Vert Lecture 9 Amniotes

amniotic egg evolved in what period?

Carboniferous

Embryonic amniotes ….

bypass aquatic larval stage, do not form functional gills, and exchange gases by diffusion through the eggshell

waterproof skin

made up of multilayered keratinous epidermis and a thick dermis, hydrophobic lipids in the skin, limits desiccation

albumen

egg white, protects embryo and provides a reservoir of water and protein

Structure of egg: Chorion

EC/ME protection and gas exchange

Structure of egg: yolk sac

nutrients, extraembyronic membrane, lies outside embryos body, nutrients transported via vessels of the circulatory system that develop in the walls of the sac

Structure of egg: Amnion

protection

Structure of egg: Chorioallantoic membrane

EC/ME/EN surface for gas exchange

Structure of egg: Allantois

ME/EN waste storage and gas exchange

amnion and chorion form from the folds of the…

ectoderm and mesoderm

allantois

outgrowth of the embryonic hindgut, composed of endoderm on the inside and mesoderm on the outside. stores nitrogenous waste, vascularizes the chorioallantoic membrane, can give rise to blood vessels

flexible leathery eggshell

generalized amniote condition

placodes

produce different types of epidermal structures, changes in gene expression caused them

metanephric kidneys

• all extant amniotes have them, drain by the ureter, improved water retention

• responsible for maintaining homeostasis of body fluids, regulating extracellular fluid volumes osmolality, ion concentrations, and pH of the blood

ammonia

• Metabolism of protein produces __

• quite toxic, but it is very soluble in water and diffuses rapidly because it is a small molecule. Common in fish, not amniotes.

• Amniote sweat and urine can
  contain small amounts

Urea

• Converted form of Ammonia, less toxic and more water soluble. Can be released in a concentrated solution in urine, thereby conserving water.

• Synapsids do this. We have urea concentrated urine

Uric acid

• Slightly soluble, readily combines with sodium and potassium to form salts—sodium or potassium urate.

• the primary nitrogenous waste product of sauropsids, however they synthesize and excrete __ and recover the water that is released when it precipitates

Lung ventilation

• coastal ventilation

• character of amniotes based on phylogenetic inference

• long trachea supported by cartilaginous rings

Lateral flange of the pterygoid bone

Jaw adductor muscles become divided, allows different modes of processing food

Second cervical vertebra modified into an axis

greater mobility of head on neck allows changes in feeding and social behavior

Astragalus bone and mesotarsal joint

indicates more limb-based (rather than axial-based) locomotion

More than one sacral vertebra

increasing use of hindlimb

Penis

used for internal fertilization

Costal aspiration

higher metabolic rates, allows loss of CO2 via lungs rather than skin

Trachea with cartilaginous rings

allows for longer neck, changes in feeding and social behavior

Amniota has two sister clades

synapsids (mammals), sauropsida (lepidosuars, turtles, crocodilians, birds)

Synapids and sauropsids split __ mya

320

Synapisd (single bar) condition

• single lower temporal fenestra on each side of head

• below fenestra is lower temporal bar

• above fenestra, postorbital and squamosal bones

Diapsid (double bar) condition

• two temporal fenestrae

• lower temporal bar below lower temporal fenestra

• upper temporal bar between lower and upper fenestrae

lower temporal bar formed by

the jugal and quadratojugal bones

convergent evolution of skull fenestration

explained by reorientation and subdivision of the adductor mandibulae in the more domed skull of basal amniotes

jaw closing muscles of a reptiliomorph are relatively simple and contained

beneath the skull roof

axial muscles power __, with the feet functioning mainly as

locomotion, pivot points around which the hindlimb rotates

three small proximal tarsal bones fuse to form the

astralagus

mesotarsal joint

distinct plane of bending, in middle of the ankle, lies between the proximal and distal tarsal bones

