Exam 1 Worksheet Short Answers Flashcards
(125 cards)
1
Q
Describe the difference between an ionic bond and a covalent bond
A
In an ionic bond, one atom has given up one or more electrons, leaving it with a positive charge, while the other atom has taken on one or more electrons, leaving it with a negative charge. The attraction between the oppositely charged cation and anion create the ionic bond.
A covalent bond is formed when two atoms share electrons, creating a stronger and more stable bond.
2
Q
How is a hydrogen bond formed?
A
When one atom has a hydrogen atom covalently bound to another atom that exerts a stronger pull on the shared electrons, this creates a polar covalent bond. The hydrogen atom in the bond has a slight positive charge (delta +), and it will be attracted to other molecules with slight negative (delta -) atoms or to outright negatively charged atoms. Thus, the hydrogen bond is a weak bond formed by attractions of opposites, similar to an ionic bond, but weaker because the hydrogen atom involved is not fully + charged.
3
Q
Explain why ions interact easily with water.
A
Water molecules are formed by polar covalent bonds between an oxygen and each of its two hydrogen partners. The hydrogen atoms are thus each delta +, and available to hydrogen bond with any negatively charged atoms (anions). The oxygen atom of a water molecule has a delta2- charge and will be attracted to any positively charged atom (ie: cations). Thus, all ions have electrical attractions to water molecules: anions to the delta+ hydrogen end of the water molecule, cations to the delta 2- oxygen end of the water molecule.
4
Q
A neutral solution would have a pH of
A
7
5
Q
The pH of blood is normally in what range?
A
7.35-7.45
6
Q
A solution with a pH of 12 is
A
basic
7
Q
A solution with a pH of 2 is
A
acidic
8
Q
a solution of pH 5 has ___ times ___ hydrogen ions than a solution of pH 2
A
1000
fewer
9
Q
How would 100-fold decrease in pH affect an enzyme that normally functions at neutral pH?
A
Most enzymes are proteins, and every protein functions best at a certain pH and temperature. For most proteins, this optimum pH is close to blood pH, and this optimum temperature is close to normal body temperature. As pH conditions move away from that ideal, the bonds holding the protein in its optimum shape are affected, causing the protein to bend or unfold into a different shape. Since a protein’s function is dependent on its shape, altered protein shape leads to altered protein (in this case, enzyme) function
10
Q
What is the relationship between an enzyme and the activation energy for a chemical reaction
A
Most chemical reactions in the human body would not take place at body temperature or pH. In other words, it is improbable for two substrates to come together on their own simply by contact. But when an enzyme binds the substrates, it alters their shape enough so that they can bind with one another. The enzyme essentially lowers the energy (the “activation energy”) required for them to interact. Once a reaction has occurred between the substrates, the new product leaves the enzyme. The enzyme then returns to its original shape and is available to catalyze another reaction.
11
Q
Based on what you know about the electron shell model of carbon, explain why carbon forms the backbone of so many organic molecules
A
Carbon has an atomic number of 6, so in the electron shell model would have 4 electrons in its second shell. This atom is stable with 8 electrons in that second shell, so carbon can share pairs of electrons with one, two, three or four other atoms, including other carbon atoms. This leaves carbon as a main building block of a wide variety of organic compounds, of all lengths and branching patterns
12
Q
Why are carbohydrates considered to be “hydrated carbon”?
