Exam 2 Flashcards
Mitosis
a type of cell division by which a diploid somatic cell duplicates its DNA and divides once to produce two genetically identical diploid daughter cells.
multicellular organisms use this type of cell division for tissue growth and repair
Mitosis
Diploid (2N) cells
contain two complete sets of homologous chromosomes, which have the same size, the same shape, and carry genes for the same traits.
In order for a eukaryotic cell to reproduce itself
it must duplicate its DNA and distribute that DNA to the resulting daughter cells.
Human somatic cells contain
23 pairs of homologous chromosomes
The cell cycle
an orderly sequence of events that describes the life of a cell.
occurs between successive divisions of a cell and is the longest portion of the cell cycle.
Interphase
the first “Gap” phase (G1)
a cell duplicates its organelles, synthesizes proteins, grows, and carries out its metabolic activities
how long do Typical somatic cells spend in G1
8-10 hours
the “Synthesis” phase (S)
the DNA molecules are replicated in order to produce two identical copies of the DNA
how long do Typical somatic cells spend in S
6-8 hours
the second “Gap” phase (G2)
cell growth continues, proteins that are needed for cell division get synthesized, and centrioles are replicated
how long do Typical somatic cells spend in G2
4-6 hours
describes division of the nucleus, which is followed by division of the cytoplasm.
Mitosis
how long do Typical somatic cells spend in Mitosis
1-2 hours
The length of the cell cycle varies from one type of cell to another.
Some cells (skin) will divide continuously
Some cells (liver) divide very slowly unless organ is damaged
If damaged, cells divide more rapidly
Some cells (nerve cells, heart muscle) lose their ability to divide and get replaced by scar tissue when they dieHow many stages are required to divide the nucleus in mitosis
five sequential stages
PROPHASE
The first stage; chromatin in the nucleus condenses into thick, rod-shaped chromosomes
Each chromosome consists of identical pair of chromatids joined together at centromere
the nuclear membrane starts to disintegrate
nucleoli disappear
pairs of centrioles migrate toward opposite poles of the cell
Mitotic spindle
PROMETAPHASE.
The second stage; microtubules form a spindle apparatus with fibers that attach one identical chromatid to one pole of the cell and the other identical chromatid to the opposite pole of the cell
chromosomes migrate toward the center of the cell as pairs of chromatids
METAPHASE
The third stage; chromosomes line up randomly along a metaphase plate at the center of the cell with one chromatid located on each side of the cell’s “equator”
ANAPHASE
The fourth stage; centromeres split and microtubules pull the identical chromatids apart
chromatids migrate toward opposite poles of the cell as they become daughter chromosomes
Only use term chromatid when attached by centromere, once separate they are daughter chromosomes
TELOPHASE.
The final stage; daughter chromosomes decondense and form a tangled mass of chromatin
a new nuclear envelope forms around each tangled mass of chromatin
the spindle apparatus is disassembled
nucleoli reappear
Cytokinesis
begins during late anaphase or early telophase as the cytoplasm divides.
A variety of factors are needed to initiate cell division.
sufficient cytoplasm must exist to be distributed to the daughter cells
DNA replication must be completed
an adequate supply of nutrients must be available to the cell
maturation promoting factor, cdc2 proteins, and cyclin must be present
adjacent cells die and create space for new cells to occupy
Certain factors can halt cell division.
withdrawal of nutrients or growth factors
contact inhibition blocks cell division when cells touch one another
apoptosis is the orderly, genetically programmed death of a cell
Meiosis
another type of cell division by which a diploid germ cell duplicates its DNA and divides twice to produce four genetically different haploid gametes.
germ cells
special reproductive cells in the gonads that produce eggs or sperm
Haploid (N) cells
contains only one complete set of chromosomes.
