Endocrine System Flashcards
The Endocrine Glands
- Pineal gland
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid gland
- Thymus
- Adrenal glands
- Kidneys
- Pancreas
- Ovaries
- Uterus (in females)
- Testes (in males)
Exocrine glands
Secrete into a duct that carries the secretion to the body surface or one of the body cavities. Sweat glands, salivary glands, etc
Endocrine glands
Secrete hormones into the extracellular fluid that surrounds the cells that make up the gland. The secretion then usually passes into the capillaries to be transported by the blood.
Hormones
Chemicals secreted by endocrine glands, that are transported throughout the body in the blood. They change the functioning of cells by
1.changing the type,
2. activities
3. or quantities of proteins produced.
Steroid hormones
Oestrogen, progesterone, cortisol and aldosterone. Lipid soluble meaning they do not dissolve in water. They are slow to have an effect, but the effect is long lasting.
Protein and amine hormones
Water soluble. Because they are not lipid soluble, they are unable to diffuse across the cell membrane. Instead they work by attaching to receptor proteins in the membrane of the target cell. They are quick to cause an effect but is short lasting.
Specific in terms of hormone receptors
Each type of receptor will bind with only one specific molecule.
Saturation in terms of hormone receptors
Once all the receptor molecules are occupied by hormone molecules the addition of more hormones does not produce any greater effect.
Enzyme amplification
One hormone does not cause the manufacture or activation of just one molecule of an enzyme, it activates thousands of molecules. One hormone could trigger the production of more than a billion enzyme molecules. Thus a very small stimulus can produce a very large effect.
Hormone clearance
Once a hormone has produced the required effect, it must be turned off. This is done by breaking down the hormone molecules. Some hormones are broken down in the target cells, but most are broken down in the liver and kidneys. Degraded hormones are then excreted in either the bile or the urine.
Hypothalamus
Has roles in both the nervous and endocrine systems, and serves as a connection between the 2 systems. It is located at the base of the brain, below the thalamus and above the pituitary gland. About the size of an almond
Hypothalamus function
It regulates body temperature, water balance and heart rate, in addition to increasing or decreasing the secretions of other glands. It secretes releasing factors and inhibiting factors which travel through blood vessels to the anterior lobe of the pituitary gland.
Other hormones produced, pass along the nerve fibres to the posterior lobe of the pituitary gland where they are then released.
Releasing factors
Stimulate the secretion of a hormone
Inhibiting factors
Slow down the secretion of a hormone
Pituitary gland
Lies just under the hypothalamus and is joined to the hypothalamus by a stalk called the infundibulum. It is not much bigger than a large pea, about 13 mm in diameter. But is absolutely vital. Consists of an anterior and a posterior lobe which functions separately.
Anterior lobe
Has no nerves connecting it to the hypothalamus, rather they are connected by a complex network of blood vessels lying in the infundibulum.
Which hormones are released by the anterior lobe
- FSH
- LH
- GH
- TSH
- ACTH
- PRL
Posterior lobe
Is joined to the hypothalamus by nerve fibres that come from nerve fibres that come from nerve cell bodies in the hypothalamus and pass through the infundibulum to the posterior lobe.
Which hormones are released by the posterior lobe
- Oxytocin
- ADH
Why is the pituitary gland not a true endocrine gland?
Because it does not secrete substances. It simply stores and releases hormones.
Follicle stimulating hormone (FSH)
In Women: Stimulates development of the follicles that contain eggs in the ovary of the female.
In Men: Stimulates the production and maturation of sperm in the testes.
Luteinising hormone (LH)
In Women: Works with FSH to bring about ovulation and to form a structure called the corpus luteum after ovulation.
In Men: Stimulates interstitial cells in the testes to secrete male sex hormones.
Growth Hormone (GH)
Stimulates body growth, particularly the skeleton. It increases the rate at which amino acids are taken up by cells and built into proteins. It is secreted throughout life to maintain the size of organs once maturity is reached.
Thyroid-stimulating hormone (TSH)
Stimulates production and release of hormones from the thyroid gland.
Adrenocorticotropic hormone (ACTH)
Controls production and release of some of the hormones from the cortex of the adrenal glands.
Prolactin (PRL)
Works with other hormones to initiate and maintain milk production in females.
Oxytocin (OT)
Stimulates contraction of the muscles in the uterus. It is released in large quantities during labour. Also stimulates contraction of cells in the mammary glands resulting in release of milk during breastfeeding.
Pineal gland
Found deep inside the brain. Starts about the size of a pea when a child, and gradually decreases in size after puberty. It’s role remains something of a mystery, however it is known that it secretes melatonin.
Melatonin
Involved in the regulation of sleep patterns. Production of melatonin by the pineal gland is stimulated by darkness, and inhibited by light.
Thyroid gland with metabolism
Located in the neck, just below the larynx. Consists of 2 lobes that lie on either side of the trachea, and are joined by a narrow piece of tissue that lies across the front of the trachea. The follicular cells in the thyroid gland secrete 2 hormones in response to TSH. Thyroxine (T4) and Triiodothyronine (T3).
