Mammal Characteristics – Soft Anatomy: Special Skin Glands

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Mammal Characteristics –Soft Anatomy: Special Skin Glands• Endocrine Control:

– Nursing also stimulates the release of oxytocin, thus allowing "milk letdown" (squeezing of milk into milk ducts)

– Lactation and nursing forces a close relationship between mother & young; closely linked to parental investment

Mammal Characteristics –Soft Anatomy: Special Skin Glands

• What constitutes milk?

1) lipids - major energy source2) protein3) sugars (mainly lactose)4) minerals5) water

Mammal Characteristics –Soft Anatomy: Special Skin Glands• Evolution of Mammary glands

– mammary areas (Monotremes = egg laying mammals)

* no nipples, milk soaks fur; young lick/suck milk from fur; mammary areas scattered over ventral surface

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Mammal Characteristics –Soft Anatomy: Special Skin Glands• Evolution of Mammary glands

– nipples (1st found in Marsupials = pouched mammals)

* nipples with mammary hair scattered inside pouch

Marsupials


Marsupial “Pouches”

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• Remaining mammal Orders, i.e., pouchlessmammals, also have nipples but....

* nipples arranged along a primitive line, related to the loss of a pouch


• Arrangement of Nipples along the Primitive Line:

1) inguinal: nipples in groin area; e.g., cow

2) abdominal

3) pectoral: e.g., bats, manatee, higher primates


• Sweat Glands - allow secretion of some wastes & provide evaporative cooling- Broadly distributed in

humans and some ungulates

- Spatial restricted in some mammals (e.g., carnivores, rodents)

- Not found in whales, some bats, and some rodents

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• Sebaceous Glands -connected with the hair follicle- Provides oil for

lubrication of skin & hair (water repellency)

• Scent Glands & Musk Glands – Various uses:

- Mate attractant- Territory marker- Defense


• Adipose tissue (fat) - of special importance to mammals- store energy; heat &

H2O source; insulation

Mammal Characteristics –Physiology

• Circulatory System: - Four-chambered heart,

2 atria 2 ventricles

- (relative to fish, amphibians & birds)

- Double circulatory system - heart split into 2 halves, right & left function as distinct organs

(systemic vs. pulmonary circulation)

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• Circulatory System: - Erythrocytes (rbc) lack

nuclei (i.e., enucleate); carry more oxygen

- Variable heart rates & body size

e.g., masked shrew = ~780 beats/min

mink = ~300 beats/minelephant = ~35 beats/min

Bird rbc (ovoid shaped)

Mammal rbc (except camel)(disc shaped)

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• Respiratory System:trachea

bronchi

bronchioles

alveoli (respiratory surface)

-Numerous clusters of alveoli increases surface area (SA) of lungs


• Respiratory System:- Large muscle

separating thoracic & abdominal cavities (diaphragm) contracts...

- increase volume of thoracic cavity/ decrease pressure, air moves into lungs

- exhale = reverse process

• How do reptiles breath?


• Reproductive System:- Two functional ovaries (platypus only left ovary)

- Ova fertilized in oviduct

- Most mammals are viviparous, except

Monotremes = oviparous

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Mammal Characteristics –Reproductive Physiology

mono = onetremata = opening

-Referring to cloacaopening through which eggs and waste pass


• Marsupials

-still not full development to gestation in a uterus

-not full differentiating of reproductive and excretory systems


- Implantation of embryo in uterine wall for varying lengths of time

- Embryo supplied with nutrients via the placenta

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choriovitelline placenta: found in marsupials

- yolk sac forms a placenta- simple contact with

maternal cells = lack vascularization


chorioallantoic placenta: found in majority of mammals

- rapid diffusion of nutrients between mother & embryo

Villi – highly vascularized


Peramelid placenta:combination of chorioallantoic & choriovitelline placenta found in Order Peramelemorphia

- lacks villi = less SA for exchange

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- Many male mammals have penis supported by a bone (baculum or os penis)