Meiosis requires ___ nuclear divisions to separate and distribute the DNA into gametes.
two
the first nuclear division (Meiosis I)
a reduction division because number of chromosomes gets reduced from diploid (2N) to haploid (N)
the second nuclear division (Meiosos II)
an equatorial division; chromatids that comprise a chromosome get separated and distributed to different gametes
prophase I
DNA condenses into visible chromosomes.
homologous chromosomes pair up to form a tetrad
maternal and paternal chromatids within a tetrad exchange pieces of DNA during crossing-over
Produces new gene combinations on chromatid
nuclear envelope disintegrates
nucleoli disappear
centrioles assemble microtubules into a spindle apparatus
metaphase I
tetrads line up at the center of the cell.
pair of chromatids that make up each homologous chromosome lie on opposite sides of the cell’s equator
anaphase I
tetrads separate and the two chromatids that make up each homologous chromosome move toward opposite poles of the cell.
telophase I
the cytoplasm gets divided and two haploid cells result.
unpaired chromosomes decondense into a tangled mass of chromatin
a new nuclear envelope forms around each tangled mass of chromatin
the spindle apparatus is disassembled
nucleoli reappear
Interkinesis
a quiet phase, during which time each haploid daughter cell prepares to divide again.
Major difference between meiosis II and Mitosis
meiosis II involves haploid cells, while mitosis involves diploid cells
The second nuclear division of meiosis II
similar to mitosis because the pairs of non-identical chromatids are separated and distributed into four gametes.
The first meiotic division reduces ….
the number of chromosomes from 46 in the diploid germ cell to 23 in each haploid daughter cell.
The second meiotic division separates …
each of the 23 pairs of chromatids in each daughter cell and distributes them into a pair of gametes.
Cancer
refers to any disease characterized by uncontrolled cell division that produces abnormal tumors or neoplasms.
benign tumors
tend to grow slowly and don’t spread to other organs, but they interfere with normal body function and/or appearance
malignant tumors
non-encapsulated, they grow rapidly, and they spread to other organs by way of blood or lymph
do not exhibit contact inhibition and easily break loose from tumor to ‘seed’ growth of new tumors
Malignant cells
enclosed within fibrous capsule
Most benign tumors
Contact inhibition
cells come into contact with another cell and they stop cell division temporarily
Metastasis
describes the spread of cancerous cells to other parts of the body.
the initial invasion of malignant cells into the surrounding tissue
produces a primary tumor that competes for space and nutrients and ultimately destroys normal tissue
secondary tumors
malignant cells may detach from this primary tumor and establish secondary tumors with new networks of blood vessels that provide nutrients for rapid growth
approximately _____ of cancer deaths result from metastasis
90%
how is cancer named
according to the cells or tissues from which the primary tumor arises.
carcinomas
arise from epithelial cells
melanomas
arise from pigment-producing melanocytes in the skin
sarcomas
arise from bone cells or muscle cells
leukemia
arises from abnormal white blood cells produced in the bone marrow
lymphomas
arise from lymph nodes
90% of all cancers are
carcinomas
______ of cancers are caused by environmental carcinogens that cause mutations.
60% to 70%
oncogenes
mutant forms of normal genes called proto-oncogenes
code for proteins that stimulate cell division, cell growth, cell adhesion
Proto- oncogenes
produce excess growth- factor or abnormal produce excess growth- factor or abnormal growth-factor receptors that stimulate continual cell division
Oncogenes
tumor suppressor genes
inhibit cell division or inactivate carcinogens
Loss of, or damage to, tumor suppressor genes…
can trigger cancer
the “accelerator” of the cell cycle
oncogenes
the “brakes” on the cell cycle
tumor suppressor genes
most cancers are treated by
surgical removal of the malignancy
chemotherapy
administers drugs that poison malignant cells
radiation therapy
destroys the chromosomes in malignant cells in order to prevent cell division
malignant cells are vulnerable to …
chemotherapy and radiation therapy because they divide faster than normal cells
treatment is often difficult because…
the variety of cells in a tumor may respond differently to different chemicals and radiation
DNA is composed of
two long chains of deoxynucleotides
each deoxynucleotide contains
the sugar deoxyribose, which has a phosphate group attached to the 5’ carbon and a nitrogenous base attached to the 1’ carbon
Nitrogenous bases of DNA
adenine, guanine, cytosine, and thymine
The DNA molecule takes the shape of
a double helix.
