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Animal Diversity and the Body Plan

•  Much of the diversity of animal life centers around the divergence of the body plan.

•  What are some of the important events that shape the evolution of animal body plans?

•  These body plans have formed the framework for subsequent natural selection as form and function coevolve.

•  The basic animal body plan centers around fundamental levels of organization.


•  Levels of Organization:

•  Cells organized into tissues which are organized into organs.

•  What is this increase in complexity with increasing levels of organization known as?

•  It is the subtle (and not-so-subtle) modifications of basic tissues and organ systems that permit form to match function via the process of natural selection.


•  Tissues and types of tissues 1.  Epithelial tissue 2.  Connective tissue 3.  Muscle tissue 4.  Nervous tissue

•  Organized into organ systems

TISSUES

•  Sheets of cells with similar structure and a common function

•  Cell structure studied by histology –  the study of the

microscopic anatomy of cells and tissues

TISSUES

•  Four basic types of tissues:

1.  Epithelial 2.  Connective 3.  Muscle 4.  Nervous

Connective tissue •  Binds and supports

other tissues in the body

•  Comprised of cells separated by non-living material, which is called extracellular matrix

•  Ability to stretch and contract passively

Digestion •  The function of the digestive system is to

prepare food (by mechanical and chemical breakdown) for absorption into the blood or lymphatic system.

•  The resulting nutrients provide the energy that animals need for growth, reproduction, activity and life.

Digestion

•  Many different signals cause reactions within the digestive tract.

•  Can you think of any? •  Sight, smell, taste or even thought of

food can cause (cephalic trigger): Salivation, gastric juice production and

gastric contraction These all prepare the digestive tract for

food.

Digestion

•  Once food is in the stomach (gastric trigger)…

•  The contents and volume initiate reflexes that cause production of more gastric secretions and more gastric motility.

Digestion

•  And the food moves into the intestines (intestinal trigger)…

•  Results in secretion of bicarbonate, enzymes, bile, and increases contractions to mix food with all of these substances.

Sensory system- used to locate food (chemosensory, visual, electrosensory, thermosensory, etc.)

Physical structures used to mechanically break up food

Chemical processes that break food into forms that can be transported in the body and metabolized into other molecules. (enzymatic breakdown)

Undigested material is expelled from the animal

The inner surface of the gastrointestinal tract is contiguous with the external environment!

Digestion

Digestion

Basic dietary strategies:

Carnivory

Herbivory

Omnivory

Feeding structures: specialized mouthparts that assist feeding

Very diverse! Mouthparts may manipulate, suck, crush, shred, etc.

Let’s go on a tour of some interesting mouthparts…..

Snail Radula- rasping mouthparts

Cone snail harpoon

Moths and Butterflies- sucking mouthparts

Darwin’s orchid:

•  Nectar at end of 30cm long spur

•  Charles Darwin theorized that a pollinator must exist with a tongue at least that long.

•  Was not believed at the time

After Darwin's death, the predicted pollinator was discovered, a hawk moth now named Xanthopan morganii praedicta (praedicta meaning predicted).

Specializations in bird beaks

Mammal teeth

Shape of mammalian teeth reflects the nature of the diet.

Mouth

Mechanical breakdown

Saliva moistens and lubricates food

Enzymes in saliva (amylase) does minimal starch breakdown

Lysozymes in saliva are also antibacterial.

Esophagus- transport food to stomach

Stomach

Reservoir for food (2-3 hours)

Food is churned into chyme (liquid food) by mixing with gastric juices

Protein digestion begins

Usually acidic (acid needed to activate enzymes)

Gastric Brooding Frog, Rheobatrachus silus in southeast Queensland. In 1974 it was reported to be unique in the animal kingdom in swallowing its eggs, incubating its young in its stomach, and giving birth to baby frogs through its mouth. This news attracted worldwide attention, but one winter the total population disappeared. It has not been seen for 25 years.

http://www.environment.gov.au/soe/2006/publications/emerging/frogs/index.html

Not ALL vertebrate stomachs are acidic!

Liver

Produces bile salts (stored in gall bladder) to emulsify fats so they can be digested and absorbed. (also plays many other important roles)

Pancreas

Exocrine gland: secretes enzymes into small intestines to digest fats, carbohydrates and proteins.

Endocrine gland: secretes…what?

