Chapter 23 Digestive System

Front 1

Function of Digestive System

Back 1

-prepare food for cellular utilization by physically and chemically breaking down food
-nutrients carried around in blood to tissues

Front 2

Beginnings of gastroenterology 1825-1833

Back 2

-Dr. William Beaumont performed experiments on a guy who got shot in the stomach by holding food over the hole and observing digestion

Front 3

Digestive Processes: 1. INGESTION

Back 3

1. INGESTION:
-physical intake of food into the mouth

Front 4

Digestive Processes: 2. PROPULSION

Back 4

2. PROPULSION:
-food moving through oral cavity down digestive tract

includes:
a. SWALLOWING: voluntary
b. PARASTALSIS: invloluntary, propel food from esophagus down GI tract

Front 5

Digestive Processes: 3. MECHANICAL DIGESTION

Back 5

3. MECHANICAL DIGESTION
-physically breaking down food
-includes chewing, mixing with saliva, churning (moving around in stomach), segmentation (contraction/relaxation within the intestine)

Front 6

Digestive Processes: 4. CHEMICAL DIGESTION

Back 6

4. CHEMICAL DIGESTION
-enzymatic breakdown of food molecules into basic units
-mostly occurs in stomach & small intestine
-ex. break down carbohydrates into monosaccharides, proteins into amino acids, etc

Front 7

Digestive Processes: 5. ABSORPTION

Back 7

5. ABSORPTION
-absorb basic units of food into blood
-passage of molecules through the mucous membrane of the small intestine: blood/lymph

Front 8

Digestive Processes: 6. DEFECATION

Back 8

6. DEFECATION
-discharge of indigestible wastes

Front 9

Alimentary canal

Back 9

-Alimentary canal is your gastrointestinal tract, a long continuous tube
~9 meters in length
-goes from mouth to anus

-includes oral cavity, pharynx, esophagus, stomach, small intestine, & large intestine

Front 10

Accessory digestive organs

Back 10

-help break down food and provide enzymes
-include teeth, tongue, liver (bile), salivary glands, gallblader (stores bile), pancreas (stores digestive enzymes)

Front 11

Serous membranes

Back 11

-MESENTERY---secured within abdomen
-PARIETAL PERITONEUM---contact w/ abdominal wall
----GREATER OMENTUM (double layer of parietal peritoneum, links greater curvature of stomach to posterior abdominal wall)
----LESSER OMENTUM: goes from lesser curvature of ---------------------------------stomach to liver
----MESOCOLON
---------2 different kinds of Mesocolon: TRANSVERSE & -----------------------------------------------------SIGMOID

-Peritoneal cavity is filled w/ fluid
-VISCERAL PERITONEUM

Front 12

4 Layers (TUNIC) of the GI tract

Back 12

1. Mucosa (innermost)
2. Submucosa
3. Muscularis (externa)
4. Serosa (outermost); aka visceral peritoneum

Front 13

Layers of the GI tract: 1. MUCOSA

Back 13

1. MUCOSA
-absorptive & secretory (absorbs nutrients from the lumen of the GI tract)
-made of simple columnar epithelium
-has goblet cells

-has 3 different sublayers:
1. EPITHELIAL
2. LAMINA PROPRIA: small capillaries that feed goblet cells, also absorb nutrients
3. MUSCULARIS MUCOSA: smooth muscle tissue; local movement as needed, move food around

Front 14

Layers of the GI tract: 2. SUBMUCOSA

Back 14

2. SUBMUCOSA
-made of vascular connective tissue
-keeps tube alive
-gives tube its elastic properties

Front 15

Layers of the GI tract: 3. MUSCULARIS (externa)

Back 15

3. MUSCULARIS (externa)
-made of 2 layers of muscle:
a. CIRCULAR LAYER (innermost)-contracts and makes tube skinnier
b. LONGITUDINAL LAYER-makes tube shorter
-both layers work together to propel food down the tube
-pulverize, churn, peristalsis, & pyloric sphincter (concentrated layer of muscle)

Front 16

Layers of the GI tract: 4. SEROSA

Back 16

-synonymous with visceral peritoneum
-only found within abdominal cavity
-organs will have this serosa
-binding & protective

Front 17

MOUTH

Back 17

includes:
1. ORAL CAVITY--cheeks, lips, soft/hard palate, tongue at base
2. VESTIBULE--space between cheeks & lips

purpose of the mouth
-to create a bolus by mechanical/chemical means
-BOLUS---moistened mass of food
-SALIVA---adds enzymes

