Biology - Digestive System

what liver takes up from hepatic portal vein

-excess sugar ---> creates glycogen (storage form of glucose) -fats --> stores it as triacylglycerols the liver can also reverse these processes producing glucose for the rest of the body through glycogenolysis and gluconeogenesis and mobilizing fats in lipproteins

nasopharynx

1st part of pharynx, behind the nasal cavity

oropharynx

2nd part of pharynx, at the back of the mouth

laryngopharynx

3rd part of the pharynx, above the vocal chords

aminopeptidase

Aminopeptidase is a peptidase secreted by glands in duodenum that removes N-terminal amino acid from peptide. Released by duodenum.

hormones involved in feeding behavior

Antidiuretic hormone (ADH)/vasopresin aldosterone glucagon ghrelin leptin cholescystokinin

Pancreatic juices

CCK promotes the secretion of pancreatic juices into the duodenum. Pancreatic juices are a complex mixture of several enzymes in a bicarbonate rich alkaline solution. This bicarobnate helps neutralize acidic chyme as well as provide working environemnt for digestive enzymes which are active around pH 8.5. Pancreatic juices contain enzymes that can digest all three types of nutrients: carbs, fats and proteins

Dipeptidases

Dipeptidases cleave peptide bonds of dipeptides to release free amino acids. Unlike carbohydrates which must be broken down into monosaccharide for absorption, di- and even tripeptides can be absorbed across the small intestine wall.

Trypsinogen

Enteropeptidase is an enzyme critical for activation of trypsinogen, a pancreatic protease to trypsin. Trypsin initiates an activation cascade.

pyloric glands

Found in the Antrum and Pylorus of the stomach. Contain G cells that secrete gastrin, a peptide hormone that induces parietal cells in stomach to secrete more HCl and signls stomach to contract, mixing contents.

Gastroesophageal reflux disease

GERD: weakness in lower esophageal sphincter/cardiac sphincter. This results in heartburn sypmtoms afer eating. As food and acid reflux enter the lower esophagus, they irritate the less protected mucosa, stimulating pain receptors. These receptors localize pain poorly so the general burning sensation in the lower chest --> heartburn

parietal cell

Hydrogen ions in the stomach are secreted by parietal cells as hydrocloric acid, and cleaves pepsinogen into pepsin. Also secrete intrinsic factors, a glycoprotein involved in proper absorption of Vitamin B

Liver detoxification

The liver also detoxifies both endogenous compounds (made in body) and exogenous compounds (brought in from environment) Liver modifies ammonia, toxic waste product of amino acid metabolism, to urea which can be excreted by kidneys.

vitamins

absorbed in the small intestine. Can be categorized as either fat soluble or water soluble

pH and enzyme activity in the digestive system

acidic environment of stomac nd basic environment of duodenum point out important correlatoin between pH and enzyme activity. Pepsin is active in stomach and works best at pH 2. Pancreatic enzymes are active in duodenum and work best at pH 8.5.

transcellulary

across cell membrane, a method by which water passes alongside passing paracellularly

Substances absorbed directly in stomach

alcohol and aspirin but stomach is mainly an organ for digestion

which lands of the body are innervated by the parasympathetic nervous system

all glands of the body EXCEPT sweat glands

water soluble vitamins

all other vitamins (B complex and C) are water soluble. absorbed along with water, amino acids, and carbohydrates, across the endothelial cells of small intestine, passing directly into plasma.

lipase

also found in saliva, along side salivary amylase. Lipase catalyzes the hydrolysis of lipids.

lower esophageal sphincter

also known as cardiac sphincterc. As peristalsis squeezes the bolus toward the stomach, when it approaches the stomach, this muscular ring relaxes and opens to allow passage of food.

cardiac sphincter

also known as lower esophageal sphincter. As peristalsis squeezes the bolus toward the stomach, when it approaches the stomach, this muscular ring relaxes and opens to allow passage of food.

intracellular digestion

as a part of metabolism, involves the oxidation of glucose and fatty acids for energy.

what parts of alimentary canal have digestion

begins in the oral cavity and continues in the stomach and the first part of the small intestine (duodenum)

digestive tract

begins with oral cavity, followed by pharynx, etners esophagus, transports food into stomach, travels down small intestine, then large intestine, and then waste products enter the rectum. salivary glands, pancreas, liver, and gallbladder help to provide enzymes and lubrication necessary to aid the digestion of food

