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Lecture #9 – Animal Nutrition and Digestion
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Key Concepts: Animals are heterotrophic!
Nutritional needs – what animals get from food Food processing The human digestive system
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Critical Thinking Is this animal approaching the fruit or the flower??? Why???
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Critical Thinking Is this animal approaching the fruit or the flower??? The flower!!! Why??? Butterflies pollinate while drinking nectar; frugivores eat fruits and distribute seeds!
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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
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Critical Thinking Why do we eat??? Specifically, what do we get from food???
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Critical Thinking Why do we eat??? Specifically, what do we get from food??? Energy Carbon skeletons Essential nutrients Amino acids Fatty acids Vitamins Minerals
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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
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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
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Why we eat – carbon skeletons
Animals need organic carbon scaffolds to build our own organic molecules – such as???
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Why we eat – carbon skeletons
Animals need organic carbon scaffolds to build our own organic molecules – such as carbohydrates, lipids, proteins and nucleic acids These are the 4 main categories of macromolecules common to all forms of life Animals can’t make organic molecules from CO2
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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
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Essential Amino Acids Most animals use the same 20 amino acids to make what???
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Essential Amino Acids Most animals use the same 20 amino acids to make proteins (including enzymes!) 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
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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
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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????
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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 Phospholipid membranes Energy storage Cushioning and insulation Steroids and some hormones
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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
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Critical Thinking Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why???
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Critical Thinking Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why??? Water soluble vitamins dissolve in blood Excesses are filtered and excreted in urine Fat soluble vitamins dissolve into our adipose tissue Excesses are stored in fat and can become toxic
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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
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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
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Mineral Functions??? Calcium – Phosphorous – Sulfur – Potassium –
Chlorine – Sodium – Magnesium – Iron –
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Some Mineral Functions
Calcium – bones and teeth; nerve and muscle fx. Phosphorous – bones and teeth; ATP; nucleic acids; membranes Sulfur – in some amino acids Potassium – pH and solute balance; nerve fx. Chlorine – pH and solute balance; nerve fx. Sodium – pH and solute balance; nerve fx. Magnesium – enzyme cofactor Iron – hemoglobin; e- carrier; enzyme cofactor
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Food Processing Ingestion Absorption Digestion Elimination
Diagram – food procession in a small mammal
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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
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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
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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
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Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes
Diagram – sponges and their choanocytes
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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
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Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles
Diagram – two cell layers in cnidarians Images – a jellyfish and a flatworm
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Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles
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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 – single opening for incoming food and outgoing waste is inefficient – food and waste mix More complex animals have a digestive tube with an opening for ingestion and one for elimination
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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
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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???
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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??? It allows for specialization along the digestive tract
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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
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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
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Diagram – the human digestive tract
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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
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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
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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
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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
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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
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Diagram – the somach lining and secreting cells
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Ulcers….. Stomach lining replaces itself by mitosis about every 3 days
Lesions still sometimes occur Ulcer risk factors???
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Ulcers….. Stomach lining replaces itself by mitosis about every 3 days Lesions still sometimes occur Ulcer risk factors Helicobacter pylori Tobacco Alcohol Caffeine Aspirin Chocolate! Ouch!!
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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
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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
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Diagram – the cells lining the stomach, secretion of digestive juices
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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
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Diagram – the human small intestine
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Four levels of folding function to increase surface area – tube, interior folds, villi, microvilli
Diagram – levels of folding in the human small intestine
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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
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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
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Pancreas secretes enzymes and bicarbonate; liver secretes bile
Diagram – the pancreas, liver and gall bladder; structure and function
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Digestive enzymes and substrates
Chart – digestive enzymes; point of secretion and substrate; same on next slide
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Most digestion in duodenum (1st 25cm)
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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
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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
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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
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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)
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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
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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
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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
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Critical Thinking Where will the levels of blood sugar and other nutrients vary the most??? The hepatic portal vein Levels are stabilized in the liver before blood is circulated to the rest of the body
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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.
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Diagrams – the cecum in omnivores (humans) vs
Diagrams – the cecum in omnivores (humans) vs. specialized herbivores (koalas)
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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
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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
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Diagram – the human digestive tract with the large intestine highlighted
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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)
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Critical Thinking How might diet affect tooth evolution? Carnivores –
Herbivores – Omnivores –
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Critical Thinking How might diet affect tooth evolution?
Carnivores – eat meat only – puncture, rip, shred, crush Herbivores – eat plants only – bite, grind Omnivores – eat both – combo teeth
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Ripping, crushing and shredding teeth
Biting and grinding teeth Combo of teeth for biting, tearing, grinding and crushing Diagram – differences in tooth structure
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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)
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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
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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)
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Extra compartments house symbiotic micro-organisms – food is often regurgitated and / or re-consumed
Diagram – the digestive system of a cow
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Review – Key Concepts: Animals are heterotrophic! Nutritional needs
Energy Carbon skeletons Essential nutrients Food processing The human digestive system Diet as a selection pressure
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