digestive system

what are the two kinds of gut tracts

1. blind gut

2. tube within a tube

blind gut

no cavity between gut and body wall

one opening and primitive form

tube within a tube

• flow through digestive tube

• body cavity between gut and body wall

• separate openings (mostly)

• advanced

digestive enzymes

• carbohydrases

• proteases

• lipases

• nulcleases

what is the purpose of enzymes

allow chemical reactions to occur at lower temperatures: allow for reactions to occur at normal body temperature

what are the five phases of food processing

1. ingestion

2. digestion

3. transport

4. absorption

5. egestion

ingestion

food is taken into the body and moves into a digestive cavity (usually called the alimentary canal)

digestion

food is broken down into smaller amounts

transport

through alimentary canal

absorption

ions, water, and small molecules diffuse or ate transported into the circulatory system (nutrients, vitamins, hormones)

egestion

undigested materials and other wastes are passed from the body (elimination or excretion)

what is the alimentary canal a

digestive tract or GI tube

• single elongate tube with an opening at both ends

• contains smooth muscle cells and lined with epithelial cells

  • synthesize and secrete digestive enzymes

  • secrete hormones and transport digested materials

how many regions of the GI tract are there

5- different environments for different processes

general structure of GI tract

• lumen lined epithelial and glandular cells

• secretory cells release a protective layer of mucus

• other cells release hormones

• glands release acid, enzyme, water and ions

epithelial cells are linked by tight junctions and surrounded by layers of tissue made of smooth muscle, neurons, connective tissues and blood vessels

region of reception

• bucal cavity (mouth and structures)

• ingestion and digestion site

• includes the jaws, teeth cheeck muscle tounge salviary glands

• includes the pharyns- back of mouth cavity which is the point where digestive and respiratory systems cross

region of conduction

• esophagus- tube carrying materials from mouth cavity to rest of the alimentary canal - “neck region” through chest

• conducts food from pharynx to stomach

peristalsis

rhytmic wave-like contractions which propel food forward in GI tract (of smooth muscle)

region of storage (more digestion)

stomach- saclike organ evolved for storing food, muscular nature helps break food (partial protein digestion) regulates rate of emptying into the small intestines

secretions -HCl kils microbes, dissolves particular matter (parietal cells)

pepsinogen- converted into pepsin to being protein digestion- epithelium coated with alkaline mucus

lumen cavity in stomach- pepsinogen and hcl make pepsin for protein breakdown

region of terminal digestion and absorption

small intestine (nearly all digestion of food and absorption of food)

Hydrolytic enzymes found on apical surface of epithelial cells or secreted by pancrease into lumen

production of digestion absorbed across epithelial cells and enter blood

surface area specializations of the SI

• small intestine specialized to carry out the bulk of digestion and absorption

  • muscosal infoldings

  • villi- finger l ike projections border (ext of plasma membrane)

specializations increase the likelihood of food particle encountering digestive enzyme and being absorbed

what are the 3 regions of the small intestine

1. duodenum- lots of secretion into this regtion mostly digestion

2. Iejunum

3. Lieum

last two are mainly absorption

surface modification that increase the surface area of the SI

1. plicare circulares

   • large folds of the epithelial lining

   • increase 2-3 times

2. villus

   • finger like projections

   • increase 10 times

3. microvilli

   • folding of the plasma membrane of the cells lining the villus

   • increase 20 times

large intestine

function is to compact and eliminate feces (soem h2O) wasteeeee

waste

• water- 75

• inorganic substances 5

• roughages 8

• fat 5

• undigested protein, dead cells and bile 2

limited vitamin synthesis by resident bacteria

anus

opening at posterior end of alimentary canal for the release of waste material

cloaca (some vertebrates)

chamber receiving contents of digestive, reproductive and urinary tract opening to the outside

pancreas

secrete enzymatic juice through the pancreatic duct into the duodenum of the SI

liver

produces bile (assists enzymes in breakdown of large fat globules into smaller forms)

gall bladder

storage of bile (secretes into SI as needed)