UNIT 10 - DIGESTIVE SYSTEM Flashcards
what is the overall function of the digestive system?
-to hydrolyze macromolecules found in food
-to provide the body with a continual supply of water, electrolytes, vitamins, and nutrients
why must the body hydrolyze macromolecules?
-the larger macromolecules cannot cross the plasma membrane
-subunit molecules like monosaccharides, amino acids, fatty acids, and glycerol can cross the plasma membrane by facilitated diffusion and active transport
what is the specific function of the esophagus?
-simple passage of food
what is the specific function of the stomach?
-temporary storage of food
what is the specific function of the small intestine?
-digestion and absorption
what is the basic overview of the digestive system?
-movement of food through the alimentary tract
-secretion of digestive enzymes
-absorption of good products
-blood circulation to carry away absorbed substances
-control by local nerves and hormonal systems
what are the stages of digestion?
-ingestion
-mechanical digestion
-chemical digestion
-movement
-absorption
-elimination
what is ingestion?
-intake of food via the mouth
what is mechanical digestion?
-chewing in the mouth and contractions of smooth muscles in the stomach
what is chemical digestion?
-digestive enzymes hydrolyze macromolecules into subunits
what is movement?
-food is passed from one organ to the next
-typically by contractions of smooth muscle (peristalsis)
-indigestibles are expelled through the tract
what is absorption?
-movement of nutrients across the GI tract wall into the blood and delivered to the cells
what is elimination?
-removal of indigestible wastes (defecation)
what is contained within the lumen of the GI tract?
-food or feces
what are the layers of the digestive tract?
-mucosa
-submucosa
-muscularis
-serosa
what is the mucosa layer of the digestive tract?
-innermost layer
-produces mucus for protection
-produces digestive enzymes
what is the submucosa layer of the digestive tract?
-loose connective tissue
-contains blood vessels, lymphatic vessels, and nerves
what is the muscularis layer of the digestive tract?
-2 layers of smooth muscle
-inner circular layer and an outer longitudinal layer
-moves food along the GI tract
-EXCEPTIONS
what is the serosa layer of the digestive tract?
-outer lining
-part of the peritoneum (visceral peritoneum)
what is diverticulosis?
-condition where the mucosa of any part of the GI tract (large intestine typically) pushes through the other layers and forms pouches where food collects
-pouches/weak spots in the muscularis layer
what is diverticulitis?
-when the pouches become infected (inflamed)
-happens to 10-25 percent of people with diverticulosis
what is inflammatory bowel disease (IBD)
-chronic diarrhea, abdominal pain, fever, and weight loss
-includes crohn’s disease and ulcerative colitis
what is irritable bowel syndrome (IBS)?
-powerful and abnormal (coordination of) contractions of the muscularis cause abdominal pain, constipation, gas, urgent/explosive stools (diarrhea)
-underlying cause is not known
-accentuated with stress and anxiety
-spastic colon
what is the purpose of the oral cavity?
-receives food and begins mechanical and chemical digestion
what does the roof of the mouth separate?
-the nasal cavity from the oral cavity
what are the two parts of the roof of the mouth?
-hard bony palate
-soft palate
what makes the soft palate?
-muscle
-ends in the uvula
what are the tonsils? where are the located?
-lymphatic tissue that protect from disease
-in the back of the mouth on either side of the tongue
-single pharyngeal tonsil in the nasopharynx (called the adenoids)
what is the purpose of the teeth?
-mechanically digest food
how many teeth are in the mouth of a child? an adult?
-20 smaller deciduous teeth (child)
-32 larger permanent teeth (adult)
what are the two main divisions of the tooth?
-crown (above the gumline)
-root (below the gumline)
what are the layers of the teeth?
-enamel (hard outer layer)
-dentin (thick bonelike layer)
-pulp (nerves and blood vessels)
-periodontal membranes (anchor to the jawbone)
how does tooth decay and cavities occur?
-when bacteria metabolize sugar and produce acids that erode teeth
-can become painful if the nerves of the pulp are reached
what is gingivitis?
-inflammation of the gums
-can spread to the periodontal membrane (causes loosening of the teeth)
how many salivary glands are in the oral cavity? what is their purpose?
