15-17 Flashcards
What is the fundamental problem of animal nutrient acquisition?
How to get small organic molecules containing carbon, nitrogen and sulphur
What are autotrophs, name 2 examples
Organisms that can fix inorganic substances into organic
- plants
- some bacteria
What are heterotrophs?
Organisms which cannot fix inorganic carbon and nitrogen and so rely on autotrophs
- to eat/digest
- symbiosis with fixer - like some hydra symbiont with green alga
What are the 6 main categories of molecules that animals need to acquire?
- Carbohydrates
- Fats
- Amino Acids
- Minerals
- Vitamins
- Roughage
Why do animals need carbohydrate? where do they get it?
- energy
- carbon skeletons of other organic molecules
from - sugars and starches from milk, fruits, seeds and plant storage organs
- basically none from meat or fish
Why do animals need fats, where do they get them?
- for energy, insulation, padding, build other molecules, cell membranes, myelin
- some essential fatty acids are needed
- fats and oils from cell membranes, adipose tissue, oily fish, milk
- some seeds and fruits give enough (avocado and nuts)
What are the mammalian energy sources?
2 main
- brain requires glucose
- cannot use fat
- most carbs into fat for storage and carbs cannot be retrieved from these stores and so need carbs in diet
Why do animals need amino acids, where do get them?
- constructing proteins and also emergency energy source
- needed for growth and reproduction
- maintenance (like hail and nails)
- digestive enzymes need to be made everyday
- cell lining intestines-half replaced in 4 days
- need some in diets as cannot make
- rest from other amino acids and glucose
- from proteins in seeds, milk, eggs and meat/fish
Why is only a little bit of protein needed in daily diet?
cell and protein breakdown gives some amino acids as recycled
- only that which is lost and the essential amino acids to be taken in
Why do animals need minerals? where do they get them?
inorganic cations and anions
- body fluids = Na, K, Cl, Mg, Ca, Phosphate
- crystalline bone = Ca, phosphate
- Thyroxine = Iodine
- Haemoglobin = Fe
- Enzymes cofactors = Mg, Zn, Cu (cytochromes)
Why do animals need vitamins? where do they get them?
organic molecules we require in small quantities but cannot synthesise
a nutrient can be a vitamin for one animal but not for others - Vit C for us and guinea pigs but not for other mammals
What is roughage
- why do we need it
- where do we get it from
- near-indigestible to animals
- cellulose and chitin
- our gut flora extract some nutrients
- without we would be constipated
What is digestion?
Simply it is hydrolysis of macromolecules into monomers that can be absorbed
Polysaccharides —>sugars
Proteins —> amino acids
Fats —> fatty acids and glycerol
How do intestinal parasites get food?
in host - bathed in monomer food already foraged and digested by host
What is intracellular digestion and how does it work?
- single-celled animals internalise particles of foodstuffs and digest them within cell
- Amoeba extends pseudopodia
- phagocytosis—>so in vesicle
- Lysosome with digestive enzymes fuse
- digested absorbed
- waste exocytosis
What is extracellular digestion?
- take food into an internal cavity which is not within a cell
- most have entrance (mouth) and exit (anus or cloaca)
- some ‘batch reactor’ hydra or pitcher plants where one entrance/exit
What are the 4 main sections of an extracellular digestive system (with tube)
- Headgut
- Foregut
- Midgut
- hindgut
What does the headgut do?
specialised for tearing/biting/sucking food
- maybe toxins/anticoagulants/ digestive enzymes
What does the foregut do?
stores food between meals and also grinds it —>through muscular action as most dont chew
What does the midgut do?
secretes digestive enzymes into a fluid slurry
- where most absorption occurs
- small nutrient molecules and water
What does the hindgut do?
resorbs last of water and nutrients
- prepare remains for evacuation through intestinal exit
- some have fermentation chambers here
What parts of nutrient acquisition require energy?
x 5
1) Chewing, squeezing, grinding and peristalsis
2) Synthesis of digestive enzymes
3) Secretion of enzymes, electrolytes
4) Absorption of digestive products
5) Foraging
How do we know what to eat?
1) highly nutritious and non-toxic
- mainly off taste and copying other animals
2 for nice tastes=higher conc to activate = mM to M scale
25 for bitter/nasty=smaller conc=μm to detect
What part of the brain monitors day-to-day weight and overall hunger?
