nutrition, osmoregulation &...

© 2014 Pearson Education, Inc.

Nutrition, Osmoregulation & Excretion

(Reference- chapters 41, 44)


The Need to Feed

§  Food is taken in, taken apart, and taken up in the process of animal nutrition

§  In general, animals fall into three categories

§  Herbivores eat mainly plants and algae

§  Carnivores eat other animals

§  Omnivores regularly consume animals as well as plants or algae

§  Most animals are opportunistic feeders


Nutrition

§  An animal’s diet must provide

§  Chemical energy for cellular processes

§  Organic building blocks for macromolecules

§  Essential nutrients


Essential Nutrients

§  Materials that an animal cannot assemble from simpler organic molecules are called essential nutrients, and must be obtained from diet

§  Essential amino acids- meat, eggs, and cheese provide all essential amino acids and are thus “complete” proteins

§  Essential fatty acids- include certain unsaturated fatty acids; fatty acid deficiencies are rare

§  Vitamins- organic molecules required in the diet in very small amounts

§  Minerals- simple inorganic nutrients, usually required in small amounts


Mechanical digestion

Chemical digestion (enzymatic hydrolysis)

Nutrient molecules enter body cells

Undigested material

INGESTION

DIGESTION

ABSORPTION

ELIMINATION

1

2

3

4

Food processing: ingestion, digestion, absorption, and elimination


Suspension Feeding

§  Many aquatic animals are suspension feeders, which sift small food particles from the water

Filter feeding Baleen


Substrate Feeders

§  Substrate feeders are animals that live in or on their food source

Caterpillar

Feces


Fluid Feeders

§  Fluid feeders suck nutrient-rich fluid from a living host


Bulk Feeders

§  Bulk feeders eat relatively large pieces of food


§  Digestion is the process of breaking food down into molecules small enough to absorb

§  Mechanical digestion, such as chewing, increases the surface area of food

§  Chemical digestion splits food into small molecules that can pass through membranes; these are used to build larger molecules

§  In chemical digestion, the process of enzymatic hydrolysis splits bonds in molecules with the addition of water


Figure 41.8

Esophagus

Esophagus

Esophagus

Crop

Crop

Crop

Gizzard

Gizzard

Intestine

Intestine

Anus

Anus

Anus

Mouth

Mouth

Mouth

Stomach

Foregut Midgut Hindgut

Rectum

Gastric cecae

(a) Earthworm

(b) Grasshopper

(c) Bird

Pharynx


Digestion in Mammals

§  The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts

§  Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder

§  Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal

§  Valves called sphincters regulate the movement of material between compartments


Figure 41.9

Tongue

Salivary glands

Oral cavity

Pharynx

Esophagus

Sphincter Liver

Stomach

Gall- bladder

Small intestine

Pancreas

Large intestine

Sphincter

Rectum

Anus

Duodenum of small intestine


Absorption in the Small Intestine

§  The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen

§  The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption

§  Transport across the epithelial cells can be passive or active depending on the nutrient


Figure 41.14a

LUMEN OF SMALL INTESTINE Epithelial cell

Triglycerides

Fatty acids Monoglycerides

Triglycerides

Triglycerides are broken down to fatty acids and monoglycerides by lipase.

Monoglycerides and fatty acids diffuse into epithelial cells and are reformed into triglycerides.

1

2


Evolutionary adaptations of vertebrate digestive systems correlate with diet

§  Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet

Carnivore Herbivore

Omnivore

Incisors Canines Premolars Molars


Stomach and Intestinal Adaptations

§  Many carnivores have large, expandable stomachs

§  Herbivores and omnivores generally have longer alimentary canals than carnivores, reflecting longer time to digest vegetation

Small intestine

Carnivore

Stomach

Cecum

Colon (large intestine)

Small intestine

Herbivore


Mutualistic Adaptations

§  Some intestinal bacteria produce vitamins; intestinal bacteria also regulate the development of the intestinal epithelium and immune function

§  Scientists have found more than 400 bacterial species in the human digestive tract

