DIGESTIVE SYSTEM: CHAPTER 22 Flashcards
WHAT ARE THE MAIN FUNCTIONS OF THE DIGESTIVE SYSTEM
key term 1
- take in food
- break food down into nutrients
- absorb molecules into bloodstream
- rid body of indigestible remains
EXPLAIN THE PARTS OF THE DIGESTIVE PROCESS
key term 1, IPM DAD,
- injestion: eating
- propulsion: movement of food through the alimentary canal (GI Tract). includes swallowing and peristalsis
- mechanial breakdown: chewing and mixing food with saliva and churning food in the small intestine via segmentation
- digestion: series of catabolic steps that involves enzymes to brwakdown complex food molecules into chemical building blocks-
- absorption: passage of digested fragments into the lumen of GI tract into blood or lymph
- defacation: elimination of indigestible substances via anus in form of feces
WHAT IS PERISTALSIS AND SEGMENTATION?
key term 1
presitalsis: uses alternating waves of contraction and relaxation to propell food
segmentation: local contriction of small intestine to mix/churn food with digestive juices
WHAT ARE THE 2 MAJOR GROUPS OF ORGANS IN THE DIGESTIVE SYSTEM? WHAT ORGANS ARE WITHIN THEM?
key term 1
1) alimentary canal: aka the gastrointestinal (GI) tract. it is a muscular tube that runs down from the mouth to the anus and works to digest and absorb food.
- organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
2) accessory organs: teeth, tongue, gallbladder and digestive glands including the salivary glands, pancreas, and liver.
WHAT IS THE ENTERIC NERVOUS SYSTEM
- it is the GI tracts own nervous system and it controls motility. it is also called the gut brain
- enteric neurons: communicate with eachother throughout the GI tract via short reflexes
WHAT ARE THE 4 BASIC LAYERS THAT ALL THE DIGESTIVE ORGANS HAVE?
key term 2
mucosa, submucosa, muscularis externa, serosa
WHAT ARE THE FUNCTIONS OF THE MUCOSA
KT 2
- is the innermost layer that lines the lumen
- functions: produces mucous, hormones, and digestive enzymes. absorbs end products of digestion and protexts from infectious disease
- made up of 3 sublayers: lamina propria, epithelium, and muscularis mucosa
WHAT ARE THE FUNCTIONS OF THE SUBMUCOSA AND WHAT IS IT MADE OF
KT2
- consists of alveolar connective tissue
- contains many elastic tissue to maintain organ shape when storing large meals
- consists of blood and lymphatic vessels, lymphoid focciles and the submucosal plexus that supply’s surrounding GI tract tissue
FUNCTIONS OF MUSCULARIS EXTERNA
KT2
- is responsible for segmentation and pristalsis
- contains circular and longtitidinal tissue
- when circular tissue thickens it can create spincters.
FUNCTIONS OF THE SEROSA
KT2
- is the outermost layer that contains an epithelium called visceral peritoneum
- in the esophagus the serosa is replaced by adventita which is a dense connective tissue that holds esophagus to surrounding structures
- restroperitoneal organs have both adventita and serosa.
HOW DOES THE MOUTH CONTRIBUTE TO DIGESTION? WHAT ARE SOME ASSOCIATED ORGANS IN THE MOUTH
KT3
- is where food is cheweed and enyme-containing saliva begins the process of digestion (of starch)
- organs: tongue, teeth, salivary glands, mouth
FUNCTIONS OF THE TONGUE
KT3
- occupies floor of the mouth and consists of bundles of skeletal muscle
functions:
- gripping, repositioning, and mixing food during chewing.
- formation of bolus (mixture of food and saliva)
- initialting swallowing, speech, and taste
WHAT DO THE EXTRINSIC AND INTRINSIC MUSCLES OF THE TONGUE DO
KT3
intrinsic: alters shape of tongue
exterinsic: alter tongue position
WHAT IS THE FUNCITON OF THE SALIVARY GLANDS. WHAT ARE THE 2 TYPES OF SALIVARY GLANDS?
KT3
- cleanes mouth
- dissolves food and chemicals for taste
- moistens food
- begins breakdown of strach using salivary amylase
major (exterinsic) salivary glands: located outside of the oral cavity and produces most saliva
minor (intrinsic) salivary glands: located in oral cavity and helps keeo mouth moist
WHAT ARE THE 2 TYPES OF CELLS THAT SALIVARY GLANDS ARE COMPOSED OF? WHAT DO THEY PRODUCE?
