The Nervous System & The Endocrine System: Year 8 Biology Final Exam Summary

2.1 The Endocrine System

Hormone and Glands
> The chemical messengers called hormones are released in one part of the body, revel through blood, and affect cells in other parts of the body.
> The endocrine system is made up of glands that release hormones into the blood. Hormones deliver messages throughout the body.

Hormones: act by binding to specific chemical receptors on cell membranes or within cells.
> Cells with receptors for a particular hormone are called target cells. No receptors= hormone has no effect.
> Full effect may take several minutes, hours, or days.
> Many endocrine functions depend on the effects of two opposing hormones.
Example: insulin (Beta cells of pancreas) prompts liver to convert blood glucose to glycogen to store. Glucagon (Alpha cells of pancreas) prompts liver to convert glycogen to glucose and release it in the blood.
> Both work together to mantain homeostasis.

Glands: an organ that produces and releases a substance, or secretion.
> Exocrine glands: release their secretions through tube-like structures (called ducts) either out of the body or directly into the digestive system. Sweat, tears, digestive enzymes.
> Endocrine glands: release their hormones directly into the blood, which transports the secretions throughout the body.

Your endocrine glands:

1. Hypothalamus: makes hormones that control the pituitary gland and hormones that are stored in the pituitary gland.
2. Pituitary gland: produces hormone that regulate many of the other endocrine glands and some organs.
3. Parathyroid glands: four glands that release parathyroid hormone (regulates the level of calcium in blood).
4. Thymus: during childhood, the thymus release thymosin, which stimulates T cell development and proper immune response.
5. Adrenal glands: release hormones that helps the body respond to stress.
6. Pineal gland: releases melatonin, which is involved in rhythmic activities– daily sleep-wake cycles.
7. Pancreas: produces insulin and glucagon which regulate the level of glucose in your body.
8. Thyroid: produces thyroxine, which regulates metabolism throughout body.
9. Ovaries: produces estrogen and progesterone. Estrogen– development of female secondary sex characteristics & development of eggs. Progesterone– prepares uterus for a fertilized egg.
10. Testes: produce testosterone, which is responsible for sperm production and development of male secondary sex characteristics.

Prostaglandins: nearly all cells have been shown to produce small amounts of hormonelike substances called prostaglandins.
> Modified fatty acids that are produced by a wide range of cells. Only affect nearby cells and tissues. "Local hormones."
> Some cause smooth muscles (uterus, bronchioles, and blood vessels) to contract.
> One group of prostaglandins cause sensation of pain in most headaches. Aspirin helps stop the pain because it inhibits the synthesis of these prostaglandins.

Hormone Action
Two groups– steroid hormones: produces from a lipid called cholesterol. Non-steroid hormones– include proteins, small peptides, and modified amino acids.

Steroid Hormones
> Because they're lipids, they can easily cross cell membranes.
> Once in the cell, steroid hormones can enter the nucleus cand change the pattern of gene expression in a target cell.
> Effects especially powerful and long lasting.

1. A steroid hormone enters a cell by passing directly across membrane.
2. Once inside, the hormone binds to a receptor and forms a hormone-receptor complex.
3. The hormone-receptor complex enters the nucleus of the cell, where it binds to regions of DNA that control gene expression.
4. This binding initiates the transcription of specific genes to messenger RNA. (mRNA).
5. The mRNA moves into the cytoplasm and direct protein synthesis.

Nonsteroid Hormones
> Generally cannot pass through cell membrane of their target cells.
> Bind to receptors on cell membranes and cause release of secondary messengers that affect cell activities.

1. A nonsteroid hormone bind to receptors on the cell membrane.
2. The binding of the hormone activates enzymes on the inner surface of cell membranes.
3. These enzymes release secondary messengers such as calcium ions, nucleotides, and even fatty acids to relay the hormone's message within the cell. One common secondary messender is cAMP (cylic AMP), which is produced from ATP.
4. These secondary messengers can activate or inhibit a wide range of cell activities.

One more chapter and im doneee!!