1. Carbohydrates

2. Lipids

3. Proteins

4. Vitamins

5. Minerals

6. Ions

7. Water

Process of nutrient acquisition, digestion, and absorption

- Takes place along the GI tract

- Secretory cells

- Absorptive cells

- Muscle cells

- Neurons

1. Assimilation

2. Egestion

- Nutrients from food can be oxidized to provide energy

- Energy from food must match metabolic requirements

- body size

- activity

- growth rate

- reproductive state

- environmental stress

Energy content of a gram of a specific macromolecule

- protein and carbohydrates = 4kcal/g

- fat = 9kcal/g

- Group of unrelated molecules with diverse functions

- Many participate in catalysis as cofactors for enzymes

- Some are antioxidants

- Usually categorized on solubility:

- Fat-soluble: K, A, D, E

- Water soluble: B, C

- Obtained in diet or from bacteria living in the GI tract

- Can be toxic if you take too many fat-soluble vitamins

Metabllic elements that participate in protein structure:

- Calcium

- Phosporus

- Iron

- Copper

- Zinc

- most are absorbed along the GI tract by specific transporters

They must be obtained by the diet:

- Phenylalanine

- isoleucine

- leucine

- lysine

- hystadine

- threonine

- tryptophan

- methionine

- valine

Animal tissues provide higher protein quality than plant tissues

- supplies all amino acid requirements

- some plants provide low levels of specific amino acids, and therefore a combination of plants are required to fulfill a.a. requirements

Omega-3 or omega-6

- omega-3 must be ingested as gamma-linoleic acid (plant seeds, poultry, eggs, nuts

- omega-6 must be ingested as alpha-linoleic acid (cold water fish)

Enzymes convert macromolecules to forms that can be absorbed and processed

- Lipases

- Proteases

- Amylases

- Nucleases

Most digestion takes place extracellularly (at the lumen of the GI tract)

- Break down proteins into shorter polypeptides

- Peptidases cleave successive amino acids

- Break down polysaccharides into oligosaccharides

- Disaccharidases (maltase, sucrease, lactase)

Digestion in many animals benefits from the assistance of symbiotic organisms

- bacteria

- fungi

- photosynthetic organisms

1. Enterosymbionts

- live within the lumen of the GI tract

- often in an enlarged region called the cecum

2. Exosymbionts

- Actively cultivated outside the body

3. Endosymbionts

- Grow in interstitial spaces or within host cells

- Zoochlorellae (green algae) produce carbon skeleton, glucose and maltose

1. Polysaccharides

- Glycogen: storage carb of mammalian muscle and liver

- Starch: storage carb of plants

- Cellulose: cannot be digested by human enzymes (plant cell wall)

- Chitin: exoskeletons of arthropods, plankton

2. Disaccharides

- Sucrose

- Lactose

- Maltose

- Polysaccharides and disaccharides are broken down to monosaccharides (e.g. fructose, glucose, galactose)

- Monosaccharides are absorbed by epithelial cells in the intestine (enterocytes)

- Most using sodium dependent transporters (amino acid-Na⁺ cotransporters)

- there are a variety of transporters that carry amino acids overall

1. Simple lipids

- Fatty acids, triacylglycerol, sterols (cholesterol)

2. Compound lipids

- phospholipids, lipoproteins

- Dominate biological membranes

- Two classes:

1. Phosphoglycerides

2. Sphingolipids

- Are broken down by phospholipases

Cholesterol --> Prenenolone --> Progesterone

Progesterone --> Cortisol, Corticosterone & Testosterone

Corticosterone --> Aldosterone

Testosterone --> Estrogen

Digestion and import of lipids is complicated by their hydrophobicity

- GI tract secretes bile that emulsified lipids into small droplets (micelles)

- Dietary fats are broken down into fatty acids and monoglycerides (by lipases)

- Lipids diffuse across cell membrane into enterocyte

Short chain fatty acids and glycerol: in the blood (as lipoprotein complexes)

Triglycerides, long fatty acid chains, cholesterol, and monoacylglycerides: coated by proteins as chylomicrons

1. Mouth, pharynx, esophagus

- mechanical breakdown of food

2. Stomach

- acidic compartment

3. Upper or small intestines

- Digestion and absorption

4. Lower or large intestines

- Abosrption of water

5. Anus

- release of indigestible material

1. Duodenum

2. Jejunum

3. Ileum

1. Incisors

- piercing and tearing flesh

2. Canines

- piercing and tearing flesh

3. Premolars

4. Molars

1. Orbital gland

2. Sublingual gland

3. Parotid gland

4. Mandibular gland

1. Lubricates food

2. Dissolves food so nutriends can bind to gustatory receptors

3. Cleanses mouth with antimicrobial properties

4. Contains enzymes that initiate digestion

Salivation is controlled by nerve signals

- Parasympathetic nerves stimulate salivation

- Sympathetic nerves inhibit salivation

1. Foregut

- esophagus, stomach, anterior section of the duodenum

- forms buds tht become the pancreas and liver

2. Midgut

- Posterior part of the duodenum, jejunum, ileum, cecum, and large intestine

3. Hindgut

- colon and rectum

1. Increasing gut length

2. Increasing surface undulations

- circular folds

- villi

- microvilli

Specialized compartments increase efficiency of digestion

- compartments have specializations (pH, enzymes, types of secretory and absorptive cells)

1. Tight junctions

- prevent leakage across epithelium

2. Mucous neck cells

- secrete mucus

3. Parietal cells

- secrete hydrochloric acid (HCl)

4. Chief cells

- secrete the protease pepsin

5. Enteroendocrine cells

- secrete hormones into the blood (e.g. gastrin)

1. Mucosa

2. Submucosa

- blood and lymphatic vessels, nerves

3. Circular smooth muscle

4. Longitudinal smooth muscle

Mucosal Cells

1. Enterocytes

- absorptive cells with microvilli

2. Goblet cells

- secrete mucus

3. Enteroendocrine cells

- secrete hormones

4. Paneth cells

- secrete antimicrobial molecultes (lysozyme)

Crypt of lieberkuhn

- secretes sucrase, maltase, lactase, peptidase

Solution of digestive chemicals and liver waste products

- produced in the liver and stored in the gallbladder

- contains phospholipids (aids in uptake of lipids)

- contains bile salts (emulsify fats)

- Bile duct opens into small intestine

1. Proteases - breakdown protein

2. Amylase - breaks down glycogen and starch

3. Lipases - breaks down triglycerides

4. Nucleases - break down nucleic acids

- Food moves along the GI tract by contractions of smooth muscle (controlled by nerves and hormones)

- must be fast enough to minimize amount of indigestible material in the GI tract but slow enough to allow for digestion and absorption (Rate will vary according to diet)

Longitudinal: controls length, peristalsis

Circular: controls diameter, segmentation

- Myogenic and neurogenic control of smooth muscle contraction

A nerve network between the muscle layers of the intestines.

- Receives signals from the sympathetic and parasympathetic nervous systems