Proper fat digestion depends on

bile and lipase. Bile gets the fats into solution and increases their SA by placing them micelles (mechanical digestoin). vs. Lipase can come in to hydrolyze the ester bonds holding lipids together (chemical digestion)

emulsify

bile salts emulsify fats and cholesterol into micelles in the small intestine.

major components of bile

bile slats (emulsify fats), pigments (especially bilirubin), and cholesterol

mastication

breaking up of large food particles into small particles by using teeth tongue and lips. This process is called mastication. chewing increases surface area-to-volume ratio of the food --> allowing more surface area for enzymatic digestion as it passes through the gut tube. It also moderates the size of food particles entering the lumen of the alimentary canal; food particles that are too large --> obstructive risk in the tract

exocrine functions of pancreas

bulk of pancreas is made of exocrine cells - acinar cells

cirrhosis

can occur from chronic alcohol consumption, hepatitis C, autoimune hepatitis, and fatty lier disease. It is scarring of liver and this scar tissue builds up --> increased resistance within the portal vein --> portal hypertension --> backup of fluid within the portal system --> swollen veins in digestive system especially esophagus which may rupture and cause life threatening bleeding. This manifests as hematemesis: vomitting of blood. Also causes bleeding disorders because clotting factor production is disrupted. Also, improper disposal of ammonia --> increased ammonia in blood whic affets mentation. Cirrohosis can cause liver cancer.

salivary amylase/ptylain

capable of hydrolzing starch into smaller sugars (maltose and dextrins). Found in saliva

three main energy sources

carbohydrates, fats, and proteins

pancreatic juices can digest

carbs, fats, and proteins

leptin

cholecystokinin do opposite of glucagon and ghrelin, stimulating feelings of satiety. Works alongside cholecystokinin

clotting factors

clotting factors used during blood coagulation. Synthesized by the liver alongside albumin

enteric nervous system

collection of one hundred million neurons that govern function of gastrointestinal system. These neurons are present in the walls of digestive tract and trigger peristalsis. This system can function independently of the brain and spinal cord, although it is heavily regulated by the autonomic nervous system, increasing secretions from the exocrine glands and promoting peristalsis.

gastric juice

combination of secretions from parietal cells and chief cells (pepsin and HCl). Stomach acid is also important because it kills most harmful bacteria (except H pylori, which is usually asymptomatic but can cause inflammation, ulcers, and even gastric cancers).

chemical digestion of carbohydrates ends where?

completed in the small intestine but initiated in the mouth. This is done by pancreatic amylase, which is synonymous with salivary amylase.

middle third of esophagus

composed of skeletal and smooth mucle

top third of esophagus

composed of skeletal muscle. Top of the esophagus is under somatic (voluntary) motor control

bottom third of esophagus

composed of smooth muscle only, bottom of esophagus and most of the rest of the GI tract is under autonomic (involuntary) control.

bile ducts

connect the liver with both the gallbladder and small intestine. Bile is producted in liver and travels down bile ducts where it is stored in gallbladder or secreted into duodenum.

mucosa of stomach

contains gastric glands and pyloric glands. Also important to prevent auto-digestion in stomach due to harsh environment created by HCl and other enzymes

fundus

contains mainly gastric glands just like the body of the stomach

body (stomach)

contains mainly gastric glands like the fundus of the stomach

pylorus

contains mainly pyloric glands like the antrum of the stomach

antrum

contains mostly pyloric glands like the pylorus of the stomach

Bile

copmlex fluid composed of bile salts, pigments, and cholesterol. Release is stimulated by CCK.

micelles

created by emulsification of carbs and fats by bile salts. Micelles increase surface area of fats, increasing the rate at which lipase can act.

Bile salts

derived from cholesterol. THey are not enzymes and do not directly perform on chemical digestion (enzymatic cleavage of chemical bonds). Role: mechanical digestion of fats and ultimately facilitate the chemical digestion of lipids. Bile salts have hydrophobic and hydrophillic regions allowing them to serve as bridge between aqueous and liquid environments. lot like soaps and detergents for hand wash. In small intestine, bile salts emulsify fats and cholesterol into micelles. Wihtout bile, fats would spontaneously separate out of aqueous mixture in the duodenum and would not be accessible to pancreatic lipase.

chyme

digestion of solid food in the stomach results in an acidic, semi-fluid mixture known as chyme. Combined mechanical and chemical digestive activites of the stomach results in a significant increase in the surface area of the now unrecognizable food particles so when chyme reaches intestines, absorption of nutrients can be maximized.