-3 pairs
-secrete saliva
what is contained within saliva?
-salivary amylase
-lysozyme
what is the purpose of salivary amylase?
-begins carbohydrate/starch digestion
what is lysozyme?
-antibacterial enzyme
what is the function of the tongue?
assists in mechanical breakdown and movement of food
-forms a bolus and moves it towards the pharynx
-covered in taste buds
what do the mouth and nasal passages lead to?
-the pharynx
what does the pharynx open into?
-esophagus (food passage)
-trachea (air passage)
-are both parallel to each other
-trachea is in front of the esophagus
where does the esophagus lead to?
-stomach
-muscular tube
is swallowing voluntary or involuntary?
-starts as a voluntary mechanism
-once food or drink is pushed back to the pharynx it becomes an involuntary reflex
how does the body ensure that the food enters the esophagus instead of the trachea?
-trachea moves up under the epiglottis to cover the glottis which opens to the larynx
how does the body ensure that the food enters the esophagus instead of the nasal passage?
-soft palate moves back to close off the nasal passage
what is a sphincter? how do they aid in the digestive system?
-ring of muscle that acts as a valve
-when it contracts it stops food from moving through
-when it relaxes (release of NO and VIP) it allows food to pass through
what is an important sphincter in the first part of the digestive system? what does it prevent?
-lower esophageal sphincter (between the esophagus and stomach)
-prevents acid reflux if closing properly
what are the functions of the stomach?
-stores food
-starts digestion of proteins
-controls the release of chyme in the small intestine
-does not absorb nutrients
what does the stomach absorb?
-alcohol because it is fat soluble and can pass through membranes easily
what is the muscularis layer of the stomach?
-3 layers instead of 2 (for mechanical digestion)
-circular, longitudinal, and oblique layers
how often does the stomach contract?
-every 20 seconds
what is special about the mucosa in the stomach?
-deep fold called rugae (increase stomach capacity)
-has gastric pits with gastric glands
-many different cell types in the epithelium
what is produced by the gastric glands?
-gastric juice
-2L per day
what is contained within the gastric juice?
-pepsin
-HCL
-mucus
-lipase
-intrinsic factors
what is the function of pepsin?
-digests dietary proteins into shorter peptide chains
where is protein digestion completed?
-in the small intestine
what is the function of HCL in the stomach?
-kills bacteria and activates pepsin via pepsinogen
-acidic (pH of 2)
how does HCL and pepsinogen act to activate pepsin?
-pepsinogen is a zymogen secreted by chief cells
-HCL removes some of its amino acids to form pepsin
what is a zymogen?
-digestive enzymes secreted as inactive proteins
-converted to active enzymes by removing some of their amino acids
what is the purpose of mucus within the stomach?
-traps invaders
-protects stomach cells (apical layer) from the high acidity
what is the purpose of lipase within the stomach?
-breaks down tri or diglycerides into smaller pieces
what is the purpose of intrinsic factor within the stomach?
-glycoprotein secreted by parietal cells to combine with vitamin B12
-forms a complex that resists digestion and gets absorbed in the terminal ileum by pinocytosis
-vitamin B12 is then transported to the liver where it is stored
what are the different cells of the epithelium in the stomach mucosa? what do they secrete?
-mucus cells (mucus)
-parietal cells (HCL + intrinsic factor)
-chief cells (pepsinogen + lipase)
-endocrine cells
what are the different endocrine cells of the epithelium in the stomach mucosa? what do they secrete?
-G cells (gastrin)
-D cells (somatostatin)
-enterochromaffine (tin) cells (histamine)
-P/D cells (ghrelin)
what are the phases of digestion?
-cephalic phase
-gastric phase
-intestinal phase
what occurs within the cephalic phase?
-senses (think about food, taste or smell food, put food in your mouth)
-triggers the brain (medulla oblongata)
-vagus nerve triggers the stomach to increase acidity by secreting gastrin + acetylcholine (both increase HCL) also secretes pepsin
-no food in the stomach
what occurs within the gastric phase?
-senses (food distending the stomach wall)
-afferent vagus nerve triggers the medulla oblongata (brain)
-efferent vagus nerve triggers the release of pepsin, acetylcholine, and gastrin (increase pH) in the stomach
-food in the stomach
what occurs within the intestinal phase?
