Tissues, organs, and organ system

Which of the following are never multicellular?

1. Fungi2. Animals3. Plants4. Bacteria5. All can be multicellular

Outline

• Stem cells• Kinds of Tissues• Organs• Organ systems• Homeostasis

All human life begins with a single cell

All the cells of your body come from that single cell

• The process by which one cell becomes many kinds of cells is called differentiation

• There are approximately 200 cell types in the human body

• And 100 trillion cells

Cell differentiation becomes more and more specific during development

• Cells which can differentiate into any kind of cell are called totipotent

• Cells which can differentiate into more than one cell are called pluripotent

Cells differentiate according to signals from their neighbors

• One of the major promises of stem cells comes from this fact

• Stem cells can thus be used to heal damaged tissue, such as nervous tissue, cardiac tissue, or bone marrow

Tissues

Groups of similar cells working toward a common task

There are four major types of human tissue

• Epithelial• Connective• Muscle• Nervous

Epithelial tissue forms body surfaces and lines body cavities

• Squamous tissue- flat, easily passed• Cuboidal- cube-shaped, often secretory• Columnar- Oblong, often formed in glands• Ciliated- featuring cilia

Epithelial tissue is bound to connective tissues by a basement membrane

• Basement membrane- acellular surface made of proteins and polysaccharides

• Usually connects epithelia to loose connective tissue

Epithelial cells can form glands

• A gland- a collection of cells which secrete a product

• Exocrine- release substances through ducts or tubes

Endocrine glands secrete hormones directly into the body

• Hormone- a signalling chemical which is released in one part of the body and affects another part of the body

• Examples- Insulin, Follicle stimulating hormone, testosterone

Connective tissues are diverse in structure

• They include bone, cartilage, adipose tissue (fat cells), blood, etc.

• Most connective tissue exists in an extracellular matrix

• Fibers add flexibility, durability, and strength

Collagen adds tensile strength, elastin flexibility

The extracellular matrix often determines the properties of connective tissues

• Fibrous connective tissues

• Loose- • Dense• Elastic

Adipocytes have very little

extracellular matrix

• Sits beneath skin• Provides insulation,

energy storage• Also protects organs

Bone is a kind of connective tissue

• Osteocytes are surrouned by a matrix rich in collagen and calcium

• Chondrocytes of cartilage

• Blood is also a tissue

Muscle tissue• Contractile tissue• For movement of

body, blood, organs

• Three major kinds– Smooth – Skeletal– Cardiac

• All contain actin and myosin fibers for contraction

Smooth muscle

• Involuntary muscle• Forms contractile

linings of organs and blood vessels

• Found in digestive system, e. g. esophagus

Skeletal muscle

• Mounted on bones for body movement

• Striated• Mostly voluntary

(sometimes involuntary, e. g. reflexes)

• Individual muscles wrapped in connective tissue sheath

Cardiac muscle

• Involuntary muscle of the heart

• Cells communicate with each other closely to allow simultaneous contraction

• Irregular striations

Skeletal, cardiac muscle striations are bands of actin and myosin

Neurons carry messages• Neurons are the basic

unit of the nervous system

• Many connections are the cause of brain’s complexity

• Length increases speed and fidelity of communication

• Neurons communicate with electrochemical signals

Generalized neuron structure

Glial cells provide support

• Schwann cells provide protection, electric insulation

• Astrocytes provide nutrition

The cells in tissues are held together with transmembrane proteins

• Tight junctions- ensures passage of substances through cells

• Adhering junctions allow stretching

• Gap junctions- allow cell-to-cell communication between adjacent cells in a tissues

Protein junctions bind membrane layers to a basement membrane

• Tight junctions usually sit higher- prevent leakage

• Adherens band form a ring around epidermal cells in membrane

• Hemidesmosomes bind epithelial cells to basement membrane

• Gap junctions allow communication between cells

Membranes cover and protect organs and other surfaces

• Two major kinds of membranes:– Epithelial– Connective tissue

• Two major kinds of epithelial membranes:– Mucous: contain glands

to secrete substances– Serous: secrete only

serous fluid

Fig. 4.7, p. 75

When a fertilized egg begins to divide, which cells form first?

1 2 3 4 5

20% 20% 20%20%20%1. bone marrow2. Adipose3. stem cells4. neural5. heart

Muscle that is NOT striped and is involuntary is

1 2 3 4 5

20% 20% 20%20%20%1. cardiac.2. skeletal.3. striated.4. smooth.5. both cardiac and smooth.

