3d-human Digestive System 2009

Human Digestive System Chapter 10.2 Ms. Ho

Functions of the Digestive System Ingestion  Digestion  Absorption  Excretion 

*Note: alternate terms for the Digestive Tract are GI (gastrointestinal) Tract & Alimentary Canal

Mouth and Oral Cavity 

Mouth opens to the Oral Cavity  Teeth  Salivary

Glands

 Tongue  Other

Structures: uvula, soft palate, hard palate, tonsils

Teeth Structure & Function     

Mechanical digestion OR breakdown of food Incisors: bite & cut Canines: tearing & shreading Bicuspids/Premolars: pierce & tear Molars: crush & grind

How are teeth modified in organisms?

Carnivore

Herbivore

Omnivore

Salivary Glands 

Food is mixed with saliva that is produced by 3 pairs of salivary glands  Parotid

(largest)  Sublingual (smallest)  Submandibular 

Uses ducts (tubular canals) to transport secretions to mouth

Saliva Presence of food triggers nervous reflex in salivary glands  release saliva via ducts  Saliva is 99% water, mucus (glycoprotein) & enzymes (i.e. salivary amylase)  Function: 

 protects

lining of oral cavity from abrasion & lubricates food for easier swallowing  chemical digestion: amylase breaks down polysaccharide (amylose  maltose)

Functions of the Tongue   



Helps mix saliva & food together Positions food on molars for chewing Moves food around until it forms a bolus (food ball) & pushes it back to pharynx Primary organ for taste

Tongue & Taste Buds 

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Muscle containing papillae “pimple-like” structure on upper surface of tongue that houses the taste buds 4 sensory tastes:  Sweet  Salty  Sour  Bitter

Location of Taste Buds

Q: Are you a Super-taster?

Other Oral Cavity structures Uvula: flap of tissue covering nasal cavity when swallowing food  Tonsils: lymphoid tissue on either side of uvula in back of throat that produces antibodies  Hard Palate: roof of mouth, hard ridges  Soft Palate: further back in mouth ending in the uvula 

Pharynx   



Common passageway for food, liquids, and air Pharynx muscles assist in swallowing of bolus Region connecting oral cavity & pharynx is the “Oropharynx” Epiglottis: flap of tissue that covers over opening of trachea (glottis) prevents food from entering airway

Swallowing Food 

Trachea moves up against epiglottis to close the opening & prevent food from entering the trachea



Mucin is secreted by back of throat & esophagus wall

Structure of the Esophagus  

Muscular, flexible tube, ~25cm long 3 layers:  Mucosa

(inner): lining covered in mucus  Submucosa (middle): nerves, blood & lymph vessels  Muscularis (outer): circular & longitudinal muscle

Function of the Esophagus 

To conduct food from the pharynx to the stomach

Cross-sectional View

Peristalsis A series of wave-like contractions that propels food along the digestive tract 

Q: What is it called when food moves upwards?

Structure of the Stomach      

J-shaped muscular sac, stretches with food 3 layers of muscles: Longitudinal (outside), Circular (middle) & Oblique (inner folds) Inner lining is folded into accordion-like ridges called “rugae”  inc SA Ridges contain gastric glands that produce gastric juice (enzymes, mucus, HCl) for chemical digestion Cardiac sphincter: ring of muscle controlling entrance into stomach Pyloric sphincter: ring of muscle controlling exit out of stomach

Stomach Q: How many litres of food can the stomach hold when fully expanded? Q: How long does it take your stomach to empty after a meal?

Functions of the stomach Bulk storage of undigested food  Mechanical breakdown of food via rhythmic contractions (mixing of fluids)  Chemical Digestion: breaks chemical bonds via hydrochloric acid (pH 2) and enzymes (pepsin & lipase)  End product is “chyme” partially digested food in a semi-liquid state 

Stomach Lining

Mixing & Rhythmic Contractions

Structure of the Small Intestine Consist of a series of loops loosely attached to the back of the abdomen  Name is from small diameter (approx. 2.5 to 3cm diameter, 7m in length)  Mesentery: layer of connective tissue that holds small intestine together to prevent entangling of intestine in abdominal cavity  Ileocecal valve: ring of muscles (sphincter) that controls movement of material from small intestine to large intestine 

3 Sub-regions of Small Intestine Duodenum  Jejunum  Ileum 

Function of the Small Intestine 

Most of the chemical digestion of macromolecules & absorption of nutrients occurs here



90% of products are absorbed in small intestines Other 10% absorption occurs in stomach & large intestines

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Structure of Intestinal Wall Lining has folded finger-like projections called “villi”  increase SA  Each villus has many microscopic folds called “microvilli”  further increase SA to maximize absorption  Network of capillaries & tiny lymph vessel called “lacteal” extend into hollow core of each villus 