Hypothalamus - Arcuate nucleus
- Leptin from adipose tissue
- Insulin
both enter hypothalamus
What is said to be the ‘hunger centre’ of brain
Lateral hypothalamus
What is said to be the satiety centre of the brain?
ventro-medial nucleus of the hypothalamus
What happens after starvation causes leptin levels to fall?
promote hunger drive
- also heighten sensitivity of reward systems in forebrain
- lessen pituitary secretion of TSH and reproductive hormones
What are temporary satiety signals?
- warn hypothalamus that meal eaten and will be digested
- sweet taste
- stomach stretching
- hormone CCK
What is CCK and when is it released?
- during digestion from duodenum
- control of stomach emptying and secretions, bile and pancreatic secretion
- measure of food in GIT
- important satiety signal
What does GIT stand for?
Gastro-intestinal tract
In humans what is the ‘headgut’?
The mouth
- chew and bite
- saliva
What is the foregut of humans?
stomach
- stores food between meals
- mixes it using smooth muscles
- secretes acid and proteolytic enzymes
- warms food to speed reactions and melt/soften fat
- absorbs ethanol
- stomach secretes intrinsic factor needed for later absorption of Vit B12
- releases chyme into small intestine (midgut) = liquid slurry
What is the midgut in humans?
- small intestine
- first bit is duodenum
- chyme mixed with bile from liver and pancreatic juice
- both alkaline to neutralise stomach acid
- Pancreas juices contain digestive enzymes
- bile stored in gallbladder and contains bile salts which are detergents so easy digestion by lipases
- next is jejunum and then ileum
- lots of fluid secretion
What is the livers job during digestions?
absorb substances that enter blood
- carried directly there by hepatic portal vein
- detoxifies (like ethanol)
- converts absorbed nutrients into final forms for metabolism or storage
What is the hindgut in humans?
large intestine
- sphincter between ileum, caecum and colon
- caecum not very large
- colon responsible for final water absorption
- also contains bacteria that extract some last nutrients from roughage
- make vits = K
What are the two kinds of secretion that make up saliva?
1) serous - fluid, with electrolytes = Na+, Cl-, K+, and proteins (like amylase)
2) Mucus - contains glycoprotein mucin
What are the glands that release saliva?
1) Parotid glands only serous and produced by one set of cells
2) Submandibular = mixed
3) Sublingual = mixed
- mucus is released by mucous cells
what is mucin?
glycoprotein in saliva that makes mucus when in contact with water
- long peptide strands
- polysaccharide side chains which resist proteolytic digestion in stomach
- high negative charge so very hydrophilic
Functions of saliva
x 9
- Forming and lubricating a food bolus to allow swallowing
- Lubricate mouth and throat - speech and swallowing
- initiating starch digestion - amylase
- Neutralising acid that builds up in plaque
- Neutralise acid regurgitated by stomach
- Secreting urea
- route of excretion (just not in humans)
- heat loss (when sweating not possible)
- incapacitate prey by - anticoagulants, poisons, ‘glue’ to catch insects
What is in saliva apart from mucus and serous?
- enzymes - amylase, also others
- immunoglobulins, lysozyme, lactoferrin, lactoperoxidase. Bacteriocidal
- some animals, toxins, anticoagulants
How can GIT protect against microorganisms?
1) bacteriocides and antibodies in saliva
2) throat and small intestine have lymph nodes
3) Stomach acid is pH1.5, so kills bacteria
4) absorbed substances go to liver - detoxified
5) Bitter and sour tastes associated with toxins
6) Pain and nausea from poisoning—>vomiting
How are salivary glands structured?
- branching ducts ending in acini
- serous cells in acini and mucus secreting cells at necks of acini
- parasympathetic innervation from cranial nerves = salivation
Overview of saliva secretion
- fluids and electrolytes actively secreted
- some ions into acinus and other ions follow to balance electrical gradient
- water follows to maintain osmotic
- saliva then follows down ducts and electrolyte composition altered by further active transport = secondary changes
how is the base level of acini cells maintained?
- in salivary glands
- sodium ATPase in basal cell-membrane maintains Na+ gradient
- 2Cl-, K+, Na+ cotransporter uses this to drive Cl- into cell from blood side (secondary active transport)
- build up of Cl- leads to internal negativity and greater outward Cl- gradient
How is primary secretion of saliva activated/carried out?
