Nutrition Flashcards
Why do animals eat
Ultimate explanation
Proximate explanation
Ultimate explanation
– to provide the nutrients required to maintain the body and to perform processes/activities
Proximate explanation
homeostasis, nerve signals, hormones, hunger, hedonic rewards
What percentage of dry weight of food is made up of protein, carbs and fat
90%
Energy content of protein
17kJ (4.1 kcal) per gram
Energy content of carbs
17kJ (4.1 kcal) per gram
Energy content of fat
37kJ (8.8 kcal) per gram
Energy content of ethanol
29kJ (7.0 kcal) per gram
Number of amino acids
23
Essential amino acids
Protein in the diet provides specific amino acids that are unable to be synthesised at a sufficient rate for optimal performance
Most animals – 9 essential AAs
First identified in rats – common across spp
Some differences – e.g. arginine (NE humans), taurine (E cats)
Number of Essential amino acids
9 (in most animals)
Classifying carbs
Absorbable
Digestible
Fermentable
Non-fermentable
Absorbable carbs
Monosaccharides e.g. glucose, fructose
Digestible carbs
Di-/Polysaccharides e.g. sucrose, starch
Fermentable carbs
Oligosaccharides e.g. pectin, gum
Carbohydrates that cannot be digested are transported to the intestine where gut bacteria break them down by fermentation into short chain fatty acids. These can then be absorbed by the gut cells and used in metabolism and other processes. These include soluble “fibre” such as pectin, gums and hemicelluloses.
Non-Fermentable carbs
– Cellulose*, lignin, waxes
Functions of carbs
Primary energy source (even for carnivores)
Insulin regulates blood glucose level
Storage (Glycogen)- in liver and muscle
Excess carbs converted to fat for storage
Used to build amino acids, fatty acids
Protects protein
Importance of fats
Energy dense - improve palatability and texture of food.
Glycerol backbone, 3 chains of fatty acids
Provider of EFA’s
Essential cell membrane component
Prostaglandins
Absorption, storage and transport of fat-soluble vitamins
Type of fat important to health
Essential fatty acids
such as linoleic, α-linolenic acids. EFA’s are important for kidney function and reproduction. They are essential components of cell membranes and are needed for prostoglandin synthesis. Prostaglandins are hormone-like lipid compounds that are produced throughout the body. Fats are also essential for the absorption, storage and transport for fat-soluble vitamins (A, D, E and K). The type of fat is important, saturated fats are solid at room temperature and are more prone to forming plaques and blocking arteries, and as such should be limited in the diet. They also contribute to the biosynthesis of LDL or ‘bad cholesterol’. Mono and polyunsaturated fats are an important part of the diet.
Fat soluble vitamins
A
D
E
K (cats)
Stored in body better than water soluble vitamins
Daily intake less critical
Water soluble vitamins
B-Complex Vitamins
C
Poorly stored in body
Frequent intake
needed
Excesses lost via urine
Number of basic vitamins
14
Vitamin A
Essential in diet
Vision – night blindness- used to form rhodopsin
Vitamin A is also essential for healthy skin, particularly the respiratory tract as it is necessary for the correct functioning of mucus producing cells.
Antioxidant
Plants - β-carotene (carotenoid)
Animal sources – vitamin A
Vitamin D
Ca absorption/resorption
Linked to dietary conc. Ca & P
Can be synthesised from lipid compounds in skin.
The main function of vitamin D is in bone health. It maintains skeletal calcium balance by stimulating calcium absorption in the intestine and resorption of Ca from bone. Vitamin D is one we can make ourselves, if we have adequate exposure to sunlight. Exposure to UV-B converts cholesterol in the skin to vitamin D.
Vitamin E
Antioxidant - protects cell membranes
Regulates activity of some enzymes.
Neurological functions/wound healing
Stored in liver, excreted in bile
Vitamin K
Important in blood clotting
Made by gut microflora
Newborn babies given vitamin k injection.
Vitamin K regulates the formation of several blood clotting factors (factors VII, IX, X and XII).