‘side of the ladder’
the sugar of one deoxynucleotide is linked to the phosphate group of the next deoxynucleotide by a covalent bond, which creates sugar phosphate chain
‘rungs of the ladder’
complementary base pairs are held together by hydrogen bonds
The two chains that make up the DNA double helix are
antiparallel
Unwinding
an enzyme breaks the hydrogen bonds that hold complementary base pairs together ‘unzipping’ DNA double helix
Pairing
free deoxynucleotides in the nucleoplasm form hydrogen bonds with deoxynucleotides on each template to create complementary base pairs
Joining
deoxynucleotides attached to the template are joined together by covalent bonds to form a “daughter” strand that is complementary to its “parent” strand template
DNA replication is semiconservative
because each replicated DNA molecule consists of one original “parent” strand plus one newly synthesized complementary “daughter” strand.
why are Errors in DNA replication are quite rare
because enzymes “proofread” the daughter strand and correct mistakes in complementary base pairing.
mutations
Uncorrected errors that are passed on to next generation
RNA is composed of
one chain of ribonucleotides.
each ribonucleotide contains
the sugar ribose, which has a phosphate group attached to the 5’ carbon and a nitrogenous base attached to the 1’ carbon
Nitrogenous bases of RNA
adenine, guanine, cytosine, and uracil
RNA can exist as
a long, single strand or a twisted structure with hairpin loops.
messenger RNA (mRNA)
carries coded genetic information from the DNA in the nucleus to ribosomes in the cytoplasm
ribosomal RNA (rRNA)
holds ribosome subunits together during protein synthesis
transfer RNA (tRNA)
) binds to a specific amino acid in the cytoplasm and delivers it to a ribosome to be incorporated into a growing polypeptide
transcription
the process by which genetic information that is stored in DNA is copied into a strand of messenger RNA
the sense strand
its sequence of deoxynucleotides contains coded information that “makes sense” for synthesizing a protein
the template strand,
it will be transcribed into molecule of messenger RNA
pre- mRNA
contains exons that code for segment of a protein and introns that do not code for any part of protein
Introns
must be removed from pre-mRNA and exons must be spliced together to produce functional mRNA molecule
After transcription is completed,
the two strands of DNA are rejoined and the mRNA passes out of the nucleus and into the cytoplasm where translation will occur.
must be linked together in the correct sequence to synthesize a protein.
Amino acids
codon
Three consecutive ribonucleotides in mRNA
the four ribonucleotides that make up mRNA must somehow specify____ different amino acids that are used in protein synthesis
20
there are three “stop codons” that halt protein synthesis
UAA, UAG, UGA
Translation
the process by which the genetic information that was coded into mRNA gets converted into a protein.
bind to mRNA and search for the start codon (AUG) in order for translation to begin.
The two ribosome subunits
Additional tRNA molecules
bring their amino acids to the ribosome according to the codons in the mRNA strand.
Gregor Mendel
Our understanding of heredity comes from his experiments
why did Mendel chose to study garden peas
because they were easy to grow, they expressed distinct traits without intermediate effects, and he could control the breeding.
pure-breeding
peas that are self-pollinated produce offspring with same traits as the parents
hybrids
peas that are cross-pollinated produce offspring with a mixture of parental traits
Law of Segregation
each organism contains two “factors” for any given trait and these factors separate during gamete formation, so each gamete contains only one factor for each trait
Law of Independent Assortment
members of one pair of factors separate independently of members of another pair of factors so all possible combinations of factors can occur in the gametes
a gene
a segment of DNA on a chromosome that controls the expression of structural, physical, or even behavioral traits
locus
The location of a particular gene on a chromosome
contain both members of a pair of homologous chromosomes, so they possess two copies of any particular gene.
