lecture exam 5 - chapter 24

GI tract

alimentary canal, muscular tube that winds through body and is responsible for the digestion and absorbtion of food

GI tract structures

oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus

accessory structures of digestive organs

assist in breakdown of foodstuffs, not part of GI tract, teeth, tongue, gallbladder, salivary glands, liver, pancreas

functions of digestive system

ingestion, mastication, secretion, digestion, absorption (most important), elimination

ingestion

taking materials into the digestive tract

mastication

chewing

secretion

lubricate, liquify, digest

propulsion

movement of materials along the digestive tract, deglutition, peristalsis, mass movements

digestion

mechanical: chewing, mixing, churning food

chemical: digestive enzymes break down food

absorbtion

most important, movement of nutrients from the GI tract to blood or lymph

elimination

elimination of indigestible solid wastes

local regulation of digestive system

enteric nervous sytem, nerve plexuses located in walls of digestive tract, regulates digestive activity, submucosal and myenteric nerve plexuses

local regulation of digestive tract - submucosal nerve plexuses and myenteric nerve plexuses

submucosal: regulates glands and smooth muscle in mucosa

myenteric: controls Gi tract mobility

general regulation of digestive system

Coordination with cns, may initiate reflexes because of sight, smell, taste of food, primarily parasympathetic input (rest and digest), sympathetic input ibhibits muscle contraction, secretion, decrease of blood flow to the digestive tract

nervous regulation of digestive system

3 major types of enteric neurons: sensory neurons, motor neurons, interneurons, nervous system regulation involves both general and local regulation

sensory neurons of nervous regulation

detect changes in chemical compostition of GI tract (what did we eat and what chemicals do we release to break it down)

motor neurons of nervous regulation

stimulate or inhibit smooth muscle contraction and glandular secretions

interneurons of nervous regulation

connect sensory neurons to motor neurons within the ENS

peritoneum

serous membrane that lines the abdominopelvic cavity and organs

peritonuem layers

mesenteries, retroperitoneal, greater omentum, lesser omentum

mesenteries

routes by which vessels and nerves pass from body wall to the organs

retroperitoneal 

organs located posterior to the peritoneum

greater omentum

connects greater curvature of stomach to transverse colon

lesser omentum

connects lesser curvature of stomach and duodenum to the liver and diaphragm

how many adult teeth

32 (20 deciduous teeth), replacement starts around age 5 and ends around 11

types of teeth

incisors, canines, premolars, molars

crown of teeth

exposed part of tooth above gingiva (gum), covered by a protective enamel, acellular material composed of hydroxyapatite (hardest substance)

neck of tooth

enameled part of tooth below gingiva

root of tooth

portion of tooth embedded in jawbone, composed of dentin, within dentin the root is the pulp cavity (filled with pulp, blood vessels, nerves)

periodontal ligaments of teeth

anchor teeth in the sockets (alveoli)

chewing (mastication)

incisors and canines bite or cut off food, premolars and molars grind

muscles involved in mastication

masster and temporalis mainly, medial and lateral pterygoids

mastication reflex

comes from medulla oblongata, descending pathways from cerebrum provide conscious control and controls basic movements involved in chewing, when you put food in your mouth the reflex is to chew but you can stop if you want (conscious control)

salivary glands

produce and secrete saliva, compound acinar glands, serous and mucus secretions (serous: enzymes, ions, mucin) (mucus: muscous)

3 pairs of salivary glands

parotid, submandibular, sublingual

saliva secretions from salivary glands function

cleanses mouth, moistens and dissolves food and chemicals, aids in bolus formation, contains enzymes that break down starch

saliva components

1L of saliva a day, 97-99.5% water and slightly acidic solution, - electrolytes, digestive enzymes (salivary amylase), proteins (mucin, lysozyme, defensins, IgA), metabolic wastes (urea, aric acid)

control of salivation

primarily parasympathetic, secrete saliva in response to ingested food that or thought of food, sympathetic stimulation can ibhibit saliva production

pharynx in digestion role

transports food and fluid to esophagus and air to trachea

parts of pharynx involved in digestion

posterior walls of oropharynx and laryngopharynx contain a group of muscles called pharyngeal constrictors that contribute to swallowing

structure of esophagus

upper and lower esophageal sphincters regulate movement, mucous glands produce lubricating mucus, passes through esophageal hiatus of the diaphragm

function of esophagus

transports food from pharynx to stomach

phases of swallowing

voluntary phase, pharyngeal phase, esophageal phase

voluntary phase of swallowing

deglutition, a bolus of food is moved by tongue from oral cavity to pharynx

pharyngeal phase of swallowing

reflex causes by stimulation of stretch receptors in pharynx,- soft palate closes nasopharynx, -epiglottis vestibular folds and vocal folds close opening to larynx,- pharyngeal  muscles move blous to the esophagus by contracting and constricting

esophageal phase of swallowing

a reflex initiated by stretch receptors in the esophagus, wave of contraction (peristalsis) moves food to stomach

stomach

temporary storage tank where chemical breakdown of protein begins and food is converted from bolus to chyme

gastropharyngeal opening of stomach

opens to esophagus superiorly

pyloric orfice of stomach

opens to duodenum inferiorly

major regions of stomach

cardiac (connects to esophagus), fundus (upper and rounded below diaphragm), body, pyloric (distal)

lateral sides of stomach have

greater and lesser curvatures that are attachment points for greater and lesser omentum