A
Most carbohydrate molecules are built with carbon atoms that have a hydrogen and an OH group as two of its bonding partners
13
Q
Name the four classes of organic molecules
A
Carbohydrates, lipids, proteins, and nucleic acids
14
Q
Carbohydrates:
A
Its building block - monosaccharides (and disaccharides)
Whether it is hydrophilic or hydrophobic - hydrophilic
The most common forms of the molecule in the body- glucose and its storage form glycogen are important energy molecules; other polysaccharides are found within cells and in extracellular space
15
Q
Proteins:
A
Its building block amino acids
Whether it is hydrophilic or hydrophobic most proteins as a whole are hydrophilic, though within a protein there can be stretches of amino acids that are hydrophobic
The most common forms of the molecule in the body : membrane proteins, enzymes, structural proteins, signaling proteins – there is no end to the classes of important proteins we will find in the human body
16
Q
lipids
A
Its building block fatty acids, glycerol, cholesterol
Whether it is hydrophilic or hydrophobic generally hydrophobic; phospholipids (which are amphipathic) are an important class of lipids with one end hydrophobic and the other hydrophilic
The most common forms of the molecule in the body: cholesterol, phospholipids, fatty acids, glycerol, triglycerides, steroid hormones
17
Q
nucleic acids
A
Its building block deoxyribonucleotides, ribonucleotides
Whether it is hydrophilic or hydrophobic hydrophilic
The most common forms of the molecule in the body DNA, RNA, ATP
18
Q
What is meant by the primary structure of a protein? Secondary? Tertiary? Quaternary?
A
The primary structure simply describes the linear sequence of amino acids in the protein
The secondary structure occurs when amino acids in the primary structure form hydrogen bonds with neighboring amino acids, causing the protein to bend or fold into an alpha helix or a pleated sheet shape
The tertiary structure occurs when amino acids find new neighbors after the protein twisted into its secondary shape; new bonds form and alter the shape into its final form. For most proteins, the tertiary structure is its final shape, and the protein has some function for the body in this final shape.
The quaternary shape of a protein is when one or more proteins, each in their tertiary shape, bind together to form a new conglomerate protein. Each protein part of this bigger protein is now referred to as a protein subunit of the final protein. Usually the tertiary proteins that come together here are not functional on their own – they must form the complex quaternary structure protein to have a function. Only some proteins in the body have a quaternary structure
19
Q
Why are temperature and pH important factors in protein function?
A
Every protein functions best at a certain pH and temperature. For most proteins, this optimum pH is close to blood pH, and this optimum temperature is close to normal body temperature. As pH conditions move away from that ideal, the bonds holding the protein in its optimum shape are affected, causing the protein to bend or unfold into a different shape. Since a protein’s function is dependent on its shape, altered protein shape leads to altered protein function.
20
Q
The four bases used in RNA molecules are
A
guanine, cytosine, adenine, and uracil
21
Q
The four bases used in DNA molecules are
A
guanine, cytosine, adenine, and thymine
22
Q
What are some key differences between RNA and DNA molecules?
A
The sugar molecule used in the nucleotide (ribose in RNA, deoxyribose in DNA)
RNA is single stranded, DNA is double stranded
RNA moves from the nucleus to the cytoplasm, DNA stays in the nucleus (there is also some DNA in mitochondria, which we will not talk about in this course)
23
Q
How is the structure of an ATP molecule related to its function in the body?
A
ATP is an adenosine nucleotide (adenine base off a sugar-phosphate unit) with two additional phosphates, making for 3 total phosphates (“triphosphate”). The terminal phosphate is cleaved, leaving an ADP molecule (adenosine diphosphate), a phosphate, and the energy liberated from the bond which can now power cell reactions.
24
Q
the building blocks of carbohydrates are
A
monosaccharides
25
```
which of the following substances is hydrophobic?
Fatty acid
Nucleic acid
Amino Acid
Glucose
```
fatty acid
26
in an RNA molecule, the backbone of the linear strand if formed by covalent bonds between which groups on adjacent nucleotides
ribose and phosphate
27
most enzymes derive from which class of organic molecules
protein
28
Which portion of the plasma membrane is hydrophobic, and why?
The portion of the phospholipid molecule with the fatty acid tail is hydrophobic because of its nonpolar nature. When phospholipid molecules arrange in a bilayer, the fatty acid tails from each layer of the bilayer face one another, forming a hydrophobic interior to the membrane
29
Which portion of the plasma membrane is hydrophilic, and why?
The portions of the phospholipid molecules contain the phosphate group is charged, and is therefore hydrophilic. The head groups on the inner layer of the bilayer face the interior of the cell (in other words, face the cytoplasm) and the head groups on the outer layer of the bilayer face the exterior of the cell (in other words, face the extracellular fluid)
30
Why do we say that “phospholipids give the plasma membrane its structure, but proteins give the plasma membrane its function?”