-chyme creates 3 responses
-impulses medulla oblongata to decrease vagus activity
-local reflexes create direct action and the stomach wall decreases mixing and grinding
-release of local hormones via the blood (somatostatin, cholecystokinin, GIP, and secretin)
-gastric secretion is inhibited
how does the stomach empty?
-within 2-6 hours
-pyloric sphincter
how does the pyloric sphincter work?
-small diameter (less than 2mm)
-only allows a small amount of chyme to enter the small intestine
-liquid food passes faster
what occurs if chyme enters the esophagus?
-it will produce a burning sensation in the chest
-esophagus lining is thinner than the stomach lining
what causes gastroesophageal reflux disease (GERD)?
-pregnancy
-excess fat pushing on the stomach
-failure of the lower esophageal sphincter
-chronic heartburn
which side should you lay on to prevent reflux?
-left side
how does vomiting occur?
-strong contractions of the abdominal muscles and the diaphragm forces contents of the stomach into the esophagus and the oral cavity
what does the diaphragm seperate?
-thoracic and abdominal cavities
why does the stomach make noise?
-stomach digestion moves gas
-squeezing gas produces a noise
why does the stomach growl when empty?
-brain asks the muscles to contract to stimulate hunger (moves air)
what are the characteristics of the small intestine?
-small diameter (2.5 cm)
-3-6 meters long
-30m squared
-has 3 sections
-primary digestive organ
-absorption occurs here
what are the accessory organs to the small intestine?
-liver
-pancreas
-pancreatic duct
-gallbladder
-bile duct
what are the 3 sections of the small intestine?
-duodenum
-jejunum
-ileum
what does the pancreas do?
-secretes digestive enzymes into the duodenum through the pancreatic duct
-secretes sodium bicarbonate to neutralize chyme
why must chyme be neutralized?
-other enzymes cannot act
-pH of 2 to a pH of 8
what is the purpose of the duodenum?
-to reduce poly-carbohydrates and convert them to glucose with the help of the pancreas
what digestive enzymes does the pancreas secrete?
-pancreatic amylase
-trypsin (class: protease)
-lipase
-nuclease
what is the purpose of pancreatic amylase?
-digest carbohydrates (ex: starch into maltose)
-maltose is not absorbable
what does the small intestine produce at the apical layer of cells (enterocytes)?
-brush border enzymes
-ex: maltase + lactase + (amino)peptidase
what are the steps in processing carbohydrates?
-step 1: pancreatic amylase
-step 2: maltase + lactase
what is the purpose of maltase?
-digests maltose into glucose which is absorbable
what is the purpose of lactase?
-digests lactose into glucose
what is lactose?
-primary sugar in milk
what does it mean to be lactose intolerant?
-after ingesting milk and other dairy products, experience diarrhea, gas, bloating, and abdominal cramps
-cannot digest lactose properly
why does diarrhea occur with lactose intolerance?
-undigested lactose causes fluid retention in the small intestine
why does gas, bloating, and cramps occur with lactose intolerance?
-bacteria break down the lactose anaerobically
what is celiac disease?
-autoimmune response against a protein called gliadin (present in gluten) naturally found in grains such as wheat, barley, and rye
-presence of gliadin in the small intestine results in an inflammatory response (damages the villi and microvilli of the intestine)
-leads to abdominal pain, diarrhea, and malnutrition
what is the purpose of trypsin?
-digests proteins into di or tripeptides (can be absorbed)
-di or tripeptides are further broken down into amino acids by peptidase
what are proteases?
-class of digestive enzymes that digest proteins
what is the purpose of aminopeptidase?
-brush border enzyme that digests peptides into amino acids
what is the purpose of the gallbladder?
-stores bile produced by the liver and releases it into the duodenum via the bile duct
what is the purpose of bile?
-emulsifies fat
what are the approximate percentages of our dietary caloric intake?
-carbohydrates (50)
-proteins (25)
-fats (25)
what is the purpose of lipase?
-hydrolyzes fats into glycerol and fatty acids
-more efficient compared to gastric lipase
what other places have lipase secreted?