Insulin and glucagon which regulate glucose metabolism.

Small intestines •  Where the bulk of chemical digestion occurs •  Where most nutrient and water absorption

occurs •  With so much absorption happening, what

might characterize the small intestines? •  Large surface area! Due to length, folds, villi,

microvilli and brush border •  Food remains here ~3-10 hours

Movement through the digestive tract

•  Food moves through by involuntary muscular contractions of the smooth muscle tissue found in the walls of the digestive tract.

•  Peristalsis is waves of contractions of the longitudinal and circular muscles of the gut.

Surface Area! Surface area can be increased in the gut by: increasing the length of the gut and increasing the surface undulations.

In general, the relative length of the gut reflects the digestibility of the diet.

Animals with diets that are difficult to digest often have longer guts to increase digestion efficiency (and absorption of nutrients).

Carnivores generally have shorter guts than herbivores

•  Like other vertebrates, ruminant Artiodactyla (including deer, cows, and their relatives) are unable to digest plant material directly, because they lack enzymes to break down cellulose in plant cell walls.

•  Digestion in ruminants occurs sequentially in a four-chambered stomach.

•  Plant material is initially taken into the Rumen, where it is processed mechanically and exposed to bacteria than can break down cellulose (foregut fermentation).

•  The Reticulum allows the animal to regurgitate and reprocess particulate matter ("chew its cud").

•  More finely-divided food is then passed to the Omasum, for further mechanical processing.

•  The mass is finally passed to the true stomach, the Abomassum, where the digestive enzymes break down the bacteria so as to release nutrients.

Large intestine

•  Some water and salt reabsorption

•  Bacterial fermentation of undigested food

•  Rectum stores waste (undigestible materials) that exit the anus.

What happens in your large intestines?

•  Recovery of water and salts. •  Formation of feces- remains of food is dehydrated, mixed

with bacteria and mucus. •  Bacteria ferment undigested carbohydrates… may

produce socially embarrassing gases! •  Bacteria also synthesize vitamins; e.g. vitamin K is

essential for normal blood clotting. •  Normal feces: 75% water, 25% food waste and bacteria •  Color is due to compounds from bile that are not

absorbed. •  Smell is produced by bacteria.

Water Balance •  In the process of producing and secreting

various digestive juices, the GI tract passes a large quantity of water into the gut lumen.

•  In humans, this volume is usually ~8L/day (1.5 X blood volume)

•  Clearly you do not lose this much through your digestive system (à dehydration)

•  Nearly all is recovered by the intestines- most occurs by solute uptake with water following by osmosis. Note we cannot directly pump water!

Fluid Entering GI Lumen Fluid Absorbed

1500 ml (food and beverage) 1500 ml

2500 ml

1500 ml 500 ml

1500 ml 1000 ml

10,000 ml

9,000 ml

850 ml

150 ml 10,000 ml

Hormones act to enhance or inhibit water absorption (by altering solute uptake).

Circulation & Gas Exchange

General •  Exchanging materials

with environment - happens at cellular level via diffusion

•  Therefore aqueous environment essential –  easy in aquatic,

unicellular or simple multicellular animals

–  simple diffusion inadequate for larger animals

Transport of internal fluids & Gas Exchange

•  Not differentiated in many organisms

•  Highly interconnected in all.

•  Circulatory system: hemolymph, blood

•  Respiratory system: transport of O2 and CO2: body ⇔environment via gills or lungs, trachea systems on land

Circulation

1.  Gastrovascular cavity –  Cnidarians,

Flatworms: few cell layers, all tissues bathed directly

Circulation

2.  Open –  Mollusks (except

cephalopods), Arthropods

–  Hemolymph baths internal organs directly in sinuses

Circulation

3.  Closed –  Annelids,

Cephalopods, vertebrates

–  blood confined to vessels, and transported to tissues/cells

Basic structure of closed system

1.   vessels: arteries ⇒arterioles ⇒ capillaries ⇒ tissues ⇒ venules ⇒ veins

2.   pump: muscular walls of arteries (heart)

3.   Unidirectional: heart ⇒gills ⇒ systemic circuit

Basic structure of closed system

4.  Double circulatory system of tetrapods –  pulmonary –  systemic

Heart - Tetrapod

•  Chambers •  Atrium: receives

blood returning from systemic & pulmonary circuits

•  +O2 from pulmonary •  -O2 from systemic

Heart - Tetrapod

•  Ventricle: receives blood from atrium, contracts (very muscular) to push blood out

