Lecture #9 – Animal Nutrition and Digestion

Key Concepts: Animals are heterotrophic! Nutritional needs – what animals get from food Food processing The human digestive system

Critical Thinking Is this animal approaching the fruit or the flower??? Why???

Critical Thinking Is this animal approaching the fruit or the flower??? Why???

Animals are always consumers Only photosynthesis can convert solar energy to usable chemical energy Plants store chemical energy Animals eat plants (or other animals) ….of course this is somewhat simplified…. but NO animals are autotrophic

Critical Thinking Why do we eat??? Specifically, what do we get from food???

Critical Thinking Why do we eat??? Specifically, what do we get from food???

Why we eat – energy Animals generate ATP by aerobic respiration Main substrate is carbohydrates Fats are also used Proteins are used as a “last resort” Digestion converts consumed polymers to the monomers used in respiration

Remember bioenergetics Managing the energy budget is essential to maintaining animal function ATP powers basal metabolism, other activities; maintains homeostasis; etc… Animals must eat to make ATP Diagram – bioenergetics and the fate of food

Why we eat – carbon skeletons Animals need organic carbon scaffolds to build our own organic molecules – such as???

Why we eat – carbon skeletons Animals need organic carbon scaffolds to build our own organic molecules – such as

Why we eat – essential nutrients Molecules that animals cannot make at all Do not have the right biosynthetic pathways Must be eaten in pre-assembled form Some common to all animals; some specialized Essential amino acids Essential fatty acids Vitamins Minerals

Essential Amino Acids Most animals use the same 20 amino acids to make what???

Essential Amino Acids Most animals use the same 20 amino acids to make Most animals can only synthesize about half Remaining amino acids must be consumed All animal proteins are complete – contain all the essential amino acids All plant proteins are incomplete – missing some of the essential amino acids

Human vegetarian diets must mix plant groups to obtain all essential amino acids Chart – essential amino acids; overlap between grains and legumes Grass and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies Grains and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies

Essential Fatty Acids Some unsaturated fatty acids cannot be synthesized Most animals (especially humans!) get adequate essential fatty acids from their diet We use fatty acids for????

Essential Fatty Acids Some unsaturated fatty acids cannot be synthesized Most animals (especially humans!) get adequate essential fatty acids from their diet We use fatty acids for

Vitamins Organic molecules used in small quantities Water soluble vitamins usually function as coenzymes Fat soluble vitamins function in nutrient absorption, as antioxidants, etc.. Deficiencies are rare with an adequate, balanced diet

Critical Thinking Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why???

Critical Thinking Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why???

for a general under-standing Study table in text for a general under-standing Table – essential vitamins; sources and functions Don’t memorize, just grasp significance

Minerals Inorganic elements Many different functions Some required in small amounts; some in larger Requirements vary by taxon Many different functions Some metabolic; some structural Know top 8 minerals and their main functions

Mineral Functions??? Calcium – Phosphorous – Sulfur – Potassium – Chlorine – Sodium – Magnesium – Iron –

Some Mineral Functions Calcium – Phosphorous – Sulfur – Potassium – Chlorine – Sodium – Magnesium – Iron –

Food Processing Ingestion Absorption Digestion Elimination Diagram – food procession in a small mammal

Evolution of Compartmentalization Food digestion must be contained Why??? Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination

Evolution of Compartmentalization Food digestion must be contained Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination

Evolution of Compartmentalization Food digestion must be contained Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination

Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes Diagram – sponges and their choanocytes

Evolution of Compartmentalization Food digestion must be contained Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination

Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles Diagram – two cell layers in cnidarians Images – a jellyfish and a flatworm

Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles Problem???

Evolution of Compartmentalization Food digestion must be contained Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening – More complex animals have a digestive tube with an opening for ingestion and one for elimination

Hands On Be sure to examine specimens and comment on structure-function relationships Be sure to examine Cnidarians at the aquarium and comment on structure-function relationships

Evolution of Compartmentalization Food digestion must be contained Avoids digestion of body cells and tissues Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination

Critical Thinking The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste Can you think of another advantage for the 2-hole tube plan???

Two hole tube digestive plan – essentially an open tube that passes through the body

Critical Thinking The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste Can you think of another advantage for the 2-hole tube plan???