colon

divided into ascending, transverse, descending, and sigmoid colons. Main function to absorb water and salts from undigested material left over from the small intestine. Small intestine absorbs much more wate than colon, so colon primarily concentrates the remaining material to form feces.

cholecystokinin

does opposite of glucagon and ghrelin, stimulating feelings of satiety. Works alongside leptin.

jejunum and ileum

duodenum is primarily involved with digestion. Jejenum and ileum are involve din absorption of nutrients. Small intestine is lined with villi, which are small finger-like projections from the epithelial lining. Each villus has many microvilli --> increasing surface area available for absorption. In the middle of each villus is both a capillary bed for absorption of water soluble nutrients and a lacteal - lympathetic channel that takes up fats for transport into lymphatic system

microvilli

each villus has microvilli which drastically increase the surface area available for absoprtion. At the middle of each villus is both a capillary bed available for absorption. In addition at the middle of each villus is both a capillary bed for absorption of water soluble nutrients and lacteal - lymphatic channel that takes up fats for transport into lymphatic

chemical digestion

enzymatic cleavage of chemical bonds such as the peptide bonds of proteins or glycosidic bonds of starches.

acinar cells

exocrine cells of pancreas. Make majority of cells in pancreas. These cells produce pancreatic juices.

greater curvature

external curvature of the stomach is called greater curavture

large intestine

food goes from small intestine to large intestine. Final part of the gastrointestinal tract. Primarily involved in water absorption. Large diameter but shorter length than small intestine. Three major sections: cecum, colon, and the rectum.

small intestine

food goes to small intestine from stomach consists of 3 segments: duodenum, jejunum, and ileum. Up to 7 meters. Duodenum - mainly digestion Jejunum and Ileum - absoprtion

epiglottis

food is prevented from entering the larynx during swallowing by a cartilaginous structure that folds down to cover laryngeal inlet called the epiglottis. Failure of this mechanism -> aspiration of food and chokig

pyloric sphincter

food leaves stomach through pyloric sphincter and enters duodenum

esophagus

from pharynx, food enters esophagus which transports food into the stomach muscular tube that connects pharynx to the stomach. Top third of esophagus is composed of skeletal muscle and bottom third is composed of smooth muscle. Middle third is mix of both. Top of esophagus is under somatic control and bottom is under autonomic control. no digestion occurs in the esophagus except for enzymatic activity that was initiated by the salivary enzymes in the mouth.

stone formation in gallbladder

gallbladder is common site of cholesterol or bilirubin stone formation --> causes inflammation of galbladder. Stones may travel into bile ducts and get stuck in biliary tree. In some cases, stones can get caught just before entering the duodenum, resulting in blockage of not only the biliary tree but the pancreatic duct as well --> pancreaitis. stone formation is nothing mor ethan precipitation of a solid once its cocentration has reached the Ksp of hte compound. Comon in the gallbladder because bile is concentrated there.

stomach

highly muscular organ with capacity of approximately two liters. Located in the upper left quadrant of the abdominal cavity, under the diaphragm. Stomach uses hydrochloric acid and enzymes to digest food, creating a harsh environment and the mucosa is quite thick to prevent autodgiestion. Four main anatomical divisions: fundus, body, antrum, and pylorus Aspirin and Alcohol are absorbed directly form stomach but stomach is mainly organ of digestion

Nonsteroidal anti-inflammatory drugs (NSAIDs)

ibuprofen, naproxen, and aspirin can disrupt mucus production within the stomach. THis leaves mucsa of stomach unprotected and irritation results. Can be in form of gastritis, inflammation of mucosa of the stomach or gastric ulcers, deep wounds in the suface of the stomach.