•  Pulmonary to lungs back to atria ⇒ventricle ⇒ systemic

Heart - Tetrapod

•  Ventricle undivided in amphibians (3 chambers) •  partially divided in most reptiles (3ish chambers) •  completely divided in birds & crocs, mammals (i.e.

four chambers, no mixing of unoxygenated and oxygenated blood)

Heart - Tetrapod

•  Valves: assure one-way flow: atrioventricular (AV); semilunar valves (base of pulmonary artery, aorta)

Cardiac cycle 1.   Heart beat: •  Diastole: relaxation of

the heart muscles (atria and ventricles fill)

•  contraction = systole –  FIRST, atrial systole –  “lub” - recoil of blood

against closed AV valve –  SECOND, ventricular

systole –  “dub” - recoil against

semilunar valve •  cycle ca 0.8 sec. in

human at rest

Cardiac cycle

2.   Heart rate = beats/min –  affected by oxygen debt, temperature,

hormones etc. 3.   Stroke volume = the amount of

blood pumped in a single contraction

4.   Cardiac output = vol blood/min by left ventricle (rate & vol/beat dependent)

Cardiac cycle 5.  SA node (pacemaker) in wall of right atrium sets

pumping rhythm •  AV node acts as relay

•  Pacemaker

Blood flow 1.  Obeys laws of fluid

dynamics; flows under pressure, faster in larger vessels, slowest in capillaries

2.  Elastic quality of arteriole walls helps smooth out pressure

3.   Blood pressure: peripheral resistance of arterial walls, measured in mm mercury

Blood flow •  The critical exchange of

substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries

•  The difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end

Blood

•  Connective tissue: cells in a liquid matrix “plasma”,

•  solutes (salts, electrolytes for osmotic balance) dissolved in water (90%)

•  Average human 4-6 liters

Blood

•  RBCs - Erythrocytes –  most numerous –  major function: O2 transport

via hemoglobin

•  WBCs – Leukocytes –  travel in interstitial fluid to

fight infections –  5 kinds targeted at different

types of pathogens •  Platelets

–  Chips of marrow cells involved in clotting.

RESPIRATION

•  Mitochondrial respiration consumes O2 and produces CO2.

•  Animals need to exchange gasesà respiration

•  Animals that are larger than a few cells cannot rely on diffusion (remember this occurs slowly over long distances)

•  Animals rely on bulk flow then diffusion: there is an intimate relationship between the circulatory system and the respiratory system.

Structure

•  Only requires a thin, moist simple squamous epithelium w/rich blood supply, interfaces with medium (air or water)

•  Many animals have specialized respiratory organs with large surface areas (to maximize gas exchange): gills (outpocketings, water) or lungs (infolding, air)

•  Remember the skin is also an important gas exchange surface for some animals (cutaneous gas exchange).

Gills •  External extensions

of pharynx, feathery, delicate

•  Advantages: water keeps gills constantly moist

•  Disadvantages: [O2] in water is low compared to air

Air

•  high [O2] , easier to ventilate •  but respiratory surface looses H2O

through evaporation •  air utilized via invaginating respiratory

surface into body

Tracheae - Insects •  tiny air tubes via spiracles •  carry gases directly to tissues, do not use

circulatory system

Lungs

•  vascularized mantel of land snails

•  booklungs - spiders •  air sacs of terrestrial

vertebrates

Mammalian Lung •  Paired invaginations

restricted to single location, circ system must bridge gap to other parts of body

•  Trachea, bronchus, bronchiole, alveoli

•  Ventilation: negative pressure breathing - rib cage and diaphragm

Birds

•  anterior and posterior air sacs •  two cycles inhalation and exhalation required

Homeostasis: Thermoregulation

I.  Thermal Environments II.  Strategies for responding to thermal

environments. III.  Responses to seasonal temperature

changes. IV.  Why thermoregulate? V.  How do organisms thermoregulate?

I.  Ectotherms. II.  Endotherms.

Strategies for responding to thermal environments

•  Some confusing terminology… –  Endotherm –  Ectotherm –  Poikilotherm –  Warm-blooded –  Cold-blooded –  Homeotherm –  Heterotherm* –  Stenotherm* –  Eurytherm*

* terms not used in your textbook


Classic distinctions •  Poikilothermy: body

temperature fluctuates with environment.

