digestive system part 2

name the accessory organs associated with the small intestine

liver

• digestiven function is production of bile

• has four lobes named right, left, caudate and quadrate

• has a falciform ligament which separates the right and left lobes

• has hepatocytes, which filter and process nutrient rich blood

gallbladder

• stores, concentrates and releases bile

• thin-walled sac

• is going to release that bile through the cystic duct

pancreas

• produces enzymes (chemical digestion)

• produces bicarbonate (neutralizes acid)

what feeds and drains the liver

hepatic artery

hepatic portal vein

• is deoxygenated

• nutrient rich blood

hepatic vein

describe the portal triad at each corner of a lobule

consists of:

bile/hepatic ductule

portal arteriole

• branch of the hepatic artery

hepatic venule

• branch of the hepatic portal vein

• nutrient rich blood from the digestive organs

other than the portal triad, what three things does the lobule have

central vein

• at the center of each lobule

• drains blood from lobule

• these merge to form the hepatic vein

hepatic sinusoids

• blood from hepatic portal veins and arterial blood are going to mix

• flows toward center vein

• nutrient absorption happens here

• has hepatic macrophages (kupffer cells)

bile caniculus

• they carry bile by hepatocytes to the bile/hepatic ductule in portal triad

what is bile

• an alkaline solution

• is produced by hepatocytes

functions

• emulsification (bile,salts, lecithin)

• neutralize acidic chyme (HCO3-)

• elimination of bilirubin

what is the function of hepatocytes

• to produce 900 ml bile per day, its digestive function

• process blood-borne nutrients

• store any fat-soluble vitamins

• detoxification

what is the biliary apparatus

the network of ducts draining the liver

right and left hepatic —— common hepatic ducts combines with cystic duct——- common bile ducts

what are the endocrine and exocrine functions of the pancreas

endocrine

• secretion of insulin and glucagon

exocrine

• produce pancreatic juice

• assists with digestion

• exocrine acinar cells have pancreatic juice containing digestive enzymes

• exocrine pancreatic duct cells secrete alkaline bicarbonate fluid

describe pancreatic juice

• is formed from secretions of acinar cells and pancreatic duct cells

• is alkaline because has pH of 8

• has important components of electrolytes (primarily HCO3-) and enzymes

• drains through the main pancreatic duct

what does pancreatic amylase digest

carbohydrates

what does pancreatic proteases digest

proteins

what does pancreatic lipases digest

triglycerides

what does pancreatic nucleases digest

nucleic acids

what is the hepatopancreatic ampulla

is going to recieve

• bile from common bile duct

• pancreatic juice from main pancreatic duct

what is the hepatopancreatic sphincter

regulates the movement of bile and pancreatic juice into the duodenum

what is the major duodenal papilla

is the projection in the duodenal wall, the junction of the common bile duct and main pancreatic duct

what is going to happen when chyme enters the small intestine

• free fatty acids are going to stimulate release of cholecystokinin

• acidity is going to stimulate the release of secretin

what does cholecystokinin (CCK) cause

• gallbladder to contract and release bile

• pancreas to release enzyme rich pancreatic juice

• hepatopancreatic ampulla is going to open

what does secretin cause

the release of HCO3- that contains a solution from liver and ducts of pancreas

what is the job of the large intestine

• absorption of water, electrolytes and vitamins

• watery chyme will be compacted into feces

• is going to store the feces until eliminated through defecation

• propel feces toward anus

• colon is not essential for life

what are the regions of the small intestine

cecum

• starts at ileocecal valve

• chyme enters here from the ileum

vermiform appendix

• a thin sac

• is a part of MALT system

• is a bacterial storehouse, can recolonize gut when necessary

what is appendicitis

• mostly due to fecal matter obstructing the appendix

• pain referred to T10 around umbilicus, eventually to RLQ

• nausea or vomitting, abdominal tenderness, fever

• is surgically removed via appendectomy

• may burst if left untreated

• peritonitis can happen, an infection in abdominopelvic cavity

what is the colon regions of the small intestine in order

ascending colon to right colic/hepatic flexure to transverse colon to left colic/ splenic flexure to descending colon to sigmoid colon

describe the rectum

• expands to store the feces

• three rectal valves stop feces from passing with gas

describe the anal canal

• lined with stratified squamous epithelium

• opens to exterior at anus

• anal sinuses are here, they are depressions in anal canal wall and release mucus when pressure is exerted

what are the two anal sphincters

internal anal sphincter

• involuntary smooth muscle

external anal sphincter

• voluntary skeletal muscle

what is teniae coli

they are longitudinal bundles of smooth muscle on the large intestine

what are haustras

pocketlike sacs on the large intestine

describe the mucosa in the large intestine

from cecum to rectum— simple columnar epithelium

anal canal—- stratified squamous epithelium

intestinal glands

goblet cells—- secrete mucin and are for lubrication

lymphatic nodules—- are in lamina propria

what is the microbiota doing in the gut

• normal flora in large intestine is going to breakdown carbohydrates, protiens and lipids remaining in chyme

