Tissues

Learning Objectives By the end of this class you should understand: The four tissue types in humans The nature and purpose of stem cells The structural classifications of epithelial tissues and the relationship to their functions The different categories and functions of connective tissue The primary categories and purposes of muscle and neural tissue

Stem Cells The initial fertilized human cell (zygote) is a totipotent stem cell – Can turn into any cell in the human body – A stem cell is immortal and continues to undergo mitosis

Adult cells Most tissues in the body are made of adult (amitotic) cells – A layer of stem cells remains to replenish these cells – These stem cells are NOT totipotent but are still stem cells (e.g. base of skin) These adult cells are arranged into tissues – Group of similar specialized cells that work together

Human Tissues There are four classifications of human tissues Epithelial tissue Connective tissue Muscle tissue Nervous tissue

Tissue Functions Epithelial: Form boundaries between different environments and secrete things Connective: Support, protect and transport Muscle: Contracts (produces force) Nervous: Transmits electrical impulses

Electrical Activity Muscle tissue and Nervous tissue are electrically active – Use ion pumps to create electrical voltage – Use voltage to send signals quickly over long distances Electrically active tissue responds to electrical currents

Epithelial Tissue Epithelial tissues all form boundaries between different environments – Wrapped around most organs – Form exterior of skin and interior of blood vessels, digestive/urinary tracts, etc – Glandular tissue secretes substances into these environments

Epithelial Tissue Types Different epithelial tissues have different structures – The function of any tissue is determined by its structure Epithelial cells may be squamous (flat), columnar (tall) or cuboidal (not too flat or tall) Epithelial tissue may be simple (one layer) or stratified (many layers)

Glandular Tissue A gland is any epithelial tissue that releases a substance that leaves the tissue – Sweat/Mucus/Saliva – Signal molecules (hormones) Any secretion that stays in the bloodstream is called endocrine Any secretion that leaves the bloodstream is called exocrine

What about Digestive Juices? Endocrine tissue releases chemicals into the bloodstream The digestive tract is technically outside the body – Digestive secretions are from exocrine glands

Connective Tissue Connective tissues are the broadest category of tissues – Support, protect, and transport Fibrous connective tissues serve various protective and structural purposes There are also four “special” connective tissues – You have already heard of these!

Muscle Tissue All muscle tissue is stimulated by electrical signals – Some muscle tissue is voluntary (stimulated by nerves coming from the conscious brain) – Other muscle tissue is involuntary (stimulated either by the unconscious brain or automatically)

Muscle Tissue Types Skeletal Muscle – Voluntary – Attached to bones Cardiac Muscle – Heart muscle – Involuntary – Autorhythmic Smooth Muscle – Involuntary – Wrapped around hollow organs such as stomach

Nervous Tissue Nervous tissue consists of two types of cells: – Neurons: electrically active signal cells – Glial cells or neuroglia: Support cells that protect neurons

Brain Tissue

Organs An organ is made of two or more tissues – Almost all have one or more connective tissue layers around the outside An organ serves a specific overall function to regulate homeostasis in some way An organ works with other organs in an organ system

Integumentary System The integumentary system consists of your skin and skin appendages – Can you name all four? We will use this as a model organ and model organ system – Note the different types of tissue found throughout the organ

Skin The skin consists of two layers: – The epidermis (outer part) comprised mostly of epithelial tissue – The dermis (inner part) comprised mostly of connective tissue and blood vessels The skin has a layer below called the hypodermis which is most of the body’s fat reserves

Skin Stem Cells Keratinocyte stem cells (basal cells) live at the bottom of the epidermis, close to the blood supply of the dermis – They are constantly undergoing mitosis Some of the cells become adult keratinocytes and slowly shrivel up and die and become tough – Keratin is also the protein in your hair and nails

Thermoregulation The skin is the key to maintaining body temperature – Heating: arrector pili (smooth muscles) raise goosebumps – Cooling: sweat is produced to evaporate for cooling Blood is flushed to skin for cooling or pulled away to conserve heat Controlled by hypothalamus in brain

Negative Feedback Loop

Homeostasis Homeostasis is maintained by negative feedback loops – Positive feedback loops are self-amplifying and dangerous if not controlled Thermoregulation is just one example of these negative feedback loops

Thermoregulation

That’s the basics! Muscle tissue will be covered in chapters 6 & 8 Nervous tissue will be covered in chapters 11 & 12 Other organ systems that preserve homeostasis will be covered after exam #1!