•  Homeothermy: body temperature remains constant

•  Ectothermy: body temperature regulated by external sources.

•  Endothermy: body temperature regulated by internal metabolic sources.

•  Poikilothermy/Homeothermy & ectothermy/endothermy vary on a continuum.


More distinctions

•  Homeothermy: Body temperature remains constant.

•  Heterothermy: Body temperature varies.

•  Note that endothermy & ectothermy are distinguished by source of heat, not body temperature.

•  Organisms can be poikilothermic homeotherms. How?

•  Organisms can be endothermic heterotherms. How?


More terminology

•  Eurythermic: wide tolerance range. •  Stenothermic: narrow tolerance range.

•  Examples: Tropical vs. Arctic terrestrial animals.

•  Examples: Polar fish vs. intertidal fish.

Antarctic Ice Fish thermal tolerance range 6 ºC (-1.8º to 4ºC) Intertidal goby thermal tolerance

range >30 ºC (8º to 40ºC)

Physiological Ecology I.  Thermal environments. II.  Strategies for responding to thermal

environments. III.  Responses to seasonal temperature changes. IV.  Why thermoregulate? V.  How do organisms thermoregulate?


How do organisms respond to seasonal temperature changes?

•  Acclimation. •  Hibernation & Estivation.

Acclimation

•  Changes in physiological or biochemical processes in response to some environmental factor.

•  Permits organisms to tolerate temperatures one season that would be fatal or sub-optimal in another.

Acclimation •  Involves biochemical or

physiological adjustments. •  Changes are relatively short

term and are reversible. •  Not all organisms can

acclimate. –  Depends on the amount of

variation in the environment. –  In what environments/

organisms would you expect to see acclimation?

Hibernation & Estivation •  State of reduced metabolism

that may last several months.

•  To avoid cold: hibernation. •  To avoid heat: estivation. •  Must rely on stored energy

reserves. •  Lower metabolic rate

reduces loss of these reserves.

Hibernating ground squirrels may have core temperatures as low as -2ºC

Estivating lungfishes seal themselves in a mud/mucus ball as lake beds begin to dry up

Check out this website on frozen frogs! It’s very, very cool

Why thermoregulate?

Biochemistry •  Increased rate of many chemical reactions. •  Affects solubility. •  Too high temperatures denatures proteins. •  Too low temperatures result in freezing.

Why thermoregulate? Thermal neutral zone

•  The range of environmental temperatures over which the metabolic rate of a homeothermic animal does not change.

•  Not a problem for poikilothermic homeotherms (external environment does not vary).

•  Big problem when external environment varies considerably.

•  Permits endothermic homeotherms to live in environments with higher temperature fluctuations.

Thermoregulation

•  Regulation of body temperature. •  Must manipulate heat gain and loss. •  Via energy transfer processes:

Hs = Hm ± Hcd ± Hcv ± Hr - He

•  What are these variables?


•  Hs: Heat stored in the body (this is what is being thermoregulated!)

•  Hm: Metabolic heat (heat gain through cellular respiration)

•  Hcd: Conduction (transfer of heat between two objects).

•  Hcv: Convection (transfer of heat between solid and liquid or air).

•  Hr: Radiation (transfer through electromagnetic radiation).

•  He: Evaporation (heat loss due to evaporation).

Temperature regulation in ectotherms

•  Temperature dependent upon external environment. –  What variables of Hs = Hm ± Hcd ± Hcv ± Hr - He

can we ignore?

•  How then, do they thermoregulate? –  Which variables can they manipulate?


•  Can manipulate conduction, convection, and radiation.

•  Behavioral patterns –  Habitat selection –  Posture

•  Color •  Growth form


•  When it is too cold the problem is to increase heat storage (maximize the “+” aspect of the equation; minimize the “-” aspect).



•  When it is too hot the problem is to keep heat storage low (minimize the “+” aspect of the equation; maximize the “-” aspect).


Temperature regulation in endotherms

•  Endotherms can maintain body temperatures using cellular respiration.

•  This is energetically expensive (high metabolic costs).

•  Can mitigate this using other mechanisms that have negligible metabolic costs. –  Behavioral & Physiological –  These manipulate Hcd, Hcv, and Hr.

