The Integumentary System

Integument is skin Skin and its appendages make up the integumentary system A fatty layer (hypodermis) lies deep to it Two distinct regions  Epidermis  Dermis

Functions of skin Protection  Cushions and insulates and is waterproof  Protects from chemicals, heat, cold, bacteria  Screens UV Synthesizes vitamin D with UV Regulates body heat Prevents unnecessary water loss Sensory reception (nerve endings)

Epidermis Four types of cells  Keratinocytes – deepest, produce keratin (tough fibrous protein)  Melanocytes - make dark skin pigment melanin  Merkel cells – associated with sensory nerve endings Layers (from deep to superficial)  Stratum basale or germinativum – single row of cells attached to dermis; youngest cells  Stratum spinosum – spinyness is artifactual; tonofilaments (bundles of protein) resist tension  Stratum granulosum – layers of flattened keratinocytes producing keratin (hair and nails made of it also)  Stratum corneum – horny layer (cells dead, many layers thick) (see figure on next slide)

Epithelium: layers (on left) and cell types (on right)

Remember… Four basic types of tissue  Epithelium – epidermis just discussed  Connective tissue - dermis  Muscle tissue  Nervous tissue

Dermis Strong, flexible connective tissue: your “hide” Cells: fibroblasts, macrophages, mast cells, WBCs Fiber types: collagen, elastic, reticular Rich supply of nerves and vessels Critical role in temperature regulation (the vessels) Two layers (see next slides)  Papillary – areolar connective tissue; includes dermal papillae  Reticular – “reticulum” (network) of collagen and reticular fibers

* Dermis layers * * * Dermal papillae

Epidermis and dermis of (a) thick skin and (b) thin skin (which one makes the difference?)

Hypodermis “Hypodermis” (Gk) = below the skin “Subcutaneous” (Latin) = below the skin Also called “superficial fascia” “fascia” (Latin) =band; in anatomy: sheet of connective tissue Fatty tissue which stores fat and anchors skin (areolar tissue and adipose cells) Different patterns of accumulation (male/female)

Skin color Three skin pigments  Melanin: the most important  Carotene: from carrots and yellow vegies  Hemoglobin: the pink of light skin Melanin in granules passes from melanocytes (same number in all races) to keratinocytes in stratum basale  Digested by lysosomes  Variations in color  Protection from UV light vs vitamin D?

Skin appendages Derived from epidermis but extend into dermis Include  Hair and hair follicles  Sebaceous (oil) glands  Sweat (sudoiferous) glands  Nails

Nails Of hard keratin Corresponds to hooves and claws Grows from nail matrix

Hair and hair follicles: complex Derived from epidermis and dermis Everywhere but palms, soles, nipples, parts of genitalia * “arrector pili” is smooth muscle * Hair papilla is connective tissue ________________ Hair bulb: epithelial cells surrounding papilla

Functions of hair  Warmth – less in man than other mammals  Sense light touch of the skin  Protection - scalp Parts  Root imbedded in skin  Shaft projecting above skin surface Make up of hair – hard keratin Three concentric layers  Medulla (core)  Cortex (surrounds medulla)  Cuticle (single layers, overlapping)

Sweat glands Entire skin surface except nipples and part of external genitalia Prevent overheating 500 cc to 12 l/day! (is mostly water) Humans most efficient (only mammals have) Produced in response to stress as well as heat

Review What are the top and bottom layers of the epidermis What are the 4 cell types within the epidermis What structures reside in the dermis? The role that the integumentary system plays? Order these skin layers superficial to deep: dermis, hypodermis, epidermis. Where might you find keratin?

