Pancreas: Structure and Location
The pancreas is located in the abdominal cavity, behind and slightly below the stomach, between the duodenum and spleen. It is both an exocrine and endocrine gland. The endocrine part consists of small clusters of cells called the islets of Langerhans, scattered among the exocrine tissue.
Types of Endocrine Cells in Pancreas
- Alpha (α) cells – secrete glucagon
- Beta (β) cells – secrete insulin
- Delta (δ) cells – secrete somatostatin or Growth Hormone Inhibiting Hormone (GHIH)
- F-cells – secrete pancreatic polypeptide
These endocrine cells are richly supplied with blood and innervated by both sympathetic and parasympathetic nerves.
Pancreatic Hormones and Their Functions
1. Insulin
Produced by beta cells of the islets of Langerhans, insulin facilitates the transport of glucose into cells and promotes energy storage.
- Enhances glycogenesis – conversion of glucose into glycogen.
- Promotes lipogenesis – conversion of glucose into fatty acids.
- Reduces gluconeogenesis – formation of glucose from non-carbohydrate sources.
All these actions lead to a decrease in blood glucose levels, producing a hypoglycemic effect.
2. Glucagon
Secreted by alpha cells, glucagon has opposite effects to insulin. It raises blood glucose levels by:
- Stimulating glycogenolysis – conversion of glycogen to glucose in the liver.
- Promoting gluconeogenesis – formation of glucose from amino acids and fats.
3. Somatostatin
Secreted by delta cells, somatostatin acts locally to inhibit the secretion of insulin and glucagon, helping to regulate pancreatic hormone balance.
4. Pancreatic Polypeptide
Produced by F-cells, this hormone regulates the release of digestive enzymes from the pancreas.
Regulation of Pancreatic Hormone Secretion
- Chemical control: Blood glucose levels are the major regulatory factor.
- Hormonal control: Gastrointestinal hormones like secretin, gastrin, and cholecystokinin promote insulin secretion.
- Neural control: Parasympathetic stimulation (acetylcholine) enhances insulin release, whereas sympathetic transmitters (epinephrine and norepinephrine) inhibit it.
Pancreatic Disorders
Diabetes Mellitus
The most common endocrine disorder of the pancreas is diabetes mellitus, characterized by high blood glucose levels (hyperglycemia), glucose in urine (glycosuria), excessive urination (polyuria), thirst (polydipsia), and hunger (polyphagia).
Types of Diabetes Mellitus
1. Insulin-Dependent Diabetes Mellitus (IDDM):
This type results from an absolute deficiency of insulin, often due to autoimmune destruction of beta cells. Patients require regular insulin injections. Lack of glucose uptake leads to fat and protein breakdown, causing ketoacidosis and weight loss.
Chronic complications include atherosclerosis, ischemic heart disease, gangrene, and diabetic retinopathy.
2. Non-Insulin Dependent Diabetes Mellitus (NIDDM):
This more common type occurs in individuals over 40 years old. It is due to insulin resistance rather than insulin deficiency. It can be controlled with diet, exercise, and oral hypoglycemic drugs that enhance insulin sensitivity or stimulate its secretion.
Gonads
The gonads are reproductive organs that produce gametes — sperm in males and oocytes in females — and also secrete sex hormones.
Ovaries (Female Gonads)
- Located in the female pelvic cavity, each ovary produces estrogens (estradiol and estrone) and progesterone.
- Together with FSH and LH from the anterior pituitary, these hormones regulate the menstrual cycle, maintain pregnancy, and prepare mammary glands for lactation.
- Estrogens promote female secondary sexual characteristics such as breast development and widening of hips.
- The ovaries also secrete inhibin (inhibits FSH secretion) and relaxin (RLX) during pregnancy to relax pelvic ligaments and dilate the cervix during labor.
Testes (Male Gonads)
- Located in the scrotum, the testes produce the main male sex hormone testosterone.
- Testosterone regulates sperm production and promotes male secondary sexual characteristics such as deeper voice, muscle growth, and beard formation.
- Testes also secrete inhibin, which inhibits FSH secretion to regulate spermatogenesis.
Detailed Notes
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