Endocrine system Flashcards
Negative Feedback
Output shuts off the original effect of the stimulus or reduces its intensity.
Cause variable to change in direction opposite to that of the initial change.
Eg regulation of body temperature and controlling blood sugar levels.
Positive Feedback
Result or response enhanced the original stimulus so that the response is accelerated.
Usually control infrequent events that do not require continuous adjustments.
Eg labour contractions and blood clotting
Hormones:
chemical messengers secreted by cells into extra cellular fluids. Regulate metabolic function of other cells in the body
Major processes controlled: Reproduction Growth and development Maintenance of electrolyte Regulation of cellular metabolism Mobilisation of body defences
Two types of glands
Exocrine: produce non hormonal substances eg sweat and saliva and have ducts that carry these substances to membrane surface
Endocrine: produce hormones and lack ducts. Hormones are released into surrounding tissue fluid that have typically rich vascular and lymphatic drainage
Main types of hormones
Water Soluble: amino acid based and vary greatly in size.
They act on receptors in the plasma membrane as they can not enter the cell
Lipid Soluble: steroids are synthesised from cholesterol
Act on receptors inside the cells which directly activate genes as they can pass through the cell membrane.
Hormones Action
May affect all the cells of the body or only particular groups of cells (target cells) or particular organs
Hormones circulate to almost all tissues but only affect those which have receptors for the particular hormone.
Typical changes brought about: Alters membrane permeability Stimulates synthesis of enzymes and other proteins Activated or deactivates enzymes Induces secretory activity Stimulates mitosis
Hormones: Anterior Pituitary
Follicle Stimulating Hormone (FSH) - growth of follicles or production of sperm
Lutenising Hormone - ovulation and maintenance of corpus luteum/secretion of testosterone
Growth Hormone- growth and protein synthesis
Thyroid Stimulating Hormone (TSH) - stimulates the secretion if hormones from thyroid
Adrenocorticotropic Hormone (ACTH) - secretion of hormones from adrenal cortex
Prolactin- milk production
Hormones: posterior pituitary gland
Antidiuretic Hormone (ADH) - reabsorption of water
Oxytocin- contraction of uterus during childbirth
Hormones: thyroid
Thyroxine - increases metabolic rate therefore Oxygen consumption and heat production
Calcitonin - decreases blood calcium levels by inhibiting the breaking down of bone and filtration of calcium
Hormones: parathyroids
Parathyroid hormone - increases the levels of calcium in the blood, increases rate at which bone is broken down.
Hormones: thymus
Thymosins- stimulates development of T lymphocytes
Hormones:Adrenal Cortex
Aldosterone - increases reabsorption Of Sodium and excretion of K+
Cortisol - promoted normal metabolism and repair and helps body deal with stress
Hormones: adrenal medulla
Adrenaline and Noradrenaline - fight or flight response, reinforces the effects of sympathetic nervous system
Hormones: pancreas
Insulin - stimulates uptake of glucose
Glucagon - stimulates the breakdown of glycogen and fat therefore increases blood glucose levels.
Hormones: Testes
Androgens - stimulate sperm production, growth of skeleton and muscle as well as male sexual characteristics
