homeostasis Flashcards
KMS
define hormone
chemical substance secreted in minute amounts by glands, carried by the blood, which alters the activity of one or more specific target organs, and is eventually broken down by liver
what biomolecules can make up hormones?
either protein or steroid (lipid)
contrast endocrine and excocrine glands
Endocrine: ductless glands that produce hormones and secrete them directly into bloodstream, which the blood carries to target organ or tissue
Exocrine: glands with ducts that produce a secretion that is carried by the duct
state at least 1 example of endocrine and exocrine gland
endocrine
* hypothalamus
* testes
* pancreas (islets of Langerhans)
exocrine
* salivary
* sweat
both
* pancreas (pancreatic juice through pancreatic duct)
define homeostasis
maintenance of a constant internal environment
explain why homeostasis is important
cells function well only within a narrow range of conditions, so large changes can result in cells not functioning efficiently, or even dying, and homeostasis ensures a stable internal environment in organism with minimal unavoidable disturbances,
thus allowing the organism to function more efficiently, as cells are maintained in an internal environment with optimal conditions, as well as with a degree of independence from the external environment, as the organism is not adversely affected by changes in external environment
state how the internal environment differs at cellular and tissue level
cellular level
cytoplasm constituents are controlled by
* cell surface membrane (rates at which molecules are exchanged are controlled by diffusion and osmotic gradients, and active transport mechanisms
* enzyme activity, controlled by the rate of protein synthesis
tissue level
tissue fluid formed when higher blood pressure at the arterial ends of capillaries force blood plasma out of the capillaries, with features that need to be kept constant:
* temperature
* pH
* concentration of respiratory gases
* concentration of essential molecules
* concentration of ions
* concentration of toxic substances
define reference point
the optimal level in a homeostatic control system
describe the components of a control system and how it achieves negative feedback
1- Stimulus
any change or deviation from normal condition
2- Receptor
detects the stimulus from reference point, and relays the information to control centre
3- Control centre
compares information with reference point, and sends an appropriate signal to the effector if there is deviation
4- Effector
carries out the appropriate response based on signal received from control centre to counteract the initial deviation which results in an effect that is picked up by receptor, which relays information to the control centre and returns the system to normal, optimal conditions, after comparison against reference point
this process is negative feedback
define negative feedback
mechanism that counteract changes in internal environment and restore it to the reference point
explain why blood glucose level regulation is important
glucose is the ideal substrate for cellular respiration, preferred fuel molecule for both cardiac and skeletal muscles, and the only metabolic fuel molecule used by the brain.
a drastic decrease in blood glucose level could lead to fainting, convulsions, coma and finally death
where is insulin and glucagon produced
insulin: beta cells of the islets of Langerhans in the pancreas
glucagon: alpha cells of the islets of Langerhans in the pancreas
explain how concentration of glucose in blood is maintained (explain together)
blood glucose concentration is monitored constantly by islets of Langerhans in the pancreas
an increase or decrease in blood glucose levels causes the beta cells or alpha cells respectively of islets of Langerhans in the pancreas to produce insulin or glucagon respectively
which are transmitted via the bloodstream to all parts of the body
insulin travel to liver and muscles cells, causing the following responses
* increase permeability of cell membranes to glucose, thus increasing uptake of glucose from blood by cells
* increase rate of cellular respiration and hence rate of oxidation of glucose in cells
* stimulate liver and muscle cells to increase rate of glycogenesis to convert excess glucose to glycogen for storage
glucagon travels to the liver cells, causing the following responses
* stimulate conversion of stores glycogen back to glucose
* conversion of non-carbohydrate sources such as pyruvate, amino acids, and glycerol to glucose
the decrease or increase in blood glucose concentrations back to reference point is detected by beta cells or alpha cells in islets of Langerhans respectively which decreases the secretion of insulin or glucagon respectively
the circulating insuling or glucagon is then broken down in the liver and excreted by the kidneys
contrast type 1 and type 2 diabetes mellitus.
Type 1: pancreas fails to produce enough functional insulin
Type 2: body cells no longer respond / are desensitised to insulin produced by pancreas
state signs and symptoms of diabetes, and treatment
signs and symptoms
* increase in blood glucose
* glucose found in urine
* excessive thirst and urination
* tiredness
* loss of weight
treatment
* insulin injection (only for Type 1)
* controlled diet and exercose
* taking medicine
explain why temperature regulation is important
enzymes in the body can only work within a certain range of temperatures, and changes in the body temperature may result in enzyme inactivation or even denaturation
state which body organ produces the most heat
liver
explain how body temperature is maintained
body temperature is monitored constantly by thermoreceptors in the skin and hypothalamus
an increase or decrease in temperature of external environment is detected by thermoreceptors in the skin which sends nerve impulses to the hypothalamus
an increase / decrease in blood temperature is also directly detected by thermoreceptors in the hypothalamus when warm / cool blood flows thorugh it
the hypothalamus in brain sends out nerve impulses to relevant body parts, where corrective processes occur to restore the temperature back to normal
when body tempeartures needs to be raised:
* arterioles in skin dilate while shunt vessels constrict, to allow more blood to flow through blood capillaries under skin surface. thus, more heat is lost through skin by radiation, convection and conduction
* sweat glands become more active, so there is increased production of sweat, and as more sweat evaporates from surface of skin, more latent heat of vaporisation is removed from the body
* the metabolic rate of body slows down thus less heat is produced within the body
these processes decrease blood temperature to reference point
when body temperature needs to be lowered:
* arterioles in skin constrict while shunt vessels dilate, to allow less blood to flow through blood capillaries under skin surface. thus, more less is lost through skin by radiation, convection and conduction
* sweat glands become less active, so there is decreased production of sweat, and as less sweat evaporates from surface of skin, less latent heat of vaporisation is removed from the body
* the metabolic rate of body increases thus more heat is produced within the body
* sometimes, ‘shivering’ also occurs when above reactions are insufficient to prevent drop in body temperature, and this spasmodic contraction of muscles increases heat production
these processes increase blood temperature to reference point
this decrease or increase in blood temperature back to reference point is detected by thermoreceptors, which stops the homeostatic action
processes are vice versa
where is ADH produced
hypothalamus in the brain (and is released by the pituitary gland)
explain why blood plasma water potential regulation is important
if blood plasma is too dilute, water molecules enter the cells by osmosis, so the cells swell and burst
if blood plasma is too concentrated, water molecules move out of the cells by osmosis, so the cells become dehydrated, shrink, and are thus unable to carry out metabolic functions
explain how blood plasma water potential is maintained
blood plasma water potential is monitored constantly by osmoreceptors in the hypothalamus
an increase or decrease in water potential of blood plasma above or below reference point is detected by osmosreceptors in the hypothalamus in the brain, which stimulates the pituitary gland
if blood plasma water potential needs to be decreased
* pituitary gland RELEASES less ADH into the bloodstream, causing the walls of distal convoluted tubule and collecting duct to be less permeable to water
* kidney tubules reabsorb less water back into blood capillaries
* more urine is produced
* urine is more dilute
these actions decrease blood plasma water potential back to reference point
if blood plasma water potential needs to be increased
* pituitary gland RELEASES more ADH into bloodstream, causing the walls of distal convoluted tubule and collecting duct to be more permeable to water
* kidney tubules reabsorb more water back into blood capillaries
* less urine is produced
* urine is more concentrated
these actions increase blood plasma water potential back to reference point
this decrease or increase in blood plasma water potential back to reference point is detected by the osmoreceptors, which causes secretion of ADH to return to norm