Acidic nature

important for digestion and also important for killing bacteria. Also helps denature proteins and can break down some intramolecular bonds that hold food together.

chemical digestion of fats is initiated

in the mouth by lipase.

chemical digestion of carbohydrates is initiated where?

in the mouth. Salivary amylase is in charge of that. Synonymous with pancreatic amylase which is active in the small intestine

pepsinogen

inactive form zymogen form of pepsin. Part of the make up of gastric juice alongside parietal cells. Pepsinogen is cleaved by HCl into pepsin.

sympathetic nervous system effect on salivation

increases viscosity of saliva in mouth --> dry mouth/tacky sensation during fight or fight response

pancreatitis

inflammation of the pancreas. Caused by gallstones or excessive consumption of alcohol. Results from premature activation of pancreatic enzymes and autodigestion of the pancreatic tissue. Can result in diabeties and reduced digestion of proteins and fats

lesser curvature

internal cuvature of the stomach is called lesser curvature

Two types of digestion

intracellular digestion extracellular digestion

sympathetic division - digestive system

involve din inhibition of digestive activities, decrease of secretions from exocrine glands, and inhibition of peristalsis during periods of high sympathetic activity, blood flow is decreased to the digestive tract and gut motility slos sgnificantly

digestion

involves the breakdown of food into its constittuent organic molecules: lipids into free fatty acids and glycerol, starches and other carbohydrates into monosacchardise and proteins into amino aids. Digestion can be subdivided into mechanical and chemical processes. begins int eh oral cavity and continues in the stomach and the FIRST part of the small intestine (duodenom)

absorption

involves the transport of products of digestion from the digestive tract into the circulatory system for distribution to the body's tissues and cells

lipoprotein

is a biochemical assembly that contains both proteins and lipids, bound to the proteins, which allow fats to move through the water inside and outside cells. The proteins serve to emulsify the lipid molecules. Process done by liver

billary tree

is a system of vessels that directs these secretions from the liver, gallbladder and pancreas through a series of ducts into the duodenum. Specifically, it secretes bile out.

gluconeogenesis

is the metabolic process by which organisms produce sugars (namely glucose) for catabolic reactions from non-carbohydrate precursors. Process done by liver.

mechanical digestion

is the physical breakdown of large food particles into smaller food particles but does not involve breaking of chemical bonds

how is swallowing initated

it is initiated in the muscles of the oropharynx which constitute the upper esophageal sphincter

Most absorption in small intestine takes place in

jejunum and illeum, only MINOR involvement in absorption can be found in duodenum

bacteria in the digestive system

large intestine and een small intestine home to many bacteria. 30% of dry matter in stool consists of bacteria. Most are anerobes. Relationship is symbiotic, bacteria are provided with food and byproducts produced by bacteria are beneficial to humans bacteria in gut produce vitamin K essentail for clotting factors and biotin (vitamin B) which is coenzyme for many metabolic enzymes.

rugae

lining of the stomach is thrown into folds called rugae

hepatic portal vein

liver also receives all blood draining from abdominal portion of digestive tract through hepatic portal vein. Thyy to the right side of the heart. is nutrient rich blood can be processed by liver before draining into inferior vena cava on its way to the right side of heart

albumin

liver also synthesizes certain proteins necessary for proper body function. Albumin, a protein that maintains plasma oncotic pressure and also serves as a carrier for many drugs and hormones

liver

located in upper right uadrant of abdomen and contains two unique structures for communicating with digestive system: bile ducts and the hepatic portal vein Functions of liver: processing of nutrients (glycogenesis and glycogenolysis, storage and mobilization of fats, gluconeognesis, production of urea, detoxification of chemicals, production of bile, and synthesis of albumin and clotting factors

gallbladder

located just beneath the liver and both stores and concentrates bile. Upon release of CCK, gallbladder contracts and pushes bile out to the billary tree. The bile duct system merges with pancreatic duct before emptying out into the duodenum.

bilirubin

major pigment in bile is bilirubin which is a byproduct of the breakdown of hemoglobin. Bilirubin travels to the liver where it is conjugated (attached to a protein) and secreted into the bile for excretion If liver is unable to process or excrete bilirubin (from liver damage, excessive RBC destruction, or blockage of the bile ducts) jaundice or yellowing of the skin may occur.

appendix

mall fingerlike projection that was once thought to vestigial, ut recent evidences suggests that it may have a role in warding off certain bacterial infections and repopulating the large intestine with normal flora afterdiarrhea. Appendicitis - surgical emergency.

oral cavity

mouth plays role in both mechanical and chemical digestion of food -mechanical: breaking up of large food particles into small particles by using teeth, tongue, and lips (mastication) -chemical: breakdown of chemical bonds in the macromolecules that make up food. This relies on enzymes from saliva produced by three pairs of salivary glands (salivary amylase - hydrolyzes starch into small sugars (maltose and dextrins) while lipase catalyzes hydrolysis of lipids). Amount of chemical digestion in mouth is minimal because food does not stay in mouth fr long.

