digestion

Through oral cavity

Breaking down macromolecules into smaller molecules
Mechanical (chewing), chemical (enzymatic hydrolysis)

Occurs in small intenstine, smaller molcules absorbed into bloodstream

As feces, stored in rectum and eliminated through anus (also called egestion)

Break down large carbon compounds in food to yield ions and smaller compounds that can be absorbed

Lining of small intestine with epithelium that absorbs nutrients on inner surface

Tissue layer containing blood and lymph vessels

Longitudinal muscle with circular muscle inside it

Outer coat

Waves of muscle contraction that pass along intestine. Circular muscles contract behind food constrict gut to prevent it from going backwards, longitudinal muscles contract where the food is located moves it along the gut. Controlled by nervous system and occurs in only one direction, away from mouth

Food is only moved a couple cm at a time, progression is slower to allow time for digestion. Main function of peristalsis in intestine is to churn semi-digested food to mix with enzymes, speeding up digestion

Contains 2 types of gland tissue: small groups of cells secrete insulin and glucagon into blood, remainder synthesizes and secretes digestive enzymes into gut
Mediated by hormones synthesized and secreted by stomach
Small groups of gland cells cluster around ends of tubes called ducts, into which enzymes are secreted
Enzymes are synthesized in pancreatic gland cells on ribosomes on rough endoplasmic recticulum, processed in Golgi apparatus and secreted by exocytosis
Ducts with pancrease merge into larger ducts, finally forming one pancreatic duct, where pancreatic juice is secreted into lumen of small intestine

Through oral cavity

DIgests starch into maltose (salivary and pancreatic)

Digests triglycerides into fatty acids and glycerol or fatty acids and monoglycerides

Digests phospholipids into fatty acids, glycerol, and phosphate

Digests proteins and polypeptides into shorter peptides

Digests DNA and RNA into nucleotides

Digests maltose into glucose

Digests lactose into glucose and galactose

Digests sucrose into glucose and fructose

Proteases that digest peptides

DIgests dipeptides into amino acids

Sphincter muscle at top of stomach lets bolus in
Gastric juices released, low pH kills harmful bacteria and helps break down food
Stomach churns regularly, turning food mixture into chyme
Pepsin (a protease) is secreted into stomach and breaks protein into smaller polypeptides

Amylopectin has some 1,6 bonds which amylase cannot break. In the membranes of microvilli, maltase, glucosidase, and dextrinase digest maltose, maltotriose, and dextrins into glucose

Acidic chyme enters first part of small intestine (duodenum) through sphincter muscle a squirt at a time
Bile and pancreatic enzymes and bicarbonate added
Majority of digestiion occurs in duodenum

An alkaline detergent that emulsifies fats (coats and breaks into small globules), made in liver and stored in gallbladder

Major part of large intestine, absorbs water and salts
Diarrhea occurs when lining is irritated and not enough water is absorbed, constipation occurs when too much water is absorbed

Some further digestion of carbohydrates

Process of taking substances into cells and blood
Nutrients pass through layer of cells into body tissue
Nutrients have to pass from lumen of small intestine to capillaries or lacteal in villi, must first be absorbed into epithelium cells

Finger-like projection of mucosa that increases surface area of absorption

Brush-like projections on epithelial (lining) cells of sides of villi (brush border)

Thin epithelial layer allows nutrients to pass through easily, blood capillaries are close to epithelium
Proteins channels in microvilli membrane allow for faciliated diffusion and active transport to rapidly transport nutrients
Mitochondria in epithelium provide ATP for active transport
Lacteal (branch of lymph system in center of villus) carries away fats after absorption, joins blood stream
Nutrients absorbed by capillaries connect to hepatic portal vein which goes to liver for detoxification before main bloodstream
Bacteria and other larger substances too big to get through brush border

Products of digestion: glucose, fructose, other monosaccharides, amino acids, fatty acids, monoglycerides, glycerol, bases from digestion of nucleotides
Mineral ions, vitamins

Digested into fatty acids and monoglycerides, which are absorbed by simple diffusion into villus epithelium cells. Fatty acids also absorbed by facilitated diffusion by fatty acid transporters. Once inside epithelium cells, fatty acids are combined with monoglycerides to produce triglycerides. Triglycerides combine with cholesterol and form phospholipid particles, which are released by exocytosis and enter the lacteal and get carried away by lymph or enter villi blood capillaries

Glucose is polar so cannot pass through plasma membrane by simple diffusion. Sodium-potassium pumps create low concentration of sodium ions in epithelium cells, sodium-glucose co-transporter proteins in microvilli transfer sodium and glucose from intestinal lumen to epithelium cells (faciliated diffusion). Glucose channels allow glucose to move by facilitated diffusion to inside the villus and on into capillaries

Amylose has unbranched chains of glucose (1,4) and is digested by amylase into maltose and maltotriose

Amylopectin has some 1,6 bonds which amylase cannot break. In the membranes of microvilli, maltase, glucosidase, and dextrinase digest maltose, maltotriose, and dextrins into glucose