•  Can mitigate this using strategies that decrease Hm and He.


Negligible metabolic costs

•  Vasomotor responses •  Postural changes •  Insulation adjustments •  Microclimate choices

How can conductance and convection change?

•  Insulation –  Pilomotor response

(goosebumps) –  Seasonal fur –  Fat/blubber

•  Vasoconstriction & vasodilation

•  Burrow or huddle (can also decrease Hr)

•  Counter-current exchange.

Decreasing metabolic costs

•  Avoidance and habitat selection

•  Nocturnal activity •  Hibernation or

estivation •  Torpor

Decreasing metabolic costs

•  Avoidance and habitat selection

•  Nocturnal activity •  Hibernation or estivation •  Torpor: Facultative

decrease of metabolic rate. –  Are hummingbirds

homeothermic???

Hummingbirds can have an active body temperature of 40ºC (=104ºF). This is the highest body temperature of any bird. During torpor they may lower this to 12ºC!

Manipulating He

•  Sweat (animals). •  Breathing.

–  Panting.

•  All are tied in with vasomotor control. –  Evaporative surfaces

often heavily vascularized.

Why did endothermy evolve?

•  Metabolically expensive--costs involved. –  Difficult if food is

scarce. –  Metabolic costs

increase 10X--need to eat more.

•  What are the benefits?

Why did endothermy evolve? •  Metabolically

expensive--costs involved.

•  What are the benefits? –  Increased locomotor

activity via increased aerobic ability.

–  Increased responsiveness in varying environments.

–  Ability to exploit more diverse environments.

Summary

•  Animals and plants use numerous mechanisms to cope with temperature variation.

•  There is a broad continuum of thermoregulatory strategies.

•  Thermoregulation can be accomplished through numerous behavioral, morphological, and physiological pathways.

Homeostasis: Osmoregulation & Excretory Systems

Osmoregulation

•  Balances the uptake and loss of water and solutes

•  Cells & tissues are bathed in internal fluids, cannot tolerate dramatic changes in osmotic content – Regardless of external environment: – Marine, freshwater, terrestrial; transitional,

fluctuating

Osmolarity •  Concentrations of solutes

in fluids –  Measured in milliosmoles/

L

•  Hyperosmotic: higher solute concentration

•  Hypoosmotic: lower solute concentration

•  Isoosmotic: equal osmolarity

Osmolarity •  Water and salts will

move down their concentration gradients

•  This presents different challenges for marine, freshwater, and terrestrial organisms.

Transport Epithelium •  Is the specialized tissue

that regulates solute movement.

•  Active transport of ions, small molecules.

•  Controls permeability to water.

Osmoconformers •  Body fluids are

isoosmotic with environment.

•  Most marine invertebrates.

•  Any freshwater? •  Do not lose or gain

water. •  Are there costs to this?

Osmoregulators

•  Adjust internal osmolarity: body fluids have different osmolarity from environment.

•  What they do depends on habitat, adaptation, and phylogeny.

Tolerance

•  Most animals (whether osmoconformers or osmoregulators) cannot tolerate broad changes in external osmolarity: Stenohaline (what does this word remind you of?)

Tolerance

•  Euryhaline animals can tolerate broad changes.

•  Example: salmon travel from freshwater to saltwater to freshwater to breed

Osmoregulators: Chondrichtyes

•  Which animals are these?

•  Where do they live (for the most part)?

•  Sharks and relatives are hyperosmotic (gain water through osmosis). –  Because retain urea

dissolved in body fluids

Urine gets rid of excess water. Salt gland gets rid of excess

sodium.

Osmoregulators: Marine Osteichthyes

•  What kind of animals are these?

•  Bony fishes evolved in freshwater, maintain ancestral freshwater osmolarity

•  Are therefore strongly hypoosmotic (lose water through osmosis).