-stomachs parietal cells
-salivary glands
what does the mucosa of the small intestine include?
-fingerlike projections called villi
-cells that cover the villi have microvilli
-increase SA for absorption
what is the purpose of the microvilli?
-give the villi a fuzzy brush border that contains enzymes to complete digestion
where are nutrients finally absorbed?
-into the enterocytes/villi containing blood capillaries and a small lymphatic capillary called a lacteal
what enters the blood capillaries pf villi?
-monosaccharides
-di or tripeptides
-amino acids
what enters the lacteal/lymphatic vessel?
-glycerol and fatty acids form lipoprotein droplets called chylomicrons which enter
what does vitamin and mineral absorption sometimes require?
-specific transport proteins
what are the characteristics of the pancreas?
-located behind the stomach
-4 sections
-produces pancreatic juice (exocrine)
-also an endocrine gland
what are the 4 sections of the pancreas?
-head
-isthmus
-body
-tail
what does pancreatic juice contain?
-sodium bicarbonate
-pancreatic amylase
-lipase
-trypsin
how is the pancreas a endocrine gland?
-secretes the hormone insulin when blood glucose levels rise
-stimulates cells to take up glucose from the blood
what is type 1 diabetes?
-can not produce insulin
-body can not use glucose
-muscle and fat cannot take up glucose
-spillover urine
-can lead to hyperglycemia
-normally diagnosed in childhood
-treatment = insulin injection
what is type 2 diabetes?
-body’s cells are insulin-resistant
-normally occurs in adulthood (9/10)
-risk factors : obesity, inactivity, family history
what are the characteristics of the liver?
-largest gland in the body
-lies mainly in the upper right abdominal cavity under the diaphragm
-has lobules
-stores vitamins
-produces bile (500-700mL/day)
-involved in blood glucose homeostasis
what are the lobules of the liver?
-structural and functional units
-filter blood and remove poisonous substances
what brings blood to the liver? where does the blood come from?
-hepatic portal vein
-blood from the GI tract
how is the liver involved in blood glucose homeostasis?
-converts glycerol and amino acids to glucose
what is contained within bile?
-bile salts
-water
-cholesterol
-bicarbonate
-bilirubin
what is bilirubin?
-green pigment formed from the breakdown of haemoglobin produced by macrophages
how do dead blood cells leave the body?
-via feces
what are the many functions of the liver?
-destroys old RBCs
-detoxifies blood
-stores iron, B12, A, D, E, K vitamins
-stores glucose as glycogen
-makes plasma proteins (albumins and fibrinogen from amino acids)
-produces urea from breaking down amino acids
-regulates blood cholesterol level (converts some to bile salts)
what is hepatitis?
-inflammation of the liver
-A, B, C, D, E strains of virus
-viruses are most common causes
-other infections, toxic substances, and autoimmune diseases can also cause hepatitis
what is hepatis A?
-usually acquired from sewage contaminated drinking water and food
-vaccines are available
what is hepatitis B?
-usually from sexual contact
-also from blood transfusions or contaminated needles
-more contagious than AIDS (spread in the same way)
-vaccines are available
what is hepatitis C?
-usually acquired by infected blood
-can lead to chronic hepatitis, liver cancer, and death
what is cirrhosis?
-chronic disease
-liver becomes fatty and then filled with fibrous scar tissue
-often seen in alcoholics due to malnutrition and excessive alcohol that the liver is forced to break down
-can also cause hepatitis
what is the biliary tree?
-bile ducts
-gallbladder
what do the bile ducts allow for?
-allow for bile and bile salts secreted by the liver to reach the duodenum
what are the characteristics of the gallbladder?
-pear shaped organ below the liver
-stores and concentrates (up to 80%) bile between meals (40-70mL)
-absorbs fatty acids and fat soluble vitamins by forming micelles (emulsification)
-facilitate protein digestion by denaturing dietary proteins to accelerate their cleavage by pancreatic proteases
what is jaundice?
-liver disease can cause bile pigments to leak into the blood (bilirubin)
-a yellowish tint to the whites of eyes and skin
what are gallstones/calculus?
-made of a stone-like material (pigment, calcium, and cholesterol) from bile
what controls the secretion of digestive juices?
