47 Digestive PPT

4/17: updated through slide 86

the movement of organic molecules, electrolytes (inorganic ions), vitamins, and water across the digestive epithelium and into the interstitial fluid of the digestive tract

absorption

the splitting of carbohydrates, proteins, lipids, and nucleic acids in foods into chemical subunits small enough to be absorbed into an animal’s body fluids and cells

digestion

what is a calorie? a kilocalorie?

the amount of energy requires to raise the temperature of 1 gram of water by 1^o C. A kilocalorie (kcal) equals 1000 calories

how are nutrients classified by composition?

simple inorganic nutrients - do not contain carbon. ex. calcium, magnesium, zinc, iron, potassium, etc

complex organic nutrients - contain carbon. ex. carbs, lipids, proteins, vitamins

What are minerals?

a nutrient made of a single chemical element

what are the three broad groups of conditions of malnutrition?

undernutrition, micronutritient-related malnutrition, and overnutrition

what are essential nutrients?

nutrients the body cannot synthesize on its own. these have to be obtained in the diet. these include essential amino acids, essential fatty acids, and essential minerals. varies from animal to animal

what are vitamins?

organic molecules required in small quantities that the animal can’t synthesize itself. many are coenzymes that assist in enzymatic reactions

how does the body respond to undernutrition?

the body uses stored fats and glycogen first, then proteins. use of proteins as fuel leads to muscle wastage and in the long term, organ and brain damage, which can lead to death.

list and define the 4 feeding methods

fluid feeders - inject liquid foods, like nectar or blood (e.g., mosquitoes, hummingbirds)

suspension feeders - ingest small organisms that are suspended in water (e.g., clams, baleen whales)

deposit feeders - ingest particles of organic matter from solid material they live in or on (earthworms, crabs)

bulk feeders - consume sizeable food items whole or in large chunks (most mammals, reptiles, birds, and amphibians)

what is biological hydrolysis?

the cleavage of biomolecules where a water molecule is consumed to effect the separation of a larger molecule into component parts

breakdown of food molecules occurs by ___, in which chemical bonds are broken by the addition of H⁺ and OH^-.

enzymatic hydrolysis

list the four types of enzymes and what they hydrolyze

amylases - hydrolyze starches

lipases - fats and other lipids

proteases - proteins

nucleases - nucleic acids

Sponges and some cnidarians break down food exclusively by what process? describe this process

intracellular digestion. food particles are trapped by choanocytes (specialized cells lining the body wall), which take them in by endocytosis and transport them to amoeboid cells which digest the particles intracellularly

how do animals with sac-like digestive systems digest food?

they have a single mouth that serves as both the entrance for food and exit for undigested material. these animals lack a separate vascular system, instead having a gastrovascular cavity that circulates nutrients and other materials through various tissue layers. digestion begins in the gastrovascular cavity and is completed intracellularly

what is extracellular digestion?

digestion that occurs outside body cells, in a pouch or tube enclosed within the body.

___ cells secrete enzymes that digest food

epithelial

how is the inside of the digestive tube (lumen) considered functionally external?

it opens to the external environment

list the five steps of digestion in order

mechanical processing (mastication), secretion of enzymes (and other digestive aids), enzymatic hydrolysis, absorption, elimination

describe earthworm (annelid) digestion

earthworms are deposit feeders that feed on organic soil particles. muscular activity moves particles through the esophagus into the crop, where they are stored and mixed with mucus. this mixture enters the gizzard, which contains grains of sand that helps grind the mixture into fine particles. then it enters a long intestine, where enzymatic hydrolysis and reabsorption happens. undigested residue exits through the anus

describe digestion in an insect

herbivorous insects tear plant parts into small particles with hard external mouth parts. digestion begins in the pharynx, then food moves through the esophagus, crop, and gizzard to the stomach. in the stomach, food is hydrolyzed, undigested contents move to the intestine for further digestion and absorption. at the end of the intestine, water is absorbed, remnants exit through the anus

describe digestion in birds

a bird eats a seed by swallowing it whole. saliva moistens the seeds, then the seeds pass through the pharynx and tube-like anterior end of the esophagus to the pouch-like crop, which stores food. the glandular portion of the stomach (proventriculus) secretes digestive enzymes and acids. seeds are ground in the gizzard. in the intestine, the liver secretes bile and pancreas adds digestive enzymes. the products are absorbed and the rest leaves though the anus

the digestive tract is also called the:

gastrointestinal (GI) tract or alimentary canal

list the digestive organs in order

mouth, pharynx, esophagus, stomach, small and large intestines, rectum, and anus

what are the accessory organs involved in digestion?

