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The Digestive System Chapter 23.

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Presentation on theme: "The Digestive System Chapter 23."— Presentation transcript:

1 The Digestive System Chapter 23


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


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.

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