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Anatomy and Physiology

In humans, the trachea divides into the two main bronchi that enter the roots of the

lungs. The bronchi continue to divide within the lung, and after multiple divisions, giverise to bronchioles. The bronchial tree continues branching until it reaches the level of

terminal bronchioles, which lead to alveolar sacs. Alveolar sacs are made up of clusters

of alveoli, like individual grapes within a bunch. The individual alveoli are tightly

wrapped in blood vessels and it is here that gas exchange actually occurs.

Deoxygenated blood from the heart is pumped through the pulmonary artery to the

lungs, where oxygen diffuses into blood and is exchanged for carbon dioxide in the

hemoglobin of the erythrocytes. The oxygen-rich blood returns to the heart via the

pulmonary veins to be pumped back into systemic circulation

Human lungs are located in two cavities on either side of the heart. Though similar

in appearance, the two are not identical. Both are separated into lobes by fissures, with

three lobes on the right and two on the left. The lobes are further divided into segments

and then into lobules, hexagonal divisions of the lungs that are the smallest subdivision

visible to the naked eye. The connective tissue that divides lobules is often blackened in

smokers. The medial border of the right lung is nearly vertical, while the left lung

contains a cardiac notch . The cardiac notch is a concave impression molded to

accommodate the shape of the heart. Lungs are to a certain extent 'overbuilt' and have

a tremendous reserve volume as compared to the oxygen exchange requirements when

at rest. Such excess capacity is one of the reasons that individuals can smoke for years

without having a noticeable decrease in lung function while still or moving slowly; in

situations like these only a small portion of the lungs are actually perfused with blood for

gas exchange. As oxygen requirements increase due to exercise, a greater volume of

the lungs is perfused, allowing the body to match its CO2/O2 exchange requirements.

Additionally, due to the excess capacity, it is possible for humans to live with only one

lung, with the other compensating for its loss.

The environment of the lung is very moist, which makes it hospitable for bacteria.

Many respiratory illnesses are the result of bacterial or viral infection of the lungs.

Inflammation of the lungs is known as pneumonia; inflammation of the

pleura surrounding the lungs is known as pleurisy.

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In addition to their function in respiration, the lungs also:

Alter the pH of blood by facilitating alterations in the partial pressure of Carbon

dioxide Filter out small blood clots formed in veins Filter out gas micro-bubbles occurring in

the venous blood stream such as those created after scuba diving during

decompression

Influence the concentration of some biologic substances and drugs used in medicine

in blood

Convert angiotensin I to angiotensin II by the action of angiotensin-converting

enzyme

May serve as a layer of soft, shock-absorbent protection for the heart, which thelungs flank and nearly enclose.

Immunoglobulin-A is secreted in the bronchial secretion and protects against

respiratory infections.

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Anatomy and physiology

In humans, the kidneys are located in the abdominal cavity, and lie in

a retroperitoneal position. There are two, one on each side of the spine. The asymmetry

within the abdominal cavity caused by the liver typically results in the right kidney being

slightly lower than the left, and left kidney being located slightly more medial than theright. The left kidney is approximately at the vertebral level T12 to L3, and the right

slightly lower. The right kidney sits just below the diaphragm and posterior to the liver,

the left below the diaphragm and posterior to the spleen. Resting on top of each kidney

is an adrenal gland. The upper (cranial) parts of the kidneys are partially protected by

the eleventh and twelfth ribs, and each whole kidney and adrenal gland are surrounded

by two layers of fat (the perirenal and pararenal fat) and the renal fascia. Each adult

kidney weighs between 125 and 170 grams in males and between 115 and 155 grams

in females. The left kidney is typically slightly larger than the right.

The kidney has a bean-shaped structure, each kidney has concave and

convex surfaces. The concave surface, the renal helium, is the point at which the renal

artery enters the organ, and the renal vein and ureter leave. The kidney is surrounded

by tough fibrous tissue, the renal capsule, which is itself surrounded by perinephric fat,

renal fascia (of Gerota) and paranephric. The anterior (front) border of these tissues is

the peritoneum, while the posterior (rear) border is the transversalis fascia.

The superior border of the right kidney is adjacent to the liver; and the spleen, for the

left border. Therefore, both move down on inhalation.

The kidney is approximately 1114 cm in length, 6 cm wide and 4 cm thick.

The substance, or parenchyma, of the kidney is divided into two major

structures: superficial is the renal cortex and deep is the renal medulla. Grossly, these

structures take the shape of 8 to 18 cone-shaped renal lobes, each containing renal

cortex surrounding a portion of medulla called a renal pyramid. Between the renal

pyramids are projections of cortex called renal columns. Nephrons, the urine-producing

functional structures of the kidney, span the cortex and medulla. The initial filtering

portion of a nephron is the renal corpuscle, located in the cortex, which is followed by

a renal tubule that passes from the cortex deep into the medullary pyramids. Part of the

renal cortex, a medullary ray is a collection of renal tubules that drain into a

single collecting duct. The tip, or papilla, of each pyramid empties urine into a minor

calyx, minor calyces empty into major calyx, and major calyces empty into the renal

pelvis, which becomes the ureter.