Chapter 9: Homeostasis and Hormonal Control Flashcards
Define homeostasis.
- Maintenance of a
- constant internal environment to
- restore the norm
- in response to environment changes
- through corrective processes
What is the importance of homeostasis?
A stable internal environment allows an organism to be independent of changes in the external environment
Explain the principles of homeostasis.
- Homeostasis is the maintenance of a constant internal environment through the process of corrective mechanisms and negative feedback;
- Where a stimulus will trigger a corrective mechanism that will revert the change back to the norm
What is meant by negative feedback?
Negative feedback is the body’s reaction to bring about an opposite effect to the changes detected through a negative feedback loop.
What are the components of a negative feedback loop?
- Normal/set point to be maintained
- Stimulus, a change from normal conditions
- Receptors that detect the stimulus
- Corrective mechanism that brings about a reverse effect of the stimulus
- Effector, organ or cell that responds to a stimulus (carries out CM)
- Feedback to receptors that the condition has been restored to normal state (CM decreases)
-
What is the process by which blood water potential is maintained?
Osmoregulation
What are the processes that occur within the body when blood water potential increases above the norm?
Stimulus:
- Blood water potential increases above the norm
Receptor:
- Hypothalamus in brain detects stimulus
Corrective Mechanism:
- Pituitary gland releases less ADH
- Cells in walls of distal convoluted tubule and collecting duct become less permeable to water
- Less water is selectively reabsorbed by kidney tubules back into the bloodstream
Effects:
- More water is excreted
- Urine produced becomes more diluted
- Blood water potential increases back to norm
- Feedback is sent to the hypothalamus and ADH production increases
What are the processes that occur within the body when blood water potential decreases above the norm?
Stimulus:
- Blood water potential decreases above the norm
Receptor:
- Hypothalamus in brain detects stimulus
Corrective Mechanism:
- Pituitary gland releases more ADH
- Cells in walls of distal convoluted tubule and collecting duct become more permeable to water
- More water is selectively reabsorbed by kidney tubules back into the bloodstream
Effects:
- Less water is excreted
- Urine produced becomes more concentrated
- Blood water potential decreases back to norm
- Feedback is sent to the hypothalamus and ADH production decreases
Why does blood water potential need to be kept within narrow limits?
blood wp too high-> body cells burst
blood wp too low-> body cells crenate
What are the processes that occur within the body when blood glucose concentration increases above the norm?
Stimulus:
- Blood glucose conc. increases above norm
Receptor:
- Islets of Langerhans in the pancreas is stimulated
Corrective mechanism:
- Islets of Langerhans secrete more insulin which is transported by blood to liver and muscle cells
- Insulin
-> stimulates liver and muscle cells to convert excess glucose into glycogen for storage for liver and muscle cells
->increases permeability of cell surface membranes to glucose for increased glucose uptake by cells
->increases oxidation of glucose during tissue respiration
Effects:
- Blood glucose conc. decreases back to norm
- Feedback is sent to the pancreas and insulin production falls
What are the processes that occur within the body when blood glucose concentration decreases below the norm?
Stimulus:
- Blood glucose conc. decreases above norm
Receptor:
- Islets of Langerhans in the pancreas is stimulated
Corrective mechanism:
- Islets of Langerhans secrete more glucagon which is transported by blood to liver and muscle cells
- Glucagon
-> stimulates liver and muscle cells to convert stored glycogen into glucose
-> converts fats and amino acids into glucose
Effects:
- Blood glucose conc. increases back to norm
- Feedback is sent to the pancreas and glucagon production falls
In what situations would blood water potential be expected to rise?
Drinking a lot of water
In what situations would blood water potential be expected to fall?
When sweating excessively due to high physical activity
Define the term hormone.
Hormones are chemical substances secreted in minute quantities by endocrine glands that are transported through the bloodstream to target organs where they exert their effects.
What is the function of a hormone?
- Influences the growth, development and activity of an organism
- Controls and coordinates body activities
What happens to a hormone after performing its function?
- Destroyed in liver
- Excreted in kidney
Provide some example of hormones and their respective functions in the human body.
(4 pts.)
- Oxytocin helps in delivery of baby out of the mother’s womb during childbirth
- Human Growth Hormone (HGH) increases the height of a child
- Adrenaline prepares the body for “fight-or-flight” during dangerous encounters
- Sex hormones are responsible for physical and emotional changes during puberty
What are the differences between and endocrine gland and an exocrine gland?
(+ named examples of each)
Endocrine gland:
- Ductless glands
- Transport their secretions via the bloodstream to target organs
- e.g. adrenal gland, pituitary gland, pancreas
Exocrine gland:
- Ducts present
- Transport their secretions via ducts to target organs
- e.g. sweat gland, salivary gland, pancreas
What are some examples of endocrine glands and their secretions? [in syllabus]
(5 pts.)
Pituitary gland: ADH
Hypothalamus: regulates secretion of some hormones
Ovary: Oestrogen, Progesterone
Testes: Testosterone
Pancreas: Insulin, Glucagon
What are the effects of a lack of secretion of insulin?
- Abnormally high blood glucose concentration
- Tissue cells cannot store or utilise glucose
- Symptoms include weak body, continual weight loss, glucose present in urine
- Could lead to diabetes mellitus
What are the effects of over-secretion of insulin?