Most membranes are built using phospholipid molecules, arranged in a bilayer which serves as a barrier to most substances; the inner, hydrophobic region of the bilayer is impermeable to any polar, charged, or large molecule. Since the primary job of the plasma membrane is to separate the inside of the cell from the outside world, the phospholipid bilayer provides this structure.
While some types of proteins are found on all body cells, other proteins are unique to one cell type or another. Thus, every cell in the body has an array of proteins in its plasma membrane giving every cell a unique identity. These proteins serve a wide variety of functions, so having different proteins gives each cell unique functions
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Transport proteins
move non-lipid soluble solutes across the membrane in either direction
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Receptor proteins
bind signals (e.g. hormones) from other cells and initiate a change within the cell
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Anchoring proteins
attach the cell to its surroundings
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Membrane enzymes
catalyze cell reactions on either the inner or outer surface of the membrane
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Cell-to-Cell proteins
attach cells to other cells
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Recognition proteins
allow cells of the immune system to recognize the cell as self or as foreign
37
Explain the “fluid-mosaic model” of the cell membrane
As the phospholipid molecules are not bonded together, they move freely around within the lipid bilayer and between inner and outer layers of the lipid bilayer. The term mosaic refers to the wide variety (mosaic) of different proteins located in the membrane. Vesicles of membrane and proteins are constantly being added to the plasma membrane, and removed from the plasma membrane, so the complement of proteins in any one cell is always changing
38
what is the relationship of cholesterol to the plasma membrane
cholesterol stabilizes the lipid bilayer
39
how does a water molecule move across the plasma membrane
it moves through the center of an aquaporin molecule
40
if a cell were placed in an isotonic solution, what would happen to the cell size
the cell size would not change
41
Describe the structure of the nuclear membrane
The nuclear membrane is a double membrane, so there are two phospholipid bilayers, one inside the other. Proteins embedded in these membranes form pores (“nuclear pores”) which control movement of substances between the cytoplasm and the nucleoplasm.
42
What is a nucleolus?
A nucleolus is a small, dark, spherical area in the nucleus. These represent areas where there is a lot of activity around particular regions of the DNA, busy transcribing DNA into mRNA and creating ribosomal and tRNA. Nucleoli are a common feature in cells whose principal activity is protein synthesis – cells that make peptide hormones, for example.
43
What is the difference between chromatin and chromosomes?
Chromatin is the loose, uncoiled appearance of DNA in the nucleus; this is what is seen in most stages of the cell cycle. Chromosomes are the most tightly compacted appearance of DNA, seen only during mitosis
44
Explain the relationship between a chromosome and a gene
A gene is a small segment of DNA which carries the genetic code to make a piece of RNA. Some of these RNA transcripts become transfer RNA or ribosomal RNA, but usually when people refer to a gene they mean a segment of DNA is transcribed into messenger RNA. Since messenger RNA is translated into a protein, the term gene most commonly refers to a segment of DNA coding for a protein. Each chromosome contains many genes along its length
45
How do the terms “transcription” and “translation” relate to the process by which a protein is produced from information contained in a gene?
The gene is the segment of DNA containing the information to make the protein. Transcription is the process in which a sequence of bases on the template strand of DNA is used to make a segment of messenger RNA containing a sequence of bases complementary to it. Translation is the process in which the messenger RNA is used to build a sequence of amino acids to form a protein.
46
Where in the cell does this transcription occur?
In the nucleus
47
Where in the cell does translation occur?
At ribosomes in the cytoplasm
48
Describe the structure of a tRNA molecule and relate it to its function in the cell.
tRNA stands for transfer RNA. This is a single strand RNA molecule, bent into a cloverleaf shape. There are two regions of importance on a tRNA molecule. One is at the end, where it binds one of the 20 different amino acids. The other important region is a sequence of 3 bases exposed in another area of the molecule called the anticodon. Transfer RNA picks up amino acids in the cytoplasm and shuttles them to the growing protein at the ribosome; the anticodon helps place it in the correct position during translation. After an amino acid is removed from the tRNA by the ribosome, it leaves the ribosome, and returns to the cytoplasm to pick up another amino acid.
