What is homeostasis
Is the maintenance of a constant internal environment, it is important that the cells environment is at an optimal level for normal cell and body function
What is a paracrine?
Paracrine’s are secreted by all cells in a particular tissue and move through extra cellar fluid.
What is a hormone?
A chemical substance produced in the body that controls and regulates the activity of certain cells or organs. Hormones are only able to influence cells that have the correct receptor for the hormone. Hormone receptors are specific, saturation can also occur.
What are the two types of hormones?
Protein / amine hormones and steroid hormones
What are protein or amine hormones?
- Water soluble
- Cannot cross cell membrane
- Secondary messenger substances diffuses through cell
- Have to bind to a receptor, then a secondary receptor which under goes events such as enzymes
e. g. Insulin + Insulin receptor ——> glucose enters cell
What are steroid hormones?
- Lipid soluble
- Can diffuse across cell membranr
- Enters target cell
- Combines with receptor protein inside the cell ( on mitochondria, other organelles or a nucleus)
- Hormone receptor complex activates genes controlling the formation of proteins
What does ‘hormone clearance’ refer to?
Once a hormone has completed its job it is turned off. Hormone molecules are broken down in a target cell or liver & kidneys -Degraded hormones are excreted in bile or urine.
Explain the features of the hypothalamus
- Located at the base of the brain
- Regulates many body functions i.e. temp, water balance and heart rate
- Many functions of the hypothalamus are carried out in pituitary gland
In which two ways are the hormones carried in the body?
Carried in the blood to anterior love and there they inhibit or stimulate the release of hormones made in Anterior lobe
Passed through nerve fibres from the hypothalamus of the posterior lobe where they are secreted
Explain the features of the pituitary gland
- Located under hypothalamus
- Infundibulum connects pituitary gland to hypothalamus
- Called ‘master gland’ because it regulates the activity of other glands
- Contain two lobes; anterior and posterior
What is the role of the anterior lobe?
- At front
- Releases hormones; FSH, LH, GH, TSH, ACTH, PRL
- Hypothalamus regulates these hormones by secreting, releasing an inhibiting factors into the extra cellar fluid around the cells of the hypothalamus & then these are carried by blood to anterior lobe
What is the role of the posterior lobe?
- At rear
- Release oxytocin and antidiuretic hormone but these are not produced in the posterior lobe, they are produced in special nerve cells in hypothalamus
- Nerve cells have long extensions that pass through the infundibulum to the posterior lobe
- Stay in the posterior lobe until they are ready for release
- Nerve impulses iniate the release of hormones into blood stream
What hormones does the anterior lobe release?
Follicle stimulating hormone(FSH) Luteininsing hormone (LH) Growth hormone (GH) Thyroid stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Prolactin (PRL)
What hormones does the posterior pituitary lobe release?
Antiduiretic hormone (ADH) Oxytocin (OT)
Features of the thyroid gland?
- Located in the neck below larynx
- Contains 2 lobes
- Secretes thyroxine in response to TSH
- controls body metabolism & body temperature
- Message travels from hypothalamus –> anterior pituitary–> TSH–> thyroid–> thyroxine
Features of parathyroid glands
- Located at the back of the thyroid gland, contains 4 lobes
- Secretes parathyroid hormone
- controls calcium & phosphate levels in the blood
What are the adrenal glands?
Two glands one above each kidney
Inner = arenal medulla
Outer = adrenal cortex
Role of the adrenal medulla?
Helps body prepare for life threatening situations - fight or flight response uses noradrenaline and is part of the sympathetic divison of autonomic nervous system
What does the adrenal cortex do?
Acts on kidneys to reduce amount of sodium and increase amount of potassium in urine therefore removing potassium in urine and keeping high amounts of sodium monitored by aldesterone & cortisol which deals with stress and repair of damaged tissues
What is the role of the pancreas?
The pancreas are both an exocrine and endocrine gland it is an endocrine gland when it secretes insulin and glycogen but an exocrine gland when it secretes pancreatic juices.
What is the role of insulin?
Reduces the amount of glucose in the blood (blood sugar level) it does this by promoting the uptake of glucose from the body by the cells of the body
What is the role of glucagon?
Works opposite to insulin. Increases blood sugar level by promoting the breakdown of glycogen to glucose in the liver
List 4 other endocrine glands
- Heart
- Kidneys
- Placenta
- Stomach and small intestine
How do nerve impulses travel in an unmyelinated fibre?
Travels steadily, depolarisation of one area of the membrane causes a local current flow between neighbouring areas of membrane. This causes depolarisation immediatly adjacent to the site of the original stimulus