Avemetatarsalians

evolved an upright posture and bipedalism, and the plane of motion in the ankle joint secondarily sampled to a mesotarsal joint

dorsoventral flexion

up and down of the spine, does not conflict with lung ventilation

locomotion based on axial muscles works only for

short dashes

lizards that retain ancestral modes of locomotion and ventilation are limited to

short bursts of activity

all amniotes share the presence of a post pulmonary septum, a

sheet of connective tissue in the coelom that separates lungs from digestive organs and forms separate pleural (lungs) and peritoneal (abdominal) cavities

the mammalian diaphragm represents __of post pulmonary septum

muscularization

Synapsid Lungs

• air passes from trachea through a series of progressively smaller passages

• begins with primary bronchi and extends through 23 branch points, final branches end in alveoli

Sauropsid Lungs

• ventilated by unidirectional flow of air over gas-exchange structures called faveoli

Gastralia

• bones in the ventral abdominal wall

• basal amniote character

Sauropsid lung evolution and features

• mobile gastrula

• air sacs

• extended sternum

• immobile lungs

• uncinate processes

Mobile gastralia

• retained in extant crocs

• contraction pulls the gastrula posteriorly, increasing the volume of the abdominal and pulmonary cavities and producing inhalation

extended sternum

• functionally replaced the lost gastrula as a method of ventilating the lungs

• becomes extend posteriorly, and caudal end pivots up and down

air sacs

evolved indepdenlty in pterosaurs and saurischian dinos, retained in birds

immobile lungs

• characteristic of some derived sauropsids

• firmly anchored to dorsal ribs and vertebral column

Uncinate processes

• projections on the ribs seen in maniraptoran Dinos

• muscles that contribute to the forceful movements of the ribs and sternum during inhalation and exhalation

Sauropsid lung evolution and features

• gular pump of monitors

• muscular sling of turtles

• pelvic ventilation of crocs

• hepatic piston of crocs

Gular pump of monitors

ventilate lungs while running by drawing air into gular region through the nares, then closing the arial valves and forcing the air into the lungs by contraction of the gular muscles

Muscular sling of turtles

use a sling created by abdominal muscles, forces viscera upward and compresses the lungs between the viscera and carapace for exhalation

Pelvic ventilation of crocs

• derived character.

• The pubic bones project anteriorly from the
  pelvis and are not fused to the ilium and ischium. The ischiopubic muscles originate on the ischium and insert on the pubic bones; contraction of these muscles causes the pubic bones to rotate ventrally and posteriorly, and that movement increases the volume of the abdominal cavity, allowing the pulmonary cavity and lungs to expand

Hepatic piston of crocs

Extant crocodylians use movement of the liver to ventilate the lungs. The abdominal muscles contract during exhalation, forcing the liver to move toward the head, thus reducing the volume of the pulmonary
cavity. During inhalation, the diaphragmaticus muscle draws the liver posteriorly, increasing the volume of the pulmonary cavity.

Avian respiration

• air capillaries radiate from the
  parabronchi (sometimes called parabronchial lungs).

• Air capillaries intertwine closely with vascular capillaries that carry blood. Air and blood flow pass in opposite directions in a cross-current exchange

• Two groups of air sacs, anterior and posterior, are large, ~9x the volume of
  the lungs, poorly vascularized, and do not participate in gas exchange; they are reservoirs that store air during parts of the cycle to create a through-flow lung.

• Two respiratory cycles are required to move a unit of air through the lung.

• the volumes of the secondary and tertiary bronchi
  and the air capillaries change very little during ventilation, so the blood vessels are not stretched at each respiratory cycle. As a result, the walls of the air capillaries and blood capillaries of birds are thinner than 0.5 μm, reducing the distance O2 and CO2 must diffuse. Rapid diffusion of gas
  between blood and air is probably one of the
  mechanisms that allows birds to breathe at very high elevations.

