ch 24 digestive system PP

gastrointestinal GI tract

long tube that is open at both ends for transit of food during processing

named portions of GI tract

esophagus

stomach

small intestine

large intestine

rectum

accessory digestive organs

teeth

tongue

salivary glands

liver

gallbladder

pancreas

GI tract

oral cavity

pharynx

esophagus

stomach

small intestine

large intestine

anal canal

accessory structures are not

part of the GI tract but they do contribute to food processing

6 basic processes involved in digestion

ingestion

secretion

motility

digestion

absorption

defecation

enteric nervous system

submucosal plexus

myenteric plexus

autonomic nervous system

parasympathetic

sympathetic

absorption

digested substances are transported from the lumen of the GI tract through the epithelium

most nutrients are absorbed into the

blood capillaries

lipids and lipid-soluble vitamins are absorbed into the

lymphatic capillaries

primary types of motility of GI tract

mixing

propulsion

peritoneum

largest serous membrane in body

parts of peritoneum

lesser omentum

mesocolon

mesentery

greater omentum

parietal peritoneum

visceral peritoneum

peritoneal cavity

falciform ligament

salivary glands

lie outside mouth and empty their contents into ducts which deliver saliva into oral cavity

3 pairs of salivary glands

parotid

submandibular

sublingual

opening of parotid duct is near

second maxillary molar

tongue

together with associated muscle forms floor of oral cavity

tongue is compoesd of

skeletal muscle covered with mucous membrane

the tongue participates in

chewing

swallowing

speech

upper and lateral surfaces of tongue are

covered with papillae some of which have taste buds

mechanical digestion in mouth

chewing mixes food with saliva and forms a bolus which can easily be swallowed

chemical digestion in mouth

salivary amylase converts polysaccharides to disaccharides

pharynx

funnel shaped tube that extends from internal nares to the esophagus posteriorly and to larynx anteriorly

pharynx is composed of

skeletal muscle and lined with mucous membrane

esophagus

collapsible muscular tube that lies posterior to trachea and connects pharynx to stomach

voluntary phase of oral digestion

bolus of food is pushed by tongue against hard palate and then moves toward oropharynx

features of voluntary phase of oral digestion

hard palate

bolus

oral cavity

oropharynx

tongue

epiglottis

pharyngeal phase of oral cavity

as bolus moves into oropharynx soft palate and uvula close off nasopharynx and larynx elevates so epiglottis closes over laryngeal opening

features of pharyngeal phase

soft palate and uvula elevate and close off nasopharynx

uvula

bolus

epiglottis closes over laryngeal opening

esophageal phase of oral digestion

bolus passes through esophagus and enters stomach

inferior esophageal sphincter opens

peristaltic contractions of esophageal muscle push bolus toward stomach

features of esophageal phase

soft palate, uvula, and epiglottis return to preswallowing position

superior esophageal sphincter closes

esophagus

bolus

pharynx activity

pharyngeal stage of deglutition

pharynx result

moves bolus from oropharynx to laryngopharynx and into esophagus

closes air passageways

esophagus activity

relaxation of upper esophageal sphincter

esophageal stage of deglutition (peristalsis)

relaxation of lower esophageal sphincter

secretion of mucus

esophagus result

permits entry of bolus from laryngopharynx to esophagus

pushes bolus down esophagus

permits entry of bolus into stomach

lubricates esophagus for smooth passage of bolus

stomach

j-shaped enlargement of GI tract

parts of stomach

fundus

cardia

body

lesser curvature

greater curvature

pyloric antrum

pyloric canal

pyloric sphincter

pylorus

functions of stomach

mixes saliva food and gastric juice to form chyme

serves as a reservoir for food before release into small intestine

secretes gastric juice which has HCl, pepsin, intrinsic factor, and gastric lipase