KT3
- Serous cells: produce watery secretion containin enzymes, glycoproteins, and ions
- mucous cells: produce mucous thats thickly concentration with glycoproteins
the watery secretions+mucous=saliva
WHAT IS THE COMPOSITION OF SALIVA
KT3. HINT: 6 of them
- mostly water (95-97.5%)
- contains electrolytes: Na, K, Cl, HCO3-, PO4 2-
- slightly acidic (6.75-7)
- salivary amylase and linguinal lipase
- metabolic wastes: uric acid and urea
- lysozyme, Iga, defensins and nitric oxide from nitrates in food protect against microorganisms
HOW IS SALIVA SECRETION REGULATED?
KT 3
Major salivary glands are activated by the parasympathetic nervous system when:
- injested food triggers mechanoreceptors and chemorecptors to the mouth sending signals to salviatory nuceli in the brain stem which triggers parasynpathetic impulses along cranial nerves IX and VII to glands.
^^ smells/ sight of food or upset stomach can also act as a stimulant
strong sympathatic stimulation inhibits salivation which causes dry mouth
WHAT ARE THE MECHANISMS OF MASTICATION AND DEGLUTITION
KT 4
mastication: process of chewing that tears food and grinds it into smaller fragments
deglutition swallowing. the pharynx and esophagus are channels to pass frood from the mouth to the stomach. deglutition is their main functions. it has 2 phases.
- buccal phase: voluntary contraction of the tongue
- pharyngeal-esophageal phase involuntary phase that primarily involves the vagus nerve (controlled by swallowing center in medulla and pons)
WHAT IS THE GASTROESOPHAGEAL (CARDIAC) SPHINCTER
- it surrounds the cardial orifice
- it keeps the orifice closed when food isn’t being digested and mucus cells prevent acid reflex and protect esophagus
WHAT ARE THE 5 PARS OF THE MASTICATION AND DEGLUTITION PROCESS
1) buccal phaseupper esophegeal sphincter closed, tongue pressed against hard palate forcing bolus into oropharynx
2) pharyngeal esophageal phase begins: tongue blocks mouth, soft palate and uvula rise closing nasopharynx, larynx rises so epiglottis is closed, upper esophageal sphincter relaxes so food can enter esophagus
3) pharyngeal esophageal phase continues: contrictor muscles of pharynx contract forcing food into esophagus inferiorly. supper esophageal sphincter contracts after food enters.
4) presitalsis moves food down esophagus into stomach
5) gastrophageal sphincter surrounding cardial oridice opens and closes after food enters to prevent regurtitaion.
WHAT IS THE STOMACH? WHAT DOES IT DO?
KT5. what happens when stomach is empty?
stomach: temporary storage tank that starts chemical breakdown of protein digestion
- converts bolus into chyme
- when it is empty, sotmach mucosa folds called rugae
WHAT ARE THE 4 TUNICS IN THE STOMACH? WHAT ARE SOME MODIFICATIONS TO THEM
KT 5
- mucosa: consists of simple columnar epithelium entirely composed of mucous cells (secretes alkaline mucus). it is dotted with gastric pits which lead to gastric glands which produce gastric juice
- submucosa
- muscularis externa: has a 3rd layer apart from the circular and longtitudinal called the oblique layer. it allows stomach to pummel chyme which increases physical breakdown
- serosa
WHAT ARE THE TYPES OF CELLS IN THE STOMACH? WHAT DO THEY DO?
KT6
- Mucous neck cells: secrete thin aicdic mucous of unknown function
- parital cells: secretes HCL (denatures proteins and activates pepsin which breaks plant walls and kills bacteria) and intrinsic factor (glycoprotein needed for absorption of vitamin B12)
- cheif cells: secretes pepsinogen which will later activate by HCL to pepsin (digests proteins). also secretes lipases.
