Internal gill structures of aquatic vertebrates

INTERNAL GILLS

·         Pouched gills: in agnathans – lamp rays

·         Septal gills: in chondrichthyes

·          Aseptal gills: in osteichthyes

Pouched gills

·         Large sac like branchial pouches which are lined with primary gill lamellae.

·         Water goes through mouth àpharynx àpore shaped internal gill slitsàbranchial pouches.

·         Water leaves the branchial pouches through pore shaped external gill slits.

Septal gills

·         Branchial pouches are narrow chambers.

·         Between the branchial chambers, para branchial chambers are present with external gill slits. External gill slits are small and slit shaped.

·         Distal tips of the interbranchial septa can act as valves to close the external gill slits.

·         Gill lamellae runs along the interbranchial septa towards the body surface.

·         Internal gill slits rise from the pharynx and run into each branchial chamber.

Aseptal (non-septal) gills

·         Operculum covers the gills.

·         A single large opercula cavity is present with one valved external gill slit.

·         Interbranchial septa are greatly reduced.

·         Therefore gill lamellae extend freely into the opercula cavity.

(diagram: http://people.eku.edu)

Comparative anatomy of the animal body covering

INVERTEBRATE BODY COVERING

Protozoan body covering

·         Plasma membrane acts as the body covering.

·         Some have an additional gelatinous outer layer.

·         Some have a complex body covering called Pellicle. Ex:- Paramecium

Pellicle

·         Two membranes are present as outer alveolar membrane and outer alveolar membrane.

·         Between those two an alveolar cavity is present.

·         Some have cilia in the pellicle.

Poriferan body covering

·         Thin.

·         Two types of epidermis.

-          Pinacoderm: outer epidermis. Single layer of Pinacocytes. Pinacocytes are scale like falttened cells.

-          Choanoderm: inner epidermis. Single layer of choanocytes. Choanocytes are oval shaped cells with a flagellum on each.

·         Between those to lies the mesoglea or mesenchyma.

·         It’s a jelly like layer consist of spicules and amoebocytes, enclosing a central cavity called spongocoel.

·         Spicules supply strength and amoebocytes give rise to new cells.

·         Ostia are located on the wall.

Cnidarian body covering

·         Similar to that of Poriferan.

·         Outer epidermis: Cuticle is present.

                             Consist of small cubicle cells.

·         Inner gastrodermis: Mainly consist of columnar epithelial cells.

·         Mesoglea: Jelly like layer.

Platyhelminthes, nematode, annelid and arthropod body covering.

·         Single layer epidermis is present.

·         Cuticle is present on the epidermis.

·         Some arthropods have an inner layer of dermis.

VERTEBRATE BODY COVERING

·         Body covering is called as skin.

·         It has a multilayered structure.

·         Consist of two layers as epidermis and dermis.

Epidermis

·         Multilayered.

·         Avascular.

·         Forms structures such as feathers, claws, scales…etc.

·         From top to bottom of the epidermis;

-          Stratum corneum: Dead keratinized cells are on the surface.

-          Stratum germinativum

-          Basal lamina.

Dermis

·         Fibrous connective tissue with blood vessels, nerves and sensory receptors.

·         Fish scales are derived from the dermis.

Fish skin

·         Relatively thin.

·         Derivatives of the skin;

-          Scales: Bony scales derived from dermis.

             Bone cells come into the dermis and secrete scales. Afterwards they leave. Dentine and enamel layers are later deposited on those scales.

-          Melanophores: Star shaped cells that lie under the epidermis.

-          Glands

                                                                                     I.            Mucous glands: unicellular mucous producing glands. Mucous reduce friction when swimming. Produce mucous cocoon to protect from predators and heat in dry seasons. Also prevent invasion of bacteria.

                                                                                  II.            Poison glands: produce poisonous substances.

                                                                               III.            Light emitting glands: aids to attraction, species recognition and avoid predators.

Amphibian skin

·         Thin, moist skin.

·         Can breathe through the skin.

·         Derivatives of the skin

-          Glands

                                                                         I.            Mucous glands: keep the skin moist

                                                                      II.            Granular poison glands: parotid and parotoid glands.

-          Chromatophores: present in epidermis and dermis. Gives colorization.

·         No scales except for some species.

Reptilian skin

·         Thick, dry skin.

·         Stratum corneum is hardened with dead keratinized cells.

·         Can observe two layers in the epidermis.

-          Outer epidermal generation

-          Inner epidermal generation

·         Therefore they can shed scales or called as molting.

·         Scent producing glands are present in some.

·         No mucous glands.

