exam 3 - digestive system

nutrients

molecules + ions needed for metabolic processes / to sustain life

includes carbohydrates, proteins, lipids, minerals, vitamins, water

carbohydrate digestion in the oral cavity

salivary amylase begins digestion here

is inactivated in the stomach due to low pH

carbohydrate digestion in the small intestine

facilitated by pancreatic amylase and brush border enzymes

pancreatic amylase in carb digestion

1. pancreatic amylase produced by pancreas and released to SI

2. pancreatic amylase continues starch digestion begun by salivary amylase

3. brush border enzymes continue to digest starch into glucose / digest lactose and sucrose into monosaccharides

brush border enzymes in carb digestion

1. dextrinase and glucoamylase

2. maltase

3. lactase

4. sucrase

dextrinase and glucoamylase function

break bons between glucoses of oligosaccharides

maltase lactase and sucrase functions

maltase - breaks bond 2 glucoses of maltose

lactase = digests lactose into glucose and galactose

sucrase = digests sucrose to glucose and fructose

absorption of carbohydrates

monosaccharides are absorbed across SI epithelial lining into the blood

blood transports to the liver where fructose and galactose are converted to glucose

glucose taken up for energy / converted to glycogen and fat

cellulose

component plant cell wall

we lack enzyme to digest it - it is fiber that adds bulk to the lumen content

protein digestion

protein broken down by proteolytic enzymes and proteases - released as inactive and must be activated

begins in the stomach lumen with pepsin

protein digestion steps in SI

1. inactive trypsinogen, chymotrypsinogen, procarboxypeptidase released from pancreas into SI

2. enteropeptidase activates trypsinogen to trypsin

3. trypsin activates more trypsin, chymotrypsin, carboxypeptidase

4. activated pancreatic proteolytic enzymes break down protein to peptides and amino acids

5. brush border enzymes complete breakdown of proteins to amino acids

trypsin and chymotrypsin action

• Break bonds between specific amino acids

• Produce smaller strands of peptides

carboxypeptidase action

• Breaks bond between amino acid on carboxyl end and the remaining protein

dipeptidase action

Brush border enzyme

breaks final bond between two amino acids

Aminopeptidase

brush border enzyme

generates free amino acids

absorption proteins

free amino acids absorbed across SI epithelial lining

• co transported with Na across apical membrane

• facilitated diffusion across basolateral membrane

used as building blocks for new proteins or converted to glucose

what lipids require enzymes and which dont to be broken down

triglycerides require enzyme

cholesterol doesnt

triglyceride breakdown in the stomach

lingual lipase - component of saliva that is activated in the stomach

gastric lipase - from chief cells

30% of triglycerides are broken down this way into diglyceride and FA, no participation of bile salts

lipid digestion in the small intestine

1. bile salts released by liver and gallbladder, emulsify lipid droplets to form micelles

2. pancreatic lipase released from the pancreas, functions within micelles to digest triglycerides into monoglyceride and 2 FAs

Emulsification

separation large lipid droplets to smaller lipid droplets

occurs by bile salts which are recovered by active transport in the last portion of the ileum

amphipathic molecule - nonpolar tails line fat droplet and heads face aqueous fluid forming micelle

allows greater access pancreatic lipase to triglyceride

absorption of lipids

1. lipid transported to simple columnar epithelial lining by micelles, enters cell, bile salts reused stay in the lumen

2. triglycerides reform with cholesterol and other lipids are wrapped in protein

3. chylomicrons formed and exocytosed

4. enter lacteals and lymph capillaries in SI

5. enter blood and deliver lipids to liver etc

nucleic acids

nucleotide polymers DNA and RNA

sugar + phosphate group + N base

nucleic acid breakdown

In small intestine

• deoxyribonuclease / ribonuclease released by pancreas breaks phosphodiester bone

• brush border enzymes:

  • phosphatase - breaks bond holding phosphate

  • nucleosidase - breaks bond between sugar and N base

• components are absorbed across epithelium SI

water absorption

mostly in the SI, partially in LI - rest passed in feces

absorbed across epithelium into blood vessels by osmosis

minerals

inorganic ions - Ca Na K I Zn Mg P Fe

vitamin absorption (water / fat soluble)

fat soluble - ADEK in SI with lipids in micelles

water soluble - BC, diffusion/active transport, B12 receptor mediated endocytosis - intrinsic factor required

pernicious anemia

condition resulting from lack of intrinsic factor needed for B12 absorption

absorptive (fed) state

time eating, digesting, absorbing - about 4 hours after meal

increase in concentrations glucose, triglycerides, amino acids

blood glucose in maintained 70-110mg/dL

main hormone of the absorptive (fed) state

Insulin

insulin

released by B cells of pancreas in response to increasing blood sugar

stimulates liver and muscle cells to form glycogen

increases uptake triglycerides from blood,

stimulates lipogenesis, inhibits lipolysis in adipose

most cells increase amino acid uptake and accelerate protein synthesis

post absorptive (fasting) state

time between meals

body relies on stored nutrients and works to maintain nutirent levels

main hormone of postabsorptive state

GLUCAGON

Glucagon

released by a cells of pancreas in response to decreasing blood sugar

stimulates liver increase in breakdown of glycogen

stimulates gluconeogenesis from noncarbs

stimulates adipose breakdown of triglycerides

no effects on amino acids or proteins in cells

cholesterol synthesis

in the liver

1. FA are transported in blood enter hepatocytes

2. broken down into acetyl coa (beta oxidation)

