1. The Digestive System
Chapter 23

2. OVERVIEW

3. Introduction
Digestion is the mechanical and chemical breakdown of food into forms that cells can absorb.
Mechanical Digestion – breaks down food into smaller pieces
Chemical Digestion – decomposes food into smaller molecules
Add these terms to vocabulary list…
The digestive system consists of:
The alimentary canal – extends from mouth to anus
Accessory glands –secrete chemicals into the alimentary canal.

4. Human digestive system
After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested.
Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours.
In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

5. The Alimentary Canal
If stretched out, the alimentary canal is about 8 meters long.
That’s 26 feet!

6. Structure of the wall Mucosa – mucous membrane
Epithelial tissues on a bed of connective tissue
This layer absorb nutrients, secrete chemicals, and protect the underlying layers.
Submucosa – Beneath the mucosa
Loose connective tissue
Blood vessels, nerves, and lymphatic vessels
This layer nourishes the surrounding tissues, and carries away nutrients.
Muscular –
Decrease and increase the diameter of the A.C. to push food through
Serosa – serous membrane
Secretes serous fluid, which lubricates the A.C.

7. Movements of the Alimentary Canal
Muscles of the A.C. provide two basic movements:
Segmentation – mixing movement
Smooth muscles contract and relax, mixing foods with digestive juices
Peristalsis – propelling movement
Smooth muscles contract in a wave-like motion pushing food through the alimentary canal

8. The Mouth (ORAL CAVITY)
Receives food
Mechanically breaks up solid particles using TEETH & TONGUE
Chemically digest food using saliva.
This action is called mastication
Makes a BOLUS (wet ball of food)
The mouth also functions as an organ of speech, and sensory reception.

9. Salivary Glands Secrete saliva
Saliva moistens the food, and begins the digestion of carbohydrates
Three pairs of major salivary glands, include:
Parotid glands
Submandibular
Sublingual

10. SALIVA = water + mucus + amylase
Salivary Glands
SALIVA = water + mucus + amylase
Parotid glands
Secrete clear watery fluid
Rich in salivary amylase – begins the chemical digestion of carbohydrates
Submandibular glands
Secretes a mixed saliva with both watery fluid and mucus
Sublingual glands
Secrete primarily mucus

11. The palate and uvula The palate forms the roof of the oral cavity
Hard Palate - bony roof of the mouth
Formed by the palatine bones and portions of the maxilla
Soft Palate - Muscular arch
Uvula – cone-shaped projection
During swallowing, muscles draw the soft palate and the uvula upward preventing food from entering the nasal cavity.

12. The teeth Teeth are the hardest structures in the body
primary (deciduous) teeth numbering 20
Usually erupt through the gums from age of 6 months to 2 years
secondary (permanent) teeth numbering 32
Usually begin to erupt at 6 years
3rd molars = wisdom teeth, which may erupt between years of age

13. Types of teeth Incisors-
blade shaped teeth that bite or cut off large pieces of food
Adult – 8
Child – 8
Canines-
cone shaped teeth that grasp and tear food
Adult – 4
Child – 4
Premolars –
flattened surface for grinding food
Adult – 8
Child – 0
Molars –
flattened surface for grinding food
Adult – 12
Child – 8

14. The tongue Thick, muscular organ
Manipulate foods and aids in swallowing
Mucous Membrane
Frenulum
Root
Anchored to the hyoid bone.
Covered with lingual tonsils
Papillae – projections on the surface of the tongue.
Some provide friction, others house taste buds.

15. Pharynx
The back of the throat.
Deglutition (swallowing)
3 parts

16. Swallowing Epiglottis flap of cartilage
closes trachea (windpipe) when swallowing
food travels down esophagus

17. esophagus Peristalsis
involuntary muscle contractions to move food along
Esophageal Hiatus – opening in the diaphragm, passage for esophagus
Hiatal hernia – part of the stomach protrudes through the hiatus.

18. Stomach 2 sphincters (valves) 3 layers of muscle
Secretes gastric juices
(enzymes + HCl)
Mechanically and chemically breaks down food

19. stomach Fundus = top portion Pyloris = funnel-shaped lower portion
Rugae – gastric folds line the stomach

20. Gastric Juice Acidic (pH 1.5-2.5) (HCl)
Pepsin- an enzyme that breaks down large proteins into amino acids.
HCl activates pepsin
BOLUS + GASTRIC JUICE = chyme.

23. Accessory Organs
Pancreas
Gall Bladder
Liver

24. Pancreas
An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine)
Pancreatic juice digests all major nutrient types.
“ENZYME COCKTAIL” includes enzymes top break down all compounds: proteins, lipids and carbohydrates
Alkaline (base) neutralizes acidic chyme coming from stomach.