Tubular system allows for specialization and efficiency Diagram – development of specialization in 2-hole tubular digestive tracts in earthworms, insects and birds Specialization based on habitat and diet Both divergent and convergent patterns have emerged All mammals have a cecum Both earthworms and birds have developed crops

The Human Digestive System Relatively straightforward adaptations to an omnivorous diet Tube running from mouth to anus with specialized regions for food processing, absorption, and elimination of wastes Accessory glands supply lubrication, digestive enzymes and other secretions Schematic diagram – the human digestive system

Diagram – the human digestive tract

Oral cavity, pharynx and esophagus allow for chewing and swallowing food Teeth cut and grind Tongue mixes and pushes bolus to back Saliva lubricates food, protects the mouth lining, buffers pH, kills bacteria, and begins the digestion of carbohydrates Diagram – the oral cavity, pharynx and esophagus; same diagram on next two slides

Oral cavity, pharynx and esophagus allow for chewing and swallowing food Epiglottis tips down to direct food from pharynx to esophagus (so you don’t breathe your food) Diagram – specifically the function of the epiglottis

Oral cavity, pharynx and esophagus allow for chewing and swallowing food Peristaltic contractions in esophagus push food to stomach Food does not fall by gravity – remember our quadruped ancestors… Sphincter (ring) muscles also control passage of food

Stomach continues the action… Stores food (very folded and stretchy) Muscle contractions mix food Lining secretes gastric juice Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria Pepsin begins protein hydrolysis Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor Controls passage of food into small intestine

Stomach continues the action… Stores food (very folded and stretchy) Muscle contractions mix food Lining secretes gastric juice Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria Pepsin begins protein hydrolysis Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor Controls passage of food into small intestine

Diagram – the somach lining and secreting cells

Ulcers….. Stomach lining replaces itself by mitosis about every 3 days Lesions still sometimes occur Ulcer risk factors???

Ulcers….. Stomach lining replaces itself by mitosis about every 3 days Lesions still sometimes occur Ulcer risk factors

Other animals can get ulcers, too From a student’s extra credit  Causes include stress, diet, genetic abnormalities, microbial infections, very finely ground grains, heredity, bile reflux that destroys stomach lining

Stomach continues the action… Stores food (very folded and stretchy) Muscle contractions mix food Lining secretes gastric juice Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria Pepsin begins protein hydrolysis Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor Controls passage of food into small intestine Partly based on liquidity of food – drink water to get over the over-stuffed feeling

Diagram – the cells lining the stomach, secretion of digestive juices

The Small Intestine Completes digestion and absorbs monomers Some absorption occurs in other parts of the digestive tract, but most in the SI More than 6m long Multiple levels of folding increase SA Surface area about 600m2!! Most digestion occurs in the first 25cm of the small intestine Enzymatic hydrolysis Most absorption occurs in the latter 5.75m of the small intestine

Diagram – the human small intestine

Four levels of folding function to increase surface area – tube, interior folds, villi, microvilli Diagram – levels of folding in the human small intestine

Increased surface area, especially of transport epithelia, is a hallmark of large, complex, multi-dimensional animals Factoids from humans: Lungs have 100 m2 of surface area (almost 1/2 as big as room) Small intestine has surface area of a tennis court 80 km of tubules in a single kidney 100,000 km of blood vessels = almost 3X circumference of earth

The Small Intestine Completes digestion and absorbs monomers Some absorption occurs in other parts of the digestive tract, but most in the SI More than 6m long Multiple levels of folding increase SA Surface area about 600m2!! Most digestion occurs in the first 25cm of the small intestine Enzymatic hydrolysis Most absorption occurs in the latter 5.75m of the small intestine

Pancreas secretes enzymes and bicarbonate; liver secretes bile Diagram – the pancreas, liver and gall bladder; structure and function

Digestive enzymes and substrates Chart – digestive enzymes; point of secretion and substrate; same on next slide

Most digestion in duodenum (1st 25cm)

The Small Intestine Completes digestion and absorbs monomers Some absorption occurs in other parts of the digestive tract, but most in the SI More than 6m long Multiple levels of folding increase SA Surface area about 600m2!! Most digestion occurs in the first 25cm of the small intestine Enzymatic hydrolysis Most absorption occurs in the latter 5.75m of the small intestine

Monomers cross into epithelial cells, then into interstitial fluid, then into the lymph or bloodstream Diagram – close-up of villi and microvilli Some transport is facilitated, some active Each villus includes lymph and blood vessels

Fat Digestion Fats are hydrophobic Diagram – fat digestion process; same next slide Fats are hydrophobic Bile salts emulsify large fat droplets into smaller droplets  more surface area Lipase digestion produces fatty acids and mono-glycerides These monomers form into micelles

