Ch 23 - Digestive System

Digestive system main function

absorb nutrients

Mechanical digestion

breakdown of objects without breaking thier chemical bonds

often this changes their state of matter (ex. solid to liquid)

increases surface area & speeds up digestion

chemical digestion

breaking down objects inot smaller pieces by breaking chemical bonds

Ingestion

putting food inot the GI tract thorugh the mouth

Oral cavity

teeth

tongue

salivary glands

perfroms both mecahnical and chemical digestion

Mastication

chewing

first step of mechanical digestion to increase surface and breakdown food

muscles of mastication

temporalis

masseters

medial and lateral pterygoid

Salivary glands

parotid gland

sublingual glnad

submandibular gland

saliva composition

1.0-1.5L produced each day

98-99.5% H2O

Fluids and digestive enzymes help digest food

• Salivary amylase (digest carbs)

• Lingual lipase (digest fats)

Mucin glycoproteins

Normal pH range: 6.35-6.85

• Buffers neutralize acids

• pH can range from 6.2-7.6

Antimicrobial enzymes

• Immunoglobulins

• Lysozymes, peroxidases, defensins

can vary

bolus

mashed up food and saliva

Structure of the tooth

crown, neck, and root

enamel, dentin, gingiva (gum), pulp cavity, root canal

• enamel is made of calcium slats like bone

• dentin is made of sugar. this is where you get cavities

deciduous teeth

baby teeth

permanent teeth

adult teeth

eventually replace deciduous teeth

incisors

8 total

4 on top, 4 on bottom

Canines (cuspids)

4 total

2 on top, 2 on bottom

premolars (bicuspids)

8 total

4 on top, 4 on bottom

molars

12 total

6 on top, 6 on bottom

4 third molars - “wisdom teeth”

How many teeth do adult typically have

32

Deglutition (swallowing) phases

buccal phase

pharyngeal phase

esophageal phase

final phase

Buccal phase

tongue pushes up against hard palate

soft palate closed

pharyngeal phase

hyoid pulls up and foward

epiglottis shuts

esophageal phase

pharynx contracts

peristalsis in esophagus

final phase

lower esophageal sphinter opesn

bolus enters the stomach

peristalsis

series of wave-like contractions

involuntary muscular contractions

propulsion

movmenet of food through the GI tract

Functions of the stomach

storage: 2-4 L

mechanical digestion

• acid breakdown of food

• churning

chemical digestion

• enzymatic breakdown of sugars and proteins

signaling and hormone production

Cells of the stomach

parietal cells

mucus cells

chief cells

G-cells

parietal cells

hydrochloric acid (Hcl)

secrete intrinsic factor

• helps absorb vitamin b12

mucus cells

aka foveolar cells

secrete mucus

mucus blocks acid

chief cells

secrete pepsinogen

G-cells

type of enteroendocrine cell

secrete gastrin

Parietal cell acid Production

produce HCl by combing H+ and Cl-

H+ comes from CO2 (breathing) and H2O (digestion) combing to make carbonic acid (H2CO3)

Cl- is pumped inot the cell

H+ and Cl- combine into HCl in the stomach

ulcers

what happnes if mucus doens’t block the acid

gastric acid eats away at stomach lining causing peptic ulcers

can also happen at the duodenum

peptic ulcers & helicobacter pylori

Most people with helicobacter pylori infections are asymptomatic

Causes gastritis and peptic ulcers

Invades mucosal layer and secretes proteases and toxins

Can reduce mucus amount.

Pepsinogen

precursor to pepsin

pepsin

protease

• chemically breaks proteins into smaller proteins and amino acids

Gastrin (stomach)

peptide hormone secreted by G-cells

increases tomach motility

• increases muscular movement

stimulates acids and enzyme production

Regulation of Gastric Activity

1. cephalic phase

2. gastric phase

3. intestinal phase

cephalic phase

food is going down the esophagus

before food gets to the stomcah you are in this phase

there are many triggers like smell and taste that tells the stomach that food is coming

things like the vagus nerve activates the stoamch which activates mucus, pepsinogen, HCL, gastrin

Gastric Phase

cuases stomach to stretch

rises stomach pH

causes more mucus and pepsinogen

increases acid amount so you can combat change in pH

also turns on muscular activity in the stomach

Intestinal phase

digesrted food becomes chyme

• liquified

• acidic

not all chyme goes to small intestine, pyloric sphincter conrols amount of food leaving the stomach

• controls how hungry you are if there is more chyme in your stomach you feel fuller.