25. Pancreas

26. LIVER

27. Liver Functions
The liver carries on many important metabolic activities, including:
Glycogenesis: producing glycogen from glucose
Glycolysis: breakdown of glycogen into glucose
Gluconeogenesis: converts non-carbohydrates to glucose
Oxidizes fatty acids
Synthesizes phospholipids and cholesterol
Forms urea
Synthesizes plasma proteins
Stores glycogen, iron, and vitamins A, D, and B12
Phagocytosis of worn out RBCs and foreign substances
Removes toxins such as alcohol and certain drugs from the blood

28. Liver
Function: produces bile
BILE breaks up fats

29. GALL BLADDER It stores bile between meals
It concentrates bile by reabsorbing water
The gall bladder itself does not produce bile
Bile duct –
a long tube that carries BILE
Connects the liver, pancreas, and gall bladder to the duodenum (small intestine)

31. GALLSTONES
GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder
Can either be “passed” (OUCH!!) or surgically removed

32. Small intestine Function Structure chemical digestion
major organ of digestion & absorption
absorption through lining
over 6 meters!
small intestine has huge surface area = 300m2 (~size of tennis court)
Structure
3 sections
duodenum = most digestion
jejunum = absorption of nutrients & water
ileum = absorption of nutrients & water
About every 20 seconds, the stomach contents are mixed by the churning action of smooth muscles.
As a result of mixing and enzyme action, what begins in the stomach as a recently swallowed meal becomes a nutrient-rich broth known as acid chyme.
At the opening from the stomach to the small intestine is the pyloric sphincter, which helps regulate the passage of chyme into the intestine.
A squirt at a time, it takes about 2 to 6 hours after a meal for the stomach to empty.

33. Duodenum pancreas liver gall bladder 1st section of small intestines
acid food from stomach
mixes with digestive juices from:
pancreas
liver
gall bladder

34. Absorption in the SI
Much absorption is thought to occur directly through the wall without the need for special adaptations
Almost 90% of our daily fluid intake is absorbed in the small intestine.
Villi - increase the surface area of the small intestines, thus providing better absorption of materials

35. Villi increase surface area. More surface area = More absorption

36. Appendix
Vestigial organ

37. appendicitis inflammation of the appendix due to infection
Common treatment is removal of the appendix via surgery

38. The Large Intestine
The large intestine is named because of its diameter
It has four parts:
Cecum – blind pouch
Ileocecal sphincter
The appendix projects from the cecum.
Colon
(ascending, transverse, descending, sigmoid)
Rectum - straight
Anal canal
The anus – is guarded by two sphincter muscles
external anal sphincter – composed of skeletal muscle
internal anal sphincter – composed of smooth muscle

39. Large intestines (colon)
Function
re-absorb water
use ~9 liters of water every day in digestive juices
> 90% of water reabsorbed

40. Large Intestine Solid materials pass through the large intestine.
These are undigestible solids (fibers).
Water is absorbed.
Vitamins K and B are reabsorbed with the water.
Rectum- solid wastes exit the body.

41. feces Poop, excrement, solid waste, etc…
Feces is composed of materials not digested or absorbed, and include: Water, Electrolytes, Mucus, Bacteria, and Bile pigments
Approximately 1/3 of the dry weight of feces is bacteria.
The color of feces is provided by bile pigments altered by bacteria .

42. diarrhea
a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine.
This results in increased, multiple, watery feces.
This condition may result in severe dehydration, especially in infants

43. constipation
a condition in which the large intestine is emptied with difficulty.
Too much water is reabsorbed
Solid waste hardens

44. Bacterial flora Escherichia coli (E. coli)
Living in the large intestine is a community of helpful bacteria
Escherichia coli (E. coli)
produce vitamins
vitamin K; B vitamins
generate gases
by-product of bacterial metabolism
methane, hydrogen sulfide

45. Rectum undigested materials Last section of colon (large intestines)
eliminate feces
undigested materials
extracellular waste
mainly cellulose from plants
roughage or fiber
masses of bacteria

46. Anal Canal / Anus… Last Stop
Exit or opening for solid wastes
Regulated by anal sphincter (valve)
Anal sphincter surrounded by muscles
Elimination aided by abdominal muscles

47. Hemorrhoids
Very common, especially during pregnancy and after childbirth.
Result from increased pressure in the veins of the anus. The pressure causes the veins to bulge and expand, making them painful, particularly when you are sitting..
Symptoms
Anal itching
Anal ache or pain,
especially while sitting
Bright red blood on
toilet tissue, stool, or
in the toilet bowl
Pain during bowel
movements
One or more hard tender lumps near the anus

48. Episiotomy
This…

49. Notebooks Due Monday, April 14 Must include: RESPIRATORY SYSTEM
DIGESTIVE SYSTEM
URINARY SYSTEM
See website for DIGESTIVE SYSTEM powerpoint to help finish notes on chart.