homeostatis & hormonal control Flashcards
define homeostasis and homeostatic control and explain
> homeostasis (definition): maintenance of a constant internal environment
- this helps an organism to be independent. of the changes in external environment
homeostatic control (definition): occurs when body reacts to bring about an opposite egged to the changes detected
- this is known as the negative feedback process
describe the process when there is negative feedback taking place:
1) normal/set point that needs to be maintained
2) stimulus which is a change from normal condition in the internal environment
3) receptors that detect the stimulus
4) control center where info from receptor is received & compare with set point & commands to effector despatched from here
5) correct mechanism that runs about reserve effect of the stimulus
6) effector: carrying out corrective mechanism
7) response: change in condition (back to normal)
define hormone and explain what it is and does
> hormone (definition): it is a chemical messenger produced in a minute quantities by an endocrine gland
- it is transported by the bloodstream to targets organs which are effectors
- hormones influence growth, development & activity of an organism
- after performing the functions, they are destroyed in the liver (unit 1) and excreted by kidneys
production of hormones
> hormones produced by exocrine/endocrine glands
- eg. sweat glands have ducts for carrying sweat out of the body
- hormones are produced by ductless glands (a ductless gland does not have a duct to carry away its secretion, the hormone produced by a ductless gland is secreted directly into bloodstream)
secreted into bloodstream then distributes the hormone around the body (known as endocrine glands)
glands that are purely endocrine gland (production only hormones) - eg. pituitary gland that secretes ADH
other glands: pancreas produces both hormones and other secretions:
1) pancreas produces pancreatic juice, which is carried by pancreatic duct to duodenum
2) pancreas also contains special groups of cells known as the islets of Langerhans (secretes the hormones insulin and glucagon into bloodstream)
- hence, pancreas is considered both an endocrine & exocrine gland
functions of different endocrine glands (pituitary gland, hypothalamus, ovary, testis and pancreas)
pituitary gland:
- it plays an important role as a ‘controller’ (it secretes a no. of hormones, which control the secretion of hormones of several other endocrine glands)
- thus, it is often referred to as the ‘master gland’ (it also secretes the antidiuretic hormone, ADH
hypothalamus
- it is an endocrine gland that regulates the secretion of some hormones
ovary
- secretes oestrogen and progesterone
testis
- secretes testosterone
pancreas
- islets of Langerhans in pancreas secrete insulin and glucagon
how does pancreas play a part in homeostasis and hormonal control
> pancreas produces both hormones & pancreatic juice
pancreatic gland produces pancreatic juice is transported to duodenum by ducts
- islets of Langerhands are endocrine glands that contain 2 types of cells:
1) alpha (a) cells: secretes glucagon directly into blood
2) beta (b) cells: secretes insulin directly into blood
when BGC increase above normal (effects of insulin - LACK & EXCESSIVE)
> insulin decreases BGC by:
1) increasing the rate of cells respiration
2) making cell membranes more permeable to glucose
3) stimulating the liver & muscle cells to convert glucose to glycogen for storage
4) increasing the sue of glucose for tissue respiration
when there is a LACK of insulin
- increases BGC by:
- glucose cannot be stored or ultimates by tissue cells (hence, BGC rises and some glucose is subsequently lost in the urine, resulting in a rise to diabetes)
when there is EXCESSIVE insulin
- abnormal decrease in BGC such that:
- low BGC results in a condition called shock
- seizures or fits, collapsing or passing out may follow
when BGC decrease below normal (effects of glucagon)
> islets of Langerhans in pancreas increases secretion of glucagon when BGC is low (stimulates liver cells to) :
glucagon increases BGC by:
1) conversion of glycogen to glucose (in liver cells)
2) conversion of amino acids to glucose (in liver cells)
what is ADH (anti-diuretic hormone)
- ADH is produced by a region of the brain called the hypothalamus & is secreted by the pituitary gland
- amount of water in the blood plasma is controlled by the ADH
- released by the pituitary gland, it increases water reabsorption in nephrons
diabetes (type 1 and type 2)
1) type 1 diabetes (hereditary) : islets of Langerhans are not able to produce/secrete sufficient insulin
2) type 2 diabetes;
risk factors: (type 2)
> obesity
- accumulation of an excessive amount of body fat (insulin resistance)
> age
- deficiency of insulin secretion/production
> family history
- this can be passed down (inherited diabetes type 2)
> blood lipid levels
- risk is increased if you have high level of “bad cholesterol or LDH & low levels of good ‘cholesterol’ or HDL in the blood
> sedentary lifestyle
- less active = greater the risk of
- physical activities help control your weight by suing ip excess glucose to provide energy for muscle contractions & make their liver & muscle cells more sensitive to insulin