- baculum not found in: *monotremes*hoofed animals *N. A. insectivores *elephants *whales *humans


• Reproductive System:- Testes usually contained in a scrotum outside the body

cavity -- cooling for testes & sperm viability• Digestive System:

- Salivary glands lubricate food for swallowing & begin digestion

- Teeth provide mechanical breakdown; dental patterns suggestive of diet

- Stomach - storage & refinement- Small Intestine - digest & absorb; completion of

digestion, numerous enzymes at work

Digestion

- Large Intestine - water absorption; some food digestion & absorption of nutrients (bacteria, source of vitamin K)

- Complex digestive system in some herbivores - adaptation to high cellulose diet, including symbiotic bacteria

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Two Strategies for High Cellulose Diet:

1) Cecal fermentation(e.g., horses, rabbits)

- cecum with microorganisms

- caprophagy (rabbits)

Digestion - Herbivores

Two Strategies for High Cellulose Diet:

2) Multi-chambered stomach (4 chambers)

(ruminants = cows, sheep, deer….)

- “stomachs” with symbiotic bacteria

rumen reticulum omasumabomasum

Digestion - Herbivores


• Excretory System:- Includes kidney with

nephrons housed within

- Loop of Henle for water conservation

- excretion of urea, not uric acid

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• Sensory System :1) Olfaction

- sensitive sense of smell in some, e.g., insectivores

- absent in porpoises & dolphins

- Vomeronasal organ (flehmen)


• Sensory System :1) Olfaction

- also good in carnivores & rodents

- poor in apes-relation to inter- and intra-

specific relations


• Sensory System :2) Hearing

- well developed in most mammals; substitute for vision in some

- external pinna unique to mammals (capture & funnel incoming sound waves)

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• Sensory System :2) Hearing

- 3 ear ossicles or bones (malleus, incus, stapes)


• Sensory System :3) Vision

- vertebrate eye design- reduced function in some,

e.g., insectivores- nocturnal vs. diurnal



- nocturnal vs. diurnal- rods & cones

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- tapetum lucidum


• Sensory System :4) Touch

- vibrissae (tactile hairs)


• Sensory System :4) Touch

- Seismic communication (fossorial species)

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Mammal Characteristics Physiology

• Thermoregulation & Metabolism:- Importance of adipose tissue- Heat production via cellular respiration- Heat loss via evaporative cooling- Heat conservation via torpor (reduce metabolism &

body temperature)


• Thermoregulation & Metabolism:- High metabolic cost of endothermy

basal rate of metabolism: minimal cost of maintaining normal body temperature during rest

- General trend = basal rate of metabolism increases with decreasing body size

* SA greater relative to volume in smaller mammals

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• Nervous System:Includes: - Central Nervous System (brain & spinal cord)- Peripheral Nervous System (sensory & motor)- Large brain mass relative to other vertebrates


• Nervous System:- Huge increase in cerebrum (= neopallium) SA via folding (convoluted neopallium)

neopallium = control center; center of sensory & motor areas, information processing


• Nervous System:- Wrinkling of the neopallium

implies that the surface of the brain is simply trying to keep pace with the increased volume of the brain; wrinkling is not a function of intelligence

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“Primitive” mammals and intelligence

Quiring & Crile's Curvelog brain weight directly proportional to log body weight

log body weight

log

brai

n w

eigh

t

Higher primatesdolphins

shrewsW

woodchuck

elephant

opossum

dog


• Nervous System:- Placental mammals have a

mass of nerve tissue which provides a bridge between the cerebral hemispheres (= corpus callosum); monotremes & marsupials do not have this feature

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Mammal Characteristics Skeletal Structure

- Relative to reptiles:1) more complete ossification(hardened by Ca salt) & fusion of bones

- Advantages:a) stable anchor for musclesb) joint formation


- Relative to reptiles:2) simplified, i.e., optimal

reduction in number of parts- Advantages: a) saves developmental

/maintenance costsb) more flexible axial skeleton

(i.e., head, backbone, ribs)c) increased limb speed

(appendicular skeleton)


