T10: Cell Turnover

What is CELL TURNOVER?

The process of replacing old and damaged cells with new cells.

What processes are involved in CELL TURNOVER?

1. Cell division 2. The maturation of cells 3. The shedding of aged cells

What are the functions of CELL TURNOVER?

1. Helps maintain tissue health 2. Supports repair 3. Prevents cell buildup 4. Prevents dysfunction

What determines the ultimate structure of the clone of cells that develops from the fertilized egg?

The genome of the fertilized egg.

What is the earliest stage of development?

A fertilized egg or zygote.

What does it mean when early embryonic cells are described as potent?

They possess the ability to develop into an entire organism.

What happens as development proceeds?

1. Cells divide 2. Cells gradually become specialized through differentiation

What does differentiation give rise to?

The various tissues and organs of the body.

What examples of organisms are shown in the slide?

1. Sea urchin 2. Mouse

What controls the process of development?

1. Regulated gene expression 2. Cell signaling 3. Developmental pathways

What does the genome of the zygote contain?

A complete set of genetic instructions required to guide the development of a multicellular organism.

What happens as the zygote divides through mitosis?

It produces a clone of genetically identical cells.

What directs differentiation in genetically identical cells?

Gene expression patterns.

What influences gene expression patterns?

1. Intrinsic genetic factors 2. Extrinsic signals

What are examples of extrinsic signals?

1. Chemical gradients 2. Cell-to-cell interactions

What provides the blueprint for development?

The genome.

What determines the ultimate structure and function of the organism?

1. How genetic information is regulated 2. How genetic information is expressed over time

What are tissues?

Organized mixtures of many cell types.

What are tissues in multicellular organisms made of?

Multiple specialized cell types that work together to perform a specific function.

How are cells structurally supported in tissues?

1. Embedded in and supported by an extracellular matrix 2. Arranged in a highly structured way

What cell types are found in epithelial tissue?

1. Epithelial cells 2. Some immune cells 3. Stem cells

What structures and cell types are included in connective tissue?

1. Bone 2. Blood 3. Fibroblasts 4. Immune cells 5. Adipocytes

What cell types mainly make up nerve tissue?

1. Neurons 2. Glial cells

What are the two main layers of mammalian skin?

1. Epidermis 2. Dermis

What cell types are found in the epidermis?

1. Keratinocytes 2. Melanocytes 3. Langerhans cells 4. Merkel cells

What are the functions of keratinocytes?

1. Most abundant cells in the epidermis 2. Produce keratin for protection

What are the functions of melanocytes?

1. Produce melanin 2. Give the skin its color 3. Provide protection against UV radiation

What are the functions of Langerhans cells?

1. Immune cells in mammalian skin 2. Help detect and fight pathogens

What are the functions of Merkel cells?

Involved in touch sensation.

What cell types are found in the dermis?

1. Fibroblasts 2. Macrophages 3. Mast cells 4. Endothelial cells 5. Nerve cells 6. Adipocytes

What are the functions of fibroblasts?

1. Produce collagen 2. Produce extracellular matrix components

What are the functions of macrophages?

1. Function in immune self-defense 2. Involved in inflammatory responses

What are the functions of endothelial cells?

Line the blood vessels within the dermis.

What are the functions of nerve cells in the dermis?

Transmit sensory information within the dermis.

What are the functions of adipocytes?

1. Store fat 2. Provide insulation for the skin

What are the three factors that contribute to tissue stability?

1. Cell communication 2. Selective cell-to-cell adhesion 3. Cell memory

Why is cell-to-cell interaction important?

1. Maintains tissue organization 2. Regulates cellular behavior 3. Vital to the survival of the cell

How do cells exchange signals during cell communication?

1. Through specialized junctions 2. Through signaling molecules

What activities are coordinated by cell communication?

1. Growth 2. Differentiation 3. Response to environmental changes

What mediates selective cell-to-cell adhesion?

1. Adhesion proteins 2. Junctional complexes

What are the functions of selective cell-to-cell adhesion?

1. Helps cells recognize specific neighboring cells 2. Helps cells attach to specific neighboring cells

Why is selective adhesion important?

1. Maintains the structural integrity of tissues 2. Prevents abnormal cell movement

Why is adhesion especially important in epithelial tissues?

Tightly connected cells form protective barriers.

What is cell memory?

The ability of cells to retain information about their identity and previous interactions.

What does cell memory allow daughter cells to do?

Maintain specialized functions after cell division.

What do these factors ensure?

1. Proper tissue development 2. Repair 3. Homeostasis

What can disruption of cell communication, cell adhesion, and cellular memory contribute to?

Diseases such as cancer.

What do cells lose in cancer?

1. Normal growth control 2. Tissue organization

What are stem cell self-renewal and differentiation essential for?

1. Cell turnover 2. Tissue maintenance

What unique ability do stem cells have?