Diploid cells
contain only one member of a pair of homologous chromosomes, so they possess only one copy of any particular gene
haploid cells
alleles
Alternate or contrasting forms of a gene
genotype
The combination of the two alleles for a particular trait
if the same allele is received from each parent, the genotype is ______________ and organism is _______________
homozygous; pure-breeding
if contrasting alleles are received from the parents, the genotype is _______________ and organism is _____________
heterozygous; hybrid
phenotype
Only one allele is usually expressed at any time and the physical expression of the genotype
dominant allele
the allele that is expressed when two contrasting forms of a gene are present at the same time
recessive allele
the allele that is not expressed when two contrasting forms of a gene are present at the same time
represented with lower case letters
Recessive allele
represented with capital letters
Dominant allele
the first letter of a __________ trait is typically selected to represent that trait
Recessive
monohybrid cross
follows one pair of contrasting traits from pure-breeding parents through hybrid offspring (F1) to a third generation (F2).
monohybrid testcross
uses a homozygous recessive individual to determine the genotype of an individual that displays the dominant phenotype.
if all of the offspring from the testcross display the dominant phenotype, the tested individual must be
homozygous dominant
if one-half of the offspring from the testcross display the dominant phenotype and one-half display the recessive phenotype, the tested individual must be
heterozygous
dihybrid cross
follows two pairs of contrasting traits simultaneously from pure-breeding parents (P) through hybrid offspring (F1) to a third generation (F2).
Incomplete dominance
describes a situation in which neither allele may be completely dominant, so a heterozygous genotype produces an intermediate phenotype between the dominant and recessive phenotypes.
Codominance
describes a situation where there are more than two alleles and each allele may specify a particular substance that is expressed by the heterozygous genotype.
Epistasis
occurs when genes at two different loci interact to control a single trait.
Pleiotropy
describes a situation in which a single gene affects more than one trait.
Humans have____ pairs of autosomes and ______ pair of sex chromosomes
22; 1
autosomes
the same in males and females and carry most of our genes
sex chromosomes
different in males and females and determine our sex
Genotype XX
produces female phenotype
Genotype XY
produces male phenotype
are not truly homologous, because the Y chromosome is shorter and shaped differently than the X chromosome
human sex chromosomes
X-linked genes
Any genes carried on non-homologous portion of X chromosome
have only one copy of an X-linked gene, so they express whatever trait is controlled by the allele they have for that gene.
Males
will only express a recessive sex-linked trait if they carry two copies of the X-linked recessive allele.
Females
called carriers if they possess one recessive allele but express dominant trait
heterozygous females
passed from a father to his daughter, who becomes a carrier
X-linked genes
inherited by a daughter only if her father has the trait and her mother is at least a carrier
sex-linked traits
tissue
consists of similar cells that have a common embryonic origin and are designed to work together to perform a particular function.
Tissues differ from one another according to
the types of cells that are present and the matrix that surrounds these cells.
a matrix
composed of various fibers within a ground substance
Ground substance
can be hard or semisolid or liquid; contains water, gases, minerals, nutrients, wastes, other chemicals
Tissues are classified as
epithelial (covering) or connective (support) or muscle (movement) or nervous (control).
There are _____ primary germ (inal) layers that give rise to all mature tissues.
three
Ectoderm
the outer layer and it produces the epidermis and nervous system.
Mesoderm
the middle layer and it produces muscle, bone, blood, and most of the other connective tissues.
Endoderm
the inner germ and it produces mucous membranes and digestive glands.
Epithelial tissue
consists of cells that are tightly packed together with little extracellular material between them.
apical surface
always free and exposed to a body cavity or lumen of an internal organ or an exterior body surface
basal surface
attaches to adjacent connective tissue
Epithelial tissue attaches to
underlying connective tissue by a basement membrane.
basal lamina
contains collagen fibers and other proteins
reticular lamina
contains reticular fibers and other proteins
is avascular and depends on blood from the underlying connective tissue, but it can quickly regenerate.
Epithelial tissue
Location of Epithelial tissue
covers body surfaces, lines body cavities and forms the secretory structure of glands to function in protection, absorption, and secretion, respectively.