H. pylori


Mutualistic Adaptations in Herbivores

§  Many herbivores have fermentation chambers, where mutualistic microorganisms digest cellulose

§  The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants

Reticulum

Esophagus

Rumen

Omasum Abomasum

Intestine

4

3

2

1


Regulation of Digestion

§  Each step in the digestive system is activated as needed

§  The enteric division of the nervous system helps to regulate the digestive process

§  The endocrine system also regulates digestion through the release and transport of hormones


Regulation of Energy Storage

§  The body stores energy-rich molecules that are not needed right away for metabolism

§  In humans, energy is stored first in the liver and muscle cells in the polymer glycogen

§  Excess energy is stored in fat in adipose cells

§  When fewer calories are taken in than expended, the human body expends liver glycogen first, then muscle glycogen and fat


Figure 41.UN04

Veins to heart

Lymphatic system

Hepatic portal vein

Liver

Mouth Esophagus

Stomach Lipids

Absorbed food (except lipids)

Absorbed water

Secretions from salivary glands

Secretions from gastric glands

Small intestine Secretions from liver

Secretions from pancreas Large intestine

Anus

Rectum


Osmoregulation

•  Physiological systems of animals operate in a fluid environment

•  Relative concentrations of water and solutes must be maintained within fairly narrow limits

•  Osmoregulation controls solute concentrations and balances water gain and loss


•  Water enters and leaves cells by osmosis •  Osmolarity (solute concentration of a solution)

determines movement of water across a membrane •  If two solutions are iso-osmotic, water molecules cross

the membrane at equal rates in both directions

•  If two solutions differ in osmolarity, net flow of water is from the hypo-osmotic to the hyper-osmotic solution


Figure 44.2

Solutes Water

Selectively permeable membrane

Net water flow

Hypoosmotic side: • Lower solute concentration • Higher H2O concentration

Hyperosmotic side: • Higher solute concentration • Lower H2O concentration


Osmoregulatory Challenges and Mechanisms

•  Osmoconformers (only some marine animals) are iso-osmotic with their surroundings and do not regulate osmolarity

•  Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment


•  Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarity

•  Euryhaline animals can survive large fluctuations in external osmolarity


Marine Animals •  Most marine invertebrates are osmoconformers •  Many marine vertebrates and some marine

invertebrates are osmoregulators •  Marine bony fishes are hypo-osmotic to seawater •  They balance water loss by drinking large amounts of

seawater and eliminating the ingested salts through their gills and kidneys


Figure 44.4a

Osmoregulation in a marine fish

Gain of water and salt ions from food

Excretion of salt ions from gills

Osmotic water loss through gills and other parts of body surface

Excretion of salt ions and small amounts of water in scanty urine from kidneys

SALT WATER

Gain of water and salt ions from drinking seawater

Water Salt

Key


Freshwater Animals •  Freshwater animals constantly gain water by

osmosis from their hypo-osmotic environment •  Lose salts by diffusion and maintain water balance

by drinking almost no water and excreting large amounts of dilute urine

•  Salts lost by diffusion are replaced in foods and by uptake across the gills


Figure 44.4b

Osmoregulation in a freshwater fish

Gain of water and some ions in food

FRESH WATER

Uptake of salt ions by gills

Osmotic water gain through gills and other parts of body surface

Excretion of salt ions and large amounts of water in dilute urine from kidneys

Water Salt

Key


Animals That Live in Temporary Waters

•  Some aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state (anhydrobiosis)

Hydrated tardigrade Dehydrated tardigrade

• 50 µm


Land Animals •  Reducing water loss is key to survival on land •  Body coverings of terrestrial animals limit dehydration •  Desert animals get water savings behaviors such as a

nocturnal lifestyle •  Land animals maintain water balance by eating moist

food and producing water metabolically through cellular respiration


Energetics of Osmoregulation

•  Osmoregulators must expend energy to maintain osmotic gradients

•  The amount of energy differs based on – How different the animal’s osmolarity is from its

surroundings – How easily water and solutes move across the

animal’s surface – Work required to pump solutes across the membrane


Excretion

•  The type and quantity of an animal’s waste products can greatly affect water balance

