What Is The Role Of Smooth Muscles and diaphragm in the human body?

Smooth muscles is also known as –

1. Non-striated muscles
2. Involuntary muscles
3. Visceral muscles

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Location :-

These muscles are present in almost all organs, for example :-

1. In wall of digestive tract
2. Respiratory tract
3. Urinary bladder, ureter, urethra
4. Blood vessel wall
5. Muscle of iris, eyeball

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Smooth muscle structure :-

Smooth muscle fibers are fusiform, elongated cell of different length. The nucleus is single and centrally placed, well-defined myofibrils and sarcomeres are absent in smooth muscle cells.

Absence of dark and light bands gives it non-striated appearance. The contractile protein are action, myosin and tropomyosin.

Smooth muscle fibers are surrounded by connective tissue, but you won’t find any tendons in this particular muscle type.

Type :-

1. Single unite fibers
2. Multi unit fibers

Single unite fibers :- The muscles are arranged in single sheet or bundles. Ex.- Muscle fibers in the wall of GIT , uterus, ureters.

Multi unite fibers :- The muscle fibers are individuals and each is supplied by a single nerve. These fibers do not exhibit spontaneous contraction. ex.- Ciliary muscle of eye, smooth muscle of blood vessels.

Diaphragm :-

Diaphragm is the muscular sheet that separates the abdominal cavity and thoracic cavity. It has mainly 2 surfaces.

a.) Superior surface :-

The diaphragm is in two halves-right and left. Each half is known as suprapleural membrane.

b.) Inferior surface :-

Inferior surface is also called ‘ thoraco-abdominal surface’ .

Large opening in the diaphragm :-

1. Aortic opening :- It lies at the lower border of 12th thoracic vertebra. It transmits – aorta, thoracic, ducts and azygous vein.
2. Oesophageal opening :- It lies in the muscular part of the diaphragm. It transmits :-
   • Esophagus
   • Gastric nerve
   • Left gastric artery
   • Vena Caval opening :- It is lies in the central tendon of diaphragm. It transmits :-

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➥ Inferior vena cava

➥ Branches of phrenic nerves

Small opening in the diaphragm :-

There are several small openings in the diaphragm which allow passage of following structures –

• Splanchnic nerves
• Sympathetic chain
• Sub- costal nerves
• Epigastric vessels

Thymus :-

Thymus is a lymphoid organ situated in the lower part of the neck extending to the superior mediastinum of thorax.

External features :- Thymus is a bi-lobed structure. It has two pyramid shaped lobes connected by areolar tissue.

weight = 10-15 gm at birth , 30-40 gm or puberty

Relations :-

• Anterior = Sternum
• Posterior =Arch of aorta, trachea.
• Laterally = Lungs.
• Inferior = Heart

Blood supply :- The thymousis supplied by branches from internal thoracic and inferior thyroid arteries.

Vein drain thoracic :- left brachio cephalic, internal thoracic vein and inferior thyroid veins.

Function :-

• It controls lymphopoiesis and regulates the numbers of lymphocytes.
• It regulates the development of lymphoid tissue.

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Histology :-

Parenchyma of the thymus gland contains lymphoid tissue. Cells of lymphoid tissue forms T and B lymphocytes. Lymphoid cell of thymus gland secrets thymosin hormone.

Function of thymus gland :-

Endocrine :- Thymus gland secrets maintains normal function of different lymphoid organs.

Thymus gland forms T and B lymphocyte cell. T lymphocyte cell is related with cell mediated immunity which B lymphocyte are related with antibody mediated immunity.