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Bone marrow

This photograph shows the bone marrow.
Red bone marrow fills the head of the femur, and a spot of yellow bone marrow is visible in the center. The white reference bar is 1 cm.

Thymus

The thymus    gland is a bilobed organ found in the space between the sternum and the aorta of the heart ( [link] ). Connective tissue holds the lobes closely together but also separates them and forms a capsule.

Location, structure, and histology of the thymus

The left panel of this figure shows the head and chest of a woman and the location of the thymus is marked. The top right panel shows a micrograph of the thymus and the bottom right panel shows a magnified view of the structure of the thymus.
The thymus lies above the heart. The trabeculae and lobules, including the darkly staining cortex and the lighter staining medulla of each lobule, are clearly visible in the light micrograph of the thymus of a newborn. LM × 100. (Micrograph provided by the Regents of the University of Michigan Medical School © 2012)

View the University of Michigan WebScope at (External Link) to explore the tissue sample in greater detail.

The connective tissue capsule further divides the thymus into lobules via extensions called trabeculae. The outer region of the organ is known as the cortex and contains large numbers of thymocytes with some epithelial cells, macrophages, and dendritic cells (two types of phagocytic cells that are derived from monocytes). The cortex is densely packed so it stains more intensely than the rest of the thymus (see [link] ). The medulla, where thymocytes migrate before leaving the thymus, contains a less dense collection of thymocytes, epithelial cells, and dendritic cells.

Aging and the…

Immune system

By the year 2050, 25 percent of the population of the United States will be 60 years of age or older. The CDC estimates that 80 percent of those 60 years and older have one or more chronic disease associated with deficiencies of the immune systems. This loss of immune function with age is called immunosenescence. To treat this growing population, medical professionals must better understand the aging process. One major cause of age-related immune deficiencies is thymic involution, the shrinking of the thymus gland that begins at birth, at a rate of about three percent tissue loss per year, and continues until 35–45 years of age, when the rate declines to about one percent loss per year for the rest of one’s life. At that pace, the total loss of thymic epithelial tissue and thymocytes would occur at about 120 years of age. Thus, this age is a theoretical limit to a healthy human lifespan.

Thymic involution has been observed in all vertebrate species that have a thymus gland. Animal studies have shown that transplanted thymic grafts between inbred strains of mice involuted according to the age of the donor and not of the recipient, implying the process is genetically programmed. There is evidence that the thymic microenvironment, so vital to the development of naïve T cells, loses thymic epithelial cells according to the decreasing expression of the FOXN1 gene with age.

It is also known that thymic involution can be altered by hormone levels. Sex hormones such as estrogen and testosterone enhance involution, and the hormonal changes in pregnant women cause a temporary thymic involution that reverses itself, when the size of the thymus and its hormone levels return to normal, usually after lactation ceases. What does all this tell us? Can we reverse immunosenescence, or at least slow it down? The potential is there for using thymic transplants from younger donors to keep thymic output of naïve T cells high. Gene therapies that target gene expression are also seen as future possibilities. The more we learn through immunosenescence research, the more opportunities there will be to develop therapies, even though these therapies will likely take decades to develop. The ultimate goal is for everyone to live and be healthy longer, but there may be limits to immortality imposed by our genes and hormones.