49
What types of proteins are assembled on free ribosomes?
Proteins that do not need to be bound to membranes, or to be sequestered inside vesicles
50
What types of proteins are assembled on fixed ribosomes?
Three classes of proteins need to be synthesized associated with phospholipid membranes, and so are all produced in the rough endoplasmic reticulum. Here, the endoplasmic reticulum provides the membrane while the ribosome fixed to it creates the protein. One class of proteins made in rER is lysosomal enzymes; they are sequestered within the cisternae of the ER as they are produced, transported to the Golgi within a vesicle, and come out of the Golgi still within a vesicle, now called a lysosome. The role of the membrane in this case is to protect the cytoplasm from the digestive enzymes in the lysosome. A second class of proteins made in rER are those that will work at the plasma membrane; these proteins need to thread back and forth through the phospholipid membrane, or tie to phospholipid molecules, processes which need to be completed at the time of synthesis. These proteins are carried to the plasma membrane from the Golgi via vesicles; when the vesicles meet the surface, the entire vesicle fuses into the surface, adding new proteins to the membrane as well as the phospholipids of the vesicle. Finally, proteins to be exported from the cell are produced in rER. These proteins are sequestered in the cisternae of the ER, transported in vesicles to the Golgi, and come out of the Golgi as secretory vesicles. Secretory vesicles merge into the plasma membrane, but the protein contents of the vesicle are released into the extracellular space, a process called exocytosi
51
Describe how a protein destined to become an integral membrane protein is translated, processed, and inserted in the membrane. What organelles are involved
As the messenger RNA for an integral membrane protein begins transcription on a free ribosome, the first few amino acids in the protein sequence are recognized by molecules in the cell as specifying that this is a protein that needs to finish synthesis associated with membrane. The ribosome/mRNA complex moves as a unit to the ER and attaches to its surface. The ribosome then resumes translation, but the protein is now threaded through the membrane of the ER as it is synthesized, with hydrophobic amino acids embedded in the fatty acid center of the membrane, and hydrophilic amino acids on either side of the membrane. When the synthesis of the membrane is completed, it moves with its membrane as a unit to the Golgi apparatus, where final modifications of the protein are made. The protein/membrane unit (usually with many more than one protein embedded in the membrane) moves as a vesicle from the Golgi to the cell surface. There, it will be inserted as a unit into the plasma membrane. Every time membrane proteins are added to the cell surface, membrane is added with them.
52
Enzymes such as RNA polymerase are required in the process of transcription. How do you think this molecule would be produced and how would it get to its site of action?
Proteins required in transcription are needed in the nucleus (where transcription occurs). This molecule is synthesized on a free ribosome in the cytoplasm, and directed through a nuclear pore into the nucleus where it has its action. Because this protein is not tied to membrane, it would not need to be made at rough endoplasmic reticulum by a fixed ribosome.
53
Microfilaments
the smallest; comprised of the protein actin, and located just inside the plasma membrane where they provide structural support and aid in cell movement
54
Intermediate filaments
intermediate in size, about twice the diameter of actin filaments; located throughout the cell and provide structural support and stabilize organelle position
55
Microtubules
largest of the cytoskeletal elements, about twice the diameter of intermediate filaments; provide strength to cell and involved in movement of organelles and (at the time of cell division) the chromosomes
56
Centriole
nonmembranous; located in the centrosome region and serves as the anchoring structure for the microtubule system
57
Golgi Apparatus
membranous; located between the rER and the plasma membrane; receives vesicles from rER with newly synthesized proteins and further modifies the proteins before shipping them to their final destinations
58
Lysosome
membranous; contains numerous types of digestive enzymes (lipases for breaking down lipids, amylases for breaking down carbohydrates, proteases for breaking down proteins); will fuse with endocytotic vesicles and break down materials brought in from outside cell
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Mitochondria
membranous (with a double membrane); energy sources and oxygen are taken in, and carbon dioxide and ATP are produced
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Ribosome
nonmembranous; site of protein synthesis
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Rough Endoplasmic Reticulum
membranous; network of membrane with ribosomes attached when producing proteins that need to be attached to membrane or sequestered inside membrane.
