Homeostasis Flashcards
In broad terms and in relation to homesotatic mechanisms, the body “effectors” are
Muscles and Glands
What are homeostatic responses generally aimed at maintaining ?
The internal Milieu, i.e. physico-chemical conditions in the ECF
Homeostatic mechanisms generally respond to …
A. changing variables, which therefore tend to oscillate
B. Deviations from the set point
What is negative feedback ?
When the effector negates the stimulus.
What is the difference between positive and negative feedback?
Positive feedback occurs to INCREASE the change or output: the result of a reaction is amplified to make it occur more quickly. Negative feedback occurs to REDUCE the change or output: the result of a reaction is reduced to bring the system back to a stable state.
What is a set point?
Is a balanced physiological value for a variable.
What is a sensor ?
Sensor or receptor monitors variations from the set point and detects the change.
What is integration?
The integration or control center takes the received information and sends signals to effectors.
What is an effector ?
any muscles or glands that receives information from the integrating center and acts to bring about the changes needed to maintain homeostasis.
What is oscillation?
The value always oscillates about the set point in a system controlled by negative feedback.
What is the difference between efficient and less efficient ?
The efficient has low tolerance for change and requires high levels of ATP.
A less efficient has high tolerance for change and it will take more time to response because oscillations will be larger.
What is a circadian rhythm ?
The set points of some controlled variables are not constantly and can vary, often with the diurnal (circadian) rhythm approximately a 24 hour daily cycle.
An example is the temperature (1 or 2 while slepping) and the cortisol secretion.
What are the components of human thermoregulatory homeostatic system when increasing the temperature?
1.Stimulus: blood temperature warmer than hypothalamic set point.
2. It activated the heat loss center in the hypothalamus: Skin blood vessels and integumentary system.
3. The body temperature decreases and the hypothalamus heat-loss center shuts-off
The body temeperature is usually ?
35.8c-38.2c
What happen with skin blood vessels and sweat glands work to decrease the body temperature?
*Skin blood vessels: they dilate capillaries become flushed with warm blood, heat radiates from skin surface.
*Sweat glands: secrete perspiration, which is vaporized by the body heat, helping to cool it down.
What are the components of human thermoregulatory homeostatic system when DECREASING the temperature?
1.Stimulus: blood temperature cooler than hypothalamic set point.
2. It activated the heat promoting center in the hypothalamus: Skin blood vessels and skeletal muscles
3. The body temperature increases and the hypothalamus heat promoting center shuts-off
What happen with skin blood vessels and skeletal muscle work to increase the body temperature?
The skin blood vessels: constrict blood is diversify from skin capillaries and withdrawn to deeper tissues; minimizes overall heat loss from skin surface.
What are the two types of receptor that participate in thermoregulation homeostasis?
*Shell or peripheral receptors
*Deep body temperature receptors
Describe how and why fever is generated, and what aspects of homeostatic control are altered during a feverish period
-During inflammation e.g. infection, autoimmune disorders, macrophages and other cells release cytokines- interleukins, tumour necrosis factor.
-Cytokines act on the hypothalamus - release prostaglandins which reseat the hypothalamic set point to a higher level- heat promoting mechanisms activated.
-Vasoconstriction, reduced heat loss, skin cools, shivering commences and chills as body temperature rises.
-Once the immune system (+antibiotics/antiviral drugs) has reversed the disease process, the hypothalamic set point returns to normal.
-Heat loss mechanism is activated
*Fever mau assist control of infections by increasing the metabolic rate, increasing phagocytic activity (neutrophils) and inhibition of bacteria growth (increased temperature, sequestration of iron, copper and zinc by the liver)
Describe one of the examples you were given of positive feedback.
Regulation of clotting
1. Break or tear in blood vessel wall
2. clotting occurs as platelets adhere to site and release chemicals.
3. release chemicals attract more platelets.
4.Clotting proceeds until brake is sealed by newly formed clot.
Give another example of positive feedback
1- push baby against the cervix
2. the cervical stretch
3. Stimulates the production in the hypothalamus of oxytocin
4. oxytocin is stored by the posterior pituitary and released in the bloodstream.
5. Oxytocin causes uterine contraction
the delivery of the baby stops the cycle
What is the difference between normal positive feedback
They are limited duration loops and they stop when the process had been driven to completion.
Where is the nephrone located?
In the kidneys
What does the nephron do ?