3. acetyl coa turned into cholesterol by HMG-CoA reductase enzyme

4. cholesterol is released into blood in very low density lipoproteins or synthesized into bile salts

lipoproteins

lipids with protein wrap for transport

• chylomicrons

• very low density lipoproteins

• low density lipoproteins

• high density lipoproteins

rate the liver lipoproteins from most to least lipid

VLDL - most lipid

LDL

HDL - least lipid

lipid transport from liver to peripheral tissue

VLDL - released to blood circulate blood releasing triglycerides to peripheral tissues (adipose) become LDL

LDL - high in cholesterol, deliver to cells; bind to LDL receptor on plasma membranes of cells, endocytosis, cholesterol added to membrane, may be used to produce steroids

lipid transport from tissue to liver

HDLs - protein formed in liver, released to blood without lipid, circulates blood and fills with lipids

makes cholesterol available to steroid producing tissue but not engulfed, transports lipid back to liver and excess cholesterol is turned into bile salts in liver

ATP generation with glucose

4 stages of cellular respiration

1. glycolysis

2. intermediate stage

3. citric acid cycle

4. electron transport chain

glycolysis

anaerobic in cytoplasm

glucose into 2 pyruvate molecules, 2 ATP formed, 2 NADH from NAD+

in conditions of insufficient O2 pyruvate is turned into lactate

intermediate stage

aerobic in mitochondria

pyruvate into acetyl CoA, CO2 formed, NADH produced

citric acid cycle

acetyl CoA enters citric acid cycle

CO2 ATP FADH2 NADH formed in cycle turn

electron transport chain

H and e- transfer from NADH and FADH2

ATP formed through oxidative phosphorylation

ATP generation from lipids

1. glycerol enter glycolysis - converted to glucose by liver

2. carbons of FA removed - acetyl CoA formed - beta oxidation

3. acetly CoA enters citric acid cycle

ATP generation with amino acids

1. deamination - amine group of amino acid removed by hepatocytes, converted to urea, excreted through kidney in urine

2. amino acid enters metabolic pathway at glycolysis, intermediate stage or citric acid cycle depending on amino acid

interconversion

change of one biomolecule into another

due to biochemical pathway associated with cellualr respiration

examples of interconversion

1. glucose becomes acetyl coA becomes triglyceride and is stored instead of citric acid cycle

2. protein and fat on low carb diets goes through pathway reversal and is converted to glucose

metabolic rate

measure of energy used in a given time period

• basal metabolic rate

• total metabolic rate

Basal metabolic rate BMR

energy that is used at rest - not eaten in 12 hours, relaxed, temp 20C

measured by calorimeter or respirometer

BMR varies with

age - decreases 1% per year after 60 years age

lean body mass - more = higher BMR

body surface area - higher = higher BMR

ethnicity

thyroid hormone effect on BMR

TH increases BMR

• hyperthyroidism = higher BMR

• hypothyroidism = lower BMR

total metabolic rate

BMR + metabolism associated with activity

factors affecting TMR

amount skeletal muscle and activity - increases with higher activity

food intake - increases with ingestion decreases after absorption

changes in environment - increases with colder temp

temperature regulation

heat produced due to metabolic rate

97-99F 36.1-37.2C

neural and hormonal controls

core body temp

head and torso (vital portions of body) - temp maintained about constant

maintained by allowing fluctuation in periphery

neuronal control of body temp

hypothalamus and nervous system

hypothalamus body temp control

motor pathways to sweat glands, skeletal muscles, peripheral blood vessels

monitors blood temp

• body temp increases - HT stimulates sweat glands and vasodilates peripheral vessels

• body temp decreases - HT inhibits sweat glands, vasoconstricts peripheral vessels

nervous system body temp control

induces skeletal muscle contractions to generate heat - shivering

behavioral changes - initiated in cortex in response to temperature

hormonal control of body temp

regulated by many hormones

• thyroid epinephrine norepinephrine GH testosterone

thyroid hormone control of body temp

establishes metabolic rate

raises body temp by increasing rate of all cells

when body temp drops - HT: TRH - AP: TSH - Thyroid Gland: TH

6 main functions of digestive system

ingestion

motility

secretion

digestion

absorption

elimination

ingestion

introduction of solid and liquid nutrients into the oral cavity

first step in process

motility

voluntary and involuntary muscular contractions

mixing and moving materials through GI tract

secretion

process of producing and releasing fluid products facilitating digestion

• enzymes, acid, bile

digestion

breakdown of ingested food into smaller structures

mechanical digestion

material is physically broken down by chewing and mixing

chemical digestion

involves enzymes to break chemical bonds

change large complex molecules into smaller molecules

absorption

transport of digested molecules electrolytes vitamins and water from GI tract into blood or lymph

elimination

expulsion of indigestible components that are not absorbed

4 tunics of GI tract

mucosa

submucosa

muscularis

adventitia (or serosa)