B-complex vitamins
Form co-enzymes - involved with normal metabolic function – mostly involved in breakdown of macronutrients
There are 8 B vitamins and choline which make up the B complex of vitamins.
They are used to form co-enzymes which are involved with normal metabolic function – energy metabolism and synthetic pathways and they are water soluble.
B9, or folic acid is involved in the production of red blood cells, metabolism of amino and nucleic acids and cell division and the correct development of the neural tube. It is particularly important in pregnant women and infants, with deficits increasing the risk of spina bifida, a condition where the spine does not form correctly during gestation.
Herbivores and B-complex vitamins
Ruminants – produced by bacteria in rumen e.g., cows, sheep
Cecal digesters – fermentation in caecum, coprophagy e.g., rabbits, mice
Colonic digesters – may not absorb enough from colon, some ingestion of soil, e.g., elephant, horse
Vitamin C - ascorbic acid
Important in wound healing, blood vessel/cartilage maintenance
Antioxidant activity
High levels in immune cells
Produced by most animals except bats, guinea pigs, capybaras, many monkeys and apes (including humans)
Vitamin C is a co factor in at least 8 enzymatic reactions, including those involved in the synthesis of collagen, an important structural protein, used in wound healing and maintenance of blood vessels and cartilage.
It is required to synthesise carnitine, which transports fatty acids into mitochondria to generate energy and it is used in the synthesis of neurotransmitters.
It is used in the synthesis and breakdown of tyrosine.
It has antioxidant activity, so it is protective against oxidative damage and it is found in high levels in immune cells. Its precise function is unknown but it does deplete during infections and it is thought to be involved in the activity of phagocytes and lymphocytes.
Macro minerals
CalciumChlorideMagnesiumPhosphorousPotassium
Sodium
What are macro minerals
Those found in the body in large quantities - over 5 g
Micro minerals
Arsenic
Chromium
Cobalt
Copper
Fluoride
Iodine
Iron
Manganese
Nickel
Selenium
Silicon
Vanadium
Zinc
Calcium
Most abundant mineral in the body.
Important for bones, teeth, muscle contraction
Secretion of hormones, digestive enzymes and neurotransmitters
99% Ca stored in skeletal tissues
Phosphorus
Second most abundant mineral.
85% Ph stored in bones and teeth - maintains structure with Ca.
Important for DNA/RNA, energy transfer during metabolism (ATP), phospholipids
Ca:Ph ratio 1:1 to 2:1
Hunger
the physiological response to a lack of nutrients in the stomach/bloodstream
Hedonic mechanism
Pleasure associated with foods – rewarding, makes animal want to keep eating
Gustatory mechanisms of reward
Food reward modulated by palatability
Consume sweet/salty foods past repletion, avoid sour/bitter foods even when food deprived.
Flavours are indicative of nutritional value.
Modified by post-ingestion cues – e.g. lithium chloride
Extreme food seeking behaviour
Outbreak - Mormon crickets band together, start marching.
Marching bands – 10km long, can travel 2km per day.
Do not strip landscape – searching for particular foods?
Flowers, seed heads, the leaves of legumes, carrion, animal faeces, urine-soaked soil and each other.
Seeking salt and protein?
Classification of ingestion
Filter feeding
Deposit feeding
Fluid feeding
Bulk feeding
Filter feeding
obtaining nutrients from particles suspended in water
Typically pass water over a specialized filtering structure.
E.g. Whale shark, flamingo, lots of aquatic invertebrates
Deposit feeding
Feed by obtaining nutrients from particles suspended in soil.
E.g. earthworm, sea cucumbers, fiddler crabs, sand dollars (echinoderms).
Fluid feeding
Obtaining nutrients by consuming other organisms’ fluids.
Plant sap - Aphids, shield bugs,
Nectar – butterflies, bees
Blood - mosquitoes, assassin bugs, ticks, mites, fleas, leeches, vampire bats
Blood feeding especially important for transmission of diseases in animals.
Bulk feeding
Obtaining nutrients by eating some or all of an organism.