*It filters the blood fluid via nephrones
*Almost all of this fluid, and everything it contains is reabsorbed and returned to the body.
* Toxic wastes are excreted, and the amount of water and salt retained or lost in the final urine or will depend on the bodies needs.
Describe how Na+ and water are reabsorbed in the proximal convoluted tubule
-Na+ is removed from the cells lining the PCT by the Na+/K+ ATPase pump. the resultant concentration gradient between the lumen of the nephron and the inside of the cells allows for the facilitated transport of NA+ intro cells lining the PCT. water follows sodium, glucose and amino acids into the cells of the PTC by osmosis.
-This is obligatory water reabsorption- cannot be varied to respond to body’s needs
Renal function: ADH inserts aquaporins into the collecting duct. Why and to what effect ?
-ADH is released from the posterior pituitary gland stimulated by increased osmolarity of ECF or fall in blood pressure e.g. hemorrhage, or blood volume.
- Inserts aquaporins channels into the distal nephron allowing increased absorption of water from the tubule *correction of the initial stimulus.
When stimulates renin secretion and what is the end result of this ?
Two things: the first is a decrease in blood pressure sensed by a loss of stretch in the small arteries feeding the kidney, and the second is reduced sodium concentrations in the distal convoluted tubule (sensed by cells found in the macula densa). The most potent stimulus to renin secretion is both.
How do the kidneys regulate blood pressure and volume?
By removing more or less water.
What is the action of the hormone vasopressin or Antidiuretic hormone?
It causes the kidneys to retain more water by increasing water permeability of the COLLECTING DUCT.
What does it cause the release of Aldosterone in the kidney?
Aldosterone acts on the DISTAL TUBULE a and collecting tubule to increase reabsorption of sodium and calcium
What is Renin?
It is a enzyme created in response to low pressure. It initiates a two step process
1. Angiotensin I
2. hormone Angiotensin II
What does Angiotensin II do?
It increases blood pressure in several ways:
*Vasoconstriction (constricts blood vessels)
*Promotes the release of vasopressin and aldosterone
*Stimulates thirst centers in the brain that encourage water intake
What happens when RBC count drops hypoxia ?
The kidneys that is the regulator (and liver) secretes Erythropoietin to initiate erythropoiesis so erythrocytes are synthesised.
How does calcium homeostasis happens?
1.When there is low calcium in the blood the parathyroid hormone (PTH) is secreted.
2. This stimulates the kidney to produce calcitriol.
What is the action of calcitriol?
It promotes absorption of dietary calcium in the small intestine and increases calcium reabsorption by the kidney.
What is the anatomy of the kidney ?
the Kidney is connected to the ureter which takes urine to the urinary bladder and finally to the urethra.
How does the glomerular capsule ?
Leaky capillaries allow fluid and small molecules through but not cells and proteins. They filtrate about 180 L filtrate that finds its way into the bowman’s capsule.
What are the parts of the nephron?
- glomerulus,
- proximal convoluted tubule,
- loop of Henle,
- distal proximal tubule
How does blood enters and leaves the kidney?
It enters through the renal artery (afferent arteriole) and leaves through the blood vain efferent arteriole.
Where is the blood plasma filtered (general) ?
Blood plasma is filtered through the bowman’s capsule. The filtrate moves through the renal tubule alongside the network of blood capillaries before draining in the collecting duct.
What happens in the PCT proximal convoluted tubule
It is the major site of absorption of sodium(active), magnesium(15-25%), potassium(passive),chloride(passive), calcium. Glucose 100%( active, secondary transport ), Amino Acids 100% (active), Urea (passive). Water by osmosis.
-salts, glucose and amino acids, and that these are mostly actively pumped (requiring ATP) across the wall of the PCT and into the kidney interstitium.
What is reabsorption?
Is when water and solutes within the PCT are transported to the bloodstream.
What happens in the descending and ascending loop of henle
- The loop of Henle allows the establishment of a very salty renal medulla; at 1200 mOsmol it is ~4x the osmolarity of other body tissues (which are ~300 mOsmol).
- The collecting ducts traverse this salty medulla.
The cells here are permeable to water and thus the salt and urea concentration rises within the fluid by the time it reaches the bend. Water leaves by facilitated transport passive
ASCENDING The ascending limb is permeable to sodium chloride, which passes out of the tubule into the medullary tissue surrounding it. ( active transport )
how many nephrons does a kidney has ?
1 million