1st inhalation birds

volume of thorax increase, air → posterior air sacs. air in parabronchi → anterior air sacs

1st exhalation birds

volume of thorax decreases, air in posterior sacs → parabronchi. air in anterior sacs → exterior

2nd inhalation birds

air into anterior sacs → new air into posterior

2nd exhalation birds

air leaves through trachea → posterior to parabronchi

Amniote circulation

• to sustain high levels of cellular metabolism, O2 must be transported rapidly from the lungs to the muscles, and CO2 must move out of the muscles

• heart and blood vessels of the circulatory system are pipelines through which oxygen is distributed to the tissues

mammals retain the __ arch as the aorta, while birds retain the _

left, right

Both lineages (synapsids and sauropsids) __ to a single arch, likely due to

independently reduced, advantages tied to high blood pressure and flow rates

Challenges of high blood pressure? What evolved to protect?

thin and delicate lung tissue can be damaged. Therefore, amniotes evolved separate pressure systems for systemic (body) and pulmonary (lung) circulation.

Mammals and birds have solved the problem of maintaining different blood pressures in the systemic and pulmonary circuits by

separating the ventricle into systemic and pulmonary sides with a permeant septum

Hearts with a ventricular septum: Mammals and birds (pathway)

Deoxygenated blood from posterior returns via inferior vena cava → blood from head, neck, and upper limbs return via paired anterior cardinal veins (superior vena cava in mammals) → this bloodstream enters the right atrium → passes through the right atrioventricular valve into the right ventricle→ through pulmonary semilunar valve into the pulmonary artery→ oxygenated blood then returns from the lungs via the right and left pulmonary veins, entering the left atrium and → passing through the left atrioventricular valve into the left ventricle → exits via the aorta

the ventricular septum allows mammals and birds to maintain blood pressure in the systemic (left) circuit that are _ times the pressure in the pulmonary (right) circuit

6-8

Turtles and lepidosaurs lack what?

a ventricular septum

Turtle and Lepisosaurs heart consist of three main ventricular compartments:

• Cavum pulmonale

• Cavum venosum

• Cavum arteriosum

Turtle and Lepisosaurs heart pathway

deoxygenated blood enters the right atrium → flows into the cave venosum→ oxygenated blood from the left atrium enters the cave arteriosum

• blood redirected between circuits through right to left or left to right shunts

Cavum pulmonale

connected to the pulmonary artery

Cavum venosum

connected to the left and right aortic arches

Cavum arteriosum

receives oxygenated blood from the lungs and connects to the cave venosum

Physiological advantages of intracardiac shunting

• allows flexible blood flow between circuits

• high rate of blood flow during warming carries heat from the skin to the core of the body, whereas low heart rate during cooling delays transport of heat from the core to the skin

• turtles use right-to-left shunt to reduce blood flow to the temporarily nonfunctional lungs during diving and when retracted into their shells

• most species of lizards and turtles heat more than 40% faster than they cool

Crocodilian hearts

• have a ventricular septum, prevents intracardiac shunting

• use extra cardiac shunt controlled by pressure differences between two circuits

• when basking, crocs increase blood flow with right to left shunt through limbs to warm themselves

Blood flow control in crocs

• right aorta open from the left ventricle and receives oxygenated blood

• left aorta and pulmonary artery both exit from the right ventricle

• blood flow controlled by the relative resistance to flow in the systemic versus pulmonary circuits

Blood flow in crocs, activity vs rest

• during activity, high left ventricular pressure ensures both aortas receive only oxygenated blood via the foramen of Panizza, preventing deoxygenated blood from entering circulation

• at rest, equal ventricular pressures allow some deoxygenated blood to flow into the left aorta, supplying the viscera, while the brain continues receiving oxygenated blood

What does the croc ventricular system suggest?

ancient crocs may have been active predators with high metabolic rates and blood pressures

The basis of vertebrate kidney function is the __. Each of these consists of a _ that filters the blood

nephron, glomerulus

loop of Henle

(a portion of the nephron) is a derived character of mammals and is largely responsible for their ability to produce concentrated urine