- enteroendocrine cells: secretes histamine (activates parietal cells to secrete HCL), and gasrtin (increases HCL secretion via parasympathetic nerve fibers)
WHAT IS THE MUCOSAL BARRIER? WHAT DOES IT DO?
it protects the stomach from the harsh digestive conditions by having a:
- thick layer of bicarbonate rich mucous
- tight juctions between epithelial cells
- ensuring damaged cells are replaced quickly
WHAT ARE THE PROCESSES CARRIED OUT BY THE STOMACH
HINT: 7
- breakdown of food
- holding area for food
- delivers chyme to small intestine
- denatures proteins via HCL
- pepsin carries out enzymic digestion of protein
- lipid soluble asprin and alcohol absorbed into blood
- only stomach factor essential to life is secretion of intrinsic factor for vitamin B12 absorption
EXPLAIN THE REGULATION/PHASES OF GASTRIC SECRETION AND
KT7
1) CEPHALIC (REFLEX) PHASE: conditioned reflex triggers by aroma, taste, sight, and thought
gastric phase, intestinal phase
EXPLAIN THE GASTRIC PHASE OF GASTRIC SECRETION REGULATION
KT7
2) GASTRIC PHASE
stimulation
- ditension activate strech receptors which send short and long reflexes which increase secretory activity
- rising Ph, caffeine, partially injested proteins activate enteroendocrine G cells to secretion gastrin
^^ gastrin increase HCL release by parital cells by binding to receptors on parietal cells or stimulating enteroendocrine glands to release histamine
Inhibition: is caused by Low ph, time between meals, during digestion as a negative feedback mechanism. also inhibited by sympathetic stimulation
More protein=more HCL=decline in Ph= less gastrin secretion
EXPLAIN THE INTESTINAL PHASE OF GASTRIC SECRETION REGULATION
KT7
stimulation: partially dijested food enters small intestine causing intestinal (ecteric) gastrin to be released. causes gastric glands to continue secretory activities, however this is breif.
inhibition: protect stomach from being overhwelmed by too much chyme and acidity.
- distension of duodenum due to entry of chyme
- acidic chyme
- fatty chyme
- hypotonic chyme
- enterogastric reflex: enteric nervous syetm short reflex, sympathetic nervous system long reflexes.
- enterogastrones: secretes secretin and cholecytokinin which inhibit gastric secretion
EXPLAIN THE PHASES OF GASTRIC MOTILITY
KT7
- Propulsion: Peristalic waves move from fundus towards pylorus
- grinding: most vigourous peristalsis and mixing action occurs near pylorus. pyloric end acts as a pump that delivers small amt of chyme to duodemun
- retropulsion: peristalic wave closes the pyloric valve, forcing most of the content of the pyloris backwards into the stomach
EXPLAIN REGUATION OF GASTRIC EMPTYING
KT 7
- usually empties in 4 hours but an increase of fatty chyme can increase time to 6 hours or more
duodenum prevents overfilling by controlling how much chyme enters
- duodenal receptors repsond to strech and chemical signals
- enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling (decrease contractile force and rate of stomach emptying)
WHAT ARE THE DIGESTIVE FUNCTIONS OF THE LIVER, GALLBLADDER AND PANCREAS
KT 8
- Liver: produces bile (fat emulsifier)
- gallbladder: stores bile
- pancreas: supplies enzymes for digestion as well as bicarbonate to neutralize stomach acid
WHAT ARE THE METABOLIC FUNCTIONS OF THE LIVER
KT 10. HINT: 5 of them
- Carb metabolism (glucose to glycogen and vise versa)
- fat metabolism (storage and synthesis of fatty acids and cholestral)
- protein metabolism(breaks down amino acids for ATP production and synthesize plasma proteins)
- vitamin/mineral storage: (Vitamin A and Vitamin D and B12)
- biotransformation functions: detoxification
HOW DOES BILE ASSIST WITH DIGESTION
KT 8
Bile: responsible for fat emulsification. contains:
- bile salts: cholestral derivatives that function in fat emulsification and absorption
- cholestral, triglycerides, phospholipids, and electrolytes
EXPLAIN BILE ENTEROHEPATIC CIRCULATION
it is a recycling method that conserves bile salts.
1) reabsorbed into blodd by ileum
2) returned to liver via hepatic portal vein
3) resecreted into newly formed bile
about 95% of bile sats are secreted, meaning only 5% are newly synthesized.
EXPLAIN THE GROSS ANATOMY OF THE LIVER, INCLUDING BIL DUCTS, COMMON HEPATIC DUCT, CYSTIC DUCT, LIVER LOBULES, AND PORTAL TRIAD
the bile duct: is formed by unuon of the common hepatic and cystic ducts
common hepatic duct: leaves liver
cystic duct: connects liver to gallbladder
liver lobules: hexagonal structures that contain hepatocytes that filter and process nutrient rich blood
portal triad: located in the corner of each lobule and it contains a branch of the hepatic artery, hepatic portal vein and bile duct which receives bile from bile canaliculi
BREIFLY EXPLAIN THE GALLBLADDER.