ingest food

necessary to supply the body with nutrients.

does mechanical or chemical dgestion occur in the esphagus

no, except for continued enzymatic activity initiated in the mouth by salivary enzymes. Thus digestion, that occurs prior to entrance of bolus in stomach is minimal compared to digestion that occurs in the stomach/small intestine.

enteropeptidase

not a brush border enzyme but secreted the duodenum. Involved in the activation of other digestive enzymes from acessory organs of digestion. Enzyme critical for activation of trypsinogen, a pancreatic protease to trypsin. Enteropeptidase can also activate procarboxypeptidases A and B to their acive forms

water absoprtion

occurs in the small intestine. Much of the water in chyme is the result of secretions. The average person consumes up to two liters of fluid per day, but secretions into the upper GI tract may total up to 7 liters/day. To maintain proper fluid levels, much of this fluid must be reabsorbed by osmosis. As solutes are drawn into bloodstream, water is drawn with it, eventually reaching capillaries. Water passes not only transcelluarly (across cell membrane) but also paracellularly (squeezing between cells to reach the blood)

fat soluble vitamins

only four fat-soluble vitamins (A, D, E, and K). ADEK They dissolve directly into chylomicrons to enter the body. Failure to digest and absorb fa properly, which can be due to pathologies in the liver, gallbladder, pancreas, or small intestine ---> deficiencies in fat soluble vitamins

anus

opening through which wastes are eliminated. Contains two sphincters: the internal and external anal sphincter

major and minor duodenal papillae

openings of the pancreatic duct into the duodenum. Acinar cells secrete their products into these ducts.

extracellular digestion

our diets do not consist of pure glucose and fatty acids; rather these substances must be extracted from our food. Process by which these nutrients are obtained from food occurs within the lumen of the alimenetary canal and is known as extracellular digestion. Technically, this is outside the ody as it isouside the clel borders.

bolus

our muscular tongue forms food into a bolus, which is forced back to the pharynx and swallowed

accessory organs of digestion

pancreas, liver, and gall balldder. Acessory organs of digestion originate as outgrowths of endoderm from gut tube during development

pancreatic lipase

pancrease secretes pancreatic lipase which is capable of breaking down fats into free fatty acids and glycerol

duct system

pancreatic juices transferred to duodenum via a duct system that runs along the imddle of the pancreas. Like all exocrine cells, aciar cells secrete their products into ducts. These ducts empty into duodenum through major and minor duodenal paillae

Tryspinogen

pancreatic peptidase. Enteropeptidase activates trypsinogen into tryspin which can activate the other zymogens and also procarboxypeptidases A and B to active forms.

the three pairs of salivary glands

parotid submandibular sublingual other microscopic salivary glands are scattered throughout the upper digestive system. Parasympathetic nervous system is responsible for promoting salivation but the sympathetic nervous system has some input in these glands as well. It inreases the viscosity of saliva which is why dry mouth and even a tacky sensation nthe mouth occurs during fight or flight response

internal anal sphincter

part of anus, under involuntary control

external anal sphincter

part of anus, under voluntary control (somatic

Pancreatic amylase

part of pancreatic juice, specifically it breaks down large polysaccharides into small disaccharides and is responsible for carbohydrate digestion.

cecum

part of the large intestine. It is simply an outpocketing that accepts fluid exiting the small intestine through the ileocecal valve and is the site of the appendix. Consists many aerobic bacteria though most bacteria in digestive system are anearobes.

secretin

peptide hormone that causes pancreatic enzymes to be released into duodenum. It also regulates pH of digestive tract by reducing HCl secretion for parietal cells and increasing bicarbonate secretion from the pancreas. It is also an enterogastrone: hormone that slows motility through digestive tract.

brush border enzymes

present on luminal surface of cells lining duodenum and break down dimers and tmiers of biomolecules into absorable monomers. I.e. Disacaridases and peptidases

mucous cells

produce bicarbonate rich mucs that protects the muscular wall from harshly acidic (pH = 2) and proteolytic environment of the stomach. Located in gastic glands in the lining of the stomach.

saliva

produced in salivary glands. Aids in chemical and mechanical digestion (lubrication/mositening of food) and breakdown of macromolecules in food. Saliva contains salivary amylase/ptylain and lipase.

parasympathetic nervous system effect on salivation

promotes salivation

pepsin

proteolytic enzyme. Created by pepsinogen which is cleaved by HCl. Pepsin digests proteins by cleaving peptide bonds near aromatic amino acids resulting in short peptide fragments. Most active at low pH which is unique among human enzymes as most human nezymes are most active at physiological pH.