Simple Epithelium
Consists of one layer of epithelial cells, with every cell touching the basement membrane.
Simple squamous epithelium
consists of thin, flat cells, each with one central nucleus.
Simple squamous epithelium functions
in diffusion, osmosis, and filtration
Location of Simple squamous epithelium
located in lungs and kidneys and small intestine
Mesothelium lines
abdominal, pleural, and pericardial cavities
Endothelium lines
heart and blood vessels
Simple cuboidal epithelium
consists of squarish cells with a central spherical nucleus.
Simple cuboidal epithelium functions
absorption and secretion
Location of Simple cuboidal epithelium
kidney tubules and the lining of the ducts of salivary glands
Simple columnar epithelium
consists of elongated rectangular cells with a single nucleus located near the base of the cell.
Simple columnar epithelium functions
in secretion and absorption
non-ciliated columnar epithelium
in the small intestine contains goblet cells that secrete mucus and microvilli that increase surface area to enhance absorption
ciliated columnar epithelium
in uterine tubes moves oocytes toward the uterus
Pseudostratified columnar epithelium
consists of cells of different heights that rest on the same basement membrane, but the nuclei are located at different levels so it appears that there are multiple layers.
Pseudostratified columnar epithelium functions
secretes mucus and moves the mucus by ciliary action
Locations of Pseudostratified columnar epithelium
located in the upper respiratory tract and in portions of the male reproductive tract
is named according to the shape of the cells in the apical layer. Have multiple layers
Stratified epithelium
Stratified squamous epithelium
consists of multiple layers of cells and is the most widespread epithelium in the body.
deep cuboidal or columnar cells
become squamous near the apical surface
Stratified squamous epithelium functions
protects against pathogens, resists abrasion, and retards water loss
keratinized epithelium on the skin surface
contains a layer of dead squamous cells filled with waterproof keratin protein
non-keratinized epithelium locations
covers tongue and lines mouth, esophagus, anal canal, and vagina; lacks the surface layer of dead squamous cells so it is moist and slippery
Stratified cuboidal epithelium
consists of two or more layers of cube-shaped cells.
Stratified cuboidal epithelium functions
in protection, limited secretion, and absorption
Locations of Stratified cuboidal epithelium
in the ducts of sweat glands and in ovaries and testes
Stratified columnar epithelium
quite rare and found only in limited regions of the pharynx, larynx, anal canal, and male urethra.
Transitional epithelium
consists of round or cuboidal cells that become squamous in shape as the tissue gets stretched.
Transitional epithelium permits:
distension of an organ or structure
Locations of Transitional epithelium
in the ureters, urinary bladder, and part of the urethra
Connective tissue
the most abundant, widely distributed, and variable tissue in the body.
All connective tissues arise from
embryonic mesenchyme
Functions of connective tissue.
binds organs together and provides support for organs and other tissues
allows various body movements
protects internal organs
protects the body against disease-causing organisms
stores energy
transports nutrients, wastes, and gases through the body
Connective Tissue consists of
fibers, with widely separated cells surrounded by different kinds of ground substance.
fibroblasts
large, flat, spindle-shaped cells with branching processes
Blasts
undifferentiated cells that synthesize and secrete fibers and ground substance
macrophages
large irregular cells that phagocytize bacteria and cellular debris
leukocytes
white blood cells that protect against bacteria and toxins
plasma cells
round or irregular cells that secrete proteins, which can attack or neutralize foreign substances in body
mast cells
large cells located near blood vessels that secrete heparin to inhibit blood clotting and secrete histamine to dilate blood vessels and increase blood flow
adipocytes
large, rounded cells that store triglycerides
Types of fibers found in connective tissue.
collagen fibers, elastic fibers, and reticular fibers
collagen fibers
consist of collagen proteins that provide great strength and flexibility
elastic fibers
consists of elastin proteins that can easily stretch and recoil
reticular fibers
thin collagen fibers coated with glycoproteins that provide support for blood capillaries, nerves, and muscles
Ground substance
supports cells and fibers and affects how a tissue functions.
glycosaminoglycans
play an important role in regulating water and electrolytes
proteoglycans
form thick colloids that hold tissues together
adhesive glycoproteins
bind membrane proteins to collagen fibers
Areolar connective tissue
consists of collagen fibers, elastic fibers, and reticular fibers and all of the cell types, which are embedded in a semi-fluid ground substance.
