Cell Turnover and Growth Processes

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Questions and Answers

What characteristic distinguishes embryonic stem cells from adult stem cells?

Embryonic stem cells are found in differentiated tissues.

Adult stem cells are capable of becoming totipotent.

Embryonic stem cells can give rise to any cell in the body. (correct)

Adult stem cells have a virtually limitless self-renewal capacity.

Where are tissue (adult) stem cells primarily found?

In undifferentiated tissues only

Within differentiated tissues (correct)

In the inner mass of the blastocyst

In the blood circulation

Which type of stem cells are characterized by continuously proliferating cells with a short life span?

Embryonic stem cells

Permanent stem cells

Stable stem cells

Labile stem cells (correct)

What defines permanent stem cells?

They do not persist long into postnatal life. Signup and view all the answers

Which of the following is NOT a source of adult stem cells?

Inner mass of the blastocyst Signup and view all the answers

What is the main role of the G1/S checkpoint in the cell cycle?

To monitor the integrity of DNA before replication Signup and view all the answers

What type of growth refers to an increase in the number of cells by mitosis?

Multiplicative growth Signup and view all the answers

Which phase of the cell cycle is primarily responsible for DNA synthesis?

S phase Signup and view all the answers

What happens to a cyclin after it has completed its round of phosphorylation?

It degrades to regulate CDK levels Signup and view all the answers

Which process involves the specialization of a cell and expression of specific genes?

Differentiation Signup and view all the answers

What is the purpose of morphogenesis during embryogenesis?

To develop structural shape and form Signup and view all the answers

Which of the following is NOT a characteristic of stem cells?

High rate of DNA synthesis Signup and view all the answers

What physiological condition is an example of cell proliferation?

Endometrial tissue during menstrual cycle Signup and view all the answers

Which type of protein forms complexes with CDKs to allow them to phosphorylate substrates?

Cyclins Signup and view all the answers

Which of the following statements about the role of CDKIs is correct?

They can broadly inhibit all CDKs Signup and view all the answers

Which is NOT a type of cell growth described?

Fibrous growth Signup and view all the answers

How can growth be increased according to the content?

By increasing the rate of cell proliferation Signup and view all the answers

What occurs if DNA damage is deemed beyond repair during the cell cycle?

The cell undergoes senescence or apoptosis Signup and view all the answers

What is the primary function of the G2/M checkpoint in the cell cycle?

To assess DNA integrity before mitosis Signup and view all the answers

What are the main factors affecting the size of a cell population?

Cell proliferation and apoptosis Signup and view all the answers

Which statement accurately reflects the relationship between the microenvironment and cell proliferation?

The microenvironment can both inhibit and stimulate proliferation Signup and view all the answers

Study Notes

Cell Turnover

Cell turnover is a presentation on the topic of cell turnover, growth, differentiation, and morphogenesis.
The presentation was given by Dr N Buthelezi in the Department of Anatomical Pathology.
The date of the presentation was January 20, 2025.

Learning Objectives

The learning objectives cover definitions of growth, differentiation, and morphogenesis.
The objectives also cover the cell cycle, types of stem cells, and various tissue types.

Growth, Differentiation, and Morphogenesis

Growth is the process of increasing size through the synthesis of specific tissue components.
Types of growth include:
- Multiplicative: An increase in the number of cells via mitosis, crucial during embryogenesis and in all tissues.
- Auxetic: An increase in the size of individual cells (e.g., skeletal muscle).
- Accretionary: An increase in intercellular tissue components (e.g., bone, cartilage).
- Combined: A combination of these growth types.

Maintaining Cell Populations

Cell proliferation is vital for development and maintaining homeostasis in steady-state tissues.
Cell proliferation also replaces dead or damaged cells.
Cell populations depend on proliferation rates and apoptosis.
Cell proliferation can be stimulated by pathological and physiological conditions.
Physiological examples include endometrial tissue during the menstrual cycle and thyroid tissue during pregnancy.
Pathological stimulation can include after cell death or tissue injury.

Cell Cycle

The cell cycle is a sequence of events leading to cell division.
The cell cycle comprises the following phases:
- G1: Presynthetic growth phase
- Restriction point
- G1/S checkpoint
- S: DNA synthesis
- G2: Premitotic growth
- G2/M checkpoint
- M: Mitosis
The cell cycle's phases have checkpoints to ensure proper DNA replication and prevent damage.

Cell Cycle Regulation

The cell cycle is controlled by activators and inhibitors.
- Cyclins and Cyclin-Dependent Kinases (CDKs)
- CDK inhibitors (CDKIs).
CDKs phosphorylate protein substrates, regulated by cyclin activity.
Cyclin levels fluctuate, affecting CDK activity.

Cyclin-Dependent Kinase Inhibitors

p21 (CDKN1A), p27 (CDKN1B), and p57 (CDKN1C) are broadly inhibitory to CDKs, stopping their activity, which prevents cell cycle progression.
p15 (CDKN2B) p16 (CDKN2A), p18 (CDKN2C), and p19 (CDKN2D) are more selective, impacting CDK4 and CDK6 specifically.

Stem Cells

Stem cells are undifferentiated cells capable of differentiating into various cell types.
Characteristics of stem cells:
- Self-renewal: Maintaining the stem cell pool.
- Asymmetric division: One daughter cell differentiates, while the other retains self-renewal capacity.
Types of stem cells:
- Embryonic stem cells (ES cells): From the inner cell mass of the blastocyst, have virtually limitless self-renewal capacity and can become any cell type (totipotent).
- Tissue stem cells (adult stem cells): Located in differentiated tissues, producing only cell types specific to that tissue (pluripotent, multipotent).
Examples of tissues/locations for stem cells: Bone marrow, hair follicle bulge, eye limbus, canals of Haller in the liver, and supraventricular zone in the brain.
Labile stem cells proliferate continuously, have a brief lifespan, and render tissues susceptible to radiation or drugs (e.g., hematopoietic cells).
Stable stem cells divide infrequently under normal conditions, rapidly dividing when cells are lost (e.g., liver, endocrine glands, bone)
Permanent stem cells' active stem cells do not stay in the system long after birth and cannot be replaced when lost. (e.g., neurons, cardiac muscle).

References

Kumar V, Abbas AK, Fausto N, Aster JC. Robbins and Cotran pathologic basis of disease.
Cross S. Underwood's Pathology: A Clinical Approach. Elsevier Health Sciences; 2018 Mar 9.

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Description

This quiz explores the concepts of cell turnover, growth, differentiation, and morphogenesis as presented by Dr. N Buthelezi in the Department of Anatomical Pathology. It covers essential learning objectives related to the cell cycle, types of stem cells, and various tissue types necessary for understanding these biological processes.