Front 18

Accessory organs of the mouth: TONGUE

Back 18

-made of skeletal muscle; considered a mucous membrane
-has INTRINSIC FIBERS---control shape of tongue (rolling tongue)
-has EXTRINSIC FIBERS---control location of tongue

-Anterior 2/3 of tongue---seen in oral cavity
-Posterior 1/3 of tongue---is in the pharynx

-tongue moves food during chewing & swallowing
-70% of people can roll their tongues; believed to be hereditary, but 1/3 of twins are different

Front 19

Accessory organs of the mouth: PAPILLAE

Back 19

-FILIFORM PAPILLAE: simply friction bumps for grasping/touching food (NO TASTE)
-FUNGIFORM PAPILLAE: tastebuds
-VALLATE PAPILLAE: v-shaped line surrounded by lingual salivary glands, larger, tastebuds

Front 20

Accessory organs of the mouth: SALIVARY GLANDS

Back 20

-food dissolved by saliva through chemical digestion
-cleanses teeth (prevents tooth decay)
-1-1.5 liters of saliva produced per day
-Glands: PAROTID, SUBMANDIBULAR, SUBLINGUAL
-Extrinsic salivary glands: anticipation of eating
-Parotid: near ear, LARGEST of salivary glands, makes most saliva when you eat
-Submandibular gland: near mandible
-Sublingual gland: inferior to tongue

Front 21

Accessory organs of the mouth: TEETH

Back 21

-humans have Heterodont dentition (we have multiple tooth morphologies)
1. INCISORS: nipping
2. CANINES: sharper, piercing/tearing
3. PREMOLARS/BICUSPIDS: grinding
4. MOLARS: grinding

-we have 2 sets of teeth: (Diphyodonts)
-start with 20 deciduous teeth (baby teeth)---all in by the time we're about 2 years old
-we have 32 permanent teeth, the pulp of baby teeth is reabsorbed and the teeth fall out
-Wisdom teeth---last molars to erupt around 17-25 years old, often impacted, pushes against roots of other teeth and causes shifting

Front 22

Tooth anatomy

Back 22

CROWN--exposed tooth
NECK---just near gumline, links crown to embedded root
ROOT---anchors tooth in place

tooth layers:
ENAMEL---external, hardest substance in body; 90% hydroapetite (high concentration)
DENTIN---deep to enamel, makes up most of the tooth; harder than bone
PULP: vascular & nervous tissue

Front 23

PHARYNX (throat)

Back 23

made up of 3 parts:
1. NASOPHARYNX---superior
2. OROPHARYNX---middle
3. LARYNGOPHARYNX---inferior

-food passes through middle & inferior pharynx
-constrictor muscles: circular; contract in sequence to help propel food down pharynx during swallowing (superior, middle, inferior)

Front 24

ESOPHAGUS

Back 24

-mid-neck to start of stomach at cardiac orfice
-collapsible muscular tube ~25 cm in length
-upper 1/3: skeletal muscle
-middle 1/3: mixed
-lower 1/3: smooth muscle; has all 4 layers

-muscularis layer varies throughout esophagus

Front 25

Swallowing (DEGLUTITION) mechanisms

Back 25

3 phases
1. mouth closed and bolus elevated against palate (voluntary)
2. passage of bolus through pharynx. Larynx elevated and sequential contraction of constrictor muscles (voluntary)
3. entry of bolus through esophagus via peristalsis (involuntary)

Front 26

STOMACH

Back 26

-distensible, j-shaped "holding organ"
-food churned & combined w/ gastric secretions to form chyme
-in food eating contests, lean people win bc they have more elastic tissue (not surrounded by a lot of fat)

-the BOLUS is changed to CHYME
-the stomach has a 3rd layer of smooth muscle (2 layers in all other parts:
1. LONGITUDINAL---outer
2. CIRCULAR---middle
3. OBLIQUE---inner (gives another direction of pull so stomach can churn better)---unlike the rest of the muscularis in the GI tract

Front 27

PYLORIC SPHINCTER

Back 27

-valve in the stomach that lets chyme go from the stomach into the SMALL INTESTINE
-(note that there's no valve that guards the stomach and esophagus---this lets us regurgitate (vomit), which protects us from poisons; also it is the cause of heartburn/acid reflux---acid from the stomach goes into the esophagus, the hydrochloric acid literally digests the esophagus)
-mice have a cardiac sphincter only, can't throw up

Front 28

Chemicals of the stomach

Back 28

-the stomach lining has holes and at the bottom of the holes, there is production of secretions
-PARIETAL CELLS---produce hydrochloric acid
-CHIEF CELLS---produce pepsinogen (enzyme)