Gastric Activity Regulated by

gastrin

baroreceptors - neurons detecting stretch and pressure

chemoreceptors - neurons detecting increased pH

Small intestine

duodenum

jejunum

ileum

Duodenum

first segment of the small intestine

primary site for chemical digestion

receives: bile and pancreatic enzymes

helps break down fats, proteins, and carbohydrates

Jejunum

middle section of the small intestines

main site to absorb nutrients

circular folds, villi, and microbilli increase surface area to absorb broken down food

Ileum

final part of the small intestine

longest

thinner circular folds, smaller villi

“peyers” patches - lymphoid tissue

absrobs and recycles bile acids

absorbs vitamin B12

has lots of smaller vessels which allows for higher level of absorption

Stomach & duodenum relationship

receives acidic chyme

begins neutralization and digestion

liver and duodenum relationship

sends bile to help break down fats

Gallbladder and duodenum relationship

releases stored bile for fat digestion

pancrease and duodenum relationship

rleases enzymes and bicarbonate

digest carbs, proteins, and fats; neutralizes acids

Duodenal hormones

gastrin

secretin

cholecystokinin (CCK)

glucose dependent insulinotropic polypeptide (GIP)

gastrin (duodenum)

peptide hormone

produced by the duodenum and stomach

increase overall stomach activity

secretin

peptide hormone

increase bicarbonate secretion by the pancrease

increase bile production by the liver

Cholecystokinin (CCK)

fatty acids and amino acids stimulate release

inhibits gastrci emptying

increases bile production

suppresses hunger

glucose dependent insulinotropic polypeptide (GIP)

decreases gastric acid

stimulated by hihg glucose content in chyme

stimulates release of insulin from pancreas

hepatic artery

oxygenated blood to supply liver

portal vein

deoxygenated nutrient rich blood to supply liver

Kupffer cells

resident (fixed) macrophages in the liver

dispose of pathogens, foreign particles, debris

recycle cell debris adn large molecules

releases inflammatory cytokines

Hepatocytes

~80% of livers mass

Major functions

• plasma proteins production

• carbohydrate metabolism

• fat and lipid metabolism

• drug metabolism and detoxification

Detoxification

first pass effect (metabolism)

enzymes metabolize chemicals that pass through the liver

liver enzymes can incativate drugs or activates prodrugs

bile and lvier enzyme help in excretion of drugs and metabolites

Liver plasma protein production

serum albumins

fibrinogen and clotting factors

complementt proteins

Lipoprotiens (LDL and HDL0

• transport cholestrol, triglycerides, fat

liver carbohydrate metabolism

gluconeogenesis

glycogen formation and catabolism

converts carbohydrates —> fatty acids

Liver fat and lipid metabolism

major site of fatty acid synthesis

can convert excess carbs —> fatty acids

breakdown excess lipids inot energy and ketons

synthesize cholesterol and bile acids

fatty liver disease

too much fat accumulates in the liver and now liver grows

less function and more fat cells —> causes cirrhosis

bile

dark green-yellow fluid mixture

95-98% h2o

made from bile salts and acids

made partly by bilirubin

used to absorb lipids and fats

bile acids and salts

made from cholesterol

amphipathic - has both hydrophobic and hydrophilic sites

breaks upf at droplets and makes them solube

forms micelles

micelles

smaller bubbles of phospholipids that have the hydrophobic part on the outside

Bile emulsification

breakdown of large fat globule using bile salts inot tiny fat droplets

Galbladder

located underside of the liver

stores and concentrates bile

releases bile inot the duodenum when fatty food enters

helps digestion by emulsying fats

Route of BIle

liver —> galbladder —> common bile duct —> duodenal papilla —> duodenum

Duodenal ampulla (ampulla of vater)