Most vertebrates, many invertebrates. Includes herbivores, omnivores, carnivores.
Filter feeder mouth
The obvious one is some structure that can filter particles from the water. In baleen whales they either swim open mouthed and continuously filter, or they lunge at a concentration of krill gulp a large mouthful of water then squeeze the water out through their baleen.
These are long hairlike structures that hang from the upper jaw and capture krill, which are small crustaceans. Barnacles are small crustaceans that as adults become affixed to a surface and filter feed. They cement themselves to a surface by their heads and the feathery structures that you see poking out of the shell are their feet. These filter tiny plankton from the water and pass them to the mouth, and from there into the stomach. Sea squirts are tunicates. Sea squirts feed by taking in water through the oral or incurrent siphon, which is equivalent to a mouth.
The water enters the mouth and pharynx, flows through mucus-covered gill slits (also called pharyngeal stigmata) into a water chamber called the atrium, then exits through the atrial siphon. Tentacles at the opening to the pharynx and cilia inside the pharynx trap particles which are passed to the stomach.
Deposit feeders mouth
The gut of the earthworm is a straight tube which extends from the worm’s mouth to its anus. It is differentiated into a buccal cavity (generally running through the first one or two segments of the earthworm), pharynx (running generally about four segments in length), oesophagus, crop, gizzard (usually) and intestine.
Food enters the mouth. The pharynx acts as a suction pump; its muscular walls draw in food. In the pharynx, the pharyngeal glands secrete mucus. Food moves into the oesophagus, where calcium (from the blood and ingested from previous meals) is pumped in to maintain proper blood calcium levels in the blood and food pH. From there the food passes into the crop and gizzard. In the gizzard, strong muscular contractions grind the food with the help of mineral particles ingested along with the food. Once through the gizzard, food continues through the intestine for digestion.
Benthic sea cucumbers (not all spp), just like earthworms, use feeding tentacles to push sediment towards the mouth. This is then passed through the intestine where nutrients are absorbed and filtered sediments are excreted through the anus.
Fluid feeders mouth
First of all a comparison of two insect fluid feeders. They are both flies, in the order diptera, both feed on blood but the modes of feeding and the adaptation of the mouthparts are quite different. First, mosquitoes, which have delicate syringe-like mouthparts. Here the labium is like a sword sheath housing the other mouth parts which together form a hollow needle. The mosquito inserts this needle into the skin and searches around for a capillary, then sucks up the blood. The horsefly in comparison, uses its mandibles and maxillae to cut into the skin, they then use their labium as a sponge to lap up the blood that wells out. This is a much coarser way to access the blood.
This is why a mosquito can bite you without you having any idea it has happened, but a horsefly bite really hurts!
Bird mouth
Birds tend to be bulk feeders with some exceptions, for example flamingos are considered to be filter feeders. Birds do not have teeth so they use their beaks and tongues to pick up and manipulate food. In some cases the beak can also break up food.
For example, many predatory birds have sharp beaks that can tear flesh into small pieces. Finches that feed on seeds tend to have large, heavy beaks that can crush the seeds before they are swallowed. Other birds swallow food whole, for example, most fish-eating birds and pecking birds, like chickens. In many birds mastication is carried out after swallowing in the gizzard, which is a muscular stomach that can grind food, sometimes with the aid of grit or stones that birds swallow.
Reptile mouth
Most reptiles are carnivorous but despite having teeth tend not to use them to masticate food but rely on their digestive juices to break down food.
Crocodiles and alligators swallow stones and these may aid in the breakdown of food in the stomach, which is muscular and acts as a gizzard. Some reptiles will use their teeth much as mammalian carnivores, to tear off chunks of food that are small enough to be digested. Some reptiles are herbivorous, such as iguanas, and much like herbivorous mammals use their tongue to manipulate and teeth to break off small pieces of plant matter which are then digested in the stomach with the aid of microbes. All snakes are carnivorous. They use their teeth, modified into fangs to deliver venom, which also contains digestive enzymes, helping to start the process of digestion before ingestion. They do not chew, instead they swallow their prey whole. Muscular contractions and strong digestive juices help to break down the food.
