Digestive System

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Digestion• Processing of food• Types

– Mechanical (physical)• Chew• Tear• Grind• Mash• Mix

– Chemical• Catabolic reactions• Enzymatic hydrolysis

– Carbohydrate– Protein– Lipid

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Digestion

• Phases– Ingestion– Movement– Digestion– Absorption

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Digestive System Organization

• Gastrointestinal (Gl) tract (Alimentary canal)– Tube within a tube– Direct link/path between organs– Structures

• Mouth• Oral Cavity• Pharynx• Esophagus• Stomach• Duedenum • Jejenum• kIleum• Cecum• Ascending colon• Transverse colon

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Digestive System Organization• Descending colon• Sigmoid colon• Rectum• Anus

• Accessory structures– Not in tube path– Organs

• Teeth• Tongue• Salivary glands• Liver• Gall bladder• Pancreas

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Anatomy of the Mouth and Throat

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The Major Salivary Glands

Major Salivary GlandsParotid gland(25%)• is the largest of the three glands and is located below and in front of the ears, • secretes a fluid rich in amylase• Becomes infected and swollen with the mumps

Submandibular Glands(70%)• located in the floor of the mouth on the inside surface of the lower jaw• Secretes mostly a serous fluid

Sublingual glands(5%)• Are the smallest of the salivary glands and is located on the floor of the mouth

under the tongue.

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Saliva-Functions and composition

Saliva Functions• Moistens the mouth• Digest a little starch and fat• Cleanses the teeth• Inhibits bacterial growth• Dissolves molecules so they can

stimulate taste buds• Dilute and buffer foods• Moistens food and binds particles

together to aid in swallowing(Bolus formation)

Saliva –Composition • Is a hypotonic solution of 99% water

and other solutes• pH of 6.8 to 7.0• Solutes in saliva• Salivary amylase- an enzyme that

begins starch digestion• Lingual lipase- activated by stomach

acid and digest fat after the food is swallowed

• Mucus- binds and lubricates the food mass and aids in swallowing

• Lysozyme- kills bacteria

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Mastication(Chewing)• Mastication is a repetitive sequence of jaw opening and closing with a

profile in the vertical plane called the chewing cycle. • Mastication consists of a number of chewing cycles. • The human chewing cycle consists of three phases:1. Opening phase: the mouth is opened and the mandible is depressed 2. Closing phase: the mandible is raised towards the maxilla3. Occlusal or intercuspal phase: the mandible is stationary and the teeth

from both upper and lower arches approximate

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Deglutition (swallowing)• Sequence

– Voluntary stage• Push food to back of

mouth– Pharyngeal stage

• Raise– Soft palate– Larynx – Tongue to soft palate

– Esophageal stage• Contract pharyngeal

muscles• Open esophagus• Start peristalsis

Phases of Deglutition• Coordinated by swallowing center in the medulla oblongata and ponsBuccal phase• The voluntary stage in which the tongue collects food, presses it against the plate to

form a bolus, and pushes it back into the oropharynxPharyngeal-esophageal phase• Three actions block food and drink from reentering the mouth or entering the nasal

cavity or larynx• The root of the tongue blocks the oral cavity• The soft palate rises and blocks the nasopharynx• The muscles pull the larynx up against the epiglottis to close the airway that leads to the

tracheaEsophageal Stage- Food is moved through the esophagus by peristalsis (the wave like

muscle contractions of the inner circular and outer longitudinal muscles).• At the end of the pharyngeal stage of the swallow, it must relax to allow the bolus to

enter the esophagus.

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Structure of GI tract

Structure of GI tractMucosa• The inner layer of the tract that is a mucous membrane that is composed of a

layer of epithelium- simple columnar in most of the GI tract• a thin layer of smooth muscle ( is responsible for the mucosal folds, or rugae, that serves to increase

the surface area for digestion.)• Is the most highly differentiated layer of the GI tract.

Submucosa• binds the mucosa to the underlying muscle layer. • blood vessels, lymphatics, a nerves plexus, glands that secrete lubricating mucus into the lumen• A thick layer of muscle that under lies the submucosa • begins at the mouth where it is composed of a mixture of smooth and striated muscle (for voluntary

swallowing) and the external sphincter where it is skeletal. • At the distal pharynx it turns into all smooth muscle that courses throughout the rest of the tract. • The involuntary smooth muscle consist of an inner circular and an outer longitudinal layer.

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Structure of GI tract..ctdSerosaThe outermost layer of the GI tract. • Composed of a thin layer of r tissue topped by a serous membrane

(mesothelium) • Begins in the lower 3 to 4 cm of the esophagus and ends with the sigmoid

colon• When the outer fibrous layer is attached to surrounding tissue it is called

adventitia• See this at the oral cavity, pharynx, most of the esophagus, and the rectum It

secretes fluid that allows the tract structures to glide over each other without friction. It is also referred to as visceral peritoneum.