Organs

• Collections of tissue which form functions together

• Heart, kidney, etc.• Contained in body

cavities-– Cranial/spinal– Thoracic– Abdominal/pelvic

The heart is an organ• Main tissue: the tissue

forming the greatest mass of the organ

• Heart: cardiac muscle• Sporadic tissues: tissues

comprising a minority of the mass of the organ

• Nervous tissue, connective tissue (blood vessels, etc.)

SUPERIOR (of two body parts, the one closer to head)

INFERIOR(of two body parts,

the one farthest from head)

frontal plane (aqua)

midsagittal plane (green)

ANTERIOR(at or near front of body)

distal (farthest from trunk or from point of origin of a body part)

proximal (closest to trunk or to point of origin of a body part)

POSTERIOR (at or near back of body)

transverse plane (yellow)

Fig. 4.8b, p. 76

Organ Systems work together toward collections of general tasks

Fig. 4.9, p. 77

UrinarySystem

LymphaticSystem

RespiratorySystem

DigestiveSystem

ReproductiveSystem

The integumentary system includes the body’s largest organ,

the skin• Many kinds of

tissue, each comprised of many kinds of cells

• Smooth muscle- for contraction

• Adipose cells- connective tissue

• Sweat/sebaceous glands (endocrine or exocrine?)

Functions of the skin

• Protect body from foreign invaders

• Protect against • Detect environmental

information• Regulate temperature• Synthesize vitamin D

There are 3 basic layers to the skin

• Epidermis, dermis, and hypodermis

• Epidermis- source of structures such as hair follicles, sweat/sebaceous glands

• Made mostly of keratinocytes,

• Melanocytes give skin its color

There are 5 basic layers to epidermis

• Corneum, lucidum, granulosum, spinosum, and basale

• Corneum stratum:– stratified sqamous epithelium– empty, dead cells

• Lucidum- Only in callous forming regions

• Spinosum- cells are keratinized• Basale- source of “Epidermal

stem cells”

There are 3 basic layers to the skin• Dermis

– mostly loose connective tissue– Provides flexibility– Vascularized– Nerve endings terminate – Separation of dermis from

epidermis causes a blister

• Hypodermis/subcutis:– Fatty tissue (50% of body)– Connects skin to bone or

muscle

One cm2 has:• 200 nerve endings• 100 sweat glands• 10 hairs with muscles• 15 oil glands• 12 heat receptors• 25 pressure receptors• 2 cold receptors • 3 blood vessels

Activity-Determine the resolving power of skin

• Procedure1. Prepare 4 tape-bound pin pairs, d = .3cm, .5cm,

1.0cm, 1.5cm2. Determine resolution at ~high fidelity (.8 or

better) for: fingertips, back of hand, forearm, back of neck

3. Record data4. Present results5. Interpret results

Epidermal/dermal layers in closeup

Which of the following statements is false concerning the outermost layer of the

epidermis?1. It is the first to experience any abrasion.2. Keratin provides waterproofing.3. Millions of cells are worn off daily.4. Its cells are undergoing rapid cell division.5. It is called the stratum corneum.

Homeostasis

Homeostasis means “staying the same”

• Recall: Living things do not exist at equilibrium

• Living things do exist at “steady state”

• Living things work to maintain a stable internal environment

G = 0

A closed hydroelectric system

G < 0

A closed system eventually reaches equilibrium

The body works to maintain a constant, stable internal environment

• This requires changes to account for an unstable external environment

• Homeostatic mechanisms exist throughout the body

• Temperature, blood pH, dO2, [glucose], etc. are all regulated by negative feedback

A thermostat operates by negative feedback

• The classic homeostatic mechanism analogy

• How does it work?• What mechanisms must

it contain in order to function properly?

• What is its cost?

Fig. 4.14c, p. 82

smooth muscles in arterioles in skin sweat glands

sweating

adjustment in heat loss

vasoconstriction, vasodilation

adjustment in loss or

conservation of metabolic heat

skeletalmuscles

muscle tone,

shivering

adjustments in muscle activity (in metabolic

heat output)

voluntary changes in behavior

adjustments in heat gain or heat loss

motor neurons

hormonal signals from “thermostat” centers in

hypothalamus

The price of minimizing entropy is the constant expenditure of free energy

Why do you think homeostasis with respect to temperature and

pH might be important?Think of mechanisms and structures

which might depend on a stable internal environment.

A few human body mechanisms operate on positive feedback

• Some are regulated by positive feedback

Other Positive feedback mechanisms in real life

More positive feeback loops

A large increase in the body’s core temperature will cause what change in proteins?

1. Denaturation2. an increase in function3. Replication4. doubling of the rate of a reaction5. a small reduction in the rate of reaction

Which of the following involves a positive feedback mechanism?

1. temperature control2. childbirth3. glucose concentration4. absorption of toxins5. muscle concentration