secretes gastrin into blood

cells in stomach

surface mucous cell

mucus neck cell

parietal cell

chief cell

g cell

surface mucus cell

secretes mucus

mucus neck cell

secretes mucus

parietal cell

secretes hydrochloric acid and intrinsic factor

chief cell

secretes pepsinogen and gastric lipase

g cell

secretes hormone gastrin

phases of stomach digestion

cephalic phase

gastric phase

intestinal phase

cephalic phase

cephalic reflex

initiated by thought smell sight or taste of food or sounds of food prep

cephalic reflex 1

receptors- special senses

cephalic reflex 2

sensory input

increased nerve signals relayed from cerebral cortex and hypothalamus to medulla oblongata

cephalic reflex 3

medulla oblongata integrates input from higher brain centers

cephalic reflex 4

motor output

increased nerve signals relayed along vagus nerve from medulla oblongata to stomach

cephalic reflex 5

effector

stomach stimulated to increase both its force of contraction and release of secretions

gastric phase

gastric reflex and gastrin release

initiated by presence of food in stomach

gastric reflex 1

receptors

baroreceptors in stomach wall detect stretch; chemoreceptors detect protein or high pH in stomach contents

gastric reflex 2

sensory input

increased nerve signals relayed to medulla oblongata

gastric reflex 3

medulla oblongata integrates sensory input

gastric reflex 4

motor output

increased nerve signals relayed along vagus nerve from medulla oblongata to stomach

gastric reflex 5

effector

stomach stimulated to increase both its force of contraction and release of secretions

gastric reflex in addition, the presence of food in stomach causes

release of gastrin which targets stomach to increase both its force of contraction and release of secretions esp HCl

gastrin also stimulates contraction of pyloric sphincter

intestinal phase

intestinal reflex and CCK and secretin release

initiated by presence of acidic chyme in duodenum

intestinal reflex 1

receptors

chemoreceptors in intestinal wall detect acidic chyme or low pH in stomach contents

intestinal reflex 2

sensory input

decreased nerve signals relayed to medulla oblongata

intestinal reflex 3

medulla oblongata integrates sensory input

intestinal reflex 4

motor output

decreased nerve signals relayed along vagus nerve from medulla oblongata to stomach

intestinal reflex 5

effector

stomach inhibited to decrease both its force of contraction and release of secretions

intestinal reflex in addition, the presence of

fatty chyme in duodenum causes release of cholecystokinin CCK which decreases the force of contraction in stomach

presence of acidic chyme causes release of secretin which inhibits release of stomach secretions

majority of digestion and absorption occur in

the small intestine

small intestine parts

duodenum

jejunum

ileum

functions of small intestine

segmentation

peristalsis

completes digestion of carbohydrates, proteins, lipids

begins and completes digestion of nucleic acids

absorbs 90% nutrients and water that pass through digestive system

segmentation

mixes chime with digestive juices and bring food into contact with mucosa for absorption

peristalsis

propels chime through small intestine

circular folds

increase surface area for digestion and absorption in the small intestine

circular folds aka

plicae circulares

intestinal juice

provides a vehicle for absorption of substances from chyme as they come in contact with villi

brush border enzymes

found on surfaces of microvilli of absorptive cells

break down food products

mechanical digestion in SI

segmentation

peristalsis

segmentation does

localized contractions

peristalsis does

propulsive contractions

chemical digestion in SI of

carbohydrates

proteins

lipids

nucleic acids

pancreas is a gland that

lies posterior to stomach

produces enzymes that digest carbohydrates, proteins, fats, and nucleic acids

produces sodium bicarbonate which buffers stomach acid

empties its contents into duodenum

liver

makes bile which is important in emulsification of fats

gallbladder

stores bile until it is needed

liver is composed of

hepatocytes

bile canaliculi

hepatic sinusoids

blood supply of liver

oxygenated blood from hepatic artery and nutrient-rich, deoxygenated blood from hepatic portal vein

hepatic sinusoids

central vein

hepatic vein

inferior vena cava

right atrium of heart

functions of liver and gallbladder

carbohydrate, lipid and protein metabolism

processing of drugs and hormones

bilirubin excretion

bile salt synthesis

storage

phagocytosis

vitamin D activation