Digestive System

Nutritional requirements

needed to provide cell energy demands for:

• Growth

• maintenance

• building and repairing tissue

• regulating cellular activities

Nutrients

Chemicals that must be obtained in order to survive

types:

• Macromolecules

• minerals

• vitamins

• water

Macromolecule

Large complex molecule composed of multiple smaller molecules linked together covalently

Types:

• carbohydrates

• lipids

• proteins

• nucleic acids

Carbohydrates

Contain: carbon hydrogen, and oxygen

Functions:

• Energy storage (quick energy use for cells

• structural (materials to build cell walls)

Monosaccharides (carbohydrate)

Simple sugars

Example:

• glucose

• fructose

Disaccharides (carbohydrate)

Double sugars

Example:

• sucrose

• lactose

Polysaccharides (carbohydrate)

Long strands of simple sugars

Example:

• Starch

• glycogen

• cellulose

Lipids

• Contain: carbon, hydrogen, oxygen (less oxygen than carbohydrates)

• hydrophobic

Lipid Function

• source if long term energy storage

• cushion and insulate internal organs

• major component of cell membranes

• hormones

Fats (Lipids)

Triglycerides

• 3 fatty acid chains linked to glycerol

Unsaturated:

• liquid at room temperature (ex: olive oil)

Saturated:

• solid at room temperature (ex: butter)

Proteins

• Made of Amino acids

• Broken down by liver to provide energy during starvation

Protein function

• structural support (blood cells, body tissues, muscles)

• aid movement (muscle contraction)

• Biological catalysts (enzymes)

• defence from disease

• transport substances

Nucleic Acids

• biological macromolecules

• composed of nucleotides

(nucleotides = phosphate group, sugar, nitrogen base)

Breaking down macromolecules

• large macromolecules → small molecules (so they can be absorbed)

Hydrolysis reaction

chemical reaction where water breaks down macromolecules to smaller molecules

Water

• Vital for proper functioning of all cells and organs

• transporting dissolved nutrients into cells

• flushing toxins from cells

• lubricating tissues and joints

• forming essential body fluids (blood, mucus)

• regulate body temperature

• eliminating waste materials (urine, sweat)

Minerals

• inorganic element needed in small amounts

• help chemical reactions

• build bones and cartilage

• absorbed into bloodstream

Mineral Example

Calcium:

• from dairy and leafy greens

• help bone formation, muscle contraction

Potassium:

• fruits and vegetables

• help nerve conduction and muscle contraction

Vitamins

• organic compounds needed in small amounts

• help develop tissue

• fight and resist disease

Fat soluble vitamins

• vitamin A, D, E, K

• only vitamin A and D can be stored

Water soluble

• vitamin B and C

• sometimes removed when cooked in water

Vitamin examples

Vitamin A:

• Eggs, milk, vegetables

• growth and repair, antioxidant

Vitamin E:

• leafy greens, fruits, grains

• antioxidant, protect red blood cells

Ingestion

• Taking food in

• 5-10 seconds

Digestion

• catabolism

• breaking down food

• 2-6 hours

• Can be mechanical or chemical

Absorption

• taking nutrients in

• 5-6 hours

Egestion

• releasing waste

• after 12-24 hours

Mechanical digestion

• food mass is shredded, torn and churned

• occurs in mouth, esophagus, and stomach

• walls churn and squeeze bolus

chemical digestion

• chemicals and enzymes break down food

• occurs in mouth, stomach, and small intestine

• bolus mixes with gastric juice

Enzymes

• proteins formed by secretory cells and secreted into digestive tract

• not functional at high temperatures

• end with “-ase"

substrate

molecule which an enzyme acts on

Hormone

chemical regulator secreted in part of body then transported to cause a response

Gastrin (hormone)

stimulates stomach wall to secrete enzymes and chemicals for chemical digestion

Metabolism

• Total of chemical reactions in body

• Anabolism + catabolism

Catabolism

Breaking large molecules to small

Anabolism

process of connecting small molecules to form large ones

Digestion results

• produces nutrients to be diffused into cells

• produce waste

Oral cavity

1. Lips, tongue, teeth, jaw muscle break down food

2. mixes with saliva and amylase

3. begins chemical digestion of carbohydrates

4. bolus forms and is swallowed

Hard Palate

• Hard front part of mouth toof

• made of bone and skin

• breaks down food

soft palate

• back part of mouth roof

• made of muscle

• expands for swallowing

uvula

• pointed structure hanging from soft palate

• directs food down esophagus

Parotid Gland (salivary gland)

• below skin in front of ears

• secrete watery fluid containing salivary amylase

*amylase helps chemical digestion of starch into sugar

sublingual glands (salivary gland)

• below tongue on floor of mouth

submandibular gland (salivary gland)

below roof of tongue in throat

Swallowing

• bolus of food crosses respiratory tract by swallowing

• swallowing: empties mouth and ensures food does not enter trachea

• epiglottis closes trachea

Esophagus

• Muscular tube that connects pharynx and stomach

Peristalsis

• series of coordinated muscular contractions

• propels food along digestive tract → stomach

Stomach

• J-shaped stretchable organ

• reservoir for food

• sphincters control movement of food in and out of stomach

Cardiac Sphincter

between stomach and esophagus

pyloric sphincter

between stomach and small intestines

Gastric Juice

• lined with gastric glands that secrete juice when stimulated

• made of hydrochloric acid, salt, enzymes, water, mucus

• mucus coats stomach walls as protection from gastric juice

Stomach Pt2

• Rugae allow stomach to expand

• 3 layers of muscle fibres allowing contraction and relaxing

• churns and mechanically breaks up food mixing it with gastric juice

Mucous secreting cells

• lubricates stomach wall to protect from gastric juice

Parietal Cell

secrete hydrochloric acid

chief cell

secrete pepsinogen

Small intestine

• digestion completes

• macromolecule broken down absorbed into circulatory system

• carries nutrients to cells and tissues in body

Small intestine functions

1. breaks down carbohydrates, proteins, fats, and nucleic acids

2. absorbs:

• monosaccharides

• amino acids

• fatty acids and glycerol

• nitrogen bases sugars and phosphates

Microvilli and Villi

• small intestine are lined with villi

• microvilli line villi

• increase surface area for absorption

• Villi 10x

• microvilli 500x

Duodenum

• 25-30 cm U-shaped

• food passes from stomach

• receives secretions from pancreas and gallbladder

jejunum

• after duodenum

• 2.5 m long with lots of folds

• breaks down remaining proteins and carbohydrates

Ileum

• after jejunum

• 3 m long

• few and small villi

• absorbs nutrients

• pushes undigested material into large intestine

Accessory Organs

• not part of alimentary canal

• connected to canal by ducts

• provide support to digestive tract

• fluids from organs necessary

Pancreas

• finger shaped

• 15 cm

• below stomach

• secretes hormones and enzymes

liver

• creates 1 L bile a day

• Bile is detergent to breakdown or emulsify fat

• produces bile and secretes it to small intestine

• regulates metabolism

• removes toxins using catalase enzyme

Gallbladder

• under right lobe of liver

• stores and concentrates bile

large intestine

• 1.5 m long

• large diameter

• absorbs water, salt, vitamins

• absorbs water mainly (90%)

Sections of large intestine

1. cecum

2. colon

3. rectum

4. anus

Large intestine Pt2

• anaerobic bacteria break down undigested water

• leftover matter forms feces pushed into rectum by muscular contractions

• poop exits through anus