Fat Absorbtion Micelles are tiny enough to diffuse into epithelial cells Monomers are recombined into fats in the epithelial cells Fats mix with cholesterol and are coated with proteins Resulting globules are transported into the lymph, and eventually into the blood (at shoulder ducts)

Intestinal blood vessels drain directly into the hepatic portal vein Nutrients get sent straight to the liver for metabolic processing Diagram – how blood vessels absorb nutrients; same next slide

Intestinal blood vessels drain directly into the hepatic portal vein From the liver, the blood goes straight to the heart for distribution throughout the body

Critical Thinking Where will the levels of blood sugar and other nutrients vary the most??? Diagram – circulation patterns in humans showing relationship between circulation and major organs

Critical Thinking Where will the levels of blood sugar and other nutrients vary the most???

The large intestine, AKA the colon Connected to SI at T junction Dead-end of T is the cecum Appendix extends off cecum Cecum functions as fermentation chamber in many animals, especially herbivores Human cecum is small, relatively functionless Appendix contributes to immune function, but is dispensable Appendix may function to repopulate intestines with beneficial bacteria after intestinal infections Cecum is very large in herbivores. Last point from October 2007 P&C review of a Duke study on appendix function. Adaptive value in sparse populations where individuals can’t pick up germs from other people (as in before we were overpopulated), or in areas that still suffer from intestinal diseases that cause diarrhea (cholera, dysentery) that clear out the gut bacteria.

Diagrams – the cecum in omnivores (humans) vs Diagrams – the cecum in omnivores (humans) vs. specialized herbivores (koalas)

The large intestine, AKA the colon Remainder of LI is ~ 1.5m Main function is to absorb water 7l of fluid is secreted into intestinal lumen Additional water is consumed in diet SI and LI together absorb ~ 90% Inflammation of LI reduces water absorption  diarrhea LI also houses both commensal and mutualistic bacteria Live on undigested or unabsorbed materials Produce important vitamins (K, B’s, folic acid, biotin) Some produce stinky gasses as a byproduct of metabolism

The large intestine, AKA the colon Final section of LI is the rectum Feces are produced as water is absorbed from waste organic materials Waste includes LOTS of bacteria; cellulose 40% of the dry weight of feces is bacteria Feces are stored in the rectum When the “time” comes, feces are eliminated through the anus Sphincter muscles control elimination One is voluntary, one involuntary Some, but not complete control over defecation

Diagram – the human digestive tract with the large intestine highlighted

Diet is a selection pressure Dentition Different tooth shapes for ripping and grinding Length of small intestine Herbivores typically have much longer SI Other compartments and symbioses Fermentation chambers that house micro-organisms that can digest cellulose (animals lack cellulases) Enlarged ceca (first feces are re-eaten) Esophageal pouches (crops in some birds, the “stomachs” of ruminants)

Critical Thinking How might diet affect tooth evolution? Carnivores – Herbivores – Omnivores –

Critical Thinking How might diet affect tooth evolution? Carnivores – Herbivores – Omnivores –

Ripping, crushing and shredding teeth Biting and grinding teeth Combo of teeth for biting, tearing, grinding and crushing Diagram – differences in tooth structure

Diet is a selection pressure Dentition Different tooth shapes for ripping and grinding Length of small intestine Herbivores typically have much longer SI Other compartments and symbioses Fermentation chambers that house micro-organisms that can digest cellulose (animals lack cellulases) Enlarged ceca (first feces are re-eaten) Esophageal pouches (crops in some birds, the “stomachs” of ruminants)

Most plant material is tough and fibrous – the longer digestive tract in herbivores allows more time and space for digestion and absorption of both nutrients and water Diagram – differences in the digestive tract of carnivore vs. herbivore

Cecum in magenta…..

Diet is a selection pressure Dentition Different tooth shapes for ripping and grinding Length of small intestine Herbivores typically have much longer SI Other compartments and symbioses Fermentation chambers that house micro-organisms that can digest cellulose (animals lack cellulases) Enlarged ceca (first feces are re-eaten) Esophageal pouches (crops in some birds, the “stomachs” of ruminants)

Extra compartments house symbiotic micro-organisms – food is often regurgitated and / or re-consumed Diagram – the digestive system of a cow

Review – Key Concepts: Animals are heterotrophic! Nutritional needs Energy Carbon skeletons Essential nutrients Food processing The human digestive system Diet as a selection pressure

Hands On Begin your careful dissection of the rat Follow instructions in lab manual Answer questions on lab handout Be careful, delicate and precise!!!!