Digestive System

1
Digestive System
2
Digestive system functions

• Ingestion
• Mixing and movement of food.
• Peristalysis
• Digestion of foods.
• Chemical
• Mechanical
• Absorption of digested foods.
• Defecation.

3
Layers of the GI tract

• Alimentary canal vs Accessory organs.
• Wall of GI tract is composed of four layers
  (inside-gtoutside)
• Mucosa
• Submucosa
• Muscularis
• Serosa
• Peritoneum
• Mesentery

4
Layers of the GI tract
5
Salivary Glands
Tortora 516

• Saliva is secreted from 3 pairs of glands
• Parotid glands (back)
• Submandibular glands (jaw)
• Sublingual (below tongue)
• Composition of saliva
• 99.5 water
• 0.5 solutes
• Salivary amylase- (digestive enzyme for starch)
• Mucus (lubrication)
• lysozyme (kills bacteria)

6
Control of Salivary Glands

• Parasympathetic ANS stimulates production of
  saliva.
• Stimuli
• Food touching the tongue
• Smell
• Taste
• Thought of food.

7
Chewing

• Mechanical digestion involves
• Muscular manipulation by the tongue
• Teeth grind food into smaller pieces
• Saliva mixes in
• Result a soft, flexible, easily swallowed mass
  called a bolus

8
Swallowing
Tortora Pages 519-520

• Voluntary stage
• Bolus is pushed to back of mouth by tongue.
• Pharyngeal stage
• Breathing stops.
• Bolus passes through pharynx
• Esophageal stage
• Peristalysis
• Heartburn

9
Esophagus
Tortora Pages 518-520

• Connects mouth to stomach.
• Lies behind the trachea (flat side)
• Passes through the diaphragm
• Contains two layers of smooth muscle.
• Food has to pass over trachea _at_ epiglottis

10
Stomach
520-521

• J shaped, lies under diaphragm.
• A mixing chamber and holding reservoir- size
  varies
• Divided into four areas
• Cardia
• Fundus
• Body
• Pylorus/ Pyloric sphincter
• Rugae

11
Wall of Stomach
Tortora Pages 439-443

• 4 layers
• Mucosa
• Submucosa
• Muscularis 3 layers of muscle
• Longitudinal layer
• Circular layer
• Oblique layer
• Serosa

12
Gastric Gland secretions
Tortora Page 522

• Mucous cells
• Mucus
• Chief cells
• Pepsinogen
• Parietal Cells
• HCL
• Intrinsic factor (B12)
• G cells
• Gastrin (hormone)

13
Stomach Digestion
Tortora 522-523

• Mechanical digestion
• Bolus converted to chyme.
• Mixing waves push chyme into duodenum.
• Pyloric sphincter releases into SI
• Chemical digestion
• Pepsin breaks down proteins into peptides.
• Lipase digests triglycerides (in acid) into
  diglycerides

14
Stomach Absorption
Tortora 523

• Mucus protects the stomach lining from being
  digested itself
• Little absorption of nutrients here
• Stomach wall does absorb
• Water
• Electrolytes
• Some drugs (aspirin)
• Alcohol

15
Pancreas
Tortora 523

• Pancreas lies behind the stomach
• Secretions pass through pancreatic duct into
  duodenum
• Pancreatic juice Bicarbonate counteracts acid
  from chyme
• Digestive enzymes
• Islets of Langerhans produce hormones insulin

16
Enzymes produced by the pancreas that work in the
small intestine

1. Pancreatic amylase turns starches to
   dissacharides
2. Trypsin - proteins to
   polypeptides.
3. Chymotrypsin - proteins to peptides.
4. Carboxypeptidase - proteins to peptides.
5. Pancreatic lipase - triglycerides to fatty
   acids monoglcerides
6. Ribonuclease -nucleic acid digestion

17
Liver
Tortora 524-525

• Heaviest gland in the body 3 lbs.
• Involved in filtration,
• storage (glycogen), protein metabolism, and
  excretion
• Produces bile
• Emulsifies lipids (fats)
• Bile leaves liver through cystic duct.

18
Gall Bladder
Tortora 525-526

• Bile (made in the liver) is stored in the gall
  bladder.
• Carried by cystic duct to common bile duct, then
  released into duodenum.
• Bile emulsifies lipids

Gall stones (crystallized cholesterol)
19
Small Intestine
Tortora 526-527

• Composed of
• Duodenum
• Jejunum
• Ileum
• Food is released through ileocecal sphincter into
  the cecum

20
Small Intestine

• Mucosa
• Villi extend from wall of sm. intestine.
• Capillary network
• Lacteal- lymph
• Duodenal glands-secrete alkaline mucus
• Microvilli-increases surface area for absorption

21
Enzymes produced by small intestine

• Maltase maltose to glucose
• Sucrase sucrose to glucose
  fructose
• Lactase lactose to glucose
  galactose
• Peptidases peptides to amino acids
• Ribonuclease RNA to sugar bases
• Deoxyribonuclease DNA to sugar bases

22
Absorption in the Small Intestine
Tortora 530

• Carbohydrates proteins move into capillaries.
• Fatty acids monoglycerides move into the
  lacteal (lymph capillaries)

23
Large Intestine/ colon
Tortora 532-533

• 5 ft in length/2.5 inches diameter
• Ileocecal sphincter allows material to pass from
  sm. intestine to the colon
• Has ascending, transverse, descending, and
  sigmoid portions.
• Puckered due to contraction of muscular bands
  (teniae coli)

24
Digestion and absorption

• Bacteria ferment digest food- releasing H2,
  CO2, methane gases (flatulence)
• Bacteria produce vitamin B K (absorbed by
  colon)
• Bacteria break down bilirubin- brown color
• Absorbs much of the water and ions, forming
  feces.

25
Appendix
Tortora 532

• Structure
• Short finger-like extension of the lg. intestine
• Attaches to the cecum
• Stores a sample of healthy colon bacteria, to
  re-colonize the colon after an intestinal
  disease.
• Appendicitis inflammation requiring removal of
  the appendix

26
Inflamed appendix
27
Defecation reflex
Tortora 533-534

• Mass peristalysis pushes contents from the
  sigmoid colon to the rectum
• Stretch receptors initiate the defecation reflex
• Initiated by food in the stomach/ ANS
  controlled.
• Internal sphincter- (involuntary) opens
• External sphincter releases (voluntary control)
• downward pushing of the diaphragm push out the
  feces

28
Colon cancer
Healthy colon

• One of the deadliest cancers
• Detected by stool samples, or sigmoid/colonoscopie
  s
• Polyp removal using a wire snare