Tissues, organs, and organ systems

Which of the following are never multicellular?

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

Outline

• Introduction-Stem cells• Kinds of Tissues• Organs• Organ systems• The skin• Disorders of the skin• Homeostasis

All human life begins with a single cell

After 3 mitotic divisions, the individual has 8 identical cells

After many divisions, a solid morula becomes a hollow blastula

Morula Blastula

During gastrulation, cells begin to differentiate

Gastrula Gastrula invagination

Frog eggs develop similarly

In vertebrates, 3 kinds of tissue layers (“germ layers”):-Ectoderm: becomes skin, nervous system-Mesoderm: bones, muscles, sex cells, etc.-Endoderm: digestive sys, liver, glands, etc.

All the cells of your body come from that original 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

Adults have some stem cells left

• In places where continual growth and differentiation is necessary– Blood– Hair follicles– Breast tissue– Skin

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

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

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

UrinarySystem

LymphaticSystem

RespiratorySystem

DigestiveSystem

ReproductiveSystem

The Skin

The integumentary system includes the body’s largest organ,

the skin• All 4 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 impact, abrasions

• 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

The epidermis is made primarily of epithelial cells

• New Cells are formed from the basal layer

• Stratum Basale- source of “Epidermal stem cells”

• Cells die and become keratinized (filled with keratin) on the way up

• Spinosum- cells are keratinized

Keratin

• A tough, fibrous protein• Found in hair, nails,

reptile scales, bird beaks, whale baleen

• Holds out water• As hair, skin & nail cells

die, they become keratinized- filled with keratin

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

Disorders of the skin

• Acne• Albinism and Vitiligo• Melanoma

Acne is caused by infection in follicles

Albinisim and vitiligo

Figure 4.12

Melanoma is the deadliest form of skin cancer

Identifying melanoma• Rember your ABCD• Look out for “ugly

ducklings”• Fair skinned people- be

vigilant for light melanoma

• Better yet, avoid it altogether– Wear a hat– Skip the tanning salon– Wear sunscreen?

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 & Skeletal System

Lecture Outline

• Homeostasis• Midterm review• Begin Chapter 9- Senses• Cow eye dissection lab

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?

Cycle of Homeostasis- a receptor, a control center, and an effector

Figure 4.13

Homeostasis

• Then, a control center, such as the brain, integrates the information coming from all receptors and sends out an appropriate response

• The effector carries out the response returning the system to homeostasis again

Homeostasis

• The thermostat for the body is located in the hypothalamus

• Hyperthermia, abnormally elevated body temperature, and hypothermia, abnormally low body temperature, are both life-threatening conditions that result when this mechanism fails

In the human body, the brain controls most Homeostasis mechanisms

Figure 4.14 (1 of 2)

The hypothalamus receives information about changes in the envoronment and responds

Figure 4.14 (2 of 2)

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.

Insulin & Glucagon work together to regulate blood sugar levels

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