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Smooth Endoplasmic Reticulum
membranous; network of membranes (without ribosomes) that serve as the site of carbohydrate and lipid synthesis
63
Which of the following structures is the center of activity in the process of transcription?
nucleolus
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In which of the following structures would you find deoxyribonucleic acid
chromatin
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The organelle responsible for directing newly formed proteins to their destination in the cell is the
golgi apparatus
66
microfilaments
form a web of protein strands under the plasma membrane
67
What does it mean if a cell is in the G0 stage?
A cell in G0 stage has ceased to cycle and no longer divides. These cells are basically stuck in the activities of early G1, performing all the day-to-day activities of an adult cell except division
68
Distinguish between the following similar words: chromosome, chromatin, chromatid
Chromosomes are the DNA in its most compact state and are visible during cell division
Chromatin is the name for DNA during interphase, when it is unwound and spread out within the nucleus and accessible for transcription or copy
Chromatids are the special case for compact chromosomes when the duplicate chromosomes formed by DNA synthesis are compacted as chromosomes but tied to their duplicate chromosome; the two bonded chromosomes are referred to as twin chromatids or sister chromatids
69
Distinguish between the following similar words: centriole, centrosome, centromere
Centrioles are organelles comprised of tubulin protein and serve as the anchoring point in the cell for the microtubule array (microtubules are also made of the protein tubulin).
The region of the cell containing the pair of centrioles, along with a network of proteins, forms an organizing area called the centrosome.
The centromere is the region where two sister chromatids are joined together; they are pulled apart during anaphase by separation at the centromere.
70
Briefly describe the process by which a chromosome is duplicated
The DNA strands are separated, and each strand has DNA polymerase molecules attached. Deoxyribonucleotides (the building blocks of DNA) within the nucleus form hydrogen bonds with the exposed complementary bases, and the DNA polymerase links the new nucleotides together to form a new strand of DNA. Each chromosome formed in DNA synthesis contains one of the original strands (called the parent strand) and one newly synthesized strand. The end result is two identical DNA double helix molecules that remain joined to one another somewhere along their length at a region called the centromere
71
Describe the role of the centrioles in cell division
Centrioles are the anchoring point for the microtubule array in the cell. Centrioles are duplicated prior to cell division, resulting in two pairs of centrioles entering mitosis. During prophase, one pair of centrioles moves to each end (pole) of the cell. The microtubules re-align between these two centriole regions as the mitotic spindle.
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G1
basic cell maintenance activities, growth in size, duplication of organelles, prep for S phase
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S
duplication of each of the 46 chromosomes, resulting in 46 chromatid pairs
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G2
synthesis of the proteins needed for mitosis, final cell growth
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Prophase
centriole pairs move to opposite poles and microtubules arrange into spindle; nuclear membrane disappears
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Metaphase
chromatids line up along center of spindle as the metaphase plate
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Anaphase
microtubules pull twin chromatids apart, with each end of cell getting 46 daughter chromosomes
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Telophase
nuclear membrane reappears, mitotic spindle disappearsand chromosomes unwind to chromatin
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cytokinesis
the division of the cytoplasm and formation of two cells
80
how does a tumor form? what is metastasis?
Tumors form when cells lose the normal controls regulating the cell cycle. This may be due to DNA damage or to other signaling problems. Normally there are genes coded in the DNA that stimulate entry into cell division, and also proteins coded in DNA that inhibit cell division. DNA mutations can affect either of these gene groups, resulting in over-stimulation of division, or under-repression of cell division. Both conditions lead to uncontrolled division and the formation of tumors. Other cancers occur when signals from outside the cell trigger uncontrolled cell division. A tumor is an abnormal solid mass of cells formed from uncontrolled cell division.
Sometimes cells in a tumor mutate further, and develop the ability to move away from their neighbor cells, digest away the barriers that hold them in position, and travel through body tissues, blood, or lymph to form new tumors in other parts of the body. This process is called metastasis.
81
In a cell which divides every 50 days, which stage of the cell cycle is likely to be of longest duration?