Zollinger-Ellison syndrome

rare disease results from gastrin-secreting tumor (gastrinoma). This tumor is found in pancreas typically. THe excess gastrin leads to excess HCl prodcution by parietal cells. Most common sign of this disease is an intractable ulcer disease.

heartburn

receptors in the lower esophagus localize pain poorly so the general burning sensation in the lower chest is heart burn. Also, a symptom of GERD (which is weakness in cardiac/lower esophageal sphincter

endocrine functions of pancreas

release of insulin, glucagon, and somatostatin. These ormones are important for maintenance of proper lood sugar levels. Hormonal function of pancreas is limited to cells residing in islets of Langerhans scattered throughout the organ

gastric glands

respond to signals from the vagus nerve of the parasympathetic nervous system, activated by the brain i response to sight, taste, smell of food. Gastric glands have 3 different types of cells: mucous cells, chief cells, and parietal cells

Duodenum

responsible for majority of chemical digestion and has some involvment in absorption. Presence of chyme in duodenum causes release of brush border enzymes like disaccharidases and peptidases. Also secretes enteropeptidases. Lastly, it also secretes hormones like secretin and cholecystokinin into blood stream

celic deisease

reults from immune reaction against gluten. Immune system develops antibodies against certain components of gluten which cross react with elements of small intestine --> damage to mucosa. Results in diarrhea and discomfort. Also can result in inability to absorb fat and fat soluble vitamins. They are NOT allergies.

peristalsis

rhythmic contractions of gut tube in order to move materials through the system. They are governed by the enteric nervous system which are neurons found in the walls of the digestive tract Under normal circumstances, peristalsis proceeds down the digestive tract. Certain conditions, such as exposure to chemicals, infectious agents, and physical stimulation in the posterior pharynx, and even cognitive stimulation can lead to reversal of peristalsis - emesis (vomitting)

Alimentary canal

runs from mouth to anus and sectioned off by sphincters or circular smooth muscles around the canal and can contract to allow compartmentalization of function.

which organs provide enzyme and lubrication for digestion of food

salivary glands pancreas liver gallbladder

G cells

secrete gastrin. Found in pyloric glands in Antrum and Pylorus of Stomach

chief cells

secrete pepsinogen

Gastrin

secreted by G cells in the pyloric glands of Antrum and Pylorus of stomach Induces parietal cells in stoach to secrete more HCl and signals stomach to contract, mixing its contents

intrinsic factor

secreted by parietal cells in the stomach. It is a glycoprotein that is involved in proper absorption of Vitamin B

ghrelin

secreted by stomach and pancreas, stimulate feelings of hunger alongside glucagon

glucagon

secreted by the pancreas stimulate feelings of hunger alongside ghrelin

cholecystokinin (CCK)

secreted in response to entry of chyme, specifically amino acids and fat in chyme into the duodenum. Peptide hormone that stimulates the release of both bile and pancreatic juices and also acts in the brain where it promotes satiety. Also promotes secretion of pancreatic juices into the duodenum.

hormones released by duodenum

secretin and cholecystokinin released into bloodstream

enterogastrone

secretin is an enterogastrone, which is a hormone that slows motility through digestive tract. Slowing of motility allows increased time for digestive enzymes to act on chyme, especially fats.

pharynx

shared pathway for both food entering the digestive system and air entering the respiratory system cavity that leads from the mouth and posterior nasal cavity to the esophagus. The pharynx connects not only to the esophagus but also to the larynx which is a part of the respiratory tract. three parts to the pharynx: nasopharynx, oropharynx, and larynxgopharynx

how are simple sugars and amino acids absorbed

simple sugars such as glucose, fructose, and galactose, and amino acids are absorbed by secondary active transport and facilitated diffusion into the epithelial cells lining the small intestine. These substances then move across the epithelial cells into the intestinal capillaries. Blood is constantly passing by the epithelial cells in the capillaries, carrying the carbohydrate and amino acid molecules away from the epithelial cells ---> creates concentration gradient such that the blood always has a lowering concentration of monosaccharides and amino acids than inside epithelial cells into teh capillaries. The absorbed molecules then go to the liver via the hepatic portal circulation

