BIO 202: Unit Two Exam - Digestive System, Nutrition, and Metabolism

digestion

breakdown of food into a usable form

absorption

uptake of nutrients into the epithelial cells of the digestive tract then blood then lymph

muscularis externa

thick layer of smooth muscle that does work of pushing things through digestive tract

• inner circular layer: squeezes 

• outer longitudinal layer: pushes

enteric nervous system

nervous system built into the wall of the digestive system

• myenteric plexus: neurons between muscularis externa layers

• submucosal plexus: deals with submucosa

neural control of digestive tract

• short myenteric reflexes: stretch or chemical stimulation acts through myenteric plexus

• long vasovagal reflexes: parasympathetic stimulation of digestive motility and secretion 

hormonal control of digestive tract

gastrin and secretin stimulate distant parts of the digestive tract

paracrine control of digestive tract

chemical messengers that diffuse through tissue fluids to stimulate target cells

salivary amylase

enzyme that begins starch digestion in the mouth

lingual lipase

enzyme that is activated by stomach acid and digests fat after food is swallowed

lysozyme

enzyme that kills bacteria

pyloric glands

glands near the pylorus

• mucous cells

• parietal cells

gastric glands

glands in the stomach 

• mucous cells

• parietal cells

• chief cells

• stem cells 

• enteroendocrine cells 

mucous cells

secrete mucous to help neutralize acid and protect the duodenum from damage

parietal cells

secrete hydrochloric acid, intrinsic factor, and ghrelin

• also use carbonic anhydrase to catalyze reaction between CO2 and H2O

chief cells

secrete gastric lipase and pepsinogen

stem cells

repair and replace old cells

enteroendocrine cells

secrete hormones and paracrine messengers that regulate digestion

zymogens

digestive enzymes that are secreted as inactive proteins to prevent them from digesting the same cells that produce them

• converted to active enzymes after removing amino acids

• trypsinogen → trypsin

• chymotrypsinogen → chymotrypsin

• procarboxypeptidase → carboxypeptidase

pepsinogen

zymogen secreted by chief cells

• HCl removes its amino acid to form pepsin that can digest proteins into shorter peptide chains

• autocatalytic effect

intrinsic factor

glycoprotein that is secreted by parietal cells

• binds vitamin B12 so intestinal cells in small intestine can absorb it by endocytosis 

vitamin B12

essential vitamin that is needed to synthesize hemoglobin and prevent pernicious anemia

epithelial cell replacement

main method to protect the stomach in which cells are replaced after 3-6 days

mucous coat

method to protect stomach by resisting action of acid and enzymes

tight junction

method to protect stomach, between epithelial cells to prevent gastric juice from digesting connective tissue

stimulation of gastric function

• vagus nerve

• histamine

• gastrin hormone

• intestinal gastrin

inhibition of gastric function

• sympathetic signals

• secretin hormone

• cholecystokinin (CCK)

hepatocytes

cells of the liver that absorb glucose, amino acids, vitamins, and nutrients from blood for metabolism after a meal

• remove and degrade hormones, toxins, bile pigments, and drugs

• secrete albumin, lipoproteins, clotting factors, and angiotensinogen into blood

bile canaliculi

collect bile made by hepatocytes

hepatic portal system

drains blood returning from digestive organs and allows the liver to act as a check for nutrients

bile

yellow-green fluid that contains minerals, cholesterol, neutral fats, bile pigments, and bile acids

• bilirubin is its principal pigment that is derived from decomposition of hemoglobin

segmentation in small intestine

purpose is to mix and chern NOT to move material as in peristalsis to make sure digestive enzymes can work on contents

carbohydrate digestion

oligosaccharides (maltose, sucrose, lactose, and fructose) contact brush border enzymes that act upon them to make glucose

carbohydrate absorption

glucose is absorbed with sodium as they are cotransported in secondary active transport 

• sodium-potassium pump creates sodium vacuum that draws sodium into core of villus and tags glucose along 

protein digestion

pancreatic enzymes hydrolyze polypeptides into short oligopeptides then brush border enzymes finish task to produce free amino acids

• begins in the stomach and is completed in the small intestine

emulsification

process that unclumps lipids

• big fat globules are broken up and coated by lecithin and bile acids to become smaller globules

lipid digestion

emulsified droplets are acted upon by pancreatic lipase into free fatty acids and monoglycerides that are then taken up by micelles

lipid absorption

free fatty acids and monoglycerides are transported to smooth ER, resynthesized into triglycerides, and made into chylomicrons that are taken up by lacteals of villi into lymph until they reenter the bloodstream

nucleases

hydrolyze DNA and RNA to nucleotides

• nucleosidases and phosphatases then split nucleotides into phosphate ions, ribose or deoxyribose sugar, and nitrogenous bases