G1 phase
82
In which stage of the cell cycle would the DNA appear as chromosomes visible with a light microscope?
anaphase
83
The process by which a cell breaks away from its primary tumor and migrates to a distant site in the body to establish a new tumor is called
metastasis
84
define tissue
A tissue is a collection of embryologically related, specialized cells (and sometimes their secretions) that work together to perform specialized functions
85
name the four tissue types the body
epithelial, connective, muscle, and nervous
86
gap junctions
proteins extend between cells, linking together in the extracellular space to form a pore connecting the cytoplasm of one cell with the cytoplasm of the adjacent cell, allowing rapid and direct movement of ions between cells
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tight junctions
the plasma membrane of one cell is directly linked by proteins right against the surface of the adjacent cell, leaving no extracellular space between cells; the cells appear to be fused together
88
Desmosomes
proteins link one cell to another across the extracellular space, but there is space between cells for materials to move. This junction anchors cells together rather that fusing them together
89
Describe how a sheet of cells can function as a tissue that separates compartments in the body
Because all the cells in the sheet are linked together, substances cannot pass from one surface of the sheet to the opposite surface by passing in the extracellular fluid between cells. Instead, the cells must transport (via passive or active transport processes) the substance across their plasma membrane at one side of the sheet, through the cytoplasm, and out of the cell across the plasma membrane on the other side of the sheet. In this way, the sheet regulates permeability between compartments, much as a plasma membrane regulates permeability between the inside and outside of a single cell
90
Contrast the process of Direct Communication with Paracrine Communication between two cells
In direct communication, the two cells are close enough together to be connected by a gap junction. The gap junction forms a pore between the two cells, so that signals, carried by ion movement, can pass from the cytoplasm of one cell directly into the cytoplasm of the adjacent cell without having to pass through a membrane. In paracrine communication, the two cells are not in physical contact, but must be close enough for a chemical released by one cell to diffuse to the extracellular space to reach the adjacent cell. Because this process relies on signaling molecules moving across a membrane and diffusing through the extracellular space over a small distance, it is slower and less efficient than direct communication
91
What is the function of a desmosome
Forms a physical attachment between neighboring cells
92
Which of the following forms of communication allows a neuron to signal its target cell with a neurotransmitter?
synaptic communication
93
explain the polarity of epithelium
different sides of the cell have different characteristics and perform different functions
94
explain the avascularity of epithelium
no blood vessels pass between epithelial cells
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Apical surface specializations
the apical surface often has special features such as microvilli or cilia
96
What are the differences between cilia and microvilli?
Cilia are long, fingerlike extensions from the apical surface, have a core of microtubules, and exhibit synchronized movements allowing the cells to move materials (such as mucous) over that surface in the extracellular space. Microvilli are short extensions off the apical surface, increasing the surface area of the plasma membrane, usually allowing the cells more transport activity across that surface of the cell.
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Lateral interdigitations
membranes of adjacent cells form complex, interlinking networks; the cells are not physically linked at this area, but the interlocking membranes hinder the movement of materials through the space between cells
98
What is the difference between an endocrine gland and an exocrine gland?
Endocrine glands secrete their products into the extracelllar fluid; the products diffuse to nearby blood vessels and are carried away in the bloodstream. Exocrine glands secrete their products directly into ducts, pipes which carry the secretions toward a particular location and onto the epithelial surface at that organ
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Merocrine gland
products are released from secretory granules by exocytosis at the plasma membrane
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Holocene gland
the entire cell breaks down, releasing the product along with all other cell components and destroying the cell in the process
101
What do we mean when we refer to an epithelial cell as polarized
One side of the cell is specialized to function differently from the opposite side
102
Which type of epithelium would be optimal for an organ surface exposed to abrasion
Stratified squamous
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In which type of gland secretion is the entire cell shed in its product
holocrine
104
List functions of connective tissue
Energy storage (adipose tissue = fat)
Defending body from disease (white blood cells)
Structural framework of body (bones of skeleton)
Supports and interconnects tissues and organs (CT proper, cartilage)
Transport of materials in fluids (blood, lymph)
105
What is extracellular matrix?