Mucosa

inner lining mucous membrane

• epithelium

• lamina propria

• muscularis mucosa

epithelium of mucosa tunic

in contact with lumen contents

• simple columnar epithelium allowing for secretion and absorption

• portions that must withstand abrasion are nonkeratinized stratified squamous epithelium

lamina propria of mucosa tunic

composed of areolar tissue, small blood vessels, and nerves

absorption occurs when substances move into these vessels

muscularis mucosae of mucosa tunic

smooth muscle deep to lamina propria

contractions facilitate release of secretions into lumen, increase contact of materials with mucosa

submucosa tunic

areolar dense irregular CT

blood vessels lymph vessels and nerves

• submucosal nerve plexus

• MALT / GALT

• aggregated lymphoid nodules of the ileum

submucosal nerve plexus of submucosa tunic

nerves and ganglia innervating smooth muscle and glands

MALT / GALT of submucosa tunic

prevents ingested microbes from crossing GI tract wall

aggregated lymphoid nodules of ileum (peyer patches) of submucosa tunic

large aggregates of lymphatic nodules in distal small intestine

muscularis tunic

composed of smooth muscle

• inner circular layer

• outer longitudinal layer

• myenteric nerve plexus

inner circular layer of muscularis tunic

smooth muscle cells oriented circumferentially within GI tract

contraction constricts tube lumen

outer longitudinal layer of muscularis tunic

cells oriented lengthwise along GI tract

contraction shortens tube

myenteric nerve plexus of muscularis tunic

axons and ganglia between layers control contractions

muscularis tunic functions

mixing - backward and forward motion, lack directional movement, blends ingested materials with secretions

propulsion - directional movement of materials through GI tract, occurs by peristalsis, sequential contraction of muscularis, GI tract wall moves like a wave, inner circular layer thickened at locations to form sphincter - closes off lumen and control spassage of contents to next section of GI tract

adventitia tunic

areolar CT

found outside the peritoneal cavity

serosa tunic

areolar CT plus outer covering visceral peritoneum

• only intraperitoneal organs have serosa

GI regulation through

Enteric nervous system

Autonomic Nervous System

nerve reflexes

hormonal control

Enteric Nervous System

sensory and motor neurons within submucosal plexus and myenteric plexus

innervate smooth muscle and glands GI tract

coordinate mixing and propulsion reflexes

Autonomic Nervous System

parasympathetic innervation promotes GI tract activity

sympathetic innervation opposes GI tract activity

Nerve reflexes controlling GI tract wall

baroreceptors - detect stretch

chemoreceptors - monitor chemical contents lumen

short reflex - local reflex, ENS, coordinates small segments of GI tract

long reflex - sensory input to CNS and autonomic motor output, coordinates GI tract motility, secretions, accessory digestive organs

serous membranes of abdominal cavity

peritoneum - serous membrane associated with abdominopelvic cavity

• parietal peritoneum - lines inside surface of abdominal wall

• visceral peritoneum - covers surface of organs within abdominopelvic cavity

• peritoneal cavity - potential space between these 2 layers, lubricating serous fluid secreted from both layers, allows free movement abdominal organs

intraperitoneal organs

organs completely surrounded by visceral peritoneum

• stomach, most SI, part of LI

retroperitoneal organs

lie directly against posterior abdominal wall, only anterolateral portion covered by peritoneum

• have adventitia not serosa

• most duodenum, pancreas, ascending and descending colon, rectum

mesentery

a double layer of peritoneum

supports suspends and stabilizes intraperitoneal GI organs

blood and lymph vessels nerves are sandwiched between folds

associated with specific organs

parts of mesentery

greater omentum

lesser omentum

falciform ligament

mesentery proper

mesocolon

oral cavity and salivary glands

mechanical digestion begins

slaiva secreted from salivary glands in response to food

contains salivary amylase - digestion starch

mixed with ingested materials to form bolus

pharynx

bolus moved to pharynx during swallowing

mucus secreted to facilitate swallowing

esophagus

bolus transported from pharynx into stomach

lubricated by mucus secretions

stomach

bolus mixed with gastric secretions by smooth muscle ocntractions

secretions produced by epithelial cells of stomach

chyme formed from mixing

duodenum also considered part of upper GI tract

oral cavity portions

oral cavity

vestibule

oral cavity proper

lips - labial frenulum

palate - hard palate, transverse palatine folds, soft palate

uvula

fauces - palatoglossal arch, palatopharyngeal arch

tongue - papillae, lingual frenulum

salivary glands

produce saliva

• intrinsic salivary glands

• extrinsic salivary glands