → myosin head in high energy straight position
- no ATP present: myosin heads cannot detach from actin, will be stuck on actin in a contracted position (rigor)
- no Ca 2+ present: inability to contract (flaccid)
motor unit
- all fibers in a skeletal muscle don’t fire simultaneously during a contraction → a group of muscle cells innervated by a single motor neuron = motor unit
- delicate movements = small motor units
- gross movements = large motor units
- strength of a contraction: depends on
- number of motor units being used
- size of motor units being used
- frequency of action potentials
mucous neck cells
make and secrete mucus into gastric pits, mucus is alkaline → protects from corrosion
*** different from goblet cells (secrete mucous in lining of intestines and respiratory tract)
cheif cells
make and secrete pepsinogen (zymogen) into gastric pits
parietal cells
secrete HCl into gastric pits → pH = 2 → converts pepsinogen into pepsin
g cells
make and secrete gastrin → released into the blood → circulates back to parietal and cheif cells stimulating them to release HCl and pepsinogen