bile enters the duodenum using the common bile duct

pancreatic enzyme enter the duodenum using the pancreatic duct

both ducts will combine into one vessel ccalled the duodenal ampulla before entering the duodenum

opening of the duodenum

Pancrease function

endocrine—> bloodstream

• pancreatic islets

• pancreatic blood vessels

• secrete hormones

exocrine —> epithelial surfaces

• pancreatic acini

  • pancreatic juice

• pancreatic ducts

• secrete enzymes

Path of pancreatic juice

pancreatic acini —> pancreatic ducts —> duodenal ampulla —> duodenum

pancreatic juice

enable digestion and nutreints absorption

secreted by pancreatic acini and epithelial cells

exocrine secretion

alkaline/basic pH

contains many eyzmes

~1 liter of pancretic juice produced each day

Pancreatic enzymes

carbohydrase

lipases

protease

carbohydrase

pancreatic amylase

Lipases

pancreatic lipase

sterol esterase

• breks down ester inot fatty acids and cholesterol

phosphlipase

• brekas phosphlipids into fatty acids

protease

elastase

chymotrypsin

• activates in the duodenum

trypsin

• activates in the duodenum

Circular folds

large folds of mucosa and submucosa

function

• slow movement of chyme

• increase surface area

Villi

finger-like projections of the mucosa

contains: blood capillaries and lumph vessel

function:

• greatly increase surface area

• allows nutreints to enter blood and lymph quickly

Microvilli

tiny projections ont eh apical surface of epithelia cells

form the brush border

functions

• maximize surface area

• contains enzymes for final digestion

• enhance absorption of nutreints into cells

Brush border enzymes

protease

break dimers into monomers

maltase, lactase, sucrase

maltase

breaks maltose into 2 units of glucose

lactase

breaks lactose inot galactose and glucose

sucrase

breaks sucrose inot fructose and glucose

Villi vessels

capillaries - absorb sugars and proteisn to blood stream

Lacteals - come from lymphatic system, absorbs fats to the lymphatic system

chyle

lymph from small intestine containg fat droplets

Segmentation

migration motility complex

• special form of peristalsis

• cyclic waves of contraction

• “pockets'“ of intestinal contents

• contractions push contents backwards and forwards

Large Intestine Anatomy

cecum

ascending colon

hepatic flexure

transverse colon

splenic flexure

descending colon

sigmoid colon

rectum

anus

large intestine functions

reabsorption of water

feces compaction

storage of fecal matter

vitamin absorption

Appendix

worm like

lengths vary from 5-35 centimeters

possible functions

• reservoir of symbiotic gut microbes

• lymphoid tissue and immunity

Appendicitis

infected appendix

often indicated by pain in right lower quadrant

requires surgical removal

failure to do so can lead to septic shock

Internal anal sphincter

smooth muscle

not under voluntary control; parasympathetic

reflexes triggered by distension (stretching)

External anal sphincter

skeletal muscle

voluntary control

Fecal color identification

fecal matter is often important to detec specific medical condtions

pale/clay colored feces is cuased by lack of stercobilin

red or black feces can be caused by blood in the GI tract (internal bleeding)

Digestion of Red Blood Cells

Dead RBCs are digested in the liver and spleen

the major component of RBC is heme and needs to be digested

• iron is recycled

heme is broken down into biliverdin and then bilirubin

Bile to urobilin & stercobilin

bile salts contain bilirubin which gives it a green color

bile is degraded in the iintestines by bacteria to form urobilin and stercobilin

most of the urobilin stays in the large intestine but a small amount enter the bloodstream

Color of pee

urobilin in the bloodstream needs to be removed by the kidneys

giving urine its yellow color

color of feces

the rest of stercobilin and urobilin is excreted out as feces

stercobilin gives poop its brown color

Defecation

expelling feces from teh GI tract via the anus