Flashcards in Homeostatic Control, Excretion and Thermoregulation (Chapter 14) Deck (64)
What is homeostasis?
- The maintenance of internal conditions despite variations in the external environment, within narrow limits us
- It uses control systems in the body to keep internal conditions near constant
What does homeostasis require?
- Information about the conditions inside the body and the surroundings, which are detected by sensory cells
- This information to be transferred between different parts of the body
Name 6 physiological factors controlled in homeostasis in mammals
1) core body temperature
2) metabolic wastes especially CO2 and urea
3) blood pH
4) blood glucose concentration
5) water potential of blood
6) concentration of CO2 and O2 (respiratory gases) in the blood
What is the internal environment of an organism?
All conditions inside the body/conditions in which the cells function
What is the immediate environment for a cell?
The tissue fluid that surrounds it
What are 3 features of tissue fluid that influence cell activities?
2) water potential
3) concentration of glucose
How does temperature influence cell activities?
- Low temperatures slow down metabolic reactions
- At high temperatures, proteins (incl enzymes) are denatured and cannot function
How does water potential influence cell activities?
- If the water potential decreases, water may move out of cells by osmosis, causing metabolic reactions in the cell to slow or stop
- If the water potential increases, water may enter the cell, causing it to swell and maybe burst
How does the concentration of glucose influence cells activties?
- Glucose is the fuel for respiration ∴ lack of it causes respiration to slow or stop, depriving the cell of an energy source
- Too much glucose may cause water to move out of the cell by osmosis, again disturbing the metabolism of the cell
How does homeostasis work?
By controlling the composition of blood and ∴ the composition of tissue fluid (using different control mechanisms for different aspects of the blood and tissue fluid)
What do most control mechanisms in living organisms use to maintain homeostatic balance?
A negative feedback control loop, involving a receptor and effector (muscles and glands)
How does negative feedback work?
1) the receptor detects stimuli (external or internal) that are involved with the condition being regulated
2) these receptors send information (input) about the changes they detect through to nervous system to a central control in the brain or spinal cord
3) the central control instructs an effector to carry out an action (output)
4) continuous monitoring of the factor by receptors produces a steady stream of information to the control centre that makes continuous adjustments to the output
5) ∴ the factor fluctuates around a particular set point (ideal value)
What is the aim of negative feedback?
To keep changes in the factor within narrow limits
What are the actions of negative feedback called and why?
- Corrective actions because their effect is to correct and reverse the change
- An increase in the factor results in something happening that makes the factor decrease and vice versa
Why do homeostatic mechanisms involve negative feedback?
- Because it minimises the difference between the actual value of the factor and the set point
- The factor never stays exactly constant, but fluctuates a little above and below the set point
What two coordination systems in the body transfer information between different parts of the body?
Nervous and endocrine
How is information transferred in the nervous system?
Information in the form of electrical impulses is transmitted along neurones
How is information transferred in the endocrine system?
Chemical messengers called hormones that travel in the blood, in a form of long-distance cell signalling
What is thermoregulation?
The control of body temperature, involving both the endocrine and nervous system
What is excretion?
The removal of unwanted products of metabolism
What two excretory products are formed in humans in much greater quantities than others?
How is CO2 an excretory product?
1) it is produced continuously by cells respiring aerobically
2) the waste CO2 is transported from the respiring cells to lungs in the bloodstream
3) gas exchange occurs within the lungs and CO2 diffuses from the blood into the alveoli - it is excreted in the air we breathe out
How is urea an excretory product?
1) it is produced in the liver from excess amino acids and transported to the kidneys, in solution in blood plasma
2) kidneys remove urea from blood and excrete it, dissolved in water, as urine
What happens when more protein is eaten than is needed?
- The excess cannot be stored in the body, however amino acids provide useful energy
- To make use of this energy, the liver removes the amino groups
What is deamination?
The process where the liver removes the amino groups from amino acids
What happens during deamination?
- The amino group (-NH2) of an amino acid and an extra hydrogen atom are removed and combine to produce NH3 and a keto acid
Where does deamination take place?
In liver cells
What happens to NH3 formed in deamination?
1) it is converted immediately to urea, which is less soluble and less toxic, by combining it with CO2 in the urea cycle
2) urea diffuses from liver cells into the blood plasma
3) as blood passes through the kidneys, urea is filtered out and excreted
Why must NH3 be immediately converted to urea?
It is very soluble and highly toxic ∴ this prevents damage from NH3 building up in the blood