The material that fills in the space between cells of connective tissue – contains fibers and ground substance
106
Where do the fibers in the extracellular matrix come from?
They are made from proteins secreted by the primary cell type of that connective tissue: fibroblasts in CT proper, Chondroblasts/cytes in cartilage, Osteoblasts/cytes in bone
107
Compare the three fiber types of connective tissue – collagen, elastic, and reticular – in terms of their relative sizes and strengths
Collagen fibers are biggest and strongest, and used in support tissues. Reticular fibers are the finest diameter and provide the least strength to a tissue. Elastic fibers are intermediate in size and strength, but offer the ability to resist deformation of the tissues (resiliency – returning the tissue to its original state)
108
Which connective tissue cell type is responsible for scar formation?
fibroblasts
109
Why is it difficult for cartilage to heal?
Cartilage is avascular, meaning that blood vessels do not run within it. This means oxygen and nutrients must diffuse through the firm cartilage matrix material to reach the chondrocytes within, an inefficient process which limits the ability of cartilage to repair after injury
110
Compare the two processes by which cartilage grows: appositional and interstitial growth. (key vocab: chondroblasts, chondrocytes, cell division, perichondrium, lacunae, extracellular matrix)
In appositional growth, stem cells in the perichondrium at the edges of cartilage differentiate into chondroblasts, which start secreting materials into the extracellular matrix. As this matrix material matures, the chondroblasts mature into chondrocytes, which are now trapped in fluid-filled pockets called lacunae within the cartilage. Thus, appositional growth is growth of new cartilage at the edges of existing cartilage.
Interstitial growth occurs as mature chondrocytes in lacunae divide an form daughter cells. These chondrocytes continue to secrete matrix materials and maintain the cartilage matrix around them, pushing the cartilage outward from within
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Dense irregular connective tissue
contains randomly directed bundles of collagen fibers
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Perichondrium
is the connective tissue proper directly surrounding cartilage
113
Compare the arrangement of compact bone with that of spongy bone. Where in a long bone would each type be located? (key vocab: osteon, central canal, canaliculi, lacunae, blood vessels, osteocytes)
Compact bone, also called dense bone, is formed from small units called osteons. Osteons contain osteocytes, which maintain the collagen and mineralized ground substance of the hard extracellular matrix. Each osteon has a central canal in its center containing blood vessels. Osteocytes are arranged in concentric circles around the central canal, each osteocyte lying in a lacuna with processes reaching out to other osteocytes through small tunnels in the matrix called canaliculi. Oxygen and nutrients from the artery in the central canal percolate through the canaliculi to reach the osteocytes, keeping them alive and providing the materials needed for them to maintain the bone. Compact bone comprises the thick wall of the diaphysis of a long bone, and forms a thin covering to the epiphyses of long bones and flat bones.
Spongy bone also contains osteocytes in lacunae, interconnected through canaliculi. There are no osteon units in spongy bone. The bone forms as thin spicules, called trabeculae. Trabeculae contain the same extracellular matrix (collagen fibers and mineralized ground substance) but are thin and branch with spaces between them. The relatively open area created between trabeculae gives the bone a sponge-like appearance, but unlike a sponge the trabeculae are hard spikes of bone because of the mineralized matrix. The spaces are filled with fluid that is constantly replenished by blood vessels within the spongy bone. Osteocytes in spongy bone receive oxygen and nutrients by diffusion through the canaliculi which open into the fluid.
114
Describe how a bone thickens through the process of appositional growth. (key vocab: osteoblasts, osteocytes, cell division, periosteum, osteon, extracellular matrix, blood vessels)
In appositional growth, progenitor cells in the inner part of the periosteum are triggered to differentiate into osteoblasts. Osteoblasts begin to secrete collagen molecules which form collagen fibers in the extracellular space. Osteoblasts also secrete ground substance which binds calcium salts from nearby blood vessels, turning the ground substance around the collagen very hard. Thus, in appositional growth, new bone is added along the sides of existing bone, making the bone thicker and stronger. This process can occur throughout life.