nutrients

substances in food needed for growth and maintenance

• used for metabolic fuel, cell structures, and molecular synthesis

macronutrients

nutrients that make up bulk of ingested food

• carbohydrates, lipids, proteins

micronutrients

nutrients that are required but only in small amounts

• vitamins and minerals

carbohydrates primary source

plants and starch in grains and vegetables 

• insoluble fiber: cellulose in veggies

• soluble fiber: pectin in apples and citruses 

excess of carbohydrates

diabetes, nutritional deficits, obesity, GI irritation, and elevated triglycerides in plasma

deficit of carbohydrates

tissue wasting and metabolic acidosis resulting from accelerated fat use for energy

lipid primary source

triglycerides

• saturated fats: meat, dairy, tropical oils

• unsaturated fats: seeds, nuts, olive oil, vegetable oils

excess of lipids

obesity and high risk of cardiovascular disease

deficit of lipids

weight loss, fat stores, problems controlling heat, and tissue proteins being catabolized for energy

complete proteins

contain all needed essential amino acids

• eggs, milk, fish, most meats, and soybeans 

incomplete proteins

lack some essential amino acids

• legumes, nuts, and cereals

all of none protein rule

all amino acids needed must be present for protein synthesis to occur, if not, amino acids are used for energy

excess of protein

obesity, enhanced calcium, excretion, bone loss, high cholesterol, and kidney stones

deficit of protein

weight loss, tissue wasting, retarded growth, anemic, and edema due to deficit in plasma proteins

protein nitrogen balance

refers to homeostatic state in which rate of protein synthesis equals rate of breakdown and loss

positive nitrogen balance

synthesis exceeds breakdown

• normal in children, pregnancy, and tissue repair

negative nitrogen balance

breakdown exceeds synthesis

• seen in stress, burns, infection, injury, poor diet proteins, and starvation

vitamins

organic compounds that are crucial in helping the body use nutrients

• function as coenzymes that allow enzymes to function correctly 

water soluble vitamins

not stored in the body and are excreted if not used within 1 hour

• B complex and C absorbed with water

• B12 absorption requires intrinsic factor

fat soluble vitamins

stored in the body (except K) and are absorbed with lipid digestion products

• vitamins A, D, E and K

minerals

work with vitamins to ensure proper body function

• calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium, and iron

anabolism

synthesis of large molecules from small molecules

catabolism

hydrolysis of complex structures to simple ones

cellular respiration

catabolic breakdown of food fuels whereby energy from food is captured to form ATP

phosphorylation

enzymes shift high-energy phosphate groups of ATP to other molecules

stage 1 of processing nutrients

nutrients are digested into absorbable units that are absorbed into blood and transported to cells

• carbohydrates → glucose and sugar

• fats → fatty acids and glycerol

• proteins → amino acids

stage 2 of processing nutrients

cellular processing happens in the cytoplasm

• anabolism: synthesis of nutrients into macronutrients

• catabolism: nutrients are broken down to pyruvic acid and acetyl CoA

stage 3 of processing nutrients

oxidative breakdown of intermediates into CO2, water, and ATP in mitochondria

substrate-level phosphorylation

high energy phosphate groups are directly transferred from phosphorylated substrates to ADP

• substrate is source of phosphate (ADP + P → ATP)

oxidative phosphorylation

chemiosmotic process that couples movement of substances across membranes 

• energy released from food oxidation is used to pump H+ across inner mitochondrial membrane to create concentration gradient 

complete glucose catabolism

requires three pathways

• glycolysis

• krebs cycle

• electron transport chain and oxidative phosphorylation

glycolysis

breaks down glucose into pyruvic acid in the cytosol

krebs cycle

oxidizes pyruvic acid into CO2 in the mitochondrial matrix

electron transport chain and oxidative phosphorylation

generates most ATP in mitochondrial matrix

• phase I: ETC creates proton (H+) gradient using electrons removed from food

• phase II: chemiosmosis uses energy of proton gradient to synthesize ATP

glycogenesis

process of forming glycogen with excess glucose 

• mostly occurs in the liver and skeletal muscle cells 

glycogenolysis

breakdown of glycogen via glycogen phosphorylase

• in response to low blood glucose and under the influence of glucagon

gluconeogenesis

process of forming new glucose from noncarbohydrate sources

• occurs in the liver when blood glucose levels drop to protect against damaging effects of hypoglycemia

lipid catabolism

two building blocks of triglycerides are oxidized separately 

• glycerol breakdown

• fatty acid breakdown

beta oxidation

occurs in the mitochondria, fatty acids are converted into acetyl coA which generates ketones

• makes blood acidic and lowers pH

lipogenesis

triglyceride synthesis that occurs when cellular ATP and glucose levels are high

• glycerol and fatty acids not needed for energy are stored as triglycerides

true

true or false: glucose is easily converted to fat because acetyl coA is an intermediate in glucose catabolism and the starting point for fatty acid synthesis

lipolysis

breakdown of stored fats into glycerol and fatty acids

• accelerated when carbohydrate intake is inadequate