CTR - 10 - Homeostasis Flashcards
What is a set point?
The desired value of a variable
What is a stimulus?
Deviation from a set point
What is negative feedback?
To reduce or correct a deviation from the set point (negate the stimulus)
Why is there oscillation?
Due to large between receptor and response (slight overcorrections)
What happens to oscillations in a more efficient homeostatic system?
Less oscillation (but this requires energy = costly)
Homesotasis is concerned with the ______ but changes are often detected ________.
ECF, but changes are often detected in the blood
Who said this:
Organ systems create and control composition of the internal milieu, and constantly is required for body cells to operate
Claude Bernard
Who said this:
Numerous agents/processes act together to control particular variables
Walter Cannon
Gain = ?
correction / error
What is the importance of maintaining body temperature?
Enzymatic reaction rates are temperature dependent.
T or F? Shell temperature and rectal temperature are accurate representations of core temperature.
Shell = NO Retal = YES
A fever results in ____________
A shift (increase) in the hypothalamic set point (greater than 37 degrees celsius)
How do you know when a fever is broken? What does this mean?
Set point returns to normal. Sweating to cool the body back down to regular set point.
What temperatures does heat stress occur at? What is another name for heat stress? Symptoms
Heat exhaustion. 37.5 - 39
Elevated core body temp Mental confusion Fainting Dehydration Headache Heat loss mechanisms ARE functional
Corrective responses
What temperatures does heat stroke occur at? What is another name for heat stress? Symptoms
Hyperpyrexia. Greater than 40
Brain and hypothalamic activity is depressed - thermoregulatory mechanisms work less effectively –> POSITIVE FEEDBACK
Elevated core body temp Behave/speak inappropriately Confused Clammy/dry skin Not request shade or fluids
What is positive feedback? 2 physiological examples
Error in signalling - acceleration into catastrophe.
Blood clotting
Childbirth (oxytcoin)
What is the primary excretory organ?
Kidneys
What % of blood flow goes to the kidneys?
25%
The nephrons filter a total of _____
180 L of blood per day
How many nephrons?
2 million (1 million per kidney)
How much of the filtered blood is reabsorbed?
99%
What is reabsorbed in the PCT?
Glucose, water, Na+, Cl-, amino acids
How is glucose reabsorbed in the PCT?
secondary active transport
How are amino acids reabsorbed in the PCT?
secondary active transport
What is the osmolarity of the medulla?
1200 mOsm
How does ADH affect the kidney?
Inserts aquaporins into the collecting duct –> increases water reabsorption
What are eryhtrocytes?
Red blood cells
How many red blood cells are produced?
2 million per second (and removed)
How many haemoglobin molecules per RBC?
300 million
What is a hypoxic tissue?
Tissue getting insufficient oxygen
What is an anoxic tissue>
Tissue getting NO Oyxgen
What is another name for a RBC?
Erythrocyte
What does the ________ release to regulate RBC concentration?
Kidney, releases erythropoietin (EPO)
What does EPO do (broadly)?
Increases RBC count
Where does EPO act?
On red bone barrow - releasing RBC
What is acclimatisation?
Change in set point instigated by environmental change
Change in set point instigated by environmental change. What is this?
Acclimatisation
What happens if there is too little/much calcium?
Too little: Heart and muscle contraction Nerve action (APs) Blood coagulation Cell division
Too much
- precipitates out in blood (with phosphate) forming clots
Why is blood glucose regulation important?
Too high (diabetes) Too low (decreased CNS activity)
What are the roles of insulin?
Conversion of glucose to glycogen in liver (if stores filled up, sorted as fat)
Uptake of glucose into tissue cells (by binding to receptors, increasing facilitated diffusion of glucose into cells)
Stimulus for insulin release?
High blood glucose (amino aids, and fatty acids too)!
glucose enters beta cells via ________?
GLUT (glucose transporters)
How does glucose affect beta cells?
eneters via GLUT, increases ATP production, causes K+ channels to close, depolarisation, opens Ca2+ channels, insulin released from vesicles via exostosis
How is glucose reabsorbed from the kidney (BG)? Structures?
lumen of nephron –> tubular cell
- secondary active transport against concentration gradient (with sodium) - via co-transport carrier
- facilitated diffusion out of tubular cell to interstitial fluid via glucose carrier
What are signs of diabetes mellitus?
Sweet urine
Wake up many times to urinate (osmosis)
What is the real threshold?
300 mg / 100 mL
Greater than this, glucose is excreted, as transporters are maxed out.
What does diabetes mellitus mean?
Sweet urine
Type II accounts for _____
90%
Type II accounts for _____
10%
What are some consequences of diabetes mellitus?
Blindness Amputation of lower limbs Kind failure Impotence Cardiovascular disease Acidosis Metabolic anomalies
What are the first and second actions of glucagon?
Firstly - glycogenolysis (glucogen –> glucose in liver)
Gluconeogenesis - formation of new glucose from fat cells
Why is chronic stress diabetogenic?
Chornic stress -> increases cartels levels
Which is a stimulus for glucagon release
Increases blood glucose –> can lead to diabetes mellitus
What is diabetes insipidus?
Inability to concentrate urine
Diuresis can be 3-15 L per day
What are the causes of diabetes insipidus?
Neurogenic (insufficient production or release of ADH from posterior pituitary - tumours)
Nephrogenic (end stage kidney disease - no receptors for ADH = cannot retain water)
Pscyhogenic = vastly increase water intake
What is cardiac output?
Volume of blood pumped from heart per minute
CO = SV x HR
What three factors maintain blood pressure? Structures?
Adequate Cardiac output - heart
Sufficient peripheral resistance = smooth muscle in small arteries
Adequate blood volume = kidneys
Baroreceptors are _______ receptors
Stretch
Falling BP = less stretch
Rising BP = more stretch
Baroreceptors signal the ___________
Sympathetic nervous system
What does angiotensin II do?
Vasocontrstion
Increase ADH release from post pituitary
Increase aldosterone from adrenal cortex
