14- hormonal communication Flashcards
(35 cards)
what is an endocrine gland?
It’s a group of cells that are specialised to secrete chemicals- these chemicals are hormones, and are secreted directly into the bloodstream.
How is hormone release triggered?
This can occur as a result of a change in concentration of a particular substance e.g. blood glucose conc, or as a result of another hormone or nerve impulse.
What are target cells?
Once secreted, the hormones are transported in the blood plasma all over the body. They diffuse out of the blood and bind to specific receptors for that hormone, found on the membrane or cytoplasm of cells in the target organs, known as target cells.
How do steroid hormones work?
They’re lipid soluble, so can pass through the lipid components of a cell membrane and bind to steroid hormone receptors to form a hormone- receptor complex. The receptors may be present in the cytoplasm or the nucleus, depending on the hormone. The hormone-receptor complex formed acts as a transcription factor which in turn facilitates or inhibits the transcription of a specific gene. e.g. oestrogen
What is a non-steroid hormone?
They’re hydrophilic so cannot pass directly through the cell membrane. Instead, they bind to specific receptors on the cell surface membrane of the target cell. This triggers a cascade of reaction mediated by chemicals called second messengers. e.g. adrenaline
Give 8 characteristics of the hormonal system.
Communication is by chemicals called hormones.
Transmission is by the bloodstream.
Transmission is usually relatively slow.
Hormones travel to all parts of the body, but only target organs respond.
Response is widespread.
Response is slow
Response is often long lasting
Effect may be permanent and irreversible.
Give 8 key features of the nervous system.
Communication is by nerve impulses.
Transmission is by neurones
Transmission is very rapid
Nerve impulses travel to specific parts of the body
Response is localised
Response is rapid
Response is short lived
Effect is temporary and reversible.
What are the adrenal glands?
They’re two small glands that measure approx. 3cm high and 5 cm long. They’re located on top of each kidney and are made up of 2 distinct parts, surrounded by the capsule.
What are the 2 parts of the adrenal glands?
Adrenal cortex- outer region of the glands. This produces hormones that are vital to life, e.g. cortisol and aldosterone.
Adrenal medulla- the inner region of the glands. This produces non-essential hormones e.g. adrenaline- helps the body react to stress.
What are the 3 main types of hormones produced by the adrenal cortex?
Glucocorticoids
Mineralocorticoids
Androgens
What are glucocorticoids?
Include cortisol which helps regulate metabolism by controlling how the body converts fats, proteins and carbohydrates into energy. It also helps to regulate blood pressure and cardiovascular function in response to stress.
Another glucocorticoid hormone released is corticosterone. It works with cortisol to regulate the immune system and supresses inflammatory reactions. The release of these hormones is controlled by the hypothalamus.
What are mineralocorticoids?
The main one produced is aldosterone which helps control blood pressure by maintaining the balance between salt and water concentrations in the blood and bodily fluids. Its release is mediated by signals triggered by the kidney.
What are androgens?
Small amounts of male and female sec hormones are released. Their impact is relatively small compared with the larger amounts of hormones e.g. oestrogen and testosterone, released by the ovaries or testes after puberty, but they are still important, especially in women after the menopause.
What hormones are produced by the adrenal medulla?
They’re released when the sympathetic nervous system is stimulated.
Adrenaline- This increases the heart rate, sending blood quickly to the muscles and brain. It rapidly increases blood glucose conc. levels by converting glycogen to glucose in the liver.
Noradrenaline- works with adrenaline in response to stress, producing effects such as increased HR , widening of pupils, widening of air passages in the lungs, and the narrowing of blood vessels in non-essential organs (resulting in higher blood pressure)
What are the 2 main functions of the pancreas?
Exocrine gland- to produce enzymes and release them via a duct into the duodenum
endocrine gland- to produce hormones and release them into the blood.
Explain the role of the pancreas as an exocrine gland.