-together these secretions help break down food into something usable for energy

Front 29

Mucosa

Back 29

-Gastric pits
-Gastric glands

Front 30

SMALL INTESTINE

Back 30

-named for its DIAMETER, not length
-3 meters long and 2.4 cm (1 inch) wide
-here is where digestion is actually completed and nutrients are absorbed into bloodstream

-3 sections:
a. DUODENUM
-25 cm long
-valve that wraps around pancreas
-Duodenal papilla---common bile duct & pancreatic duct
-bile--breaks down fatty foods

b. JEJUNUM---where absorption takes place; 1 m long

c. ILEUM---attaches to large intestine; 2 m long

Front 31

Structural modifications in SMALL INTESTINE

Back 31

-modifications increase surface area in small intestine
-surface area 1800 sq ft
1. can see ridges w/ naked eye; circular folds (PLICAE CIRCULARE); big ridges
2. each ridge is lined w/ VILLI (fingers)
3. at apical surface of each cell that lines villi, there are MICROVILLI

allows chyme to pass through and be absorbed

Front 32

VILLI

Back 32

-LACTEAL:
-green vessels; lymphatic capillaries; responsible for absorbing fatty acids (fat)

-CAPILLARIES:
-red/blue vessels inside villi; critical for absorbing proteins (amino acids) and sugars

Front 33

Mechanical activities of small intestine

Back 33

1. RHYTHMIC SEGMENTATION
-coordinated contractions of circular smooth muscle
-churning of chyme
-every bit of chyme must come in contact w/ small intestine wall
-chyme doesn't go anywhere

2. PENDULAR MOVEMENTS
-requires coordination of circular and longitudinal contraction
-move chyme back and forth (actually moving chyme around)
-first circular contraction, then longitudinal contraction

3. PERISTALSIS
-goes from one end of the GI tract to the other, moving the chyme from the small intestine towards large intestine

DIGESTIVE PROCESSES ARE FINISHED IN THE SMALL INTESTINE

Front 34

LARGE INTESTINE

Back 34

-about half as long as small intesine (~1.5 meters long), but 6.5 cm in diameter
-receives undigested food from small intestine
-last chance to absorb nutrients & electrolytes
-goal is to remove waste products
-passes feces out of GI tract

INTERNAL ANAL SPHINCTER
-made of smooth muscle & involuntary

EXTERNAL ANAL SPHINCTER
-made of skeletal muscle & voluntary

Front 35

APPENDICITIS

Back 35

-infection/inflammation of the appendix (accessory organ)
-pain in lower right quadrant
-found where ileum and large intestine come together (easy for infection to happen)
-related to lymphatic system
-our bodies can function without it

Front 36

LIVER

Back 36

-LARGEST internal organ (1.4 kg/ 3 lbs)
-largest gland? it secretes bile...
-Bile production & ~500 documented functions
-hepatic portal system
-liver can store nutrients, vitamins, sugars
-synthesis, storage & release (break down toxins), vitamins, carbs, lipids

-blood flow in the liver
-2 cells thick----functions reliant on diffusion; good blood supply/ houses capillary bed

-from hepatic portal vein there's nutrient-rich, oxygen poor blood and from the hepatic arteries there's oxygen rich blood; the 2 bloods mix, the liver pulls out toxins and breaks them down, pulls out sugars/proteins and stores them

Front 37

GALLBLADDER

Back 37

-muscular sac that stores extra bile
-don't necessarily need the gallbladder
-if you haven't eaten a lot of fatty foods in a while, the bile gets stored for later use
-when you eat fatty foods, it contracts and shoots extra bile right into the duodenum to help facilitate fat absorption
-GALLSTONES: from cholesterol in bile, block cystic duct; the surgeon will suck out the gallbladder; you'll have a steady flow of bile instead of extra storage

Front 38

PANCREAS

Back 38

-pancreatic enzymes: fats, sugars, proteins
-it is both an exocrine (secretes out of body) AND an endocrine (secretes into bloodstream) gland
-utilizes sugar

EXOCRINE FUNCITON:
-exocrine pancreatic duct empties into duodenum

ENDOCRINE FUNCTION:
-endocrine is responsible for hormones insulin and glucagon which maintain homeostasis relative to blood sugar levels
--ISLET CELLS: produces insulin and glucagon
-if blood sugar is too HIGH: body releases insulin from pancreas; causes liver/fat cells, skeletal muscles to uptake sugar out of bloodstream
-if blood sugar is too LOW: pancreas releases glucagon; sugar that is stored in the liver is released into bloodstream

Pancreatic cancer is arguably the worst cancer to get because it is so easily spread since the pancreas has a direct connection to the bloodstream