salivary glands, teeth, tongue, pancreas, liver, and gallbladder

What are the essential amino acids?

lysine, tryptophan, phenylanine, threonine, valine, methionine, leucine, isoleucine, and histidine (in infants)

what are the two essential fatty acids?

linoleic acid and linolenic acid

what are linolenic and linoleic acid essential for?

they are both required for synthesis of phospholipids that form parts of biological membranes and certain hormones

what are the classes of vitamins?

fat-soluble and water-soluble

where does the body store vitamins?

fat-soluble vitamins are stored in adipose tissues, and any excess water-soluble vitamins are excreted in the urine

how does the body make and activate vitamin D in response to UV light?

the skin contains 7-dehydrocholesterol, and a photochemical cleavage results in the formation of vitamin D. vitamin D enters the circulation, bound to vitamin D-binding protein (synthesized in the liver). vitamin D is hydroxylated in the liver, then again in the kidney. it is now active

what is the importance of vitamin K?

it is required for making blood clotting factors in the liver. humans can’t make vitamin K, but much of the requirement is supplied by bacterial activity in the large intestine

what are macrominerals?

minerals that are required in large amounts (>100mg per day). calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur. trace minerals are required in small amounts

list the four major layers of the gut

(innermost:) mucosa, submucosa, muscularis, serosa/serous layer

what is the mucosa?

the innermost layer of the GI wall, facing the lumen of the tube. it contains epithelial and glandular cells, and lines the digestive tract.

describe epithelial and glandular cells

epithelial cells absorb digested nutrients and seal off the digestive contents from body fluids

glandular cells secrete enzymes, lubricating mucus that aids digestion, and substances that adjust the pH of the digestive contents

what is the submucosa?

a thick layer of elastic connective tissue that contains neuron networks (the enteric nervous system), blood and lymph vessels, and small glands

what is the muscularis?

two smooth muscle layers that play an essential role in mechanical processing and in moving materials along the digestive tract.

what are the two layers of the muscularis?

circular layer and longitudinal layer

how do the circular and longitudinal layers work together?

contraction of circular muscles and relaxation of the longitudinal muscles lengthens the gut, and vise versa. these muscles produce peristalsis (a wave of contractions that passes along the gut, constricting the gut and pushing the contents onward)

what is the serosa?

the outermost layer of the GI wall, made of serous membrane. the serosa is also the visceral layer of the peritoneum (the serous membrane that lines the abdominopelvic cavity and covers its organs)

sphincter muscles are rings of ___ muscle

smooth

what do the sphincters of the GI system do?

they form valves between major regions of the digestive tract. they control the passage of digestive contents from one region to the next.

list the sphincter muscles described in lecture

pharyngoesophageal (upper esophageal)

gastroesophageal (lower esophageal)

pyloric sphincter (exit of the stomach, between the pylorus and the duodenum)

ileocecal

what is heartburn and acid indigestion a result of?

the backward flow of stomach acid up into the esophagus

what is GERD?

gastroesophageal reflux disease. is often mild, can generally be treated by avoiding certain foods, smoking, etc.