Drinking constantly. Get rid of salts through chloride

cells in gills and urine

Osmoregulators: Marine Reptiles

•  Have salt glands •  Marine birds: nasal

salt glands •  Crocodile tears •  Marine turtles and

cloacal salt glands •  Marine iguanas:

nasal salt glands

Freshwater animals

•  Problems are opposite to marine

•  ALL animals are hyperosmotic to freshwater, so osmotically take in water

•  Constantly urinating •  Expend energy to

maintain salts

Terrestrial animals

•  Desiccation greatest threat to life on land

•  Humans die if water loss exceeds 12%

•  Helps explain why so few colonizations of terrestrial environments

Water balance in terrestrial animals

•  Water balance is acquisition vs loss

•  Acquisition –  Wd = drinking –  Wf = food –  Wa = absorption

•  Loss –  We = evaporation –  Ws = secretions

•  Overall –  Wia = Wd + Wf + Wa - We - Ws

Adaptations to terrestriality involve maximizing acquisition

while minimizing loss


•  Acquisition strategies when water is limiting: –  Condense fog. –  Metabolic water from food

(oxidation of glucose). •  Water conservation:

–  Prevent evaporation with waterproofing cuticle.

–  Restrict time or place of activity.

–  Concentrate urine or feces.


•  Acquisition strategies when water is limiting:

–  Condense fog. –  Metabolic water from

food (oxidation of glucose).

•  Water conservation: –  Prevent evaporation

with waterproofing cuticle.

–  Minimize evaporation through behavior or morphological structures.








•  Estivation, nocturnality –  Concentrate urine or feces.





–  Minimize evaporation through behavior or morphological structures.



Nitrogenous wastes

•  Nitrogenous wastes come from the metabolic breakdown of proteins or DNA.

•  Byproduct is ammonia, which is highly toxic to tissues.

•  Not a problem for aquatic animals: simply rid ammonia into aqueous environment

Nitrogenous wastes

•  Terrestrial animals cannot do this.

•  Expend energy to convert ammonia into less toxic form.

•  Mammals produce urea –  Does not require dilution

by lots of water –  Water soluble, removed

from fetus via placenta

Nitrogenous wastes

•  Terrestrial animals cannot do this.

•  Expend energy to convert ammonia into less toxic form.

•  Why does this not work for animals with shelled eggs?

•  Reptiles (including birds) and insects produce uric acid –  Precipitate, paste-like, not

water-soluble –  Concentrations in pocket in

egg, does not contaminate interstitial fluids

The Excretory System •  These nitrogenous wastes are

removed from the bloodstream by the excretory system

•  Four components: 1.  Filtration: nonselective, water

and solutes 2.  Reabsorption: returns valuable

substances to body fluids 3.  Secretion: eliminates toxins

and excess salts 4.  Excretion: altered filtrate

(urine) leaves body

Excretory Systems •  Varies widely across animal taxa •  BUT similar theme where form meets function: network of tubules that provide

a large surface area for the exchange of water and solutes •  Protonephridia in flatworms •  Simple tubular system with flame bulb filtration

–  Interstitial fluid ⇒ flame bulb filtration ⇒ external environment

Excretory systems •  Metanephridia: most annelids

–  Excretory tubules with internal opening.

–  Closed circulatory system: metanephridia surrounded by capillaries.

–  Metanephridia take in filtrate, selectively reabsorb solutes.

–  Terrestrial & freshwater annelids (?) live in hypoosmotic environment, metanephridia eliminate large amounts of water.

–  Marine annelids isoosmotic, eliminate ammonia wastes.

Excretory systems

•  Malphighian Tubules: Terrestrial arthropods

•  Open circulatory system •  Dead end tips open into

hemolymph •  Transport epithelium

secretes nitrogenous wastes and solutes into tubules (water follows, how?)

•  Transports to rectum, water and solutes reabsorbed, uric acid eliminated

Excretory systems •  Vertebrate kidney •  Paired compact organs,

principal site of water balance and salt regulation

•  Each kidney is supplied with blood by a renal artery and drained by a renal vein

•  Urine exits each kidney through a duct called the ureter

•  Both ureters drain into a common urinary bladder, and urine is expelled through a urethra

Kidney •  The nephron is the functional unit of the kidney

–  Single long tubule and a ball of capillaries called the glomerulus

–  Bowman’s capsule surrounds and receives filtrate from the glomerulus

Kidney •  Filtration occurs as blood pressure forces fluid from the blood in the

glomerulus into the lumen of Bowman’s capsule •  Filtration of small molecules is nonselective •  The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous

wastes, and other small molecules

Kidney •  From Bowman’s capsule, the filtrate passes through three regions of

the nephron: the proximal tubule, the loop of Henle, and the distal tubule

•  Fluid from several nephrons flows into a collecting duct, all of which lead to the renal pelvis, which is drained by the ureter

