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Small intestine

This diagram shows the small intestine. The different parts of the small intestine are labeled.
The three regions of the small intestine are the duodenum, jejunum, and ileum.

The jejunum    is about 0.9 meters (3 feet) long (in life) and runs from the duodenum to the ileum. Jejunum means “empty” in Latin and supposedly was so named by the ancient Greeks who noticed it was always empty at death. No clear demarcation exists between the jejunum and the final segment of the small intestine, the ileum.

The ileum    is the longest part of the small intestine, measuring about 1.8 meters (6 feet) in length. It is thicker, more vascular, and has more developed mucosal folds than the jejunum. The ileum joins the cecum, the first portion of the large intestine, at the ileocecal sphincter    (or valve). The jejunum and ileum are tethered to the posterior abdominal wall by the mesentery. The large intestine frames these three parts of the small intestine.

Parasympathetic nerve fibers from the vagus nerve and sympathetic nerve fibers from the thoracic splanchnic nerve provide extrinsic innervation to the small intestine. The superior mesenteric artery is its main arterial supply. Veins run parallel to the arteries and drain into the superior mesenteric vein. Nutrient-rich blood from the small intestine is then carried to the liver via the hepatic portal vein.

Histology

The wall of the small intestine is composed of the same four layers typically present in the alimentary system. However, three features of the mucosa and submucosa are unique. These features, which increase the absorptive surface area of the small intestine more than 600-fold, include circular folds, villi, and microvilli ( [link] ). These adaptations are most abundant in the proximal two-thirds of the small intestine, where the majority of absorption occurs.

Histology of the small intestine

Illustration (a) shows the histological cross-section of the small intestine. The left panel shows a small region of the small intestine, along with the blood vessels and the muscle layers. The middle panel shows a magnified view of a small region of the small intestine, highlighting the absorptive cells, the lacteal and the goblet cells. The right panel shows a further magnified view of the epithelial cells including the microvilli. Illustrations (b) shows a micrograph of the circular folds, and illustration (c) shows a micrograph of the villi. Illustration (d) shows an electron micrograph of the microvilli.
(a) The absorptive surface of the small intestine is vastly enlarged by the presence of circular folds, villi, and microvilli. (b) Micrograph of the circular folds. (c) Micrograph of the villi. (d) Electron micrograph of the microvilli. From left to right, LM x 56, LM x 508, EM x 196,000. (credit b-d: Micrograph provided by the Regents of University of Michigan Medical School © 2012)

Circular folds

Also called a plica circulare, a circular fold    is a deep ridge in the mucosa and submucosa. Beginning near the proximal part of the duodenum and ending near the middle of the ileum, these folds facilitate absorption. Their shape causes the chyme to spiral, rather than move in a straight line, through the small intestine. Spiraling slows the movement of chyme and provides the time needed for nutrients to be fully absorbed.

Villi

Within the circular folds are small (0.5–1 mm long) hairlike vascularized projections called villi (singular = villus) that give the mucosa a furry texture. There are about 20 to 40 villi per square millimeter, increasing the surface area of the epithelium tremendously. The mucosal epithelium, primarily composed of absorptive cells, covers the villi. In addition to muscle and connective tissue to support its structure, each villus contains a capillary bed composed of one arteriole and one venule, as well as a lymphatic capillary called a lacteal    . The breakdown products of carbohydrates and proteins (sugars and amino acids) can enter the bloodstream directly, but lipid breakdown products are absorbed by the lacteals and transported to the bloodstream via the lymphatic system.