Triiodothyronine (T3)
- Has 3 iodine atoms attached
- 20% of thyroid hormones produced
- More active than Thyroxine but doesn’t last as long
Thyroxine (T4)
- Has 4 iodine atoms attached
- 80% of thyroid hormones produced
- Less active than Triiodothyronine but lasts longer
- Once released enzymes convert it into T3
Thyroxine in terms of metabolism
Thyroxine controls body metabolism by regulating reactions in which complex molecules are broken down to release energy, and other reactions in which complex molecules are synthesized from simple ones. The overall effect is to bring about the release of energy, and because some of the energy is released in the form of heat. To maintain body temperature
Thyroid gland role with calcium and phosphate
Regulates the levels of calcium and phosphate in the blood through the release of calcitonin by c-cells. These actions allow calcium and phosphate concentrations to decrease.
Calcitonin with calcium
When the concentration of calcium in the blood increases, the thyroid gland releases calcitonin which reduces the reabsorption of calcium by the kidneys and the breakdown of bone.
Calcitonin with phosphate
If the concentration of phosphate in the blood becomes too high, calcitonin acts to move phosphate into bone and reduces its reabsorption by the kidneys.
Parathyroid glands
Located in the rear surface of the lobes of the thyroid gland. There are usually 4 parathyroid glands, although some people have more. Each is about the size of a small pea.
Parathyroid glands function
Secrete parathyroid hormone (PTH or parathormone) which increases calcium levels in the blood and phosphate excretion in the urine.
Thymus
Located in the chest just above the heart and just behind the sternum. It is largest in children, then begins to shrink after puberty.
Thymus function
Secretes a group of hormones called thymosins, which influence the maturation of disease-fighting cells called T-lymphocytes.
Adrenal glands
There are 2 adrenal glands, one immediately above each kidney. Each adrenal gland has an inner adrenal medulla and outer adrenal cortex. They are quite different in their structure and function, thus they are really 2 separate endocrine glands.
Adrenal medulla
Produces adrenaline and noradrenaline.
Adrenaline or ephinephrine
Similar effect to that of the sympathetic division of the ANS. It helps to prepare the body for a reaction to a threatening situation. Fight or flight responses.
Noradrenaline or norepinephrine
Has effects similar to adrenaline. In particular, it increases the rare and force of the heartbeat.
Adrenal cortex
More than 20 different hormones are produced in the adrenal cortex and they are known collectively as corticosteroids. The 2 main ones aldosterone and cortisol.
Aldosterone
Acts on the kidney to reduce the amount of sodium and increase the amount of potassium in the urine.
Cortisol
With related hormones, promotes normal metabolism, helping the body to withstand stress and to repair damaged tissues.
Pancreas
Soft organ, approximately 15cm long. Lies just below the stomach and alongside the duodenum, the first part of the small intestine. It is both an exocrine and endocrine gland.
Exocrine part of the pancreas
Secretes digestive enzymes into the small intestine through the pancreatic duct.
Endocrine part of the pancreas
Made up of clusters of special cells called islets of Langerhans (also called pancreatic islets). These cells secrete two important hormones insulin and glucagon.
Insulin
Secreted by the beta cells of the islets of Langerhans. It reduces the amount of glucose in the blood (blood sugar level.) It does this by promoting the uptake of glucose from the blood by the cells of the body. The level of secretion of insulin by the pancreas is determined by the amount of glucose in the blood and is controlled through a negative feedback system.
How does insulin reduce blood sugar level in the liver
Insulin causes the conversion of glucose to glycogen and fat.
How does insulin reduce blood sugar level in skeletal muscles
It causes formation of glycogen from glucose.
How does insulin reduce blood sugar level in fat storage tissue
It causes glucose to be converted into fat.
Glucagon
Secreted by the alpha cells of the islets of Langerhans, acts in the opposite way to insulin. It works to increase the blood glucose level, by mainly promoting the breakdown of glycogen to glucose in the liver. It also stimulates the breakdown of fat in the liver and in fat storage tissues.
Gonads
The testes and the ovaries.
Androgens
Known as the male sex hormones. They are responsible for the development and maintenance of the male sex characteristics. In males androgens are produces by the testes. Females also produce androgens in the ovaries, adrenal glands and fat cells, however lower levels are produced.
Other endocrine tissues
- Stomach
- Small intestine
- Kidneys
- The heart
- The placenta
Stomach and small intestine as an endocrine gland
Both secrete hormones that coordinate the exocrine glands of the digestive system.
Kidneys as an endocrine gland
Secrete hormones, including erythropoietin (EPO) - a hormone thar stimulates the production of red blood cells by the bone marrow.
The heart as an endocrine gland
Secretes a hormone that helps to reduce blood pressure.
The placenta as an endocrine gland
Secretes a number of hormones during pregnancy that help to maintain the pregnancy, stimulate development of the foetus and stimulate the mother’s mammary glands.