115
Describe the process of intramembranous ossification
Intramembranous ossification occurs during development, where bone forms within loose connective tissues (C.T. proper) of skin, which is why it is sometimes called “dermal” bone. Here, undifferentiated cells in the connective tissue are triggered to differentiate into osteoblasts, which start to produce collagen and ground substance and lay down bone. Cells locked into the new matrix are now called osteocytes. Bone continues to grow outward, into a plate of bone. Eventually blood vessels will invade the center and remodel the inner portion of bone into spongy bone, while the outer shell is compact bone. In this process, “flat” bones, such as those of the skull, are formed over time, but the process went from connective tissue proper directly into bone, without any intervening cartilage phase
116
Why does bone usually heal well
Unlike cartilage, bone is HIGHLY vascular. This is necessary if bone is to serve as the ready source of calcium ions needed to maintain homeostasis. It also provides a steady supply of oxygen and nutrients for osteoblasts during the healing process
117
Where in bone is calcium stored?
Extracellular matrix
118
What is the definition of a joint? Name the three kinds of joints in the body based on the material holding the bones together
A joint is a place where two bones meet; there is no requirement that the bones move relative to one another. Bones may be held together by connective tissue proper (fibrous joints), by cartilage (cartilagenous joints) or by a connective tissue capsule enclosing a fluid filled space between bones (synovial joint)
119
Name the major body cavities, and the contents they protect
The cranial cavity contains the brain.
The orbit contains the eyeball.
The nasal cavity has no special contents; it is the opening of the airway for respiration. Paranasal sinuses are spaces in the bones adjacent to the nasal cavity which lighten the bones, cause sound to resonate, and need to drain fluid into the nasal cavity.
The oral cavity contains the tongue and related structures.
The thoracic cavity contains the heart, lungs, and other structures.
The abdominal cavity contains most of the digestive organs, as well as kidneys and spleen
The pelvic cavity contains the bladder, rectum, and reproductive organs
120
How are skull bones held together in the adult? How is this different in the newborn?
Skull bones are held together as suture joints, with connective tissue proper (collagen) holding the bones together and preventing shifting of the bones. In the newborn, the bones have bigger gaps and more connective tissue between them (making up the fontanelles), which left some room for movement as the baby’s head p
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Describe the organization of the vertebral column
The vertebral column comprises a series of bones (vertebrae) stacked on one another vertically. The bones are aligned with their vertebral bodies facing anteriorly and spines facing posteriorly, with the vertebral foramina lined up over one another to create the vertebral canal. This provides a long continuous tube to protect the spinal cord. Having individual bones with intervertebral discs between allows for a limited range of movement of the spine, allowing us to flex and extend, laterally flex, and rotate our torso without disturbing the fragile spinal cord tissue.
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What are primary and secondary curvatures of the spine?
The primary curves are within the thoracic and sacral levels of the spine, formed when embryonic development of the thoracic and pelvic organs forced a posterior bend to the vertebral column in those regions. As babies learn to hold themselves upright, the cervical and lumbar “secondary” curvatures form to counteract the primary curvatures and redistribute weight evenly in a vertical line down the vertebral column
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What are the costal cartilages and why are they important
Costal cartilages hold the anterior ends of the ribs to the sternum, completing the enclosure of the thoracic organs.
Because these cartilages have more “give” than the bony ribs, they add some “give” to the thoracic wall as it changes size during breathing.
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Describe an area of the skeleton where stability has been compromised in order to increase mobility
The shoulder joint has very little contact between the rounded head of the humerus and the glenoid cavity of the scapula, its socket. This allows for great range of motion at the shoulder, allowing the upper limb great variety of movement. However, without much “fit” between the bones, the shoulder joint relies on other, “soft” tissues to hold the bones together – ligaments and tendons of the four rotator cuff muscles.
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Describe an area of the skeleton where mobility has been compromised in order to increase stability
The sacrum is a bone of the vertebral column, formed from the fusion of 5 sacral vertebrae into a single bone. This means there are no movement within the sacrum, and consequently no flexion or rotation of the vertebral column at that level. However, having the bones fused together at the sacral level provides great structural support at the bottom of the spine, which bears the weight of all the body superior to it