- main function is to store bile
- has a honeycomb shape which allows it to expand as it fills
- muscular contraxtions release bile into the cystic duct
EXPLAIN THE EXOCRINE AND ENDOCRINE FUNCTIONS OF THE PANCREASE
endocrine: produces insulin and glucagon by pacreatic islet cells
exocrine: produces pancreatic juisces producded by secretory cells called acini
WHAT IS THE COMPOSITION OF PANCREATIC JUICE
it is a watery alkaline solution that contains electrolytes (HCO3- mainly), and digestive enzymes like
- proteases- for proteins, is secreted inactive to prevent self digestion (tripsinogen –> tripsin)
- amylase- for carbs
- lipases- for lipids
- nucleases- for nucleic acids
BREIFLY EXPLAIN THE FUNCTION OF THE HEPATOPANCREATIC SPHINCTER HAPETAPANCREATIC AMPULLA, PANCREATIC DUCT AND BILE DUCT
hepatopancreatic sphincter: controls the entry of bile and chyme into the duodenum
The bile duct, **pancreatic duct ** unite in a wall of the duedenum called the hepatopancreatic ampulla:
WHAT ARE THE NEURAL AND HORMONAL CONTROLS OF BILE AND PANCREATIC SECRETION INTO THE SMALL INTESTINE
KT 9
HORMONAL: enteroendocrine secrete
- secretin: it is stimulated by acidic chyme entering the duodenum. and stimulates duct cells to secrete pancreatic juice and bile-(weakly)
- cholecytokinin (CCK): is stimulated by protein rich fatty chyme. stimulated acini to secrete pancreatic juice and contracts gallbladder and relaxes hepatopancreatic sphincter to release bile
NEURAL
- the vagus nerve reflexes weakly stimulate gallbladdercontraction and pencreatic secretion during gastric and cephalic phases
NAME THE EVENTS OF PANCREATIC JUICE AND BILE ENTERING THE SMALL INTESTINE
KT 9
1) secretin is triggers by acidic chyme and cholecytokinin is triggered by fat and protein rich chyme
2) pancreatic secretion: secretin causes duct cells and cholecytokinin caused acini to secrete pancreatic juice. vagus nerve weakly helps with pancreatic juice secretion
3) bile secretion: bile salts coming from the enterohepatic circulation are strongest stimulant for bile release. secretin weakly helps
4) gallbladder contraction: cholecytokinin causes gallbladder to contract and vagus nerve weakly helps
5) hepatopancreatic sphincter relaxtion: cholecytokinin causes hepatopancreatic sphincter to relax and bile and pancreatic juices enter duodenum
BREIFLY DESCRIBE THE SMALL INTESTINE, WHAT ARE IT’S SUBDIVISIONS?
small intestine: major organ of digestion and absorption. joints the large intestine at the ileocecal valve
- duodenum: mostly retroperoneal, has the most features and curves around the pancrease
- jujunum: attacked posteriorly by mesentery
- ileum: attached posteriorly by mesentery, joints large intestine at ileocecal valve
WHAT ARE SOME MODIFICATIONS OF THE SMALL INTESTINE FOR ABSORPTION
KT11
- modifications allow for an increased surface area = more nutrient absorption
- circular folds: permanent folds that force chyme to slowly spiral through lumen, gives more time for nutient absorption
- villi: fingerlike projections of mucosa that contain dense capillary bed and lymphtaic capillary called lacteal for absorption
- microvilli: cytoplasmic extensions from mucosal cells that give fuzy appreance called the brush border that contains brush border enzymes that are used for final carb and protein digestion
WHAT ARE THE TYPES OF CELLS FOUND IN THE SMALL INTESTINE
-
enterocytes: make up bulk of epithelium, simple columnar absorptive cells.