Mammal mouth- unusual animals
The anteater’s tongue is covered with thousands of tiny hooks called filiform papillae which are used to hold the insects together with large amounts of saliva. We have these papillae too, they are the rougher bumps on our tongues at the front and down the centre that don’t contain taste buds. Their function in humans isn’t so obvious but they might aid in creating the bolus of food and manipulating it around the mouth. After manipulating the insects into a ball, swallowing and the movement of the tongue are aided by side-to-side movements of the jaws. The anteater’s stomach, similar to a bird’s gizzard, has hardened folds and uses strong contractions to grind the insects; a digestive process assisted by small amounts of ingested sand and dirt. The tongue is attached to the sternum and moves very quickly, flicking 150 times per minute.
The duck billed platypus is a carnivore that has no teeth and has an extended upper and lower jaw. The bill is in fact a sensory organ that has mechano- and electroreceptors. When diving in silty water the platypus closes its eyes, nostrils and ears and so hunts entirely via sensing movement and tiny changes in the electrical field around its bill caused by worms and crustaceans in the water or riverbed. It carries prey in its cheek pouches and takes them to the surface where they are eaten. In place of teeth there are hard ridges on the jaw that are used to masticate the prey before swallowing.
Mammals mouth
Lips, teeth and tongue grasp and manipulate food.
Pigs use snout to root in ground and pointed lower lip to convey feed into mouth.
Teeth tear/masticate food
Tongue tastes food
Saliva – moistens and softens food, initiates digestion.
Incisors
cutting teeth, implanted in front of incisive bones of maxilla and anterior part of mandible.
Canines
used to hold food for tearing, situated behind the incisors.
Molars
mainly for chewing. Broad irregular grinding surfaces
Carnassial teeth
shearing meat, last upper premolar in maxilla, very large, 3 roots – found in carnivores only
Continuous eruption
Teeth grow throughout life
Continuous wear
E.g., Rabbits, horses, rodents.
Mastication and digestion
Some spp – saliva contains alpha - amylase
Amylase breaks down starch into maltose
Maltose – disaccharide of glucose.
Amylase - inhibited by stomach pH.
Mucus
Protects lining
Produced in all parts
Gastrin
Hormone - stimulates gastric gland to secrete
pepsinogen and HCl
Pepsinogen
Acted upon by HCl to produce pepsin
HCl
Low pH needed for pepsin. Softens food, kills microbes (and bacteria from rumen).
Rennin (chymosin)
Coagulates milk to < rate of passage (activated by HCl)
Found in young mammals
Intestine - midgut
Majority of digestion and absorption
Surface area increased by villi
Enzymes break down nutrient molecules into building blocks:
Protein»_space; Amino Acids
Carbs»_space; Simple Sugars
Fats»_space; Fatty Acids
Nucleic Acid»_space; Nucleotide
Secretin/CCK
Hormones triggers secretion of bile from liver and bicarbonate and enzymes from pancreas
Bile
Common bile duct from liver carriesbile salts – emulsifies fat, activates lipases (Inverts form fatty acid-amino acid and glycolipid complexes).
Pancreatic juices
Trypsin, chymotrypsin, procarboxypeptidases, pancreatic amylase, pancreatic lipase, bicarbonates
Intestinal juices
Trypsin, chymotrypsin, carboxypeptidases, amylase, lipase, bicarbonates, disaccharidases, peptidases, nucleotidases, lysozymes, chitinases, gluconases
Vertebrates also have bicarbonate and disaccharides
Ruminants - foregut
Herbivores
4 parts to stomach
Cattle, goats, sheep
Non-ruminants - foregut
Herbivores
1 part to stomach
Camels, llamas, whales
Caecal - Hindgut
Herbivores
1 part to stomach
Rabbits, guinea pigs, chinchillas
Colonic - Hindgut
Omnivores/ carnivores
1 part to stomach
Ferrets, cats, dogs, pigs, primates, humans
Site of fermentation of indigestible foods
Ruminants
Non-ruminants
Caecal
Colonic
Jejunum
each villus has a vein and artery for collection and transport of digested nutrients, and a lacteal, which is a lymph capillary for the collection of fats. Each villus is coated with an epithelial layer of cells covered in microvilli, which are called enterocytes. The layer of microvilli that cover the villus are referred to as the “brush border” .
