Pancreas The pancreas is a retroperitoneal organ that forms as an outgrowth of the duodenal lining. Situated posterior to the stomach it is pinkish in color and

about 15 cm long, running from the loop of the duodenum on the right to the spleen on the left. It has four basic regions: a head, neck, body, and tail. The pancreas has two functional parts, the exocrine pancreas and the endocrine pancreas. The endocrine portion of the pancreas forms as small clusters of cells, the pancreatic islets, distributed among the exocrine acinar cells of the pancreas. They are far less numerous (approximately 5% of the pancreas) than the cells of the exocrine pancreas. There are four distinct cell types within the pancreatic islets: alpha or A cells, beta or B cells, delta or D cells, and F cells. The alpha (20%) and beta (70%) cells constitute the greater part of the pancreatic islets and produce the hormones glucagon and insulin, respectively. The other 10% of the islet cells are delta and F cells, which secrete somatostatin and pancreatic polypeptide, respectively.

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Photomicrographs of pancreas

200x (left), 640x (right)

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Pancreas in situ

Anteror view

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Ovaries The ovaries are ovoid organs about the size of an unshelled almond and occupy the boundary zone between the abdominal and pelvic

cavities. They consist of a dull white fi brous tissue embedded with oocytes, the “egg” cells of the female. Surrounding the oocytes are numerous follicular cells that undergo changes during the female menstrual cycle. The follicular cells are the endocrine cells of the ovary that produce the female steroidal hormones.

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Sagittal section of female pelvis

Medial view

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Testes The testes are oval-shaped organs about 2 inches (5 cm) long and 1 inch (2.5 cm) wide that occupy the scrotal sac of a male. They are covered by a tough fibrous tunic and

wrapped in a serous sac that separates them from the external tissues that surround them. Internally, the testes consist of numerous small compartments created by connective tissue bands that project inward from the outer fibrous tunic. Each testicular compartment is occupied by a thin, highly coiled seminiferous tubule. This thin tube is the site of sperm production. Situated between the tubules are the interstitial cells (of Leydig). It is these large interstitial cells that secrete the steroidal hormones in the testis.

1 Testis

2 Interstitial (Leydig) cell

3 Basement membrane

4 Sertoli cell

5 Spermatogonium

6 Primary spermatocyte

7 Secondary spermatocyte

8 Spermatid

9 Seminiferous tubule

10Tunica albuginea

11Epididymis

12Spermatic cord

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Photomicrograph of testis

40x

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Sagittal section of left testis

Medial view

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16 Cardiovascular System

If you have ever planted a garden of significant size, you have probably experienced the importance of an irrigation system. At its simplest, an irrigation system is

a network of channels or furrows that deliver needed water from one main source to the roots of all the garden’s plants. Like an irrigation system, the body’s blood vessels form an extensive network of “irrigation channels” to deliver needed fluid — in this case the homeostatically maintained blood — to all the body’s cells. In fact, this delivery system is probably the most phenomenal irrigation network imaginable. Emanating from a muscular pump, the heart, these vessels form an extensive system of tubular roadways that carry nourishing blood away from the heart and toward the tissues. They

then make a “U-turn” through small permeable, exchange vessels, the capillaries, which feed all the body’s cells. Here, life-supporting molecules, such as water, oxygen, glucose, and amino acids are delivered to the cells, and the by-products of cellular metabolism are picked up from the surrounding tissue fluid. The blood then flows back to the heart through a series of return vessels, the veins, that parallel the delivery vessels. This circular pattern of flow to and from the heart constitutes the vascular (blood vessel) component of the cardiovascular (circulatory) system. This irrigation network

is so impressive, that if all the blood vessels of the body were placed end-to-end they would extend 25,000 miles (96,500 km), which is approximately two times the equatorial circumference of the earth.

The irrigation network of blood vessels are of no value without a pump. The heart is the dual, self-regulating pump that generates the pressure to drive the blood through this impressive irrigation

network. It pumps the blood through two cycles — a pulmonary cycle to pick up oxygen from the lungs and a systemic cycle to deliver the oxygen to all the cells of the body. Soon after conception, and up until death, the heart pumps blood. It averages approximately 70 beats per minute, or about 3 billion contractions in an average lifetime.

The final aspect of the cardiovascular system is the accessory drainage network — the lymphatics. These small vein-like vessels insure that the cardiac return equals the cardiac output. This chapter will depict the anatomy of this amazing muscular pump and the vascular and lymphatic roadways that distribute the blood throughout the body.

Find more information about the cardiovascular system in

R E A L A N AT O M Y

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