The Intestinal Wall

*Note: only 2 layers of muscles (circular & longitudinal muscle) instead of 3 like the stomach (no oblique muscle)

Cross-section of Small Intestines

Surface of Intestinal Wall

Cross-section of Villus

Absorption within Small Intestines 

Nutrients are absorbed across Intestinal cells (Villus) either via the: 



Blood Capillaries – amino acids & monosaccharides Lacteal – glycerol & fatty acids

Functions within each Region Duodenum: (first 25cm, U-shaped) chemical digestion occurs here, chyme mixes w/ digestive juices from pancreas, liver, gall bladder & intestinal wall  Jejunum: (~3m long) most absorption of nutrients occur here, highly folded inner lining contains lots villi & intestinal glands  Ileum: (~4m long) contains fewer & smaller villi, absorb nutrients & push undigested material into large intestine 

Intestinal Movements 



Peristalsis: series of wave-like muscular contractions & relaxations Rhythmical Segmentation: mixing contractions that knead material back and forth without propelling it forward at a very fast rate

Structure of the Large Intestine Large upside-down U-shaped organ  Approx. 1.5m in length & 8cm in diameter  Three main sections: ascending colon, transverse colon & descending colon  Chyme enters caecum a small pouch connected to ascending colon  host to large # of bacteria that breakdown cellulose  Appendix a finger-like projection at the tip of caecum  function is still a mystery 

3 sections of the Large Intestine Ascending  Transverse  Descending 

Functions of the Large Intestine    

Complete absorption of nutrients Reabsorb water, minerals & other useable materials  prevents dehydration Absorb vitamins K & B (biotin, folic acid) produced by bacteria (E. coli) Form, compact & store fecal matter (waste & undigested material) prior to defecation

*Note: movement of material via peristalsis

Structure of the Large Intestines

Rectum & Anal Canal Last portion of the digestive tract:  Rectum: where feces are stored until eliminated  Anal Canal: between rectum & anus passageway for feces, ends in Internal (involuntary) and External (voluntary) anal sphincters  allows body to control timing of elimination 

Digestive Questions  



How long does it take to digest a meal? How is gas produced within along the digestive tract (2 ways)? How does one get diarrhea & how does it happen?

Accessory Organs Pancreas, Liver & Gall Bladder

Accessory Organs Large organs outside the digestive tract that aids in chemical digestion  Chemical secretions are carried by ducts that empties into the digestive tract  3 Main Accessory Organs: 

  

Liver Gall Bladder Pancreas

Liver, Gall Bladder & Pancreas

Structure of the Liver  

Largest internal organ, brownish-red in colour, divided into 2 large lobes (L & R) Located just beneath the diaphragm

Function of the Liver  

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

Liver performs over 500 functions: Produces bile (greenish-yellow liquid) that contains bile salts from cholesterol that helps to emulsify large fat globules into smaller fat droplets (easier fat digestion & lipase action) Emulsification: is a process that involves molecules attracted to water at one end and fats at the other end creating a suspension of small fat droplets  stable emulsion Bile released via hepatic duct

Functions of the Liver 

Plays major role in metabolism (set of chemical reactions that maintains life):  Demolition:

breaks down old RBC  Recycler: parts of decomposed Hb are recycled to make bile salts  Storehouse: collects excess chemical in blood (i.e. fat soluble vitamins, glucose  glycogen)  Detoxification centre: detoxifies poisons ingested in food & water (i.e. alcohol)

Gall Bladder Hollow, pear-shaped organ on the underside of the liver  Not involved in enzyme production  Storage warehouse for bile, release is triggered by hormone via cystic duct 

Gall Bladder

Structure of the Pancreas Leaf-shaped gland, ~20cm in length  Located close to curve of stomach, attached to the duodenum  Pancreatic juice enters duodenum via pancreatic duct 

The Pancreas

Pancreas Produces over 28 digestive enzymes that breaks down lipids (lipase), carbohydrates (amylase) & proteins (trypsin, peptidase)  Produces pancreatic juice, alkaline substance (NaHCO3) that neutralizes acidic chyme, so other enzymes can function  Produces insulin (hormone that regulates blood glucose levels), allows glucose to enter cells 

Pancreas & Diabetes Hypoglycemic: abnormally low-levels of glucose in blood (pancreas sends out too much insulin to break down sugar)  Hyperglycemic: extremely high glucose levels or diabetes (pancreas can’t make enough insulin or body can’t use insulin) 

 Type

1: insulin dependent  Type 2: non-insulin dependent  Type 3: gestinational diabetes

Accessory Organs & their ducts

Summary of the Digestive System