Drosophila gut
a tubular epithelial organ composed of a monolayer of cells surrounded by muscles. The gut is divided into the foregut, the midgut, and the hindgut, based on the developmental origin.
The crop stores the food ingested by the flies, and the first half of the cardia belongs to the foregut. The Malpighian tubules, a functional equivalent of the mammalian kidney, connect at the midgut-hindgut junction.
The midgut is the main site of digestion, and most studies of Drosophila gut immunity have focused on this compartment. (B) A cross section of the adult Drosophila midgut. The adult midgut contains several types of cells: absorptive enterocytes (ECs), secretory enteroendocrine cells (EEs), and pluripotent intestinal stem cells (ISCs). Muscle cells are present under the basement membrane of epithelial cells. Between the lumen and epithelia, a semipermeable non-cellular structure, the peritrophic matrix, protects the enterocytes from abrasive particles and pathogens. In addition, a mucus layer lies between the peritrophic matrix and ECs along the midgut
Why do herbivores have longer digestive systems than carnivores
allows a longer transit time, increasing time and surface area for absorption of nutrients from harder to digest plant material.
Fat absorption
Micelles -> fatty acids and monoglycerides
Diffuse across cell membrane of enterocyte
Recombined into fat (TAG) in the ER
Packaged into lipoproteins (+cholesterols and vitamins) – Chylomicrons- released by exocytosis
Too large for capillaries – enter lymph via lacteals –transported to blood.
Chylomicrons then flow into the circulation via lymphatic vessels, which drain into the general circulation at the large veins in the chest. When large numbers of chylomicrons are being absorbed, the lymph draining from the small intestine appears milky and the lymphatics are easy to see. That lymph passes through mesenteric lymph nodes (LN) and then into larger lymphatics.
Monosaccharides absorption
Hydrophilic - can’t diffuse across lipid cell membrane.
Monosaccharides carried across membrane into enterocyte via specific transporters.
Transported across basal membrane into blood via diffusion gradient.
moves across the basal cell membrane through a glucose uniporter (GluT2) via the diffusion gradient and from there into blood where it is carried around the body, either to be used in cells and the brain as required or stored in the liver as glycogen. Fructose is transported in exactly the same way but using a different transporter.
Amino acid and small peptide absorption
The lumenal plasma membrane of the absorptive cell bears at least four sodium-dependent amino acid transporters - one each for acidic, basic, neutral and amino acids. These transporters bind amino acids only after binding sodium. The fully loaded transporter then undergoes a conformational change that dumps sodium and the amino acid into the cytoplasm, followed by its reorientation back to the original form. Thus, absorption of amino acids is also absolutely dependent on the electrochemical gradient of sodium across the epithelium. Further, absorption of amino acids, like that of monosaccharides, contributes to generating the osmotic gradient that drives water absorption. The basolateral membrane of the enterocyte contains additional transporters which export amino acids from the cell into blood. These are not dependent on sodium gradients. There is virtually no absorption of peptides longer than four amino acids. However, there is abundant absorption of di- and tripeptides in the small intestine. These small peptides are absorbed into the small intestinal epithelial cell by cotransport with H+ ions via a transporter called PepT1. Once inside the enterocyte, the vast bulk of absorbed di- and tripeptides are digested into amino acids by cytoplasmic peptidases and exported from the cell into blood. Only a very small number of these small peptides enter blood intact. In the first place, very few proteins get through the gauntlet of soluble and membrane-bound proteases intact. Second, “normal” enterocytes do not have transporters to carry proteins across the plasma membrane and they certainly cannot permeate tight junctions.