Questions & Answers

write short notes on ligaments,curves and moverment of vertebral column.
mutesi Reply
what is the Analysis
ROHIT Reply
what is Anatomy
ROHIT Reply
Cutting Up
Nonie
it's a organs and bouns reading
AJITH
Cutting Up
Nonie
what
AJITH
Cutting Up
Nonie
to dissect
Nonie
what usually cause blood pressurae
Abdullateef Reply
too much salt in the diet
Abuusu
older age
Abuusu
Even family history of high blood pressure
Abuusu
yes
Yaqub
too much salt in the diet
Yaqub
stress is the leading factor
Richard
smoking and too much alcohol consumption
Annu
obesity can also cause hypertension
Yaqub
high temperature of the body high salt of the body
Drs
how does the temperature affect the blood pressure?
Chidiebere
sex
Onavwie
What sex.?
Arshad
Male
Vikas
i mearnt gender,there's increased blood pressure in male than female
Onavwie
Why
Vikas
guys, read the question, involuntary pumping of heart causes the blood pressure in the arteries, he has not asked about high or low BP.
Jess
explain the cellular mechanism that produces tetanus and summation
Jenica Reply
epithelial cells polerity
jitendra Reply
tissues
Deepak
demonstrate the fluid replacement in the body
John Reply
the red blood cells is in the long bones or flat bones?
isbii
as age increases, the bone elongates .. will the joint vanish?
Sushruth Reply
what is anatomy?
Ivy Reply
structure
Allonda
discuss the organization of the body
Mwila Reply
explain the cellular mechanism that produces tetanus and summation
Chayanne Reply
explain why the muscle doesn't respond to low stimulus voltages
Chayanne
how would muscle contractions be affected if skeletal muscle fibers did have T - tubules?
Chayanne
tetanus is a disease caused by a bacteria causing rigidity and spasms of volutary muscles.. there is a prolonged construction of muscles caused by repeated stimuli
Marcus
muscles follow the "all or none law" when it comes to reponse to stimuli... muscle construction would have been affected because the T tubules are the conducting tracts that transport the or move the action potential in deporalizing the other parts of cell hence the muscle wont act as a single cell
Marcus
Skeletal muscle fibers do have t tubules that's how action potential propagates to spread throughout the muscle. Tetanus production is a phenomenon which is better explained in time rather then cellularly. Action potentials either separated in time or space are summated on the muscle and
Vikas
When the stimulus frequency hits more than 25 the individual twitches from the fibers summate and the muscle as a whole contracts. Cellulary, a good amount of calcium needs to be accumulated as is done by twitches adding together.
Vikas
what is the names of tarsus?
Fathia Reply
the region of the foot containing the seven tarsal bones.
Manja
the tarsal bones
Marcus
how the valves keep the blood moving in one direction?
Nonie Reply
They open and close during blood circulation,
Denis
Then valve open labb sound and valve close dabb sound
HARDIK
The valves for example the semilunar valves act to prevent back flow of blood from arteries to ventricles during ventricular diastole and help to maintain pressure on the major arteries .The aortic semilunar valve separate the left ventricle from opening of the aorta.
Denis
thank you
Nonie
😷
HARDIK
hi
Shakir
hello
Manja
Yes
kannan
what are estrogen and progesterone ? and their functions
Emmanuel
it's a body hormones and this is spread by women and it's can help to reproduction system...
HARDIK
yhe I also wana know
Lemasyanji
can we introduce ourselves and share contact?
Emmanuel
🤔
HARDIK
thanks
Emmanuel
i want ti study medicine.. what are the main course?
Emmanuel
Progesterone helps to maintain the endometrium wall which is later shed out of the body during the menstrual cycle
Smisha
Estrogen is another ovarian hormone which helps the primary follicle to develop into graafian follicle and cause ovulation
Smisha
what is decstro cardiac
priyanshi
Right sided heart in a guy
Vikas
Dextrocardia is a condition where the. heart lies in the right side of the thorax instead of the left and it occurs when the heart loops to the left instead of the right.
Idoko
hii
Vikas
can any talk me a scope of anatomy and physiology
Vikas
please
Vikas
It has valves that OPEN and close during circulation
xiao
What does the Thyroid gland means
Solomon Reply
It's a gland in your neck produces thyroid hormone maintains body metabolism
Vikas
how many joints are in the human foot?
Roghayeh Reply
I believe that is 33 joints
Ana
26 bones and 33 joints.
Amin
thank u.
Roghayeh
thanks
antouman

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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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