Dissecting the Fetal Pig Sus scrofa

Introduction to Mammals Of all the classes of animal life, mammals are considered to be the most advanced. Examples: dogs, cats, squirrels, pigs, whales, horses, sheep, and HUMANS! Vary greatly in size…from 2 inches (the shrew) to 100 feet long (the blue whale)

Mammalian Characteristics Vertebrates (have backbones) Presence of lungs (breathe air) Warm-blooded (endothermic)  This means that the body temperature of a mammal stays the same, no matter what the outside temperature is 4 chambered heart

Mammalian Characteristics, cont’d Give birth to live young  Monotremes – mammals that lay eggs  EX: the platypus and the echidna (spiny anteater) Body Hair Produce milk (have mammary glands) Platypus Echidna

Mammalian Characteristics, con’t Less Obvious Characteristics  The diaphragm separates the heart and lungs from the stomach  Lower jaw has one bone on each side  Different types of teeth adapted to different uses (tearing, chewing)  Brains are much more highly developed than any other animal

Comparative Anatomy Study of similarities and differences in the anatomy (structure) of organisms Many aspects of structure and function are identical between different species of mammals  Homologous Structures – same structure (embryologically speaking), different function (have a common evolutionary descent) EX: wings of bats and arms of humans  Analogous Structures – different structure, same function (evolved in a similar environment) EX: wings of bats and wings of insects

Comparative Anatomy Fetal PigsHumans KingdomAnimalia PhylumChordata ClassMammalia OrderArtiodactylaPrimates FamilySuidaeHominidae GenusSusHomo SpeciesScrofasapiens

Why Fetal Pigs? The fetal pig is a mammal, like humans. Nearly all the structures are the same or very similar in anatomy. Fetal pigs are NOT bred for the purpose of dissection. They are a by-product of the pork food industry. Fetal pigs are NOT killed for the purpose of dissection. Those that are not dissected are used for fertilizer or discarded. Fetal pigs are relatively inexpensive. Even in the extra large size, when the structures are well-developed, they can be obtained for about 1/3 the cost of a similarly sized cat. Most people do not think of pigs as “pets.”

Advantages to Dissection Dissection is a hands-on, investigatory kind of activity for students. Dissection allows students to "test the truthfulness" of what they see in books. Dissection impresses on students the normal variation that is present in the natural world. No two fetal pigs, even though they are perfectly normal, will look exactly the same. In fact, to do well on practicals, students MUST looks at several examples of each structure in different animals. Occasionally, quite significant anatomical variations (anomalies) will be noticed.

Safety and Handling Sharps  All Dissecting tools should be considered dangerous.  Notify your teacher IMMEDIATELY if you are cut.  Handle probes, dissection scissors, razor blades, etc. with extreme caution.  Always cut away from you, never toward yourself or another person.  Dissection specimens should be properly mounted in the dissection pan before cutting.

Safety and Handling, cont’d Do not place your hands near your mouth or eyes while handling preserved specimens. Most of the preservatives in use today are non-toxic to the skin, but they may cause minor skin irritations. If the preservative gets on your skin, wash with soap and warm water. If the preservative gets in your eyes, rinse them thoroughly with the safety eyewash. Wear lab gloves and goggles at all times! Lab gloves and paper towels go in the regular trash. Skin and pieces of pig go into the separate plastic bag at the front of the room (NOT down the sink).

Dissection Helpful Points Actual cutting should be kept to a MINIMUM Tissue are picked and teased apart with needle probes, forceps, and blunt probes in order to trace the pathways of blood vessels, nerves, muscles, and other structures. NEVER CUT OR MOVE MORE THAN IS NECESSARY TO EXPOSE A GIVEN PART. Compare dissections with other students, especially students whose pig is of a different sex. You will be responsible for both sexes on the lab practical (test).

Determine the Sex of your Pig Female: Look for a single urogenital opening just ventral to the anus. A prominent genital papilla projects from the urogenital opening. Male: Look for the scrotum, a sac-like swelling containing the testes and located ventral to the anus. The male urogenital opening is faintly visible just posterior to the umbilicus. Note that males as well as females have multiple nipples = teats = mammary papillae.

Female Male