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Pancreas

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High-magnification light microscopy of stained pancreas tissue. The central islet of Langerhans shows tightly packed cells stained pink, each with a dark purple nucleus. Surrounding cells also show pink cytoplasm and dark nuclei, but with differently stained granules. The overall composition highlights the islet's cellular density against a background of surrounding tissue.
Figure 1: Microscopic view of cells of a pancreas islet, stained pink and purple. Nuclei visible in each cell.

The pancreas contains clusters of endocrine cells responsible for producing and secreting hormones involved in regulating blood glucose levels.

Diagram illustrating the macroanatomy of the pancreas adjacent to the stomach and small intestine. The diagram labels the head, body, and tail of the pancreas, as well as the respective locations of the stomach and small intestine.
Figure 2: Anatomical diagram showing the pancreas, stomach, and small intestine.

Location

The pancreas sits posterior to the stomach. It is nestled in the curvature of the duodenum. The duodenum is the first section of the small intestine that connects to the stomach. The pancreas consists of a head tucked into the duodenum. A body is situated posterior to the stomach. The tail tapers and extends laterally. A main pancreatic duct drains secretions and squirts them into the duodenum through the hepatopancreatic ampulla.

Exocrine Tissue

Upon first view, the pancreas seems to have a homogenous distribution of cells. At higher magnifications, the acinar cells of the digestive system are clearly distinguished. They can be differentiated from the clusters of endocrine cells of the pancreatic islets.

Pancreatic Islets

The pancreatic islets are dispersed throughout the acinar cells of the pancreas. They are most abundant in the tail and body of the pancreas. Within each islet, the endocrine cells are highly organized. Different cell types are distributed in specific regions.  Beta cells are typically found in the center of the islet, surrounded by alpha and delta cells.

Cells

Beta cells are the most abundant cell type in the pancreatic islets. These cells are clustered at the center of the pancreatic islet. Their purple nucleus is darkly stained purple with a light pink cytoplasm.

Alpha are usually found around the outside rim of the pancreatic islet. These cells have a darkly stained nucleus and a reddish cytoplasm.

Delta cells produce somatostatin. This hormone inhibits the release of both insulin and glucagon. It also inhibits other digestive hormones.

PP cells (pancreatic polypeptide cells) produce pancreatic polypeptide, a hormone involved in regulating pancreatic enzyme secretion and appetite regulation.

Microscopic section of a pancreas, stained with H&E. The image displays a roughly triangular section against a blank white background. Deep purple acinar cells occupy most of the field, interspersed with white adipose tissue. Delicate white connective tissue septa divide the acini. Few visible blood vessels demonstrate pink staining. This composition allows for detailed examination of pancreatic cellular and structural features.
Figure 3: Microscopic view of pancreatic tissue stained purple with white spots.
Microscopic view of pancreas tissue stained with Hematoxylin and Eosin (H&E). Deep purple-stained acinar cells form lobules separated by thin white connective tissue. Lighter pink vessels are visible, with round, clear islets of Langerhans distributed throughout.
Figure 4: Pancreas histology stained purple and pink with white spots and vessels.
High-magnification light microscopy of stained pancreas tissue. The central islet of Langerhans shows tightly packed cells stained pink, each with a dark purple nucleus. Surrounding cells also show pink cytoplasm and dark nuclei, but with differently stained granules. The overall composition highlights the islet's cellular density against a background of surrounding tissue.
Figure 5: Microscopic view of cells of a pancreas islet, stained pink and purple. Nuclei visible in each cell.

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Illustration and histological image of a pancreatic islet. The main illustration shows an Islet of Langerhans with labeled alpha, beta, delta, and F cells and a capillary. A detail shows a section of the pancreas, while another image focuses on islet histology.
Figure 6: Pancreas islet histology showing various cell types: alpha, beta, delta, F cells, and capillary.

Glucose Homeostasis

Diagram illustrating the glucose regulation feedback loop. When blood sugar is high, the pancreas releases Insulin. Insulin stimulates glycogen formation in the liver, stimulates glucose uptake from tissue cells, and lowers blood sugar. When blood sugar is low, pancreas release glucagon, which stimulates glycogen breakdown in the liver, and raises blood sugar. The diagram shows the liver, pancreas, tissue cells, insulin, glucagon, glucose, and glycogen.
Figure 7: Glucose regulation feedback loop showing the roles of insulin, glucagon, liver, and pancreas in maintaining blood sugar levels.

Alpha cells produce glucagon. This hormone raises blood glucose levels. It stimulates the breakdown of glycogen (stored glucose) in the liver. It also promotes the release of glucose into the bloodstream.

Beta cells are the most abundant cell type in the pancreatic islets. They produce insulin, which is a hormone that lowers blood glucose levels. This hormone works by promoting the uptake and storage of glucose in cells.

Antagonistic Hormones

Antagonistic hormones are hormones that produce the opposite effect from each other. Insulin and glucagon are antagonistic as are PTH and calcitonin that regulate calcium homeostasis. Insulin responds to a high level of glucose and triggers effectors that lower blood glucose. Conversely, glucagon responds to a low level of glucose and trigger effectors that raise blood glucose. Of course, this creates a fluctuation of glucose around an ideal set point.

The image contains two graphs arranged vertically. The top graph plots "Blood Glucose" (y-axis) against time marked by "Breakfast," "Lunch," and "Dinner" (x-axis) with a green sinusoidal line. The bottom graph plots "Hormone Level" (y-axis) against "Time" (x-axis), displaying a blue sinusoidal line for "Insulin" and a red sinusoidal line for "Glucagon," with a legend to the right. Vertical dashed lines connect corresponding points across both graphs. The composition is clean and simple, focusing on the data representation.
FIgure 8: Graph showing blood glucose levels and hormone levels (insulin and glucagon) over time, correlated with meal times.

Figures 1 and 3-6: Pancreas, H&E, 40X ( Slide 188B)
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

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