- Relative to reptiles:2) simplified, i.e., optimal

reduction in number of parts- Advantages: d) increased range of movement

of limbse) decreased weight/mass

= quick movement/unit energy ratio

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• e.g., jaw, pelvic girdle, and pectoral girdle

- reduction in # jaw bones in mammals relative to reptiles

- fusion of pelvic girdle (ischium-ilium-pubis), but not in monotremes

fusion, ossification & simplification in pectoral girdle (Fig. 2-13, p. 22)

• Broad stance• Limbs not in line with

center of gravity (CoG)

• Energy-intensive movement

• Upright stance• Limbs more in line

with CoG• More energy efficient

movement

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Mammal Characteristics Skeletal Development

• Reptiles a) continuous bone

growth during much of life (indeterminantgrowth)

b) ossification within an ever growing cartilaginous cap at end of bones

c) lack well-formed joints

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• Mammalsa) bone growth only during

early years of life (determinant growth)

b) ossification occurs early = muscles attachment points & articularsurfaces (bone meets bone), thus well-formed joints are possible


• Mammalsc) epiphysis: articular surface

of long bones

diaphysis: bone shaft

epiphyseal plate: cartilage zone between epiphysis & diaphysis; bone elongation growth (i.e., metaphysis)


• Mammals

- As young mammal matures, epiphyseal plate becomes ossified & epiphyseal line forms; useful for rough age estimate (immature vs. adult)

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Axial Skeleton (head, backbone, ribs)

Five Vertebral Divisions:

1) cervical (neck) -typical 7 cervical vertebrae

2) thoracic (chest) - ribattachment




3) lumbar (lower back) -largest vertebrae; back muscles

4) sacral (pelvis region) -attachment for pelvic girdle

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5) caudal (tail)


Appendicular Skeleton (limbs)Classic "1 block of bone -- 2

block of bone" pattern

• "1 block" refers to 1st long bone leading from axial skeleton

• 1 bone = femur or humerus


Appendicular Skeleton (limbs)• "2 block" refers to 2nd

series of long bones

• 2 bones = tibia & fibula or radius & ulna, respectively

• "1 block – 2 block" pattern began in crossopterygians, an ancestor of amphibian and land mammals

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Appendicular Skeleton (limbs)

• crossopterygians (= lobe-finned fish) in fossil record ~360 mybp

• All represents thought extinct except for coelacanth

Mammal Characteristics Appendicular Skeleton

• Pectoral Girdle- scapula & clavicle (attachment

to sternum)- interclavicle - found in

monotremes; gone in marsupials & placentals

- coracoid & acromion reduced to processes (marsupials & placentals)

- scapula embedded in muscle/no direct articulation to axial skeleton

Comparison of pectoral girdle

echidnaAncient mammal-like reptile

placental mammal

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• Pectoral Girdle- clavicle reduced or absent in

cursorial mammals (runners)- stride length & impact cushion


• Articulations (joints)sutural joints: immovable joint;

found in skullsymphyseal joints: slightly

movable; found in jaw;intervertebral discs; symphysis pubis in humans*

synovial joints: extensive movement; synovial fluid for

lubrication


• Articulations (joints)symphysis pubis in humans* hormonal action in a pregnant

woman causes symphysispubis, sacroiliac & other joints to soften/become flexible....

* widening of pelvic cavity for childbirth

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Some Synovial Joints:

1) gliding: side-to-side/ back-and-forthe.g., intercarpal, intertarsal, sternoclavicular joints

- some marine mammals have mainly gliding joints



2) hinge: bending in 1 plane, only

e.g., knee & elbow



3) ball-and-socket: greatest range of movement in several planes;

e.g., humerus-scapula articulation; femur-pelvic girdle articulation

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Evolution of Skeletal Structure

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Mammal Characteristics – Soft Anatomy: Special Skin Glands

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