stomach wall layers

external serosa, muscularis (3 layers (longitudnal, circular, oblique) (unlike most othet digestive organs with 2), submucosa, mucosa

mucosa of stomach wall layers

simple columnar epithelium, surface mucus cells produce mucous with bicarbonate, proteins, stomach lining, protects from acids and ulcers

empty stomach volume and feature

50mL volume but can hold a gallon, rugae are folds visible in empty stomach

peristalsis

moves food distally through digestive tract, smooth muscle contraction, relaxation ahead of bolus causing digestive tract to expand and contraction behind bolus to move it

gastric pits

contain glands that secrete gastric juices, mucus neck cells, parietal cells, chief cells, endocrine cells

mucus neck cells in gastric pit

secrete acidic mucus

parietal cells in gastric pit

secrete HCl and intrinsic factor

chief cells in gastric pit

produce pepsinogen, pepsinogen activated to pepsin by HCl in stomach and pepsin itself via positive feedback mechanism

endocrine cells of gastric pit

regulatory hormones, gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), somatostatin

chyme

ingested food (bolus) mixed with gastric juices

gastric juices include

mucus, pepsinogen, HCL, instrinsic factor, gastrin and histamine

mucus in gastric juices function

protects stomach lining from acidic chyme and pepsin

pepsinogen in gastric juices function

converted to pepsin which digests proteins

HCl in gastric juices funciton

promotes pepsin activity and removes microorganisms

instrinsic factors in gastric juices function

necessary for B12 activity

gastrin and histamine in gastric juices funciton

regulate stomach secretions

cephalic phase of stomach secretions

initiated by sight, smell, taste or thought of food, nerve impulses from medulla stimulate HCl, pepsinogen, gastrin, histamine secretion

gastric phase of stomach secretions

initiated by distension of the stomach which stimulates gastrin secretion and activates cns and local reflexes that promote further secretion

gastrointestinal phase

acidic chyme enters the duodenum and stimulates neuronal reflexes and the secretion of hormones (CCK, secretin) that inhibit gastric secretions

mixing waves - movement of stomach

mix the stomach contents with stomach secretions to form chyme, more liwuid part of chyme pushed towards pyloric sphincter and more solid center moves back towards body of stomach

peristaltic waves - movement of stomach

move chyme distally duodenum, stronger than mixing waves, liquid part of chyme to pyloric sphincter and solid part to body

hunger contractions - movement of stomach

result of mixing and peristaltic waves in stomach

vomiting - movement of stomach

reverse peristaltic contractions

small intestine

digestion is finished and nutrients are absorbed

why is small intestine called small intestine

diameter not length, large intestine is wider in diameter, small intestine is longer but smaller in diameter

duodenum of small intestine

chyme exits stomach at pyloric sphincter and moves to duodenum, curves to left (head of pancreas sits here), contains major and minor duodenal papillae

duodenal papillae

where pancreatic ducts and liver ducts empty their secretions

duodenal histology - structural modifications that increase surface area

circular folds, vili (stationary, contain capillaries and lacteals, folds of mucosa), microvilli (folds of cell membranes of absrorbtive cells)

intestinal glands

pits in mucosa between vili, absorptive cells, goblet cells, endocrine cells, granular cells

absorbtive cells of intestinal glands

produce digestive enzymes and absorb digested food

goblet cells of intestinal glands

produce protective mucus

endocrine cells of intestinal glands

produce regulatory hormones

granular cells of intestinal glands

protect intestinal epithelium from bacteria

ileum and jejunum of small intestine

gradual decrease in diameter and thickness of intestinal wall, number of intestinal folds and number of vili further away from stomach, major site of nutrient absorption

peyers patches in ileum and jejunum of small intestine

lymphatic nodules numerous in mucosa and submucosa, similar to tonsils, trap foreign molecules

ileocecal junction

where the ileum meets cecum of large intestine, ileocecal sphincter and ileocecal valce

secretions of small intestine

stimulated by chemical or tactile irritation, vagal (parasympathetic) stimulation and secretin, fluid primarily composed of water, electrolytes, mucus

mucus in small intestine secretions

protects against digestive enzymes and stomach acids

digestive enxymes of small intestine secretions

bind to absorptive cells of intestinal walls disaccharidase (break down disaccharides to monosaccharides), peptides (hydrolyze peptide bonds), nucleases (break down nucleic acids)

segmental contractions of small intestine

mix intestinal contents, not moving distally, segments alternate between contraction and relaxation whcih spreads out material and material becomes more diffuse. (lighter in color)

peristaltic contractions of small intestine

propel chyme distally down small intestine

what stimulates small intestine movement

distension of intestinal wall, local reflexes, and pns

chyme movement in small intestine

ileocecal sphincter remains slightly contracted until peristaltic waves reach it then relaxes allowing chyme to move to cecum, distension of cecum by chyme casuses ileocecal valve to reflexivly contract which prevents more chyme from entering the cecum, increases digestion and absorbtion in small intestine by slowing progress of chyme - prevents backflow

4 external lobes of liver

right lobe, left lobe, caudate lobe, quadrate lobe

lobules of liver

Hexagonal-shaped lobules are the structural and functional units of the liver, composed of hepatocyte (liver cell) plates radiating outward from a central vein, portal triads found at each of the 6 corners of each lobule

portal triad

hepatic duct, hepatic artery, hepatic portal vein

hepatic duct of portal triad

conducts bile to duodenum

hepatic artery of portal triad

supplies o2 rich blood to liver

hepatic portal vein of portal triad

carries venous blood with nutrients from digestive viscera