Bird skin

·         Thin but horny scales are on legs and feet.

·         Claws and beak present.

·         Derivatives of the epidermis:

-          Feathers

                                                                 I.            Contour feathers: Cover the body.

                                                              II.            Flight feathers: Cover the wings. Large and stiffer.

                                                           III.            Down feathers:  lie beneath the contour feathers. Fluffy barbs.

                                                           IV.            Bristle feathers: Short and stiff but the barbs are absent.

·         Stratum corneum is not keratinized like in mammals.

·          Dermis lacks ossification.

·         Glands: mainly secrete lipids.

-          Uropygial gland: Single, branched alveolar gland located above the base of the tail. Produces fatty and waxy secretion. This is later spread over feathers to make waterproof.

-          Wax glands: lie in the external ear canal

Mammalian skin

·         Thick epidermis.

·         Transitional layers can be seen between stratum corneum and stratum germinativum.

·         Stratum corneum is thick and forms foot pads in many mammals.

·         Glands:

-          Sebaceous glands: alveolar branched glands that produce oil and wax.

-          Sweat glands: tubular coiled glands.

-          Mammary glands

Fundamentals of thermodynamics:- 1st law, 2nd law and 3rd law short notes

·         Deals with energy and the energy changes.

Thermodynamics can only give information about a system when it is at equilibrium state; a time-invariant state.

When it is based on the concept of equilibrium it’s known as “Equilibrium thermodynamics”.

When it is based on the concept of time-invariant state it’s known as “Thermodynamics of Steady state” or “non-equilibrium thermodynamics”.

Equilibrium thermodynamics: - Only with closed and isolated systems.

System

·         Open: Both matter and energy can transfer between system and surroundings.

·         Closed: Only energy can transfer.

·         Isolated: Neither energy nor matter can transfer.

·         Homogenous system: Consists of a single phase.

·         Heterogeneous system: Consist of two or more phases.

Isothermal: Constant T

Isobaric: Constant P

Isochoric: Constant V

Adiabatic: No heat transfer between the system and the surroundings.

Heat and work do not belong to system and are NOT properties of thermodynamics.

They are operations which performed on the system to alter its energy.

Properties

·         Extensive: Describe and depend on the size of the system. (Mass, volume, pressure…)

·         Intensive: Does not depend on the size of the system. (Molar volume, Molecular weight, Temperature…)

First law

Introduces the concept of internal energy.

·         DQ = U + W

From 1^st law;

When isothermal: DU= 0

                              DQ = DW

At constant volume: DW = 0

                                  DQ = DU

W = - PDV   it is a minus value for a closed system in expansion

W=nRTln.V_f / V_i   Can be taken for an isothermal expansion of a gas

Heat capacity

C=dQ/dT

At constant P: C_p= (dH/dT)_p

At constant V: C_v= (dU/dT)_v

To know how the reaction proceeds we need to know;

·         Enthalpy-H

·         Entropy-S

Enthalpy

DH^o  = å n H^o_products  - å n H^o_reactants

DH = U + PV

DH = C_pdT (as above mentioned in heat capacity)

DH = mCDǾ

Second Law

Describes entropy. Entropy is an idea of randomness in a reaction.

S>0 reaction is spontaneous

S<0 reaction is non spontaneous

S=0 reaction is at equilibrium

·         DS  =  DQ/T

At constant pressure

DS  =  DH/T

Also;

DS_universe  =  DS_system  +  DS_surroundings

DS^o  =  å n S^o_products  -  å n S^o_reactants

Third law

Absolute Entropy, S, =  0  at 0  Kelvins for a perfect crystal of a pure substance.

DG,  Gibbs Free Energy

The maximum amount of energy available to do useful work on the surroundings.

·         DG  = D H – T D S

DG  <  0  (-) Spontaneous

DG  >  0 (+) Spontaneous in the opposite direction       DG  =  0  equilibrium

·         DG^o  =   DH^o  -  T DS^o

DS (+), DH (-) Spontaneous at all temperature

DS (+), DH (+) Spontaneous at high temperatures (where exothermicity is relatively unimportant)     

    

DS (-), DH (-) Spontaneous at low temperatures

            (where exothermicity is dominant)

DS(-), DH (+)  Process not spontaneous at any temperature (reverse process is spontaneous at all temperatures)

·         DG  = DG^o  +  RT ln Q

                       Q  =  Reaction Quotient.

Free energy at equilibrium

·         G  =  0

·         So DG^o  =  -RT ln Q_equilibrium

              Q_equiliibrium  =  K_p (gases)

                                 =  K_c  (solution)