Questions & Answers

what is stumac
Abdussalam Reply
What is phagocytosis
Mohamed Reply
Phagocytosis, process by which certain living cells called phagocyte
Sadashiv
It is the process that is carried out by the immune system of the body, that certain specialized immune cells (macrophages, Nks, dendritic cells, etc) that engulf and neutralize the foreign substances that invades the body.
Wesley
So that they can be predicate out of the body.
Wesley
phagocytosis is the process by which living cell or yh plasma membrane engulf large molecules into it internal environment ... it also known as food feeding
Boateng
all that you are say what does it mean?
Dzah
simply is the way the immune system fights foreign bodies by engulfing them..
Dzah
by the help of the immune cells...
Dzah
what are the six types of connective tissues
Athieno Reply
describe the structure of the liver
Atwebembeire Reply
what is specific name for spinal cord
Stanley Reply
what is the best description for skeletal muscular
Stanley
what is the best description for skeletal muscular
Stanley
costs of bones of skeleton, their joint s and voluntary
grace
what are examples of long bones
grace
example of long bones will be the femur tibia and humerus and even radius
Nina
so basically long bones are mostly in you hands and feets
Nina
skeletal muscular are voluntary and are attached to the bone by tendon which help maintain the posture and position of the body and it also protects internal organs in the abdominal region
Nina
The specific name for spinal cord is coccygeal segment
Sandra
Smallest unit of life
Kimberly Reply
cell
Adnan
The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Therefore, it is sometimes called the building block of life. Some organisms, such as bacteria or yeast, are unicellular—consisting only of a single cell—while others, for instance, mammalians, a
Adnan
cells are the building blocks of life
Stanley
Describe the complications of fracture
Zaifa Reply
functions of connective tissue
renah Reply
what is a local potential
Nandi Reply
potential of neurons
vipin
response of neurons against sodium ion Chanel
vipin
The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside. At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.
Adnan
what is tissues
Addai Reply
are groups of specialized cell that perform they same activity
Deng
a group of specialized cells of the same structure and function
Malenga
a group of specialized cells that have the same structure and perform the same function
Cantiago
what is meant by control center?
Freeman Reply
what is anatomy
Ajibola Reply
is the study of the structure of the body and their relationship to each refers to the shapes iyo sizes
Khadar
If water touches hydrophobic tail, what will happen as negative effect?
Sayo
is the study of structural of the human body and their function
Masiame
What is the function of the Trachea
Samuel
what is a blastomere?
Toluba Reply
In biology, a blastomere is a type of cell produced by cleavage (cell division) of the zygote after fertilization and is an essential part of blastula formation.
Adnan
what is cell
Shivaani
Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. ... Cells have many parts, each with a different
Adnan
function
Adnan
cell is a membrane bound unit that contains the fundamentals molecules of life
Sushma
A1
Adnan
excellent
Adnan
movement,reproduction, excretion, respiration ,growth ,nutrition, response to external stimuli.
Sushma
good
Adnan
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Adnan
questions pushy ja sukty hy kya
Maryam
jwab forun milta hy ya ak do din k bad
Maryam
Maryam Riaz sister what you say
Adnan
i want to say that k kush questions k answer mil sukty hy mjhy
Maryam
inshallah
Adnan
zaror mere behen
Adnan
question kari
Adnan
hn mil mil sakte h na esly
Ziya
Which muscle of the gluteal region originates from lumber spine? a. Gluteus medius b. Psoas major c. Iliacus d. Gluteus maximus
Maryam
sweet sister's
Adnan
question tu kari Inshallah Allah behtar kariga
Adnan
to mcqs kia to hy
Maryam
answer ni mila abhi
Maryam
wait sister
Adnan
what is the functional unit of kidneys
Khadar
nephron is the functional unit of kidney
Maryam
Maryam Riaz sister option. d. gluteus maximus
Adnan
thanks
Maryam
sorry Maryam Riaz sister
Adnan
option b. psoas major
Adnan
right answer this one
Adnan
nephron is the functional unit of kidney
Ihsan
I discussed with to my teachers
Adnan
d
Ihsan
d. is right option bro
Adnan
yes
Ihsan
what is cell
Shilpa
cell is the smallest unit of life
Maryam
ok
Shilpa
Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. ... Cells have many parts, each with a different
Adnan
function
Adnan
Maryam Riaz sister I m clear option d. also right thank you ihan bro
Adnan
type structure function origin insertion action of muscles
DAMINI Reply
get anatomyka app
Raghvendra
what you ask especially
Raghvendra
oxygn amount in our body
Tg Reply
A normal level of oxygen is usually 95% or higher. Some people with chronic lung disease or sleep apnea can have normal levels around 90%. The “SpO2” reading on a pulse oximeter shows the percentage of oxygen in someone's blood
Adnan

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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