•  Among the most significant wastes are nitrogenous products of protein breakdown

•  Animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid (differ in toxicity and the energy costs of producing them)


Figure 44.7a

Most aquatic animals, including most bony fishes

Mammals, most amphibians,

sharks, some bony fishes

Many reptiles (including birds),

insects, land snails

Ammonia Urea Uric acid


Excretory Processes

•  Most excretory systems produce urine by refining a filtrate derived from body fluids

•  Key functions of most excretory systems – Filtration: Filtering of body fluids – Reabsorption: Reclaiming valuable solutes – Secretion: Adding nonessential solutes and wastes to

the filtrate – Excretion: Processed filtrate containing nitrogenous

wastes is released from the body


Excretory systems

•  Flatworms have protonephridia- a network of dead-end tubules connected to external openings

•  Each segment of an earthworm has a pair of open-ended metanephridia

•  In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation


Kidneys •  Kidneys, the excretory organs of vertebrates,

function in both excretion and osmoregulation •  The many tubules of kidneys are highly organized •  The vertebrate excretory system also includes ducts

and other structures that carry urine from the tubules out of the kidney and out of the body


Figure 44.12a

Excretory Organs Kidney Structure Nephron Types

Renal artery

Renal vein

Ureter

Renal artery and vein

Ureter

Urethra

Urinary bladder

Kidney


Solute Gradients and Water Conservation

•  The mammalian kidney’s ability to conserve water is a key terrestrial adaptation

•  Hyperosmotic urine can be produced only because considerable energy is expended to transport solutes against concentration gradients

•  The two primary solutes affecting osmolarity are NaCl and urea


Adaptations of the Vertebrate Kidney to Diverse Environments

•  Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in various habitats


Case Study: Kidney Function in the Vampire Bat

•  The South American vampire bat feeds at night on the blood of large birds and mammals, and can alternate rapidly between producing large amounts of dilute urine and small amounts of very hyperosmotic urine


Birds and Other Reptiles •  Birds conserve water by excreting uric acid instead

of urea •  Other reptiles reabsorb water from wastes in the

cloaca


Freshwater Fishes and Amphibians

•  Freshwater fishes conserve salt and excrete large volumes of very dilute urine

•  Kidney function in amphibians is similar to freshwater fishes

•  Amphibians conserve water on land by reabsorbing water from the urinary bladder


Marine Bony Fishes

•  Marine bony fishes are hypoosmotic compared with their environment

•  Kidney filtration rates are low, and very little urine is excreted


Hormonal circuits link kidney function, water balance, and blood pressure

•  Mammals control the volume and osmolarity of urine in response to changes in salt intake and water availability

•  A combination of nervous and hormonal controls manages the mammalian kidney, and also contribute to homeostasis for blood pressure and blood volume


Antidiuretic Hormone

•  Antidiuretic hormone, ADH, regulates water conservation

•  Osmoreceptor cells in the hypothalamus monitor blood osmolarity and regulate release of ADH from the posterior pituitary

•  When osmolarity rises above its set point, ADH release into the blood stream increases

•  ADH reduces urine volume and lowers blood osmolarity

•  Alcohol is a diuretic as it inhibits the release of ADH


Figure 44.UN02

Animal Inflow/Outflow Urine

Freshwater fish. Lives in water less concentrated than body fluids; fish tends to gain water, lose salt

Marine bony fish. Lives in water more concentrated than body fluids; fish tends to lose water, gain salt

Terrestrial vertebrate. Terrestrial environment; tends to lose body water to air

Drinks water Salt in (by mouth)

H2O and salt out

Moderate volume of urine

Urine is more concentrated than body fluids

Small volume of urine

Urine is slightly less concentrated than body fluids

Large volume of urine

Urine is less concentrated than body fluids

H2O in

H2O out Salt in Drinks water

Salt out

Does not drink water Salt in (active transport by gills)

Salt out (active transport by gills)

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