crypts: produce intestinal juice that acts as carrier fluid for absorbing nutrients from chyme
villi: absorption of nutrients and electrolytes
goblet cells: mucous secreting cells found in epithelia of villi and crypts
enteroendocrine cells: source of enterogastrones like cholecytokinin and secretin
antimicrobial cells maintian bacterial flora and stem cells maintain a high turnover
EXPLAIN THE DIGESTIVE PROCESS IN THE SMALL INTESTINE
-
after a meal: segmentation triggered by intrinsic pacemaker cells, also controlled by long and short reflexes and hormones (acetylcholine and norepinephrine)
-between meals: true presitalsis is causes by a rise in hormones. meal remnants, bactera, and debris and moved towards the large intestine. complete trip from duodenum to ileum takes about 2 hours. - ileoecal valve control: ileocecal sphincter relaxes in the prescence of the hormone gastrin and admits chyme into the large intestine
WHAT IS THE MAIN FUNCTION OF THE LARGE INTESTINE? WHAT’S ITS UNIQUE FEATURE? WHAT ARE ITS SUBDIVISIONS?
**main function: ** water absorption, stores residues temporarily and then eliminates them as feces
unique feature: haustra, which are pocket-like sacs cause by tone of muscularis
subdivisions:
- cecum: first part of small large intestine
- appendix: MALT, bacterial storehouse, twisty shape makes it susceptible to blockages
- colon: have several regions that are retroperitoneal
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum: rectal valves stop feces from being pased with gas (flatus)
- anal canal: last segment of large intestine that opens to exterior at anus, has 2 sphincters called the internal anal sphincter (smooth muscle), and external anal sphincter (skeletal muscle)
EXPLAIN THE DIGESTIVE PROCESS IN THE LARGE INTESTINE
food remains in the large intestine for about 12-24 hours. there is no further digestion except for bacterial and salts, water, and vitamins are absorbed.
motility of large intestine
- Haustral contractions: slow segmenting movements mostly in ascending and descending colon last 1 min and occur every 30 mins
- mass movements: (mass presitalsis): long- slow moving contractile waves that move feces towards rectum. occur 3-4x per day. feces stored in descending and sigmoud colon and finish dehydrating it. usually occurs after eating via gastrocolic reflex
EXPLAIN THE DEFECATION PART OF LARGE INTESTINE DIGESTIVE PROCESS
defecation:
- mass movements force feces into rectum
- distension initiates defecation reflex which triggers contraction of the sigmoid colon and rectum, relaxes anal sphincter and voluntary control allows control of external anal sphincter. muscles of the rectum will contract to expell feces which is assisted by valsavas maneuver.
EXPLAIN DIGESTION OF CARBOHYDRATES
- only monosaccharides can be absorbed (glucose, fructose, galactose)
- begins in the mouth with salivary amylase
1) pancreatic amylase: breaks down starch or glycogen that escaped salivary amylase into oligosaccharides and disaccharides.
2) brush borders enzymes **maltase ** and sucrase further break these into lactose,maltose, and sucrose and then into monosaccharides
3) monosaccharides are cotransporyed to apical membranr of absorbative epithelial cells (mostly by 2ndary active transport with Na)
4) monosaccarides ecit across the basolateral membrane by facililated diffusion
EXPLAIN DIGESTION OF PROTEINS
proteins are broken from large polypeptides –> small polypeptides –> amino acids and monomers
digestion first begins in the stomach when pepsinogen is converted to pepsin and digests proteins.
1) pancreatic protease trypsin cleaves proteins into smaller peptides while carboxypeptidase takes off one amino acid at time from the end
2) brush border enzymes break oligopeptides and dipeptides into individual amino acids
3) amino acids are cotransported across apical membrane of absorptive epithelial cells via 2ndary active transporters like Na or H
4) amino acids exit across basolateral membrane via facilitated difusion
EXPLAIN ABSORPTION OF LIPIDS
- emulsification: triglycerides and their breakdown products are insoluble in H2O, so bile salts break large fat gobules into smaller ones
- digestion: pancreatic lipases break down fat into monoglyceride and 2 free fatty acids
- micelle formation: products from digestion become coated with bile salts
- diffusion lipid products leave micelles and cross epithelial membrane via diffusion
- chylomicron formation: lipid products are converted back into triglycerides forming a chylomicron
- chylomicron transport: chylomicrons are exocytosed from basolateral side and enter lymphatic lacteal –> eventually emptied into venous blood at thoracic duct
- once in blood, chylomicrons are broken into free fatty acids and gkycerol by lipoprotein lipase so they can be used by cells.
- short-chain fatty acids can diffuse directy into blood