Most of the pancreas is made up of exocrine glandular tissue. This tissue is responsible for producing digestive enzymes and alkaline fluids known as pancreatic juices. The enzymes and juice are secreted into ducts which eventually lead to the pancreatic duct. From here, theyre released into the duodenum, the top part of the small intestine. The pancreas produces three important types of digestive enzymes;
Amylase- break down starch into simple sugars. e.g. pancreatic amylase.
protease- breals down proteins into amino acids, e.g. trypsin
lipases- break down lipids into fatty acids and glycerol e.g pancreatic lipase
explain the role of the pancreas as an endocrine gland.
It’s responsible for producing insulin and glucagon. These hormones play an essential role in controlling blood glucose conc. Within the exocrine tissue there are small regions called islets of Langerhans. The cells in the islets of Langerhans are responsible for producing insulin and glucagon, and secreting these hormones directly into the blood stream.
What are the different types of cells in the islets of Langerhans?
alpha cells- produce and secrete glucagon
beta cells- produce and secrete insulin
alpha cells are larger and more numerous than beta cells within an islet. Using standard staining techniques it is very difficult to tell the difference. If a differential stain is used, the cell types will be different colours.
how does blood glucose concentration increase?
diet- when you eat carbohydrate rich foods such as pasta and rice and sweet foods such as cakes, the carbs they contain are broken down in the digestive system to release glucose. The glucose released is absorbed into the bloodstream and blood glucose conc rises
glycogenolysis- glycogen stored in the liver and muscle cells is broken down into glucose which is released into the bloodstream, increasing blood glucose conc.
gluconeogenesis- the production of glucose from non-carbohydrate sources. e.g. the liver is able to make glucose from glycerol and amino acids. This glucose is released into the bloodstream and causes an increase in blood glucose conc.
How is blood glucose conc. decreased
Respiration- some of the glucose in the blood is used by cells to release energy. This is required to perform normal body functions. However, during exercise, more glucose is needed as the body needs to generate more energy in order for muscle cells to contract. The higher the level of physical activity, the higher the demand for glucose and the greater the decrease of blood glucose conc.
glycogenesis - the production of glycogen. When blood glucose conc. is too high, excess glucose taken in through the diet is converted into glycogen which is stored in the liver.
What is the role of insulin?
It is produced by the beta cells in the islets of Langerhans in the pancreas. If the blood glucose conc is too high, the beta cells detect this rise in blood glucose conc and respond by secreting insulin. Virtually all body cells have insulin receptors on their cell membrane surface membrane. when insulin binds to its glycoprotein receptor, it causes a change in the tertiary structure of the glucose transport protein channels. This causes the channels to open allowing more glucose to enter the cell. Insulin also activates the enzyme within some cells to convert glucose to glycogen and fat.
How does insulin lower blood glucose conc. ?
- Increasing the rate of absorption of glucose by cells, in particular skeletal muscle cells
- Increasing the respiratory rate of cells- this increases their need for glucose and causes a higher uptake of glucose from the blood.
- Increasing the rate of glycogenesis- insulin stimulates the liver to remove glucose from the blood by turning the glucose into glycogen and storing it in the liver and the muscle cells.
- Increasing the rate of glucose to fat conversion
- Inhibiting the release of glucagon from the alpha cells of the islets of Langerhans.
What is the role of glucagon?
It is produced by the alpha cells in the islets of langerhans in the pancreas. If the blood glucose conc is too low, the alpha cells detect this, and respond by secreting glucagon directly into the bloodstream. Unlike insulin, the only cells in the body which have glucagon receptors are the liver cells and fat cells- therefore these are the only cells that can respond to glucagon.
How does glucagon raise blood glucose levels?
- Glycogenolysis: the liver breaks down its glycogen store into glucose and releases it back into the bloodstream.
- reducing the amount of glucose absorbed by the liver cells
- Increasing gluconeogenesis: increasing the conversion of amino acids and glycerol into glucose in the liver.