• B complex vitamins and vitamin K are synthesized, where it is absorbed from large intestine into blood

• produces gases (CO2, hydrogen, hydrogen sulfide, methane)

what is feces

• undigested food residues

• mucus

• sloughed off epithelial cells

• millions of bacteria

• shut enough water for smooth passage

what are haustral contractions

• haustrum fills with feces

• the distension stimulates reflex contractions in muscularis

• slow segmental movements move contents along the colon

what is the gastrocolic reflex

• initiated by stomach digestion

• results in mass movements

• slow and powerful

• properly fecal material toward rectum

• activated three to four times per day

describes the steps in defecation reflex

1) feces move into rectum, stimulating stretch receptors

2) receptors transmit signals to spinal cord, spinal cord reflex intiated

3) nerve signals relayed along parasympathetic axons to sigmoid colon, rectum, and internal anal sphincter

4) parasympathetic output is increased, contraction of rectum and sigmoid colon happens as well as relaxation of internal anal sphincter

5) voluntary defecation happens, so external anal sphincter relaxes allowing feces to pass. This is learned at about age 3 and involves valsalva maneuver

what is diarrhea

• water stools

• large intestine does not have enough time to absorb water from feces

• irritation of colon due to bacteria or jostling of of digestive viscera (common in marathon runners)

• prolonged diarrhea may result in dehydration and electrolyte imbalance

what is compensation

• compacted feces

• feces are going to remain in colon for extended periods of time

• too much water is absorbed

• stool is hard and difficult to pass

• may result from insufficient fiber or fluid in diet, or improper bowel habits or lack of exercise

what is chemical digestion

• catabolic process in which larg food molecules are broken down into monomers that are small enough to be absorbed through gastrointestinal tract lining

• enzymes are going to carry out hydrolysis

what is catabolism

metabolic pathway that breaks molecules down into smaller units

what is a monomer

a “building block” that forms the basic unit for large molecules

what are enzymes

substances that accelerate chemical reactions

what is hydrolysis

breaking down a substance using water

where are the main sites of carbohydrate digestion

the oral cavity and small intestine

what substances can only be absorbed by the small intestine

monosaccharides

• glucose

• fructose

• galactose

what comes from the salivary glands in the oral cavity

salivary amylase

• it breaks bonds between glucose molecules within the starch molecule

• is inactivated by low pH of stomach

is there any carbohydrate digestion in the stomach

No as no carbohydrate digesting enzymes are secreted by the gastric glands

how are monosaccharides absorbed

across small intestine epithelial lining

what is cellulose

• carbohydrate component of plant cell wall

• is not digested as we lack enzymes to chemically digest cellulose

• is part of fiber adding “bulk” to lumen content

describe protein digestion overall

• occurs in stomach and small intestine

• proteins are long chains of amino acid with peptide bonds

• amino acids can be absorbed across intestinal wall

• enzymes are going to target the peptide bonds between the amino acids

• enzymes are released as inactive enzymes that must be activated

describe protein digestion in the stomach

• low pH of stomach denatures proteins to facilitate chemical breakdown

• HCI is released by parietal cells

• pepsin is here

• HCI activates the inactive pepsinogen into active pepsin

what do pancreatic proteases in small intestine do

• break down large polypeptides into smaller polypeptides

• they are trypsin, chymotrypsin and carboxypeptidase

• released in inactive form (tripsinogen, chymotrypsinogen and procarboxypeptidase)

what does enteropeptidase in the small intestine do

• synthesized in small intestine

• activates trypsinogen to trypsin

what does trypsin in the small intestine do

• activates more trypsinogen to trypsin

• activates chymotrypsinogen to chymotrypsin

• activates procarboxypeptidase to carboxypeptidase

what does trypsin and chymotrypsin in the small intestine do

• break any bonds between amino acids

• proteins are now small strands of proteins

what does carboxypeptidase and other brush boarder enzymes do in the small intestine

• small chains of amino acids and dipeptides become amino acids

where does free amino acids get absorbed

in the small intestine epithelial lining into the blood

where does lipid digestion occur

• in the stomach and small intestine

how does triglycerides get broken down

• composed of glycerol and three fatty acids

• enzymes are required to break these bonds

does cholesterol need to be broken down for reabsorbtiion

no they do not

what happens to lingual lipase in the stomach

• is activated when it reaches the sotmach

where is gastric lipase produced

chief cells

describe emulsification in the small intestine

• bile salts form micelles

• allows for greater access of pancreatic lipase to triglycerides

describe pancreatic lipase in the small intestine

• triglycerides become monoglycerides and fatty acids

• no brush border enzymes are required to digest fats

describe lipid absorbtion

• triglycerides are reassembled in epithelial cells

• form chylomicrons and will enter lacteals

describe nucleic acid digestion

• occurs in small intestine

• DNA and RNA digested and made into sugar, phosphate, and nitrogenous base

• pancreatic nucleases made DNA and RNA into nucleotide monomers

• brush boarder enzymes make the monomers into bases, sugars and ions

• products are then absorbed across epithelium of small intestine