Areolar connective tissue binds:
epithelium to deeper tissue and provides strength and support
Areolar connective tissue description
thin, delicate membranes that are located beneath skin
Areolar connective tissue are also located:
between the skin and muscles and around blood vessels and nerves
Reticular connective tissue
consists of reticular fibers and fibroblasts.
Reticular connective tissue functions as
a support framework
location of Reticular connective tissue
in lymph nodes, in the spleen, and in bone marrow
Adipose tissue
contains few fibers, but has numerous adipocytes filled with large fat droplets.
Adipose tissue functions
as a protective cushion, insulates against heat loss, and stores energy
Locations of Adipose tissue
in subcutaneous “fat layers” beneath the skin, in the breasts and hips, and around the kidneys, heart, and various joints
amount of adipose tissue in the body depends upon
the amount of food consumed
Dense regular connective tissue
contains parallel bundles of collagen fibers.
Dense regular connective tissue’s orderly arrangement:
provides strength
Dense regular connective tissue is a principal component of :
tendons and ligaments
Dense irregular connective tissue
contains collagen fibers that are randomly arranged.
Dense irregular connective tissue provides:
strength to resist unpredictable stresses
Location of Dense irregular connective tissue
between the skin and underlying muscle, and in protective capsules around the kidneys, liver, and other internal organs
Elastic connective tissue
contains branching elastic fibers and fibroblasts.
Elastic connective tissue function
permits stretching
Location of Elastic connective tissue
in lungs and respiratory passageways, walls of elastic arteries, and in vocal cords
Marfan syndrome
a hereditary defect in elastic fibers that causes joint and vision problems
Cartilage
Consists of collagen fibers and elastic fibers and mature chondrocytes embedded in a semisolid matrix containing chondroitin sulfate
blood supply of cartilage
cartilage lacks its own blood supply so it depends on diffusion from nearby tissues to obtain nutrients
low rate of metabolism and cell division in cartilage
causes repair of injured cartilage to occur very slowly
cartilage is usually surrounded by
a perichondrium (‘around the cartilage’) sheath of dense irregular CT
Hyaline cartilage description
has a glossy, bluish-white appearance and is the most abundant type.
functions of Hyaline Cartilage
functions as a matrix for bone development and provides friction-free movement at joints
locations and names of hyaline cartilage
Articular cartilage- located attends of long bones
Costal cartilage- located at ends of ribs
Other locations- tip of nose, parts of larynx, trachea, and bronchi
Elastic cartilage contains
chondrocytes within a web-like mesh of elastic fibers.
Elastic cartilage functions
provides strength and flexible elastic support
Elastic cartilage locations
maintains the shape of the external ear and epiglottis
Fibrocartilage contains
chondrocytes among collagen fibers, but it has no perichondrium.
Fibrocartilage functions
absorbs shock and provides support
Fibrocartilage lactions
◦located in the pubic symphysis at the front of the pelvis and in the intervertebral discs
◦forms shock-absorbing pads in the knees
Bone Tissue: two types of _______________________ tissue make up most of the bone mass of the skeleton
osseous
spongy bone
consists of columns and plates called trabeculae
compact bone
◦consists of dense calcified rings called osteons
the hardest type of connective tissue;
compact bone
osteocytes
mature bone cells
Bone tissue functions
•provides physical support for the body, protects internal organs, provides leverage for muscle action, and stores calcium and phosphorus.