Divide and produce two types of cells.

What are the two types of cells produced when a stem cell divides?

1. One daughter cell remains a stem cell through self-renewal 2. Another cell becomes a precursor cell committed to differentiation

What happens to precursor cells?

1. Continue to divide 2. Gradually become specialized

What are terminally differentiated cells?

Cells that develop specific structures and functions.

Why is the differentiation process important?

Ensures a continuous supply of new cells needed to replace old, damaged, and dead cells.

What tissues require continuous replacement?

1. Skin 2. Blood 3. Intestinal lining

Why is the balance between self-renewal and differentiation important?

1. Maintains tissue homeostasis 2. Maintains normal organ function

What happens if stem cells fail to self-renew?

Tissues may lose their ability to regenerate.

What can uncontrolled proliferation contribute to?

Diseases such as cancer.

What are the roles of stem cells in multicellular organisms?

1. Cell turnover 2. Cell growth 3. Tissue repair

What concepts are presented in the figure?

1. Self-renewal 2. Differentiation 3. Tissue maintenance 4. Regeneration

Where does rapid cell turnover occur in the intestinal epithelium?

1. Villi 2. Crypts of Lieberkühn

Where are stem cells located in the intestinal epithelium?

At the base of the crypts.

What do stem cells in the intestinal epithelium do?

Continuously divide to produce precursor cells.

What specialized epithelial cells do precursor cells differentiate into?

1. Absorptive brush border cells 2. Mucus-secreting goblet cells

What happens as intestinal cells mature?

1. Migrate upward along the villus toward the lumen of the gut 2. Become fully differentiated

What functions do mature intestinal epithelial cells perform?

1. Nutrient absorption 2. Mucus secretion

What happens when cells reach the tip of the villus?

1. Undergo cell death 2. Are shed into the intestinal lumen

How long does epithelial turnover in humans typically take?

3 to 6 days.

Why is constant renewal of intestinal cells necessary?

The gut lining is continuously exposed to: 1. Mechanical stress 2. Digestive enzymes 3. Microorganisms

What processes work together to maintain the intestinal epithelium?

1. Stem cell activity 2. Cell migration 3. Cell shedding

What do these processes help maintain?

1. Intestinal homeostasis 2. Tissue repair 3. Proper digestive function

Where are the stem cells that renew the epidermis located?

1. Basal layer 2. Stratum basale

What is the stratum basale?

The innermost layer of the epidermis.

What processes are involved in epidermal renewal?

1. Differentiation 2. Migration

What cells are present in the basal layer?

1. Epidermal stem cells 2. Basal keratinocytes

What do epidermal stem cells produce?

1. New stem cells 2. Transit amplifying cells

What is the function of new stem cells?

Maintain the stem cell pool.

What happens to transit amplifying cells?

1. Proliferate briefly 2. Eventually differentiate

What happens to newly formed keratinocytes?

Migrate upward through the epidermal layers.

What epidermal layers do keratinocytes pass through?

1. Stratum spinosum 2. Stratum granulosum 3. Stratum lucidum 4. Stratum corneum

What happens as keratinocytes move upward?

1. Undergo terminal differentiation 2. Accumulate keratin

What forms the protective waterproof barrier of the skin?

Dead keratinocytes.

What happens to the dead skin cells over time?

They are continuously shed off.

How long does complete renewal of the epidermis take in healthy adult skin?

Approximately 28 days.

What stem cell gives rise to all circulating blood cell types?

Hematopoietic stem cell (HSC).

Where do hematopoietic stem cells primarily reside?

In the bone marrow.

What is the function of hematopoietic stem cells?

Continuous production of all differentiated blood cells.

What is hematopoiesis?

The process of blood cell formation.

Where does hematopoiesis primarily occur?

In the bone marrow.

When can hematopoiesis occur in other organs?

During stress or disease conditions.

Why is bone marrow important?

It is the only site that can generate blood cells in large and appropriate amounts.

What does blood cell renewal depend on?

The condition and production of hematopoietic stem cells.

What is hematopoiesis?

The continuous process by which all circulating blood cells are produced.

Where are hematopoietic stem cells mainly located?

In the bone marrow.

What are the characteristics of hematopoietic stem cells?

1. Self-renewal 2. Differentiation into all blood cell types

What happens during asymmetrical division of hematopoietic stem cells?

1. One daughter cell remains a stem cell 2. One daughter cell becomes a progenitor or precursor cell

Why does one daughter cell remain a stem cell during asymmetrical division?

To maintain the stem cell pool.

What does the other daughter cell become during asymmetrical division?

A progenitor or precursor cell committed to a specific blood cell lineage.

What are the two major blood cell lineages?

1. Myeloid lineage 2. Lymphoid lineage

What blood cells arise from the myeloid lineage?

1. Erythrocytes 2. Granulocytes 3. Monocytes 4. Platelets