Kidney •  Vasa recta are capillaries that serve the

loop of Henle •  The vasa recta and the loop of Henle

function as a countercurrent system

Kidney •  The mammalian kidney conserves water by

producing urine that is much more concentrated than body fluids

•  The cooperative action and precise arrangement of the loops of Henle and collecting ducts are largely responsible for the osmotic gradient that concentrates the urine

•  NaCl and urea contribute to the osmolarity of the interstitial fluid, which causes reabsorption of water in the kidney and concentrates the urine

Urine Concentration in the Kidney

•  Loop of Henle maintains interstitial gradient of NaCl –  Increases in the

descending limb –  Decreases in the

ascending limb –  Energy is expended

to maintain the gradient between the medulla and cortex

Urine Concentration in the Kidney

•  Urea diffuses into the interstitial fluid of the medulla from the collecting duct

•  Filtrate makes three trips between the cortex and medulla

•  As filtrate flows past interstitial fluid of increasing osmolarity, more water moves out by osmosis, conserving water and concentrating urine.

Diversity of the Kidney

•  Reptiles tend to have shorter loops of Henle, conserve by elimination of uric acid (energetically expensive)

•  Mammals in arid environments have extremely long loops

Summary

•  Maintaining homeostasis in osmolarity presents a challenge for all animals.

•  Habitat (marine, freshwater, terrestrial) and phylogeny affect the solutions found in the diversity of animals.

•  Homeostasis and excretion of waste are intricately linked.

The Nervous System

Functional organization of the Nervous System

•  Most animals are bilaterally symmetrical •  Allows for cephalization: concentration

of sense organs and nervous integration centers at the anterior end of the body.

•  Animals move in a particular direction.

•  Vertebrate CNS (central nervous system) is encased in bone and cartilage (brain and spinal cord).

•  The rest is the peripheral nervous system.

The brain and the spinal cord are made up of gray matter (neuron cell bodies and dendrites) and white matter (bundles of axons and associated myelin sheaths).

CNS development •  The brain and spinal cord

develop from a hollow tube (neural tube).

•  The posterior portion forms the spinal cord and the anterior portion swells and forms 3 (basic) sections of brain.

•  The brain and spinal cord are hollow (ventricles in the brain) filled with cerebrospinal fluid (CSF).

Vertebrate Brains

•  Brain size and structure varies greatly among vertebrates (birds and mammals have much larger relative brain sizes than other tetrapods).

•  Presumably this allows for more complex integration.

Vertebrate Brains

•  All vertebrates have the same basic structure of the brain, no new structures, just enlarged sections of brain.

•  In birds and mammals, the forebrain is enlarged.

•  FOREBRAIN: •  Telencephalon →cerebrum •  Diencephalon →hypothalamus, thalamus, epithalamus.

•  FOREBRAIN: •  Telencephalon →cerebrum

• Specialized for information processing, perception, voluntary movement, learning

•  Diencephalon →hypothalamus, thalamus, epithalamus.

• Specialized for processing and integrating sensory information, coordinating behavior, and maintaining homeostasis.

Corpus callosum connects the two hemispheres allowing them to communicate.

MIDBRAIN is greatly reduced in mammals. Important for some coordination and sensory integration.

HINDBRAIN includes the medulla oblongata15, pons14 and cerebellum25-29. Often called the “primitive brain”. Supports vital body functions (breathing, circulation and coordination of movement). Cerebellum integrates sensory input from eyes, ears and muscleà coordination.

The mammalian cerebrum integrates and interprets sensory information and initiates voluntary movements.

Highly folded- WHY?

Four Regions (based on names of bones that overlie them)

Frontal lobe: reasoning, planning of action and movement, and some aspects of speech.

Parietal lobe: movement, orientation, recognition and perception of stimuli.

Occipital lobe: visual processing

Temporal lobe: perception and recognition of auditory stimuli, memory and speech.

Some regions of the brain are organized topographically (homunculus).

The best examples of these are the somatosensory cortex and the primary motor cortex.

In these regions, various parts of the body are represented by disproportionate areas of the brain.

The size of the cortical region typically reflects the number of sensory or motor neurons present in that body part, rather than the size of that body part.