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Peristalsis and Segmentation

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Law of Gut

• Peristaltic Movement

+• Movement towards gravity(Mouth to anus)

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Esophagus

• Usually collapsed (closed)• Functions

– Secrete mucous– Transport food

• Sphincters– Upper– Lower

Esophagus..ctdEsophagus• A straight muscular tube about 25-30 cm long• It begins at the level of the cricoid cartilage, inferior to the larnyx behind the trache a

and extends through the chest cavity, pierces the diaphragm at the esophageal hiatus , and meets with the stomach at an opening called the cardiac orifice.

• It transports food to the stomach and secretes mucus, which aids transport.

• The inferior segment is constricted forming the lower esophageal sphincter which, along with the diaphragm, closes to prevent back flow of stomach contents

• Heartburn- when HCl from the stomach regurgitates back into the lower esophagus resulting in a burning sensation.

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Stomach

• Usually “J” shaped• Left side, anterior to the spleen• Mucous membrane

– G cells – make gastrin– Goblet cells – make mucous– Gastric pit – Oxyntic gland – Parietal cells – Make HCl– Chief cells – Zymogenic cells

• Pepsin• Gastric lipase

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Anatomy of the Stomach

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Stomach• 3 muscle layers

– Oblique– Circular– Longitudinal

• Regions– Cardiac sphincter– Fundus– Antrum (pylorus)– Pyloric sphincter

• Vascular• Inner surface thrown into

folds – Rugae• Contains enzymes that work

best at pH 1-2

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Stomach• Functions

– Mix food– Reservoir– Start digestion of

• Protein• Nucleic acids• Fats

– Activates some enzymes– Destroy some bacteria– Makes intrinsic factor – B

12 absorption– Destroys some bacteria

– Absorbs• Alcohol• Water• Lipophilic acid• B 12

Stomach-Phases

HCl Generation

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Small Intestine

• Extends from pyloric sphincter ileocecal valve

• Regions– Duodenum– Jejenum– Ileum

• Movements– Segmentation– Peristalsis

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Small Intestine• Absorbs

– 80% ingested water– Electrolytes– Vitamins– Minerals– Carbonates

• Active/facilitated transport• Monosaccharides

– Proteins• Di-/tripeptides• Amino acids

– Lipids• Monoglycerides• Fatty acids• Micelles• Chylomicrons

Small Intestine-structure

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Structure of the Villi in the Small Intestine

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Small Intestine• Secretes digestive

enzymes– Peptidases

• Amino-• Di-• Tri-

– Sucrases– Maltase– Lactase– Saccharidases

• Di-• Tri-

– Lipase– Nucleases

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Small Intestine

• Control• Requires pancreatic

enzymes & bile to complete digestion

Absorption at intestine

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Large Intestine

• Extends from ileocecal valve to anus• Regions

– Cecum – Appendix– Colon

• Ascending• Transverse• Descending

– Rectum– Anal canal

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Anatomy of the Large Intestine

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Large Intestine

• Histology– No villi– No permanent circular folds– Smooth muscle

• Taeniae coli• Haustra

– Epiploic appendages– Otherwise like rest of Gl tract

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Large Intestine• Functions

– Mechanical digestion• Haustral churning• Peristalsis• Reflexes

– Gastroileal– Gastrocolic

– Chemical digestion –Bacterial digestion

• Ferment carbohydrates• Protein/amino acid

breakdown

– Absorbs•More water•Vitamins

– B– K

– Concentrate/eliminate wastes

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Feces Formation and Defecation• Chyme dehydrated to

form feces• Feces composition

– Water– Inorganic salts– Epithelial cells– Bacteria– Byproducts of digestion

• Defecation– Peristalsis pushes feces into

rectum– Rectal walls stretch

• Control– Parasympathetic– Voluntary

Defecation

Summary-Digestion and absorption

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Excretory System

The Kidney

Nephron

Figure 26.13b

Countercurrent Multiplication and Concentration of Urine

Glomerulus

Glomerular Filtrate

Ureters and Urinary Bladder

Urinary Bladder

Composition of Urine

Urinary bladder structure

Innervations of urinary bladder

Micturition

Skin and sweat glands

Functions

• Skin performs the following functions:• Protection• Sensation• Heat regulation • Control of evaporation• Storage and synthesis• Absorption• Water resistance

Perspiration

• Perspiration (sweating, transpiration or diaphoresis) is the production of a fluid consisting primarily of water as well as various dissolved solids (chiefly chlorides), that is excreted by the sweat glans in the skin of mammals

Liver

Internal structure-liver

Functions-Liver

Liver cells

Intestinal juices daily secretions

Bile secretion

Composition of Bile

Enterohepatic circulation

Gall bladder-function