Blood description
•a fluid connective tissue whose ground substance is called plasma.
blood composition
•Suspended in the plasma are red blood cells, white blood cells, platelets, and fibers.
blood functions
•transport cells and dissolved substances throughout the body
Nerve tissue composition
•consists of neurons and supporting cells called neuroglia, or glial cells
Neruon processes
◦extending from the cell body are single axons that transmit signals away from the cell body; and branched dendrites receive signals from nearby neurons
the cell body of a neuron contains
the nucleus and other organelles
neuron functions
specialized for detecting stimuo and transmitting nerve signals to other cells
nerve tissue locations
• in the brain, spinal cord, and in peripherl nerves
an excitable tissue that responds quickly to external stimuli by undergoing a change in the membrane potential of its cells.
nerve tissue and cardiac muscle tissue
Skeletal muscle consists
of long, cylindrical multinucleate cells called muscle fibers
skeletal muscle function
•Most skeletal muscle attaches to bones to move body parts.
skeletal muscle description
striated and its contractions are under voluntary control.
Cardiac muscle consists
of branched uninucleate myocytes held together by intercalated discs.
Cardiac muscle is found in
the wall of the heart
cardiac muscle description
•striated like skeletal muscle, but its contractions are involuntary.
Smooth muscle is called_________________and it consists of
visceral muscle; spindle-shaped uninucleate cells
Smooth muscle is found in
the walls of the stomach, bladder, uterus, and blood vessels
smooth muscle description
not striated and its contractions are involuntary.
Cell junctions are
•contact points between the plasma membranes of tissue cells.
Tight junctions
•work like “zippers” to connect cells in epithelium that lines body cavities.
tight junctions function
◦prevent digestive juices from seeping between the epithelial cells that line the stomach and intestines which would cause digestion of underlying CT
Desmosomes
work like “snaps” to attach adjacent cells to one another in tissues that need to resist mechanical stresses.
Were are desmosomes common
◦common among cells in the superficial layer of the skin and between myocytes
Gap junctions
use protein channels, called connexons, to form tiny, fluid-filled channels between adjacent cells.
Glands are composed of
•epithelial cells that produce or release aqueous secretions.
exocrine glands secrete
their products into ducts to be released at the surface of the body or into the lumen of another organ
endocrine glands
have no ducts and secrete hormones into the extracellular fluid
can be classified as unicellular or multicellular
exocrine glands
unicellular exocrine glands
could be mucous cells or goblet cells
multicellular glands
are usually enclosed within a capsule that is divided into lobes, which are subdivided into lobules
Multicellular exocrine glands include
salivary glands, pancreas, mammary glands
Exocrine glands can also be classified according to
the type of substances they secrete
serous glands
produce thin watery fluids, such as perspiration or tears
mucous glands
produce the glycoprotein mucin that absorbs water to become sticky mucus
Merocrine (eccrine) glands
release their secretions by exocytosis.
examples of merocrine glands
salivary, sweat, pancreatic glands
Apocrine glands are similar to
merocrine glands
examples of apocrine glands
sweat glands in armpit or mammary glands
Holocrine glands produce
secretions that consist of dead cell fragments and chemicals.
examples of holocrine glands
oil glands in skin
The largest membrane
cutaneous membrane (skin)
cutaneous membrane
consists of a layer of stratified squamous epithelium resting on top of a layer of underlying connective tissue.
the only dry membrane in the body
the cutaneous membrane
A mucous membrane (mucosa)
consist of a layer of epithelium, a layer of areolar connective tissue called the lamina propria, and a layer of smooth muscle called the muscularis.
location of mucous membrane
◦mostly lines body cavities and/or tracts that open to the exterior
function of mucous membrane
mucus moistens and lubricates the tissue and traps bacteria and foreign particles
A serous membrane (serosa)
consists of a thin layer of areolar connective tissue that is covered with simple squamous epithelium.
location of serous membrane
lines internal body cavities, forms pleurae that cover the lungs, forms the pericardium that covers the heart, and forms the peritoneum that covers the abdominal organs
function of serous membrane
watery serous fluid lubricates these membranes to reduce friction
A synovial membrane
•consists only of connective tissue without any epithelium.
location and function of synovial membrane
lines joint cavities and secretes a slippery synovial fluid that lubricates and nourishes the cartilage that covers the ends of the bones