Peripheral Nervous System

•  Afferent neurons- carry sensory information to integrating centers.

•  Efferent neurons- carry signals from integrating centers to govern physiological responses and behaviors.

Peripheral Nervous System

Autonomic Nervous System

•  Involuntary, homeostatic regulation of most physiological functions.

•  Made up of sympathetic, parasympathetic and enteric nervous systems.

•  Sympathetic: “fight or flight”, active during stress or physical activity.

•  Parasympathetic: “rest and digest”, most active during rest.

Autonomic Nervous System

•  Maintain homeostasis via: – Dual innervation: parasympathetic vs.

sympathetic – Creates antagonistic action (stimulate or

inhibit) – Basal tone: even at rest they produce

some action potentials so that increases and decreases in AP frequency can alter the response in the target organ.

Autonomic Nervous System •  All autonomic

pathways contain two (2) neurons in series: –  Preganglionic (in

the central nervous system)

–  Postganglionic (efferent neuron in the periphery)

Anatomical Differences •  Cell bodies of

preganglionic neurons are in different regions of the CNS –  Sympathetic arise

in the thoracic lumbar region

–  Parasympathetic arise in the hindbrain, cranial and sacral regions.

Anatomical Differences

•  Locations of postganglionic neurons are different: –  Sympathetic: close to

spinal cord –  Parasympathetic: close

to effector organ •  So, sympathetic have

short preganglionic and long postganglionic neurons, and vice versa for parasympathetic.

Anatomical Differences

•  Sympathetic preganglionic neurons synapse with 10 or more postganglionic neuronsà widespread effects

•  Parasympathetic preganglionic neurons synapse with 3 or fewer postganglionic neuronsà more localized effects.

Neurotransmitters

•  For both systems, the preganglionic neurons release stimulatory neurotransmitter.

•  Postganglionic in parasympathetic:

•  Inhibitory or stimulatory, but slower acting.

Neurotransmitters •  Sympathetic:

postganglionic cell typically releases norepinephrine.

•  Results in flight or fight response.

•  For instance, the heart rate will increase and the pupils will dilate, energy will be mobilized, and blood flow diverted from other non-essential organs to skeletal muscle.

Regulation •  Autonomic NS regulates

primarily through reflex arcs- simple neural circuits that do not involve the conscious centers of the brain.

•  Sympathetic and parasympathetic often work antagonistically.

•  Ex: control of blood pressure

Somatic Motor Pathways

•  Control skeletal muscle. •  Usually under conscious (voluntary)

control… a.k.a. “voluntary nervous system”.

•  Can you think of an example when muscle control is not under conscious control?

•  Reflexes!

Reflex

•  Patellar tendon (knee jerk) reflex- monosynaptic stretch reflex.

Efferent Motor Pathways are different from the Autonomic N.S. •  Only control one type of effector organ:

skeletal muscle. •  Cell bodies of motor neurons are located in

the CNS, never in ganglia outside of the CNS. •  Monosynaptic- only one synapse between the

CNS and effector organ- can be LONG neurons.

•  Neurotransmitter always excitatory.

Efferent Motor Pathways are different from the Autonomic N.S.

•  Synapse at neuromuscular junction splits into a cluster of axon terminals that branch out over the motor end plate. This allows the neuron to contact more than one muscle fiber.

•  Synaptic cleft is very narrow- diffusion across of NT is very rapid. •  All motor neurons release acetylcholine (ACh). •  Effect of ACh on skeletal muscle is ALWAYS excitatory.

•  Vertebrate skeletal muscle is characterized by a hierarchy of smaller and smaller units

•  A skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle

•  Each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally

Bundle of muscle fibers

Muscle

Single muscle fiber (cell)

Nuclei

Z lines

Plasma membrane

Myofibril

Sarcomere

Skeletal Muscle

•  Skeletal muscle is also called striated muscle because the regular arrangement of myofilaments creates a pattern of light and dark bands

•  The functional unit of a muscle is called a sarcomere, and is bordered by Z lines

Skeletal Muscle

Fig. 50-25

Bundle of muscle fibers

TEM

Muscle

Thick filaments (myosin)

M line

Single muscle fiber (cell)

Nuclei

Z lines

Plasma membrane

Myofibril

Sarcomere

Z line Z line

Thin filaments (actin)

Sarcomere

0.5 µm

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