L4: pancreas, thyroid gland, pineal gland and hormone receptors

Where is the pancreas located

• retroperitoneal

• Lies in a loop formed between inferior border of the stomach and proximal portion of the SI

Pancreas description

• slender, pale organ with modular texture

• 20-25cm in length

• 80g in weight

• Has endocrine and exocrine functions

2 pancreatic regions

Exocrine and endocrine

Exocrine pancreas

• 99 percent of volume

• Cluster of cells and attached ducts

• Secrete basic, enzyme rich fluid

• Fluid flows through intestinal tract through pancreatic ducts

Pancreatic acini

Cluster of cells in exocrine pancreas

Endocrine pancreas

• 1 percent of volume

• Smalls groups of hormone producing cells scattered in clusters called pancreatic islets or islets of langerhans

How many pancreatic islets in a typical pancreas

2 million

cells in pancreatic islets

• alpha

• beta

• delta

• pancreatic polypeptide

alpha cells

• produce glucagon

• raises blood glucose

• increases rate of glycogen breakdown and glucose release by liver

beta cells

• produce insulin

• increases glucose uptake and utilization by cells

• increases glycogen production in liver and skeletal muscles

delta cells

• produce somatostatin

• identical to growth hormone-inhibiting hormone

• suppresses the release of glucagon and insulin

• slows rate of food absorption and enzyme secretion in intestinal tract

somatostatin

a type of peptide hormone

PP cells

• produces PP

• inhibits gallbladder contraction

• regulates production of some pancreatic enzymes

• can help control rate of nutrient absorption

feedback loop when glucose is high

1. stimulus: homeostasis disturbed by excess glucose

2. receptors: beta cells in pancreas

3. secretes insulin

4. effector: all body cells respond

5. homeostasis restored by lowered glucose levels

how do body cells respond when restoring high blood sugar

• increased rate of glucose transport into target cells

• increased rate of glucose use and ATP generation

• increased coversion of glucose to glycogen

• increased aa absorption and protein synthesis

• increased triglyceride synthesis in adipose cells

normal blood sugar range

70-110 mg/dL

feedback loop when glucose is too low

1. stimulus: low blood sugar

2. receptor: alpha cells in pancreas

3. releases glucagon

4. effectors: liver, skeletal muscle, adipose cells respond to increase glucose production

how do effectors respond to low blood sugar

• increased breakdown of glycogen to glucose in liver and skeletal muscles

• increased breakdown of fat to fatty acids in adipose tissue

• increased synthesis and release of glucose in liver

diabetes mellitus

high glucose concentrations in blood and urine

diabetes mellitus causes

• inadequete insulin production, synthesis of abnormal insulin molecules or production of defective receptor proteins due to genetics

• pathological conditions such as injury to pancreas or immune disorders

type I diabetes

inadequete insulin production from beta cells

type II diabetes

body produces normal amounts of insulin but tissues do not respond properly due to insulin resistance

problems caused by diabetes

• diabetic retinopathy

• increased risk of heart attack

• diabetic nephropathy

• diabetic neuropathy

• reduced blood flow to distal portions of limbs

diabetic retinopathy

damages retina blood vessels

diabetic nephropathy

damage to kidneys

diabetic neuropathy

nerve damage

pineal gland

• in midbrain

• produces melatonin from molecules of serotonin

• collaterals from the visual pathway enter the pineal gland and affect the rate of production of melatonin

• rate lowest during the day and highest during the night

pinealocytes

pineal gland cells

functions of melatonin

• setting circadian rhythms

• inhibiting reproductive functions

• protecting against damage by free radicals

where is thyroid gland located

• neck

• posterior to thyroid cartilage

• anterior to trachea

feedback loop with thyroid gland

• TRH released by hypothalamus

• enters anterior pit gland which secretes TSH

• TSH enters thyroid gland

• thyroid gland releases T3 and T4 hormones and targets relavant organs

• T3 and T4 inhibits hypothalamus and anterior pit gland

thyroid gland histology

• contains large number of thyroid follicles

• contains colloids

• contains clear (C) cells

• contains cuboidal epithelial cells

colloid

• a globular protein called thyroglobulin (tyrosine)

• within cavities

• fluid + substances

C cells

produce calcitonin

calcitonin

lowers blood calcium