if untreated, can lead to serious changes in the esophageal lining (Barrett esophagus)

describe the food journey through the oral cavity

mastication occurs, the food forms a bolus. salivary glands secrete saliva containing salivary amylase, mucus, bicarbonate ions, and lysozyme (kills bacteria)

describe the food journey through the pharynx and esophagus

the swallowing reflex moves the bolus into the pharynx. the epiglottis prevents food from entering the trachea. peristalsis in the esophagus moves the bolus downward and through the gastroesophageal sphincter

acid reflux occurs as a failure of the ___ sphincter

gastroesophageal

describe the swallowing reflex

the reflex begins when the bolus reaches the pharynx. the pressure of the tongue seals back of mouth and prevents the bolus from backing up. larynx moves upward, pushing the glottis against the epiglottis to prevent bolus from entering airway. bolus enters esophagus, circular muscles of the esophagus contract behind the food. later, longitudinal muscles contract to open up the esophagus, this series of alternating contractions and relaxations move the bolus to the stomach.

a large distensible sack, muscular elastic organ with the largest diameter of any part of the gastrointestinal tract

the stomach

what are the four major functions of the stomach?

storage of ingested food

mechanical breakdown of ingested food

disruption of chemical bonds in food through the action of acid and enzymes

production of intrinsic factor, a glycoprotein needed for the absorption of B12 in the small intestine

what happens to ingested substances once in the stomach?

they combine with the secretions of the glands of the stomach and form a mixture of partially digested food (chyme)

in the stomach, what are the layers of the muscularis?

the outer longitudinal, middle circular, inner oblique layer

when the stomach’s volume is relaxed (empty), the mucosa has prominent folds called

rugae

what are the invaginations of the mucous layer of the stomach?

gastric pits that secrete gastric juice

what are the components of gastric juice?

pepsinogen (pepsin precursor)

hydrochloric acid

lubricating mucus

what cells in gastric pits secrete pepsinogen?

chief cells

what do parietal cells in gastric pits do?

they secrete H+ and Cl- ions that form HCl in the lumen of the stomach. they also secrete intrinsic factor

what are mucous cells (goblet cells)?

cells in the gastric pits that secrete alkaline mucus that protects the stomach lining from acidic environment in the stomach

What is the importance of HCl in the stomach?

keeps a low pH, denatures proteins and inactivates most of the enzymes in food, acidity breaks down plant cell walls, converts pepsinogen to pepsin

most of the important digestive and absorptive steps of digestion take place in the

small intestine

what are the microscopic extensions that cover the ridges of the lining of the small intestine?

intestinal villi

what are the epithelial cells covering the villi that have a brush border of fingerlike projections of plasma membrane?

microvilli

the ___ provides digestive enzymes as well as buffers that help neutralize chyme

pancreas

the liver secretes ___, which is stored in the ___

bile, gallbladder

what is bile?

bile is a substance that contains buffers and bile salts, which facilitate the digestion and absorption of lipids

what are the 3 segments of the small intestine?

duodenum - receives chyme from the stomach and digestive secretions from the pancreas and liver

jejunum - the bulk of chemical digestion and nutrient absorption occurs here

ileum - the final segment, also the longest

the intestinal lining has a series of transverse folds called

circular folds

how does bile enter the digestive tract?

bile from the liver, stored in the gallbladder, and bile from the pancreas collect in a common duct that empties into the lumen of the duodenum

break maltose, lactose, and sucrose into individual monosaccharides

disaccharidases

hydrolyze small peptides to individual monosaccharides

aminopeptidases

break nucleic acids into nucleosides

nucleotidases

convert nucleosides to nitrogenous bases, five-carbon sugars, and phosphates

nucleosidases

what do brush border cells absorb?

they absorb water-soluble products of digestion. this occurs by active transport, water follows by osmosis.

lactose is broken into what components? by what enzyme?

glucose and galactose by lactase

what is lactose intolerance?

the inability to synthesize lactase, leading to no absorption of lactose. the lactose is then broken down by bacteria, producing excessive methane and CO₂ , causing discomfort

how are monoglycerides and fatty acids absorbed?

water insoluble products of fat digestion pass through the membrane and enter the cytoplasm as micelles. fatty acids and monoglycerides are combined into triglycerides and packaged into chylomicrons (small droplets covered by a protein coat). chylomicrons are secreted into the interstitial fluid of the submucosa and taken up by the lymphatic system