DIGESTIVE SYSTEM: CHAPTER 22 Flashcards

Question

WHAT ARE THE PROCESSES CARRIED OUT BY THE STOMACH | HINT: 7

Answer 1

- 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

Answer 2

1) **CEPHALIC (REFLEX) PHASE**: conditioned reflex triggers by aroma, taste, sight, and thought **gastric phase, intestinal phase**

Answer 3

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

Answer 4

**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

Answer 5

- **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

Answer 6

- 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)

Answer 7

- **Liver**: produces bile (fat emulsifier) - **gallbladder**: stores bile - **pancreas**: supplies enzymes for digestion as well as bicarbonate to neutralize stomach acid

Answer 8

- **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

Answer 9

**Bile**: responsible for fat emulsification. contains: - **bile salts:** cholestral derivatives that function in fat emulsification and absorption - cholestral, triglycerides, phospholipids, and electrolytes

Answer 10

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.

Answer 11

**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**

Answer 12

- 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

Answer 13

**endocrine**: produces insulin and glucagon by pacreatic islet cells **exocrine**: produces pancreatic juisces producded by secretory cells called **acini**

Answer 14

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

Answer 15

**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**:

Answer 16

**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

Answer 17

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

Answer 18

**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

Answer 19

- 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

Answer 20

- **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

Answer 21

- **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

Answer 22

**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)

Answer 23

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**

Answer 24

**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.

Answer 25

- 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

Answer 26

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

Answer 27

- **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