-nervous system and digestive hormones
-parasympathetic nervous system stimulates gastric secretions when looking at or smelling food
what is an example of how the digestive secretions are regulated?
-protein rich meal causes G cells to produce the gastrin hormone (increases secretory activity of the gastric glands, increase in HCL) (stomach)
-HCL in chyme stimulates the release of secretin by S cells, proteins and fat in chyme stimulates the release of cholecystokinin (CCK) from I cells (duodenum)
-the release of these two hormones causes the liver to increase bile production and causes the gallbladder to contract and release stored bile (fat digestion) also increases pancreatic juice production to buffer acidity
what does the large intestine include?
-cecum
-colon
-rectum
-anal canal
what are the characteristics of the large intestine?
-larger in diameter than the small intestine
-shorter in length than the small intestine
-receives 1-2L of chyme per day
-no villosity
why does the large intestine not have villi?
-limited absorption function
-most absorption is already done in the small intestine
what are the characteristics of the caecum?
-first portion of the large intestine
-vermiform appendix projects off the caecum
what is the purpose of the vermiform appendix?
-fights infections (immune cells)
what is appendicitis?
-inflamed appendix
-can cause peritonitis
what is peritonitis?
-life threatening infection of the peritoneum
what are the different parts of the colon?
-ascending colon (right side of the body)
-transverse colon (across abdominal cavity)
-descending colon (left side of the body)
-sigmoid colon (S shape)
what is the rectum?
-last portion of the large intestine
-opens at the anus where defecation occurs
what does the colon recieve?
-liquid containing water and electrolytes
-some amount of unabsorbed nutrients
-unabsorbable substances (fibers)
what are the functions of the large intestine?
-absorbs water and ions from feces to prevent dehydration
-moves the chyme
-forms feces
-absorbs vitamins produced by intestinal flora
-forms gas
what is the purpose of intestinal flora in the large intestine?
-break down indigestible material and produce B complex vitamins and vitamin K
-convert unabsorbed amino acids into various gases (indole + mercaptan) (contribute to odor)
what is not produced by the large intestine? what is not absorbed by the large intestine?
-digestive enzymes (produces mucus defensin)
-does not absorb nutrients
what are the characteristics of feces?
-3/4 water
-1/4 solid waste
-bacteria and dietary fiber (indigestible remains) make up the solid wastes
-bacteria digesting indigestible material causes odor and gas
-stercobilin (breakdown product of bilirubin) and oxidized iron causes the brown colour
how does defacation occur?
-peristalsis forces feces into the rectum
-stretching of the rectal wall initiates nerve impulses to the spinal cord
sigmoid and rectal muscles contract (puborectalis and anal sphincters relax)
-allows feces to exit via the anus
what can inhibit defacation?
-contracting the external anal sphincter
-skeletal muscle (voluntary to a certain point)
why does diarrhea occur?
-increased peristalsis and failure to absorb water from the feces
-either due to an infection or nervous stimulation
why does constipation occur?
-dry hard deces (less water)
-may be controlled with water and fiber intake
what are hemorrhoids? why do they occur?
-enlarged inflamed blood vessels of the anus
-due to chronic constipation, pregnancy, aging, and intercourse
what is ulcerative colitis?
-affects the large intestine and rectum
-results in diarrhea, rectal bleeding, abdominal cramps, and urgency to defecate
what is crohn’s disease?
-usually in the small intestine
-ulcers in the intestinal wall (painful + bleed b/c they erode the submucosal layer (nerves + blood vessels)
-cannot absorb nutrients in the affected areas
-causes diarrhea, weight loss, abdominal cramping, anemia, bleeding, and malnutrition
-most common IBD
what are polyps?
-small growths on the colon lining
-can be benign or cancerous
what is the expected outcome of polyps that are detected as cancerous?
-a complete cure if colon cancer is detected while still confined to a polyp
what raises the risk of colon cancer?
-increased dietary fat
what can impact colon cancer?
-fibers in the diet
-regular elimination reduces the time that the colon wall is exposed to cancer-promoting agents in the feces
how can the inside of the large intestine be checked?
-colonoscopy
-swallowing a camera
