Exocrine gland: a gland that secretes hormones directly into the blood- NO DUCTS.
Endocrine gland: a gland that secretes molecules into a duct which carries molecules to targeted cells.
- Molecules that are released by endocrine glands directly into the blood act as messengers, carrying a signal from the endocrine gland to the specific targets.
- Cells that are receiving hormones have specific complementary receptors.
There are two types of hormones:
- Protein and peptide hormones like adrenaline.These do not enter the cell.
- Steroid hormones like sex hormones.
Adrenaline is released by the adrenal medulla.
1. Adrenaline receptor site has a shape complementary to the adrenaline.
2. Adrenaline activates the enzyme adenyl cyclase.
3. Adenyl cyclase converts ATP into cAMP, which activates other enzymes inside the cell.
ATP ---> cAMP (second messenger) ---> activate enzymes
Adrenal cortex- the adrenal cortex uses cholesterol to make steroids:
Mineral cortocoids: help control Na+ and K+ levels in the blood.
Glucocortocoids: help control metabolism of carbohydrates in the liver.
Regulation of Blood Glucose
Pancreatic duct: made by tubules which have groups of exocrine cells which release digestive enzymes.
Islet of Langerhans:these contain alpha and beta cells.
- Alpha cells: these manufacture/ secrete glucagon- ENDOCRINE
- Beta cells: these manufacture/ secrete insulin- ENDOCRINE
Rise in Blood glucose:
1. Detected by beta cells, insulin secreted.
2. Detected by hepatocytes and muscle cells. Glucose converted to glycogen (glycogenesis)- when glucose produced from amino acids its gluconeogenesis.
Fall in blood glucose:
1. Detected by alpha cells, glucagon secreted.
2. Detected by hepatocytes, glycogen converted to glucose (glycogenolysis).
Control of insulin levels
Insulin level control occurs in the beta cells in the pancreas.
1. Cell membrane has potassium and calcium ion channels. Potassium OPEN- make the inside of cell negative (-70mV).
2. When blood glucose concentration is HIGH, glucose moves into the cell.
3.Glucose is metabolised to form ATP. ATP CLOSES potassium ion channels.
4. Accumulation of potassium ions alters potential difference of the cell- it becomes less negative.
5. Change in potential difference triggers the calcium channels to OPEN.
6. Calcium ions cause the vesicles of insulin to fuse with the cell membrane: released by exocytosis.