- Abnormally low blood glucose concentration
- Symptoms include hunger, rapid heartbeat, irritability
- May lapse into a coma or even die in severe cases
What is diabetes mellitus?
A condition where blood glucose conc. cannot be regulated, usually caused by insufficient insulin secretion. This leads to persistently high blood glucose concentration. As kidneys are unable to fully selectively reabsorb glucose back into blood capillaries, glucose is excreted in urine.
Signs and symptoms include:
- consistently high blood glucose conc.
- presence in glucose in urine after a meal
- healing of wounds is slow and difficult
- frequent urination
- weight loss
What is Type 1 Diabetes?
- Early-onset diabetes
- Insufficient or no insulin production as cells in pancreas that produce insulin are destroyed
- Inherited condition
- Treatment: Insulin injection at early stage
What is Type 2 Diabetes?
- Late-onset diabetes
- Insulin produced but target cells (e.g. muscle or liver cells) do not respond well to insulin OR
- Insufficient production of insulin
- Risk factors:
-obesity
-sedentary lifestyle
-unhealthy diet
-family history
-high levels of bad cholesterol and low levels of good cholesterol
-age - Treatment: oral medication, control of dietary intake and exercising
How do you reduce the risk of Type 2 Diabetes?
- eat healthy foods (e.g. fruits and vegetables-> low in calories, high in fibre)
- engage in more active physical activities (use up excess glucose)
-glucose provides energy for muscular contractions
-liver and muscle cells become more sensitive to insulin - avoid long periods of inactivity (e.g. sitting for too long)
- maintain a healthy body weight that suits age and height
What are the similarities between endocrine and nervous controls?
- Contains detector that detects stimulus
- Contains signal or message that is transmitted
- Contains an effector (target organ/ cell that carries out response)
What are the differences between endocrine and nervous controls?
Endocrine: Involves hormones (chemical substances)
Nervous: Involves neurones (nerve impulses)
Endocrine: Chemical transmission
Nervous: Chemical and Electrical transmission
Endocrine: Hormones transported by blood
Nervous: Nerve impulses transmitted by neurones
Endocrine: Slower transmission and relatively slow-acting
Nervous: Rapid transmission and response
Endocrine: Can cause long-term or short-term changes
Nervous: Often causes short-term changes
Endocrine: May be voluntary or involuntary
Nervous: Always involuntary
Endocrine: Usually localised response (e.g. one muscle)
Nervous: Widespread responses (usually affects more than one target organ)
What are the key structures of the skin?
(state)
- Blood vessels
- Hair follicle
- Sweat glands
- Sensory receptors
What are the functions of the skin?
- Protection from injury
- Protection from water loss
- Detection of changes in the environment
- Production of sweat
- Temperature regulation
What are the processes that occur within the body when body temperature increases above the norm?
Stimulus:
* Blood and skin temperatures increase above the norm
Receptor:
* Thermoreceptors on the skin detect this change and send the information to the hypothalamus in the brain
* Thermoreceptors in the hypothalamus in the brain also detect the increase in the temperature of blood flowing through it
Corrective mechanism + effect:
1. Vasodilation occurs
* Arterioles in skin dilate
* Shunt vessels constrict
* More blood flows to capillaries in skin
-More heat loss at skin surface through conduction, convection and radiation
2. Production of sweat increases
* Sweat glands become more active
-More latent heat of vaporisation is lost due to evaporation of water in sweat
3. Rate of metabolic activities decreases
-reduced heat production
-reduced heat released within the body
What are the processes that occur within the body when body temperature decreases above the norm?
Stimulus:
* Blood and skin temperatures decrease above the norm
Receptor:
* Thermoreceptors on the skin detect this change and send the information to the hypothalamus in the brain
* Thermoreceptors in the hypothalamus in the brain also detect the decrease in the temperature of blood flowing through it
Corrective mechanism + effect:
1. Vasoconstriction occurs
* Arterioles in skin constrict
* Shunt vessels dilate
* Less blood flows to capillaries in skin
-Less heat loss at skin surface through conduction, convection and radiation
2. Production of sweat decreases
* Sweat glands become less active
-Less latent heat of vaporisation is lost due to evaporation of water in sweat
3. Rate of metabolic activities increases
-increased heat production
-more heat released within the body
4. Shivering
- reflex contraction of muscles in the body
- muscle cells undergo respiration
- heat is released and transported via blood to the rest of the body
5. ‘Goose Pimples’
- hair erector muscles contract
- layer of air trapped at skin surface to retain heat
How do you increase heat gain by the body?
- Metabolic activities such as cellular respiration (esp. in liver and muscle cells)
- Vigorous muscular exercise
- Consumption of hot food and drinks
- Being in a warm environment
How do you lose heat within the body?
- Through skin surface via conduction, convection and radiation
- Loss of latent heat of vaporisation through evaporation of water in sweat
- Exhaled air from lungs
- Faeces and urine
Describe the relationship between the liver and the kidney in managing metabolic wastes.
The liver is where deamination of amino acids occurs to produce urea. Urea is carried by the renal artery to the kidney, where it is removed from the bloodstream and excreted in urine.
Describe the relationship between the liver and the pancreas in a person whose intake is only water for 24 hours.
Low blood glucose stimulates the Islets of Langerhans in the pancreas to produce glucagon that is released into the blood to the liver. Glucagon stimulates the liver cells to convert stored glycogen into glucose and convert fats and amino acids into glucose for maintenance of constant blood glucose levels.
