Ch 20 Stem Cells and Tissue Removal Textbook Info (Exam 4)

What basic requirements are shared by all specialized tissues?

• mechanical strength

• oxygen

• nutrient supply

• waste disposal

• nerve innervation

• immune defense

• support for specialized cells

What cell type provides mechanical strength in tissues?

fibroblasts and related cells in connective tissue

What cell type lines blood vessels in tissues?

endothelial cells

What is the function of endothelial cells in tissues?

they line blood vessels and provide oxygen, nutrients, and waste disposal

How are most tissues innervated?

by nerve cell axons ensheathed by Schwann cells

What role do Schwann cells play in tissue structure?

they wrap around axons to provide electrical insulation

What cells are responsible for clearing dead or damaged cells and debris?

macrophages

Which cells help fight infection in tissues?

macrophages, lymphocytes, and other white blood cells

What is the function of the supporting apparatus in tissues?

to maintain the principal specialized cells, such as muscle ccells, gland cells, or blood-forming cells

What are the main factors contributing to tissue stability?

• cell communication

• selective cell adhesion

• cell memory

How dcoes cell communication contribute to tissue stability?

cells monitor signals from other cells and adjust behavior accordingly; this ensures proper proliferation and survival

What is selective cell adhesion and why is it important?

the tendency of cells to stick to similar OR specific cell types using adhesion molecules like caherins, helping maintain tissue structure

What molecules are involved in selective cell adhesion?

cadherins and other cell adhesion molecules

How does cell memory help maintain tissue stability?

cells retain their specialized gene expression patterns and pass them on to daughter cells during division, preserving identity

What ensures that a fibroblast produces another fibroblast when it divides?

cell memory, which maintains the pattern of gene expression

Fibroblasts provide

structural support

Endothelial cells

line blood vessels

Schwann cells

insulate nerve axons

Immune cells like macrophages

clear debris and fight infection

Cell communication is when

cells exchange signals to regulate growth, survival, and behavior

Selective cell adhesion is when

cells use specific adhesion molecules (like cadherins) to stick to appropriate neighbors and matrix components, keeping them in the right place

Cell memory is when specialized cells

maintain their identity through stable gene expression patterns and pass this identity to their progeny

What is an example of tissue with very low or no cell turnover?

nervous tissue - most nerve cells last a lifetime without replacement

Which cells are responsible for removing old bone matrix?

osteoclasts

What type of cells deposit new bone matrix?

osteoblasts

Osteoclasts are

akin to macrophages

Osteoblasts are

related to fibroblasts

Where are old RBC destroyed?

in the liver and spleen by phagocytic cells

What effect does high-dose ionizing radiation have on tissues?

it blocks cell division, halting tissue renewal

Why are control mechanisms important in adult tissues?

to maintain balance between cell production and cell loss

How does cancer relate to normal cell turnover?

cancer arises when normal controls on cell renewal are violated, allowing mutant cells to proliferate excessively

Where are new RBC produced?

in the bone marrow by blood-forming precursor cells

What are terminally differentiated cells?

cells that are fully specialized, cannot divide, and lie at the end of their developmental pathway

How are terminally differentiated cells replaced?

by proliferating precursor cells derived from self-renewing stem cells

What are key properties of stem cells?

they are undifferentiated, can divide indeinitely, and can either self-renew or give rise to differentiated cells via precursor cells

What is the role of precursor cells?

they divide and generate terminally differentiated cells but typically do not perform specialized functions themselves

Are stem cells and precursor cells kept in the same tissue as their progeny?

yes, they usually remain within the same resident tissue

Are stem cells developmentally flexible?

no, under normal conditions they are developmentally restricted, meaning they only give rise to specific cell types

What happens to precursor cells in the intestine?

they move upward in the epithelial layer, differentiate into absorptive or secretory cells, and are eventually shed at the villi tips

Where are stem and precursor cells located in the skin?

in the basal layer of the epidermis, attached to the basal lamina

How do skin cells move during differentiation?

outward, perpendicular to the basal layer, eventually being shed from the surface

Can one stem cell type produce multiple differentiated cell types?

yes, for example, intestinal stem cells give rise to absorptive cells, goblet cells, and other secretory cells

What is hematopoiesis?

the process of blood-cell formation from a common hematopoietic stem cell in the bone marrow

What types of cells does hematopoiesis produce?

all blood cells, including red blood cells (for oxygen transport) and many types of white blood cells (for immunity)

Why do stem-cell systems require control mechanisms?

to ensure that new differentiated cells are generated in the correct locations and in the right numbers

What do these control mechanisms rely on?

extracellular signals exchanged between stem cells, their progeny, and other nearby cell types

What type of signaling proteins promote proliferation in intestinal stem cells?

wnt proteins

Where are Wnt signals active in the intestine?

at the base of each intestinal crypt, where they promote stem cell and precursor cell proliferation

How is Wnt signaling confined to the crypt base?

other long-range signals produced in the crypt prevent Wnt pathway activation outside the crypt

What other roles do crypt cells play besides producing Wnt signals?

they exchange signals that regulate cell diversification into either secretory or absorptive cells

What happens if the signaling mechanisms in the intestine are disrupted?

the structure of the gut lining is disrupted, potentially leading to disease

What are two major roles of stem cells in the body?

continual tissue renewal and repair of damaged tissue

What is an example of using stem cells for tissue repair in animals?

transfusing hematopoietic stem cells into irradiated mice to regenerate blood cells and prevent anemia or infection

What are embryonic stem (ES) cells?

pluripotent stem cells derived from early embryos that can proliferate indefinitely and differentiate into nearly all cell types

What does it mean that ES cells are pluripotent?

they can give rise to all tissues and cell types of the body, including reproductive germ-line cells

What can ES cells be induced to do in culture?

differentiate into a wide variety of specific cell types using appropriate extracellular signals

What are induced pluripotent stem (iPS) cells?

cells that are reprogrammed from adult differentiated cells into an ES-like, pluripotent state

What type of adult cells are commonly reprogrammed into iPS cells?

fibroblasts

What properties do iPS cells share with embryonic stem (ES) cells?

ability to proliferate indefinitely, differentiate into many cell types, and (in mice) contribute to tissue formation