- Parasympathetic nerve stimulation
- Ca2+ gated anion channels in luminal cell-membrane open
- Cl- and HCO3- now leave into acini lumen
- Negative potential draws Na+ from plasma to saliva between acinus
- Water follows down osmotic gradient
How are secondary changes to saliva in the ducts made?
- saliva down ducts
- Na+ reabsorbed in exchange fro K+
- Cl- reabsorbed in exchange for HCO3-
- Ducts impermeable to water so no water movement
- as net ion uptake, saliva hypotonic to plasma
- final concentrations depend on flow rate
How can HCO3- concentration increase with increasing flow?
- unlike all others which decrease, just at different rates depending on flow
Dont know…
Why does an active gland need 10x greater blood flow than exercising muscle?
needs a lot of energy, so glucose and oxygen
- at peak flow salivary glands secrete 1ml per minute per gram of gland
What are released in parasympathetic nerve endings to promote secretion?
- also vasodilators
1. ACh
2. VIP = vasoactive intestinal peptide
What is the definition of digestion?
Process by which enzymes and acids in the GI tract hydrolyse ingested large molecules into smaller ones suitable for absoption
What are examples of structural carbohydrates?
Most plants have cellulose
- unbranched polymer of glucose with C1-C4 bonds in the β configuration
- insoluble in water
- resistant to most acids and enzymes
Chitin
- invertebrates and fungi
- N-acetyl-glucosamine
What are storage carbohydrates?
Starch
- plants = 10% amylose and 90% amylopectin
Glycogen
C1-C6 similar to amylopectin
Examples of transport carbohydrates
Disaccharides
- maltose, sucrose, lactose, fructose
What carbohydrates can humans not indigestible
Cellulose
Chitin
How is starch digested?
α-amylase in saliva and pancreatic juice - into smaller oligosaccharides - 2-10 monomers Maltose (glucoamylase) Maltotriose (same enzyme) Larger unbranched polymers
Lactase and sucrase
The disaccharides and larger oligosaccharides must be monomers to be digested
What is the importance of microvilli
large surface area and have many digestive enzymes- not secreted in juices but bound to luminal membranes
How is the small intestine adapted to secretion and absorption?
- Surface area
- microvilli, villi, valvulae
roughly 600x increase in surface area
How are carbohydrates absorbed?
DIAGRAM
- Glucose and galactose have one carrier so compete
- SGLT1 using Na+ down its electrochem gradient
Then out of cell into blood by GLUT2 which is facilitated diffusion
FRUCTOSE
- GLUT5 FD
- enters blood by GLUT2 in comp with GandG
Digestion of chitin?
Many animals cant digest chitin
- secrete chitinases
How do animals digestion of cellulose?
Mostly exploit bacteria which produce cellulases
- most have fermentation chamber in the intestine
What happens in foregut fermenters?
foregut greatly expanded and stomach with multiple chambers or blind ended appendages
ANAEROBIC
What happens in hindgut fermenters
- hindgut enlarges with one or more blind ending caeca
(horses)
ANAEROBIC
How is cellulose digested by bacteria?
cellulose + bacteria
—>
small molecules + gas + energy for bacterial growth
Digestion in the cow?
4 chambered stomach
- reticulum and rumen are main fermentation vats and micro-organisms break down cellulose, synthesise vits and conserve/recycle nitrogen
Omasum feeds products of fermentation to abomasum
- acid, enzymes
Glucose not available to cow - used by bacteria
use VFA and Amino acids
What are VFAs?
Volatile fatty acids
- acetic acid
- proprionic acid
- butyric acid
Absorbed into stomachs
- absorbed by simple diffusion as pH is such that they are not ionised
- A and B by liver to long-chain fatty acids
- P into glucose
How do cows lose gas?
Eructation (burping)
- 1-2 litres per minute
- 190 litres of methane a day
Amino acids use in cows
Bacteria produce amino acids from essential one in leaves and urea in saliva
- any protein first de-aminated
- produce ammonia
- diffuses through rumen wall into cow
- into urea which goes into saliva
Amino acids can also be a source of glucose synthesis in the liver by gluconeogenesis
DIAGRAM
How do carnivores get glucose?
- ingest almost no carbohydrates
- made in liver by gluconeogenesis from amino acids