Stomach secretes this many products

six 1. HCl (kills microbes, denatures proteins, and converts pepsinogen into pepsin) 2. Pepsinogen (cleaved to pepsin into the stomach, an enzyme that partially digests proteins) 3. Mucous (protects mucosa) 4. Bicarbonate (protects mucosa) 5. Water (Dissolves and dilutes ingested material) 6. Intrinsic factor (required for normal absoprtion of vitamin B12)

how are fats absorbed

small fatty acids will follow same process as carbohydrates and amino acids by diffusing directly into the intestinal capillaries. They do not require transporters because they are nonpolar so they can easily traverse the cellular membrane. Larger fats, glycerol,and cholesterol move separately into the intestinal cells but then reform into triglycerides. The triglycerides and esterified cholesterol molecules are packaged into insoluble chylomicrons

villi

small finger-like projections that line the epithelial lining. Each villus has microvilli.

lacteals

small vessels that form the beginning of the lymphatic system. These lacteals converge and enter venous circulation through the thoracic duct in the base of the neck, which empties into the left subclavian vein.

paracellularly

squeezing between cells, a method by which water passes alongside passing transcellularly

upper esophageal sphincter

swallowing is initiated in the muscles of the oropharynx which constitute of the upper esophageal sphincter.

glycogeolysis

the breakdown of glycogen (n) to glucose-6-phosphate and glycogen (n-1). Done by liver

parasympathetic division - digestive system

the enteric nervous system an function independently of the rain and SC although it is heavily regulated by the ANS. The parasympathetic nervous system is involved in digestive activities, increasing secretions from exocrine glands and promoting peristalsis The fact that we often feel sleepy and lethargic after eating a big meal (Food coma) is due to parasympathetic activity.

salivary glands

there pairs of salivary glands that release saliva that has enzymes for chemical digestion. Saliva also aids in mechnical digestion by moistening and lubricating food. Salivary glands are innervated by parasympathetic nervous system. Presence of food in oral cavity triggers neural circuit --> increased parasympathetic stimulation of these glands. Salivation can also be triggered by signals that food is near, such as smell or sight

ADH and aldosterone

trigger sensation of thirst, encouraging behavior of fluid consumption

chyllomicrons

triglycerides and esterified chlesterol molecules are packaged into insoluble chylomicrons. Rather than entering the bloodstream, chylomicrons enter the lymphatic circulation through lacteals. These lacteals converge and enter venous circulation through the thoracic duct in the base of the neck, which empties into the left subclavian vein.

pancreatic peptidases

trypsinogen, chymotrypsinogen, and carboxypeptidases A and B are released into their zymogen form but once activated are responsible for protien digestion. Enteropeptidase produced by duodneum is the master switch.

pancreas

two different roles in body: exocrine and endocrine functions

Peptidases

type of brush border enzyme. Includes: dipeptidases and aminopepidases. Break down proteins (peptides). Aminopeptidase is a peptidase secreted by glands in duodenum that removes N-terminal amino acid from peptide. Dipeptidases cleave peptide bonds of dipeptides to release free amino acids. Unlike carbohydrates which must be broken down into monosaccharide for absorption, di- and even tripeptides can be absorbed across the small intestine wall.

disaccharidases

type of brush border enzyme. Includes: maltase (maltose) isomaltase (isomaltose), lactase (lactose), and sucrase (sucrose). Lack of a particular disaccharidase causes inability to break down corresponding dissacharide. Then bacteria in the intestines are able to hydrolyze the disaccharide producing methane gas as a byproduct. Undigested disaccharides can have an osmotic effect, pulling water into stool and causing diarrhea.

lactose intolerant people

unable to digest lactose --> undigested lactose has an osmotic effect pulling water into the stool and causing diarrhea. This is why they have bloating, flatulence, and possibly diarrhea after ingesting dairy products.

H pylori

usually asymptomatic but can cause inflammation, ulcers, and even gastric cancers. Not killed by stomach acid

ileocecal valve

vlave that accepts fluid exiting the small intestine into the cecum.

emesis

vomiting. Exposure to chemicals, infectious agents, physical stimulation in posterior pharynx, and even cognitive stimulation can lead to reversal of peristalsis which is vomitting/emesis

rectum

waste products of digestion enter the rectum where feces are stored until the appropriate time of release. Feces consists of indigestible material, water, bacteria,a nd certain digestive secretions that aren't reabsorbed (enzymes and some bile)