Download Animal Systems - Miss-Sussmans

Animal Systems
The Digestive System
Higher Organisms
All have same basic challenges
*obtain nutrients
*distribute nutrients through body
*void wastes
*respond to environment
*reproduce
All have similar ways of dealing with challenges – the body systems
The Digestive System
Not need by autotrophs, only heterotrophs
Digestion:
Large food molecules break down into simpler molecules absorbed by
body for cell activities
Simple Animals:
intracellular digestion – food vacuoles
ex. Hydra – encloses captured food in vacuole
where lysosomes containing digestive
juices fuse & break down food
The Digestive System
Complex Animals:
extracellular digestion – digestive tract (gastrovascular cavity)
ex. Grasshopper – food passes through specialized regions of gut
mouth  esophagus  crop (storage organ) 
stomach  intestine  rectum  anus
The Human Digestive System
Structures
*Mouth
*Esophagus
*Stomach
*Small intestine
*Large intestine
*Accessory Organs
- salivary glands, pancreas, liver, gall bladder
4 Kinds of Molecules Broken Down
1. Starch (sugar)
2. Proteins
3. Fats
4. Nucleic acids (RNA, DNA)
1st Stop: The Mouth a.k.a. Oral Cavity
Ingestion – food enters oral cavity
Mechanical Digestion – chewing (mastication) – bolus
Chemical Digestion – saliva
* secreted by salivary glands (1st accessory organ)
* contains salivary amylase – enzyme breaks down starch into
maltose (2 glucose molecules: disaccharide)
Bolus moves through pharynx into
esophagus
Pharynx – both food & air pass through
*epiglottis – flap of connective
tissue that closes when food
swallowed to prevent from going
into trachea
Esophagus – tube-like organ that moves
bolus from mouth to stomach
*peristalsis – wave-like contractions
(involuntary) move bolus down
2nd Stop: The Stomach
Thick muscular sac that:
- temporarily stores ingested food
- partially digests proteins
- kills bacteria
Chemical Digestion
Gastric juices
- secreted by parietal cells (epithelial)
- contains:
1. HCl – (pH = 2)  kills most bacteria
- stomach cells secrete mucous for protection
2. pepsin (pepsinogen) – proteins  smaller peptides
- activated by low pH (HCl)
The Stomach
Mechanical Digestion
- churning action
- bolus now called chyme
- enters small intestine through the pyloric sphincter
3rd Stop: The Small Intestine
3 Regions – 23 ft long in avg. man
*Duodenum – connects stomach to jejunum
*Jejunum – connects duodenum to ileum
*Ileum – connects jejunum to large intestine
Chemical Digestion
- All 4 kinds of molecules completely digested
- intestinal walls secrete:
1. Maltase, Lactase, Sucrase – carbs  simple sugars
2. Peptidases – proteins  peptides
Small Intestine
Chemical Digestion
The pancreas (2nd accessory organ) plays large role in chemical digestion
- secretes enzymes through pancreatic duct
1. Pancreatic amylase – starch  disaccharides
2. Trypsin/Chymotrypsin – proteins  dipeptides
3. Pancreatic lipase – lipids (fats)  fatty acids & glycerol
4. Ribo-/Deoxyribonucleases – nucleic acids  nucleotides
- secretes bicarbonate through duct
*neutralizes acid coming into small intestine from stomach
Small Intestine
Mechanical Digestion
Bile – emulsifier: fats  smaller fat droplets
*makes more accessible for pancreatic lipase
*enters through bile duct, merges with pancreatic duct
*made in the liver (3rd accessory organ)
*stored in gall bladder (4th accessory organ)
Small Intestine
Enzyme
Origin
Food it Digests
Peptidases (proteases)
Intestinal walls
Proteins
Maltase, Lactase, Sucrase
Intestinal walls
Carbs
Pancreatic Amylase
Pancreas
Starch
Trypsin, Chymotrypsin
(Proteases)
Pancreas
Proteins
Pancreatic lipase
Pancreas
Fats
Small Intestine
Absorption
- simplified molecules absorbed
villi & microvilli – folds that increase surface area
*capillary – in each villus absorbs into bloodstream (diffusion)
*lacteals – lymph vessels in villi that absorb fatty acids
4th Stop: The Large Intestine
Smaller, thicker intestine that:
- reabsorbs H2O & salts
- harbors harmless bacteria
* break down undigested food
* provide us w/ essential vitamins (K)
Elimination
Feces – undigested food
*moves into rectum & expelled
Hormones’ Role in Digestion
Hormone
Function
Gastrin
Stimulates stomach cells to produce
gastric juices
Secretin
Stimulates pancreas to produce
bicarbonate & pancreatic enzymes
Cholecystokinin (CCK)
Stimulates secretion of pancreatic
enzymes & bile